A cell-based screen identifies ATR inhibitors with synthetic lethal properties for cancer-associated mutations

Abstract

Available ATR inhibitors also show activity against related DNA-damage response kinases such as ATM and DNA-PKcs. Now a cell-based screen leads to the identification of two compounds with potent activity against ATR in tissue culture, including one that is specific for ATR. These compounds are particularly toxic for cells showing oncogene-induced replicative stress, even more so in the absence of p53. Oncogene activation has been shown to generate replication-born DNA damage, also known as replicative stress. The primary responder to replicative stress is not Ataxia-Telangiectasia Mutated (ATM) but rather the kinase ATM and Rad3-related (ATR). One limitation for the study of ATR is the lack of potent inhibitors. We here describe a cell-based screening strategy that has allowed us to identify compounds with ATR inhibitory activity in the nanomolar range. Pharmacological inhibition of ATR generates replicative stress, leading to chromosomal breakage in the presence of conditions that stall replication forks. Moreover, ATR inhibition is particularly toxic for p53-deficient cells, this toxicity being exacerbated by replicative stress–generating conditions such as the overexpression of cyclin E. Notably, one of the compounds we identified is NVP-BEZ235, a dual phosphatidylinositol-3-OH kinase (PI3K) and mTOR inhibitor that is being tested for cancer chemotherapy but that we now show is also very potent against ATM, ATR and the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs).