Liebmann J E, Hahn S M, Cook J A, Lipschultz C, Mitchell J B, Kaufman D C
Radiation Oncology Branch, National Cancer Institute, Bethesda, Maryland 20892.
Cancer Res. 1993 May 1;53(9):2066-70.
Taxol is a naturally occurring chemotherapeutic agent that is active against a variety of tumors. Taxol is believed to act by binding tightly to microtubules and preventing their disaggregation. Others have shown that depletion of cellular glutathione results in the disaggregation of microtubules, presumably by allowing the oxidation of some or all of the cysteine residues in tubulins. We studied the effect of glutathione (GSH) depletion by L-buthionine sulfoximine (L-BSO) on taxol cytotoxicity in two human tumor lines. After a 24-h incubation in 5 mM L-BSO, the breast adenocarcinoma line MCF-7 and the lung adenocarcinoma line A549 were exposed to varying concentrations of taxol for 24 h. GSH levels were undetectable in cells treated with L-BSO. At the highest concentrations of taxol (50 nM), control MCF-7 cells had 10% cell survival and control A549 cells had only 1% cell survival as assessed by clonogenic assay. Pretreatment with 5 mM L-BSO resulted in a 3-fold increase in survival of MCF-7 cells and a 10-fold increase in survival of A549 cells. Pretreatment with L-BSO had no effect on taxol uptake into A549 or MCF-7 cells, as assessed by measurement of binding of [3H]taxol to cells. Following exposure to 37 nM taxol for 24 h, both cell lines had over 80% of their population in G2/M and bromodeoxyuridine labeling showed that taxol markedly reduced the percentage of cells in S phase. L-BSO pretreatment had no effect on the cell cycle in either cell line in the absence of taxol. However, in cells treated with taxol, L-BSO increased the percentage of cells in S phase by 3-fold in both cell lines. We conclude that depletion of cellular GSH by L-BSO results in resistance to taxol in MCF-7 and A549 cells. Resistance to taxol mediated by GSH depletion is not due to alterations in cellular uptake of taxol by L-BSO. L-BSO increased the S-phase fraction of taxol-treated cells in both cell lines. These data suggest that GSH depletion interferes with cell cycle changes induced by taxol. The alteration in taxol-induced cell cycle effects may account for the resistance to taxol produced by L-BSO.
紫杉醇是一种天然存在的化疗药物，对多种肿瘤具有活性。据信紫杉醇通过紧密结合微管并阻止其解聚来发挥作用。其他人已经表明，细胞内谷胱甘肽的耗竭会导致微管解聚，推测是通过使微管蛋白中的一些或所有半胱氨酸残基氧化来实现的。我们研究了L-丁硫氨酸亚砜胺（L-BSO）诱导的谷胱甘肽（GSH）耗竭对两种人类肿瘤细胞系中紫杉醇细胞毒性的影响。在5 mM L-BSO中孵育24小时后，将乳腺腺癌细胞系MCF-7和肺腺癌细胞系A549暴露于不同浓度的紫杉醇中24小时。用L-BSO处理的细胞中未检测到GSH水平。通过克隆形成试验评估，在最高浓度的紫杉醇（50 nM）下，对照MCF-7细胞的细胞存活率为10%，对照A549细胞的细胞存活率仅为1%。用5 mM L-BSO预处理导致MCF-7细胞的存活率增加3倍，A549细胞的存活率增加10倍。通过测量[3H]紫杉醇与细胞的结合来评估，用L-BSO预处理对紫杉醇进入A549或MCF-7细胞没有影响。在暴露于37 nM紫杉醇24小时后，两个细胞系中超过80%的细胞处于G2/M期，溴脱氧尿苷标记显示紫杉醇显著降低了S期细胞的百分比。在没有紫杉醇的情况下，L-BSO预处理对任一细胞系的细胞周期均无影响。然而，在用紫杉醇处理的细胞中，L-BSO使两个细胞系中S期细胞的百分比增加了3倍。我们得出结论：L-BSO诱导的细胞内GSH耗竭导致MCF-7和A549细胞对紫杉醇产生抗性。由GSH耗竭介导的对紫杉醇的抗性不是由于L-BSO改变了细胞对紫杉醇的摄取。L-BSO增加了两个细胞系中紫杉醇处理细胞的S期比例。这些数据表明，GSH耗竭干扰了紫杉醇诱导的细胞周期变化。紫杉醇诱导的细胞周期效应的改变可能是L-BSO产生对紫杉醇抗性的原因。
