SCH900776 is an agent targeting cell cycle checkpoint kinase 1 (Chk1) with potential radiosensitization and chemosensitization activities. It specifically binds to and inhibits Chk1, which may result in tumor cells bypassing Chk1-dependent cell cycle arrest in the S and G2/M phases to undergo DNA repair prior to entry into mitosis; tumor cells may thus be sensitized to the DNA-damaging effects of ionizing radiation and alkylating chemotherapeutic agents.