MRP/GST SYNERGY AND MDR

我们认为多药耐药相关蛋白(MRP)和 谷胱甘肽S转移酶(GSTs)协同作用 对多种抗癌药物的多药耐药性(MDR)。通过协同，我们 意味着MRP和MRP的增加对耐药性的总影响 GST大于MRP和GST对耐药的影响之和 商品及服务税独立执行。我们认为，这种协同作用的机制 涉及药物或其有毒代谢物的结合，以 谷胱甘肽(GSH)。据认为，这些谷胱甘肽毒素结合物 是更好的MRP相关药物外排泵的底物 未结合药物或代谢物。 这一假设很吸引人，因为虽然GST可以共轭一些 抗癌药物联合GSH、GST升高对耐药的影响 一直是不一致的。因此，有人建议，第二次 基因产物可能是GSTs充分产生耐药性所必需的。 最近的报道强烈表明，MRP是一种依赖于ATP的GSH- 共轭导出器。因此，MRP是第二种模式的首选 GST介导的耐药相关基因产物。 为了验证这一假设，我们将使用模型亲本细胞系 表现低基础水平的MRP和GST。通过稳定地转染这些基因 细胞，衍生的细胞系将建立表达增加的 具有或不具有随之而来的 GST同工酶。将对这些细胞系进行相对耐药性检查 一系列药物和外来毒素的细胞毒性作用。 仅表达的细胞的细胞毒性剂量-反应数据的比较 MRP增加与表达MRP-GST水平增加的细胞相比 同工酶组合将允许鉴定和定量 MRP和GSTs之间的药效学相互作用。此外， 细胞内GSH池的抗性与维持的关系 将会被探索。有了这些衍生的细胞系，相对的 对药物结合酶，如GSTs的耐药性的贡献，以及 可以对MRP进行评估。这些细胞将被用来检验我们的假设 GST和MRP可以协同作用授予高水平抗性 选择抗肿瘤药物。为了研究任何一种 观察MRP与GST同工酶、药物动力学的协同作用 蓄积和外排将在衍生细胞系中确定。 这些药代动力学研究将确定GST是否升高 水平促进药物出口，通过形成GSH-药物结合物，在 MRP升高的细胞。

We propose that the multidrug resistance-associated protein (MRP) and glutathione S-transferases (GSTs) cooperate synergistically to confer high level multidrug resistance (MDR) to many anticancer drugs. By synergy we mean that the total effect on drug resistance of increases in both MRP and GST is greater than the sum of the effects on drug resistance of MRP and GST taken independently. We suggest that the mechanism of this synergy involves the conjugation of drugs, or their toxic metabolites, to glutathione (GSH) by GSTs. It is believed that these GSH-toxin conjugates are better substrates for the MRP-associated drug efflux pump than are the unconjugated drugs or metabolites. This hypothesis is appealing because, while GSTs can conjugate a number of anticancer drugs with GSH, the effect of increased GST on drug resistance has been inconsistent. Consequently, it has been suggested that a second gene product may be necessary for GSTs to fully confer drug resistance. Recent reports have strongly indicated that MRP is an ATP-dependent, GSH- conjugate exporter. Therefore, MRP is the prime candidate for the second gene product involved in GST-mediated drug resistance. To test this hypothesis, we will use model parental cell lines that express low basal levels of MRP and GST. By stable transfection of these cells, derivative cell lines will be established that express increased levels of MRP with or without concomitantly increased levels of the isozymes of GST. These cell lines will be examined for relative resistance to the cytotoxic effects of a panel of drugs and xenobiotic toxins. Comparison of cytotoxicity dose-response data for cells that express only increased MRP versus cells that express increased levels of MRP-GST isozyme combinations will allow the identification and quantitation of pharmacodynamic interactions between MRP and GSTs. Additionally, the relationship between resistance and maintenance of intracellular GSH pools will be explored. With these derivative cell lines, the relative contributions to resistance of drug conjugating enzymes, such as GSTs, and MRP can be evaluated. These cells will be used to test our hypothesis that GST and MRP can cooperate synergistically to confer high level resistance to select antineoplastic drugs. In order to examine the mechanism of any observed synergy between MRP and the isozymes of GST, the kinetics of drug accumulation and efflux will be determined in the derivative cell lines. These pharmacokinetic studies will establish whether or not increased GST levels facilitate drug export, by the formation GSH-drug conjugates, in cells having increased MRP.