Discovery of pyrido[3,2-d]pyrimidin-6(5H)-one derivatives as checkpoint kinase 1 (CHK1) inhibitors with potent antitumor efficacy.

Checkpoint kinase 1 (CHK1) plays a crucial role in the DNA damage response pathway, making it an attractive target for cancer therapy. Herein, we present the synthesis, optimization, and evaluation of selective CHK1 inhibitors with a pyrido[3,2-d]pyrimidin-6(5H)-one scaffold. Among them, compound 11 showed single-digit nanomolar potency against CHK1 (IC: 0.55 nM) with good kinase selectivity. Notably, 11 showed anti-proliferative effect in MV-4-11 cells singly (IC = 202 nM) and a synergistic effect in combination with gemcitabine in HT-29 cells (IC = 63.53 nM). Furthermore, the combination of 11 and gemcitabine exhibited synergistic effect in the HT-29 xenograft mouse model. Overall, this work provides a strong foundation for the development of selective CHK1 inhibitors and the therapeutic strategy for cancer.