Studies on filarial GST as a target for antifilarial drug development-in silico and in vitro inhibition of filarial GST by substituted 1,4-naphthoquinones

Eleven 1,4-naphthoquinone analogues with different amino substitutions at position 3 of the quinone ring earlier reported for macrofilaricidal activity were selected and screened against purified cytosolic GST isolated from the bovine filarial worm Setaria digitata and IC₅₀ values were determined. Of the 11 compounds tested, 8 showed good inhibition against S. digitata GST. The IC₅₀ values of the most effective macrofilaricidal compounds—11 2-(4-methylpiperazin-1-yl)naphthalene-1,4-dione] and 9 {2-(1,3-dimethylbutyl)amino]naphthalene -1,4-dione}—were 0.872 and 0.994 mM, respectively. Compounds 9 and 11 were further studied for type of enzyme inhibition and found to exhibit competitive and uncompetitive inhibition kinetics, respectively, with respect to substrate GSH. All 11 compounds were in agreement with Lipinski’s rule of five and passed through the FAFDrugs ADME/tox filter. Molecular docking was carried out using the modeled 3D structure of wbGST PDB ID:1SFM as receptor and substituted naphthoquinones as ligands using AutoDock 4.0. The binding energy of nine compounds varied from −9.15 to −6.58 Kcal mol⁻¹, whereas compounds 8 and 10 did not show any binding to the receptor. Among the compounds studied, compound 7 {2-3-(diethylamino) propyl]aminonaphthalene-1,4-dione} showed maximum affinity towards wbGST as it exhibited the lowest binding energy, followed by compounds 11 and 9. However compound 7 was not macrofilaricidal while 11 and 9 exhibited macrofilaricidal activity. The results of in silico and in vitro studies with the synthesized 1,4 -naphthoquinone analogues on filarial GST and in vitro macrofilaricidal activity against adult bovine filarial worm S. digitata open up a promising biochemical target for antifilarial drug development.