Complementary RNA interference and compound screens to identify novel therapeutic targets for mismatch repair deficient cancers
Madeleine Hewish1, Sarah A. Martin1, Christopher J. Lord2, David Cunningham3, Alan Ashworth1
1Gene Function and Regulation Group, Institute of Cancer Research, London, UK, 2Breakthrough Breast Cancer Research Centre, Institute of Cancer Research, London, UK, 3Royal Marsden Hospital, London and Surrey, UK
Proffered paper presentation
Background
Synthetic lethal interactions represent a means of selectively targeting cancers characterised by tumour suppressor gene loss. Two genes are synthetically lethal when loss of function of one gene is compatible with viability but loss of both is not. Where one gene in a synthetic lethal relationship is a tumour suppressor, the other becomes a candidate target. The Mismatch Repair (MMR) gene MLH1 represents a promising candidate for a synthetic lethal approach given that loss of MLH1 expression occurs in 15% of sporadic colorectal cancers, and that MLH1 deficiency has been associated with a poor response to systemic chemotherapy in ovarian, testicular and gastric cancers. Mutation of MLH1 occurs in 40% of cancers associated with Lynch syndrome.
Methods
Using a human colorectal cell line model (HCT116) and its isogenic comparator (HCT116+Chr3), we used an RNA interference approach to systematically target 779 kinases and kinase-related genes. Using a commercially available siRNA library, we identified candidate genes whose loss of function is synthetically lethal with MLH1 deficiency. Complementary to this, we also screened compound libraries to identify drugs to which MLH1-deficient cells are more sensitive.
Results
From the primary siRNA screen, a total of 31 potential hit genes were identified and taken forwards for validation in a secondary screen. Data from primary and secondary siRNA screens will be presented, together with validatory work in other MLH1-deficient cell line models. From the compound screens, 15 compounds caused selective loss of cellular viability in MLH1-deficient cells. Data from the initial compound screens and subsequent validatory experiments will be presented.
Conclusion
Complementary RNA interference and compound screens have been utilised to identify drugs and targets for use in the treatment of MMR deficient cancers. Gene expression array profiling, gene ontology annotations and network analyses are being used to further inform mechanistic investigation of hit genes.
