Abstract B91: Combined ATM and ATR kinase inhibition selectively kills p53-mutated non-small cell lung cancer (NSCLC) cells.

Introduction: Cancer cells frequently exhibit defects in components of the DNA-damage response (DDR) and may as a consequence become highly dependent on remaining DDR pathways to survive DNA damage. Targeting such remaining DDR pathways to confer synthetic lethality has become a valuable new strategy for personalised cancer therapy, and an attractive target for this approach is the central DDR kinase Ataxia Telangiectasia and Rad3 related (ATR). Several small molecule inhibitors of ATR are now entering clinical development. However, the challenges remain to identify patient subgroups that might benefit from ATR inhibitors, and to integrate these agents with standard therapies. Two important components of the DDR, Ataxia Telangiectasia Mutated (ATM) and p53, are commonly mutated and inactivated in lung cancer. In this study, we therefore evaluate the potential of ATR kinase inhibition for the treatment of ATM- or p53-deficient human NSCLC, both as single agent and in combination with ionizing radiation (IR). Methods: We used proliferation and clonogenic survival assays to measure the sensitivity of a panel of NSCLC cell lines to the selective ATR kinase inhibitor VE-821. Inhibition of ATR mediated signalling was assessed by immunoblotting. Immunofluorescence and chromosome analysis were used to assess the induction of DNA damage following treatment of cells with either VE-821 alone, or in combination with the selective ATM inhibitor KU55933. FACS analysis was used to measure cell cycle phase distribution and DNA content. Results: NSCLC cells deficient in both ATM and p53 were highly sensitive to ATR inhibition (IC 50 0.7 µM), but there was no clear association between sensitivity and mutation status of either ATM or p53 alone (IC 50 3.9 - 8.9 µM). We observed similar relative sensitivities in clonogenic survival assays and in combination with IR. This increased cytotoxicity of ATR inhibition in a combined ATM- and p53-deficient background was associated with formation of giant micronucleated cells and evidence of mitotic catastrophe within 48 h of treatment. Furthermore, we found a marked increase in VE-821-induced chromosomal damage in cells deficient in ATM and p53, compared with cells deficient in either gene alone. We confirmed this dependency on p53 mutation status and ATM function for sensitivity to ATR inhibition by treating p53-mutated NSCLC cells with a combination of VE-821 and KU55933. In this setting, inhibition of ATM markedly sensitised tumour cells to VE-821 treatment, as shown by a reduction in clonogenic survival and an increase in chromosomal damage. Conclusion: Our data suggest that in NSCLC the functional status of both ATM and p53 determines the cellular response to ATR inhibition and that combined ATM and ATR kinase inhibition selectively kills p53 mutant cells. A combination of ATM and ATR inhibitors may therefore have a broad utility for the treatment of p53 mutated NSCLC. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B91. Citation Format: Anika M. Weber, Sivan M. Bokobza, Aoife M. Devery, Anderson J. Ryan. Combined ATM and ATR kinase inhibition selectively kills p53-mutated non-small cell lung cancer (NSCLC) cells. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B91.