Fig. 2. Binding and inhibition of CYP17A1 with compound 1 compared to abiraterone.

A Titration of CYP17A1 with increasing concentrations (red→blue) of 1 yields difference spectra with increases at 430 nm, consistent with Fe—CN coordination. B Plots of the absorbance changes due to titration with 1 (blue) and abiraterone (black) reveal that both compounds bind very tightly. Protein concentration is 200 nM and the tight binding equation was used. C CYP17A1 progesterone hydroxylation is inhibited by both compounds, but more potently by abiraterone (black) than by 1 (blue). Both binding assays and inhibition assays were performed in triplicate and all points are shown, although some points overlap.