Cisplatin is the most effective chemotherapy drug for the treatment of ovarian cancer. Its usefulness in the clinic is restricted by dose-limiting nephrotoxicity and the development of drug-resistance within the tumor. During the previous funding period our studies demonstrated that the nephrotoxicity of cisplatin is due to the metabolism of cisplatin-glutathione conjugate through a GGT- mediated pathway in the kidney. We further demonstrated that this GGT-mediated toxicity is specific to the kidney. When GGT was transfected into tumor cells it reduced the toxicity of cisplatin rather than increasing it as was seen in the kidney. These findings indicate that there are two distinct mechanisms of cisplatin toxicity. The delineation of these two mechanisms would provide the opportunity to inhibit the side effects of cisplatin without compromising its antitumor activity. The current proposal focuses on defining the mechanisms by which cisplatin exerts its toxic effects and identifying the mechanism by which tumor cells develop resistance to cisplatin. The first specific aim is to further characterize the unstable cisplatin-glutathione conjugate that is a substrate for GGT and follow its metabolism within the kidney. A series of cisplatin-glutathione conjugates will be tested as substrates for GGT-mediated activation to nephrotoxins by LLC-PK1 cells and human renal proximal tubule cells. Cisplatin-glutathione conjugates will be isolated by HPLC and their structure determined by Mass Spectrometry. The pathway by which they are metabolized will be determined with the use of selective inhibitors of enzymes within the pathways. Inhibitors that block the activation of cisplatin in vitro will be tested for their ability to block the nephrotoxicity of cisplatin in vivo. The second specific aim is to identify the mechanism by which tumors become resistant to cisplatin in vivo. Human epithelial ovarian tumors will be propagated in nude mice. Half the mice will be treated with cisplatin. Cisplatin resistant tumors will be isolated after several courses of treatment. mRNA will be isolated from these tumors and differentially expressed genes will be isolated by representational differential analysis.
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