Discovery of Novel 5-(Pyridazin-3-yl)pyrimidine-2,4(1,3)-dione Derivatives as Potent and Orally Bioavailable Inhibitors Targeting Ecto-5'-nucleotidase.

Ecto-5-nucleotidase (CD73) is overexpressed in a variety of cancers and associated with the immunosuppressive tumor microenvironment, making it an attractive target for cancer immunotherapy. Herein, we designed and synthesized a series of novel (pyridazine-3-yl)pyrimidine-2,4(1,3)-dione derivatives as CD73 inhibitors. These compounds exhibited remarkable inhibitory activity against CD73 in both enzymatic biochemical and cellular assays. Among them, compound proved to be one of the most potent inhibitors and an uncompetitive inhibitor with no obvious cytotoxicity. This compound showed high metabolic stability in rat liver microsomes and favorable pharmacokinetic profiles in rats ( = 3.37 h, = 50.24%). Importantly, orally administered significantly inhibited tumor growth in the triple-negative breast cancer 4T1 mouse model (TGI = 73.6%, 50 mg/kg). Immunoassays suggested that remarkably increased the infiltration of positive immune cells, thereby reinvigorating antitumor immunity. These results demonstrate that is a potent CD73 inhibitor worthy of further development.