GDC-0575, also known as ARRY-575 and RG7741, is a potent and selective inhibitor of cell cycle checkpoint kinase 1 (Chk1) with an IC50 of 1.2?nM. Chk1 inhibitor GDC-0575 specifically binds to and inhibits Chk1; this may result in tumor cells bypassing Chk1-dependent cell cycle arrest in the S and G2/M phases, which permits the cells to undergo DNA repair prior to entry into mitosis.