RF34 | PMON202 The Human Metabolic Profile of Estetrol

OBJECTIVES: Estetrol (E4), a native estrogen produced by the fetal human liver, has four hydroxyl-groups, making it structurally distinct from other estrogens. We determined the human metabolic profile of E4, which is recently marketed combined with drospirenone as a novel contraceptive and is currently in development for the relief of menopausal symptoms. Method: We studied the in vitro metabolism of E4 using human hepatocytes, human liver microsomes and recombinant CYP enzymes in reaction phenotyping studies to evaluate the role of human cytochrome P450 enzymes, UDP-glucuronosyltransferases (UGT) and sulfotransferases (SULT). Furthermore, we evaluated the in vivo metabolism of E4 in an open-label, non-randomised phase 1 human absorption, distribution, metabolism, and excretion study, in which six healthy postmenopausal participants received a single oral solution containing 15 mg [(14)C]-E4. We analysed blood (up to 240h), urine and faecal samples (up to 312h). Metabolite profiling and identification was performed using liquid chromatography with tandem mass spectrometry. RESULTS: The in vitro studies showed that E4 undergoes extensive phase 2 metabolism to form glucuronide and sulphate conjugates. UGT2B7 is the key enzyme catalysing the direct glucuronidation of E4 and SULT1E1 is the dominant sulfotransferase for sulphate conjugation in vitro. Unlike for other estrogens, oxidative phase 1 metabolism by P450 enzymes does not play a major role in the metabolism of E4. Following oral administration of E4 to humans, the major metabolites observed in human plasma were E4-16-glucuronide, E4-3-glucuronide and E4-glucuronide-sulfate (respectively 62%, 17% and 9% of radioactivity at the time of maximum plasma concentration [Tmax]). At Tmax, unchanged E4 accounts for only 7.5% of plasma radioactivity. Main metabolites quantified in urine during the first 6 hours after administration were E4-16-glucuronide and E4-3-glucuronide (respectively 77.4% and 16.5% of urine radioactivity). Approximately 69% of the total administered radioactivity was recovered in urine and 22% in faeces. Mass spectrometry showed that E4 was not present in urine but was detected in faeces and that E4 is not converted back into one of the other natural estrogens (estriol, estradiol, estrone). CONCLUSIONS: Altogether, these data suggest that E4 has a unique metabolic profile. E4 is a terminal end-product of estrogen metabolism, which is not converted back, in vivo, into active metabolites like estriol, estradiol or estrone. Unlike for other estrogens, CYP450 enzymes do not play a major role in the metabolic pathway of E4. Presentation: Monday, June 13, 2022 12:30 p.m. - 2:30 p.m., Monday, June 13, 2022 12:48 p.m. - 12:53 p.m.