RESUMEN
A series of 2,2'-dihydroxybenzophenones and their carbonyl N-analogues were studied as potential inhibitors against human glutathione transferase M1-1 (hGSTM1-1) purified from recombinant E. coli. Their screening revealed an inhibition against hGSTM1-1 within a range of 0-42% (25 µM). The IC50 values for the two stronger ones, 16 and 13, were 53.5 ± 5.6 µΜ and 28.5 ± 2.5 µΜ, respectively. The results were compared with earlier ones for isoenzymes hGSTP1-1 and hGSTA1-1 involved in MDR. All but one bind more strongly to A1-1, than M1-1 and P1-1, the latter being a poor binder. An order of potency A1-1 > > M1-1 > P1-1 meritted 13, 14 and 16 as the most potent inhibitors with hGSTM1-1. Enzyme kinetics with hGSTM1-1 (Km(CDNB) 213 ± 10 µΜ and Km(GSH) 303 ± 11 µΜ) revealed a competitive modality for 16 (Ki(16) = 22.3 ± 1.1 µΜ) and a mixed one for 13 versus CDNB (Ki(13) = 33.3 ± 1.6 µM for the free enzyme and Ki(13) ' = 17.7 ± 1.7 µM for the enzyme-CDNB complex). 5- or 5'-Bromo- or phenyl-substituted (but not in combination) inhibitors, having a H-bonded oxime weakly acidic group of a small volume, are optimal candidates for binding hGSTM1-1. The outcome of the isoenzyme trilogy identified good binder leads for the investigated GSTs involved in MDR.