Understanding drug resistance in cancers with DNA repair mutations (360G-Wellcome-206721_Z_17_Z)

The DNA damage response (DDR) is critical for maintaining genome stability. Cancer mutations have been identified in many genes linked to DNA repair, for example in ~20% of primary prostate cancers. Genes like BRCA1 are essential for mediating high-fidelity template-based Homologous Recombination (HR) repair of DNA double strand breaks (DSB). The absence of BRCA1 increases mutagenic repair and the risk of developing cancer, but also sensitises cells to treatments that generate DSBs, such as the DDR enzyme inhibitor olaparib. Cancer cells which are BRCA1-deficient can evolve drug-resistance by additional mutations which restore HR; for example, BRCA1-/- 53BP1-/- cells, which are olaparib resistant. Our aim is to identify genes which when ‘inhibited’ re-sensitise for example BRCA1-/- 53BP1-/- cells, to olaparib, and in doing so gain additional mechanistic insights into HR regulation. This can be best achieved by conducting a CRISPR/cas9 genetic screen using a highly focused guide library containing 10 guides per gene, in order to reveal genes which are synthetically lethal with drug-resistant genotypes. By screening with guides which target protein kinases, we aim to establish druggable candidates which can be inhibited to extend the remit of pre-existing cancer therapies for HR-proficient cancers, as well as re-sensitise BRCA1-deficient cancers which have become treatment-resistant.