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

New insights into SYK targeting in solid tumors

Spleen tyrosine kinase (SYK) is predominantly expressed in hematopoietic cells and has been extensively studied for its pivotal role in B cell malignancies and autoimmune diseases. In epithelial solid tumors, SYK shows a paradoxical role, acting as a tumor suppressor in some cancers while driving tumor growth in others. Recent preclinical studies have identified the role of SYK in the tumor microenvironment (TME), revealing that SYK signaling in immune cells, especially B cells, and myeloid cells, promote immunosuppression, tumor growth, and metastasis across various solid tumors. This review explores the emerging roles of SYK in solid tumors, the mechanisms of SYK activation, and findings from preclinical and clinical studies of SYK inhibitors as either standalone treatments or in combination with immunotherapy or chemotherapy for solid tumors.

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.

A phase I study of TAK-659 and paclitaxel in patients with taxane-refractory advanced solid tumors

BACKGROUND

Paclitaxel resistance limits durability of response in patients with initial clinical benefit. Overexpression of spleen tyrosine kinase (SYK) has been proposed as a possible resistance mechanism. This phase I trial evaluated the safety and preliminary activity of the SYK inhibitor TAK-659 combined with paclitaxel in patients with advanced taxane-refractory solid tumors.

PATIENTS AND METHODS

Patients with advanced solid tumors and prior progression on taxane-based therapy received intravenous infusion of paclitaxel on days 1, 8, and 15 plus oral TAK-659 daily in 28-day cycles. The dose-escalation phase included six cohorts treated at different dose levels; the dose-expansion phase included patients with ovarian cancer treated at the highest dose level. Toxicity was graded using the National Cancer Institute Common Terminology Criteria for Adverse Events version 5.0. Efficacy was evaluated using Response Evaluation Criteria in Solid Tumors version 1.1.

RESULTS

Our study included 49 patients. Maximum tolerated dose was not reached, but higher rates of adverse events were observed at higher dose levels. There were no treatment-related deaths. The most common treatment-related adverse events of any grade were increased aspartate aminotransferase (n = 31; 63%), increased alanine aminotransferase (n = 26; 53%), decreased neutrophil count (n = 26; 53%), and decreased white blood cell count (n = 26; 53%). Most adverse events were either grade 1 or 2. In the 44 patients with evaluable disease, 12 (27%) had stable disease as the best overall response, including three patients with prolonged stable disease, and 4 patients (9%) achieved a partial response.

CONCLUSIONS

The combination of paclitaxel and TAK-659 showed preliminary activity possibly overcoming resistance to taxane-based therapy as well as a tolerable safety profile in patients with advanced solid tumors.

A novel natural Syk inhibitor suppresses IgE-mediated mast cell activation and passive cutaneous anaphylaxis

Spleen tyrosine kinase (Syk) plays a crucial role as a target for allergy treatment due to its involvement in immunoreceptor signaling. The purpose of this study was to identify natural inhibitors of Syk and assess their effects on the IgE-mediated allergic response in mast cells and ICR mice. A list of eight compounds was selected based on pharmacophore and molecular docking, showing potential inhibitory effects through virtual screening. Among these compounds, sophoraflavanone G (SFG) was found to inhibit Syk activity in an enzymatic assay, with an IC50 value of 2.2 μM. To investigate the conformational dynamics of the SYK-SFG system, we performed molecular dynamics simulations. The stability of the binding between SFG and Syk was evaluated using root mean square deviation (RMSD) and root mean square fluctuation (RMSF). In RBL-2H3 cells, SFG demonstrated a dose-dependent suppression of IgE/BSA-induced mast cell degranulation, with no significant cytotoxicity observed at concentrations below 10.0 μM within 24 h. Furthermore, SFG reduced the production of TNF-α and IL-4 in RBL-2H3 cells. Mechanistic investigations revealed that SFG inhibited downstream signaling proteins, including phospholipase Cγ1 (PLCγ1), as well as mitogen-activated protein kinases (AKT, Erk1/2, p38, and JNK), in mast cells in a dose-dependent manner. Passive cutaneous anaphylaxis (PCA) experiments demonstrated that SFG could reduce ear swelling, mast cell degranulation, and the expression of COX-2 and IL-4. Overall, our findings identify naturally occurring SFG as a direct inhibitor of Syk that effectively suppresses mast cell degranulation both in vitro and in vivo.

Identification and structural characterization of small molecule inhibitors of PINK1

Mutations in PINK1 and Parkin cause early-onset Parkinson's Disease (PD). PINK1 is a kinase which functions as a mitochondrial damage sensor and initiates mitochondrial quality control by accumulating on the damaged organelle. There, it phosphorylates ubiquitin, which in turn recruits and activates Parkin, an E3 ubiquitin ligase. Ubiquitylation of mitochondrial proteins leads to the autophagic degradation of the damaged organelle. Pharmacological modulation of PINK1 constitutes an appealing avenue to study its physiological function and develop therapeutics. In this study, we used a thermal shift assay with insect PINK1 to identify small molecules that inhibit ATP hydrolysis and ubiquitin phosphorylation. PRT062607, an SYK inhibitor, is the most potent inhibitor in our screen and inhibits both insect and human PINK1, with an IC50 in the 0.5-3 µM range in HeLa cells and dopaminergic neurons. The crystal structures of insect PINK1 bound to PRT062607 or CYC116 reveal how the compounds interact with the ATP-binding pocket. PRT062607 notably engages with the catalytic aspartate and causes a destabilization of insert-2 at the autophosphorylation dimer interface. While PRT062607 is not selective for PINK1, it provides a scaffold for the development of more selective and potent inhibitors of PINK1 that could be used as chemical probes.

A phase Ib study evaluating the recommended phase II dose, safety, tolerability, and efficacy of mivavotinib in combination with nivolumab in advanced solid tumors

Mivavotinib (TAK-659/CB-659), a dual SYK/FLT3 inhibitor, reduced immunosuppressive immune cell populations and suppressed tumor growth in combination with anti-PD-1 therapy in cancer models. This dose-escalation/expansion study investigated the safety, pharmacokinetics, pharmacodynamics, and preliminary efficacy of mivavotinib plus nivolumab in patients with advanced solid tumors. Patients received oral mivavotinib 60-100 mg once-daily plus intravenous nivolumab 3 mg/kg on days 1 and 15 in 28-day cycles until disease progression or unacceptable toxicity. The dose-escalation phase evaluated the recommended phase II dose (RP2D; primary endpoint). The expansion phase evaluated overall response rate (primary end point) at the RP2D in patients with triple-negative breast cancer (TNBC). During dose-escalation (n = 24), two dose-limiting toxicities (grade 4 lipase increased and grade 3 pyrexia) occurred in patients who received mivavotinib 80 mg and 100 mg, respectively. The determined RP2D was once-daily mivavotinib 80 mg plus nivolumab 3 mg/kg. The expansion phase was terminated at ~50% enrollment (n = 17) after failing to meet an ad hoc efficacy futility threshold. Among all 41 patients, common treatment-emergent adverse events (TEAEs) included dyspnea (48.8%), aspartate aminotransferase increased, and pyrexia (46.3% each). Common grade ≥3 TEAEs were hypophosphatemia and anemia (26.8% each). Mivavotinib plasma exposure was generally dose-proportional (60-100 mg). One patient had a partial response. Mivavotinib 80 mg plus nivolumab 3 mg/kg was well tolerated with no new safety signals beyond those of single-agent mivavotinib or nivolumab. Low response rates highlight the challenges of treating unresponsive tumor types, such as TNBC, with this combination and immunotherapies in general. TRIAL REGISTRATION ID: NCT02834247.

Characterization of covalent inhibitors that disrupt the interaction between the tandem SH2 domains of SYK and FCER1G phospho-ITAM

RNA sequencing and genetic data support spleen tyrosine kinase (SYK) and high affinity immunoglobulin epsilon receptor subunit gamma (FCER1G) as putative targets to be modulated for Alzheimer's disease (AD) therapy. FCER1G is a component of Fc receptor complexes that contain an immunoreceptor tyrosine-based activation motif (ITAM). SYK interacts with the Fc receptor by binding to doubly phosphorylated ITAM (p-ITAM) via its two tandem SH2 domains (SYK-tSH2). Interaction of the FCER1G p-ITAM with SYK-tSH2 enables SYK activation via phosphorylation. Since SYK activation is reported to exacerbate AD pathology, we hypothesized that disruption of this interaction would be beneficial for AD patients. Herein, we developed biochemical and biophysical assays to enable the discovery of small molecules that perturb the interaction between the FCER1G p-ITAM and SYK-tSH2. We identified two distinct chemotypes using a high-throughput screen (HTS) and orthogonally assessed their binding. Both chemotypes covalently modify SYK-tSH2 and inhibit its interaction with FCER1G p-ITAM, however, these compounds lack selectivity and this limits their utility as chemical tools.

Review and prospects of targeted therapies for Spleen tyrosine kinase (SYK)

Spleen tyrosine kinase (SYK) is a non-receptor tyrosine kinase. The dysregulation of SYK is closely related to the occurrence and development of allergic diseases, autoimmune diseases and cancer. SYK has become an attractive target for drug discovery due to its important biological functions. This article reviews the biological function of SYK, the relationship between SYK and disease, and therapies targeting SYK. In addition, inspired by new technologies such as proteolysis targeting chimeras (PROTACs) and phosphatase recruiting chimeras (PHORCs), we propose the development of new therapeutic approaches for targeting SYK, such as SYK PROTACs and SYK PHORCs, which may overcome deficiencies of existing methods.

Cancer cell-intrinsic PD-1: Its role in malignant progression and immunotherapy

Programmed cell death protein-1 (PD-1), also called CD279, is coded by the PDCD1 gene and is constitutively expressed on the surface of immune cells. As a receptor and immune checkpoint, PD-1 can bind to programmed death ligand-1/programmed death ligand-2 (PD-L1/PD-L2) in tumor cells, leading to tumor immune evasion. Anti-PD-1 and anti-PD-L1 are important components in tumor immune therapy. PD-1 is also expressed as an intrinsic variant (iPD-1) in cancer cells where it plays important roles in malignant progression as proposed by recent studies. However, iPD-1 has received much less attention compared to PD-1 expressed on immune cells although there is an unmet medical need for fully elucidating the mechanisms of actions to achieve the best response in tumor immunotherapy. iPD-1 suppresses tumorigenesis in non-small cell lung cancer (NSCLC) and colon cancer, whereas it promotes tumorigenesis in melanoma, hepatocellular carcinoma (HCC), pancreatic ductal adenocarcinoma (PDAC), thyroid cancer (TC), glioblastoma (GBM), and triple-negative breast cancer (TNBC). In this review, we focus on the role of iPD-1 in tumorigenesis and development and its molecular mechanisms. We also deeply discuss nivolumab-based combined therapy in common tumor therapy. iPD-1 may explain the different therapeutic effects of anti-PD-1 treatment and provide critical information for use in combined anti-tumor approaches.

Characterization of covalent inhibitors that disrupt the interaction between the tandem SH2 domains of SYK and FCER1G phospho-ITAM

RNA sequencing and genetic data support spleen tyrosine kinase (SYK) and high affinity immunoglobulin epsilon receptor subunit gamma (FCER1G) as putative targets to be modulated for Alzheimer's disease (AD) therapy. FCER1G is a component of Fc receptor complexes that contain an immunoreceptor tyrosine-based activation motif (ITAM). SYK interacts with the Fc receptor by binding to doubly phosphorylated ITAM (p-ITAM) via its two tandem SH2 domains (SYK-tSH2). Interaction of the FCER1G p-ITAM with SYK-tSH2 enables SYK activation via phosphorylation. Since SYK activation is reported to exacerbate AD pathology, we hypothesized that disruption of this interaction would be beneficial for AD patients. Herein, we developed biochemical and biophysical assays to enable the discovery of small molecules that perturb the interaction between the FCER1G p-ITAM and SYK-tSH2. We identified two distinct chemotypes using a high-throughput screen (HTS) and orthogonally assessed their binding. Both chemotypes covalently modify SYK-tSH2 and inhibit its interaction with FCER1G p-ITAM.

Optimization of a series of novel, potent and selective Macrocyclic SYK inhibitors

Spleen tyrosine kinase (SYK) is a non-receptor cytoplasmic kinase. Due to its pivotal role in B cell receptor and Fc-receptor signalling, inhibition of SYK has been a target of interest in a variety of diseases. Herein, we report the use of structure-based drug design to discover a series of potent macrocyclic inhibitors of SYK, with excellent kinome selectivity and in vitro metabolic stability. We were able to remove hERG inhibition through the optimization of physical properties, and utilized a pro-drug strategy to address permeability challenges.

Discovery of 3-(1H-benzo[d]imidazole-2-yl)-1H-pyrazol-4 -amine derivatives as novel and potent syk inhibitors for the treatment of hematological malignancies

Spleen tyrosine kinase (Syk) is an important oncogene and signal transduction mediator that is mainly expressed in hematopoietic cells. Syk plays a key role in the B cell receptor (BCR) signaling pathway. Abnormal activation of Syk is closely related to the occurrence and development of hematological malignancies. Therefore, Syk is a potential target for the treatment of various hematologic cancers. Starting from compound 6(Syk, IC₅₀ = 15.8 μM), we performed fragment-based rational drug design for structural optimization based on the specific solvent-accessible region, hydrophobic region, and ribose region of Syk. This resulted in the discovery of a series of novel 3-(1H-benzo [d]imidazole-2-yl)-1H-pyrazol-4-amine Syk inhibitors, which led to the identification of 19q, a highly potent Syk inhibitor that exhibited excellent inhibitory activity on Syk enzyme (IC₅₀ = 0.52 nM) and showed potency against several other kinases. In addition, compound 19q effectively reduced phosphorylation of downstream PLCγ2 level in Romos cells. And it also exhibited antiproliferative activity in multiple hematological tumour cells. More gratifyingly, 19q showed impressive efficacy at a low dosage (1 mg/kg/day) in the MV4-11 mouse xenograft model without affecting the body weight of the mice. These findings suggest that 19q is a promising new Syk inhibitor for treating blood cancers.

Population Pharmacokinetics of Mivavotinib (TAK-659), a Dual Spleen Tyrosine Kinase and FMS-Like Tyrosine Kinase 3 Inhibitor, in Patients With Advanced Solid Tumors or Hematologic Malignancies

Mivavotinib (TAK-659), an orally administered, small-molecule, dual inhibitor of spleen tyrosine kinase and FMS-like tyrosine kinase 3 (SYK/FLT3), is under development for the treatment of patients with advanced malignancies. In this analysis, we evaluated the population pharmacokinetics (PK) of mivavotinib and its sources of variability (covariates) in adult patients with advanced solid tumors, or relapsed/refractory B-cell lymphomas or acute myeloid leukemia, using pooled data from 159 patients enrolled in 2 phase 1/2 clinical studies. A 2-compartment model with first-order linear elimination and a first-order absorption rate (and associated lag time) adequately described the PK of mivavotinib in this patient population. The population estimates of apparent clearance (CL/F) and apparent central compartment volume (V_c /F) were 31.6 L/h and 893 L, respectively, resulting in a half-life of ≈20 hours. In the final model, creatinine clearance was included as a covariate of CL/F, and sex as a covariate of V_c /F. Simulations showed that steady-state exposure to mivavotinib increased with decreasing renal function. Expanding eligibility by enrolling patients with moderate renal impairment in phase 1 increased the diversity of patients in early trials and allowed the model to inform dose adjustment in patients with moderate renal impairment in future trials. In addition, simulations showed median steady-state trough concentration of mivavotinib following 70 mg twice daily and 160 mg daily dosing to be commensurate with 100 ng/mL, the level leading to >90% FLT3 inhibition per ex vivo plasma immune assays and considered a potential exposure threshold required for FLT3-driven efficacy.

Phase I study of novel SYK inhibitor TAK-659 (mivavotinib) in combination with R-CHOP for front-line treatment of high-risk diffuse large B-cell lymphoma

Background: TAK-659, a novel oral SYK inhibitor, has demonstrated efficacy in heavily pretreated diffuse large B-cell lymphoma (DLBCL). We report results of a phase I single-institution escalation study of front-line treatment with R-CHOP and TAK-659 in treatment-naïve high-risk DLBCL. Methods: Patients with high-risk DLBCL were treated with R-CHOP for 1 cycle, followed by combined R-CHOP and TAK-659 for an additional five cycles, with TAK-659 dosing escalated from 60 mg, to 80 mg, to 100 mg daily, based on a 3 + 3 design. The primary objective was to determine the safety and establish the maximum tolerated dose (MTD) of TAK-659 in this setting. Results: Twelve patients were enrolled. Dose level 3 (100 mg) was established as the MTD. Dose level 1 (60 mg) maintained a similar area under the curve (AUC) to the MTD. With a median follow-up of 21 months, 92% of patients achieved complete response (CR). The most common treatment-emergent adverse events were lymphopenia (100%), infection (50%, n = 3 opportunistic), aspartate aminotransferase elevation (100%), and alanine aminotransferase elevation (83%). Conclusion: A TAK-659 dose of 60 mg was well tolerated, did not require dose modifications, and maintained a similar AUC to the MTD. The combination of R-CHOP and TAK-659 in patients with newly diagnosed high-risk DLBCL produces promising CR rates.

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.

Heterogeneity of Patient-Derived Acute Myeloid Leukemia Cells Subjected to SYK In Vitro Inhibition

Acute myeloid leukemia (AML) is an aggressive hematological malignancy with a dismal prognosis. The cytoplasmic spleen tyrosine kinase (SYK) is highly expressed by hematopoietic cells and has emerged as a potential therapeutic target. In this study, we evaluated the in vitro antileukemic effects of five SYK inhibitors, fostamatinib, entospletinib, cerdulatinib, TAK-659, and RO9021, in a consecutive AML patient cohort. All inhibitors demonstrated a concentration-dependent antiproliferative effect, although there was considerable heterogeneity among patients. For fostamatinib and TAK-659, the antiproliferative effects were significantly higher in FLT3 mutated patients compared to nonmutated patients. Fostamatinib, entospletinib, TAK-659, and RO9021 induced significant apoptosis in primary AML cells, although the proapoptotic effects of the SYK inhibitors were less pronounced than the antiproliferative effects. Finally, most of the SYK inhibitors caused a significant decrease in the release of cytokines and chemokines from primary AML cells, indicating a potent inhibitory effect on the release of these leukemic signaling molecules. We concluded that the SYK inhibitors had antileukemic effects in AML, although larger studies are strongly needed to identify which patient subsets will benefit most from such a treatment.

Tumor cell SYK expression modulates the tumor immune microenvironment composition in human cancer via TNF-α dependent signaling

BACKGROUND

The expression of SYK in cancer cells has been associated with both tumor promoting and tumor suppressive effects. Despite being proposed as anticancer therapeutic target, the possible role of SYK in modulating local adaptive antitumor immune responses remains uncertain. Using detailed analysis of primary human tumors and in vitro models, we reveal the immunomodulatory effect of SYK protein in human solid cancer.

METHODS

We spatially mapped SYK kinase in tumor cells, stromal cells and tumor-infiltrating leukocytes (TILs) in 808 primary non-small cell lung carcinomas (NSCLCs) from two cohorts and in 374 breast carcinomas (BCs) from two independent cohorts. We established the associations of localized SYK with clinicopathologic variables and outcomes. The immunomodulatory role of SYK on tumor cells was assessed using in vitro cytokine stimulation, transcriptomic analysis and selective SYK blockade using a small molecule inhibitor. Functional responses were assessed using cocultures of tumor cells with peripheral blood lymphocytes. T cell responses in baseline and post-treatment biopsies from patients with BC treated with a SYK inhibitor in a phase I clinical trial were also studied.

RESULTS

Elevated tumor cell or leukocyte SYK expression was associated with high CD4⁺ and CD8⁺ TILs and better outcome in both NSCLC and BC. Tumor cell SYK was associated with oncogenic driver mutations in EGFR or KRAS in lung adenocarcinomas and with triple negative phenotype in BC. In cultured tumor cells, SYK was upregulated by TNFα and required for the TNFα-induced proinflammatory responses and T cell activation. SYK blockade after nivolumab in a phase I clinical trial including three patients with advanced triple negative BC reduced TILs and T cell proliferation. Our work establishes the proinflammatory function of tumor cell SYK in lung and breast cancer. SYK signaling in cultured tumor cells is required for T cell activation and SYK blockade limits adaptive antitumor immune responses and tumor rejection in patients with cancer.

CONCLUSIONS

Together, our results establish the immunomodulatory role of SYK expression in human solid tumors. This information could be used to develop novel biomarkers and/or therapeutic strategies.

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.

Fused pyrrolo-pyridines and pyrrolo-(iso)quinoline as anticancer agents

This work emphasizes the synthesis strategies and antiproliferative related properties of fused pyrrolo-pyridine (including indolizine and azaindoles) and pyrrolo-(iso)quinoline derivatives recently reported in literature.

Immune targeted therapy for diffuse large B cell lymphoma

Diffuse large B-cell lymphoma (DLBCL), the most common subtype of non-Hodgkin lymphoma, is highly heterogeneous and invasive. Although the majority of DLBCL patients show a good response to rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone treatment, approximately one-third of patients still have a poor prognosis. Many immune-targeted drugs, such as bispecific T-cell engagers and CAR T-cell therapy, have been proven effective for refractory and relapsed patients. This article reviews the progress of immune targeted therapy for DLBCL.

Integration of FRET and sequencing to engineer kinase biosensors from mammalian cell libraries

The limited sensitivity of Förster Resonance Energy Transfer (FRET) biosensors hinders their broader applications. Here, we develop an approach integrating high-throughput FRET sorting and next-generation sequencing (FRET-Seq) to identify sensitive biosensors with varying substrate sequences from large-scale libraries directly in mammalian cells, utilizing the design of self-activating FRET (saFRET) biosensor. The resulting biosensors of Fyn and ZAP70 kinases exhibit enhanced performance and enable the dynamic imaging of T-cell activation mediated by T cell receptor (TCR) or chimeric antigen receptor (CAR), revealing a highly organized ZAP70 subcellular activity pattern upon TCR but not CAR engagement. The ZAP70 biosensor elucidates the role of immunoreceptor tyrosine-based activation motif (ITAM) in affecting ZAP70 activation to regulate CAR functions. A saFRET biosensor-based high-throughput drug screening (saFRET-HTDS) assay further enables the identification of an FDA-approved cancer drug, Sunitinib, that can be repurposed to inhibit ZAP70 activity and autoimmune-disease-related T-cell activation.

A novel dual HDAC and HSP90 inhibitor, MPT0G449, downregulates oncogenic pathways in human acute leukemia in vitro and in vivo

Acute leukemia is a highly heterogeneous disease; therefore, combination therapy is commonly used for patient treatment. Drug–drug interaction is a major concern of combined therapy; hence, dual/multi-target inhibitors have become a dominant approach for cancer drug development. HDACs and HSP90 are involved in the activation of various oncogenic signaling pathways, including PI3K/AKT/mTOR, JAK/STAT, and RAF/MEK/ERK, which are also highly enriched in acute leukemia gene expression profiles. Therefore, we suggest that dual HDAC and HSP90 inhibitors could represent a novel therapeutic approach for acute leukemia. MPT0G449 is a dual effect inhibitor, and it showed cytotoxic effectiveness in acute leukemia cells. Molecular docking analysis indicated that MPT0G449 possessed dual HDAC and HSP90 inhibitory abilities. Furthermore, MPT0G449 induced G₂ arrest and caspase-mediated cell apoptosis in acute leukemia cells. The oncogenic signaling molecules AKT, mTOR, STAT3, STAT5, MEK, and ERK were significantly downregulated after MPT0G449 treatment in HL-60 and MOLT-4 cells. In vivo xenograft models confirmed the antitumor activity and showed the upregulation of acetyl-histone H3 and HSP70, biomarkers of pan-HDAC and HSP90 inhibition, with MPT0G449 treatment. These findings suggest that the dual inhibition of HDAC and HSP90 can suppress the expression of oncogenic pathways in acute leukemia, and MPT0G449 represents a novel therapeutic for anticancer treatment.

An Overview of the Biological Activity of Pyrrolo[3,4-c]pyridine Derivatives

Pyrrolo[3,4-c]pyridine is one of the six structural isomers of the bicyclic ring system containing a pyrrole moiety fused to a pyridine nucleus. The broad spectrum of pharmacological properties of pyrrolo[3,4-c]pyridine derivatives is the main reason for developing new compounds containing this scaffold. This review presents studies on the biological activity of pyrrolo[3,4-c]pyridines that have been reported in the scientific literature. Most of these derivatives have been studied as analgesic and sedative agents. Biological investigations have shown that pyrrolo[3,4-c]pyridines can be used to treat diseases of the nervous and immune systems. Their antidiabetic, antimycobacterial, antiviral, and antitumor activities also have been found.

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.

Dual Kinase Targeting in Leukemia

Pharmacological cancer therapy is often based on the concurrent inhibition of different survival pathways to improve treatment outcomes and to reduce the risk of relapses. While this strategy is traditionally pursued only through the co-administration of several drugs, the recent development of multi-targeting drugs (i.e., compounds intrinsically able to simultaneously target several macromolecules involved in cancer onset) has had a dramatic impact on cancer treatment. This review focuses on the most recent developments in dual-kinase inhibitors used in acute myeloid leukemia (AML), chronic myelogenous leukemia (CML), and lymphoid tumors, giving details on preclinical studies as well as ongoing clinical trials. A brief overview of dual-targeting inhibitors (kinase/histone deacetylase (HDAC) and kinase/tubulin polymerization inhibitors) applied to leukemia is also given. Finally, the very recently developed Proteolysis Targeting Chimeras (PROTAC)-based kinase inhibitors are presented.

Strategies for Targeting the NLRP3 Inflammasome in the Clinical and Preclinical Space

Inhibiting the NLRP3 inflammasome mediates inflammation in an extensive number of preclinical models. As excitement in this field has grown, several companies have recently initiated testing of direct NLRP3 inhibitors in the clinic. At the same time, the NLRP3 inflammasome is part of a larger pro-inflammatory pathway, whose modulation is also being explored. Multiple targets in this pathway are already impinged upon by molecules that have been through clinical trials. These data, informed by the growing mechanistic understanding of the NLRP3 inflammasome in the preclinical space, provide a rich backdrop to assess the current state of the field. Here we explore attempts to inhibit the NLRP3 inflammasome in light of clinical and preclinical data around efficacy and safety.

Novel potent and selective pyrazolylpyrimidine-based SYK inhibitors

Hybridisation of amino-pyrimidine based SYK inhibitors (e.g. 1a) with previously reported diamine-based SYK inhibitors (e.g. TAK-659) led to the identification and optimisation of a novel pyrimidine-based series of potent and selective SYK inhibitors, where the original aminomethylene group was replaced by a 3,4-diaminotetrahydropyran group. The initial compound 5 achieved excellent SYK potency. However, it suffered from poor permeability and modest kinase selectivity. Further modifications of the 3,4-diaminotetrahydropyran group were identified and the interactions of those groups with Asp512 were characterised by protein X-ray crystallography. Further optimisation of this series saw mixed results where permeability and kinase selectivity were increased and oral bioavailability was achieved in the series, but at the expense of potent hERG inhibition.

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.

Discovery of Lanraplenib (GS-9876): A Once-Daily Spleen Tyrosine Kinase Inhibitor for Autoimmune Diseases

Spleen tyrosine kinase (SYK) is a critical regulator of signaling in a variety of immune cell types such as B-cells, monocytes, and macrophages. Accordingly, there have been numerous efforts to identify compounds that selectively inhibit SYK as a means to treat autoimmune and inflammatory diseases. We previously disclosed GS-9973 (entospletinib) as a selective SYK inhibitor that is under clinical evaluation in hematological malignancies. However, a BID dosing regimen and drug interaction with proton pump inhibitors (PPI) prevented development of entospletinib in inflammatory diseases. Herein, we report the discovery of a second-generation SYK inhibitor, GS-9876 (lanraplenib), which has human pharmacokinetic properties suitable for once-daily administration and is devoid of any interactions with PPI. Lanraplenib is currently under clinical evaluation in multiple autoimmune indications.

Apigenin and Abivertinib, a novel BTK inhibitor synergize to inhibit diffuse large B-cell lymphoma in vivo and vitro

Background: Apigenin, a flavonoid phytochemical extracted from fruits and vegetables, has shown anti-neoplastic effects in a variety of malignant tumors. DLBCL is the most common type of aggressive lymphoma in adults with a poor prognosis. Small-molecule inhibitors like BTK inhibitors have demonstrated extended period of disease control. Whereas the effects of the synergetic inhibition of the two have not been elucidated.

Methods: We assessed the efficacy of Apigenin alone or combined with Abivertinib to inhibit DLBCL progression. Cell viability was examined using the cell proliferation cell proliferation assay (MTS). Apoptotic cells and cell cycle evaluation were detected by Annexin V-FITC and DNA staining solution respectively. Western blot was used to explore the potential mechanism, and the in vivo effects of the two drugs were performed by a DLBCL xenograft BALB/c nude mice model.

Results: Our results demonstrated that Apigenin can inhibit the proliferation and clone forming of DLBCL cells. Apigenin also induces apoptosis by down-regulating BCL-XL and activating Caspase family. In addition, Apigenin down-regulates cell cycle proteins including CDK2/CDK4/CDK6/CDC2/p-RB to increase G2/M phase arrest. Mechanically, our data demonstrate that Apigenin leads to a significant reduction of the expression of pro-proliferative pathway PI3K/mTOR to inhibit DLBCL cells survival. Moreover, our in vitro and in vivo results show that Apigenin can synergize with Abivertinib, a novel BTK inhibitor, in treating DLBCL visa synergistically inducing apoptosis and inhibiting the p-GS3K-β and its downstream targets.

Conclusions: Collectively, our study suggests that Apigenin exerts improving anti-lymphoma effect of BTK inhibitors and provides hope to targeted therapy of those develop resistance.

Preclinical efficacy for a novel tyrosine kinase inhibitor, ArQule 531 against acute myeloid leukemia

BACKGROUND

Acute myeloid leukemia (AML) is the most common type of adult leukemia. Several studies have demonstrated that oncogenesis in AML is enhanced by kinase signaling pathways such as Src family kinases (SFK) including Src and Lyn, spleen tyrosine kinase (SYK), and bruton's tyrosine kinase (BTK). Recently, the multi-kinase inhibitor ArQule 531 (ARQ 531) has demonstrated potent inhibition of SFK and BTK that translated to improved pre-clinical in vivo activity as compared with the irreversible BTK inhibitor ibrutinib in chronic lymphocytic leukemia (CLL) models. Given the superior activity of ARQ 531 in CLL, and recognition that this molecule has a broad kinase inhibition profile, we pursued its application in pre-clinical models of AML.

METHODS

The potency of ARQ 531 was examined in vitro using FLT3 wild type and mutated (ITD) AML cell lines and primary samples. The modulation of pro-survival kinases following ARQ 531 treatment was determined using AML cell lines. The effect of SYK expression on ARQ 531 potency was evaluated using a SYK overexpressing cell line (Ba/F3 murine cells) constitutively expressing FLT3-ITD. Finally, the in vivo activity of ARQ 531 was evaluated using MOLM-13 disseminated xenograft model.

RESULTS

Our data demonstrate that ARQ 531 treatment has anti-proliferative activity in vitro and impairs colony formation in AML cell lines and primary AML cells independent of the presence of a FLT3 ITD mutation. We demonstrate decreased phosphorylation of oncogenic kinases targeted by ARQ 531, including SFK (Tyr416), BTK, and fms-related tyrosine kinase 3 (FLT3), ultimately leading to changes in down-stream targets including SYK, STAT5a, and ERK1/2. Based upon in vitro drug synergy data, we examined ARQ 531 in the MOLM-13 AML xenograft model alone and in combination with venetoclax. Despite ARQ 531 having a less favorable pharmacokinetics profile in rodents, we demonstrate modest single agent in vivo activity and synergy with venetoclax.

CONCLUSIONS

Our data support consideration of the application of ARQ 531 in combination trials for AML targeting higher drug concentrations in vivo.

Tyrosine Kinases in Autoimmune and Inflammatory Skin Diseases

Tyrosine kinases relay signals from diverse leukocyte antigen receptors, innate immune receptors, and cytokine receptors, and therefore mediate the recruitment and activation of various leukocyte populations. Non-receptor tyrosine kinases of the Jak, Src, Syk, and Btk families play major roles in various immune-mediated disorders, and small-molecule tyrosine kinase inhibitors are emerging novel therapeutics in a number of those diseases. Autoimmune and inflammatory skin diseases represent a broad spectrum of immune-mediated diseases. Genetic and pharmacological studies in humans and mice support the role of tyrosine kinases in several inflammatory skin diseases. Atopic dermatitis and psoriasis are characterized by an inflammatory microenvironment which activates cytokine receptors coupled to the Jak-Stat signaling pathway. Jak kinases are also implicated in alopecia areata and vitiligo, skin disorders mediated by cytotoxic T lymphocytes. Genetic studies indicate a critical role for Src-family kinases and Syk in animal models of autoantibody-mediated blistering skin diseases. Here, we review the various tyrosine kinase signaling pathways and their role in various autoimmune and inflammatory skin diseases. Special emphasis will be placed on identification of potential therapeutic targets, as well as on ongoing preclinical and clinical studies for the treatment of inflammatory skin diseases by small-molecule tyrosine kinase inhibitors.

Dual FLT3 inhibitors: Against the drug resistance of acute myeloid leukemia in recent decade

Acute myeloid leukemia (AML) is a malignant disease characterized by abnormal growth and differentiation of hematopoietic stem cells. Although the pathogenesis has not been fully elucidated, many specific gene mutations have been found in AML. Fms-like tyrosine kinase 3 (FLT3) is recognized as a drug target for the treatment of AML, and the activation mutations of FLT3 were found in about 30% of AML patients. Targeted inhibition of FLT3 receptor tyrosine kinase has shown promising results in the treatment of FLT3 mutation AML. Unfortunately, the therapeutic effects of FLT3 tyrosine kinase inhibitors used as AML monotherapy are usually accompanied by the high risk of resistance development within a few months after treatment. FLT3 dual inhibitors were generated with the co-inhibition of FLT3 and another target, such as CDK4, JAK2, MEK, Mer, Pim, etc., to solve the problems mentioned above. As a result, the therapeutic effect of the drug is significantly improved, while the toxic and side effects are reduced. Besides, the life quality of AML patients with FLT3 mutation has been effectively improved. In this paper, we reviewed the studies of dual FLT3 inhibitors that have been discovered in recent years for the treatment of AML.

Overview of Targeted Drugs for Mature B-Cell Non-hodgkin Lymphomas

The improved knowledge of pathogenetic mechanisms underlying lymphomagenesis and the discovery of the critical role of tumor microenvironments have enabled the design of new drugs against cell targets and pathways. The Food and Drug Administration (FDA) has approved several monoclonal antibodies (mAbs) and small molecule inhibitors (SMIs) for targeted therapy in hematology. This review focuses on the efficacy results of the currently available targeted agents and recaps the main ongoing trials in the setting of mature B-Cell non-Hodgkin lymphomas. The objective is to summarize the different classes of novel agents approved for mature B-cell lymphomas, to describe in synoptic tables the results they achieved and, finally, to draw future scenarios as we glimpse through the ongoing clinical trials. Characteristics and therapeutic efficacy are summarized for the currently approved mAbs [i.e., anti-Cluster of differentiation (CD) mAbs, immune checkpoint inhibitors, chimeric antigen receptor (CAR) T-cell therapy, and bispecific antibodies] as well as for SMIs i.e., inhibitors of B-cell receptor signaling, proteasome, mTOR BCL-2 HDAC pathways. The biological disease profiling of B-cell lymphoma subtypes may foster the discovery of innovative drug strategies for improving survival outcome in lymphoid neoplasms, as well as the trade-offs between efficacy and toxicity. The hope for clinical advantages should carefully be coupled with mindful awareness of the potential pitfalls and the occurrence of uneven, sometimes severe, toxicities.

Discovery of a Natural Syk Inhibitor from Chinese Medicine through a Docking-Based Virtual Screening and Biological Assay Study

Spleen tyrosine kinase (Syk) is a critical target protein for treating immunoreceptor signalling-mediated allergies. In this study, a virtual screening of an in-house Chinese medicine database followed by biological assays was carried out to identify novel Syk inhibitors. A molecular docking method was employed to screen for compounds with potential Syk inhibitory activity. Then, an in vitro kinase inhibition assay was performed to verify the Syk inhibitory activity of the virtual screening hits. Subsequently, a β-hexosaminidase release assay was conducted to evaluate the anti-mast cell degranulation activity of the active compounds. Finally, tanshinone I was confirmed as a Syk inhibitor (IC₅₀ = 1.64 μM) and exhibited anti-mast cell degranulation activity in vitro (IC₅₀ = 2.76 μM). Docking studies showed that Pro455, Gln462, Leu377, and Lys458 were key amino acid residues for Syk inhibitory activity. This study demonstrated that tanshinone I is a Syk inhibitor with mast cell degranulation inhibitory activity. Tanshinone I may be a potential lead compound for developing effective and safe Syk-inhibiting drugs.

Spleen Tyrosine Kinase Inhibitor TAK-659 Prevents Splenomegaly and Tumor Development in a Murine Model of Epstein-Barr Virus-Associated Lymphoma

The novel SYK and FLT3 inhibitor TAK-659 prevents the enlargement of spleen and tumor development in a mouse model of EBV-associated lymphoma by counteracting the activation of cellular kinase SYK through the viral LMP2A gene by inducing cell death in tumor cells but not in nontumor cells. These findings indicate that TAK-659 may be a very effective nontoxic therapeutic molecule especially for EBV-positive hematologic malignancies.

Epstein-Barr virus (EBV) is associated with several B and epithelial cell cancers. EBV-encoded latent membrane protein 2A (LMP2A) contributes to cellular transformation by mimicking B cell receptor signaling. LMP2A/MYC double transgenic mice develop splenomegaly and B cell lymphoma much faster than MYC transgenic mice do. In this study, we explored the potential therapeutic efficacy of a novel spleen tyrosine kinase (SYK) and FLT3 inhibitor TAK-659 for development of a treatment option for EBV-associated malignancies. In our transgenic model, TAK-659 treatment totally abrogated splenomegaly and tumor development in LMP2A/MYC mice in both pretumor and tumor cell transfer experiments. TAK-659 treatment killed tumor cells, but not host cells within the spleen and tumors. Furthermore, TAK-659 treatment abrogated metastasis of tumor cells into bone marrow. Our data also show that TAK-659 inhibits SYK phosphorylation and induces apoptosis in LMP2A/MYC tumor cells at low nanomolar concentrations. Therefore, TAK-659 may provide an effective therapeutic option for treatment of LMP2A-positive EBV-associated malignancies and should be explored further in clinical trials.

IMPORTANCE The novel SYK and FLT3 inhibitor TAK-659 prevents the enlargement of spleen and tumor development in a mouse model of EBV-associated lymphoma by counteracting the activation of cellular kinase SYK through the viral LMP2A gene by inducing cell death in tumor cells but not in nontumor cells. These findings indicate that TAK-659 may be a very effective nontoxic therapeutic molecule especially for EBV-positive hematologic malignancies.

Syk inhibitors in clinical development for hematological malignancies

Spleen tyrosine kinase (Syk) is a cytosolic non-receptor protein tyrosine kinase (PTK) and is mainly expressed in hematopoietic cells. Syk was recognized as a critical element in the B-cell receptor signaling pathway. Syk is also a key component in signal transduction from other immune receptors like Fc receptors and adhesion receptors. Several oral Syk inhibitors including fostamatinib (R788), entospletinib (GS-9973), cerdulatinib (PRT062070), and TAK-659 are being assessed in clinical trials. The second generation compound, entospletinib, showed promising results in clinical trials against B-cell malignancies, mainly chronic lymphoid leukemia. Syk inhibitors are being evaluated in combination regimens in multiple malignancies.

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.