Network pharmacology and transcriptomics reveal androgen receptor as a potential protein target for 6PPD-quinone

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPD-quinone, or 6PPD-Q) has received increasing attention as an emerging hotspot contaminant. The occurrence of 6PPD-Q in dust and fine atmospheric particles indicates substantial human exposure to this toxicant but the hazards of 6PPD-Q to human health is unknown. We used in silico approaches to identify potential human protein targets of 6PPD-Q and conducted preliminary validation through an in vitro cell proliferation assay and an in vivo transcriptomic analysis of prostate tissues from 6PPD-Q-treated mice. Receptor-based reverse screening and network pharmacology identified four hub targets of 6PPD-Q that were closely related to prostate carcinogenesis. Among these four targets, 6PPD-Q exhibited a strong binding tendency to androgen receptor (AR) with a binding free energy of -23.04 kcal/mol. A support vector machine (SVM) model for predicting chemicals with AR agonism or AR-inactivity was established with good prediction performance (mean prediction accuracy: 0.92). SVM prediction and AR-mediated cell-based assays, with a known AR agonist and a proposed AR inactive agent as positive and negative controls, confirmed that 6PPD-Q displayed AR agonism. Upregulation of Ar mRNA expression (FC = 1.29, p = 0.0404) and its related prostate cancer pathway was observed in the prostate of mice exposed to environmentally realistic concentrations of 6PPD-Q, suggesting a potential role in promoting prostate carcinogenesis. These findings provide evidence that 6PPD-Q agonized AR to exert downstream gene transactivation and imply its prostate cancer risks to humans.