Checkpoint kinase 1 (Chk1) regulates S and G2-M phase cell cycle checkpoints in response to DNA damage. CHIR124 is a cell-permeable, quinolone-based inhibitor of Chk1 (IC50 = 0.3 nM in vitro). It demonstrates high selectivity for Chk1 by displaying inhibitory values 2,000-fold higher against Chk2 (IC50 = 0.7 μM). In synergy with topoisomerase I poisons or ionizing radiation, CHIR124 can inhibit the growth of p53-mutant solid tumor cells both in vitro and in a xenograft model, potentiating tumor apoptosis.
