SCH 900776

SCH 900776 is a novel and more selective Chk1 inhibitor that potently inhibits Chk1 and abrogates cell-cycle arrest induced by SN38. Checkpoint kinase 1 (CHK1) is an essential serine/threonine kinase that responds to DNA damage and stalled DNA replication. SCH 900776 reduced the growth-inhibitory concentration of hydroxyurea by 20- to 70-fold. Additionally, SCH 900776 suppresses accumulation of the Chk1 pS296 autophosphorylation in a dose-dependent manner. SCH 900776 exposure phenocopies short interfering RNA-mediated CHK1 ablation and interacts synergistically with DNA antimetabolite agents in vitro and in vivo to selectively induce dsDNA breaks and cell death in tumor cell backgrounds. SCH 900776 is currently in phase I clinical trials.