Molecular Biology Flashcards
What are the 4 phases of the cell growth cycle?
G1
S
G2
M
Name some of the characteristics of tumour angiogenesis
Uncontrolled expression of pro-angiogenic factors
Disorganised vascular structure (lack of pericytes often)
Low integrity vessels that can collapse, causing hypoxia
Leaky microvasculature
How can we target Ras as an anti-cancer therapy?
Due to it having a lipid acid modification that allows it to bind to the membrane, we can inhibit the modification using peptidomimetics
…..These haven’t really worked though….
Why is losing the function of tumour suppressor genes (TSGs) more rare?
As they are recessive, so you need to lose both genes to see the effect
Becomes more common if you inherit one recessive gene
What are the 4 stages of asymmetric cell division?
Stem cell (totipotent)
Restricted potential stem cell (multipotent)
Progenitor cell (unipotent)
Terminally differentiated cell
What’s the difference between a benign and a malignant tumour?
Benign –> Non cancerous, localised, look like normal cells, surrounded by a fibrous capsule
Malignant –> Grow and divide rapidly, relatively undifferentiated, high nucleus to cytoplasm ratio, less defined border, can become metastatic
What part in cancer does Telomerase play?
Telomerase (reverse transcriptase enzyme) adds tandem repeats to the end of chromosomes to prevent them from being killed
Present in cancer cells and so prevent them from dying naturally….whilst not being present in most somatic cells naturally
How does p53 work?
It is normally complexed to the inhibitor MDM2 protein, rendering it…..inactive
When stressors are present, MDM2 is inhibited, allowing p53 to function
It works as a tetramer, so if one of the 4 units becomes mutated/damaged, the entire thing is non-functional but yet very stable, so it isn’t degraded! –> Meaning cells won’t die
What are 3T3 cells?
And what happens when they become transformed?
Fibroblasts
When transformed they have their RAS constitutively active due to a loss of p53, so the cells don’t stop proliferating
They also have less cell-to-cell contact, so the chance of them becoming metastatic increases
What is retinoblastoma?
A tumour in the retina
Recessive
Derived from a single cell (clonal) mutation to do with pRb
What is the main treatment for Gastro-Intestinal Stromal Tumours (GIST)?
Glivec (imatinib)
Driven by c-kit receptor activity
What are the 3 types of immunotherapy that can be used for metastatic cancer?
Ipilimumab –> Blocks CTLA4, enhancing the effects of T cells
Pembrolizumab/Nivolumab –> Block PD1, which increases the immune response by preventing the tumour cells from turning off T cells
What is VEGF-VEGFR?
A tyrosine kinase receptor that causes downstream signalling leading to angiogenesis
Eg, PI3K/AKT for cell survival
FAK for cell adhesion and migration
Ras –> ERK for proliferation
What are the 4 resistance mechanisms to anti-angiogenic drugs?
Metabolic adaption –> Finding nutrients from places other than the blood vessels
Re-vascularisation –> By expressing other factors like bFGF/PDGF
Co-option of normal peritumoural blood vessels and vascular mimicry –> The tumour cells mimic the endothelial cells
Drugs improve the blood supply –> Which means more nutrients can get to the tumour!
What is Li Fraumeni Syndrome?
An inherited disorder of mutated p53
Why can HER2 become constitutively active?
As the valine (which is hydrophobic and happy in its place) is mutated to glutamine, causing the receptor to close
- Known as the Neu oncoprotein
What is the Philadelphia Chromosome?
In CML there is a translocation between chromosomes 9 and 22, causing 9 to get longer and 22 smaller
BCR becomes partnered with ABL in chromosome 22, which means BCR can’t block the kinase domain, meaning cell division can occur
What is TEL-PDGF(B) receptor fusion in CMML?
A translocation between chromosomes 5 (TEL) and 12 (PDGF)
This causes the PFGF kinase to always be active, with the helix-loop region of TEL inducing oligomerisation
Glivec (imatinib) can be used to treat this
Mutations in what will result in EGFR inhibitors not working?
K-Ras, as occurs after the EGFR in the molecular pathway
What are the 3 things that can cause mutations?
Chemical carcinogens
Radiation
Viruses (HPV)
What is the Src tyrosine kinase?
In a healthy cell the Src genes tyrosine (Y) is phosphorylated, putting it into its inactive form, preventing cell growth….then when needed phosphatase removed it, allowing it to be active
In a cancerous cell the C-terminal tyrosine is mutated/non-existent and so the inactive form cannot be made…leading to a constitutionally active kinase (which drives cell growth)
When constitutively active, the cells have less cell-to-cell contact and so are more likely to become metastatic
What are the functions of the following drugs?
Aflibercept
Bevacizumab (Avastin)
Ramucirumab
Aflibercept –> A fake receptor that competes with all VEGFRs for the angiogenic proteins
Bevacizumab (Avastin) –> An anti VEGF-A antibody
Ramucirumab –> An anti VEGFR-2 antibody
What are the 3 ways of preventing tumour angiogenesis?
Inhibiting production of angiogenic proteins
Neutralising angiogenic proteins
Inhibit receptors for angiogenic proteins
What type of cells commonly become cancerous?
Fast replicating cells such as the epithelium, GI and lungs
What are the 3 stages of CML?
Initial chronic stage (mild)
Accelerated phase that develops after 4 years (when diagnosis usually occurs)
Acute leukaemic phase (blast crisis)
How can resistance to Glivec (imatinib) occur?
Resistance builds by BCR-ABL over-expressing
Point mutations mean that it can’t bind, due to its specificity –> Nilotinib/Dasatinib then needed
No drugs are active against the T315I mutation! (except experimental JAK-2 inhibitors)
What is C-Abl?
A non-receptor protein tyrosine kinase
It has a nuclear internalisation and is activated by DNA damage
Interacts with p53 and Rb to regulate gene transcription
Glivec (imatinib) inhibits this kinase by starving it of ATP
What are the 3 ways that we can target the metastatic cascade?
Seeding –> invasion/extravasation/EMT
Dormancy –> Keep the cells dormant for as long as possible, or activate them to kill them
Metastatic colonisation –> Target the signalling pathways for this
How does Herceptin (Trastuzumab) work?
Binds to HER2+ cells, attracting the immune system (via its Fc region) to kill the cell
Also uncouples Src activation, increases p27 expression and promotes Antibody Dependent Cellular Cytotoxicity (ADCC)
What are the 2 theories for site-specific metastasis?
First Pass Organ –> They recolonise in the first organ they come to
Seed and Soil Hypothesis –> Will only recolonise in an environment that supports their growth
- Eg, correct growth factors, adhesion factors and selective chemotaxis
What 2 things can occur if a mutation occurs in the EFGR?
Ligand independence –> Due to constitutive dimerisation - This is the erbB oncoprotein for the EGFR (caused by a deletion)
Over-expression –> Due to gene amplification
What does p53 regulate the expression of?
p21 cyclin-dependent kinase inhibitor
MDM2 (which inhibits p53)
Bax (a pro-apoptopic protein)
What are the 6 different types of tumour suppressor genes (TSGs)?
Growth/development suppressors
Cell cycle checkpoint proteins
Cell cycle inhibitors
Inducers of apoptosis
DNA repair enzymes
Developmental pathways
How many mutations are needed for a cell to become cancerous?
3-7
Often benign cells will be one mutation short of becoming malignant
Where do the following cancers arise from?
Carcinoma
Adenocarcinoma
Sarcoma
Leukaemia
Carcinoma –> Epithelial cells
Adenocarcinoma –> Glandular tissue (eg, the breast)
Sarcoma –> Connective tissue and muscle
Leukaemia –> Blood cell derived sarcomas
Describe the metastatic cascade
Primary tumour growth
Angiogenesis
Detachment and invasion into surrounding tissues
Intravasation into lymphatics/capillaries
Survival in the circulation
Arrest in new area/secondary organ
Extravasation into the secondary tissue (lots of cells die at this point)
Establishment of microenvironment
What is angiogenesis?
The formation of new blood vessels
= neoangiogensis in cancer (driven by hypoxic conditions)
This needs to occur due to the rate that tumours grow, and so they need lots of nutrients and oxygen
Explain the Wnt pathway
Wnt is a ligand that binds to frizzled sequesters of GSK-3 (a kinase) allowing B-catenin to act as a transcription factor –> Driving cyclin-D and C-Myc expression and so cell proliferation
End result is a loss of function of APC (a tumour suppressor gene), so the inhibitor complex can’t form, allowing B-catenin to be free/active
How does HPV cause cancerous effects?
Interact with key regulatory proteins
E5 –> Causes prolonged activation of PDGFR
E6/7 –> Inhibit pRB and p53
Why does are tumours heterogenous?
Due to the asymmetric division of stem cells
How does the Hh pathway work?
Sonic, Desert and Indian bind to patched TSG, causing the inhibition of the smoothened TSG to be inhibited (so activated)
This causes Gli transcription factors to be released, causing cell proliferation
So LOF of the patched TSG will cause cancer
What role does Denosumab have in cancer?
It prevents the activation of osteoclasts, which prevents the formation/release of growth factors
How does Iressa and Tarceva work?
Block ATP, so prevent phosphorylation of kinases
Tarceva only works on hyper-mutated forms of cancer
How do you detect if a cancer is HER2+?
Immunohistochemistry –> Scale of 0-3 with 3 meaning +ve
FISH ELISA –> Detects the cleavage product in the patients serum
How does a loss of function in pRB or p16 affect cell division?
pRB –> LOF will remove inhibition (let go) of E2F, allowing it to be constitutively active. This also causes the pathway to be cyclin D/GF independent
p16 –> LOF means that the cycle can’t be stopped to repair DNA, so mutations are passed on to daughter cells and accumulate
What are the 3 ways that proto-oncogenes can be converted to oncogenes?
All via a gain of function mutation
Point mutation
Gene amplification
Chromosomal translocation
What is Ras?
Part of EGFR signalling, that can still be targeted after EGFR is constitutively active
Mutations of Ras causes it to always be active, with mutations being different in different cancers (eg, prostate point mutation will be different to that of the lung)
What is ADVEXIN?
Adenoviral transfer of p53 into a tumour cell
How do circulating tumour cells (CTCs) go about extravasation into the secondary tissue?
Using selectins, CD44 and integrins to drag the cancer cells through the basement membrane
What type of stem cell can become cancerous?
Undifferentiated ones that have left their niche
This is because cells need to have the potential to divide to become cancerous
So for a differentiated cell to become cancerous, it must require the ability to differentiate
What is leukaemia?
A cancer of the white blood cells, which produces tonnes of immature blood cells due to unregulated proliferation
These cells squeeze normal cells out of the bone marrow
Originates from stem/progenitor cells
You can’t get leukaemia of RBCs as they don’t have a nucleus! So no DNA that can be mutated!
What’s an EMT?
Epithelial to Mesenchymal Transition
This occurs to allow carcinomas to have more motility and be more invasive
How are leukaemia’s classified?
Either acute/chronic
The site of origin (myeloid or lymphoid)
Define Epigenetics
Study of changes to an organism in terms of gene expression, as opposed to the alteration of the genetic code
Effects are usually mediated by histone modification (methylation)
What is the Cancer Stem Cell Hypothesis?
Stem cell niche is expanded
Cancer stem cells then adapt to a different niche…allowing explansion
Cancer stem cells become niche independent, so self-renewal is cell-autonomous
Allows progenitor cells to be converted to cancer stem cells
