Gene-specific Oligonucleotide Probes for a, p, TT,and Microsomal Rat Glutathione S-transferases: Analysis of Liver Transferase Expression and Its Modulation by Hepatic Enzyme Inducers and Platinum Anticancer Drugs1

Glutathione S-transferases (GSTs) play an important role in the detoxification of diverse electrophilic chemicals, including anticancer drugs. Gene-specific Oligonucleotide probes were developed to monitor the expression of individual GST mRNAs in livers of adult male rats treated with drugs and other chemical modulators of GST expression. Northern blot analysis of total liver RNA using probes specific for individual GSTs belonging to classes a (GSTs Yal, Ya2, Ye), u (GSTs Ybl, Yb2, Yb3), »(GST Yp), and GSTm, demonstrated the expression in liver of all but Yp mRNA. Kidney GST expression was at least as high as that in liver for GSTs Yal, Yc, and Yp, while it was substan tially lower but still detectable for GSTs Ya2, Yb2, and <.S 1„¿ „. Several of the liver GST class a mRNAs, in particular Ya2, were inducible by pretreatment of rats with phénobarbital or isosafrole. In contrast, dexamethasone preferentially induced Ybl, Yb2, and Ya2, while two other inducers of liver drug metabolism, isoniazid and clofibrate, were less effective with respect to GST induction. GSTms mRNA was induced to a small extent or not at all by the agents tested. Treatment of adult male rats with the anticancer drug cisplatin increased liver expression of GST Yc mRNA and suppressed Yal mRNA levels with little or no major effect on several other GST mRNAs. Western blot analysis of liver cytosols prepared from the cisplatin-treated rats revealed corresponding changes in GST Yc and Ya protein levels. Comparable changes in liver GST Yal and Yc expression were effected by the cisplatin analogue iproplatin but not by carboplatin or transplatin. This pattern of response to these platinum drugs is comparable to that seen with respect to platinum drug-induced gonadal toxicity and modulation of liver cytochrome P450 expression, suggesting a common mechanistic basis for these diverse effects of platinum anticancer drugs on hepatic enzymes of drug metabolism. Together, these studies demonstrate the utility of Oligonucleotide probes for phenotyping liver tissue for the expression of GST enzymes that can contribute to anticancer drug metabolism and resistance. They also raise the possibility of drug-drug interactions involving cisplatin and alkylating agent anticancer drugs that can be metabolized in liver by «-class GSTs.