POTENT AND SELECTIVE INHIBITORS OF LEUKOTRIENE A(4) HYDROLASE - EFFECTS ON PURIFIED ENZYME AND HUMAN POLYMORPHONUCLEAR LEUKOCYTES

Leukotriene (LT) A(4) hydrolase (EC 3.3.2.6) is a bifunctional zinc me talloenzyme that catalyzes the hydrolysis of the unstable epoxide inte rmediate LTA(4) into the proinflammatory substance LTB(4) and also exh ibits an amidase/peptidase activity toward synthetic substrates. Based on proposed reaction mechanisms for other zinc hydrolases, we have sy nthesized inhibitors of LTA(4) hydrolase and evaluated their effects o n the formation of LTB(4) from LTA(4) using both purified enzyme and i ntact polymorphonuclear leukocytes, The two most effective inhibitors, an alpha-keto-beta-amino ester (compound IV) and a thioamine (compoun d VIII), exhibited IC50 values of 1.9 +/- 0.9 and 0.19 +/- 0.12 mu M ( mean +/- SD, n = 4), respectively. Compounds IV and VIII were also pot ent inhibitors of LTB(4) biosynthesis in ionophore stimulated polymorp honuclear leukocytes with IC50 < 200 nM. At higher concentrations, the biosynthesis of 5-hydroxy-eicosatetraenoic acid was also inhibited wi th IC50 approximate to 10 mu M for both substances. In contrast, leuko cyte 15-lipoxygenase and platelet LTC(4) synthase activity were not in hibited by these substances at the highest concentrations tested, 50 a nd 10 mu M, respectively. Compounds IV and VIII thus exhibit selectivi ty among enzyme activities in the arachidonic acid cascade. In conclus ion, we describe two compounds that are among the most potent and sele ctive inhibitors of LTA(4) hydrolase and LTB(4) biosynthesis by intact polymorphonuclear leukocytes, described thus far.