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  • Title: Exploration of in vitro pro-drug activation and futile cycling by glutathione S-transferases: thiol ester hydrolysis and inhibitor maturation.
    Author: Ibarra C, Grillo MP, Lo Bello M, Nucettelli M, Bammler TK, Atkins WM.
    Journal: Arch Biochem Biophys; 2003 Jun 15; 414(2):303-11. PubMed ID: 12781783.
    Abstract:
    In addition to glutathione (GSH) conjugating activity, glutathione S-transferases (GSTs) catalyze "reverse" reactions, such as the hydrolysis of GSH thiol esters. Reverse reactions are of interest as potential tumor-directed pro-drug activation strategies and as mechanisms for tissue redistribution of carboxylate-containing drugs. However, the mechanism and specificity of GST-mediated GSH thiol ester hydrolysis are uncharacterized. Here, the GSH thiol esters of ethacrynic acid (E-SG) and several nonsteroidal antiinflammatory agents have been tested as substrates with human GSTs. The catalytic hydrolysis of these thiol esters appears to be a general property of GSTs. The hydrolysis of the thiol ester of E-SG was studied further with GSTA1-1 and GSTP1-1, as a model pro-drug with several possible fates for the hydrolysis products: competitive inhibition, covalent enzyme adduction, and sequential metabolism. In contrast to hydrolysis rates, significant isoform-dependent differences in the subsequent fate of the products ethacrynic acid and GSH were observed. At low [E-SG], only the GSTP1-1 efficiently catalyzed sequential metabolism, via a dissociative mechanism.
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