Abstract A24: A genome-wide RNAi screen identifies synthetic lethality of CX-5461 with homologous recombination repair deficiency in ovarian cancer

Abstract Cancer is characterized by deregulated cell growth and proliferation, both of which are associated with hyperactivation of ribosome biogenesis. Inhibition of ribosome biogenesis using CX-5461, a specific inhibitor of RNA polymerase I-dependent transcription, has shown therapeutic efficacy in a MYC driven B-cell lymphoma mouse model, which is enhanced when used in combination with the mTORC1 inhibitor Everolimus. However, the therapeutic potential of CX-5461 in solid cancers is yet to be determined. Our preliminary data utilizing a panel of 36 ovarian cancer (OVCA) cell lines suggest that acute CX-5461 treatment results in cell cycle arrest and does not induce apoptosis. We hypothesize that the identification of genes that can be targeted to cooperate with CX-5461 will define novel drug combinations for the improved treatment of OVCA. Therefore, we performed a genome-wide RNAi screen to identify synthetic lethal genes with CX-5461 in the high-grade serous ovarian cancer (HGSOC) cell line OVCAR4. Pathway enrichment analysis of the candidate hits showed significant enrichment in the homologous recombination DNA repair (HR) pathway. Synergy with CX-5461 was validated in multiple HGSOC cell lines by both genetic and pharmacological inhibition of HR pathway components. We are currently investigating the mechanism of this synergy and will further assess efficacy in vivo. As HR deficiency is observed in 20% of OVCA patients, we suggest that future application of our studies will lead to new therapeutic options to improve the survival of this cohort of patients. Citation Format: Shunfei Yan, Keefe T. Chan, Kaylene J. Simpson, Elaine Sanij, Karen E. Sheppard, Katherine M. Hannan, Ross D. Hannan, Richard B. Pearson. A genome-wide RNAi screen identifies synthetic lethality of CX-5461 with homologous recombination repair deficiency in ovarian cancer [abstract]. In: Proceedings of the AACR Special Conference on DNA Repair: Tumor Development and Therapeutic Response; 2016 Nov 2-5; Montreal, QC, Canada. Philadelphia (PA): AACR; Mol Cancer Res 2017;15(4_Suppl):Abstract nr A24.