P1.14-41 The Combination of the PARP Inhibitor Olaparib and the ATR Inhibitor VE-821 Selectively Targets ATM-Deficient Lung Cancer Cells

Abstract

The driving principle behind precision medicine is to specifically target genetic variations that arise in tumorigenesis while leaving normal cells unaffected. Mutations in Ataxia Telangiectasia Mutated (ATM) may offer such a therapeutic target. ATM is mutated in approximately 12% of lung cancers and up to 40% of lung adenocarcinoma have been reported to lack ATM protein expression. ATM is an apex signaling kinase that responds to DNA-double strand breaks, playing a direct role in DNA repair as well as the initiation of signaling cascades that can lead to cell cycle arrest and apoptosis. We asked whether ATM-deficient human lung cancer cells are sensitive to the poly-ADP ribose polymerase (PARP) inhibitor olaparib, and investigated the mechanism of action of olaparib in these cells. We analyzed drug sensitivity for 61 lung adenocarcinoma cell lines from the Genomics of Drug Sensitivity in Cancer (GDSC) project and deleted ATM from lung adenocarcinoma A549 cells using CRISPR/Cas9. We determined the effects on cell viability using trypan blue exclusion and clonogenic survival assays. To investigate the mechanism of sensitivity of ATM-deficient cells to PARP and ATR inhibitors we used flow cytometry and cell viability assays as above. We observed a positive correlation between olaparib IC50 values and ATM mRNA expression. ATM mutant cell lines were more sensitive to olaparib compared to ATM wild-type cell lines or cell lines with amplified ATM. Additionally, ATM-deficient lung cancer cells were sensitive to olaparib, as are lung cancer cells (A549) with CRISPR/Cas9 deletion of ATM. Mechanistically, olaparib caused the temporary and reversible accumulation of G2 phase cells in ATM-deficient cells which manifested as a decrease in proliferation in both the trypan blue exclusion assay and clonogenic survival assay. Olaparib did not induce cell death in ATM-deficient cells, however cell death was induced when olaparib was used in combination with the ATR inhibitor VE-821. We show that olaparib acts as a cytostatic agent in ATM-deficient lung cancer cells, inducing a reversible and temporary growth arrest in G2 phase. Only when combined with the ATR inhibitor VE-821 was cell death observed and only in ATM-deficient cells. Our data suggest that patients with ATM-deficient lung cancer could benefit from combinatorial treatment with PARP and ATR inhibitors.