CHEK1 and neoplasm: From collective studies of berzosertib in combination with carboplatin, irinotecan, cisplatin, or gemcitabine in multiple preclinical tumor models, the total plasma concentration needed to reach 50% of maximal inhibition (IC50) of p-Chk1 in humans was estimated to be approximately 110 ng/mL (95% confidence interval (CI) 62–158 ng/mL) after adjustment for species differences in plasma protein binding [17].