SB 218078 is an inhibitor of checkpoint kinase 1 (Chk1) that blocks phosphorylation of cdc25 with an IC50 value of 15 nM. It less potently inhibits cdc2 and PKC (IC50s = 250 and 1,000 nM, respectively) and causes 85% inhibition of PKD1 at 1 μM. SB 218078 releases G2 cell cycle arrest induced by γ-irradiation or the topoisomerase I inhibitor topotecan . In this way, SB 218078 enhances the cytotoxicity of DNA-damaging compounds.
