exploiting genomic instability Flashcards
why is it important to understand genomic instability?
to understand molecular causes of disease, which would lead to better diagnostics, improved new technologies like CRISPR
understanding biological basis of ageing
to develop new treatments for disease like cancer
to educate public on lifestyle choices - e.g. population studies reveal which areas have high rates of certain cancers and what environmental factors may be contributing to that
give five ways in which cancer cells are naturally susceptible to DNA damage
Increased metabolism - take up more glucose, known as the Warburg effect
Reduced contact inhibition - so can grow out of control and invade other tissues
Lack of cell cycle checkpoints (hyperproliferation). Resistant to apoptosis
Unstable genomes
Mutations in DDR genes - like BRCA1 - e.g. 50% of cancers have mutated p53. the result is a loss of certain DNA repair pathways, more damage accumulates etc…
what are PARPs?
why are PARP inhibitors used?
PARP = poly ADP-Ribose Polymerase - involved in BER, ssDNA repair
A family of enzymes
DNA damage occurs, PARPs detect and bind to the sites of damage, particularly single-strand breaks.
Upon binding, PARPs add PAR chains to themselves and other target proteins. This causes the recruitment of DNA repair proteins to the damage site, promoting the repair process
why are PARP inhibitors used to treat cancer?
are they used alone?
stopping BER, the SSB repair pathway, in cancer cells overloads the cells with damage until they can no longer function
PARP inhibitors are often used alongside chemotherapy drugs, to overload the cancer cells with damage and prevent repair
how are cancer cells treated with synthetic lethality?
cancer cells are usually deficient in some DNA repair pathways, and so rely heavily on others
synthetic lethality is the idea that you use drugs to knock out a DNA repair pathway the cancer cells are reliant on, so while healthy cells have redundancy in that they can switch to a different repair pathway, the cancer cells cannot
what makes cancer cells very susceptible to synthetic lethality?
they divide super quickly, and with fewer cell cycle check points, so accumulate damage very quickly
what is a problem that occurs when treating cancer cells with synthetic lethality?
Tumours - grow quickly and so are unstable - they ‘evolve’ and become resistant to drug being used
that is, the chemotherapy acts as an environmental stress, selecting for cells that can tolerate it
how can cancer cells ‘evolve’ to be resistant to drugs knocking out DNA repair pathways?
Reversion mutations - sometimes cancer cells gain beneficial mutations, where you’ve got mutations in DNA repair genes (what you want), but mutating even further can e.g. delete an inhibitory exon, and the gene becomes somewhat functional again
what is cisplatin and how does it work?
a chemotherapy drug
Alkylating agent, kills cells by ‘cytotoxic’ effect
Chloride ions get replaced by water, the compound becomes more reactive, binds to guanine in DNA (and maybe adenine) causing adducts/kinks (intrastrand, 90%), or interstrand, linking strands together…
this can prevent unwinding in DNA replication (and transcription)
with chemotherapy drugs like cisplatin, what are the downsides?
cancer cells lack the necessary repair pathways to fix the lesions chemotherapy causes, and while normal cells are better able to repair the lesions (as they too will be damaged), fast dividing cells like those lining the gut and hair cells, are significantly impacted
cancer cells can become resistant to cisplatin, e.g. they can actually develop pumps to increase efflux of the drug
what is radiotherapy and how does it work?
different types?
its main area for improvement?
how often it is used?
Uses X-rays, gamma rays and even neutron and proton therapy to cause DNA damage - ionising radiation damages DNA backbone, DSBs etc…
also impacts water, creating ROS that then cause damage
Can be external beam therapy (EBRT), or internal
the focus is trying to target the radiotherapy as much as possible to reduce damage to healthy cells
50% of cancer patients receive some form of radiotherapy
what is Gamma Knife Therapy?
Or stereotactic radiosurgery
Very good at focusing high energy gamma radiation, often used in head and neck cancers as they are hard to access
what is a forward genetic screen and how is it being used in cancer treatment?
you cause DNA damage, look at the phenotype, then find the genes that cause the phenotype
a study has used forward genetic screens -
Lots of cancer cells deficient in MMR (mismatch repair)
Intentionally knocked out DNA repair pathways
Applied drugs used for this kind of cancer
Had a look at the resistant cancer cells
Sequenced their genome/found hallmark mutations that indicate developing resistance to said treatment
In future - can look out for this in patients in order to potentially change treatment plan
