Complex Metabolism of the Novel Neurosteroid, Ganaxolone, in Humans: A Unique Challenge for Metabolites in Safety Testing Assessment.

The human pharmacokinetics, metabolism, and excretion of [14C]-ganaxolone (GNX) were characterized in healthy male subjects (n = 8) following a single 300-mg (150 µCi) oral dose. GNX exhibited a short half-life of 4 hours in plasma, whereas total radioactivity had a half-life of 413 hours indicating extensive metabolism to long-lived metabolites. Identification of the major GNX circulating metabolites required extensive isolation and purification for liquid chromatography-tandem mass spectrometry analysis, together with in vitro studies, NMR spectroscopy, and synthetic chemistry support. This revealed that the major routes of GNX metabolism involved hydroxylation at the 16α-hydroxy position, stereoselective reduction of the 20-ketone to afford the corresponding 20α-hydroxysterol, and sulfation of the 3α-hydroxy group. This latter reaction yielded an unstable tertiary sulfate, which eliminated the elements of H2SO4 to introduce a double bond in the A ring. A combination of these pathways, together with oxidation of the 3ß-methyl substituent to a carboxylic acid and sulfation at the 20α position, led to the major circulating metabolites in plasma, termed M2 and M17. These studies, which led to the complete or partial identification of no less than 59 metabolites of GNX, demonstrated the high complexity of the metabolic fate of this drug in humans and demonstrated that the major circulating products in plasma can result from multiple sequential processes that may not be easily replicated in animals or with animal or human in vitro systems. SIGNIFICANCE STATEMENT: Studies on the metabolism of [14C]-ganaxolone in humans revealed a complex array of products that circulated in plasma, the two major components of which were formed via an unexpected multi-step pathway. Complete structural characterization of these (disproportionate) human metabolites required extensive in vitro studies, along with contemporary mass spectrometry, NMR spectroscopy, and synthetic chemistry efforts, which served to underscore the limitations of traditional animal studies in predicting major circulating metabolites in man.

Disposition, profiling and identification of emixustat and its metabolites in humans.

1. Emixustat is a small molecule that potently inhibits retinal pigment epithelium 65 isomerohydrolase. Emixustat is in clinical development for the treatment of various retinopathies (i.e. Stargardt disease and diabetic retinopathy). 2. A human absorption, distribution, metabolism, and excretion (ADME) study was conducted with a single dose of [14C]-emixustat in healthy male subjects. Total 14C content in plasma, urine, and faeces was determined using accelerator mass spectrometry (AMS), and metabolic profiles in pooled plasma and urine were investigated by both HPLC-AMS and 2D LC-MS/MS. 3. After a single, oral 40-mg dose of [14C]-emixustat, recovery of total 14C was nearly complete within 24 h. Urine was the major route of 14C elimination; accounting for > 90% of the administered dose. 4. Biotransformation of emixustat occurred primarily at two structural moieties; oxidation of the cyclohexyl moiety and oxidative deamination of the 3R-hydroxypropylamine, both independently and in combination to produce secondary metabolites. Metabolite profiling in pooled plasma samples identified 3 major metabolites: ACU-5124, ACU-5116 and ACU-5149, accounting for 29.0%, 11.5%, and 10.6% of total 14C, respectively. Emixustat was metabolized in human hepatocytes with unchanged emixustat accounting for 33.7% of sample radioactivity and predominantly cyclohexanol metabolites observed.

Absorption, Distribution, Metabolism, and Excretion of the Androgen Receptor Inhibitor Enzalutamide in Rats and Dogs.

BACKGROUND AND OBJECTIVES: Enzalutamide is an androgen receptor inhibitor that has been approved in several countries. Absorption, distribution, metabolism, and excretion (ADME) data in animals would facilitate understanding of the efficacy and safety profiles of enzalutamide, but little information has been reported in public. The purpose of this study was to clarify the missing ADME profile in animals. METHODS: ADME of 14C-enzalutamide after oral administration as Labrasol solution were investigated in non-fasted male Sprague-Dawley rats and beagle dogs. RESULTS: Plasma concentrations of 14C-enzalutamide peaked in rats and dogs at 6-8 h after a single oral administration. In most tissues, radioactivity concentration peaked at 4 h after administration. Excluding the gastrointestinal tract, tissues with the highest concentration of radioactivity were liver, fat, and adrenal glands. The tissue concentrations of radioactivity declined below the limit of quantitation or <0.89 % of maximum concentration by 168 h post-dose. Two known metabolites (M1 and M2) and at least 15 novel possible metabolites were detected in this study. M1 was the most abundant metabolite in both rats and dogs. Unchanged drug was a minor component in excreta. In intact rats, the mean urinary and fecal excretion of radioactivity accounted for 44.20 and 49.80 % of administered radioactivity, respectively. In intact dogs, mean urinary and fecal excretion was 62.00 and 22.30 % of the administered radioactivity, respectively. CONCLUSIONS: Rapid oral absorption was observed in rats and dogs when 14C-enzalutamide was administered as Labrasol solution. Tissue distribution in rats was clarified. The elimination of enzalutamide is mediated primarily by metabolism. Species differences were observed in excretion route.