Some 3-(4-aminophenyl)pyrrolidine-2,5-diones as all-trans-retinoic acid metabolising enzyme inhibitors (RAMBAs)

A series of (+/-)-3-(4-aminophenyl) pyrrolidin-2,5-diones substituted in the 1-, 3- or 1,3- position with an aryl or long chain alkyl function are weak inhibitors of the metabolism of all-trans retinoic acid (RA) by rat liver microsomes (68-75% inhibition) compared with ketoconazole (85%). Further studies with the 1-cyclohexyl analogue (1) (IC50 = 98.8 muM, ketoconazole, 22.15 muM) showed that it was not stereoselective in its inhibition. (+/-)-(1) was not an inhibitor of pig brain microsomal enzyme (ketoconazole, IC50 = 20.9 muM), had little effect on human liver microsomal enzyme (19.3%, ketoconazole, 81.6%) or human placental microsomal enzyme (9.8%, ketoconazole 73.9%) but was a weak inhibitor of human and rat skin homogenates (52.6% and IC50 = 211.6 muM respectively; ketoconazole, 38.8% and 85.95 muM). In RA-induced cell cultures of human male genital fibroblasts and HaCat cells, (+/-)-(1) was a weak inhibitor (c. 53% at 200 muM) whereas ketoconazole showed high potency (c. 65% at 0.625 muM and 0.25 muM respectively). The nature of the induced target enzyme is discussed.