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.

Comparative Study of Dermal Pharmacokinetics Between Topical Drugs Using Open Flow Microperfusion in a Pig Model.

PURPOSE: Accurate methods to determine dermal pharmacokinetics are important to increase the rate of clinical success in topical drug development. We investigated in an in vivo pig model whether the unbound drug concentration in the interstitial fluid as determined by dermal open flow microperfusion (dOFM) is a more reliable measure of dermal exposure compared to dermal biopsies for seven prescription or investigational drugs. In addition, we verified standard dOFM measurement using a recirculation approach and compared dosing frequencies (QD versus BID) and dose strengths (high versus low drug concentrations). METHODS: Domestic pigs were topically administered seven different drugs twice daily in two studies. On day 7, drug exposures in the dermis were assessed in two ways: (1) dOFM provided the total and unbound drug concentrations in dermal interstitial fluid, and (2) clean punch biopsies after heat separation provided the total concentrations in the upper and lower dermis. RESULTS: dOFM showed sufficient intra-study precision to distinguish interstitial fluid concentrations between different drugs, dose frequencies and dose strengths, and had good reproducibility between studies. Biopsy concentrations showed much higher and more variable values. Standard dOFM measurements were consistent with values obtained with the recirculation approach. CONCLUSIONS: dOFM pig model is a robust and reproducible method to directly determine topical drug concentration in dermal interstitial fluid. Dermal biopsies were a less reliable measure of dermal exposure due to possible contributions from drug bound to tissue and drug associated with skin appendages.

Employing zero-inflated beta distribution in an exposure-response analysis of TYK2/JAK1 inhibitor brepocitinib in patients with plaque psoriasis.

Brepocitinib is an oral selective dual TYK2/JAK1 inhibitor and based on its cytokine inhibition profile is expected to provide therapeutic benefit in the treatment of plaque psoriasis. Efficacy data from a completed Phase 2a study in patients with moderate-to-severe plaque psoriasis were utilized to develop a population exposure-response model that can be employed to inform dose selection decisions for further clinical development. A modeling approach that employs the zero-inflated beta distribution was used to account for the bounded nature and distributional characteristics of the Psoriasis Area and Severity Index (PASI) score data. The developed exposure-response model provided an adequate description of the observed PASI scores across all the treatment arms tested and across both the induction and maintenance dosing periods of the study. In addition, the developed model exhibited a good predictive capacity with regard to the derived responder metrics (e.g., 75%/90%/100% improvement in PASI score [PASI75/90/100]). Clinical trial simulations indicated that the induction/maintenance dosing paradigm explored in this study does not offer any advantages from an efficacy perspective and that doses of 10, 30, and 60 mg once-daily may be suitable candidates for clinical evaluation in subsequent Phase 2b studies.

Model-Informed Assessment of Probability of Phase 3 Success for Ritlecitinib in Patients with Moderate-to-Severe Ulcerative Colitis.

Ritlecitinib, an oral Janus kinase 3/tyrosine kinase expressed in hepatocellular carcinoma family inhibitor, was evaluated in patients with ulcerative colitis (UC) in a phase 2b trial. Model-informed drug development strategies were applied to bridge observations from phase 2b to predictions for a proposed phase 3 study design to assess the probability of achieving the target efficacy outcome. A longitudinal exposure-response model of the time course of the 4 Mayo subscores (rectal bleeding, stool frequency, physician's global assessment, and endoscopic subscore) in patients with UC receiving placebo or ritlecitinib was developed using population modeling approaches and an item response theory framework. The quantitative relationships between the 4 Mayo subscores accommodated the prediction of composite endpoints such as total Mayo score and partial Mayo score (key endpoints from phase 2b), and modified clinical remission and endoscopic remission (proposed phase 3 endpoints). Clinical trial simulations using the final model assessed the probability of candidate ritlecitinib dosing regimens (including those tested in phase 2b and alternative) and phase 3 study designs for achieving target efficacy outcomes benchmarked against an approved treatment for moderate-to-severe UC. The probabilities of achieving target modified clinical remission and endoscopic improvement outcomes at both weeks 8 and 52 for ritlecitinib 100 mg once daily was 74.8%. Model-based assessment mitigated some of the risk associated with proceeding to pivotal phase 3 trials with dosing regimens of which there was limited clinical experience.

Population pharmacokinetic modeling of oral brepocitinib in healthy volunteers and patients with immuno-inflammatory diseases.

The objective of this population pharmacokinetic (PK) analysis was to characterize the concentration-time profile of brepocitinib plasma concentration after single- and multiple-oral administration in healthy volunteers (HVs) and patients with immuno-inflammatory diseases. Blood samples from phase I HV and phase II clinical studies of patients with alopecia areata, psoriasis, psoriatic arthritis, ulcerative colitis (UC), vitiligo, and hidradenitis suppurativa were analyzed using a nonlinear mixed-effects modeling approach. Effects of patients' characteristics on brepocitinib exposure were investigated. Overall, 8552 brepocitinib plasma concentrations from 775 individuals were included in the analysis. The PKs of brepocitinib were adequately described by a two-compartment model with first-order absorption and a lag time for tablet formulation, dose-dependent bioavailability, and Box-Cox transformed interindividual variabilities on apparent clearance (CL/F) and apparent central volume of distribution (Vc/F). For a typical 70-kg non-Asian female patient with baseline aspartate aminotransferase of 22 unit/liter, CL/F and Vc/F estimates were 17.5 L/h and 88.5 L, respectively. Asians had a higher exposure (independent of body weight), caused by a 10% lower CL/F when compared to other individuals. Independent of baseline body weight, the male population showed 13% higher Vc/F compared to the female population. Patients with UC were predicted to have 46% slower absorption rate compared to other individuals. The PKs of brepocitinib were well-characterized by a two-compartment model with first-order absorption and dose-dependent bioavailability. Several covariates, such as race and sex, were identified to have statistically significant, but not clinically meaningful, effects on the estimated PK parameters.

Master protocols and other innovative trial designs in inflammation and immunology to expedite clinical drug development.

Master protocol designs, such as umbrella and basket studies, allow multiple compounds or multiple target populations to be evaluated simultaneously within a single protocol, and have been widely adopted in oncology clinical trials. These novel designs can also be applied in other therapeutic areas, where they could have several benefits over conducting traditional randomized controlled trials. Here, we detail Pfizer's recent implementations of master protocol designs in inflammation and immunology clinical studies, focusing on the opportunities for cost and resource savings and how these designs can expedite the time required to bring new treatments to patients in need.

Brepocitinib, Zimlovisertib, and Ropsacitinib in Hidradenitis Suppurativa.

BACKGROUND: Hidradenitis suppurativa (HS) is a debilitating, inflammatory skin disease with limited treatment options and partially understood pathophysiology. Using an umbrella trial design, three kinase inhibitor immunomodulators with different mechanisms of action were evaluated. METHODS: This phase 2a, double-blind, parallel-group trial enrolled adults with moderate to severe HS who were then randomly assigned (1:1:1:1) to once-daily brepocitinib 45 mg (a JAK1/TYK2 inhibitor), zimlovisertib 400 mg (an IRAK4 inhibitor), ropsacitinib 400 mg (a TYK2 inhibitor), or matching placebo for 16 weeks. The primary end point was the percentage of participants achieving HS clinical response (HiSCR) at week 16. Safety, including treatment-emergent adverse events (TEAEs), was monitored throughout. RESULTS: Totals of 52, 47, 47, and 48 participants were assigned to brepocitinib, zimlovisertib, ropsacitinib, and placebo, respectively. At week 16, 28% were lost to follow-up and assumed to be nonresponders; HiSCR occurred in 33.3% (16/48) of participants receiving placebo and in 51.9% (27/52), 34.0% (16/47), and 37.0% (17/46) of those receiving brepocitinib, zimlovisertib, and ropsacitinib (difference in percentage points vs. placebo [90% confidence interval], 18.7 [2.7 to 34.6], 0.7 [−15.2 to 16.7], and 3.5 [−12.6 to 19.6]), respectively. TEAEs occurred more frequently with active treatment (brepocitinib, 30 [57.7%]; zimlovisertib, 26 [55.3%]; ropsacitinib, 29 [61.7%]; placebo, 23 [47.9%]). Most TEAEs (infections, skin disorders, and gastrointestinal symptoms) were mild; there were no deaths. CONCLUSIONS: Participants with moderate to severe HS treated with brepocitinib experienced greater clinical response, whereas those on zimlovisertib and ropsacitinib did not, compared with placebo. These results favor the JAK/STAT pathway as an immunologic target in HS and did not confirm a role for selective IRAK4 or TYK2 inhibition. These results should be confirmed in larger studies with longer follow-up. (Funded by Pfizer; ClinicalTrials.gov registration number, NCT04092452.)

Baseline serum and stool microbiome biomarkers predict clinical efficacy and tissue molecular response after ritlecitinib induction therapy in ulcerative colitis.

BACKGROUND AND AIMS: Ritlecitinib, an oral JAK3/TEC family kinase inhibitor, was well- tolerated and efficacious in the phase 2b VIBRATO study in participants with moderate-to-severe ulcerative colitis (UC). The aim of this study was to identify baseline serum and microbiome markers that predict subsequent clinical efficacy and to develop noninvasive serum signatures as potential real-time noninvasive surrogates of clinical efficacy after ritlecitinib. METHODS: Tissue and peripheral blood proteomics, transcriptomics, and fecal metagenomics were performed on samples before and after 8-week oral ritlecitinib induction therapy (20 mg, 70 mg, 200 mg, or placebo once daily, N=39, 41, 33, and 18, respectively). Linear mixed models were used to identify baseline and longitudinal protein markers associated with efficacy. The combined predictivity of these proteins was evaluated using a logistic model with permuted efficacy data. Differential expression of fecal metagenomic was used to differentiate responders and nonresponders. RESULTS: Peripheral blood serum proteomics identified 4 baseline serum markers (LTA, CCL21, HLA-E, MEGF10) predictive of modified clinical remission (MR), endoscopic improvement (EI), histologic remission (HR), and integrative score of tissue molecular improvement. In responders, 37 serum proteins significantly changed at Week 8 compared with baseline (FDR<0.05); of these, changes in 4 (IL4R, TNFRSF4, SPINK4, and LAIR-1) predicted concurrent EI and HR responses. Fecal metagenomics analysis revealed baseline and treatment response signatures that correlated with EI, MR, and tissue molecular improvement. CONCLUSIONS: Blood and microbiome biomarkers stratify endoscopic, histologic, and tissue molecular response to ritlecitinib, which may help guide future precision medicine approaches to UC treatment.