Cancer Flashcards
1
Q
What is metaplasia? Give an example
A
A reversible change in which one adult cell type (usually epithelial) is replaced by another adult cell type
e.g. Barrett’s oesophagus
2
Q
What is dysplasia?
A
An abnormal pattern of growth in which some of the cellular and architectural features of malignancy are present
- Pre-invasive stage with intact basement membrane
- Loss of architectural orientation
- Loss in uniformity of individual cells
- Nuclei: hyperchromatic, enlarged
- Mitotic figures: abundant, abnormal, in places where not usually found
3
Q
Where is dysplasia common?
A
1) Cervix- HPV infection
2) Bronchus- Smoking
3) Colon- Ulcerative Colitis
4) Larynx- Smoking
5) Stomach- Pernicious anaemia
6) Oesophagus- Acid reflux
4
Q
What is neoplasia?
A
An abnormal autonomous proliferation of cells unresponsive to normal growth control mechanisms
5
Q
What are the characteristics of a benign tumour?
A
- Do not metastasise
- Encapsulated
- Usually well differentiated
- Slowly growing
- Normal mitoses
6
Q
When are benign tumours fatal?
A
Dangerous places: - meninges - pituitary Secretes something dangerous: - insulinoma Gets infected: - bladder Bleeds: - stomach Ruptures: - liver adenoma Torts (twisted): - ovarian cyst
7
Q
What are the characteristics of a malignant tumour?
A
- Invade surrounding tissues
- Spread to distant sites
- No capsule
- Well to poorly differentiated
- Rapidly growing
- Abnormal mitoses
8
Q
What is a metastasis?
A
A discontinuous growing colony of tumour cells, at some distance from the primary cancer
- They depend on the lymphatic and vascular drainage of the primary site
- Lymph node involvement has a worse prognosis
9
Q
What is Duke’s staging of bowel cancer?
A
Describes the progression of the cancer
Dukes A: Growth limited to wall; nodes megative
Dukes B: Growth beyond musc propria; nodes negative
Dukes C1: Nodes positive; apical lymph node negative
Dukes C2: Apical lymph node positive
10
Q
What are the different types of benign epithelial tumours? Give examples.
A
- Of surface epithelium = PAPILLOMA
e. g. skin, bladder - Of glandular epithelium = ADENOMA
e. g. stomach, thyroid, colon, kidney, pituitary, pancreas
11
Q
What is a carcinoma?
A
A malignant tumour derived from epithelium
12
Q
What are the different types of carcinoma?
A
- Squamous cell
- Adenocarcinoma
- Transitional cell
- Basal cell carcinoma
13
Q
Give an example of a benign soft tissue tumour.
A
Osteoma
14
Q
What is a sarcoma?
A
A malignant tumour derived from connective tissue (mesenchymal) cells
15
Q
What are the different types of sarcomas?
A
- Fat = Liposarcoma
- Bone = Osteosarcoma
- Cartilage = Chondrosarcoma
- Striated muscle = Rhabdomyosarcoma
- Smooth muscle = Leiomyosarcoma
- Nerve sheath = Malignant Peripheral Nerve Sheath Tumour
16
Q
What is leukaemia?
A
A tumour of white blood cells:
A malignant tumour of bone marrow-derived cells which circulate in the blood
17
Q
What is lymphoma?
A
A tumour of white blood cells:
A malignant tumour of lymphocytes (usually) in lymph nodes
18
Q
What is a teratoma? What are the differences between men and women?
A
A tumour derived from germ cells, which have the potential to develop into tumours of all three germ cell layers: 1. Ectoderm 2. Mesoderm 3. Endoderm Women → mostly benign Men → All malignant
19
Q
What is a hamartoma?
A
A localised overgrowth of cells and tissues native to the organ
- Cells are mature but architecturally abnormal
- Common in children, and should stop growing when they do
e. g. bile duct hamartomas, bronchial hamartomas
20
Q
What is a benign tumour of glandular tissue?
A
An adenoma
21
Q
What is a malignant tumour derived from soft tissue?
A
Sarcoma
22
Q
What is the criteria for assessing differentiation of a malignant tumour?
A
Evidence of normal function still present with production of: - keratin - mucin - bile - hormones Various grading systems for: - breast - prostate - colon No differentiation, ANAPLASTIC carcinoma
23
Q
What is the most important thing when it comes to assessing the prognosis of cancer?
A
The stage
24
Q
What is described by the grade of a tumour?
A
Describes it’s degree of differentiation
25
What is described by the stage of a tumour?
Describes how far it has spread
26
What occurs during M-phase?
Mitosis:
- Nuclear division
- Cell division (cytokinesis)
27
What occurs during interphase?
Duplication
- DNA
- Organelles
- Protein synthesis
28
What are the stages of interphase? What happens in each phase?
G₀ - Cell cycle machinery dismantled
G₁ phase (Gap) - Decision point
S phase - Synthesis of DNA / protein
G₂ phase (Gap) - Decision point
29
What happens during S phase?
- DNA replication
- Protein synthesis: initiation of translation and elongation increased; capacity is also increased
- Replication of organelles (centrosomes, mitochondria, Golgi etc) in case of mitochondria, needs to coordinate with replication of mitochondrial DNA
30
What is the centrosome? What are it's functions?
Consists of two centrioles (barrels of nine triplet microtubules)
Functions: microtubules organising centre (MTOC) and mitotic spindle
31
What are the phases of mitosis?
```
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis
```
32
When does condensation of chromatin occur?
Prophase
33
What is the process (and size) of the condensation of chromatin?
1) Short region of DNA double helix (2nm)
2) "Beads-on-a-string" form of chromatin (DNA wrapped around histones) (11nm)
3) 30nm chromatin fibre of packed nucleosomes
4) Extended scaffold-associated form (Chromatin bound to chromosome scaffold)
5) Condensed scaffold-associated form
6) Chromosome
34
What is the kinetochore?
The belt of protein around the centromere of a chromosome which microtubules attach to
35
What happens during prophase?
- Replicated chromosomes condense
- Duplicated centrosomes migrate to opposite sides of the nucleus and organise the assembly of spindle microtubules
- Mitotic spindle forms outside nucleus between the 2 centrosomes
36
What is the process of spindle formation?
- Radial microtubule arrays (ASTERS) form around each centrosome (microtubule organising centers - MTOC)
- Radial arrays meet
- Polar microtubules form
37
What occurs during metaphase?
Chromosomes align at the equator of the spindle
| Prometaphase: Early prometaphase → late prometaphase
38
What happens in early prometaphase?
- Breakdown of nuclear membrane
- Spindle formation largely complete
- Attachment of chromosomes to spindle via kinetochores (centromere region of chromosome)
39
What happens in late prometaphase?
- Microtubule from opposite pole is captured by sister kinetochore
- Chromosomes attached to each pole congress to the middle
- Chromosome slides rapidly towards centre along microtubules
40
What occurs during anaphase?
- Paired chromatids separate to form two daughter chromosomes
- Cohesin holds sister chromatids together
- Anaphase A and B
41
What happens during anaphase A?
- Breakdown cohesin
- Microtubules shorter
- Daughter chromosomes pulled toward opposite spindle poles
42
What happens during anaphase B?
1- Daughter chromosomes migrate towards poles
| 2- Spindle poles (centrosomes) migrate apart
43
What occurs during telophase?
- Daughter chromosomes arrive at spindle
- Nuclear envelope reassembles at each pole
- Assembly of contractile ring
44
What is cytokinesis?
Cytoplasm of both daughter cell condenses
- Acto-myosin ring contracts
- New membrane inserted
- Midbody begins to form
- Chromatin decondenses. Nuclear structures reform
- Interphase microtubule array reassembles
45
When is the Spindle Assembly checkpoint?
During the transition out of metaphase (prometaphase and metaphase)
- Senses completion of chromosome alignment and spindle assembly (monitors kinetochore activity)
46
What is required for the spindle assembly checkpoint? When does anaphase occur?
```
Requires:
- CENP-E
- BUB protein kinases
BUBs dissociate from kinetochore when chromosomes are properly attached to the spindle
When all dissociate, anaphase proceeds
```
47
What is the normal attachment of microtubules to kinetochores?
Amphelic attachment
| One microtubule from each centrosome attaches to one sister chromatid
48
What is merotelic attachment of microtubules to kinetochores? Does it produce a checkpoint signal? What is the result?
One microtubule from one centrosome attaches to one sister chromatid. Two microtubules from the other centrosome attach to both sister chromatids
No checkpoint signal
Causes chromosome loss at cytokinesis
49
What is syntelic attachment of microtubules to kinetochores? Does it produce a checkpoint signal? What is the result?
Two microtubules from one centrosome attach to both the sister chromatids
May or may not produce a checkpoint signal
If no checkpoint signal then both sister chromatids will be drawn to the same pole
50
What is monotelic attachment of microtubules to kinetochores? Does it produce a checkpoint signal?
One microtubule from one centrosome attaches to one sister chromatid
Will produce a checkpoint signal
51
What is a checkpoint signal?
When a chromatid is not attached to a microtubule, or both are attached to a microtubule attached to the same centrosome a checkpoint signal is generated.
Anaphase cannot proceed until there are no checkpoint signals
52
What causes aneuploidy?
1) Misattachment of microtubules to kinetochores
2) Aberrant centrosome / DNA duplication
If cell cycle or DNA / centrosome replication causes the daughter cells to have multipolar spindles when cytokinesis occurs the cell can cause aberrant cytokinesis
53
Why can inducing gross chromosome mis-segregations be used as an anti-cancer therapy?
- Alters microtubule dynamics
- Produces unattached kinetochores
- Causes long-term mitotic arrests
- Can lead to apoptotic cell death
54
What can go wrong during the cell cycle? What causes these?
1. Cell cycle arrest
- at checkpoints (G1 and spindle checkpoint)
- can be temporary (i.e. following DNA repair)
2. Programmed cell death (apoptosis)
- DNA damage too great and cannot be repaired
- chromosomal abnormalities
- toxic agents
55
Where are the cell cycle checkpoints? What effects do tumours have on checkpoints?
G₁ checkpoint
G₂ checkpoint
Metaphase (spindle) checkpoint
Tumours block these checkpoints then exit the cell cycle at G₀. They then dismantle cell cycle apparatus (deregulation of cell cycle)
56
In the absence of stimulus what phase are cells in?
G₀
57
What is the process of signalling in a cell, causing a cell to exit G₀?
Cell responds to extracellular factors and is modulated by other pathways
- A dimeric ligand bind to the receptor and causes it to form a dimer
- Amino acids are then phosphorylated in the kinase domain causing activation of the receptor
• This causes a conformational change in the receptor; changing it's activity
• It also creates a docking site for other protein
- Activation of the receptor triggers a kinase cascade and the binding of adaptor proteins
58
What is the role of c-Myc?
c-Myc is a transcription factor. It stimulates the expression of cell cycle genes. Upregulation of of Myc triggers entry into S-phase
59
What is the process of growth factor stimulation of signalling pathways?
```
Mitogenic growth factor
(i.e. growth signals from other cells e.g. Hepatocyte Growth Factor released after liver damage)
↓
Receptor protein tyrosine kinase
↓
Small G (GTP-binding) protein (Ras)
↓
Kinase cascade
↓
Immediate early genes (c-Jun, c-Fos, c-Myc- transcription factors) - control the expression of other genes
```
60
How does growth factor initiate a response in the cell?
- GF dimer binds to the tyrosine kinase receptor with ligand binding
- Each phosphorylated tyrosine bound to the receptor binds intracellular signalling proteins forming a signalling hub to initiate the cascade
- Grb2 binds to exchange factor Sos which activated Ras which then allows transmission of the signal
61
What does Herceptin do?
Blocks the action of EGF receptors by blocking ligand binding to the receptor preventing further activation of the receptor
62
What do adapter proteins bind to on growth factor receptors?
Phosphorylated tyrosines
63
What are the domains of Grb2?
SH3-SH2-SH3
64
What does SH3 domains bind to in Grb2?
Proline rich regions
65
How does Ras bind to growth factor receptors and induce the kinase cascade? Give an example of a factor than can activate Ras
- Cannot bind to the receptor directly- must bind to Grb2
- Ras binds GDP, and when it is activated GTP which allows it to signal the kinase cascade
Activated by exchange factors e.g. Sos
Ras has a lipid modification to bind it to the membrane
66
What are the different types of oncogenic mutation in Ras? What is the outcome of these mutations?
```
V12Ras- constitutively active
- Glycine → Valine
- Prevents GAP binding by preventing inactivation
L61Ras- constitutively active
- Glutamine → Leucine
- Prevents GTP hydrolysis
```
67
What does Ras do?
Controls the cell cycle
68
When Ras is active what process does it induce?
1. Activates kinase I (Raf)
2. Raf phosphorylates kinase II (MEK)
3. MEK phosphorylates kinase III (ERK)
This then:
- Changes protein activity
- Changes gene expression (e.g. c-Myc, cell proliferation)
69
What is the activity of cyclin-dependent kinases regulated by?
- Interaction with cyclins
| - Phosphorylation
70
What cyclin-Cdk pair cause the cell to enter mitosis?
Cdk 1-mitotic cyclin B
| - Forms mitosis promoting factor which is the mitotic checkpoint
71
What cyclin-Cdk pair trigger DNA replication machinery in the cell?
Cdk-Scyclin
72
What is the process of formation of Mitosis Promoting Factor
1. Cdk1 binds cyclin B to form inactive MPF
2. Cdk-activating kinase (CAK) and Wee1 (inhibitory kinase) phosphorylate inactive MPF
3. Phosphatase Cdc25 phosphorylates again to produce active MPF
Positive feedback: Active MPF further activates Cdc25 to drive mitosis
73
Signals from fully attached kinetochores during mitosis cause cyclin B to be degraded. What effect does this have?
- Cdk1 inactivated
- Key substracts dephosphorylated
- Mitosis progresses
74
What cyclin and Cdk pair are present in the G₁ phase of the cell cycle?
Cdk2 (G1/S-Cdk)
| Cyclin E
75
What cyclin and Cdk pair are present in the S phase of the cell cycle?
Cdk2 (S-Cdk)
| Cyclin A
76
What is the role of cyclin D? What stimulates transcription of this factor?
c-Myc stimulates transcription of cyclin D
| Cyclin D bind to Cdk4 or Cdk-6 which allows the cells entry into G₁
77
What is the timing process of release of cyclins/Cdks throughout the cell cycle?
```
Cdk4/6-cyclin D
- end of G₁
Cdk2-cyclin E
- end of G₁ →⅔ of S
Cdk2-cyclin A
- mid-S → metaphase (mid-mitosis)
Cdk1-cyclin B
- start of mitosis → anaphase-telophase
```
78
What do Cdks do?
They phosphorylate proteins (on Serine or Threonine) to drive cell cycle progression
Cdk1-cyclin B
- MPF
- Phosphorylate subset of proteins during mitosis such as nuclear lamins
- Then disassemble and break down the nuclear envelope
Cdk2-cyclin E
- Phosphorylate proteins which control start of the cell cycle
- e.g. Retinoblastoma protein
79
What is the role of Retinoblastoma (Rb) protein?
Rb is a "tumour suppressor"
Found at G₀
- Active Rb protein binds to E2F making it an inactive transcription factor
- Cdk4/6-cyclin D and Cdk2-cyclin E causes phosphorylation of pRb to make it the inactive form
- This releases E2F for gene transcription
80
What are the two families of Cdk inhibitors?
INK4 family:
- G₁ phase CKIs
- Inhibit Cdk4/6 by displacing cycD
CIP/KIP family
- S phase CKIs
- Inhibit all Cdks by bindings to the Cdk/cyc complex
They much be degraded to allow cell cycle progression
81
Give examples of different oncogenes and the cancer they cause.
- EGFR/HER2 → mutationally activated or overexpressed in many breast cancers
- Ras → mutationally activated in many cancers (inhibitors of membrane attachment)
- Cyclin D1 → overexpressed in 50% of breast cancers
- B-Raf → mutationally activated in melanomas
- c-Myc → overexpressed in many tumours
82
What treatment is used for HER2-positive metastatic breast cancer?
Herceptin antibody
83
What are the different tumour suppressors in breast cancer?
- Rb → inactivated in many cancers
| - p27ᴷᴵᴾ¹ → underexpression correlates with poor prognosis in many malignancies
84
Where is cancer incidence lowest in the world? Why is this?
Asia
| Diagnosis of cancer is lower due to less advanced medical care
85
What are the five most common cancers worldwide?
- Lung
- Breast
- Bowel
- Prostate
- Stomach
86
What are the main anti-cancer treatment modalities?
- Surgery
- Radiotherapy
- Chemotherapy
- Immunotherapy
87
What types of genetic mutations cause cancer?
- Chromosome translocations
- Gene amplification (copy number variations)
- Point mutations within promoter or enhancer regions of genes
- Deletions or insertions
- Epigenetic alterations to gene expression
- Can be inherited (e.g. BRCA gene)
88
What are the causes of cancer and they're relevant proportions?
⅓ of cancer = poor lifestyle choices
| ⅔ of cancer = random mutations
89
What are the different types of systemic therapy to treat cancer?
1. Cytotoxic chemotherapy
| 2. Targeted therapies
90
What are the different types of cytotoxic chemotherapy? How do they work?
1. Alkylating agents
2. Antimetabolites
3. Anthracyclines
4. Vinca alkaloids and taxanes
5. Topoisomerase inhibitors
"Select" rapidly dividing cells by targeting their structures (mostly the DNA)
91
What are the different types of targeted therapies?
- Small molecule inhibitors
| - Monoclonal antibodies
92
How is cytotoxic chemotherapy administered? Describe it.
Given intravenously or by mouth (occassionally)
Works systemically
Non "targeted" - affects all rapidly dividing cells in the body
Given post-operatively; adjuvant
- Pre-operatively: neoadjuvant
- As monotherapy or in combination
- With curative or pallative intent
93
What is the mechanism of action of alkylating agents?
Add alkyl groups to guanine residues in DNA
Cross-link (intra, inter, DNA-protein) DNA strands and prevents DNA from uncoiling at replication
Trigger apoptosis (via checkpoint pathway)
Encourage mis-pairing - oncogenic
94
What is the mechanism of action of pseudo-alkylating agents? Give examples of drugs
Add platinum to guanine residues in DNA
Same mechanism of cell death as alkylating agents
Examples: carboplatin, crisplatin, oxaliplatin
95
Give examples of different types of alkylating agents.
- Chlorambucil
- Cyclophosphamide
- Dacarbazine
- Temozolomide
96
What are the side effects of alkylating and pseudoalkylating agents?
- Hair loss (except carboplatin)
- Nephrotoxicity
- Neurotoxicity (can be permanent)
- Ototoxicity (platinums)
- Nausea, vomiting and diarrhoea
- Immunosuppression
- Tiredness
97
What is the mechanism of action of anti-metabolites?
Masquarades as purine or pyramidine residues leading to inhibition of DNA synthesis, DNA double strand breaks and apoptosis
- Blocks DNA replication (DNA-DNA) and transcription (DNA-RNA)
- Can be purine (A or G), pyramidine (T/U or C) or folate antagonists (which inhibit dihydrofolate reductase required to make folic acid, an important building block for all nucleic acids - especially T)
98
Give examples of anti-metabolite cancer treatments. Which one of these is one of the most common chemotherapy drugs?
- Methotrexate (folate)
- 6-mercaptopurine
- Decarbazine
- Fludarabine (purine)
- 5-flurouracil *MOST COMMON*
- Capecitabine
- Gemcitabine (pyramidine)
99
What are the side effects of anti-metabolites?
- Hair loss (alopecia)- not 5FU or capecitabine
- Bone marrow suppression causing anaemia, neutropenia and thrombocytopaenia
- Increased risk of neutropenic sepsis (and death) or bleeding
- Nausea and vomiting (dehydration)
- Mucositis and diarrhoea
- Palmar-plantar erythrodysesthesia (PPE)
- Fatigue
100
What is the mechanism or action of anthracyclines? Give examples of the drug
- Inhibit transcription and replication by intercalating (i.e. inserting between) nucleotides within the DNA/RNA strand
- Also block DNA repair - mutagenic
- They create DNA and cell membrane damaging free oxygen radicals
Examples: doxorubicin, epirubicin
101
What are the side effects of anthracyclines?
- Cardiac toxicity (arrhythmias, heart failure) - probably due to damage induced by free radicals
- Alopecia
- Neutropenia
- Nausea and vomiting
- Fatigue
- Skin changes
- Red urine (doxorubicin "the red devil")
102
What is the mechanism of action of vinca alkaloids and taxanes?
- Originally derived from natural sources
- Work by inhibiting assembly (vinca alkaloids) or disassembly (taxanes) of mitogenic microtubules causing dividing cells to undergo mitotic arrest
103
What are the side effects of microtubule targeting drugs?
- Nerve damage: peripheral neuropathy, autonomic neuropathy
- Hair loss
- Nausea
- Vomiting
- Bone marrow suppression (neutropenia, anaemia etc)
- Arthralgia
- Allergy
104
What is the mechanism of action of topoisomerase inhibitors?
- Topoisomerases are required to prevent DNA torsional strain during DNA replication and transcription
- They induce temporary single strand (topo1) or double strand (topo2) breaks in the phosphodiester backbone of DNA
- They protect the free ends of DNA from aberrant recombination events
- Drugs such as anthracyclines have anti-topoisomerase effects through their action on DNA
- Specific topoisomerase inhibitors include Topotecan and irinotecan (topo I) and etoposide (topo II) alter binding of the complex to DNA and allow permanent DNA breaks
105
What are the side effects of topoisomerase inhibitors?
- Irinotecan: Acute cholinergic type syndrome - diarrhoea, abdominal cramps and diaphoresis (sweating). Therefore given with atropine
- hair loss
- Nausea and vomiting
- Fatigue
- Bone marrow suppression
106
What are the resistance mechanisms of cancer to treatments?
- DNA repair mechanisms upregulated and DNA damage is repaired
- DNA adducts replaced by Base Excision repair (using PARP)
- Drug effluxed from the cell by ATP-binding cassette (ABC) transporters
107
What are the advantages and disadvantages on dual kinase inhibitors?
Advantage: Prevents feedback loops (parallel pathways or activation of feedback cascades)
Disadvantage: Increase toxicities
108
What are the 10 hallmarks of the cancer cell?
1. Self-sufficient
2. Insensitive to anti-growth signals
3. Anti-apoptotic
4. Pro-invasive and metastatic
5. Pro-angiogenic
6. Non-senescent
7. Dysregulated metabolism
8. Evades the immune system
9. Unstable DNA
10. Inflammation
109
Give examples of receptors which are overexpressed in cancer?
HER-2
- Amplified and overexpressed in 25% of breast cancer
EGFR
- Overexpressed in breast and colorectal cancer
PDGFR
- Glioma (brain cancer)
110
Give examples of ligand which is overexpressed in cancer?
VEGF
| - prostate cancer, kidney cancer, breast cancer
111
Give an example of constitutive (ligand independent) receptor activation in cancer?
EGFR (lung cancer)
| FGFR (head and neck cancers, myeloma)
112
What are the suffixes associated with monoclonal antibodies? Include examples
```
-momab
(derived from mouse antibodies)
-ximab
(chimeric) e.g. cetuximab
-zumab
(humanised) e.g. bevacizumb, trastuzumab
-mumab
(fully human) e.g. panitumumab
```
113
What is the action of monoclonal antibodies?
- Neutralise the ligand
- Prevent receptor dimerisation
- Cause internalisation of receptor
- Activate Fcγ-receptor-dependent phagocytosis or cytolysis induces complement-dependent cytotoxicity (CDC) or antibody-dependent cellular cytotoxicity (ADCC)
114
Give an example of a monoclonal antibody used in oncology?
- Bevacizumab binds and neutralises VEGF. Improves survival in colorectal cancer
- Cetuximab targets EGFR
115
What is the mechanism of action of small molecule inhibitors?
- Bind to the kinase domain of the tyrosine kinase within the cytoplasm, and block autophosphorylation and downstream signalling
116
Where is the BCR-Abl translocation in CML?
Between chromosomes 9 and 22
117
What is Glivec?
A small molecule inhibitor which targets the ATP-binding region withing the kinase domain
118
What intracellular receptor does small molecule inhibitor Erlotinib act on?
EGFR
119
What intracellular receptor does small molecule inhibitor Gefitinib act on?
EGFR
120
What intracellular receptor does small molecule inhibitor Lapatinib act on?
EGFR
| HER2
121
What intracellular receptor and intracellular kinases does small molecule inhibitor Sorafinib act on?
Intracellular receptor
- VEGFR
Intracellular kinase
- Raf kinase
122
What intracellular kinase does small molecule inhibitor Dasatinib act on?
Src kinase
123
What intracellular kinase does small molecule inhibitor Torcinibs act on?
mTOR inhibitors
124
What effect does inhibiting VEGF have on a tumour?
Alters blood flow to the tumour
125
What effect does inhibiting AKT have on a tumour?
Blocks apoptosis resistance mechanisms
126
What is the benefit to using cancer drugs which act of receptors rather than cytotoxic drug?
Less toxicity
127
What is the main disadvantage to using monoclonal antibodies or small molecule inhibitors?
Resistance
128
What are the resistance mechanisms to targeted therapies?
- Mutations in ATP-binding domains (e.g. BCR-Abl fusion gene and ALK gene, targeted by Glivec and crizotinib respectively)
- Intrinsic resistance (Herceptin effective in 85% HER2+ breast cancers, suggesting other driving pathways)
- Intragenic mutations
- Upregulation of downstream or parallel pathways
129
What is the action of Anti-sense oligonucleotides?
- Single-stranded, chemically modified DNA-like molecule 17-22 nucleotides in length
- Complementary nucleic acid hybridisation to target gene hindering translation of specific mRNA
- Recruits RNase H to cleave target mRNA
- Good for "undruggable" targets
130
How is targeting b-Raf a successful therapy option in cancer?
- Activating mutation of b-Raf identified in 60% of melanomas
- Substitution of glutamic acid for valine (V600E) causes a 500-fold increase in activity
- b-Raf inhibitor (Vemurafenib) showed dramatic Phase 1 activity in melanoma (80% PR or CR)
- Extends life-span by 7 months
- Side effects: arthralgia, skin rash and photosensitivity
131
How is immune modulation via programmed cell death a successful therapy option in cancer?
- Present on the surface of cancer cells
- Required to maintain T cell activation
- After binding the ligand PDL1, the body's T cells can no longer recognise tumour cells as foreign
- If either is blocked the immune system is stimulated
- Nivolumab is anti-PD1 antibody
132
What external influences are detected by cells?
Chemical- hormones, growth factors, ion concentrations, ECM, molecules on other cells, nutrients and dissolved gas (O₂/CO₂) concentrations
Physical- mechanical stresses, temperature, the topography or "layout" of the ECM and other cells
133
What external factors can influence cell division?
- Growth factors
- Cell-cell adhesion
- Cell-ECM adhesion
134
What is the process of a cell settling on a culture surface?
- Cell settles on culture surface
- Spreads
- Acquires motility
It is not passive or gravity dependent. Energy is requires to modulate cell adhesion and the cytoskeleton during spreading
135
What is the requirement of cells to respond to growth factors?
Cells must be bound to ECM (with a degree of spreading) to be fully competent:
- For responding to soluble growth factors
- To begin protein synthesis and proliferation (DNA synthesis)
136
What are cell-ECM adhesion molecules?
Cells have receptors on their surface which bind specifically to ECM molecules
- these are often linked, at their cytoplasmic domains, the cytoskeleton
- This arrangement means that there is mechanical continuity between ECM and the cell interior
137
What are integrins?
Heterodimer complexes of α and β subunits that associate extracellularly by their "head" regions. Each of the "tail" regions spans the plasma membrane
- They are the most important ECM receptors
- Recognise short, specific peptide sequences
- More than 20 combinations of α/β known
- Each combination specifically binds a particular peptide sequence
- Peptide sequences are found in more than one ECM molecule
138
What is peptide sequence RGD found in?
- Fibronectin
- Vitronectin
- Fibrinogen (plus others)
139
How are integrins bound to the actin cytoskeleton?
Via actin-binding proteins
140
What does a cluster of integrin complexes form?
- Focal adhesions (mostly)
- Hemidesmosomes
These are involved in signal transduction and bind to specific adhesion molecules on some cells
141
How are integrins involved in cell signal transduction?
- Integrin complexes binding to ECM can stimulate the complex to produce a signal inside the cell
"outside-in" integrin signalling
- A signal generated inside the cell (e.g. hormone binding to receptor) can act on an integrin complex to alter the affinity of an integrin (i.e. alter its affinity for its ECM binding)
"inside-out" integrin signalling
142
What is "outside-in" signalling in cells?
A cell can receive information about its surroundings from its adhesion to ECM
- e.g. the composition of the ECM will determine which integrin complexes bind and which signals it receives
- this can alter the phenotype of the cell
143
How do focal adhesions sense the mechanical properties of their surroundings?
The amount of force that is generated at a focal adhesion depends on both the force generated by the cytoskeleton (F cell) and the stiffness of the ECM
144
Following integrin activation what conformational changes occur with the complex?
- "Inside-out" activation extends the flexed complex (↑ affinity)
- Ligand-binding opens the legs of the complex allowing cytoplasmic signalling molecules to bind (outside-in signalling)
145
What effect does the ECM have on the phenotype of cells?
Profound effect e.g.
In interstitial matrix (type I collagen)
- mammary epithelium does not differentiate to secretory cells
In basal lamina matrix (basement membrane)
- mammary cells organise into "organoids" and produce milk proteins
146
What is the ERK MAP kinase cascade required for cyclin D expression?
Growth factor binds to tyrosine kinase receptor
```
Ras
↓
Raf (MAPKKK)
↓
MEK (MAPKK)
↓
ERK (MAPK)
↓
Gene expression (proliferation)
```
147
What is the mechanism of anchorage dependence?
Growth factor receptors and integrin signalling complexes can each activate identical signalling pathways (e.g. MAPK)
- Individually, this activation is weak and/or transient
- Together, activation is strong and sustained
- The separate signalling pathways act synergistically
148
What are short-term contact interactions between cells?
Transient interactions between cells which do not form stable cell-cell junctions
149
What are long-term contact interactions between cells?
Stable interactions resulting in formation of cell-cell junctions
150
What is contact inhibition of locomotion? What does it ensure?
When most non-epithelial cells collide they "repel" one another by paralysing motility at the contact site, promoting the formation of a motile front at another site on the cell, and moving off in the opposite direction
151
What types of cells for long-term cell-cell contacts by strongly adhering and forming specific cell-cell junctions?
- Epithelial cells (forms layers)
- Endothelial cells (forms layers)
- Neurones (synapses)
152
What is contact-induces spreading of epithelial cells?
Contact between epithelial cells leads to the mutual induction of spreading so that the total spread area of the contacted cells is greater than that of the sum of the two separated cells
This could result in a stable monolayer
153
What factors affect cell-cell adhesion?
- Ca²⁺
| - Adhesion-blocking antibody
154
What is the effect of no cell-cell junctions?
- Activated MAPK
- Decreased p27ᴷᴵᴾ¹
- High proliferation
155
What protein is thought to be the link between cell-cell adhesion and proliferation?
β-catenin
| Binds cadherin to α-catenin, which binds to actin. Binds cell to ECM
156
What effect does the APC gene have on β-catenin?
The product of the APC gene is a protein involved in degradation of β-catenin
- β-catenin is a protein involved in cell-cell adhesion
If APC is mutated then degradation is reduced
= ↑ proliferation
157
In what circumstances would β-catenin form a complex with LEF-1? What does this complex cause?
β-catenin/LEF-1 complex forms if β-catenin cytoplasmic levels rise as a result of:
- Inhibition of degradation
- Loss of cadherin-mediated adhesion
β-catenin/LEF-1 complex enters the nucleus and influences gene expression, leading to proliferation
158
Other than the β-catenin/LEF-1 complex what other adhesion-associated signalling pathways are known to influence contact-induced inhibition of proliferation?
- Clustering of cadherins after cell-cell contact is known to alter the activation of small GTPases (e.g. Rac is activated; Rho is inhibited) this can influence proliferation
- Some growth factor receptors are associated with cell-cell junctions. This reduces their capacity to promote proliferation
159
What happens if cells lose their contact inhibition?
They will:
- Proliferate uncontrollably (lose density dependence of proliferation)
- Are less adherent and will multilayer (lose contact inhibition of locomotion and anchorage dependence)
- Epithelia breakdown cell-cell contacts
- Not Hayflick limited, express telomerase
i. e. Cancer
160
Other than tumour formation, what is an important consequence of low of contact inhibition of locomotion for the progression of cancer?
Increased invasiveness leads to metastasis
161
Give examples of parts of the signal transduction pathway where proto-oncogenes can lead to uncontrolled proliferation of cells.
- If the gene coding for a component of a signalling pathway is mutated so that the protein is constitutively active, that pathway will be permanently "on"
- Receptors, signalling intermediates and signalling targets (e.g. transcription factors) are proto-oncogenes
- This can result in loss of growth factor dependence
162
What is a proto-oncogene?
The normal cellular gene corresponding to the mutant gene which promotes uncontrolled cell proliferation
163
What oncogenes can arise from proto-oncogene Ras?
V12Ras (Gly12Val mutation)
| L61Ras (Gln61Leu mutation
164
What oncogene arises from proto-oncogene c-Raf?
v-Raf (deletion of regulatory domain)
165
What oncogene arises from proto-oncogene c-Jun?
v-Jun (deletion of regulatory domain)
166
What percentage of all cancers are caused by a mutation in Ras? What cancer is this mutation most frequent in?
≈30%
| Pancreatic cancer
167
How does a primary carcinoma cell metastasise?
- Cell-cell adhesion must be down-regulated (e.g. cadherin levels reduced)
- The cells must be motile
- Degradation of ECM must take place; matrix metaloproteinase (MMP) levels increased in order to migrate through basal lamina and interstitial ECM
- The degree of carcinoma cell-cell adhesion is an indicator of how differentiated the primary tumour is, and indicates its invasiveness and the prognosis
168
What are the steps in tumour progression?
1. Homeostasis
2. Genetic alterations
3. Hyper-proliferation
4. De-differentiation (non-reversible)
- Disassembly
- Cell-cell contacts
- Lose polarity
5. Invasion
- Increased motility
- Cleavage ECM proteins (allows cells to migrate)
169
What are the sequential events involved in metastasis?
1. Epithelial cells in primary tumours are tightly bound together
2. Metastatic tumour cells become mobile mesenchyme-type cells and enter the bloodstream
3. Metastatic cells then travel through the bloodstream to a new location in the body
4. Metastatic cells exit the circulation and invade a new organ
5. Cancer cells lose their mesenchymal characteristics and form a new tumour
170
What are the different types of tumour cell migration?
- Amoeboid migration
- Mesenchymal (single cell) migration
- Mesenchymal (chains) migration
- Cluster/cohort migration
- Multicellular strands/sheet migration
171
What is amoeboid cell migration? What cancers does this occur in?
```
Single, autonomous cell invasion
Occurs in:
- Lymphoma
- Leukaemia
- SCLC
```
172
What is mesenchymal cell migration? What cancers does this occur in?
```
Single cell or chains. Single cell opens up the trail and other cells follow
Occurs in:
- Fibrosarcoma
- Glioblastoma
- Anaplastic tumours
```
173
What is cluster/cohort cell migration? What cancers does this occur in?
Lots of cells migrate together. Requires coordination with neighbouring cells
Occurs in:
- Epithelial cancer
- Melanoma
174
What is multicellular strand/sheet cell migration? What cancers does this occur in?
Lots of cells migrate together in strands or sheets. Requires coordination between neighbouring cells
Occurs in:
- Epithelial cancer
- Vascular tumours
175
What genes are upregulated in invasive cells compared to primary tumours?
Genes involved in:
- Cytoskeleton regulation
- Motility machinery
176
What are the different stimuli that can make a cell move?
- Organogenesis and morphogenesis
- Wounding
- Growth factors/chemoattractants
- Dedifferentiation (tumours)
177
What specialised structures allow a cell to move?
- Focal adhesion
- Lamellae
- Filopodium
178
What are filopodia in cells?
Cell structure used for motility
| Finger-like projections rich in actin filaments made up of bundles of parallel filaments
179
What is the function of plaque in cells?
Hold integrins in place and produces force in a cell
| - Contains vinculin
180
What are lamellipodia in cells?
Cell structure used for motility
Sheet-like protrusions rich in actin filaments
- Protrusions lay down lamella and recycle the cell membrane to allow it to move
- Branched and crosslinked filaments
181
What is hapoptatic motility?
No particular direction to movement of the cell
182
What are the steps involved in cell motility?
1. Extension
2. Adhesion
3. Translocation
4 De-adhesion
183
What is G-actin?
Small soluble actin subunits
184
What is F-actin?
Large filamentous actin polymer
185
How does a cell change direction of motility in response to a signal such as a nutrient source?
1. Disassembly of filaments and rapid diffusion of subunits
| 2. Reassembly of filaments at a new site
186
What are stress fibres in a cell?
Bundles of antiparallel fibres that have contractile properties to move the cell
187
What are the different outcomes of remodelling G-actin?
- F-actin
- Sequestering
- Nucleating
188
What are the different outcomes of remodelling F-actin?
- G-actin
- Bundling
- Motor proteins
- Side-binding
- Capping
- Cross-linking
- Severing
189
What is the process of nucleation of actin?
1. ARP complex formed from Arp2, Arp3 and other proteins (minus end)
2. Actin monomers join on (two actin subunits wide) toward the plus end
Limiting step in actin dynamics - formation of trimers to initiate polymerisation
Becomes energetically favourable to polymerise
190
What is the process of elongation of actin?
Profilin competes with thymosin for binding to actin monomers and promotes assembly
Monomer binding:
- Profilin
Sequestering:
- β4-thymosin
- ADF/cofilin (do not inhibit polymerisation)
191
What proteins are involved in capping actin? What is the function of capping?
```
+ End:
- Cap Z
- Gelsolin
- Fragmin / severin
- End:
- Tropomodulin
- Arp complex
Capping controls the length of filaments
```
192
What is the function of severing actin filaments? What proteins are involved?
- In an unsevered population, actin filaments grow and shrink relatively slowly
- In severed populations, actin filaments grow and shrink more rapidly
Severing proteins:
- Gelsolin
- ADF/Cofilin
- Fragmin/severin
193
What proteins are involved in cross-linking and bundling of fibres?
- α-actinin (ladder rung H)
- fascin (H)
- fimbrin (H)
- filamin (V cross links perpendicular fibres)
- spectrin (α + β long links)
- dystrophin (actin to plasma membrane)
- villin
- vinculin
194
What angle does actin branch at? What is the branching protein?
70°
| Arp complex
195
What causes the gel-sol transition? (Rigid→Can flow)
Actin filament severing
196
Give examples of diseases caused by dysregulation of the actin cytoskeleton.
- High blood pressure
- Wiskott-Aldrich Syndrome- WAS (immunodeficiency, eczema, autoimmunity)
- Epidermolysis Bullosa (Hereditary blistering disease)
- Bullous Pemphigoid (autoimmune disease)
197
What types of actin remodelling are involved in the different stages of cell motility?
1. Extension
- Disassembly
- Nucleation
- Branching
- Severing
- Capping
- Bundling
- Polymerisation
2. Adhesion
- Gel/sol transition
- Attachment ECM
3. Translocation
- Contraction
4. De-adhesion
- Detachment
198
What types of actin remodelling are involved in lamellae protrusion?
- Polymerisation
- Disassembly
- Branching
- Capping
Net filament assembly at leading edge
Net filament disassembly behind leading edge
199
What types of actin remodelling are involved in filopodia?
- Actin polymerisation
- Bundling
- Crosslinking
Nucleate the filaments then fibres form which polymerise and grow
200
What are the signalling mechanisms that regulate the actin cytoskeleton?
1. Ion flux changes (i.e. intracellular calcium)
2. Phosphoinositide signalling (phospholipid binding)
3. Kinases/phosphatases (phosphorylation cytoskeletal proteins)
4. Signalling cascades via small GTPases
201
What are the best-known members of the Ras super-family? What activates these proteins?
- Rac
- Rho
- Cdc42
These proteins are examined by receptor tyrosine kinase, adhesion receptors and signal transduction pathways
Expression levels are upregulated in different human tumours
202
What does activation of Cdc42 stimulate?
Filopodia
203
What does activation of Rac stimulate?
Lamellipodia
204
What does activation of Rho stimulate?
Stress fibres
205
What small GTPases are involved in the different stages of cell migration?
1. Extension
- Rac (actin polymerisation; branching)
2. Adhesion
- Rac (focal adhesion assembly)
- Rho
3. Translocation
- Rho (stress fibres; tension; contraction)
4. De-adhesion
- Rho
206
What is the function of Cdc42 in cell motility?
- Filopodia
- Polarised moility
- Actin Polymerisation
207
Why do we need apoptosis?
- To remove harmful cells from the body (e.g. cells with viral infection or DNA damage)
- To remove developmentally defective cells (e.g. B-lymphocytes expressing antibodies against self antigen)
- To remove excess/unnecessary cells (e.g. eliminating excess neurons during brain development, sculpting of digits during limb development)
- To remove obsolete cells (e.g. mammary epithelium after lactation period)
208
What is necrosis? What is the sequence of events that occur during necrosis?
Unregulated cell death associated with trauma, cellular disruption and an inflammatory response
1. Plasma membrane becomes permeable
2. Cell swells and cellular membranes rupture
3. Proteases are released leading to autodigestion and cell dissolution
4. Localised inflammation
209
What is apoptosis? What is the sequence of events that occur in apoptosis?
Regulated/programmed cell death involving a controlled disassembly of cellular contents without disruption and no inflammation
1. Latent Phase: death pathways are activated, but cells appear morphologically the same
2. Execution phase
- Loss of microvilli, intercellular junctions and plasma membrane asymmetry (phosphatidylserine lipid appears in outer leaflet) → cell shrinkage
- Chromatin and nuclear condensation with DNA fragmentation
- Formation of membrane blebs and fragmentation into membrane-enclosed apoptotic bodies
The plasma membrane remains intact. Apoptotic bodies are then phagocytosed by neighbouring cells and roaming macrophages
210
What does DNA modification in apoptosis cause?
- Fragmentation of DNA ladders (seen in agarose gel)
| - Formation of more "ends" (which can be labelled fluorescently with TUNEL assay
211
What are the different types of programmed call death?
It is a graded response with features of both apoptosis and necrosis
- Apoptosis-like
- Necrosis-like
212
What is the role of caspases during apoptosis?
Cysteine-dependent aspartate-directed proteases are the executioners of apoptosis. They execute via a cascade activated by proteolysis
213
What are the different classes of caspases?
```
Effector caspases (3, 6 and 7)
- Similar molecular organisation.
- Start off as a single chain polypeptide with two subunits (large +small) that are released by proteolytic cleavage during maturation
Initiator caspases (2, 8, 9 and 10)
- Same pair of subunits
- Extra targeting subunit (protein-protein interacting domain) which directs them to a particular location
CARD (Caspase recruitment domain)
DED (Death effector domain)
```
214
How are procaspases activated?
Proteolytic cleavage to form a large and small subunit (as well as a targeting subunit in initiator caspases)
- Cleaved by the caspases themselves
- The protein then refolds into an active hetero-tetrameric caspase molecule
215
What is the caspase cascade?
Once apoptosis is initiated, the initiator caspases cleave and activate the effector caspases, which then go on to carry out the apoptotic programme in two ways:
- Cleaving and inactivating various proteins and complexes (e.g. nuclear lamins→nuclear breakdown)
- Activating enzymes by direct cleavage, or cleavage of inhibitor molecules (e.g. protein kinases and nucleus such as Caspase Activated DNase
216
What are the mechanisms of caspase activation?
Death by design
- Receptor mediated (extrinsic) pathways
Death by default
- Mitochondrial (intrinsic) pathways
217
What is the Death receptor and how is it activated in cell death?
An extracellular cysteine-rich domain, single transcellular domain and cytoplasmic tail with a "death domain"
Activated when it encounters secreted or transmembrane "death ligands" (e.g. TNF or Fas)
218
What are the adapter proteins and what is their function?
FADD
- Positive regulator (required for the death pathway to be activated)
- Promotes cell death
- Contains two domains: DED (death effector domain) and DD (death domain)
FLIP
- Negative regulator (inhibits the death pathway)
- Allows it to be regulated
- Contains two DED domains
219
What is the death receptor signalling pathway?
1. Death ligand binds to death receptor (i.e. Fas receptor is engaged by Fas ligand), which is present on the surface of cytotoxic T-lymphocytes
2. Death receptor undergoes trimerisation (process of bringing 3 receptors into closer proximity), which brings the 3 cytoplasmic death domains together
3. The trimerised death domains recruits the positive adaptor protein FADD by its own DD
4. The binding of FADD causes the recruitment and oligomerisation (proteolytic activation) of procaspase 8
5. Binding of caspase 8 (by its own DED) to the FADD protein leads to the formation of a DISC (death inducing signaling complex)
6. DISC formation results in cross-activation of procaspase 8, whereby they cleave each other within the complex (due to close proximity). The active caspase 8 is then released, and it cleaves effector caspases to execute the death programme.
220
What inhibits the death receptor activation of caspase 8?
FLIP
221
What causes death by default? (programmed cell death)
Mitochondrial regulation of apoptosis is the intrinsic pathway whereby cellular stresses (e.g. lack of/overstimulation by growth factors, DNA damage etc) cause a loss of mitochondrial membrane potential
This results in a release of cytochrome C and other apoptosis-inducing factors which stimulat the formation of the apoptosome complex
222
What is the apoptosome complex?
Contains APAF-1 (apoptotic activating factor 1), cytochrome C, ATP and procaspase 9
- At one end Apaf-1 contains a number of repeats that are involved in protein-protein interactions
- At the other end there is an ATPase domain
- At the fron there is a caspase recruitment domain (CARD) also found in some initiator caspases (e.g. caspase 9)
223
What is the apoptosome?
When cytochrome C binds to the WD-40 repeats on Apaf-1 it form a heptamer (apoptosome).
This requires ATP
- The CARD domains at the centre of the heptamer are capable of interacting with CARD domains on procaspase-9 (7 bind in total)
- The close proximity of the procaspase 9s mean they can cross-cleave and activate each other to produce caspase 9. This is released and is able to trigger the caspase cascade → apoptosis
224
How can you differentiate between the two apoptotic mechanisms? What mechanism brings these two pathways together?
- Mitochondrial-mediated pathway requires ATP
- Protein Bid brings accelerates the cell death process by bringing the two pathways together
- Bid can be cleaved by caspase 8. Once cleaves it can go to the mitochondria and promote the release of cytochrome C, therefore recruiting the mitochondrial-mediated pathway
225
What are the Bcl-2 family? What are the two categories within this family?
Intrinsic modulators of apoptosis
- Anti-apoptotic proteins: localised to the mitochondrial membrane, and inhibit apoptosis(e.g. Bcl-2 and Bcl-xL)
- Pro-apoptotic proteins: move between the cytosol and the mitochondrial membrane, promoting apoptosis (e.g. Bid, Bad and Bax
226
What does growth factor binding to the tyrosine kinase receptor cause?
Dimerisation and phosphorylation of the tyrosine kinase receptor
227
What does phosphorylation of the tyrosine kinase receptor cause?
Initiates signal transduction pathways, as well as creates docking sites for adaptor proteins (which can bind and mediate the protein-protein interactions within the pathways
- One of the docking sites is for adaptor protein Grb2, which mediates the Ras pathway
- Another site triggers the PI3-kinase pathway involved in cell survival and anti-apoptotic effects
228
What is PI3-K? What does it do?
Phosphatidylinositol 3-kinase is a lipid kinase involved in growth control and cell survival
- Has a targeting subunit, adaptor subunit and a catalytic subunit
- It phosphorylates PIP2→PIP3, which is recognised by the adapter subunit of protein kinase B (PKB/Akt)
- Akt is then recruited to the cell membrane and is activated, with anti-apoptotic effects
- Akt phosphorylates Bad which is then held in an inactive heterodimer in the cytoplasm along with other pro-apoptotic proteins (Bid and Bax) by the BH3 domains of the anti-apoptotic Bcl-2/xL proteins
- With the pro-apoptotic proteins held in inactive heterodimers, cell survival and proliferation are prompted
229
What stops Akt from functioning? What happens when this occurs?
- When growth factors are absent Akt fails to come to the cell membrane
- This means Bad is dephosphorylated and is released from it's heterodimer
- It then goes to the mitochondrial membrane, where it can bind through its own BH3 domain to the BH3 domains of the anti-apoptotic Bcl-2 family members and displace the pro-apoptotic Bcl-2 family members
- Once the pro-apoptotic family members are released from inhibition, they form a pore in the mitochondrial membrane, which allows cytochrome C to escape into the cytosol and induce apoptosis
230
What are the roles of Akt?
- Phosphorylates and inactivates Bad
- Phosphorylates and inactivates caspase 9 (initiator caspase)
- Inactivates FOXO transcription factors (FOXOs usually promote expression of apoptosis-promoting genes)
- Other effects include stimulation of protein synthesis (MAPK/ERK pathway)
231
What are the extrinsic regulators of programmed cell death?
PTEN- a lipid phosphatase that counteracts the production of Akt therefore reducing the regulation of cell survival and promoting apoptosis
IAPs (inhibitors of apoptosis proteins) regulate programmed cell death by binding to procaspases and preventing their activation, and binding to active caspases and inhibiting their activity
232
What role do tumour suppressors play in cancer?
Tumour suppressors promote apoptosis (e.g. PTEN). These are often deleted/inactivated in many cancers
233
What role do proto-oncogenes play in cancer?
Proto-oncogenes promote apoptosis
| Oncogenes inhibit apoptosis, and therefore are harmful. These are often overexpressed in cancers (e.g. Bcl-2 and Akt)
234
What is the cancer cell phenotype?
- Disregard of signals to stop proliferating
- Capacity for sustained proliferation
- Evasion of apoptosis
- Ability to invade
- Ability to promote angiogenesis
235
Give examples of proto-oncogenes.
- Myc
- Ras
- Erb
- Sis
236
What are the methods by which proto-oncogenes become carcinogenic?
- Mutation (point mutation of deletion)
- Gene amplification (Multiple gene copies)
- Chromosomal translocation (Chimaeric genes)
- Insertional mutagenesis (e.g. viral infection
237
What causes the proto-oncogene to become carcinogenic in Burkitt's lymphoma?
Chimaeric genes
| Chromosomal translocation
238
What is the Philadelphia Chromosome?
Chromosome 9 + 22 has two key areas:
- ABL region
- BCR region
In normal circumstances, replication occurs normally
Occassionally there is a chromosomal translocation, and ABL swaps over to chromosome 22. The result of the combination of BCR and ABL leads to cancer
239
How does mutant Ras have carcinogenic effects?
When bound to GTP, Ras is active and can phosphorylate Raf via kinase activity, then GTP is dephosphorylated to GDP. This passes a signal down the cascade and generates a signal for proliferation.
Once GTP is dephosphorylated and Ras is inactive.
Mutant Ras fails to dephosphorylate GTP and remains active
240
What is the role of tumour suppressor genes?
Regulate cellular proliferation and maintain cell integrity (e.g. retinal blastoma cell)
- Each cell has two copies of each tumour suppressor genes, therefore changes in one gene copy is usually insufficient to promote cancer
- Mutation or loss of both copies mean complete loss of control
241
What is retinoblastoma? What causes it?
Malignant cancer of developing retinal cells, which is due to either sporadic or hereditary disease
- Sporadic disease usually involving one eye
- Hereditary cases tend to be bilateral and multifocal
It is due to the mutation of the RB1 tumour suppressor gene on chromosome 13914
- RB1 encodes a nuclear protein that is involved in the regulation of the cell cycle
Present as a chalky eye, and treatment requires removal of the eye
242
What are the functions of tumour suppressor genes?
- Regulate cell proliferation
- Maintain cellular integrity
- Regulate cell growth
- Regulate the cell cycle
- Regulate nuclear transcription factors
- Involved in DNA repair proteins
- Cell adhesion molecules
- Cell death regulators
Effectively they suppress the neoplastic phenotype
243
What is the most common tumour suppressor gene involved in cancer?
p53
244
What is p53? What does it do?
A tumour suppressor gene which works in conjunction with MDM2 (when bound, p53 is inactive)
- p53 is involved in a wide range of activities, including regulating p53 target genes and protein-protein interactions
- Mutants act in a dominant manner therefore mutation of a single copy is sufficient to get dysregulation (this is because it forms a dimer)
245
What causes Familial Adenomatous Polyposis? What is FAP?
It results from a deletion in chromosome 5q21 which results in loss of APC gene. This gene is involved in cell adhesion and signalling
- Sufferers develop multiple benign adenomatous polyps of the colon, but there is a 90% risk of developing colorectal carcinoma following the development of polyps
- APC participates in the WNT signalling pathway to alter transcription and growth by helping to control activity of B-catenin thereby preventing uncontrolled growth
- Loss of APC results in hyperproliferation of the epithelium (loss of tumour suppressor function)
246
What method produces and carcinogenic oncogene and a tumour suppressor gene?
Oncogene: Specific translocations/point mutation
| Tumour suppressor gene: Deletions or mutations
247
Are oncogenes dominant or recessive? Are they hereditary?
Dominant at cell level
| Mutations rarely hereditary
248
Are tumour suppressor genes dominant or recessive? Are they hereditary?
Recessive at cell level
| Mutations can be inherited
249
What types of cancer are caused by oncogenes?
Leukaemia and lymphoma
250
What types of cancer are caused by tumour suppressor genes?
Solid tumours
251
Give examples of effects of insufficient angiogenesis.
- Baldness
- MI (Ischaemia)
- Limb fractures
- Thrombosis
252
Give examples of excessive angiogenesis.
- Retinal disease
- Cancers
- Atherosclerosis
- Obesity
253
What is the model of sprouting angiogenesis?
1. Selection of sprouting endothelial cells as a result of stimulation by growth factors and inhibitors (ECM degradation; lateral inhibition; change in polarity)
2. Sprout outgrowth and guidance (Invasive behaviour; maintenance of junctions, deposition of new ECM, EC proliferation)
3. Sprout fusion and lumen formation (Stalk-cell proliferation; vacuole formation and fusion; tip cells encountering repulsion and adhesion)
4. Perfusion and maturation (Stabilisation of EC-EC adhesion; stabilisation of PC contacts; ↓ EC proliferation; ↑ pro-quiescent signals)
254
What are the inhibitors of angiogenesis?
```
- Thrombospondin-1
The statins
- Angiostatin
- Endostatin
- Canstatin
- Tumstatin
```
255
What are the activators of angiogenesis?
- VEGFs
- FGFs
- PDGFB
- EGF
- LPA
256
In the presence of oxygen what stops angiogenesis from occurring?
HIF-α binds to pVHL and degrades in a proteasome.
257
Why does angiogenesis occur in the absence of oxygen?
No hydroxyproline so HIF-α does not bind to pVHL and instead binds to HIF-ß and causes transcription of hypoxia-inducible genes:
- VEGF
- PDGF-ß
- TGF-α
- EPO
258
What are the different members of the VEGF family?
```
VEGF-A
VEGF-B
VEGF-C
VEGF-D
PIGF (Placental growth factor)
```
259
What are the different tyrosine kinase receptors?
- VEGFR-1
- VEGFR-2
- VEGFR-3
Co-receptors:
- Nrp1
- Nrp2
(Neuropilin)
260
What receptor is the major mediator of VEGF-dependent angiogenesis? What does it do?
VEGFR-2
| Activates signalling pathways that regulate endothelial cell migration, survival and proliferation
261
What is the process of sprouting angiogenesis?
Specialised endothelial tip cells lead the outgrowth of blood-vessel sprouts towards gradients of VEGF
Tip cells selection is based on Notch signalling between adjacent endothelial cells at the angiogenic front
262
What is the Canonical Notch signalling pathway in angiogenesis?
- Notch receptors and ligands are membrane-bound proteins that associate through their extracellular domains
- Delta/jagged ligand on the tip cell binds to Notch receptor on stalk cells
- The intracellular domain of Notch (NICD) translocates to the nucleus and binds to the transcription factor RBP-J
263
What is the process of selection of tip cells in angiogenesis?
1. In stable blood vessels, Dll4 and Notch signalling maintain quiescence
2. VEGF activation increases expression of DII4
3. Dll4 drives Notch signalling, which inhibits expression of VEGFR2 in the adjacent cell
4. Dll4-expressing tip cells acquire a motile, invasive and sprouting phenotype
5. Adjacent cells (Stalk cells) form the base of the emerging sprout, proliferate to support sprout elongation
264
What is the role of macrophages in vessel anastomosis?
- Significant role in physiological and pathological angiogenesis
- Macrophages carve out tunnels in the ECM, providing avenues for subsequent capillary infiltration
- Tissue-resident macrophages were shown to be associated with angiogenic tip cells during anastomosis
265
What is the role of VE-cadherin in angiogenesis?
It is essential for vessel stabilisation and quiescence
- Constitutively expressed at junctions
- Homophilic interaction mediates adhesion between endothelial cells and intracellular signalling
- Controls contact inhibition of cell growth
- Promotes survival of EC
266
What cells help to stabilise neovessels?
Mural cells (progenitor cells)
- Smooth muscle cells stabilise arterioles
- Pericytes stabilise capillaries
267
What are the effects of Ang-1 and Ang-2 on the Tie2 receptor?
Angiopoietin-1 and Angiopoietin-2 are antagonistic ligands of the Tie2 receptor
- Ang-1 binding to Tie2 promotes vessel stability and inhibits inflammatory gene expression
- Ang-2 antagonises Ang-1 signalling, promotes vascular instability and VEGF-dependent angiogenesis
268
What is the sprouting angiogenesis summary?
1. Initiation
2. Selection
3. Tip-cell navigation
4. Stalk elongation
5. Fusion
6. Perfusion and oxygenation
7. Maturation and stabilisation
8. Quiescence
269
At what size do tumours require new vessels?
>1mm
270
How do tumours induce angiogenesis in the host?
Once a tumour grows larger than 1mm it requires a new vessel network.
Tumour secretes angiogenic factors that stimulate migration, proliferation and neovessel formation by endothelial cells in adjacent established vessels
Newly vascularised tumour no longer relies solely on diffusion from host vasculature fascilitating progressive growth
271
What is the angiogenic switch?
A discrete step in tumour development that can occur at different stages in the tumour-progression pathway, depending on the nature of the tumour and its microenvironment
272
What are the characteristics of tumour blood vessels?
- Irregularly shaped, dilated, tortuous
- Not organised into definitive venules, arterioles and capillaries
- Leaky and haemorrhagic, partly due to the overproduction of VEGF
- Perivascular cells often become loosely associated
- Some tumours may recruit endothelial progenitor cells from the bone marrow
273
What agents can target the VEGF pathway as a treatment option for cancer? Give examples
- Anti-VEGF antibodies (e.g. bevacizumab)
- Soluble VEGF receptors (e.g. VEGF-Trap)
- Anti-VEGFR antibodies (e.g. IMC-1121b)
- Small-molecule VEGFR inhibitors (e.g. vatalanib, sunitinib, ZD6474, AZD2171)
274
How does VEGFR1 (Flt-1) stop tumour growth?
Inhibits VEGF
- VEGFR1 binds to VEGF and "mops it up" preventing it from stimulating angiogenesis
- Flt-1 expression reduces tumour growth in vivo, without affecting tumour cell growth in vitro: effect on vasculature
275
What is Avastin? What are its uses in cancer?
Anti-VEGF humanised mouse antibody
(bevacizumab) used alone or with other drugs to treat:
- Cervical cancer: not gotten better with other treatment, has metastasized or recurred
- Colorectal cancer metastasized
- Glioblastoma: not gotten better with other treatment
- Non-small cell lung cancer: locally advanced, not suitable for surgery, metastasized or recurred
- Ovarian epithelial, fallopian tube, primary peritoneal cancer: recurred. For patients who do not respond to platinum chemotherapy
- Renal cell cancer: metastasized
276
What are the side effects and limitations of Avistin?
```
Side effects:
- GI perforation
- Hypertension
- Proteinuria
- Venous thrombosis
- Haemorrhage
- Wound healing complications
Limitations:
- No overall survival advantage over chemotherapy alone
- No quality-of-life or survival advantage
```
277
What are the strategies of anti-angiogenic therapies?
Anti-angiogenic therapy which normalises the vasculature:
- reduces hypoxia
- increase efficacy of conventional therapies
However, sustained/aggressive anti-angiogenic therapy may damage healthy vasculature leading to loss of vessels, creating vasculature resistant to further treatment and inadequate for delivery of oxygen/drugs.
278
What are the potential mechanisms of resistance to anti-VEGF therapy in cancer?
1. VEGF inhibition aggravates hypoxia increasing tumour's production of other angiogenic factors or increases tumour invasiveness
2. Tumour's vessels may be less sensitive due to vessel lining by tumour cells or endothelial cells derived from tumours etc
3. Tumour cells that recruit pericytes may be less responsive to VEGF therapy
279
What are the different ways in which tumours form blood vessels?
Angiogenesis:
- Tumour cells secrete factors to stimulate vessel growth
- Vessel growth into tumour mass
Vasculogenic Mimicry:
- Tumour cells organise themselves to form vessel-like channels
- Vessels hook up to channels within the tumour mass
280
What is Age-Related Macular Degeneration?
Abnormal growth of choroidal blood vessels
- "Leaky" vessels cause oedema
- Visual impairment
281
What is the "tumour-on-a-chip" platform?
The development of a microphysiological system that incorporates human cells in a 3D extracellular matrix (ECM), supported by perfused human microvessel
Incorporates tumour cells and vasculature to improve drug screening
- Can be used for drug screening
282
What can damage DNA?
```
Chemicals
- Dietary (40% of human cancers)
- Lifestyle (30% due to smoking)
- Environmental
- Occupational
- Medical (Iatrogenic)
- Endogenous
Radiation
- Ionizing
- Solar
- Cosmic
DNA damage can lead to mutation. Mutation may lead to cancer
```
283
What types of DNA damage are caused by carcinogens?
- DNA adducts and alkylation
- Base dimers and chemical cross-links
- Base hydroxylations and abasic sites formed
- Double and single strand breaks
Double strand breaks are the most dangerous and likely to cause cancer; single strand breaks are easier to repair
284
What are the phase I and phase II stages of metabolism?
Phase I
- Addition of functional groups
e.g. oxidations, reductions, hydrolysis
- mainly cytochrome P450-mediated
Phase II
- Conjugation of Phase I functional groups
e.g. sulphation, glucuronidation, acetylation, methylation, amino acid and glutathione conjugation
- Generates polar (water soluble) metabolites
285
What are polycyclic aromatic hydrocarbons?
- Common environmental pollutants
Formed from:
- combustion of fossil fuels
- combustion of tobacco
286
What is the two-step process of epoxidation of B[a]P?
1. Lipophylic material. In food and in the atomosphere. It is everywhere
2. Oxidised. Epoxide = very reactive
3. Detoxifes and produces a diol
4. Produces another epoxide with diol = VERY DNA DAMAGING. Spontaneously breaks off and get a charge around carbon- very reactive- reacts with DNA and RNA
5. Causes DNA adduction
287
What is the significance of Aflatoxin B₁ in cancer?
- Formed by Aspergillus flavus mould commonly on poorly stored grains and peanuts
- Aflatoxin B₁ is a potent human liver carcinogen, especially in Africa and Far-East (where they cannot afford to test for it)
288
How does solar (UV) radiation cause cancer?
Pyrimidines in DNA form dimers as a result of solar radiation. The dimer is a mutagenic lesion
Fair skin has a higher incidence of skin cancer
289
How does ionising radiation cause cancer?
- Generates free radicals in cells
- Includes oxygen free radicals
• Super oxide radical: O₂･
• Hydroxyl radical: HO･
- Possess unpaired electrons
• Electrophilic and therefore seek out electron-rich DNA
290
What effect do oxygen free radicals have on DNA?
```
Cause:
- Double and single strand breaks
- Apurinic and apyrimidinic sites
- Base modifications
• Ring-opened guanine and adenine
• Thymine and cytosine glycols
• 8-hydroxyadenine and 8-hydroxyguanine (mutagenic)
```
291
What enzyme system is most frequently involved in the activation of chemicalss to metabolites that can damage DNA?
Cytochrome P450
292
What are the different types of DNA repair?
1. Direct reversal of DNA damage
2. Base excision repair
3. Nucleotide excision repair
4. During- or post-replication repair
293
How is DNA repaired by direct reversal of DNA damage?
- Photolyase splits cyclobutant pyrimidine-dimers
| - Methyltransferases and alkyltransferases remove alkyl groups from bases
294
How is DNA repaired by base excision repair?
- DNA glycosylases and apurinic/apyrimidinic endonucleases and other enzyme partners
- A repair polymerases (e.g. Polβ) fills the gap and DNA ligase completes the repair
295
How is DNA repaired by nucleotide excision repair?
- Xeroderma pigmentosum proteins (XP proteins) assemble at the damage. A stretch of nucleotides either side of the damage are excised.
- Repair polymerases (e.g. Polδ/β) fill the gap and DNA ligase completes the repair
296
How is DNA repaired during- or post-replication?
- Mismatch repair
| - Recombinational repair
297
What are the two types of excision repair of DNA damage?
- Base excision repair pathway
| - Nucleotide excision repair pathway
298
What is the fate of carcinogenic damage to DNA?
1. Efficient repair → Normal cell
2. Apoptosis
3. Incorrect repair/altered primary sequence → DNA replication and cell division: fixed mutations
- Transcription/translation giving aberrant proteins
- Carcinogenesis if critical targets are mutated: oncogenes, tumour suppressor genes
299
What is the process of testing new drugs for possible DNA damage?
1. Structural alerts / SAR
2. In vitro BACTERIAL gene mutation assay e.g. Ames test with S. typhimurium
3. In vitro MAMMALIAN CELL assay e.g. chromosome aberration, TK mutation in mouse lymphoma cell Micronucleus assay
4. In vivo MAMMALIAN assay e.g. Bone marrow micronucleus test transgenic rodent mutation assay
5. Investigate in vivo MAMMALIAN assays
300
What is the Ames test? What is it used for?
Tests for mutagenicity of chemicals
Chemical to be tested
+ rat liver enzyme preparation (S9)
Conversion of chemical to reactive metabolite?
Bacteria that do not synthesise histidine e.g. Salmonella strain
On histadine-free media: if mutations occur in bacterial genome then bacteria acquire ability to synthesise histidine = colonies
301
What is the process and use of in vitro micronucleus assays?
- Cells treated with chemical and allowed to divide
- Cytokinesis blocked using cytochalasin-B
- Binucleate cells assessed for presence of micronuclei
- Can stain the kinetochore proteins to determine if chemical treatment caused clastgenicity (chromosomal breakage) or aneuploidy (chromosomal loss)
302
What is the use of a bone narrow micronucleus assay?
Treat animals with chemical and examine bone marrow cells or peripheral blood erythrocytes or micronuclei
303
Which of the following is involved in the repair of damaged DNA?
1. Mutation
2. Epoxidation
3. DNA adduction
4. Base excision repair
5. Sister chromatid exchange
4. Base excision repair
304
What factors contribute to the aetiology of colorectal cancer?
- Environmental (diet) factors
| - Genetic factors
305
What are the functions of the colon?
- Extraction of water from faeces (electrolyte balance)
- Faecal reservoir (evolutionary advantage)
- Bacterial digestion for vitamins (e.g. B and K)
306
What are the protective mechanisms that eliminate genetically defective cells in the colon?
- Natural loss
- DNA monitors
- Repair enzymes
307
What is a polyp?
Any projection from a mucosal surface into a hollow viscus and may be hyperplastic, neoplastic, inflammatory, hamartomatous etc
308
What is an adenoma?
A benign neoplasm of the mucosal epithelial cells
309
What are the different types of colonic polyp?
- Metaplastic/hyperplastic
- Adenomas
- Juvenile
- Peutz Jeghers
- Lipomas
- Others (essentially any circumscribed intramucosal lesions)
310
What are hyperplastic polyps?
- Very common
- <0.5cm
- 90% of all colon polyps
- Often multiple
- No malignant potential
- 15% have k-ras mutation
Microscopic: Individual glands show a typical serration of their mid-portion
311
What are the different types of colonic adenoma and their percentage occurrence?
```
- Tubular (>75% tubular)
90%
- Tubulovillous (25-50% villous)
10%
- Villous (>50% villous)
- (Flat)
- (Serrated)
```
312
What is the microscopic structure of adenomas?
Tubular
- Columnar cells with nuclear enlargement, elongation, multilayering and loss of polarity
- Increased proliferative activity
- Reduced differentiation
- Complexity/disorganisation of architecture
Villous
- Mucinous cells with nuclear enlargement, elongation, multilayering and loss of polarity
- Exophytic, frond-like extensions
- Rarely may have hypersecretory function and result in excess mucus discharge and hypokalaemia
313
What is dysplasia?
Literally 'Bad growth'
Abnormal growth of cells with some features of cancer
Subjective analysis
Indefinite low grade and high grade
314
What is APC?
Adenomatous Polyposis Coli (FAP)
- 5q21 gene mutation
- Site of mutation determines clinical variants (classic, attenuated, Gardner, Turcot)
- Many patients have prophylactic colectomy <30
315
Who is affected by Colonic Adenoma? What are the risks associated with this?
- 25% of adults have adenomas at age 50
- 5% of these become cancers if left
- Large polyps have higher risk than small ones (so 5% >1cm 50-60; 15% at 75)
- Cancers stay at a curable stage for 2 years
316
What is the progression from adenoma to carcinoma?
- Most colorectal cancers arise from adenomas
- Residual adenoma in 10-30% of colorectal cancers
- Adenomas and cancer have similar distribution
- Adenomas usually precede cancer by 15 years
- Endoscopic removal of polyps decreases the incidence of subsequent colorectal cancer
317
What are the genetic pathways associated with colorectal cancer?
- Adenoma carcinoma sequence
APC, Kras, Smads, p53, telomerase activation
- Microsatellite instability
Microsatellites are repeat sequences prone to misalignment. Some microsatellites are in coding sequences of genes which inhibits growth or apoptosis e.g. TGFbR11
Mismatch repair genes (MSH2, MLH1 + 4 others). Recessive genes requiring 2 hits.
HNPCC-germline mutation in these genes
318
What are the two main pathways involved in the genetic predisposition of colorectal cancer?
Two main pathways:
- FAP - inactivation of APC tumour suppressor genes
- HNPCC - microsatellite instability
319
Describe the prevalence of colonic carcinoma?
- 35000 cases per year in the UK
- 10% of cancer related deaths
- Ages range 50-80. Sporadic rare <30
- High in U.S., Eastern Europe, Australia
- Low in Japan, Mexico and Africa
- Dietary Factors: High fat, low fibre, high red meat, refined carbohydrates
320
What foods are though to increase the risk of colorectal cancer?
- Food containing 5-10k bioactive chemicals
- Food containing carcinogens
- It also containing anticancer agents
- Heat modifies chemicals further
- Bacterial modifies food residues
321
How does cooking food at high temperatures contribute to carcinogenesis?
```
Heterocyclic amines
PhIP
↓oxidation
N-OH-PhIP
+
Deoxyguanosine
↓
Mutagenesis
```
322
What dietary deficiencies contribute to colorectal cancer?
- Folates
Coenzyme for nucleotide synthesis and DNA methylation
- MTHFR
Deficiency leads to disruption in DNA synthesis causing DNA instability (strand breaks and uracil incorporation) → mutations
Decreased methionine synthesis leads to genomic hypomethylation and focal hypermethylation → gene activation and silencing
323
What are the anticancer food elements?
- Vitamin C - ROS scavenger
- Vitamin E - ROS scavenger
- Isothiocyanates (cruciferous veg)
- Polyphenols (green tea, fruit juice)
Activate MAPK
↓
Regulates phase2 detoxifying enzymes as well as other genes (e.g. glut-S transferase) and reduce DNA oxidation
Other mechanisms:
- Garlic associated apoptosis (ajoene, allicin)
- Green tea
EGCG-induced telomerase activity
324
What is the clinical presentation of colorectal cancer?
- Change in bowel habit
- Bleeding PR
- Unexplained Fe deficiency anaemia
Also:
- Mucus PR
- Bloating
- Cramps ('colic')
- Constitutional (weight loss, fatigue)
325
What are the macroscopic features of colorectal cancer?
Small carcinomas may be present within larger polypoid adenomas, pedunculated or sessile
326
What is the distribution of colorectal cancer?
- Caecum/ascending colon 22%
- Transverse colon 11%
- Descending colon 6%
- Rectosigmoid 55%
327
What are the microscopic features of carcinomas?
- Adenocarcinomas Grade 1-3
- Mucinous carcinomas
- Signet ring cell
- Neuroendocrine
328
What is grading?
Proportion of gland differentiation relative to solid areas or nests and cords of cells without lumina
~10% well differentiated
~70% moderately differentiated
~20% poorly differentiated
329
What clinical features affect prognosis?
```
Improved prognosis:
- Diagnosis in asymptomatic patients
- Rectal bleeding as presenting symptom
Diminished prognosis:
- Bowel obstruction/perforation
- Age <30
- Preoperative serum CEA (High)
- Distant metastases (Severe)
Colon better than rectum OR
Left colon better than right
- Tumour location
```
330
What pathological features affect prognosis?
```
Diminished prognosis:
- Increased depth of bowel wall penetration
- Mucinous (colloid) or signer ring cell
- Venous invasion
- Lymphatic invasion
- Perineural invasion
- 1-4 nodes better than >4 nodes
Improved prognosis
- Local inflammation and immunologic reaction
Well > poorly differentiated
- Degree of differentiation
```
331
What are the treatment options for the different grades of colorectal cancer?
I: Surgery
II: Surgery + 5FU
III: Surgery + 5FU/Leucovorin
IV: Surgery + Metastectomy + Chemo + Palliative RT
332
Who is screened as high risk for colon cancer?
- Previous adenoma
- 1st degree relative affected by colorectal cancer before the age of 45
- 2 affected first degree relatives
- Evidence of dominant familial cancer trait including colorectal, uterine and other cancers
- UC and Crohn's disease
- Hereditable cancer families (include other sites)
333
What is the population screening programme for colon cancer?
Faecal Occult Blood (FOB)
Positives referred for:
60-75 years- colonoscopy
55-60 years- sigmoidoscopy
334
What is population screening?
The practice of investigating apparently healthy individuals with the object of detecting unrecognised disease or people with an exceptionally high risk of developing disease, and of intervening in ways that will prevent the occurrence of disease or improve the prognosis when it develops
335
A 76 year old man presents with new onset rectal bleeding to the GP. What must be excluded in the first instance?
Colorectal malignancy
336
What are many colorectal cancers derived from?
Adenomas
337
What is stated in a report on a polyp?
1. High or low grade dysplasia
2. Is there also invasive cancer
3. Is it completely excised
338
What differentiates adenocarcinoma from carcinoma?
In adenocarcinoma there is no invasion into the muscularis mucosae
339
What is TNM grading of colorectal cancer?
T1- Tumour in the lamina propria (inner lining)
T2- Tumour invades into the muscularis interna
T3- Tumour invades through the muscularis externa
T4- Tumour invades into surrounding tissue
340
What are the different grades of colorectal cancer?
- Well/moderately differentiated
| - Poorly differentiated
341
What is more important, stage or grade?
Stage
342
What are the different types of breast carcinoma in situ?
- Ductal carcinoma in situ
- Lobular carcinoma in situ
In situ = noninvasive
343
How is breast cancer T staged?
Based purely on size
T1: <2cm
T2: 2-5cm
T3: >5cm
344
When are lymph nodes removed in breast cancer?
A few removed to sample and check for invasion
| If there is invasion more would be removed
345
What are the common types of skin cancer?
1. Malignant melanoma
2. Papilloma (squamous, benign, from warts)
3. Basal cell carcinoma (derived from sweat glands)
4. Squamous cell carcinoma
346
How are non-melanoma skin cancers staged?
Based on size and invasion into underlying tissue
347
What is the most common cancer in men and women aged 15-24?
Blood cancers
348
What is leukaemia?
"White blood"
| Bone marrow disease and not all patient have abnormal cells in the blood
349
What causes leukaemia?
Results from a series of mutations in a single lymphoid or myeloid stem cell
These mutations lead the progeny of that cell to show abnormalities in proliferation, differentiation or cell survival leading to steady expansion of the leukaemic clone
350
How is leukaemia different from other cancer?
Most cancer exist as a solid tumour, however, it is uncommon for patients with leukaemia to have tumours. More often they have leukaemic cells replacing normal bone marrow cells and circulating freely in the blood stream
351
What are benign and malignant leukaemias?
```
Benign = chronic
Malignant = acute
```
352
What cells are affected in lymphoid leukaemia?
B or T cell lineage
353
What cells are affected in meyloid leukaemia?
Any combination of granulocytic, monocytic, erythroid or megakaryocytic cell
354
What are the different types of leukaemia?
- Acute lymphoblastic leukaemia
- Acute myeloid leukaemia
- Chronic lymphocytic leukaemia
- Chronic myeloid leukaemia
355
What mutations have been recognised to cause leukaemia? What else increases the risk of leukaemia?
- Mutation in a known proto-oncogene
- Creation of a novel gene, e.g. a chimaeric or fusion gene
- Dysregulation of a gene when translocation bring it under the influence of the promoter or enhancer of another gene
- Loss of function of a tumour-suppressor gene (resulting from a deletion or mutation of the gene)
- Tendency to increased chromosomal breaks
- If the cell cannot repair DNA normally
- Inherited or other constitutional abnormalities can contribute to leukaemogenesis (e.g. Down's syndrome, chromosomal fragility syndromes, defects in DNA repair, inherited defects of tumour-suppressor genes)
356
What causes leukaemogenic mutations?
- Irradiation
- Anti-cancer drugs
- Cigarette smoking
- Chemicals (benzene)
357
What is the difference between acute and chronic myeloid leukaemia?
In AML cells continue to proliferate but they no longer mature so there is:
- A build up of myeloblasts (blast cells) in the bone marrow with spread into the blood
- A failure of production of normal functioning end cells such as neutrophils, monocytes, arythrocytes, platelets
In CML the responsible mutations usually affect a gene encoding a protein in the signalling pathway between a cell surface receptor and the nucleus
The protein encoded may be either a membrane or a cytoplasmic protein
358
In AML what is normally affected by mutation?
Mutations usually affect transcription factors so that the transcription of multiple genes is affected
359
What happens to affected cells in CML?
Cell kinetics and function are not as seriously affected as in AML
However, the cell becomes independent of external signals, there are alterations in the interaction with stroma and there is reduced apoptosis so that cells survive longer and the leukaemic clone expands progressively
360
What happens to production of cells in AML and CML?
AML: Failure of production of end cells
CML: Increased production of end cells
361
What is the difference between acute and chronic lymphoid leukaemias?
ALL: Increase in very immature cells (lymphoblasts) with a failure of these to develop into mature T and B cells
CLL: the leukaemic cells are mature, although abnormal, T cells or B cells
362
How does leukaemia cause the disease characteristics?
Accumulation of abnormal cells leading to:
- Leucocytosis
- Bone pain (if leukaemia is acute)
- Hepatomegaly
- Splenomegaly
- Lymphadenopathy (if lymphoid)
- Thymic enlargement (is T lymphoid)
- Skin infiltration
363
What are the metabolic effects of leukaemic cell proliferation?
- Hyperuricaemia
- Renal failure
- Weight loss
- Low grade fever
- Sweating
364
What are the effects of crowding of normal cells in leukaemia?
- Anaemia
- Neutropenia
- Thrombocytopenia
365
What happens to immune function in CLL?
Loss of normal immune function as a result of loss of normal T cell and B cell function
366
Who is most affected by ALL?
Children
367
What is thought to cause some leukaemias in infants and young children?
- Irradiation in utero
- In utero exposure to certain chemicals
- Epsteine-Barr viruc infection
Rarely ALL results from exposure to a mutagenic drug
368
What is thought to cause B-lineage ALL?
Delayed exposure to a common pathogen or, conversely, that early exposure to pathogens protects
369
What are the clinical features of ALL?
Resulting from an accumulation of abnormal cells
- Bone pain
- Hepatomegaly
- Splenomegaly
- Lymphadenopathy
- Thymic enlargement
- Testicular enlargement
Resulting from crowding out of normal cells
- Fatugue, lethargy, pallor, breathlessness (caused by anaemia)
- Fever and other features of infection (caused by neutropenia)
- Bruising, petechiae, bleeding (caused by thrombocytopenia)
370
What are the haematological features of ALL?
- Leucocytosis with lymphoblasts in the bloos
- Anaemia (normocytic, normochromic)
- Neutropenia
- Thrombocytopenia
- Replacement of normal bone marrow cells by lymphoblasts
371
What investigations are conducted into ALL?
- Blood count and film
- Check of liver and renal function and uric acid
- Bone marrow aspirate
- Cytogenetic/molecular analysis
- Chest X-ray
372
What is the use of cytogenetic and molecular genetic analysis in ALL?
Useful for managing the individual patient because it gives information about prognosis
Hyperdiploidy: good prognosis
t(4;11): poor prognosis
373
What are the leukaemiogenic mechanisms of ALL?
- Formation of a fusion gene (caused by translocation)
- Dysregulation of a proto-oncogene by juxtaposition of it to the promoter of another gene, e.g. a T-cell receptor gene
- Point mutation in a proto-oncogene
374
What causes production of ETV6-RUNX1 fusion gene? How is it detected?
t(12;21)(p12;q22)
Detected using FISH (Fluorescence in situ hybridization)
ETV6 = green probe
RUNX1 = red probe
ETV6-RUNX1 = yellow
375
What is the treatment for ALL?
```
Supportive
- Red cells
- Platelets
- Antibiotics
Systemic chemotherapy
Intrathecal chemotherapy
```
376
What is happenings to mortality rates from cancer in high- and low-income countries
Cancer rates are decreasing in high-income countries but not in low-income countries
377
What is happening to the total cancer burden?
It is increasing due to demographic changes (ageing populations, increasing size) and Westernization of lifestyles
378
What is cancer incidence related to?
- Age
- Common environmental causes
- Geographical variation and secular trends
379
What are the well-defined risk factors for cancer?
- Smoking
- Diet
- Alcohol consumption
380
What is the leading female cancer?
Breast cancer
| 1 in 5 cancer deaths among women
381
Why are cancer deaths are decreasing?
- Early diagnosis
- Chemo/radiotherapies
- Hormonal therapies
382
What is the cellular organisation of the mammary gland?
```
Inner layer (luminal epithelial cells) which produce milk and grow in response to hormones (during menstrual cycle/pregnancy)- some of these cells are slightly vacuolated
Outer layer (myoepithelial cells) which have the ability to contract in response to hormones
```
383
How do pathology labs test for oestrogen sensitivity of breast cancer tumours?
Immunohistochemical staining using antibodies against the Human Oestrogen Receptor (ER)
Scored by the lab: 0, weak, medium, high expression
384
What percentage of breast cancers are oestrogen receptor positive?
80%
385
What is the mechanism of the oestrogen receptor?
Activated by binding oestrogen (steroid hormone- lipophilic- gets across membrane easily)
Nuclear receptor = transcription factor. Gene expression is induced by binding to specific DnA sequences called Oestrogen Response Elements
Displaces hsp90 and allows oestrogen to bind forming a dimer
This translocates to the nucleus and induces transcription factor
386
What important genes are regulated by oestrogen?
- Progesterone receptor (PR) (differentiation in the mammary gland - makes these cells also susceptible to progesterone as well as oestrogen)
- Cyclin D1 (important regulator of the cell cycle)
- C-myc (cell's ability to survive)
- TGF-α
387
How does the oestrogen receptor contribute to breast cancer?
The oestrogen-induced gene products increase cell proliferation, resulting in breast cancer
388
How is oestrogen used to treat breast cancer?
⅓ of premenopausal women with advanced breast cancer will respond to oophorectomy
Breast cancer in postmenopausal women responds to high-dose therapy with synthetic oestrogens (chronic stimulation causes the tumour to stop responding = tumour regression)
ER is overexpressed in around 70% if cancers (oestrogen regulated the expression of genes involved in cellular proliferation leading to breast cancer
389
What is the role os surgery in breast cancer?
Alone it has a very high curative index
390
How is endocrine therapy achieved?
- Ovarian suppression
- Blocking oestrogen production by enzymatic inhibition
- Inhibiting oestrogen responses
391
Where are oestrogens produced in the body?
- Ovary (main source of oestrogen biosynthesis)
| - Some produced from androgens (from adrenals) being peripherally converted to oestrogens
392
How is ovarian ablation conducted? What are the major problems with this and how are they overcome?
- Surgical oophorectomy
- Ovarian irradiation
Major problems associated with this are morbidity and irreversibility
To overcome these issues treatments to produce medical ovarian ablation have been developed
393
What drugs induce reversible and reliable medical ovarian ablation? How do they work? Give examples
Luteinising Hormone Releasing Hormone (LHRH) agonists
LHRH agonsists bind to LHRH receptors in the pituitary leading to receptor down-regulation and suppression of LH release and inhibition of ovarian function, including oestrogen production
e.g. Goserelin, Buserelin, Leuprolide, Triptorelin
394
What are the targets for breast cancer treatment?
- LHRH agonists (target LH release- useful in premenopausal women)
- Antioestrogens
- Aromatase inhibitors (Useful in postmenopausal women who have low circulating oestrogen because aromatisation occurs at peripheral sites)
395
What is the mechanism of Tamoxifen? What is it's use and side effects?
Anti-oestrogen
- Competitive inhibitor of oestradiol binding to the ER
- Negates the stimulatory effect of oestrogen by blocking the ER, causing the cell to be held at the G1 phase of the cell cycle
- Endocrine treatment of choice for metastatic disease in postmenopausal patients (approximately ⅓ patients respond)
Few side effects reported- hot flushes (29%) most commonly reported during Tamoxifen therapy
396
What are the advantages and disadvantages of SERMs? Give an example
Tamoxifen
Advantages
- Osteoporosis- common post menopause. Tamoxifen has oestrogenic effects in the bone
- Atherosclerosis- oestrogen lowers LDL cholesterol and raises HDL. Tamoxifen has oestrogenic effects in the CVS
Disadvantages
- Links to thromboembolic effects
- Causes endometrial thickening, hyperplasia and fibroids following years of therapy
397
What drugs have been derived from Tamoxifen? Describe them.
- Toremifene: Structural derivative of tamoxifen with similar antioestrogenic and oestrogenic properties
ICI 182,780: No oestrogen-like effects but does control oestrogen-stimulated growth
Raloxifene (Evista)- Anti-tumour agent in animals. Agonist in bone, no activity in breast and uterus. Used for osteoporosis in post-menopausal women
398
What is the role of Tamoxifen in breast cancer prevention?
Reduces the incidence of contralateral breast cancer by ⅓. Clinical trials focussed on high-risk patients:
- Previous benign breast cancer pathology (5 years)
- Previous family history
38% reduction in overall breast cancer incidence
399
What problems are associated with using Tamoxifen in breast cancer prevention? How are these problems overcome?
- Increase incidence of endometrial cancer
- Stroke
- DVT
- Cataracts
Prevention trials are being conducted with:
- Raloxifene/Faslodex (SERM)
- Aromatase Inhibitors
400
How is oestrogen blocked by enzymatic inhibition? When is this treatment utilised?
Aromatase inhibitors
In postmenopausal women the major source of oestrogens are from the conversion of adrenal hormones
- This enzymatic conversion occurs at extra-adrenal or peripheral sites such as fat, liver and muscle
- This conversion is catalysed by the aromatase enzyme complex
401
What is aromatase? How is it involved in breast cancer?
Aromatase consists of a complex containing a cytochrome P450 heme containing protein and flavoprotein NADPH cytochrome P450 reductase
- It catalyses 3 separate steroid hydroxylations involved in the conversion of androstenedione to estrone
- Aromatase can metabolise androsteindione, which is produced by the adrenal glands. This leads to the production of Estrone Sulphate, which is circulated in the plasma
402
What are the different types of aromatase inhibitors used to treat breast carcinoma? Describe the action of each inhibitor. Give examples
Type 1: Mechanism-based, or suicide, inhibitors
- Competes with natural substrate for enzyme binding
- Enzyme then acts on inhibitor to produce a reactive alkylating species which form covalent bonds at or near the enzyme active site
- IRREVERSIBLE
e.g. Exemestane- S.E. mild- hot flushes, nausea and fatigue
Type 2: Competitive inhibitors
- Binds to the active site and prevents product formation
- Only as long as the inhibitor occupies the catalytic site
- REVERSIBLE
e.g. Anastrozole
403
What is the use of progestins in breast cancer?
Progesterone is the dominant naturally occurring progestin
- Complex response- influences both proliferation and differentiation
- Used in the endocrine treatment of uterine and breast cancer with clinically proven antineoplastic properties
- Second or third line therapy for metastatic breast cancer following oestrogen
- Principle progestin: Megestrol acetate
404
What are the clinical problems associated with endocrine therapy treatment of breast cancer? What is the solution?
- Initial response but eventual relapse
- Relapse due to resistance during prolonged endocrine therapy
- NOT due to tumours becoming ER-independent
- Recent data shows that resistant tumours have mutated ER
Solution:
- Continue to use endocrine therapies as these are successful
- But, require additional therapeutic agents/strategies for endocrine resistant, metastatic disease
405
What are the risk factors for breast cancer?
Risk factors- Exposure to oestrogen
- Early age of onset of menarche
- Late age of menopause
- Age at first full-term pregnancy
- Some forms of the contraceptive pill
- Hormone replacement therapy
- Obesity
- Diet, physical activity, height, medication (Aspirin)
406
What is the screening programme for breast cancer?
- Mammography for all women 50-64 (being extended to 70) once every 3 years
- 70% of women attend
407
What types of skin cancer are derived from keratinocytes?
- Basal cell carcinoma
| - Squamous cell carcinoma (e.g. non-melanoma skin cancer)
408
What types of skin cancer are derived from melanocytes?
Malignant melanomas
409
What types of skin cancer are derived from vasculature?
- Kaposi's sarcoma
| - Angiosarcoma
410
What types of skin cancer are derived from lymphocytes?
Mycosis fungoides
411
What are the potential causes of skin cancer?
```
Genetic syndromes
- Gorlin's syndrome (defect in PTCH gene)
- xeroderma pigmentosum (defect in DNA repair)
Viral infections
- HHV8 in Kaposi's sarcoma
- HPV in SCC
UV light
- BCC
- SCC
- malignant melanoma
Immunosuppression
- drugs
- HIV
- old age
- leukaemia
```
412
What is the presentation of malignant melanoma?
- Pigmented
- Irregular border
- Irregular pigmentation
- Characteristic of skin cancer
- Particularly in the South West of England
413
What is the most common cause of skin cancer?
Basal cell carcinoma
414
What is the presentation of basal cell carcinoma?
- Pearly
| - Dilated vessels on the surface
415
What type of UV light causes skin cancer?
- UVB is more significant in skin carcinogenesis even though 100 times more UVA reaches the surface of the earth.
- UVA also has an effect on skin carcinogenesis but to a lesser extent than UVB
- UVA is the major cause of skin ageing
- UVA is used therapeutically to treat psoriasis
416
How does UVB light cause skin cancer?
- UVB directly induces abnormalities in DNA (e.g. mutations)
- UVB induces photoproducts (mutations)
- Affects C and T; usually repaired quickly by nucleotide excision repair
- Causes cross-linking of thymine dimers
417
How does UVA light cause skin cancer?
- DNA forms pyramidine dimers but less efficiently than UVB
| - Free radicals which damage DNA and cell membrane
418
UV damage to DNA leads to mutations in which genes?
- Cell division
- DNA repair
- Cell cycle arrest
419
How is UV induced DNA damage repaired?
- Photoproducts are removed by a process called nucleotide excision repair
- Xeroderma pigmentosum
Genetic condition with defective nucleotide excision repair
420
What mutations cause skin cancer?
1. Mutations that stimulate uncontrolled cell proliferation
e. g. abolishing control of the normal cell cycle (p53 gene)
2. Mutations that alter responses to growth stimulating / repressing factors
3. Mutations that inhibit programmed cell death (apoptosis)
421
What is sunburn?
Rapid accumulation of mutations in DNA leading to keratinocyte cell apoptosis
- Apoptosis removes UV damaged cells in the skin which might otherwise become cancer cells
422
What are the immunomodulatory effects of UV light?
UVA and UVB effect the expression of genes involved in skin immunity
- Depletes Langerhans cells in the epidermis
Reduced skin immunocompetence and immunosurveillance
- Basis for UV phototherapy for e.g. psoriasis
Further increases the cancer causing potential of sun exposure
Sunlight dampens down effects of Langerhans cells which decrease immune system in skin making it more prone to cancer
423
What are the Fitzpatrick Phototypes?
I - Always burns, never tans
II - Usually burns, sometimes tans
III - Sometimes burns, usually tans
IV - Never burns, always tans
V - Moderate constitutive pigmentation - Asian
VI - Marked constitutive pigmentation - Afrocaribbean
424
What are the dendritic cells within the epidermis?
Melanocytes
| They interdigitate with around 20 cells
425
What are the different types of melanin? How is it produced?
- Eumelanin: brown or black (produced in blonde, brown or black haired people)
- Phaeomelanin: yellowish or reddish brown (produced in ginger people)
Melanin is formed from tyrosine via a series of enzymes
426
What causes differences in hair colour and skin types?
MCR1 gene
- >20 gene polymorphism
- Variation in eumelanin:phaeomelanin produced
(Also dictates skin sensitivity to UV damage)
427
What is a malignant melanoma? What are the causes and risks?
Malignant tumour of melanocytes
- Melanocytes become abnormal
- Atypical cells and architecture
Caused by:
- UV exposure
- Genetic factors
Risks of metastasis
428
What is Lentigo Maligna?
```
Melanoma in situ
Proliferation of malignant melanocytes within the epidermis (does not pass through the BM)
No risk of metastasis
- Irregular shape
- Flat
- Light and dark brown colours
- Size usually >2cm
- Commonly on the face
```
429
What is a Superficial spreading malignant melanoma?
- Lateral proliferation of malignant melanocytes
- Invades basement membrane
- Risk of metestasis
430
How do you diagnose superficial spreading malignant melanoma?
```
ABCD rule:
Asymmetry
Border irregularity
Colour variation (dark brown-black: colour important indicator severity)
Diameter >0.7mm and increasing
Erythema
```
431
What is a nodular malignant melanoma?
- Vertical proliferation of malignant melanocytes (no previous horizontal growth)
- Risk of metastasis
- Can be weepy and ulcerative
432
What can arise with a superficial spreading melanoma?
Nodular melanoma arising within a superficial spreading melanoma
- Downward proliferation of malignant melanocytes
- Following previous horizontal growth
- Nodule developing within irregular plaque
- Prognosis will become worse
433
What melanoma occurs on the hands and feet?
Acral lentiginous melanoma
434
What is an amelanotic melanoma?
No longer produces melanin- usually diagnosed on removal
435
What are the different types of malignant melanoma?
- Superficial spreading
- Nodular
- Lentigo maligna melanoma
- Acral lentiginous
- Amelanotic
436
What is Breslow thickness?
Measurement from granular layer to bottom of a melanoma- indicates the prognosis
437
What are the main risk factors for the development of melanoma?
- Family history of dysplastic nevi or melanoma
- UV irradiation
- Sunburns during childhood
- Intermittent burning exposure in unacclimatized fair skin
- Atypial/dysplastic nevus syndrome
- Personal history of melanoma
- Skin type I or II
438
What is squamous cell carcinoma? What are the causes and risks?
```
Malignant tumour of keratinocytes
Occurs more commonly:
- On the lips
- Men with sticking out ears
- Women on the legs
```
```
Caused by:
- UV exposure
- HPV
- Immunosuppression
- May occur in scars or scarring processes
Risk of metastasis
```
439
What is basal cell carcinoma? What are the causes?
Malignant tumour arising from basal layer of epidermis
- Slow growing
- Invades tissue but does not metastasis
- Common on face
Caused by:
- Sun exposure
- Genetics
440
What is mycosis fungoides?
Not a fungal infection
Lymphoma specifically affecting the skin
Skin have their own population of lymphocytes
441
What is Kaposi's sarcoma? What is it associated with?
Tumour of endothelial cells of the lymphatics
442
What is epidermodysplasia veruciformis?
- Rare autosomal recessive condition
- Predisposition to HPV induced warts and SCCS
(genetic)
443
What test is carried out on blood samples to detect prostate cancer? What does this detect?
PSA test
Damage to the prostate result in PSA (prostate specific antigen) which is normally secreted and joins seminal fluid, but is prevented from entering the body via any other route by the basement membrane.
444
What is the Gleason Pattern for grading of prostate cancer?
1. Small, uniform glands
2. More stroma between glands
3. Distinctly infiltrative margins
4. Irregular masses of neoplastic glands
5. Only occasional gland formation
The two largest areas of tumour are found and scored and the two scores are quoted plus theis sum
__ + __ , __
2-4 considered low grade
5-7 intermediate
8-10 high
445
Why is hormone therapy used to treat prostate cancer?
- Can be the best form of treatment for some prostate cancer patients, due to the possibility of the tumour remaining latent for the patients lifespan
- In patients over 70 "watchful waiting/active observation" in low grade tumours is the favoured approach
446
When is radical prostatectomy used in prostate cancer?
Only effective for tumours confined to the prostate gland and has reported side-effects of incontinence and/or impotence in the majority of people who undergo the operation due to the proximity of nerves controlling these functions
447
What is the mechanisms of the prostate cancer treatment leuprolide and flutamide?
The prostate is an androgen dependent gland
Responds to:
Testosterone
Dihydrotestosterone (3x more potent)
Androgens (5x less potent)
Leuprolide is an GnRH receptor agonist on the pituitary; stimulates release of LH
- It is very potent with a high affinity
- Initially stimulates LH release, but eventually causes downregulation of the receptor
Flutamide is an androgen receptor antagonist which stops the action of the weak androgens circulating from the adrenals and testes
448
If a patient with prostate cancer is being treated with anti-androgen treatment what mechanism could cause recurrence of the disease?
Mutations can occur in the tumour, causing them to respond to other ligands, such as oestrogens or even the anti-oestrogens
