ABBV-105, a selective and irreversible inhibitor of Bruton's tyrosine kinase, is efficacious in multiple preclinical models of inflammation

Comprehensive Characterization of Bruton's Tyrosine Kinase Inhibitor Specificity, Potency, and Biological Effects: Insights into Covalent and Noncovalent Mechanistic Signatures

Uncovering a drug's mechanism of action and possible adverse effects are critical components in drug discovery and development. Moreover, it provides evidence for why some drugs prove more effective than others and how to design better drugs altogether. Here, we demonstrate the utility of a high-throughput in vitro screening platform along with a comprehensive panel to aid in the characterization of 15 Bruton's tyrosine kinase (BTK) inhibitors that are either approved by the FDA or presently under clinical evaluation. To compare the potency of these drugs, we measured the binding affinity of each to wild-type BTK as well as a clinically relevant resistance mutant of BTK (BTK C481S). In doing so, we discovered a considerable difference in the selectivity and potency of these BTK inhibitors to the wild-type and mutant proteins. Some of this potentially contributes to the adverse effects experienced by patients undergoing therapy using these drugs. Overall, noncovalent BTK inhibitors showed stronger potency for both the wild-type and mutant BTK when compared with that of covalent inhibitors, with the majority demonstrating a higher specificity and less off-target modulation. Additionally, we compared biological outcomes for four of these inhibitors in human cell-based models. As expected, we found different phenotypic profiles for each inhibitor. However, the two noncovalent inhibitors had fewer off-target biological effects when compared with the two covalent inhibitors. This and similar in-depth preclinical characterization of drug candidates can provide critical insights into the efficacy and mechanism of action of a compound that may affect its safety in a clinical setting.

Bruton's tyrosine kinase: A promising target for treating systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic systemic autoimmune disorder involving multiple organs and systems. There is growing evidence that autoreactive B cells occupy a central role in the occurrence and progression of SLE due to their ability to generate pathogenic autoantibodies. Small molecule inhibitors targeting Bruton's tyrosine kinase (BTK), a crucial intracellular kinase regulating B cell development and function, emerge as a new strategy to treat SLE in recent years and are superior to biologic agents depleting B cells in many aspects. Supportive data obtained from lupus-prone mice preliminarily demonstrated the promising therapeutic potential of BTK inhibition. However, these BTK inhibitors, including elsubrutinib, evobrutinib, etc., mostly face with unsatisfactory efficacy and certain safety issues during clinical use, driving the quest for new-generation inhibitors with improved potency and higher selectivity. This paper elaborates the importance of BTK involvement in SLE pathogenesis, reviews the clinical research progress of BTK inhibitors for SLE and discusses limitations and challenges the drugs met in development, in order to contribute to a deeper understanding of disease mechanism and provide a reference for new-generation BTK inhibitor research.

Efficacy and Safety of Upadacitinib or Elsubrutinib Alone or in Combination for Patients With Systemic Lupus Erythematosus: A Phase 2 Randomized Controlled Trial

OBJECTIVE

The 48-week, phase 2 SLEek study (NCT03978520) evaluated the efficacy and safety of upadacitinib (JAK inhibitor) and elsubrutinib (BTK inhibitor) alone or in combination (ABBV-599) in adults with moderately to severely active systemic lupus erythematosus (SLE).

METHODS

Patients were randomized 1:1:1:1:1 to elsubrutinib 60 mg and upadacitinib 30 mg once daily (ABBV-599 high dose), elsubrutinib 60 mg and upadacitinib 15 mg once daily (ABBV-599 low dose), elsubrutinib 60 mg once daily (QD), upadacitinib 30 mg QD, or placebo QD. The primary endpoint was the proportion of patients achieving both Systemic Lupus Erythematosus Responder Index 4 (SRI-4) and glucocorticoid dose ≤10 mg QD at week 24. Additional assessments through week 48 included British Isles Lupus Assessment Group-Based Composite Lupus Assessment (BICLA) and Lupus Low Disease Activity State (LLDAS) responses, number of flares, time to first flare, and adverse events.

RESULTS

The study enrolled 341 patients. The ABBV-599 low dose and elsubrutinib arms were discontinued after a planned interim analysis showed lack of efficacy (no safety concerns). More patients achieved the primary endpoint with upadacitinib (54.8%; P = 0.028) and ABBV-599 high dose (48.5%; P = 0.081) versus placebo (37.3%). SRI-4, BICLA, and LLDAS response rates were higher for both upadacitinib and ABBV-599 high dose versus placebo at weeks 24 and 48. Flares were reduced, and time to first flare through week 48 was substantially delayed with both upadacitinib and ABBV-599 high dose versus placebo. No new safety signals were observed beyond those previously reported for upadacitinib or elsubrutinib.

CONCLUSION

Upadacitinib 30 mg alone or in combination with elsubrutinib (ABBV-599 high dose) demonstrated significant improvements in SLE disease activity and reduced flares and were well tolerated through 48 weeks.

Inhibitors of Bruton's tyrosine kinase as emerging therapeutic strategy in autoimmune diseases

Bruton's tyrosine kinase (BTK) is a cytoplasmic, non-receptor signal transducer, initially identified as an essential signaling molecule for B cells, with genetic mutations resulting in a disorder characterized by disturbed B cell and antibody development. Subsequent research revealed the critical role of BTK in the functionality of monocytes, macrophages and neutrophils. Various immune cells, among which B cells and neutrophils, rely on BTK activity for diverse signaling pathways downstream of multiple receptors, which makes this kinase an ideal target to treat hematological malignancies and autoimmune diseases. First-generation BTK inhibitors are already on the market to treat hematological disorders. It has been demonstrated that B cells and myeloid cells play a significant role in the pathogenesis of different autoimmune diseases such as multiple sclerosis, rheumatoid arthritis, systemic lupus erythematosus and primary Sjögren's syndrome. Consequently, second-generation BTK inhibitors are currently being developed to treat these disorders. Despite the acknowledged involvement of BTK in various cell types, the focus on B cells often overshadows its impact on innate immune cells. Among these cell types, neutrophils are often underestimated in the pathogenesis of autoimmune diseases. In this narrative review, the function of BTK in different immune cell subsets is discussed, after which an overview is provided of different upcoming BTK inhibitors tested for treatment of autoimmune diseases. Special attention is paid to BTK inhibition and its effect on neutrophil biology.

Safety, pharmacokinetics and pharmacodynamics of HWH486 capsules in healthy adults: A randomized, double-blind, placebo-controlled, phase I dose-escalation study

OBJECTIVES

HWH486 inhibits Bruton's tyrosine kinase and therefore shows promise as a treatment against rheumatoid arthritis and chronic spontaneous urticaria. This phase I trial assessed tolerability, safety, pharmacokinetics and pharmacodynamics of a single oral dose of HWH486 capsules in healthy adults.

METHODS

A single-center, randomized, double-blind, placebo-controlled, dose-escalation study from 10 to 800 mg was conducted in 96 healthy Chinese adults, of whom 80 received HWH486 and 16 received placebo.

RESULTS

A total of 96 subjects were enrolled, and all completed the study. In the HWH486 group, mean Tmax ranged from 1.03 to 2.00 h, and mean T1/2 ranged from 0.85 to 8.67 h across the dose range from 10 to 800 mg. Mean Cmax increased linearly with dose, while mean AUC0-t increased non-linearly. Occupancy of Bruton's tyrosine kinase peaked within 0.50-4.00 h after administration across the dose groups, and the delay until peak occupancy decreased with increasing dose. Twenty-five subjects (31.25 %) in the HWH486 group experienced 35 treatment-emergent adverse events, while four subjects (25.00 %) in the placebo group experienced eight such events.

CONCLUSIONS

HWH486 is well tolerated and safe in healthy adults, in whom it can strongly bind Bruton's tyrosine kinase. These findings justify clinical studies of HWH486 efficacy against autoimmune diseases.

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.

Bruton's tyrosine kinase inhibition suppresses neutrophilic inflammation and restores histone deacetylase 2 expression in myeloid and structural cells in a mixed granulocytic mouse model of asthma

Asthmatic inflammation is not a single homogenous inflammation but may be categorized into several phenotypes/endotypes. Severe asthma is characterized by mixed granulocytic inflammation in which there is increased presence of neutrophilic numbers and unresponsiveness to corticosteroids. Neutrophilic oxidative stress and histone deacetylase 2 (HDAC2) dysregulation in the pulmonary compartment are thought to lead to corticosteroid insensitivity in severe asthma with mixed granulocytic inflammation. Bruton's tyrosine kinase (BTK) is a no-receptor tyrosine kinase which is expressed in innate immune cells such as neutrophils and dendritic cells (DCs) where it is incriminated in balancing of inflammatory signaling. We hypothesized in this study that BTK inhibition strategy could be utilized to restore corticosteroid responsiveness in mixed granulocytic asthma. Therefore, combined therapy of BTK inhibitor (ibrutinib) and corticosteroid, dexamethasone was administered in cockroach allergen extract (CE)-induced mixed granulocyte airway inflammation model in mice. Our data show that CE-induced neutrophilic inflammation was concomitant with HDAC2 expression and upregulation of p-NFkB expression in airway epithelial cells (AECs), myeloid cells and pulmonary tissue. Further, there were increased expression/release of inflammatory and oxidative mediators such as MUC5AC, TNF-α, GM-CSF, MCP-1, iNOS, nitrotyrosine, MPO, lipid peroxides in AECs/myeloid cells/pulmonary tissue. Dexamethasone alone significantly attenuated eosinophilic inflammation and inflammatory cytokines but was not able to control oxidative inflammation. Ibrutinib alone markedly reduced neutrophilic infiltration and oxidative inflammation, and restored HDAC2 without having any significant effect on eosinophilic inflammation. These data suggest that BTK inhibition strategy may be used in conjunction with dexamethasone to treat both neutrophilic and eosinophilic inflammation, i.e. mixed granulocytic asthma.

Comparison of Intermolecular Interactions of Irreversible and Reversible Inhibitors with Bruton’s Tyrosine Kinase via Molecular Dynamics Simulations

Bruton’s tyrosine kinase (BTK) is a key protein from the TEC family and is involved in B-cell lymphoma occurrence and development. Targeting BTK is therefore an effective strategy for B-cell lymphoma treatment. Since previous studies on BTK have been limited to structure-function analyses of static protein structures, the dynamics of conformational change of BTK upon inhibitor binding remain unclear. Here, molecular dynamics simulations were conducted to investigate the molecular mechanisms of association and dissociation of a reversible (ARQ531) and irreversible (ibrutinib) small-molecule inhibitor to/from BTK. The results indicated that the BTK kinase domain was found to be locked in an inactive state through local conformational changes in the DFG motif, and P-, A-, and gatekeeper loops. The binding of the inhibitors drove the outward rotation of the C-helix, resulting in the upfolded state of Trp395 and the formation of the salt bridge of Glu445-Arg544, which maintained the inactive conformation state. Met477 and Glu475 in the hinge region were found to be the key residues for inhibitor binding. These findings can be used to evaluate the inhibitory activity of the pharmacophore and applied to the design of effective BTK inhibitors. In addition, the drug resistance to the irreversible inhibitor Ibrutinib was mainly from the strong interaction of Cys481, which was evidenced by the mutational experiment, and further confirmed by the measurement of rupture force and rupture times from steered molecular dynamics simulation. Our results provide mechanistic insights into resistance against BTK-targeting drugs and the key interaction sites for the development of high-quality BTK inhibitors. The steered dynamics simulation also offers a means to rapidly assess the binding capacity of newly designed inhibitors.

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.

Safety and efficacy of elsubrutinib or upadacitinib alone or in combination (ABBV-599) in patients with rheumatoid arthritis and inadequate response or intolerance to biological therapies: a multicentre, double-blind, randomised, controlled, phase 2 trial

BACKGROUND

ABBV-599 is a novel fixed-dose combination of the Bruton's tyrosine kinase (BTK) inhibitor elsubrutinib and the Janus kinase (JAK) inhibitor upadacitinib under investigation for the treatment of autoimmune diseases. We aimed to determine whether ABBV-599 could increase the treatment response for patients with active rheumatoid arthritis compared with inhibiting either pathway alone, while maintaining an acceptable safety profile.

METHODS

We conducted a multicentre, double-blind, parallel-group, dose-exploratory, randomised, controlled, phase 2 trial at 75 community sites in eight countries in Europe and North America. We enrolled patients who were 18 years or older with rheumatoid arthritis and inadequate response or intolerance to biological disease-modifying antirheumatic drugs. Eligible patients were randomly assigned (3:2:2:2:2:1) via interactive response technology to receive daily, orally administered ABBV-599 (ie, upadacitinib 15 mg plus elsubrutinib 60 mg), elsubrutinib 60 mg, elsubrutinib 20 mg, elsubrutinib 5 mg, upadacitinib 15 mg, or placebo. Randomisation was stratified by the number of previous biological disease-modifying antirheumatic drugs. The investigator, study site personnel, and patients were masked throughout the study. The primary endpoint was change from baseline in disease activity score of 28 joints with C-reactive protein (DAS28-CRP) at week 12 for all patients who received a study drug. Pharmacokinetics and safety were also assessed. This study is registered with ClinicalTrials.gov, number NCT03682705.

FINDINGS

Between Oct 8, 2018, and March 26, 2020, 242 patients were randomly assigned to receive ABBV-599 (n=62), elsubrutinib 60 mg (n=41), elsubrutinib 20 mg (n=39), elsubrutinib 5 mg (n=41), upadacitinib 15 mg (n=40), or placebo (n=19). Of the 242 patients, 204 (84%) were female, 38 (16%) were male, and 220 (91%) were White; the mean age at baseline was 58·0 years (SD 11·3). Compared with placebo, the least squares mean changes from baseline in DAS28-CRP were -1·44 (90% CI -2·03 to -0·85; p<0·0001) for ABBV-599, -0·40 (-1·03 to 0·23; p=0·29) for elsubrutinib 60 mg, -0·20 (-0·85 to 0·44; p=0·61) for elsubrutinib 20 mg, -0·21 (-0·84 to 0·41; p=0·57) for elsubrutinib 5 mg, and -1·75 (-2·38 to -1·13; p<0·0001) for upadacitinib. No significant improvements in efficacy measures for elsubrutinib alone (any dose) versus placebo were detected, despite adequate plasma exposure and target engagement. Treatment-emergent adverse events were observed in 113 (47%) of 242 patients, with similar proportions for all groups.

INTERPRETATION

Significant improvements in disease activity metrics of rheumatoid arthritis with ABBV-599 were driven by the JAK inhibitor upadacitinib with no discernible effect by the BTK inhibitor elsubrutinib.

FUNDING

AbbVie.

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.

The Development of BTK Inhibitors: A Five-Year Update

Bruton's tyrosine kinase (BTK) represented, in the past ten years, an important target for the development of new therapeutic agents that could be useful for cancer and autoimmune disorders. To date, five compounds, able to block BTK in an irreversible manner, have been launched in the market, whereas many reversible BTK inhibitors (BTKIs), with reduced side effects that are more useful for long-term administration in autoimmune disorders, are under clinical investigation. Despite the presence in the literature of many articles and reviews, studies on BTK function and BTKIs are of great interest for pharmaceutical companies as well as academia. This review is focused on compounds that have appeared in the literature from 2017 that are able to block BTK in an irreversible or reversible manner; also, new promising tunable irreversible inhibitors, as well as PROTAC molecules, have been reported. This summary could improve the knowledge of the chemical diversity of BTKIs and provide information for future studies, particularly from the medicinal chemistry point of view. Data reported here are collected from different databases (Scifinder, Web of Science, Scopus, Google Scholar, and Pubmed) using "BTK" and "BTK inhibitors" as keywords.

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.

Btk Inhibitors: A Medicinal Chemistry and Drug Delivery Perspective

In the past few years, Bruton’s tyrosine Kinase (Btk) has emerged as new target in medicinal chemistry. Since approval of ibrutinib in 2013 for treatment of different hematological cancers (as leukemias and lymphomas), two other irreversible Btk inhibitors have been launched on the market. In the attempt to overcome irreversible Btk inhibitor limitations, reversible compounds have been developed and are currently under evaluation. In recent years, many Btk inhibitors have been patented and reported in the literature. In this review, we summarized the (ir)reversible Btk inhibitors recently developed and studied clinical trials and preclinical investigations for malignancies, chronic inflammation conditions and SARS-CoV-2 infection, covering advances in the field of medicinal chemistry. Furthermore, the nanoformulations studied to increase ibrutinib bioavailability are reported.

The Results of Well-conducted Negative Clinical Trials Should Be Reported in a Peer-reviewed Journal

We expect that the pathogenesis, manifestations, and successful management of disease will be fully reported in peer-reviewed journals. However, there are multiple publications addressing the likelihood that clinical trials that do not report a positive result are underreported in the medical literature, with a maximum of 50% of negative studies published, even after 5 years of availability of their results1,2.

Type I Interferons in Systemic Autoimmune Diseases: Distinguishing Between Afferent and Efferent Functions for Precision Medicine and Individualized Treatment

A sustained increase in type I interferon (IFN-I) may accompany clinical manifestations and disease activity in systemic autoimmune diseases (SADs). Despite the very frequent presence of IFN-I in SADs, clinical manifestations are extremely varied between and within SADs. The present short review will address the following key questions associated with high IFN-I in SADs in the perspective of precision medicine. 1) What are the mechanisms leading to high IFN-I? 2) What are the predisposing conditions favoring high IFN-I production? 3) What is the role of IFN-I in the development of distinct clinical manifestations within SADs? 4) Would therapeutic strategies targeting IFN-I be helpful in controlling or even preventing SADs? In answering these questions, we will underlie areas of incertitude and the intertwined role of autoantibodies, immune complexes, and neutrophils.

Comparative Analysis of BTK Inhibitors and Mechanisms Underlying Adverse Effects

The cytoplasmic protein-tyrosine kinase BTK plays an essential role for differentiation and survival of B-lineage cells and, hence, represents a suitable drug target. The number of BTK inhibitors (BTKis) in the clinic has increased considerably and currently amounts to at least 22. First-in-class was ibrutinib, an irreversible binder forming a covalent bond to a cysteine in the catalytic region of the kinase, for which we have identified 228 active trials listed at ClinicalTrials.gov. Next-generation inhibitors, acalabrutinib and zanubrutinib, are approved both in the United States and in Europe, and zanubrutinib also in China, while tirabrutinib is currently only registered in Japan. In most cases, these compounds have been used for the treatment of B-lymphocyte tumors. However, an increasing number of trials instead addresses autoimmunity and inflammation in multiple sclerosis, rheumatoid arthritis, pemphigus and systemic lupus erythematosus with the use of either irreversibly binding inhibitors, e.g., evobrutinib and tolebrutinib, or reversibly binding inhibitors, like fenebrutinib. Adverse effects (AEs) have predominantly implicated inhibition of other kinases with a BTKi-binding cysteine in their catalytic domain. Analysis of the reported AEs suggests that ibrutinib-associated atrial fibrillation is caused by binding to ERBB2/HER2 and ERBB4/HER4. However, the binding pattern of BTKis to various additional kinases does not correlate with the common assumption that skin manifestations and diarrhoeas are off-target effects related to EGF receptor inhibition. Moreover, dermatological toxicities, diarrhoea, bleedings and invasive fungal infections often develop early after BTKi treatment initiation and subsequently subside. Conversely, cardiovascular AEs, like hypertension and various forms of heart disease, often persist.

Small molecule approaches to treat autoimmune and inflammatory diseases (Part I): Kinase inhibitors

Autoimmune and inflammatory diseases place a huge burden on the healthcare system. Small molecule (SM) therapeutics provide much needed complementary treatment options for these diseases. This digest series highlights the latest progress in the discovery and development of safe and efficacious SMs to treat autoimmune and inflammatory diseases with each part representing a class of SMs, namely: 1) protein kinases; 2) nucleic acid-sensing pathways; and 3) soluble ligands and receptors on cell surfaces. In this first part of the series, the focus is on kinase inhibitors that emerged between 2018 and 2020, and which exhibit increased target and tissue selectivity with the aim of increasing their therapeutic index.

Immunosuppressive agents for rheumatoid arthritis: a systematic review of clinical trials and their current development stage

Aims

With the arrival of conventional synthetic (csDMARDs), biological (bDMARDS) and then targeted synthetic (tsDMARDs) disease-modifying anti-rheumatic drugs, the therapeutic arsenal against rheumatoid arthritis (RA) has recently expanded. However, there are still some unmet needs for patients who do not achieve remission and continue to worsen despite treatments. Of note, most randomized controlled trials show that, for methotrexate-inadequate responders, only 20% of patients are ACR70 responders. With our better understanding of RA pathogenesis, finding new treatments is a necessary challenge. The objective of our study was to analyse the whole pipeline of immunosuppressive and immunomodulating drugs evaluated in RA and describe their mechanisms of action and stage of clinical development.

Methods

We conducted a systematic review of all drugs in clinical development in RA, in 17 online registries of clinical trials.

Results

The search yielded 4652 trials, from which we identified 243 molecules. Those molecules belong to csDMARDs (n = 22), bDMARDs (n = 118), tsDMARDs (n = 103). Twenty-four molecules are already marketed in RA in at least one country: eight csDMARDs, 10 bDMARDs and six tsDMARDs. Molecules under current development are mainly bDMARDs (n = 34) and tsDMARDs (n = 33). Seven of those have reached phase III. A large number of molecules (150/243, 61.7%) have been withdrawn.

Conclusion

Despite the availability of 24 marketed molecules, the development of new targeted molecules is ongoing with a total of 243 molecules in RA. With seven molecules currently reaching phase III, we can expect an increase in the armamentarium in the years to come.

Driving Potency with Rotationally Stable Atropisomers: Discovery of Pyridopyrimidinedione-Carbazole Inhibitors of BTK

Bruton's tyrosine kinase (BTK) has been shown to play a key role in the pathogenesis of autoimmunity. Therefore, the inhibition of the kinase activity of BTK with a small molecule inhibitor could offer a breakthrough in the clinical treatment of many autoimmune diseases. This Letter describes the discovery of BMS-986143 through systematic structure-activity relationship (SAR) development. This compound benefits from defined chirality derived from two rotationally stable atropisomeric axes, providing a potent and selective single atropisomer with desirable efficacy and tolerability profiles.

Discovery of BIIB068: A Selective, Potent, Reversible Bruton's Tyrosine Kinase Inhibitor as an Orally Efficacious Agent for Autoimmune Diseases

Autoreactive B cell-derived antibodies form immune complexes that likely play a pathogenic role in autoimmune diseases. In systemic lupus erythematosus (SLE), these antibodies bind Fc receptors on myeloid cells and induce proinflammatory cytokine production by monocytes and NETosis by neutrophils. Bruton's tyrosine kinase (BTK) is a non-receptor tyrosine kinase that signals downstream of Fc receptors and plays a transduction role in antibody expression following B cell activation. Given the roles of BTK in both the production and sensing of autoreactive antibodies, inhibitors of BTK kinase activity may provide therapeutic value to patients suffering from autoantibody-driven immune disorders. Starting from an in-house proprietary screening hit followed by structure-based rational design, we have identified a potent, reversible BTK inhibitor, BIIB068 (1), which demonstrated good kinome selectivity with good overall drug-like properties for oral dosing, was well tolerated across preclinical species at pharmacologically relevant doses with good ADME properties, and achieved >90% inhibition of BTK phosphorylation (pBTK) in humans.

Fenebrutinib versus Placebo or Adalimumab in Rheumatoid Arthritis: A Randomized, Double-Blind, Phase II Trial (ANDES Study)

OBJECTIVE

To evaluate fenebrutinib, an oral and highly selective non-covalent inhibitor of Bruton's tyrosine kinase (BTK), in patients with active rheumatoid arthritis (RA).

METHODS

Patients with RA and inadequate response to methotrexate (cohort 1, n=480) were randomized to fenebrutinib (50 mg once daily, 150 mg once daily, 200 mg twice daily), 40 mg adalimumab every other week, or placebo. Patients with RA and inadequate response to tumor necrosis factor inhibitors (cohort 2, n=98) received fenebrutinib (200 mg twice daily) or placebo. Both cohorts continued methotrexate therapy.

RESULTS

In cohort 1, American College of Rheumatology scores (ACR50) at week 12 were similar for fenebrutinib 50 mg once daily and placebo, and higher for fenebrutinib 150 mg once daily (28%) and 200 mg twice daily (35%) than placebo (15%) (p=0.017; p=0.0003). Fenebrutinib 200 mg twice daily and adalimumab (36%) were comparable (p=0.81). In cohort 2, more patients achieved ACR50 with fenebrutinib 200 mg twice daily (25%) than placebo (12%) (p=0.072). The most common adverse events for fenebrutinib included nausea, headache, anemia, and upper respiratory tract infections. Fenebrutinib had significant effects on myeloid and B cell biomarkers (CCL4 and rheumatoid factor). Fenebrutinib and adalimumab caused overlapping as well as distinct changes in B cell and myeloid biomarkers.

CONCLUSION

Fenebrutinib demonstrated efficacy comparable to adalimumab in patients with an inadequate response to methotrexate, and safety consistent with existing immunomodulatory therapies for RA. These data support targeting both B and myeloid cells via this novel mechanism for potential efficacy in the treatment of RA.

Design of Potent and Selective Covalent Inhibitors of Bruton's Tyrosine Kinase Targeting an Inactive Conformation

Bruton's tyrosine kinase (BTK) is a member of the TEC kinase family and is selectively expressed in a subset of immune cells. It is a key regulator of antigen receptor signaling in B cells and of Fc receptor signaling in mast cells and macrophages. A BTK inhibitor will likely have a positive impact on autoimmune diseases which are caused by autoreactive B cells and immune-complex driven inflammation. We report the design, optimization, and characterization of potent and selective covalent BTK inhibitors. Starting from the selective reversible inhibitor 3 binding to an inactive conformation of BTK, we designed covalent irreversible compounds by attaching an electrophilic warhead to reach Cys481. The first prototype 4 covalently modified BTK and showed an excellent kinase selectivity including several Cys-containing kinases, validating the design concept. In addition, this compound blocked FcγR-mediated hypersensitivity in vivo. Optimization of whole blood potency and metabolic stability resulted in compounds such as 8, which maintained the excellent kinase selectivity and showed improved BTK occupancy in vivo.

Efficacy and Pharmacodynamic Modeling of the BTK Inhibitor Evobrutinib in Autoimmune Disease Models

Because of its role in mediating both B cell and Fc receptor signaling, Bruton's tyrosine kinase (BTK) is a promising target for the treatment of autoimmune diseases such as rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). Evobrutinib is a novel, highly selective, irreversible BTK inhibitor that potently inhibits BCR- and Fc receptor-mediated signaling and, thus, subsequent activation and function of human B cells and innate immune cells such as monocytes and basophils. We evaluated evobrutinib in preclinical models of RA and SLE and characterized the relationship between BTK occupancy and inhibition of disease activity. In mouse models of RA and SLE, orally administered evobrutinib displayed robust efficacy, as demonstrated by reduction of disease severity and histological damage. In the SLE model, evobrutinib inhibited B cell activation, reduced autoantibody production and plasma cell numbers, and normalized B and T cell subsets. In the RA model, efficacy was achieved despite failure to reduce autoantibodies. Pharmacokinetic/pharmacodynamic modeling showed that mean BTK occupancy in blood cells of 80% was linked to near-complete disease inhibition in both RA and SLE mouse models. In addition, evobrutinib inhibited mast cell activation in a passive cutaneous anaphylaxis model. Thus, evobrutinib achieves efficacy by acting both on B cells and innate immune cells. Taken together, our data show that evobrutinib is a promising molecule for the chronic treatment of B cell-driven autoimmune disorders.

Merits and Pitfalls in the Characterization of Covalent Inhibitors of Bruton's Tyrosine Kinase

In vitro analysis of covalent inhibitors requires special consideration, due to the time-dependent and typically irreversible nature of their target interaction. While many analyses are reported for the characterization of a final candidate, it is less clear which are most useful in the lead optimization phase of drug discovery. In the context of identifying covalent inhibitors of Bruton's tyrosine kinase (BTK), we evaluated multiple techniques for characterizing covalent inhibitors. Several methods qualitatively support the covalent mechanism of action or support a particular aspect of interaction but were not otherwise informative to differentiate inhibitors. These include the time dependence of IC₅₀, substrate competition, mass spectrometry, and recovery of function after inhibitor removal at the biochemical and cellular level. A change in IC₅₀ upon mutation of the targeted BTK C481 nucleophile or upon removal of the electrophilic moiety of the inhibitor was not always a reliable indicator of covalent inhibition. Determination of k_inact and K_I provides a quantitative description of covalent interactions but was challenging at scale and frequently failed to provide more than the ratio of the two values, k_inact/K_I. Overall, a combination of approaches is required to assess time-dependent, covalent, and irreversible inhibitors in a manner suitable to reliably advance drug candidates.