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Binding to Cellular Macromolecules as a Possible Mechanism for the Cytotoxicity of Misonidazole¹

Physics Division, Ontario Cancer Institute, Toronto, Ontario, Canada

Reduction of the nitro group occurred when [¹⁴C]misonidazole was treated with zinc dust in aqueous solution in the presence of ammonium chloride. When the reduction mixture was allowed to react with calf thymus DNA or bovine albumin, radioactivity was bound to both DNA and protein. Under the same conditions, misonidazole did not bind to these macromolecules. Analysis of the reduction mixture indicated that the hydroxylamine, amine, and hydrazo derivatives of mizonidazole were the major products. In a number of tissues of C3H mice after administration of [¹⁴C]misonidazole, radioactivity was detected in the DNA, RNA, and protein fractions. Similar results were also obtained with Chinese hamster ovary cells incubated with the drug in the absence of oxygen. It is postulated that nitroreduction and binding of the nitroreduction products to macromolecules is a probable mechanism for the mutagenic and cytotoxic properties of misonidazole.

¹ Supported by the Ontario Cancer Treatment and Research Foundation and the National Cancer Institute of Canada.

Received 10/ 1/79. Accepted 3/19/80.

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