2-and 3-substituted 1,4-naphthoquinone derivatives as subversive substrates of trypanothione reductase and lipoamide dehydrogenase from Trypanosoma cruzi: Synthesis and correlation between redox cycling activities and in vitro cytotoxicity

Trypanothione reductase (TR) is both a valid and an attractive target for t he design of new trypanocidal drugs. Starting from menadione, plumbagin, an d juglone, three distinct series of 1,4-naphthoquinones (NQ) were synthesiz ed as potential inhibitors of TR from Trypanosoma cruzi (TcTR). The three p arent molecules were functionalized at carbons 2 and/or 3 by various polyam ine chains. Optimization of TcTR inhibition and TcTR specificity versus hum an disulfide reductases was achieved with the 3,3'-[polyaminobis(carbonylal kyl)]bis(1,4-NQ) series 19-20, in which an optimum chain length was determi ned for inhibition of the trypanothione disulfide reduction. The most activ e derivatives against trypanosomes in cultures were also studied as subvers ive substrates of TcTR and lipoamide dehydrogenase (TcLipDH). The activitie s were measured by following NAD(P)H oxidation as well as coupling the reac tions to the reduction of cytochrome c which permits the detection of one-e lectron transfer. For TcTR, 20(4-c) proved to be a potent subversive substr ate and an effective uncompetitive inhibitor versus trypanothione disulfide and NADPH. Molecular modeling studies based on the known X-ray structures of TcTR and hGR were conducted in order to compare the structural features, dimensions, and accessibility of the cavity at the dimer interface of TcTR with that of hGR, as one of the putative NQ binding sites. TcLipDH reduced the plumbagin derivatives by an order of magnitude faster than the corresp onding menadione derivatives. Such differences were not observed with the p ig heart enzyme. The most efficient and specific subversive substrates of T cTR and TcLipDH exhibited potent antitrypanosomal activity in in vitro T. b rucei and T. cruzi cultures. The results obtained here confirm that reducti on of NQs by parasitic flavoenzymes is a promising strategy for the develop ment of new trypanocidal drugs.