Lucumi A, Robledo S, Gama V, Saravia N G
Facultad de Salud, Universidad del Valle, Cali, Colombia AA 5445.
Antimicrob Agents Chemother. 1998 Aug;42(8):1990-5. doi: 10.1128/AAC.42.8.1990.
The emergence of Leishmania less sensitive to pentavalent antimonial agents (SbVs), the report of inhibition of purified topoisomerase I of Leishmania donovani by sodium stibogluconate (Pentostam), and the uncertain mechanism of action of antimonial drugs prompted an evaluation of SbVs in the stabilization of cleavable complexes in promastigotes of Leishmania (Viannia). The effect of camptothecin, an inhibitor of topoisomerase, and additive-free meglumine antimoniate (Glucantime) on the stabilization of cleavable DNA-protein complexes associated with the inhibition of topoisomerase was assessed in the human promonocytic cell line U-937, promastigotes of L. (Viannia) panamensis selected for SbV resistance in vitro, and the corresponding wild-type strain. The stabilization of cleavable complexes and the 50% effective dose (ED50) of SbVs for parasites isolated from patients with relapses were also evaluated. The median ED50 for the wild-type strain was 16. 7 microg of SbV/ml, while that of the line selected for resistance was 209.5 microg of SbV/ml. Treatment with both meglumine antimoniate and sodium stibogluconate (20 to 200 microg of SbV/ml) stabilized DNA-protein complexes in the wild-type strain but not the resistant line. The ED50s of the SbVs for Leishmania strains from patients with relapses was comparable to those for the line selected for in vitro resistance, and DNA-protein complexes were not stabilized by exposure to meglumine antimoniate. Cleavable complexes were observed in all Leishmania strains treated with camptothecin. Camptothecin stabilized cleavable complexes in U-937 cells; SbVs did not. The selective effect of the SbVs on the stabilization of DNA-protein complexes in Leishmania and the loss of this effect in naturally resistant or experimentally derived SbV-resistant Leishmania suggest that topoisomerase may be a target of antimonial drugs.
对五价锑剂（SbV）敏感性降低的利什曼原虫的出现、葡糖酸锑钠（喷他脒）对杜氏利什曼原虫纯化拓扑异构酶I抑制作用的报道以及锑剂作用机制的不确定性，促使人们对SbV在稳定利什曼原虫（维扬利什曼原虫）前鞭毛体中可裂解复合物方面进行评估。在人单核细胞系U-937、体外选择的对SbV耐药的巴拿马利什曼原虫（维扬利什曼原虫）前鞭毛体及其相应野生型菌株中，评估了拓扑异构酶抑制剂喜树碱和无添加剂葡甲胺锑酸盐（葡糖胺锑）对与拓扑异构酶抑制相关的可裂解DNA-蛋白质复合物稳定化的影响。还评估了可裂解复合物的稳定化以及SbV对复发患者分离出的寄生虫的50%有效剂量（ED50）。野生型菌株的ED50中位数为16.7微克SbV/毫升，而选择的耐药株的ED50为209.5微克SbV/毫升。用葡甲胺锑酸盐和葡糖酸锑钠（20至200微克SbV/毫升）处理可稳定野生型菌株中的DNA-蛋白质复合物，但不能稳定耐药株中的复合物。复发患者的利什曼原虫菌株对SbV的ED50与体外选择的耐药株相当，且暴露于葡甲胺锑酸盐不能稳定DNA-蛋白质复合物。在用喜树碱处理的所有利什曼原虫菌株中均观察到可裂解复合物。喜树碱可稳定U-937细胞中的可裂解复合物；SbV则不能。SbV对利什曼原虫中DNA-蛋白质复合物稳定化的选择性作用以及在天然耐药或实验获得的SbV耐药利什曼原虫中这种作用的丧失表明，拓扑异构酶可能是锑剂的作用靶点。
