PF-477736

PF-477736 is a selective, potent, and ATP-competitive small molecule inhibitor of checkpoint kinase 1 (Chk1), with a Ki of 0.49 nM for Chk1 and over 100-fold selectivity against Chk2[2][4][7]. Developed by Pfizer as an investigational anticancer agent, it was primarily studied in combination with chemotherapeutics such as gemcitabine for the treatment of advanced solid tumors[3][5]. Chk1 plays a critical role in the DNA damage response by regulating cell cycle checkpoints (notably G2/M) and facilitating homologous recombination repair. Inhibition of Chk1 by PF-477736 abrogates cell cycle arrest following DNA damage, increases replicative stress, impairs homologous recombination repair (HRR), and can sensitize tumor cells to DNA-damaging agents or PARP inhibitors[8][10]. Preclinical studies also suggest that PF-477736 can inhibit vascular smooth muscle cell proliferation via the Chk1/p53/CD44 pathway[6].