The mutagenicity of benzimidazole and benzimidazole derivatives. VI. Cytogenetic effects of benzimidazole derivatives in the bone marrow of the mouse and the Chinese hamster.

Methyl benzimidazole-2-ylcarbamate (MBC) was mutagenic in mice by the micro-nucleus test. Other benzimidazole derivatives, with the exception of the parent compound of MBC, benomyl, and the very closely related substance 2-benzimidazolylurea, did not produce micro-nuclei in mouse bone marrow. Evidence is presented that MBC acts through inhibition of mitosis and that for this action the carbamoyl group is a necessary but not a sufficient condition. It is also demonstrated that for this particular type of mutagenic activity a threshold limit exists, which seems to be in the order of less than 10 mug MBC per ml blood.