Novel pyridine bioisostere of cabozantinib as a potent c-met kinase inhibitor: Synthesis and anti-tumor activity against hepatocellular carcinoma

Two novel bioisosteres of cabozantinib, 3 and 4, were designed and synthesized. The ben-zene ring in the center of the cabozantinib structure was replaced by trimethylpyridine (3) and pyridine (4), respectively. Surprisingly, the two compounds showed extremely contrasting mesenchy-mal–epithelial transition factor (c-Met) inhibitory activities at 1 μM concentration (4% inhibition of 3 vs. 94% inhibition of 4). The IC50 value of compound 4 was 4.9 nM, similar to that of cabozantinib (5.4 nM). A ligand-based docking study suggested that 4 includes the preferred conformation for the binding to c-Met in the conformational ensemble, but 3 does not. The anti-proliferative activity of compound 4 against hepatocellular carcinoma (Hep3B and Huh7) and non-small-cell lung cancer (A549 and H1299) cell lines was better than that of cabozantinib, whereas 3 did not show a signifi-cant anti-proliferative activity. Moreover, the tumor selectivity of compound 4 toward hepatocellu-lar carcinoma cell lines was higher than that of cabozantinib. In the xenograft chick tumor model, compound 4 inhibited Hep3B tumor growth to a much greater extent than cabozantinib. The present study suggests that compound 4 may be a good therapeutic candidate against hepatocellular carci-noma.