title: Exploration of in vitro pro-drug activation and futile cycling by glutathione S-transferases: thiol ester hydrolysis and inhibitor maturation.
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.
authors.affiliation: Department of Medicinal Chemistry, University of Washington, Seattle, WA 98195-7610, USA.
authors.forename: Catherine
authors.initials: C
authors.lastname: Ibarra
authors.forename: Mark P
authors.initials: MP
authors.lastname: Grillo
authors.forename: Mario
authors.initials: M
authors.lastname: Lo Bello
authors.forename: Marzia
authors.initials: M
authors.lastname: Nucettelli
authors.forename: Theo K
authors.initials: TK
authors.lastname: Bammler
authors.forename: William M
authors.initials: WM
authors.lastname: Atkins
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D001667:Binding, Competitive; D002384:Catalysis; D002853:Chromatography, Liquid; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D004950:Esterases / Q000378:metabolism; D004952:Esters / Q000378:metabolism; D004976:Ethacrynic Acid / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D051549:Glutathione S-Transferase pi; D005982:Glutathione Transferase / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D006868:Hydrolysis; D007527:Isoenzymes / Q000737:chemistry; D007700:Kinetics; D008780:Methyltransferases; D008956:Models, Chemical; D011355:Prodrugs / Q000378:metabolism*; D021241:Spectrometry, Mass, Electrospray Ionization; D013438:Sulfhydryl Compounds / Q000378:metabolism; D013997:Time Factors
chemical_list: D000970:Antineoplastic Agents; D004791:Enzyme Inhibitors; D004952:Esters; D007527:Isoenzymes; D011355:Prodrugs; D013438:Sulfhydryl Compounds; D008780:Methyltransferases; C022742:thiol S-methyltransferase; C496556:GSTP1 protein, human; D051549:Glutathione S-Transferase pi; D005982:Glutathione Transferase; D004950:Esterases; D005978:Glutathione; D004976:Ethacrynic Acid