Proof of concept for the clinical effects of oral rilzabrutinib, the first Bruton tyrosine kinase inhibitor for pemphigus vulgaris: the phase II BELIEVE study

Pemphigus relapse: Mechanisms, risk factors, and agents associated with disease recurrence

Pemphigus represents a spectrum of potentially life-threatening autoimmune-mediated skin blistering conditions caused by antibody production against desmoglein 1 and 3 (anti-DSG 1 and 3) in keratinocytes. Greater than 50% of pemphigus patients experience relapse, which complicates long-term medical management, including risks associated with re-treatment and complications such as infection and dehydration. This review aims to elucidate mechanisms, risk factors, and medications associated with pemphigus relapse. Mechanisms of relapse include the persistence of auto-reactive B-cell populations post-treatment and CD20- B-cell populations that reactivate after B-cell depletion therapy. Risk factors for relapse include high body surface area (BSA) of pemphigus involvement, high body mass index, high severity according to the Pemphigus Disease Area Index (PDAI) at onset, treatment delay, and high anti-DSG1 and DSG3 titers post-treatment. Targeted B-cell localization is associated with better clinical outcomes, including less frequent relapses. Rituximab is currently the gold standard of treatment for moderate-severe pemphigus and has relapse rates of 11%-44% in selected studies, with a mean time to relapse of 5.8 months to 36 months following treatment. Relapse rates across lymphoma dosing (375 mg/m2) versus rheumatoid arthritis dosing (1 g dosing weekly) was inconsistent; however, more frequent dosing, earlier treatment, and higher cumulative dosing were associated with lower relapse rates. Alternative agents that have clinical efficacy include corticosteroid monotherapy, mycophenolate mofetil, azathioprine, and intravenous immunoglobulin. Future studies should include head-to-head comparators over long follow-up periods to identify the best treatment agents associated with the least relapse risk.

Disease modification in chronic spontaneous urticaria

Chronic spontaneous urticaria (CSU) is a debilitating, inflammatory skin condition characterized by infiltrating immune cells. Available treatments are limited to improving the signs and symptoms. There is an unmet need to develop therapies that target disease-driving pathways upstream of mast cell activation to inhibit or delay the progression of CSU and associated comorbidities. Here, we aim to define disease modification due to a treatment intervention and criteria that disease-modifying treatments (DMTs) must meet in CSU. We have defined disease modification in CSU as a favorable treatment-induced change in the underlying pathophysiology and, therefore, the disease course, which is clinically beneficial and enduring. A DMT must fulfil the following criteria: (1) prevents or delays the progression of CSU, (2) induces long-term, therapy-free clinical remission, which is the sustained absence of CSU signs and symptoms without the need for treatment, and (3) affects the underlying mechanism of CSU, as demonstrated by an effect on disease-driving signals and/or a biomarker. DMTs in CSU should slow disease progression, achieve long-lasting disease remission, target disease-driving mechanisms, reduce mast cell-activating IgE autoantibodies, target cytokine profile polarization, and normalize the gut microbiome and barrier. Treating CSU at the immune system level could provide valuable alternatives to pharmacotherapy in CSU management. Specific DMTs in CSU are yet to be developed, but some show potential benefits, such as inhibitors of Bruton's Tyrosine Kinase, IL-4 and IL-13. Future therapies could prevent CSU signs and symptoms, achieve long-term clinical benefits after discontinuing treatment, and prevent associated concomitant disorders.

Bruton Tyrosine Kinase Inhibition Decreases Inflammation and Differentially Impacts Phagocytosis and Cellular Metabolism in Mouse- and Human-derived Myeloid Cells

Bruton tyrosine kinase (BTK) is a kinase expressed by various immune cells and is often activated under proinflammatory states. Although the majority of BTK-related research has historically focused on B cells, understanding the role of BTK in non-B cell populations is critical given myeloid cells also express BTK at comparable levels. In this study, we investigated and compared how BTK inhibition in human and murine myeloid cells alters cell phenotype and function. All experiments were performed using two BTK inhibitors (evobrutinib and tolebrutinib) that are currently in late-stage clinical trials for the treatment of multiple sclerosis. Assays were performed to assess the impact of BTK inhibition on cytokine and microRNA expression, phagocytic capacity, and cellular metabolism. In all cells, both evobrutinib and tolebrutinib significantly decreased phosphorylated BTK and LPS-induced cytokine release. BTK inhibition also significantly decreased the oxygen consumption rate and extracellular acidification rate in myeloid cells, and significantly decreased phagocytosis in murine-derived cells, but not human macrophages. To further elucidate the mechanism, we also investigated the expression of microRNAs known to impact the function of myeloid cells. BTK inhibition resulted in an altered microRNA expression profile (i.e., decreased miR-155-5p and increased miR-223-3p), which is consistent with a decreased proinflammatory myeloid cell phenotype. In summary, these results provide further insights into the mechanism of action of BTK inhibitors in the context of immune-related diseases, while also highlighting important species-specific and cell-specific differences that should be considered when interpreting and comparing results between preclinical and human studies.

Updates on the Management of Autoimmune Bullous Diseases

Background

Autoimmune bullous diseases are associated with high morbidity and mortality. Traditionally, systemic corticosteroids and conventional immunosuppressive agents have been the mainstay of treatment, but their broad immunosuppressive effects and long-term complications have prompted the exploration of newer more targeted therapies.

Materials and Methods

This review explores the evolving landscape of therapeutic options for immunobullous diseases, with a particular focus on pemphigus, bullous pemphigoid (BP), and mucous membrane pemphigoid, by searching PubMed, clinicaltrials.gov, and Cochrane databases for published literature from 2014 to 2023.

Results/Discussion

We discuss emerging treatments for pemphigus such as B cell modulatory drugs, anti-inflammatory drugs, those inhibiting autoantibody half-life or blister-inducing activity, and stem cell therapy, while offering insights into the level of evidence, potential benefits, and limitations of each approach. The role of biologics and novel therapies like rituximab, omalizumab, and dupilumab in reshaping the management of BP is also discussed.

Conclusion

The article highlights the need for further research, clinical trials, and comparative studies to determine the most effective and safest treatment options for patients with immunobullous diseases.

Targeting Bruton's tyrosine kinase (BTK) as a signaling pathway in immune-mediated diseases: from molecular mechanisms to leading treatments

Bruton's tyrosine kinase (BTK), a nonreceptor tyrosine kinase, plays a remarkable role in the transmission and amplification of extracellular signals to intracellular signaling pathways. Various types of cells use the BTK pathway to communicate, including hematopoietic cells particularly B cells and T cells. The BTK pathway plays a role in controlling the proliferation, survival, and functions of B cells as well as other myeloid cells. First, second, and third-generation BTK inhibitors are currently being evaluated for the treatment of immune-mediated diseases in addition to B cell malignancies. In this article, the available evidence on the action mechanisms of BTK inhibitors is reviewed. Then, the most recent data obtained from preclinical studies and ongoing clinical trials for the treatment of autoimmune diseases, such as pemphigus vulgaris, pemphigus foliaceus, bullous pemphigoid, systemic lupus erythematosus, Sjögren's disease, rheumatoid arthritis, systemic sclerosis, multiple sclerosis, myasthenia gravis, and inflammatory diseases such as psoriasis, chronic spontaneous urticaria, atopic dermatitis, and asthma are discussed. In addition, adverse effects and complications associated with BTK inhibitors as well as factors predisposing patients to BTK inhibitors complications are discussed.

The potential of Bruton's tyrosine kinase (BTK) inhibitors in the pharmacotherapeutic management of immune and dermatological disease

INTRODUCTION

The review article explores the evolving role of Bruton's tyrosine kinase (BTK) inhibitors in immune-mediated dermatological conditions, addressing significant gaps in current treatment approaches.

AREAS COVERED

The review comprehensively discusses the mechanisms of action of BTK inhibitors, including irreversible and reversible inhibitors. Clinical applications of BTK inhibitors in dermatological diseases such as pemphigus, chronic spontaneous urticaria (CSU), hidradenitis suppurativa (HS), systemic lupus erythematosus (SLE), and atopic dermatitis are explored, highlighting recent advancements and ongoing clinical trials. Potential advantages of BTK inhibitors over existing therapies and challenges in translating preclinical findings to clinical outcomes are discussed.

EXPERT OPINION/COMMENTARY

BTK inhibitors represent a promising therapeutic avenue for immune-mediated dermatological conditions, offering oral administration, targeted pathway inhibition, and a favorable safety profile compared to biologic therapies. Ongoing research and clinical trials hold the potential to address unmet needs and reshape the therapeutic landscape in dermatology.

Efficacy and Safety of Rilzabrutinib in Pemphigus: PEGASUS Phase 3 Randomized Study

TRIAL DESIGN

Pemphigus is a rare but life-threatening autoimmune disease requiring long-term treatment that minimizes corticosteroid (CS) exposure while providing consistent disease control. The phase 2 pemphigus study of oral, reversible, covalent Bruton tyrosine kinase inhibitor rilzabrutinib demonstrated rapid and sustained efficacy with well-tolerated safety.

METHODS

Adults (aged 18-80 years) were randomized 1:1 to 400 mg rilzabrutinib (n = 65) or placebo (n = 66) twice daily (with CS ≤ 0.5 mg/kg/d) for 37 weeks in the phase 3 PEGASUS study in moderate-to-severe pemphigus vulgaris/pemphigus foliaceus.

RESULTS

The primary endpoint of complete remission from week 29 to week 37 with the amended endpoint CS dose ≤10 mg/d was not significant for 13 of 54 (24%) rilzabrutinib versus 10 of 55 (18%) placebo patients with PV (P = .45). Secondary endpoints showed numerical but nonsignificant improvements with rilzabrutinib (vs placebo) in reduced CS use, prolonged complete remission duration, and faster time to first complete remission.

CONCLUSIONS

Overall, rilzabrutinib was well-tolerated, with similar adverse events reported in both groups. Using minimal CS dose ≤10 mg/d and excluding remote observations, the primary efficacy endpoint was not met. However, results from a prespecified sensitivity analysis using CS dose ≤5 mg/d, considering all observations, and including all patients support Bruton tyrosine kinase inhibition as a viable therapeutic approach for pemphigus.

Effects of Quinidine or Rifampin Co-administration on the Single-Dose Pharmacokinetics and Safety of Rilzabrutinib (PRN1008) in Healthy Participants

This open-label, phase 1 study was conducted with healthy adult participants to evaluate the potential drug-drug interaction between rilzabrutinib and quinidine (an inhibitor of P-glycoprotein [P-gp] and CYP2D6) or rifampin (an inducer of CYP3A and P-gp). Plasma concentrations of rilzabrutinib were measured after a single oral dose of rilzabrutinib 400 mg administered on day 1 and again, following a wash-out period, after co-administration of rilzabrutinib and quinidine or rifampin. Specifically, quinidine was given at a dose of 300 mg every 8 hours for 5 days from day 7 to day 11 (N = 16) while rifampin was given as 600 mg once daily for 11 days from day 7 to day 17 (N = 16) with rilzabrutinib given in the morning of day 10 (during quinidine dosing) or day 16 (during rifampin dosing). Quinidine had no significant effect on rilzabrutinib pharmacokinetics. Rifampin decreased rilzabrutinib exposure (the geometric mean of Cmax and AUC0-∞ decreased by 80.5% and 79.5%, respectively). Single oral doses of rilzabrutinib, with or without quinidine or rifampin, appeared to be well tolerated. These findings indicate that rilzabrutinib is a substrate for CYP3A but not a substrate for P-gp.

What is novel in the clinical management of pemphigus vulgaris?

INTRODUCTION

Pemphigus, an uncommon autoimmune blistering disorder affecting the skin and mucous membranes, currently with mortality primarily attributed to adverse reactions resulting from treatment protocols. Additionally, the existing treatments exhibit a notable recurrence rate. The high incidence of relapse and the considerable adverse effects associated with treatment underscore the imperative to explore safer and more effective therapeutic approaches. Numerous potential therapeutic targets have demonstrated promising outcomes in trials or preliminary research stages. These encompass anti-CD-20 agents, anti-CD-25 agents, TNF-α inhibition, FAS Ligand Inhibition, FcRn inhibition, BAFF inhibition, Bruton's tyrosine kinase (BTK) inhibition, CAAR T Cells, JAK inhibition, mTOR inhibition, abatacept, IL-4 inhibition, IL-17 inhibition, IL-6 inhibition, polyclonal Regulatory T Cells, and autologous hematopoietic stem cell transplantation.

AREAS COVERED

The most significant studies regarding the impact and efficacy of the mentioned treatments on pemphigus were meticulously curated through a comprehensive search conducted on the PubMed database. Moreover, the investigations of interest cited in these studies were also integrated.

EXPERT OPINION

The efficacy and safety profiles of the other treatments under discussion do not exhibit the same level of robustness as anti-CD20 therapy, which is anticipated to endure as a critical element in pemphigus treatment well into the foreseeable future.

Aberrant B cell receptor signaling in circulating naïve and IgA+ memory B cells from newly-diagnosed autoantibody-positive rheumatoid arthritis patients

OBJECTIVE

Altered B cell receptor (BCR) signaling has been implicated in the pathogenesis of rheumatoid arthritis (RA). Here we aimed to identify signaling aberrations in autoantibody-positive and autoantibody-negative RA patients by performing a comprehensive analysis of the BCR signaling cascade in different B cell subsets.

METHODS

We first optimized phosphoflow cytometry for an in-depth analysis of BCR signaling across immunoglobulin isotypes in healthy donors. Subsequently, we compared BCR signaling in circulating B cell subsets from treatment-naïve, newly-diagnosed autoantibody-positive RA and autoantibody-negative RA patients and healthy controls (HCs).

RESULTS

We observed subset-specific phosphorylation patterns of the BCR signalosome in circulating B cells from healthy donors. Compared with HCs, autoantibody-positive RA patients displayed enhanced responses to BCR stimulation for multiple signaling proteins, specifically in naïve and IgA+ memory B cells. Whereas in unstimulated healthy donor B cells, the phosphorylation status of individual signaling proteins showed only limited correlation, BCR stimulation enhanced the interconnectivity in phosphorylation within the BCR signalosome. However, this strong interconnectivity within the BCR signalosome in stimulated B cells from HCs was lost in RA, especially in autoantibody-positive RA patients. Finally, we observed strong correlations between SYK and BTK protein expression, and IgA and IgG anti-citrullinated protein antibody concentrations in serum from autoantibody-positive RA patients.

CONCLUSION

Collectively, the isotype-specific analysis of multiple key components of the BCR signalosome identified aberrant BCR signaling responses in treatment-naïve autoantibody-positive RA patients, particularly in naïve B cells and IgA+ memory B cells. Our findings support differential involvement of dysregulated BCR signaling in the pathogenesis of autoantibody-positive and autoantibody-negative RA.

A Comprehensive Review of Small-Molecule Inhibitors Targeting Bruton Tyrosine Kinase: Synthetic Approaches and Clinical Applications

Bruton tyrosine kinase (BTK) is an essential enzyme in the signaling pathway of the B-cell receptor (BCR) and is vital for the growth and activation of B-cells. Dysfunction of BTK has been linked to different types of B-cell cancers, autoimmune conditions, and inflammatory ailments. Therefore, focusing on BTK has become a hopeful approach in the field of therapeutics. Small-molecule inhibitors of BTK have been developed to selectively inhibit its activity and disrupt B-cell signaling pathways. These inhibitors bind to the active site of BTK and prevent its phosphorylation, leading to the inhibition of downstream signaling cascades. Regulatory authorities have granted approval to treat B-cell malignancies, such as chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL), with multiple small-molecule BTK inhibitors. This review offers a comprehensive analysis of the synthesis and clinical application of conventional small-molecule BTK inhibitors at various clinical stages, as well as presents promising prospects for the advancement of new small-molecule BTK inhibitors.

Applications of oxetanes in drug discovery and medicinal chemistry

The compact and versatile oxetane motifs have gained significant attention in drug discovery and medicinal chemistry campaigns. This review presents an overview of the diverse applications of oxetanes in clinical and preclinical drug candidates targeting various human diseases, including cancer, viral infections, autoimmune disorders, neurodegenerative conditions, metabolic disorders, and others. Special attention is given to biologically active oxetane-containing compounds and their disease-related targets, such as kinases, epigenetic and non-epigenetic enzymes, and receptors. The review also details the effect of the oxetane motif on important properties, including aqueous solubility, lipophilicity, pKa, P-glycoprotein (P-gp) efflux, metabolic stability, conformational preferences, toxicity profiles (e.g., cytochrome P450 (CYP) suppression and human ether-a-go-go related gene (hERG) inhibition), pharmacokinetic (PK) properties, potency, and target selectivity. We anticipate that this work will provide valuable insights that can drive future discoveries of novel bioactive oxetane-containing small molecules, enabling their effective application in combating a wide range of human diseases.

Efficacy and safety of Bruton's tyrosine kinase inhibitors in the treatment of pemphigus: A comprehensive literature review and future perspective

Bruton's tyrosine kinase (BTK) is a protein involved in B-cell-receptor signaling and B-cell proliferation. The pathophysiology of several autoimmune diseases, such as pemphigus disorder, relies on the BTK signaling pathway. Therefore, BTK inhibitors were found to be beneficial alternatives to conventional treatmentsThe current study aimed to assess the efficacy and safety of BTK inhibitors in treating pemphigus. A complete search was performed on databases including PubMed/MedLine, Scopus, Web of Science, as well as Google Scholar search engine for studies published by September 20th, 2023. The current review indicates that BTK inhibitors alone or in combination with conventional treatments are promising options in the management of pemphigus. The overall safety profile of BTK inhibitors has been acceptable, and the reported adverse reactions were not severe or life-threatening.

Bullous Pemphigoid Occurring after Stopping Imatinib Therapy of CML: Is a Continuation of Post-Treatment Follow-Up Needed?

Advancements and the use of tyrosine kinase inhibitors (TKIs) have revolutionized the treatment of Chronic Myeloid Leukemia (CML), achieving unprecedented success rates and expanding their applications to various neoplasms. However, the use of TKIs is not without its drawbacks. Skin, gastrointestinal, and central nervous systems are particularly susceptible to adverse effects, including a higher incidence of autoimmune responses in treated individuals. In this report, we present a unique case of bullous pemphigoid, a rare autoimmune disease, which has not been previously associated with TKI therapy as an adverse effect, particularly appearing after discontinuing Imatinib® treatment.

Autoimmune blistering diseases: promising agents in clinical trials

INTRODUCTION

Treatment options for autoimmune bullous diseases (AIBD) are currently limited to corticosteroids and traditional immunomodulants and immunosuppressants that are associated with unfavorable adverse effect profiles. The most frequent AIBDs, i.e. bullous pemphigoid, pemphigus vulgaris, and mucous membrane pemphigoid, impose a high disease burden onto affected patients and can be detrimental due to infections, exsiccosis, and impaired food intake. Significant progress has been made in elucidating disease mechanisms and key mediators by in vivo and in vitro models, thus identifying a multifaceted range of possible drug targets. However, except for rituximab for pemphigus vulgaris, no new drugs have been approved for the treatment of AIBDs in the last decades.

AREAS COVERED

This review covers new drug developments and includes ongoing or completed phase 2 and 3 clinical trials. Studies were identified by querying the registries of ClinicalTrials.gov and Cochrane Library.

EXPERT OPINION

Promising results were shown for a variety of new agents including nomacopan, efgartigimod, omalizumab, dupilumab, as well as chimeric autoantibody receptor T cells. Clinical translation in the field of AIBDs is highly active, and we anticipate significant advances in the treatment landscape.

New small molecules in dermatology: for the autoimmunity, inflammation and beyond

OBJECTIVE AND DESIGN

The discovery of new inflammatory pathways and the mechanism of action of inflammatory, autoimmune, genetic, and neoplastic diseases led to the development of immunologically driven drugs. We aimed to perform a narrative review regarding the rising of a new class of drugs capable of blocking important and specific intracellular signals in the maintenance of these pathologies: the small molecules.

MATERIALS/METHODS

A total of 114 scientific papers were enrolled in this narrative review.

RESULTS

We describe in detail the families of protein kinases-Janus Kinase (JAK), Src kinase, Syk tyrosine kinase, Mitogen-Activated Protein Kinase (MAPK), and Bruton Tyrosine Kinase (BTK)-their physiologic function and new drugs that block these pathways of intracellular signaling. We also detail the involved cytokines and the main metabolic and clinical implications of these new medications in the field of dermatology.

CONCLUSIONS

Despite having lower specificity compared to specific immunobiological therapies, these new drugs are effective in a wide variety of dermatological diseases, especially diseases that had few therapeutic options, such as psoriasis, psoriatic arthritis, atopic dermatitis, alopecia areata, and vitiligo.

B-cell targeted therapy of pemphigus

Pemphigus is an autoimmune disease that causes blistering and erosion of the skin and mucous membranes because of autoantibodies against desmoglein, which plays an important role in adhesion between epidermal keratinocytes. Treatment of pemphigus has long been centered on corticosteroids, and the guidelines for management of pemphigus have recommended high-dose systemic corticosteroids as the first-line treatment. While guideline-based treatment has been shown to be beneficial in patients with pemphigus, it has also become clear that this treatment is accompanied by significant burden and risk. The challenge for future pemphigus treatment is to maximize efficacy while minimizing risk during the course of the disease. In this regard, treatment targeting B cells is expected to become increasingly important as autoreactive B cells in pemphigus patients are thought to play a major role in the production of autoantibodies, which form the basis of the pathogenesis. The recent expansion of insurance coverage to rituximab, a monoclonal antibody against CD20, for refractory pemphigus in the USA, Europe, and Japan has opened up a new era of pemphigus treatment by enabling treatment strategies with drugs targeting B cells in patients. Here, we discuss the current status and future prospects of pemphigus treatment, focusing on rituximab and Bruton's tyrosine kinase inhibitors, which are expected to become essential drugs for pemphigus treatment in the future.

Towards multiomic analysis of oral mucosal pathologies

Oral mucosal pathologies comprise an array of diseases with worldwide prevalence and medical relevance. Affecting a confined space with crucial physiological and social functions, oral pathologies can be mutilating and drastically reduce quality of life. Despite their relevance, treatment for these diseases is often far from curative and remains vastly understudied. While multiple factors are involved in the pathogenesis of oral mucosal pathologies, the host's immune system plays a major role in the development, maintenance, and resolution of these diseases. Consequently, a precise understanding of immunological mechanisms implicated in oral mucosal pathologies is critical (1) to identify accurate, mechanistic biomarkers of clinical outcomes; (2) to develop targeted immunotherapeutic strategies; and (3) to individualize prevention and treatment approaches. Here, we review key elements of the immune system's role in oral mucosal pathologies that hold promise to overcome limitations in current diagnostic and therapeutic approaches. We emphasize recent and ongoing multiomic and single-cell approaches that enable an integrative view of these pathophysiological processes and thereby provide unifying and clinically relevant biological signatures.

Advancement in therapeutic strategies for immune-mediated oral diseases

BACKGROUND

Immune-mediated diseases are a diverse group of conditions characterized by alteration of cellular homeostasis and inflammation triggered by dysregulation of the normal immune response. Several immune-mediated diseases exhibit oral signs and symptoms. Traditionally, these conditions are treated with corticosteroids or immunosuppressive agents, including azathioprine, cyclophosphamide, and thalidomide. Recent research into the developmental pathways of these diseases has led to the exploration of novel approaches in treatment. This review examines newer treatment modalities for the management of immune-mediated diseases with oral presentations. Topical calcineurin inhibitors (TCIs) such as tacrolimus and pimecrolimus have been employed successfully in managing oral lichen planus and pemphigus vulgaris. Biologic agents, comprising monoclonal antibodies, fusion proteins, and recombinant cytokines, can provide targeted therapy with fewer adverse effects. Neutraceutical agents comprising aloe vera, curcumin, and honey are commonly used in traditional medicine and offer a holistic approach. They may have a place as adjuvants to current standard therapeutic protocols. Photodynamic therapy (PDT) and low-level laser therapy (LLLT) utilize a specific wavelength of light to achieve desired cellular change. While the use of PDT in immune-mediated diseases is contentious, LLLT has shown positive results. Newer therapeutic modalities involve kinase inhibitors, S1P₁ receptor modulators, MSCs, and iRNA providing targeted treatment of specific diseases.

Existing and Investigational Medications for Refractory Chronic Spontaneous Urticaria: Safety, Adverse Effects, and Monitoring

Treatment of chronic spontaneous urticaria (CSU) is responsive to H1 antihistamines administered up to four times the recommended US Food and Drug Administration dose in approximately 50% of patients. However, when patients do not respond to these first-line agents, evidence-based guidelines using Grading of Recommendations, Assessment, Development, and Evaluations methodology have provided direction for second- and third-line treatments that can effectively treat patients with CSU. Some patients remain refractory to these advanced treatments; therefore, alternative treatments with a lower certainty of evidence may be necessary. Regardless of the therapies used to treat CSU patients, it is essential for clinicians to be knowledgeable about the mechanism of action, efficacy, and safety and monitoring recommendations of the treatments prescribed. This review provides a comprehensive review of the adverse effects and monitoring recommendations for agents in use for CSU treatment as well as those currently undergoing investigation for CSU treatment.

[Pemphigus: current and future treatment strategies]

Pemphigus diseases are a group of organ-specific autoimmune diseases which are characterised by the production of autoantibodies against intra-epidermal adhesion molecules and structural proteins of skin and mucosae. Depending on the entity, patients develop blisters and erosions on the skin and/or mucosae. According to the AWMF S2k guidelines for diagnosis and therapy of pemphigus diseases, a systemic therapy is recommended. Initially, high-dose, oral corticosteroids in combination with immunosuppressive drugs as corticosteroid-sparing agent, usually azathioprine or mycophenolate mofetil, can be used. Furthermore, rituximab, a monoclonal antibody directed against CD20 on B cells, was recently approved for pemphigus vulgaris and moderate or severe pemphigus foliaceus.

BTK inhibitors in the treatment of hematological malignancies and inflammatory diseases: mechanisms and clinical studies

Bruton's tyrosine kinase (BTK) is an essential component of multiple signaling pathways that regulate B cell and myeloid cell proliferation, survival, and functions, making it a promising therapeutic target for various B cell malignancies and inflammatory diseases. Five small molecule inhibitors have shown remarkable efficacy and have been approved to treat different types of hematological cancers, including ibrutinib, acalabrutinib, zanubrutinib, tirabrutinib, and orelabrutinib. The first-in-class agent, ibrutinib, has created a new era of chemotherapy-free treatment of B cell malignancies. Ibrutinib is so popular and became the fourth top-selling cancer drug worldwide in 2021. To reduce the off-target effects and overcome the acquired resistance of ibrutinib, significant efforts have been made in developing highly selective second- and third-generation BTK inhibitors and various combination approaches. Over the past few years, BTK inhibitors have also been repurposed for the treatment of inflammatory diseases. Promising data have been obtained from preclinical and early-phase clinical studies. In this review, we summarized current progress in applying BTK inhibitors in the treatment of hematological malignancies and inflammatory disorders, highlighting available results from clinical studies.

Blasenbildende Autoimmundermatosen – Klinik, Diagnostik und neue Therapieansätze

Diese Arbeit gibt eine Übersicht über die Gruppe blasenbildender Autoimmundermatosen und stellt deren wichtigste Vertreter, das bullöse Pemphigoid, den Pemphigus vulgaris sowie den Pemphigus foliaceus, vor. Die häufigste der insgesamt seltenen blasenbildenden Autoimmundermatosen ist das bullöse Pemphigoid (BP). Es betrifft vor allem Patienten jenseits des 60. Lebensjahrs. Charakterisiert ist es typischerweise durch das Auftreten praller Blasen, die mit einem heftigen Juckreiz einhergehen. Ein längeres, sogenanntes prämonitorisches Stadium ohne Blasenbildung ist nicht ungewöhnlich. Es gibt außerdem Varianten mit anderem Erscheinungsbild wie das lokalisierte BP. Der diagnostische Goldstandard ist die direkte Immunfluoreszenzmikroskopie einer periläsional entnommenen Hautbiopsie, welche lineare Ablagerungen von IgG und C3 an der Basalmembran zeigt. Vervollständigt wird die Diagnostik durch die indirekte Immunfluoreszenzmikroskopie sowie weiterführende ELISA-Untersuchungen, mittels derer zirkulierende Autoantikörper im Patientenserum nachgewiesen werden können. Das wichtigste Zielantigen ist BP180, ein hemidesmosomales, von Keratinozyten exprimiertes Protein. Ergänzend kann eine histopathologische Untersuchung erfolgen, die allerdings nur Hinweise zur Spaltebene und zum (meist Eosinophilen-dominierten) Infiltratmuster geben kann und alleine nicht zur Diagnosestellung ausreicht. Die Pathogenese des BP ist Gegenstand der wissenschaftlichen Diskussion. Medikamente wie Dipeptidylpeptidase-4-Inhibitoren können Auslöser sein; Assoziationen zu neurologischen Erkrankungen finden sich häufig. Entsprechend aktueller Leitlinien wird das BP mit topischen bzw. systemischen Glukokortikoiden ggf. in Kombination mit Doxyzyklin, Dapson oder einem Immunsuppressivum behandelt. Bei Therapieresistenz werden intravenöse Immunglobuline oder der anti-CD-20-Antikörper Rituximab eingesetzt. Aufgrund einer vergleichsweise hohen Mortalität bedingt durch Patientenalter und iatrogener Immunsuppression werden neue Therapieansätze gesucht. Fallserien, Kohortenanalysen und Phase 1-/2-Studien mit anti-IgE-Antikörpern und Inhibitoren der eosinophilen Granulozyten sowie des Komplementsystems zeigen teils vielversprechende Effekte. Die wichtigsten Vertreter der Pemphiguserkrankungen sind der Pemphigus vulgaris (PV), der Pemphigus foliaceus (PF) und der sehr seltene paraneoplastische Pemphigus (PNP). Klinisch präsentiert sich der PV mit meist enoralen Schleimhauterosionen und teilweise zusätzlichen Erosionen an der freien Haut. Der PF manifestiert sich nur an der freien Haut. Wie beim BP wird die Diagnose mittels direkter Immunfluoreszenzmikroskopie gestellt, welche beim PV und PF netzförmige Ablagerungen von IgG und C3 innerhalb der Epidermis zeigt. Die häufigsten Zielantigene sind die Desmogleine 1 und 3. Genetische Prädispositionen für den PV und PF sind bekannt und Grund für eine global unterschiedliche Häufigkeit. Der PNP ist immer mit einer malignen Erkrankung assoziiert und von einem progredienten Verlauf mit hoher Mortalität geprägt. Therapeutisch erfordern die Pemphiguserkankungen oft aggressivere Ansätze als das BP. Neben systemischen Glukokortikoiden und Immunsuppressiva wird für den PV und PF der anti-CD-20-Antikörper Rituximab empfohlen. Neue Therapieansätze sind die Hemmung der Bruton-Tyrosinkinase sowie des neonatalen Fc-Rezeptors (FcRN). In einer Phase 2-Studie zeigte Efgartigimod, ein Antagonist des FcRN, eine hohe Therapieeffektivität für Patienten mit PV und PF.

Current and Innovated Managements for Autoimmune Bullous Skin Disorders: An Overview

Autoimmune bullous skin disorders are a group of disorders characterized by the formation of numerous blisters and erosions on the skin and/or the mucosal membrane, arising from autoantibodies against the intercellular adhesion molecules and the structural proteins. They can be classified into intraepithelial or subepithelial autoimmune bullous dermatoses based on the location of the targeted antigens. These dermatoses are extremely debilitating and fatal in certain cases, depending on the degree of cutaneous and mucosal involvement. Effective treatments should be implemented promptly. Glucocorticoids serve as the first-line approach due to their rapid onset of therapeutic effects and remission of the acute phase. Nonetheless, long-term applications may lead to major adverse effects that outweigh the benefits. Hence, other adjuvant therapies are mandatory to minimize the potential harm and ameliorate the quality of life. Herein, we summarize the current therapeutic strategies and introduce promising therapies for intractable autoimmune bullous diseases.

Immunotherapy for Pemphigus: Present and Future

Pemphigus is a chronic and severe autoimmune bullous disease caused by autoantibodies targeting adhesion molecules between keratinocytes. It requires 2–3 years on average to manage the disease. To date, although Rituximab combined with short-term systemic glucocorticoids was accepted as first-line therapy, systemic glucocorticoids remain the primary therapeutic option for pemphigus patients, successfully decreasing morbidity and mortality from pemphigus. However, novel therapeutic strategies are desirable due to the low efficacy in some subset of patients and the long-term severe adverse effects of traditional therapies. Recently, immunotherapy has proved to be encouraging for disease control or cure. Based on the current understanding of the immune mechanisms of pemphigus, we review the immune targets and corresponding agents applied in practice or under clinical trials. The goals of the novel treatments are to improve the quality of life of pemphigus patients by improving efficacy and safety, minimizing side effects, achieving fast disease control, or curing the disease.

A thorough QTc study to evaluate the effects of oral rilzabrutinib administered alone and with ritonavir in healthy subjects

This study aimed to define the clinically relevant supratherapeutic dose of rilzabrutinib, an oral Bruton tyrosine kinase (BTK) inhibitor, and evaluate potential effects of therapeutic and supratherapeutic exposures on cardiac repolarization in healthy subjects. This was a two-part phase I study (anzctr.org.au ACTRN12618001036202). Part A was a randomized, open-label, three-period, single-dose crossover study (n = 12) with rilzabrutinib 100 mg ± ritonavir 100 mg or rilzabrutinib 1200 mg. Part B was a randomized, double-blind, placebo-controlled, four-way, single-dose crossover study (n = 39) with matched placebo, rilzabrutinib 400 mg ± ritonavir 100 mg, or moxifloxacin (positive control). Primary objectives: part A - pharmacokinetics (PK) of rilzabrutinib ± ritonavir, safety, and optimal dose for Part B; Part B - effect of rilzabrutinib therapeutic and supratherapeutic concentration on electrocardiogram (ECG) parameters. ECGs and PK samples were serially recorded before and post-dose. In part A, rilzabrutinib 100 mg + ritonavir led to 17-fold area under the concentration-time curve (AUC0-∞ ) and 7-fold maximum plasma concentration (Cmax ) increases over rilzabrutinib alone. Rilzabrutinib 1200 mg was discontinued due to mild-to-moderate gastrointestinal intolerance. In Part B, rilzabrutinib 400 mg + ritonavir increased rilzabrutinib mean AUC0-∞ from 454 to 3800 ng h/mL and Cmax from 144 to 712 ng/mL. The concentration-QTc relationship was slightly negative, shallow (-0.01 ms/ng/mL [90% CI -0.016 to -0.001]), and an effect >10 ms on QTcF could be excluded within the observed range of plasma concentrations, up to 2500 ng/mL. Safety was similar to other studies of rilzabrutinib. In conclusion, rilzabrutinib, even at supratherapeutic doses, had no clinically relevant effects on ECG parameters, including the QTc interval.

What protein kinases are crucial for acantholysis and blister formation in pemphigus vulgaris? A systematic review

Pemphigus vulgaris (PV) is a potentially fatal autoimmune blistering disease characterized by cell-cell detachment (or acantholysis) and blister formation. While the signaling mechanisms that associate with skin/mucosal blistering are being elucidated, specific treatment strategies targeting PV-specific pathomechanisms, particularly kinase signaling, have yet to be established. Hence, the aim of this review was to systematically evaluate molecules in the class of kinases that are essential for acantholysis and blister formation and are therefore candidates for targeted therapy. English articles from PubMed and Scopus databases were searched, and included in vitro, in vivo, and human studies that investigated the role of kinases in PV. We selected studies, extracted data and assessed risk of bias in duplicates and the results were reported according to the methodology outlined by the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA). The risk of bias assessment was performed on in vivo studies utilizing SYRCLE's risk of bias tool. Thirty-five studies were included that satisfied the pathogenicity criterion of kinases in PV, the vast majority being experimental models that used PV sera (n = 13) and PV-IgG (n = 22). Inhibition of kinase activity (p38MAPK, PKC, TK, c-Src, EGFR, ERK, mTOR, BTK, and CDK2) was achieved mostly by pharmacological means. Overall, we found substantial evidence that kinase inhibition reduced PV-associated phosphorylation events and keratinocyte disassociation, prevented acantholysis, and blocked blister formation. However, the scarce adherence to standardized reporting systems and the experimental protocols/models used did limit the internal and external validity of these studies. In summary, this systematic review highlighted the pathogenic intracellular events mediated by kinases in PV acantholysis and presented kinase signaling as a promising avenue for translational research. In particular, the molecules identified and discussed in this study represent potential candidates for the development of mechanism-based interventions in PV.

Mechanisms Causing Acantholysis in Pemphigus-Lessons from Human Skin

Pemphigus vulgaris (PV) is an autoimmune bullous skin disease caused primarily by autoantibodies (PV-IgG) against the desmosomal adhesion proteins desmoglein (Dsg)1 and Dsg3. PV patient lesions are characterized by flaccid blisters and ultrastructurally by defined hallmarks including a reduction in desmosome number and size, formation of split desmosomes, as well as uncoupling of keratin filaments from desmosomes. The pathophysiology underlying the disease is known to involve several intracellular signaling pathways downstream of PV-IgG binding. Here, we summarize our studies in which we used transmission electron microscopy to characterize the roles of signaling pathways in the pathogenic effects of PV-IgG on desmosome ultrastructure in a human ex vivo skin model. Blister scores revealed inhibition of p38MAPK, ERK and PLC/Ca2+ to be protective in human epidermis. In contrast, inhibition of Src and PKC, which were shown to be protective in cell cultures and murine models, was not effective for human skin explants. The ultrastructural analysis revealed that for preventing skin blistering at least desmosome number (as modulated by ERK) or keratin filament insertion (as modulated by PLC/Ca2+) need to be ameliorated. Other pathways such as p38MAPK regulate desmosome number, size, and keratin insertion indicating that they control desmosome assembly and disassembly on different levels. Taken together, studies in human skin delineate target mechanisms for the treatment of pemphigus patients. In addition, ultrastructural analysis supports defining the specific role of a given signaling molecule in desmosome turnover at ultrastructural level.

FcRn Antagonism Leads to a Decrease of Desmoglein-Specific B Cells: Secondary Analysis of a Phase 2 Study of Efgartigimod in Pemphigus Vulgaris and Pemphigus Foliaceus

Background

Immunoglobulin G (IgG) levels are maintained by the IgG-recycling neonatal Fc-receptor (FcRn). Pemphigus vulgaris and pemphigus foliaceus are debilitating autoimmune disorders triggered by IgG autoantibodies against mucosal and epidermal desmogleins. Recently, a phase 2 clinical trial (NCT03334058; https://clinicaltrials.gov/NCT03334058) was completed in participants with pemphigus using efgartigimod, an FcRn inhibitor, in combination with prednisone. Efgartigimod demonstrated an early effect on diease activity and was well tolerated. In addition to the safety and efficacy assessment, clinical trials present an opportunity to gain more insights into the mechanism of disease, the mode of action of treatment, and potential for corticosteroid-sparing activity.

Objective

The aim of our study was to assess the impact of FcRn antagonism by efgartigimod on immunological parameters known to be directly involved in pemphigus pathology, such as cellular and serological responses.

Methods

We investigated total and antigen-specific IgG subclass level kinetics during and after treatment, assessed antigen-specific B-cell responses, followed T- and B-cell immunophenotypes, and analyzed how different immunophenotypes link to clinical response.

Results

Treatment resulted in reduction of total IgG as well as autoreactive IgG antibody levels. Surprisingly, unlike total IgG and vaccine- or natural-infection-elicited IgG, which returned to baseline levels after stopping efgartigimod treatment, autoreactive antibody levels remained low in several study participants. Efgartigimod showed no effect on total leukocytes, neutrophils, monocytes, or lymphocytes in patients treated with extended efgartigimod therapy. Intriguingly, antigen-specific analyses revealed a loss of desmoglein-specific B cells in several participants responding to efgartigimod, in line with prolonged reduction of pathogenic IgG levels.

Conclusions

Efgartigimod treatment of participants with pemphigus improved their conditions and exerted an immunomodulatory effect beyond the blockade of IgG recycling. Further studies in larger populations with an appropriate placebo control are needed to confirm these potentially important observations to establish long-term clinical responses in autoimmune diseases.

Bruton's Kinase Inhibitors for the Treatment of Immunological Diseases: Current Status and Perspectives

The use of Bruton's tyrosine kinase (BTK) inhibitors has changed the management of patients with B-cell lymphoid malignancies. BTK is an important molecule that interconnects B-cell antigen receptor (BCR) signaling. BTK inhibitors (BTKis) are classified into three categories, namely covalent irreversible inhibitors, covalent reversible inhibitors, and non-covalent reversible inhibitors. Ibrutinib is the first covalent, irreversible BTK inhibitor approved in 2013 as a breakthrough therapy for chronic lymphocytic leukemia patients. Subsequently, two other covalent, irreversible, second-generation BTKis, acalabrutinib and zanubrutinib, have been developed for lymphoid malignancies to reduce the ibrutinib-mediated adverse effects. More recently, irreversible and reversible BTKis have been under development for immune-mediated diseases, including autoimmune hemolytic anemia, immune thrombocytopenia, multiple sclerosis, pemphigus vulgaris, atopic dermatitis, rheumatoid arthritis, systemic lupus erythematosus, Sjögren's disease, and chronic spontaneous urticaria, among others. This review article summarizes the preclinical and clinical evidence supporting the role of BTKis in various autoimmune, allergic, and inflammatory conditions.

Translational autoimmunity in pemphigus and the role of novel Bruton tyrosine kinase inhibitors

Bruton tyrosine kinase (BTK) is involved in a multifarious inflammatory and autoimmune process. As a result, BTK has emerged as a promising novel remedial target for amalgamated autoimmune diseases. Medicament corporations have recently devoted considerable attention to the evolution of BTK inhibitors. Pemphigus is an uncommon and often fatal autoimmune illness. Blisters and erosions on cutaneous surfaces and mucous membranes are crippling symptoms of pemphigus vulgaris, which are caused by immunoglobulin G autoantibodies binding to keratinocyte proteins, resulting in keratinocyte adhesion defects. Although systemic corticosteroids and adjuvant medications are used to treat pemphigus, some patients are resistant to these. BTK inhibitors inhibit B-cell signaling, which is clinically useful in treating pemphigus. Assorted clinical trials are underway to assess the safety, tolerability, and pharmacokinetics of distinct BTK inhibitors, including PRN473 and remibrutinib. The current review evaluates translational autoimmunity in pemphigus and discusses BTK inhibitors in the treatment of pemphigus.

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Pemphigus is severe, and potentially fatal B-cell-mediated autoimmune illness.

•Systemic corticosteroids are used to treat pemphigus, some patients are resistant.

•Bruton Tyrosine Kinase (BTK) is involved in a variety of auto-immune processes.

•As a result, BTK has emerged as a new therapeutic target including pemphigus.

•The current review evaluates the translational autoimmunity in pemphigus.

•This review also depicts the role of BTK inhibitors in treatment of pemphigus.

Discovery of Reversible Covalent Bruton's Tyrosine Kinase Inhibitors PRN473 and PRN1008 (Rilzabrutinib)

Bruton's tyrosine kinase (BTK), a Tec family tyrosine kinase, is critical in immune pathways as an essential intracellular signaling element, participating in both adaptive and immune responses. Currently approved BTK inhibitors are irreversible covalent inhibitors and limited to oncology indications. Herein, we describe the design of covalent reversible BTK inhibitors and the discoveries of PRN473 (11) and rilzabrutinib (PRN1008, 12). These compounds have exhibited potent and durable inhibition of BTK, in vivo efficacy in rodent arthritis models, and clinical efficacy in canine pemphigus foliaceus. Compound 11 has completed phase 1 trials as a topical agent, and 12 is in phase 3 trials for pemphigus vulgaris and immune thrombocytopenia.

Bruton's tyrosine kinase inhibition-An emerging therapeutic strategy in immune-mediated dermatological conditions

Bruton's tyrosine kinase (BTK), a member of the Tec kinase family, is critically involved in a range of immunological pathways. The clinical application of BTK inhibitors for B‐cell malignancies has proven successful, and there is strong rationale for the potential benefits of BTK inhibitors in some autoimmune and allergic conditions, including immune‐mediated dermatological diseases. However, the established risk‐to‐benefit profile of “first‐generation” BTK inhibitors cannot be extrapolated to these emerging, non‐oncological, indications. “Next‐generation” BTK inhibitors such as remibrutinib and fenebrutinib entered clinical development for chronic spontaneous urticaria (CSU); rilzabrutinib and tirabrutinib are being studied as potential treatments for pemphigus. Promising data from early‐phase clinical trials in CSU suggest potential for these agents to achieve strong pathway inhibition, which may translate into measurable clinical benefits, as well as other effects such as the disruption of autoantibody production. BTK inhibitors may help to overcome some of the shortcomings of monoclonal antibody treatments for immune‐mediated dermatological conditions such as CSU, pemphigus, and systemic lupus erythematosus. In addition, the use of BTK inhibitors may improve understanding of the pathophysiological roles of mast cells, basophils, and B cells in such conditions.

Autoimmune Pemphigus: Latest Advances and Emerging Therapies

Pemphigus represents a group of rare and severe autoimmune intra-epidermal blistering diseases affecting the skin and mucous membranes. These painful and debilitating diseases are driven by the production of autoantibodies that are mainly directed against the desmosomal adhesion proteins, desmoglein 3 (Dsg3) and desmoglein 1 (Dsg1). The search to define underlying triggers for anti-Dsg-antibody production has revealed genetic, environmental, and possible vaccine-driven factors, but our knowledge of the processes underlying disease initiation and pathology remains incomplete. Recent studies point to an important role of T cells in supporting auto-antibody production; yet the involvement of the myeloid compartment remains unexplored. Clinical management of pemphigus is beginning to move away from broad-spectrum immunosuppression and towards B-cell-targeted therapies, which reduce many patients’ symptoms but can have significant side effects. Here, we review the latest developments in our understanding of the predisposing factors/conditions of pemphigus, the underlying pathogenic mechanisms, and new and emerging therapies to treat these devastating diseases.

Immunopathology and Immunotherapy of Inflammatory Skin Diseases

Recently, there have been impressive advancements in understanding of the immune mechanisms underlying cutaneous inflammatory diseases. To understand these diseases on a deeper level and clarify the therapeutic targets more precisely, numerous studies including in vitro experiments, animal models, and clinical trials have been conducted. This has resulted in a paradigm shift from non-specific suppression of the immune system to selective, targeted immunotherapies. These approaches target the molecular pathways and cytokines responsible for generating inflammatory conditions and reinforcing feedback mechanisms to aggravate inflammation. Among the numerous types of skin inflammation, psoriasis and atopic dermatitis (AD) are common chronic cutaneous inflammatory diseases. Psoriasis is a IL-17–mediated disease driven by IL-23, while AD is predominantly mediated by Th2 immunity. Autoimmune bullous diseases are autoantibody-mediated blistering disorders, including pemphigus and bullous pemphigoid. Alopecia areata is an organ-specific autoimmune disease mediated by CD8⁺ T-cells that targets hair follicles. This review will give an updated, comprehensive summary of the pathophysiology and immune mechanisms of inflammatory skin diseases. Moreover, the therapeutic potential of current and upcoming immunotherapies will be discussed.

Effects of the Btk-Inhibitors Remibrutinib (LOU064) and Rilzabrutinib (PRN1008) With Varying Btk Selectivity Over Tec on Platelet Aggregation and in vitro Bleeding Time

Background: Bruton tyrosine kinase inhibitors (BTKi) are used in B-cell malignancies and in development against various autoimmune diseases. Since Btk is also involved in specific pathways of platelet activation, BTKi might be considered to target platelet GPVI/GPIb-mediated atherothrombosis and platelet FcγRIIA-dependent immune disorders. However, BTKi treatment of patients with B-cell malignancies is frequently associated with mild bleeding events caused possibly by off-target inhibition of Tec. Here, we compared the platelet effects of two novel BTKi that exhibit a high (remibrutinib) or low (rilzabrutinib) selectivity for Btk over Tec.

Methods and Results: Remibrutinib and rilzabrutinib were pre-incubated with anticoagulated blood. Platelet aggregation and in vitro bleeding time (closure time) were studied by multiple electrode aggregometry (MEA) and platelet-function analyzer-200 (PFA-200), respectively. Both BTKi inhibited atherosclerotic plaque-stimulated GPVI-mediated platelet aggregation, remibrutinib being more potent (IC₅₀ = 0.03 μM) than rilzabrutinib (IC₅₀ = 0.16 μM). Concentrations of remibrutinib (0.1 μM) and rilzabrutinib (0.5 μM), >80% inhibitory for plaque-induced aggregation, also significantly suppressed (>90%) the Btk-dependent pathways of platelet aggregation upon GPVI, von Willebrand factor/GPIb and FcγRIIA activation stimulated by low collagen concentrations, ristocetin and antibody cross-linking, respectively. Both BTKi did not inhibit aggregation stimulated by ADP, TRAP-6 or arachidonic acid. Remibrutinib (0.1 μM) only slightly prolonged closure time and significantly less than rilzabrutinib (0.5 μM).

Conclusion: Remibrutinib and rilzabrutinib inhibit Btk-dependent pathways of platelet aggregation upon GPVI, VWF/GPIb, and FcγRIIA activation. Remibrutinib being more potent and showing a better profile of inhibition of Btk-dependent platelet activation vs. hemostatic impairment than rilzabrutinib may be considered for further development as an antiplatelet drug.

Patent highlights April–May 2021

A snapshot of noteworthy recent developments in the patent literature of relevance to pharmaceutical and medical research and development.

Bruton's Tyrosine Kinase Inhibition as an Emerging Therapy in Systemic Autoimmune Disease

Systemic autoimmune disorders are complex heterogeneous chronic diseases involving many different immune cells. A significant proportion of patients respond poorly to therapy. In addition, the high burden of adverse effects caused by "classical" anti-rheumatic or immune modulatory drugs provides a need to develop more specific therapies that are better tolerated. Bruton's tyrosine kinase (BTK) is a crucial signaling protein that directly links B-cell receptor (BCR) signals to B-cell activation, proliferation, and survival. BTK is not only expressed in B cells but also in myeloid cells, and is involved in many different signaling pathways that drive autoimmunity. This makes BTK an interesting therapeutic target in the treatment of autoimmune diseases. The past decade has seen the emergence of first-line BTK small-molecule inhibitors with great efficacy in the treatment of B-cell malignancies, but with unfavorable safety profiles for use in autoimmunity due to off-target effects. The development of second-generation BTK inhibitors with superior BTK specificity has facilitated the investigation of their efficacy in clinical trials with autoimmune patients. In this review, we discuss the role of BTK in key signaling pathways involved in autoimmunity and provide an overview of the different inhibitors that are currently being investigated in clinical trials of systemic autoimmune diseases, including rheumatoid arthritis and systemic lupus erythematosus, as well as available results from completed trials.

Bruton Tyrosine Kinase Inhibition and Its Role as an Emerging Treatment in Pemphigus

Bruton Tyrosine Kinase (BTK) has a key role in multiple pathways involved in inflammation and autoimmunity. Therefore, BTK has become a new therapeutic target for a group of hematologic and autoimmune disorders. The pharmaceutical industry has invested in the clinical development of BTK inhibitors during the last decade. Ibrutinib, for example, which was the first BTK inhibitor to be used in clinical trials, has two approved indications, mantle cell lymphoma and chronic lymphocytic leukemia, and remains under evaluation for additional indications. Rillzabrutinib (PRN1008) is a new, highly potent and selective inhibitor of BTK. Early studies performed in canine pemphigus demonstrated effectiveness. A proof-of-concept, multicenter, phase 2 trial has recently showed the efficacy and safety of oral rilzabrutinib in pemphigus vulgaris. In this mini review, we present evidence regarding the mechanisms affected by BTK inhibition and the concept of BTK inhibition as an emerging new treatment in pemphigus.

Mechanism-based therapeutic targets of pemphigus vulgaris: A scoping review of pathogenic molecular pathways

Pemphigus vulgaris (PV) is a potentially fatal autoimmune blistering disease characterised by cell-cell detachment or acantholysis. The mechanisms which follow antibody (Ab) binding and culminate in acantholytic changes and skin/mucosal blistering have not been fully clarified. Current treatment strategies are not specific to PV pathophysiology and although life-saving, harbour considerable side effects. We aimed to systematically assess the molecules amenable to targeted treatments that follow Ab binding and are associated with PV acantholysis. The resulting scoping review was conducted under PRISMA-ScR guidelines with clear inclusion and exclusion criteria and focused specifically on kinases, caspases, proteases, hydrolytic enzymes and other molecules of interest postulated to take part in the pathophysiology of PV. The review process resulted in the identification of 882 articles, of which 56 were eligible for qualitative synthesis. From the included articles, the majority (n = 42) used PV-IgG as the pathogenic agent, mainly via in vitro (n = 16) and in vivo (n = 10) models. Twenty-five molecules were found to play a pathogenic role in PV, including uPA, ADAM10, EGFR, Src, PKC, cdk2, ERK, PLC, calmodulin, NOS, p38MAPK and caspase-3. Selective inhibition of these molecules resulted in varying degrees of reduction in acantholysis and blistering. The pathogenic molecules identified in this review represent potential candidates for clinical translation.

Preclinical Mechanisms of Topical PRN473, a Bruton Tyrosine Kinase Inhibitor, in Immune-Mediated Skin Disease Models

The expression of Bruton tyrosine kinase (BTK) in B cells and innate immune cells provides essential downstream signaling for BCR, Fc receptors, and other innate immune cell pathways. The topical covalent BTK inhibitor PRN473 has shown durable, reversible BTK occupancy with rapid on-rate and slow off-rate binding kinetics and long residence time, resulting in prolonged, localized efficacy with low systemic exposure in vivo. Mechanisms of PRN473 include inhibition of IgE (FcεR)-mediated activation of mast cells and basophils, IgG (FcγR)-mediated activation of monocytes, and neutrophil migration. In vivo, oral PRN473 was efficacious and well tolerated in the treatment of canine pemphigus foliaceus. In this study, we evaluated in vitro selectivity and functionality, in vivo skin Ab inflammatory responses, and systemic pharmacology with topically administered PRN473. Significant dose-dependent inhibition of IgG-mediated passive Arthus reaction in rats was observed with topical PRN473 and was maintained when given 16 h prior to challenge, reinforcing extended activity with once-daily administration. Similarly, topical PRN473 resulted in significant dose-dependent inhibition of the mouse passive cutaneous anaphylaxis IgE-mediated reaction. Multiday treatment with topical PRN473 in rodents resulted in low-to-no systemic accumulation, suggesting that efficacy was mainly due to localized exposure. Reduced skin Ab inflammatory activity was also confirmed with oral PRN473. These preclinical studies provide a strong biologic basis for targeting innate immune cell responses locally in the skin, with rapid onset of action following once-daily topical PRN473 administration and minimal systemic exposure. Dose-dependent inhibition in these preclinical models of immune-mediated skin diseases support future clinical studies.