The interactions of a number of steroid-metabolizing cytochromes P450 with abiraterone D4A metabolite: spectral analysis and molecular docking.

The interactions of pharmacologically active 3-keto-Δ4-metabolite of anticancer drug abiraterone (D4A) with steroid-metabolizing cytochromes P450 (CYP51A1, CYP11A1, CYP19A1) was studied by absorption spectroscopy and molecular docking. Both abiraterone and D4A induce type I spectral changes of CYP51A1, one of the enzymes of cholesterol biosynthesis. We have revealed that D4A did not induce spectral changes of CYP11A1, the key enzyme of pregnenolone biosynthesis, unlike abiraterone (type II ligand of CYP11A1). On the contrary, D4A interacts with the active site of CYP19A1, the key enzyme of estrogen biosynthesis, inducing type II spectral changes, while abiraterone does not. Spectral analysis allowed us to calculate spectral dissociation constant (KS) for each complex of cytochrome P450 with respective ligands. The data were supported by molecular docking. The obtained results broaden understanding of interactions of D4A with some of the key steroid-metabolizing cytochromes P450 and allow one to predict possible disproportions of steroid metabolism.

Estimation of the inhibiting impact of abiraterone D4A metabolite on human steroid 21-monooxygenase (CYP21A2).

Abiraterone D4A metabolite, the product of 3ß-hydroxysteroid dehydrogenase activity toward abiraterone, may serve as a potential antitumor agent for the treatment of prostate cancer. The main adverse effect of abiraterone is the disruption of corticosteroid biosynthesis, and the more pharmacologically active abiraterone D4A metabolite may have the same issues. We therefore estimated the inhibiting impact of the abiraterone D4A metabolite on one of the key corticosteroidogenic enzymes - human steroid 21-monooxygenase (CYP21A2). Molecular docking of D4A into the active site of CYP21A2 has been predicted to be similar to abiraterone binding with the enzyme. Abiraterone D4A metabolite, similar to abiraterone, induces type II spectral changes of CYP21A2. The spectral dissociation constant for the abiraterone D4A metabolite-CYP21A2 complex was calculated as 3.4 ±â€¯0.5 µM. Abiraterone D4A metabolite demonstrates competitive/mixed type CYP21A2 inhibition with an inhibitory constant of 1.8 ±â€¯0.8 µM, as obtained by Dixon plot. These results make it possible to predict the adverse effects of the new perspective candidate compound for antitumor therapy.

In vitro interactions of abiraterone, erythromycin, and CYP3A4: implications for drug-drug interactions.

Potential drug-drug interactions of the antitumor drug abiraterone and the macrolide antibiotic erythromycin were studied at the stage of cytochrome P450 3A4 (CYP3A4) biotransformation. Using differential spectroscopy, we have shown that abiraterone is a type II ligand of CYP3A4. The dependence of CYP3A4 spectral changes on the concentration of abiraterone is sigmoidal, which indicates cooperative interactions of CYP3A4 with abiraterone; these interactions were confirmed by molecular docking. The dissociation constant (Kd ) and Hill coefficient (h) values for the CYP3A4-abiraterone complex were calculated as 3.8 ± 0.1 µM and 2.3 ± 0.2, respectively. An electrochemical enzymatic system based on CYP3A4 immobilized on a screen-printed electrode was used to show that abiraterone acts as a competitive inhibitor toward erythromycin N-demethylase activity of CYP3A4 (apparent Ki  = 8.1 ± 1.2 µM), while erythromycin and its products of enzymatic metabolism do not affect abiraterone N-oxidation by CYP3A4. In conclusion, the inhibition properties of abiraterone toward CYP3A4-dependent N-demethylation of erythromycin and the biologically inert behavior of erythromycin toward abiraterone hydroxylation were demonstrated.