Targeting BTK in CLL: Beyond Ibrutinib

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 the overall response rate at Week 12 according to the Castleman 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 considered with caution and probably avoided. This trial was registered at www.clinialtrials.gov as #NCT04743687.

Targeting the B cell receptor signaling pathway in chronic lymphocytic leukemia

Aberrant signal transduction through the B cell receptor (BCR) plays a critical role in the pathogenesis of chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL). BCR-dependent signaling is necessary for the growth and survival of neoplastic cells, making inhibition of down-stream pathways a logical therapeutic strategy. Indeed, selective inhibitors against Bruton's tyrosine kinase (BTK) and phosphoinositide 3-kinase (PI3K) have been shown to induce high rates of response in CLL and other B cell lymphomas. In particular, the development of BTK inhibitors revolutionized the treatment approach to CLL, demonstrating long-term efficacy. While BTK inhibitors are widely used for multiple lines of treatment, PI3K inhibitors are much less commonly utilized, mainly due to toxicities. CLL remains an incurable disease and effective treatment options after relapse or development of TKI resistance are greatly needed. This review provides an overview of BCR signaling, a summary of the current therapeutic landscape, and a discussion of the ongoing trials targeting BCR-associated kinases.

Kinase-impaired BTK mutations are susceptible to clinical-stage BTK and IKZF1/3 degrader NX-2127

Increasing use of covalent and noncovalent inhibitors of Bruton's tyrosine kinase (BTK) has elucidated a series of acquired drug-resistant BTK mutations in patients with B cell malignancies. Here we identify inhibitor resistance mutations in BTK with distinct enzymatic activities, including some that impair BTK enzymatic activity while imparting novel protein-protein interactions that sustain B cell receptor (BCR) signaling. Furthermore, we describe a clinical-stage BTK and IKZF1/3 degrader, NX-2127, that can bind and proteasomally degrade each mutant BTK proteoform, resulting in potent blockade of BCR signaling. Treatment of chronic lymphocytic leukemia with NX-2127 achieves >80% degradation of BTK in patients and demonstrates proof-of-concept therapeutic benefit. These data reveal an oncogenic scaffold function of mutant BTK that confers resistance across clinically approved BTK inhibitors but is overcome by BTK degradation in patients.

Treatment of Double-Refractory Chronic Lymphocytic Leukemia-An Unmet Clinical Need

Recent years have seen significant improvement in chronic lymphocytic leukemia (CLL) management. Targeting B-cell lymphoma (BCL-2) and Bruton's kinase (BTK) have become the main strategies to restrain CLL activity. These agents are generally well tolerated, but the discontinuation of these therapies happens due to resistance, adverse effects, and Richter's transformation. A growing population of patients who have previously used both BTK inhibitors and BCL2 suffer from the constriction of the following regimens. This review explores the resistance mechanisms for both ibrutinib and venetoclax. Moreover, we present innovative approaches evaluated for treating double-refractory CLL.

Real-world analysis of adverse event rates after initiation of ibrutinib among Medicare beneficiaries with chronic lymphocytic leukemia

BACKGROUND

The first-generation BTK inhibitor ibrutinib is a standard-of-care therapy in the treatment of chronic lymphocytic leukemia (CLL) despite potential side effects that often lead to discontinuation.

METHODS

This study used 2013-2019 claims data to describe the incidence rate of adverse events (AEs) among elderly Medicare beneficiaries newly initiating ibrutinib for CLL.

RESULTS

The final sample contained 11,870 Medicare beneficiaries with CLL (mean age 77.2) newly initiating ibrutinib, of whom 65.2% discontinued over mean follow-up of 2.3 years. The overall incidence rate of AEs was 62.5 per 1000 patient-months for all discontinuers and 32.9 per 1000 patient-months for non-discontinuers. Discontinuers had a higher incidence rate of AEs per 1000 patient-months compared with non-discontinuers for all AEs examined, including infection (22.8 vs. 14.5), atrial fibrillation (15.1 vs. 7.0), anemia (21.9 vs. 14.5), and arthralgia/myalgia (19.5 vs. 13.6).

CONCLUSION

In this first real-world study of a national sample of elderly US patients treated with ibrutinib, we found a clear unmet need for improved management of ibrutinib-related AEs and/or new treatments to improve real-world outcomes in patients with CLL.

Rituximab combined with Bruton tyrosine kinase inhibitor to treat elderly diffuse large B-cell lymphoma patients: Two case reports

BACKGROUND

Diffuse large B-cell lymphoma (DLBCL) is a common aggressive non-Hodgkin's lymphoma (NHL), accounting for 30%-40% of adult NHLs. This report aims to explore the efficacy and safety of rituximab combined with Bruton tyrosine kinase inhibitors (BTKis) in the treatment of elderly patients with DLBCL.

CASE SUMMARY

The clinical data of two elderly patients with DLBCL who received rituximab combined with BTKi in our hospital were retrospectively analyzed, and the literature was reviewed. The patients were treated with chemotherapy using the R-miniCHOP regimen for two courses. Then, they received rituximab in combination with BTKi.

CONCLUSION

The treatment experience in these cases demonstrates the potential efficacy of rituximab combined with BTKi to treat elderly DLBCL patients, thus providing a new treatment strategy.

Ibrutinib directly reduces CD8+T cell exhaustion independent of BTK

Introduction

Cytotoxic CD8+ T cell (CTL) exhaustion is a dysfunctional state of T cells triggered by persistent antigen stimulation, with the characteristics of increased inhibitory receptors, impaired cytokine production and a distinct transcriptional profile. Evidence from immune checkpoint blockade therapy supports that reversing T cell exhaustion is a promising strategy in cancer treatment. Ibrutinib, is a potent inhibitor of BTK, which has been approved for the treatment of chronic lymphocytic leukemia. Previous studies have reported improved function of T cells in ibrutinib long-term treated patients but the mechanism remains unclear. We investigated whether ibrutinib directly acts on CD8+ T cells and reinvigorates exhausted CTLs.

Methods

We used an established in vitro CTL exhaustion system to examine whether ibrutinib can directly ameliorate T cell exhaustion. Changes in inhibitory receptors, transcription factors, cytokine production and killing capacity of ibrutinib-treated exhausted CTLs were detected by flow cytometry. RNA-seq was performed to study transcriptional changes in these cells. Btk deficient mice were used to confirm that the effect of ibrutinib was independent of BTK expression.

Results

We found that ibrutinib reduced exhaustion-related features of CTLs in an in vitro CTL exhaustion system. These changes included decreased inhibitory receptor expression, enhanced cytokine production, and downregulation of the transcription factor TOX with upregulation of TCF1. RNA-seq further confirmed that ibrutinib directly reduced the exhaustion-related transcriptional profile of these cells. Importantly, using btk deficient mice we showed the effect of ibrutinib was independent of BTK expression, and therefore mediated by one of its other targets.

Discussion

Our study demonstrates that ibrutinib directly ameliorates CTL exhaustion, and provides evidence for its synergistic use with cancer immunotherapy.

Structure of BTK kinase domain with the second-generation inhibitors acalabrutinib and tirabrutinib

Bruton's tyrosine kinase (BTK) is the target of the therapeutic agent, Ibrutinib, that treats chronic lymphocyte leukemia (CLL), mantle cell lymphoma (MCL) and other B cell malignancies. Ibrutinib is a first in class, covalent BTK inhibitor that limits B-cell survival and proliferation. Designing new inhibitors of BTK has been an important objective for advancing development of improved therapeutic agents against cancer and autoimmune disorders. Based on the success of Ibrutinib, several second-generation irreversible BTK inhibitors have been developed that exhibit fewer off-target effects. However, the binding-mode and their interaction with Btk have not been experimentally determined and evaluated at atomic resolution. Here we determined the first crystal structure of the BTK kinase domain in complex with acalabrutinib. In addition, we report a structure of the BTK/tirabrutinib complex and compare these structures with previously solved structures. The structures provide insight in the superior selectivity reported for acalabrutinb and guide future BTK inhibitor development.

Detailed safety profile of acalabrutinib vs ibrutinib in previously treated chronic lymphocytic leukemia in the ELEVATE-RR trial

ELEVATE-RR demonstrated noninferior progression-free survival and lower incidence of key adverse events (AEs) with acalabrutinib vs ibrutinib in previously treated chronic lymphocytic leukemia. We further characterize AEs of acalabrutinib and ibrutinib via post hoc analysis. Overall and exposure-adjusted incidence rate was assessed for common Bruton tyrosine kinase inhibitor-associated AEs and for selected events of clinical interest (ECIs). AE burden scores based on previously published methodology were calculated for AEs overall and selected ECIs. Safety analyses included 529 patients (acalabrutinib, n = 266; ibrutinib, n = 263). Among common AEs, incidences of any-grade diarrhea, arthralgia, urinary tract infection, back pain, muscle spasms, and dyspepsia were higher with ibrutinib, with 1.5- to 4.1-fold higher exposure-adjusted incidence rates. Incidences of headache and cough were higher with acalabrutinib, with 1.6- and 1.2-fold higher exposure-adjusted incidence rate, respectively. Among ECIs, incidences of any-grade atrial fibrillation/flutter, hypertension, and bleeding were higher with ibrutinib, as were exposure-adjusted incidence rates (2.0-, 2.8-, and 1.6-fold, respectively); incidences of cardiac events overall (the Medical Dictionary for Regulatory Activities system organ class) and infections were similar between arms. Rate of discontinuation because of AEs was lower for acalabrutinib (hazard ratio, 0.62; 95% confidence interval, 0.41-0.93). AE burden score was higher for ibrutinib vs acalabrutinib overall and for the ECIs atrial fibrillation/flutter, hypertension, and bleeding. A limitation of this analysis is its open-label study design, which may influence the reporting of more subjective AEs. Overall, event-based analyses and AE burden scores demonstrated higher AE burden overall and specifically for atrial fibrillation, hypertension, and hemorrhage with ibrutinib vs acalabrutinib. This trial was registered at www.clinicaltrials.gov as #NCT02477696.

Treatment Refractoriness in Chronic Lymphocytic Leukemia: Old and New Molecular Biomarkers

Chronic lymphocytic leukemia (CLL) is the most common leukemia in adults. Despite its indolent clinical course, therapy refractoriness and disease progression still represent an unmet clinical need. Before the advent of pathway inhibitors, chemoimmunotherapy (CIT) was the commonest option for CLL treatment and is still widely used in areas with limited access to pathway inhibitors. Several biomarkers of refractoriness to CIT have been highlighted, including the unmutated status of immunoglobulin heavy chain variable genes and genetic lesions of TP53, BIRC3 and NOTCH1. In order to overcome resistance to CIT, targeted pathway inhibitors have become the standard of care for the treatment of CLL, with practice-changing results obtained through the inhibitors of Bruton tyrosine kinase (BTK) and BCL2. However, several acquired genetic lesions causing resistance to covalent and noncovalent BTK inhibitors have been reported, including point mutations of both BTK (e.g., C481S and L528W) and PLCG2 (e.g., R665W). Multiple mechanisms are involved in resistance to the BCL2 inhibitor venetoclax, including point mutations that impair drug binding, the upregulation of BCL2-related anti-apoptotic family members, and microenvironmental alterations. Recently, immune checkpoint inhibitors and CAR-T cells have been tested for CLL treatment, obtaining conflicting results. Potential refractoriness biomarkers to immunotherapy were identified, including abnormal levels of circulating IL-10 and IL-6 and the reduced presence of CD27⁺CD45RO^- CD8⁺ T cells.

The Management of Relapsed or Refractory Waldenström's Macroglobulinemia

Waldenström's macroglobulinemia (WM) is an immunoglobulin M monoclonal gammopathy produced by a bone marrow lymphoplasmacytic lymphoma, an indolent non-Hodgkin lymphoma in which the cure is still an unmet challenge. Combinations with alkylating agents, purine analogs, and monoclonal antibodies, Bruton tyrosine kinase, and proteasome inhibitors are used for the treatment of relapsed and refractory patients. Moreover, new additional agents can be seen on the horizon as potential effective therapies. No consensus on a preferred treatment in the relapsed setting is available yet.

Synergistic disruption of BTK and BCL-2 causes apoptosis while inducing ferroptosis in double-hit lymphoma

Double-hit lymphoma (DHL) is an aggressive subset of Diffuse Large B-cell Lymphoma (DLBCL) with poor outcomes and without satisfying treatment options. BTK inhibitor monotherapy is ineffective to suppress aggressive lymphoma. Hence, combination with other potential agents is warranted. Here, we demonstrated the second generation of BTK inhibitor, zanubrutinib, and a BCL-2 inhibitor, navitoclax, worked in synergistic manner to suppress DHL. Comprehensive in silico approach by interrogating single-cell to bulk-level profiling was employed along with in vitro and in vivo validation in DHL cell lines. Ablation of BTK enhanced sensitivity to navitoclax and suppressed proliferation of DHL cells. Combination of second generation of BTK inhibitor with navitoclax synergistically suppressed DLBCL cells with higher synergy score in DHL subset. The drug combination triggered apoptosis and ferroptosis, with the latter being characterized by reactive oxygen species (ROS) accumulation, extensive lipid peroxidation, and depletion of reduced glutathione. Moreover, ablation of BTK sensitized DHL cells to ferroptosis. Mechanistically, disruption of BTK and BCL-2 triggered ferroptosis by downregulating NRF2 and HMOX1, while deactivating GPX4. Combination of zanubrutinib and navitoclax effectively suppressed tumor growth in vivo. Our data suggest that zanubrutinib and navitoclax synergistically suppressed DHL by inducing apoptosis and ferroptosis.

2-Arachidonoylglycerol Modulates CXCL12-Mediated Chemotaxis in Mantle Cell Lymphoma and Chronic Lymphocytic Leukemia

To survive chemotherapy, lymphoma cells can relocate to protective niches where they receive support from the non-malignant cells. The biolipid 2-arachidonoylglycerol (2-AG), an agonist for the cannabinoid receptors CB1 and CB2, is released by stromal cells in the bone marrow. To investigate the role of 2-AG in lymphoma, we analyzed the chemotactic response of primary B-cell lymphoma cells enriched from peripheral blood of twenty-two chronic lymphocytic leukemia (CLL) and five mantle cell lymphoma (MCL) patients towards 2-AG alone and/or to the chemokine CXCL12. The expression of cannabinoid receptors was quantified using qPCR and the protein levels visualized by immunofluorescence and Western blot. Surface expression of CXCR4, the main cognate receptor to CXCL12, was analyzed by flow cytometry. Phosphorylation of key downstream signaling pathways activated by 2-AG and CXCL12 were measured by Western blot in three MCL cell lines and two primary CLL samples. We report that 2-AG induces chemotaxis in 80% of the primary samples, as well as 2/3 MCL cell lines. 2-AG induced in a dose-dependent manner, the migration of JeKo-1 cell line via CB1 and CB2. 2-AG affected the CXCL12-mediated chemotaxis without impacting the expression or internalization of CXCR4. We further show that 2-AG modulated p38 and p44/42 MAPK activation. Our results suggest that 2-AG has a previously unrecognized role in the mobilization of lymphoma cells by effecting the CXCL12-induced migration and the CXCR4 signaling pathways, however, with different effects in MCL compared to CLL.

Costunolide covalently targets NACHT domain of NLRP3 to inhibit inflammasome activation and alleviate NLRP3-driven inflammatory diseases

The NLRP3 inflammasome's core and most specific protein, NLRP3, has a variety of functions in inflammation-driven diseases. Costunolide (COS) is the major active ingredient of the traditional Chinese medicinal herb Saussurea lappa and has anti-inflammatory activity, but the principal mechanism and molecular target of COS remain unclear. Here, we show that COS covalently binds to cysteine 598 in NACHT domain of NLRP3, altering the ATPase activity and assembly of NLRP3 inflammasome. We declare COS's great anti-inflammasome efficacy in macrophages and disease models of gouty arthritis and ulcerative colitis via inhibiting NLRP3 inflammasome activation. We also reveal that the α-methylene-γ-butyrolactone motif in sesquiterpene lactone is the certain active group in inhibiting NLRP3 activation. Taken together, NLRP3 is identified as a direct target of COS for its anti-inflammasome activity. COS, especially the α-methylene-γ-butyrolactone motif in COS structure, might be used to design and produce novel NLRP3 inhibitors as a lead compound.

BMX controls 3βHSD1 and sex steroid biosynthesis in cancer

Prostate cancer is highly dependent on androgens and the androgen receptor (AR). Hormonal therapies inhibit gonadal testosterone production, block extragonadal androgen biosynthesis, or directly antagonize AR. Resistance to medical castration occurs as castration-resistant prostate cancer (CRPC) and is driven by reactivation of the androgen-AR axis. 3β-hydroxysteroid dehydrogenase-1 (3βHSD1) serves as the rate-limiting step for potent androgen synthesis from extragonadal precursors, thereby stimulating CRPC. Genetic evidence in men demonstrates the role of 3βHSD1 in driving CRPC. In postmenopausal women, 3βHSD1 is required for synthesis of aromatase substrates and plays an essential role in breast cancer. Therefore, 3βHSD1 lies at a critical junction for the synthesis of androgens and estrogens, and this metabolic flux is regulated through germline-inherited mechanisms. We show that phosphorylation of tyrosine 344 (Y344) occurs and is required for 3βHSD1 cellular activity and generation of Δ4, 3-keto-substrates of 5α-reductase and aromatase, including in patient tissues. BMX directly interacts with 3βHSD1 and is necessary for enzyme phosphorylation and androgen biosynthesis. In vivo blockade of 3βHSD1 Y344 phosphorylation inhibits CRPC. These findings identify what we believe to be new hormonal therapy pharmacologic vulnerabilities for sex-steroid dependent cancers.

Current state of NK cell-mediated immunotherapy in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) has become one of the most common hematological diseases in western countries, with an annual incidence of 42/100,000. Conventional chemotherapy and targeted therapeutic drugs showed limitations in prognosis or in efficiency in high-risk patients. Immunotherapy represented is one of the most effective therapeutic approaches with the potential of better effect and prognosis. Natural killer (NK) cells are good options for immunotherapy as they can effectively mediate anti-tumor activity of immune system by expressing activating and inhibiting receptors and recognizing specific ligands on various tumor cells. NK cells are critical in the immunotherapy of CLL by enhancing self-mediated antibody-dependent cytotoxicity (ADCC), allogeneic NK cell therapy and chimeric antigen receptor-natural killer (CAR-NK) cell therapy. In this article, we reviewed the features, working mechanisms, and receptors of NK cells, and the available evidence of the advantages and disadvantages of NK cell-based immunotherapies, and put forward future study directions in this field.

Proteolysis-targeting chimaeras (PROTACs) as pharmacological tools and therapeutic agents: advances and future challenges

Proteolysis-targeting chimaeras (PROTACs) have been developed to be an emerging technology for targeted protein degradation and attracted the favour of academic institutions, large pharmaceutical enterprises, and biotechnology companies. The mechanism is based on the inhibition of protein function by hijacking a ubiquitin E3 ligase for protein degradation. The heterobifunctional PROTACs contain a ligand for recruiting an E3 ligase, a linker, and another ligand to bind with the protein targeted for degradation. To date, PROTACs targeting ∼70 proteins, many of which are clinically validated drug targets, have been successfully developed with several in clinical trials for diseases therapy. In this review, the recent advances in PROTACs against clinically validated drug targets are summarised and the chemical structure, cellular and in vivo activity, pharmacokinetics, and pharmacodynamics of these PROTACs are highlighted. In addition, the potential advantages, challenges, and prospects of PROTACs technology in disease treatment are discussed.

Bruton's tyrosine kinase inhibitors in the treatment of primary central nervous system lymphoma: A mini-review

Primary central nervous system lymphoma (PCNSL) is a highly aggressive brain tumor with poor prognosis if no treatment. The activation of the NF-κB (nuclear factor kappa-B) is the oncogenic hallmark of PCNSL, and it was driven by B cell receptor (BCR) and Toll-like receptor (TLR) signaling pathways. The emergence of Bruton's tyrosine kinase inhibitors (BTKis) has brought the dawn of life to patients with PCNSL. This review summarizes the management of PCNSL with BTKis and potential molecular mechanisms of BTKi in the treatment of PCNSL. And the review will focus on the clinical applications of BTKi in the treatment of PCNSL including the efficacy and adverse events, the clinical trials currently being carried out, the underlying mechanisms of resistance to BTKi and possible solutions to drug resistance.

Immunotherapy approaches for hematological cancers

Hematological cancers such as leukemia, lymphoma, and multiple myeloma have traditionally been treated with chemo and radiotherapy approaches. Introduction of immunotherapies for treatment of these diseases has led to patient remissions that would not have been possible with traditional approaches. In this critical review we identify main disease characteristics, symptoms, and current treatment options. Five common immunotherapies, namely checkpoint inhibitors, vaccines, cell-based therapies, antibodies, and oncolytic viruses, are described, and their applications in hematological cancers are critically discussed.

Synergistic Effects of Zanubrutinib Combined With CD19 CAR-T Cells in Raji Cells in Vitro and in Vivo

Background and Objects: Bruton's tyrosine kinase inhibitors are commonly used and effective for lymphoma and chronic lymphocytic leukemia (CLL). Ibrutinib might improve the effect of anti-cluster of differentiation 19 (CD19) chimeric antigen receptor (CD19 CAR) T-cell therapy in lymphoma, but the effects of zanubrutinib combined with CAR-T cells is unclear. Methods: We selected a low effect-target ratio (E:T = 1:3) to study this synergistic effect in vitro. The programed cell death protein 1 (PD-1) expression in CD19 CAR-T cells and immune phenotype of T lymphocytes were analyzed by flow cytometry (FCM). We selected CD19 CAR-T cells of a patient with diffuse large B cell lymphoma (DLBCL) to study the synergistic effect of zanubrutinib with CAR-T cells by bioluminescence imaging monitoring. The CD19 CAR-T cells expansion in mice was compared by FCM. Results: Zanubrutinib and ibrutinib had dose-dependent toxicity on both CAR-T cells and lymphoma cells. But there was no significant synergistic effect of the CD19 CAR-T cells combined with zanubrutinib/ibrutinib in vitro. The PD-1 expression in CD19 CAR-T cells increased when the CD19 CAR-T cells were co-cultured with Raji cells and decreased when ibrutinib was added in culture, but zanubrutinib had no such effect. The extinction of luciferase expression was more obvious in the polytherapy group of ibrutinib and CD19 CAR-T cell than that in the other groups. Moreover, the proportion of CAR-T cells in the combination therapy group of CD19 CAR-T cells and ibrutinib was higher than that of the polytherapy group of CD19 CAR-T cells with zanubrutinib group. The synergistic effect could be observed obviously in mice receiving ibrutinib combined with CD19 CAR-T cells. But zanubrutinib cannot perform joint therapy effect either in vitro or in mice. Conclusion: Zanubrutinib might have no joint therapy effect with CD19 CAR-T cells neither in vitro nor in mice, but the mechanism of different curative effects requires our further research and exploration.

Bruton tyrosine kinase inhibitors in B-cell lymphoma: beyond the antitumour effect

Targeting B-cell receptor signalling using Bruton tyrosine kinase (BTK) inhibitors (BTKis) has become a highly successful treatment modality for B-cell malignancies, especially for chronic lymphocytic leukaemia. However, long-term administration of BTKis can be complicated by adverse on- and/or off-target effects in particular cell types. BTK is widely expressed in cells of haematopoietic origin, which are pivotal components of the tumour microenvironment. BTKis, thus, show broad immunomodulatory effects on various non-B immune cell subsets by inhibiting specific immune receptors, including T-cell receptor and Toll-like receptors. Furthermore, due to the off-target inhibition of other kinases, such as IL-2-inducible T-cell kinase, epidermal growth factor receptor, and the TEC and SRC family kinases, BTKis have additional distinct effects on T cells, natural killer cells, platelets, cardiomyocytes, and other cell types. Such mechanisms of action might contribute to the exceptionally high clinical efficacy as well as the unique profiles of adverse effects, including infections, bleeding, and atrial fibrillation, observed during BTKi administration. However, the immune defects and related infections caused by BTKis have not received sufficient attention in clinical studies till date. The broad involvement of BTK in immunological pathways provides a rationale to combine BTKis with specific immunotherapies, such as immune checkpoint inhibitor or chimeric antigen receptor-T-cell therapy, for the treatment of relapsed or refractory diseases. This review discusses and summarises the above-mentioned issues as a reference for clinicians and researchers.

Bruton’s Tyrosine Kinase Inhibitor Zanubrutinib Effectively Modulates Cancer Resistance by Inhibiting Anthracycline Metabolism and Efflux

Zanubrutinib (ZAN) is a Bruton’s tyrosine kinase inhibitor recently approved for the treatment of some non-Hodgkin lymphomas. In clinical trials, ZAN is often combined with standard anthracycline (ANT) chemotherapy. Although ANTs are generally effective, drug resistance is a crucial obstacle that leads to treatment discontinuation. This study showed that ZAN counteracts ANT resistance by targeting aldo-keto reductase 1C3 (AKR1C3) and ATP-binding cassette (ABC) transporters. AKR1C3 catalyses the transformation of ANTs to less potent hydroxy-metabolites, whereas transporters decrease the ANT-effective concentrations by pumping them out of the cancer cells. In our experiments, ZAN inhibited the AKR1C3-mediated inactivation of daunorubicin (DAUN) at both the recombinant and cellular levels. In the drug combination experiments, ZAN synergistically sensitised AKR1C3-expressing HCT116 and A549 cells to DAUN treatment. Gene induction studies further confirmed that ZAN did not increase the intracellular level of AKR1C3 mRNA; thus, the drug combination effect is not abolished by enzyme induction. Finally, in accumulation assays, ZAN was found to interfere with the DAUN efflux mediated by the ABCB1, ABCG2, and ABCC1 transporters, which might further contribute to the reversal of ANT resistance. In summary, our data provide the rationale for ZAN inclusion in ANT-based therapy and suggest its potential for the treatment of tumours expressing AKR1C3 and/or the above-mentioned ABC transporters.

BTK-independent regulation of calcium signalling downstream of the B-cell receptor in malignant B-cells

BTK inhibitors (BTKi) have dramatically improved outcomes for patients with chronic lymphocytic leukaemia (CLL) and some forms of B-cell lymphoma. However, new strategies are needed to enhance responses. Here we have performed a detailed analysis of the effects of BTKi on B-cell receptor (BCR)-induced signalling using primary malignant cells from CLL patients and B-lymphoma cell lines. Although BTK is considered as a key activator of PLCγ2, BTKi (ibrutinib and acalabrutinib) failed to fully inhibit calcium responses in CLL samples with strong BCR signalling capacity. This BTKi-resistant calcium signalling was sufficient to engage downstream calcium-dependent transcription and suppress CLL cell apoptosis and was entirely independent of BTK and not just its kinase activity as similar results were obtained using a BTK-degrading PROTAC. BTK-independent calcium signalling was also observed in two B-lymphoma cell lines where BTKi had little effect on the initial phase of the calcium response but did accelerate the subsequent decline in intracellular calcium. In contrast to BTKi, calcium responses were completely blocked by inhibition of SYK in CLL and lymphoma cells. Engagement of BTK-independent calcium responses was associated with BTK-independent phosphorylation of PLCγ2 on Y753 and Y759 in both CLL and lymphoma cells. Moreover, in CLL samples, inhibition of RAC, which can mediate BTK-independent activation of PLCγ2, cooperated with ibrutinib to suppress calcium responses. BTK-independent calcium signalling may limit the effectiveness of BTKi to suppress BCR signalling responses and our results suggest inhibition of SYK or dual inhibition of BTK and RAC as alternative strategies to strengthen pathway blockade.

Medicinal Chemistry Strategies for the Development of Bruton's Tyrosine Kinase Inhibitors against Resistance

Despite significant efficacy, one of the major limitations of small-molecule Bruton's tyrosine kinase (BTK) agents is the presence of clinically acquired resistance, which remains a major clinical challenge. This Perspective focuses on medicinal chemistry strategies for the development of BTK small-molecule inhibitors against resistance, including the structure-based design of BTK inhibitors targeting point mutations, e.g., (i) developing noncovalent inhibitors from covalent inhibitors, (ii) avoiding steric hindrance from mutated residues, (iii) making interactions with the mutated residue, (iv) modifying the solvent-accessible region, and (v) developing new scaffolds. Additionally, a comparative analysis of multi-inhibitions of BTK is presented based on cross-comparisons between 2916 unique BTK ligands and 283 other kinases that cover 7108 dual/multiple inhibitions. Finally, targeting the BTK allosteric site and uding proteolysis-targeting chimera (PROTAC) as two potential strategies are addressed briefly, while also illustrating the possibilities and challenges to find novel ligands of BTK.

Exploiting the ubiquitin system in myeloid malignancies. From basic research to drug discovery in MDS and AML

The ubiquitin-proteasome system is the crucial homeostatic mechanism responsible for the degradation and turnover of proteins. As such, alterations at this level are often associated with oncogenic processes, either through accumulation of undegraded pathway effectors or, conversely, excessive degradation of tumor-suppressing factors. Therefore, investigation of the ubiquitin- proteasome system has gained much attraction in recent years, especially in the context of hematological malignancies, giving rise to efficient therapeutics such as bortezomib for multiple myeloma. Current investigations are now focused on manipulating protein degradation via fine-tuning of the ubiquitination process through inhibition of deubiquitinating enzymes or development of PROTAC systems for stimulation of ubiquitination and protein degradation. On the other hand, the efficiency of Thalidomide derivates in myelodysplastic syndromes (MDS), such as Lenalidomide, acted as the starting point for the development of targeted leukemia-associated protein degradation molecules. These novel molecules display high efficiency in overcoming the limitations of current therapeutic regimens, such as refractory diseases. Therefore, in this manuscript we will address the therapeutic opportunities and strategies based on the ubiquitin-proteasome system, ranging from the modulation of deubiquitinating enzymes and, conversely, describing the potential of modern targeted protein degrading molecules and their progress into clinical implementation.

[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.

Cardiotoxicity of BTK inhibitors: ibrutinib and beyond

INTRODUCTION

The development of Bruton<apos;>s Tyrosine Kinase (BTK) inhibitors has transformed the treatment of B-cell malignancies and other non-malignant conditions. Management of the unique cardiotoxic profile of these agents requires prompt recognition and a multi-disciplinary approach.

AREAS COVERED

The increasing indications and addition of newer agents to clinical practice and emergence of BTK inhibitor-related cardiac adverse events have complicated the management decisions for utilization of this class of therapy. We review the incidence, mechanisms, and management approaches for BTK inhibitor-related atrial fibrillation, hypertension, and ventricular arrhythmias.

EXPERT OPINION

The newer BTK inhibitor acalabrutinib represents a new standard of care in front-line chronic lymphocytic leukemia (CLL) given the results of the ELEVATE-RR trial demonstrating comparable efficacy and a more favorable toxicity profile especially with regard to cardiac adverse events as compared to ibrutinib. Often not recognized by clinicians, BTK inhibitor-induced hypertension is common and can be severe, requiring prompt recognition and initiation or adjustment of anti-hypertensive medications to prevent major adverse cardiac outcomes. Novel BTK inhibitors in development are being designed to overcome the patterns of resistance from first-generation agents and to minimize off-target kinase activity, with promising toxicity profiles in early trials.

Recent development of BTK-based dual inhibitors in the treatment of cancers

Bruton's tyrosine kinase (BTK) is a promising target in the treatment of various cancers. Despite the early success of BTK inhibitors in the clinic, these single-target drug therapies have limitations in their clinical applications, such as drug resistance. Several alternative strategies have been developed, including the use of dual inhibitors, to maximize the therapeutic potential of anticancer drugs. In this review, we highlight the scientific background and theoretical basis for developing BTK-based dual inhibitors, as well as the status of these agents in preclinical and clinical studies, and discuss further options in this field. We posit that these advances in BTK-based dual inhibitors confirm their feasibility for the treatment of refractory tumors, including those with drug resistance, and provide a framework for future drug design in this field. Accordingly, we anticipate increasingly rapid progress in the development of novel potent dual inhibitors and advanced clinical research on BTK-based dual inhibitors.

A Novel Finding of Lichenoid Drug Reaction From Ibrutinib Therapy

Ibrutinib is Burton’s tyrosine kinase inhibitor used in the treatment of chronic lymphocytic leukemia and other conditions. This drug has been generally thought to be well tolerated, although studies have identified a few distinct adverse effects, including gastrointestinal discomfort, nausea, diarrhea, and atrial fibrillation. Regarding cutaneous findings, ibrutinib has only been linked to two self-limiting forms of mild rashes generally. In this report, we discuss a lichenoid drug reaction to ibrutinib in a patient with chronic lymphocytic leukemia severe enough to result in drug discontinuation. This adverse effect has not been previously reported to our knowledge.

Druggable Molecular Pathways in Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL), the most common type of leukemia in adults, is characterized by a high degree of clinical heterogeneity that is influenced by the disease’s molecular complexity. The genes most frequently affected in CLL cluster into specific biological pathways, including B-cell receptor (BCR) signaling, apoptosis, NF-κB, and NOTCH1 signaling. BCR signaling and the apoptosis pathway have been exploited to design targeted medicines for CLL therapy. Consistently, molecules that selectively inhibit specific BCR components, namely Bruton tyrosine kinase (BTK) and phosphoinositide 3-kinase (PI3K) as well as inhibitors of BCL2, have revolutionized the therapeutic management of CLL patients. Several BTK inhibitors and PI3K inhibitors with different modes of action are currently used or are in development in advanced stage clinical trials. Moreover, the restoration of apoptosis by the BCL2 inhibitor venetoclax offers meaningful clinical activity with a fixed-duration scheme. Inhibitors of the BCR and of BCL2 are able to overcome the chemorefractoriness associated with high-risk genetic features, including TP53 disruption. Other signaling cascades involved in CLL pathogenesis, in particular NOTCH signaling and NF-kB signaling, already provide biomarkers for a precision medicine approach to CLL and may represent potential druggable targets for the future. The aim of the present review is to discuss the druggable pathways of CLL and to provide the biological background of the high efficacy of targeted biological drugs in CLL.

The Mysterious Actor-γδ T Lymphocytes in Chronic Lymphocytic Leukaemia (CLL)

Chronic lymphocytic leukaemia (CLL) is the most common leukaemia among adults. It is the clonal expansion of B cells expressing CD19 and CD5. Despite significant progress in treatment, CLL is still incurable. γδ T cells comprise an important subset of the cytotoxic T cells. Although γδ T cells in CLL are dysfunctional, they still can possibly be used for immunotherapy. The current paper reviews our understanding of γδ T lymphocytes in CLL.

The Role of Bruton's Kinase Inhibitors in Chronic Lymphocytic Leukemia: Current Status and Future Directions

The use of Bruton's tyrosine kinase (BTK) inhibitors has changed the management and clinical history of patients with chronic lymphocytic leukemia (CLL). BTK is a critical molecule that interconnects B-cell antigen receptor (BCR) signaling. BTKis are classified into two categories: irreversible (covalent) inhibitors and reversible (non-covalent) inhibitors. Ibrutinib was the first irreversible BTK inhibitor approved by the U.S. Food and Drug Administration in 2013 as a breakthrough therapy in CLL patients. Subsequently, several studies have evaluated the efficacy and safety of new agents with reduced toxicity when compared with ibrutinib. Two other irreversible, second-generation BTK inhibitors, acalabrutinib and zanubrutinib, were developed to reduce ibrutinib-mediated adverse effects. Additionally, new reversible BTK inhibitors are currently under development in early-phase studies to improve their activity and to diminish adverse effects. This review summarizes the pharmacology, clinical efficacy, safety, dosing, and drug-drug interactions associated with the treatment of CLL with BTK inhibitors and examines their further implications.

Utility of Bruton’s Tyrosine Kinase Inhibitors in Light Chain Amyloidosis Caused by Lymphoplasmacytic Lymphoma (Waldenström’s Macroglobulinemia)

Of the variety of immunoglobulin related amyloidosis (AL), immunoglobulin M (IgM) related AL represents only 6 to 10% of affected patients, and the majority of these cases are associated with underlying non-Hodgkin's Lymphoma including Waldenström's macroglobulinemia (WM). Ibrutinib, acalabrutinib, and zanubrutinib are Bruton tyrosine kinase (BTK) inhibitors approved for certain indolent B cell non-Hodgkin's lymphoma (NHL). BTK is a nonreceptor kinase involved in B-cell survival, proliferation, and interaction with the microenvironment. We retrospectively evaluated the tolerability and effectiveness of BTK inhibitors ibrutinib and acalabrutinib therapy in (n = 4) patients with IgM-related AL amyloidosis with underlying WM. Treatment was well tolerated with both hematologic and organ response in patients with AL amyloidosis in the setting of WM. Atrial fibrillation led to the discontinuation of ibrutinib in one patient, and acalabrutinib caused significant thumb hematoma needing dose reduction in another patient. All patients evaluated had the MYD88 mutation. This may explain the good response to BTK inhibitors therapy in our series. BTK inhibitors should be further investigated in larger prospective studies for treatment of AL amyloidosis in patients with lymphoplasmacytic lymphoma/WM.

Outcomes for Recurrent Mantle Cell Lymphoma Post-Ibrutinib Therapy: A Retrospective Cohort Study from a Japanese Administrative Database

INTRODUCTION

Treatment options in patients with mantle cell lymphoma (MCL) failing ibrutinib are limited, with no standard therapies defined. This study aimed to investigate real-world treatment patterns and outcomes for patients with MCL following ibrutinib.

METHODS

This study utilized a de-identified hospital-based claims database (Medical Data Vision) in Japan. Eligible patients were adults who were diagnosed with MCL and had received antitumor drugs between December 2010 and July 2020. Patients were followed from the first antitumor drug treatment until the end of available data up to July 2021. Time-to-event analyses utilized the Kaplan-Meier method. Factors for receiving post-ibrutinib therapy were explored with logistic regression analysis.

RESULTS

Of the 1386 patients who started antitumor drug therapy, 247 patients received and discontinued ibrutinib at any line of therapy. Among them, 137 patients (55.5%) received subsequent therapy. The median age at the end of ibrutinib therapy was 77 (range 42-95), and 44 patients had a dependent activity of daily living (ADL). Factors negatively associated with receiving post-ibrutinib therapy after discontinuation of ibrutinib were age ≥ 75 years (odds ratio [95% CI] 0.46 [0.26-0.80]) and emergency hospital admissions (0.37 [0.17-0.84]). Immediate post-ibrutinib therapy regimens were highly diverse, with BR (bendamustine, rituximab) only prescribed in more than 10% of patients. The median duration of post-ibrutinib therapy was 1.5 months (95% CI 1.07-2.07). The median overall survival from the end of ibrutinib therapy in patients regardless of the receipt of post-ibrutinib therapy (n = 247), in those who did not receive post-ibrutinib therapy (n = 110), and in those who received post-ibrutinib therapy (n = 137) was 5.6 months (95% CI 3.8-8.7), 2.3 months (95% CI 1.2-3.9), and 8.7 months (95% CI 5.6-13.8), respectively. The most common adverse event during post-ibrutinib therapy was infection, with the use of anti-infectives (17%).

CONCLUSIONS

Patients with MCL previously treated with ibrutinib have poor ability to carry out ADL and experience very poor outcomes. New safe, effective therapies are needed.

Structure-based virtual screening and biological evaluation of novel small-molecule BTK inhibitors

Bruton tyrosine kinase (BTK) is linked to multiple signalling pathways that regulate cellular survival, activation, and proliferation. A covalent BTK inhibitor has shown favourable outcomes for treating B cell malignant leukaemia. However, covalent inhibitors require a high reactive warhead that may contribute to unexpected toxicity, poor selectivity, or reduced effectiveness in solid tumours. Herein, we report the identification of a novel noncovalent BTK inhibitor. The binding interactions (i.e. interactions from known BTK inhibitors) for the BTK binding site were identified and incorporated into a structure-based virtual screening (SBVS). Top-rank compounds were selected and testing revealed a BTK inhibitor with >50% inhibition at 10 µM concentration. Examining analogues revealed further BTK inhibitors. When tested across solid tumour cell lines, one inhibitor showed favourable inhibitory activity, suggesting its potential for targeting BTK malignant tumours. This inhibitor could serve as a basis for developing an effective BTK inhibitor targeting solid cancers.

The role of Bruton's tyrosine kinase in the immune system and disease

Bruton's tyrosine kinase (BTK) is a TEC kinase with a multifaceted role in B-cell biology and function, highlighted by its position as a critical component of the B-cell receptor signalling pathway. Due to its role as a therapeutic target in several haematological malignancies including chronic lymphocytic leukaemia, BTK has been gaining tremendous momentum in recent years. Within the immune system, BTK plays a part in numerous pathways and cells beyond B cells (i.e. T cells, macrophages). Not surprisingly, BTK has been elucidated to be a driving factor not only in lymphoproliferative disorders but also in autoimmune diseases and response to infection. To extort this role, BTK inhibitors such as ibrutinib have been developed to target BTK in other diseases. However, due to rising levels of resistance, the urgency to develop new inhibitors with alternative modes of targeting BTK is high. To meet this demand, an expanding list of BTK inhibitors is currently being trialled. In this review, we synopsize recent discoveries regarding BTK and its role within different immune cells and pathways. Additionally, we discuss the broad significance and relevance of BTK for various diseases ranging from haematology and rheumatology to the COVID-19 pandemic. Overall, BTK signalling and its targetable nature have emerged as immensely important for a wide range of clinical applications. The development of novel, more specific and less toxic BTK inhibitors could be revolutionary for a significant number of diseases with yet unmet treatment needs.

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.

Pyrrolo[2,1-f][1,2,4]triazine: a promising fused heterocycle to target kinases in cancer therapy

Cancer is the second leading cause of death worldwide responsible for about 10 million deaths per year. To date several approaches have been developed to treat this deadly disease including surgery, chemotherapy, radiation therapy, hormonal therapy, targeted therapy, and synthetic lethality. The targeted therapy refers to targeting only specific proteins or enzymes that are dysregulated in cancer rather than killing all rapidly dividing cells, has gained much attention in the recent past. Kinase inhibition is one of the most successful approaches in targeted therapy. As of 30 March 2021, FDA has approved 65 small molecule protein kinase inhibitors and most of them are for cancer therapy. Interestingly, several kinase inhibitors contain one or more fused heterocycles as part of their structures. Pyrrolo[2,1-f][1,2,4]triazine is one the most interesting fused heterocycle that is an integral part of several kinase inhibitors and nucleoside drugs viz. avapritinib and remdesivir. This review articles focus on the recent advances made in the development of kinase inhibitors containing pyrrolo[2,1-f][1,2,4]triazine scaffold.

Acalabrutinib Versus Ibrutinib in Previously Treated Chronic Lymphocytic Leukemia: Results of the First Randomized Phase III Trial

PURPOSE

Among Bruton's tyrosine kinase inhibitors, acalabrutinib has greater selectivity than ibrutinib, which we hypothesized would improve continuous therapy tolerability. We conducted an open-label, randomized, noninferiority, phase III trial comparing acalabrutinib and ibrutinib in patients with chronic lymphocytic leukemia (CLL).

METHODS

Patients with previously treated CLL with centrally confirmed del(17)(p13.1) or del(11)(q22.3) were randomly assigned to oral acalabrutinib 100 mg twice daily or ibrutinib 420 mg once daily until progression or unacceptable toxicity. The primary end point was independent review committee-assessed noninferiority of progression-free survival (PFS).

RESULTS

Overall, 533 patients (acalabrutinib, n = 268; ibrutinib, n = 265) were randomly assigned. At the data cutoff, 124 (46.3%) acalabrutinib patients and 109 (41.1%) ibrutinib patients remained on treatment. After a median follow-up of 40.9 months, acalabrutinib was determined to be noninferior to ibrutinib with a median PFS of 38.4 months in both arms (95% CI acalabrutinib, 33.0 to 38.6 and ibrutinib, 33.0 to 41.6; hazard ratio: 1.00; 95% CI, 0.79 to 1.27). All-grade atrial fibrillation/atrial flutter incidence was significantly lower with acalabrutinib versus ibrutinib (9.4% v 16.0%; P = .02); among other selected secondary end points, grade 3 or higher infections (30.8% v 30.0%) and Richter transformations (3.8% v 4.9%) were comparable between groups and median overall survival was not reached in either arm (hazard ratio, 0.82; 95% CI, 0.59 to 1.15), with 63 (23.5%) deaths with acalabrutinib and 73 (27.5%) with ibrutinib. Treatment discontinuations because of adverse events occurred in 14.7% of acalabrutinib-treated patients and 21.3% of ibrutinib-treated patients.

CONCLUSION

In this first direct comparison of less versus more selective Bruton's tyrosine kinase inhibitors in CLL, acalabrutinib demonstrated noninferior PFS with fewer cardiovascular adverse events.

The road to chemotherapy-free treatment in chronic lymphocytic leukaemia

PURPOSE OF REVIEW

The treatment landscape of chronic lymphocytic leukaemia (CLL) has tremendously evolved in the last decades, from chemo to chemoimmunotherapy (CIT) and, eventually, to pathway inhibitors that target critical pathways for leukaemic cells survival. Also, treatment goals are moving towards achieving undetectable minimal residual disease with little toxicity.

RECENT FINDINGS

We performed a thorough review of the history of treatment approvals by both the Food and Drug Administration (FDA) and the European Medicines Agency (EMA). This review especially focuses on therapies that are currently approved by both agencies. The indications and particular characteristics of each drug are examined.

SUMMARY

Currently available treatment approaches for CLL offer the opportunity to individualize therapy for every single patient with CLL. Inhibitors of B-cell receptor (BCR) signalling pathways and antiapoptotic proteins are nowadays the treatment of choice for most CLL patients, but CIT can be an option for younger and fit patients with low-risk disease [mutated IGHV, no del(11q) or del(17p)/TP53 mutations].

The Role of BTK Inhibition in the Treatment of Chronic Lymphocytic Leukemia: A Clinical View

The B cell receptor (BCR) signaling pathway is functional and has critical cell survival implications in B cell malignancies, such as chronic lymphocytic leukemia (CLL). Orally administered small molecule tyrosine kinase inhibitors of members of the BCR signaling pathway have proven to be transformational in treatment of CLL. The first-generation inhibitor, ibrutinib, covalently binds to the C481 amino acid of Bruton's tyrosine kinase (BTK), thereby irreversibly inhibiting its kinase activity, and interferes with the biology of the cells, ultimately resulting in CLL cell death and therapeutic response. Remissions are not deep to the point of considering discontinuation for most patients, but BTK-inhibitor-based therapy provides exceptional long-term disease control with continuous treatment. There are in-class toxicities and more selective second- and subsequent-generation agents and reversible inhibitors have been developed with the intent of reducing toxicities. Also, strategies to subvert resistance have included tighter or alternative, non-covalent, inhibitor binding. Furthermore, other strategies to deplete BTK protein, such as degraders, are in development and being tested in the clinic. Ultimately, the development and approval of these agents targeting BTK have ushered in a new era of chemotherapy-free treatments with remarkably improved survival outcomes for patients with CLL.

The resistance mechanisms and treatment strategies of BTK inhibitors in B-cell lymphoma

Bruton's tyrosine kinase inhibitors (BTKi) have revolutionized the treatment of B‐cell lymphoma (BCL). These drugs interfere with the mechanisms underlying malignant B‐cell pathophysiology, allowing better drug response as well as low toxicity. However, these multiple mechanisms also lead to drug resistance, which compromised the treatment outcome and needs to be solved urgently. This review focuses on genomic variations (such as BTK and its downstream PCLG2 mutations as well as Del 8p, 2p+, Del 6q/8p, BIRC3, TRAF2, TRAF3, CARD11, MYD88, and CCND1 mutations) and related pathways (such as PI3K/Akt/mTOR, NF‐κB, MAPK signaling pathways, overexpression of B‐cell lymphoma 6, platelet‐derived growth factor, toll‐like receptors, and microenvironment, cancer stem cells, and exosomes) involved in cancer pathophysiology to discuss the mechanisms underlying resistance to BTKi. We have also reviewed the newly reported drug resistance mechanisms and the proposed potential treatment strategies (the next‐generation BTKi, proteolysis‐targeting chimera‐BTK, XMU‐MP‐3, PI3K‐Akt‐mTOR pathway, MYC or LYN kinase inhibitor, and other small‐molecule targeted drugs) to overcome drug resistance. The findings presented in this review lay a strong foundation for further research in this field.

Kinase Inhibition in Relapsed/Refractory Leukemia and Lymphoma Settings: Recent Prospects into Clinical Investigations

Cancer is still a major barrier to life expectancy increase worldwide, and hematologic neoplasms represent a relevant percentage of cancer incidence rates. Tumor dependence of continuous proliferative signals mediated through protein kinases overexpression instigated increased strategies of kinase inhibition in the oncologic practice over the last couple decades, and in this review, we focused our discussion on relevant clinical trials of the past five years that investigated kinase inhibitor (KI) usage in patients afflicted with relapsed/refractory (R/R) hematologic malignancies as well as in the pharmacological characteristics of available KIs and the dissertation about traditional chemotherapy treatment approaches and its hindrances. A trend towards investigations on KI usage for the treatment of chronic lymphoid leukemia and acute myeloid leukemia in R/R settings was observed, and it likely reflects the existence of already established treatment protocols for chronic myeloid leukemia and acute lymphoid leukemia patient cohorts. Overall, regimens of KI treatment are clinically manageable, and results are especially effective when allied with tumor genetic profiles, giving rise to encouraging future prospects of an era where chemotherapy-free treatment regimens are a reality for many oncologic patients.

Progress in the development of small molecular inhibitors of the Bruton's tyrosine kinase (BTK) as a promising cancer therapy

Bruton tyrosine kinase (BTK) is a key kinase in the B cell antigen receptor signal transduction pathway, which is involved in the regulation of the proliferation, differentiation and apoptosis of B cells. BTK has become a significant target for the treatment of hematological malignancies and autoimmune diseases. Ibrutinib, the first-generation BTK inhibitor, has made a great contribution to the treatment of B cell malignant tumors, but there are still some problems such as resistance or miss target of site mutation. Therefore, there is an imperative need to develop novel BTK inhibitors to overcome these problems. Besides, proteolysis targeting chimera (PROTAC) technology has been successfully applied to the development of BTK degradation agents, which has opened a fresh way for the BTK targeted treatment. This paper reviews the biological function of BTK, the discovery and development of BTK targeted drugs as a promising cancer therapy. It mainly reviews the binding sites and structural characteristics of BTK, structure-activity relationships, activity and drug resistance of BTK inhibitors, as well as potential treatment strategies to overcome the resistance of BTK, which provides a reference for the rational design and development of new powerful BTK inhibitors.

Severe infections in patients with lymphoproliferative diseases treated with new targeted drugs: A multicentric real-world study

Background

Lymphoid neoplasms treatment has recently been renewed to increase antitumor efficacy and conventional chemotherapies toxicities. Limited data have been published about the infection risk associated with these new drugs, therefore this study analyzes the infectious complications in patients with lymphoproliferative diseases (LPD) treated with monoclonal antibodies (obinutuzumab, ofatumumab, brentuximab, nivolumab, or pembrolizumab), BTK inhibitors (ibrutinib and acalabrutinib), PI3K inhibitors (idelalisib) and BCL2 inhibitors (venetoclax).

Methods

Multicenter retrospective study of 458 LPD patients treated with targeted therapies in real‐life setting, in 18 Spanish institutions, from the time of their commercial availability to August 2020.

Results

Severe infections incidence was 23% during 17‐month median follow‐up; cumulative incidence was higher in the first 3–6 months of targeted drug treatment and then decreased. The most frequent etiology was bacterial (54%). Nine (6%) Invasive fungal infections (IFI) were observed, in its majority in chronic lymphocytic leukemia (CLL) patients treated predominantly with ibrutinib. Significant risk factors for severe infection were: severe lymphopenia (p = 0.009, OR 4.7, range 1.3–1.7), combined targeted treatment vs single agent treatment (p = 0.014 OR 2.2 range 1.1–4.2) and previous rituximab (p = 0.03 OR 1.8, range 1.05–3.3). Infection‐related mortality was 6%. In 22% of patients with severe infections, definitive discontinuation of the targeted drug was observed.

Conclusion

A high proportion of patients presented severe infections during follow‐up, with non‐negligible attributable mortality, but infection incidence is not superior to the one observed during the chemotherapy era. In selected cases with specific risk factors for infection, antimicrobial prophylaxis should be considered.