Vol. 27, Issue 2, 303-308, February 1999

Cytochrome P-450 Isoforms Involved in Carboxylic Acid Ester Cleavage of Hantzsch Pyridine Ester of Pranidipine

Shoji Kudo, Hiroshi Okumura, Gohachiro Miyamoto, and Takashi Ishizaki

Tokushima Research Institute, Otsuka Pharmaceutical Co., Ltd, Tokushima, Japan (S.K., H.O., G.M.); and Department of Pharmacology and Therapeutics, Graduate School of Clinical Pharmacy, Kumamoto University, Kumamoto, Japan (T.I.)

Cytochrome P-450 (CYP) isoforms responsible for the cleavage of Hantzsch pyridine ester at the 3-position of pranidipine were studied in vitro using cDNA-expressed human CYP enzymes. CYP1A1, 1A2, 2D6, and 3A4 cleaved the ester with a catalytic activity of 5.5, 0.93, 13.1, and 22.4 nmol/30 min/nmol P-450, respectively. CYP2A6, 2B6, 2C8, 2C9, 2C19, and 2E1 were not involved in the de-esterification. The K_m and V_max values for the de-esterification were 11.8 µM and 0.47 nmol/min/nmol P-450 in the CYP2D6-catalyzed reaction and 8.7 µM and 0.84 nmol/min/nmol P-450 in the CYP3A4-catalyzed reaction. The intrinsic clearance (V_max/K_m) of the de-esterification by CYP3A4 was 2-fold greater than that by CYP2D6. Quinidine almost completely inhibited the CYP2D6-mediated de-esterification at the concentration of 1 × 10⁶ M. Ketoconazole and troleandomycin inhibited the CYP3A4-mediated reaction in a dose-related manner. The results indicate that although the multiple CYP isoforms can catalyze the de-esterification, CYP3A4 and 2D6 are the major isoforms.