Inhibition of Brain Human Steroid 5α-Reductase 1 by Dithiocarbamates: A Comprehensive Enzymatic and Structural Analysis

We investigated the inhibitory effects of dithiocarbamates (DTCs) on human steroid 5α-reductase 1 (SRD5A1), an enzyme crucial for the conversion of testosterone or pregnenolone into neuroactive steroids. Utilizing a comprehensive approach that included enzyme assays, molecular docking simulations, and both structure-activity relationship (SAR) and 3D quantitative SAR (3D-QSAR) analyses, we assessed the potency and interaction mechanisms of DTCs with SRD5A1 in human SF126 cells. Our results demonstrated that zinc dibutyldithiocarbamate, disulfiram, ferbam, thiram, and ziram displayed significant inhibitory activity against SRD5A1, with IC 50 values of 1.10, 1.62, 2.31, 1.74, and 1.84   μM, respectively. Kinetic studies indicated that these compounds function as mixed inhibitors, suggesting a multifaceted interaction with the enzyme's active site. These DTCs effectively penetrated the cell membrane of SF126 cells to inhibit SRD5A1 at ≥ 5   μM. Molecular docking analyses revealed that these compounds interacted with a distinct domain located between the NADPH and testosterone binding sites of SRD5A1, primarily through sulfur bonds, which are a fundamental component of the DTC structure. Experimental validation of the inhibitory mechanism was achieved by demonstrating that the co-incubation of dithiothreitol, a sulfhydryl-reducing agent, significantly reversed the inhibitory effects of zinc dibutyldithiocarbamate and thiram. SAR analysis revealed a negative correlation between LogP, molecular weight, and IC 50 values, and a positive correlation between LogS, lowest binding energy, and IC 50 values. The 3D-QSAR analysis further indicated that hydrogen bond acceptor and hydrophobic region capabilities significantly contribute to the primary inhibition. In conclusion, this research significantly advances our understanding of the SAR of sulfur-containing DTCs as inhibitors of human SRD5A1, providing valuable insights for identifying toxicity of DTCs targeting this enzyme.