Interactions of glutathione S-transferase-π with ethacrynic acid and its glutathione conjugate

Sanjay Awasthi, Sanjay K. Srivastava, Faiyaz Ahmad, Hassan Ahmad, G. A.S. Ansari

Research output: Contribution to journalArticlepeer-review

128 Scopus citations


Ethacrynic acid, a diuretic drug known to be an inhibitor of glutathione S-transferases (GSTs), has been shown to enhance the cytotoxicity of the alkylating agent class of chemotherapeutic drugs in cultured cancer cells resistant to alkylating agents. This action of ethacrynic acid is presumably mediated by inhibition of GSTs which are implicated in detoxification of alkylating agents. In addition to being an inhibitor of GSTs, ethacrynic acid also interacts with GSTs as a substrate for conjugation with GSH to yield an ethacrynic acid-GSH conjugate. This conjugate is formed both enzymatically and non-enzymatically and itself is a GST inhibitor. Since ethacrynic acid-GSH conjugate is itself likely to be able to mediate reversal of alkylating agents through GST inhibition, we have synthesized and purified the ethacrynic acid-GSH conjugate, studied the kinetics of inhibition of human lung π-class GST by ethacrynic acid and the conjugate, and compared the kinetics of the enzymatic and non-enzymatic formation of the conjugate using an HPLC method. Results of our studies showed that the ethacrynic acid-GSH conjugate was a more potent inhibitor of human lung GST-π than ethacrynic acid (Ki = 1.5 vs. 11.5 μM, respectively) and that their mechanisms for GST inhibition were distinct (competitive and non-competitive, respectively). Comparison of enzymatic and non-enzymatic rates of conjugate formation in vitro indicated that GST-γ catalyzed a rapid conjugation of ethacrynic acid with GSH at a concentration of ethacrynic acid an order of magnitude above that required to nearly completely inhibit GST catalyzed conjugation of 1-chloro-2,4-dinitrobenzene. However, because of the rapid non-enzymatic reaction, and the inhibition of GST-π with the accumulation of the conjugate in the reaction mixture, the overall quantity of the conjugate formed after 150 min was nearly identical in the presence or absence of GST-π. Results of these studies suggest that inhibition of GSTs by ethacrynic acid-GSH conjugate may be the main mechanism through which ethacrynic acid reverses alkylating agent resistance.

Original languageEnglish (US)
Pages (from-to)173-178
Number of pages6
JournalBiochimica et Biophysica Acta (BBA)/Protein Structure and Molecular
Issue number2
StatePublished - Jul 10 1993
Externally publishedYes


  • Conjugate
  • Enzyme inhibition
  • Ethacrynic acid
  • Glutathione
  • Glutathione S-transferase

ASJC Scopus subject areas

  • Structural Biology
  • Biophysics
  • Biochemistry
  • Molecular Biology


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