Inhibition of rat and human glutathione S-transferase isoenzymes by ethacrynic acid and its glutathione conjugate.
Ethacrynic acid, a potent inhibitor of glutathione S-transferases (GST), has been shown to enhance the cytotoxicity of chlorambucil in drug resistant cell lines, but a definite mechanism has not been established. Both covalent binding to GST and reversible inhibition of GST have been reported. In the present study no irreversible inhibition was observed: for all rat GST tested, inactivation was complete within 15 sec at 0 degree, and dialysis of GST after incubation with ethacrynic acid gave complete recovery of enzyme activity for all isoenzymes tested. Moreover, the inhibition was competitive towards 1-chloro-2,4-dinitrobenzene and non-competitive towards glutathione for rat isoenzyme 1-1. Strong inhibition of both human and rat GST of the alpha-, mu- and pi-classes was obtained with ethacrynic acid, while conjugation of ethacrynic acid with glutathione did not abolish its inhibiting properties. For the alpha-, mu- and pi-class I50 values (microM) were 4.6-6.0, 0.3-1.9 and 3.3-4.8, respectively for ethacrynic acid, and 0.8-2.8, less than 0.1-1.2 and 11.0, respectively for its glutathione conjugate. Of all isoenzymes tested the human isoenzyme mu is most sensitive to the action of both ethacrynic acid and its glutathione conjugate.
Ploemen
J H
JH
TNO-CIVO Toxicology and Nutrition Institute, Department of Biological Toxicology, Zeist, The Netherlands.
van Ommen
B
B
van Bladeren
P J
PJ
D000818:Animals; D004137:Dinitrochlorobenzene / Q000494:pharmacology; D004976:Ethacrynic Acid / Q000494:pharmacology*; D005978:Glutathione / Q000494:pharmacology*; D005982:Glutathione Transferase / Q000037:antagonists & inhibitors*; D006801:Humans; D007527:Isoenzymes / Q000037:antagonists & inhibitors*; D007700:Kinetics; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains
D004137:Dinitrochlorobenzene; D007527:Isoenzymes; D005982:Glutathione Transferase; D005978:Glutathione; D004976:Ethacrynic Acid