CHEK1 and neoplasm: Synthetic lethal vulnerabilities are exploited therapeutically by combining inhibitors against a tumor deficiency in the DDR protein: CHK1 inhibitor (MK-8776) is used with gemcitabine (antimetabolite) in solid tumors [239], WEE1 Inhibitor (AZD-1775) with gemcitabine, cisplatin, or carboplatin (DNA damaging agents) in advanced solid tumors [240] or in combination with a checkpoint kinase CHK1 inhibitor (PF-0047736) in acute lymphoblastic leukemia [241], and a DNA-PK and mTOR dual inhibitor (CC-115) in hematopoietic and solid cancer cells [242].