Cancer Flashcards
1
Q
What is metaplasia?
A
A reversible change in which one adult cell type (usually epithelial) is replace by another adult cell type
- Adaptive
2
Q
What is dysplasia?
A
- An abnormal pattern of growth in which some of the cellular and architectural features of malignancy are present
3
Q
How does dysplasia appear?
A
- Loss of architectural orientation
- Loss in uniformity of individual cells
4
Q
How do nuclei appear in dysplasia?
A
Hyperchromatic
Enlarged
5
Q
How do mitotic figures appear in dysplasia?
A
Abundant
Abnormal
In places where they are not usually found
6
Q
Where is dysplasia common?
A
- Cervix- HPV infection
- Bronchus- Smoking
- Colon- UC
- Larynx- Smoking
- Stomach - Pernicious anaemia
- Oesophagus- acid reflux
7
Q
What is neoplasia/tumour/malignancy?
A
An abnormal autonomous proliferation of cells unresponsive to normal growth control mechanisms
8
Q
How do benign tumours differ from malignant tumours?
A
1) Do not invade/ do not metastasise
2) Encapsulated
3) Usually well differentiated
4) Slowly growin
5) Normal mitoses
9
Q
When can benign tumours be fatal?
A
1) When in a dangerous place e.g. meninges, pituitary
2) Secretes something dangerous: insulinoma
3) Gets infected: bladder
4) Bleeds: stomach
5) Ruptures: liver adenoma
6) Torts (twisted): ovarian cyst
10
Q
What are the characteristics of a malignant tumour?
A
1) Invade surrounding tissues
2) Spread to distant sites
3) No capsule
4) Well to poorly differentiated
5) Rapidly growing
6) Abnormal mitoses
11
Q
What is a metastasis?
A
A discontinuous growing colony of tumour cells, at some distance from the primary cancer
12
Q
What does a metastasis depend on?
A
The lymphatic and vascular drainage of the primary site
13
Q
What is a benign tumour of the surface epithelium?
A
Papilloma
e.g. skin, bladder
14
Q
What is a benign tumour of the glandular epithelium?
A
Adenoma
e.g. stomach, thyroid, colon, kidney, pituitary, pancreas
15
Q
What is a carcinoma?
A
Malignant tumour derived from epithelium
16
Q
What are the different types of carcinomas?
A
- Squamous cell
- Adenocarcinoma
- Transitional cell
- Basal cell carcinoma
17
Q
What is a sarcoma?
A
A malignant tumour derived from connective tissue (mesenchymal) cells
18
Q
What are the different types of sarcomas?
A
Fat= liposarcoma Bone= osteosarcoma Cartilage= chondrosarcoma Muscle striated= rhabdomyosarcoma Muscle smooth= leiomyosarcoma Nerve sheath= malignant peripheral nerve sheath tumour
19
Q
What are the tumours of white blood cells?
A
Leukaemia
Lymphoma
20
Q
What is leukaemia?
A
A malignant tumour of bone marrow derived cells which circulate in the blood
21
Q
What is lymphoma?
A
A malignant tumour of lymphocytes (usually) in lymph nodes
22
Q
What is teratoma?
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
23
Q
How do gonadal teratomas differ in males and females?
A
Males= all malignant Females= most are benign
24
Q
What is hamartoma?
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
25
What is the criteria for assessing differentiation of a malignant tumour?
- Evidence of normal function still present production of keratin, mucin, bile and hormones
- Various grading systems, for Ca breast, prostate colon
- There is no differentiation for anaplastic carcinoma
26
What does the grade of a tumour describe?
Its degree of differentiation
27
What does the stage of tumour describe?
How far it has spread
28
What is more important (stage or grade) when determining prognosis?
Stage is more important.
29
What does the rate of cell division depend on?
1) Embryonic vs adult cells
2) Complexity of system
3) Necessity of renewal
4) State of differentiation (some cells never divide i.e. neurons)
5) Presence of tumour cells
30
Why is appropriate regulation cell division important?
- Premature, aberrant mitosis results in cells death
- In addition to mutations in oncogenes and tumour suppressor genes, most solid tumours are aneuploid
- Various cancer cell lines show chromosome instability
- Perturbation of protein levels of cell cycle regulators is found in different tumours
- Contact inhibition of growth
- Attacking the machinery that regulates chromosome segregation is one of the most successful anti-cancer strategies n clinical use
31
What is the cell cycle?
Orderly sequence of events in which a cell duplicates its contents and divides in two
32
What is the order of the eukaryotic cell cycle?
```
M phase
Interphase
G0
G1
S
G2
```
33
What occurs during the M phase?
Mitosis
- Nuclear division
- Cell division (cytokinesis)
34
What occurs during interphase
Duplication
- DNA
- Organelles
- Protein synthesis
35
Why is mitosis the most vulnerable period of the cell cycle?
- Cells are more easily killed (irradiation, heat shock, chemicals)
- DNA damage can not be repaired
- Gene transcription is silenced
36
What occurs during the S phase?
Replication for division
- DNA replication
- Protein synthesis: initiation of translation and elongation increased; capacity is also increased
- Replication of organelles (centrosome, mitochondria, Golgi, etc)
In the case of mitochondria, this needs to coordinate with the replication of mitochondrial DNA
37
What is the centrosome?
- Consists of two centrioles (barrels of nine triplet microtubules)
- Functions: microtubule organising center (MTOC) and mitotic spindle
38
What are the six different phases of mitosis?
```
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis
```
39
What occurs during prophase?
- Replicated chromosome condense to avoid breaking
- Duplicated centrosomes migrate to opposite sides of the nucleus and organise the assembly of spindle microtubules
- Outside the nucleus, the mitotic spindle assembles between the two centrosomes
40
What does each condensed chromosome consist of?
2 sister chromatids, each with a kinetochore
41
How does the mitotic spindle form?
- Radial microtubule arrays (ASTERS) form around each centrosome (microtubule organising centres MTOC)
- Radial arrays meet
- Polar microtubules form
- Microtubules are in a dynamic state
42
What occurs during early prometaphase?
- Breakdown of the nuclear membrane
- Spindle formation is largely complete
- Attachment of the chromosome to spindle via kinetochores (centromere region of chromosome)
43
What occurs during 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
44
What occurs during metaphase?
The attached chromosome have undergone active movement and are lined up at the midline of the spindle.
The kinetochores of each sister chromatid are attached to opposite poles of the spindle
45
What occurs during anaphase?
- Paired chromatids separate to form two daughter chromosomes
- Cohesin holds sister chromatids together
- Consists of Anaphase A and B
46
What occurs during anaphase A?
- Breakdown cohesin
- Microtubules get shorter
- Daughter chromosome pulled toward opposite spindle poles
47
What occurs during anaphase B
1) Daughter chromosomes migrate towards poles
| 2) Spindle poles (centrosomes) migrate apart
48
What occurs during telophase?
- Daughter chromosome arrive at the spindle
- Nuclear envelope reassembles at each pole
- Assembly of contractile ring
49
What is cytokinesis?
The stage where the cytoplasm is divided into two daughter cells by the contractile ring of actin and myosin filaments.
Each daughter cell now has its own nucleus
50
What is the Spindle- assembly checkpoint?
Controls the transition out of metaphase into anaphase by sensing completion of chromosome alignment and spindle assembly.
- Achieved by monitoring kinetochore activity
- Requirements for this include CENP-E and BUB protein kinases
- BUBs dissociate when chromosomes are properly attaches to the spindle
- When all has dissociated, anaphase proceeds
51
What is aneuploidy?
Abnormal number of chromosomes
52
What are the different ways in which aneuploidy can be caused?
1) Mis-attachment of spindle to kinetochores
2) Aberrant mitosis
3) Anti-cancer therapy
53
What are the types of attachment of the spindle to kinetochores?
Amphelic attachment= normal: kinetochores do not produce a checkpoint signal
Merotelic attachment= spindle attachment from the same centrosome to both kinetochores
Monotelic attachment= movement of both pairs of chromatids to the same pole
Synthelic attachment= movement of both pairs of chromatids to the same pole, but in this case they are attached to different spindles
54
Why does merotelic attachment have negative consequences?
Results in aneuploidy
- Kinetochores won't produce a checkpoint signal which indicates something is wrong
- There is a loss of a chromosome at cytokinesis
55
Why can synthelic attachment result in aneuploidy?
Both sister chromatids are at the same pole
| - These sister chromatids are likely to break and their kinetochores may or may not produce checkpoint signals
56
Why does aberrant mitosis result in aneuploidy?
Results in 4 instead of 2 centrosomes being produced
| - This leads to a multi-polar spindle with abnormal cytokinesis following. This results in 4 daughter cells
57
Why can anti-cancer therapy induce aneuploidy?
- Drugs have been developed to induce chromosome mis-segregation with the aim of this to lead to apoptosis of the cancer cell
- This is achieved by either inhibiting attachment-error-correction mechanisms, or inhibiting checkpoint protein kinases
58
Give examples of anti-cancer therapies that can result in aneuploidy
- Taxanes and vinca alkaloids
- Used in breast and ovarian cancers
- Produces unattached kinetochores
- Causes long-term mitotic arrest
59
What might happen if something goes wrong during the cell cycle?
1) Cell cycle arrest
- At check points (G1 and spindle check point)
- Can be temporary, allowing time for DNA repair
2) Programmed cell death (apoptosis)
- DNA damage too great and cannot be repaired
- Chromosome abnormalities
- Toxic agents
60
What is the G1/S checkpoint influenced by?
Growth factors
61
What is the G2/M checkpoint influenced by?
DNA damage
62
What is the Metaphase checkpoint influenced by?
Sister chromatid alignment
63
During the cell cycle, what occurs in the absence of stimulus?
The cells go into G0 (quiescent phase)
- This is how most differentiated cells in the body exist where they are able to perform specific functions without dividing
64
What does exit from the G0 phase require?
- Is highly regulated
- Requires growth factors and intracellular signalling cascades
- This does not happen in tumour cells
65
How are signalling cascades activated?
In response to extracellular ligands that bind to cell surface receptors and trigger an intracellular signal
66
What happens to the intracellular signal that is triggered by a signalling cascade?
- Amplified
- Integrated
- Modified by other pathways before diverging to have effects on metabolism, gene expression and the cytoplasm
67
Give an example of an intracellular signalling cascade
EGF (epidermal growth factor) and PDGF (platelet-derived growth factor) attach to their respective receptors (receptor protein tyrosine kinase)
- These are found in a monomeric, inactive state
68
During a signalling cascade, what happens in the presence of a ligand?
- Receptors form dimers
| - Are activated by phosphorylation of amino acid residues in the kinase domain
69
During a signalling cascade, how does phosphorylation to activate receptors occur?
Via the transfer of phosphate from ATP to a hydroxyl group on serine, threonine and tyrosine.
70
During a signalling cascade when the receptor is activated, how does the added phosphate group alter protein function?
- The phosphate group is negatively charged
- It causes a change in conformation leading to a change in activity (+ve or -ve)
- Creating a docking site for another protein
71
During a signalling cascade, what does activation of a receptor result in?
- Intracellular kinase cascade mediated by adaptor proteins which bind to the newly created docking site
72
What do protein kinase cascades result in?
Lead to signal amplification, diversification and opportunity for regulation
73
Why are their protein kinase cascades?
Frequently the protein regulated by a kinase is another kinase, and so on
74
How can protein kinase cascades be reversed?
By phosphatases
75
How long does G1 last?
10 hours
76
How long does the S phase last?
9 hours
77
How long does G2 last?
4 hours
78
Which stages are interphase?
G1
G0
G2
79
What is c-Myc?
A transcription factor which stimulates the expression of cell cycle genes
- Has an important role in G1
80
What are they key components of signalling pathways?
1) Regulation of enzyme activity by protein phosphorylation (kinases)
2) Adapter proteins
3) Regulation by GTP-binding proteins
81
How does growth factor stimulate signalling pathways?
Mitogenic growth factor -> Receptor protein tyrosine kinase -> Small G (GTP-binding) protein (Ras) -> Kinase cascade -> Immediate early genes- control the expression of other genes
82
What does the first 15 minutes of growth factor stimulation of signalling pathways consist of?
- The mitogenic growth factor binding to the cell surface receptor protein tyrosine kinase
- Phosphorylation of RTPK initiates the kinase cascade which provides additional docking sites and activates Ras
83
What does the Ras binding stimulate?
Stimulates and mediates early-response gene expression from the MAPK/ERK cascade e.g. c-Myc expression
84
What does the last hour of growth factor stimulation of signalling pathways involve?
Stimulation of expression of delayed-response genes which leads to the activation of the cell-cycle control system
85
What happens following phosphorylation of receptor protein tyrosine kinase?
Additional docking sites are formed.
| Adapter proteins such as Grb2 dock to the phosphorylated site
86
What happens when Grb2 binds to the phosphorylated site?
Recruits inactive Ras protein to the cytosolic surface of the plasma membrane. The inactive Ras protein is associated with a GDP molecule.
87
How do Ras-activating proteins activate Ras?
Using exchange factor Sos, which exchanges a phosphate from a GTP molecule associate with the Ras-activating protein for the GDP molecule associated with Ras
88
How is Ras deactivated?
G-proteins act as a molecular switch, turning Ras off.
| They do this through GTP hydrolysis using GTPase activating proteins (GAP)
89
How is Ras oncogenically activated?
Mutations that increase the amount of active GTP-loaded Ras.
| The mutations either prevent GAP binding or prevent GTP hydrolysis.
90
What does Ras activate one it is in its active GTP-loaded form?
Protein kinase cascade.
Specifically= Extracellular signal-regulated kinase (ERK) cascade
Gernerically= Mitogen-activated protein kinase (MAPK) cascades
91
What are the generic and specific names of the protein kinase cascde
```
Kinase I-
Generic name: MAP-KKK
Specific: Raf
Kinase 2-
Generic name: MAP-KK
Specific: MEK
Kinase 3-
Generic name: MAP-K
Specific: ERK
```
92
What does ERK go on to stimulate?
Changes in cell protein and gene expression (eg c-Myc) in order to promote cell division
93
What do mutated Ras and c-Myc act as?
Oncogenes
| Lead to uncontrolled cell division and tumour proliferation
94
What is cell cycle control based on?
Cyclin-dependent kinases (Cdks)
| - They are present in proliferating cells throughout the cell cycle
95
How is the activity of cyclin-dependent kinases (Cdks) regulated?
- Through their interaction with cyclins
| - Their phosphorylation
96
What are cyclins?
- Proteins which activate Cdks
- Transiently expressed at specific points in the cell cycle
- Level of expression if highly regulated
- They are synthesised and then degraded
- Form cyclin-Cdk complexes of which different complexes trigger different events in the cell cycle
97
What are the different cyclin-Cdk complexes which trigger different events in the cell cycle?
S phase: Cdk2/Cyclin A
Mitosis: Cdk1/Cyclin B
G1 progression: Cdk2/Cyclin E
98
What types of genes are activated by the Ras-ERK pathway?
c-jun, c-fos, c-myc encoding transcription factors
99
How does mitotic cyclin B interact with Cdk1?
They form a complex which acts as the mitosis promoting factor (MPF)
100
How is the mitosis promoting factor (MPF) activated?
Requires activating phosphorylation using CAK (cdk activating kinase)
- As well as removal of the inactivating phosphorylation by inhibitory kinase - Wee1
101
What determines whether the mitosis promoting factor becomes activated?
The balance between CAK and Wee1
102
Why is mitosis promoting factor activated at the end of interphase?
WEE1 is removed at the end of interphase using CDC25 phosphatase.
- There is positive feedback
103
How does mitosis progress?
Cdk1/cycB active- then mitosis is on hold and the key substrates are phosphorylated.
A signal from fully attached kinetochores causes cyclin B to be degraded
- Cdk1 inactivated
- Key substrates dephosphorylated
- Mitosis progresses
104
How does growth factor stimulation of signalling pathways promote G0 to G1 transition?
c-Myc is an immediate early gene transcription factor.
| - c-Myc stimulates transcription of cyclin D which is required for re-entry into the cell cycle from G0
105
How does Cyclin D stimulate progression from G1 into the S phase?
Cyclin D activate cdk4 and cdk6 which stimulates cyclin E production which is required for the cell cycle to progress
106
What is the purpose of Cdks
Sequentially activated by cyclins and stimulate the synthesis of genes required for the next phase
e.g. CycD/Cdk4/6 stimulates the expression of CycE
- This gives direction and timing to the cycle
107
How Cdks work?
They phosphorylate proteins (or Serine or threonine) to drive cell cycle progression
108
What do MPF target?
Nuclear lamins.
| The phosphorylation of which causes the breakdown of the nuclear envelope
109
What does Cdk4/6- Cyclin D target?
Retinoblastoma protein
The phosphorylation of which inactivates the protein
Releases E2F transcription factor, driving gene transcription of Cyclin E and allowing the progression of the cell cycle from G1 > S phase
110
How can the Cdk5/6-cyclin D complex have negative effects.
```
Retinoplastoma protein (pRB) is a tumour supressor which acts as a break on the cell cycle until it receives the signal from the Cdk4/6-Cyclin D complex
- Is the tumor suppressor is lost, uncontrolled cell division may occur
```
111
How Cdk inhibitors (CKIs) regulate Cdks
Inhibit them to prevent progression through the cell cycle, which is important in ensuring the integrity of the cell cycle is maintained
112
What are the two familiess of CDk inhibitors (CKIs)
INK4
| CIP/KIP
113
How does the INK4 family inhibit Cdks
Inhibits Cdk4/6 by displacing cyc D
| - Arrest G1 at the restriction checkpoint
114
How does the CIP/KIp family inhibt Cdks
Inhibits all Cdks especially in the S phase
| - Does this by binding to the Cdk/cyc complex
115
What codes for INK4?
p16
116
What codes for CIP/KIP?
p27
117
How can problems with Cdk inhibitors result in cancers?
- Loss of INK4 inhibition
- Over-production of cdk4/cyclin D
- Loss of retinoblastoma protein (highly prevalent in lung cancer)
118
How can cell cycle regulatory proteins lead to cancer and act as oncogenes?
- EGFR/HER2= mutationally activated or over-expressed in many breast cancers
- Ras= mutationally activated in many cancers
- Cyclin D1
- B-Raf
- c-Myc
119
Why may Ras lead to cancer?
When mutationally activated.
| They are inhibitors of membrane attachment
120
Which tumour suppressors and cell cycle regulatory proteins are inactivated in cancer?
Rb
| p27KIP1
121
What are the types of genetic mutations that cause cancer?
- Chromosome translocation
- Gene translocation
- Gene amplification (copy number variation)
- Point mutations within promotor or enhancer regions of genes
- Deletions or insertions
- Epigenetic alterations to gene expression
- Can be inherited
122
What are the components of cytotoxic chemotherapy?
1) Alkylating agents
2) Antimetabolites
3) Anthracyclines
4) Vinca alkaloids and taxanes
5) Topoisomerase inhibitors
123
How is cytotoxic chemotherapy administered?
- Given intravenously or by mouth
- 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 palliative intent
124
How do alkylating agents act in cytotoxic chemotherapy?
- Add alkyl groups to guanine residues in DNA
- Cross-link DNA strands and prevent DNA from uncoiling at replication
- Trigger apoptosis (at checkpoint pathway
- Encourage miss-pairing- oncogenic
125
What are pseudo-alkylating agents?
- Add platinum to guanine residues in DNA
- Same mechanism of cell death as alkylating agents
E.G. Carboplatin, cisplatin, oxaliplatin
126
Give examples of alkylating agents
Chlorambucil
Cycophosphamide
Dacarbazine
Temozolomide
127
What are the side effects of alkylating and pseudoalkylating agents?
- Cause hair loss ( not carboplatin)
- Nephrotoxicity
- Neurotoxicity
- Ototoxicity (platinums)
- Nausea
- Vomiting
- Diarrhoea
- Immunosuppression
- Tiredness
128
How do anti-metabolites act in cytotoxic chemotherapy?
Masquerade as purine or pyrimidine residues leading to inhibition of DNA synthesis, DNA double strand breaks and apoptosis
- Block DNA replication and transcription
- Can be purine (adenine and guanine), pyrimidine or folate antagonists
- Examples= methrorextate (folate), 6-mercaptopurine, carbazine and fludarabine
129
What are the side effects of anti-metabolites?
- Hair loss (alopecia): not 5FU or capecitabine
- Bone marrow suppression causing anaemia, neutropenia and thrombocytopenia
- Increased risk or neutropenic sepsis (and death) or bleeding
- Nausea and vomiting (dehydration)
- Mucositis and diarrhoea
- Palamar-plantar erthrodysethesia (PPE)
- Fatigue
130
How do anthracyclines work in cytotoxic chemotherapy?
- 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
- E.g. doxorubicin, epirubicin
131
What are the side effects of anthracyclines?
- Cardiac toxicity (arrhythmias, heart failure)
- Alopecia
- Neutropenia
- Nausea and vomiting
- Fatigue
- Skin changes
- Red urine
132
How do vinca alkaloids and taxanes work in cytotoxic chemotherapy?
Inhibit assembly (vinca alkaloids or disassembly (taxanes) of mitotic microtubules causing dividing cells to undergo mitotic arrest
133
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
134
How do topoisomerase inhibitors work in cytotoxic chemotherapy?
- Topoisomerases are required to prevent DNA torsional strain during DNA replication and transcription
- 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 anthacyclines have anti-toposomerase effects through their action on DNA
- Specific topoisomerase inhibitors include Tpotecan and irinotecan (topo I) and etoposide (topo II) alter binding of the complex to DNA and allow permanent DNA breaks)
135
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, vomiting
- Fatigue
- Bone marrow suppression
136
How can a resistant cell survive?
- Drug effluxed from the cell by ATP-binding cassette (ABC) transporters
- DNA adducts replaced by Base Excision repair (using PARP)
- DNA repair mechanisms are up-regulated and DNA damage is repaired so the DNA double strand does not break
137
What are the ten hallmarks of a cancer cell?
1) Self-sufficient
2) Insensitive to anti-growth signals
3) Anti-apoptoctic
4) Pro-invasive and metastatic
5) Pro-angiogenic
6) Non-senscent
7) Dysregulated metabolism
8) Evades the immune system
9) Unstable DNA
10) Inflammation
138
What receptors are over-expressed in cancers?
HER2: amplified and over-expressed in 25% breast cancer
EGFR: over-expressed in breast cancer and colorectal cancer
PDGFR: glioma (brain cancer
139
What ligands are over-expressed in cancers?
VEGF: prostate cancer, kidney cancer, breast cancer
140
What are the different monoclonal antibodies?
- momab ( derived from mouse antibodies)
- ximab (chimeric) e.g. cetumixab
- zumab (humanised) e.g. bevacizumab, trastuzumab
- mumab (fully human) e.g. panitumumab
141
What do monoclonal antibodies target?
The extracellular component of the receptor
- They neutralise the ligand
- Prevent receptor dimerisation
- Cause internalisation of receptor
- mAbs also activate Fcy-receptor-dependent phagocytosis or cytolysis induced complement-dependent cytotoxicity (CDC) or antibody-dependent cellular cytotoxicity (ADCC)
142
Which monoclonal antibodies are used in oncology?
- Bevacizumab binds and neutralises VEGF. Improves survival colorectal cancer
- Cetuximab targets EGFR
143
What is the mechanism of small molecule inhibitors (SMIs)?
Bind to the kinase domain of the tyrosine kinase within the cytoplasm and block autophosphorylation and downstream signalling
- Also act on intracellular kinases therefore can affect cell signalling pathways
144
What is Glivec?
A small molecule inhibitor that targets the ATP binding region within the kinase domain
145
Give examples of SMIs inhibiting receptors
Erlotinib (EGFR)
Gefitinib (EGFR)
Lapatinib (EGFR/HER2)
Sorafinib (VEGFR)
146
Give examples of SMIs inhibiting intracellular kinases
Sorafinib (Raf kinase)
Dasatinib (Src kinase)
Torcinib (mTOR inhibitors)
147
What are the advantages of SMIs
- Can target TKs without an extracellular domain or which are constitutively activated (ligand independent)
- Pleiotropic tagets (useful in heterogenic tumours/cross talk)
- Oral administration
- Good tissue penetration
- Cheap
148
What is a disadvantage of SMIs and monoclonal antibodies?
Resistance
149
What are the different resistance mechanisms to targeted therapies?
- Mutations in ATP-binding domain (e.g. BCR-Abl fusion genes 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
150
What are 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
151
What is cell behaviour?
The term used to describe the way cells interact with their external environment and their reactions to this, particularly proliferative and motile responses of cells
152
What external influences are detected by cells?
- Chemical: hormones, growth factors, ion concentrations, ECM, molecules on other cells, nutrients and dissolve gas (O2/CO2) cells
- Physical: mechanical stresses, temperature, the topography or layout of the ECM and other cells
153
What is cell-spreading dependent on?
Gravity dependent
| Energy is required to modulate cell adhesion and the cytoskeleton during spreading
154
What is the importance of cell- ECM adhesion?
- In suspension, cells do not significantly synthesise protein or DNA
- Cells require to be attached to ECM (and a degree of spreading is required) to begin protein synthesis and proliferation (DNA synthesis)
- Attachment to ECM may be required for survival (e.g. epithelia, endothelia)
- i.e. anchorage dependence
155
What are cell-ECM adhesion molecules?
- Cells have receptors on their cell surface which bind specifically to ECM molecules
- These molecules are often linked at their cytoplasmic domains, to the cytoskeleton
- This arrangement means that there is mechanical continuity between ECM and the cell interior
156
What are integrins?
Heterodimer complexes of alpha and beta subunits that associate extracellularly by their ‘head’ regions. Each of the ‘tail’ regions spans the plasma membrane.
- Recognise short, specific, peptide sequences
- More than 20 combinations of alpha/beta known
- Each combination specifically binds a particular peptide sequence
- Such peptide sequences found in more than one ECM molecule e.g. RGD found in fibronectin, virtonectin, fibrinogen plus others
- Linked via actin binding proteins to the actin cytoskeleton
157
What do integrin complexes cluster to form?
Focal adhesions
Hemidesmosome (alpha6Beta4- linked to the cytokeratin network)
- These clusters are involved in signal transduction
- Integrins also bind to specific adhesion molecules to some cells
158
How can ECM receptors (e.g. integrins) act to transduce signals?
- ECM binding to an integrin complex can stimulate the complex to produce a signals inside the cell i.e. ‘outside-in’ integrin signalling
- A signal generated inside the cell can act on an integrin complex to alter the affinity of an integrin i.e. inside out integrin signalling (e.g. in inflammation or blood-clotting, switching on adhesion of circulating leukocytes
159
What is outside- in signalling
- 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
160
Describe the density-dependence of cell division
- When cells in culture form a confluent monolayer, they cease proliferating and slow down many other metabolic activities.
This used to be known as contact inhibition of cell division
- Another set of experiments have now suggested that it is competition for external growth factors and not cell-cell contact responsible. This is known as the density dependence of cell division.
161
What is the ERK MAP kinase Cascade?
- The pathway by which growth factors induce gene expression and cell proliferation is known as the ERK MAP kinase cascade
- The signal starts when a growth factor binds to the receptor on the cell surface and ends when the DNA in the nucleus expresses a protein and produces some change in the cell, such as cell division.
- The proteins included are MAPK which communicate by adding phosphate groups to a neighbouring protein- acts as an on or off switch
- The extracellular growth factor binds to the membrane ligand. This allows Ras to swap its GDP for a GTP. It can now activate MAP3K, which activates MAP2K which activates MAPK. MAPK can now activate a transcription factor, such as myc
162
What is proliferation dependent on?
Density (e.g. growth factor)
| Anchorage (e.g. ECM)
163
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
164
What are the types of contact interactions between cells?
Short term: transient interactions between cells which do not form stable cell-cell junctions
Long-term: stable interactions resulting in formation of cell-cell junctions
165
What is the cell-cell contact between non-epithelial cells?
- Contact inhibition of locomotion
- When non-epithelial cells collide they do not form stable cell-cell contacts
- They repel one another by paralysing motility at the contact site, promoting the formation of a motile front at another at another site on the cell and moving off in the opposite direction
- The contact inhibition of locomotion is responsible for preventing multilayering of cells in culture and in vivo
166
What are the long-term cell-cell contacts?
- Upon contact, some cell types strongly adhere and form specific cell-cell junctions (adherens junctions, desmosomes, tight junctions, gap junctions)
- This is true of epithelial cells and endothelial cells, which form layers and neurones forming synapses
167
How are cell-cell junctions arranged in epithelia?
As continuous belts (zonula) or as discrete spots (macula)
168
What causes contact-induced spreading of epithelial cells?
Contact between epithelial cells leads to the mutation induction of spreading.
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
169
How does cell-cell adhesion affect cell proliferation?
The formation of cell-cell junctions occurs when the MAP Kinase pathway is active, there is increase p27kIP1. It results in low proliferation
170
Give examples of SMIs inhibiting receptors
Erlotinib (EGFR)
Gefitinib (EGFR)
Lapatinib (EGFR/HER2)
Sorafinib (VEGFR)
171
Give examples of SMIs inhibiting intracellular kinases
Sorafinib (Raf kinase)
Dasatinib (Src kinase)
Torcinib (mTOR inhibitors)
172
What are the advantages of monoclonal antibodies?
- High target specificity
- Cause ADCC, complement mediated cytotoxicity and apoptosis infuction
- Can be radiolabelled
- Cause target receptor internalisation
- Long half-life (lower dosing frequency)
- Good for haematological malignancies
- Liked by regulatory authorities (FDA)
173
What external factors can influence cell division?
Growth factors, cell-cell adhesion and cell-ECM adhesion
174
How are adherens junctions mediated?
- By cadherins
- Molecules that span the plasma membrane and associated with identical molecules on adjacent cells
- Cadherin in the transmembrane homophilic cell adhesion molecule (Ca++ dependent) that associated with beta-catenin intracellular
- Beta-catenin then associates with an alpha-catenin molecule which associates with an actin filament
175
Is Beta-catenin the link between cell-cell adhesion and proliferation?
- When bound to cadherin, Beta-catenin is not available for LEF-1 binding
- In adenomatous polyposis coli (APC), the ATP gene-product is involved in the degradation of the junction-associated molecule beta-catenin
- Results in an overgrowth of the colon epithelium which results in thousands of polyps
176
What are the dynamics of beta-catenin?
- APC part of a complex that phosphorylates Beta-catenin. When it does so, it targets it for degradation. If beta-catenin hangs around in the cytoplasm, it gets targeted with LEF-1, goes into the nucleus and switches on proliferation
177
What is the mechanism for contact inhibition of proliferation?
- When bound to cadherin at the membrane, beta catenin is not available for LEF-1 binding and nuclear effects
- Normally, cytoplasmic beta-catenin rapidly degraded
- If beta-catenin cytoplasmic levels rise as a result of inhibition of degradation or loss of cadherin-mediated adhesion, beta-catenin/lef-1 complex enters nucleus and influences gene expression, leading to proliferation
178
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
179
In what ways can cells lose their social skills?
- Proliferate uncontrollably (lose density dependence of proliferation)
- Are less adherant and will multilayer (lose contact inhibition of locomotion and anchorage dependence)
- Epithelia breakdown cell-cell contacts
- Not Hayflick limited, express telomerase i.e. cancer
180
What is the mechanism of short-circuiting leading to uncontrolled proliferation?
- If a 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 mechanism arises as a result of loss of growth factor dependence
181
What oncogene?
Mutant gene with promotes uncontrolled cell proliferation
182
What is a proto-oncogene?
Normal cellular gene corresponding to the oncogene
183
What proportion of cancers is Ras mutated in?
30%
184
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 metalloproteinase (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
185
What molecular mechanisms regulate motility?
- Microfilaments
- Regulation of actin dynamics
- Cytoskeletal proteins
- Signalling proteins
186
What are the steps in tumours progression?
1) Homeostasis
2) Genetic alterations
3) Hyper-proliferation
4) De-differentiation
- Disassembly cell-cell contacts
- Loss polarity
5) Invasion
- Increased motility
- Cleavage ECM proteins
187
What acts as stimuli for cells to move?
- Organogenesis and morphogenesis
- Wounding
- Growth factors/chemoattractants
- Dedifferentiation (tumours)
188
Where does a cell go when it is stimulated to move?
It changes shape to achieve polarity and will therefore have a directionality to the movement
189
When does the cell know when to stop moving and how to move?
When to stop: contact-inhibition motility
| How to move: specialised structures (focal adhesion, lamellae, filopodium)
190
How does the cell attach to ECM proteins
- Attachment to substratum is important for cell movements
- Focal adhesions are sites at which the cell attaches to proteins which make the ECM
- Filamentous actin lies beneath the membrane, it hooks the focal adhesions to the cytoskeletons via integrins
- Integrins interact with various cytoskeletal proteins to form a plaque on the intracellular side
191
What are filopodia?
Finger like protrusions that are rich in actin
- Structures used for cell motility
- Protrude from the cell to sense where they want to attach and direction of movement
- Vinuncilin is the protein that overlies these protrusions
192
What are lamellipodia?
Sheet like protrusions that are rich in actin filaments
- Structures used for motility
- Attach to the substratum and when they move back, the structures are called ruffles
193
Why is control of cell movement needed?
- Within a cell to coordinate what is happening in different parts
- Regulate adhesion/release of cell-extracellular matrix receptors
- From outside to respond to external influences
194
What are the different types of motility?
Hapoptatic: movement with no direction
Chemotactic: movement in which the cell senses a stimulus and goes towards it
195
How do cells regulate their shape changes by regulating their actin cytoskeleton?
- Actin can be found as small soluble globular monomers (G-actin) or in a large polymerised filamentous polymer (F-actin)
- If there is a signal like a nutrient source at one end of the cell the F-actin at the other end will disassemble and the subunits will diffuse tot he side with the signal. There is reassembly of the subunits at the new site and this facilitates movement
196
How does the arrangement of actin filaments allow a variety of structure to be made?
Lamellipodium: has branched and crosslinked filaments
Filopodium: bundle of parallel filaments
Stress fibers: has antiparallel arrangement which forms contractile bundles
197
What is the purpose of the motor proteins and in the remodelling of actin filaments?
Motor: They provide contraction.
| Other proteins bind to stabilise the filaments
198
What is actin dynamics?
The cycle between G-actin and F-actin
| - Remodelling of actin filaments is driven by different binding proteins
199
What is the nucleation step in actin dynamics?
The rate limiting step in actin dynamics- it involves the formation of trimers to initiate polymerisation
- Arp 2 & 3 (actin-related proteins) are similar to actin, and form a complex on which the trimers of actin can attach (on the minus end)
- Elongation of the filament can then occur from the Arp2/3 complex
200
What is the elongation step in actin dynamics?
- Brings monomers (usually sequestered) to the filament
- Profilin binds to the monomers and help elongate the filament
- Thymosin is a sequestering protein which prevents polymerisation
- There is a balance between these two proteins to regulate filament growth, as profilin competes with thymosin for binding to actin monomers and promote assembly
201
What is the purpose of branching in actin dynamics?
Branched filaments form a precise 70 degree angle.
| Arp complex binds to the filament to provide nucleation a a different site
202
What is the purpose of capping proteins in actin dynamics?
- Prevent further growth of the filament
- Capping proteins include Cap Z, Gelsolin, Fragmin and Severin at the plus end. Tropomodulin and Arp are proteins at the minus end
- Can be used to regulate directionality of growth
203
What proteins are involved in cross-linking and bundling of actin dynamics?
```
alpha-actinin
fimbrin
filamin
spectrin
villin
vinculin
```
204
What is the purpose of servering in actin dynamics?
- Used to prevent low rate of growth/shrinking of very long filaments
- In unsevered population actin filaments grow and shrink relatively slowly
- In severed population actin filaments grow and shrink more rapidly
- Severing proteins include: gelsolin, ADF/cofilin, fragmin/severin
- E.g., severin is used in the gel-sol transition
205
What are activities of actin during cell movement?
Disassemble, nucleation, branching, severing, capping and bundling
206
What actin activities are involved during lamellae protrusion?
Polymerisation, disassembly, branching, capping
- During protrusion there is net filament assembly at the leading edge, and net filament disassembly behind the leading edge
207
What actin activities are involved in the formation of filopodia?
Actin polymerisation, bundling and cross-linking to form the tight parallel bundles
208
Which signalling mechanisms 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
209
How is the actin cytoskeleton controlled by small G proteins?
- Rho subfamily of small GTPases belongs to the Ras super family
Family members: Rac, Rho, Cdc43 best known
- Participate in a variety of cytoskeletal processes
- These proteins are activated by receptor tyrosine kinase, adhesion receptors and signal transduction pathways
- Expression levels are up-regulated in different human tumours
210
How do small GTPases participate in cell migration?
- Rac is an important protein for lamellar protrusion
- It controls the actin branching
- Rho is important in the cell contraction
- Rho is also important in the retraction of the cell to the rear ie. the arrangement of stress fibres and tension
- Both rac, rho and CDC42 control how the cells form focal adhesions
- Rho gives a very strong adhesion whereas cdc43 has a more docile adhesion
- Cdc42 regulates filopodia, polarised motility and actin polymerisation
211
Why is programmed cell death important?
To remove-
1) Harmful cells (e.g. cells with viral infection, DNA damage)
2) Developmentally defective cells (e.g. B lymphocytes expressing antibodies against self antigens)
3) Excess/unnecessary cells (embryonic development e.g. brain to eliminate excess neurons, liver regeneration, sculpting of digits and organs)
4) Obsolete cells (e.g. mammary epithelium at the end of lactation)
5) Exploitation- chemotherapeutic killing of cells
212
What is necrosis and apoptosis?
Necrosis: unregulated cell death associated with trauma, cellular disruption and an inflammatory response
Apoptosis: regulated cell death; controlled disassembly of cellular contents without disruption: no inflammatory response
213
What happens during necrosis?
- Plasma membrane becomes permeable
- Cell swelling and rupture of cellular membranes
- Release of proteases leading to autodigestion and dissolution of the cell
- Localised inflammation
214
What happens during the latent phase of apoptosis?
Death pathways are activated, but cells appear morphologically the same
215
What happens during the execution phase of apoptosis?
- Loss of microvilli and intercellular junctions
- Cell shrinkage
- Loss of plasma membrane asymmetry (phospatidylserine lipid appears in outer leaflet)
- Chromatin and nuclear condensation
- DNA fragmentation
- Formation of membrane blebds
- Fragmentation into membrane-enclosed apoptotic bodies
- There is no inflammation as plasma membrane remains intact
216
What is the result of DNA modification in apoptosis?
- Fragmentation of DNA ladders (seen in agarose gel)
| - Formation of more 'ends' (which can be labelled fluorescently in a TUNEL asasay)
217
What are apoptosis-like PCD and necrosis-like PCD?
Apoptosis-like PCD: some, but not all, features of apoptosis. Display of phagocytic recognition molecules before plasma membrane lysis
Necrosis-like PCD: variable features of apoptosis before cell lysis: aborted apoptosis
218
What are the mechanisms of apoptotic cell death?
1) The executioners- Caspases
2) Initiating the cell death programme
- death receptors
- mitochondria
3) The Bcl-2 family
219
What are caspases?
Cysteine-dependent aspartate-directed proteases
- Executioners of apoptosis
- Activated by proteolysis
- Cascade of activation
220
What are the classes of caspases?
```
Effector caspases (3,6 and 7)
Initiator caspases ( 2,8,9 and 10)
- Initiator caspases have subunits either called CARD or DED
CARD- Caspase Recruitment Domain
DED- Death Effector Domain
```
221
How do caspases maturation?
- Procaspases (zymogens) are single chain polypeptides. To be activated they undergo proteolytic cleavage to form a large and small subunit
- These cleavages are done by the caspases themselves
- Cleavage of the inactive procaspase precursor is followed by folding of 2 large and 2 small chains to form an active L2S2 heterotretamer
222
What do caspase cascades consist of?
- Amplification
- Divergent responses
- Regulation
- Initiator caspases trigger apoptosis by cleaving and activating
- Effector caspases carry out the apoptotic programme
223
How do effect caspases execute the apoptotic programme?
- Cleave and inactivate proteins or complexes (e.g. nuclear lamins leading to nuclear breakdown)
- Activate enzymes (include protein kinases: nucleases e.g. Caspase Activated DNase, CAD) by direct cleavage, or cleavage or inhibitory molecules
224
What are the mechanisms of caspase activation?
1) Death by deign- receptor-mediated (extrinsic) pathways
| 2) Death by default- mitochrondrial (intrinsic) death pathway
225
What do death receptors consist of and how are they activated?
Extracellular cysteine-rich domain
Single transcellular domain
Cytoplasmic tail with 'death domain'
- They are activated when they encounter secreted or transmembrane trimeric ligands (TNF or Fas) called DEATH LIGANDS
226
What are the adaptor proteins in the death by design pathway?
- FADD- a positive regulator which promotes cell death
= The two domains of FADD are DED (death effector domain) and DD (death domain)
- FLIP- a negative regulator which inhibits the death pathway
- FLIP contains two DED domains
227
What is the death receptor signalling process?
1) Death ligand binds to the death receptor (i.e. Fas receptor engaged by Fas ligand)
2) Death receptor undergoes trimerisation which brings the 3 cytoplasmic DD domains together
3) Trimerised death domains recruit the positive adaptor protein by its own DD
4) Binding of FADD causes recruitment and oligomerisation of procaspase 8
5) Binding of caspase 8 leads to formation of a DISC (death inducing signalling complex)
6) DISC formation results in cross-activation of procaspase8 where they cleave each other within the complex. Active caspase 8 is release where it cleaves effector caspases to execute the death programme
228
What inhibits death receptor activate of caspase 8?
FLIP
- It has caspase homology in DED domain but no proteolytic activity therefore it competes with the procaspase
- Competes for binding to receptor tails
- Incorporates into receptor/procaspase complexes and interferes with transcleavage
229
What happens during mitochondrial regulation of apoptosis?
- Loss of mitochondrial membrane potential
- Release of cytochrome c
- Release of other apoptosis inducing factors
- Formation of the apoptosome complex
230
What is the apoptosome complex?
' Wheel of death'- Contains APAF-1, cycotchrome c, ATP and procaspase 9
- Each APAF-1 in the heptameric apoptosome can potentially bind a procaspase 9
- Oligomerisation brings multiple procaspase9s close together, resulting in cleavage, activation and release as active caspase 9 tetramer, which initiates a caspase cascade leading to apoptosis
- Procaspase 9 binds to CARD
231
What links the receptor mediated and mitochondria mediated death pathways?
A protein called Bid
| - Caspase 8 cleaved Bid which enhances the release of mitochondrial proteins, thus engaged the intrinsic pathway
232
Why does apoptosis require energy?
- The apoptosome requires ATP
| - Energy levels in the cell may determine whether death is by necrosis or apoptosis
233
What is the Bcl-2 Family?
Proteins that are intrinsic modulators of apoptosis
- 3 groups, all of which contain the BH3 domain
- Members of the family are in two categories:-
Anti apoptotic proteins: localised to mitochrondrial membrane and inhibit apoptosis (Bcl-2, Bcl-xL)
Pro-apopotic proteins: move between the cytosol and the mitochondrial membrane promoting apoptotis (Bid, Bad, Bax, Bak)
234
What is the role of the PI3'-Kinase signalling pathway in cell cycle and apoptosis regulation?
PI3'-K is a lipid kinase involved in growth control and cell survival
- Activate kinase PKB/Akt which is anti-apoptotic
- PKB phosphorylates the BAD and causes it to inactivate leading to cell survival
- When growth factors are absent, PkB fails to come to the cell membrane so Bad is dephosphorylated and is released from its heterodimer.
- Bad will displace Bcl-2/-cL from Bax/Bak leading to apoptosis
235
What is the role of PBK/Akt?
1) Phosphorylates and inactivates Bad
2) Phosphorylates and inactivates caspase 9
3) Inactivates FOXO transcription factors (FOXOs promote expression of apoptosis-promoting genes)
4) Other e.g. stimulates ribosome production and protein synthesis
236
What is PTEN?
A lipid phosphatase and extrinsic regulator which counteracts PI3-K signalling. It reduces the regulation of cell survival and promotes apoptosis
237
What are IAPs?
Inhibitors of apoptosis proteins
- They regulate programmed cell death
- Bind to procaspases and prevent their activation. Bind to active caspases and inhibit their activity
238
What are the characteristics of the cancer cell phenotype?
- Disregard of signals to stop proliferating
- Disregard of signals to differentiate
- Capacity of sustained proliferation
- Evasion of apoptosis
- Ability to invade
- Ability to promote angiogenesis
239
What are pro-oncogenes?
They code for essential proteins involved in the maintenance of cell growth division and differentiation
- Can be converted into oncogene due to mutation
240
What will a point mutation or deletion of a proto oncogene lead to?
Aberrantly active protein
241
What will gene amplification of a proto-oncogene lead to?
Overproduction of normal protein
242
What is the result of chromosomal translocation (chimaeric genes) or insertional mutagenesis of proto-oncogenes?
- Strong enhancer increases normal protein levels e.g. Burkitt's lymphoma
- Fusion to actively transcribed gene overproduces protein or fusion protein is hyperactive e.g. Philadelphia chromosome
243
What are the consequences of mutant RAS?
- Upon binding GTP, Ras becomes active
- Dephosphorylation of the GTP to GDP switches RAS off
- Mutant RAS fails to dephosphorylate GTP and remains active
244
What tumours are associated with the SRC oncogene?
Breast, colon, lung
| - Cytoplasmic location
245
What tumours are associated with the MYC oncogene?
Burkitt's lymphoma
246
What tumours are associated with the JUN oncogene?
Lung
247
What tumours are associated with the Ha-RAS oncogene?
Bladder
248
What tumours are associated with the Ki-RAS oncogene?
Colon
| Lung
249
Why is mutation or deletion of one gene copy usually insufficient to promote cancer?
- Typically proteins whose function it is to regulate proliferation, maintain cell integrity
- Each cell has two copies of each tumour suppressor gene
- Mutation or loss of both copies means loss of control
250
What features contribute to inherited cancer susceptibility?
- Family history of related cancers
- Unusually early age of onset
- Bilateral tumours in paired organs
- Synchronous or successive tumours
- Tumours in different organ systems in the same individual
- Mutation inherited through the germline
251
What is retinoblastoma?
- Malignant cancer of developing retinal cells
- Sporadic disease that usually involved one eye
- Hereditary cases can be unilateral, bilateral and multifocal
252
What causes retinoblastoma?
Mutation of the RB1 tumour suppressor gene on chromosome 13q14
- RB1 encodes a nuclear protein that is involved in the regulation of the cell cycle
253
What are the functional classes of tumour suppressor genes?
- Regulate cell proliferation
- Maintain cellular integrity
- Regulate cell growth
- Regulate the cell cycle
- Nuclear transcription factors
- DNA repair proteins
- Cell adhesion molecule
- Cell death regulators
- They suppress the neoplastic phenotype
254
What tumours are associated with the BRCA1 tumour suppressor gene?
Breast
Ovarian
Prostate
255
What tumours are associated with the PTEN tumour suppressor gene?
Prostate
| Glioblastoma
256
What tumours are associated with the APC tumour suppressor gene?
Colon
257
Why is a mutation in a single copy of the P53 tumour suppressor gene enough to get dysregulation?
Mutants act in a dominant manner
258
What is Familial adenomatous polyposis coli?
- Due to a deletion in 5q21 resulting in the loss of the APC tumour suppressor gene
- Involved in cell adhesion and signalling
- Sufferers develop multiple benign adenomatous polyps of the colon
- 90% risk of developing colorectal carcinoma
259
How does the APC tumour suppressor gene work?
- Participates in the WNT signalling pathway
| - APC protein helps control the activity of beta-catenin and thereby prevents uncontrolled growth
260
What steps lead to the development of colorectal cancer
- Damage to the APC
- Hyperproliferation of the epithelium (loss of tumour suppressor function)
- DNA hypomethylation is epigenetic modification of the epithelial cell. Combins with the action of a mutated RAS gene (oncogene) this will push the polyps to develop into an adenoma
- Mutation of p53 will result in a carcinoma
- Matastases
261
What are the differences between oncogenes and tumour suppressor genes?
```
Oncogene:
- Gene active in a tumour
- Specific translocation/point mutations
- Mutations rarely hereditary
- Dominant at cell level
- Broad tissue specificity
- Leukaemia and lymphoma
Tumour suppressor gene:
- Gene inactive in a tumour
- Deletions or mutations
- Mutations can be inherited
- Recessive at cell level
- Considerable tumour specificity
- Solid tumours
```
262
What steps are needed to make a blood vessel?
- Vasculogenesis (bone marrow progenitor cell)
- Angiogenesis (sprouting)
- Arteriogenesis (collateral growth)
263
What are the inhibitors of angiogenesis?
```
- Thrombospondin-1
The statins:
- Angiostatin
- Endostatin
- Canstatin
- Turnstatin
```
264
What are the activators of angiogenesis?
- VEGFs
- FGFs
- PDGFB
- EGF
- LPA
265
What is the initial stimulus for angiogenesis?
Hypoxia
- It is sensed in cells by the transcription factor HIF (hypoxia-inducible factor) which leads to the expression of hypoxia-inducible genes
- Encodes VEGF which is the signal to initiate blood vessel formation via endothelium activation
266
What is pVHL?
von Hippel-Lindau tumour suppressor gene
| - Controls levels of HIF
267
What is vascular endothelial growth factor (VEGF) and its receptors?
- Family of 5 members: VEGF-A, VEGF-B, VEGF-C, VEGF-D and placental growth factor (PIGF)
- Three tyrosine kinase receptors: VEGF receptor (VEGFR)-1 VEGFR-2 and VEGFR-3: an co-receptors neuropilin Nrp1 and Nrp2
- VEGFR-2 is the major mediator of VEGF-dependent angiogenesis, activating signalling pathways that regulate endothelial cell migration, survival, proliferation
268
What happens in sprouting angiogenesis?
Specialised endothelial tip cells lead the outgrowth of blood-vessel sprouts towards gradients of VEGF
269
What is the canonical notch signalling pathway?
- Notch receptors and ligands are membrane-bound proteins that associate through their extracellular domains
- The intracellular domain of Notch (NICD) translocates to the nucleus and binds to the transcription factor RBP-J
270
What is involved in tip cell selection?
1) In stable blood vessel DII4 and Notch signalling maintain quiescence
2) VEGF activation increases expression of DII4
3) DII4 drives Notch signalling which inhibits expression of VEGFR2 in the adjacent cell
4) DII4-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
271
How do macrophages participate in vessel anastomosis?
- Macrophages have been shown to carve out tunnels in the extra cellular matrix thereby providing avenues for subsequent capillary infiltration
- Tissue resident macrophages were shown to be associated with angiogenic tip cells during anastomosis
272
What is the purpose of VE-cadherin?
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
273
What is the purpose of mural cells?
- Help stabilise the neovessels
274
What is involved in vessel stabilisation?
Pericytes
| Mural cells
275
How do signalling pathways control stability?
- The Angiopoietin-Tie2 ligand-receptor system?
- Ang-1 and Ang-2 are antagonistic ligands of the Tie2 receptor
- Ang-1 binding to the Tie2 promotes vessel stability and inhibits inflammatory gene expression
- Ang-2 antagonises Ang-1 signalling, promotes vascular instability and VEGF-dependent angiogenesis
276
Describe tumour angiogenesis and neovasculature
- Tumours less than 1mm3 receive oxygen and nutrients by diffusion from host vasculature
- Larger tumours require 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 which facilitates progressive growth
277
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
278
What are the characteristics of tumour blood vessels?
- Irregularly shapes, dilated, tortuous
- Not organised into definitive venules, arteriole and capillaries
- Leaky and hemorrhagic, partly due to overproduction of VEGF
- Perivascular cells often become loosely associated
- Some tumours may recruit endothelial progenitor cells from the bone marrow
279
How does anti-angiogenic therapy normalise the vasculature?
- Reduced hypoxia
| - Increases efficacy of conventional therapies
280
What are the problems with sustained/aggressive anti-angiogenic therapy?
May damage healthy vasculature leading to loss of vessels, creating vasculature resistant to further treatment and inadequate for deliver of oxygen/drugs
281
What is Avastin
Monoclonal antibody which inhibits VEGF
282
What are the side effects of Avastin therapy for cancer?
- GI perforation
- Hypertension
- Proteinuria
- Venous thrombosis
- Haemorrhage
- Would healing complications
283
How does therapeutic angiogenesis help coronary artery disease and peripheral artery disease?
Promotes neo-vascularisation to prevent ischaemic damage
284
What types of damage can occur to DNA as a result of carcinogens?
- Base dimers and chemical cross links
- Base hydroxylations and abasic sites formed
- DNA adducts and alkylation
- Double and single strand breaks
285
What does mammalian metabolism consist of?
Phase I:
- Addition of functional groups e.g. oxidations, reductions, hydrolysis
- Mainly cytochrome P540-mediated
Phase II:
- Conjugation of Phase I functional groups e.g. sulfation, glucuronidation, acetylation, methylation, amino acid and glutathion conjugation
- Generates polar (water soluble) metabolites
286
What are polycyclic aromatic hydrocarbons?
- Common environmental pollutants
- Formed from combustion of fossil fuels
- Formed from combustion of tobacco
287
What is aflatoxin B1?
- Formed by Aspergillus flavus mould
- Common on poorly stored grains and peanuts
- Aflatoxin B1 is a potent human liver carcinogen, especially in Africa and Far-East
288
How is 2-napthylamine metabolised?
- CYP1A2 converts the amine to a hydroxylamine. This is toxic and will damage cells and DNA
- A phase II enzyme detoxifies the substrate by adding a sugar molecule to it. However in the bladder, the new metabolite is labile in the acid pH of the urine. This generate s a positively charged amino group that is a highly DNA-reactive electrophile
- DNA is particular electron-rich because of all the nitrogenous bases. The new metabolite reacts with the DNA, forming DNA adducts
289
How does UV radiation act as a carcinogen?
- High energy and attacks DNA
- Cross links thymidine to form pyrimidine dimers
- Skin cancer
290
How does ionising radiation act as a carcinogen?
- Generates free radicals in cells
- Includes oxygen free radicles (super oxide radical, hydroxyl radical)
- Possess unpaired electrons (electrophilic and therefore seek out electron-rich DNA)
- Radicals attack DNA leading to double and single strand breaks often in apurinic and apyrimidinic sites
- Radials cause base modifications such as ring-opened guanine and adenine, thymine and cytosine glycols and 8-hydroxyadenine & 8-hydroxyguanine (mutagenic)
291
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
292
What happens during direct reversal of DNA damage?
- Photolyase splits cyclobutane pyrimidine dimers
| - Methyltransferases and alkyltransferases remove alkyl groups from bases
293
What happens during base excision repair?
- Mainly for apurinic/apyrimidinic damage
- DNA glycoslyases and apurinic/apyrimidinic endonucleases and other enzyme partners
- A repair polymerase fills the gap and DNA ligase completes the repair
294
What happens during nucleotide excision repair?
- Mainly for bulky DNA adducts
- Xeroderma pigmentosum proteins assemble at the damage. A stretch of nucleotides either side of the damage are excised
- Repair polymerases fill the gap and DNA ligase completes the repair
295
What are the two pathways of excision repair?
- Base excision repair pathway: the chain remains intact
| - Nucleotide excision repair pathway: a stretch of DNA is removed therefore the chain does not remain in tact
296
What is the Ames test?
A crude bacterial test looking at potential mutagenicity of chemicals, ie the ability of the chemical to cause DNA damage
297
How can chromosomal aberrations be detected in mammalian cells?
Treat mammalian cells with chemical in presence of liver s9.
| Look for chromosomal damage
298
How is cytokinesis blocked in an in vitro micronucleus assay?
Treat with cytochalasin-B
299
What is the function of the colon?
- Extraction of water from faeces (electrolyte balance)
- Faecal reservoir (evolutionary advantage)
- Bacterial digestion for vitamins (e.g. B and K)
300
What is the number of cells that die in the colon?
2-5 million die per minute
- Proliferation renders cells vulnerable
- APC mutations prevent cell loss
301
What is a polyp?
Any projection from a mucosal surface into a hollow viscus and may be hyperplastic, neoplastic, inflammatory, hamartomatous
302
What is an adenoma?
A benign neoplasm of the mucosal epithelial cells
303
What are the different types of colonic polyps?
- Metaplastic/hyperplastic (no malignant potential and 15% have k-ras mutation)
- Adenomas
- Juvenile
- Peutz Jeghers
- Lipomas
- Others
304
What are the different types of colonic adenomas?
- Tubular (90%)
- Tubulovillous (10%)
- Villous
- Flat
- Serrated
305
What is the microscopic structure of a tubular adenoma?
- Columnar cells with nuclear enlargement, elongation, multilayering and loss of polarity
- Increased proliferative activity
- Reduced differentiation
- Complexity/disorganisation of architecture
306
What is the microscopic structure of villous adenomas?
- Mucinous cells with nuclear enlargement, elongation, multilayering and loss of polarity
- Exophytic, frond-like extensions
- Rarely may have hypersecretory function and result in excess mucous discharge and hypokalaemia
307
What is colonic dysplasia?
Abnormal growth of cells with some features of cancer. Requires subjective analysis, may be indefinite, low grade and high grade
308
What is Adenomatous polyposis coli (APC/FAP)?
A disease caused by a 5q21 mutation.
- Site of mutation determines clinical variants
- Many patients will have a prophylactic colectomy
309
From where do most colonic carcinomas arise?
From adenomas
- There is a residual adenoma in 10 to 30% of carcinomas
- Adenomas and carcinomas have similar distribution and adenomas usually precede cancer by 15 years
310
What genetic pathways are involved in the progression from adenomas to carcinomas?
- The adenoma carcinoma sequence: Involves APC, K-ras, p53 and telomerase activation
- Microsatellite instability: Microsatellites are repeat sequences prone to misalignment. Some microsatellites are in coding sequences of genes which inhibit growth or apoptosis e.g. TGFbR11.
Mismatch repair genes are are recessive genes requiring 2 hits
311
What are the two main pathways of genetic predisposition to colonic carcinoma
FAP: inactivation of APC tumour suppressor genes
HNPCC: micro-satellite instability
312
What is the most common mutation in colon cancer?
Inactivation of APC
| When APC does not an inactivating mutation, beta catenin does
313
What dietary factors contribute to colonic carcinoma?
High fat
Low fibre
High red meat
Refined carbohydrates
314
How does food contribute to carcinoma?
- Contains 5,000-10,000 bioactive chemicals
- Food also contains carcinogens and anti-cancer agents
- Heat modified chemicals further and bacteria can modify food residues
- Heteocyclic amines (HCAs) are generated when meat is cooked at high temperatures and these may cause mutations
315
Why are dietary deficiencies significant in colorectal cancer?
- Folates are important, as a co-enzyme is needed for nucleotide synthesis and DNA methylation
- MTHFR deficiency leads to a disruption in DNA synthesis causing DNA instability (strand breaks and uracil incorporation) leading to mutations.
Decreased methionine synthesis leads to genomic hypomethylation and focal hypermethylation leading to gene activation and silencing
316
What are the various anti-cancer 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 and reduces DNA oxidation
317
What is the clinical presentation of colorectal cancer?
- Altered bowel habit
- Rectal bleeding
- Unexplained Fe deficiency- anaemia
- Mucous
- Bloating
- Cramps 'colic'
- Constitutional weight loss, fatigue
318
What are the macroscopic features of colonic carcinomas?
- Small carcinomas may present with large polypoid adenomas, pedunculated or sessile
- Caecum/ascending colon: 22%
- Transverse colon- 11%
- Descending colon- 6%
- Rectosigmoid- 55%
319
What is grading?
The proportion of gland differentiation relative to solid areas of nests and cord of cells without lumina
320
What is the Dukes Classification?
```
Dukes A:
- Growth limited to wall
- Nodes negative
Dukes B
- Growth beyond musc propria
- Nodes negative
Dukes C1:
- Nodes postive
- Apical LN negative
Dukes C2:
- Apical LN positive
```
321
How do clinical features affect prognosis?
- Diagnosis in asymptomatic patients: Improved prognosis
- Rectal bleeding presenting as symptoms: Improved prognosis
- Bowel obstruction/perforation: Diminished prognosis
- Tumour location: Colon better than rectum, Left colon better than right colon
- Age
322
How do pathological features affect prognosis?
- Depth of bowel wall penetration: Increased penetration diminished prognosis
- Number of regional lymph nodes involved: 1-4 nodes better than >4 nodes
- Degree of differentiation: Well >poorly differentiation
- Mucinous or signet ring cell: Diminished prognosis
Venous invasion:
- Diminished prognosis
- Lymphatic invasion: Diminished prognosis
Perineural invasion: Diminished prognosis
Local inflammation and immunological reaction: Improved prognosis
323
What are the treatment options available for colorectal cancer?
Surgery, with concurrent treatment with 5FU, leucovorin, metastatectomy, chemotherapy and palliative care
324
How are patients selected for screening for high risk 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
325
What is 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 the disease or improve the prognosis when it develops
326
What is the criteria for a screening programme?
1) Importance of the disease- condition should be important in respect to the seriousness and/or frequency
2) The natural history of the disease must be known in order to
- identify where screening can take place
- enable the effects of any intervention to be assessed
327
What are the characteristics of screening for colorectal cancer?
- Simple and acceptable to the patients
- Sensitive and selective
- Screening population should have equal access to screening procedure
- Cost effectiveness
328
What is FOB?
Fecal Occult Blood Test
- Most people ages 60-69 are screened ever 2 years and positive are referred for colonoscopy
- It is relatively insensitive and produces some false positives
329
What are the different types of skin cancer?
1) Keratinocyte derives
e. g. basal cell carcinoma, squamous cell carinoma aka non melanoma skin cancer (NMSC)
2) Melanocyte derived
e. g. malignant melanoma
3) Vasculature derived
e. g. Kaposi's sarcoma, angiosarcoma
4) Lymphocyte derived
e. g. Mycosis fungoides
330
What are the causes of skin cancer?
Accumulation of genetic mutations lead to uncontrolled cell proliferation
Genetic syndromes: Gorlin's syndrome
Xeroderma pigmentosum
Viral infections: HHV8 in Kaposi's sarcoma
HYPV in SCC
UV light: BCC, SCC, Malignant melanoma
Immunosuppression: drugs, HIV, old age, leukaemia
331
Why is sunlight needed?
- Essential for photosynthesis (plants)
- Infrared spectra provide warmth
- Effect on human mood
- Stimulates the production of vitamin D in the skin
332
What is the most important wavelength in skin carcinogens?
UVB (280-315)
333
Which wavelength is a major cause of skin ageing?
UVA (315-400)
| - Contributes to skin carcinogenesis
334
What is the action of UVB
- Directly induces abnormalities in DNA eg mutations
- UVB induces photoproducts (mutations)
- Affects pyrimidines ie Cytosine (C) and Thyme (T) bases
- Usually repaired quickly by nucleotide excision repair
335
How does UVA contribute to skin carcinogenesis?
- DNA forming cyclobutane butane pyrimidine dimers but less efficiently than UVB
- Free radicals which damage DNA and cell membrane
336
What is the consequence of UV induced skin carcinogenesis?
UV damage to DNA leads to mutations in specific genes
- Cell division
- DNA reapir
- Cell cycle arrest
337
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
338
What mutations cause cancer?
1) Mutations that stimulate uncontrolled cell proliferations 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)
339
How is sunburn caused?
- UV leads to keratinocyte cell apoptosis
- Sun burn cells are apoptotic cells in UV overexposed skin
- Apoptosis removes UV damaged cells in the skin which might otherwise become cancer cells
340
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
341
What are the Fitzpatrick phototypes?
Host response to UV is determined by genetic influences especially skin phototype
1) Always burns, never tans
2) Usually burns, sometimes tans
3) Sometimes burns, usually tans
4) Never burns, always tans
5) Moderate constitutive pigmentation- Asian
6) Marked constitutive pigmentation- Afrocarribean
342
What is melanin?
- Melanin pigmentation is responsible for skin colour
- Produced by melanocytes within the basal layer of the epidermis
- Skin colour depends on the amount and type of melanin produced, not the density of melanocytes (which is fairly constant)
- Melanin dictates skin sensitivity to UV damage
343
What two types of melanin are formed?
Eumelanin- brown or black
Phaeomelanin- yellowish or reddish brown
- Melanin is formed from tyrosine via a series of enzymes
344
What is MCR1?
Melanocortin 1 receptor
- Leading role in pigmentation following UV exposure, regulating changes in the skin and hair pigmentation phenotype
- In response to UV, it promotes a switch from phaeomelanin to eumelanin and therefore has a key role in tanning
- >20 gene polymorphisms
345
What is malignant melanoma?
- Malignant tumour of melanocytes: melanocytes become abnormal, atypical cells and architecture
- Caused by UV exposure and genetic factors
- Risk of metastasis
346
What is lentigo maligna?
(melanoma in situ)
- Proliferation of malignant melanocytes within the epidermis
- Risk of metastasis
- Irregular shape
- Light and dark brown colours
- Size is usually >2 cm
347
How does malignant melanoma superficially spread?
- Lateral proliferation of malignant melanocytes
- Invade basement membrane
- Risk of metastasis
348
How is superificial spreading of malignant diagnosed?
ABCD rule
- Asymmetry
- Border irregular
- Colour variation (dark brown-black)
- Diameter >0.7 mm and increasing
- Erythema
349
How does nodular malignant melanoma proliferate?
- Vertical proliferation of malignant melanocytes
(no previous horizontal growth)
- Risk of metastasis
350
How does nodular melanoma arise within a superficial spreading melanoma?
- Downward proliferation of malignant melanocytes
- Following previous horizontal growth
- Nodule developing within irregular plaque- prognosis will become worse
351
What are the different types of malignant melanoma?
- Superficial spreading
- Nodular
- Lentigo maligna melanoma
- Acral lentignous
- Amelanotic
352
How is prognosis of melanoma established?
Breslow thickness
| - Measurement from granular layer to bottom of tumour
353
What are the risk factors for the development of melanoma?
- Genetic markers (e.g. CDKN2A mutations
- Family history of dysplastic nevi or melanoma
- Ultraviolet irradiation
- Sunburns during childhood
- Intermittent burning exposure in unacclimatised fair skin
- Number (>50) and size (>5 mm) of melanocytic nevi
- Congenital nevi
- Number of atypical nevi (>5)
- Atypical/dysplastic nevus syndrom
- Personal history of melanoma
- High socioeconomic status
- Skin type I,II
- Equatorial latitudes
- DNA repair defects (e.g. xeroderma pigmentosum)
- Immunosuppression
354
What is squamous cell carcinoma?
- Malignant tumour of keratinocytes
- Caused by UV exposure, HPV, Immunosuppression, May occur in scars or scarring processes
- Risk of metastasis
355
What is basal cell carcinoma?
- Malignant tumour arising from basal layer of epidermis
- Caused by sun exposure, genetics
- Slow growing
- Invades tissue, but does not metastasise
- Common on face
356
What is epidermodysplasia veruciformis?
Rare autosome recessive condition
| - Predisposition to HPV induced warts and SCCs
357
Why is the incidence of breast cancer rising whereas the mortality is falling?
- Early diagnosis
- Chemo/radiotherapies
- Hormonal therapies
358
What is the cellular organisation of the mammary gland?
A layer of myoepithelial cells, some of which are slightly vacuolated, is just seen around the luminal cells, making contact with the basement membrane
359
What are the major histological types of invasive breast cancer?
- Infiltrating ductal carcinoma (IDC) many of which feature no special type of histological structure, account for almost 80% of breast cancers
- Ductal carcinoma in situ (DCIS)
- Infiltrating lobular carcinoma (ILC)
- Tubular carcinoma
- Medullary carcinoma
- Mucinous carcinoma
- Inflammatory breast cancer
360
What is used in immunohistochemical staining?
Antibodies against the human oestrogen receptor
| - About 80% of breast cancers are oestrogen-receptor positive
361
How does oestrogen receptor act as a growth factor?
- The receptor is activated upon oestrogen binding
- Exists in the cytoplasm, bound to hsp90. Oestrogen crosses the cell membrane, and once bound to the nuclear/oestrogen receptor, displaces hsp90
- Receptor dimerises, and translocates to the nucleus where it binds to DNA sequences calls oestrogen response elements
- This increases the expression of oestrogen-induced gene products which increase cell proliferation, inhibit apoptosis and may result in breast cancer
362
What is the role of the oestrogen receptor in breast cancer?
- Some breast cancers like normal breast, are sensitive to the effects of oestrogen
- One third of premenopausal women with advanced breast cancer will respond to oophorectomy
- The receptor is over expressed in 50% of breast cancers. Presence is indicative of a better prognosis
363
What are treatment approaches for breast cancer?
- Surgery
- Radiation therapy
- Chemotherapy
- Endocrine therapy
364
How does endocrine therapy treat breast cancer?
- Ovarian suppression
- Blocking oestrogen production by enzymatic inhibition
- Inhibiting oestrogen responses
365
How are target tissue controlled hormonally?
- The ovaries in premenopausal women make the majority of oestrogen, under the control of pituitary gonadotrophins, which is under the control of the LHRH from the hypothalamas
- Aromatisation of androgens is also a source of peripheral oestrogen
366
What is ovarian ablation?
- The ovary is the major source of oestrogen biosynthesis in pre-menopausal women
- Ovarian ablation aims to eliminate this source.
- It can be carried out by surgical oophorectomy, ovarian irradiation
- Major problems with this procedure are morbidity and irreversibility
367
How can reversible and reliable medical ovarian ablation be achieved?
- Using lutenising hormone releasing hormone agonists
- LHRH agonists binds to LHRH receptors in the pituitary leading to receptor down-regulation and suppression of LH release and inhibition of ovarian function, including oestrogen production
368
Give examples of LHRH agonists?
Goserelin
Buserelin
Leuprolide
Triptorelin
369
What is Tamoxifen?
Anti-oestrogen used be inhibit oestrogen action
- Most commonly used due to its demonstrated efficacy and low incidence side effects
- Competitive inhibitor of oestradiol binding to the ER
- Endocrine treatment of choice for metastatic disease in postmenopausal patients
- Is a SERM- selective oestrogen receptor modulator
370
How is Tamoxifen administered?
As a pro-drug: Tamoxifen Citrate which is metabolised in the GI tract to generate 4-hydroxymoxifen (active component) and endoxifen
- Tamoxifen citrate is metabolised in the gut to form the active drug
371
How do anti-oestrogens negate the stimulatory effects of oestrogen?
Blocking the ER which causes the cell to be held at the G1 phase of the cell cycle
372
What effects does tamoxifen have on bone?
- Oestrogen is important to maintain bone in premenopausal women. After menopause, hormone replacement therapy is often recommended to prevent the development of osteoporosis. The long-term of an anti-oestrogen has the potential to precipitate premature osteoporosis
- Tamoxifen has oestrogenic effect in bone
373
What effect does tamoxifen have in the cardiovascular system?
Oestrogen lowers LDL cholesterol levels and raises HDL levels. Following menopause, women are at the same risk for coronary heart disease as me. Long term administration of an antioestrogen could produce a population at risk for premature coronary heart disease
- Tamoxifen has oestrogenic effects in the cardiovascular system
374
What are the undesirable effects of tamoxifen?
Endometrial thickening, hyperplasia and fibroids following several years of therapy
375
How does tamoxifen effect the breast, liver and heart and bone?
Breast= reduces breast cancer
Liver and heart= Lowers cholesterol, reduces atherosclerosis and heart attacks
Bone= maintains density to help prevent bone loss
376
What are the negative effects of tamoxifen on the hypothalamus, eye, liver and uterus?
```
Hypothalamus= Increases vasomotor symptoms
Eye= Increases cataracts
Liver= Increases thromboembolism
Uterus= Promotes endometrial cancer fibroids, polyps and vaginal discharge
```
377
What additional drugs have been developed to target breast cancer?
- Toremifene: structural derivative of tamoxifen
- ICI 182 780: pure anti-oestrogen
- Raloxifene: anti-tumour agent with no activity in breast or uterus but protective in bone therefore used for osteoporosis
378
What problems are used in using Tamoxifen in prevention of breast cancer?
- Increase incidence of endometrial cancer
- Stroke
- Deep vein thrombosis
- Cataracts
379
What does aromatase consist of?
A complex containing a cytochrome P450 heme containing protein and a NADPH cytochrome p450 reductase
- The enzyme complex catalyses 3 separate steroid hydroxylation involved in the conversion of androstenedione to estrone
- Aromatase can metabolise androsteinidione which is produced by the adrenal glands. This leads to the production of estrone sulphate which is circulated in the plasma
380
How are aromatase inhibitors used in breast cancer?
In postmenopausal women, the major source of oestrogen derives not from the ovaries but from the conversion of the adrenal hormones androstenedione and to a lesser extent- testosterone to estrone
- 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
381
How are aromatase inhibitors classified?
1) Suicide inhibitors- destroy active site
- Initially compete with the natural substrate for active site but then on binding they form covalent bonds which results in irreversible inactivation of aromatase
2) Competitive inhibitors- bind reversible to the active site. These are more clinically useful as have fewer side effects
382
Give an example of a suicide aromatase inhibitor
Exemestane
- Single dose administration reveals a major reduction in plasma oestrogen with only mild side effects reported, including hot flushes, nausea and fatigue
383
Give an example of a competitive aromatase inhibitor
Anastrozole
384
What is the role of progestins in breast cancer?
- Progesterone- the dominant naturally occurring progestin
- Progestins are used in the endocrine treatment of uterine and breast cancer with clinically proven antineoplastic properties
- Progestin therapy for metastatic breast cancer has been used principally as a second or third-line therapy following selective oestrogen
- The principle progestin used for metastatic breast cancer has been megestrol acetate
385
What are the risk factors of breast cancer?
- Early age of onset of menarche
- Late age to menopause
- Age at first full term pregnancy
- Some forms of the contraceptive pill
- Hormone replacement therapy
- Obesity
- Diet, physical activity, height, medication (aspirin)
386
What does leukaemia result from?
- 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 which leads to steady expansion of the leukaemic clone
387
How does leukaemia differ from other cancers?
- Most cancers exist as a solid tumour
- 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
- Leukaemia is different because haemopoietic and lymphoid cells behave differently from other body cells
- Normal haemopoietic stem cells can circulate in the blood and both the stem cells and the cells derived from them can enter tissues
- Normal lymphoid stem cells recirculate between tissues and blood
388
How are leukaemias described?
- Leukaemias that behave regularly 'benign' are called chronic- the disease goes on for a long time
- Leukaemias that behave in a 'malignant' manner are called acute- meaning if they are not treated the disease is very aggressive and the patients dies quite rapidly
389
How is leukaemia classified?
- Depending on the cell of origin, it can be lymphoid or myeloid
- Lymphoid can be B or T lineage
- Myeloid can be any combination of granulocytic, monocytic, erythroid or megakaryocytic
- Examples:
Acute lymphoblastic leukaemia (ALL)
Acute myeloid leukaemia (AML)
Chronic lymphocytic leukaemia (CLL)
Chronic myeloid leukaemia (CML
390
Why do people get leukaemia?
- Loss of function of a tumour-suppressor gene (deletion or mutation)
- Tendency to increased chromosome breaks, likelihood of leukaemia increases
- If the cell cannot repair DNA normally, an error may persist whereas in a normal person the defect would be repaired
391
What leukaemogenic mutations result in 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 brings it under the influence of the promoter or enhancer of another gene
392
What inherited or constitutional abnormalities can contribute to leukaemogenesis?
- Down's syndrome
- Chromosomal fragility syndromes
- Defects in DNA repair
- Inherited defects of tumour-suppressor genes
393
What are the identifiable causes of leukaemogenic mutations?
- Irradation
- Anti-cancer drugs
- Cigarette smoking
- Chemicals: benzene
394
What happens in Acute myeloid leukaemia?
1) Cells continue to proliferate but they no longer mature so there is
- A build of the most immature cells- myeloblasts (blast cells) in the bone marrow with spread into the blood
- A failure of production of normal functioning end cells- neutrophils, monocytes, erythrocytes, platelets
2) In AML the responsibly mutations usually affect transcription factors so the transcription of multiple genes in affected
395
What happens in Chronic myeloid leukaemia?
- 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 receptor or a cytoplasmic protein
- Cell kinetics and function are not as seriously affected as in AML
- The cell becomes independent of external signals, there are alterations in the interaction with the stroma and there is reduced apoptosis so that cells survive longer and the leukaemic clone expands progressively
396
With regards to to the production of end cells, how does AML and CML differ?
```
AML= Failure of production of end cells
CML= Increased production of end cells
```
397
What is the difference between acute and chronic lymphoid leukaemias?
- Acute lymphoblastic leukaemia has an increase in very immature cells (lymphobalasts) with a failure of these to develop into mature T and B cells
- Chronic lymphoid leukaemias: The leukaemic cells are mature although are abnormal T or B cells
398
What characteristics does accumulation of abnormal cells in leukaemia cause?
- Leucocytosis
- Bone pain (if leukaemia is acute)
- Hepatomegaly
- Splenomegaly
- Lymphadenopathy (if lymphoid)
- Thymic enlargement (if T lymphoid)
- Skin infiltration
399
What characteristics do the metabolic effects of leukaemic cell proliferation in leukaemia cause?
- Hyperuricaemia
- Renal failure
- Weight loss
- Low grade fever
- Sweating
400
What characteristics does the crowding out of normal cells in leukaemia cause?
- Anaemia
- Neutropenia
- Thrombocytopenia
401
What is a standard feature of chronic lymphoid leukaemia?
Loss of normal immune function as a result of loss of normal T cell and B cell function
402
What is acute lymphoblastic leukaemia largely a disease of?
Children
- Suggests that is may result from delayed exposure to a common pathogen
- Family size, new towns, socio-economic class, early social interactions, variations between countries
403
What are the clinical features of acute lymphoblastic leukaemia that result from the accumulation of abnormal cells?
- Bone pain
- Hepatomegaly
- Splenomegaly
- Lymphadenopathy
- Thymic enlargment
- Testicular enlargement
404
What are the clinical features of acute lymphoblastic leukaemia that result from the crowding out of normal cells?
```
Caused by anaemia:
- Fatigue
- Lethargy
- Pallor
- Breathlessness
Caused by neutropenia:
- Fever and other features of infection
Caused by thrombocytopenia:
- Bruising
- Petechiae
- Bleeding
```
405
What are the haematological features of acute lymphoblastic leukaemia?
- Leucocytosis with lymphoblasts in the blood
- Anaemia (normocytic, normochromic)
- Neutropenia
- Thrombocytopenia
- Replacement of normal bone marrow cells by lymphoblasts
406
What are the investigations for acute lymphoblastic leukaemia?
- Blood count and film
- Check of liver and renal function and uric acid
- Bone marrow aspirate
- Cytogenetic/molecular analysis
- Chest X-ray
407
Why is cytogenic and genetic analysis useful in acute lymphoblastic leukaemia?
- Cytogenic/molecular genetic analysis is useful for managing the individual patient as it gives more information about prognosis
- It advances the knowledge of leukaemia as it has permitted the discovery of leukaemogenic mechanisms
- Hyperdiploidy reveals a good prognosis
- Recipricol translocation between chromosome 4 & 11 is a poor prognosis
408
What are the leukamogenic mechanisms of acute lymphoblastic leukaemia?
- Formation of a fusion gene (translocation)
- Dysregulation of proto-oncogene by juxtaposition of it to the promoter of another gene e.g. T-cell receptor gene
- Point mutation in a proto-oncogene
409
How is acute lymphoblastic leukaemia treated?
1) Supportive
- Red cells
- Platelets
- Antibiotics
2) Systemic chemotherapy
3) Intrathecal chemotherapy
