Safety, Pharmacokinetics, and Pharmacodynamics in Healthy Volunteers Treated With GDC-0853, a Selective Reversible Bruton's Tyrosine Kinase Inhibitor

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.

Safety, pharmacokinetics, and pharmacodynamics of sofnobrutinib, a novel non-covalent BTK inhibitor, in healthy subjects: First-in-human phase I study

Bruton's tyrosine kinase (BTK) is a potential therapeutic target for allergic and autoimmune diseases. This first-in-human phase I study evaluated safety, pharmacokinetic, and pharmacodynamic profiles of sofnobrutinib (formerly AS-0871), a highly selective, orally available, non-covalent BTK inhibitor, in healthy adult subjects. Single ascending doses (SAD; 5-900 mg) and multiple ascending doses (MAD; 50-300 mg twice daily [b.i.d.] for 14 days [morning dose only on Day 14]) of sofnobrutinib were tested. In the entire study, all adverse events (AEs) were mild or moderate, and no apparent dose-proportional trend in severity or frequency was observed. No serious treatment-emergent AEs, cardiac arrythmias, or bleeding-related AEs were reported. In the SAD part, sofnobrutinib exhibited approximately dose-dependent systemic exposures up to 900 mg with rapid absorption (median time to maximum concentration of 2.50-4.00 h) and gradual decline (mean half-lives of 3.7-9.0 h). In the MAD part, sofnobrutinib showed low accumulation after multiple dosing (mean accumulation ratios of ≤1.54) and reached a steady state on ≤Day 7. Single dosing of sofnobrutinib rapidly and dose-dependently suppressed basophil and B-cell activations in ex vivo whole blood assays. Multiple dosing of sofnobrutinib achieved 50.8%-79.4%, 67.6%-93.6%, and 90.1%-98.0% inhibition of basophil activation during the dosing interval of 50, 150, and 300 mg b.i.d., respectively. Based on pharmacokinetic-pharmacodynamic analysis, half-maximal inhibitory concentration (IC50) of sofnobrutinib for basophil activation was 54.06 and 57.01 ng/mL in the SAD and MAD parts, respectively. Similarly, IC50 for B-cell activation was 187.21 ng/mL. These data support further investigation of sofnobrutinib in allergic and autoimmune diseases.

Therapeutic potential and recent progression of BTK inhibitors against rheumatoid arthritis

Rheumatoid arthritis (RA) is a complex chronic inflammatory illness that affects the entire physiology of human body. It has become one of the top causes of disability worldwide. The development and progression of RA involves a complex interplay between an individual's genetic background and various environmental factors. In order to effectively manage RA, a multidisciplinary approach is required, as this disease is complicated and its pathophysiological mechanism is not fully understood yet. In majority of arthritis patients, the presence of abnormal B cells and autoantibodies, primarily anti-citrullinated peptide antibodies and rheumatoid factor affects the progression of RA. Therefore, drugs targeting B cells have now become a hot topic in the treatment of RA which is quite evident from the recent trends seen in the discovery of various B cell receptors (BCRs) targeting agents. Bruton's tyrosine kinase (BTK) is one of these recent targets which play a role in the upstream phase of BCR signalling. BTK is an important enzyme that regulates the survival, proliferation, activation and differentiation of B-lineage cells by preventing BCR activation, FC-receptor signalling and osteoclast development. Several BTK inhibitors have been found to be effective against RA during the in vitro and in vivo studies conducted using diverse animal models. This review focuses on BTK inhibition mechanism and its possible impact on immune-mediated disease, along with the types of RA currently being investigated, preclinical and clinical studies and future prospective.

Novel and Emerging Treatments to Target Pathophysiological Mechanisms in Various Phenotypes of Multiple Sclerosis

The objective is to comprehensively review novel pharmacotherapies used in multiple sclerosis (MS) and the possibilities they may carry for therapeutic improvement. Specifically, we discuss pathophysiological mechanisms worth targeting in MS, ranging from well known targets, such as autoinflammation and demyelination, to more novel and advanced targets, such as neuroaxonal damage and repair. To set the stage, a brief overview of clinical MS phenotypes is provided, followed by a comprehensive recapitulation of both clinical and paraclinical outcomes available to assess the effectiveness of treatments in achieving these targets. Finally, we discuss various promising novel and emerging treatments, including their respective hypothesized modes of action and currently available evidence from clinical trials. SIGNIFICANCE STATEMENT: This comprehensive review discusses pathophysiological mechanisms worth targeting in multiple sclerosis. Various promising novel and emerging treatments, including their respective hypothesized modes of action and currently available evidence from clinical trials, are reviewed.

BTK signaling-a crucial link in the pathophysiology of chronic spontaneous urticaria

Chronic spontaneous urticaria (CSU) is an inflammatory skin disorder that manifests with itchy wheals, angioedema, or both for more than 6 weeks. Mast cells and basophils are the key pathogenic drivers of CSU; their activation results in histamine and cytokine release with subsequent dermal inflammation. Two overlapping mechanisms of mast cell and basophil activation have been proposed in CSU: type I autoimmunity, also called autoallergy, which is mediated via IgE against various autoallergens, and type IIb autoimmunity, which is mediated predominantly via IgG directed against the IgE receptor FcεRI or FcεRI-bound IgE. Both mechanisms involve cross-linking of FcεRI and activation of downstream signaling pathways, and they may co-occur in the same patient. In addition, B-cell receptor signaling has been postulated to play a key role in CSU by generating autoreactive B cells and autoantibody production. A cornerstone of FcεRI and B-cell receptor signaling is Bruton tyrosine kinase (BTK), making BTK inhibition a clear therapeutic target in CSU. The potential application of early-generation BTK inhibitors, including ibrutinib, in allergic and autoimmune diseases is limited owing to their unfavorable benefit-risk profile. However, novel BTK inhibitors with improved selectivity and safety profiles have been developed and are under clinical investigation in autoimmune diseases, including CSU. In phase 2 trials, the BTK inhibitors remibrutinib and fenebrutinib have demonstrated rapid and sustained improvements in CSU disease activity. With phase 3 studies of remibrutinib ongoing, it is hoped that BTK inhibitors will present an effective, well-tolerated option for patients with antihistamine-refractory CSU, a phenotype that presents a considerable clinical challenge.

A review of Bruton's tyrosine kinase inhibitors in multiple sclerosis

Bruton's tyrosine kinase (BTK) inhibitors are an emerging class of therapeutics in multiple sclerosis (MS). BTK is expressed in B-cells and myeloid cells, key progenitors of which include dendritic cells, microglia and macrophages, integral effectors of MS pathogenesis, along with mast cells, establishing the relevance of BTK inhibitors to diverse autoimmune conditions. First-generation BTK inhibitors are currently utilized in the treatment of B-cell malignancies and show efficacy in B-cell modulation. B-cell depleting therapies have shown success as disease-modifying treatments (DMTs) in MS, highlighting the potential of BTK inhibitors for this indication; however, first-generation BTK inhibitors exhibit a challenging safety profile that is unsuitable for chronic use, as required for MS DMTs. A second generation of highly selective BTK inhibitors has shown efficacy in modulating MS-relevant mechanisms of pathogenesis in preclinical as well as clinical studies. Six of these BTK inhibitors are undergoing clinical development for MS, three of which are also under investigation for chronic spontaneous urticaria (CSU), rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). Phase II trials of selected BTK inhibitors for MS showed reductions in new gadolinium-enhancing lesions on magnetic resonance imaging scans; however, the safety profile is yet to be ascertained in chronic use. Understanding of the safety profile is developing by combining safety insights from the ongoing phase II and III trials of second-generation BTK inhibitors for MS, CSU, RA and SLE. This narrative review investigates the potential of BTK inhibitors as an MS DMT, the improved selectivity of second-generation inhibitors, comparative safety insights established thus far through clinical development programmes and proposed implications in female reproductive health and in long-term administration.

Bruton's Tyrosine Kinase Inhibitors for Multiple Sclerosis Treatment: A New Frontier

Multiple sclerosis (MS) can cause significant disability to patients via relapse-associated worsening and progression independent of relapses. The causes of neuronal and myelin damage can include lymphocyte-mediated inflammation and microglial activation. Bruton's tyrosine kinase (BTK) is an enzyme that mediates B cell activation and the proinflammatory phenotype of microglia. Inhibiting BTK provides a novel therapeutic target for MS but also has a complicated pharmacology based on binding specificity, CNS penetration, half-life, and enzyme inhibition characteristics. Multiple agents are being studied in phase 3 trials, and each agent will have unique efficacy and safety profiles that must be considered individually.

A randomized, controlled single, and multiple ascending dose trial of the safety, pharmacokinetics and pharmacodynamics of SN1011 in healthy subjects

The purpose of this study was to investigate the safety, tolerability, pharmacokinetics, and pharmacodynamics of SN1011, a novel Bruton tyrosine kinase (BTK) inhibitor, and food effects in healthy subjects. In this phase I trial, subjects received single ascending doses (SADs) of SN1011 (100 to 800 mg), multiple ascending doses (MADs) of SN1011 (200 to 600 mg), or placebo q.d. Additionally, 12 subjects randomly received a single dose of SN1011 600 mg under fasting states and then fed states, vice versa. Safety was assessed per Common Terminology Criteria for Adverse Events version 5.0. Pharmacokinetic parameters were calculated by noncompartmental analysis and BTK receptor occupancy in peripheral blood monocytes was determined. Seventy-one healthy subjects were dosed in five SAD cohorts, three MAD cohorts, and one food effect cohort, with 57 receiving SN1011 and 14 receiving placebo. No serious adverse events (AEs) were reported. There was no correlation between AE occurrences and SN1011 exposure. The three most frequent AEs with SN1011 were increased blood triglycerides, decreased neutrophil count, and decreased leucocyte count. SN1011 exhibited a dose-proportional increase in maximum plasma concentration and area under the time concentration curve following single and multiple dose administrations, with an accumulation ratio of 1.5 to 2.2 after multiple dose administrations. No difference in SN1011 exposure was observed between fed states. BTK receptor occupancy remained above 83% over 24 h after single administration and remained above 80% for the MAD groups for 10 days of continuous q.d. administration. SN1011 was well-tolerated and safe after single or multiple exposures to healthy subjects, supporting further clinical development of SN1011 for treatment of autoimmune diseases.

Shared learning from a physiologically based pharmacokinetic modeling strategy for human pharmacokinetics prediction through retrospective analysis of Genentech compounds

The quantitative prediction of human pharmacokinetics (PK) including the PK profile and key PK parameters are critical for early drug development decisions, successful phase I clinical trials, and the establishment of a range of doses to enable phase II clinical dose selection. Here, we describe an approach employing physiologically based pharmacokinetic (PBPK) modeling (Simcyp) to predict human PK and to validate its performance through retrospective analysis of 18 Genentech compounds for which clinical data are available. In short, physicochemical parameters and in vitro data for preclinical species were integrated using PBPK modeling to predict the in vivo PK observed in mouse, rat, dog, and cynomolgus monkey. Through this process, the in vitro to in vivo extrapolation (IVIVE) was determined and then incorporated into PBPK modeling in order to predict human PK. Overall, the prediction obtained using this PBPK-IVIVE approach captured the observed human PK profiles of the compounds from the dataset well. The predicted Cmax was within 2-fold of the observed Cmax for 94% of the compounds while the predicted area under the curve (AUC) was within 2-fold of the observed AUC for 72% of the compounds. Additionally, important IVIVE trends were revealed through this investigation, including application of scaling factors determined from preclinical IVIVE to human PK prediction for each molecule. Based upon the analysis, this PBPK-based approach now serves as a practical strategy for human PK prediction at the candidate selection stage at Genentech.

Bruton tyrosine kinase inhibitors for multiple sclerosis

Current therapies for multiple sclerosis (MS) reduce both relapses and relapse-associated worsening of disability, which is assumed to be mainly associated with transient infiltration of peripheral immune cells into the central nervous system (CNS). However, approved therapies are less effective at slowing disability accumulation in patients with MS, in part owing to their lack of relevant effects on CNS-compartmentalized inflammation, which has been proposed to drive disability. Bruton tyrosine kinase (BTK) is an intracellular signalling molecule involved in the regulation of maturation, survival, migration and activation of B cells and microglia. As CNS-compartmentalized B cells and microglia are considered central to the immunopathogenesis of progressive MS, treatment with CNS-penetrant BTK inhibitors might curtail disease progression by targeting immune cells on both sides of the blood-brain barrier. Five BTK inhibitors that differ in selectivity, strength of inhibition, binding mechanisms and ability to modulate immune cells within the CNS are currently under investigation in clinical trials as a treatment for MS. This Review describes the role of BTK in various immune cells implicated in MS, provides an overview of preclinical data on BTK inhibitors and discusses the (largely preliminary) data from clinical trials.

Bruton's Tyrosine Kinase Inhibitors: The Next Frontier of B-Cell-Targeted Therapies for Cancer, Autoimmune Disorders, and Multiple Sclerosis

Bruton's tyrosine kinase (BTK) is an important protein belonging to the tyrosine kinase family that plays a key role in the intracellular signaling and proliferation, migration, and survival of normal and malignant B-lymphocytes and myeloid cells. Understanding the role of BTK in the B-cell signaling pathway has led to the development of BTK inhibitors (BTKi) as effective therapies for malignancies of myeloid origin and exploration as a promising therapeutic option for other cancers. Given its central function in B-cell receptor signaling, inhibition of BTK is an attractive approach for the treatment of a wide variety of autoimmune diseases that involve aberrant B-cell function including systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and multiple sclerosis (MS). Here, we review the role of BTK in different cell signaling pathways, the development of BTKi in B-cell malignancies, and their emerging role in the treatment of MS and other autoimmune disorders.

Battling BTK mutants with noncovalent inhibitors that overcome Cys481 and Thr474 mutations in Waldenström macroglobulinemia therapy: structural mechanistic insights on the role of fenebrutinib

Recently, the non-covalent Bruton tyrosine kinase (BTK) inhibitor fenebrutinib was presented as a therapeutic option with strong inhibitory efficacy against a single (C481S) and double (T474S/C481S) BTK variant in the treatment of Waldenström macroglobulinemia (WM). However, the molecular events surrounding its inhibition mechanism towards this variant remain unresolved. Herein, we employed in silico methods such as molecular dynamic simulation coupled with binding free energy estimations to explore the mechanistic activity of the fenebrutinib on (C481S) and (T474S/C481S) BTK variant, at a molecular level. Our investigations reveal that amino acid arginine contributed immensely to the total binding energy, this establishing the cruciality of amino acid residues, Arg132 and Arg156 in (C481S) and Arg99, Arg137, and Arg132 in (T474S/C481S) in the binding of fenebrutinib towards both BTK variants. The structural orientations of fenebrutinib within the respective hydrophobic pockets allowed favorable interactions with binding site residues, accounting for its superior binding affinity by 24.5% and relative high hydrogen bond formation towards (T474S/C481S) when compared with (C481S) BTK variants. Structurally, fenebrutinib impacted the stability, flexibility, and solvent accessible surface area of both BTK variants, characterized by various alterations observed in the bound and unbound structures, which proved enough to disrupt their biological function. Findings from this study, therefore, provide insights into the inhibitory mechanism of fenebrutinib at the atomistic level and reveal its high selectivity towards BTK variants. These insights could be key in designing and developing BTK mutants' inhibitors to treat Waldenström macroglobulinemia (WM).

Pirtobrutinib inhibits wild-type and mutant Bruton's tyrosine kinase-mediated signaling in chronic lymphocytic leukemia

Pirtobrutinib (LOXO-305), a reversible inhibitor of Bruton’s tyrosine kinase (BTK), was designed as an alternative strategy to treat ibrutinib-resistant disease that develops due to C481 kinase domain mutations. The clinical activity of pirtobrutinib has been demonstrated in CLL, but the mechanism of action has not been investigated. We evaluated pirtobrutinib in 4 model systems: first, MEC-1, a CLL cell line overexpressing BTK^WT, BTK^C481S, or BTK^C481R; second, murine models driven by MEC-1 overexpressing BTK^WT or BTK^C481S; third, in vitro incubations of primary CLL cells; and finally, CLL patients during pirtobrutinib therapy (NCT03740529, ClinicalTrials.gov). Pirtobrutinib inhibited BTK activation as well as downstream signaling in MEC-1 isogenic cells overexpressing BTK^WT, BTK^C481S, or BTK^C481R. In mice, overall survival was short due to aggressive disease. Pirtobrutinib treatment for 2 weeks led to reduction of spleen and liver weight in BTK^WT and BTK^C481S cells, respectively. In vitro incubations of CLL cells harboring wild-type or mutant BTK had inhibition of the BCR pathway with either ibrutinib or pirtobrutinib treatment. Pirtobrutinib therapy resulted in inhibition of BTK phosphorylation and downstream signaling initially in all cases irrespective of their BTK profile, but these effects started to revert in cases with other BCR pathway mutations such as PLCG2 or PLEKHG5. Levels of CCL3 and CCL4 in plasma were marginally higher in patients with mutated BTK; however, there was a bimodal distribution. Both chemokines were decreased at early time points and mimicked BCR pathway protein changes. Collectively, these results demonstrate that pirtobrutinib is an effective BTK inhibitor for CLL harboring wild-type or mutant BTK as observed by changes in CCL3 and CCL4 biomarkers and suggest that alterations in BCR pathway signaling are the mechanism for its clinical effects. Long-term evaluation is needed for BTK gatekeeper residue variation along with pathologic kinase substitution or mutations in other proteins in the BCR pathway.

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.

[18F]BTK-1: A Novel Positron Emission Tomography Tracer for Imaging Bruton's Tyrosine Kinase

PURPOSE

Bruton's tyrosine kinase (BTK) is a key component of B cell receptor (BCR) signaling, and as such a critical regulator of cell proliferation and survival. Aberrant BCR signaling is important in the pathogenesis of various B cell malignancies and autoimmune disorders. Here, we describe the development of a novel positron emission tomography (PET) tracer for imaging BTK expression and/or occupancy by small molecule therapeutics.

METHODS

Radiochemistry was carried out by reacting the precursor with [¹⁸F]fluoride on a GE FX-FN TracerLab synthesis module to produce [¹⁸F]BTK-1 with a 6% decay-corrected radiochemical yield, 100 ± 6 GBq/µmol molar activity, and a radiochemical purity of 99%. Following intravenous administration of [¹⁸F]BTK-1 (3.63 ± 0.59 MBq, 0.084 ± 0.05 µg), 60-min dynamic images were acquired in two xenograft models: REC-1, an efficacious mantle cell lymphoma model, and U87MG, a non-efficacious glioblastoma model. Subsequent studies included vehicle, pretreatment (10 min prior to tracer injection), and displacement (30 min post-tracer injection) studies with different reversible BTK inhibitors to examine BTK binding. Human radiation dosimetry was estimated based on PET imaging in healthy rats.

RESULTS

Uptake of [¹⁸F]BTK-1 was significantly higher in BTK expressing REC-1 tumors than non-BTK expressing U87MG tumors. Administration of BTK inhibitors prior to tracer administration blocked [¹⁸F]BTK-1 binding in the REC-1 tumor model consistent with [¹⁸F]BTK-1 binding to BTK. The predicted effective dose in humans was 0.0199 ± 0.0007 mSv/MBq.

CONCLUSION

[¹⁸F]BTK-1 is a promising PET tracer for imaging of BTK, which could provide valuable information for patient selection, drug dose determination, and improving our understanding of BTK biology in humans.

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.

Semi-Mechanistic PK/PD Modeling and Simulation of Irreversible BTK Inhibition to Support Dose Selection of Tirabrutinib in Subjects with RA

Tirabrutinib is an irreversible, small-molecule Bruton's tyrosine kinase (BTK) inhibitor, which was approved in Japan (VELEXBRU) to treat B-cell malignancies and is in clinical development for inflammatory diseases. As an application of model-informed drug development, a semimechanistic pharmacokinetic/pharmacodynamic (PK/PD) model for irreversible BTK inhibition of tirabrutinib was developed to support dose selection in clinical development, based on clinical PK and BTK occupancy data from two phase I studies with a wide range of PK exposures in healthy volunteers and in subjects with rheumatoid arthritis. The developed model adequately described and predicted the PK and PD data. Overall, the model-based simulation supported a total daily dose of at least 40 mg, either q.d. or b.i.d., with adequate BTK occupancy (> 90%) for further development in inflammatory diseases. Following the PK/PD modeling and simulation, the relationship between model-predicted BTK occupancy and preliminary clinical efficacy data was also explored and a positive trend was identified between the increasing time above adequate BTK occupancy and better efficacy in treatment for RA by linear regression.

Discovery and Preclinical Characterization of BIIB091, a Reversible, Selective BTK Inhibitor for the Treatment of Multiple Sclerosis

Multiple Sclerosis is a chronic autoimmune neurodegenerative disorder of the central nervous system (CNS) that is characterized by inflammation, demyelination, and axonal injury leading to permeant disability. In the early stage of MS, inflammation is the primary driver of the disease progression. There remains an unmet need to develop high efficacy therapies with superior safety profiles to prevent the inflammation processes leading to disability. Herein, we describe the discovery of BIIB091, a structurally distinct orthosteric ATP competitive, reversible inhibitor that binds the BTK protein in a DFG-in confirmation designed to sequester Tyr-551, an important phosphorylation site on BTK, into an inactive conformation with excellent affinity. Preclinical studies demonstrated BIB091 to be a high potency molecule with good drug-like properties and a safety/tolerability profile suitable for clinical development as a highly selective, reversible BTKi for treating autoimmune diseases such as MS.

Bruton's Tyrosine Kinase Inhibition in Multiple Sclerosis

PURPOSE OF REVIEW

Multiple sclerosis (MS) is an inflammatory disease of the central nervous system (CNS) with a chronic and often progressive disease course. The current disease-modifying treatments (DMTs) limit disease progression primarily by dampening immune cell activity in the peripheral blood or hindering their migration from the periphery into the CNS. New therapies are needed to target CNS immunopathology, which is a key driver of disability progression in MS. This article reviews Bruton's Tyrosine Kinase Inhibitors (BTKIs), a new class of experimental therapy that is being intensely evaluated in MS. We focus on the potential peripheral and central mechanisms of action of BTKIs and their use in recent clinical trials in MS.

RECENT FINDINGS

There is evidence that some BTKIs cross the blood-brain barrier and may be superior to currently available DMTs at dampening the chronic neuroinflammatory processes compartmentalized within the CNS that contribute to progressive worsening in people withMS (pwMS). Recently, evobrutinib and tolebrutinib have shown efficacy in phase II clinical trials, and there are numerous ongoing phase III clinical trials of various BTKIs in relapsing and progressive forms of MS. Results from these clinical trials will be essential to understand the efficacy and safety of BTKIs across the spectrum of MS and keydifferences between specific BTKIs when treating pwMS. Inhibition of BTK has emerged as an attractive strategy to target cells of the adaptive and innate immune system outside and within the CNS. BTKIs carry great therapeutic potential across the MS spectrum, where key pathobiology aspects seem confined to the CNS compartment.

Review of the development of BTK inhibitors in overcoming the clinical limitations of ibrutinib

Bruton's tyrosine kinase (BTK) regulates multiple important signaling pathways and plays a key role in the proliferation, survival, and differentiation of B-lineage cells and myeloid cells. BTK is a promising target for the treatment of hematologic malignancies. Ibrutinib, the first-generation BTK inhibitor, was approved to treat several B-cell malignancies. Despite the remarkable potency and efficacy of ibrutinib against various lymphomas and leukemias in the clinics, there are also some clinical limitations, such as off-target toxicities and primary/acquired drug resistance. As strategies to overcome these challenges, second- and third-generation BTK inhibitors, BTK-PROTACs, as well as combination therapies have been explored. In this review, we summarize clinical developments of the first-, second- and third-generation BTK inhibitors, as well as recent advances in BTK-PROTACs and ibrutinib-based combination therapies.

Bruton's Tyrosine Kinase Inhibition for the Treatment of Rheumatoid Arthritis

Bruton’s tyrosine kinase (BTK) inhibitors are an emerging class of drugs that inhibit B cell receptor activation, FC-γ receptor signaling, and osteoclast proliferation. Following on approval for treatment of hematologic malignancies, BTK inhibitors are now under investigation to treat a number of different autoimmune diseases, including rheumatoid arthritis (RA). While the results of BTK inhibitors in RA animal models have been promising, the ensuing human clinical trial outcomes have been rather equivocal. This review will outline the mechanisms of BTK inhibition and its potential impact on immune mediated disease, the types of BTK inhibitors being studied for RA, the findings from both preclinical and clinical trials of BTK inhibitors in RA, and directions for future research.

Next-generation Bruton's tyrosine kinase inhibitor BIIB091 selectively and potently inhibits B cell and Fc receptor signaling and downstream functions in B cells and myeloid cells

Objectives

Bruton's tyrosine kinase (BTK) plays a non-redundant signaling role downstream of the B-cell receptor (BCR) in B cells and the receptors for the Fc region of immunoglobulins (FcR) in myeloid cells. Here, we characterise BIIB091, a novel, potent, selective and reversible small-molecule inhibitor of BTK.

Methods

BIIB091 was evaluated in vitro and in vivo in preclinical models and in phase 1 clinical trial.

Results

In vitro, BIIB091 potently inhibited BTK-dependent proximal signaling and distal functional responses in both B cells and myeloid cells with IC₅₀s ranging from 3 to 106 nm, including antigen presentation to T cells, a key mechanism of action thought to be underlying the efficacy of B cell-targeted therapeutics in multiple sclerosis. BIIB091 effectively sequestered tyrosine 551 in the kinase pocket by forming long-lived complexes with BTK with t _1/2 of more than 40 min, thereby preventing its phosphorylation by upstream kinases. As a key differentiating feature of BIIB091, this property explains the very potent whole blood IC₅₀s of 87 and 106 nm observed with stimulated B cells and myeloid cells, respectively. In vivo, BIIB091 blocked B-cell activation, antibody production and germinal center differentiation. In phase 1 healthy volunteer trial, BIIB091 inhibited naïve and unswitched memory B-cell activation, with an in vivo IC₅₀ of 55 nm and without significant impact on lymphoid or myeloid cell survival after 14 days of dosing.

Conclusion

Pharmacodynamic results obtained in preclinical and early clinical settings support the advancement of BIIB091 in phase 2 clinical trials.

Efficacy, Safety, and Pharmacodynamic Effects of the Bruton's Tyrosine Kinase Inhibitor Fenebrutinib (GDC-0853) in Systemic Lupus Erythematosus: Results of a Phase II, Randomized, Double-Blind, Placebo-Controlled Trial

OBJECTIVE

Fenebrutinib (GDC-0853) is a noncovalent, oral, and highly selective inhibitor of Bruton's tyrosine kinase (BTK). The efficacy, safety, and pharmacodynamics of fenebrutinib in systemic lupus erythematosus (SLE) were assessed in this phase II, multicenter, randomized, placebo-controlled study.

METHODS

Patients who had moderately to severely active SLE while receiving background standard therapy were randomized to receive placebo, fenebrutinib 150 mg once daily, or fenebrutinib 200 mg twice daily. Glucocorticoid taper was recommended from weeks 0 to 12 and from weeks 24 to 36. The primary end point was the SLE Responder Index 4 (SRI-4) response at week 48.

RESULTS

Patients (n = 260) were enrolled from 44 sites in 12 countries, with the majority from Latin America, the US, and Western Europe. The SRI-4 response rates at week 48 were 51% for fenebrutinib 150 mg once daily (P = 0.37 versus placebo), 52% for fenebrutinib 200 mg twice daily (P = 0.34 versus placebo), and 44% for placebo. British Isles Lupus Assessment Group-based Combined Lupus Assessment response rates at week 48 were 53% for fenebrutinib 150 mg once daily (P = 0.086 versus placebo), 42% for fenebrutinib 200 mg twice daily (P = 0.879 versus placebo), and 41% for placebo. Safety results were similar across all arms, although serious adverse events were more frequent with fenebrutinib 200 mg twice daily. By week 48, patients treated with fenebrutinib had reduced levels of a BTK-dependent plasmablast RNA signature, anti-double-stranded DNA autoantibodies, total IgG, and IgM, as well as increased complement C4 levels, all relative to placebo.

CONCLUSION

While fenebrutinib had an acceptable safety profile, the primary end point, SRI-4 response, was not met despite evidence of strong pathway inhibition.

The Use of Bruton's Tyrosine Kinase Inhibitors to Treat Allergic Disorders

Purpose of review

Studies show that inhibitors of Bruton’s tyrosine kinase (BTKis), currently FDA-approved for the treatment of B cell malignancies, can prevent IgE-mediated reactions through broad inhibition of the FcεRI signaling pathway in human mast cells and basophils. This review will summarize recent data supporting the use of these drugs as novel therapies in various allergic disorders.

Recent findings

Recent studies have shown that BTKis can prevent IgE-mediated degranulation and cytokine production in primary human mast cells and basophils. Two oral doses of the second-generation BTKi acalabrutinib can completely prevent moderate passive systemic anaphylaxis in humanized mice and even protect against death during severe anaphylaxis. Furthermore, two doses of ibrutinib can reduce or eliminate skin prick test responses to foods and aeroallergens in allergic subjects. BTKis in development also show efficacy in clinical trials for chronic urticaria. Unlike other therapies targeting IgE, such as omalizumab, BTKis appear to have rapid onset and transient effects, making them ideal candidates for intermittent use to prevent acute reactions such as IgE-mediated anaphylaxis.

Summary

These studies suggest that BTKis may be capable of preventing IgE-mediated anaphylaxis, paving the way for future trials in food allergy and urticaria.

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.

Targeting Bruton tyrosine kinase using non-covalent inhibitors in B cell malignancies

B cell receptor (BCR) signaling is involved in the pathogenesis of B cell malignancies. Activation of BCR signaling promotes the survival and proliferation of malignant B cells. Bruton tyrosine kinase (BTK) is a key component of BCR signaling, establishing BTK as an important therapeutic target. Several covalent BTK inhibitors have shown remarkable efficacy in the treatment of B cell malignancies, especially chronic lymphocytic leukemia. However, acquired resistance to covalent BTK inhibitors is not rare in B cell malignancies. A major mechanism for the acquired resistance is the emergence of BTK cysteine 481 (C481)  mutations, which disrupt the binding of covalent BTK inhibitors. Additionally, adverse events due to the off-target inhibition of kinases other than BTK by covalent inhibitors are common. Alternative therapeutic options are needed if acquired resistance or intolerable adverse events occur. Non-covalent BTK inhibitors do not bind to C481, therefore providing a potentially effective option to patients with B cell malignancies, including those who have developed resistance to covalent BTK inhibitors. Preliminary clinical studies have suggested that non-covalent BTK inhibitors are effective and well-tolerated. In this review, we discussed the rationale for the use of non-covalent BTK inhibitors and the preclinical and clinical studies of non-covalent BTK inhibitors in B cell malignancies.

Bleeding by Bruton Tyrosine Kinase-Inhibitors: Dependency on Drug Type and Disease

Bruton tyrosine kinase (Btk) is expressed in B-lymphocytes, myeloid cells and platelets, and Btk-inhibitors (BTKi) are used to treat patients with B-cell malignancies, developed against autoimmune diseases, have been proposed as novel antithrombotic drugs, and been tested in patients with severe COVID-19. However, mild bleeding is frequent in patients with B-cell malignancies treated with the irreversible BTKi ibrutinib and the recently approved 2nd generation BTKi acalabrutinib, zanubrutinib and tirabrutinib, and also in volunteers receiving in a phase-1 study the novel irreversible BTKi BI-705564. In contrast, no bleeding has been reported in clinical trials of other BTKi. These include the brain-penetrant irreversible tolebrutinib and evobrutinib (against multiple sclerosis), the irreversible branebrutinib, the reversible BMS-986142 and fenebrutinib (targeting rheumatoid arthritis and lupus erythematodes), and the reversible covalent rilzabrutinib (against pemphigus and immune thrombocytopenia). Remibrutinib, a novel highly selective covalent BTKi, is currently in clinical studies of autoimmune dermatological disorders. This review describes twelve BTKi approved or in clinical trials. By focusing on their pharmacological properties, targeted disease, bleeding side effects and actions on platelets it attempts to clarify the mechanisms underlying bleeding. Specific platelet function tests in blood might help to estimate the probability of bleeding of newly developed BTKi.

Antineoplastic kinase inhibitors: A new class of potent anti-amoebic compounds

Entamoeba histolytica is a protozoan parasite which infects approximately 50 million people worldwide, resulting in an estimated 70,000 deaths every year. Since the 1960s E. histolytica infection has been successfully treated with metronidazole. However, drawbacks to metronidazole therapy exist, including adverse effects, a long treatment course, and the need for an additional drug to prevent cyst-mediated transmission. E. histolytica possesses a kinome with approximately 300–400 members, some of which have been previously studied as potential targets for the development of amoebicidal drug candidates. However, while these efforts have uncovered novel potent inhibitors of E. histolytica kinases, none have resulted in approved drugs. In this study we took the alternative approach of testing a set of twelve previously FDA-approved antineoplastic kinase inhibitors against E. histolytica trophozoites in vitro. This resulted in the identification of dasatinib, bosutinib, and ibrutinib as amoebicidal agents at low-micromolar concentrations. Next, we utilized a recently developed computational tool to identify twelve additional drugs with human protein target profiles similar to the three initial hits. Testing of these additional twelve drugs led to the identification of ponatinib, neratinib, and olmutinib were identified as highly potent, with EC₅₀ values in the sub-micromolar range. All of these six drugs were found to kill E. histolytica trophozoites as rapidly as metronidazole. Furthermore, ibrutinib was found to kill the transmissible cyst stage of the model organism E. invadens. Ibrutinib thus possesses both amoebicidal and cysticidal properties, in contrast to all drugs used in the current therapeutic strategy. These findings together reveal antineoplastic kinase inhibitors as a highly promising class of potent drugs against this widespread and devastating disease.

Every year, nearly a hundred thousand people worldwide die from infection by the intestinal parasite Entamoeba histolytica, despite the widespread availability of metronidazole as a treatment. Here we report that six anticancer drugs of the kinase inhibitor class possess potent anti-amoebic properties, with one of them killing both actively dividing parasite and its transmissible cysts. These anticancer kinase inhibitors, including the dual-purpose drug with both amoebicidal and cysticidal activities may be used to treat amoebiasis, especially in cancer patients or in life-threatening brain- and liver-infecting forms of the disease.

Small-Molecule Kinase Inhibitors for the Treatment of Nononcologic Diseases

Great successes have been achieved in developing small-molecule kinase inhibitors as anticancer therapeutic agents. However, kinase deregulation plays essential roles not only in cancer but also in almost all major disease areas. Accumulating evidence has revealed that kinases are promising drug targets for different diseases, including cancer, autoimmune diseases, inflammatory diseases, cardiovascular diseases, central nervous system disorders, viral infections, and malaria. Indeed, the first small-molecule kinase inhibitor for treatment of a nononcologic disease was approved in 2011 by the U.S. FDA. To date, 10 such inhibitors have been approved, and more are in clinical trials for applications other than cancer. This Perspective discusses a number of kinases and their small-molecule inhibitors for the treatment of diseases in nononcologic therapeutic fields. The opportunities and challenges in developing such inhibitors are also highlighted.

Fenebrutinib in H1 antihistamine-refractory chronic spontaneous urticaria: a randomized phase 2 trial

Bruton's tyrosine kinase (BTK) is crucial for FcεRI-mediated mast cell activation and essential for autoantibody production by B cells in chronic spontaneous urticaria (CSU). Fenebrutinib, an orally administered, potent, highly selective, reversible BTK inhibitor, may be effective in CSU. This double-blind, placebo-controlled, phase 2 trial (EudraCT ID 2016-004624-35 ) randomized 93 adults with antihistamine-refractory CSU to 50 mg daily, 150 mg daily and 200 mg twice daily of fenebrutinib or placebo for 8 weeks. The primary end point was change from baseline in urticaria activity score over 7 d (UAS7) at week 8. Secondary end points were the change from baseline in UAS7 at week 4 and the proportion of patients well-controlled (UAS7 ≤ 6) at week 8. Fenebrutinib efficacy in patients with type IIb autoimmunity and effects on IgG-anti-FcεRI were exploratory end points. Safety was also evaluated. The primary end point was met, with dose-dependent improvements in UAS7 at week 8 occurring at 200 mg twice daily and 150 mg daily, but not at 50 mg daily of fenebrutinib versus placebo. Asymptomatic, reversible grade 2 and 3 liver transaminase elevations occurred in the fenebrutinib 150 mg daily and 200 mg twice daily groups (2 patients each). Fenebrutinib diminished disease activity in patients with antihistamine-refractory CSU, including more patients with refractory type IIb autoimmunity. These results support the potential use of BTK inhibition in antihistamine-refractory CSU.

Safety, pharmacokinetics and pharmacodynamics of BI 705564, a highly selective, covalent inhibitor of Bruton's tyrosine kinase, in Phase I clinical trials in healthy volunteers

Aims

To evaluate the safety, pharmacokinetics and pharmacodynamics of single‐ and multiple‐rising doses (MRDs) of BI 705564 and establish proof of mechanism.

Methods

BI 705564 was studied in 2 placebo‐controlled, Phase I clinical trials testing single‐rising doses (1–160 mg) and MRDs (1–80 mg) of BI 705564 over 14 days in healthy male volunteers. Blood samples were analysed for BI 705564 plasma concentration, Bruton's tyrosine kinase (BTK) target occupancy (TO) and CD69 expression in B cells stimulated ex vivo. A substudy was conducted in allergic, otherwise healthy, MRD participants. Safety was assessed in both studies.

Results

All doses of BI 705564 were well tolerated. Geometric mean BI 705564 plasma terminal half‐life ranged from 10.1 to 16.9 hours across tested doses, with no relevant accumulation after multiple dosing. Doses ≥20 mg resulted in ≥85% average TO that was maintained for ≥48 hours after single‐dose administration. Functional effects of BTK signalling were demonstrated by dose‐dependent inhibition of CD69 expression. In allergic participants, BI 705564 treatment showed a trend in wheal size reduction in a skin prick test and complete inhibition of basophil activation. Mild bleeding‐related adverse events were observed with BI 705564; bleeding time increased in 1/12 participants (8.3%) who received placebo vs 26/48 (54.2%) treated with BI 705564.

Conclusion

BI 705564 showed efficient target engagement through durable TO and inhibition of ex vivo B‐cell activation, and proof of mechanism through effects on allergic skin responses. Mild bleeding‐related adverse events were probably related to inhibition of platelet aggregation by BTK inhibition.

Oral Bruton tyrosine kinase inhibitors block activation of the platelet Fc receptor CD32a (FcγRIIA): a new option in HIT?

Activation of the platelet Fc-receptor CD32a (FcγRIIA) is an early and crucial step in the pathogenesis of heparin-induced thrombocytopenia type II (HIT) that has not been therapeutically targeted. Downstream FcγRIIA Bruton tyrosine kinase (BTK) is activated; however, its role in Fc receptor-induced platelet activation is unknown. We explored the potential to prevent FcγRIIA-induced platelet activation by BTK inhibitors (BTKi's) approved (ibrutinib, acalabrutinib) or in clinical trials (zanubrutinib [BGB-3111] and tirabrutinib [ONO/GS-4059]) for B-cell malignancies, or in trials for autoimmune diseases (evobrutinib, fenebrutinib [GDC-0853]). We found that all BTKi's blocked platelet activation in blood after FcγRIIA stimulation by antibody-mediated cross-linking (inducing platelet aggregation and secretion) or anti-CD9 antibody (inducing platelet aggregation only). The concentrations that inhibit 50% (IC50) of FcγRIIA cross-linking-induced platelet aggregation were for the irreversible BTKi's ibrutinib 0.08 µM, zanubrutinib 0.11 µM, acalabrutinib 0.38 µM, tirabrutinib 0.42 µM, evobrutinib 1.13 µM, and for the reversible BTKi fenebrutinib 0.011 µM. IC50 values for ibrutinib and acalabrutinib were four- to fivefold lower than the drug plasma concentrations in patients treated for B-cell malignancies. The BTKi's also suppressed adenosine triphosphate secretion, P-selectin expression, and platelet-neutrophil complex formation after FcγRIIA cross-linking. Moreover, platelet aggregation in donor blood stimulated by sera from HIT patients was blocked by BTKi's. A single oral intake of ibrutinib (280 mg) was sufficient for a rapid and sustained suppression of platelet FcγRIIA activation. Platelet aggregation by adenosine 5'-diphosphate, arachidonic acid, or thrombin receptor-activating peptide was not inhibited. Thus, irreversible and reversible BTKi's potently inhibit platelet activation by FcγRIIA in blood. This new rationale deserves testing in patients with HIT.

Understanding the Effect of Hydroxypropyl-β-Cyclodextrin on Fenebrutinib Absorption in an Itraconazole-Fenebrutinib Drug-Drug Interaction Study

Cyclodextrins are widely used pharmaceutical excipients, particularly for insoluble compounds dosed orally, such as the oral solution of itraconazole, which is frequently used in clinical drug–drug interaction studies to inhibit cytochrome P450 3A. Since cyclodextrins act by forming inclusion complexes with their coformulated drug, they could have an unintended consequence of affecting absorption if they form a strong complex with the potential victim drug in an itraconazole drug–drug interaction study. This observation was made in a drug–drug interaction study with the Bruton’s tyrosine kinase (BTK) inhibitor fenebrutinib and itraconazole, in which, relative to the control group, the expected increase in fenebrutinib maximum plasma concentration (C_max) was not observed in the itraconazole group, and a delay in time to reach maximum plasma concentration (T_max) was observed in the itraconazole group. The in vitro binding constant between fenebrutinib and hydroxypropyl‐β‐cyclodextrin was determined to be 2 × 10⁵ M⁻¹, and the apparent permeability of fenebrutinib across a Madin‐Darby canine kidney cell monolayer decreased in a cyclodextrin concentration‐dependent manner. This observation was confirmed in vivo, in a pentagastrin‐pretreated dog model, in which fenebrutinib was administered with or without cyclodextrin; a reduction in C_max, a prolonged T_max, and increased fenebrutinib recovery in feces replicated the previous observation in healthy volunteers and supported the hypothesis that complexation with cyclodextrin decreased rate and extent of fenebrutinib absorption. Physiologically‐based pharmacokinetic modeling was used to translate the in vitro effect of cyclodextrin on fenebrutinib apparent permeability to the in vivo effect on absorption, which was then confirmed using the in vivo dog pharmacokinetic data.

Physiologically-Based Pharmacokinetic Model-Informed Drug Development for Fenebrutinib: Understanding Complex Drug-Drug Interactions

Fenebrutinib is a CYP3A substrate and time‐dependent inhibitor, as well as a BCRP and OATP1B transporter inhibitor in vitro. Physiologically‐based pharmacokinetic (PBPK) modeling strategies with the ultimate goal of understanding complex drug‐drug interactions (DDIs) and proposing doses for untested scenarios were developed. The consistency in the results of two independent approaches, PBPK simulation and endogenous biomarker measurement, supported that the observed transporter DDI is primarily due to fenebrutinib inhibition of intestinal BCRP, rather than hepatic OATP1B. A mechanistic‐absorption model accounting for the effects of excipient complexation with fenebrutinib was used to rationalize the unexpected observation of itraconazole‐fenebrutinib DDI (maximum plasma concentration (C_max) decreased, and area under the curve (AUC) increased). The totality of the evidence from sensitivity analysis and clinical and nonclinical data suggested that fenebrutinib is likely a sensitive CYP3A substrate. This advanced PBPK application allowed the use of model‐informed approach to facilitate the development of concomitant medication recommendations for fenebrutinib without requiring additional clinical DDI studies.

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.

Population Pharmacokinetics, Efficacy Exposure-response Analysis, and Model-based Meta-analysis of Fenebrutinib in Subjects with Rheumatoid Arthritis [corrected]

Purpose

Fenebrutinib (GDC-0853), a Bruton’s tyrosine kinase (BTK) inhibitor was investigated in a Phase 2 clinical trial in patients with rheumatoid arthritis (RA). Our aim was to apply a model-informed drug development (MIDD) approach to examine the totality of available clinical efficacy data.

Methods

Population pharmacokinetics (popPK) modeling, exposure-response (E-R) analysis, and model-based meta-analysis (MBMA) of fenebrutinib were performed based on the Phase 2 data.

Results

PopPK of fenebrutinib after oral administration was described using a 3-compartment model with linear elimination and a flexible absorption transit compartment model. Healthy subjects had a 52% higher apparent clearance than patients. E-R analyses based on longitudinal ACR20, ACR50, and ACR70 and DAS28 (CRP) data modeled fenebrutinib effect with an E_max function, and an efficacy plateau was achieved within the exposure range obtained in the Phase 2 clinical trial. Based on literature data, a summary-level clinical efficacy database was constructed, and MBMA determined ACR20, ACR50, and ACR70 responder rates in the placebo and adalimumab arms of the Phase 2 clinical trial were found to be consistent with historical data for these treatments.

Conclusions

Our multi-pronged approach applied MIDD to maximize knowledge extraction of efficacy data and enabled robust interpretation from a Phase 2 clinical trial.

Electronic supplementary material

The online version of this article (10.1007/s11095-019-2752-y) contains supplementary material, which is available to authorized users.

Complex DDI by Fenebrutinib and the Use of Transporter Endogenous Biomarkers to Elucidate the Mechanism of DDI

Mechanistic understanding of complex clinical drug-drug interactions (DDIs) with potential involvement of multiple elimination pathways has been challenging, especially given the general lack of specific probe substrates for transporters. Here, we conducted a clinical DDI study to evaluate the interaction potential of fenebrutinib using midazolam (MDZ; CYP3A), simvastatin (CYP3A and OATP1B), and rosuvastatin (BCRP and OATP1B) as probe substrates. Fenebrutinib (200 mg) increased the area under the curve (AUC) of these probe substrates twofold to threefold. To evaluate the mechanism of the observed DDIs, we measured the concentration of coproporphyrin I (CP-I) and coproporphyrin III (CP-III), endogenous biomarkers of OATP1B. There was no change in CP-I or CP-III levels with fenebrutinib, suggesting that the observed DDIs were caused by inhibition of CYP3A and BCRP rather than OATP1B, likely due to increased bioavailability. This is the first published account using an endogenous transporter biomarker to understand the mechanism of complex DDIs involving multiple elimination pathways.

Current and emerging treatments for chronic spontaneous urticaria

OBJECTIVE

To review the published literature on current and new treatments for chronic spontaneous urticaria (CSU) and to provide guidance on the potential use of these therapeutics.

DATA SOURCES

A PubMed search was performed to include English-language articles with the keywords chronic spontaneous urticaria, pathophysiology, quality of life, and treatments, with a preference to those articles written in the last 5 years. ClinicalTrials.gov was reviewed for recent relevant clinical trials related to potential CSU therapeutics.

STUDY SELECTIONS

Literature was included if it provided information related to the current understanding of the pathophysiology and management of CSU as well as potential novel therapeutics currently in development.

RESULTS

CSU has a significant effect on patients' quality of life. Current therapies include antihistamines, leukotriene receptor antagonists, omalizumab, and immunosuppressants; however, additional treatments are needed. New therapeutics under investigation include IgG1 anti-IgE monoclonal antibodies (ligelizumab), chemoattractant rector-homologous molecule expressed on T_H2 cells antagonists (AZD1981), Bruton tyrosine kinase inhibitors (fenebrutinib), anti-siglec-8 monoclonal antibody (AK002), and topical spleen tyrosine kinase inhibitors (GSK2646264). We review the mechanisms of action as well as recently published data from clinical trials regarding the efficacy and safety of these treatments.

CONCLUSION

The development of new treatments for CSU will lead to improved options for patients and may assist with improving our understanding of disease pathophysiology.

Absence of Pharmacokinetic Interactions between the Bruton's Tyrosine Kinase Inhibitor Fenebrutinib and Methotrexate

Fenebrutinib (GDC-0853) is an orally administered small molecule inhibitor of Bruton's tyrosine kinase being investigated for treatment of rheumatoid arthritis in patients with inadequate responses to methotrexate (MTX). This study interrogated the potential for pharmacokinetic drug interactions between fenebrutinib and MTX. Eighteen healthy male subjects were enrolled in the study. They received a single oral dose of MTX (7.5 mg) on day 1 followed by a 13-day washout period. Subsequently, on days 15-20 the participants received 200 mg of fenebrutinib twice daily. On day 21, they received a 7.5 mg dose of MTX and a 200 mg dose of fenebrutinib under fasting conditions. The geometric mean ratios of MTX area under the plasma concentration-time curve (AUC) and C _max on day 21 relative to day 1 (90% confidence interval [CI]) were 0.96 (0.88-1.04) and 1.05 (0.94-1.18), respectively. The geometric mean ratios of fenebrutinib AUC and C _max for day 21 relative to day 20 (90% CI) were 1.03 (0.95-1.11) and 1.02 (0.90-1.15), respectively. The combination treatment was well tolerated, with an adverse event profile similar to that reported in other MTX trials. These results indicate that there is no clinically significant pharmacokinetic interaction between fenebrutinib and MTX.

Pharmacokinetic-pharmacodynamic models that incorporate drug-target binding kinetics

Pharmacokinetic/pharmacodynamic (PK/PD) models predict the effect time course resulting from a drug dose. In this review, we summarize the development of mechanistic PK/PD models that explicitly integrate the kinetics of drug-target interactions into predictions of drug activity. Such mechanistic models are expected to have several advantages over approaches in which concentration and effect are linked using variations of the Hill equation, and where preclinical data are often used as a starting point for modeling drug activity. Instead, explicit use of the full kinetic scheme for drug binding enables time-dependent changes in target occupancy to be calculated using the kinetics of drug-target interactions and drug PK, providing a more precise picture of target engagement and drug action in the non-equilibrium environment of the human body. The mechanistic PK/PD models also generate target vulnerability functions that link target occupancy and effect, and inform on the sensitivity of a target to engagement by a drug. Key factors such as the rate of target turnover can also be integrated into the modeling which, together with target vulnerability, provide additional information on the PK profile required to achieve the desired pharmacological effect and on the utility of kinetic selectivity in developing drugs for specific targets.

From Biology to Therapy: The CLL Success Story

Chemoimmunotherapy has been the standard of care for patients with chronic lymphocytic leukemia (CLL) over the last decade. Advances in monoclonal antibody technology have resulted in the development of newer generations of anti-CD20 antibodies with improved therapeutic effectiveness. In parallel, our knowledge about the distinctive biological characteristics of CLL has progressively deepened and has revealed the importance of B-cell receptor (BCR) signaling and upregulated antiapoptotic proteins for survival and expansion of malignant cell clones. This knowledge provided the basis for development of novel targeted agents that revolutionized treatment of CLL. Ibrutinib and idelalisib inhibit the Bruton tyrosine kinase (BTK) and phosphoinositide 3-kinase (PI3K) delta, respectively, thus interfering with supportive signals coming from the microenvironment via the BCR. These drugs induce egress of CLL cells from secondary lymphoid organs and remarkably improve clinical outcomes, especially for patients with unmutated immunoglobulin heavy-chain genes or with p53 abnormalities that do not benefit from classical treatment schemes. Latest clinical trial results have established ibrutinib with or without anti-CD20 antibodies as the preferred first-line treatment for most CLL patients, which will reduce the use of chemoimmunotherapy in the imminent future. Further advances are achieved with venetoclax, a BH3-mimetic that specifically inhibits the antiapoptotic B-cell lymphoma 2 protein and thus causes rapid apoptosis of CLL cells, which translates into deep and prolonged clinical responses including high rates of minimal residual disease negativity. This review summarizes recent advances in the development of targeted CLL therapies, including new combination schemes, novel BTK and PI3K inhibitors, spleen tyrosine kinase inhibitors, immunomodulatory drugs, and cellular immunotherapy.

Emerging Therapies in Chronic Spontaneous Urticaria

Chronic spontaneous urticaria (CSU) is characterized by typically short-lived and fleeting wheals, angioedema or both, which occur spontaneously and persist for longer than 6 weeks. This term is applied to the most common subtype of chronic urticaria. The underlying pathophysiology for CSU involves mast cell and basophil degranulation with release of histamine, leukotrienes, prostaglandins and other inflammatory mediators. Although a variety of treatments exist, many patients do not tolerate or benefit from the existing therapies and even require more effective treatments. Omalizumab is currently the only licensed biologic for antihistamine-refractory CSU, and novel drugs are under development. This article reviews its current status regarding pathogenesis and approach to treatment as well as therapeutic agents that are under development for the treatment of CSU.