[The interactions of abiraterone and its pharmacologically active metabolite D4A with cytochrome P450 2C9 (CYP2C9)]

Interactions of cytochrome P450 2C9 (CYP2C9) were studied with the antitumor drug abiraterone and its pharmacologically active metabolite D4A, promising as an agent for prostate cancer treatment. It was shown by absorption spectroscopy, that both investigated compounds induced spectral changes of CYP2C9, indicating interactions of the pyridine nitrogen atom with the heme iron ion of the active site of the enzyme, but interactions of the ligands with the enzyme could be mediated by a water molecule bound to the heme iron ion. Based on the spectral changes, the values of dissociation constants (KS) for complexes of abiraterone and D4A with CYP2C9 were calculated as 1.73±0.14 μM and 3.95±0.16 μM. Both compounds inhibited O-demethylase activity of CYP2C9 towards its substrate. At 100 μM concentration of naproxen the concentrations of abiraterone, D4A and sulfaphenazole inhibiting CYP2C9 activity by 50% (IC50) were determined as 13.9 μM, 40 μM and 41 μM, respectively. The obtained results can be used for prognosis of drug-drug interactions at CYP2C9 level during administration of abiraterone or D4A as an antitumor agent for prostate cancer treatment in complex pharmacotherapy.