Evaluating the Role of Janus Kinase Pathways in Platelet Homeostasis Using a Systems Modeling Approach

Janus kinase inhibitors modify the fatty acid profile of extracellular vesicles and modulate the immune response

Background

Janus kinase inhibitors (jakinibs) are immunomodulators used for treating malignancies, autoimmune diseases, and immunodeficiencies. However, they induce adverse effects such as thrombosis, lymphocytosis, and neutropenia that could be mediated by extracellular vesicles (EVs). These particles are cell membrane-derived structures that transport cellular and environmental molecules and participate in intercellular communication. Jakinibs can modify the content of EVs and enable them to modulate the activity of different components of the immune response.

Objective

to evaluate the interactions between immune system components of healthy individuals and EVs derived from monocytic and lymphoid lineage cells generated in the presence of baricitinib (BARI) and itacitinib (ITA) and their possible effects.

Methods

EVs were isolated from monocytes (M) and lymphocytes (L) of healthy individuals, as well as from U937 (U) and Jurkat (J) cells exposed to non-cytotoxic concentrations of BARI, ITA, and dimethyl sulfoxide (DMSO; vehicle control). The binding to and engulfment of EVs by peripheral blood leukocytes of healthy individuals were analyzed by flow cytometry using CFSE-stained EVs and anti-CD45-PeCy7 mAb-labeled whole blood. The effect of EVs on respiratory burst, T-cell activation and proliferation, cytokine synthesis, and platelet aggregation was evaluated. Respiratory burst was assessed in PMA-stimulated neutrophils by the dihydrorhodamine (DHR) test and flow cytometry. T-cell activation and proliferation and cytokine production were assessed in CFSE-stained PBMC cultures stimulated with PHA; expression of the T-cell activation markers CD25 and CD69 and T-cell proliferation were analyzed by flow cytometry, and the cytokine levels were quantified in culture supernatants by Luminex assays. Platelet aggregation was analyzed in platelet-rich plasma (PRP) samples by light transmission aggregometry. The EVs' fatty acid (FA) profile was analyzed using methyl ester derivatization followed by gas chromatography.

Results

ITA exposure during the generation of EVs modified the size of the EVs released; however, treatment with DMSO and BARI did not alter the size of EVs generated from U937 and Jurkat cells. Circulating neutrophils, lymphocytes, and monocytes showed a 2-fold greater tendency to internalize ITA-U-EVs than their respective DMSO control. The neutrophil respiratory burst was attenuated in greater extent by M-EVs than by L-EVs. Autologous ITA-M-EVs reduced T-cell proliferation by decreasing IL-2 levels and CD25 expression independently of CD69. A higher accumulation of pro-inflammatory cytokines was observed in PHA-stimulated PBMC cultures exposed to M-EVs than to L-EVs; this difference may be related to the higher myristate content of M-EVs. Platelet aggregation increased in the presence of ITA-L/M-EVs by a mechanism presumably dependent on the high arachidonic acid content of the vesicles.

Conclusions

Cellular origin and jakinib exposure modify the FA profile of EVs, enabling them, in turn, to modulate neutrophil respiratory burst, T-cell proliferation, and platelet aggregation. The increased T-cell proliferation induced by BARI-L/M-EVs could explain the lymphocytosis observed in patients treated with BARI. The higher proportion of arachidonic acid in the FA content of ITA-L/M-EVs could be related to the thrombosis described in patients treated with ITA. EVs also induced a decrease in the respiratory burst of neutrophils.

Momelotinib in Myelofibrosis Patients With Thrombocytopenia: Post Hoc Analysis From Three Randomized Phase 3 Trials

The oral activin A receptor type I, Janus kinase 1 (JAK1), and JAK2 inhibitor momelotinib demonstrated symptom, spleen, and anemia benefits in intermediate- and high-risk myelofibrosis (MF). Post hoc analyses herein evaluated the efficacy and safety of momelotinib in patients with MF and thrombocytopenia (platelet counts <100 × 109/L) from randomized phase 3 studies: MOMENTUM (momelotinib versus danazol; JAK inhibitor experienced); SIMPLIFY-1 (momelotinib versus ruxolitinib; JAK inhibitor naïve); and SIMPLIFY-2 (momelotinib versus best available therapy; JAK inhibitor experienced); these studies were not statistically powered to assess differences in thrombocytopenic subgroups, and these analyses are descriptive. The treatment effect of momelotinib versus ruxolitinib on week 24 response rates (spleen volume reduction ≥35%/Total Symptom Score reduction ≥50%/transfusion independence) was numerically comparable or better in thrombocytopenic patients versus the overall JAK inhibitor naive population; rates were preserved with momelotinib in thrombocytopenic patients but attenuated with ruxolitinib (momelotinib: 27%/28%/67% overall versus 39%/35%/61% in thrombocytopenic group; ruxolitinib: 29%/42%/49% overall versus 0%/22%/39% in thrombocytopenic group, respectively). In contrast to ruxolitinib, momelotinib maintained high dose intensity throughout the treatment. In the JAK inhibitor experienced population, thrombocytopenic patients had the following: (1) numerically higher symptom and transfusion independence response rates with momelotinib than in control arms; and (2) preserved spleen, symptom, and transfusion independence response rates with momelotinib relative to the overall study populations. The safety profile of momelotinib in thrombocytopenic patients was also consistent with the overall study population. In summary, momelotinib represents a safe and effective treatment option for patients with MF and moderate-to-severe thrombocytopenia.

Pharmacodynamics of Janus kinase inhibitors for the treatment of atopic dermatitis

INTRODUCTION

Atopic dermatitis (AD) is the most common inflammatory skin disorder. Despite the high disease burden, the therapeutic options are limited and their efficacy in controlling AD might be partially satisfactory.

AREAS COVERED

Most of the key mediators in AD pathogenesis act through the JAK/STAT signaling pathway, which represents a valid therapeutic target. The first generation of JAK inhibitors, namely tofacitinib and ruxolitinib, inhibit multiple JAKs, whereas newer JAK inhibitors show more selective inhibitory effects for specific JAKs. The aim of this review was to discuss the role of the JAK/STAT pathway in AD and its inhibition, with a special focus on pharmacodynamic properties. We checked the English-language literature, published in the last 15 years using PubMed, Google Scholar, and Scopus.

EXPERT OPINION

JAK inhibitors have different selectivity for various JAK molecules, which influences their pharmacodynamics, efficacy and safety profile. Since many key cytokines in AD signal through JAK1, and as the selective JAK1 inhibition may be effective, avoiding the concomitant inhibition of JAK2- and JAK3-dependent pathways could be associated with additional safety issues. Therefore, selective JAK1 inhibitors may represent promising therapeutic agents for AD, as they might prevent off-target effects of JAK inhibitors, especially related to the hematologic profile.

Population Pharmacokinetic-Pharmacodynamic Modeling of Platelet Time-Courses Following Administration of Abrocitinib

Aims

Abrocitinib is a selective Janus kinase 1 inhibitor for the treatment of moderate‐to‐severe atopic dermatitis. Herein we describe the time‐course of drug‐induced platelet reduction following abrocitinib administration, identify covariates affecting platelet counts, and determine the probability of patients experiencing thrombocytopaenia while receiving abrocitinib.

Methods

This analysis included data from two Phase 2 and three Phase 3 studies in psoriasis and atopic dermatitis patient populations administered abrocitinib 10–400 mg QD orally for up to 12 weeks, with platelet counts determined up to week 16. A semi‐mechanistic model was developed to assess the impact of baseline platelet counts (170, 220 and 270 × 1000/μL), age and race on the platelet nadir and week 12 counts with once‐daily abrocitinib 200 mg or 100 mg.

Results

Decreases in platelet counts were transient with the nadir occurring on average 24 days (95% prediction interval, 23–24) after continuous administration of abrocitinib 200 mg QD. Following administration of once‐daily abrocitinib 200 mg, the probabilities of thrombocytopaenia (<150 × 1000/μL) at the nadir were 8.6% and 95.5% for the typical patient with baseline platelet count of 270 × 1000/μL or 170 × 1000/μL, respectively. Adolescents had a lower probability of thrombocytopaenia compared with adults; platelet count distribution was similar in Asian and Western patients at the nadir and at week 12.

Conclusion

This analysis supports the safety of once‐daily abrocitinib 200 mg and 100 mg dosing regimens, with low probability of thrombocytopaenia during treatment, except for higher risk of low‐grade thrombocytopaenia that diminished after 4 weeks in patients with low baseline platelet counts.

Janus kinase inhibitors for the therapy of atopic dermatitis

The JAK-STAT pathway is involved in the signaling of multiple cytokines driving cutaneous inflammation in atopic dermatitis (AD). Janus kinase (JAK) inhibitors target individual receptor-associated kinases, thereby preventing the mediation of inflammatory signals. Several JAK inhibitors with varying mechanism of action, potency, and safety represent potential therapeutic options for AD in both topical and systemic application. The JAK1/2 selective JAK inhibitor baricitinib was the first substance from this class of drugs approved by the EMA for the systemic oral treatment of AD. The clinical development program of the JAK1 selective inhibitors upadacitinib and abrocitinib is finalized with positive results for AD. The PAN-JAK inhibitor delgocitinib was the first substance being approved for the treatment of AD (in Japan). This review article covers the rising data on investigational and approved JAK inhibitors in the context of the treatment of AD.

Integrated Safety Analysis of Abrocitinib for the Treatment of Moderate-to-Severe Atopic Dermatitis From the Phase II and Phase III Clinical Trial Program

Background

Pivotal phase III studies demonstrated that abrocitinib, an oral, once-daily, JAK1-selective inhibitor, is effective treatment for moderate-to-severe atopic dermatitis (AD) as monotherapy and in combination with topical therapy.

Objective

The aim of this study was to evaluate the long-term safety of abrocitinib 200 mg and 100 mg in an integrated analysis of a phase IIb study, four phase III studies, and one long-term extension study.

Methods

Two cohorts were analyzed: a placebo-controlled cohort from 12- to 16-week studies and an all-abrocitinib cohort including patients who received one or more abrocitinib doses. Adverse events (AEs) of interest and laboratory data are reported.

Results

Total exposure in the all-abrocitinib cohort (n = 2856) was 1614 patient-years (PY); exposure was ≥ 24 weeks in 1248 patients and ≥ 48 weeks in 606 (maximum 108 weeks). In the placebo-controlled cohort (n = 1540), dose-related AEs (200 mg, 100 mg, placebo) were nausea (14.6%, 6.1%, 2.0%), headache (7.8%, 5.9%, 3.5%), and acne (4.7%, 1.6%, 0%). Platelet count was reduced transiently in a dose-dependent manner; 2/2718 patients (200-mg group) had confirmed platelet counts of < 50 × 10³/mm³ at week 4. Incidence rates (IRs) were 2.33/100PY and 2.65/100 PY for serious infection, 4.34/100PY and 2.04/100PY for herpes zoster, and 11.83/100PY and 8.73/100PY for herpes simplex in the 200-mg and 100-mg groups, respectively. IRs for nonmelanoma skin cancer, other malignancies, and major adverse cardiovascular events were < 0.5/100PY for both doses. Five venous thromboembolism events occurred (IR 0.30/100PY), all in the 200-mg group. There were three deaths due to gastric carcinoma (diagnosed at day 43), sudden death, and COVID-19.

Conclusion

Abrocitinib, with proper patient and dose selection, has a manageable tolerability and longer-term safety profile appropriate for long-term use in patients with moderate-to-severe AD.

Trial Registries

ClinicalTrials.gov: NCT02780167, NCT03349060, NCT03575871, NCT03720470, NCT03627767, NCT03422822.

Video abstract

Quantitative systems pharmacology model of thrombopoiesis and platelet life-cycle, and its application to thrombocytopenia based on chronic liver disease

Platelets are produced by hematopoietic stem cells via megakaryocytes in the bone marrow and play a critical role in hemostasis. The aim of this study was to develop a new platelet model based on the thrombopoiesis and platelet life-cycle by a quantitative systems pharmacology modeling approach, which could describe changes in platelet count profiles in platelet-related diseases and drug intervention. The proposed platelet model consists of 44 components. The model was applied to thrombopoiesis of a thrombopoietin receptor agonist, lusutrombopag. It could well describe the observed platelet count profiles after administration of lusutrombopag for both healthy subjects and patients with chronic liver disease and thrombocytopenia. This model should be useful for understanding the disease progression of platelet-related conditions, such as thrombocytopenia and for predicting platelet count profiles in various disease situations related to platelets and drug administration in drug development.

JAK Inhibitors in Rheumatoid Arthritis: An Evidence-Based Review on the Emerging Clinical Data

Janus kinase (JAK) Inhibitors are the latest drug class of disease-modifying medication to emerge for the treatment of rheumatoid arthritis (RA). They are a small molecule-targeted treatment and are the first oral option to compare favourably to existing biologic disease-modifying anti-rheumatic drugs (DMARDs). Tofacitinib, baricitinib and upadacitinib are the first 3 JAK inhibitors to become commercially available in the field and are the core focus of this review. To date, they have demonstrated comparable efficacy to tumour necrosis factor (TNF) inhibitors in terms of American College of Rheumatology (ACR) response rates and disease activity (DAS28) scores with similar cost to the benchmark adalimumab. This narrative review article aims to synthesise and distil the key available trial data on JAK inhibitor efficacy and safety, along with their place in the ACR and European League Against Rheumatism (EULAR) guidelines for RA. The novel mechanism of action of the JAK/STAT pathway is highlighted along with the potential effects of modulating each pathway. The rapid onset of action, role in attenuation of central pain processing and effect on structural damage and radiographic progression are also all examined in detail. We also explore the latest meta-analyses and comparative performance of each of the 3 available JAKs in an effort to determine which is most efficacious and which has the most favourable safety profile. Post marketing concerns regarding thromboembolism risk and herpes zoster infection are also discussed. Additionally, we review the cost-benefit analyses of the available JAK inhibitors and address some of the pharmacoeconomic considerations for real-world practice in the UK and US by detailing the raw acquisition cost and the value they provide in comparison to the benchmark biologic adalimumab and the anchor DMARD methotrexate.

Kinetic-Pharmacodynamic Model of Platelet Time Course in Patients With Moderate-to-Severe Atopic Dermatitis Treated With Oral Janus Kinase 1 Inhibitor Abrocitinib

The oral Janus kinase 1 (JAK1) inhibitor abrocitinib reduced signs and symptoms of atopic dermatitis (AD) in a placebo‐controlled, randomized, double‐blind, phase IIb trial (dose range 10–200 mg). A kinetic‐pharmacodynamic (K‐PD) model consisting of proliferation, maturation, and blood circulation compartments was developed to characterize platelet count changes during the study. The K‐PD model consisted of a drug elimination constant, four system parameters describing platelet dynamics, variance terms, correlation, and residual errors. Overall, these patients exhibited mean transit time from progenitor cells to platelets of 8.2 days (longer than the reported megakaryocyte life span), likely arising from JAK1‐induced perturbations of platelet progenitor homeostasis. The final model described dose‐related platelet count declines until nadir at treatment week 4 and return to baseline levels thereafter. The model was deemed suitable to support the design of subsequent abrocitinib AD trials and indicated limited clinically relevant platelet reductions in the range of doses studied.