A potent, nonpeptidyl 1H-quinolone antagonist for the gonadotropin-releasing hormone receptor.

Extensive development of the structure-activity relationships of a screening lead determined three important pharmacophores for gonadotropin-releasing hormone (GnRH) receptor antagonist activity. Incorporation of the 3,4,5-trimethylphenyl group at the 3-position, 2-(2(S)-azetidinyl)ethoxy group at the 4-position, and N-4-pyrimidinylcarboxamide at the 6-position of the quinolone core resulted in the identification of 4-(2-(azetidin-2(S)-yl)ethoxy)-7-chloro-2-oxo-3-(3,4,5-trimethylphenyl)-1,2-dihydroquinoline-6-carboxylic acid pyrimidin-4-ylamide (1) as a potent antagonist of the GnRH receptor. A 10(4)-fold increase in in vitro binding affinity is observed for the GnRH receptor as compared to the initial screening lead. Compound 1 exhibits nanomolar binding activity and functional antagonism at the human receptor and is 7-fold less active at the rhesus receptor. Intravenous administration of compound 1 to rhesus monkeys results in a significant decrease of the serum levels of downstream hormones, luteinizing hormone (79% decrease in area under the curve) and testosterone (92% decrease in area under the curve), at a dose of 3 mg/kg. Quinolone 1 is a potent nonpeptidyl antagonist for the human GnRH receptor that is efficacious for the suppression of luteinizing hormone and testosterone in primates.

Biotransformation of finasteride (MK-0906) by Selenastrum capricornutum (green algae).

Finasteride (MK-0906), a drug used for the treatment of benign prostatic hyperplasia, is a highly specific inhibitor of steroid 5 alpha-reductase, an enzyme that converts testosterone (T) to dihydrotestosterone (DHT) in animals and humans. In a study to evaluate the effect of finasteride on the growth of green alga, Selenastrum capricornutum, the parent drug was not detected by HPLC in the posttreatment (14 day) samples, suggesting complete biotransformation. Thermospray LC/MS, followed by NMR analysis, indicated that the major algal metabolite was 11 alpha-hydroxy-finasteride. This metabolite has negligible in vitro bioactivity against human prostatic 5 alpha-reductase; its potency is only 2% that of finasteride. The primary metabolite of finasteride produced by the green alga involved a biotransformation not previously observed in mammalian and human studies. The green alga effectively deactivates the drug, thereby mitigating any potential environmental impact.

Capillary column GLC-mass spectrometric assay with selected-ion monitoring for timolol and [13C3]timolol in human plasma.

A method for the measurement of the beta-blocker timolol and its 13C3-labeled analog in human plasma is described. A known amount of an internal standard, [2H9]timolol, is added to each plasma sample. The method employs a reversed-phase C18 cartridge for isolation of the drug-containing fraction, capillary column GLC of the trimethylsilyl derivatives, and detection via selected-ion monitoring. The ions monitored for quantification (m/e 86 from timolol and m/e 89 and 95 from the 13C3- and 2H9-labeled analogs, respectively) arise from the side chains of the three compounds [e.g., CH2N+HC(CH3)3 for m/e 86]. Plasma levels of timolol and [13C3]timolol in human subjects given 5 or 10 mg of each compound were followed simultaneously for 12 hr postdosing. A detection level of 0.5 ng/ml of plasma was found. No evidence was found for a metabolic kinetic isotope effect since the ratios of the two species of drug in the plasma samples were the same as the ratios in the administered dose.

Biochemical and biomedical applications of capillary column GLC using SIM.

This report focuses on recent applications of capillary column GLC to the analysis of drugs and metabolites, other xenobiotics, natural products, and environmental contaminants in samples of biological origin. The increasing use of selected ion monitoring, combined with stable isotope methods as a means of GLC detection and quantification, is emphasized. Specific topics covered include the use of capillary column GLC for 1) determining the pharmacokinetics of timolol (BLOCADREN) in human volunteers by simultaneous oral and intravenous administration of this beta-blocker and its 13C3-labeled analog; 2) measuring residue levels of the forced molting agent, xylonidine, in yolk and albumen of chicken eggs; 3) monitoring animal plasma and tissues for the depletion of 5-hydroxy-1,3-dioxane and 4-hydroxymethyl-1,3-dioxolane (isomeric components of glycerol formal, an animal drug formulation component); 4) detecting 13C, 15N-methyltryptamine (a biosynthesis product from 13C, 15N-tryptamine) in human urine; and 5) measuring estradiol levels in biological samples.

High-performance liquid chromatographic determination of N-(2-methyl-2-propyl)-3-oxo-4-aza-5 alpha-androst-1-ene-17 beta-carboxamide, a 4-azasteroid, in human plasma from a phase I study.

A sensitive and selective high-performance liquid chromatographic method has been developed for the quantitative determination of N-(2-methyl-2-propyl)-3-oxo-4-aza-5 alpha-androst-1-ene-17 beta-carboxamide (I) in human plasma. I, a 5 alpha-reductase inhibitor and a potential therapeutic agent for benign prostatic hyperplasia, is a member of the family of compounds referred to as the 4-azasteroids. The 4-N-methyl analogue of the drug was used as the internal standard and calibration curves were developed at two levels of sensitivity to cover a large dynamic range of plasma concentrations. Drug was isolated from biological fluids with a solid-phase C18 extraction column; the analyte was further purified by adsorption and desorption from a second extraction column (CN cartridge). Evaluation of the isolation method revealed that it was reproducible and drug recoveries equalled ca. 90%. Chromatography was carried out on a C8 column (5 micron) with ultraviolet detection at 210 nm. The detection limit was ca. 10 ng/ml for I. Human plasma levels are reported for I following single-dose oral administration of 50,200 and 400 mg of drug; urinary excretion data are reported for a single volunteer given 400 mg of I.

Comparative metabolic disposition of ivermectin in fat tissues of cattle, sheep, and rats.

In the study of the metabolic disposition of ivermectin in cattle, sheep, and rats, a group of nonpolar metabolites was detected in the fat tissues of these animals. Upon saponification or esterase treatment, these nonpolar metabolites gave rise to polar products that were similar to the ivermectin metabolites present in the liver. A hypothesis was thus proposed that the polar ivermectin metabolites produced in the liver were esterified and stored in the fat as nonpolar entities, which can be reconverted back to the polar metabolites chemically or enzymatically. To substantiate this hypothesis, the regeneration of polar metabolites from the nonpolar metabolites was studied and hydrolysis products were characterized to establish the basic structure of the alcohol portion of the metabolites. Furthermore, chromatographic comparisons were made between radiolabeled in vivo metabolites and synthetic fatty acid ester samples. These results established the general structural class of the ivermectin nonpolar metabolites and also confirmed the unusual metabolic pathway of ivermectin disposition in fat tissue.

Disposition and pharmacokinetics of [14C]finasteride after oral administration in humans.

The disposition of [14C]finasteride, a competitive inhibitor of steroid 5 alpha-reductase, was investigated after oral administration of 38.1 mg (18.4 microCi) of drug in six healthy volunteers. Plasma, urine, and feces were collected for 7 days and assayed for total radioactivity. Concentrations of finasteride and its neutral metabolite, omega-hydroxyfinasteride (monohydroxylated on the t-butyl side chain), in plasma and urine were determined by HPLC assay. Mean excretion of radioactivity equivalents in urine and feces equaled 39.1 +/- 4.7% and 56.8 +/- 5.0% of the dose, respectively. The mean peak plasma concentrations reached for total radioactivity (ng equivalents), finasteride, and omega-hydroxyfinasteride were 596.5 +/- 88.3, 313.8 +/- 99.4, and 73.7 +/- 11.8 ng/ml, respectively, at approximately 2 hr; the mean terminal half-life for drug and metabolite was 5.9 +/- 1.3 and 8.4 +/- 1.7 hr, respectively. Of the 24-hr plasma radioactivity, 40.9% was finasteride, 11.8% was the neutral metabolite, and 26.7% was characterized as an acidic fraction of radioactivity. Binding of [14C]finasteride to plasma protein was extensive (91.3 to 89.8%), with a trend suggesting concentration dependency (range 0.02 to 2 micrograms/ml). Little of the dose was excreted in urine as parent (0.04%) or omega-hydroxyfinasteride (0.4%). Urinary excretion of radioactivity was largely in the form of acidic metabolite(s)--18.4 +/- 1.7% of the dose was eliminated as the omega-monocarboxylic acid metabolite. Finasteride was scarcely excreted unchanged in feces. In humans, finasteride is extensively metabolized through oxidative pathways.(ABSTRACT TRUNCATED AT 250 WORDS)

Disposition and metabolism of finasteride in dogs.

Finasteride (FIN) is a potent 5 alpha-reductase inhibitor that has shown clinical success in treating men with benign prostatic hyperplasia. In the study of biological effects and metabolism of FIN in animals, the dog serves as the primary modality. This study was conducted to determine the pharmacokinetics and fate of FIN after oral administration of single doses of [14C]FIN to dogs at 10 and 80 mg/kg (N = 2 and 3, respectively), and also after intravenous infusion at 5 mg/kg (N = 2). Plasma, urine, and feces were analyzed for total 14C content. Parent drug and metabolites in plasma and excreta were measured by HPLC/UV/radioassay and identified by NMR spectroscopy and MS, FIN was subject to extensive biotransformation before excretion. Structures were determined for the major metabolites in plasma, urine, and feces. The primary metabolic events for FIN were hydroxylation of the t-butyl side chain to give hydroxymethyl-FIN (metabolite I), which is oxidized further to form the carboxylic acid derivative (metabolite IV), and hydroxylation at positions B alpha and 15. Terminal half-life of FIN after the intravenous dose was 3.4 hr. Plasma clearance and volume of distribution at steady-state were 4.8 ml/min/kg and 1.1 liter/kg. Dogs showed rapid absorption after oral administration of the low dose, with Cmax reached in the 1-2 hr, bioavailability was estimated to be > 90%. After either dosing route, 45% of the plasma radioactivity (as represented by AUC) was parent drug, 43% was metabolite I, and 1% was metabolite IV. After oral administration, the 80 mg/kg dose was absorbed slowly, with the highest levels of radioactivity in plasma reached in 4-30 hr. Average Cmax value for FIN and metabolite I increased in a dose-related, but nonproportional, manner. Compared with the 10 mg/kg dose, it seems the higher dose was reasonably well-absorbed, as indicated by the nearly proportional increase of AUC values of total radioactivity and FIN. Composition of plasma metabolites observed at the 80 mg/kg dose level was similar to that observed previously for the low dose, suggesting that an increase in plasma exposure was effected in dogs receiving FIN at 80 mg/kg in toxicity studies. Most of the administered radioactivity was recovered in feces after all doses. Little of the intravenous and low oral doses, but > 50% of the 80 mg/kg oral dose, was excreted as intact FIN, suggesting that metabolism might have been saturated at the high dose.

Magnetic resonance imaging of the efficacy of specific inhibition of 5 alpha-reductase in canine spontaneous benign prostatic hyperplasia.

A leading role for prostatic levels of dihydrotestosterone (DHT) in the pathogenesis of benign prostatic hyperplasia is well established, if incompletely understood. The present study provides initial confirmation that 5 alpha-reductase inhibition alone is sufficient to prevent prostatic accumulation of DHT and to produce epithelial regression in the canine prostate. In dogs treated with the specific 5 alpha-reductase inhibitor finasteride, prostatic volume decreased to one-third of the baseline volume, while the prostatic concentration of DHT fell fivefold: both were constant in placebo control dogs. Demonstration that MR imaging can serve as accurate modality to assess prostatic volume was provided by serial measurements of the canine prostate and by correlation of the last imaging measurement with the weight of the excised prostate. Significant intensity changes were observed in T2-weighted images measured post-treatment; these changes correlated with the histopathology of the prostate. These results suggest that beyond quantifying regression, multiecho T2 measurements can be useful in probing accompanying changes occurring on the cellular level.

Orally bioavailable, indole-based nonpeptide GnRH receptor antagonists with high potency and functional activity.

Stereospecific introduction of a methyl group to the indole-3-side chain enhanced activity in our tryptamine-derived series of GnRH receptor antagonists. Further improvements were achieved by variation of the bicyclic amino moiety of the tertiary amide and by adjustment of the tether length to a pyridine or pyridone terminus. These modifications culminated in analogue 24, which had oral activity in a rat model and acceptable oral bioavailability and half-life in dogs and monkeys.