Effect of misonidazole pretreatment on nitrogen mustard-induced DNA cross-linking in mouse tissues in vivo

Abstract

Summary In the present study we have used the alkaline elution technique to study the effect of misonidazole (MISO) on the initial amount of DNA cross-linking in various normal and neoplastic tissues of C3H mice treated with nitrogen mustard (HN2) in vivo. Tissue samples for analysis of the cross-links were prepared 1 h after injection with HN2 to minimize the effect of subsequent repair processes on the yield of lesions. For mice receiving HN2 alone, the greatest level of cross-linking was found in spleen and jejunum, with the liver showing the lowest level. In animals that had been pretreated with MISO (1 mg g -1, i.p.) for 0.5 h prior to injection with HN2, the amount of cross-linking in the spleen and jejunum was not affected by MISO; however, in all other tissues that were examined, cross-linking was enhanced by MISO to a varying extent depending on the specific tissue. The greatest enhancement was observed in the liver ( x 6) and kidney (x 3.1), both of these tissues showing a greater enhancement than either of the two fibrosarcomas. The potentiation of HN2 cross-linking in a particular tissue correlated well with two cellular processes that are known to be nitroreduction-dependent in vitro, namely, the degree of MISO-induced GSH depletion and the binding of MISO to cellular macromolecules. Thus, the potentiation of cross-linking in normal tissues such as liver and kidney, and by inference in tumours, may be intimately related to the generation and/or accumulation of nitro-reduced MISO metabolites in those tissues.The potentiation of many antitumour drugs by the hypoxic cell radiosensitizer misonidazole (MISO) is now well documented (McNally, 1982;Millar, 1982;Siemann, 1982Siemann, , 1984. However, the mechanisms of chemosensitization, and in particular the role of hypoxia, have not been completely elucidated. Hypoxia during the MISO pretreatment stage has been found to be essential for the in vitro potentiation of all chemotherapy drugs studied to date, including the enhanced cytotoxicity of the bifunctional alkylating agent nitrogen mustard (HN2) to V79 cells (Stratford et al., 1980) and EMT6 tumour spheroids (Twentyman, 1982a(Twentyman, , 1982b. A requirement of hypoxia for MISO enhancement in vivo may explain why tumours generally seem to be sensitized to a greater extent than most normal tissues, although the exact situation regarding the involvement of hypoxia in vivo is unclear. However, Wheeler et al. (1984) recently showed that, at least for the drug BCNU, hypoxia induced by clamping of the leg was clearly critical for sensitization by MISO of a subcutaneous rat 9L tumour.We recently reported (Murray & Meyn, 1984) that pretreatment of mice with MISO enhanced the in vivo DNA cross-linking activity of HN2 in a murine fibrosarcoma, a tumour that contains a substantial fraction of hypoxic cells (Stone & Milas, 1978;Grdina et al., 1976