Bruton's tyrosine kinase is required for activation of IkappaB kinase and nuclear factor kappaB in response to B cell receptor engagement

Long-read single-cell RNA sequencing enables the study of cancer subclone-specific genotypes and phenotypes in chronic lymphocytic leukemia

Bruton tyrosine kinase (BTK) inhibitors are effective for the treatment of chronic lymphocytic leukemia (CLL) due to BTK's role in B cell survival and proliferation. Treatment resistance is most commonly caused by the emergence of the hallmark BTK C481S mutation that inhibits drug binding. In this study, we aimed to investigate cancer subclones harboring a BTK C481S mutation and identify cells with co-occurring CLL driver mutations. In addition, we sought to determine whether BTK-mutated subclones exhibit distinct transcriptomic behavior when compared to other cancer subclones. To achieve these goals, we use scBayes, which integrates bulk DNA sequencing and single-cell RNA sequencing (scRNA-seq) data to genotype individual cells for subclone-defining mutations. Although the most common approach for scRNA-seq includes short-read sequencing, transcript coverage is limited due to the vast majority of the reads being concentrated at the priming end of the transcript. Here, we utilized MAS-seq, a long-read scRNA-seq technology, to substantially increase transcript coverage and expand the set of informative mutations to link cells to cancer subclones in six CLL patients who acquired BTK C481S mutations during BTK inhibitor treatment. In two patients who developed two independent BTK-mutated subclones, we find that most BTK-mutated cells have an additional CLL driver gene mutation. When examining subclone-specific gene expression, we find that in one patient, BTK-mutated subclones are transcriptionally distinct from the rest of the malignant B cell population with an overexpression of CLL-relevant genes.

From development to clinical success: the journey of established and next-generation BTK inhibitors

Over the past decade, Bruton's tyrosine kinase (BTK) has emerged as a pivotal therapeutic target for B-cell malignancies and autoimmune diseases, given its essential role in B-cell development and function. Dysregulation of BTK signalling is implicated in a range of hematologic cancers, including Waldenström's macroglobulinaemia (WM), mantle cell lymphoma (MCL), and chronic lymphocytic leukaemia (CLL). The development of BTK inhibitors (BTKIs), starting with ibrutinib, has revolutionized the treatment of these malignancies by inhibiting B-cell receptor (BCR) signalling and inducing apoptosis in malignant B-cells. Despite the impressive clinical efficacy of ibrutinib, challenges such as resistance mutations and off-target effects remain. To address these issues, next-generation BTKIs, including acalabrutinib, orelabrutinib, zanubrutinib, and pirtobrutinib, have been developed, offering improved specificity and reduced toxicity profiles. This review highlights the therapeutic potential of BTK-targeted therapies in treating B-cell malignancies, discusses recent advancements with FDA-approved BTKIs, and explores the latest clinical outcomes from ongoing trials of novel inhibitors.

Tumor microenvironment as a novel therapeutic target for lymphoid leukemias

Lymphoid leukemias represent a significant global health burden, leading to substantial morbidity and mortality. The intricate interplay between leukemic cells and their surrounding tumor microenvironment (TME) is pivotal in disease initiation, progression, and therapeutic resistance. Comprising a dynamic milieu of stromal, immune, and leukemic cell populations, the TME orchestrates a complex network of signaling pathways and molecular interactions that foster leukemic cell survival and proliferation while evading immune surveillance. The crosstalk between these diverse cellular components within the TME not only fuels tumor progression but also confers resistance to conventional therapies, including the development of multi-drug resistance (MDR). Recognizing the pivotal role of the TME in shaping disease outcomes, novel therapeutic approaches targeting this dynamic ecosystem have emerged as promising strategies to complement existing anti-leukemic treatments. As a result, drugs that target the TME have been developed as complementary strategies to those that directly attack tumor cells. Thus, a detailed understanding of the TME components and their interactions with tumor cells is critical. Such knowledge can guide the design and implementation of novel targeted therapies for lymphoid leukemias.

The function of serine/threonine-specific protein kinases in B cells

The serine/threonine-specific protein kinases (STKs) are important for cell survival, proliferation, differentiation, and apoptosis. In B cells, these kinases play indispensable roles in regulating important cellular functions. Multiple studies on human and other animal cells have shown that multiple STKs are involved in different stages of B cell development and antibody production. However, how STKs affect B cell development and function is still not completely understood. Considering that B cells are clinically important in immunity and diseases, our understanding of STKs' roles in B cells is in great need of investigation with current technologies. Investigating serine/threonine kinases will not only deepen our insight into B cell-related disorders but also facilitate the identification of more effective drug targets for conditions like lymphoma and systemic lupus erythematosus.

Tyrosine kinases: multifaceted receptors at the intersection of several neurodegenerative disease-associated processes

Tyrosine kinases (TKs) are catalytic enzymes activated by auto-phosphorylation that function by phosphorylating tyrosine residues on downstream substrates. Tyrosine kinase inhibitors (TKIs) have been heavily exploited as cancer therapeutics, primarily due to their role in autophagy, blood vessel remodeling and inflammation. This suggests tyrosine kinase inhibition as an appealing therapeutic target for exploiting convergent mechanisms across several neurodegenerative disease (NDD) pathologies. The overlapping mechanisms of action between neurodegeneration and cancer suggest that TKIs may play a pivotal role in attenuating neurodegenerative processes, including degradation of misfolded or toxic proteins, reduction of inflammation and prevention of fibrotic events of blood vessels in the brain. In this review, we will discuss the distinct roles that select TKs have been shown to play in various disease-associated processes, as well as identify TKs that have been explored as targets for therapeutic intervention and associated pharmacological agents being investigated as treatments for NDDs.

Discovery and Preclinical Characterization of BIIB129, a Covalent, Selective, and Brain-Penetrant BTK Inhibitor for the Treatment of Multiple Sclerosis

Multiple sclerosis (MS) is a chronic disease with an underlying pathology characterized by inflammation-driven neuronal loss, axonal injury, and demyelination. Bruton's tyrosine kinase (BTK), a nonreceptor tyrosine kinase and member of the TEC family of kinases, is involved in the regulation, migration, and functional activation of B cells and myeloid cells in the periphery and the central nervous system (CNS), cell types which are deemed central to the pathology contributing to disease progression in MS patients. Herein, we describe the discovery of BIIB129 (25), a structurally distinct and brain-penetrant targeted covalent inhibitor (TCI) of BTK with an unprecedented binding mode responsible for its high kinome selectivity. BIIB129 (25) demonstrated efficacy in disease-relevant preclinical in vivo models of B cell proliferation in the CNS, exhibits a favorable safety profile suitable for clinical development as an immunomodulating therapy for MS, and has a low projected total human daily dose.

Factors Governing B Cell Recognition of Autoantigen and Function in Type 1 Diabetes

Islet autoantibodies predict type 1 diabetes (T1D) but can be transient in murine and human T1D and are not thought to be directly pathogenic. Rather, these autoantibodies signal B cell activity as antigen-presenting cells (APCs) that present islet autoantigen to diabetogenic T cells to promote T1D pathogenesis. Disrupting B cell APC function prevents T1D in mouse models and has shown promise in clinical trials. Autoantigen-specific B cells thus hold potential as sophisticated T1D biomarkers and therapeutic targets. B cell receptor (BCR) somatic hypermutation is a mechanism by which B cells increase affinity for islet autoantigen. High-affinity B and T cell responses are selected in protective immune responses, but immune tolerance mechanisms are known to censor highly autoreactive clones in autoimmunity, including T1D. Thus, different selection rules often apply to autoimmune disease settings (as opposed to protective host immunity), where different autoantigen affinity ceilings are tolerated based on variations in host genetics and environment. This review will explore what is currently known regarding B cell signaling, selection, and interaction with T cells to promote T1D pathogenesis.

Bruton's tyrosine kinase ablation inhibits B cell responses and antibody production for the prevention of chronic rejection in cardiac transplantation

Chronic rejection is the primary cause of late allograft failure, however, the current treatments for chronic rejection have not yielded desirable therapeutic effects. B cell activation and donor-specific antibody (DSA) production are the primary factors leading to chronic rejection. Bruton's tyrosine kinase (BTK) plays a key role in the activation and differentiation of B cells and in antibody production. This study investigated the efficacy of blocking BTK signalling in the prevention of chronic rejection. BTK signalling was blocked using the BTK inhibitor ibrutinib and gene knockout. In vitro assays were conducted to examine the consequences and underlying mechanisms of BTK blockade in regards to B cell activation, differentiation, and antibody secretion. Additionally, we established a cardiac transplantation mouse model of chronic rejection to explore the preventive effects and mechanisms of BTK ablation on chronic rejection. Ablating BTK signalling in vitro resulted in the inhibition of B cell activation, differentiation, and antibody production. In vivo experiments provided evidence that ablating BTK signalling alleviated chronic rejection, leading to reduced damage in myocardial tissue, neointimal hyperplasia, interstitial fibrosis, inflammatory cell infiltration, and C4d deposition. Allograft survival was prolonged, and B cell responses and DSA production were inhibited as a result. We confirmed that ablation of BTK signalling inhibited B cell response by blocking downstream PLCγ2 phosphorylation and inhibiting the NF-κB, NFAT, and ERK pathways. Our findings demonstrated that ablation of BTK signalling inhibited B cell activation and differentiation, reduced DSA production, and effectively prevented chronic rejection.

Long-read single-cell RNA sequencing enables the study of cancer subclone-specific genotype and phenotype in chronic lymphocytic leukemia

Bruton's tyrosine kinase (BTK) inhibitors are effective for the treatment of chronic lymphocytic leukemia (CLL) due to BTK's role in B cell survival and proliferation. Treatment resistance is most commonly caused by the emergence of the hallmark BTKC481S mutation that inhibits drug binding. In this study, we aimed to investigate whether the presence of additional CLL driver mutations in cancer subclones harboring a BTKC481S mutation accelerates subclone expansion. In addition, we sought to determine whether BTK-mutated subclones exhibit distinct transcriptomic behavior when compared to other cancer subclones. To achieve these goals, we employ our recently published method (Qiao et al. 2024) that combines bulk DNA sequencing and single-cell RNA sequencing (scRNA-seq) data to genotype individual cells for the presence or absence of subclone-defining mutations. While the most common approach for scRNA-seq includes short-read sequencing, transcript coverage is limited due to the vast majority of the reads being concentrated at the priming end of the transcript. Here, we utilized MAS-seq, a long-read scRNAseq technology, to substantially increase transcript coverage across the entire length of the transcripts and expand the set of informative mutations to link cells to cancer subclones in six CLL patients who acquired BTKC481S mutations during BTK inhibitor treatment. We found that BTK-mutated subclones often acquire additional mutations in CLL driver genes, leading to faster subclone proliferation. When examining subclone-specific gene expression, we found that in one patient, BTK-mutated subclones are transcriptionally distinct from the rest of the malignant B cell population with an overexpression of CLL-relevant genes.

Readministration of high-dose adeno-associated virus gene therapy vectors enabled by ImmTOR nanoparticles combined with B cell-targeted agents

Tolerogenic ImmTOR nanoparticles encapsulating rapamycin have been demonstrated to mitigate immunogenicity of adeno-associated virus (AAV) gene therapy vectors, enhance levels of transgene expression, and enable redosing of AAV at moderate vector doses of 2 to 5E12 vg/kg. However, recent clinical trials have often pushed AAV vector doses 10-fold to 50-fold higher, with serious adverse events observed at the upper range. Here, we assessed combination therapy of ImmTOR with B cell-targeting drugs for the ability to increase the efficiency of redosing at high vector doses. The combination of ImmTOR with a monoclonal antibody against B cell activation factor (aBAFF) exhibited strong synergy leading to more than a 5-fold to 10-fold reduction of splenic mature B cells and plasmablasts while increasing the fraction of pre-/pro-B cells. In addition, this combination dramatically reduced anti-AAV IgM and IgG antibodies, thus enabling four successive AAV administrations at doses up to 5E12 vg/kg and at least two AAV doses at 5E13 vg/kg, with the transgene expression level in the latter case being equal to that observed in control animals receiving a single vector dose of 1E14 vg/kg. Similar synergistic effects were seen with a combination of ImmTOR and a Bruton's tyrosine kinase inhibitor, ibrutinib. These results suggest that ImmTOR could be combined with B cell-targeting agents to enable repeated vector administrations as a potential strategy to avoid toxicities associated with vector doses above 1E14 vg/kg.

Identification of immune infiltration-related biomarkers in carotid atherosclerotic plaques

Atherosclerosis is a chronic lipid-driven inflammatory response of the innate and adaptive immune systems, and it is responsible for several cardiovascular ischemic events. The present study aimed to determine immune infiltration-related biomarkers in carotid atherosclerotic plaques (CAPs). Gene expression profiles of CAPs were extracted from the Gene Expression Omnibus database. Differentially expressed genes (DEGs) between the CAPs and control groups were screened by the "limma" package in R software. Immune cell infiltration between the CAPs and control groups was evaluated by the single sample gene set enrichment analysis. Key infiltrating immune cells in the CAPs group were screened by the Wilcoxon test and least absolute shrinkage and selection operator regression. The weighted gene co-expression network analysis was used to identify immune cell-related genes. Hub genes were identified by the protein-protein interaction (PPI) network. Receiver operating characteristic curve analysis was performed to assess the gene's ability to differentiate between the CAPs and control groups. Finally, we constructed a miRNA-gene-transcription factor network of hub genes by using the ENCODE database. Eleven different types of immune infiltration-related cells were identified between the CAPs and control groups. A total of 1,586 differentially expressed immunity-related genes were obtained through intersection between DEGs and immune-related genes. Twenty hub genes were screened through the PPI network. Eventually, 7 genes (BTK, LYN, PTPN11, CD163, CD4, ITGAL, and ITGB7) were identified as the hub genes of CAPs, and these genes may serve as the estimable drug targets for patients with CAPs.

Influence of Bruton's Tyrosine Kinase (BTK) on Epithelial-Mesenchymal Transition (EMT) Processes and Cancer Stem Cell (CSC) Enrichment in Head and Neck Squamous Cell Carcinoma (HNSCC)

Constitutively active kinases play a crucial role in carcinogenesis, and their inhibition is a common target for molecular tumor therapy. We recently discovered the expression of two oncogenic isoforms of Bruton's Tyrosine Kinase (BTK) in head and neck squamous cell carcinoma (HNSCC), Btk-p80 and BTK-p65. However, the precise role of BTK in HNSCC remains unclear. Analyses of a tissue microarray containing benign and malignant as well as inflammatory tissue samples of the head and neck region revealed the preferential expression of BTK-p80 in malignant tissue, whereas BTK-p65 expression was confirmed in over 80% of analyzed metastatic head and neck tumor cases. Therefore, processes associated with metastasis, like cancer stem cell (CSC) enrichment and the epithelial-mesenchymal transition (EMT), which in turn depend on an appropriate cytokine milieu, were analyzed. Treatment of HNSCC-derived cell lines cultured under 3D conditions with the BTK inhibitor AVL-292 caused reduced sphere formation, which was accompanied by reduced numbers of ALDH1A1+ CSCs as well as biological changes associated with the EMT. Moreover, we observed reduced NF-κB expression as well as altered NF-κB dependent pro-tumorigenic and EMT-associated cytokine release of IL-6, IFNγ, and TNFα when BTK activity was dampened. Therefore, an autocrine regulation of the oncogenic BTK-dependent process in HNSCC can be suggested, with BTK inhibition expected to be an effective treatment option for HNSCC.

Zanubrutinib Ameliorates Cardiac Fibrosis and Inflammation Induced by Chronic Sympathetic Activation

(1) Background: Heart failure (HF) is the final stage of multiple cardiac diseases, which have now become a severe public health problem worldwide. β-Adrenergic receptor (β-AR) overactivation is a major pathological factor associated with multiple cardiac diseases and mediates cardiac fibrosis and inflammation. Previous research has demonstrated that Bruton's tyrosine kinase (BTK) mediated cardiac fibrosis by TGF-β related signal pathways, indicating that BTK was a potential drug target for cardiac fibrosis. Zanubrutinib, a second-generation BTK inhibitor, has shown anti-fibrosis effects in previous research. However, it is unclear whether Zanubrutinib can alleviate cardiac fibrosis induced by β-AR overactivation; (2) Methods: In vivo: Male C57BL/6J mice were treated with or without the β-AR agonist isoproterenol (ISO) to establish a cardiac fibrosis animal model; (3) Results: In vivo: Results showed that the BTK inhibitor Zanubrutinib (ZB) had a great effect on cardiac fibrosis and inflammation induced by β-AR. In vitro: Results showed that ZB alleviated β-AR-induced cardiac fibroblast activation and macrophage pro-inflammatory cytokine production. Further mechanism studies demonstrated that ZB inhibited β-AR-induced cardiac fibrosis and inflammation by the BTK, STAT3, NF-κB, and PI3K/Akt signal pathways both in vivo and in vitro; (4) Conclusions: our research provides evidence that ZB ameliorates β-AR-induced cardiac fibrosis and inflammation.

Microenvironmental control of hematopoietic stem cell fate via CXCL8 and protein kinase C

Altered hematopoietic stem cell (HSC) fate underlies primary blood disorders but microenvironmental factors controlling this are poorly understood. Genetically barcoded genome editing of synthetic target arrays for lineage tracing (GESTALT) zebrafish were used to screen for factors expressed by the sinusoidal vascular niche that alter the phylogenetic distribution of the HSC pool under native conditions. Dysregulated expression of protein kinase C delta (PKC-δ, encoded by prkcda) increases the number of HSC clones by up to 80% and expands polyclonal populations of immature neutrophil and erythroid precursors. PKC agonists such as cxcl8 augment HSC competition for residency within the niche and expand defined niche populations. CXCL8 induces association of PKC-δ with the focal adhesion complex, activating extracellular signal-regulated kinase (ERK) signaling and expression of niche factors in human endothelial cells. Our findings demonstrate the existence of reserve capacity within the niche that is controlled by CXCL8 and PKC and has significant impact on HSC phylogenetic and phenotypic fate.

Real-World Clinical Outcomes and Adverse Events in Patients with Chronic Lymphocytic Leukemia Treated with Ibrutinib: A Single-Center Retrospective Study

Background and Objectives: The treatment of chronic lymphocytic leukemia (CLL) has acquired new targeted therapies. In clinical trials, ibrutinib improved outcomes safely. Real-world data called for a reappraisal of ibrutinib strategies. We report on a single center's experience with ibrutinib monotherapy, aiming to explore the outcomes, tolerability, and prognosis of CLL patients in routine clinical practice. Materials and Methods: Data were collected from all CLL patients treated with ibrutinib at Fundeni Clinical Institute, Bucharest, Romania, between January 2016 and June 2021. Results: A total of one hundred twenty-three CLL adult patients were treated with ibrutinib. Of the patients, 87% had relapsed/refractory CLL. The median age at ibrutinib initiation was 65 years; 44.7% of patients were staged Rai III/IV. At 32-month median follow-up, the median progression-free survival (PFS) was 50 months, the overall survival (OS) was not reached, and the overall response rate (ORR) was 86.2%. The age or number of previous therapies did not impact outcomes or tolerability. An Eastern Cooperative Oncology Group performance status (ECOG PS) score ≥ 2 and shorter time from initiation of last therapy (TILT) before ibrutinib predicted inferior PFS. Baseline characteristics had no impact on the OS except for TILT in R/R CLL patients. Drug-related adverse events (AEs) of any grade and grade ≥ 3 AEs were reported in 82.1% and 30.9% of the patients, respectively. Infections were the most common AEs (29.3%). Drug discontinuation was permanent in 43.9% of patients, mainly due to disease progression (17.1%) and toxicity (8.9%). Patients with a Cumulative Illness Rating Scale (CIRS) score ≥ 6 had a higher risk for toxicity-related discontinuation. An ECOG PS ≥ 2 predicted an increased rate of permanent discontinuation and grade ≥ 3 AEs. Conclusions: The outcomes of this study align with the results from ibrutinib clinical trials. Our study demonstrated that poor patient fitness, early relapse before ibrutinib, and permanent ibrutinib discontinuation are essential outcome determinants. Patient comorbidity burden and fitness were significant predictors for ibrutinib intolerance.

Research-based flow cytometry assays for pathogenic assessment in the human B-cell biology of gene variants revealed in the diagnosis of inborn errors of immunity: a Bruton's tyrosine kinase case-study

Introduction

Inborn errors of immunity (IEI) are an expanding group of rare diseases whose field has been boosted by next-generation sequencing (NGS), revealing several new entities, accelerating routine diagnoses, expanding the number of atypical presentations and generating uncertainties regarding the pathogenic relevance of several novel variants.

Methods

Research laboratories that diagnose and provide support for IEI require accurate, reproducible and sustainable phenotypic, cellular and molecular functional assays to explore the pathogenic consequences of human leukocyte gene variants and contribute to their assessment. We have implemented a set of advanced flow cytometry-based assays to better dissect human B-cell biology in a translational research laboratory. We illustrate the utility of these techniques for the in-depth characterization of a novel (c.1685G>A, p.R562Q) de novo gene variant predicted as probably pathogenic but with no previous insights into the protein and cellular effects, located in the tyrosine kinase domain of the Bruton's tyrosine kinase (BTK) gene, in an apparently healthy 14-year-old male patient referred to our clinic for an incidental finding of low immunoglobulin (Ig) M levels with no history of recurrent infections.

Results and discussion

A phenotypic analysis of bone marrow (BM) revealed a slightly high percentage of pre-B-I subset in BM, with no blockage at this stage, as typically observed in classical X-linked agammaglobulinemia (XLA) patients. The phenotypic analysis in peripheral blood also revealed reduced absolute numbers of B cells, all pre-germinal center maturation stages, together with reduced but detectable numbers of different memory and plasma cell isotypes. The R562Q variant allows Btk expression and normal activation of anti-IgM-induced phosphorylation of Y551 but diminished autophosphorylation at Y223 after anti IgM and CXCL12 stimulation. Lastly, we explored the potential impact of the variant protein for downstream Btk signaling in B cells. Within the canonical nuclear factor kappa B (NF-κB) activation pathway, normal IκBα degradation occurs after CD40L stimulation in patient and control cells. In contrast, disturbed IκBα degradation and reduced calcium ion (Ca2⁺) influx occurs on anti-IgM stimulation in the patient's B cells, suggesting an enzymatic impairment of the mutated tyrosine kinase domain.

Resistance to Bruton tyrosine kinase inhibition in chronic lymphocytic leukaemia and non-Hodgkin lymphoma

Bruton tyrosine kinase inhibitors (BTKi) have transformed the therapeutic landscape of chronic lymphocytic leukaemia (CLL) and non-Hodgkin lymphoma. However, primary and acquired resistance to BTKi can be seen due to a variety of mechanisms including tumour intrinsic and extrinsic mechanisms such as gene mutations, activation of bypass signalling pathways and tumour microenvironment. Herein, we provide an updated review of the key clinical data of BTKi treatment in CLL, mantle cell lymphoma, and diffuse large B-cell lymphoma (DLBCL). We incorporate the most recent findings regarding mechanisms of resistance to covalent and non-covalent inhibitors, including ibrutinib, acalabrutinib, zanubrutinib and pirtobrutinib. We also cover the clinical sensitivity of certain molecular subtypes of DLBCL to an ibrutinib-containing regimen. Lastly, we summarise ongoing clinical investigations aimed at overcoming resistance via use of BTKi-containing combined therapies or the novel non-covalent BTKi. The review article targets an audience of clinical practitioners, clinical investigators and translational researchers.

B Cell Activation Results in IKK-Dependent, but Not c-Rel- or RelA-Dependent, Decreases in Transcription of the B Cell Tolerance-Inducing Gene Ets1

Ets1 is a key transcription factor in B cells that is required to prevent premature differentiation into Ab-secreting cells. Previously, we showed that BCR and TLR signaling downregulate Ets1 levels and that the kinases PI3K, Btk, IKK, and JNK are required for this process. PI3K is important in activating Btk by generating the membrane lipid phosphatidylinositol (3,4,5)-trisphosphate, to which Btk binds via its PH domain. Btk in turn is important in activating the IKK kinase pathway, which it does by activating phospholipase Cγ2→protein kinase Cβ signaling. In this study, we have further investigated the pathways regulating Ets1 in mouse B cells. Although IKK is well known for its role in activating the canonical NF-κB pathway, IKK-mediated downregulation of Ets1 does not require either RelA or c-Rel. We also examined the potential roles of two other IKK targets that are not part of the NF-κB signaling pathway, Foxo3a and mTORC2, in regulating Ets1. We find that loss of Foxo3a or inhibition of mTORC2 does not block BCR-induced Ets1 downregulation. Therefore, these two pathways are not key IKK targets, implicating other as yet undefined IKK targets to play a role in this process.

Kinase-deficient BTK mutants confer ibrutinib resistance through activation of the kinase HCK

The Bruton's tyrosine kinase (BTK) inhibitor ibrutinib irreversibly binds BTK at Cys⁴⁸¹, inhibiting its kinase activity and thus blocking transduction of B cell receptor (BCR) signaling. Although ibrutinib is durably effective in patients with B cell malignancies, many patients still develop ibrutinib-resistant disease. Resistance can arise because of mutations at the ibrutinib-binding site in BTK. Here, we characterized the mechanism by which two BTK mutations, C481F and C481Y, may lead to ibrutinib resistance. Both mutants lacked detectable kinase activity in in vitro kinase assays. Structural modeling suggested that bulky Phe and Tyr side chains at position 481 sterically hinder access to the ATP-binding pocket in BTK, contributing to loss of kinase activity. Nonetheless, BCR signaling still propagated through BTK C481F and C481Y mutants to downstream effectors, the phospholipase PLCγ2 and the transcription factor NF-κB. This maintenance of BCR signaling was partially achieved through the physical recruitment and kinase-independent activation of hematopoietic cell kinase (HCK). Upon BCR activation, BTK C481F or C481Y was phosphorylated by Src family kinases at Tyr⁵⁵¹, which then bound to the SH2 domain of HCK. Modeling suggested that this binding disrupted an intramolecular autoinhibitory interaction in HCK. Activated HCK subsequently phosphorylated PLCγ2, which propagated BCR signaling and promoted clonogenic cell proliferation. This kinase-independent mechanism could inform therapeutic approaches to CLL bearing either the C481F or C481Y BTK mutants.

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.

Btk Supports Autoreactive B Cell Development and Protects against Apoptosis but Is Expendable for Antigen Presentation

Bruton's tyrosine kinase (Btk) propagates B cell signaling, and BTK inhibitors are in clinical trials for autoimmune disease. Although autoreactive B cells fail to develop in the absence of Btk, its role in mature cells is unknown. To address this issue, a model of conditional removal (Btk flox/Cre-ERT2 ) was used to excise Btk from mature transgenic B cells that recognize the pathophysiologic autoantigen insulin. Anti-insulin B cells escape central tolerance and promote autoimmune diabetes, mimicking human autoreactive cells. Lifelong Btk deficiency was previously shown to eliminate 95% of anti-insulin B cells, but in this model, mature anti-insulin B cells survived for weeks after targeted Btk deletion, even when competing with a polyclonal repertoire. BCR-stimulated cells could still signal via Syk, PLCy2, and CD22, but failed to upregulate the antiapoptotic protein Bcl-xL, and proliferation was impaired. Surprisingly, Btk-depleted anti-insulin B cells could still present Ag and activate T cells, a critical function in promoting T cell-mediated islet cell destruction. Thus, pharmacologic targeting of Btk may be most effective by blocking expansion of established autoreactive cells, and preventing emergence of new ones.

Is there a role for anti-CD20 antibodies in CLL?

Anti-CD20 monoclonal antibodies (mAbs) have revolutionized the treatment of chronic lymphocytic leukemia (CLL) by improving survival of patients with CLL in conjunction with chemotherapy. However, the novel targeted agents such as Bruton tyrosine kinase inhibitors (BTKis) and venetoclax have now mostly replaced chemotherapy in frontline treatment of CLL. Several clinical trials have been conducted to examine the role of anti-CD20 mAbs in combination with BTK inhibitors and venetoclax. Addition of rituximab to ibrutinib does not improve progression-free survival (PFS) of treatment-naive patients with CLL, possibly related to ibrutinib's antagonistic effect on anti-CD20 antibodies. Alternatively, addition of a glycoengineered anti-CD20 mAb obinutuzumab to a more selective BTKi acalabrutinib may improve PFS but does not improve overall survival of patients with CLL in the frontline setting, pending long-term follow-up. Thus, we suggest that the addition of an anti-CD20 mAb to a BTKi is of most benefit to patients with autoimmune cytopenia or rapidly progressive disease. In contrast to BTKis, combination of fixed-duration venetoclax and anti-CD20 mAb can induce deep remission with high rates of undetectable minimal residual disease, correlating with improved survival of patients with CLL in both frontline and relapsed/refractory settings. In this review, we discuss clinical trials of BTKis and venetoclax that have investigated the role of anti-CD20 mAbs in frontline and relapsed settings of CLL treatment. We also provide an algorithm suggesting how anti-CD20 mAbs may be incorporated in the treatment of patients with CLL, including specific scenarios.

Protein Kinase CK1α Sustains B-Cell Receptor Signaling in Mantle Cell Lymphoma

Mantle Cell Lymphoma (MCL) is still an incurable B-cell malignancy characterized by poor prognosis and frequent relapses. B Cell Receptor (BCR) signaling inhibitors, in particular of the kinases BTK and PI3Kγ/δ, have demonstrated clinically meaningful anti-proliferative effects in B cell tumors. However, refractoriness to these drugs may develop, portending a dismal prognosis. Protein kinase CK1α is an emerging pro-growth enzyme in B cell malignancies. In multiple myeloma, this kinase sustains β-catenin and AKT-dependent survival and is involved in the activation of NF-κB in B cells. In this study, we analyzed the role of CK1α on MCL cell survival and proliferation, on the regulation of BCR-related BTK, NF-κB, PI3K/AKT signaling cascades and the effects of CK1α chemical inhibition or gene silencing in association with the BTK inhibitor Ibrutinib or the PI3Kγ/δ inhibitor Duvelisib. CK1α was found highly expressed in MCL cells as compared to normal B cells. The inactivation/loss of CK1α caused MCL cell apoptosis and proliferation arrest. CK1α sustained BCR signaling, in particular the NF-κB, AKT and BTK pathways by modulating the phosphorylation of Ser 652 on CARD11, Ser 536 p65 on NF-κB, Ser 473 on AKT, Tyr 223 on BTK, as well as the protein levels. We also provided evidence that CK1α-mediated regulation of CARD11 and BTK likely implicates a physical interaction. The combination of CK1α inhibition with Ibrutinib or Duvelisib synergistically increased cytotoxicity, leading to a further decrease of the activation of BCR signaling pathways. Therefore, CK1α sustains MCL growth through the regulation of BCR-linked survival signaling cascades and protects from Ibrutinib/Duvelisib-induced apoptosis. Thus, CK1α could be considered as a rational molecular target for the treatment of MCL, in association with novel agents.

Quantitative proteomics identifies PTP1B as modulator of B cell antigen receptor signaling

This study analyses the function of the protein tyrosine phosphatase 1B identifying its binding partners and dephosphorylation targets for modulating B cell antigen receptor signaling.

B cell antigen receptor (BCR) signaling is initiated by protein kinases and limited by counteracting phosphatases that currently are less well studied in their regulation of BCR signaling. Here, we used the B cell line Ramos to identify and quantify human B cell signaling components. Specifically, a protein tyrosine phosphatase profiling revealed a high expression of the protein tyrosine phosphatase 1B (PTP1B) in Ramos and human naïve B cells. The loss of PTP1B leads to increased B cell activation. Through substrate trapping in combination with quantitative mass spectrometry, we identified 22 putative substrates or interactors of PTP1B. We validated Igα, CD22, PLCγ1/2, CBL, BCAP, and APLP2 as specific substrates of PTP1B in Ramos B cells. The tyrosine kinase BTK and the two adaptor proteins GRB2 and VAV1 were identified as direct binding partners and potential substrates of PTP1B. We showed that PTP1B dephosphorylates the inhibitory receptor protein CD22 at phosphotyrosine 807. We conclude that PTP1B negatively modulates BCR signaling by dephosphorylating distinct phosphotyrosines in B cell-specific receptor proteins and various downstream signaling components.

Bruton's Tyrosine Kinase Inhibition as an Emerging Therapy in Systemic Autoimmune Disease

Systemic autoimmune disorders are complex heterogeneous chronic diseases involving many different immune cells. A significant proportion of patients respond poorly to therapy. In addition, the high burden of adverse effects caused by "classical" anti-rheumatic or immune modulatory drugs provides a need to develop more specific therapies that are better tolerated. Bruton's tyrosine kinase (BTK) is a crucial signaling protein that directly links B-cell receptor (BCR) signals to B-cell activation, proliferation, and survival. BTK is not only expressed in B cells but also in myeloid cells, and is involved in many different signaling pathways that drive autoimmunity. This makes BTK an interesting therapeutic target in the treatment of autoimmune diseases. The past decade has seen the emergence of first-line BTK small-molecule inhibitors with great efficacy in the treatment of B-cell malignancies, but with unfavorable safety profiles for use in autoimmunity due to off-target effects. The development of second-generation BTK inhibitors with superior BTK specificity has facilitated the investigation of their efficacy in clinical trials with autoimmune patients. In this review, we discuss the role of BTK in key signaling pathways involved in autoimmunity and provide an overview of the different inhibitors that are currently being investigated in clinical trials of systemic autoimmune diseases, including rheumatoid arthritis and systemic lupus erythematosus, as well as available results from completed trials.

Hierarchy of signaling thresholds downstream of the T cell receptor and the Tec kinase ITK

The strength of peptide:MHC interactions with the T cell receptor (TCR) is correlated with the time to first cell division, the relative scale of the effector cell response, and the graded expression of activation-associated proteins like IRF4. To regulate T cell activation programming, the TCR and the TCR proximal interleukin-2-inducible T cell kinase (ITK) simultaneously trigger many biochemically separate signaling cascades. T cells lacking ITK exhibit selective impairments in effector T cell responses after activation, but under the strongest signaling conditions, ITK activity is dispensable. To gain insight into whether TCR signal strength and ITK activity tune observed graded gene expression through the unequal activation of distinct signaling pathways, we examined Erk1/2 phosphorylation or nuclear factor of activated T cells (NFAT) and nuclear factor (NF)-κB translocation in naïve OT-I CD8⁺ cell nuclei. We observed the consistent digital activation of NFAT1 and Erk1/2, but NF-κB displayed dynamic, graded activation in response to variation in TCR signal strength, tunable by treatment with an ITK inhibitor. Inhibitor-treated cells showed the dampened induction of AP-1 factors Fos and Fosb, NF-κB response gene transcripts, and survival factor Il2 transcripts. ATAC sequencing analysis also revealed that genomic regions most sensitive to ITK inhibition were enriched for NF-κB and AP-1 motifs. Specific inhibition of NF-κB during peptide stimulation tuned the expression of early gene products like c-Fos. Together, these data indicate a key role for ITK in orchestrating the optimal activation of separate TCR downstream pathways, specifically aiding NF-κB activation. More broadly, we revealed a mechanism by which variations in TCR signal strength can produce patterns of graded gene expression in activated T cells.

Bruton's tyrosine kinase inhibition induces rewiring of proximal and distal B-cell receptor signaling in mice

Bruton′s tyrosine kinase (Btk) is a crucial signaling molecule in BCR signaling and a key regulator of B‐ cell differentiation and function. Btk inhibition has shown impressive clinical efficacy in various B‐cell malignancies. However, it remains unknown whether inhibition additionally induces changes in BCR signaling due to feedback mechanisms, a phenomenon referred to as BCR rewiring. In this report, we studied the impact of Btk activity on major components of the BCR signaling pathway in mice. As expected, NF‐κB and Akt/S6 signaling was decreased in Btk‐deficient B cells. Unexpectedly, phosphorylation of several proximal signaling molecules, including CD79a, Syk, and PI3K, as well as the key Btk‐effector PLCγ2 and the more downstream kinase Erk, were significantly increased. This pattern of BCR rewiring was essentially opposite in B cells from transgenic mice overexpressing Btk. Importantly, prolonged Btk inhibitor treatment of WT mice or mice engrafted with leukemic B cells also resulted in increased phosho‐CD79a and phospho‐PLCγ2 in B cells. Our findings show that Btk enzymatic function determines phosphorylation of proximal and distal BCR signaling molecules in B cells. We conclude that Btk inhibitor treatment results in rewiring of BCR signaling, which may affect both malignant and healthy B cells.

Current and future therapies for primary Sjögren syndrome

Primary Sjögren syndrome (pSS) is a systemic autoimmune disease that is characterized by a triad of symptoms that affect all patients (dryness, pain and fatigue). In addition, systemic involvement can affect between one-third and one-half of patients. The management of patients with pSS has been negatively affected by a lack of effective treatments; however, knowledge of the epidemiology of pSS has increased, and advances in developing classification criteria, systemic disease activity scoring and patient-reported outcomes have been made during the past decade. Progress has also been made in understanding the mechanisms that underlie the pathogenesis of pSS, which has enabled a more targeted therapeutic approach to be taken. At present, therapeutic decisions rely on the evaluation of symptoms and systemic manifestations and are mostly formed on the basis of experience rather than evidence, and on similarities with other autoimmune diseases, although the 2019 management recommendations from EULAR are now being used to inform clinical management of pSS. This Review summarizes the available evidence for systemic treatments for pSS and includes discussions of advances in outcome assessment, the current evidence for DMARD use and an overview of promising future therapeutics.

Bruton's tyrosine kinase inhibition in the treatment of preclinical models and multiple sclerosis

Significant progress has been made in understanding the immunopathogenesis of multiple sclerosis (MS) over recent years. Successful clinical trials with CD20-depleting monoclonal antibodies have corroborated the fundamental role of B cells in the pathogenesis of MS and reinforced the notion that cells of the B cell lineage are an attractive treatment target. Therapeutic inhibition of Bruton's tyrosine kinase (BTK), an enzyme involved in B cell and myeloid cell activation and function, is regarded as a next-generation approach that aims to attenuate both errant innate and adaptive immune functions. Moreover, brain-penetrant BTK inhibitors may impact compartmentalized inflammation and neurodegeneration within the central nervous system by targeting brain-resident B cells and microglia, respectively. Preclinical studies in animal models of MS corroborated an impact of BTK inhibition on meningeal inflammation and cortical demyelination. Notably, BTK inhibition attenuated the antigen-presenting capacity of B cells and the generation of encephalitogenic T cells. Evobrutinib, a selective oral BTK inhibitor, has been tested recently in a phase 2 study of patients with relapsing-remitting MS. The study met the primary endpoint of a significantly reduced cumulative number of Gadolinium-enhancing lesions under treatment with evobrutinib compared to placebo treatment. Thus, the results of ongoing phase 2 and 3 studies with evobrutinib, fenobrutinib, and tolebrutinib in relapsing-remitting and progressive MS are eagerly awaited. This review article introduces the physiological role of BTK, summarizes the pre-clinical and trial evidence, and addresses the potential beneficial effects of BTK inhibition in MS.

BTK Inhibitors in Chronic Lymphocytic Leukemia: Biological Activity and Immune Effects

Bruton´s tyrosine kinase (BTK) inhibitor (BTKi)s block the B-cell receptor (BCR) signaling cascade by binding to the BTK enzyme preventing the proliferation and survival of malignant and normal B cells. During the past decade, the clinical use of BTKis for the treatment of B-cell malignancies has exponentially grown, changing the treatment landscape for chronic lymphocytic leukemia (CLL) in particular. At present, three different covalent BTKis, ibrutinib, acalabrutinib and zanubrutinib, are FDA-approved and many new inhibitors are under development. Despite having remarkable selectivity for BTK, the first-in-class BTKi ibrutinib can also bind, with various affinities, to other kinases. The combined inhibition of BTK (“on-target” effect) and other kinases (“off-target” effect) can have additive or synergistic anti-tumor effects but also induce undesired side effects which might be treatment-limiting. Such “off-target” effects are expected to be more limited for second-generation BTKis. Moreover, the blockade of BCR signaling also indirectly affects the tumor microenvironment in CLL. Treatment with BTKis potentially impacts on both innate and adaptive immunity. Whether this affects infection susceptibility and vaccination efficacy requires further investigation. Here, we summarize the available knowledge on the impact of BTKis on the immune system and discuss the possible clinical implications. Indeed, a deeper knowledge on this topic could guide clinicians in the management and prevention of infections in patients with CLL treated with BTKis.

TRPM5 Negatively Regulates Calcium-Dependent Responses in Lipopolysaccharide-Stimulated B Lymphocytes

B cells produce high amounts of cytokines and immunoglobulins in response to lipopolysaccharide (LPS) stimulation. Calcium signaling cascades are critically involved in cytokine production of T cells, and the cytosolic calcium concentration is regulated by calcium-activated monovalent cation channels (CAMs). Calcium signaling is also implicated in B cell activation; however, its involvement in the cytokine production of LPS-stimulated B cells remains less well characterized. Here, we show that the transient receptor potential melastatin 5 channel (TRPM5), which is one of the CAMs, negatively modulates calcium signaling, thereby regulating LPS-induced proliferative and inflammatory responses by B cells. LPS-stimulated B cells of Trpm5-deficient mice exhibit an increased cytosolic calcium concentration, leading to enhanced proliferation and the production of the inflammatory cytokines interleukin-6 and CXCL10. Furthermore, Trpm5-deficient mice show an exacerbation of endotoxic shock with high mortality. Our findings demonstrate the importance of TRPM5-dependent regulatory mechanisms in LPS-induced calcium signaling of splenic B cells.

Bruton's tyrosine kinase: an emerging targeted therapy in myeloid cells within the tumor microenvironment

Bruton’s tyrosine kinase (BTK) is a non-receptor kinase belonging to the Tec family of kinases. The role of BTK in B cell receptor signaling is well defined and is known to play a key role in the proliferation and survival of malignant B cells. Moreover, BTK has been found to be expressed in cells of the myeloid lineage. BTK has been shown to contribute to a variety of cellular pathways in myeloid cells including signaling in the NLRP3 inflammasome, receptor activation of nuclear factor-κβ and inflammation, chemokine receptor activation affecting migration, and phagocytosis. Myeloid cells are crucial components of the tumor microenvironment and suppressive myeloid cells contribute to cancer progression, highlighting a potential role for BTK inhibition in the treatment of malignancy. The increased interest in BTK inhibition in cancer has resulted in many preclinical studies that are testing the efficacy of using single-agent BTK inhibitors. Moreover, the ability of tumor cells to develop resistance to single-agent checkpoint inhibitors has resulted in clinical studies utilizing BTK inhibitors in combination with these agents to improve clinical responses. Furthermore, BTK regulates the immune response in microbial and viral infections through B cells and myeloid cells such as monocytes and macrophages. In this review, we describe the role that BTK plays in supporting suppressive myeloid cells, including myeloid-derived suppressor cells (MDSC) and tumor-associated macrophages (TAM), while also discussing the anticancer effects of BTK inhibition and briefly describe the role of BTK signaling and BTK inhibition in microbial and viral infections.

Incorporating Novel Targeted and Immunotherapeutic Agents in Treatment of B-Cell Lymphomas

The introduction of novel targeted agents and immunotherapeutic modalities into the treatment of B-cell lymphomas has drastically shifted the treatment landscape. In diffuse large B-cell lymphoma, recent approvals of CAR T-cell therapy, the antibody-drug conjugate polatuzumab, and the anti-CD19 monoclonal antibody tafasitamab have provided efficacious options for patients with relapsed and refractory disease. These immunotherapies attempt to harness power from the patient's own immune system to eradicate lymphoma. In chronic lymphocytic leukemia, oral targeted kinase inhibitors such as ibrutinib and acalabrutinib (Bruton tyrosine kinase inhibitors) and venetoclax (BCL2 inhibitor) are now favored over chemoimmunotherapy for upfront treatment because of improved progression-free survival across all subgroups (including high-risk subgroups such as unmutated immunoglobulin variable heavy chain and chromosome 17p deletion). In indolent lymphomas, several PI3K inhibitors are approved for treatment of relapsed disease. However, uptake of these agents has been limited because of toxicity concerns. Combination of lenalidomide and rituximab has been a safe and effective immune modality for patients with refractory indolent lymphomas; it is currently being used as a backbone to bring other targeted agents such as tazemetostat (EZH2 inhibitor) into earlier lines of treatment. In this article, we will review novel commercially available agents in the treatment of relapsed/refractory diffuse large B-cell lymphoma, treatment-naïve chronic lymphocytic leukemia, and relapsed/refractory indolent lymphomas. We will evaluate clinical trials that led to their approval and will provide an outlook into the future novel agents currently under investigation in B-cell malignancies.

Nurse-Like Cells and Chronic Lymphocytic Leukemia B Cells: A Mutualistic Crosstalk inside Tissue Microenvironments

Chronic lymphocytic leukemia (CLL) is the most common adult leukemia in Western countries and is an example of hematological disease where cooperation between genetic defects and tumor microenvironmental interaction is involved in pathogenesis. CLL is a disease that is considered as "addicted to the host"; indeed, the crosstalk between leukemic cells and the tumor microenvironment is essential for leukemic clone maintenance supporting CLL cells' survival, proliferation, and protection from drug-induced apoptosis. CLL cells are not innocent bystanders but actively model and manipulate the surrounding microenvironment to their own advantage. Besides the different players involved in this crosstalk, nurse-like cells (NLC) resemble features related to leukemia-associated macrophages with an important function in preserving CLL cell survival and supporting an immunosuppressive microenvironment. This review provides a comprehensive overview of the role played by NLC in creating a nurturing and permissive milieu for CLL cells, illustrating the therapeutic possibilities in order to specifically target and re-educate them.

Ibrutinib for improved chimeric antigen receptor T-cell production for chronic lymphocytic leukemia patients

Chimeric antigen receptor T (CART) cells targeting CD19 have shown promising results in the treatment of chronic lymphocytic leukemia (CLL). However, efficacy seems to be inferior compared to diffuse large B-cell lymphoma or acute lymphoblastic leukemia. Impaired T-cell fitness of CLL patients may be involved in treatment failure. Less-differentiated naïve-like T cells play an important role in CART expansion and long-term persistence in vivo. These cells are sparse in CLL patients. Therefore, optimization of CART cell production protocols enriching less differentiated T cell subsets may overcome treatment resistance. The B-cell receptor inhibitor ibrutinib targeting Bruton's tyrosine kinase (BTK) is approved for the treatment of CLL. Besides BTK, ibrutinib additionally inhibits interleukin-2-inducible T-cell kinase (ITK) which is involved in T-cell differentiation. To evaluate the effect of ibrutinib on CART cell production, peripheral blood mononuclear cells from nine healthy donors and eight CLL patients were used to generate CART cells. T-cell expansion and phenotype, expression of homing and exhaustion makers as well as functionality of CART cells were evaluated. CART cell generation in the presence of ibrutinib resulted in increased cell viability and expansion of CLL patient-derived CART cells. Furthermore, ibrutinib enriched CART cells with less-differentiated naïve-like phenotype and decreased expression of exhaustion markers including PD-1, TIM-3 and LAG-3. In addition, ibrutinib increased the cytokine release capacity of CLL patient-derived CART cells. In summary, BTK/ITK inhibition with ibrutinib during CART cell culture can improve yield and function of CLL patient-derived CART cell products.

Promises and pitfalls of targeted agents in chronic lymphocytic leukemia

Targeted agents have significantly improved outcomes for patients with chronic lymphocytic leukemia, particularly high-risk subgroups for whom chemoimmunotherapy previously offered limited efficacy. Two classes of agent in particular, the Bruton tyrosine kinase inhibitors (e.g., ibrutinib) and the B-cell lymphoma 2 inhibitor, venetoclax, induce high response rates and durable remissions in the relapsed/refractory and frontline settings. However, maturing clinical data have revealed promises and pitfalls for both agents. These drugs induce remissions and disease control in the majority of patients, often in situations where modest efficacy would be expected with traditional chemoimmunotherapy approaches. Unfortunately, in the relapsed and refractory setting, both agents appear to be associated with an inevitable risk of disease relapse and progression. Emerging patterns of resistance are being described for both agents but a common theme appears to be multiple sub-clonal drivers of disease progression. Understanding these mechanisms and developing effective and safe methods to circumvent the emergence of resistance will determine the longer-term utility of these agents to improve patients' quality and length of life. Rational drug combinations, optimised scheduling and sequencing of therapy will likely hold the key to achieving these important goals.

BCR-Induced Ca2+ Signals Dynamically Tune Survival, Metabolic Reprogramming, and Proliferation of Naive B Cells

B cell receptor (BCR) engagement induces naive B cells to differentiate and perform critical immune-regulatory functions. Acquisition of functional specificity requires that a cell survive, enter the cell cycle, and proliferate. We establish that quantitatively distinct Ca2+ signals triggered by variations in the extent of BCR engagement dynamically regulate these transitions by controlling nuclear factor κB (NF-κB), NFAT, and mTORC1 activity. Weak BCR engagement induces apoptosis by failing to activate NF-κB-driven anti-apoptotic gene expression. Stronger signals that trigger more robust Ca2+ signals promote NF-κB-dependent survival and NFAT-, mTORC1-, and c-Myc-dependent cell-cycle entry and proliferation. Finally, we establish that CD40 or TLR9 costimulation circumvents these Ca2+-regulated checkpoints of B cell activation and proliferation. As altered BCR signaling is linked to autoimmunity and B cell malignancies, these results have important implications for understanding the pathogenesis of aberrant B cell activation and differentiation and therapeutic approaches to target these responses.

Acalabrutinib and Its Therapeutic Potential in the Treatment of Chronic Lymphocytic Leukemia: A Short Review on Emerging Data

Recently, the treatment landscape for chronic lymphocytic leukemia (CLL) has changed dramatically due to the development of drugs targeting proteins in the B cell antigen receptor (BCR) pathway. Acalabrutinib, a second-generation Bruton's tyrosine kinase (BTK) inhibitor, was recently FDA approved for treatment of treatment naïve and relapsed refractory CLL. Acalabrutinib was designed as a more selective BTK inhibitor as compared to ibrutinib in an attempt to mitigate some of the treatment limiting toxicities seen with ibrutinib such as atrial fibrillation and bleeding. In preclinical studies, acalabrutinib was demonstrated to have efficacy in CLL in both patient blood samples and murine models. A multinational phase 1/2 study demonstrated the efficacy and safety of acalabrutinib monotherapy in treatment naïve, relapsed refractory and ibrutinib-intolerant CLL patients. Subsequent phase 3 studies, ASCEND and ELEVATE-TN, compared acalabrutinib monotherapy or combination acalabrutinib and obinutuzumab to standard of care treatments and demonstrated acalabrutinib's improved efficacy and tolerability. Currently, a phase 3 study is ongoing to compare acalabrutinib to ibrutinib monotherapy (NCT02477696). In the setting of recent FDA approval, real-world evidence will help to elucidate the optimal use of acalabrutinib in the treatment of CLL.

RNA-binding protein Ptbp1 is essential for BCR-mediated antibody production

The RNA-binding protein polypyrimidine tract-binding protein-1 (Ptbp1) binds to the pyrimidine-rich sequence of target RNA and controls gene expression via post-transcriptional regulation such as alternative splicing. Although Ptbp1 is highly expressed in B lymphocytes, its role to date is largely unknown. To clarify the role of Ptbp1 in B-cell development and function, we generated B-cell-specific Ptbp1-deficient (P1BKO) mice. B-cell development in the bone marrow, spleen and peritoneal cavity of the P1BKO mice was nearly normal. However, the P1BKO mice had significantly lower levels of natural antibodies in serum compared with those of the control mice. To investigate the effect of Ptbp1 deficiency on the immune response in vivo, we immunized the P1BKO mice with T-cell-independent type-2 (TI-2) antigen NP-Ficoll and T-cell-dependent (TD) antigen NP-CGG. We found that B-cell-specific Ptbp1 deficiency causes an immunodeficiency phenotype due to defective production of antibody against both TI-2 and TD antigen. This immunodeficiency was accompanied by impaired B-cell receptor (BCR)-mediated B-cell activation and plasmablast generation. These findings demonstrate that Ptbp1 is essential for the humoral immune response.

Naquotinib exerts antitumor activity in activated B-cell-like diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL), the most common type of B-cell non-Hodgkin lymphoma (NHL), is categorized into two major subtypes, activated B-cell-like (ABC) and germinal center B-cell-like (GCB). The ABC subtype is associated with worse prognosis than the GCB subtype using currently available therapies such as combination treatment with rituximab plus standard cytotoxic chemotherapy. The B-cell receptor (BCR) pathway is activated in ABC DLBCL, suggesting that inhibition of this pathway could provide an alternative strategy for treatment. Naquotinib is an irreversible tyrosine kinase inhibitor (TKI) originally designed to target the epidermal growth factor receptor (EGFR). As sequence alignment analysis indicates that irreversible EGFR-TKIs also inhibit Bruton's tyrosine kinase (BTK), here, we characterized the inhibitory effects of naquotinib against BTK in comparison to ibrutinib, acalabrutinib, tirabrutinib and spebrutinib. Naquotinib inhibited BTK kinase activity with similar potency to that for EGFR activating mutations. In vivo, naquotinib induced tumor regression and suppressed tumor recurrence in TMD8 and OCI-Ly10, ABC DLBCL cell line xenograft models, at a lower dose than the clinically relevant dose. Compared to other BTK inhibitors, naquotinib showed faster onset and comparable inhibition of BTK following incubation with cell lines for 3 and 20 h. In addition, naquotinib showed longer continuous inhibition of BTK following removal of the compound, lasting for at least 26 h after removal. Pharmacokinetics studies in the TMD8 xenograft model showed higher concentration and slower elimination of naquotinib in tumors than other BTK inhibitors. These data suggest that naquotinib may have therapeutic potential in ABC DLBCL patients.

A non-covalent inhibitor XMU-MP-3 overrides ibrutinib-resistant BtkC481S mutation in B-cell malignancies

BACKGROUND AND PURPOSE

Bruton's tyrosine kinase (BTK) plays a key role in B-cell receptor signalling by regulating cell proliferation and survival in various B-cell malignancies. Covalent low-MW BTK kinase inhibitors have shown impressive clinical efficacy in B-cell malignancies. However, the mutant BtkC481S poses a major challenge in the management of B-cell malignancies by disrupting the formation of the covalent bond between BTK and irreversible inhibitors, such as ibrutinib. The present studies were designed to develop novel BTK inhibitors targeting ibrutinib-resistant BtkC481S mutation.

EXPERIMENTAL APPROACH

BTK-Ba/F3, BTK(C481S)-Ba/F3 cells, and human malignant B-cells JeKo-1, Ramos, and NALM-6 were used to evaluate cellular potency of BTK inhibitors. The in vitro pharmacological efficacy and compound selectivity were assayed via cell viability, colony formation, and BTK-mediated signalling. A tumour xenograft model with BTK-Ba/F3, Ramos and BTK(C481S)-Ba/F3 cells in Nu/nu BALB/c mice was used to assess in vivo efficacy of XMU-MP-3.

KEY RESULTS

XMU-MP-3 is one of a group of low MW compounds that are potent non-covalent BTK inhibitors. XMU-MP-3 inhibited both BTK and the acquired mutant BTKC481S, in vitro and in vivo. Further computational modelling, site-directed mutagenesis analysis, and structure-activity relationships studies indicated that XMU-MP-3 displayed a typical Type-II inhibitor binding mode.

CONCLUSION AND IMPLICATIONS

XMU-MP-3 directly targets the BTK signalling pathway in B-cell lymphoma. These findings establish XMU-MP-3 as a novel inhibitor of BTK, which could serve as both a tool compound and a lead for further drug development in BTK relevant B-cell malignancies, especially those with the acquired ibrutinib-resistant C481S mutation.

Safety, Tolerability, Pharmacokinetics, Target Occupancy, and Concentration-QT Analysis of the Novel BTK Inhibitor Evobrutinib in Healthy Volunteers

Bruton's tyrosine kinase (BTK) is a key regulator of B cell receptor and Fc receptor signaling, and a rational therapeutic target for autoimmune diseases. This first‐in‐human phase I, double‐blind, placebo‐controlled trial investigated the safety, tolerability, pharmacokinetics (PK), target occupancy, and effects on QT interval of evobrutinib, a highly selective, oral inhibitor of BTK, in healthy subjects. This dose escalation trial consisted of two parts. Part 1 included 48 subjects in 6 ascending dose cohorts (25, 50, 100, 200, 350, and 500 mg) randomized to a single dose of evobrutinib or placebo. Part 2 included 36 subjects in 3 ascending dose cohorts (25, 75, and 200 mg/day) randomized to evobrutinib or placebo once daily for 14 days. Safety and tolerability, as well as PK and target occupancy (total and free BTK in peripheral blood mononuclear cells), were assessed following single and multiple dosing. PK parameters were determined by noncompartmental methods. QT interval was obtained from 12‐lead electrocardiogram recordings and corrected for heart rate by Fridericia's method (QTcF). Treatment‐emergent adverse events (TEAEs) were mostly mild, occurring in 25% of subjects after single dosing, and 48.1% after multiple dosing. There was no apparent dose relationship regarding frequency or type of TEAE among evobrutinib‐treated subjects. Absorption was rapid (time to reach maximum plasma concentration (T_max) ~ 0.5 hour), half‐life short (~ 2 hours), and PK dose‐proportional, with no accumulation or time dependency on repeat dosing. BTK occupancy was dose‐dependent, reaching maximum occupancy of > 90% within ~ 4 hours after single doses ≥ 200 mg; the effect was long‐lasting (> 50% occupancy at 96 hours with ≥ 100 mg). After multiple dosing, full BTK occupancy was achieved with 25 mg, indicating slow turnover of BTK protein in vivo. Concentration‐QTcF analyses did not show any impact of evobrutinib concentration on corrected QT (QTc). In summary, evobrutinib was well‐tolerated, showed linear and time‐independent PK, induced long‐lasting BTK inhibition, and was associated with no prolongation of QT/QTc interval in healthy subjects. Evobrutinib is, therefore, suitable for investigation in autoimmune diseases.

Evaluating Acalabrutinib In The Treatment Of Mantle Cell Lymphoma: Design, Development, And Place In Therapy

Mantle cell lymphoma (MCL) is an incurable intermediate-grade lymphoma representing 5-6% of non-Hodgkin's lymphomas diagnosed in the United States. The introduction of inhibitors of Bruton's tyrosine kinase (BTK) into targeted therapy for MCL has significantly improved outcomes in patients with relapsed/refractory (R/R) disease. Since the initial approval of the first-generation inhibitor, ibrutinib, several second-generation inhibitors have been explored. Acalabrutinib, a second-generation BTK inhibitor, has demonstrated impressive efficacy in clinical trials along with a safety profile that thus far appears improved compared to ibrutinib. The results of a Phase II trial in patients with R/R MCL led to the approval of acalabrutinib in this patient population while fueling further exploration of acalabrutinib in several ongoing clinical trials.

Decoding inflammation, its causes, genomic responses, and emerging countermeasures

Inflammation is the mechanism of diseases caused by microbial, autoimmune, allergic, metabolic and physical insults that produce distinct types of inflammatory responses. This aetiologic view of inflammation informs its classification based on a cause‐dependent mechanism as well as a cause‐directed therapy and prevention. The genomic era ushered in a new understanding of inflammation by highlighting the cell's nucleus as the centre of the inflammatory response. Exogenous or endogenous inflammatory insults evoke genomic responses in immune and non‐immune cells. These genomic responses depend on transcription factors, which switch on and off a myriad of inflammatory genes through their regulatory networks. We discuss the transcriptional paradigm of inflammation based on denying transcription factors’ access to the nucleus. We present two approaches that control proinflammatory signalling to the nucleus. The first approach constitutes a novel intracellular protein therapy with bioengineered physiologic suppressors of cytokine signalling. The second approach entails control of proinflammatory transcriptional cascades by targeting nuclear transport with a cell‐penetrating peptide that inhibits the expression of 23 out of the 26 mediators of inflammation along with the nine genes required for metabolic responses. We compare these emerging anti‐inflammatory countermeasures to current therapies. The transcriptional paradigm of inflammation offers nucleocentric strategies for microbial, autoimmune, metabolic, physical and other types of inflammation afflicting millions of people worldwide.

Regulatory B lymphocytes: development and modulation of the host immune response during disease

The role of B lymphocytes (B cells) in immunogenic responses has become increasingly important over the past decade, focusing on a new B-cell subtype: regulatory B-cells (Bregs). These Bregs have been shown to possess potent immunosuppressive activities and have identified as key players in disease control and immune tolerance. In this review, the occurrence of Breg type in various conditions, along with evidence supporting discovered functions and proposed purposes will be explored. An example of such regulatory functions includes the induction or suppression of various T lymphocyte phenotypes in response to a particular stimulus. Should Bregs prove effective in mediating immune responses, and correlate with favorable disease outcome, they may serve as a novel therapeutic to combat disease and prevent infection. However, the induction, function and stability of these cells remain unclear and further investigation is needed to better understand their role and therapeutic efficacy.

Optimization of novel reversible Bruton's tyrosine kinase inhibitors identified using Tethering-fragment-based screens

Since the approval of ibrutinib for the treatment of B-cell malignancies in 2012, numerous clinical trials have been reported using covalent inhibitors to target Bruton's tyrosine kinase (BTK) for oncology indications. However, a formidable challenge for the pharmaceutical industry has been the identification of reversible, selective, potent molecules for inhibition of BTK. Herein, we report application of Tethering-fragment-based screens to identify low molecular weight fragments which were further optimized to improve on-target potency and ADME properties leading to the discovery of reversible, selective, potent BTK inhibitors suitable for pre-clinical proof-of-concept studies.

NF-κB Signaling in Macrophages: Dynamics, Crosstalk, and Signal Integration

The nuclear factor-κB (NF-κB) signaling pathway is one of the best understood immune-related pathways thanks to almost four decades of intense research. NF-κB signaling is activated by numerous discrete stimuli and is a master regulator of the inflammatory response to pathogens and cancerous cells, as well as a key regulator of autoimmune diseases. In this regard, the role of NF-κB signaling in immunity is not unlike that of the macrophage. The dynamics by which NF-κB proteins shuttle between the cytoplasm and the nucleus to initiate transcription have been studied rigorously in fibroblasts and other non-hematopoietic cells, but many questions remain as to how current models of NF-κB signaling and dynamics can be translated to innate immune cells such as macrophages. In this review, we will present recent research on the dynamics of NF-κB signaling and focus especially on how these dynamics vary in different cell types, while discussing why these characteristics may be important. We will end by looking ahead to how new techniques and technologies should allow us to analyze these signaling processes with greater clarity, bringing us closer to a more complete understanding of inflammatory transcription factor dynamics and how different cellular contexts might allow for appropriate control of innate immune responses.