Dimethandrolone, a Potential Male Contraceptive Pill, is Primarily Metabolized by the Highly Polymorphic UDP-Glucuronosyltransferase 2B17 Enzyme in Human Intestine and Liver

Abstract

Dimethandrolone undecanoate (DMAU), an oral investigational male hormonal contraceptive, is a prodrug that is rapidly converted to its active metabolite, dimethandrolone (DMA). Poor and variable oral bioavailability of DMA after DMAU dosing is a critical challenge to develop it as an oral drug. The objective of our study was to elucidate the mechanisms of variable pharmacokinetics of DMA. We first identified DMA metabolites formed in vitro and in vivo in human hepatocyte incubation and serum samples following oral DMAU administration in men, respectively. The metabolite identification study revealed two metabolites, DMA-glucuronide (DMA-G; major) and the androstenedione analog of DMA (minor), in the hepatocyte incubations. After oral DMAU administration, only DMA-G was detected in serum, which was >100-fold compared with DMA levels, supporting glucuronidation as the major elimination mechanism for DMA. Next, 13 clinically relevant UDP-glucuronosyltransferase (UGT) enzymes were tested for their involvement in DMA-G formation, which revealed a major role of UDP-glucuronosyltransferase 2B17 (UGT2B17) isoform with a smaller contribution of UGT1A9 in DMA-G formation. These data were confirmed by dramatically higher DMA glucuronidation rates (>200- and sevenfold) in the high versus the null UGT2B17-expressing human intestinal and liver microsomes, respectively. Since human UGT2B17 is a highly variable enzyme with a 20%-80% gene deletion frequency, the in vitro data suggest a major role of UGT2B17 polymorphism on the first-pass metabolism of DMA. Further, considering DMA is a selective and sensitive UGT2B17 substrate, it could be used as a clinical probe of UGT2B17 activity. SIGNIFICANCE STATEMENT: Dimethandrolone (DMA) is an active metabolite of dimethandrolone undecanoate (DMAU), an investigational male hormonal contraceptive. Previous studies have indicated poor and inconsistent bioavailability of DMAU following oral administration. This study found that UDP-glucuronosyltransferase 2B17-mediated high intestinal first-pass metabolism is the key mechanism of variable DMA bioavailability.

Graphical abstract

Fig. 1.

(A) DMAU is an ester prodrug that is rapidly metabolized to its active metabolite, DMA. Sequential metabolism of DMA is not well characterized. (B) The mechanism of action of DMAU involves suppression of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) secretion from the pituitary gland, leading to a cessation of spermatogenesis. (C) Chemical structures of DMA and testosterone.

Fig. 2.

The relative amounts of DMA (open bar) and DMA-G (filled bar) formed in human hepatocytes at (A) 1 µM and (B) 10 µM DMA concentrations at 60 and 120 minutes. No DMA was detected at 1 µM DMA incubation, suggesting its rapid elimination to form DMA-G. The ratios of DMA-G to DMA concentrations were twofold at 10 µM hepatocyte incubations, confirming higher formation of the metabolite compared with the parent.

Fig. 3.

(A) MS response of DMA-G formation in 13 rhUGT2B17 enzymes. UGT1A9 and UGT2B17 were the only enzymes involved in DMA metabolism. (B) DMA metabolism kinetics in the rhUGT2B17 system. (C and D) DMA-G formation kinetics in the high (red) versus null (blue) UGT2B17-expressing HIM (n = 2 high expressors and n = 3 low expressors) and HLM (n = 3 high and null expressors). The data points represent the mean ± standard deviation. (E and F) The estimated f_{m, UGT2B17} was 99.6% and 86%, respectively, in the high-expressing intestinal and liver microsomes, respectively. (G) Michaelis-Menten parameters and UGT2B17 protein abundance in rhUGT2B17 and the high versus null UGT2B17-expressing HIMs and HLMs, respectively.

Fig. 4.

Pharmacokinetic profiles of DMA-G (red circle) and DMA (blue square) following an oral administration of 100 mg DMAU. The systemic exposure (AUC) of DMA-G was >100-fold than DMA serum concentrations, confirming glucuronidation as the major mechanism of DMA disposition.

Fig. 5.

Potential approaches to develop safe and effective oral DMAU delivery. In the first approach, subjects can be stratified into null, mid, and high expressors of UGT2B17 for effective clinical trials. Second, DMA can be administered with a specific UGT2B17 inhibitor to avoid the confounding effect of UGT2B17 metabolism in the first-pass elimination tissues such as intestine and liver.