Targeting Bruton's Tyrosine Kinase Research Articles

Mutation in Bruton Tyrosine Kinase (BTK) A428D confers resistance To BTK-degrader therapy in chronic lymphocytic leukemia

Targeting BTK has profoundly changed the face of CLL treatment over the past decade. Iterative advances in the cat and mouse game of resistance and redesign have moved BTK inhibitors from covalent to non-covalent and now targeted protein degraders. However, contrary to the presumption that protein degraders may be impervious to mutations in BTK, we now present clinical evidence that a mutation in the kinase domain of BTK, namely A428D, can confer disease resistance to a BTK degrader currently in clinical trials, that is BGB-16673. Modeling of a BTK A428D mutation places a negatively charged aspartic acid in place of the hydrophobic side chain of alanine within the binding pocket of another BTK-degrader in clinical development, namely NX-2127, suggesting that CLL cells with BTK A428D also may be resistant to NX-2127, as they already are known to be with either non-covalent or covalent inhibitors of BTK. Consequently, the two BTK degraders furthest advanced in clinical trials potentially may select for CLL cells with BTK A428D that are resistant to all approved BTKi’s.

Inhibiting Bruton's Tyrosine Kinase to Counteract Chemoresistance and Stem Cell-Like Properties in Osteosarcoma.

Osteosarcoma, a highly aggressive bone cancer, often develops resistance to conventional chemotherapeutics, leading to poor prognosis and survival rates. The malignancy and chemoresistance of osteosarcoma pose significant challenges in its treatment, highlighting the critical need for novel therapeutic approaches. Bruton's tyrosine kinase (BTK) plays a pivotal role in B-cell development and has been linked to various cancers, including breast, lung, and oral cancers, where it contributes to tumor growth and chemoresistance. Despite its established importance in these malignancies, the impact of BTK on osteosarcoma remains unexplored. Our study delves into the expression levels of BTK in osteosarcoma tissues by data from the GEO and TCGA database, revealing a marked increase in BTK expression compared with primary osteoblasts and a potential correlation with primary site progression. Through our investigations, we identified a subset of osteosarcoma cells, named cis-HOS, which exhibited resistance to cisplatin. These cells displayed characteristics of cancer stem cells (CSCs), demonstrated a higher angiogenesis effect, and had an increased migration ability. Notably, an upregulation of BTK was observed in these cisplatin-resistant cells. The application of ibrutinib, a BTK inhibitor, significantly mitigated these aggressive traits. Our study demonstrates that BTK plays a crucial role in conferring chemoresistance in osteosarcoma. The upregulation of BTK in cisplatin-resistant cells was effectively countered by ibrutinib. These findings underscore the potential of targeting BTK as an effective strategy to overcome chemoresistance in osteosarcoma treatment.

Abstract 6069: Discovery and preclinical development of orally bioavailable potent BTK degrader, and its early clinical development for the treatment of relapsed and refractory B-cell malignancies

Abstract Background : Bruton tyrosine kinase (BTK) is an important signaling hub that activates the B-cell receptor (BCR) signaling cascade, which is critical for growth and survival of B-cell lymphoma or leukemia. BTK inhibitors have shown anti-tumor activity in patients with B-NHL. However, nearly half of the patients on current BTK inhibitors discontinue the treatment due to adverse effects and/or mutation-induced drug resistance. A degrader is a heterobifunctional chemical compound aimed at eliminating disease-causing proteins, rather than simply inhibiting proteins’ enzymatic function, through the ubiquitin-proteasome system (UPS)-mediated protein degradation. This approach offers a unique solution for addressing relapse or refractory disease by removing overexpressed and mutated proteins, unlike traditional inhibitors. We thus designed UBX-382, a degrader targeting BTK. Results : UBX-382 showed superior degradation activity for both wild-type (WT) and mutant BTK proteins in a single-digit nanomolar range of half-maximal degradation concentration when compared to the competing degrader programs in diffuse large B-cell lymphoma cell line. UBX-382 effectively addressed 7 out of 8 previously reported resistant BTK mutants in in vitro experiments and outperformed ibrutinib, ARQ-531, and MT-802 in inhibiting tumor growth in murine xenograft models harboring WT or C481S mutant BTK-expressing TMD-8 cells. Remarkably, oral dosing of UBX-382 for <2 weeks led to complete tumor regression in 3 and 10 mg/kg groups in murine xenograft models. Following this, further optimization was carried out for potency and PK profile. We nominated the candidate for IND filing and are planning a phase 1 clinical trial. For the first-in-human, open-label, multicenter, phase 1 study, patients in part 1 (dose escalation with BOIN design) had R/R B-cell malignancies and had received at least 2 prior therapies. The candidate will be administered orally at 5 mg once daily followed by 2 days, for a 7-day schedule over 28-day cycles. Part 2 (dose expansion) consisted of disease-specific cohorts, including CLL/SLL, DLBCL, MCL, FL, MZL, and WM. The primary endpoints were safety and tolerability, along with the definition of the maximum tolerated dose. Secondary endpoints included pharmacokinetics/pharmacodynamics and preliminary efficacy. Conclusions : We have discovered potent BTK degrader exhibiting excellent anti-tumor activity in vitro and in vivo. In pre-clinical safety studies, the candidate of UBX demonstrated an acceptable safety profile. The candidate of UBX is currently preparing phase 1 clinical trials for hematological malignancies. Citation Format: Song Hee Lee, Sun-Mi Yoo, Ye Seul Lim, Han Wool Kim, Je Ho Ryu, Jong Hwan Lim. Discovery and preclinical development of orally bioavailable potent BTK degrader, and its early clinical development for the treatment of relapsed and refractory B-cell malignancies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6069.

Targeting BTK in B Cell Malignancies: From Mode of Action to Resistance Mechanisms.

The B cell receptor (BCR) signaling pathway plays a crucial role in B cell development and contributes to the pathogenesis of B cell neoplasms. In B cell malignancies, the BCR is constitutively active through both ligand-dependent and ligand-independent mechanisms, resulting in continuous Bruton tyrosine kinase (BTK) signaling activation, which provides a survival and proliferation advantage to the neoplastic clone. Among B cell malignancies, those in which the most significant results were obtained by treatment with BTK inhibitors (BTKi) include chronic lymphocytic leukemia, mantle cell lymphoma, lymphoplasmacytic lymphoma, and diffuse large B cell lymphoma. Covalent BTKi (namely ibrutinib, acalabrutinib, and zanubrutinib) functions by irreversibly blocking BTK through covalent binding to the cysteine residue 481 (Cys-481) in the ATP-binding domain. Despite the high efficacy and safety of BTKi treatment, a significant fraction of patients affected by B cell malignancies who are treated with these drugs experience disease relapse. Several mechanisms of resistance to covalent BTKi, including Cys-481 mutations of BTK, have been investigated in B cell malignancies. Non-covalent BTKi, such as pirtobrutinib, have been developed and proven effective in patients carrying both Cys-481-mutated and unmutated BTK. Moreover, targeting BTK with proteolysis-targeting chimeras (PROTACs) represents a promising strategy to overcome resistance to BTKi in B cell neoplasms.

Screening and Characterization of Allosteric Small Molecules Targeting Bruton's Tyrosine Kinase.

Bruton's Tyrosine Kinase (BTK) is a nonreceptor tyrosine kinase that belongs to the TEC family. Mutations in the BTK gene cause X-linked agammaglobulinemia (XLA) leading to an arrest in B-cell development. BTK is also a drug target for B-cell lymphomas that rely on an intact B-cell receptor signaling cascade for survival. All FDA approved drugs for BTK target the ATP binding site of the catalytic kinase domain, leading to potential adverse events due to off-target inhibition. In addition, acquired resistance mutations occur in a subset of patients, rendering available BTK inhibitors ineffective. Therefore, allosteric sites on BTK should be explored for drug development to target BTK more specifically and in combination with active site inhibitors. Virtual screening against nonactive site pockets and in vitro experiments resulted in a series of small molecules that bind to BTK outside of the active site. We characterized these compounds using biochemical and biophysical techniques and narrowed our focus to compound "C2". C2 activates full-length BTK and smaller multidomain BTK fragments but not the isolated kinase domain, consistent with an allosteric mode of action. Kinetic experiments reveal a C2-mediated decrease in Km and an increase in kcat leading to an overall increase in the catalytic efficiency of BTK. C2 is also capable of activating the BTK XLA mutants. These proof-of-principle data reveal that BTK can be targeted allosterically with small molecules, providing an alternative to active site BTK inhibitors.

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

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

Real World Experience of Ibrutinib in an Ethnically Diverse Canadian Community Hospital

Chronic Lymphocytic Leukemia (CLL) is an indolent lymphoproliferative disorder commonly managed in community centers. Ibrutinib revolutionized the management of patients with CLL (2). Ibrutinib was initially considered an easy to administer, well tolerated oral medication with excellent efficacy. It was the first clinically available Bruton's Tyrosine Kinase (BTK) inhibitor widely used to treat CLL (3). Recently there have been concerns about cardiovascular toxicities leading to the use of alternative BTK inhibitors (5). Where alternative BTK inhibitors are available these toxicity concerns have led to a decline in the use of ibrutinib to treat CLL. The population served is ethnically diverse consisting of 52% South East Asian with a significant population of African origin. We suspected that the concerns regarding Ibrutinib toxicity were not seen in our patient population prompting a retrospective review of our experience. Ibrutinib therapy A total of 106 CLL patients treated with Ibrutinib were identified from which data was extracted. The mean age was 63.4 years. Patients with CLL treated with Ibrutinib from 2014 to 2021 were identified using OPIS and Meditech and data was extracted manually. Table 1 60% of patient received their initial drug funding through compassionate access, 2% via private insurance and the remaining 38% through the provincial health system. The majority of patients who received funding through compassionate access were eventually transitioned to the provincial health system for drug funding. Toxicity and outcomes Table 2 81% of treated patients never required a dose adjustment of Ibrutinib. The majority of dose reductions were of a temporary nature. We were unable to obtain accurate response data in our retrospective review. 82 of the 106 patients continue on ibrutinib therapy. It is presumed that these patients continue to benefit from therapy without disease progression although response data details were poorly recorded in the medical record. Conclusions There is a lack of data of community real world experience with Ibrutinib particularly in the Canadian setting. Community centers generally are lacking in information technology required to do retrospective audits. Our data shows that ibrutinib therapy for CLL is a reasonable and effective option with good tolerability in a patient population with high cardiovascular risk. The data is limited by the retrospective data collection. The efficacy of therapy is likely comparable to that of the published literature. These data suggest that the tolerability of Ibrutinib therapy seems better than that of the published literature (1) with a low incidence of atrial fibrillation, dose adjustments and low drug discontinuation rate. Of note Richter's transformation was also uncommon in our patient population. This is particularly of interest as our study did capture patients in the early days of ibrutinib therapy when there were concerns that Richter's transformation was more common than seen today. Many of the patients who were treated with ibrutinib would not have received the drug today because of cardiovascular concerns (4). At that time, it was the only available oral targeted agent for the treatment of chronic lymphocytic leukemia. Other agents such as Venetoclax, Acalabrutinib, Zanubrutinib and novel combinations were unavailable at that time or were not funded. These lack of options likely contribute to the persistence of Ibrutinib therapy in our patients. These data suggest that ibrutinib can be used in a high cardiovascular risk population with good efficacy and tolerability. 1.Alloucjery, M., Tomowiak, C., Lombard, T., & et al. (2021). Safety Profile of Ibrutinib: An Analysis of the WHO Pharmacovigilance Database. Front Pharmacology, 12:769315. 2.Byrd, J. C., Brown, J. R., O'Brien, S., & et al. (2014). Ibrutinib versus ofatumumab in previously treated chronic lymphoid leukemia. NEJM, 371(3):213-223. 3.Byrd, J. C., Furman, R. R., & Coutre, S. S. (2013). Targeting BTK with ibrutinib in relapsed chronic lymphocytic leukemia. NEJM, 369(1):32-42. 4.Lovell, A. R., Jammal, N., & Bose, P. (2022). Selecting the optimal BTK inhibitor therapy in CLL: rationale and practical considerations. Therapueltic Advances in Hematology, 13:1177/20406207221116577. 5.Salem, J. E., Manouchehri, A., & Bretagne, M. (2019). Targeting BTK with ibrutinib in relapsed chronic lymphocytic leukemia. J Am Coll Cardiol, 74:1667-1678.

Meta-Analysis of the Efficacy and Adverse Effects of Acalabrutinib in the Treatment of Relapsed/Refractory Chronic Lymphocytic Leukemia

Background Chronic Lymphocytic Leukemia (CLL) is the most prevalent adult leukemia and is characterized by the accumulation of small and mature appearing lymphocytes in blood, lymphoid tissue, and bone marrow. Chemoimmunotherapy and targeted therapies can improve overall survival and the duration of remission; however, CLL is prone to relapse, therefore identifying new therapeutic targets has been an important aspect of CLL research and management. B-cell receptor signaling serves an integral role in the pathogenesis of CLL and kinases involved in the BCR pathway are targets of novel therapies. The Bruton tyrosine kinase (BTK) that is immediately downstream of the B-cell receptor is a mediator of cell signaling involved in B cell survival and proliferation. Moreover, BTK is involved in CLL interaction with the tumor microenvironment. Targeting BTK with ibrutinib was a transformative advance in CLL treatment and has become a front-line therapy in the management of CLL. In recent years, newer generations of Bruton tyrosine kinase inhibitors (BTKi) have been approved in the management of CLL. Acalabrutinib is an irreversible, second generation BTKi that is more selective and potent than ibrutinib. This meta-analysis investigated the efficacy, outcomes, and hematologic adverse effects of acalabrutinib in the treatment of relapsed/refractory CLL. Methods A search was conducted using the PICOS model and PRISMA guidelines to retrieve outcome, efficacy, and adverse effect data. 12 studies were chosen after literature review and screening. In the event a study was an abstract or paper providing updated data on the same patient population of a previously published study, the most up to date information was used for analysis. The random effect meta-analysis model was used for analyses. Variables for analysis were: Overall Response Rate (ORR), Overall Discontinuation Rate, Death Rate, and Discontinuation due to Adverse Effects. Grade 3 Hematologic adverse reactions were analyzed: Anemia, Neutropenia, Thrombocytopenia. Results The analysis included a total of 796 patients (450 Males & 200 females; sum discrepancy due to absence of certain demographic information in particular studies). ORR pooled estimate: 82% (95% CI [0.82,0.75]; p<.001, I 2=81.96%), death rate: 12% (95% CI [0.06,0.19]; p<.001, I 2=87.23%), overall discontinuation rate: 35% (95% CI [0.20, 0.30]; p< .001, I 2=98.84%), discontinuation due to adverse effect: 13% (95% CI [0.10,0.15]; p=0.6, I 2=0.00), neutropenia: 18% (95% CI [0.15,0.20]; p=0.70), anemia: 9% (95% CI [0.06,0.12];p=0.18), thrombocytopenia: 7% (95% CI [0.04,0.11];p=0.09). Discussion BTK inhibitors have significantly changed the management of CLL and are utilized as either as frontline or as salvage treatment. Although, ibrutinib has shown efficacy in management of CLL, off-target toxicities and treatment resistance has been demonstrated with its use. Therefore, a greater understanding of second generation BTK inhibitors such as acalabrutinib will offer clinicians perspective in choosing a CLL management strategy. Our meta-analyses noted an ORR pooled estimate of 82% with a death rate of 12%. Deaths in the literature typically occurred either from disease progression or adverse effects. Similarly, discontinuation typically occurred due to progressive disease or adverse events. The Grade 3 hematologic adverse effects most frequently reported were anemia, thrombocytopenia, neutropenia. Clinical Grade 3 adverse effects (e.g. pneumonia, cardiac events) and baseline characteristics will be focused on in a future analysis.

Discovery of Ibrutinib-based BTK PROTACs with in vivo anti-inflammatory efficacy by inhibiting NF-κB activation

As a critical upstream regulator of nuclear factor-κB (NF-κB) activation, Bruton's tyrosine kinase (BTK) has been identified to be an effective therapeutic target for the treatment of acute or chronic inflammatory diseases. Herein, we describe the design, synthesis and structure-activity-relationship analysis of a novel series of Ibrutinib-based BTK PROTACs by recruiting Cereblon (CRBN) ligase. Among them, compound 15 was identified as the most potent degrader with a DC50 of 3.18 nM, significantly better than the positive control MT802 (DC50 of 63.31 nM). Compound 15 could also degrade BTK protein in Lipopolysaccharide (LPS)-stimulated RAW264.7 cells, and suppress the mRNA expression and secretion of proinflammatory cytokines such as IL-1β and IL-6 by inhibiting NF-κB activation. Furthermore, compound 15 reduced inflammatory responses in a mouse zymosan-induced peritonitis (ZIP) model. Our findings demonstrated for the first time that targeting BTK degradation by PROTACs might be an alternative option for the treatment of inflammatory disorders, and compound 15 represents one of the most efficient BTK PROTACs (DC50 = 3.18 nM; Dmax = 99.90%; near 100% degradation at 8 h) reported so far and could serve as a lead compound for further investigation as an anti-inflammatory agent.

Waldenström macroglobulinemia: a review of pathogenesis, current treatment, and future prospects.

Waldenström macroglobulinemia (WM) is a chronic B-cell lymphoproliferative disorder characterized by lymphoplasmacytic cell overgrowth in the bone marrow and increased secretion of IgM immunoglobulins into the serum. Patients with WM have a variety of clinical outcomes, including long-term survival but inevitable recurrence. Recent advances in disease knowledge, including molecular and genetic principles with the discovery of MYD88 and CXCR4 mutations, have rapidly increased patient-tolerable treatment options. WM patients may benefit from chemotherapy regimens that include rituximab-based regimens, alkylating drugs, proteasome inhibitors, monoclonal antibodies, and drugs targeting Bruton tyrosine kinase inhibitors. In light of these advancements, patients can now receive treatment customized to their specific clinical characteristics, focusing on enhancing the depth and durability of their response while limiting the adverse effects. Despite the rapidly developing therapeutic armament against WM, a lack of high-quality evidence from extensive phase 3 trials remains a significant challenge in the research. We believe clinical outcomes will keep improving when new medicines are introduced while preserving efficacy and minimizing toxicity.

Phase 1 Study of Acalabrutinib Plus Danvatirsen (AZD9150) in Relapsed/Refractory Diffuse Large B-Cell Lymphoma Including Circulating Tumor DNA Biomarker Assessment.

Novel targeted and immunotherapies have improved outcomes in relapsed/refractory (R/R) diffuse large B-cell lymphoma (DLBCL), but toxicities limit widespread use. The selective Bruton tyrosine kinase (BTK) inhibitor acalabrutinib has activity in patients with R/R DLBCL, but durable responses are uncommon. STAT3 inhibition has demonstrated clinical activity in DLBCL. Final results of the Phase 1 study of acalabrutinib plus STAT3 inhibitor (danvatirsen; AZD9150) in patients with R/R DLBCL are reported. Danvatirsen 200 mg intravenous infusion (Days 1, 3, 5 [Cycle 1]; weekly infusions starting Day 8, Cycle 1) was administered in combination with oral acalabrutinib 100 mg twice daily until progressive disease (PD) or unacceptable toxicity. Primary endpoints were safety and tolerability. Secondary endpoints included efficacy, pharmacokinetics, and immunogenicity. Seventeen patients received combination treatment. One dose-limiting toxicity (Grade 3 liver transaminase) occurred in one patient. The most common reason for treatment discontinuation was PD (65%). In evaluable patients (n=17), objective response rate was 24%; median duration of response was 1.9 months. All responders with available DLBCL cell-of-origin data were either activated B-cell or nongerminal center B-cell like subtype. Genetic subtype did not correlate with response. Baseline and longitudinal plasma cell-free DNA (cfDNA) concentrations were mostly higher in nonresponding patients. cfDNA changes were generally concordant with imaging. Pretreatment circulating B-cell levels were higher in responders versus nonresponders. Targeting both STAT3 and BTK in combination is safe and tolerable but efficacy is limited in R/R DLBCL. Results support evaluation of circulating tumor DNA as a biomarker for clinical response.

Discovery of novel dual Bruton’s tyrosine kinase (BTK) and Janus kinase 3 (JAK3) inhibitors as a promising strategy for rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronically systemic autoimmune disorder, which is related with various cellular signal pathways. Both BTK (Bruton’s Tyrosine Kinase) and JAK3 (Janus Kinase 3) play important roles in the pathogenesis of rheumatoid arthritis. Herein, we reported the discovery of dual BTK/JAK3 inhibitors through bioisosterism and computer-aided drug design based on the structure of BTK inhibitor ibrutinib. We reported the discovery of dual BTK/JAK3 inhibitors which are based on the structure of BTK inhibitor ibrutinib via the method of bioisosterism and computer-aided drug design) Most of the target compounds exhibited moderate to strong inhibitory activities against BTK and JAK3. Among them, compound XL-12 stood out as the most promising candidate targeting BTK and JAK3 with potent inhibitory activities (IC50 = 2.0 nM and IC50 = 14.0 nM respectively). In the in vivo studies, compound XL-12 (40 mg/kg) exhibited more potent antiarthritic activity than ibrutinib (10 mg/kg) in adjuvant arthritis (AA) rat model. Furthermore, compound XL-12 (LD50 > 1600 mg/kg) exerted improved safety compared with ibrutinib (LD50 = 750 mg/kg). These results indicated that compound XL-12, the dual BTK/JAK3 inhibitor, might be a potent drug candidate for the treatment of RA.

Pirtobrutinib targets BTK C481S in ibrutinib-resistant CLL but second-site BTK mutations lead to resistance.

Covalent inhibitors of Bruton tyrosine kinase (BTK) have transformed the therapy of chronic lymphocytic leukemia (CLL), but continuous therapy has been complicated by the development of resistance. The most common resistance mechanism in patients whose disease progresses on covalent BTK inhibitors (BTKis) is a mutation in the BTK 481 cysteine residue to which the inhibitors bind covalently. Pirtobrutinib is a highly selective, noncovalent BTKi with substantial clinical activity in patients whose disease has progressed on covalent BTKi, regardless of BTK mutation status. Using invitro ibrutinib-resistant models and cells from patients with CLL, we show that pirtobrutinib potently inhibits BTK-mediated functions including B-cell receptor (BCR) signaling, cell viability, and CCL3/CCL4 chemokine production in both BTK wild-type and C481S mutant CLL cells. We demonstrate that primary CLL cells from responding patients on the pirtobrutinib trial show reduced BCR signaling, cell survival, and CCL3/CCL4 chemokine secretion. At time of progression, these primary CLL cells show increasing resistance to pirtobrutinib in signaling inhibition, cell viability, and cytokine production. We employed longitudinal whole-exome sequencing on 2 patients whose disease progressed on pirtobrutinib and identified selection of alternative-site BTK mutations, providing clinical evidence that secondary BTK mutations lead to resistance to noncovalent BTKis.

The Evolution of Therapies Targeting Bruton Tyrosine Kinase for the Treatment of Chronic Lymphocytic Leukaemia: Future Perspectives.

The development of inhibitors of Bruton tyrosine kinase (BTK) and B-cell lymphoma 2 (BCL2) has resulted in a paradigm shift in the treatment of chronic lymphocytic leukaemia (CLL) over the last decade. Observations regarding the importance of B-cell receptor signalling for the survival and proliferation of CLL cells led to the development of the first-in-class BTK inhibitor (BTKi), ibrutinib, for the treatment of CLL. Despite being better tolerated than chemoimmunotherapy, ibrutinib does have side effects, some of which are due to the off-target inhibition of kinases other than BTK. As a result, more specific inhibitors of BTK were developed, such as acalabrutinib and zanubrutinib, which have demonstrated equivalent/enhanced efficacy and improved tolerability in large randomized clinical trials. Despite the increased specificity for BTK, side effects and treatment resistance remain therapeutic challenges. As these drugs all bind covalently to BTK, an alternative approach was to develop noncovalent inhibitors of BTK, including pirtobrutinib and nemtabrutinib. The alternative mechanisms of BTK-binding of these agents has the potential to overcome resistance mutations, something that has been borne out in early clinical trial data. A further step in the clinical development of BTK inhibition has been the introduction of BTK degraders, which remove BTK by ubiquitination and proteasomal degradation, in marked contrast to BTK inhibition. This article will review the evolution of BTK inhibition for CLL and offer future perspectives on the sequencing of an increasing number of different agents, and how this may be impacted on by mutations in BTK itself and other kinases.

Discovery of BGB-8035, a Highly Selective Covalent Inhibitor of Bruton’s Tyrosine Kinase for B-Cell Malignancies and Autoimmune Diseases

Bruton's tyrosine kinase (BTK) plays an essential role in B-cell receptor (BCR)-mediated signaling as well as the downstream signaling pathway for Fc receptors (FcRs). Targeting BTK for B-cell malignancies by interfering with BCR signaling has been clinically validated by some covalent inhibitors, but suboptimal kinase selectivity may lead to some adverse effects, which also makes the clinical development of autoimmune disease therapy more challenging. The structure-activity relationship (SAR) starting from zanubrutinib (BGB-3111) leads to a series of highly selective BTK inhibitors, in which BGB-8035 is located in the ATP binding pocket and has similar hinge binding to ATP but exhibits high selectivity over other kinases (EGFR, Tec, etc.). With an excellent pharmacokinetic profile as well as demonstrated efficacy studies in oncology and autoimmune disease models, BGB-8035 has been declared a preclinical candidate. However, BGB-8035 showed an inferior toxicity profile compared to that of BGB-3111.

Genomic Characterization of Patients in a Phase 2 Study of Zanubrutinib in BTK Inhibitor-Intolerant Patients with Relapsed/Refractory B-Cell Malignancies

Background/Introduction: Targeting Bruton tyrosine kinase (BTK) to inhibit B-cell receptor signaling is an effective way to treat B-cell malignancies. However, some patients (pts) have experienced toxicities to BTK inhibitors ibrutinib (ibr) and acalabrutinib (acala), which lead to dose reduction or treatment discontinuation. Zanubrutinib (zanu) is a potent and selective next-generation BTK inhibitor (Blood. 2021;138[suppl 1]:1410). BGB-3111-215 (NCT04116437) is an ongoing, phase 2 study of the safety and efficacy of zanu monotherapy in pts with chronic lymphocytic leukemia (CLL), small lymphocytic lymphoma (SLL), Waldenström macroglobulinemia (WM), mantle cell lymphoma (MCL), or marginal zone lymphoma (MZL) who discontinued ibr, acala, or acala and ibr because of intolerance. Here, we present the gene mutation profile of pts in this study to demonstrate the mutational landscape of pts intolerant to ibr or acala and to explore the association between gene mutations and response to zanu in ibr- and acala- intolerant pts. Methods: Peripheral blood from pts was collected before treatment and at or after the time of disease progression. Genomic DNA was isolated from peripheral blood mononuclear cells or plasma, and the mutational status of targeted genes was assessed using a targeted 106-gene next-generation sequencing (NGS) panel (PredicineHEMETM, Predicine). Samples were sequenced to a median depth of >20,000 reads, with a validated sensitivity of 0.25% mutant allele frequency for all genomic regions. Results: Samples from 63 pts were analyzed, including 63 at baseline and 5 at or after progressive disease (PD). There were 41 pts with CLL, 6 with SLL, 10 with WM, 3 with MCL, and 3 with MZL. The most common mutations at baseline were TP53 (31.7%), SF3B1 (22.2%), ATM (17.5%), NOTCH1 (17.5%), CHEK2 (14.3%), and KRAS (12.7%). Copy number variants were detected, including deletions at ATM locus (9.5%) and RB1 locus (9.5%) and amplifications at CCND2 locus (6.3%). For CLL/SLL, the frequencies of TP53 (27.7%), NOTCH1 (21.3%), SF3B1 (25.5%), ATM (21.3%), and BIRC3 (10.4%) mutations were comparable to those in other studies with high-risk relapsed/refractory CLL pts (Leukemia. 2018;32:3-91; Blood. 2014;123:3247-3254; Leuk Lymphoma. 2018;59[10]:2318-26). For WM, 5 of 10 (50%) samples harbored TP53 mutations, and 4 of 10 samples had MYD88 mutations; all harbored the L265P mutation. Among the 4 pts with MYD88 mutation, CXCR4 gene mutation was detected in 1 case. All 6 pts with MYD88 wild type also had CXCR4 wild type gene, consistent with published data (N Engl J Med. 2015;373:584-6). Baseline mutations were available for the 10 pts with PD, including 8 CLL, 1 SLL, and 1 MCL. Compared to pts without PD, pts with PD had increased frequency of certain mutations: TP53 (60%, P=0.071), ATM (50%, P=0.017), SF3B1 (50%, P=0.035), RB1 (40%, P=0.009), SETD2 (40%, P=0.009), and CDKN2A (30%, P=0.011). This finding suggests that these particular baseline mutations are associated with resistance to zanu. Five pts also had mutations detected at or after PD. Of these, 3 pts had BTK or PLCG2 mutations (submitted). One patient with CLL and without BTK or PLCG2 mutations had ATM and FBXW7 mutations (variant allele frequencies were 86% and 50%, respectively), suggesting DNA damage pathway mutations and NOTCH1 dysregulations may have contributed to disease progression in this patient. Conclusion: Exploratory analysis results confirmed that cell cycle, DNA damage, and NOTCH1 pathway genes were frequently mutated in pts with B-cell malignancies on study BGB-3111-215 (pts intolerant to ibr and/or acala). Pts with mutations associated with poor prognosis at baseline were more likely to develop PD.

DNMT3A-Mediated Oxidative Phosphorylation and Ibrutinib Resistance in Mantle Cell Lymphoma

Mantle cell lymphoma (MCL), a B cell non-Hodgkin lymphoma, is incurable with current treatment modalities. Targeting Bruton tyrosine kinase (BTK) in the early B cell receptor signaling pathway by ibrutinib has shown remarkable anti-tumor activity, with the overall response rate of 68% in relapsed/refractory MCL patients. However, almost all the responders relapsed after ibrutinib treatment, with the 1-year survival rate of 22%. To overcome primary and acquired resistance to ibrutinib, novel treatment strategies are urgently needed. The presence of a relapse-specific C481S mutation in BTK associated with acquired ibrutinib resistance has been frequently identified in chronic lymphocytic leukemia but is rare in clinical MCL specimens based on sequencing results. Thissuggests that non-genetic aberrations likely play a role in ibrutinib resistance. The recent emergence of mitochondrial oxidative phosphorylation (OXPHOS) as a driver of ibrutinib resistance warrants the necessity to identify the components that govern OXPHOS in MCL. This study identifies the de novo DNA methyltransferase 3A (DNMT3A) as a mediator of mitochondrial biogenesis and OXPHOS in MCL. Using multiomics and functional approaches, we found that DNMT3A is required and sufficient to confers ibrutinib resistance in MCL. We show that DNMT3A promotes MCL growth by enhancing mitochondrial biogenesis, mitochondrial functions and OXPHOS. These effects are mediated by its interaction with MEF2B, a transcriptional activator of MYC, to enhance MYC-mediated transcription of genes involved in mitochondrial biogenesis. More importantly, the level of DNMT3A protein increases after ibrutinib treatment in primary MCL, which is consistent with a previous finding that the expression of DNMT3A was higher in ibrutinib-resistant than in ibrutinib-sensitive MCL patients. We demonstrate that DNMT3A knockout sensitizes ibrutinib-resistant cells to ibrutinib treatment. Conversely, the overexpression of DNMT3A cDNA de-sensitizes ibrutinib-sensitive cell lines. Interestingly, the overexpression of a catalytically dead DNMT3A confers resistance to ibrutinib in ibrutinib-sensitive cell lines, suggesting that DNMT3A-mediated ibrutinib resistance is independent of its enzymatic activity. Finally, we demonstrate that targeting DNMT3A by a low dose of decitabine, which induces the degradation of DNMT3A protein, synergizes with IM156, an inhibitor of mitochondrial complex I and currently in phase I clinical trial, in killing ibrutinib-resistant cell lines and primary MCL cells. Currently, we are testing this synergistic effect using patient-derived xenograft mouse models. Therefore, our study reveals a novel noncatalytic function of DNMT3A and suggests that DNMT3A is a potential biomarker and molecular target in treating MCL (Figure 1). Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

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

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

Time-limited, chemotherapy-free treatment comes of age in chronic lymphocytic leukaemia.

The therapeutic landscape of chronic lymphocytic leukaemia has been transformed by the advent of drugs targeting Bruton tyrosine kinase and BCL2. 1 Kay NE Hampel PJ Van Dyke DL Parikh SA CLL update 2022: a continuing evolution in care. Blood Rev. 2022; 100930100930 Google Scholar Pivotal studies showed the superiority of such inhibitors for chronic lymphocytic leukaemia treatment compared with chemoimmunotherapy. 2 Byrd JC Brown JR O'Brien S et al. Ibrutinib versus ofatumumab in previously treated chronic lymphoid leukemia. N Engl J Med. 2014; 371: 213-223 Crossref PubMed Scopus (1189) Google Scholar , 3 Sharman JP Egyed M Jurczak W et al. Acalabrutinib with or without obinutuzumab versus chlorambucil and obinutuzmab for treatment-naive chronic lymphocytic leukaemia (ELEVATE TN): a randomised, controlled, phase 3 trial. Lancet. 2020; 395: 1278-1291 Summary Full Text Full Text PDF PubMed Scopus (216) Google Scholar , 4 Seymour JF Kipps TJ Eichhorst B et al. Venetoclax–rituximab in relapsed or refractory chronic lymphocytic leukemia. N Engl J Med. 2018; 378: 1107-1120 Crossref PubMed Scopus (475) Google Scholar , 5 Al-Sawaf O Zhang C Tandon M et al. Venetoclax plus obinutuzumab versus chlorambucil plus obinutuzumab for previously untreated chronic lymphocytic leukaemia (CLL14): follow-up results from a multicentre, open-label, randomised, phase 3 trial. Lancet Oncol. 2020; 21: 1188-1200 Summary Full Text Full Text PDF PubMed Scopus (112) Google Scholar Bruton tyrosine-kinase inhibitors such as ibrutinib and acalabrutinib are administered until progression or toxicity and, although highly effective, cardiovascular toxicities and mutations associated with resistance are known to ensue for some patients. 2 Byrd JC Brown JR O'Brien S et al. Ibrutinib versus ofatumumab in previously treated chronic lymphoid leukemia. N Engl J Med. 2014; 371: 213-223 Crossref PubMed Scopus (1189) Google Scholar , 3 Sharman JP Egyed M Jurczak W et al. Acalabrutinib with or without obinutuzumab versus chlorambucil and obinutuzmab for treatment-naive chronic lymphocytic leukaemia (ELEVATE TN): a randomised, controlled, phase 3 trial. Lancet. 2020; 395: 1278-1291 Summary Full Text Full Text PDF PubMed Scopus (216) Google Scholar , 4 Seymour JF Kipps TJ Eichhorst B et al. Venetoclax–rituximab in relapsed or refractory chronic lymphocytic leukemia. N Engl J Med. 2018; 378: 1107-1120 Crossref PubMed Scopus (475) Google Scholar , 5 Al-Sawaf O Zhang C Tandon M et al. Venetoclax plus obinutuzumab versus chlorambucil plus obinutuzumab for previously untreated chronic lymphocytic leukaemia (CLL14): follow-up results from a multicentre, open-label, randomised, phase 3 trial. Lancet Oncol. 2020; 21: 1188-1200 Summary Full Text Full Text PDF PubMed Scopus (112) Google Scholar Minimal residual disease-guided stop and start of venetoclax plus ibrutinib for patients with relapsed or refractory chronic lymphocytic leukaemia (HOVON141/VISION): primary analysis of an open-label, randomised, phase 2 trialThese data point to a favourable benefit–risk profile of MRD-guided, time-limited treatment with ibrutinib plus venetoclax for patients with relapsed or refractory chronic lymphocytic leukaemia, suggesting that MRD-guided cessation and reinitiation is feasible in this patient population. Full-Text PDF

Targeting Bruton Tyrosine Kinase for the Treatment of Vitreoretinal Lymphoma: Report of 11 Consecutive Patients

Background:Vitreoretinal lymphoma (VRL) is a rare intraocular malignancy, which is regarded as a part of the central nervous system lymphoma (CNSL) and shows a close relationship with CNS progression. Currently, no standard treatment approaches have been defined yet, although intravitreal methotrexate with or without systemic chemotherapy are generally used. Bruton tyrosine kinase (BTK) is a vital effector molecule in the progress of B-cell proliferation. VRL, as well as PCNSL, display typically an activated B cell-like (ABC) phenotype of diffuse large B-cell lymphoma (DLBCL), with frequent CD79B and MYD88 mutations, which may represent a strong biological rationale for the use of BTK inhibitors. Previous studies have demonstrated that BTK inhibitors could penetrate the blood-brain barrier, and achieve 70-90% response rate in patients with PCNSL. However, whether BTK inhibitors could penetrate the blood-eye barrier and provide benefits to patients with VRL remains unknown.Methods:In this retrospective study, 11 consecutive patients with VRL were treated with BTK inhibitors monotherapy (zanubrutinib 160mg orally twice daily, or orelabrutinib 150mg orally daily), and they were intended to be treated for 2 years, or till disease progression, or unacceptable toxicity, whichever occurs first. All enrolled patients were pathologically confirmed as vitreoretinal DLBCL using vitreous biopsy, and PET-CT scan were performed to rule out the systemic involvement of lymphoma. Patients with pretreated or concurrent CNSL were allowed in this study. Cytokine analysis (including IL-10 and IL-6) in the anterior chamber of the eye was done using Cytometric Bead Array (CBA) at one month after initiation of treatment, and every three months thereafter or as symptom indicated. Fundus photograph and optical coherence tomography (OCT) were done at each follow-up. Magnetic resonance imaging (MRI) of brain was done every three months. This study was approved by the Ethic Committee of Beijing Tongren Hospital and written informed consent was provided by all patients.Results:11 consecutive patients with VRL were treated since May 2020, among whom 5 patients were enrolled in our prospective study evaluating the efficacy and safety of zanubrutinib in the treatment of VRL (ChiCTR2000037921), and the other 6 patients were treated with off-label use of BTK inhibitors, and those 11 patients were analyzed combined in this report. The female to male ratio was 7:4, with a median of 61 years old (41-73). 3 patients had pretreated PCNSL and were in complete remission at the time of VRL relapse, and one patient (YSX2) had concurrent PCNSL and VRL. All the other 7 patients had isolated VRL, among whom 3 patients were diagnosed as de novo VRL and the other 4 patients were previously treated with repeated intravitreal methotrexate and had disease relapse at the time of BTK inhibitor treatment. The detailed efficacy information was shown in Figure 1. All but one patients achieved complete remission (CR) after one months of BTK inhibitor treatment, with symptoms resolved, disappearance of infiltration lesions in OCT, and IL-10 levels returned to normal. One patient (YSX2) suffered from disease progression in the brain and withdrew from the study after 2 months of treatment, while the eye symptoms were significantly improved. At a median follow up of 7.5 months (4-15), 4 patients were confirmed to have disease progression, with a progression-free survival (PFS) of 2, 7, 7.5, and 9 months, respectively. All the other 7 patients have durable CR. 4 patients treated with off-label use of zanubrutinib discontinued BTKi due to economic reasons, and remained in CR till the last follow-up. One patient (YSX1) stopped BTK inhibitor after 2 months, and suffered from disease relapse 5.5 months later without any other treatments. BTK inhibitors were well-tolerated, with grade 1 ecchymosis in 3/11 patients, grade 3 hypertension in 1/11 patients, grade 2 arthralgia in 1/11 patients, and grade 1 liver dysfunction in 2/11 patients. No patients stopped the drug due to adverse events, and one patient reduced the dosage due to uncontrolled hypertension. All patients were alive at the time of this report.Conclusions:In conclusion, targeting BTK in VRL is feasible and our findings can be a foundation for a paradigm shift in treatment options for this rare disease. A well-designed prospective study in a larger cohort of patients is needed to validate our findings. [Display omitted] DisclosuresNo relevant conflicts of interest to declare. OffLabel Disclosure:USE OF ZANUBRUTINIB FOR THE TREATMENT OF DIFFUSE LARGE B CELL LYMPHOMA