Signaling network of the Btk family kinases

Non-Receptor Tyrosine Kinases: Their Structure and Mechanistic Role in Tumor Progression and Resistance

Protein tyrosine kinases (PTKs) function as key molecules in the signaling pathways in addition to their impact as a therapeutic target for the treatment of many human diseases, including cancer. PTKs are characterized by their ability to phosphorylate serine, threonine, or tyrosine residues and can thereby rapidly and reversibly alter the function of their protein substrates in the form of significant changes in protein confirmation and affinity for their interaction with protein partners to drive cellular functions under normal and pathological conditions. PTKs are classified into two groups: one of which represents tyrosine kinases, while the other one includes the members of the serine/threonine kinases. The group of tyrosine kinases is subdivided into subgroups: one of them includes the member of receptor tyrosine kinases (RTKs), while the other subgroup includes the member of non-receptor tyrosine kinases (NRTKs). Both these kinase groups function as an "on" or "off" switch in many cellular functions. NRTKs are enzymes which are overexpressed and activated in many cancer types and regulate variable cellular functions in response to extracellular signaling-dependent mechanisms. NRTK-mediated different cellular functions are regulated by kinase-dependent and kinase-independent mechanisms either in the cytoplasm or in the nucleus. Thus, targeting NRTKs is of great interest to improve the treatment strategy of different tumor types. This review deals with the structure and mechanistic role of NRTKs in tumor progression and resistance and their importance as therapeutic targets in tumor therapy.

Enhancer-promoter hubs organize transcriptional networks promoting oncogenesis and drug resistance

Recent advances in high-resolution mapping of spatial interactions among regulatory elements support the existence of complex topological assemblies of enhancers and promoters known as enhancer-promoter hubs or cliques. Yet, organization principles of these multi-interacting enhancer-promoter hubs and their potential role in regulating gene expression in cancer remains unclear. Here, we systematically identified enhancer-promoter hubs in breast cancer, lymphoma, and leukemia. We found that highly interacting enhancer-promoter hubs form at key oncogenes and lineage-associated transcription factors potentially promoting oncogenesis of these diverse cancer types. Genomic and optical mapping of interactions among enhancer and promoter elements further showed that topological alterations in hubs coincide with transcriptional changes underlying acquired resistance to targeted therapy in T cell leukemia and B cell lymphoma. Together, our findings suggest that enhancer-promoter hubs are dynamic and heterogeneous topological assemblies with the potential to control gene expression circuits promoting oncogenesis and drug resistance.

Covalent docking-driven virtual screening of extensive small-molecule libraries against Bruton tyrosine kinase for the identification of highly selective and potent novel therapeutic candidates

Bruton tyrosine kinases (BTKs) play critical roles in various diseases, including chronic lymphatic leukemia (CLL), Waldenström Macroglobulinemia, Marginal Zone Lymphoma, Mantle Cell Lymphoma (MCL), and Graft Versus Host diseases. BTKs are a family of tyrosine kinases involved in B lymphocyte signal transduction, development, and maturation. Their overexpression can lead to cancer as they are essential for the activation of the B Cell Receptor (BCR) signaling pathway. Blocking the activation of BTKs presents a promising approach for treating CLL. This study was centered around the identification of small-molecule therapeutics that have an impact on human BTK. The covalently bound Ibrutinib molecule, recognized for its ability to inhibit BTK, was used as the query molecule. IUPAC text files containing molecular fragments of Ibrutinib were employed to virtually screen five different libraries comprising small-molecules, resulting in the screening of over 2.4 million synthesized compounds. Covalent docking simulations were applied to the selected small-molecules obtained through text mining from databases. Potent hit molecules capable of inhibiting BTKs through virtual screening algorithms were identified, paving the way for novel therapeutic strategies in the treatment of CLL.

BTK inhibitors in CLL: second-generation drugs and beyond

ABSTRACT

BTK inhibitors (BTKis) are established standards of care in multiple B-cell malignancies including chronic lymphocytic leukemia, mantle cell lymphoma, and Waldenstrom macroglobulinemia. The first-generation BTKi ibrutinib demonstrated superiority over standard chemoimmunotherapy regimens in multiple randomized trials but is limited by cardiovascular side effects such as atrial fibrillation and hypertension. Second-generation BTKis have improved selectivity and demonstrate reduced rates of cardiovascular complications in 3 head-to-head ibrutinib studies. The emergence of BTK C481S mutation has led to the development of noncovalent, "reversible" BTKis, such as pirtobrutinib, which are agnostic to the C481S mutation. However, these inhibitors are associated with resistant mutations outside the C481 hot spot. These variant non-C481 mutations are of great clinical interest because some are shared among pirtobrutinib, zanubrutinib, and acalabrutinib, with potential implications for cross resistance and treatment sequencing. Finally, BTK protein degraders with in vitro activity against C481 and non-C481 mutations are currently in clinical development. Here, we review the evolution of therapeutic BTK-targeting and discuss future directions for clinical research.

BMX deletion mitigates neuroinflammation induced by retinal ischemia/reperfusion through modulation of the AKT/ERK/STAT3 signaling cascade

Aims

Retinal ischemia/reperfusion (I/R) injury is implicated in the etiology of various ocular disorders. Prior research has demonstrated that bone marrow tyrosine kinase on chromosome X (BMX) contributes to the advancement of ischemic disease and inflammatory reactions. Consequently, the current investigation aims to evaluate BMX's impact on retinal I/R injury and clarify its implied mechanism of action.

Main methods

This study utilized male and female systemic BMX knockout (BMX-/-) mice to conduct experiments. The utilization of Western blot assay and immunofluorescence labeling techniques was employed to investigate variations in the expression of protein and tissue localization. Histomorphological changes were observed through H&E staining and SD-OCT examination. Visual function changes were assessed through electrophysiological experiments. Furthermore, apoptosis in the retina was identified using the TUNEL assay, as well as the ELISA technique, which has been utilized to determine the inflammatory factors level.

Key findings

Our investigation results revealed that the knockdown of BMX did not yield a significant effect on mouse retina. In mice, BMX knockdown mitigated the negative impact of I/R injury on retinal tissue structure and visual function. BMX knockdown effectively reduced apoptosis, suppressed inflammatory responses, and decreased inflammatory factors subsequent to I/R injury. The outcomes of the current investigation revealed that BMX knockdown partially protected the retina through downregulating phosphorylation of AKT/ERK/STAT3 pathway.

Significance

Our investigation showed that BMX-/- reduces AKT, ERK, and STAT3 phosphorylation, reducing apoptosis and inflammation. Thus, this strategy protected the retina from structural and functional damage after I/R injury.

Involvement of Protease-Activated Receptor2 Pleckstrin Homology Binding Domain in Ovarian Cancer: Expression in Fallopian Tubes and Drug Design

Studying primordial events in cancer is pivotal for identifying predictive molecular indicators and for targeted intervention. While the involvement of G-protein-coupled receptors (GPCRs) in cancer is growing, GPCR-based therapies are yet rare. Here, we demonstrate the overexpression of protease-activated receptor 2 (PAR2), a GPCR member in the fallopian tubes (FTs) of high-risk BRCA carriers as compared to null in healthy tissues of FT. FTs, the origin of ovarian cancer, are known to express genes of serous tubal intraepithelial carcinoma (STICs), a precursor lesion of high-grade serous carcinoma (HGSC). PAR2 expression in FTs may serve as an early prediction sensor for ovarian cancer. We show now that knocking down Par2 inhibits ovarian cancer peritoneal dissemination in vivo, pointing to the central role of PAR2. Previously we identified pleckstrin homology (PH) binding domains within PAR1,2&4 as critical sites for cancer-growth. These motifs associate with PH-signal proteins via launching a discrete signaling network in cancer. Subsequently, we selected a compound from a library of backbone cyclic peptides generated toward the PAR PH binding motif, namely the lead compound, Pc(4-4). Pc(4-4) binds to the PAR PH binding domain and blocks the association of PH-signal proteins, such as Akt or Etk/Bmx with PAR2. It attenuates PAR2 oncogenic activity. The potent inhibitory function of Pc(4-4) is demonstrated via inhibition of ovarian cancer peritoneal spread in mice. While the detection of PAR2 may serve as a predictor for ovarian cancer, the novel Pc(4-4) compound may serve as a powerful medicament in STICs and ovarian cancer. This is the first demonstration of the involvement of PAR PH binding motif signaling in ovarian cancer and Pc(4-4) as a potential therapy treatment.

Controlling Ibrutinib's Conformations about Its Heterobiaryl Axis to Increase BTK Selectivity

Ibrutinib is a covalent BTK inhibitor that is approved for several indications in oncology. Ibrutinib possesses significant off-target activities toward many kinases, often leading to adverse events in patients. While there have been robust medicinal chemistry efforts leading to more selective second-generation BTK inhibitors, there remains a need for new strategies to rapidly improve the selectivity of kinase inhibitors. An analysis of PDB data revealed that ibrutinib binds BTK in dihedral conformations that are orthogonal of ibrutinib's predicted low energy conformational range. Synthesis of a series of analogues with ground state conformations shifted toward orthogonality led to the discovery of an analogue with two incorporated ortho-methyl groups that possessed markedly increased BTK selectivity. This work suggests that conformational control about a prospective atropisomeric axis represents a strategy to rapidly program a compound's selectivity toward a given target.

The roles of BST-2 in murine B cell development and on virus propagation

The bone marrow (BM) stromal cell antigen-2 (BST-2), also known as tetherin, CD317, PDCA-1, or HM1.24, is a membrane protein overexpressed in several types of tumors and may act as a promising target for cancer treatment via antibody-dependent cellular cytotoxicity. BST-2 is also expressed in human BM stromal cells (BMSC), which support B cell development. While the activity of BST-2 as an antiviral factor has been demonstrated, the expression patterns and the role of BST-2 on B-cell development and activation have not been investigated, especially in vivo. In this study, Bst2 knockout (Bst2^-/- ) mice were generated to assess the role of BST-2 on B cell development and activation. It was observed that BST-2 was not expressed in BMSC or all B cell progenitors even in wild-type mice and does not play a significant role in B cell development. In addition, the loss of BST-2 had no effect on B cell activation. Furthermore and in contrast to the well-known antiviral role of BST-2, infection of vesicular stomatitis Indiana virus to the BM cells collected from the Bst2^-/- mice produced less infectious virus compared with that from the WT mice. These results suggest that murine BST-2 is different from human BST-2 in the expression pattern, physiological function, in vivo, and might possess positive role on VSV replication.

Novel Bruton's tyrosine kinase inhibitor TAS5315 suppresses the progression of inflammation and joint destruction in rodent collagen-induced arthritis

Rheumatoid arthritis is an inflammatory autoimmune disease, characterized by autoantibody production, synovial inflammation, and joint destruction. Its pathogenesis is due to environmental factors and genetic backgrounds. Bruton's tyrosine kinase is a cytoplasmic non-receptor tyrosine kinase, expressed in most hematopoietic cell lineages, except T cells and plasma cells, and regulates various immune-related signaling pathways, thereby playing a crucial role in pathogenesis. Thus, inhibiting Bruton's tyrosine kinase may prove beneficial in treating autoimmune diseases. In the present study, we characterized Bruton's tyrosine kinase inhibitor, TAS5315, in vitro and evaluated its therapeutic effects in experimental arthritis models. TAS5315 markedly inhibited Bruton's tyrosine kinase enzyme activity and suppressed the B-cell receptor signaling pathway in Ramos cells. Moreover, it suppressed the expression of CD69, CD86, and MHC class II in mouse B lymphocytes and the production of TNF-α and MIP-1α in mouse macrophages and decreased bone resorption activity in mouse osteoclasts. Furthermore, it ameliorated the pathological changes in two rodent models of collagen-induced arthritis in vivo. TAS5315 improved bone mineral density and bone intensity. Thus, these results suggest that TAS5315 could be a promising therapeutic option for the treatment of rheumatoid arthritis.

Toll-like receptor 9 signaling after myocardial infarction: Role of p66ShcA adaptor protein

During myocardial infarction, cellular debris is released, causing a sterile inflammation via pattern recognition receptors. These reactions amplify damage and promotes secondary heart failure. The pattern recognition receptor, Toll-like receptor 9 (TLR9) detects immunogenic fragments of endogenous DNA, inducing inflammation by NFκB. The p66ShcA adaptor protein plays an important role in both ischemic myocardial damage and immune responses. We hypothesized that p66ShcA adaptor protein promotes DNA-sensing signaling via the TLR9 pathway after myocardial infarction. TLR9 protein expression increased in cardiac tissue from patients with end-stage heart failure due to ischemic heart disease. Myocardial ischemia in mice in vivo induced gene expression of key TLR9 pathway proteins (MyD88 and Unc93b1). In this model, a functional link between TLR9 and p66ShcA was revealed as; (i) ischemia-induced upregulation of TLR9 protein was abrogated in myocardium of p66ShcA knockout mice; (ii) when p66ShcA was overexpressed in NFkB reporter cells stably expressing TLR9, NFkB-activation increased during stimulation with the TLR9 agonist CpG B; (iii) in cardiac fibroblasts, p66ShcA overexpression caused TLR9 upregulation. Co-immunoprecipitation showed that ShcA proteins and TLR9 may be found in the same protein complex, which was dissipated upon TLR9 stimulation in vivo. A proximity assay confirmed the co-localization of TLR9 and ShcA proteins. The systemic immune response after myocardial ischemia was dampened in p66ShcA knockout mice as interleukin-4, -17 and -22 expression in mononuclear cells isolated from spleens was reduced. In conclusion, p66ShcA adaptor may be an interaction partner and a regulator of the TLR9 pathway post-infarction.

BMX controls 3βHSD1 and sex steroid biosynthesis in cancer

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

A phosphorylation switch controls androgen biosynthesis in prostate cancer

Androgen biosynthesis enzyme 3β-hydroxysteroid dehydrogenase type 1 (3βHSD1) encoded by HSD3B1 has emerged as a potential driver for therapeutic resistance in prostate cancer. Patients with homozygous HSD3B1(1245C) inheritance are intrinsically more resistant to currently available androgen/androgen receptor-targeting (AR-targeting) drugs. In this issue of the JCI, Li et al. present data on the regulation of 3βHSD1 phosphorylation and activity by tyrosine kinase BMX. Inhibition of BMX activity by genetic or pharmacologic approaches blocked androgen biosynthesis in prostate cancer cells and inhibited tumor growth in preclinical xenograft models. The findings provide insights into mechanisms underlying castration resistance in prostate cancer and reveal a potential strategy to circumvent therapeutic resistance in patients with homozygous HSD3B1(1245C) inheritance.

Long-term safety profile of tirabrutinib: final results of a Japanese Phase I study in patients with relapsed or refractory B-cell malignancies

Tirabrutinib is a Bruton's tyrosine kinase inhibitor for treating B-cell malignancies. We report the final results of a Phase I study of tirabrutinib in 17 Japanese patients with B-cell malignancies. Patients were administered tirabrutinib at a dose of 160 mg, 320 mg, or 480 mg once daily, or 300 mg twice daily (N = 3, 3, 4, and 7, respectively). Three patients continued tirabrutinib until study completion (November 30, 2020). Adverse events (AEs) occurred in all 17 patients, with Grade 3-4 AEs in 8 (47.1%), serious AEs in 7 (41.2%), drug-related AEs in 16 (94.1%), and Grade 3-4 drug-related AEs in 6 (35.3%). Drug-related AEs reported in 3 or more patients were rash, vomiting, neutropenia, arthralgia, and malaise. One additional serious AE (benign neoplasm of the lung, unrelated to tirabrutinib) occurred after the previous data cutoff (January 4, 2018). Tirabrutinib administration and response assessment were continued for over 4 years in 4 patients. The overall response rate was 76.5% (13/17 patients). The median (range) time to response and duration of response were 0.9 (0.9-5.9) months and 2.59 (0.08-5.45) years, respectively. These findings demonstrate the long-term safety and efficacy of tirabrutinib in Japanese patients with B-cell malignancies.Clinical trial registration: JapicCTI-142682 ( http://www.clinicaltrials.jp/ ).

Co-delivery of ibrutinib and hydroxychloroquine by albumin nanoparticles for enhanced chemotherapy of glioma

Ibrutinib (IBR) is an oral covalent inhibitor of Bruton's tyrosine kinase (BTK) that has been approved for the treatment of hematological malignancies. It was reported that IBR exhibited great therapeutic potential for glioma. However, the poor water solubility and high hepatic first-pass effect restrict its anti-glioma application. Meanwhile, IBR induces cytoprotective autophagy through Akt/mTOR signaling pathway, thus leading to a compromised antitumor effect. Herein, we aimed to develop a human serum albumin (HSA) based co-delivery system (IBR&HCQ HSA NPs) encapsulating IBR and hydroxychloroquine (HCQ). The bioavailability of IBR was largely improved, and enhanced sensitivity of glioma to IBR was achieved due to inhibition effect of HCQ on IBR-induced pro-survival autophagy. The physicochemical properties of IBR&HCQ HSA NPs were characterized to optimize the formulation. Biodistribution investigation revealed that HSA NPs (20 mg/kg, i.v.) dramatically increased the accumulation of IBR in glioma, which was 5.59 times higher than that of free IBR (100 mg/kg, i.g.). CCK-8 and apoptosis assays demonstrated that IBR&HCQ HSA NPs showed maximal cytotoxicity to C6 cells. In vivo studies indicated that the survival time was significantly prolonged in IBR&HCQ HSA NPs treated mice compared to those treated with IBR HSA NPs. Taken together, the HSA-based drug delivery system of IBR and HCQ opens a new avenue for efficient treatment of glioma.

Bruton’s Tyrosine Kinase phosphorylates scaffolding and RNA-binding protein G3BP1 to induce stress granule aggregation during host sensing of foreign ribonucleic acids

The Ras-GTPase activating protein SH3 domain-binding protein 1 (G3BP1) plays a critical role in the formation of classical and antiviral stress granules in stressed and virus-infected eukaryotic cells, respectively. While G3BP1 is known to be phosphorylated at serine residues which could affect stress granule assembly, whether G3BP1 is phosphorylated at tyrosine residues and how this posttranslational modification might affect its functions is less clear. Here, we show using immunoprecipitation and immunoblotting studies with 4G10 antibody that G3BP1 is tyrosine-phosphorylated when cells are stimulated with the synthetic double-stranded RNA analog polyinosinic:polycytidylic acid to mimic viral infection. We further demonstrate via co-immunoprecipitation and inhibitor studies that Bruton’s tyrosine kinase (BTK) binds and phosphorylates G3BP1. The nuclear transport factor 2–like domain of G3BP1 was previously shown to be critical for its self-association to form stress granules. Our mass spectrometry, mutational and biochemical cross-linking analyses indicate that the tyrosine-40 residue in this domain is phosphorylated by BTK and critical for G3BP1 oligomerization. Furthermore, as visualized via confocal microscopy, pretreatment of cells with the BTK inhibitor LFM-A13 or genetic deletion of the btk gene or mutation of G3BP1-Y40 residue to alanine or phenylalanine all significantly attenuated the formation of antiviral stress granule aggregates upon polyinosinic:polycytidylic acid treatment. Taken together, our data indicate that BTK phosphorylation of G3BP1 induces G3BP1 oligomerization and facilitates the condensation of ribonucleoprotein complexes into macromolecular aggregates.

The potential of pirtobrutinib in multiple B-cell malignancies

Bruton’s tyrosine kinase (BTK) is a critical downstream signaling element from the B-cell receptor (BCR) that has been effectively inhibited in B-cell cancers by irreversible, covalent inhibitors including ibrutinib and acalabrutinib. All FDA-approved covalent BTK inhibitors rely on binding to the cysteine 481 (C481) amino acid within the active site of BTK, thus rendering it inert. While covalent BTK inhibitors have been very successful in multiple B-cell malignancies, improving both overall survival and progression-free survival relative to chemoimmunotherapy in phase 3 trials, they can be limited by intolerance and disease progression. Pirtobrutinib is a novel, highly selective, and non-covalent BTK inhibitor that binds independently of C481, and in a recent, first-in-human phase 1/2 clinical trial was shown to be extremely well tolerated and lead to remissions in relapsed/refractory patients with multiple B-cell malignancies. Here, we review the pharmacologic rationale for pursuing non-covalent BTK inhibitors, the clinical need for such inhibitors, existing safety, and resistance mechanism data for pirtobrutinib, and the forthcoming clinical trials that seek to define the clinical utility of pirtobrutinib, which has the potential to fulfill multiple areas of unmet clinical need for patients with B-cell malignancies.

Ibrutinib in the Treatment of Solid Tumors: Current State of Knowledge and Future Directions

Bruton's Tyrosine Kinase (BTK) is considered crucial in the activation and survival of both physiological and malignant B-cells. In recent years, ibrutinib, an oral BTK inhibitor, became a breakthrough therapy for hematological malignancies, such as chronic lymphocytic. However, ibrutinib's feasibility might not end there. Several other kinases with established involvement with solid malignancies (i.e., EGFR, HER2) have been found to be inhibited by this agent. Recent discoveries indicate that BTK is a potential anti-solid tumor therapy target. Consequently, ibrutinib, a BTK-inhibitor, has been studied as a therapeutic option in solid malignancies. While most preclinical studies indicate ibrutinib to be an effective therapeutic option in some specific indications, such as NSCLC and breast cancer, clinical trials contradict these observations. Nevertheless, while ibrutinib failed as a monotherapy, it might become an interesting part of a multidrug regime: not only has a synergism between ibrutinib and other compounds, such as trametinib or dactolisib, been observed in vitro, but this BTK inhibitor has also been established as a radio- and chemosensitizer. This review aims to describe the milestones in translating BTK inhibitors to solid tumors in order to understand the future potential of this agent better.

Targeted Treatment of Chronic Lymphocytic Leukemia: Clinical Utility of Acalabrutinib

In chronic lymphocytic leukemia (CLL), a deeper understanding of the disease biology led over the last decade to the development and clinical use of different targeted drugs, including Bruton tyrosine kinase (BTK) inhibitors. The first BTK inhibitor approved for clinical use is ibrutinib, which showed excellent efficacy and good tolerability. More recently, the interest is growing for novel more selective BTK inhibitors that may reduce the off-target effects of the drug, thus minimizing side effects and subsequent treatment interruptions or discontinuations. Acalabrutinib is an orally administered irreversible BTK inhibitor, characterized by the lack of inhibition towards other kinases. In this review, we present the most recent data from clinical trials on the clinical efficacy of acalabrutinib and acalabrutinib-based combinations for the treatment of patients with relapsed/refractory and treatment-naïve CLL. We delineate the safety profile of the drug, describe side effects of interest and discuss the clinical management of patients receiving acalabrutinib. Due to its efficacy and the favorable safety profile, acalabrutinib has emerged as a viable therapy option in the current landscape of multiple approved treatments for CLL.

Tyrosine kinase inhibitors as next generation oncological therapeutics: Current strategies, limitations and future perspectives

Protein kinases, a class of enzymes that govern various biological phenomena at a cellular level, are responsible for signal transduction in cells that regulate cellular proliferation, differentiation, and growth. Protein kinase enzyme mutation results in abnormal cell division leading to a pathological condition like cancer. Tyrosine kinase (TK) inhibitors, which helps as a potential drug candidate for the treatment of cancer, are continuously being developed. Majority of these drug candidates are being administered as conventional oral dosage form, which provides limited safety and efficacy due to non-specific delivery and uncontrolled biodistribution resulting into the adverse effects. A controlled drug delivery approach for the delivery of TK inhibitors may be a potential strategy with significant safety and efficacy profile. Novel drug delivery strategies provide target-specific drug delivery, improved pharmacokinetic behaviour, and sustained release leading to lower doses and dosing frequency with significantly reduced side effects. Along with basic aspects of tyrosine kinase, this review discusses various aspects related to the application of tyrosine kinase inhibitors in clinical oncological setting. Furthermore, the limitations/challenges and formulation advancements related to this class of candidates particularly for cancer management have been reviewed. It is expected that innovations in drug delivery approaches for TK inhibitors using novel techniques will surely provide a new insights for improved cancer treatment and patients' life quality.

Kinomics platform using GBM tissue identifies BTK as being associated with higher patient survival

BTK is a dominant bioactive kinase expressed within both cancer and immune cells of GBM tissue. Complex cell co-cultures might better model the impact of kinase inhibitors as therapeutics in GBM.

Better understanding of GBM signalling networks in-vivo would help develop more physiologically relevant ex vivo models to support therapeutic discovery. A “functional proteomics” screen was undertaken to measure the specific activity of a set of protein kinases in a two-step cell-free biochemical assay to define dominant kinase activities to identify potentially novel drug targets that may have been overlooked in studies interrogating GBM-derived cell lines. A dominant kinase activity derived from the tumour tissue, but not patient-derived GBM stem-like cell lines, was Bruton tyrosine kinase (BTK). We demonstrate that BTK is expressed in more than one cell type within GBM tissue; SOX2-positive cells, CD163-positive cells, CD68-positive cells, and an unidentified cell population which is SOX2-negative CD163-negative and/or CD68-negative. The data provide a strategy to better mimic GBM tissue ex vivo by reconstituting more physiologically heterogeneous cell co-culture models including BTK-positive/negative cancer and immune cells. These data also have implications for the design and/or interpretation of emerging clinical trials using BTK inhibitors because BTK expression within GBM tissue was linked to longer patient survival.

Combined Treatment with Acalabrutinib and Rapamycin Inhibits Glioma Stem Cells and Promotes Vascular Normalization by Downregulating BTK/mTOR/VEGF Signaling

Glioblastoma (GBM) is the most common primary malignant brain tumor in adults, with a median duration of survival of approximately 14 months after diagnosis. High resistance to chemotherapy remains a major problem. Previously, BTK has been shown to be involved in the intracellular signal transduction including Akt/mTOR signaling and be critical for tumorigenesis. Thus, we aim to evaluate the effect of BTK and mTOR inhibition in GBM. We evaluated the viability of GBM cell lines after treatment with acalabrutinib and/or rapamycin through a SRB staining assay. We then evaluated the effect of both drugs on GBM stem cell-like phenotypes through various in vitro assay. Furthermore, we incubated HUVEC cells with tumorsphere conditioned media and observed their angiogenesis potential, with or without treatment. Finally, we conducted an in vivo study to confirm our in vitro findings and analyzed the effect of this combination on xenograft mice models. Drug combination assay demonstrated a synergistic relationship between acalabrutinib and rapamycin. CSCs phenotypes, including tumorsphere and colony formation with the associated expression of markers of pluripotency are inhibited by either acalabrutinib or rapamycin singly and these effects are enhanced upon combining acalabrutinib and rapamycin. We showed that the angiogenesis capabilities of HUVEC cells are significantly reduced after treatment with acalabrutinib and/or rapamycin. Xenograft tumors treated with both drugs showed significant volume reduction with minimal toxicity. Samples taken from the combined treatment group demonstrated an increased Desmin/CD31 and col IV/vessel ratio, suggesting an increased rate of vascular normalization. Our results demonstrate that BTK-mTOR inhibition disrupts the population of GBM-CSCs and contributes to normalizing GBM vascularization and thus, may serve as a basis for developing therapeutic strategies for chemoresistant/radioresistant GBM.

Worsening of Dizziness Impairment Is Associated with Bone Marrow Kinase on Chromosome X Level in Patients after Mild Traumatic Brain Injury

Over 2 million people suffer from mild traumatic brain injury (mTBI) each year. Predicting symptoms of mTBI and the characterization of those symptoms has been challenging. Biomarkers that correlate clinical symptoms to disease outcome are desired to improve understanding of the disease and optimize patient care. Bone marrow kinase on chromosome X (BMX), a member of the TEC family of nonreceptor tyrosine kinases, is up-regulated after traumatic neural injury in a rat model of mTBI. The aim of this investigation was to determine whether BMX serum concentrations can effectively be used to predict outcomes after mTBI in a clinical setting. A total of 63 patients with mTBI (Glasgow Coma Score [GCS] between 13 and 15) were included. Blood samples taken at the time of hospital admission were analyzed for BMX. Data collected included demographic and clinical variables. Outcomes were assessed using the Dizziness Handicap Inventory (DHI) questionnaire at baseline and 6 weeks postinjury. The participant was asssigned to the case group if the subject's complaints of dizziness became worse at the sixth week assessment; otherwise, the participant was assigned to the control group. A receiver operating characteristic curve was constructed to explore BMX level. Significant associations were found between serum levels of BMX and dizziness. Areas under the curve for prediction of change in DHI postinjury were 0.76 for total score, 0.69 for physical score, 0.65 for emotional score, and 0.66 for functional score. Specificities were between 0.69 and 0.77 for total score and emotional score, respectively. Therefore, BMX demonstrates potential as a candidate serum biomarker of exacerbating dizziness post-mTBI.

HZ-A-005, a potent, selective, and covalent Bruton's tyrosine kinase inhibitor in preclinical development

Bruton's tyrosine kinase (BTK), a non-receptor tyrosine kinase, is a member of the Tec kinases family and is essential for B cell receptor (BCR) mediated signaling. BTK inhibitors such as ibrutinib hold a prominent role in the treatment of B cell malignancies. Here we disclose a potent, selective, and covalent BTK inhibitor, HZ-A-005, currently in preclinical development. HZ-A-005 demonstrated dose-dependent activity in two xenograft models of lymphoma in vivo. It showed highly favourable safety, pharmacokinetic (PK), and pharmacodynamic (PD) profiles in preclinical studies. On the basis of its potency, selectivity, and covalent mode of inhibition, HZ-A-005 reveals the potential to be a promising BTK inhibitor for a wide range of cancer indications.

Structural and biophysical insights into the mode of covalent binding of rationally designed potent BMX inhibitors

The bone marrow tyrosine kinase in chromosome X (BMX) is pursued as a drug target because of its role in various pathophysiological processes. We designed BMX covalent inhibitors with single-digit nanomolar potency with unexploited topological pharmacophore patterns. Importantly, we reveal the first X-ray crystal structure of covalently inhibited BMX at Cys496, which displays key interactions with Lys445, responsible for hampering ATP catalysis and the DFG-out-like motif, typical of an inactive conformation. Molecular dynamic simulations also showed this interaction for two ligand/BMX complexes. Kinome selectivity profiling showed that the most potent compound is the strongest binder, displays intracellular target engagement in BMX-transfected cells with two-digit nanomolar inhibitory potency, and leads to BMX degradation PC3 in cells. The new inhibitors displayed anti-proliferative effects in androgen-receptor positive prostate cancer cells that where further increased when combined with known inhibitors of related signaling pathways, such as PI3K, AKT and Androgen Receptor. We expect these findings to guide development of new selective BMX therapeutic approaches.

A multicenter, open-label, phase II study of tirabrutinib (ONO/GS-4059) in patients with Waldenström's macroglobulinemia

Tirabrutinib is a second-generation Bruton's tyrosine kinase inhibitor with greater selectivity than ibrutinib. Here, we conducted a multicenter, phase II study of tirabrutinib in patients with treatment-naïve (Cohort A) or with relapsed/refractory (Cohort B) Waldenström's macroglobulinemia (WM). Patients were treated with tirabrutinib 480 mg once daily. The primary endpoint was major response rate (MRR; ≥ partial response). Secondary endpoints included overall response rate (ORR; ≥ minor response), time to major response (TTMR), progression-free survival (PFS), overall survival (OS), and safety. In total, 27 patients (18 in Cohort A; 9 in Cohort B) were enrolled. The median age was 71 y, and the median serum immunoglobulin M level was 3600 mg/dL. Among the patients, 96.2% had the MYD88^L265P mutation. MRR and ORR were 88.9% and 96.3%, respectively (Cohort A: MRR, 88.9%; ORR, 94.4%; Cohort B: MRR, 88.9%; ORR, 100%). Median TTMR was 1.87 mo. PFS and OS were not reached with a median follow-up of 6.5 and 8.3 mo for Cohorts A and B, respectively. The most common adverse events (AEs) were rash (44.4%), neutropenia (25.9%), and leukopenia (22.2%), with most AEs classified as grade 1 or 2. Grade ≥ 3 AEs included neutropenia (11.1%), lymphopenia (11.1%), and leukopenia (7.4%). No grade 5 AEs were noted. All bleeding events were grade 1; none were associated with drug-related atrial fibrillation or hypertension. Although the follow-up duration was relatively short, the study met the primary endpoint. Therefore, tirabrutinib monotherapy is considered to be highly effective for both untreated and relapsed/refractory WM with a manageable safety profile. (JapicCTI-173646).

Safety considerations with targeted therapy drugs for B-cell non-Hodgkin lymphoma

INTRODUCTION

B-cell non-Hodgkin lymphomas (B-NHLs) are the most frequent hematologic malignant cancers. Molecular targeted therapy is an important aspect of B-NHL treatment alongside cytotoxic chemotherapy, radiotherapy, and immunotherapy.

AREAS COVERED

Molecular targeted therapies have changed the landscape of treatment strategies for B-NHLs since the approval of rituximab, an anti-CD20 monoclonal antibody, by the US Food and Drug Administration in 1997. Currently, several targeted therapies have been approved or are in the later-phase of clinical trials including naked antibodies, antibody-drug conjugates, and small molecules, such as Bruton's tyrosine kinase (BTK) inhibitors, phosphatidylinositol 3-kinase (PI3 K) inhibitors, enhancer of zeste homolog 2 (EZH2) inhibitors, and B-cell lymphoma 2 (Bcl-2) inhibitors. These drugs have various toxicities because of their unique mechanisms of action. In this review, the available toxicity data of the targeted therapies for B-NHLs have been summarized.

EXPERT OPINION

Recent clinical developments of targeted therapies for B-NHLs have provided several useful effective therapeutic options for patients. However, there are unique toxicities that need to be resolved. It is necessary to find out the toxicity mechanism; optimal treatment strategy for these toxicities; and novel targeted therapies that might potentially overcome the toxicities of previously approved targeted therapies.

Role of tyrosine kinases in bladder cancer progression: an overview

Background

Bladder cancer (BCa) is a frequent urothelial malignancy with a high ratio of morbidity and mortality. Various genetic and environmental factors are involved in BCa progression. Since, majority of BCa cases are diagnosed after macroscopic clinical symptoms, it is required to find efficient markers for the early detection. Receptor tyrosine-kinases (RTKs) and non-receptor tyrosine-kinases (nRTKs) have pivotal roles in various cellular processes such as growth, migration, differentiation, and metabolism through different signaling pathways. Tyrosine-kinase deregulations are observed during tumor progressions via mutations, amplification, and chromosomal abnormalities which introduces these factors as important candidates of anti-cancer therapies.

Main body

For the first time in present review we have summarized all of the reported tyrosine-kinases which have been significantly associated with the clinicopathological features of BCa patients.

Conclusions

This review highlights the importance of tyrosine-kinases as critical markers in early detection and therapeutic purposes among BCa patients and clarifies the molecular biology of tyrosine-kinases during BCa progression and metastasis.

Aberrantly expressed Bruton's tyrosine kinase preferentially drives metastatic and stem cell-like phenotypes in neuroblastoma cells

PURPOSE

Neuroblastoma, a common childhood tumor, remains one of the most elusive diseases to treat. To date, high-risk neuroblastoma is associated with low survival rates. To address this, novel and more effective therapeutic strategies must continue to be explored.

METHODS

We employed a bioinformatics approach corroborated with in vitro and in vivo data. Samples from neuroblastoma patients were retrieved and immuno-stained for Bruton's tyrosine kinase (BTK). To evaluate its effect on cellular functions, BTK expression in SK-N-BE(2) and SH-SY5Y neuroblastoma cells was downregulated using gene silencing or inhibition with ibrutinib or acalabrutinib. Xenograft mouse models were used to investigate the in vivo role of BTK in neuroblastoma tumorigenesis.

RESULTS

We found that BTK was highly expressed in primary neuroblastoma samples, preferentially in MYCN-amplified neuroblastoma cases, and was associated with a poor prognosis. Immunohistochemical staining of tissues from our neuroblastoma cohort revealed a strong BTK immunoreactivity. We also found that neuroblastoma SK-N-BE(2) and SH-SY5Y cells were sensitive to treatment with ibrutinib and acalabrutinib. Pharmacologic or molecular inhibition of BTK elicited a reduction in the migratory and invasive abilities of neuroblastoma cells, and ibrutinib considerably attenuated the neurosphere-forming ability of neuroblastoma cells. Both inhibitors showed synergism with cisplatin. In vivo assays showed that acalabrutinib effectively inhibited neuroblastoma tumorigenesis.

CONCLUSIONS

From our data we conclude that BTK is a therapeutically targetable driver of neuroblastoma.

New targets for therapy: antigen identification in adults with B-cell acute lymphoblastic leukaemia

Acute lymphoblastic leukaemia (ALL) in adults is a rare and difficult-to-treat cancer that is characterised by excess lymphoblasts in the bone marrow. Although many patients achieve remission with chemotherapy, relapse rates are high and the associated impact on survival devastating. Most patients receive chemotherapy and for those whose overall fitness supports it, the most effective treatment to date is allogeneic stem cell transplant that can improve overall survival rates in part due to a 'graft-versus-leukaemia' effect. However, due to the rarity of this disease, and the availability of mature B-cell antigens on the cell surface, few new cancer antigens have been identified in adult B-ALL that could act as targets to remove residual disease in first remission or provide alternative targets for escape variants if and when current immunotherapy strategies fail. We have used RT-PCR analysis, literature searches, antibody-specific profiling and gene expression microarray analysis to identify and prioritise antigens as novel targets for the treatment of adult B-ALL.

A regulatory SH2 domain-targeting protein binder effectively inhibits the activity of Bruton's tyrosine kinase and its drug-resistant variants

Human Bruton's tyrosine kinase (hBtk) plays a key role in growth and metabolism of B cells, but its dysfunctions cause various B-cell malignancies. Inhibitors targeting the ATP-binding pocket of hBtk have been developed, but they have several drawbacks such as adverse side effects and occurrence of drug-resistant mutations. Here, we present a protein binder which specifically binds to an allosteric regulatory SH2 domain of hBtk. The protein binder effectively inhibited the hBtk activity, indicating a critical role of the SH2 domain in allosteric regulation of the hBtk activity. Cytosolic delivery of the protein binder led to a significant inhibition on the BCR-mediated signaling and viability of B lymphoma cells. The utility of our approach was demonstrated by effective inhibition of drug-resistant hBtk variants by the protein binder. Based on the computationally predicted binding mode, the protein binder is likely to inhibit the hBtk activity by disrupting the interaction between the SH2 domain and kinase domain. The present approach can be used for developing therapeutic agents with improved efficacy for B-cell lymphoma.

BMX Represses Thrombin-PAR1-Mediated Endothelial Permeability and Vascular Leakage During Early Sepsis

RATIONALE

BMX (bone marrow kinase on the X chromosome) is highly expressed in the arterial endothelium from the embryonic stage to the adult stage in mice. It is also expressed in microvessels and the lymphatics in response to pathological stimuli. However, its role in endothelial permeability and sepsis remains unknown.

OBJECTIVE

We aimed to delineate the function of BMX in thrombin-mediated endothelial permeability and the vascular leakage that occurs with sepsis in cecal ligation and puncture models.

METHODS AND RESULTS

The cecal ligation and puncture model was applied to WT (wild type) and BMX-KO (BMX global knockout) mice to induce sepsis. Meanwhile, the electric cell-substrate impedance sensing assay was used to detect transendothelial electrical resistance in vitro and, the modified Miles assay was used to evaluate vascular leakage in vivo. We showed that BMX loss caused lung injury and inflammation in early cecal ligation and puncture-induced sepsis. Disruption of BMX increased thrombin-mediated permeability in mice and cultured endothelial cells by 2- to 3-fold. The expression of BMX in macrophages, neutrophils, platelets, and lung epithelial cells was undetectable compared with that in endothelial cells, indicating that endothelium dysfunction, rather than leukocyte and platelet dysfunction, was involved in vascular permeability and sepsis. Mechanistically, biochemical and cellular analyses demonstrated that BMX specifically repressed thrombin-PAR1 (protease-activated receptor-1) signaling in endothelial cells by directly phosphorylating PAR1 and promoting its internalization and deactivation. Importantly, pretreatment with the selective PAR1 antagonist SCH79797 rescued BMX loss-mediated endothelial permeability and pulmonary leakage in early cecal ligation and puncture-induced sepsis.

CONCLUSIONS

Acting as a negative regulator of PAR1, BMX promotes PAR1 internalization and signal inactivation through PAR1 phosphorylation. Moreover, BMX-mediated PAR1 internalization attenuates endothelial permeability to protect vascular leakage during early sepsis.

Nuclear localization of the tyrosine kinase BMX mediates VEGFR2 expression

Vascular endothelial growth factor receptors (VEGFRs) are major contributors to angiogenesis and lymphangiogenesis through the binding of VEGF ligands. We have previously shown that the bone marrow tyrosine kinase BMX is critical for inflammatory angiogenesis via its direct transactivation of VEGFR2. In the present study, we show that siRNA-mediated silencing of BMX led to a significant decrease in the total levels of VEGFR2 mRNA and protein, without affecting their stability, in human endothelial cells (ECs). Interestingly, BMX was detected in the nuclei of ECs, and the SH3 domain of BMX was necessary for its nuclear localization. Luciferase assays showed a significant decrease in the Vegfr2 (kdr) gene promoter activity in ECs after BMX silencing, indicating that BMX is necessary for Vegfr2 transcription. In addition, we found that wild-type BMX, but not a catalytic inactive mutant BMX-K445R, promoted Vegfr2 promoter activity and VEGF-induced EC migration and tube sprouting. Mechanistically, we show that the enhancement of Vegfr2 promoter activity by BMX was mediated by Sp1, a transcription factor critical for the Vegfr2 promoter. Loss of BMX significantly reduced Sp1 binding to the Vegfr2 promoter as assayed by chromatin immunoprecipitation assays. Wild-type BMX, but not a kinase-inactive form of BMX, associated with and potentially phosphorylated Sp1. Moreover, a nuclear-targeted BMX (NLS-BMX), but not cytoplasm-localized form (NES-BMX), bound to Sp1 and augmented VEGFR2 expression. In conclusion, we uncovered a novel function of nuclear-localized BMX in regulating VEGFR2 expression and angiogenesis, suggesting that BMX is a therapeutic target for angiogenesis-related diseases.

Uev1A promotes breast cancer cell survival and chemoresistance through the AKT-FOXO1-BIM pathway

Background

Ubiquitin-conjugating enzyme variant UEV1A is required for Ubc13-catalyzed K63-linked poly-ubiquitination that regulates several signaling pathways including NF-κB, MAPK and PI3K/AKT. Previous reports implicate UEV1A as a potential proto-oncogene and have shown that UEV1A promotes breast cancer metastasis through constitutive NF-кB activation. Ubc13-Uev1A along with TARF6 can also ubiquitinate AKT but its downstream events are unclear.

Methods

In this study, we experimentally manipulated UEV1 expression in two typical breast cancer cell lines MDA-MB-231 and MCF7 under serum starvation conditions and monitored AKT activation and its downstream protein levels, as well as cellular sensitivity to chemotherapeutic agents.

Results

We found that overexpression of UEV1A is sufficient to activate the AKT signaling pathway that in turn inhibits FOXO1 and BIM expression to promote cell survival under serum starvation conditions and enhances cellular resistance to chemotherapy. Consistently, experimental depletion of Uev1 in breast cancer cells inhibits AKT signaling and promotes FOXO1 and BIM expression to reduce cell survival under serum starvation stress and enhance chemosensitivity.

Conclusions

Uev1A promotes cell survival under serum starvation stress through the AKT-FOXO1-BIM axis in breast cancer cells, which unveals a potential therapeutic target in the treatment of breast cancers.

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.

Pre-clinical anti-tumor activity of Bruton's Tyrosine Kinase inhibitor in Hodgkin's Lymphoma cellular and subcutaneous tumor model

Bruton's Tyrosine Kinase (BTK) is a member of the TEC family and plays a central role in B-cell signaling, activation, proliferation and differentiation. Here we evaluated the impact of BTK inhibitor Ibrutinib on a panel of HL models in vitro and in vivo. Ibrutinib suppressed viability and induced apoptosis in 4 HL cell lines in a dose and time dependent manner. Molecular analysis showed induction of both apoptotic and autophagy markers. Ibrutinib treatment resulted in suppression of BTK and other downstream targets including PI3K, mTOR and RICTOR. Ibrutinib given at 50 mg/kg p.o daily for three weeks caused statistically significant inhibition of HL cell line derived subcutaneous xenografts (p < 0.01) in ICR-SCID mice. Molecular analysis of residual tumor tissue revealed down-regulation of BTK; its related markers and autophagy markers. Our studies are the first showing in vitro and in vivo action of BTK inhibition in classical HL. A phase II study examining the activity of ibrutinib in relapsed or refractory HL is currently enrolling (NCT02824029).

Emerging roles of aerobic glycolysis in breast cancer

Altered aerobic glycolysis is a well-recognized characteristic of cancer cell energy metabolism, known as the Warburg effect. Even in the presence of abundant oxygen, a majority of tumor cells produce substantial amounts of energy through a high glycolytic metabolism, and breast cancer (BC) is no exception. Breast cancer continues to be the second leading cause of cancer-associated mortality in women worldwide. However, the precise role of aerobic glycolysis in the development of BC remains elusive. Therefore, the present review attempts to address the implication of key enzymes of the aerobic glycolytic pathway including hexokinase (HK), phosphofructokinase (PFK) and pyruvate kinase (PK), glucose transporters (GLUTs), together with related signaling pathways including protein kinase B(PI3K/AKT), mammalian target of rapamycin (mTOR) and adenosine monophosphate-activated protein kinase (AMPK) and transcription factors (c-myc, p53 and HIF-1) in the research of BC. Thus, the review of aerobic glycolysis in BC may evoke novel ideas for the BC treatment.

Efficacy and Pharmacodynamic Modeling of the BTK Inhibitor Evobrutinib in Autoimmune Disease Models

Because of its role in mediating both B cell and Fc receptor signaling, Bruton's tyrosine kinase (BTK) is a promising target for the treatment of autoimmune diseases such as rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). Evobrutinib is a novel, highly selective, irreversible BTK inhibitor that potently inhibits BCR- and Fc receptor-mediated signaling and, thus, subsequent activation and function of human B cells and innate immune cells such as monocytes and basophils. We evaluated evobrutinib in preclinical models of RA and SLE and characterized the relationship between BTK occupancy and inhibition of disease activity. In mouse models of RA and SLE, orally administered evobrutinib displayed robust efficacy, as demonstrated by reduction of disease severity and histological damage. In the SLE model, evobrutinib inhibited B cell activation, reduced autoantibody production and plasma cell numbers, and normalized B and T cell subsets. In the RA model, efficacy was achieved despite failure to reduce autoantibodies. Pharmacokinetic/pharmacodynamic modeling showed that mean BTK occupancy in blood cells of 80% was linked to near-complete disease inhibition in both RA and SLE mouse models. In addition, evobrutinib inhibited mast cell activation in a passive cutaneous anaphylaxis model. Thus, evobrutinib achieves efficacy by acting both on B cells and innate immune cells. Taken together, our data show that evobrutinib is a promising molecule for the chronic treatment of B cell-driven autoimmune disorders.

Bruton's tyrosine kinase (Btk) inhibitor tirabrutinib suppresses osteoclastic bone resorption

Osteoclasts are responsible for bone erosion in osteoporosis and rheumatoid arthritis (RA). Both Btk and Tec kinases have essential functions in osteoclast differentiation. Tirabrutinib is a highly potent and dual oral Btk/Tec inhibitor with an IC₅₀ in the nmol/L range and significantly inhibits the M-CSF and RANKL-driven osteoclast differentiation. It was hypothesized that the in vitro activity of tirabrutinib could be demonstrated in mice bone resorption model. The RANKL model studies show that tirabrutinib significantly suppressed bone loss with the inhibition of serum TRAPCP5b and urinary CTX-1. Bone Mineral Density (BMD) loss in tirabrutinib-treated mice was 55% (P < .05), 87% (P < .001) and 88% (P < .001) for the 3, 10 and 30 mg/kg dose groups respectively.

Btk and Tec are required for osteoclast differentiation and activation based on the genetic evidence obtained from Btk and Tec double deficient mice. Tirabrutinib may be a novel therapeutic target for bone diseases, such as osteoporosis and RA.

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Btk and Tec are activated by RANKL and indispensable for osteoclastogenesis.

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Tirabrutinib is a highly potent and dual oral Btk/Tec inhibitor.

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Osteoclast differentiation is activated by RANKL, M-CSF and ITAM.

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Tirabrutinib inhibited RANKL-induced osteolyrtic bone disease.

Management of adverse effects/toxicity of ibrutinib

Bruton tyrosine kinase signaling (BTK) is critical step for B-cell development and immunoglobulin synthesis. Ibrutinib is an orally bioavailable bruton tyrosine kinase inhibitor (BTKi) and forms an irreversible covalent bound to BTK at the Cysteine-481 residue. Ibrutinib has been approved by FDA for the treatment of mantle cell lymphoma, chronic lymphocytic leukemia, Waldenstrom's macroglobulinemia, marginal zone lymphoma and chronic graft-versus-host disease in allogeneic stem cell transplantation. Ibrutinib is generally well tolerated drug with rapid and durable responses but has some side events. The most common side effects are diarrhea, upper respiratory tract infection, bleeding, fatigue and cardiac side effects. These events are generally mild (grade I-II). However atrial fibrillation (AF) and bleeding are important and may be grade III or higher side effects require strict monitoring. Here side effects of ibrutinib have been summarized and important considerations in the management of these adverse events have been reviewed.

Targeting phosphoinositide-3-kinase pathway in biliary tract cancers: A remedial route?

Biliary tract cancers (BTC) are aggressive tumours with a low survival rate. At the advent of the genomic era, various genetic mutations in cell signalling pathways have been incriminated in carcinogenesis. Genomic analysis studies have connected main components of the phosphoinositide-3-kinase (PI3K) signalling pathway to BTC. PI3K pathway playing a central role in cell signalling and being deregulated in various tumours has been studied as a target for chemotherapy. Novel compounds have also been identified in preclinical trials that specifically target the PI3K pathway in BTCs, but these studies have not accelerated to clinical use. These novel compounds can be examined in upcoming studies to validate them as potential therapeutic agents, as further research is required to combat the growing need for adjuvant chemotherapy to successfully battle this tumour type. Furthermore, these molecules could also be used along with gemcitabine, cisplatin and 5-fluorouracil to improve sensitivity of the tumour tissue to chemotherapy. This review focuses on the basics of PI3K signalling, genetic alterations of this pathway in BTCs and current advancement in targeting this pathway in BTCs. It emphasizes the need for gene-based drug screening in BTC. It may reveal various novel targets and drugs for amelioration of survival in patients with BTC and serve as a stepping stone for further research.

Whole Genome Resequencing of Arkansas Progressor and Regressor Line Chickens to Identify SNPs Associated with Tumor Regression

Arkansas Regressor (AR) chickens, unlike Arkansas Progressor (AP) chickens, regress tumors induced by the v-src oncogene. To better understand the genetic factors responsible for this tumor regression property, whole genome resequencing was conducted using Illumina Hi-Seq 2 × 100 bp paired-end read method (San Diego, CA, USA) with AR (confirmed tumor regression property) and AP chickens. Sequence reads were aligned to the chicken reference genome (galgal5) and produced coverage of 11× and 14× in AR and AP, respectively. A total of 7.1 and 7.3 million single nucleotide polymorphisms (SNPs) were present in AR and AP genomes, respectively. Through a series of filtration processes, a total of 12,242 SNPs were identified in AR chickens that were associated with non-synonymous, frameshift, nonsense, no-start and no-stop mutations. Further filtering of SNPs based on read depth ≥ 10, SNP% ≥ 0.75, and non-synonymous mutations identified 63 reliable marker SNPs which were chosen for gene network analysis. The network analysis revealed that the candidate genes identified in AR chickens play roles in networks centered to ubiquitin C (UBC), phosphoinositide 3-kinases (PI3K), and nuclear factor kappa B (NF-kB) complexes suggesting that the tumor regression property in AR chickens might be associated with ubiquitylation, PI3K, and NF-kB signaling pathways. This study provides an insight into genetic factors that could be responsible for the tumor regression property.

Ibrutinib significantly inhibited Bruton's tyrosine kinase (BTK) phosphorylation,in-vitro proliferation and enhanced overall survival in a preclinical Burkitt lymphoma (BL) model

Pediatric and adult patients with recurrent/refractory Burkitt lymphoma (BL) continue to have poor outcomes, emphasizing the need for newer therapeutic agents. Bruton's tyrosine kinase (BTK) is activated following B-cell receptor stimulation and in part regulates normal B-cell development. Ibrutinib, a selective and irreversible BTK inhibitor, has been efficacious in chronic lymphocytic leukemia (CLL), mantle cell lymphoma (MCL), Waldenström's macroglobulinemia, and marginal zone lymphoma. In this study, we investigated the efficacy of ibrutinib alone and in selective adjuvant combinations against BL in-vitro and in a human BL xenografted immune-deficient NOD.Cg-Prkdc^scidIl2rg^tm1Wjl/SzJ (NSG) mouse model. Our data demonstrated that phospho-BTK level was significantly reduced in BL cells treated with ibrutinib (p < 0.001). Moreover, we observed a significant decrease in cell proliferation as well as significant decrease in IC₅₀ of ibrutinib in combination with dexamethasone, rituximab, obinutuzumab, carfilzomib, and doxorubicin (p < 0.001). In-vivo studies demonstrated ibrutinib treated mice had a significantly prolonged survival with median survival of mice following ibrutinib treatment (32 days) (24 days) (p < 0.02). In conclusion, our findings demonstrate the significant in-vitro and preclinical in-vivo effects of ibrutinib in BL. Based on our preclinical results in this investigation, there is an on-going clinical trial comparing overall survival in children and adolescents with relapsed/refractory BL treated with chemoimmunotherapy with or without ibrutinib (NCT02703272).

BMX-Mediated Regulation of Multiple Tyrosine Kinases Contributes to Castration Resistance in Prostate Cancer

Prostate cancer responds to therapies that suppress androgen receptor (AR) activity (androgen deprivation therapy, ADT) but invariably progresses to castration-resistant prostate cancer (CRPC). The Tec family nonreceptor tyrosine kinase BMX is activated downstream of PI3K and has been implicated in regulation of multiple pathways and in the development of cancers including prostate cancer. However, its precise mechanisms of action, and particularly its endogenous substrates, remain to be established. Here, we demonstrate that BMX expression in prostate cancer is suppressed directly by AR via binding to the BMX gene and that BMX expression is subsequently rapidly increased in response to ADT. BMX contributed to CRPC development in cell line and xenograft models by positively regulating the activities of multiple receptor tyrosine kinases through phosphorylation of a phosphotyrosine-tyrosine (pYY) motif in their activation loop, generating pYpY that is required for full kinase activity. To assess BMX activity in vivo, we generated a BMX substrate-specific antibody (anti-pYpY) and found that its reactivity correlated with BMX expression in clinical samples, supporting pYY as an in vivo substrate. Inhibition of BMX with ibrutinib (developed as an inhibitor of the related Tec kinase BTK) or another BMX inhibitor BMX-IN-1 markedly enhanced the response to castration in a prostate cancer xenograft model. These data indicate that increased BMX in response to ADT contributes to enhanced tyrosine kinase signaling and the subsequent emergence of CRPC, and that combination therapies targeting AR and BMX may be effective in a subset of patients.Significance: The tyrosine kinase BMX is negatively regulated by androgen and contributes to castration-resistant prostate cancer by enhancing the phosphorylation and activation of multiple receptor tyrosine kinases following ADT. Cancer Res; 78(18); 5203-15. ©2018 AACR.

Homogeneous BTK Occupancy Assay for Pharmacodynamic Assessment of Tirabrutinib (GS-4059/ONO-4059) Target Engagement

Bruton’s tyrosine kinase (BTK) is a clinically validated target for B-cell leukemias and lymphomas with FDA-approved small-molecule inhibitors ibrutinib and acalabrutinib. Tirabrutinib (GS-4059/ONO-4059, Gilead Sciences, Inc., Foster City, CA) is a second-generation, potent, selective, irreversible BTK inhibitor in clinical development for lymphoid malignancies, including chronic lymphocytic leukemia (CLL) and diffuse large B-cell lymphoma (DLBCL). An accurate pharmacodynamic assay to assess tirabrutinib target coverage in phase 1/2 clinical studies will inform dose and schedule selection for advanced clinical evaluation. We developed a novel duplex homogeneous BTK occupancy assay based on time-resolved fluorescence resonance energy transfer (TR-FRET) to measure free and total BTK levels in a multiplexed format. The dual-wavelength emission property of terbium-conjugated anti-BTK antibody served as the energy donor for two fluorescent energy acceptors with distinct excitation and emission spectra. The assay was characterized and qualified using full-length purified recombinant human BTK protein and peripheral blood mononuclear cells derived from healthy volunteers and patients with CLL. We demonstrated assay utility using cells derived from lymph node and bone marrow samples from patients with CLL and DLBCL. Our TR-FRET-based BTK occupancy assay provides accurate, quantitative assessment of BTK occupancy in the clinical trial program for tirabrutinib and is in use in ongoing clinical studies.

A Quorum Sensing-Regulated Protein Binds Cell Wall Components and Enhances Lysozyme Resistance in Streptococcus pyogenes

The Rgg2/3 quorum sensing (QS) system is conserved among all sequenced isolates of group A Streptococcus (GAS; Streptococcus pyogenes). The molecular architecture of the system consists of a transcriptional activator (Rgg2) and a transcriptional repressor (Rgg3) under the control of autoinducing peptide pheromones (SHP2 and SHP3). Activation of the Rgg2/3 pathway leads to increases in biofilm formation and resistance to the bactericidal effects of the host factor lysozyme. In this work, we show that deletion of a small gene, spy49_0414c, abolished both phenotypes in response to pheromone signaling. The gene encodes a small, positively charged, secreted protein, referred to as StcA. Analysis of recombinant StcA showed that it can directly interact with GAS cell wall preparations containing phosphodiester-linked carbohydrate polymers but not with preparations devoid of them. Immunofluorescence microscopy detected antibody against StcA bound to the surface of paraformaldehyde-fixed wild-type cells. Expression of StcA in bacterial culture induced a shift in the electrostatic potential of the bacterial cell surface, which became more positively charged. These results suggest that StcA promotes phenotypes by way of ionic interactions with the GAS cell wall, most likely with negatively charged cell wall-associated polysaccharides.IMPORTANCE This study focuses on a small protein, StcA, that is expressed and secreted under induction of Rgg2/3 QS, ionically associating with negatively charged domains on the cell surface. These data present a novel mechanism of resistance to the host factor lysozyme by GAS and have implications in the relevance of this circuit in the interaction between the bacterium and the human host that is mediated by the bacterial cell surface.

Erythropoietin Intensifies the Proapoptotic Activity of LFM-A13 in Cells and in a Mouse Model of Colorectal Cancer

The Bruton’s tyrosine kinase (BTK) inhibitor LFM-A13 has been widely employed as an antileukemic agent, but applications in solid cancer have been found recently. The compound promotes apoptosis, has an antiproliferative effect, and increases cancer cell sensitivity to chemotherapy drugs. We decided to assess the impact of the simultaneous use of erythropoietin (Epo) and LFM-A13 on signal transduction in colon DLD-1 and HT-29 cells, as well as in tumor xenografts. The induction of apoptosis by Epo and LFM-A-13 in the cells was confirmed by phosphatidylserine externalization, loss of mitochondrial membrane potential, and modulation of the expression of apoptotic protein BAX and antiapoptotic protein BCL-2 in colon adenocarcinoma cells. Nude mice were inoculated with adenocarcinoma cells and treated with Epo and LFM-A13 in order to evaluate the degree of tumor regression. The simultaneous use of Epo and LFM-A13 severely inhibited cell growth, activated apoptosis, and also inhibited tumor growth in xenografts. The addition of Epo to LFM-A13 intensified the antiproliferative effect of LFM-A13, confirmed by the loss of mitochondrial membrane potential and the accumulation of apoptotic colon cancer cells with externalized phosphatidylserine (PS). These preclinical results suggest that the combination of Epo and LFM-A13 has a high proapoptotic activity and should be tested in the clinic for the treatment of solid tumors such as colon cancer.

The effects of DLEU1 gene expression in Burkitt lymphoma (BL): potential mechanism of chemoimmunotherapy resistance in BL

Following a multivariant analysis we demonstrated that children and adolescents with Burkitt lymphoma (BL) and a 13q14.3 deletion have a significant decrease in event free survival (EFS) despite identical short intensive multi-agent chemotherapy. However, how this deletion in the 13q14.3 region is associated with a significant decrease in EFS in children and adolescents with BL is largely unknown. The gene Deleted in Lymphocytic Leukemia 1 (DLEU1) is located in the region of 13q14.3. Here, we report that DLEU1 expression is implicated in the regulation of BL programmed cell death, cell proliferation, and expression of apoptotic genes in transcription activator-like effector nuclease (TALEN)s-induced DLEU1 knockdown and DLEU1 overexpressing BL cell lines. Furthermore, NSG mice xenografted with DLEU1 knockdown BL cells had significantly shortened survival (p < 0.05 and p < 0.005), whereas those xenografted with DLEU1 overexpressing BL cells had significantly improved survival (p < 0.05 and p < 0.0001), following treatment with rituximab and/or cyclophosphamide. These data suggest that DLEU1 may in part function as a tumor suppressor gene and confer chemoimmunotherapy resistance in children and adolescents with BL.

A novel BMX variant promotes tumor cell growth and migration in lung adenocarcinoma

The non-receptor tyrosine kinase BMX has been reported in several solid tumors. However, the alternative splicing of BMX and its clinical relevance in lung cancer remain to be elucidated. Exon1.0 array was used to identify a novel alternative splicing of BMX, BMXΔN, which was confirmed by rapid amplification of cDNA ends and reverse transcription-polymerase chain reaction. BMXΔN, resulting from exon skipping with excluding exon 1 to exon 8 of BMX gene, was found in 12% human lung adenocarcinoma specimens. BMXΔN is not found in paired pathologically normal lungs and positively correlated with EGFR mutation in lung adenocarcinomas. Moreover, BMXΔN increases cell proliferation, neoplastic transformation, and migratory property of human non-small cell lung cancer cells. The function of BMXΔN in lung cancer might be presumably due to enhanced ERK signaling.