Reductive metabolism and alkylating activity of mitomycin C induced by rat liver microsomes

Abstract

Mitomycin C, an antitumor antibiotic, is rapidly metabolized in the presence of rat liver microsomes. NADPH and anaerobic conditions are required for the process. The products isolated after reexposure to air are 2,7-diaminomitosene derivatives. Specifically, in the presence of inorganic phosphate, 1,2-cis- and -trans-2,7-diaminomitosene 1-phosphates, 1,2-cis- and -trans-2,7-diamino-1-hydroxymitosenes, and 2,7-diaminomitosene are formed. The last substance is a new mitomycin C derivative, and proof for its structure is presented. Mytomycin C has been previously postulated to be an alklating agent requiring reduction for activity (Iyer, V. N., & Szybalski, W. (1964) Science (Washington, D.C.) 145, 55]. The 1-phosphates above represent the first chemically characterized bioreductive alkylation products of the drug. 5'-Uridylic acid is alkylated analogously under these conditions, to give cis- and trans-2,7-diaminomitosene 1-(5'-uridylate), while the phosphodiester UpU and uridine itself are inert. Hydrogen gas/PtO2 gives the same results as microsomes/NADPH. The formation of the observed compounds indicates that enzymatic (or chemical) reduction of the quinone system of mitomycin C induces ring opening of the aziridine function, generating a reactive center at the C1 position as previously postulated by others (ibid.). The second alkylating center, also postulated, is not evident, however, under the conditions tested, indicating that the aziridine is the primary bioreductive alkylation function of mitomycin C. Identification of the products and mechanism of the microsomal anaerobic metabolism of mitomycin C are significant in view of the reported toxicity of the drug to anaerobic cancer cells.