Targeting β-catenin in acute myeloid leukaemia: past, present, and future perspectives

Constitutive activation of the Src-family kinases Fgr and Hck enhances the tumor burden of acute myeloid leukemia cells in immunocompromised mice

Overexpression of the myeloid Src-family kinases Fgr and Hck has been linked to the development of acute myeloid leukemia (AML). Here we characterized the contribution of active forms of these kinases to AML cell cytokine dependence, inhibitor sensitivity, and AML cell engraftment in vivo. The human TF-1 erythroleukemia cell line was used as a model system as it does not express endogenous Hck or Fgr. To induce constitutive kinase activity, Hck and Fgr were fused to the coiled-coil (CC) oligomerization domain of the breakpoint cluster region protein associated with the Bcr-Abl tyrosine kinase in chronic myeloid leukemia. Expression of CC-Hck or CC-Fgr transformed TF-1 cells to a granulocyte-macrophage colony-stimulating factor (GM-CSF)-independent phenotype that correlated with enhanced phosphorylation of the kinase domain activation loop. Both CC-Hck and CC-Fgr cell populations became sensitized to growth arrest by Src-family kinase inhibitors previously shown to suppress the growth of bone marrow cells from AML patients in vitro and decrease AML cell engraftment in immunocompromised mice. Methionine substitution of the 'gatekeeper' residue (Thr338) also stimulated Hck and Fgr kinase activity and transformed TF-1 cells to GM-CSF independence without CC fusion. TF-1 cells expressing either active form of Hck or Fgr engrafted immunocompromised mice faster and developed more extensive tumors compared to mice engrafted with the parent cell line, resulting in shorter survival. Expression of wild-type Hck also significantly enhanced bone marrow engraftment without an activating mutation. Reverse phase protein array analysis linked active Hck and Fgr to the mammalian target of rapamycin complex-1/p70 S6 ribosomal protein (mTORC-1/S6) kinase and focal adhesion kinase (Fak) signaling pathways. Combining Hck and Fgr inhibitors with existing mTORC-1/S6 kinase or Fak inhibitors may improve clinical responses and reduce the potential for acquired resistance.

Mechanism of bone-marrow mesenchymal stem cell-derived exosomes mediating microRNA-139-5p to regulate β-catenin in the modulation of proliferation and apoptosis of acute myeloid leukemia cells

OBJECTIVE

Acute myeloid leukemia (AML) stands out as a malignancy of the stem cell precursors of the myeloid lineage. Bone-marrow mesenchymal stem cell-derived exosomes (BMSC-exos) affect AML progression. We explored the effects and mechanism of BMSC-exos on AML cell proliferation and apoptosis.

METHODS

Human AML cells (MOLM-16, MV-4-11) and normal human hematopoietic cells (GM12878) cultured in vitro were treated with exos extracted from BMSCs that transfected with microRNA (miR)-139-5p-mimics, ovβ-catenin, or miR-139-5p-inhibitor. BMSC morphology was observed by a microscopy, and its adipogenic and osteogenic differentiation abilities were assessed by oil red O staining and alizarin red S staining. BMSC-exos were extracted by ultracentrifugation, and their morphology was observed by a transmission electron microscopy. BMSC-exos were identified by nanoparticle tracking analysis and Western blot. The binding sites between miR-139-5p and β-catenin were predicted by TargetScan database, and then validated by dual-luciferase reporter assay. mRNA levels of miR-139-5p and β-catenin, cell proliferation, and apoptosis were evaluated by RT-qPCR, CCK-8, and flow cytometry. The expressions of CD63, CD81, TSG101, and GRP94 and the proteins of β-catenin, Bax, and Bcl-2 were determined by Western blot.

RESULTS

miR-139-5p was poorly expressed in AML cell lines. miR-139-5p overexpression reduced AML cell viability/proliferation/Bcl-2 level, and raised apoptosis/Bax level. BMSC-exos repressed AML cell proliferation and promoted apoptosis via miR-139-5p. miR-139-5p targeted to inhibit β-catenin expression. Subsequently, up-regulated β-catenin partially counteracted the effects of miR-139-5p in BMSC-exos on AML cell proliferation and apoptosis.

CONCLUSION

BMSC-exos targeted to repress β-catenin expression by miR-139-5p, limited AML cell proliferation and facilitated apoptosis.

Decreasing of serine/threonine kinase 39 has tumour inhibiting effects on acute myeloid leukaemia by impacting the PI3K/AKT and Wnt/β-catenin signalling cascades

Serine/threonine kinase 39 (STK39) has been identified as a key regulator of tumour progression. However, whether STK39 plays a role in acute myeloid leukaemia (AML) remains undetermined. This work explored the expression and functions of STK39 in AML. STK39 was found to be overexpressed in AML and was negatively correlated with overall survival. Functionally, silencing STK39 inhibited cell proliferation, promoted cell differentiation and induced cell cycle arrest and apoptosis. The tumour inhibiting effects of STK39 downregulation were also verified by an in vivo xenograft tumour assay. Mechanistically, STK39 was closely related to the PI3K/AKT and Wnt/β-catenin signalling cascades in AML. Silencing of STK39 had suppressive effects on the PI3K/AKT and Wnt/β-catenin signalling cascades. The suppressive effect of STK39 silencing on the Wnt/β-catenin signalling cascade was significantly reversed when PI3K/AKT was reactivated. When β-catenin was re-expressed, the tumour-inhibiting effects caused by STK39 silencing were significantly eliminated. Therefore, STK39 plays a crucial role in AML and could be targeted for potential therapeutic purposes in treating AML.

Transcriptome Analysis of Beta-Catenin-Related Genes in CD34+ Haematopoietic Stem and Progenitor Cells from Patients with AML

Background

Acute myeloid leukaemia (AML) is a disease of the haematopoietic stem cells(HSCs) that is characterised by the uncontrolled proliferation and impaired differentiation of normal haematopoietic stem/progenitor cells. Several pathways that control the proliferation and differentiation of HSCs are impaired in AML. Activation of the Wnt/beta-catenin signalling pathway has been shown in AML and beta-catenin, which is thought to be the key element of this pathway, has been frequently highlighted. The present study was designed to determine beta-catenin expression levels and beta-catenin-related genes in AML.

Methods

In this study, beta-catenin gene expression levels were determined in 19 AML patients and 3 controls by qRT-PCR. Transcriptome analysis was performed on AML grouped according to beta-catenin expression levels. Differentially expressed genes(DEGs) were investigated in detail using the Database for Annotation Visualisation and Integrated Discovery(DAVID), Gene Ontology(GO), Kyoto Encyclopedia of Genes and Genomes(KEGG), STRING online tools.

Results

The transcriptome profiles of our AML samples showed different molecular signature profiles according to their beta-catenin levels(high-low). A total of 20 genes have been identified as hub genes. Among these, TTK, HJURP, KIF14, BTF3, RPL17 and RSL1D1 were found to be associated with beta-catenin and poor survival in AML. Furthermore, for the first time in our study, the ELOV6 gene, which is the most highly up-regulated gene in human AML samples, was correlated with a poor prognosis via high beta-catenin levels.

Conclusion

It is suggested that the identification of beta-catenin-related gene profiles in AML may help to select new therapeutic targets for the treatment of AML.

Epithelial-Mesenchymal Transition in Acute Leukemias

Epithelial-mesenchymal transition (EMT) is a metabolic process that confers phenotypic flexibility to cells and the ability to adapt to new functions. This transition is critical during embryogenesis and is required for the differentiation of many tissues and organs. EMT can also be induced in advanced-stage cancers, leading to further malignant behavior and chemotherapy resistance, resulting in an unfavorable prognosis for patients. Although EMT was long considered and studied only in solid tumors, it has been shown to be involved in the pathogenesis of hematological malignancies, including acute leukemias. Indeed, there is increasing evidence that EMT promotes the progression of acute leukemias, leading to the emergence of a more aggressive phenotype of the disease, and also causes chemotherapy resistance. The current literature suggests that the levels and activities of EMT inducers and markers can be used to predict prognosis, and that targeting EMT in addition to conventional therapies may increase treatment success in acute leukemias.

Differential expression levels of β-catenin are associated with invasive behavior of both functional and non-functional pituitary neuroendocrine tumor (PitNET)

BACKGROUND

Although research continues to elucidate the molecular mechanism underlying pituitary tumor pathogenesis, limited information is available on the potential role and expression profile of β-catenin in functional and non-functional pituitary neuroendocrine tumors (PitNETs).

METHODS AND RESULTS

In the current study, 104 pituitary samples (tumors and cadaveric healthy pituitary tissues) were included and the gene and protein expression levels of β-catenin were assessed by Real-Time PCR and immunohistochemistry, respectively. The correlation between expression level of β-catenin and tumor invasive feature and size as well as patient age, gender, and hormonal level was measured. The data showed that PitNET samples expressed higher levels of the β-catenin gene and protein compared to healthy pituitary tissues. Although there was no difference in β-catenin expression level between non-functioning (NF-PitNETs) and growth hormone-producing tumors (GH-PitNETs), both tumor types showed significantly elevated β-catenin levels compared to healthy pituitary tissues. The high level of β-catenin in the invasive functional and non-functional tumors is indicative of the association of β-catenin with PitNETs invasion. The expression pattern of the β-catenin gene and protein was consistently and significantly associated with these tumor types. The correlation between β-catenin and insulin-like growth factor 1 (IGF-1) in GH-PitNETs indicates the potential relevance of β-catenin and IGF-1 for GH-PitNETs.

CONCLUSIONS

The simultaneous increase in the expression of β-catenin gene and protein level in PitNET tissues and their relationship to the tumor severity indicates the possible contributing role of β-catenin and its underlying signaling mediators in PitNET pathogenesis.

Casein Kinase 2 (CK2): A Possible Therapeutic Target in Acute Myeloid Leukemia

The protein kinase CK2 (also known as casein kinase 2) is one of the main contributors to the human phosphoproteome. It is regarded as a possible therapeutic strategy in several malignant diseases, including acute myeloid leukemia (AML), which is an aggressive bone marrow malignancy. CK2 is an important regulator of intracellular signaling in AML cells, especially PI3K-Akt, Jak-Stat, NFκB, Wnt, and DNA repair signaling. High CK2 levels in AML cells at the first time of diagnosis are associated with decreased survival (i.e., increased risk of chemoresistant leukemia relapse) for patients receiving intensive and potentially curative antileukemic therapy. However, it is not known whether these high CK2 levels can be used as an independent prognostic biomarker because this has not been investigated in multivariate analyses. Several CK2 inhibitors have been developed, but CX-4945/silmitasertib is best characterized. This drug has antiproliferative and proapoptotic effects in primary human AML cells. The preliminary results from studies of silmitasertib in the treatment of other malignancies suggest that gastrointestinal and bone marrow toxicities are relatively common. However, clinical AML studies are not available. Taken together, the available experimental and clinical evidence suggests that the possible use of CK2 inhibition in the treatment of AML should be further investigated.

Proteolysis-targeting chimeras in biotherapeutics: Current trends and future applications

The success of inhibitor-based therapeutics is largely constrained by the acquisition of therapeutic resistance, which is partially driven by the undruggable proteome. The emergence of proteolysis targeting chimera (PROTAC) technology, designed for degrading proteins involved in specific biological processes, might provide a novel framework for solving the above constraint. A heterobifunctional PROTAC molecule could structurally connect an E3 ubiquitin ligase ligand with a protein of interest (POI)-binding ligand by chemical linkers. Such technology would result in the degradation of the targeted protein via the ubiquitin-proteasome system (UPS), opening up a novel way of selectively inhibiting undruggable proteins. Herein, we will highlight the advantages of PROTAC technology and summarize the current understanding of the potential mechanisms involved in biotherapeutics, with a particular focus on its application and development where therapeutic benefits over classical small-molecule inhibitors have been achieved. Finally, we discuss how this technology can contribute to developing biotherapeutic drugs, such as antivirals against infectious diseases, for use in clinical practices.

Novel Insights into the Role of Kras in Myeloid Differentiation: Engaging with Wnt/β-Catenin Signaling

Cells of the HL-60 myeloid leukemia cell line can be differentiated into neutrophil-like cells by treatment with dimethyl sulfoxide (DMSO). The molecular mechanisms involved in this differentiation process, however, remain unclear. This review focuses on the differentiation of HL-60 cells. Although the Ras proteins, a group of small GTP-binding proteins, are ubiquitously expressed and highly homologous, each has specific molecular functions. Kras was shown to be essential for normal mouse development, whereas Hras and Nras are not. Kras knockout mice develop profound hematopoietic defects, indicating that Kras is required for hematopoiesis in adults. The Wnt/β-catenin signaling pathway plays a crucial role in regulating the homeostasis of hematopoietic cells. The protein β-catenin is a key player in the Wnt/β-catenin signaling pathway. A great deal of evidence shows that the Wnt/β-catenin signaling pathway is deregulated in malignant tumors, including hematological malignancies. Wild-type Kras acts as a tumor suppressor during DMSO-induced differentiation of HL-60 cells. Upon DMSO treatment, Kras translocates to the plasma membrane, and its activity is enhanced. Inhibition of Kras attenuates CD11b expression. DMSO also elevates levels of GSK3β phosphorylation, resulting in the release of unphosphorylated β-catenin from the β-catenin destruction complex and its accumulation in the cytoplasm. The accumulated β-catenin subsequently translocates into the nucleus. Inhibition of Kras attenuates Lef/Tcf-sensitive transcription activity. Thus, upon treatment of HL-60 cells with DMSO, wild-type Kras reacts with the Wnt/β-catenin pathway, thereby regulating the granulocytic differentiation of HL-60 cells. Wild-type Kras and the Wnt/β-catenin signaling pathway are activated sequentially, increasing the levels of expression of C/EBPα, C/EBPε, and granulocyte colony-stimulating factor (G-CSF) receptor.

A Potential Off-Target Effect of the Wnt/β-Catenin Inhibitor KYA1797K: PD-L1 Binding and Checkpoint Inhibition

Introduction

The quest for small molecule inhibitors of the PD-1/PD-L1 checkpoint continues in parallel to the extensive development of monoclonal antibodies directed against this immune checkpoint. Drug screening strategies are being set up to identify novel PD-L1 inhibitors.

Methods

A virtual screening based on molecular docking with the PD-L1 protein dimer has been performed to identify a new binder. Binding of the identified ligand to PD-L1 has been validated experimentally using a microscale thermophoresis (MST) assay. The cellular effect of the compound was evidenced using a fluorescence resonance energy transfer (FRET) assay based on activation of tyrosine phosphatase SHP-2.

Results

We have identified the potent Wnt/β-catenin inhibitor KYA1797K as a weak PD-L1 binder. Molecular docking suggested that the compound can bind to the interface of a PD-L1 dimer, with a geometry superimposable to that of the reference PD-L1 inhibitor BMS-202. The atypical 2-thioxo-4-thiazolidinone motif of KYA1797K, derived from the natural product rhodanine, plays a major role in the interaction with PD-L1. Binding of KYA1797K to recombinant hPD-L1 was validated experimentally, using MST. The drug was found to bind modestly but effectively to hPD-L1. The FRET assay confirmed the weak capacity of KYA1797K to interfere with the activation of SHP-2 upon its interaction with human PD-1.

Discussion

Collectively, the data show that KYA1797K could function as a weak modulator of the PD-1/PD-L1 checkpoint. This effect may contribute, at least partially, to the reported capacity of the β-catenin inhibitor to downregulate PD-L1 in cancer cells. The work also underlines the interest to further consider the rhodanine moiety as a chemical motif for the design of new PD-L1 binders.