Isothiazolinone biocides as aromatase inhibitors: Hormonal disruption, and in silico docking and SAR/QSAR analysis

Isothiazolinone biocides, widely used in industrial, agricultural, and biomedical applications due to their unique chemical properties, have unclear effects on CYP19A1 (aromatase), a critical enzyme in placental estrogen synthesis. This study systematically assessed seven isothiazolinone biocides for their inhibitory effects on human and rat CYP19A1. Dichlorooctylisothiazolinone emerged as the most potent inhibitor, with IC₅₀ values of 5.78 μM (human) and 7.35 μM (rat), followed by octylisothiazolinone, 2-butyl-1,2-benzisothiazolin-3-one, methylchloroisothiazolinone, and methyl-isothiazolinone, all exhibiting mixed inhibition mechanisms. Structure-activity relationship (SAR) analysis revealed a negative correlation between IC₅₀ and LogP, suggesting that enhanced hydrophobicity enhances CYP19A1 inhibition. In intact BeWo cells, all above chemicals except octylisothiazolinone suppressed estradiol synthesis at ≥1 μM, whereas octylisothiazolinone required higher concentrations (10-100 μM), indicating that solubility and molecular size influence cellular inhibition efficiency as judged by computational analysis. Molecular docking and 3D-QSAR pharmacophore modeling further confirmed that hydrophobic interactions dominate enzyme binding, with hydrophobic pharmacophore features being key determinants of inhibitory activity. These findings demonstrate that isothiazolinone biocides act as CYP19A1 inhibitors, primarily driven by hydrophobic interactions, with potency modulated by physicochemical properties such as hydrophobicity, solubility, and molecular size.