Cancer biology Flashcards
1
Q
What is the percentage of breast cancer cases linked to over-expression of HER 2 gene?
A
25 %
2
Q
How does the over-expression of HER 2 result in the development of breast cancer?
A
HER 2 is a hetero dimer sub-class of EGFR receptors. Over-expression of the receptors amplify the downstream signalling pathway resulting in increased transcription factors for cell proliferation (sustaining proliferative signalling).
3
Q
What class of chemotherapy is Trastuzumab?
A
Monoclonal antibody
4
Q
How does Trastuzumab work?
A
Binds to the extracellular domain of the receptor, preventing HER2 homodimerisation and hence the downstream signalling pathway.
5
Q
How do Cetuximab and Panitumumab work and what type of cancer are they commonly used for and why?
A
Bind to the EGFR portion of the receptor and are commonly used for colorectal cancer. (A high proportion of colorectal cancer is linked to EGFR overexpression).
6
Q
How do Erlotinib and Gefitinib work?
A
They inhibit the tyrosine kinase portion of the EGFR, which is often highly expressed or mutated in non-small cell lung cancer in which the drugs are often indicated for. Upon binding to the ATOP site this prevents transphosphorylation of the tyrosine residues and hence the signal cannot be transducted.
7
Q
How would you define cancer?
A
Abnormal growth of cells in an uncontrolled way that can spread and metastasis to other tissue.
8
Q
Describe the difference between benign and malignant tumours.
A
Whilst both benign and malignant tumours have cell abnormalities and are unregulated within the body, benign tumours grow much more slowly and do not metastasise and therefore are not classified as cancerous.
Malignant tumour cells are cancerous therefore they do have cell abnormalities, they have rapid uncontrolled cell division and they ability to metastasise to other tissue.
9
Q
Describe the difference in definition between carcinomas and sarcomas.
A
Firstly both are types of cancer and are merely describing where in the body the cancer develops.
Carcinomas are cancers that originate from epithelial tissue, the tissue covering the internal and external structures and organs in the body.
Sarcomas however originate in the connective and supportive mesenchymal tissue.
10
Q
What are the four different classifications of carcinomas?
A
Adenocarcinoma when the cancer develops within an glandular secreting cell keeping the tissue moist.
Squamous cell carcinoma where the cancer develops in the squamous cells which are flat, surface covering cells which line the throat for example.
Transitional cell carcinoma are cells that stretch as the organ expands and they make up the transitional epithelium.
Basal cell carcinomas are cells deepest in the skin.
11
Q
Which organs are most affected by carcinomas?
A
Normally organs that are capable of secreting such as the breasts (milk), prostate (semen), colon (gastro-intestinal fluids) and the lungs (mucus).
12
Q
What are some examples of where sarcomas tend to occur?
A
Bone
Tendon
Cartilage
Muscle
Fat
13
Q
What are some examples of sarcomas?
A
Ewing’s sarcoma (bones or tissue around the bones)
Fibrosarcoma (fibrous connective tissue)
Glioma or astrocytoma (connective tissue in the brain)
14
Q
What is the difference in demographics that are affected by carcinomas and sarcomas?
A
Carcinomas tend to affect elderly people more whereas sarcomas are more commonly seen in young people.
15
Q
Aside from differences in where they occur and the demographics they affect, what are some of the other differences between carcinomas and sarcomas?
A
There is less vascularity in carcinomas in comparison to sarcomas and therefore sarcomas spread and metastasis more rapidly and therefore have an increasingly high malignancy and lower prognosis compared to carcinomas.
16
Q
Aside from carcinomas and sarcomas what are the other groups that cancers are divided into?
A
Myeloma
Leukemia
Lymphoma
Brain and spinal
Mixed type
17
Q
Describe the development of adenocarcinomas.
A
Normally a single mutated cell has sustained proliferative signalling, resulting in hyperplasia of cell type forming a benign adenoma before dysplasia occurs, the tumour has acquired a substantial number of mutations resulting in the development of malignancy. Now malignant the tumour cells then invade the basal lamina into the connective tissue by the developing angiogenesis into the bloodstream and are able to metastasise (invasive cancer).
18
Q
What percentage of cancers are carcinomas?
A
85%
19
Q
What percentage of cancers are sarcomas?
A
1% every year in the UK (on her slides says 12% of cancers are sarcomas)
20
Q
What are the two types of sarcomas?
A
Bone sarcomas
Soft tissue sarcomas
21
Q
What are some examples of soft tissue sarcomas?
A
Cartilage (Chondrosarcoma)
Muscle (Rhabdomyosarcoma or Leiomyosarcoma)
22
Q
What percentage of cancer cases are due to leukemia?
A
3% of all cases each year
23
Q
What percentage of cancer cases are due to lymphoma?
A
5% of all cases each year
24
Q
How is leukaemia defined?
A
Leukaemia is cancers of the immature white blood cells that proliferate and divide in the bone marrow before accumulating within the bloodstream.
25
What are the four main types of leukaemia?
Acute myeloid leukaemia
Chronic myeloid leukaemia
Acute lymphoblastic leukaemia
Chronic lymphocytic leukaemia
26
What is the difference between myeloid and lymphoblastic / lymphocytic types of leukaemia?
Myeloid leukaemia is when the cancer originates from granulocytes or monocytes within the bone marrow whereas lymphoblastic/ lymphocytic leukaemia is when the cancer originates from the lymphocytes.
27
Where do lymphomas develop?
Cancer that originates in the lymph glands or nodes within the lymphatic tissue.
28
What is the function of the lymph nodes?
To produce immune cells such as lymphocytes and to purify bodily fluids. The lymphatic system includes nodes, vessels and glands.
29
Define carcinogenesis.
It is the process in which normal cells evolve into cancerous cells as a result of an accumulation of mutations.
30
Define tumour progression.
It is defined as the irreversible change in the tumor characteristics reflecting the sequential appearance of a genetically altered subpopulation of cells with the new characteristics.
31
What is tumour progression driven by? *
Random mutations
Epigenetic alterations (changes in DNA methylation) of DNA that affects proliferation and survival
Increased expression of peptides and other mitogenic peptides*
32
What are the three main ways that DNA mutations arise?
Mistake during replication
Nucelotides undergoing spontaneous chemical changes
Effect of mutagenic agents
33
Explain the example of mistakes in DNA replication.
Incorrect base can be added due to miscorporation of nucleotides being added during replication and proofreading enzymes such as DNA polymerases fail to recognise the error.
34
What is the consequence of nucleotides undergoing spontaneous chemical changes?
Bases can be missed or purines are removed
35
What are the two types of mutagenic agents?
External mutagenic agents such as industrial chemical agents like vinyl chloride, benzo(a)pyrine- 4,5-epoxide in addition to UV and X-rays which can all cause DNA damage.
Internal mutagenic agents such as reactive oxygen species which are produced as a result of metabolism or inflammation.
36
How do reactive oxygen species result in DNA damage and hence mutation?
Reactive oxygen species produce reactive free radicals , which can cause a double strand break in the DNA as a result of ROS-conversion of guanine to 8-oxyguanine so it can pair with cytosine and adenonine which can result in double strand breaks and leads to genomic instability.
37
What mutations arise as a result of exposure chemical agents?
Chemical agents such as Asbestos, Benzo(a)pyrine-4,5-epoxide causes cross linking in the DNA strands or single or double breaks within the DNA.
38
What mutations arise as a result of exposure to UV or ionising radiation?
Ionising radiation can result in single or double breaks within the DNA strands or UV radiation specifically can cause pyrimidine linking (pyrimidine dimerisation on the intrastrand).
39
Which type of cancer has pyrimidine linking been associated with?
Melanoma
40
What is the cause of a bulge in the DNA forming as a result of deletion or insertion of a nucleotide?
Due to an intercalating agent inserting itself into the DNA and which results in the addition or subtraction of a nucleotide during replication or recombination.
41
What are some examples of an intercalating agents?
They tend to be flat, planar molecules such as benzo(a)pyrene.
42
To recap, what are the seven mechanisms of mutation?
Incorrect base
Missing base
3' deoxyribose fragments
Bulge due to the deletion or insertion of a nucleotide
Single or double breaks
Linked pyrimidines
Crossed linked strands
43
Despite all of these mutations occuring in everybody at times, how does cancer actually occur?
Cancer occurs when there is a fault with the repair enzymes which means the mutation cannot be rectified.
For example, UV induced skin cancer there is a fault with the nucleotide excision repair mechanisms.
44
Describe the mechanism in which DNA viruses can induce cancer?
The virus has infected cells by inserted their own episome (circular piece of DNA) into the host cell. The viral DNA can code for proteins that will promote cell proliferation (sustaining proliferative signalling) or code for proteins that will inhibit tumour suppressor genes (avoiding growth suppressors).
45
Describe how the human papillomavirus can lead to cancer?
Two genes human papillomavirus are E7 and E6. Both genes not only encode for onco-proteins (sustaining proliferative signalling) but they also interfere with tumour suppressor genes. E7 oncogene associates with the retinoblastoma inducing its proteosomal degradation. E6 meaning associated with p53 and hence targets its for proteasomal degradation?
46
In the majority of cervical cancers would you expect there to be a mutation in Rb or p53 or not?
According to WHO 95% of cervical cancers are believed to be linked to HPV. Therefore, it is understood HPV contains two specific oncogenes E6 and E7 which encode for the proteosomal degradation of tumour suppressors genes Rb and p53 respectively, ultimately resulting in their downregulation. Therefore in cervical cancer it is belived that it is the downregulation of the tumour suppressor genes rather than mutations that occur within them that lead to the development of cervical cancer.
47
Which human herpes viruses have been identified as being oncogenic viruses?
Epistein Barr virus (EBV) and Kaposi sarcoma associated virus (KSHV)
48
Despite only two types of HHV being identified as oncogenic, can other types of HHV cause cancer?
Yes, for examples herpes simplex 1 and 2 has been linked to prostate cancer and melanoma.
49
How does EBV cause cancer?
The virus contains genes which encodes for proteins inducing hypermethylation of the tumour suppressor gene RAS (specifically RASSF1A) which cause sustained proliferation as it is downstream of the growth receptor signalling pathway. Furthermore p16 a tumour suppressor protein undergoes homozygous deletion and methylation and hence is downregulated. p16 is a cdk inhibitor, preventing phosphorylation of the Retinoblastoma, with p16 downregulated the cyclin dependent kinase is no longer inhibited and Rb is constantly phosphorylated and inactivated.
50
How does Kaposi sarcoma associated virus cause cancer?
The virus has two specific genes vIRF3 and ORF73 both of which inhibit p53 activity and therefore p53 cell-induced apoptosis. A third viral gene ORF16 encodes the viral Bcl-2 protein (pro-survival) which also inhibits apoptosis (evading apoptosis).
51
Describe the two mechanisms in which RNA viruses induce carcinogenesis?
As RNA viruses insert themselves into into the host genome, they can induce carcinogenesis either by:
Providing and inserting an additional proliferative gene that alters the growth in the host cell
Or by insertional mutagenesis where the virus intergrates into the DNA close to a host gene, a proto-oncogene that encodes for cell growth (such as a growth factor), and the virus can then promote or enhance that gene expression.
52
Describe the direct mechanism of viral carcinogenesis.
The virus is either a DNA virus in which an episome is formed and results in viral oncogene expression or as a RNA virus insertion into the host genome can also lead to viral oncogene expression (either through insertional mutagenesis or additional proliferative genes). Viral oncogene expression then leads to sustained proliferative signalling, avoiding growth suppressors, cell survival, telomerases and increase in genetic instability leading to cancer.
53
What type is viral carcinogenesis is the virus acting internally and which is it acting externally?
Virus acts internally in direct viral carcinogenesis and acts externally in indirect viral carcinogenesis.
54
Which type of viral carcinogenesis would you expect the cancer cells to be within the monoclonal form?
Direct viral carcinogenesis as it is acting within and therefore is aiming to maintain the tumour phenotype.
55
Describe indirect viral carcinogenesis?
Virus infects cells and as a result release chemokines which attracts pro and anti-inflammatory cells to the site of viral infection. As a result of their metabolism pro-inflammatory cells release reactive oxygen species which release free radicals which can induce mutation by a double strand break and others by constant years of inflammation.
56
Explain how HIV is an example of indirect viral carcinogenesis?
At the beginning of a HIV infection, CD8+ T-cells are able to undergo their normal function but once immuno-suppression has occured there are no T-cells to immuno-suppress tumour growth and the normal defence mechanisms.
57
What type of cancers do patients with HIV normally get?
Lymphomas associated with EBV or Kaposi associated sarcoma.
58
Which types of cancer does EBV cause?
Burkitt's lymphoma
Nasopharyngeal carcinoma
59
Which type of cancer does Human herpes virus 8 cause?
Kaposi's sarcoma
Body cavity lymphoma
60
Which types of cancer does hepatitis B and C cause?
Hepatocellular carcinoma
61
Define hypertrophy of cells vs hyperplasia.
Hypertrophy is an increase in the size of cells (specifically muscle cells, normally achieved through exercise) whereas hyperplasia is the increase in the number of cells (increase in muscle fibres).
62
What is atrophy?
Reduction in size of muscle cells (opposite to hypertrophy).
63
Describe what occurs with dysplasia cells.
Often indicative of an early neoplastic stage, the cell to cell interactions are broken down and there is an expansion of immature cells with a reduction in number and size of mature cells.
64
Describe metaplasia.
When one cell types changes into another.
65
What are the four main phases in carcinogenesis?
Initiation
Promotion
Progression
Metastasis
66
What phase does hyperplasia occur?
In the promotion phase
67
Describe the process of carcinogenesis development.
Firstly a normal cell undergoes initiation step if it is exposed to a mutagen or there is a breakdown in the repair mechanisms and it becomes an initiated cell. In the promotion stage there are a series of other mutations that occur that gives rise to preneoplastic cells or dysplasia occur. At this point it is reversible however if a series of other mutations then occur neoplasia occurs and the tumour size will rapidly grow and metastasise.
68
Where does cancer originate from in colon?
In the colonic crypt epithelium
69
Describe the genetic mutations that arise in colon cells that result in the development of carcinogenesis.
The development from normal, healthy colon cells to the construction of a small benign tubular adenoma is a consequence of inhibition of a tumour suppressor gene (A PC beta catetin), DNA hypomethylation and a mutation in the proto-oncogene Ras. The progression of a small benign adenoma to a larger one is believed to be a result of inhibition of another two tumour suppressor genes including TSG 101. From the progression of a large but benign adenoma to carcinoma, T53 is inhibited.
70
Define neoplasia.
Neoplasia is a direct result of dysplasia (expansion of immature cells) and metaplasia (when one cell type converts to a less differentiated one). The state of neoplasia, genetically abnormal cells growing at an uncontrolled rate, is one that cannot be returned to normal, regulated one.
71
What is the mutation that arises in the Ras proto-oncogene?
It is a point mutation, where a guanine is converted to a thymidine (GGC to GTC) meaning that instead of a glycine being coded, a valine is coded instead.
72
What percentage of cancers are found to contain a mutation in the Ras proto-oncogene?
30%
73
Would you expect immortalised cancer cells to cause a tumour in a mouse?
No, they are not cancer cells and do not have the ability to metastasise. They most likely have a couple of mutations however they are not capable of causing cancer in a mouse.
74
Describe the beginning of Weinburg's experiment.
Took a biopsy of cells from a patient who had bladder cancer, isolated the DNA from the cells and inserted it into the immortalised cells.
75
What did Weinburg observe once he had injected the immortalised cancer cells?
Most of the cells remained with the same mutations as before the injection and behaved accordingly, however some cells had genetically mutated further and demonstrated neoplasia and had begun to colonise.
76
After the observations, what did Weinburg do?
Isolated the neoplastic cells and then injected them into the mouse. As a result a tumour did grow inside of the mouse. He then isolated the human genes from the mouse and confirmed the Ras mutation.
77
What are the four main types of mutations in the GF signalling cascade?
Gene amplification
Gene rearrangements (promoter misplacement results in a weakly expressed gene, becoming strongly expressed)
Large structural deletions
Subtle mutations (Ras)
78
In reference to the GF signalling pathway, where does gene amplification occur?
Growth factor
Receptor and tyrosine kinase domains
Transcription factor
79
In reference to the GF signalling pathway, where does gene rearrangements occur?
Transcription factor
80
In reference to the GF signalling pathway, where does large structural deletions occur?
Receptor and tyrosine kinase domains
81
In reference to the GF signalling pathway, where does subtle mutations occur?
Ras
82
Which chromosome and gene is linked to chronic myeloid leukaemia?
Philadephia chromosome and activated oncogene BCR-ABL
83
What is a fusion protein?
Proteins that are created through the joining of two genes that normally code for different proteins
84
In BCR-ABL which two chromosomes fuse together?
Chromosome 22 contains the BCR (break point cluster region) fuses with chromosome 9 which contains a protein tyrosine kinase, used for cell adhesion and growth.
85
Explain how fusion of the BCR-ABL results in the development of CML?
When the two genes BCR and ABL have fused together, and are in close proximity to each other. This new gene forms now regulates the activity of ABL (tyrosine kinase) as it has lost its regulatory domain, meaning that the tyrosine kinase domains are constantly switched one, regardless of whether a growth factor is also present. Furthermore RAS due to being downstream of the tyrosine kinases are also activated by the BCR-ABL oncogene and the PI3K and JAK STAT signalling pathway, resulting in increased production of transcription factors leading to sustained proliferative signalling.
86
Which is the negative regulator of the tyrosine kinase domain in the ABL gene?
SH3 domain present on the ABL gene
87
Is the SH3 domain of the ABL gene within the BCR-ABL gene?
No, the regulatory is not present
88
In the RAS signalling pathway which domain is targeted by the Tyrosine 177 residue on the BCR portion of the BCR-ABL gene?
When the tyrosine residue is phosphorylated it interacts with the SH2 domain of GRB2 adaptor proteins, initiating downstream signalling pathways (PIP2 and PIP3) involved in cell growth, inhibit cell cycle arrest, and inhibit tumour suppressor genes.
89
How does BCR-ABL activate the JAK signalling pathway?
Increased production of IL-13 and G-CSF which are ligands required to stimulate the tyrosine kinase receptors leading to activation of JAK and STAT-5 signalling.
90
Briefly describe how Imanitib and other tyrosine kinase inhibitors work in the treatment of cancer?
Binds to the ATP binding site preventing the phosphorylation of the tyrosine kinase residues preventing activation of growth factors and inducing the downstream signalling pathways.
91
Describe where the different cyclins and cyclin-dependent kinases are found on the cell cycle?
Cyclin D binds with Cdk-4 and 6 in the G1 phase of the cell cycle
Cyclin E binds to Cdk-2 in across the G1/S checkpoint
Cyclin A binds to Cdk-2 in the S phase and across the S/G2 checkpoint
Cyclin B binds to Cdk-1 in the M phase
92
Where does retinoblastoma act?
Acts at the G1/S checkpoint, prevents the cells from entering the S phase in the cell cycle.
93
What mutations would you expect of retinoblastoma in a cancer patient?
Cancer patients can have a deletion or a point mutation within the retinoblastoma protein, they can no longer prevent activation by binding to the E2F transcription factor.
Some viruses have domains that bind directly to the retinoblastoma protein such as E7 in the human papillomarvirus.
94
How can mutant retinoblastoma, a recessive gene cause cancer?
If a child from parents who are both carriers of a defect in the retinoblastoma gene, inherit the mutation so has Rb (+) and Rb (+) they will at high risk of developing cancer or the child just inherits one Rb (+) and then later in life acquires a second mutation, they will also develop it.
95
Define sproadic cancer.
Completely by chance of developing cancer, no family relatives with a history of cancer, just a chance event.
96
Define familial cancer.
Combination of genetic and environmental factors.
97
Is there a family history of cancer in familial cancer?
Relatives do demonstrate the same type of cancer however there is no pattern to the inheritance.
98
Define hereditary cancers.
Where there is a specific altered gene that is passed on from parent to child. These children are at risk, if positive, of developing multiple types of cancer or developing cancer at an earlier age.
99
What is the specific altered gene linked to colon cancer?
APC (adenomatous polyposis coli) gene
100
How is p53 activated what happens when it is?
When p53 is activated by phosphorylation due to DNA mutation, p21 (a cyclin dependent kinase inhibitor) is upregulated, this inhibits apoptosis and enabling cell cycle arrest due to inhibiting cyclin dependent kinases and by binding to PCNA (proliferative cell nuclear antigens) DNA repair can commence.
101
Which three viruses have linked P53 suppressor effects?
Hepatitis B
Human T-cell lympho-tropic virus
Human papillomavirus (Type 16)
102
What are the conditions for when is p53 activated?
Oxidative stress
Hypoxia
Nutrient deprivation
Replicative stress
DNA damage
Hyperproliferative signalling
Ribonucleotide depletion
Telomere attrition
103
What are the three main effects of p53?
Cell cycle arrest (association with p21)
DNA repair
Apoptosis
104
Describe p53's role in inducing apoptosis?
Inhibits BCLX-2 which is a pro-survival protein
Activates BAX signalling pathway which is a cell death effector
105
Describe the BAX signalling pathway.
BAX causes outer mitrochondrial permeabilistion which release cytochrome C from the mitrochondria into the cytosol. In the cytosol, Cytochrome C engages the apoptotic protease activating factor-1 (APAF1), and forms the apoptosome, which activates caspase-9 which triggers caspase-3 activation which dismantles the cell.
106
What is the relationship between MDM2 and p53?
MDM2 is believed to regulate p53 activity by inducing p53 degradation by the proteasome.
107
How would you expect MDM2 to be different in malignant cells in comparison to healthy ones.
MDM2 gene amplification in cancer, results in a downregulation of p53 tumour suppressor activity.
108
What cancers have the highest prevalence linked to mutations in the p53 tumour suppressor?
Ovary (about 50%)
Oesphagus
Colorectal
Head and neck
109
With the four most common types of cancer in the UK list the link to p53 mutation?
Colorectum (45%)
Lung (38%)
Breast (28%)
Prostate (13%)
110
What type of mutations occur to p53?
Missense mutations
Gene amplification of MDM2
Inactivated by viral proteins
111
What are some viral proteins that inhibit p53?
Adenovirus protein E1B
Human papillomavirus protein E6
Hepatitis B HBX
112
What is the Hayflick limit?
Healthy cells are only able to divide 20-70 times
113
What are some examples of the cellular stresses?
DNA damage
Activated oncogenes
Hypoxia
Ribonucleotide depletion
Telomere erosion
These exert different cellular responses.
114
What are some examples of cellular responses?
Apoptosis
Cell cycle arrest
DNA repair
Differentiation
Sensence
115
What is the coding for the nucleotide repeat for telomeres?
TTAGGG
116
In addition to telomeres what is also present at the end of chromosomes?
Shelterin
117
What percentage of tumours are linked to overexpression of telomerases?
85-90% of malignant tumours
118
What is the effect of overexpression of telomerases?
By-pass the crisis checkpoint by upregulating telomerases and also avoid the cell cycle checkpoints and hence are immortalised, any limitation to cell division is removed.
119
What type of mutations affect telomerases?
Telomerase promoter mutations
120
What are the four main classes of cells that make up the tumour micro-environment?
Immune cells
Stromal cells
Epithelial cells
Vascular cells
121
What are some examples of immune cells that make up a tumour micro-environment?
Myeloid derived suppressor cells
Mast cells
Macrophages
Lymphocytes
Neutrophils
Bone marrow dervied cells
Memory effector T-cells
122
What are some examples of stromal cells that make up a tumour micro-environment?
Fibroblast
Mesenchymal stromal cells
123
What are some examples of epithelial cells that make up a tumour micro-environment?
Normal epithelial cells
Invasive tumour cell, cancer stem cells
124
What are some examples of vascular cells that make up a tumour micro-environment?
Endothelial cells
Pericyte
Lymphatic endothelial cells
125
How do immune cells contribute to the cancer micro-environment?
Immune cells release reactive-oxygen species and these free radicals then can lead to the development of even more mutations.
126
How do stromal cells contribute to the cancer micro-environment?
Mesenchymal stromal cells, help aid metastasis and invasion of the tumour.
127
What are the three substances tumour promoting inflammatory cells release and how to do they help aid tumour growth?
They release vascular endothelial growth factors which then acts on the endothelial cells, helps aid angiogenesis
Also release endothelial growth factors which grows the cancer cells
Lastly secretes proteases including matrix metallo-proteases which degrade the extracellular matrix.
128
How do cells interact with the extracellular matrix?
Through integrins expressed on their cell surface.
129
What are integrins?
They are heterodimers and acts as transmembrane linkers between the extracellular matrix and the actin cytoskeleton.
130
What does the extracellular matrix release upon degradation?
Sequestered growth factors (vascular endothelial cells) helping the blood vessels grow
131
How are cancer stem cells defined?
They can form tumours when transplanted in animals but normal stem cells cannot
132
What is a key difference between cancer stem cells and normal stem cells?
Cancer stem cells have no control over their cell numbers (sustained proliferative signalling).
133
What percentage of a tumour is thought to be cancer stem cells?
Only 1%
134
What are some of the functions of cancer stem cells?
Important for the growth of new tumour cells
Chemo resistance
Express specific markers
Responsible for the epithelial mesenchymal transition
135
What is often the cause of tumour relapse?
Due to cancer stem cells being resistant to the chemotherapy (may be quiescent at the time) however they then proceed to mutate, proliferate and divide forming a secondary tumour.
136
What therapy is used to target cancer stem cells but what are some of the additional problems?
Anti-CSC therapy however it is important to understand that from the primary to the secondary tumour additional mutations can be acquired and therefore it is important to take a secondary biopsy of the tumour to understand which additional genetic mutations the tumour has now acquired.
137
What are some of the expressed specific markers that can be targeted in treating cancer stem cells?
CD 133, CD 24, CD 44, these are cell surface markers expressed on stem cells
138
What are some of the enzymes that can be targeted in treating cancer stem cells?
Aldehyde de-hydrogenase ALDH, expressed by stem cells, highly-chemo resistant stem cells have high expression of these enzymes.
139
Which transcription factor is targeted in treating cancer stem cells?
OCT-4
140
Which drug effluxs pumps are targeted in treating cancer stem cells?
Multi-drug resistant transporter1 (MDR1)
141
What are some of the activated signalling pathways in cancer stem cells that can be targetted?
Wnt / B catenin
Notch Hedgehog
142
Describe the differences in conditions between the normoxic and hypoxic environment?
Normoxic:
Well oxygenated
Low HIF-1 alpha, so responds to oxygen
Susceptible to chemo and radiotherapy
Close to blood vessels
Hypoxic:
Poorly oxygenated
Poor immune response
High HIF-1 alpha
High genetic instability
Not susceptible to chemo and radiotherapy
143
How does necrosis promote further tumour development and growth?
When cells undergo necrosis, their cell death is not controlled and therefore as a result everything is spilled out resulting in an inflammatory response and hence reactive oxygen species resulting in an increased chance of mutation.
144
How does hypoxic induced cells occur?
Cells exist in a hypoxic environment and if over time, one develops a mutation (for example p53) then a tumour is able to develop rapidly.
145
Describe the link between HIF-1 alpha and Von Hippel Lindau?
In normoxic conditions HIF-1 alpha is at low concentrations and part of the E3 ubiquitin ligase complex, von hippel lindau protein (tumour suppressor) interacts with HIF-1 alpha and targets it for degradation. In hypoxic conditions HIF-1 alpha is stabilised at higher concentrations.
146
What are some of the functions of HIF-1 alpha?
Induces transcription of many proteins including vascular endothelial growth factors which hence promotes angiogenesis.
147
How does degradation of the extracellular matrix facilitate metastasis?
Once the extracellular matrix has been degraded by matrix metallo-proteases secreted by tumour promoting inflammatory cells, this then leaves integrins exposed which can then sprout towards the blood vessels. Also due to these proteases the blood vessels are now more permeable to fluids, cancer cells from leaking out.
148
What are some of the effects of tumour promoting cells secretion of VEGF on VEGF receptors on the endothelial cell receptors?
Cause proliferation through MAPK downstream signalling
Induce proteins to break down the extracellular matrix
149
What are some of the proteases used for the degradation of the extracellular matrix?
Matrix metallo-proteases
Urokinase-type Plasminogen Activator
Urokinase-type Plasminogen Activator receptor
Plasminogen activator
150
How does degradation of the extracellular matrix facilitate angiogenesis?
Extracellular matrix is degraded by the matrix metallo-proteases secreted from the tumour inflammatory cells, this leaves the blood vessels exposed to secretions of the growth factors, they can now bind to receptors on the endothelial cell surface causing angiogenesis.
151
What are some of the other functions of VEGF?
Helps newly formed endothelial cell survive by up-regulating inhibitors of apoptosis.
Triggers endothelial cells to express proteins needed for angiogenesis.
152
How does Avastin work?
Avastin directly binds vascular endothelial growth factor (VEGF) to inhibit angiogenesis
153
How does Cetuximab work?
Antibody that binds directly to the epidermal growth factor receptor on both cancerous and non-cancerous cells.
154
Describe how proteolytic degradation between two cells occurs in a tumour microenvironment .
Macrophages (immune cells found in the tumour micro-environment) in addition to stromal cells can secretes matrix metallo-proteases which cleaves E-cadherin, the cell adhesion molecules which holds the cells together.
155
Describe the three functions of matrix-metallo proteases.
Cleaves E-cadherin between two cells
Cleaves the extracellular matrix
Activate cytokines or growth factors in the tumour micro-environment
156
What is stored within the extracellular matrix?
The extracellular matrix contains growth factors and chemokines which are inactive until it becomes degraded and then active cytokines and growth factors released are able to act upon the tumour cells.
157
What are some examples of stromal derived proteases?
Matrix metallo proteases
Serine proteases
158
What do cancer cells secrete which attracts macrophages and other stromal cells?
Colony stimulating factors
159
What are some of the cells responsible for participating in the epithelial to mesenchymal transition?
Macrophages
Stromal cells
160
Explain the positive feedback loop between macrophages and cancer cells?
Cancer cells secrete colony stimulating factors which attracts macrophages to the tumour site. These macrophages then secrete epithelial growth factors which then increases colony stimulating factor secretion from cancer cells which attracts even more macrophages and hence an increased epithelial growth factor is produced.
161
Which specific cysteine protease cleaves E-cadherin?
Cathepsin b secreted from macrophages
162
Once E-cadherin is cleaved, what do macrophages then secrete?
TNF-alpha and even more epithelial growth factor (EGF) which stops transcription of E-cadherin and instead promotes transcription of N-cadherin.
163
Describe the role of hepatocyte growth factor in EMT?
Hepatocyte growth factor is secreted from stromal cells as they release MMPs to degrade the extracellular matrix. HGF is a chemoattractant mitogen and hence they not only are responsible for attracting tumour cells but also induce actin rearrangements via Ras like GTPases.
164
What is the result of induced actin filament rearrangements within cancer cells?
The cancer cells as a result of actin rearrangement then produce flat, wide lamellipodia which are bundles of branching actin filaments meaning new adhesion are formed at the front and some are lost at the back, they branch towards the HGF.
165
What are the two interactions newly expressed N-cadherins on cancer cells form?
N-cadherins interact with and attach to stromal cells.
They also interact with endothelial cells and increase permeability into the blood vessels.
166
How do macrophages and pericytes assist in tumour cell migration?
Both cell types are located adjacent to the blood vessel. Macrophages secretes growth factors and chemokines to attract tumour cell to the blood vessel surface and pericytes also attracts factors such as CXCL12 that induces tumour cell migration, as it has the receptor CXCR4R
167
What are the five key steps in tissue invasion?
Loss of E-cadherin (cell adhesion molecules)
Changes in integrin expression
Increase in ECM degrading enzymes
Epithelial to mesenchymal transition
Increase in motility
168
How do tumour cells hide from NK cells in the bloodstream?
Covering themselves with platelet aggregates which are then removed upon extravastation
169
What are the three outcomes of tumour extravasation?
Apoptosis
Dormancy, nothing to support growth
Survival
170
What cells are crucial for macrometastasis?
Mature bone marrow derived cells, otherwise there is an angiogeneic dormancy, tumour growth is completely dependent upon angiogenesis.
171
What percentage of tumour cells successfully metastasise?
0.1%
172
Outline the key steps in tumour progression, invasion and metastasis.
Mutation
Proliferation
Angiogenesis
Primary tumour
Detachment
Intravastation
Migration
Extravastation
Invasion
Angiogenesis
Secondary tumor formation
173
Briefly describe glucose metabolism in a normal healthy cell.
In the presence of oxygen, aerobic respiration occurs in which glucose is metabolised to pyruvate which provides adenosine triphosphate by oxidative phosphorylation (ATP) for the cell in the mitrochondria, lactate is produced as a by-product.
In the absence of oxygen, anaerobic respiration occurs in which glucose is metabolised still to pyruvate but then ultimately to lactate.
174
How much ATP is produced per molecule of glucose for aerobic and anaerobic glycolysis in a normal healthy cells?
Aerobic respiration produces 36 mol per mol of glucose
Anaerobic respiration produces only 2 mol per mol of glucose
175
Describe the differences between aerobic glycolysis in cancerous cells to that of normal cells.
Whereas in normal healthy cells, lactate is only the major product under anaerobic conditions, in cancerous cells regardless of whether oxygen is present or not, after glucose is metabolised to pyruvate only 5% of the pyruvate pathway is utilised for the generation of ATP and 85% of the pathway produces lactate.
176
How much ATP is produced per molecule of glucose for aerobic and anaerobic glycolysis in a cancerous cells?
4 mol of ATP per mol of glucose
177
What are the main cellular consequences when lactate is the primary product formed as a result of aerobic glycolysis in cancer cells?
In hypoxic environments, which contributes to a proportion of the tumour micro-environment, cancerous cells are able to generate ATP more readily for mitosis than normal, healthy cells. Anaerobic respiration in healthy cells only contributes to 2 mol of ATP per mol of glucose, however aerobic glycolysis in cancerous cells contributes to double the amount (4 mol of ATP per mol of glucose).
178
How can altered cellular metabolism be exploited in improved detection of cancers?
Tumor cells not only have altered glucose metabolism but they also increase the uptake of glucose by upregulating glucose transporters, normally GLUT-1. PET scans have been programmed to detect increased uptake and utilisation of glucose by using a radiolabeled analogue of glucose (18F-fluorodeoxyglucose, FDG).
179
Describe the role of NK cells in detecting cancerous cells.
Recognise stressed cells (those with an altered metabolism for example)
Detect down-regulation of MHC-1 in tumour cells
Signal directly to T-cells
Present antigen to T-cells at the beginning of the cytotoxic T-cell activation
180
What is the role of CD8 (+) T- cells in cancer?
They recognise peptides derived from cytoplasmic proteins that are displayed bound to MHC-1 and induce apoptosis.
181
State the three different types of tumor expressed antigens.
Tumor specific antigens
Tumor antigens
Tumor associated antigens
182
What are tumour specific antigens?
Antigen expressed that is the cause of the tumour, for example an oncogene (such as a mutated RAS) or a tumour suppressor gene products (mutated p53 gene).
183
What are tumour antigens?
A protein with an abnormal structure, caused by a mutation and hence is a mutated self-protein. For example a mutated self-protein in carcinogen.
184
What are tumour associated antigens?
Mutation in a gene unrelated to the formation of the tumour but it can cause the synthesis of abnormal proteins (over-expressed self-proteins).
185
What are the three ways cancer cells inhibit T-cell induced apoptosis pathways?
Firstly cancer cells can prevent the loading of all types of tumour antigens to be presented on to the MHC-1 molecules which prevents the TCR being able to recognise the cells as cancerous and hence a downstream signalling pathway cannot be induced.
Tumour cells can also upregulate the expression of PD-Ligand1 which binds to the PD1 receptor on T-cells inhibiting and deactivating them via CD279.
Cancer cells also produce cytokines such as VEGF, IL-10, TGF-B, these all cause immuno-suppression as they attract a sub-type of T cells known as T regulatory cells and myeloid derived suppressor cells, which inhibit T-cells.
186
How can the metabolism in tumour cells affect immune responses?
Tumour cells compete for energy with immune cells and hence take away their energy resource, required for their function such as effector killing etc.
Furthermore the altered metabolism used in tumour cells lowers the pH which through signalling of VEGF and IFN-Y affects T-cell maturation and recruits myeloid derived suppressor cells which creates an immuno-suppressive environment.
187
What is the interaction between cancer cells and tumour promoting inflammatory cells?
Cancer cells release colony stimulating factor-1 and IL-1B which acts as chemo-attractants to immune cells such as macrophages and are crucial in for metastasis.
188
Where are the types of macrophages found in the tumour micro-environment?
Anti-tumour macrophages are found on the margins of the tumour microenvironment
Pro-tumour macrophages are found in the hypoxic environment
189
What are anti-tumour macrophages activated by?
IFN-Y or LPS (Lipopolysaccharide)
190
What are some of the downstream signalling effects of anti macrophage activation?
Production of immunostimulatory cytokines (key for T-cells)
Production of chemokines (key for lymphocytes)
Tumour cell lysis
Some reactive oxygen or nitrogen species but in a controlled way
Metalloproteinases, also in a controlled way
191
What are some of the downstream signalling effects of pro macrophage activation?
Pro-angiogeneic cytokines and enzymes such as VEGF and FGF
Production of reactive oxygen and nitrogen species (not in a controlled way), causing additional mutations
Production of cytokines including immuno-suppressive factors and mitogens
Production of a wide range of metallo-proteases (not in a controlled way), used to break down the ECM
Secretes tissue factors such as uPa
Produces chemotactic factors that attract monocytes, which then differentiate into macrophages.
192
What are the three substances tumour associated macrophages secrete?
Angiogeneic factors such as VEGF and IL-8, promoting angiogenesis
Matrix metallo proteases (specifically MMP-9) which digests the ECM
Release mitogenic factors which promotes tumour cell proliferation. These cell then release chemotactic factors, attracting monocytes which differentiate into macrophages and the cycle begins again.
193
What is the therapeutic target for the sustaining proliferative signalling hallmark of cancer?
EGF inhibitors
194
What is the therapeutic target for the evading growth suppressors hallmark of cancer?
Cyclin dependent kinase inhibitors
195
What is the therapeutic target for the enabling replicative immortality hallmark of cancer?
Telomerase inhibitors
196
What is the therapeutic target for the resisting cell death hallmark of cancer?
Proapoptotic BH3 mimetics
197
What is the therapeutic target for the inducing angiogenesis hallmark of cancer?
VEGF receptors
198
What is the therapeutic target for the activating invasion and metastasis hallmark of cancer?
Inhibitors if HGF/ c-met
199
What is the therapeutic target for the deregulating cellular energetics hallmark of cancer?
Aerobic glycolysis inhibitors
200
What is the therapeutic target for the tumour promoting inflammation hallmark of cancer?
Selective anti-inflammatory drugs
201
What is the therapeutic target for the avoiding immune destruction hallmark of cancer?
Immune activating anti-CTLA4 mAb
202
What is the therapeutic target for the genome instability and mutation hallmark of cancer?
PARP inhibitors
