SYK inhibition and response prediction in diffuse large B-cell lymphoma

Spleen tyrosine kinase (SYK): an emerging target for the assemblage of small molecule antitumor agents

INTRODUCTION

Spleen tyrosine kinase (SYK), a nonreceptor tyrosine kinase, has emerged as a vital component in the complex symphony of cancer cell survival and division. SYK activation (constitutive) is documented in various B-cell malignancies, and its inhibition induces programmed cell death. In some instances, it also acts as a tumor suppressor.

AREAS COVERED

Involvement of the SYK in the cancer growth, specifically in the progression of chronic lymphocytic leukemia (CLL), diffuse large B cell lymphomas (DLBCLs), acute myeloid leukemia (AML), and multiple myeloma (MM) is discussed. Therapeutic strategies to target SYK in cancer, including investigational SYK inhibitors, combinations of SYK inhibitors with other drugs targeting therapeutically relevant targets, and recent advancements in constructing new structural assemblages as SYK inhibitors, are also covered.

EXPERT OPINION

The SYK inhibitor field is currently marred by the poor translation rate of SYK inhibitors from preclinical to clinical studies. Also, dose-limited toxicities associated with the applications of SYK inhibitors have been evidenced. Thus, the development of new SYK inhibitory structural templates is in the need of the hour. To accomplish the aforementioned, interdisciplinary teams should incessantly invest efforts to expand the size of the armory of SYK inhibitors.

Promises of Protein Kinase Inhibitors in Recalcitrant Small-Cell Lung Cancer: Recent Scenario and Future Possibilities

SCLC is refractory to conventional therapies; targeted therapies and immunological checkpoint inhibitor (ICI) molecules have prolonged survival only marginally. In addition, ICIs help only a subgroup of SCLC patients. Different types of kinases play pivotal roles in therapeutics-driven cellular functions. Therefore, there is a significant need to understand the roles of kinases in regulating therapeutic responses, acknowledge the existing knowledge gaps, and discuss future directions for improved therapeutics for recalcitrant SCLC. Here, we extensively review the effect of dysregulated kinases in SCLC. We further discuss the pharmacological inhibitors of kinases used in targeted therapies for recalcitrant SCLC. We also describe the role of kinases in the ICI-mediated activation of antitumor immune responses. Finally, we summarize the clinical trials evaluating the potential of kinase inhibitors and ICIs. This review overviews dysregulated kinases in SCLC and summarizes their potential as targeted therapeutic agents. We also discuss their clinical efficacy in enhancing anticancer responses mediated by ICIs.

Spatially Exploring RNA Biology in Archival Formalin-Fixed Paraffin-Embedded Tissues

Spatial transcriptomics has emerged as a powerful tool for dissecting spatial cellular heterogeneity but as of today is largely limited to gene expression analysis. Yet, the life of RNA molecules is multifaceted and dynamic, requiring spatial profiling of different RNA species throughout the life cycle to delve into the intricate RNA biology in complex tissues. Human disease-relevant tissues are commonly preserved as formalin-fixed and paraffin-embedded (FFPE) blocks, representing an important resource for human tissue specimens. The capability to spatially explore RNA biology in FFPE tissues holds transformative potential for human biology research and clinical histopathology. Here, we present Patho-DBiT combining in situ polyadenylation and deterministic barcoding for spatial full coverage transcriptome sequencing, tailored for probing the diverse landscape of RNA species even in clinically archived FFPE samples. It permits spatial co-profiling of gene expression and RNA processing, unveiling region-specific splicing isoforms, and high-sensitivity transcriptomic mapping of clinical tumor FFPE tissues stored for five years. Furthermore, genome-wide single nucleotide RNA variants can be captured to distinguish different malignant clones from non-malignant cells in human lymphomas. Patho-DBiT also maps microRNA-mRNA regulatory networks and RNA splicing dynamics, decoding their roles in spatial tumorigenesis trajectory. High resolution Patho-DBiT at the cellular level reveals a spatial neighborhood and traces the spatiotemporal kinetics driving tumor progression. Patho-DBiT stands poised as a valuable platform to unravel rich RNA biology in FFPE tissues to study human tissue biology and aid in clinical pathology evaluation.

Spleen tyrosine kinase/FMS-like tyrosine kinase-3 inhibition in relapsed/refractory B-cell lymphoma, including diffuse large B-cell lymphoma: updated data with mivavotinib (TAK-659/CB-659)

We report an updated analysis from a phase I study of the spleen tyrosine kinase (SYK) and FMS-like tyrosine kinase 3 inhibitor mivavotinib, presenting data for the overall cohort of lymphoma patients, and the subgroup of patients with diffuse large B-cell lymphoma (DLBCL; including an expanded cohort not included in the initial report). Patients with relapsed/refractory lymphoma for which no standard treatment was available received mivavotinib 60-120 mg once daily in 28-day cycles until disease progression/unacceptable toxicity. A total of 124 patients with lymphoma, including 89 with DLBCL, were enrolled. Overall response rates (ORR) in response-evaluable patients were 45% (43/95) and 38% (26/69), respectively. Median duration of response was 28.1 months overall and not reached in DLBCL responders. In subgroups with DLBCL of germinal center B-cell (GCB) and non-GCB origin, ORR was 28% (11/40) and 58% (7/12), respectively. Median progression free survival was 2.0 and 1.6 months in the lymphoma and DLBCL cohorts, respectively. Grade ≥3 treatment-emergent adverse events occurred in 96% of all lymphoma patients, many of which were limited to asymptomatic laboratory abnormalities; the most common were increased amylase (29%), neutropenia (27%), and hypophosphatemia (26%). These findings support SYK as a potential therapeutic target for the treatment of patients with B-cell lymphomas, including DLBCL. Trial registration: ClinicalTrials.gov number: NCT02000934.

Evaluation of the Synergistic Potential of Simultaneous Pan- or Isoform-Specific BET and SYK Inhibition in B-Cell Lymphoma: An In Vitro Approach

Simple Summary

B-cell lymphomas represent the majority of non-Hodgkin lymphomas and are the most common lymphoid malignancies in the Western world. Genetic alterations or epigenetic modulations can lead to tumor initiation and tumor progression. Aside from standard care, targeted, individualized therapies can be highly effective. Here, we evaluated the impact of simultaneous specific inhibition of two key regulators involved in B lymphoid tumor progression. Spleen tyrosine kinase (SYK) is a B-cell receptor-associated kinase acting as a proto-oncogene in B-cell malignancies, while bromodomain and extra-terminal domain (BET) proteins are epigenetic reader proteins involved in histone recognition and transcription regulation. The simultaneous inhibition of SYK and BET showed enhanced anti-proliferative effects, as well as inducing a distinct combination-specific gene expression profile, suggesting SYK and BET inhibition as a promising combination in the treatment of B-cell lymphoma.

Abstract

Background: Both bromodomain and extra-terminal domain (BET) proteins and spleen tyrosine kinase (SYK) represent promising targets in diffuse large B-cell (DLBCL) and Burkitt’s lymphoma (BL). We evaluated the anti-lymphoma activity of the isoform-specific bivalent BET inhibitor AZD5153 (AZD) and the pan-BET inhibitor I-BET151 (I-BET) as single agents and in combination with SYK inhibitor Entospletinib (Ento) in vitro. Methods: The effect of the single agents on cell proliferation and metabolic activity was evaluated in two DLBCL and two BL cell lines. Proliferation, metabolic activity, apoptosis, cell cycle and morphology were further investigated after a combined treatment of AZD or I-BET and Ento. RNAseq profiling of combined AZD+Ento treatment was performed in SU-DHL-4 cells. Results: Both BET inhibitors reduced cell proliferation and metabolic activity in a dose- and time-dependent manner. Combined BET and SYK inhibition enhanced the anti-proliferative effect and induced a G0/G1 cell cycle arrest. SU-DHL-4 demonstrated a pronounced modulation of gene expression by AZD, which was markedly increased by additional SYK inhibition. Functional enrichment analyses identified combination-specific GO terms related to DNA replication and cell division. Genes such as ADGRA2, MYB, TNFRSF11A, S100A10, PLEKHH3, DHRS2 and FOXP1-AS1 were identified as possible key regulators. Conclusion: Simultaneous inhibition of BET and SYK enhanced the anti-proliferative effects, and induced a combination-specific gene expression signature.

Prognostic significance of BLK expression in R-CHOP treated diffuse large B-cell lymphoma

Background

The aim of the present study was to evaluate the prognostic significance of B-cell lymphocyte kinase (BLK) expression for survival outcomes in diffuse large B-cell lymphoma (DLBCL) patients treated with R-CHOP.

Methods

We retrospectively analyzed the medical records of 89 patients from two tertiary referral hospitals. The expression of BLK, SYK, and CDK1 were evaluated in a semi-quantitative method using an H-score, and the proportions of BCL2 and C-MYC were evaluated.

Results

A total of 89 patients received R-CHOP chemotherapy as a first-line chemotherapy. The expression rates of BLK in tumor cells was 39.2% (n = 34). BLK expression status was not significantly associated with clinical variables; however, BLK expression in tumor cells was significantly associated with the expression of both C-MYC and BCL2 (p = .003). With a median follow-up of 60.4 months, patients with BLK expression had significantly lower 5-year progression-free survival (PFS) and overall survival rates (49.8% and 60.9%, respectively) than patients without BLK expression (77.3% and 86.7%, respectively). In multivariate analysis for PFS, BLK positivity was an independent poor prognostic factor (hazard ratio, 2.208; p = .040).

Conclusions

Here, we describe the clinicopathological features and survival outcome according to expression of BLK in DLBCL. Approximately 39% of DLBCL patients showed BLK positivity, which was associated as a predictive marker for poor prognosis in patients who received R-CHOP chemotherapy.

Regulation of B-Cell Receptor Signaling and Its Therapeutic Relevance in Aggressive B-Cell Lymphomas

The proliferation and survival signals emanating from the B-cell receptor (BCR) constitute a crucial aspect of mature lymphocyte's life. Dysregulated BCR signaling is considered a potent contributor to tumor survival in different subtypes of B-cell non-Hodgkin lymphomas (B-NHLs). In the last decade, the emergence of BCR-associated kinases as rational therapeutic targets has led to the development and approval of several small molecule inhibitors targeting either Bruton's tyrosine kinase (BTK), spleen tyrosine kinase (SYK), or phosphatidylinositol 3 kinase (PI3K), offering alternative treatment options to standard chemoimmunotherapy, and making some of these drugs valuable assets in the anti-lymphoma armamentarium. Despite their initial effectiveness, these precision medicine strategies are limited by primary resistance in aggressive B-cell lymphoma such as diffuse large B-cell lymphoma (DLBCL) and mantle cell lymphoma (MCL), especially in the case of first generation BTK inhibitors. In these patients, BCR-targeting drugs often fail to produce durable responses, and nearly all cases eventually progress with a dismal outcome, due to secondary resistance. This review will discuss our current understanding of the role of antigen-dependent and antigen-independent BCR signaling in DLBCL and MCL and will cover both approved inhibitors and investigational molecules being evaluated in early preclinical studies. We will discuss how the mechanisms of action of these molecules, and their off/on-target effects can influence their effectiveness and lead to toxicity, and how our actual knowledge supports the development of more specific inhibitors and new, rationally based, combination therapies, for the management of MCL and DLBCL patients.

Herbal NF-κB Inhibitors Sensitize Rituximab-Resistant B Lymphoma Cells to Complement-Mediated Cytolysis

Background

Drug resistance remains a serious challenge to rituximab therapy in B-NHL (B cell non-Hodgkin’s lymphoma). CDC (complement-dependent cytotoxicity) has been proposed as a major antitumor mechanism of rituximab, and direct abrogation of CD59 function partially restores rituximab sensitivity with high efficacy. However, universal blockade of CD59 may have deleterious effects on normal cells. Sp1 regulates constitutive CD59 expression, whereas NF-κB and CREB regulate inducible CD59 expression.

Methods

Immunohistochemistry (IHC) assay was used to detect the expression levels of CD59 and other related molecules. Quantitative Real-time PCR (RT-PCR) analysis was used to explore the levels of transcripts in the original and resistant cells. We chose LY8 cells to test the effects of NF-κB and CBP/p300 inhibition on CD59 expression using flow cytometry (FACS). Immunoblotting analysis was employed to detect the effects of curcumin and POH. The in vitro and in vivo experiments were used to evaluate the toxicity and combined inhibitory effect on tumor cells of curcumin and POH.

Results

We demonstrated that herbal (curcumin and perillyl alcohol) blockade of NF-κB specifically suppresses the expression of inducible CD59 but not CD20, thus sensitizing resistant cells to rituximab-mediated CDC. Moreover, activation of NF-κB and CREB is highly correlated with CD59 expression in B-NHL tissues.

Conclusions

Our findings suggest the potential of CD59 expression as a predictor of therapeutic efficacy of NF-κB inhibitors in clinical application as well as the rationality of a NF-κB inhibitor-rituximab regimen in B-NHL therapy.

A Deep Insight Into CAR-T Cell Therapy in Non-Hodgkin Lymphoma: Application, Opportunities, and Future Directions

Non-Hodgkin's lymphoma (NHL) is a cancer that starts in the lymphatic system. In NHL, the important part of the immune system, a type of white blood cells called lymphocytes become cancerous. NHL subtypes include marginal zone lymphoma, small lymphocytic lymphoma, follicular lymphoma (FL), and lymphoplasmacytic lymphoma. The disease can emerge in either aggressive or indolent form. 5-year survival duration after diagnosis is poor among patients with aggressive/relapsing form of NHL. Therefore, it is necessary to understand the molecular mechanisms of pathogenesis involved in NHL establishment and progression. In the next step, we can develop innovative therapies for NHL based on our knowledge in signaling pathways, surface antigens, and tumor milieu of NHL. In the recent few decades, several treatment solutions of NHL mainly based on targeted/directed therapies have been evaluated. These approaches include B-cell receptor (BCR) signaling inhibitors, immunomodulatory agents, monoclonal antibodies (mAbs), epigenetic modulators, Bcl-2 inhibitors, checkpoint inhibitors, and T-cell therapy. In recent years, methods based on T cell immunotherapy have been considered as a novel promising anti-cancer strategy in the treatment of various types of cancers, and particularly in blood cancers. These methods could significantly increase the capacity of the immune system to induce durable anti-cancer responses in patients with chemotherapy-resistant lymphoma. One of the promising therapy methods involved in the triumph of immunotherapy is the chimeric antigen receptor (CAR) T cells with dramatically improved killing activity against tumor cells. The CAR-T cell-based anti-cancer therapy targeting a pan-B-cell marker, CD19 is recently approved by the US Food and Drug Administration (FDA) for the treatment of chemotherapy-resistant B-cell NHL. In this review, we will discuss the structure, molecular mechanisms, results of clinical trials, and the toxicity of CAR-T cell-based therapies. Also, we will criticize the clinical aspects, the treatment considerations, and the challenges and possible drawbacks of the application of CAR-T cells in the treatment of NHL.

Heightened activation of embryonic megakaryocytes causes aneurysms in the developing brain of mice lacking podoplanin

During early embryonic development in mammals, including humans and mice, megakaryocytes (Mks) first originate from primitive hematopoiesis in the yolk sac. These embryonic Mks (eMks) circulate in the vasculature with unclear function. Herein, we report that podoplanin (PDPN), the ligand of C-type lectin-like receptor (CLEC-2) on Mks/platelets, is temporarily expressed in neural tissue during midgestation in mice. Loss of PDPN or CLEC-2 resulted in aneurysms and spontaneous hemorrhage, specifically in the lower diencephalon during midgestation. Surprisingly, more eMks/platelets had enhanced granule release and localized to the lower diencephalon in mutant mouse embryos than in wild-type littermates before hemorrhage. We found that PDPN counteracted the collagen-1-induced secretion of angiopoietin-1 from fetal Mks, which coincided with enhanced TIE-2 activation in aneurysm-like sprouts of PDPN-deficient embryos. Blocking platelet activation prevented the PDPN-deficient embryo from developing vascular defects. Our data reveal a new role for PDPN in regulating eMk function during midgestation.

Inhibition of B-cell receptor signaling disrupts cell adhesion in mantle cell lymphoma via RAC2

Inhibition of the B-cell receptor (BCR) signaling pathway is highly effective in B-cell neoplasia through Bruton tyrosine kinase inhibition by ibrutinib. Ibrutinib also disrupts cell adhesion between a tumor and its microenvironment. However, it is largely unknown how BCR signaling is linked to cell adhesion. We observed that intrinsic sensitivities of mantle cell lymphoma (MCL) cell lines to ibrutinib correlated well with their cell adhesion phenotype. RNA-sequencing revealed that BCR and cell adhesion signatures were simultaneously downregulated by ibrutinib in the ibrutinib-sensitive, but not ibrutinib-resistant, cells. Among the differentially expressed genes, RAC2, part of the BCR signature and a known regulator of cell adhesion, was downregulated at both the RNA and protein levels by ibrutinib only in sensitive cells. RAC2 physically associated with B-cell linker protein (BLNK), a BCR adaptor molecule, uniquely in sensitive cells. RAC2 reduction using RNA interference and CRISPR impaired cell adhesion, whereas RAC2 overexpression reversed ibrutinib-induced cell adhesion impairment. In a xenograft mouse model, mice treated with ibrutinib exhibited slower tumor growth, with reduced RAC2 expression in tissue. Finally, RAC2 was expressed in ∼65% of human primary MCL tumors, and RAC2 suppression by ibrutinib resulted in cell adhesion impairment. These findings, made with cell lines, a xenograft model, and human primary lymphoma tumors, uncover a novel link between BCR signaling and cell adhesion. This study highlights the importance of RAC2 and cell adhesion in MCL pathogenesis and drug development.

Precursor B-ALL Cell Lines Differentially Respond to SYK Inhibition by Entospletinib

BACKGROUND

Impaired B-cell receptor (BCR) function has been associated with the progress of several B-cell malignancies. The spleen tyrosine kinase (SYK) represents a potential therapeutic target in a subset of B-cell neoplasias. In precursor B-acute lymphoblastic leukemia (B-ALL), the pathogenic role and therapeutic potential of SYK is still controversially discussed. We evaluate the application of the SYK inhibitor entospletinib (Ento) in pre- and pro-B-ALL cell lines, characterizing the biologic and molecular effects.

METHODS

SYK expression was characterized in pre-B-ALL (NALM-6) and pro-B-ALL cell lines (SEM and RS4;11). The cell lines were exposed to different Ento concentrations and the cell biological response analyzed by proliferation, metabolic activity, apoptosis induction, cell-cycle distribution and morphology. BCR pathway gene expression and protein modulations were further characterized.

RESULTS

Ento significantly induced anti-proliferative and pro-apoptotic effects in NALM-6 and SEM, while barely affecting RS4;11. Targeted RNAseq revealed pronounced gene expression modulation only in NALM-6, while Western Blot analyses demonstrated that vital downstream effector proteins, such as pAKT, pERK, pGSK3β, p53 and BCL-6, were affected by Ento exposure in the inhibitor-sensitive cell lines.

CONCLUSION

Different acting modes of Ento, independent of pre-BCR dependency, were characterized, unexpected in SEM. Accordingly, SYK classifies as a potential target structure in a subset of pro-B-ALLs.

Characterizing the structure-activity relationships of natural products, tanshinones, reveals their mode of action in inhibiting spleen tyrosine kinase

The cytosolic non-receptor protein kinase, spleen tyrosine kinase (SYK), is an attractive drug target in autoimmune, inflammatory disorder, and cancers indications. Here, we employed pharmacophore-based drug screening combined with biochemical assay and molecular dynamics (MD) simulations to identify and characterize inhibitors targeting SYK. The built pharmacophore model, phar-TanI, successfully identified tanshinone (TanI (IC50 = 1.72 μM)) and its analogs (TanIIA (IC50 = 3.2 μM), ST32da (IC50 = 46 μM), and ST32db (IC50 = 51 μM)) which apparently attenuated the activities of SYK in vitro. Additionally, the MD simulations followed by Ligplot analyses revealed that TanI and TanIIA interfered SYK activity through binding deeply into the active site. Besides, TanI and TanIIA mainly interact with residues L377, A400, V433, M448, M450, A451, E452, L453, G454, P455, and L501, which are functional hotspots for structure-based inhibitor optimization against SYK. The structure-activity relationships (SAR) study of the identified SYK inhibitors demonstrated that the pharmacophore model, phar-TanI is reliable and precise in screening inhibitors against SYK. This study disclosed the structure-function relationships of tanshinones from Traditional Chinese Medicine (Danshen), revealing their binding site and mode of action in inhibiting SYK and provides applicability in developing new therapeutic agents.

Biomarkers and novel therapeutic approaches for diffuse large B-cell lymphoma in the era of precision medicine

Despite the great efforts for better treatment options for diffuse large B-cell lymphoma (DLBCL) (most common form of non-Hodgkin lymphoma, NHL) to treat and prevent relapse, it continues to be a challenge. Here, we present an overview of DLBCL and address the diagnostic assays and molecular techniques used in its diagnosis, role of biomarkers in detection, treatment of early and advanced stage DLBCL, and novel drug regimens. We discuss the significant biomarkers that have emerged as essential tools for stratifying patients according to risk factors and for providing insights into the use of more targeted and individualized therapeutics. We discuss techniques such as gene expression studies, including next-generation sequencing, which have enabled a more understanding of the complex pathogenesis of DLBCL and have helped determine molecular targets for novel therapeutic agents. We examine current treatment approaches, outline the findings of completed clinical trials, and provide updates for ongoing clinical trials. We highlight clinical trials relevant to the significant fraction of DLBCL patients who present with complex cases marked by high relapse rates. Supported by an increased understanding of targetable pathways in DLBCL, clinical trials involving specialized combination therapies are bringing us within reach the promise of an effective cure to DLBCL using precision medicine. Optimization of therapy remains a crucial objective, with the end goal being a balance between high survival rates through targeted and personalized treatment while reducing adverse effects in DLBCL patients of all subsets.

Identification of a novel series of azabenzimidazole-derived inhibitors of spleen tyrosine kinase

Spleen Tyrosine Kinase (SYK) is a well-studied enzyme with therapeutic applications in oncology and autoimmune diseases. We identified an azabenzimidazole (ABI) series of SYK inhibitors by mining activity data of 86,000 compounds from legacy biochemical assays with SYK and other homologous kinases as target enzymes. A structure-based design and hybridization approach was then used to improve the potency and kinase selectivity of the hits. Lead compound 23 from this novel ABI series has a SYK IC₅₀ = 0.21 nM in a biochemical assay and inhibits growth of SUDHL-4 cells at a GI₅₀ = 210 nM.

Mechanisms of B Cell Receptor Activation and Responses to B Cell Receptor Inhibitors in B Cell Malignancies

The B cell receptor (BCR) pathway has been identified as a potential therapeutic target in a number of common B cell malignancies, including chronic lymphocytic leukemia, diffuse large B cell lymphoma, Burkitt lymphoma, follicular lymphoma, mantle cell lymphoma, marginal zone B cell lymphoma, and Waldenstrom's macroglobulinemia. This finding has resulted in the development of numerous drugs that target this pathway, including various inhibitors of the kinases BTK, PI3K, and SYK. Several of these drugs have been approved in recent years for clinical use, resulting in a profound change in the way these diseases are currently being treated. However, the response rates and durability of responses vary largely across the different disease entities, suggesting a different proportion of patients with an activated BCR pathway and different mechanisms of BCR pathway activation. Indeed, several antigen-dependent and antigen-independent mechanisms have recently been described and shown to result in the activation of distinct downstream signaling pathways. The purpose of this review is to provide an overview of the mechanisms responsible for the activation of the BCR pathway in different B cell malignancies and to correlate these mechanisms with clinical responses to treatment with BCR inhibitors.

Design and optimization of orally spleen tyrosine kinase (SYK) inhibitors for treatment of solid tumor

As the aim to discover orally SYK inhibitors for solid tumor treatment, a series of novel derivatives based on imidazo[1,2-a]pyrazine scaffold were designed, synthesized and evaluated. Structure-activity relationship study of both enzymatic and cellular assays led to the identification of compound 12f. The novel SYK inhibitor 12f showed potent antitumor activity against solid tumors with favorable drug-like properties of lipophilicity and solubility. 12f could induce cell apoptosis of ovarian and lung cancer cell lines. In SKOV3 xenograft mouse model, oral administration of 12f led to significant tumour regression without obvious toxicity. 12f improved the limited response of traditional SYK inhibitors in solid tumors in vitro and in vivo. Taken together, this compound may act as a promising lead compound for further development of new SYK inhibitors for solid tumor therapy.

Spleen tyrosine kinase activity regulates epidermal growth factor receptor signaling pathway in ovarian cancer

BACKGROUND

Spleen tyrosine kinase (SYK) is frequently upregulated in recurrent ovarian carcinomas, for which effective therapy is urgently needed. SYK phosphorylates several substrates, but their translational implications remain unclear. Here, we show that SYK interacts with EGFR and ERBB2, and directly enhances their phosphorylation.

METHODS

We used immunohistochemistry and immunoblotting to assess SYK and EGFR phosphorylation in ovarian serous carcinomas. Association with survival was determined by Kaplan-Meier analysis and the log-rank test. To study its role in EGFR signaling, SYK activity was modulated using a small molecule inhibitor, a syngeneic knockout, and an active kinase inducible system. We applied RNA-seq and phosphoproteomic mass spectrometry to investigate the SYK-regulated EGF-induced transcriptome and downstream substrates.

FINDINGS

Induced expression of constitutively active SYK130E reduced cellular response to EGFR/ERBB2 inhibitor, lapatinib. Expression of EGFRWT, but not SYK non-phosphorylatable EGFR3F mutant, resulted in paclitaxel resistance, a phenotype characteristic to SYK active ovarian cancers. In tumor xenografts, SYK inhibitor reduces phosphorylation of EGFR substrates. Compared to SYKWT cells, SYKKO cells have an attenuated EGFR/ERBB2-transcriptional activity and responsiveness to EGF-induced transcription. In ovarian cancer tissues, pSYK (Y525/526) levels showed a positive correlation with pEGFR (Y1187). Intense immunoreactivity of pSYK (Y525/526) correlated with poor overall survival in ovarian cancer patients.

INTERPRETATION

These findings indicate that SYK activity positively modulates the EGFR pathway, providing a biological foundation for co-targeting SYK and EGFR. FUND: Department of Gynecology and Obstetrics, Johns Hopkins University School of Medicine, NIH/NCI, Ovarian Cancer Research Foundation Alliance, HERA Women's Cancer Foundation and Roseman Foundation. Funders had no role in the design of the study and collection, analysis, and interpretation of data and in writing the manuscript and eventually in the decision to submit the manuscript.

Pathogenic B-cell receptor signaling in lymphoid malignancies: New insights to improve treatment

Signals emanating from the B-cell receptor (BCR) promote proliferation and survival in diverse forms of B-cell lymphoma. Precision medicine strategies targeting the BCR pathway have been generally effective in treating lymphoma, but often fail to produce durable responses in diffuse large B-cell lymphoma (DLBCL), a common and aggressive cancer. New insights into DLBCL biology garnered from genomic analyses and functional proteogenomic studies have identified novel modes of BCR signaling in this disease. Herein, we describe the distinct roles of antigen-dependent and antigen-independent BCR signaling in different subtypes of DLBCL. We highlight mechanisms by which the BCR cooperates with TLR9 and mutant isoforms of MYD88 to drive sustained NF-κB activity in the activated B-cell-like (ABC) subtype of DLBCL. Finally, we discuss progress in detecting and targeting oncogenic BCR signaling to improve the survival of patients with lymphoma.

Inhibition of SYK or BTK augments venetoclax sensitivity in SHP1-negative/BCL-2-positive diffuse large B-cell lymphoma

The BCL-2 inhibitor venetoclax has only limited activity in DLBCL despite frequent BCL-2 overexpression. Since constitutive activation of the B cell receptor (BCR) pathway has been reported in both ABC and GCB DLBCL, we investigated whether targeting SYK or BTK will increase sensitivity of DLBCL cells to venetoclax. We report that pharmacological inhibition of SYK or BTK synergistically enhances venetoclax sensitivity in BCL-2-positive DLBCL cell lines with an activated BCR pathway in vitro and in a xenograft model in vivo, despite the only modest direct cytotoxic effect. We further show that these sensitizing effects are associated with inhibition of the downstream PI3K/AKT pathway and changes in the expression of MCL-1, BIM, and HRK. In addition, we show that BCR-dependent GCB DLBCL cells are characterized by deficiency of the phosphatase SHP1, a key negative regulator of the BCR pathway. Re-expression of SHP1 in GCB DBLCL cells reduces SYK, BLNK, and GSK3 phosphorylation and induces corresponding changes in MCL1, BIM, and HRK expression. Together, these findings suggest that SHP1 deficiency is responsible for the constitutive activation of the BCR pathway in GCB DLBCL and identify SHP1 and BCL-2 as potential predictive markers for response to treatment with a venetoclax/BCR inhibitor combination.

Taming the Heterogeneity of Aggressive Lymphomas for Precision Therapy

Genomic analyses of diffuse large B cell lymphoma (DLBCL) are revealing the genetic and phenotypic heterogeneity of these aggressive lymphomas. In part, this heterogeneity reflects the existence of distinct genetic subtypes that acquire characteristic constellations of somatic genetic alterations to converge on the DLBCL phenotype. In parallel, functional genomic screens and proteomic analyses have identified multiprotein assemblies that coordinate oncogenic survival signaling in DLBCL. In this review, we merge these recent insights into a unified conceptual framework with implications for the design of precision medicine trials in DLBCL.

Inhibition of ovarian tumor cell invasiveness by targeting SYK in the tyrosine kinase signaling pathway

Cell motility and invasiveness are prerequisites for dissemination, and largely account for cancer mortality. We have identified an actionable kinase, spleen tyrosine kinase (SYK), which is keenly tightly associated with tumor progression in ovarian cancer. Here, we report that active recombinant SYK directly phosphorylates cortactin and cofilin, which are critically involved in assembly and dynamics of actin filament through phosphorylation signaling. Enhancing SYK activity by inducing expression of a constitutively active SYK mutant, SYK130E, increased growth factor-stimulated migration and invasion of ovarian cancer cells, which was abrogated by cortactin knockdown. Similarly, SYK inhibitors significantly decreased invasion of ovarian cancer cells across basement membrane in real-time transwell assays and in 3D tumor spheroid models. SYK inactivation by targeted gene knockout or by small molecule inhibition reduced actin polymerization. Collectively, this study reported a new mechanism by which SYK signaling regulates ovarian cancer cell motility and invasiveness, and suggest a target-based strategy to prevent or suppress the advancement of ovarian malignancies.

An Open-label, Phase II Trial of Entospletinib (GS-9973), a Selective Spleen Tyrosine Kinase Inhibitor, in Diffuse Large B-cell Lymphoma

In an open-label, phase II study, we evaluated entospletinib monotherapy for patients with relapsed or refractory diffuse large B-cell lymphoma. Entospletinib had limited activity in these patients. Seventy-four percent of the patients experienced a grade ≥ 3 adverse event. Treatment was interrupted in 42% of the patients, and the drug was discontinued in 19% of the patients.

Crystal Structures of Spleen Tyrosine Kinase in Complex with Two Novel 4-Aminopyrido[4,3-d] Pyrimidine Derivative Inhibitors

Spleen tyrosine kinase (SYK) is a cytosolic non-receptor protein tyrosine kinase. Because SYK mediates key receptor signaling pathways involving the B cell receptor and Fc receptors, SYK is an attractive target for autoimmune disease and cancer treatments. To date, representative oral SYK inhibitors, including fostamatinib (R406 or R788), entospletinib (GS-9973), cerdulatinib (PRT062070), and TAK-659, have been assessed in clinical trials. Here, we report the crystal structures of SYK in complex with two newly developed inhibitors possessing 4-aminopyrido[4,3-D]pyrimidine moieties (SKI-G-618 and SKI-O-85). One SYK inhibitor (SKI-G-618) exhibited moderate inhibitory activity against SYK, whereas the other inhibitor (SKI-O-85) exhibited a low inhibitory profile against SYK. Binding mode analysis indicates that a highly potent SYK inhibitor might be developed by modifying and optimizing the functional groups that interact with Leu377, Gly378, and Val385 in the G-loop and the nearby region in SYK. In agreement with our structural analysis, one of our SYK inhibitor (SKI-G-618) shows strong inhibitory activities on the β-hexosaminidase release and phosphorylation of SYK/Vav in RBL-2H3 cells. Taken together, our findings have important implications for the design of high affinity SYK inhibitors.

A novel ex vivo high-throughput assay reveals antiproliferative effects of idelalisib and ibrutinib in chronic lymphocytic leukemia

PI3Kδ (idelalisib) and BTK (ibrutinib) inhibitors have demonstrated significant clinical activity in chronic lymphocytic leukemia (CLL) interfering with the cross-talk between CLL cells and the lymph node microenviroment, yet their mechanism of action remains to be fully elucidated. Here, we developed an ex vivo model with the aim of reproducing the effects of the microenvironment that would help shed light on the in vivo mechanism of action of idelalisib and ibrutinib and predict their clinical efficacy in individual patients. First we explored the effects of various cell-extrinsic elements on CLL apoptosis and proliferation and found that the combination of CpG+IL2+HS5 stromal cell line + human serum +CLL plasma and erythrocyte fractions represented the best co-culture conditions to test the effects of the novel inhibitors. Then, using this assay, we investigated the impact of idelalisib and ibrutinib on both survival and proliferation in 30 CLL patients. While both drugs had a limited direct pro-apoptotic activity, a potent inhibition of proliferation was achieved at clinically achievable concentrations. Notably, up to 10% of CLL cells still proliferated even at the highest concentrations, likely mirroring the known difficulty to achieve complete responses in vivo. Altogether, this novel assay represents an appropriate ex vivo drug testing system to potentially predict the clinical response to novel inhibitors in particular by quantifying the antiproliferative effect.

Comparative High-Resolution Transcriptome Sequencing of Lymphoma Cell Lines and de novo Lymphomas Reveals Cell-Line-Specific Pathway Dysregulation

In dogs as well as humans, lymphoma is one of the most common hematopoietic malignancies. Furthermore, due to its characteristics, canine lymphoma is recognized as a clinically relevant in vivo model to study the corresponding human disease. Immortalized cell lines are widely used as in vitro models to evaluate novel therapeutic agents and characterize their molecular mechanisms. However, it is known that long-term cultivation leads to clonal selection, genetic instability, and loss of the initial heterogenic character, limiting the usefulness of cell lines as preclinical models. Herein, we present a systematic characterization and comparison of the transcriptomic landscape of canine primary B- and T-cell lymphomas, five lymphoid cell lines (CLBL-1, CLBL-1M, GL-1, CL-1, and OSW) and four non-neoplastic control samples. We found that lymphomas and cell lines exhibit a common “differentiation and proliferation signature”. However, our analysis also showed that, independently of the cell of origin, the transcriptional signatures of lymphomas are more similar to each other than they are to those of cell lines. In particular, we observed that not all common therapeutic targets are similarly expressed between lymphomas and lymphoid cell lines, and provide evidence that different lymphoid cell-lines should be used to model distinct aspects of lymphoma dysregulation.

Diffuse large B-cell lymphoma: can genomics improve treatment options for a curable cancer?

Gene-expression profiling and next-generation sequencing have defined diffuse large B-cell lymphoma (DLBCL), the most common lymphoma diagnosis, as a heterogeneous group of subentities. Despite ongoing explosions of data illuminating disparate pathogenic mechanisms, however, the five-drug chemoimmunotherapy combination R-CHOP remains the frontline standard treatment. This has not changed in 15 years, since the anti-CD20 monoclonal antibody rituximab was added to the CHOP backbone, which first entered use in the 1970s. At least a third of patients are not cured by R-CHOP, and relapsed or refractory DLBCL is fatal in ∼90%. Targeted small-molecule inhibitors against distinct molecular pathways activated in different subgroups of DLBCL have so far translated poorly into the clinic, justifying the ongoing reliance on R-CHOP and other long-established chemotherapy-driven combinations. New drugs and improved identification of biomarkers in real time, however, show potential to change the situation eventually, despite some recent setbacks. Here, we review established and putative molecular drivers of DLBCL identified through large-scale genomics, highlighting among other things the care that must be taken when differentiating drivers from passengers, which is influenced by the promiscuity of activation-induced cytidine deaminase. Furthermore, we discuss why, despite having so much genomic data available, it has been difficult to move toward personalized medicine for this umbrella disorder and some steps that may be taken to hasten the process.

Identification of distinct molecular subtypes of uterine carcinosarcoma

Uterine carcinosarcoma (UCS) is a rare but lethal neoplasm with high metastasis and recurrence rate, and to date, no molecular classification of UCS has been defined to achieve targeted therapies. In this study, we identified two distinct molecular subtypes of UCS with distinct gene expression patterns and clinicopathologic characteristics. Subtype I UCS recapitulates low-grade UCS, in contrast subtype II UCS represents high-grade UCS with higher tumor invasion rate and tumor weight. Interestingly, subtype I UCS is characterized by cell adhesion and apoptosis pathways, whereas genes over-expressed in subtype II UCS are more involved in myogenesis/muscle development. We also proposed certain potential subtype specific therapeutic targets, such as SYK (spleen tyrosine kinase) for subtype I and cell-cycle proteins for subtype II. Our findings provide a better recognition of UCS molecular subtypes and subtype specific oncogenesis mechanisms, and can help develop more specific targeted treatment options for these tumors.

Molecular Classification of Diffuse Large B-cell Lymphoma: What Is Clinically Relevant?

Major progress in the understanding of diffuse large B-cell lymphoma (DLBCL) biology has been made in the last decade. Many specific compounds have now entered early phase clinical trials. However, further efforts are needed to find an accurate, fast, reproducible, and affordable technique to translate DLBCL subtype determination by gene expression profiles into clinical application. This article discusses the advantages and drawbacks of the currently available techniques of DLBCL subtype determination as well as important prognostic implications related to the cell of origin. Furthermore, the article provides a schematic description of how molecularly defined DLBCL subtypes could guide tailored therapy.

Inhibition of monocarboxyate transporter 1 by AZD3965 as a novel therapeutic approach for diffuse large B-cell lymphoma and Burkitt lymphoma

Inhibition of monocarboxylate transporter 1 has been proposed as a therapeutic approach to perturb lactate shuttling in tumor cells that lack monocarboxylate transporter 4. We examined the monocarboxylate transporter 1 inhibitor AZD3965, currently in phase I clinical studies, as a potential therapy for diffuse large B-cell lymphoma and Burkitt lymphoma. Whilst extensive monocarboxylate transporter 1 protein was found in 120 diffuse large B-cell lymphoma and 10 Burkitt lymphoma patients’ tumors, monocarboxylate transporter 4 protein expression was undetectable in 73% of the diffuse large B-cell lymphoma samples and undetectable or negligible in each Burkitt lymphoma sample. AZD3965 treatment led to a rapid accumulation of intracellular lactate in a panel of lymphoma cell lines with low monocarboxylate transporter 4 protein expression and potently inhibited their proliferation. Metabolic changes induced by AZD3965 in lymphoma cells were consistent with a feedback inhibition of glycolysis. A profound cytostatic response was also observed in vivo: daily oral AZD3965 treatment for 24 days inhibited CA46 Burkitt lymphoma growth by 99%. Continuous exposure of CA46 cells to AZD3965 for 7 weeks in vitro resulted in a greater dependency upon oxidative phosphorylation. Combining AZD3965 with an inhibitor of mitochondrial complex I (central to oxidative phosphorylation) induced significant lymphoma cell death in vitro and reduced CA46 disease burden in vivo. These data support clinical examination of AZD3965 in Burkitt lymphoma and diffuse large B-cell lymphoma patients with low tumor monocarboxylate transporter 4 expression and highlight the potential of combination strategies to optimally target the metabolic phenotype of tumors.

Dual SYK/JAK inhibition overcomes ibrutinib resistance in chronic lymphocytic leukemia: Cerdulatinib, but not ibrutinib, induces apoptosis of tumor cells protected by the microenvironment

Ibrutinib (BTK inhibitor) has generated remarkable responses in CLL. However, the drug, to a large extent, does not cause cell death directly and does not eradicate CLL malignant clones. Inability to eradicate CLL has fostered resistance generation. Once patients become resistant, they do poorly with a median survival of 3-4 months. Novel therapeutic strategies are needed to prevent resistance, improve treatment outcome and ultimately cure the disease. Herein, we explore dual targeting of the BCR and JAK-STAT pathways with a novel single agent, cerdulatinib, which selectively inhibits both SYK (a BCR component) and JAK kinases. We demonstrated that cerdulatinib delivered potent tumor inhibition in 60 primary CLL patient samples, especially in those with poor prognostic indicators. Importantly, cerdulatinib, but not ibrutinib, is able to overcome the support of microenvironment and induces CLL cell death at clinically achievable concentrations. Notably, cerdulatinib blocked proliferation of ibrutinib-resistant primary CLL cells and of BTKC481S-transfected/ibrutinib-resistant lymphoma cells. These anti-tumor effects are well correlated with the inhibition of BCR and JAK-STAT signaling and downstream inhibition of the functions of AKT, ERK and NFκB. Collectively, our results show that simultaneous targeting of BCR and JAK-STAT pathways is a more effective strategy relative to single BTK inhibition.

HSP90 stabilizes B-cell receptor kinases in a multi-client interactome: PU-H71 induces CLL apoptosis in a cytoprotective microenvironment

Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of B cells in the hematopoietic system and lymphoid tissues. Although inhibitors targeting the B-cell receptor (BCR) pathway have been successful in the treatment of the disease, the underlying mechanisms leading to BCR over-activity in CLL are not fully understood. In this study, we found that HSP90, a highly conserved molecular chaperone, is overexpressed in CLL compared with resting B cells. HSP90 overexpression is accompanied by the overexpression of several BCR kinases including LYN, spleen tyrosine kinase, Bruton tyrosine kinase and AKT. Chemical and immune-precipitation demonstrated that these BCR constituents are present in a multi-client chaperone complex with HSP90. Inhibition of HSP90 with PU-H71 destabilized the BCR kinases and caused apoptosis of CLL cells through the mitochondrial apoptotic pathway. Further, PU-H71 induced apoptosis in the presence of stromal co-culture or cytoprotective survival signals. Finally, genetic knockdown of HSP90 and its client AKT, but not BTK, reduced CLL viability. Overall, our study suggests that the chaperone function of HSP90 contributes to the over-activity of the BCR signaling in CLL and inhibition of HSP90 has the potential to achieve a multi-targeting effect. Thus, HSP90 inhibition may be explored to prevent or overcome drug resistance to single targeting agents.

Discovery of TAK-659 an orally available investigational inhibitor of Spleen Tyrosine Kinase (SYK)

Spleen Tyrosine Kinase (SYK) is a non-receptor cytoplasmic tyrosine kinase that is primarily expressed in hematopoietic cells. SYK is a key mediator for a variety of inflammatory cells, including B cells, mast cells, macrophages and neutrophils and therefore, an attractive approach for treatment of both inflammatory diseases and oncology indications. Using in house co-crystal structure information, and structure-based drug design, we designed and optimized a novel series of heteroaromatic pyrrolidinone SYK inhibitors resulting in the selection of the development candidate TAK-659. TAK-659 is currently undergoing Phase I clinical trials for advanced solid tumor and lymphoma malignancies, a Phase Ib study in advanced solid tumors in combination with nivolumab, and PhIb/II trials for relapsed/refractory AML.

Heightened BTK-dependent cell proliferation in unmutated chronic lymphocytic leukemia confers increased sensitivity to ibrutinib

In chronic lymphocytic leukemia (CLL), patients with unmutated immunoglobulin heavy chain variable region gene (UM-CLL) have worse outcomes than mutated CLL (M-CLL) following chemotherapy or chemoimmunotherapy. However, in the era of BCR-targeted therapies, the adverse prognostic impact of unmutated IGHV seems to be diminishing, and there are clinical datasets showing unexpected improved responses in UM-CLL. We investigated the biological differences of BTK activity between these subgroups and further compared the impact of ibrutinib on molecular and cellular behaviors. Immunoblotting analysis revealed that phosphorylated active BTK is significantly higher in UM-CLL. Moreover, UM-CLL, compared to M-CLL, displayed a much higher proliferative capacity that was correlated with higher phospho-BTK and greater sensitivity to ibrutinib. In addition, BTK depletion with siRNA led to a more prominent reduction in the proliferation of UM-CLL, suggesting that elevated BTK activity is responsible for increased cell proliferation. Further, cell signaling activity by multiple measurements was consistently higher in UM-CLL accompanied by a higher sensitivity to ibrutinib. These studies link UM-CLL to elevated BCR signaling, heightened BTK-dependent cell proliferation and increased sensitivity to ibrutinib. The prognostic significance of IGHV mutation should be reevaluated in the era of new therapies targeting BCR signaling.

Inhibition of demethylase KDM6B sensitizes diffuse large B-cell lymphoma to chemotherapeutic drugs

Histone methylation and demethylation regulate B-cell development, and their deregulation correlates with tumor chemoresistance in diffuse large B-cell lymphoma, limiting cure rates. Since histone methylation status correlates with disease aggressiveness and relapse, we investigated the therapeutic potential of inhibiting histone 3 Lys27 demethylase KDM6B, in vitro, using the small molecule inhibitor GSK-J4. KDM6B is overexpressed in the germinal center B-cell subtype of diffuse large B-cell lymphoma, and higher KDM6B levels are associated with worse survival in patients with diffuse large B-cell lymphoma treated with R-CHOP. GSK-J4-induced apoptosis was observed in five (SU-DHL-6, OCI-Ly1, Toledo, OCI-Ly8, SU-DHL-8) out of nine germinal center B-cell diffuse large B-cell lymphoma cell lines. Treatment with GSK-J4 predominantly resulted in downregulation of B-cell receptor signaling and BCL6. Cell lines expressing high BCL6 levels or CREBBP/EP300 mutations were sensitive to GSK-J4. Our results suggest that B-cell receptor-dependent downregulation of BCL6 is responsible for GSK-J4-induced cytotoxicity. Furthermore, GSK-J4-mediated inhibition of KDM6B sensitizes germinal center B-cell diffuse large B-cell lymphoma cells to chemotherapy agents that are currently utilized in treatment regimens for diffuse large B-cell lymphoma.

Cerdulatinib, a novel dual SYK/JAK kinase inhibitor, has broad anti-tumor activity in both ABC and GCB types of diffuse large B cell lymphoma

B-cell receptor (BCR) and JAK/STAT pathways play critical roles in diffuse large B-cell lymphoma (DLBCL). Herein, we investigated the anti-lymphoma activity of cerdulatinib, a novel compound that dually targets SYK and JAK/STAT pathways. On a tissue microarray of 62 primary DLBCL tumors, 58% expressed either phosphorylated SYK or STAT3 or both. SYK and STAT3 are also phosphorylated in a panel of eleven DLBCL cell lines although ABC and GCB subtypes exhibited different JAK/STAT and BCR signaling profiles. In both ABC and GCB cell lines, cerdulatinib induced apoptosis that was associated with caspase-3 and PARP cleavage. The compound also blocked G1/S transition and caused cell cycle arrest, accompanied by inhibition of RB phosphorylation and down-regulation of cyclin E. Phosphorylation of BCR components and STAT3 was sensitive to cerdulatinib in both ABC and GCB cell lines under stimulated conditions. Importantly, JAK/STAT and BCR signaling can be blocked by cerdulatinib in primary GCB and non-GCB DLBCL tumor cells that were accompanied by cell death. Our work provides mechanistic insights into the actions of cerdulatinib, suggesting that the drug has a broad anti-tumor activity in both ABC and GCB DLBCL, at least in part by inhibiting SYK and JAK pathways.

Suppression of CD300A inhibits the growth of diffuse large B-cell lymphoma

CD300A is a type I transmembrane receptor protein which has shown inhibitory effects on B-cell receptor-mediated signals. In an analysis of public dataset, we found that CD300A mRNA levels were inversely correlated with the overall survival time of patients with diffuse large B-cell lymphoma (DLBCL). To decipher the role of CD300A in DLBCL, we knocked down the expression levels of CD300A in DLBCL cells and found that decreasing levels of CD300A significantly inhibited cell proliferation of OCI-Ly01, Farage, and SUDHL-4 cells, but not of VAL, OCI-Ly10, or SUDHL-8 cells. Mechanistically, reduced expression of CD300A resulted in a marked attenuation of AKT phosphorylation, a key molecular event in tumorigenesis, in OCI-Ly01, Farage, and SUDHL-4 cells. Pharmacologic inhibition of PI3K displayed a similar inhibitory effect on cell proliferation. Furthermore, using a xenograft animal model, we found that decreasing levels of CD300A in OCI-Ly01 and Farage cells significantly inhibited tumor formation in vivo. Collectively, our results suggested an oncogenic role of CD300A in DLBCL which could serve as a potential biomarker and therapeutic target for this malignant disease.

PRT062607 Achieves Complete Inhibition of the Spleen Tyrosine Kinase at Tolerated Exposures Following Oral Dosing in Healthy Volunteers

The spleen tyrosine kinase (SYK) regulates immune cell activation in response to engagement of a variety of receptors, making it an intriguing target for the treatment of inflammatory and autoimmune disorders as well as certain B‐cell malignancies. We have previously reported on the discovery and preclinical characterization of PRT062607, a potent and highly selective inhibitor of SYK that exhibits robust anti‐inflammatory activity in a variety of animal models. Here we present data from our first human studies aimed at characterizing the pharmacokinetics (PK), pharmacodynamics (PD), and safety of PRT062607 in healthy volunteers following single and multiple oral administrations. PRT062607 demonstrated a favorable PK profile and the ability to completely inhibit SYK activity in multiple whole‐blood assays. The PD half‐life in the more sensitive assays was approximately 24 hours and returned to predose levels by 72 hours. Selectivity for SYK was observed at all dose levels tested. Analysis of the PK/PD relationship indicated an IC₅₀ of 324 nM for inhibition of B‐cell antigen receptor‐mediated B‐cell activation and 205 nM for inhibition of FcεRI‐mediated basophil degranulation. PRT062607 was safe and well tolerated across the entire range of doses. Clinical PK/PD was related to in vivo anti‐inflammatory activity of PRT062607 in the rat collagen‐induced arthritis model, which predicts that therapeutic concentrations may be safely achieved in humans for the treatment of autoimmune disease. PRT062607 has a desirable PK profile and is capable of safely, potently, and selectively suppressing SYK kinase function in humans following once‐daily oral dosing.

Pre-BCR signaling in precursor B-cell acute lymphoblastic leukemia regulates PI3K/AKT, FOXO1 and MYC, and can be targeted by SYK inhibition

Precursor-B-cell receptor (pre-BCR) signaling and spleen tyrosine kinase (SYK) recently were introduced as therapeutic targets for patients with B-cell acute lymphoblastic leukemia (B-ALL), but the importance of this pathway in B-ALL subsets and mechanism of downstream signaling have not fully been elucidated. Here, we provide new detailed insight into the mechanism of pre-BCR signaling in B-ALL. We compared the effects of pharmacological and genetic disruption of pre-BCR signaling in vitro and in mouse models for B-ALL, demonstrating exquisite dependency of pre-BCR(+) B-ALL, but not other B-ALL subsets, on this signaling pathway. We demonstrate that SYK, PI3K/AKT, FOXO1 and MYC are important downstream mediators of pre-BCR signaling in B-ALL. Furthermore, we define a characteristic immune phenotype and gene expression signature of pre-BCR(+) ALL to distinguish them from other B-ALL subsets. These data provide comprehensive new insight into pre-BCR signaling in B-ALL and corroborate pre-BCR signaling and SYK as promising new therapeutic targets in pre-BCR(+) B-ALL.

Targeting B-cell receptor signaling in leukemia and lymphoma: how and why?

B-lymphocytes are dependent on B-cell receptor (BCR) signaling for the constant maintenance of their physiological function, and in many B-cell malignancies this signaling pathway is prone to aberrant activation. This understanding has led to an ever-increasing interest in the signaling networks activated following ligation of the BCR in both normal and malignant cells, and has been critical in establishing an array of small molecule inhibitors targeting BCR-induced signaling. By dissecting how different malignancies signal through BCR, researchers are contributing to the design of more customized therapeutics which have greater efficacy and lower toxicity than previous therapies. This allows clinicians access to an array of approaches to best treat patients whose malignancies have BCR signaling as a driver of pathogenesis.

Targeting childhood, adolescent and young adult non-Hodgkin lymphoma: therapeutic horizons

Non-Hodgkin lymphoma (NHL) is the third most common malignancy in children, adolescents and young adults (CAYA). NHL is a diverse set of diseases that arise at key regulatory checkpoints during B or T cell development in the bone marrow, germinal centre or thymus. While advances in the use of conventional cytotoxic agents have led to dramatic improvements in survival, these cures are associated with significant acute and long-term toxicities. Moreover, the prognosis for CAYA patients with relapsed or refractory NHL remains dismal, with the vast majority dying of their disease. Thanks to a large number of candidate-based biological studies, together with large-scale sequencing efforts, there has been an explosion of knowledge regarding the molecular pathophysiology of B- and T-NHL. This has ushered development of a flurry of novel therapeutic approaches that may simultaneously provide new hope for relapsed patients and an opportunity to reduce the therapeutic burden in newly diagnosed CAYA. Here we review a selection of the most promising new therapeutic approaches to these diseases. While the vast majority of these agents are untested in children, on-going work from many cooperative groups will soon explore their use in paediatric disease, in hope of further improving outcomes while maximizing quality of life.

A salvage chemotherapy of R-P-IMVP16/CBDCA consisting of rituximab, methylprednisolone, ifosfamide, methotrexate, etoposide, and carboplatin for patients with diffuse large B cell lymphoma who had previously received R-CHOP therapy as first-line chemotherapy

We have reported the efficacy of the salvage chemotherapy P-IMVP16/CBDCA for patients with diffuse large B cell lymphoma (DLBCL) who had previously received CHOP before the availability of rituximab (R). Here, we confirmed the efficacy of R combined with P-IMVP16/CBDCA as a salvage chemotherapy for patients with DLBCL, who had previously received R-CHOP. We retrospectively analysed 59 patients with relapse or refractory DLBCL (38 male patients and 21 female patients) presenting between June 2004 and June 2013. The patients received R 375 mg/m² on day 1, methylprednisolone 1000 mg/body for 3 days (from day 3 to day 5), ifosfamide 1000 mg/m² for 5 days (from day 3 to day 7), methotrexate 30 mg/m² on day 5 and day 12, etoposide 80 mg/m² for 3 days (from day 3 to day 5), and carboplatin 300 mg/m² on day 3 every 21 days. Patients aged 70 years or older were given 75% of the standard dose. The overall response rate (complete response + partial response) was 64.4%. The 2-year overall survival rate was 55.3%. The 2-year progression free survival rate was 34.7%. The 2-year overall survival rate was 61.5% for the relapse patients, and 15.6% for the refractory patients (p < 0.0001). One patient died because of sepsis related to the treatment regimen. Non-hematological adverse effects were mild and tolerable. The R-P-IMVP-16/CBDCA regimen displayed a significant activity in relapsed DLBCL, with acceptable toxicity, and should be considered a candidate for salvage chemotherapy. Copyright © 2016 John Wiley & Sons, Ltd.

Targeting B-cell receptor signaling kinases in chronic lymphocytic leukemia: the promise of entospletinib

The B-cell receptor signaling pathway has emerged as an important therapeutic target in chronic lymphocytic leukemia and other B-cell malignancies. Novel agents have been developed targeting the signaling enzymes spleen tyrosine kinase (SYK), Bruton’s tyrosine kinase, and phosphoinositide 3-kinase delta. This review discusses the rationale for targeting these enzymes, as well as the preclinical and clinical evidence supporting their role as therapeutic targets, with a particular focus on SYK inhibition with entospletinib.

Novel drug targets for personalized precision medicine in relapsed/refractory diffuse large B-cell lymphoma: a comprehensive review

Diffuse large B-cell lymphoma (DLBCL) is a clinically heterogeneous lymphoid malignancy and the most common subtype of non-Hodgkin's lymphoma in adults, with one of the highest mortality rates in most developed areas of the world. More than half of DLBLC patients can be cured with standard R-CHOP regimens, however approximately 30 to 40 % of patients will develop relapsed/refractory disease that remains a major cause of morbidity and mortality due to the limited therapeutic options.Recent advances in gene expression profiling have led to the identification of at least three distinct molecular subtypes of DLBCL: a germinal center B cell-like subtype, an activated B cell-like subtype, and a primary mediastinal B-cell lymphoma subtype. Moreover, recent findings have not only increased our understanding of the molecular basis of chemotherapy resistance but have also helped identify molecular subsets of DLBCL and rational targets for drug interventions that may allow for subtype/subset-specific molecularly targeted precision medicine and personalized combinations to both prevent and treat relapsed/refractory DLBCL. Novel agents such as lenalidomide, ibrutinib, bortezomib, CC-122, epratuzumab or pidilizumab used as single-agent or in combination with (rituximab-based) chemotherapy have already demonstrated promising activity in patients with relapsed/refractory DLBCL. Several novel potential drug targets have been recently identified such as the BET bromodomain protein (BRD)-4, phosphoribosyl-pyrophosphate synthetase (PRPS)-2, macrodomain-containing mono-ADP-ribosyltransferase (ARTD)-9 (also known as PARP9), deltex-3-like E3 ubiquitin ligase (DTX3L) (also known as BBAP), NF-kappaB inducing kinase (NIK) and transforming growth factor beta receptor (TGFβR).This review highlights the new insights into the molecular basis of relapsed/refractory DLBCL and summarizes the most promising drug targets and experimental treatments for relapsed/refractory DLBCL, including the use of novel agents such as lenalidomide, ibrutinib, bortezomib, pidilizumab, epratuzumab, brentuximab-vedotin or CAR T cells, dual inhibitors, as well as mechanism-based combinatorial experimental therapies. We also provide a comprehensive and updated list of current drugs, drug targets and preclinical and clinical experimental studies in DLBCL. A special focus is given on STAT1, ARTD9, DTX3L and ARTD8 (also known as PARP14) as novel potential drug targets in distinct molecular subsets of DLBCL.

Integrin-specific hydrogels as adaptable tumor organoids for malignant B and T cells

Non-Hodgkin lymphomas are a heterogeneous group of lymphoproliferative disorders of B and T cell origin that are treated with chemotherapy drugs with variable success rate that has virtually not changed over decades. Although new classes of chemotherapy-free epigenetic and metabolic drugs have emerged, durable responses to these conventional and new therapies are achieved in a fraction of cancer patients, with many individuals experiencing resistance to the drugs. The paucity in our understanding of what regulates the drug resistance phenotype and establishing a predictive indicator is, in great part, due to the lack of adequate ex vivo lymphoma models to accurately study the effect of microenvironmental cues in which malignant B and T cell lymphoma cells arise and reside. Unlike many other tumors, lymphomas have been neglected from biomaterials-based microenvironment engineering standpoint. In this study, we demonstrate that B and T cell lymphomas have different pro-survival integrin signaling requirements (αvβ3 and α4β1) and the presence of supporting follicular dendritic cells are critical for enhanced proliferation in three-dimensional (3D) microenvironments. We engineered adaptable 3D tumor organoids presenting adhesive peptides with distinct integrin specificities to B and T cell lymphoma cells that resulted in enhanced proliferation, clustering, and drug resistance to the chemotherapeutics and a new class of histone deacetylase inhibitor (HDACi), Panobinostat. In Diffuse Large B cell Lymphomas, the 3D microenvironment upregulated the expression level of B cell receptor (BCR), which supported the survival of B cell lymphomas through a tyrosine kinase Syk in the upstream BCR pathway. Our integrin specific ligand functionalized 3D organoids mimic a lymphoid neoplasm-like heterogeneous microenvironment that could, in the long term, change the understanding of the initiation and progression of hematological tumors, allow primary biospecimen analysis, provide prognostic values, and importantly, allow a faster and more rational screening and translation of therapeutic regimens.

Inhibition of Spleen Tyrosine Kinase Potentiates Paclitaxel-Induced Cytotoxicity in Ovarian Cancer Cells by Stabilizing Microtubules

Resistance to chemotherapy represents a major obstacle for long-term remission, and effective strategies to overcome drug resistance would have significant clinical impact. We report that recurrent ovarian carcinomas after paclitaxel/carboplatin treatment have higher levels of spleen tyrosine kinase (SYK) and phospho-SYK. In vitro, paclitaxel-resistant cells expressed higher SYK, and the ratio of phospho-SYK/SYK positively associated with paclitaxel resistance in ovarian cancer cells. Inactivation of SYK by inhibitors or gene knockdown sensitized paclitaxel cytotoxicity in vitro and in vivo. Analysis of the phosphotyrosine proteome in paclitaxel-resistant tumor cells revealed that SYK phosphorylates tubulins and microtubule-associated proteins. Inhibition of SYK enhanced microtubule stability in paclitaxel-resistant tumor cells that were otherwise insensitive. Thus, targeting SYK pathway is a promising strategy to enhance paclitaxel response.