Discovery of HM-279, a Potent Inhibitor of ALK5 for Improving Therapeutic Efficacy of Cancer Immunotherapy.

Activin receptor-like kinase 5 (ALK5) is a type I receptor serine/threonine kinase and responsible for the TGF-β signaling pathway. ALK5 is thought to be a key player in the tumor microenvironment to promote tumor progression by affecting the anticancer immunity. Therefore, ALK5 is an attractive drug target for modulating TGF-β signaling pathways to improve the therapeutic efficacy of cancer immunotherapy. We report the optimization of a series of thiazole analogues starting from lead compound 6, focusing on improving off-target selectivity. Compound 19f (HM-279) was identified as a potent ALK5 inhibitor with an acceptable off-target selectivity and favorable ADME/PK properties. Oral administration of HM-279 demonstrated antitumor activity in a CT26.WT colon carcinoma syngeneic mouse model as a single agent and in combination with the anti-PD-1 antibody through CD8+ T cell immunity.