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.

Mode of Action for Mitomycin C Inactivating Factors ofPseudomonas convexa4-87

“…7 ) Pan et alP) also found that NADPHcytochrome P-450 reductase and xanthine oxidase catalyzed MMC reduction under anaerobic conditions and with proper electron donors to produce these three metabolites. The desmutagenic factor of P. convexa 4-87 requires NAD(P)H to catalyze MMC reduction under aerobic conditions.…”

“…Peak VI was identified as DAM according to Tomasz and Lipman. 7 ) Identification of metabolites To identify the synthesized derivatives and reaction products, they were analyzed directly by field-desorption mass spectrometry, and their UV absorbance spectra were taken in methanol. The results were combined and are shown in Table I.…”

“…Various metabolic pathways have been postulated. 4 -6 ) Recently, Tomasz and Lipman 7 ) succeeded in identifying some metabolites of MMC generated by incubation of MMC with rat liver microsomes and NADPH under anaerobic conditions. All the metabolites thus obtained were 2,7-diaminomitosene type derivatives, in which the C-1 position was substituted.…”

Characterization of a quinone reductase activity for the mitomycin C binding protein (MRD): Functional switching from a drug-activating enzyme to a drug-binding protein

“…Therefore, MRD E55G might confer resistance to MC through fast binding and transformation of MC into three mitosenes (5, 6, and 7). The fact that 6 was the major product of MRD E55G catalyzed reaction also implies that 4 might be in an unusual configuration during the reaction, because in the normal reductive MC activation catalyzed by various flavoreductases, the trans (5) and cis (6) 1-hydroxy mitosenes were produced in almost equal amounts (12,20,21).…”

Immunological Quantitation of DT‐Diaphorase in Carcinoma Cell Lines and Clinical Colon Cancers: Advanced Tumors Express Greater Levels of DT‐Diaphorase

“…The bioreductive activation of MMC can occur via two pathways. The first is one-electron reduction, mediated by NADPH:cytochrome P450 reductase, 1,2) xanthine oxidase, 2) cytochrome b 5 reductase 3) and xanthine dehydrogenase. 4) The second is two-electron reduction.…”