The Pharmacokinetics, Metabolism, and Clearance Mechanisms of Ritlecitinib, a Janus Kinase 3 and Tyrosine-Protein Kinase Family Inhibitor, in Humans.

Ritlecitinib is an oral once-daily irreversible inhibitor of Janus kinase 3 and tyrosine-protein kinase family being developed for the treatment of moderate-to-severe alopecia areata. This study examined the disposition of ritlecitinib in male participants following oral and intravenous administration using accelerator mass spectroscopy methodology to estimate pharmacokinetic parameters and characterize metabolite profiles. The results indicated ritlecitinib had a systemic clearance of 43.7 L/h, a steady state volume of distribution of 73.8 L, extent of absorption of 89%, time to maximum plasma concentration of ~0.5 hour, and absolute oral bioavailability of 64%. An observed long terminal half-life of total radioactivity was primarily attributed to ritlecitinib binding to plasma albumin. Ritlecitinib was the main circulating drug species in plasma (~30%) with one major pharmacologically inactive cysteine conjugated metabolite (M2) at >10%. Oxidative metabolism (fractional clearance 0.47) and glutathione related conjugation (fractional clearance 0.24) were the primary routes of elimination for ritlecitinib with the greatest disposition of radioactivity shown in the urine (~71%). In vitro phenotyping indicated ritlecitinib cytochrome P450 fraction of metabolism assignments of 0.29 for CYP3A, 0.09 for CYP2C8, 0.07 for CYP1A2, and 0.02 for CYP2C9. In vitro phenotyping in recombinant human glutathione S-transferases indicated ritlecitinib was turned over by a number of cytosolic and microsomal enzyme isoforms. Significance Statement This study provides a detailed understanding of the disposition and metabolism of ritlecitinib, a JAK3 and TEC family kinase inhibitor for alopecia areata, in humans, as well as characterization of clearance pathways and PK of ritlecitinib and its metabolites. As an AMS-based ADME study design, we have expanded on reporting the standard ADME endpoints, providing key pharmacokinetic parameters like clearance, volume of distribution and bioavailability allowing for a more comprehensive understanding of drug disposition.

Integrating Clinical Variability into PBPK Models for Virtual Bioequivalence of Single and Multiple Doses of Tofacitinib Modified-Release Dosage Form.

Tofacitinib is a potent, selective inhibitor of the Janus kinase (JAK) family of kinases with a high degree of selectivity within the human genome's set of protein kinases. Currently approved formulations for tofacitinib citrate are immediate-release (IR) tablets, modified-release (MR) tablets, and IR solution. A once daily MR microsphere formulation was developed for use in pediatric patients. Demonstration of bioequivalence (BE) between the 10 mg once daily (q.d.) MR microsphere formulation and 5 mg twice daily (b.i.d.) IR solution is needed to enable the exposure-response analyses-based bridging to support regulatory approval. To assess BE between MR microsphere and IR solution, an innovative approach was utilized with physiologically-based pharmacokinetic (PBPK) virtual BE trials (VBE) in lieu of a clinical BE trial. A PBPK model was developed to characterize the absorption of different formulations of tofacitinib using Simcyp ADAM module. VBE trials were conducted by simulating PK profiles using the verified PBPK model and integrating the clinically observed intrasubject coefficient of variation (ICV) where BE was assessed with a predetermined sample size and prespecified criteria. The VBE trials demonstrated BE between IR solution 5 mg b.i.d. and MR microsphere 10 mg q.d. after a single dose on day 1 and after multiple doses on day 5. This research presents an innovative approach that incorporates clinically observed ICV in PBPK model-based VBE trials, which could reduce unnecessary drug exposure to healthy volunteers and streamline new formulation development strategies.

The Metabolism and Disposition of Brepocitinib in Humans and Characterization of the Formation Mechanism of an Aminopyridine Metabolite.

Brepocitinib is an oral once-daily Janus kinase 1 and Tyrosine kinase 2 selective inhibitor currently in development for the treatment of several autoimmune disorders. Mass balance and metabolic profiles were determined using accelerator mass spectrometry in six healthy male participants following a single oral 60 mg dose of 14C-brepocitinib (∼300 nCi). The average mass balance recovery was 96.7% ± 6.3%, with the majority of dose (88.0% ± 8.0%) recovered in urine and 8.7% ± 2.1% of the dose recovered in feces. Absorption of brepocitinib was rapid, with maximal plasma concentrations of total radioactivity and brepocitinib achieved within 0.5 hours after dosing. Circulating radioactivity consisted primarily of brepocitinib (47.8%) and metabolite M1 (37.1%) derived from hydroxylation at the C5' position of the pyrazole ring. Fractional contributions to metabolism via cytochrome P450 enzymes were determined to be 0.77 for CYP3A4/5 and 0.14 for CYP1A2 based on phenotyping studies in human liver microsomes. However, additional clinical studies are required to understand the potential contribution of CYP1A1. Approximately 83% of the dose was eliminated as N-methylpyrazolyl oxidative metabolites, with 52.1% of the dose excreted as M1 alone. Notably, M1 was not observed as a circulating metabolite in earlier metabolic profiling of human plasma from a multiple ascending dose study with unlabeled brepocitinib. Mechanistic studies revealed that M1 was highly unstable in human plasma and phosphate buffer, undergoing chemical oxidation leading to loss of the 5-hydroxy-1-methylpyrazole moiety and formation of aminopyrimidine cleavage product M2. Time-dependent inhibition and trapping studies with M1 yielded insights into the mechanism of this unusual and unexpected instability. SIGNIFICANCE STATEMENT: This study provides a detailed understanding of the disposition and metabolism of brepocitinib, a JAK1/TYK2 inhibitor for atopic dermatitis, in humans as well as characterization of clearance pathways and pharmacokinetics of brepocitinib and its metabolites.

Assessment of the Effects of Abrocitinib on the Pharmacokinetics of Probe Substrates of Cytochrome P450 1A2, 2B6 and 2C19 Enzymes and Hormonal Oral Contraceptives in Healthy Individuals.

BACKGROUND AND OBJECTIVE: Abrocitinib is an oral small-molecule Janus kinase (JAK)-1 inhibitor approved for the treatment of moderate-to-severe atopic dermatitis. In vitro studies indicated that abrocitinib is a weak time-dependent inhibitor of cytochrome P450 (CYP) 2C19/3A and a weak inducer of CYP1A2/2B6/2C19/3A. To assess the potential effect of abrocitinib on concomitant medications, drug-drug interaction (DDI) studies were conducted for abrocitinib with sensitive probe substrates of these CYP enzymes. The impact of abrocitinib on hormonal oral contraceptives (ethinyl estradiol and levonorgestrel), as substrates of CYP3A and important concomitant medications for female patients, was also evaluated. METHODS: Three Phase 1 DDI studies were performed to assess the impact of abrocitinib 200 mg once daily (QD) on the probe substrates of: (1) 1A2 (caffeine), 2B6 (efavirenz) and 2C19 (omeprazole) in a cocktail study; (2) 3A (midazolam); and (3) 3A (oral contraceptives). RESULTS: After multiple doses of abrocitinib 200 mg QD, there is a lack of effect on the pharmacokinetics of midazolam, efavirenz and contraceptives. Abrocitinib increased the area under the concentration time curve from 0 to infinity (AUCinf) and the maximum concentration (Cmax) of omeprazole by approximately 189 and 134%, respectively. Abrocitinib increased the AUCinf of caffeine by 40% with lack of effect on Cmax. CONCLUSIONS: Based on the study results, abrocitinib is a moderate inhibitor of CYP2C19. Caution should be exercised when using abrocitinib concomitantly with narrow therapeutic index medicines that are primarily metabolized by CYP2C19 enzyme. Abrocitinib is a mild inhibitor of CYP1A2; however, the impact is not clinically relevant, and no general dose adjustment is recommended for CYP1A2 substrates. Abrocitinib does not inhibit CYP3A or induce CYP1A2/2B6/2C19/3A and does not affect the pharmacokinetics of contraceptives. CLINICAL TRIALS REGISTRATION: ClinicalTrials.gov registration IDs: NCT03647670, NCT05067439, NCT03662516.

Virtual Bioequivalence Assessment of Ritlecitinib Capsules with Incorporation of Observed Clinical Variability Using a Physiologically Based Pharmacokinetic Model.

Ritlecitinib, an orally available Janus kinase 3 and tyrosine kinase inhibitor being developed for the treatment of alopecia areata (AA), is highly soluble across the physiological pH range at the therapeutic dose. As such, it is expected to dissolve rapidly in any in vitro dissolution conditions. However, in vitro dissolution data showed slower dissolution for 100-mg capsules, used for the clinical bioequivalence (BE) study, compared with proposed commercial 50-mg capsules. Hence, a biowaiver for the lower 50-mg strength using comparable multimedia dissolution based on the f2 similarity factor was not possible. The in vivo relevance of this observed in vitro dissolution profile was evaluated with a physiologically based pharmacokinetic (PBPK) model. This report describes the development, verification, and application of the ritlecitinib PBPK model to translate observed in vitro dissolution data to an in vivo PK profile for ritlecitinib capsule formulations. Virtual BE (VBE) trials were conducted using the Simcyp VBE module, including the model-predicted within-subject variability or intra-subject coefficient of variation (ICV). The results showed the predicted ICV was predicted to be smaller than observed clinical ICV, resulting in a more optimistic BE risk assessment. Additional VBE assessment was conducted by incorporating clinically observed ICV. The VBE trial results including clinically observed ICV demonstrated that proposed commercial 50-mg capsules vs clinical 100-mg capsules were bioequivalent, with > 90% probability of success. This study demonstrates a PBPK model-based biowaiver for a clinical BE study while introducing a novel method to integrate clinically observed ICV into VBE trials with PBPK models. Trial registration: NCT02309827, NCT02684760, NCT04004663, NCT04390776, NCT05040295, NCT05128058.