QSAR Modeling on Aromatase Inhibitory Activity of 23 Triazole Fungicides by Tritium-Water Release Assay

The 1,2,4-triazole fungicides are extensively used in agriculture, and their impacts on aquatic organisms by continuous release are increasingly concerned. Aromatase, a rate-limiting enzyme for androgens converting to estrogens, is considered as a potential target for triazole fungicides. To reveal and predict the aromatase inhibition capacity of the existing and future developed triazole fungicides, 23 commonly used 1,2,4-triazole fungicides were used for the evaluation of their inhibitory effects (expressed as the 50% inhibitory concentration (IC₅₀)) on human aromatase by ³H-H₂O release assay in the present study. Result showed the IC₅₀ values spanned four orders of magnitude from the strongest of 44 nM (flusilazole) to the lowest of 0.330 mM (bitertanol). The aromatase inhibitory activity of the triazoles was also verified in vivo by zebrafish use two triazoles with relatively weak inhibition. Subsequently, the Quantitative Structure-Activity Relationship (QSAR) modeling on the triazoles as aromatase inhibitors was constructed using stepwise regression analysis with the chemical structural descriptors including physicochemical, electronic and topological parameters. The optimal QSAR model was defined as pIC₅₀ = -22.936 - 2.668 E_Homo + 0.938 logD - 0.715 N_HBD. The effectiveness and robustness of the model were evaluated by internal and external validation with residual assessment. The internal validation showed that the R² and R_adj² were both higher than 0.700. The CCC and CCC_Ext were in acceptable levels as the cutoff value of 0.850. The cross-validation correlation coefficient Q² and the external predictive correlation coefficients (Q²-F1, Q²-F2, and Q²-F3) were all greater than 0.600. The results of Y-Scrambling with 2000 iterations indicated the model had no accidental correlation as the average R² of 0.166 and Q² of -0.378. The findings offered data support for the potential risks associated with triazole fungicides in aquatic environment and provided theoretical guidance to expedite drug development and risk assessment.