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The genotoxicity of the rhodium(III) complex cis-[Rh(biq)(2)Cl(2)]Cl (complex R) in cultured human lymphocytes was studied using the chromosome aberrations (CAs) assay. Lymphocyte cultures were initiated from two adult healthy non-smoking male volunteers and were exposed to the complex for a duration of 3 or 20 h prior to cell collection. The reduction in mitotic indices (MI) and the induction of CAs represented the toxic and clastogenic effects of the different treatments, respectively. Complex R proved to be an intermediate toxic clastogen with a MI(50) of 1.0 microg/ml and a minimum positive dose (MPD) of 0.1 microg/ml. Like bleomycin, complex R exerted its clastogenic effects without the need for metabolic activation and induced CAs of all types in lymphocytes treated in the G(2) and late S phases and, therefore, can be considered a radiomimetic. In addition, it induced more total CAs of chromatid-type than of chromosome-type. The reduction in the frequencies of CAs following the 20 h treatment as compared with those induced following the 3 h treatments indicated that human lymphocytes in the presence of complex R can partially tolerate the lesions involved in CA production. Based on the biological effects of complex R and the similarities between its functional group and that of bleomycin, possible mechanisms for complex R genotoxicity are discussed.

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