Silva J M, Rao D N, O'Brien P J
Faculty of Pharmacy, University of Toronto, Ontario, Canada.
Cancer Res. 1992 Jun 1;52(11):3015-21.
Trenimon belongs to a class of aziridinylbenzoquinone anticancer drugs that cross the blood-brain barrier. In this study we have investigated the molecular mechanisms for trenimon-induced toxicity in aerobic versus hypoxic conditions with the use of freshly isolated rat hepatocytes. The following evidence suggests the mechanisms for trenimon detoxification involves reduction by DT-diaphorase, while the cytotoxic mechanism involves macromolecular alkylation under hypoxic conditions as well as oxidative stress under aerobic conditions. (a) Hepatocyte cytotoxicity induced by trenimon (250 microM) under aerobic conditions ensued following an initial induction of cyanide-resistant respiration and partial oxidation of glutathione to oxidized glutathione. Trenimon reduction to the hydroquinone by the hepatocytes was rapid. Inhibition of hepatocyte DT-diaphorase by dicumarol increased trenimon-induced cytotoxicity by approximately 10-fold, and markedly inhibited hydroquinone formation. Furthermore, both cyanide-resistant respiration and oxidized glutathione formation were markedly increased, resulting in depletion of oxygen in the media. Trenimon reduction to the hydroquinone then occurred. This suggests that DT-diaphorase in normal hepatocytes prevents the formation of the semiquinone that causes cytotoxic protein alkylation and oxidative stress. (b) Hepatocyte cytotoxicity induced by trenimon (350 microM) under hypoxic conditions ensued following glutathione depletion without oxidized glutathione formation. Inactivation of hepatocyte DT-diaphorase by dicumarol under hypoxic conditions increased trenimon-induced cytotoxicity by approximately 3.5-fold and increased semiquinone radical levels 2-fold without affecting its reduction rate. This suggests that the cytotoxic mechanism involves protein alkylation by semiquinone radicals formed by reductases catalyzing a one-electron reduction of trenimon.
曲尼莫属于一类能穿过血脑屏障的氮丙啶基苯醌类抗癌药物。在本研究中，我们利用新鲜分离的大鼠肝细胞，研究了曲尼莫在有氧和缺氧条件下诱导毒性的分子机制。以下证据表明，曲尼莫解毒机制涉及由DT-黄递酶进行还原，而细胞毒性机制涉及缺氧条件下的大分子烷基化以及有氧条件下的氧化应激。(a) 在有氧条件下，曲尼莫（250微摩尔）诱导的肝细胞毒性是在最初诱导抗氰呼吸以及谷胱甘肽部分氧化为氧化型谷胱甘肽之后发生的。肝细胞将曲尼莫迅速还原为对苯二酚。双香豆素抑制肝细胞DT-黄递酶可使曲尼莫诱导的细胞毒性增加约10倍，并显著抑制对苯二酚的形成。此外，抗氰呼吸和氧化型谷胱甘肽的形成均显著增加，导致培养基中的氧气耗尽。随后曲尼莫还原为对苯二酚。这表明正常肝细胞中的DT-黄递酶可防止导致细胞毒性蛋白烷基化和氧化应激的半醌的形成。(b) 在缺氧条件下，曲尼莫（350微摩尔）诱导的肝细胞毒性是在谷胱甘肽耗竭且未形成氧化型谷胱甘肽之后发生的。在缺氧条件下，双香豆素使肝细胞DT-黄递酶失活，可使曲尼莫诱导的细胞毒性增加约3.5倍，并使半醌自由基水平增加2倍，而不影响其还原速率。这表明细胞毒性机制涉及由催化曲尼莫单电子还原的还原酶形成的半醌自由基对蛋白质的烷基化作用。
