PF-477736, also known as PF-00477736, is a potent CHK1 inhibitor with potential to enhance chemotherapy. This compound inhibits CHK1, an ATP-dependent serine/threonine kinase that is a crucial component of the S/G2 checkpoint system for DNA replication monitoring. By bypassing the final checkpoint defenses against DNA damage-induced lethal effects, PF-477736 may improve the antitumor efficacy of various chemotherapeutic agents in tumor cells with inherent checkpoint deficiencies.