Inhibition of human glutathione transferases by dinitronaphthalene derivatives

Glutathione transferase (GST) enzymes catalyze the conjugation of glutathione with reactive functional groups of endogenous compounds and xenobiotics, including halonitroaromatics. 1-Chloro-2,4-dinitrobenzene (CDNB) is one of the most commonly used substrates for GST activity assays. We have studied the interactions of dinitronaphthalene analogues of CDNB with recombinant human GST enzymes (Alpha, Mu, and Pi classes) expressed in Escherichia coli. Dinitronaphthalene derivatives were found to be GST inhibitors. The highest potency of inhibition was observed towards Mu-class GSTs, M1-1 and M2-2; IC50 values for 1-methoxy- and 1-ethoxy-2,4-dinitronaphthalene were in the high nanomolar to low micromolar range. Inhibition accompanies the formation, at the enzyme active site, of very stable Meisenheimer complex intermediates.