CHEK1 (checkpoint kinase 1) is a serine/threonine protein kinase that serves as a critical component of the DNA damage response and cell cycle checkpoint pathways. The protein functions primarily within the ATR-CHEK1 signaling cascade, which is activated by single-stranded DNA and serves as the principal direct effector of DNA damage and replication checkpoints, making it essential for cell survival 1. CHEK1 mediates cellular responses to DNA damage by regulating the S to G2/M phase transition and maintaining genomic stability through phosphorylation of downstream targets including CEP170 2. The kinase plays important roles in DNA repair processes, particularly in regulating double-strand break repair via homologous recombination 1. CHEK1 expression is significantly elevated in multiple cancer types, including multiple myeloma, lung adenocarcinoma, and thyroid cancer, where high expression correlates with poor clinical outcomes, advanced disease stages, and reduced survival 345. In multiple myeloma, CHEK1 promotes chr11 instability, drug resistance, and bone lesion formation by activating osteoclast differentiation 2. The protein's essential role in checkpoint signaling and its overexpression in cancers make it an attractive therapeutic target, with inhibition showing synergistic effects when combined with other DNA damage response pathway inhibitors 6.