ORALLY ACTIVE INHIBITORS OF HUMAN LEUKOCYTE ELASTASE. II. DISPOSITION OF L-694,458 IN RATS AND RHESUS MONKEYS

ABSTRACT: The disposition of L-694,458, a potent monocyclic ␤-lactam inhibitor of human leukocyte elastase, was studied in male SpragueDawley rats and rhesus monkeys. After iv dosing, L-694,458 exhibited similar pharmacokinetic parameters in rats and rhesus monkeys. The mean values for its plasma clearance, terminal halflife, and volume of distribution at steady state were 27 ml/min/kg, 1.8 hr, and 4.0 liters/kg in rats and 34 ml/min/kg, 2.3 hr, and 5 liters/kg in rhesus monkeys. The bioavailability of a 10 mg/kg oral dose was higher in rats (65%) than in rhesus monkeys (39%). In both species, concentrations of L-694,458 in plasma increased more than proportionally when the oral dose was increased from 10 mg/kg to 40 mg/kg. In monkeys a protracted plasma concentration-time profile was observed at 40 mg/kg, characterized by a delayed T max (8-24 hr) and a long terminal half-life (6 hr). [ 3 H]L-694,458 was well absorbed after oral dosing to rats at 10 mg/kg, as indicated by the high recovery of radioactivity in bile (83%) and urine (6%) of bile duct-cannulated rats. Only ϳ5% or less of the radioactivity in bile, urine, and feces was a result of intact L-694,458, indicating that the compound was being eliminated by metabolism, followed by excretion of the metabolites in feces, via bile. Demethylenation of the methylenedioxyphenyl group resulting in the catechol was the primary metabolic pathway in human and rhesus monkey liver microsomes. In rat liver microsomes, the major metabolite was the N-oxide of the methyl-substituted piperazine nitrogen. In rats dosed iv and orally with [ 3 H]L-694,458, concentrations of radioactivity were highest in the lung (the primary target tissue), adrenals, and liver. L-694,458 was unstable in rat blood and plasma, degrading via a pathway believed to be catalyzed by B-esterases and to involve cleavage of the ␤-lactam ring and loss of the methylpiperazine phenoxy group. In vitro studies indicated that in human liver, L-694,458 was metabolized by CYP3A and 2C isozymes, and in both monkey and human liver microsomes the compound acted as an inhibitor of testosterone 6␤-hydroxylation. Leukocyte elastase is a serine protease capable of proteolytic degradation of a variety of substrates, including elastin and collagen, which are components of connective tissue. Specific inhibitors of leukocyte elastase are being explored as potential therapeutic agents for the treatment of inflammatory diseases, such as cystic fibrosis and rheumatoid arthritis where high amounts of extracellular elastase, either free or bound to its natural inhibitors, ␣ 1 -proteinase inhibitor and secretory leukocyte proteinase inhibitor, have been detected extracellularly (1-3). Several classes of inhibitors of elastase have been synthesized and evaluated to date (4 -19). L-694,458 Materials and Methods Chemicals. L-694,458 ( Microsomes. Fresh rat liver and frozen human and rhesus monkey liver tissue were used for the preparation of microsomes. Microsomes containing 1 Abbreviations used are: L-694,458, N-[1(R)-(1,3-benzodioxol-5-yl

Identification and Mitigation of Reactive Metabolites of 2‑Aminoimidazole-Containing Microsomal Prostaglandin E Synthase‑1 Inhibitors Terminated Due to Clinical Drug-Induced Liver Injury

Two 2-aminoimidazole-based inhibitors, LY3031207 (<b>1</b>) and LY3023703 (<b>2</b>), of the microsomal prostaglandin E synthase-1 (mPGES-1) enzyme were found to cause drug-induced liver injury (DILI) in humans. We studied imidazole ring substitutions to successfully mitigate reactive metabolite (RM) formation. These studies support the conclusion that RM formation may play a role in the observations of DILI and the consideration of 2-aminoimidazoles as structure alerts, due to the high likelihood of bioactivation to generate RMs

Identification and Mitigation of Reactive Metabolites of 2‑Aminoimidazole-Containing Microsomal Prostaglandin E Synthase‑1 Inhibitors Terminated Due to Clinical Drug-Induced Liver Injury

Two 2-aminoimidazole-based inhibitors, LY3031207 (<b>1</b>) and LY3023703 (<b>2</b>), of the microsomal prostaglandin E synthase-1 (mPGES-1) enzyme were found to cause drug-induced liver injury (DILI) in humans. We studied imidazole ring substitutions to successfully mitigate reactive metabolite (RM) formation. These studies support the conclusion that RM formation may play a role in the observations of DILI and the consideration of 2-aminoimidazoles as structure alerts, due to the high likelihood of bioactivation to generate RMs

Discovery of the First α‑Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptor Antagonist Dependent upon Transmembrane AMPA Receptor Regulatory Protein (TARP) γ‑8

Transmembrane AMPA receptor regulatory proteins (TARPs) are a family of scaffolding proteins that regulate AMPA receptor trafficking and function. TARP γ-8 is one member of this family and is highly expressed within the hippocampus relative to the cerebellum. A selective TARP γ-8-dependent AMPA receptor antagonist (TDAA) is an innovative approach to modulate AMPA receptors in specific brain regions to potentially increase the therapeutic index relative to known non-TARP-dependent AMPA antagonists. We describe here, for the first time, the discovery of a noncompetitive AMPA receptor antagonist that is dependent on the presence of TARP γ-8. Three major iteration cycles were employed to improve upon potency, CYP1A2-dependent challenges, and in vivo clearance. An optimized molecule, compound (−)-<b>25</b> (LY3130481), was fully protective against pentylenetetrazole-induced convulsions in rats without the motor impairment associated with non-TARP-dependent AMPA receptor antagonists. Compound (−)-<b>25</b> could be utilized to provide proof of concept for antiepileptic efficacy with reduced motor side effects in patients