Abstract 1311: ATR inhibition sensitizes p53-deficient cancer cells to chemotherapeutic drugs

Abstract

Abstract PURPOSE: We sought to determine whether genetic inhibition of the ATR kinase would preferentially sensitize p53-deficient cancer cells to therapeutic agents that cause replication stress. EXPERIMENTAL PROCEDURES: Previous studies have shown that p53-deficient cancer cells harboring hypomorphic ATR alleles are highly sensitive to DNA damaging agents and DNA replication inhibitors that are commonly used in the clinic. We hypothesize that p53-dependent cell cycle checkpoints would prevent damaged, ATR-deficient cells from entering S-phase and mitosis, and thereby enhance cell survival. To test this hypothesis, we used a gene targeting approach to knock-in wild type p53 into cells with wild type and hypomorphic ATR alleles. The combined effects of ATR and p53 were determined by clonogenic survival assays, flow cytometry and analysis of apoptotic proteins. SUMMARY: RNAi-mediated knockdown of ATR in p53-deficient cells caused reduced survival after cisplatin treatment, compared with knockdown of ATR in isogenic p53-proficient cells. To unambiguously test whether ATR inhibition preferentially sensitizes p53-deficient cancer cells, we used a knock-in vector to replace a p53-mutant allele with a wild type allele. Homologous recombinant cells expressed wild type p53 protein and the p53 target proteins p21 and p53R2, demonstrating restoration of a functional p53 pathway. Knock-in of wild type p53 restored the G1/S checkpoint induced by ionizing radiation. Most significantly, genetic restoration of the p53 pathway rescued the survival defect of the ATR-deficient cells in response to chemotherapeutic drugs. CONCLUSIONS: Our data provide genetic evidence that p53 and ATR function synergistically to enhance the survival of human cancer cells treated with agents that cause DNA replication stress. We propose that pharmacologic inhibition of ATR would cause enhanced killing of cells with loss of p53 function following treatment with DNA replication inhibitors and DNA crosslinking agents, thereby increasing their therapeutic index. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1311.