Targeting B cell receptor signalling in cancer: preclinical and clinical advances

CRISPR-Cas9 screens identify regulators of antibody-drug conjugate toxicity

Antibody-drug conjugates (ADCs) selectively deliver chemotherapeutic agents to target cells and are important cancer therapeutics. However, the mechanisms by which ADCs are internalized and activated remain unclear. Using CRISPR-Cas9 screens, we uncover many known and novel endolysosomal regulators as modulators of ADC toxicity. We identify and characterize C18ORF8/RMC1 as a regulator of ADC toxicity through its role in endosomal maturation. Through comparative analysis of screens with ADCs bearing different linkers, we show that a subset of late endolysosomal regulators selectively influence toxicity of noncleavable linker ADCs. Surprisingly, we find cleavable valine-citrulline linkers can be processed rapidly after internalization without lysosomal delivery. Lastly, we show that sialic acid depletion enhances ADC lysosomal delivery and killing in diverse cancer cell types, including with FDA (US Food and Drug Administration)-approved trastuzumab emtansine (T-DM1) in Her2-positive breast cancer cells. Together, these results reveal new regulators of endolysosomal trafficking, provide important insights for ADC design and identify candidate combination therapy targets.

Fungal Infections with Ibrutinib and Other Small-Molecule Kinase Inhibitors

Purpose of review

Small molecule kinase inhibitors (SMKIs) have revolutionized the management of malignant and autoimmune disorders. Emerging clinical reports point toward an increased risk for invasive fungal infections (IFIs) in patients treated with certain SMKIs. In this mini-review, we highlight representative examples of SMKIs that have been associated with or are expected to give rise to IFIs.

Recent findings

The clinical use of the Bruton's tyrosine kinase inhibitor ibrutinib as well as other FDA-approved SMKIs has been associated with IFIs. The fungal infection susceptibility associated with the clinical use of certain SMKIs underscores their detrimental effects on innate and adaptive antifungal immune responses.

Summary

The unprecedented development and clinical use of SMKIs is expected to give rise to an expansion of iatrogenic immunosuppressive factors predisposing to IFIs (and other opportunistic infections). Beyond increased clinical surveillance, better understanding of the pathogenesis of SMKI-associated immune dysregulation should help devising improved risk stratification and prophylaxis strategies in vulnerable patients.

Dissecting the Prognostic Significance and Functional Role of Progranulin in Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is known for its strong dependency on the tumor microenvironment. We found progranulin (GRN), a protein that has been linked to inflammation and cancer, to be upregulated in the serum of CLL patients compared to healthy controls, and increased GRN levels to be associated with an increased hazard for disease progression and death. This raised the question of whether GRN is a functional driver of CLL. We observed that recombinant GRN did not directly affect viability, activation, or proliferation of primary CLL cells in vitro. However, GRN secretion was induced in co-cultures of CLL cells with stromal cells that enhanced CLL cell survival. Gene expression profiling and protein analyses revealed that primary mesenchymal stromal cells (MSCs) in co-culture with CLL cells acquire a cancer-associated fibroblast-like phenotype. Despite its upregulation in the co-cultures, GRN treatment of MSCs did not mimic this effect. To test the relevance of GRN for CLL in vivo, we made use of the Eμ-TCL1 CLL mouse model. As we detected strong GRN expression in myeloid cells, we performed adoptive transfer of Eμ-TCL1 leukemia cells to bone marrow chimeric Grn-/- mice that lack GRN in hematopoietic cells. Thereby, we observed that CLL-like disease developed comparable in Grn-/- chimeras and respective control mice. In conclusion, serum GRN is found to be strongly upregulated in CLL, which indicates potential use as a prognostic marker, but there is no evidence that elevated GRN functionally drives the disease.

Turning to Computer-aided Drug Design in the Treatment of Diffuse Large B-cell Lymphoma: Has it been Helpful?

INTRODUCTION

Amidst the numerous effective therapeutic options available for the treatment of Diffuse Large B-cell Lymphoma (DLBCL), about 30-40% of patients treated with first-line chemoimmunotherapy still experience a relapse or refractory DLBCL. This has necessitated a continuous search for new therapeutic agents to augment the existing therapeutic arsenal.

METHODS

The dawn of Computer-Aided Drug Design (CADD) in the drug discovery process has accounted for persistency in the application of computational approaches either alone or in combinatorial strategies with experimental methods towards the identification of potential hit compounds with high therapeutic efficacy in abrogating DLBCL.

RESULTS

This review showcases the interventions of structure-based and ligand-based computational approaches which have led to the identification of numerous small molecule inhibitors against implicated targets in DLBCL therapy, even though many of these potential inhibitors are piled-up awaiting further experimental validation and exploration.

CONCLUSION

We conclude that a successful and a conscious amalgamation of CADD and experimental approaches could pave the way for the discovery of the next generation potential leads in DLBCL therapy with improved activities and minimal toxicities.

The Ibr-7 derivative of ibrutinib exhibits enhanced cytotoxicity against non-small cell lung cancer cells via targeting of mTORC1/S6 signaling

Ibrutinib is a small molecule drug that targets Bruton's tyrosine kinase in B-cell malignancies and is highly efficient at killing mantle cell lymphoma and chronic lymphocytic leukemia. However, the anti-cancer activity of ibrutinib against solid tumors, such as non-small cell lung cancer (NSCLC), remains low. To improve the cytotoxicity of ibrutinib towards lung cancer, we synthesized a series of ibrutinib derivatives, of which Ibr-7 exhibited superior anti-cancer activity to ibrutinib, especially against epithelial growth factor receptor (EGFR) wild-type NSCLC cell lines. Ibr-7 was observed to dramatically suppress the mammalian target of Rapamycin complex 1 (mTORC1)/S6 signaling pathway, which is only slightly affected by ibrutinib, thus accounting for the superior anti-cancer activity of Ibr-7 towards NSCLC. Ibr-7 was shown to overcome the elevation of Mcl-1 caused by ABT-199 mono-treatment, and thus exhibited a significant synergistic effect when combined with ABT-199. In conclusion, we used a molecular substitution method to generate a novel ibrutinib derivative, termed Ibr-7, which exhibits enhanced anti-cancer activity against NSCLC cells as compared with the parental compound.

A Murine Model of Chronic Lymphocytic Leukemia Based on B Cell-Restricted Expression of Sf3b1 Mutation and Atm Deletion

SF3B1 is recurrently mutated in chronic lymphocytic leukemia (CLL), but its role in the pathogenesis of CLL remains elusive. Here, we show that conditional expression of Sf3b1-K700E mutation in mouse B cells disrupts pre-mRNA splicing, alters cell development, and induces a state of cellular senescence. Combination with Atm deletion leads to the overcoming of cellular senescence and the development of CLL-like disease in elderly mice. These CLL-like cells show genome instability and dysregulation of multiple CLL-associated cellular processes, including deregulated B cell receptor signaling, which we also identified in human CLL cases. Notably, human CLLs harboring SF3B1 mutations exhibit altered response to BTK inhibition. Our murine model of CLL thus provides insights into human CLL disease mechanisms and treatment.

Tolerability and activity of ublituximab, umbralisib, and ibrutinib in patients with chronic lymphocytic leukaemia and non-Hodgkin lymphoma: a phase 1 dose escalation and expansion trial

BACKGROUND

Therapeutic approaches for B-cell malignancies continue to evolve, especially with regard to combination approaches. We assessed the safety and efficacy of the triplet ublituximab, umbralisib, and ibrutinib in patients with advanced B-cell malignancies.

METHODS

We did an open-label, phase 1 study with dose-escalation and dose-expansion phases, at five centres in the USA. Eligible patients were aged 18 years or older with histologically confirmed lymphocytic leukaemia or relapsed or refractory B-cell non-Hodgkin lymphoma, had measurable disease, adequate organ function, and an Eastern Cooperative Oncology Group (ECOG) performance status of 2 or less. Patients with known CNS lymphoma, active hepatitis B or C infection, or HIV were excluded. In the dose-escalation cohort, patients were treated in cycles of 28 days with escalating doses of oral umbralisib (400, 600, or 800 mg) and fixed doses of intravenous ublituximab (900 mg) and oral ibrutinib (420 mg for patients with chronic lymphocytic leukaemia; 560 mg for patients with B-cell non-Hodgkin lymphoma) in a standard 3 × 3 design until disease progression or intolerance. In the dose-expansion phase, patients were given the recommended dose of the drug combination as determined from the dose-escalation phase. The primary endpoints were safety, dose-limiting toxicities, and the maximum tolerated dose of umbralisib, when given in combination with ublituximab and ibrutinib. Safety was assessed in patients who received at least one dose of study drug; activity was assessed in all patients who had at least one post-treatment efficacy measurement. The study is ongoing but no longer recruiting patients. This trial is registered with ClinicalTrials.gov, number NCT02006485.

FINDINGS

Between Sept 2, 2014, and Nov 6, 2017, we enrolled 46 patients: 24 in the dose-escalation cohort (n=14 chronic lymphocytic leukaemia or small lymphocytic lymphoma; n=10 B-cell non-Hodgkin lymphoma) and 22 in the dose-expansion cohort (n=9 chronic lymphocytic leukaemia or small lymphocytic lymphoma; n=13 B-cell non-Hodgkin lymphoma). 46 patients received at least one dose of study drug. The maximum tolerated dose of umbralisib was not reached. The recommended dose for the dose-expansion phase was umbralisib 800 mg orally once daily plus ibrutinib orally once daily and intravenous ublituximab 900 mg administered on days 1, 8, and 15 of cycle 1, day 1 of cycles 2-6, and on day 1 of cycles 9 and 12. 37 (84%) of 44 patients achieved an overall response (complete or partial response). The most common any-grade adverse events were diarrhoea (n=27 [59%]), fatigue (n=23 [50%]), infusion-related reaction (n=20 [43%]), dizziness (n=17 [37%]), nausea (n=17 [37%]), and cough (n=16 [35%]). Grade 3-4 adverse events were manageable with the most common being neutropenia (n=10 [22%]) and cellulitis (n=6 [13%]). Serious adverse events occurred in 11 (24%) of 46 patients and included rash (n=2 [4%]), pneumonia (n=2 [4%]), atrial fibrillation (n=2 [4%]), sepsis (n=2 [4%]), abdominal pain (n=1 [2%]), syncope (n=1 [2%]), cellulitis (n=1 [2%]), pneumonitis (n=1 [2%]), headache (n=1 [2%]), lung infection (n=1 [2%]), skin infection (n=1 [2%]), pleural effusion (n=1 [2%]), pericardial infusion (n=1 [2%]), upper gastrointestinal bleeding (n=1 [2%]), diarrhoea (n=1 [2%]), and weakness (n=1 [2%]). No deaths related to adverse events occurred.

INTERPRETATION

The combination of ublituximab, umbralisib, and ibrutinib seems to be tolerable and is associated with encouraging activity in advanced chronic lymphocytic leukaemia and B-cell non-Hodgkin lymphoma. This triplet combination will require further investigation in future studies to improve understanding of this novel, chemotherapy-free triplet combination in the management of these cancers.

FUNDING

TG Therapeutics.

TLR Signaling Is Activated in Lymph Node-Resident CLL Cells and Is Only Partially Inhibited by Ibrutinib

Chronic lymphocytic leukemia (CLL) is a malignancy of mature B cells driven by B-cell receptor (BCR) signaling and activated primarily in the lymph node. The Bruton's tyrosine kinase (BTK) inhibitor ibrutinib effectively inhibits BCR-dependent proliferation and survival signals and has emerged as a breakthrough therapy for CLL. However, complete remissions are uncommon and are achieved only after years of continuous therapy. We hypothesized that other signaling pathways that sustain CLL cell survival are only partially inhibited by ibrutinib. In normal B cells, Toll-like receptor (TLR) signaling cooperates with BCR signaling to activate prosurvival NF-κB. Here, we show that an experimentally validated gene signature of TLR activation is overexpressed in lymph node-resident CLL cells compared with cells in the blood. Consistent with TLR activation, we detected phosphorylation of NF-κB, STAT1, and STAT3 in lymph node-resident CLL cells and in cells stimulated with CpG oligonucleotides in vitro. CpG promoted IRAK1 degradation, secretion of IL10, and extended survival of CLL cells in culture. CpG-induced TLR signaling was significantly inhibited by both an IRAK1/4 inhibitor and ibrutinib. Although inhibition of TLR signaling was incomplete with either drug, the combination achieved superior results, including more effective inhibition of TLR-mediated survival signaling. Our data suggest an important role for TLR signaling in CLL pathogenesis and in sustaining the viability of CLL cells during ibrutinib therapy. The combination of ibrutinib with a TLR pathway inhibitor could provide superior antitumor activity and should be investigated in clinical studies. SIGNIFICANCE: CLL relies on the concomitant cooperation of B-cell receptor and Toll-like receptor signaling; inhibition of both pathways is superior to inhibition of either pathway alone. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/79/2/360/F1.large.jpg.

BTK signaling drives CD1dhiCD5+ regulatory B-cell differentiation to promote pancreatic carcinogenesis

The immune microenvironment of pancreatic ductal adenocarcinoma (PDAC) is comprised of a heterogeneous population of cells that are critical for disease evolution. Prominent among these are the specialized CD1d^hiCD5⁺ regulatory B (B_reg) cells that exert a pro-tumorigenic role by promoting tumor cell proliferation. Dissecting the molecular pathways regulating this immune sub-population can thus be valuable for uncovering potential therapeutic targets. Here, we investigate Bruton’s Tyrosine Kinase (BTK), a key B cell kinase, as a potential regulator of CD1d^hiCD5⁺ B_reg differentiation in the pancreatic tumor microenvironment. Treatment of cytokine-induced B cells in vitro with the high specificity BTK inhibitor Tirabrutinib inhibited CD1d^hiCD5⁺ B_reg differentiation and production of IL-10 and IL-35, essential mediators of B_reg immunosuppressive functions. The BTK signaling pathway was also found to be active in vivo in PanIN-associated regulatory B cells. Tirabrutinib treatment of mice bearing orthotopic Kras^G12D-pancreatic lesions severely compromised stromal accumulation of the CD1d^hiCD5⁺ B_reg population. This was accompanied by an increase in stromal CD8⁺IFNγ⁺ cytotoxic T cells and significant attenuation of tumor cell proliferation and PanIN growth. Our results uncover a novel role for BTK in regulating CD1d^hiCD5⁺ B_reg differentiation and emphasize its potential as a therapeutic target for pancreatic cancer.

Pulmonary Manifestations of Predominantly Antibody Deficiencies

Predominantly antibody deficiencies (PADs) are the most frequent forms of primary immunodeficiency diseases (PIDs). Commonly accompanied with complications involving several body systems, immunoglobulin substitution therapy along with prophylactic antibiotics remained the cornerstone of treatment for PADs and related complications. Patients with respiratory complications should be prescribed an appropriate therapy as soon as possible and have to be adhering to more and longer medical therapies. Recent studies identified a gap for screening protocols to monitor respiratory manifestations in patients with PADs. In the present chapter, the pulmonary manifestations of different PADs for each have been discussed. The chapter is mainly focused on X-linked agammaglobulinemia, common variable immunodeficiency, activated PI3K-δ syndrome, LRBA deficiency, CD19 complex deficiencies, CD20 deficiency, other monogenic defects associated with hypogammaglobulinemia, immunoglobulin class switch recombination deficiencies affecting B-cells, transient hypogammaglobulinemia of infancy, and selective IgA deficiency.

The importance of B cell receptor isotypes and stereotypes in chronic lymphocytic leukemia

B cell receptor (BCR) signaling is a central pathway promoting the survival and proliferation of normal and malignant B cells. Chronic lymphocytic leukemia (CLL) arises from mature B cells, expressing functional BCRs, mainly of immunoglobulin M (IgM) and IgD isotypes. Importantly, 30% of CLL patients express quasi-identical BCRs, the so-called "stereotyped" receptors, indicating the existence of common antigenic determinants, which may drive disease initiation and favor its progression. Although the antigenic specificity of IgM and IgD receptors is identical, there are distinct isotype-specific responses after IgM and IgD triggering. Here, we discuss the most important steps of normal B cell development, and highlight the importance of BCR signaling for CLL pathogenesis, with a focus on differences between IgM and IgD isotype signaling. We also highlight the main characteristics of CLL patient subsets, based on BCR stereotypy, and describe subset-specific BCR function and antigen-binding characteristics. Finally, we outline the key biologic and clinical responses to kinase inhibitor therapy, targeting the BCR-associated Bruton's tyrosine kinase, phosphoinositide-3-kinase, and spleen tyrosine kinase in patients with CLL.

Randomized trial of ibrutinib vs ibrutinib plus rituximab in patients with chronic lymphocytic leukemia

Ibrutinib, an oral covalent inhibitor of Bruton's tyrosine kinase, is an effective therapy for patients with chronic lymphocytic leukemia (CLL). To determine whether rituximab provides added benefit to ibrutinib, we conducted a randomized single-center trial of ibrutinib vs ibrutinib plus rituximab. Patients with CLL requiring therapy were randomized to receive 28-day cycles of once-daily ibrutinib 420 mg, either as a single agent (n = 104), or together with rituximab (375 mg/m²; n = 104), given weekly during cycle 1, then once per cycle until cycle 6. The primary end point was progression-free survival (PFS) in the intention-to-treat population. We enrolled 208 patients with CLL, 181 with relapsed CLL and 27 treatment-naive patients with high-risk disease (17p deletion or TP53 mutation). After a median follow-up of 36 months, the Kaplan-Meier estimates of PFS were 86% (95% confidence interval [CI], 76.6-91.9) for patients receiving ibrutinib, and 86.9% (95% CI, 77.3-92.6) for patients receiving ibrutinib plus rituximab. Similarly, response rates were the same in both arms (overall response rate, 92%). However, time to normalization of peripheral blood lymphocyte counts and time to complete remission were shorter, and residual disease levels in the bone marrow were lower, in patients receiving ibrutinib plus rituximab. We conclude that the addition of rituximab to ibrutinib in relapsed and treatment-naive high-risk patients with CLL failed to show improvement in PFS. However, patients treated with ibrutinib plus rituximab reached their remissions faster and achieved significantly lower residual disease levels. Given these results, ibrutinib as single-agent therapy remains current standard-of-care treatment in CLL. This trial was registered at www.clinicaltrials.gov as #NCT02007044.

PI3Kδ Is a Therapeutic Target in Hepatocellular Carcinoma

Class I phosphoinositide 3-kinase (PI3K) signaling is a major pathway in human cancer development and progression. Among the four PI3K isoforms, PI3Kα and PI3Kβ are ubiquitously expressed, whereas PI3Kγ and PI3Kδ are found primarily in leukocytes. Until now, PI3K targeting in solid tumors has focused on inhibiting PI3Kα-mediated and PI3Kβ-mediated cancer cell-intrinsic PI3K activity. The role of PI3Kδ in solid tumors is unknown. Here, we evaluated the effects of PI3Kδ using established hepatocellular carcinoma (HCC) cells, malignant hepatocytes derived from patients with advanced HCC, murine models, and HCC tissues using RNA sequencing, quantitative PCR, immunoblotting, immunofluorescence, microarray, liquid chromatography-tandem mass spectrometry, and kinase assay. We established a chemical carcinogenesis model of liver malignancy that reflects the malignant phenotype and the in vivo environment of advanced HCC. In this in vivo advanced HCC-mimic system using HCC cells treated with hydrogen peroxide (H₂ O₂ ), we showed that H₂ O₂ selectively increases PI3Kδ activity while decreasing that of other class I PI3Ks. Blocking PI3Kδ activity with a PI3Kδ inhibitor or small interfering RNA-mediated PI3Kδ gene silencing inhibited HCC-cell proliferation and dampened key features of malignant HCC, including the up-regulation of telomerase reverse transcriptase (TERT). Mechanistically, H₂ O₂ induced oxidative modification of the serpin peptidase inhibitor, serpin peptidase inhibitor (SERPINA3), blocking its ubiquitin-dependent degradation and enhancing its activity as a transcriptional activator of PI3Kδ and TERT. High PI3Kδ levels in HCC were found to correlate with poor survival rates, with human advanced HCC showing positive correlations between the protein levels of oxidized SERPINA3, PI3Kδ, and TERT. Thus, PI3Kδ plays significant roles in malignant liver tumors. Conclusion: Our data identify PI3Kδ inhibition, recently approved for the treatment of human B-cell malignancies, as a potential treatment for HCC.

A novel Bruton's tyrosine kinase inhibitor, acalabrutinib, suppresses osteoclast differentiation and Porphyromonas gingivalis lipopolysaccharide-induced alveolar bone resorption

BACKGROUND

Periodontitis is not only one of the most prevalent inflammatory diseases among adults, but also commonly linked to numerous systemic conditions including cardiovascular diseases, stroke, and diabetes. Although osteoclasts are responsible for the alveolar bone resorption during periodontitis pathogenesis, the development of pharmacologic strategies targeting these cells has not been vastly fruitful.

METHODS

Bone marrow macrophages were cultured in the presence of macrophage-colony stimulating factor (M-CSF) and receptor activator of nuclear factor κB ligand (RANKL) to examine the direct effect of acalabrutinib on osteoclastogenesis. Ca²⁺ oscillation and nuclear localization of NFATc1 in osteoclast precursors were examined to determine the precise molecular mechanism. LPS-induced alveolar bone loss model was employed for studying effect in in vivo bone resorption.

RESULTS

Acalabrutinib directly inhibited RANKL and LPS-induced in vitro osteoclast differentiation. In addition, acalabrutinib inhibited RANKL-induced phosphorylation of mitogen-activated protein kinases and reduced the expression of NF-κB. The inhibitory mechanism involved suppression of Ca²⁺ oscillation in osteoclast precursors resulting in the decreased NFATc1 expression and nuclear localization, which is a crucial prerequisite for osteoclastogenesis. The administration of acalabrutinib significantly reduced P. gingivalis lipopolysaccharide-induced alveolar bone erosion in mice.

CONCLUSION

These data indicate that acalabrutinib is an effective inhibitor of osteoclastogenesis both in vitro and in vivo, with a potential for a novel strategy against bone destruction by periodontitis.

Aberrant Activation of NF-κB Signalling in Aggressive Lymphoid Malignancies

Lymphoid malignancies frequently harbor genetic mutations leading to aberrant activation of nuclear factor-κB (NF-κB) signaling; in normal cells, this pathway has important roles in the control of cell growth, survival, stress responses, and inflammation. Malignancies with mutations in NF-κB pathway components can derive from all cell stages of mature B-cell development; however, aberrant NF-κB activity is particularly prevalent in aggressive subtypes of non-Hodgkin lymphoma and myeloma. NF-κB activation is mediated by two separate pathways, the canonical and alternative pathway, and five downstream transcription factor subunits. Recent findings implicate a predominant role for distinct NF-κB pathways and subunits in certain lymphoma subtypes and myeloma; findings which are complemented by the realization that individual NF-κB subunits can have unique, non-redundant biological roles in the putative tumor precursor cells, including activated B cells, germinal center B cells and plasma cells. The knowledge gained from these studies may be exploited for the development of therapeutic strategies to inhibit aberrant NF-κB activity at the level of the transcription-factor subunits and their target genes, as global inhibition of the pathway is toxic. Here, we provide an overview on the role of aberrant NF-κB activation in aggressive lymphoid malignancies and discuss the potential importance of individual NF-κB subunits in the pathogenesis of tumor subtypes.

B-cell receptor-mediated NFATc1 activation induces IL-10/STAT3/PD-L1 signaling in diffuse large B-cell lymphoma

Knowledge of programmed death ligand 1 (PD-L1) expression and its regulation in B-cell lymphoma cells is limited. Investigating mechanisms that control PD-L1 expression in B-cell lymphoma cells might identify biomarkers that predict the efficacy of immunotherapy with anti-programmed death-1/PD-L1 antibodies. In addition, identification of mechanisms that regulate PD-L1 may identify molecules that can be targeted to improve the clinical efficacy of immune checkpoint inhibitors. In this study, we used proteomic approaches and patient-derived B-cell lymphoma cell lines to investigate mechanisms that regulate PD-L1 expression. We found that PD-L1 expression, particularly in nongerminal center B cell-derived diffuse large B-cell lymphoma (DLBCL), is controlled and regulated by several interactive signaling pathways, including the B-cell receptor (BCR) and JAK2/STAT3 signaling pathways. We found that that BCR-mediated NFATc1 activation upregulates IL-10 chemokine expression in PD-L1⁺ B-cell lymphoma cells. Released IL-10 activates the JAK2/STAT3 pathway, leading to STAT3-induced PD-L1 expression. IL-10 antagonist antibody abrogates IL-10/STAT3 signaling and PD-L1 protein expression. We also found that BCR pathway inhibition by BTK inhibitors (ibrutinib, acalabrutinib, and BGB-3111) blocks NFATc1 and STAT3 activation, thereby inhibiting IL-10 and PD-L1 expression. Finally, we validated the PD-L1 signaling network in 2 primary DLBCL cohorts consisting of 428 and 350 cases and showed significant correlations among IL-10, STAT3, and PD-L1. Thus, our findings reveal a complex signaling network regulating PD-L1 expression in B-cell lymphoma cells and suggest that PD-L1 expression can be modulated by small molecule inhibitors to potentiate immunotherapies.

Copanlisib for treatment of B-cell malignancies: the development of a PI3K inhibitor with considerable differences to idelalisib

On the occasion of its recent approval for relapsed follicular lymphoma, we review the design and development of the pan-class I PI3K inhibitor copanlisib as a drug for the treatment of B-cell malignancies in comparison with other kinase inhibitors targeting B-cell-receptor signaling, in particular with strictly isoform-δ-selective idelalisib. In agreement with previously defined PI3K-inhibitor chemotypes, the 2,3-dihydroimidazo[1,2-c]quinazoline scaffold of copanlisib adopts a flat conformation in the adenine-binding pocket of the catalytic p110 subunit and further extends into a deeper-affinity pocket in contrast to idelalisib, the quinazoline moiety of which is accommodated in a newly created selectivity pocket. Copanlisib shows higher potency than other clinically developed PI3K inhibitors against all four class I isoforms, with approximately tenfold preference for p110α and p110δ. Owing to its potency and isoform profile, copanlisib exhibits cell-type-specific cytotoxicity against primary chronic lymphocytic leukemia cells and diffuse large B-cell lymphoma (DLBCL) cell lines at nanomolar concentrations. Moreover, copanlisib differs from idelalisib in regard to intravenous versus oral administration and weekly versus twice-daily dosing. In regard to adverse effects, intermittent intravenous treatment with copanlisib leads to fewer gastrointestinal toxicities compared with continuous oral dosing of idelalisib. In relapsed follicular lymphoma, copanlisib appears more effective and especially better tolerated than other targeted therapies. Copanlisib extends existing treatment options for this subtype of indolent non-Hodgkin lymphoma and also shows promising response rates in DLBCL, especially of the activated B-cell type.

Expression and Function of Tetraspanins and Their Interacting Partners in B Cells

Tetraspanins are transmembrane proteins that modulate multiple diverse biological processes, including signal transduction, cell–cell communication, immunoregulation, tumorigenesis, cell adhesion, migration, and growth and differentiation. Here, we provide a systematic review of the involvement of tetraspanins and their partners in the regulation and function of B cells, including mechanisms associated with antigen presentation, antibody production, cytokine secretion, co-stimulator expression, and immunosuppression. Finally, we direct our focus to the signaling mechanisms, evolutionary conservation aspects, expression, and potential therapeutic strategies that could be based on tetraspanins and their interacting partners.

NF-κB Activation in Lymphoid Malignancies: Genetics, Signaling, and Targeted Therapy

The NF-κB transcription factor family plays a crucial role in lymphocyte proliferation and survival. Consequently, aberrant NF-κB activation has been described in a variety of lymphoid malignancies, including diffuse large B-cell lymphoma, Hodgkin lymphoma, and adult T-cell leukemia. Several factors, such as persistent infections (e.g., with Helicobacter pylori), the pro-inflammatory microenvironment of the cancer, self-reactive immune receptors as well as genetic lesions altering the function of key signaling effectors, contribute to constitutive NF-κB activity in these malignancies. In this review, we will discuss the molecular consequences of recurrent genetic lesions affecting key regulators of NF-κB signaling. We will particularly focus on the oncogenic mechanisms by which these alterations drive deregulated NF-κB activity and thus promote the growth and survival of the malignant cells. As the concept of a targeted therapy based on the mutational status of the malignancy has been supported by several recent preclinical and clinical studies, further insight in the function of NF-κB modulators and in the molecular mechanisms governing aberrant NF-κB activation observed in lymphoid malignancies might lead to the development of additional treatment strategies and thus improve lymphoma therapy.

Pan-SRC kinase inhibition blocks B-cell receptor oncogenic signaling in non-Hodgkin lymphoma

In diffuse large B-cell lymphoma (DLBCL), activation of the B-cell receptor (BCR) promotes multiple oncogenic signals, which are essential for tumor proliferation. Inhibition of the Bruton's tyrosine kinase (BTK), a BCR downstream target, is therapeutically effective only in a subgroup of patients with DLBCL. Here, we used lymphoma cells isolated from patients with DLBCL to measure the effects of targeted therapies on BCR signaling and to anticipate response. In lymphomas resistant to BTK inhibition, we show that blocking BTK activity enhanced tumor dependencies from alternative oncogenic signals downstream of the BCR, converging on MYC upregulation. To completely ablate the activity of the BCR, we genetically and pharmacologically repressed the activity of the SRC kinases LYN, FYN, and BLK, which are responsible for the propagation of the BCR signal. Inhibition of these kinases strongly reduced tumor growth in xenografts and cell lines derived from patients with DLBCL independent of their molecular subtype, advancing the possibility to be relevant therapeutic targets in broad and diverse groups of DLBCL patients.

Depth and durability of response to ibrutinib in CLL: 5-year follow-up of a phase 2 study

The safety and efficacy of ibrutinib (420 mg) in chronic lymphocytic leukemia (CLL) were evaluated in a phase 2 study; 51 patients had TP53 aberration (TP53 cohort) and 35 were enrolled because of age 65 years or older (elderly cohort). Both cohorts included patients with treatment-naive (TN) and relapsed/refractory (RR) CLL. With the median follow-up of 4.8 years, 49 (57.0%) of 86 patients remain on study. Treatment was discontinued for progressive disease in 20 (23.3%) patients and for adverse events in 5 (5.8%). Atrial fibrillation occurred in 18 (20.9%) patients for a rate of 6.4 per 100 patient-years. No serious bleeding occurred. The overall response rate at 6 months, the primary study endpoint, was 95.8% for the TP53 cohort (95% confidence interval, 85.7%-99.5%) and 93.9% for the elderly cohort (95% confidence interval, 79.8%-99.3%). Depth of response improved with time: at best response, 14 (29.2%) of 48 patients in the TP53 cohort and 9 (27.3%) of 33 in the elderly cohort achieved a complete response. Median minimal residual disease (MRD) in peripheral blood was 3.8 × 10^-2 at 4 years, with MRD-negative (<10^-4) remissions in 5 (10.2%) patients. In the TP53 cohort, the estimated 5-year progression-free survival (PFS) was 74.4% in TN-CLL compared with 19.4% in RR-CLL (P = .0002), and overall survival (OS) was 85.3% vs 53.7%, respectively (P = .023). In the elderly cohort, the estimated 5-year PFS and OS in RR-CLL were 64.8% and 71.6%, respectively, and no event occurred in TN-CLL. Long-term administration of ibrutinib was well tolerated and provided durable disease control for most patients. This trial was registered at www.clinicaltrials.gov as #NCT01500733.

Role of Bruton's tyrosine kinase in B cells and malignancies

Bruton’s tyrosine kinase (BTK) is a non-receptor kinase that plays a crucial role in oncogenic signaling that is critical for proliferation and survival of leukemic cells in many B cell malignancies. BTK was initially shown to be defective in the primary immunodeficiency X-linked agammaglobulinemia (XLA) and is essential both for B cell development and function of mature B cells. Shortly after its discovery, BTK was placed in the signal transduction pathway downstream of the B cell antigen receptor (BCR). More recently, small-molecule inhibitors of this kinase have shown excellent anti-tumor activity, first in animal models and subsequently in clinical studies. In particular, the orally administered irreversible BTK inhibitor ibrutinib is associated with high response rates in patients with relapsed/refractory chronic lymphocytic leukemia (CLL) and mantle-cell lymphoma (MCL), including patients with high-risk genetic lesions. Because ibrutinib is generally well tolerated and shows durable single-agent efficacy, it was rapidly approved for first-line treatment of patients with CLL in 2016. To date, evidence is accumulating for efficacy of ibrutinib in various other B cell malignancies. BTK inhibition has molecular effects beyond its classic role in BCR signaling. These involve B cell-intrinsic signaling pathways central to cellular survival, proliferation or retention in supportive lymphoid niches. Moreover, BTK functions in several myeloid cell populations representing important components of the tumor microenvironment. As a result, there is currently a considerable interest in BTK inhibition as an anti-cancer therapy, not only in B cell malignancies but also in solid tumors. Efficacy of BTK inhibition as a single agent therapy is strong, but resistance may develop, fueling the development of combination therapies that improve clinical responses. In this review, we discuss the role of BTK in B cell differentiation and B cell malignancies and highlight the importance of BTK inhibition in cancer therapy.