Identification of the human P450 enzymes involved in the in vitro metabolism of the synthetic steroidal hormones Org 4060 and Org 30659

Abstract

1. The type of human P450 enzymes involved in the in vitro metabolism of Org 4060 and Org 30659, two synthetic steroidal hormones currently under clinical development by NV Organon for use in oral contraceptive and hormone replacement therapy, was investigated. 2. Both steroids were mainly hydroxylated at the 6 β -position in incubations with human liver microsomes. 3. The results from experiments with supersomes, correlation studies as well as inhibition studies with ketoconazole, a selective inhibitor of CYP3A, strongly suggest that the CYP3A family plays a significant role in the 6 β -hydroxylation of both steroids. 4. Measurements of kinetic parameters of P450 enzymes that could metabolize both steroids, combined with the fact that CYP3A4 is known to be the most abundant P450 enzyme in the human liver, indicate that CYP3A4 will be of major importance for the in vivo human metabolism of Org 4060 and Org 30659.