Interaction of anthelmintic benzimidazoles and benzimidazole derivatives with bovine brain tubulin.

The binding and inhibitory properties of 11 benzimidazoles for bovine brain tubulin were investigated. The effects of the benzimidazoles on the initial rates of microtubule polymerization were determined by a turbidimetric assay. The median inhibitory concentrations (I50) for nocodazole, oxibendazole, parbendazole, mebendazole and fenbendazole ranged from 1.97 . 10(-6) to 6.32 . 10(-6) M. Benomyl, cambendazole and carbendazim had I50 values from 5.83 . 10(-5) to 9.01 .10(-5) M. Thiabendazole had an I50 value of 5.49 . 10(-4) M. Inhibitor constants (Ki) were determined by the colchicine binding assay. Oxibendazole, fenbendazole, and cambendazole had Ki values of 3.20 . 10(-5), 1.73 . 10(-5) and 1.10 . 10(-4) M, respectively. Oxibendazole and fenbendazole were competitive inhibitors of colchicine. In contrast, cambendazole was a noncompetitive inhibitor of colchicine. The ability of these benzimidazoles to inhibit microtubule polymerization and the mode of action for the anthelmintic benzimidazoles is discussed.