VER250840 is a novel oral, selective Chk1 kinase inhibitor discovered by Vernalis Research. Chk1 is an important target within the DNA Damage Response (DDR) network and has been shown to play a key role in maintaining genomic integrity of cancer cells. Inhibition of Chk1 blocks cell cycle arrest and DNA repair, forcing cancer cells to undergo cell division with substantial DNA damage that results in their death. In both in vitro and in vivo preclinical studies, VER250840 has demonstrated an ability to target Chk1 in a range of different tumor types, as a single agent and in combination with several different cytotoxic agents. The clinical utility of DDR inhibitors for the treatment of cancer has recently been validated by the approval of inhibitors of Poly (ADP-ribose) polymerase (PARP). The opportunity to select patients most likely to respond to Chk1 inhibitors exists.