Silva J M, Khan S, O'Brien P J
Faculty of Pharmacy, University of Toronto, Ontario, Canada.
Biochem Pharmacol. 1993 Jun 9;45(11):2303-9. doi: 10.1016/0006-2952(93)90203-9.
The molecular cytotoxic mechanisms of mitomycin C (MMC) and its analogs, BMY 25282 and BMY 25067, have been investigated using isolated hepatocytes as a model system for studying toxicity to nondividing tissues. These drugs have quinone and aziridine moieties, and tumor cell cytotoxicity has been attributed to DNA alkylation and cross-linking. By contrast, the following results suggest that these drugs cause oxidative stress in nondividing cells by different mechanisms. Both hepatocytes or hepatic microsomes and NADPH were able to catalyse oxygen activation by all three drugs, suggesting that enzymatic reduction results in the formation of auto-oxidizable species. Their relative effectiveness at activating oxygen was BMY 25282 >> BMY 25067 > MMC. However, their relative cytotoxic effectiveness was BMY 25067 >> BMY 25282 > MMC, and it was increased markedly if hepatocyte glutathione-reductase or catalase was inactivated. Furthermore, ascorbate increased the toxic potencies of both BMY 25282 and MMC in catalase-inactivated hepatocytes by as much as 60- and 40-fold, respectively. Hepatocyte glutathione (GSH) oxidation was also increased. The relative resistance of normal hepatocytes to MMC and BMY 25282 can be attributed therefore, to the high levels of enzymes in hepatocytes involved in hydrogen peroxide detoxification. BMY 25067 cytotoxicity unlike that of BMY 25282 or MMC was prevented by the addition of the thiol reductant dithiothreitol. BMY 25067 also differed in being much more toxic towards GSH-depleted hepatocytes. Furthermore, BMY 25067, unlike MMC and BMY 25282, caused a rapid decrease in hepatocyte ATP levels and inhibited mitochondrial respiration. This could be prevented by the addition of the thiol reductant dithiothreitol, which restored intracellular GSH levels. Its toxic potency to catalase- or glutathione reductase-inactivated hepatocytes also was not increased by ascorbate. Therefore, the cytotoxicity of BMY 25067 can probably be attributed to oxidative stress by the aminodisulfide moiety which causes GSH and mixed disulfide formation, resulting in mitochondrial toxicity.
已使用分离的肝细胞作为研究对非分裂组织毒性的模型系统，研究了丝裂霉素C（MMC）及其类似物BMY 25282和BMY 25067的分子细胞毒性机制。这些药物具有醌和氮丙啶部分，肿瘤细胞的细胞毒性归因于DNA烷基化和交联。相比之下，以下结果表明这些药物通过不同机制在非分裂细胞中引起氧化应激。肝细胞、肝微粒体和NADPH都能够催化这三种药物的氧活化，这表明酶促还原导致形成可自动氧化的物质。它们在活化氧方面的相对效力为BMY 25282 >> BMY 25067 > MMC。然而，它们的相对细胞毒性效力为BMY 25067 >> BMY 25282 > MMC，如果肝细胞谷胱甘肽还原酶或过氧化氢酶失活，其毒性会显著增加。此外，抗坏血酸分别使BMY 25282和MMC在过氧化氢酶失活的肝细胞中的毒性效力提高了60倍和40倍。肝细胞谷胱甘肽（GSH）氧化也增加。因此，正常肝细胞对MMC和BMY 25282的相对抗性可归因于肝细胞中参与过氧化氢解毒的酶水平较高。与BMY 25282或MMC不同，BMY 25067的细胞毒性可通过添加硫醇还原剂二硫苏糖醇来预防。BMY 25067对GSH耗竭的肝细胞毒性也更大。此外，与MMC和BMY 25282不同，BMY 25067导致肝细胞ATP水平迅速下降并抑制线粒体呼吸。添加硫醇还原剂二硫苏糖醇可预防这种情况，二硫苏糖醇可恢复细胞内GSH水平。抗坏血酸也不会增加其对过氧化氢酶或谷胱甘肽还原酶失活的肝细胞的毒性效力。因此，BMY 25067的细胞毒性可能归因于氨基二硫键部分引起的氧化应激，该应激导致GSH和混合二硫键形成，从而导致线粒体毒性。
