Molecular Biology & Cancer Therapies Flashcards
What are some examples of gene therapies?
- Gene repair; correction of mutations
- Pro-drug metabolising enzyme therapy to sensitise cancer cells to cytotoxics
- Viral oncolysis; viruses that selectively target cancers
- Modification of the tumour microenvironment
- Drug resistance therapy for non-cancerous cells (allow high dose cytotoxic use)
- Immunotherapy w/GM effector T cells, APCs
What barriers have there been to cancer gene therapy?
- Commercial
- Biological
What commercial barriers are there to gene therapy?
- Costs for materials high; R&D, tailor-made etc.
- Individualised therapies requires; difficult for late phase clinical studies
- Potentially small market of suitable patients; not fiscally attractive
- Costs of patents & licenses
What biological barriers are there to gene therapy?
- Many genes may be mutated
- Variation within tumours; different clones within a tumour
- Variation between patients
- Requires majority of cancer cells to be affected; unlike gene therapy for monogenic diseases, e.g. single mutation in an enzyme
Give an example of a proposed miRNA therapy targeting antagomiRs, and what barriers prevent its successful use.
- miRNA usually an important regulating molecule; binds to 3’ UTR of target mRNAs and regulate translation
- Proposed use of anti-miRs (antagomiRs) to block oncomiR action; antagomiR complementary to oncomiR sequence
Barriers:
• Stability
• Excretion
• Cellular uptake and targeting
• Transient inhibition (rapid mRNA turnover); repeated doses required
• Off target effects; turning off other targets
• RNA v. unstable (lots of RNA enzyme)
Give an example of miRNA therapy involving tumour suppressor miRs, and barriers preventing its successful use.
- To upregulate tumour suppressor miRs
- Proposed oligonucleotides that would mimic TS miRs (synthetic versions)
Barriers (similar to antagomiRs): • Stability • Excretion • Cellular uptake and targeting • Transient inhibition (rapid mRNA turnover); repeated doses required • Off target effects
What is an example of pro-drug metabolising therapy? Give an example.
E.g. Herpes simplex TK (thymidine kinase)
- Phosphorylates pro-drugs such as valaciclovir to toxic nucleosides
- Target to dividing cells using gamma retroviral vector (viruses) or by targeting to cell surface antigen
- Not yet licensed (promising results)
> Activate drug only in vicinity of tumour (reduce systemic effects)
> mAb is conjugated to the pro-drug thus therapy is only targeted at tumour cells
What is an example of viral oncolysis/virotherapy? What is it?
- Viruses which have been engineered only to replicate in cancer cells
E.g. Adenovirus dl1520, which requires defective p53 pathway; this adenovirus normally inhibits p53 as part of its life cycle
How is the tumour microenvironment targeted? Why is this an advantageous therapy?
- Prevent angiogenesis by modifying normal cells
- Modify immune response and metastatic potential
»> Doesn’t require high efficiency of transduction (other therapies target cancer cells themselves; which requires hitting most of them to be successful (success in animal models of viruses expressing angiostatin and endostatin)
»> Target host not the cancer
How can gene therapy be used to reduce toxicity?
- Effectively increase therapeutic index
- MGMT gene removes alkylating DNA modifications; which would confer resistance to alkylating agents
»> Overexpressing MGMT in healthy cells; spared from cytotoxic effect
Describe the new therapy recently developed to treat aggressive ALL (acute lymphoblastic lymphoma) which involves T-cells?
- Donor T-cells taken from a healthy volunteer (unrelated to patient)
- Genetically modified to attack CD19+ cells; marker of B cells of ALL
- GM-T cells modified to be resistant to immunotherapy which would otherwise kill T-cells
- All of patient’s T-cells thus killed but still has GM donor T-cells
»> Then after therapy own T cells kill GM T-cells (recognised as foreign), leaving patient with self-T cells and no cancer cells.
What are mAbs?
- Proteins produced by immune system to bind specifically to foreign antigens
- Produced by B lymphocytes
What’s the difference between monoclonal and polyclonal antibodies?
Monoclonal Abs:
- Come from a single clone of B lymphocytes, targeting a single epitope (part of the antigen where antibody attaches)
Polyclonal Abs:
- Come from many clones of B lymphocytes
- In turn can target multiple epitopes of the antigen (extracted from blood of immunised animals)
What are mAbs used for? Give examples.
- Make cells visible to the immune system
e. g. against cancer cell markers (rituximab) - Stop cells dividing
e. g. against cancer cell growth factor receptors (cetuximab) - Target therapies
e. g. conjugated to drug or radioisotope (so they can exert their effect in the vicinity of cancer cells only) - Diagnosis
e. g. testing for expression of hormone receptors (HER2)
How does Rituximab work? What is its mode of action an example of?
- mAb that targets CD20 on B cells; recruiting immune cells to cancer e.g. NK (natural killer) cells
- Causes ADCC (antibody dependent cell mediated cytotoxicity)
- Causes complement mediated cytotoxicity (CDC); leads to pore in cell wall = cell death
- Kills B cells in lymphomas/leukaemias (and health B cells that also express CD20; but recovery after)
»> Makes cells visible to the immune system.
