Characteristic expression of Hck in human B-cell precursors

Revealing the Role of the Arg and Lys in Shifting Paradigm from BTK Selective Inhibition to the BTK/HCK Dual Inhibition - Delving into the Inhibitory Activity of KIN-8194 against BTK, and HCK in the Treatment of Mutated BTKCys481 Waldenström Macroglobulinemia: A Computational Approach

BACKGROUND

Despite the early success of Bruton's tyrosine kinase (BTK) inhibitors in the treatment of Waldenström macroglobulinemia (WM), these single-target drug therapies have limitations in their clinical applications, such as drug resistance. Several alternative strategies have been developed, including the use of dual inhibitors, to maximize the therapeutic potential of these drugs.

OBJECTIVE

Recently, the pharmacological activity of KIN-8194 was repurposed to serve as a 'dual-target' inhibitor of BTK and Hematopoietic Cell Kinase (HCK). However, the structural dual inhibitory mechanism remains unexplored, hence the aim of this study.

METHODS

Conducting predictive pharmacokinetic profiling of KIN-8194, as well as demonstrating a comparative structural mechanism of inhibition against the above-mentioned enzymes.

RESULTS

Our results revealed favourable binding affinities of -20.17 kcal/mol, and -35.82 kcal/mol for KIN-8194 towards HCK and BTK, respectively. Catalytic residues Arg137/174 and Lys42/170 in BTK and Arg303 and Lys75/173/244/247 in HCK were identified as crucial mediators of the dual binding mechanism of KIN-8194, corroborated by high per-residue energy contributions and consistent high-affinity interactions of these residues. Prediction of the pharmacokinetics and physicochemical properties of KIN-8194 further established its inhibitory potential, evidenced by the favourable absorption, metabolism, excretion, and minimal toxicity properties. Structurally, KIN-8194 impacted the stability, flexibility, solvent-accessible surface area, and rigidity of BTK and HCK, characterized by various alterations observed in the bound and unbound structures, which proved enough to disrupt their biological function.

CONCLUSION

These structural insights provided a baseline for the understanding of the dual inhibitory activity of KIN- 8194. Establishing the cruciality of the interactions between the KIN-8194 and Arg and Lys residues could guide the structure-based design of novel dual BTK/HCK inhibitors with improved therapeutic activities.

A new role for the SRC family kinase HCK as a driver of SYK activation in MYD88 mutated lymphomas

HCK facilitates TLR/BCR crosstalk through activation of SYK in response to mutated MYD88.

The HCK inhibitor A419259 selectively blocks SYK activation in MYD88 mutated cell lines and primary WM lymphoplasmacytic cells.

The SRC family kinase (SFK) HCK is transcriptionally upregulated and activated by mutated MYD88 (MYD88^Mut), a key adaptor for Toll-receptor signaling. HCK activates BTK, AKT, and ERK in MYD88^Mut lymphomas. SYK, a B-cell receptor (BCR) component, is activated in MYD88^Mut lymphoma cells. Although the SFK LYN serves as a trigger for SYK activation in MYD88^Mut ABC DLBCL cells, LYN activity is muted in MYD88^Mut Waldenstrom macroglobulinemia (WM) cells. We therefore investigated a role for HCK in mediating SYK activation. Overexpression of wild-type (WT) (HCK^WT) or gatekeeper mutated (HCK^Thr333Met) HCK in MYD88^Mut lymphoma cells triggered SYK activation. Conversely, HCK knockdown reduced p-SYK in MYD88^Mut lymphoma cells. Coimmunoprecipitation experiments showed that HCK was complexed with p-SYK in MYD88^Mut BCWM.1 and TMD8 cells, but not in MYD88 WT Ramos cells. Rescue experiments in MYD88^Mut lymphoma cells expressing HCK^Thr333Met led to persistent HCK and SYK activation and resistance to the HCK inhibitor A419259. Treatment of primary MYD88^Mut WM cells with A419259 reduced p-HCK and p-SYK expression. Taken together, our findings show that SYK is activated by HCK in MYD88^Mut B-cell lymphomas cells, broaden the prosurvival signaling generated by aberrant HCK expression in response to MYD88^Mut, and help define HCK as an important therapeutic target in MYD88^Mut B-cell lymphomas.

Expression of the prosurvival kinase HCK requires PAX5 and mutated MYD88 signaling in MYD88-driven B-cell lymphomas

Hematopoietic cell kinase (HCK) is an SRC family member that is aberrantly upregulated in B-cell neoplasms dependent on MYD88-activating mutations and supports their growth and survival. We showed herein that activation of Toll-like receptor (TLR) signaling in MYD88 wild-type B cells also triggered HCK expression, denoting on path regulatory function for HCK by MYD88. To clarify the signaling cascades responsible for aberrant HCK expression in MYD88-mutated B-cell lymphomas, we performed promoter-binding transcription factor (TF) profiling, PROMO weighted TF consensus binding motif analysis, and chromatin immunoprecipitation studies. We identified PAX5, and the mutated MYD88 downstream signaling mediators STAT3, NF-κB, and AP-1, as important drivers of HCK transcription. Knockdown of PAX5, a crucial regulatory factor required for B-cell commitment and identity, abrogated HCK transcription in MYD88-mutated lymphoma cells. Among AP-1 complex components, JunB showed greatest relevance to TLR/MYD88 signaling and HCK transcription regulation. In MYD88-mutated Waldenström macroglobulinemia and activated B-cell-diffuse large B-cell lymphoma cells, knockdown of MYD88 reduced phosphorylation of JunB but not c-Jun, and knockdown of JunB reduced HCK protein levels. Deletion of STAT3, NF-κB, and AP-1 binding sites reduced corresponding TFs binding and HCK promoter activity. Moreover, inhibitors to STAT3, NF-κB, and AP-1 reduced HCK promoter activity and messenger RNA levels, particularly in combination, in MYD88-mutated lymphoma cells. The findings provide new insights into the transcriptional regulation of HCK prosurvival signaling by mutated MYD88, and the importance of JunB as a downstream mediator of the MYD88-directed signaling apparatus.

Emerging Kinase Therapeutic Targets in Pancreatic Ductal Adenocarcinoma and Pancreatic Cancer Desmoplasia

Kinase drug discovery represents an active area of therapeutic research, with previous pharmaceutical success improving patient outcomes across a wide variety of human diseases. In pancreatic ductal adenocarcinoma (PDAC), innovative pharmaceutical strategies such as kinase targeting have been unable to appreciably increase patient survival. This may be due, in part, to unchecked desmoplastic reactions to pancreatic tumors. Desmoplastic stroma enhances tumor development and progression while simultaneously restricting drug delivery to the tumor cells it protects. Emerging evidence indicates that many of the pathologic fibrotic processes directly or indirectly supporting desmoplasia may be driven by targetable protein tyrosine kinases such as Fyn-related kinase (FRK); B lymphoid kinase (BLK); hemopoietic cell kinase (HCK); ABL proto-oncogene 2 kinase (ABL2); discoidin domain receptor 1 kinase (DDR1); Lck/Yes-related novel kinase (LYN); ephrin receptor A8 kinase (EPHA8); FYN proto-oncogene kinase (FYN); lymphocyte cell-specific kinase (LCK); tec protein kinase (TEC). Herein, we review literature related to these kinases and posit signaling networks, mechanisms, and biochemical relationships by which this group may contribute to PDAC tumor growth and desmoplasia.

HCK is a survival determinant transactivated by mutated MYD88, and a direct target of ibrutinib

HCK transcription and activation is triggered by mutated MYD88, and is an important determinant of pro-survival signaling. HCK is also a target of ibrutinib, and inhibition of its kinase activity triggers apoptosis in mutated MYD88 cells.

The class-specific BCR tonic signal modulates lymphomagenesis in a c-myc deregulation transgenic model

Deregulation of c-myc by translocation onto immunoglobulin (Ig) loci can promote B cell malignant proliferations with phenotypes as diverse as acute lymphoid leukemia, Burkitt lymphoma, diffuse large B cell lymphoma, myeloma… The B cell receptor (BCR) normally providing tonic signals for cell survival and mitogenic responses to antigens, can also contribute to lymphomagenesis upon sustained ligand binding or activating mutations. BCR signaling varies among cell compartments and BCR classes. For unknown reasons, some malignancies associate with expression of either IgM or class-switched Ig. We explored whether an IgA BCR, with strong tonic signaling, would affect lymphomagenesis in c-myc IgH 3′RR transgenic mice prone to lymphoproliferations. Breeding c-myc transgenics in a background where IgM expression was replaced with IgA delayed lymphomagenesis. By comparison to single c-myc transgenics, lymphomas from double mutant animals were more differentiated and less aggressive, with an altered transcriptional program. Larger tumor cells more often expressed CD43 and CD138, which culminated in a plasma cell phenotype in 10% of cases. BCR class-specific signals thus appear to modulate lymphomagenesis and may partly explain the observed association of specific Ig classes with human B cell malignancies of differential phenotype, progression and prognosis.

Involvement of the HCK and FGR src-family kinases in FCRL4-mediated immune regulation

FCRL4 is an immunoregulatory receptor expressed by a subpopulation of memory B cells. These tissue-based cells express increased levels of the src-family kinases HCK and FGR. In this study, we investigate the roles of these src-family kinases in FCRL4-mediated immunoregulation of B cells in the context of previously unrecognized palmitoylation of the receptor. We observed enhanced phosphorylation of FCRL4 on tyrosine residues in the presence of the HCK p59 or FGR. This phosphorylation was markedly reduced in assays using a palmitoylation-defective mutant of FCRL4. In reporter gene studies, we observe that FCRL4 expression enhances CpG-mediated activation of NF-κB signaling. Surprisingly, using a reporter gene linked to activation of the MAPK substrate Elk-1 in response to Ag receptor ligation, we find that FCRL4 has inhibitory activity in cells coexpressing FGR but an activating function in cells coexpressing HCK p59. We provide evidence that in primary memory B cells, expression of FCRL4 leads to increased expression of IL-10 in the presence of FGR or HCK p59 in response to CpG, but increased levels of IFN-γ only in the context of coexpression of FGR. Our study supports the specific requirement of HCK p59 and FGR src-family kinases for FCRL4-mediated immunomodulatory activity and indicates that palmitoylation serves as an additional level of regulatory control of FCRL4.

Novel molecular and cellular therapeutic targets in acute lymphoblastic leukemia and lymphoproliferative disease

While the outcome for pediatric patients with lymphoproliferative disorders (LPD) or lymphoid malignancies, such as acute lymphoblastic leukemia (ALL), has improved dramatically, patients often suffer from therapeutic sequelae. Additionally, despite intensified treatment, the prognosis remains dismal for patients with refractory or relapsed disease. Thus, novel biologically targeted treatment approaches are needed. These targets can be identified by understanding how a loss of lymphocyte homeostasis can result in LPD or ALL. Herein, we review potential molecular and cellular therapeutic strategies that (i) target key signaling networks (e.g., PI3K/AKT/mTOR, JAK/STAT, Notch1, and SRC kinase family-containing pathways) which regulate lymphocyte growth, survival, and function; (ii) block the interaction of ALL cells with stromal cells or lymphoid growth factors secreted by the bone marrow microenvironment; or (iii) stimulate innate and adaptive immune responses.

Intracellular signalling molecules as immunohistochemical markers of normal and neoplastic human leucocytes in routine biopsy samples

We have investigated whether intracellular signal transduction molecules can be used as immunohistological markers of normal and neoplastic human leucocytes in routine tissue sections. We obtained selective labelling of white cells for eight such molecules (the 'linker' molecules SLP-76 and BLNK, the Src family kinases Lyn, Fyn, Syk and Hck, and the phospholipases PLC-gamma1 and PLC-gamma2). Antibodies to SLP-76 and PLC-gamma1 selectively labelled T cells, and antibodies to BLNK, Lyn, Fyn, Syk and PLC-gamma2 labelled B cells (although Fyn immunostaining was restricted to mantle zone B cells). Antibodies to the Syk and Hck kinases labelled probable thymocyte precursors at the periphery of the thymic cortex. In addition to lymphoid cells, several other leucocyte types were immunostained (e.g. SLP-76, Lyn, Syk and Hck were found in megakaryocytes, myeloid cells and/or macrophages, and PLC-gamma2 was detected in arterial endothelium). SLP-76 and PLC-gamma1 were found in most T-cell lymphomas studied, and some B-cell lymphomas were also positive for PLC-gamma1 (e.g. diffuse large cell and Burkitt's lymphoma). The five B cell-associated markers were found in most B-cell non-Hodgkin's lymphomas, although some diffuse large B-cell lymphomas were negative (e.g. for Lyn) and anti-Fyn tended not to stain small B-cell neoplasms. The observation that a range of leucocyte signalling molecules can be detected in routine biopsies offers new possibilities for studying normal and neoplastic human white cells in diagnostic tissue samples.

Critical Role for Hematopoietic Cell Kinase (Hck)-mediated Phosphorylation of Gab1 and Gab2 Docking Proteins in Interleukin 6-induced Proliferation and Survival of Multiple Myeloma Cells

Interleukin-6 (LI-6) is a known growth and survival factor in multiple myeloma via activation of extracellular signal-regulated kinase and phosphatidylinositol 3-kinase signaling cascade. In this report we show that Grb2-associated binder (Gab) family adapter proteins Gab1 and Gab2 are expressed by multiple myeloma cells; and that interleukin-6 induces their tyrosine phosphorylation and association with downstream signaling molecules. We further demonstrate that these events are Src family tyrosine kinase-dependent and specifically identify the role of hematopoietic cell kinase (Hck) as a new Gab family adapter protein kinase. Conversely, inhibition of Src family tyrosine kinases by the pyrazolopyrimidine PP2, as in kinase-inactive Hck mutants, significantly reduces IL-6-triggered activation of extracellular signal-regulated kinase and AKT-1, leading to significant reduction of multiple myeloma cell proliferation and survival. Taken together, these results delineate a key role for Hck-mediated phosphorylation of Gab1 and Gab2 docking proteins in IL-6-induced proliferation and survival of multiple myeloma cells and identify tyrosine kinases and downstream adapter proteins as potential new therapeutic targets in multiple myeloma.

Granulocyte colony-stimulating factor directly affects human monocytes and modulates cytokine secretion

OBJECTIVE

Recent reports have indicated that monocytes express receptors for the granulocyte colony-stimulating factor (G-CSF). The direct effects of G-CSF on cytokine secretion in monocytes were examined.

MATERIALS AND METHODS

A monocytic cell line NOMO-1 that secretes multiple cytokines upon stimulation with lipopolysaccharide (LPS) was used. Normal human monocytes were purified by negative selection using magnetic beads. Cells pretreated with or without G-CSF were stimulated with LPS, and the subsequent concentrations of cytokines and chemokines in supernatants were determined by sandwich enzyme-linked immunosorbent assay.

RESULTS

NOMO-1 cells were found to express receptors for G-CSF. Although G-CSF stimulation did not induce cytokine secretion, pretreatment with G-CSF significantly attenuated LPS-stimulated secretion of the proinflammatory cytokines tumor necrosis factor-alpha and interleukin (IL)-12 in NOMO-1 cells. Simultaneously, however, G-CSF pretreatment apparently enhanced LPS-induced secretion of IL-10 and monocyte chemoattractant protein-1, whereas secretions of IL-1beta, IL-6, and IL-8 were unaffected. When normal human monocytes from healthy volunteers were similarly examined, marked individual variations in LPS-induced secretion of cytokines were observed. Although some exceptions exist, a similar tendency as to the effects of G-CSF treatment on cytokine secretions as that in NOMO-1 cells was observed in human monocytes.

CONCLUSIONS

Our data suggest that G-CSF directly affects monocytes and modulates their cytokine secretion. NOMO-1 cells can provide an alternate model for in vitro culture of monocytes to investigate the effects of G-CSF on cytokine secretion by these cells.