3-substituted 2-phenylimidazo[2,1-b]benzothiazoles: synthesis, anticancer activity, and inhibition of tubulin polymerization.

A new series of 3-substituted 2-phenylimidazo[2,1-b]benzothiazoles (3 a-h) were synthesized by C-arylation of 2-arylimidazo[2,1-b]benzothiazoles using palladium acetate as catalyst, and the resulting compounds were evaluated for their anticancer activity. Compounds 3 a, 3 e, and 3 h exhibited good antiproliferative activity, with GI50 values in the range of 0.19-83.1 μM. Compound 3 h showed potent anticancer efficacy against 60 human cancer cell lines, with a mean GI50 value of 0.88 μM. This compound also induced cell-cycle arrest in the G2/M phase and inhibited tubulin polymerization followed by activation of caspase-3 and apoptosis. A high-throughput tubulin polymerization assay showed that the level of inhibition for compound 3 h is similar to that of combretastatin A-4. Molecular modeling studies provided a molecular basis for the favorable binding of compounds 3 a, 3 e, and 3 h to the colchicine binding pocket of tubulin.