AB0756 IMMUNE-MEDIATED BASIS FOR A PHASE 2A CLINICAL STUDY COMPARING RILZABRUTINIB VS GLUCOCORTICOIDS IN RITUXIMAB-REFRACTORY PATIENTS WITH IGG4-RELATED DISEASE

Background:

IgG4-related disease (IgG4-RD) is an immune-mediated disorder causing fibro-inflammatory lesions. Although the cause remains unknown, it may be driven by interactions between B lymphocytes and CD4+ cytotoxic and regulatory T cells and is characterized by an increase in short-lived plasmablasts, circulating antibodies, and macrophages. Standard therapy mainly includes glucocorticoids (GC), limited by toxicity with long-term use (> 6 mo), and to a lesser extent, immunosuppressives (eg, rituximab). Bruton tyrosine kinase (BTK) plays an important role in the activation of multiple immune effector cells such as B cells, mast cells, eosinophils, basophils, monocytes/macrophages, and neutrophils. Dysregulation of the activation of these immune cells results in autoimmune inflammation, tissue damage, and development of fibrosis. Rilzabrutinib is a highly selective oral BTK inhibitor that targets multiple pathways of innate and adaptive immunity (with direct effects on B-cell and FcR pathways) and has the potential to inhibit antigen presentation to autoreactive T cells.

Objectives:

To provide the biological rationale for rilzabrutinib in IgG4-RD.

Methods:

Rilzabrutinib has been evaluated in biochemical, in vitro studies, and in vivo models of inflammatory diseases. Additional support is provided by the phase 2 trial for oral rilzabrutinib in patients with pemphigus vulgaris and the phase 2 trial for oral rilzabrutinib in patients with immune thrombocytopenia (ITP).

Results:

Rilzabrutinib inhibited the activity of BTK and B-cell receptor in B cells (IC50 5-123 nM) and Fc gamma receptor in IgG/Fc gamma receptor-stimulated monocytes (IC50 56 nM) and blocked IgG- and IgM-mediated antibody production in enriched B cells when stimulated in T-cell dependent (anti-CD40+IL-21) and T-cell independent (TLR-9/CpG and TNP-LPS) pathways. The impact of rilzabrutinib on innate cell pathways was further confirmed by significant dose-dependent inhibition of macrophage and neutrophil-driven passive rat Arthus reaction (P < 0.01 vs vehicle) and antibody-induced murine ITP (P < 0.05 vs vehicle). In a 12-week phase 2 pemphigus vulgaris trial, 54% of patients achieved the primary endpoint, control of disease activity (CDA) on low-dose corticosteroids by week 4, and 73% achieved it by week 12. In the phase 2 trial of ITP patients (median 6 prior therapies), rilzabrutinib 400 mg bid showed rapid and sustained improvement in platelet counts and only grade 1/2-related adverse events1. In responders, platelet counts increased as early as day 8, potentially due to innate immune mechanisms. Collectively, results in both B and innate immune cells provide an initial basis for evaluating rilzabrutinib in IgG4-RD. The ongoing phase 2a study (NCT04520451) is investigating rilzabrutinib 400 mg bid (+tapered GC) vs GC control (3:1) for 12 weeks in IgG4-RD patients refractory to rituximab. The primary objective is to evaluate the safety and ability of rilzabrutinib to induce GC-free remission at week 12. Coupled with known preclinical/clinical findings, mechanistic analyses in this ongoing IgG4-RD study will profile B and other immune cell effects pre-/post-rilzabrutinib dosing to enhance the clinical understanding of rilzabrutinib in IgG4-RD.

Conclusion:

Studies of rilzabrutinib that show beneficial effects on both B-cell and innate cell pathways provide support for its therapeutic role in immune-mediated diseases and for targeting the underlying pathophysiological effects of IgG4-RD. Effective and safe therapies that rapidly induce and maintain clinical responses, while minimizing the need for continuous GC treatment, remain an unmet need for patients with IgG4-RD.

References:

[1]Kuter et al. Res Pract Thromb Haemost. 2020;4(suppl 1): PB1318.

Disclosure of Interests:

Li Long Employee of: Principia Biopharma, a Sanofi Company, Matthew Baker: None declared, Mollie Carruthers: None declared, Alireza Meysami: None declared, Robert Spiera Consultant of: research funding and personal fees for consulting from Chemocentryx, Formation Biologics, Roche-Genentech, and Sanofi, Grant/research support from: research funding fees from BMS, Boehringer Ingelheim, Corbus, GSK, and Inflarx; personal fees from AbbVie, CSL Behring, GSK, and Janssen, Mamatha Reddy Employee of: Principia Biopharma, a Sanofi Company, Marianne Kavanagh Employee of: Principia Biopharma, a Sanofi Company, Michelle Francesco Employee of: Principia Biopharma, a Sanofi Company, Claire Langrish Employee of: Principia Biopharma, a Sanofi Company, Ann Neale Employee of: Principia Biopharma, a Sanofi Company, Puneet Arora Employee of: Principia Biopharma, a Sanofi Company, John H. Stone Consultant of: research funding and personal fees for consulting from Principia and Sanofi

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

Background

Bruton tyrosine kinase (BTK) inhibition targets B‐cell and other non‐T‐cell immune cells implicated in the pathophysiology of pemphigus, an autoimmune disease driven by anti‐desmoglein autoantibodies. Rilzabrutinib is a new reversible, covalent BTK inhibitor demonstrating preclinical efficacy as monotherapy in canine pemphigus foliaceus.

Objectives

To evaluate the efficacy and safety of oral rilzabrutinib in patients with pemphigus vulgaris in a multicentre, proof‐of‐concept, phase II trial.

Methods

Patients with Pemphigus Disease Area Index severity scores 8–45 received 12 weeks of oral rilzabrutinib 400–600 mg twice daily and 12 weeks of follow‐up. Patients initially received between 0 and ≤ 0·5 mg kg⁻¹ prednisone‐equivalent corticosteroid (CS; i.e. ‘low dose’), tapered after control of disease activity (CDA; no new lesions, existing lesions healing). The primary endpoints were CDA within 4 weeks on zero‐to‐low‐dose CS and safety.

Results

In total, 27 patients with pemphigus vulgaris were included: nine newly diagnosed (33%) and 18 relapsing (67%); 11 had moderate disease (41%) and 16 moderate to severe (59%). The primary endpoint, CDA, was achieved in 14 patients (52%, 95% confidence interval 32–71): 11 using low‐dose CS and three using no CS. Over 12 weeks of treatment, mean CS doses reduced from 20·0 to 11·8 mg per day for newly diagnosed patients and from 10·3 to 7·8 mg per day for relapsing patients. Six patients (22%) achieved complete response by week 24, including four (15%) by week 12. Treatment‐related adverse events were mostly mild (grade 1 or 2); one patient experienced grade 3 cellulitis.

Conclusions

Rilzabrutinib alone, or with much lower CS doses than usual, was safe, with rapid clinical activity in pemphigus vulgaris. These data suggest that BTK inhibition may be a promising treatment strategy and support further investigation of rilzabrutinib for the treatment of pemphigus.

What is already known about this topic?

Standard pemphigus treatment relies on systemic high‐dose corticosteroids (CS), rituximab and/or immunosuppressives, which are limited by delayed onset of action and potential toxicities.

Immune‐mediated mechanisms that are fast acting on both the innate and adaptive immune systems, are steroid sparing, and have safety profiles well suited for chronic administration are greatly needed for patients with pemphigus.

What does this study add?

Rilzabrutinib is an oral Bruton tyrosine kinase (BTK) inhibitor targeting B‐cell and other non‐T‐cell immune cells implicated in pemphigus pathophysiology.

Treatment with rilzabrutinib (with or without low‐dose CS) demonstrated rapid disease control and a well‐tolerated safety profile in patients with newly diagnosed and relapsing pemphigus vulgaris.

BELIEVE provides evidence for a promising treatment strategy via BTK inhibition, supporting further investigation of rilzabrutinib in other immune‐mediated diseases.

Linked Comment: A.M. Drucker and N.H. Shear. Br J Dermatol 2021; 185:691–692.

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