Effects of benzimidazole analogs on cultures of differentiating rodent embryonic cells

Micromass cell culture systems for rat embryo midbrain (CNS) and limb bud (LB) cells were employed to assess the in vitro developmental toxicity of the benzimidazole analogs, mebendazole (MBZ), thiabendazole (TBZ), and nocodazole (NCZ), in addition to the classic microtubule inhibitor, colchicine. Comparison was made to albendazole (ABZ), a previously studied benzimidazole anthelmintic. Two parameters for assessing developmental toxicity were measured: differentiation and cytotoxicity. The relative potencies of the benzimidazole analogs in the micromass system (NCZ greater than MBZ approximately ABZ much greater than TBZ) mirrored their effectiveness in an assay for in vitro inhibition of mammalian tubulin polymerization. Colchicine also exhibits a high affinity for mammalian tubulin and was a potent inhibitor of cell proliferation, chondrogenesis, and neuronal differentiation. Immunofluorescent staining of Day 1 LB cultures with a monoclonal antibody to beta-tubulin revealed that these agents elicited mitotic arrest. Many anti-tubulin agents are teratogenic in rats and their in vivo developmental toxicity may reflect perturbation of microtubular structure or function. With the exception of TBZ, these agents should be considered potential developmental toxicants since they inhibit cell growth and differentiation of micromass cultures at nanomolar concentrations.