Poddevin B, Riou J F, Lavelle F, Pommier Y
Laboratory of Molecular Pharmacology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892.
Mol Pharmacol. 1993 Oct;44(4):767-74.
The mechanisms of action of intoplicine (RP-60475), a 7H-benzo[e]pyrido[4,3-b]indole derivative that is presently in early clinical trials, have been investigated. Intoplicine induced both topoisomerase I- and II-mediated DNA strand breaks, using purified topoisomerases. The topoisomerase cleavage site patterns induced by intoplicine were unique, relative to those of camptothecin, 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA), and other known topoisomerase inhibitors. Both topoisomerase I- and II-induced DNA breaks decreased at drug concentrations higher than 1 microM, which is consistent with the DNA-intercalating activity of intoplicine. DNA damage was investigated in KB cells in culture by using alkaline elution. Intoplicine induced single-strand breaks (SSB) in a bell-shaped manner with respect to drug concentration (maximum frequency at 1 microM approximately 220 rad-equivalents). SSB formation was fast, whereas reversal after drug removal was slow. Similar bell-shaped curves were obtained for DNA double-strand breaks (DSB) and DNA-protein cross-links. SSB and DNA-protein cross-link frequencies were approximately equal, and no protein-free breaks were detectable, indicating the protein concealment of the breaks, as expected for topoisomerase inhibition. Comparison of SSB and DSB frequencies indicated that intoplicine produced a significant amount of SSB not related to DSB, which is consistent with concomitant inhibition of both DNA topoisomerases I and II in cells. Data derived from resistant cell lines indicated that multidrug-resistant cells were cross-resistant to intoplicine but that m-AMSA- and camptothecin-resistant cells were sensitive to intoplicine. Hence, intoplicine might circumvent topoisomerase I-mediated and topoisomerase II-mediated resistance by poisoning both enzymes simultaneously.
因托普西（RP - 60475）是一种目前正处于早期临床试验阶段的7H - 苯并[e]吡啶并[4,3 - b]吲哚衍生物，其作用机制已得到研究。利用纯化的拓扑异构酶，因托普西可诱导拓扑异构酶I和II介导的DNA链断裂。相对于喜树碱、4' -（9 - 吖啶基氨基）甲磺酰间茴香胺（m - AMSA）及其他已知的拓扑异构酶抑制剂，因托普西诱导的拓扑异构酶切割位点模式是独特的。当药物浓度高于1微摩尔时，拓扑异构酶I和II诱导的DNA断裂均减少，这与因托普西的DNA嵌入活性一致。通过碱性洗脱法对培养的KB细胞中的DNA损伤进行了研究。因托普西以钟形方式诱导单链断裂（SSB），其与药物浓度有关（在1微摩尔时频率最高，约为220拉德当量）。SSB形成迅速，而药物去除后的恢复缓慢。对于DNA双链断裂（DSB）和DNA - 蛋白质交联也获得了类似的钟形曲线。SSB和DNA - 蛋白质交联频率大致相等，且未检测到无蛋白质的断裂，这表明断裂被蛋白质掩盖，正如拓扑异构酶抑制所预期的那样。SSB和DSB频率的比较表明，因托普西产生了大量与DSB无关的SSB，这与细胞中DNA拓扑异构酶I和II同时受到抑制一致。来自耐药细胞系的数据表明，多药耐药细胞对因托普西有交叉耐药性，但对m - AMSA和喜树碱耐药的细胞对因托普西敏感。因此，因托普西可能通过同时使两种酶中毒来规避拓扑异构酶I介导和拓扑异构酶II介导的耐药性。
