Potential transition-state inhibitors of glyoxalase. I

Abstract

In the 1960s Szent-GyBrgyi and his co-workers reported the inhibition of tumor growth with extracts from normal tissues. Characterization using derivatization and spectral analysis demonstrated that the inhibitor was an a.fl dicarbonyl. Methylglyoxal is the lowest class member of the ketoaldehydes. A biological system which catalyses the formation of lactate from methylglyoxal was reported early in this century. The formation of D-lactate (not the L-lactate of glycolysis) is catalyzed by the mammalian enzymes, glyoxalase I (S-lactoyl-glutathione methylglyoxal-lyase, isomenzing; EC 4.4.1.5) and glyoxalase I1 (S-2-hydroxyacylglutathione hydrolase: EC 3.1.2.6).with glutathione (GSH) as a coenzyme. There have been a number of reports on the formation of methylglyoxal in mammalian tissue, and experimental support for the inhibition of tumor growth by inhibition of glyoxalase I has been published. However, the rapid catabolism of analogues of methylglyoxal or glutathione suggests that inhibitors that resemble the transition state may more effectively bind significantly to glyoxalase I. The transition state in the formation of S-lactoylglutathione from the hemimercaptal of methylglyoxal is an enediol. Compounds such as 3,4-dihydroxycyclobutene 1,2dione (squaric acid) (a coplanar compound) significantly inhibit yeast glyoxalase I. Here the inhibition in uitro of human red blood cell glyoxalase I with a number of compounds that resemble the transition state of methylglyoxal hemimercaptal is reported. These include the following with 150 in mM. 3.4-dihydroxy benzoic acid (0.32 m M ) , 3,4-dihydroxy benzohydroxamic acid (0.38 mM). 4-methyl-6,7-dihydroxy coumarin (0.03 mM), and 6.7-dihydroxy coumarin (0.03 mM). Coumarin was not inhibitory. Calculations based on the in uitro data and these structures may be predictive of their growth inhibitory nature in such model animal tumors as L1210 leukemia.

Theoretical investigations of the structure of potential inhibitors of the enzyme glyoxalase-I

“…7), and the MEP map is given in Figure 8. Since coumarin itself is only very weakly inhibitory [26], the lactone grouping per se does not seem to be the important feature of this molecule as far as the inhibition is concerned; and on the MEP map, this region has three minima in a negative potential ex--c-0-tending right round the 11 grouping. The minima associated with the two 0 -OH groups lie in a negative potential region similar to that observed with the enediol E, except that they are slightly farther apart due to the increased C-C distance in the ring system compared to the isolated double bond.…”

“…Apart from the CH3-groups, all these molecules are planar, and nonplanar analogs are not inhibitory [26]. In attempting to correlate the molecular electrostatic potential maps with the inhibitory effects of the various molecules, we have used a variety of criteria to which we now turn.…”

“…We then compared the V maps with those calculated for a wide variety of known inhibitors of glyoxalase I which differ significantly in their inhibition [26]. These compounds differ quite substantially in their chemical structure.…”

“…We have previously reported [26,27] the inhibition of human red blood cell glyoxalase I by a variety of different molecules. Other workers have carried out similar inhibition studies using yeast glyoxalase I [17].…”

“…We have previously described the experimental study of several potential transition state inhibitors of human red blood cell glyoxalase I, using an in v i m spectrophotometric analysis to determine their 50% inhibition concentration (Iso) [26,27]. The present article describes the results of an attempt to correlate the inhibitory potential of the compounds investigated with "reactivity indices" obtained from ab initio quantum chemical calculations on the inhibitors and various models for the transition state and intermediates in the reaction scheme of Figure 3.…”