Bruton's Tyrosine Kinase Inhibitor Research Articles

CNS Aspergillosis and Cryptococcosis with Cytomegalovirus Pneumonia in a Patient with Chronic Lymphocytic Leukemia Treated with Acalabrutinib.

Bruton's tyrosine kinase inhibitors (BTKis) are the preferred treatment for chronic lymphocytic leukemia (CLL). Despite their therapeutic benefits, these targeted agents have been associated with an increased risk of invasive infections. We describe a 68-year-old male who developed multiple bacterial, fungal and viral infections while on treatment with acalabrutinib. To our knowledge, this is the first reported case of concomitant CNS infections with Cryptococcus neoformans and Aspergillus fumigatus, along with cytomegalovirus (CMV) and herpes simplex virus type 1 (HSV-1) pneumonia while on acalabrutinib. This case adds to the scarce literature of fungal and bacterial infections associated with acalabrutinib, raising the suspicion that infection risk is a medication class effect for BTKis.

Richter transformation acquiring PLCG2 mutation during Bruton tyrosine kinase inhibitors treatment

Richter transformation acquiring <i>PLCG2</i> mutation during Bruton tyrosine kinase inhibitors treatment

Investigating bleeding adverse events associated with BTK inhibitors in the food and drug administration adverse event reporting system (FAERS)

ABSTRACT Background This study analyzed the bleeding adverse events (AEs) resulting from the treatment of B-cell lymphoma with Bruton tyrosine kinase (BTK) inhibitors, according to reports in the US Food and Drug Administration’s Adverse Event Reporting System (FAERS) Methods Bleeding AEs associated with BTK inhibitors (including ibrutinib, zanubrutinib, and acalabrutinib) from the first quarter of 2013 to the third quarter of 2023 were extracted. Reporting odds ratio (ROR) and proportional reporting ratio (PRR) were reported. Preferred Terms (PTs) of Medical Dictionary for Regulatory Activities (MedDRA) terms were mapped to System Organ Class terms (SOC) terms and analyzed bleeding AEs associated with three BTK inhibitors. Results A total of 463 cases of bleeding AEs were included. Contusion, subcutaneous hemorrhage, hematuria, and cerebral hemorrhage were included in PTs. Blood urine was present and subdural hematoma were also reported. The incidence of bleeding AEs was higher with ibrutinib (Case number = 10,696) than with zanubrutinib (Case number = 213) and acalabrutinib (Case number = 314). Conclusion Our findings indicate that bleeding AEs linked to BTK inhibitors in various conditions underscore the need for cautious clinical decision-making, particularly in nervous system disorders, injuries, poisoning, surgical complications, vascular disorders, and others.

Development of combination therapies with BTK inhibitors and dasatinib to treat CNS-infiltrating E2A-PBX1+/preBCR+ ALL

The t(1;19) translocation, which codes for the oncogenic fusion protein E2A (TCF3)-PBX1, is involved in acute lymphoblastic leukemia (ALL) and associated with a pre-B cell receptor (preBCR+) phenotype. Relapse in E2A-PBX1+ ALL patients frequently occurs in the central nervous system (CNS). Therefore, there is a medical need for the identification of CNS active regimens for the treatment of E2A-PBX1+/preBCR+ ALL.Using unbiased shRNA library screening approaches, we identified Bruton's tyrosine kinase (BTK) as a key gene involved in both proliferation and dasatinib sensitivity of E2A-PBX1+/preBCR+ ALL. Depletion of BTK by shRNAs resulted in decreased proliferation of dasatinib-treated E2A-PBX1+/preBCR+ cells compared with control-transduced cells. Moreover, combination of dasatinib with BTK inhibitors (BTKi) (ibrutinib, acalabrutinib or zanubrutinib) significantly decreased E2A-PBX1+/preBCR+ human and murine cell proliferation, reduced PLCG2 and BTK phosphorylation and total protein levels and increased disease-free survival of mice in secondary transplantation assays, reducing particularly CNS-leukemic infiltration. Hence, dasatinib with ibrutinib reduced pPLCG2 and pBTK in primary ALL patient samples, including E2A-PBX1+ ALLs.In summary, genetic depletion and pharmacological inhibition of BTK increase dasatinib effects in human and mouse E2A-PBX1+/preBCR+ ALL in most of performed assays, and the combination of dasatinib and BTKi is very effective in reducing CNS-infiltration of E2A-PBX1+/preBCR+ ALL cells in vivo.

A phase 2, open-label study of ibrutinib plus rituximab in Japanese patients with Waldenstrom's macroglobulinemia.

Ibrutinib is a first-in-class Bruton kinase inhibitor against B-cell neoplasms including Waldenström macroglobulinemia (WM). This study evaluated the efficacy and safety of ibrutinib-rituximab in Japanese patients with WM. Patients received ibrutinib 420mg orally once daily plus weekly rituximab 375mg/m2 IV (8 infusions total). The primary end point was major response rate (MRR; PR or better) by Independent Review Committee assessment. Secondary endpoints were progression-free survival (PFS), safety, pharmacokinetics, and biomarkers. Primary analysis was conducted in 16 patients [baseline, treatment naïve: 8 (50.0%); relapsed/refractory WM: 8 (50.0%)] who received ibrutinib-rituximab, after all patients completed Week 57 or end of treatment. At primary analysis, MRR was 87.5% [14/16 patients; 95% CI: 61.7, 98.4%; p < 0.0001 (null hypothesis: 32% response rate)]. At final analysis (median study intervention duration: 34.4months, median follow-up: 35.0months), MRR was unchanged at 87.5%, but VGPR [6/16 (37.5%)] and PR [8/16 (50.0%)] improved. Prior treatment status did not affect response. At final analysis, median PFS was not reached [36-month PFS rate: 86% (95% CI: 55, 96%)]. No critical safety signals were reported. This study demonstrated a positive benefit/risk profile of ibrutinib-rituximab in Japanese patients with WM, consistent with the iNNOVATE study.

BTK inhibitor falters in multiple sclerosis trials.

BTK inhibitor falters in multiple sclerosis trials.

Abstract CT147: Phase I clinical study of Bruton’s tyrosine kinase inhibitor (BTKi) HBW-3220 capsules in patients with relapsed/refractory (R/R) B-cell non-Hodgkin lymphoma (B-NHL)

Abstract Purpose: This clinical study is to evaluate HBW-3220, a novel reversible BTK inhibitor (BTKi) with an improved in vitro profile than the existing non-covalent drugs pirtobrutinib (LOXO-305, approved) and MK-1026 (Phase III). HBW-3220 shows superior inhibition against BTK wild-type and several common mutants, such as C481S, C481R, T474I, T316A, and L528W (the one predominantly enriched in patients resistant to the newer-generation BTKis), and hematopoietic cell kinase (HCK), a key contributor to the development of ibrutinib resistance associated with kinase-defective BTK. Methods: This phase I clinical study was conducted in R/R B-NHL patients who had received two or more prior lines of treatments. The dose escalation study adopts accelerated titration and a "3+3" design, with a daily single dose of 15, 30, 60, 90, 120, or 150 mg. During the dose escalation phase, the sponsor and investigators determined whether to expand the cohort of the previous dose based on the existing data. Adverse events (AEs) were assigned according to NCI Common Terminology Criteria for Adverse Events (CTCAE) v5.0. Response assessment was based on the iwCLL 2018 guidelines, the IWWM-7 consensus, or the Lugano 2014 guidelines, according to the respective disease type. Results: 28 patients have been enrolled so far, and the dose escalation study has been completed. No dose-limiting toxicity (DLT) occurred in any patient, implicating good tolerability. Adverse events (AEs), similar to other BTKis, were mostly Grade 1 or 2, including fever (38%), diarrhea (35%), headache (19%), anemia (42%), infectious pneumonia (23%), decreased neutrophils (42%), decreased platelet count (27%), increased alanine aminotransferase (23%), etc. Drug-related Grade 3 AEs included neutrophil count decreased (n=3, 11%), increased lymphocyte count (n=2, 7%), and infectious pneumonia (n=2, 7%). 21 patients underwent at least 1 response assessment (4 chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL); 4 marginal zone lymphoma (MZL); 5 mantle cell lymphoma (MCL); 3 diffuse large B-cell lymphoma (DLBCL); 5 other B-NHL), and the results are 1 complete response (CR), 6 partial response (PR), and 1 partial response with lymphocytosis (PR-L). The overall response rate (ORR) in CLL/SLL (all with prior irreversible BTKi treatment, and 2 of them with additional BCL2 inhibitor treatment), MZL, MCL, and DLBCL patients were 75% (3/4, including 1 PR-L), 50% (2/4), 40% (2/5) and 33% (1/3), respectively. Among the ORR (including CR, PR, and PR-L), 88% (7/8) were in the 90 mg and above dose group, regardless of previous BTKi treatment history or mutation status of p53 and BTK C481S. In the 90 mg and above dose group, the ORR is 47%. After oral administration, the drug exposures showed dose-dependent increases. The time to maximum plasma concentration (Tmax) was 2 hours, and the elimination half-life (T1/2) was 19 hours. Conclusions: The current data show that HBW-3220 is well tolerated, showing no DLT occurred at daily doses up to 150 mg, and has good efficacy in patients with CLL/SLL, MZL, and MCL. Citation Format: Ning Lee, Yingfu Li, Yong Mao, Guanfeng Liu, Jiang Li, Qingchun Liu. Phase I clinical study of Bruton’s tyrosine kinase inhibitor (BTKi) HBW-3220 capsules in patients with relapsed/refractory (R/R) B-cell non-Hodgkin lymphoma (B-NHL) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT147.

The effect of Bruton’s tyrosine kinase (BTK) inhibitor in the eosinophilic asthma model of mouse

Bruton’s Tyrosine kinase (BTK) plays a pivotal role as the key mediator in B cell signaling. Recent research has revealed that it is also expressed in cells critical to asthma development, such as T cells, and eosinophils. This study aims to investigate the potential of BTK inhibitor in eosinophilic asthma mouse model. BALB/c mice were sensitized with ovalbumin (OVA) via intraperitoneal injections and followed by OVA nebulizations. The mice were treated with 250 µg/ml or 500 µg/ml of ibrutinib before the second intraperitoneal injection and the first nebulization. Two days after the last OVA challenge, airway hyperresponsiveness (AHR) was assessed with methacholine, and differential cell count in bronchoalveolar lavage fluid (BALF) was performed. The cytokines were measured in BALF, and serum OVA-specific IgE and IgG antibody levels were evaluated by ELISA. The inhibitory effect of ibrutinib was also evaluated in splenic mononuclear cells, mast cells, eosinophils, and T cells in vitro. Treatment with ibrutinib significantly attenuated AHR and airway inflammation, compared to the OVA-induced positive control. The treatment also reduced IL-4, IL-5, IL-13 and IFN-γ cytokine levels and suppressed OVA-specific IgE and IgG production compared to the OVA-induced positive control. Additionally, ibrutinib decreased beta-hexosaminidase release from mast cells, type 2 cytokine productions from mononuclear cells and T cells, and eosinophilic activation markers in vitro. The results of this study suggest that ibrutinib treatment could exert anti-allergic effects by inactivating B cells and other BTK-expressing cells. Further studies are needed to investigate the potential therapeutic effect of ibrutinib on allergic diseases.

Latest Phase 3 Findings on Evobrutinib Raise Questions About the Future of BTK Inhibitors for Multiple Sclerosis

Latest Phase 3 Findings on Evobrutinib Raise Questions About the Future of BTK Inhibitors for Multiple Sclerosis

IκBε deficiency accelerates disease development in chronic lymphocytic leukemia.

The NFKBIE gene, which encodes the NF-κB inhibitor IκBε, is mutated in 3-7% of patients with chronic lymphocytic leukemia (CLL). The most recurrent alteration is a 4-bp frameshift deletion associated with NF-κB activation in leukemic B cells and poor clinical outcome. To study the functional consequences of NFKBIE gene inactivation, both in vitro and in vivo, we engineered CLL B cells and CLL-prone mice to stably down-regulate NFKBIE expression and investigated its role in controlling NF-κB activity and disease expansion. We found that IκBε loss leads to NF-κB pathway activation and promotes both migration and proliferation of CLL cells in a dose-dependent manner. Importantly, NFKBIE inactivation was sufficient to induce a more rapid expansion of the CLL clone in lymphoid organs and contributed to the development of an aggressive disease with a shortened survival in both xenografts and genetically modified mice. IκBε deficiency was associated with an alteration of the MAPK pathway, also confirmed by RNA-sequencing in NFKBIE-mutated patient samples, and resistance to the BTK inhibitor ibrutinib. In summary, our work underscores the multimodal relevance of the NF-κB pathway in CLL and paves the way to translate these findings into novel therapeutic options.

Challenges associated with the use of Bruton's tyrosine kinase inhibitors: A life‑saving therapy for chronic lymphocytic leukemia (Review)

Challenges associated with the use of Bruton's tyrosine kinase inhibitors: A life‑saving therapy for chronic lymphocytic leukemia (Review)

498 Bruton’s tyrosine kinase (BTK) inhibitors impede platelet aggregation but not adhesion to collagen.

OBJECTIVES/GOALS: The research objectives of this project are to elucidate the effects of Bruton’s tyrosine kinase inhibitors (BTKi) of varying target specificity on platelet function with regard to platelet aggregation, adhesion, spreading, and intracellular signaling as measured by kinase phosphorylation. METHODS/STUDY POPULATION: Blood from healthy volunteers was obtained and processed to obtain both washed platelets and platelet-rich plasma. The samples were then treated with one of the BTKi drugs or with vehicle (DMSO) at concentrations matching patient blood concentrations derived from clinical trials and pharmacokinetic studies. The incubated samples were then analyzed in an aggregometer using one of several agonists. Aggregation was stopped after five minutes with a perchloric acid-based lysis buffer. The samples were then analyzed by SDS-PAGE and immunoblotting to quantify BTK protein and BTK phosphorylation. Adhesion was assessed by incubating washed platelets treated with BTKi on microtiter wells coated with fibrinogen or collagen and quantifying adherent platelets by their endogenous acid phosphatase activity. RESULTS/ANTICIPATED RESULTS: We found that ibrutinib, zanubrutinib, and pirtobrutinib all completely inhibited collagen-induced platelet aggregation, whereas they did not inhibit aggregation induced by thrombin, ristocetin, arachidonic acid, or the PAR1 activator peptide SFLLRN (T6). Acalabrutinib inhibited collagen-induced platelet aggregation only at high concentrations (1-2 micromolar). At the lower concentration of 200 nanomolar, comparable to the concentration required for the other BTK inhibitors to completely inhibit platelet aggregation, acalabrutinib failed to inhibit aggregation but did inhibit auto-phosphorylation, indicating an impact on signaling. None of the BTKi drugs inhibited adhesion of platelets to collagen-coated surfaces. DISCUSSION/SIGNIFICANCE: Our data show the inhibitory effect of BTKi on collagen-induced platelet aggregation and signaling. However, it remains unclear whether the inhibition is due to an effect on BTK itself or other related kinases. Better insight into the mechanisms of platelet inhibition by BTKi may help guide the development of BTKi with a lower risk of hemorrhage.

Brentuximab Vedotin Plus Ibrutinib in Relapsed and Refractory Hodgkin Lymphoma

IntroductionBrentuximab vedotin (BV) is an antibody-drug conjugate that delivers monomethyl auristatin E (MMAE) to CD30+ cells and is safe and effective in relapsed/refractory (r/r) Hodgkin lymphoma (HL). Although most patients respond to BV, only a minority will obtain a complete response (CR), and almost all patients eventually progress.Ibrutinib is a Bruton's tyrosine kinase (BTK) inhibitor highly active in multiple subtypes of non-Hodgkin lymphoma; limited data exist regarding its use in HL. It irreversibly inhibits interleukin-2-inducible kinase (ITK) with Th1 based immune responses. As we previously observed preclinical synergy between ibrutinib and BV, we hypothesized ibrutinib may enhance the antitumor activity of BV in HL. We designed and conducted a phase II trial of ibrutinib plus BV in patients with R/R HL, and herein report the final primary analysis of safety and efficacy. MethodsThis was a multicenter phase II trial with a lead-in cohort in patients with r/r HL. Eligibility criteria included age ≥ 15 years with r/r HL after at least one prior line of therapy. Treatment consisted of 1.8 mg/kg BV intravenously every 3 weeks and ibrutinib 560 mg PO daily (420 mg PO daily in the lead-in cohort). Prior BV was allowed if patients were not refractory. The primary endpoint was the CR rate according to Lugano 2014. Secondary endpoints included toxicities, overall response rate (ORR), and duration of response (DOR). Results39 patients were enrolled onto the study, of which 67% were male; the median age was 33 (range: 17-71). 38% had extranodal disease at baseline, 51% had advanced stage disease, 51% were refractory to the prior therapy, and 21% had prior BV. Of 36 patients who were evaluable for response, the CR rate was 33% and ORR 64%; median DOR was 25.5 months. 13 patients proceeded to autologous transplant and 3 patients proceeded to allogeneic transplant for consolidation after response. The most common adverse events were nausea (67%), peripheral neuropathy (62%), diarrhea (59%), fatigue (46%), thrombocytopenia (46%), headache (41%), rash (41%), elevated ALT (38%), anemia (36%), vomiting (36%), abdominal pain (33%), fever (33%), and hypertension (33%). Six patients experienced unacceptable toxicity, defined as Gr 3/4 non-hematologic toxicity or non-resolving Gr 3/4 hematologic toxicity including one patient who died of multiorgan failure from suspected COVID-19 infection during cycle 1. DiscussionThe combination of BV and ibrutinib was active in r/r HL; however, given significant toxicity, it cannot be recommended for future development. MicroAbstractBrentuximab vedotin (BV) is highly active in Hodgkin lymphoma (HL) and is approved as monotherapy for relapsed/refractory (r/r) disease; nonetheless, depth and duration of response to BV monotherapy are limited. Ibrutinib is a Bruton's tyrosine kinase (BTK) inhibitor but also inhibits other tyrosine kinases including interleukin-2-inducible kinase (ITK) and has multiple immunomodulatory effects. We conducted a phase II trial (NCT02744612) of BV with ibrutinib in patients with r/r HL and enrolled 39 patients, 36 of whom were evaluable for response. The primary endpoint was CR with a promising rate considered to be 50%. The median follow-up time was 29.4 months, and the CR rate was 33% and ORR 64%; 2-year OS and PFS were 92% and 36%, respectively while the 2-year CIR was 64%. 6 patients experienced unacceptable toxicity defined as grade 3+ non-hematologic toxicity or grade 3+ hematologic toxicity not resolving to grade 1-2 within 7 days. Ultimately, combination therapy did not appear to be more effective than BV monotherapy but conferred additional toxicity.

A multicenter study of venetoclax-based treatment for patients with Richter transformation of chronic lymphocytic leukemia

AbstractPatients with chronic lymphocytic leukemia (CLL) who develop Richter transformation (RT) have a poor prognosis when treated with chemoimmunotherapy regimens used for de novo diffuse large B-cell lymphoma. Venetoclax, a B-cell lymphoma 2 protein inhibitor, has single-agent efficacy in patients with RT and is potentially synergistic with chemoimmunotherapy. In this multicenter, retrospective study, we evaluated 62 patients with RT who received venetoclax-based treatment outside of a clinical trial, in combination with a Bruton tyrosine kinase inhibitor (n = 28), R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone; n = 13), or intensive chemoimmunotherapy other than R-CHOP (n = 21). The best overall and complete response rates were 36% and 25%, 54% and 46%, and 52% and 38%, respectively. The median progression-free and overall survival estimates for the same treatment groups were 4.9 and 14.3 months, 14.9 months and not reached, and 3.3 and 9 months, respectively. CLL with del(17p) was associated with a lower complete response rate in the total cohort (odds ratio [OR], 0.15; 95% confidence interval [CI], 0.04-0.6; P = .01) and venetoclax-naïve subgroup (OR, 0.13; 95% CI, 0.02-0.66; P = .01). TP53-mutated CLL was associated with a lower complete response rate (OR, 0.15; 95% CI, 0.03-0.74; P = .02) and shorter progression-free survival (hazard ratio, 3.1; 95% CI, 1.21-7.95; P = .02) only in the venetoclax-naïve subgroup. No other clinical or baseline characteristics, including prior venetoclax treatment for CLL, showed statistically significant association with outcomes. Grade 3/4 neutropenia and thrombocytopenia events were most frequent with intensive chemoimmunotherapy + venetoclax; grade 3/4 infection rates were similar across treatment groups. In this difficult-to-treat patient population with RT, venetoclax-based combination regimens achieved high response rates, with durable remission and survival observed in a subset of patients.

Mouse models of CLL: in vivo modeling of disease initiation, progression, and transformation to Richter transformation

Chronic lymphocytic leukemia (CLL) is a highly complex disease characterized by the proliferation of CD5+ B cells in lymphoid tissues. Current modern treatments have brought significant clinical benefits to CLL patients. However, there are still unmet needs. Patients relapse on Bruton's tyrosine kinase inhibitors and BCL2 inhibitors and often develop more aggressive diseases including Richter transformation (RT), an incurable complication of up to ∼10% patients. This evidence underscores the need for improved immunotherapies, combination treatment strategies, and predictive biomarkers. A mouse model that can recapitulate human CLL disease and certain components of the tumor immune microenvironment represents a promising preclinical tool for such purposes. In this review, we provide an overview of CRISPR-engineered and xenograft mouse models utilizing either cell lines, or primary CLL cells suitable for studies of key events driving the disease onset, progression and transformation of CLL. We also review how CRISPR/Cas9 established mouse models carrying loss-of-function lesions allow one to study key mutations driving disease progression. Finally, we discuss how next generation humanized mice might improve to generation of faithful xenograft mouse models of human CLL.

Anti-CD19 Chimeric Antigen Receptor T-Cell Therapy for Richter Transformation: An International, Multicenter, Retrospective Study.

Outcomes for Richter transformation (RT) are poor with current therapies. The efficacy and safety of anti-CD19 chimeric antigen receptor T-cell therapy (CAR-T) for RT are not established. We performed an international multicenter retrospective study of patients with RT who received CAR-T. Patient, disease, and treatment characteristics were summarized using descriptive statistics, and modeling analyses were used to determine association with progression-free survival (PFS) and overall survival (OS). PFS and OS were estimated from the date of CAR-T infusion. Sixty-nine patients were identified. The median age at CAR-T infusion was 64 years (range, 27-80). Patients had a median of four (range, 1-15) previous lines of therapy for CLL and/or RT, including previous Bruton tyrosine kinase inhibitor and/or BCL2 inhibitor therapy in 58 (84%) patients. The CAR-T product administered was axicabtagene ciloleucel in 44 patients (64%), tisagenlecleucel in 17 patients (25%), lisocabtagene maraleucel in seven patients (10%), and brexucabtagene autoleucel in one patient (1%). Eleven patients (16%) and 25 patients (37%) experienced grade ≥3 cytokine release syndrome and immune effector cell-associated neurotoxicity syndrome, respectively. The overall response rate was 63%, with 46% attaining a complete response (CR). After a median follow-up of 24 months, the median PFS was 4.7 months (95% CI, 2.0 to 6.9); the 2-year PFS was 29% (95% CI, 18 to 41). The median OS was 8.5 months (95% CI, 5.1 to 25.4); the 2-year OS was 38% (95% CI, 26 to 50). The median duration of response was 27.6 months (95% CI, 14.5 to not reached) for patients achieving CR. CAR-T demonstrates clinical efficacy for patients with RT.

Bruton tyrosine kinase inhibitors in multiple sclerosis: evidence and expectations.

Despite availability of high-efficacy therapies for multiple sclerosis (MS), many patients experience significant disability worsening due to limited effects of currently available drugs on central nervous system (CNS)-compartmentalized inflammation. Bruton tyrosine kinase (BTK) is an intracellular signaling molecule involved in regulation of maturation, survival, migration, and activation of B cells and microglia, which are central players in the immunopathogenesis of progressive MS. Therefore, CNS-penetrant BTK inhibitors may better prevent disease progression by targeting immune cells on both sides of the blood-brain barrier. This review gives an overview on the preliminary results of clinical trials. Currently, the efficacy and safety of six BTK inhibitors are being evaluated in clinical trials in patients with relapsing and progressive MS. Evobrutinib, tolebrutinib and fenebrutinib have shown efficacy and safety in relapsing MS in phase 2 studies, and evobrutinib and tolebrutinib in their extension studies up to 3-5 years. However, evobrutinib failed to distinguish itself from the comparator drug teriflunomide in reduction of relapse rate (primary end point) in two phase 3 studies in relapsing MS. Inhibition of BTK has emerged as a promising therapeutic approach to target the CNS-compartmentalized inflammation. Results from phase 3 clinical trials will shed light on differences in efficacy and safety of BTK inhibitors and its potential role in the future MS landscape.

Computational Investigation of the Covalent Inhibition Mechanism of Bruton's Tyrosine Kinase by Ibrutinib.

Covalent inhibitors represent a promising class of therapeutic compounds. Nonetheless, rationally designing covalent inhibitors to achieve a right balance between selectivity and reactivity remains extremely challenging. To better understand the covalent binding mechanism, a computational study is carried out using the irreversible covalent inhibitor of Bruton tyrosine kinase (BTK) ibrutinib as an example. A multi-μs classical molecular dynamics trajectory of the unlinked inhibitor is generated to explore the fluctuations of the compound associated with the kinase binding pocket. Then, the reaction pathway leading to the formation of the covalent bond with the cysteine residue at position 481 via a Michael addition is determined using the string method in collective variables on the basis of hybrid quantum mechanical-molecular mechanical (QM/MM) simulations. The reaction pathway shows a strong correlation between the covalent bond formation and the protonation/deprotonation events taking place sequentially in the covalent inhibition reaction, consistent with a 3-step reaction with transient thiolate and enolates intermediate states. Two possible atomistic mechanisms affecting deprotonation/protonation events from the thiolate to the enolate intermediate were observed: a highly correlated direct pathway involving proton transfer to the Cα of the acrylamide warhead from the cysteine involving one or a few water molecules and a more indirect pathway involving a long-lived enolate intermediate state following the escape of the proton to the bulk solution. The results are compared with experiments by simulating the long-time kinetics of the reaction using kinetic modeling.

A prospective study of zanubrutinib, a Bruton tyrosine kinase inhibitor, in relapsed/refractory idiopathic multicentric Castleman disease.

Relapsed and refractory (R/R) idiopathic multicentric Castleman disease (iMCD) is a clinical challenge with no standard treatment. In this preliminary clinical trial, we investigated the efficacy and safety profiles of a Bruton tyrosine kinase inhibitor (BTKi), zanubrutinib, in patients with R/R iMCD. The primary endpoint was theoverall response rate at Week 12according to theCastleman Disease Collaborative Network (CDCN) response criteria. The trial was terminated early due to a lack of treatment response in the first enrolled 5 patients. Although 3 patients achieved symptomatic response, none of the 5 patients had an overall response by Week 12. One patient had progressive disease and the other 4 had stable disease. The study drug was well tolerated without grade 2 or higher adverse events. Our findings suggest that BTKi therapy is not effective for iMCD, and further attempts at single-agent therapy with zanubrutinib or other BTKis for iMCD should be consideredwith caution and probably avoided. This trial was registered at www.clinialtrials.gov as #NCT04743687.

Bruton Tyrosine Kinase Inhibition: an Effective Strategy to Manage Waldenström Macroglobulinemia.

The treatment of Waldenström macroglobulinemia (WM) has evolved over the past decade. With the seminal discoveries of MYD88 and CXCR warts, hypogammaglobulinemia, infections, and myelokathexis (WHIM) mutations in WM cells, our understanding of the disease biology and treatment has improved. The development of a new class of agents, Bruton tyrosine kinase inhibitors (BTKi), has substantially impacted the treatment paradigm of WM. Herein, we review the current and emerging BTKi and the evidence for their use in WM. Clinical trials have established the role of covalent BTKi in the treatment of WM. Their efficacy is compromised among patients who harbor CXCR4WHIM mutation or MYD88WT genotype. The development of BTKC481 mutation-mediated resistance to covalent BTKi may lead to disease refractoriness. Novel, non-covalent, next-generation BTKi are emerging, and preliminary results of the early phase clinical trials show promising activity in WM, even among patients refractory to a covalent BTKi. Covalent BTK inhibitors have demonstrated meaningful outcomes in treatment-naïve (TN) and relapsed refractory (R/R) WM, particularly among those harboring the MYD88L265P mutation. The next-generation BTKi demonstrate improved selectivity, resulting in a more favorable toxicity profile. In WM, BTKi are administered until progression or the development of intolerable toxicity. Consequently, the potential for acquired resistance, the emergence of cumulative toxicities, and treatment-related financial burden are critical challenges associated with the continuous therapy approach. By circumventing BTK C481 mutations that alter the binding site to covalent BTKi, the non-covalent BTKi serve as alternative agents in the event of acquired resistance. Head-to-head comparative trials with the conventional chemoimmunotherapies are lacking. The findings of the RAINBOW trial (NCT046152), comparing the dexamethasone, rituximab, and cyclophosphamide (DRC) regimen to the first-generation, ibrutinib are awaited, but more studies are needed to draw definitive conclusions on the comparative efficacy of chemoimmunotherapy and BTKi. Complete response is elusive with BTKi, and combination regimens to improve upon the efficacy and limit the treatment duration are also under evaluation in WM.