Design, Synthesis, and Structure–Activity Relationship Study of 2-Oxo-3,4-dihydropyrimido[4,5-d]pyrimidines as New Colony Stimulating Factor 1 Receptor (CSF1R) Kinase Inhibitors

Colony stimulating factor 1 receptor kinase (CSF1R) is a well validated molecular target for anticancer drug discovery. Herein, we report the design, synthesis, and structure-activity relationship study of 2-oxo-3,4-dihydropyrimido[4,5- d]pyrimidines as new orally bioavailable CSF1R inhibitors. One of the most promising compounds, 3bw, potently inhibits CSF1R kinase with an IC₅₀ value of 3.0 nM, while it is less potent against structurally related epidermal growth factor receptor (EGFR) and other kinases. The kinase inhibition of 3bw was further validated by Western blotting analysis in RAW264.7 macrophages. The molecule also potently blocks macrophage infiltration, abrogates the protumorigenic influences of macrophages, and exhibits reasonable pharmacokinetic profile. Compound 3bw may serve as a new valuable lead compound for future anticancer drug discovery.