Somhairle MacCormick

Selective killing of ATM- or p53-deficient cancer cells through inhibition of ATR

Here we report a comprehensive biological characterization of a potent and selective small-molecule inhibitor of the DNA damage response (DDR) kinase ATR. We show a profound synthetic lethal interaction between ATR and the ATM-p53 tumor suppressor pathway in cells treated with DNA-damaging agents and establish ATR inhibition as a way to transform the outcome for patients with cancer treated with ionizing radiation or genotoxic drugs.

Discovery of potent and selective inhibitors of ataxia telangiectasia mutated and Rad3 related (ATR) protein kinase as potential anticancer agents.

DNA-damaging agents are among the most frequently used anticancer drugs. However, they provide only modest benefit in most cancers. This may be attributed to a genome maintenance network, the DNA damage response (DDR), that recognizes and repairs damaged DNA. ATR is a major regulator of the DDR and an attractive anticancer target. Herein, we describe the discovery of a series of aminopyrazines with potent and selective ATR inhibition. Compound 45 inhibits ATR with a K(i) of 6 nM, shows >600-fold selectivity over related kinases ATM or DNA-PK, and blocks ATR signaling in cells with an IC(50) of 0.42 μM. Using this compound, we show that ATR inhibition markedly enhances death induced by DNA-damaging agents in certain cancers but not normal cells. This differential response between cancer and normal cells highlights the great potential for ATR inhibition as a novel mechanism to dramatically increase the efficacy of many established drugs and ionizing radiation.

Abstract 5491: Evaluation of the first potent and highly selective inhibitor of ATR kinase: An approach to selectively sensitize cancer cells to genotoxic drugs

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL DNA damaging agents have been the cornerstone of solid cancer therapy for decades yet they provide only modest benefit for patients with many tumor types. This reflects, in part, the efficient repair of DNA damage via a complex signaling and repair network known as the DNA damage response (DDR). Key regulators of the DDR are the phosphoinositol 3-kinase-like serine/threonine protein kinase (PIKK) family members ATR, ATM and DNA-PK. The DDR acts to detect DNA lesions, enforce checkpoints to halt cell cycle progression, and stimulate repair. Recent data have shown that elements of the DDR are commonly defective in cancer cells. It is widely believed that these cells become dependent on the remaining DDR pathways for survival from DNA damage. Inhibitors have been reported for a number of DDR enzymes, including ATM, DNA-PK, CHK1 and PARP, however there are no reports of drug-like ATR inhibitors. Here we disclose the in vitro characterization of a potent and highly selective ATR inhibitor (VE-821). This compound selectively blocks ATR signaling in cells (IC50 = 0.7 µM), but has little impact on ATM or DNA-PK signaling (IC50 >10 µM). Treatment with 10 µM VE-821 for 144 h causes little cell death in normal cell lines (5-11 %) but markedly higher death in cancer cell lines (28-46 %). VE-821 also dramatically sensitizes many cancer cells to multiple classes of genotoxic agents including antimetabolites, topoisomerase inhibitors and crosslinking agents; with over 10-fold increases genotoxic potency observed in some cases. In a panel of 36 lung cancer cell lines, VE-821 sensitized the cytotoxic effect of cisplatin to a far greater magnitude and over a broader subset of these lines than potent inhibitors of ATM, Chk1, or PARP. In over half of these cell lines, the IC50 of cisplatin was reduced by greater than 5 fold upon the addition of VE-821. We show that a basis for the cancer-selective effects of VE-821 is a synthetic lethal interaction between loss of ATM signaling (a frequent event in cancer resulting from loss of function of proteins such as ATM or p53) and ATR inhibition when cells encounter DNA damage. In keeping with this, ATR inhibition does not sensitize normal cells (with functional ATM) to the cytotoxic effects of genotoxic therapy. In this case a compensatory DDR is activated that is associated with marked activation of ATM, which in turn leads to reversible checkpoint arrest and a strong survival response. These studies show for the first time that a selective ATR inhibitor can preferentially sensitize cancer cells to genotoxic drugs by exploiting a synthetic lethal interaction between ATM and ATR signaling. This underpins the broad potential of ATR inhibition as a highly promising new strategy to improve the efficacy of genotoxic therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5491. doi:10.1158/1538-7445.AM2011-5491