Role of cysteine S-conjugate beta-lyase in the metabolism of cisplatin.
Cisplatin is nephrotoxic, but the mechanism by which cisplatin kills renal proximal tubule cells is not well defined. Inhibition of gamma-glutamyl transpeptidase or pyridoxal 5'-phosphate (PLP)-dependent enzymes blocks the nephrotoxicity. Our hypothesis is that cisplatin is metabolized to a renal toxin through a platinum-glutathione conjugate to a reactive sulfur-containing compound. The final step in this bioactivation is the conversion of a platinum-cysteine S-conjugate to a reactive thiol by a PLP-dependent cysteine S-conjugate beta-lyase. LLC-PK1 cells, a proximal tubule cell line with low cysteine S-conjugate beta-lyase activity, are used to study cisplatin nephrotoxicity. We proposed that the beta-elimination reaction catalyzed by cysteine S-conjugate beta-lyase is the rate-limiting step in the metabolism of cisplatin to a toxin in these cells. In this study, LLC-PK1 cells were transfected with human glutamine transaminase K, which catalyzes the beta-elimination reaction. Cisplatin was significantly more toxic in confluent monolayers of cells with increased cysteine S-conjugate beta-lyase activity. In contrast, carboplatin, a non-nephrotoxic derivative of cisplatin, was 20-fold less toxic than cisplatin in confluent cells, and its toxicity was not altered by overexpression of cysteine S-conjugate beta-lyase. We propose that carboplatin is not nephrotoxic because it is not metabolized through this pathway. Dividing cells were more sensitive to both cisplatin and carboplatin toxicity. Overexpression of cysteine S-conjugate beta-lyase activity had no effect on the toxicity of either drug. These data demonstrate that cisplatin kills quiescent renal cells by a mechanism that is distinct from the mechanism by which it kills dividing cells and that the renal toxicity of cisplatin is dependent on cysteine S-conjugate beta-lyase activity.
Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma.
Lei
L
Zhang
Marie H
MH
Hanigan
D000818:Animals; D000970:Antineoplastic Agents / Q000378:metabolism*; D015153:Blotting, Western; D013437:Carbon-Sulfur Lyases / Q000235:genetics / Q000378:metabolism*; D016190:Carboplatin / Q000494:pharmacology; D002460:Cell Line; D002945:Cisplatin / Q000378:metabolism*; D006801:Humans; D007668:Kidney; D008190:Lyases / Q000235:genetics / Q000378:metabolism*; D013552:Swine; D000637:Transaminases / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
D000970:Antineoplastic Agents; D016190:Carboplatin; D000637:Transaminases; C427605:glutamine - phenylpyruvate transaminase; D008190:Lyases; D013437:Carbon-Sulfur Lyases; C108902:cysteine-S-conjugate beta-lyase; D002945:Cisplatin