VX-803 (M4344, ATR inhibitor 2) is an ATP-competitive, orally active, and selective inhibitor of ataxia telangiectasia and Rad3 related (ATR) kinase with Ki of < 150 pM. VX-803 (M4344) potently inhibits ATR-driven phosphorylated checkpoint kinase-1 (P-Chk1) phosphorylation with IC50 of 8 nM. VX-803 (M4344) exhibits potential antineoplastic activity.
M4344 is determined to be an adenosine triphosphate (ATP)-competitive, highly potent, and tight-binding inhibitor of ATR with a Ki of < 150 pM. Minimal inhibitory activity is observed against a large panel of unrelated protein kinases, with 308 of 312 kinases tested having a measured Ki corresponding to more than 100-fold selectivity. M4344 potently inhibits ATR-driven phosphorylated checkpoint kinase-1 (P-Chk1) phosphorylation with an IC50 of 8 nM. Profiling on a selected set of cancer cell lines shows synergy with several types of DNA damaging chemotherapeutics as well as PARP1/2 and CHK1 inhibitors.[1]
In monotherapy efficacy studies M4344 shows tumor stasis to regression in tumor models with alternative lengthening of telomeres (ALT). In combination with PARP inhibitors, tumor regression can be observed in triple-negative breast cancer xenograft models.[1]
[1] Frank T. Zenke, et al. AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 369.