Rational Design of 5-(4-(Isopropylsulfonyl)phenyl)-3-(3-(4-((methylamino)methyl)phenyl)isoxazol-5-yl)pyrazin-2-amine (VX-970, M6620): Optimization of Intra- and Intermolecular Polar Interactions of a New Ataxia Telangiectasia Mutated and Rad3-Related (ATR) Kinase Inhibitor

The DNA damage response (DDR) is a DNA damage surveillance and repair mechanism that can limit the effectiveness of radiotherapy and DNA-damaging chemotherapy, commonly used treatment modalities in cancer. Two related kinases, ataxia telangiectasia mutated (ATM) and ATM and Rad3-related kinase (ATR), work together as apical proteins in the DDR to maintain genome stability and cell survival in the face of potentially lethal forms of DNA damage. However, compromised ATM signaling is a common characteristic of tumor cells, which places greater reliance on ATR to mediate the DDR. In such circumstances, ATR inhibition has been shown to enhance the toxicity of DNA damaging chemotherapy to many cancer cells in multiple preclinical studies, while healthy tissue with functional ATM can tolerate ATR inhibition. ATR therefore represents a very attractive anticancer target. Herein we describe the discovery of VX-970/M6620, the first ATR inhibitor to enter clinical studies, which is based on a 2-aminopyrazine core first reported by Charrier ( J. Med. Chem. 2011 , 54 , 2320 - 2330 , DOI: 10.1021/jm101488z ).

Abstract LB-299: Comprehensive preclinical evaluation of VE-822, the first ATR-targeted drug candidate: a novel approach to transforming the efficacy of DNA damaging agents

DNA damaging agents have been the cornerstone of cancer therapy for decades yet they provide only modest benefit for most patients. For example, standard of care for patients with non-small cell lung cancer (NSCLC) is dominated by the use of platinating drugs and ionizing radiation (IR), however outcome remains very poor with 5-year survival rates of <15% for patients that present with advanced disease. Such poor responses to DNA damaging treatment reflects, in part, the efficient repair of DNA damage via a complex signaling and repair network known as the DNA damage response (DDR). The DDR detects double strand breaks and replication stress, the most lethal forms of DNA damage, and acts to enforce checkpoints to halt cell cycle progression, and to stimulate repair. Key regulators of the DDR are the phosphoinositol 3-kinase-like serine/threonine protein kinase (PIKK) family members ATR and ATM. Recent pre-clinical data has suggested that a reliance on ATR for survival from DNA damage may be a common feature of cancer. This can arise either as a consequence of high replicative stress, for example from expression of certain oncogenes, from a hypoxic microenvironment, or from defects elsewhere in DNA damage surveillance and repair pathways. Most notably inhibition of ATR has been shown to be synthetic lethal with loss of the ATM-p53 pathway. In NSCLC defective ATM signaling, from loss of ATM expression or from defects in p53 has been reported in about 50% of tumors. Here we describe the comprehensive in vitro and in vivo profile for VE-822 a novel highly potent and selective inhibitor of ATR.

VE-822 potently inhibits ATR in biochemical assays with Ki <0.3nM and in cell assays with IC50 of 20nM. Against a large panel of NSCLC lines, low concentrations of VE-822 sensitized many lines to the cytotoxic effects of multiple DNA damaging agents; for example >90% of lines showed >3-fold shifts in IC50 for cisplatin in the presence of VE-822, with ~50% of lines showing >10-fold increases in cisplatin cytotoxicity. In contrast normal cells tolerate inhibition of ATR. In a panel of mouse xenograft models, derived from various primary human NSCLC tumor tissues, oral or IV administration of VE-822 strongly sensitized tumors to cisplatin treatment. In many cases, combinations including VE-822 led to tumor regression or extensive tumor growth delay. Inhibition of ATR activity and accumulation of DNA damage by VE-822 was observed coincident with efficacy. When administered alone or in combination with cisplatin VE-822 was well tolerated in mice at doses that block ATR activity.

These data support the potential for ATR inhibitors to substantially increase the efficacy of standard-of-care agents in diseases such as NSCLC.

Citation Format: Diane Boucher, Peter Charlton, Jean-Damien Charrier, Brinley Furey, Yong Gu, Amy Hall, Brian Hare, Howard Li, Sean Milton, Cheryl Murphy, Philip Reaper, Darin Takemoto, Taturo Udagawa, Yuxin Wang, Mark Wood, John Pollard. Comprehensive preclinical evaluation of VE-822, the first ATR-targeted drug candidate: a novel approach to transforming the efficacy of DNA damaging agents. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-299. doi:10.1158/1538-7445.AM2013-LB-299

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

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

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.

Discovery and structure-activity relationship of 3-aminopyrid-2-ones as potent and selective interleukin-2 inducible T-cell kinase (Itk) inhibitors

Interleukin-2 inducible T-cell kinase (Itk) plays a role in T-cell functions, and its inhibition potentially represents an attractive intervention point to treat autoimmune and allergic diseases. Herein we describe the discovery of a series of potent and selective novel inhibitors of Itk. These inhibitors were identified by structure-based design, starting from a fragment generated de novo, the 3-aminopyrid-2-one motif. Functionalization of the 3-amino group enabled rapid enhancement of the inhibitory activity against Itk, while introduction of a substituted heteroaromatic ring in position 5 of the pyridone fragment was key to achieving optimal selectivity over related kinases. A careful analysis of the hydration patterns in the kinase active site was necessary to fully explain the observed selectivity profile. The best molecule prepared in this optimization campaign, 7v, inhibits Itk with a K(i) of 7 nM and has a good selectivity profile across kinases.

Synthesis of (2S,4S)- and (2S,4R)-5-fluoroleucine and (2S,4S)-[5,5-2H2]-5-fluoroleucine

Syntheses of (2S,4S)- and (2S,4R)-5-fluoroleucine, and, and of (2S,4S)-[5,5-(2)H(2)]-5-fluoroleucine, have been completed. The methodology allows these compounds to be prepared in sufficient quantities for incorporation by solid-state protein synthesis into strategic sites in proteins for folding studies. X-ray structures of the epimers and have been obtained and show the presence of conformational isomerism. The torsion angles between the F-C bond and the main chain are compared with values found in a mutant of the protein ubiquitin in which (2S,4S)-5-fluoroleucine replaces leucine residues 50 and 67 in the native protein.

Synthesis of (2S,3R)-[3′,3′,3′-2H3]-valine and (2S,3S)-4-fluorovaline

A new synthesis of (2S,3R)-[3',3',3'-2H3]-valine has been completed and (2S,3S)-4-fluorovaline has been synthesised for the first time. Both compounds have been prepared by routes involving stereoselective addition to the (S)-pyroglutamate derivative and are available for studies in several areas of bio-organic chemistry.

Synthesis of (2S,3S)-3′-fluoroisoleucine

The fluorinated amino acid, (2S,3S)-3'-fluoroisoleucine 3, has been synthesised by a route involving stereoselective cuprate or photochemical addition to the compound 4, derived in turn from (2S)-pyroglutamic acid. This provides a reporter group for the hydrophobic amino acid (2S)-isoleucine for use in protein studies.