Microsomal metabolism of delavirdine: evidence for mechanism-based inactivation of human cytochrome P450 3A

ABSTRACT Administration of delavirdine, an HIV-1 reverse transcriptase inhibitor, to rats or monkeys resulted in apparent loss of hepatic microsomal CYP3A and delavirdine desalkylation activity. Human CYP3A catalyzes the formation of desalkyl delavirdine and 6Ј-hydroxy delavirdine, an unstable metabolite, while CYP2D6 catalyzes only desalkyl delavirdine. CYP2D6 catalyzed desalkyl delavirdine formation was linear with time (up to 30 min) but when catalyzed by cDNA expressed CYP3A4 or human liver microsomes the reaction rate declined progressively with time. Coincubation with triazolam showed that delavirdine caused a time-and NADPH-dependent loss of CYP3A4 activity in human liver microsomes as measured by triazolam 1Ј-hydroxylation. The catalytic activity loss was saturable and was characterized by a K i of 21.6 Ϯ 8.9 M and a k inact of 0.59 Ϯ 0.08 min Ϫ1 . An apparent partition ratio of 41 was determined with cDNA expressed CYP3A4, based on the substrate depletion method. Incubation of [ 14 C]delavirdine with microsomes from several species resulted in irreversible association with an approximately 50 kDa protein, as demonstrated by SDS-PAGE/autoradiography. Binding to the protein was NADPH dependent, glutathione insensitive, proportional to the level of CYP3A expression and was inhibited by ketoconazole, a specific CYP3A inhibitor. NADPH-dependent irreversible binding to human and rat total microsomal protein was demonstrated following exhaustive extraction of microsomal protein. Binding was decreased in the presence of glutathione and appeared to be related to expression level of CYP3A. These results suggest that delavirdine can inactivate CYP3A and has the potential to slow the metabolism of coadministered CYP3A substrates. The reverse transcriptase of HIV-1 catalyzes the transcription of viral RNA to proviral DNA, an essential step in the life cycle of HIV-1 and the progression to AIDS in humans is a potent, specific non-nucleoside inhibitor of HIV-1 reverse transcriptase Analysis of plasma drug levels in male rats treated orally or intravenously with single doses of delavirdine showed that the drug was well absorbed; however, clearance of delavirdine was diminished and half-life was increased in rats treated with increasing doses of delavirdine The in vitro metabolism of delavirdine was examined using liver microsomes from several specie

Pharmacokinetics and Metabolism in Rats, Dogs, and Monkeys of the Cathepsin K Inhibitor Odanacatib: Demethylation of a Methylsulfonyl Moiety as a Major Metabolic Pathway □ S

ABSTRACT: Odanacatib is a potent cathespin K inhibitor that is being developed as a novel therapy for osteoporosis. The disposition and metabolism of odanacatib were evaluated in rats, dogs, and rhesus monkeys after intravenous and oral administration of [ 14 C]odanacatib. Odanacatib was characterized by low systemic clearance in all species and by a long plasma half-life in monkeys (18 h) and dogs (64 h). The oral bioavailability was dependent on the vehicle used and ranged from 18% (monkey) to ϳ100% (dog) at doses of 1 to 5 mg/kg, using nonaqueous vehicles. After intravenous and oral administration to intact rats and monkeys >90% of the dose was recovered, mainly in the feces. Studies in bile duct-cannulated animals indicated that biliary secretion was the major mode of elimination of radioactivity; odanacatib also underwent some intestinal secretion. In monkeys, odanacatib was almost completely eliminated by metabolism; metabolism also played a major role in the clearance of odanacatib in rats and dogs. The major metabolic pathways were methyl hydroxylation (formation of M8 and its derivatives), methyl sulfone demethylation (formation of M4 and its derivative M5), and glutathione conjugation (formation of the cyclized cysteinylglycine adduct M6 after addition of glutathione to the nitrile group of odanacatib). The major metabolites in rats [M4 (parent-14 Da) and M5 (oxygenated derivative of M4)] were determined to arise from a novel pathway that involved oxidative demethylation of the methylsulfonyl moiety of odanacatib. Overall, odanacatib displayed species-dependent metabolism, which explains, at least in part, the divergent plasma half-life observed

DMD #37184 1 Pharmacokinetics and Metabolism in Rats, Dogs and Monkeys of the Cathepsin K Inhibitor Odanacatib: Demethylation of a Methylsulfonyl Moiety as a Major Metabolic Pathway DMD #37184 2 Running Title: Pharmacokinetics and Metabolism of Odanacatib

ABSTRACT Odanacatib is a potent cathespin K inhibitor that is being developed as a novel therapy for osteoporosis. The disposition and metabolism of odanacatib were evaluated in rats, dogs and rhesus monkeys after IV and oral administration of [ 14 C]odanacatib. Odanacatib was characterized by low systemic clearance in all species and by long plasma half-life in monkeys (18 hr) and dogs (64 hr). The oral bioavailability was dependent on the vehicle used and ranged from 18% (monkey) to ~100% (dog) at doses of 1-5 mg/kg, using non-aqueous vehicles. After IV and oral administration to intact rats and monkeys >90% of the dose was recovered mainly in the feces. Studies in bile-duct cannulated animals indicated biliary secretion was the major mode of elimination of radioactivity; odanacatib also underwent some intestinal secretion. In monkeys, odanacatib was almost completely eliminated by metabolism; metabolism also played a major role in the clearance of odanacatib in rats and dogs. The major metabolic pathways were: methyl hydroxylation (formation of M8 and its derivatives), methyl sulfone demethylation (formation of M4 and its derivative M5) and glutathione conjugation (formation of the cyclized cysteinylglycine adduct M6 following addition of glutathione to the nitrile group of odanacatib). The major metabolites in rats (M4, parent-14 Da and M5, oxygenated derivative of M4) were determined to arise from a novel pathway that involved oxidative demethylation of the methylsulfonyl moiety of odanacatib. Overall, odanacatib displayed species-dependent metabolism which at least in part explains the divergent plasma half-life observed

SARS-CoV-2 tropism, entry, replication, and propagation: Considerations for drug discovery and development.

Since the initial report of the novel Coronavirus Disease 2019 (COVID-19) emanating from Wuhan, China, Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has spread globally. While the effects of SARS-CoV-2 infection are not completely understood, there appears to be a wide spectrum of disease ranging from mild symptoms to severe respiratory distress, hospitalization, and mortality. There are no Food and Drug Administration (FDA)-approved treatments for COVID-19 aside from remdesivir; early efforts to identify efficacious therapeutics for COVID-19 have mainly focused on drug repurposing screens to identify compounds with antiviral activity against SARS-CoV-2 in cellular infection systems. These screens have yielded intriguing hits, but the use of nonhuman immortalized cell lines derived from non-pulmonary or gastrointestinal origins poses any number of questions in predicting the physiological and pathological relevance of these potential interventions. While our knowledge of this novel virus continues to evolve, our current understanding of the key molecular and cellular interactions involved in SARS-CoV-2 infection is discussed in order to provide a framework for developing the most appropriate in vitro toolbox to support current and future drug discovery efforts

Sustained Viral Response in a Hepatitis C Virus-Infected Chimpanzee via a Combination of Direct-Acting Antiviral Agents ▿

Efforts to develop novel, interferon-sparing therapies for treatment of chronic hepatitis C (HCV) infection are contingent on the ability of combination therapies consisting of direct antiviral inhibitors to achieve a sustained virologic response. This work demonstrates a proof of concept that coadministration of the nucleoside analogue MK-0608 with the protease inhibitor MK-7009, both of which produced robust viral load declines as monotherapy, to an HCV-infected chimpanzee can achieve a cure of infection

Antiviral Efficacy upon Administration of a HepDirect Prodrug of 2′-C-Methylcytidine to Hepatitis C Virus-Infected Chimpanzees▿

Hepatitis C virus (HCV) infects an estimated 170 million individuals worldwide, and the current standard of care, a combination of pegylated interferon alpha and ribavirin, is efficacious in achieving sustained viral response in ∼50% of treated patients. Novel therapies under investigation include the use of nucleoside analog inhibitors of the viral RNA-dependent RNA polymerase. NM283, a 3′-valyl ester prodrug of 2′-C-methylcytidine, has demonstrated antiviral efficacy in HCV-infected patients (N. Afdhal et al., J. Hepatol. 46[Suppl. 1]:S5, 2007; N. Afdhal et al., J. Hepatol. 44[Suppl. 2]:S19, 2006). One approach to increase the antiviral efficacy of 2′-C-methylcytidine is to increase the concentration of the active inhibitory species, the 5′-triphosphate, in infected hepatocytes. HepDirect prodrug technology can increase intracellular concentrations of a nucleoside triphosphate in hepatocytes by introducing the nucleoside monophosphate into the cell, bypassing the initial kinase step that is often rate limiting. Screening for 2′-C-methylcytidine triphosphate levels in rat liver after oral dosing identified 1-[3,5-difluorophenyl]-1,3-propandiol as an efficient prodrug modification. To determine antiviral efficacy in vivo, the prodrug was administered separately via oral and intravenous dosing to two HCV-infected chimpanzees. Circulating viral loads declined by ∼1.4 log10 IU/ml and by >3.6 log10 IU/ml after oral and intravenous dosing, respectively. The viral loads rebounded after the end of dosing to predose levels. The results indicate that a robust antiviral response can be achieved upon administration of the prodrug