CK2 negatively regulates the extinction of remote fear memory

Cognitive behavioral therapy, rooted in exposure therapy, is currently the primary approach employed in the treatment of anxiety-related conditions, including post-traumatic stress disorder (PTSD). In laboratory settings, fear extinction in animals is a commonly employed technique to investigate exposure therapy; however, the precise mechanisms underlying fear extinction remain elusive. Casein kinase 2 (CK2), which regulates neuroplasticity via phosphorylation of its substrates, has a significant influence in various neurological disorders, such as Alzheimer's disease and Parkinson's disease, as well as in the process of learning and memory. In this study, we adopted a classical Pavlovian fear conditioning model to investigate the involvement of CK2 in remote fear memory extinction and its underlying mechanisms. The results indicated that the activity of CK2 in the medial prefrontal cortex (mPFC) of mice was significantly upregulated after extinction training of remote cued fear memory. Notably, administration of the CK2 inhibitor CX-4945 prior to extinction training facilitated the extinction of remote fear memory. In addition, CX-4945 significantly upregulated the expression of p-ERK1/2 and p-CREB in the mPFC. Our results suggest that CK2 negatively regulates remote fear memory extinction, at least in part, by inhibiting the ERK-CREB pathway. These findings contribute to our understanding of the underlying mechanisms of remote cued fear extinction, thereby offering a theoretical foundation and identifying potential targets for the intervention and treatment of PTSD.

CX-4945 (Silmitasertib) Induces Cell Death by Impairing Lysosomal Utilization in KRAS Mutant Cholangiocarcinoma Cell Lines

BACKGROUND/AIM

Macropinocytosis is a non-selective form of endocytosis that facilitates the uptake of extracellular substances, such as nutrients and macromolecules, into the cells. In KRAS-driven cancers, including pancreatic ductal adenocarcinoma, macropinocytosis and subsequent lysosomal utilization are known to be enhanced to overcome metabolic stress. In this study, we investigated the role of Casein Kinase 2 (CK2) inhibition in macropinocytosis and subsequent metabolic processes in KRAS mutant cholangiocarcinoma (CCA) cell lines.

MATERIALS AND METHODS

The bovine serum albumin (BSA) uptake indicating macropinocytosis was performed by flow cytometry using the HuCCT1 KRAS mutant CCA cell line. To validate macropinosome, the Rab7 and LAMP2 were labeled and analyzed via immunocytochemistry and western blot. The CX-4945 (Silmitasertib), CK2 inhibitor, was used to investigate the role of CK2 in macropinocytosis and subsequent lysosomal metabolism.

RESULTS

The TFK-1, a KRAS wild-type CCA cell line, showed only apoptotic morphological changes. However, the HuCCT1 cell line showed macropinocytosis. Although CX-4945 induced morphological changes accompanied by the accumulation of intracellular vacuoles and cell death, the level of macropinocytosis did not change. These intracellular vacuoles were identified as late macropinosomes, representing Rab7+ vesicles before fusion with lysosomes. In addition, CX-4945 suppressed LAMP2 expression following the inhibition of the Akt-mTOR signaling pathway, which interrupts mature macropinosome and lysosomal metabolic utilization.

CONCLUSION

Macropinocytosis is used as an energy source in the KRAS mutant CCA cell line HuCCT1. The inhibition of CK2 by CX-4945 leads to cell death in HuCCT1 cells through alteration of the lysosome-dependent metabolism.

Identification of CK2α' selective inhibitors by the screening of an allosteric-kinase-inhibitor-like compound library

Protein Kinase CK2 is a holoenzyme composed of two regulatory subunits (CK2β) and two catalytic subunits (CK2α and CK2α'). CK2 controls several cellular processes including proliferation, inflammation, and cell death. However, CK2α and CK2α' possess different expression patterns and substrates and therefore impact each of these processes differently. Elevated CK2α participates in the development of cancer, while increased CK2α' has been associated with neurodegeneration, especially Huntington's disease (HD). HD is a fatal disease for which no effective therapies are available. Genetic deletion of CK2α' in HD mouse models has ameliorated neurodegeneration. Therefore, pharmacological inhibition of CK2α' presents a promising therapeutic strategy for treating HD. However, current CK2 inhibitors are unable to discriminate between CK2α and CK2α' due to their high structural homology, especially in the targeted ATP binding site. Using computational analyses, we found a potential Type IV ("D" pocket) allosteric site on CK2α' that contained different residues than CK2α and was distal from the ATP binding pocket featured in both kinases. With this potential allosteric site in mind, we screened a commercial library containing ~29,000 allosteric-kinase-inhibitor-like compounds using a CK2α' activity-dependent ADP-Glo™ Kinase assay. Obtained hits were counter-screened against CK2α revealing two CK2α' selective compounds. These two compounds might serve as the basis for further medicinal chemistry optimization for the potential treatment of HD.

8-Chloroadenosine Induces ER Stress and Apoptotic Cell Death in Cholangiocarcinoma Cells

BACKGROUND/AIM

Cholangiocarcinoma is a lethal cancer, and current chemotherapeutic drugs are not very effective. Recent studies reported that cholangiocarcinoma cells were sensitive to adenosine. One adenosine analog, 8-chloroadenosine (8-CA), was shown to be more potent than adenosine and induced apoptosis in leukemia cells. This study examined effects of 8-CA in cholangiocarcinoma cells and immortalized cholangiocytes.

MATERIALS AND METHODS

Cell growth was examined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Cell invasion was examined by transwell assay. Cell cycle and cell death were evaluated by flow cytometry. Colorimetric absorbance assay was used to assessed RNA and protein synthesis as well as mitochondrial membrane potential. Protein levels were examined by western blot analysis. Animal experiment was performed in Balb/cAJcl-Nu mice.

RESULTS

8-CA reduced cholangiocarcinoma cell growth, prevented colony formation and caused endoplasmic reticulum stress and cell-cycle arrest. Eventually, apoptosis was induced. However, treatment with 8-CA did not interfere with RNA synthesis or protein synthesis and did not alter mitochondrial membrane potential. Combination of 8-CA with several chemotherapeutic drugs in vitro was less effective than 8-CA alone and the drugs alone, except for the combination of 8-CA with hydroxychloroquine, which had an additive effect on RMCCA-1 cells. However, further in vivo study showed that treatment with 8-CA alone inhibited tumor growth more than treatment with a combination of 8-CA with hydroxychloroquine.

CONCLUSION

8-Chloroadenosine inhibited CCA cells by inducing endoplasmic reticulum stress and apoptosis. In vivo study showed that 8-CA inhibited cholangiocarcinoma tumor growth better when administered alone as compared to a combination with hydroxychloroquine.

CX-4945 inhibits fibroblast-like synoviocytes functions through the CK2-p53 axis to reduce rheumatoid arthritis disease severity

Fibroblast-like synoviocytes (FLS) mediate many pathological processes in rheumatoid arthritis (RA), including pannus formation, bone erosion, and inflammation. RA FLS have unique aggressive phenotypes and exhibit several tumor cell-like characteristics, including hyperproliferation, excessive migration and invasion. Casein kinase 2 (CK2) is reportedly overexpressed in numerous tumor types, and targeted inhibition of CK2 has therapeutic benefits for tumors. However, the expression level of CK2 and its functions in RA FLS remain unclear. Herein, we aimed to elucidate whether CK2 is responsible for the aggressive phenotypes of RA FLS and whether targeted therapy can alleviate the severity of RA. We found that CK2 subunits were elevated in RA FLS compared with osteoarthritis FLS, and the activity of CK2 also markedly increased in RA FLS. Targeted inhibition of CK2 using CX-4945 suppressed RA FLS proliferation through cell cycle arrest. Cell migration and invasion were also inhibited by CX-4945 treatment. Moreover, CX-4945 reduced Interleukin-6 (IL-6), CC motif chemokine ligand 2 (CCL2) and Matrix metalloproteinase-3 (MMP-3) secretion in RA FLS. Further proteomic investigation revealed that p53 signaling pathway significantly changes after CX-4945 treatment in RA FLS. The siRNA-mediated p53 knockdown partly abolished the anti-proliferation and reduced IL-6, MMP-3 secretion effects of CX-4945. Furthermore, CX-4945 administration alleviates arthritis severity in CIA mice. Collectively, our results demonstrated the abnormal elevation of CK2 and its positive association with abnormal phenotypes in RA FLS. Our novel findings suggest the possible therapeutic potential of CX-4945 for RA.

The synergistic therapeutic effect of imatinib and protein kinase CK2 Inhibition correlates with PI3K-AKT activation in gastrointestinal stromal tumors

BACKGROUND

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract. Casein kinase 2 (CK2) has been reported to be involved in several cellular processes in multiple cancers. However, the role of CK2 in GIST remains unclear.

AIM

We aimed to investigate the combinatorial treatment of imatinib (IM) and CK2 inhibition on the progression of GISTs.

METHODS

GIST biopsies and adjacent normal tissues were collected from patients. GIST882 and GIST48 cell lines were subjected to investigate the effect of IM and CK2 inhibition in GIST cells. CCK-8 assay, Caspase-3 activity assay, western blotting, and flow cytometry analysis were employed in the present investigation.

RESULTS

Our results showed that CK2 was highly expressed in GIST biopsies, and inhibition of CK2 resulted in decrease in cell viability and increase in apoptosis of GIST cells. Moreover, the combination treatment with CX-4945 (CX) and IM resulted in a more significant decrease in cell viability and increase in cell apoptosis compared with mono-treatment. Mechanistically, the combination treatment influenced the activation of the PI3K/AKT pathway. The activation of the PI3K/AKT pathway reversed the synergistic impacts of the combined treatment on cell viability and apoptosis.

CONCLUSION

Our results demonstrated that inhibition of CK2 combined with IM exhibited a synergistic anti-cancer effect on GIST cells through inactivation of the PI3K/AKT pathway.

The Casein Kinase 2 Inhibitor CX-4945 Promotes Cholangiocarcinoma Cell Death Through PLK1

BACKGROUND/AIM

Casein Kinase 2 (CK2) is a prosurvival protein kinase involved in cell growth/proliferation through the regulation of the cell cycle and apoptosis. CK2 is over-expressed in various cancers, which correlates with a poor prognosis. This study examined the anti-cancer effects of silmitasertib (CX-4945), a CK2 inhibitor, on cholangiocarcinoma (CCA) cells.

MATERIALS AND METHODS

The effects of CX-4945 on cell viability, cell cycle arrest, and apoptosis in the human cholangiocarcinoma cell lines TFK-1 and SSP-25 were evaluated. Alterations in posttranslational modifications and the levels of cell cycle regulators including p21, Polo-like kinase 1 (PLK1), andp53 were assessed by western blotting. Apoptotic responses were examined using Propidium iodine/Annexin V staining.

RESULTS

TFK-1 and SSP-25 cells exposed to CX-4945 showed morphologic changes and a more than 50% decrease in cell viability (p<0.05). Cell cycle arrest at the G2 phase was detected following an increase in phosphorylated PLK1 and p21. Furthermore, phospho-PLK1 induced the degradation of p53, which led to the dissociation of Bax from Bcl-xL. The cleavage of Caspase3 and PARP were also induced by CX-4945 treatment.

CONCLUSION

CX-4945 induces cell cycle arrest and cell death in cholangiocarcinoma cells via the regulation of PLK1 and p53. This may provide a novel therapeutic strategy for advanced cholangiocarcinoma.

Chemical Genetic Validation of CSNK2 Substrates Using an Inhibitor-Resistant Mutant in Combination with Triple SILAC Quantitative Phosphoproteomics

Casein Kinase 2 (CSNK2) is an extremely pleiotropic, ubiquitously expressed protein kinase involved in the regulation of numerous key biological processes. Mapping the CSNK2-dependent phosphoproteome is necessary for better characterization of its fundamental role in cellular signalling. While ATP-competitive inhibitors have enabled the identification of many putative kinase substrates, compounds targeting the highly conserved ATP-binding pocket often exhibit off-target effects limiting their utility for definitive kinase-substrate assignment. To overcome this limitation, we devised a strategy combining chemical genetics and quantitative phosphoproteomics to identify and validate CSNK2 substrates. We engineered U2OS cells expressing exogenous wild type CSNK2A1 (WT) or a triple mutant (TM, V66A/H160D/I174A) with substitutions at residues important for inhibitor binding. These cells were treated with CX-4945, a clinical-stage inhibitor of CSNK2, and analyzed using large-scale triple SILAC (Stable Isotope Labelling of Amino Acids in Cell Culture) quantitative phosphoproteomics. In contrast to wild-type CSNK2A1, CSNK2A1-TM retained activity in the presence of CX-4945 enabling identification and validation of several CSNK2 substrates on the basis of their increased phosphorylation in cells expressing CSNK2A1-TM. Based on high conservation within the kinase family, we expect that this strategy can be broadly adapted for identification of other kinase-substrate relationships.

Validation of an LC-MS/MS Method for the Quantification of the CK2 Inhibitor Silmitasertib (CX-4945) in Human Plasma

Silmitasertib (CX-4945) is currently being investigated in clinical trials against various types of cancer. The U.S. Food and Drug Administration (FDA) has already granted orphan drug designation to the compound for the treatment of advanced cholangiocarcinoma, medulloblastoma, and biliary tract cancer. Silmitasertib inhibits the serine/threonine protein kinase CK2, which exerts a proliferation-promoting and anti-apoptotic effect on cancer cells. In view of current and future applications, the measurement of silmitasertib levels in plasma is expected to play an important role in the evaluation of therapeutic and toxic concentrations in cancer patients. In the present work, we therefore present an LC-MS/MS method for the quantification of silmitasertib in human plasma. Using a simple liquid-liquid extraction with ethyl acetate and a mixture of n-hexane and ethyl acetate, this method can be performed in any laboratory with mass spectrometry. The validation was carried out according to the FDA guideline.

Sequence of CX-4945 and Cisplatin Administration Determines the Effectiveness of Drug Combination and Cellular Response in Cholangiocarcinoma Cells In Vitro

BACKGROUND

The incidence of cholangiocarcinoma (CCA) is increasing worldwide and current single chemotherapeutic drug treatments are ineffective. CX-4945 and cisplatin are currently in clinical trial for CCA treatment.

MATERIALS AND METHODS

We assessed the effects of the sequence of administration of CX-4945 and cisplatin applied in combination treatments on their efficacy in CCA cells in vitro. CCA cell viability was examined using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays. Apoptosis was examined using flow cytometry. The percentage of cells positive for phosphorylated H2A histone family member X (γ-H2AX) were measured using both flow cytometry and immunofluorescence.

RESULTS

CCA cell viability was reduced to 50% after 24 h of treatments with CX-4945 and cisplatin as single agents. Interestingly, treatment with cisplatin 6 h prior to CX-4945 treatment induced significantly more DNA damage and apoptosis than CX-4945 treatment followed by cisplatin. Unexpectedly, CX-4945 treatment followed by cisplatin was less effective than single treatment in RMCCA-1 CCA cells. In addition, a 1:1 ratio of each drug was the most effective combination in these cells.

CONCLUSION

These data demonstrate that the combination of CX-4945 and cis platin acts additively when cisplatin is applied first, at least in part due to increased DNA damage and apoptosis. Furthermore, treatment with CX-4945 prior to cisplatin treatment reduces the efficacy of this drug combination in CCA cells.

CK2 Activity Mediates the Aggressive Molecular Signature of Glioblastoma Multiforme by Inducing Nerve/Glial Antigen (NG)2 Expression

Nerve/glial antigen (NG)2 expression crucially determines the aggressiveness of glioblastoma multiforme (GBM). Recent evidence suggests that protein kinase CK2 regulates NG2 expression. Therefore, we investigated in the present study whether CK2 inhibition suppresses proliferation and migration of NG2-positive GBM cells. For this purpose, CK2 activity was suppressed in the NG2-positive cell lines A1207 and U87 by the pharmacological inhibitor CX-4945 and CRISPR/Cas9-mediated knockout of CK2α. As shown by quantitative real-time PCR, luciferase-reporter assays, flow cytometry and western blot, this significantly reduced NG2 gene and protein expression when compared to vehicle-treated and wild type controls. In addition, CK2 inhibition markedly reduced NG2-dependent A1207 and U87 cell proliferation and migration. The Cancer Genome Atlas (TCGA)-based data further revealed not only a high expression of both NG2 and CK2 in GBM but also a positive correlation between the mRNA expression of the two proteins. Finally, we verified a decreased NG2 expression after CX-4945 treatment in patient-derived GBM cells. These findings indicate that the inhibition of CK2 represents a promising approach to suppress the aggressive molecular signature of NG2-positive GBM cells. Therefore, CX-4945 may be a suitable drug for the future treatment of NG2-positive GBM.

Mechanistic Basis for In Vivo Therapeutic Efficacy of CK2 Inhibitor CX-4945 in Acute Myeloid Leukemia

Simple Summary

Acute Myeloid Leukemia is an aggressive disease with poor outcomes. New targeted therapies that can boost the effects of currently used chemotherapy medications without added toxicity are needed. Targeting an overactive kinase, called the protein Kinase CK2 in AML, helps leukemia cells undergo cell death and helps certain chemotherapy drugs work better. Here, we present evidence that CX-4945, a CK2 inhibitor drug, effectively kills leukemia cells in mouse models and shows the mechanism of action responsible for these effects. Leukemia cells are more sensitive to a decrease in CK2 kinase levels than normal cells. Our results show that inhibiting CK2 kinase makes AML cells more susceptible to anthracycline-induced cell death. Anthracyclines like daunorubicin and doxorubicin are widely used to treat leukemia in children and adults. A rational combination of protein kinase CK2 inhibitors with the standard of care chemotherapy may help treat AML more effectively.

Abstract

Protein Kinase CK2 (Casein Kinase 2 or CK2) is a constitutively active serine-threonine kinase overactive in human malignancies. Increased expression and activity of CK2 in Acute Myeloid Leukemia (AML) is associated with a poor outcome. CK2 promotes AML cell survival by impinging on multiple oncogenic signaling pathways. The selective small-molecule CK2 inhibitor CX-4945 has shown in vitro cytotoxicity in AML. Here, we report that CX-4945 has a strong in vivo therapeutic effect in preclinical models of AML. The analysis of genome-wide DNA-binding and gene expression in CX-4945 treated AML cells shows that one mechanism, by which CK2 inhibition exerts a therapeutic effect in AML, involves the revival of IKAROS tumor suppressor function. CK2 phosphorylates IKAROS and disrupts IKAROS’ transcriptional activity by impairing DNA-binding and association with chromatin modifiers. Here, we demonstrate that CK2 inhibition decreases IKAROS phosphorylation and restores IKAROS binding to DNA. Further functional experiments show that IKAROS negatively regulates the transcription of anti-apoptotic genes, including BCL-XL (B cell Lymphoma like–2 like 1, BCL2L1). CX-4945 restitutes the IKAROS-mediated repression of BCL-XL in vivo and sensitizes AML cells to apoptosis. Using CX-4945, alongside the cytotoxic chemotherapeutic drug daunorubicin, augments BCL-XL suppression and AML cell apoptosis. Overall, these results establish the in vivo therapeutic efficacy of CX-4945 in AML preclinical models and determine the role of CK2 and IKAROS in regulating apoptosis in AML. Furthermore, our study provides functional and mechanistic bases for the addition of CK2 inhibitors to AML therapy.

Phosphoproteomic Landscape of AML Cells Treated with the ATP-Competitive CK2 Inhibitor CX-4945

Casein kinase 2 (CK2) regulates a plethora of proteins with pivotal roles in solid and hematological neoplasia. Particularly, in acute myeloid leukemia (AML) CK2 has been pointed as an attractive therapeutic target and prognostic marker. Here, we explored the impact of CK2 inhibition over the phosphoproteome of two cell lines representing major AML subtypes. Quantitative phosphoproteomic analysis was conducted to evaluate changes in phosphorylation levels after incubation with the ATP-competitive CK2 inhibitor CX-4945. Functional enrichment, network analysis, and database mining were performed to identify biological processes, signaling pathways, and CK2 substrates that are responsive to CX-4945. A total of 273 and 1310 phosphopeptides were found differentially modulated in HL-60 and OCI-AML3 cells, respectively. Despite regulated phosphopeptides belong to proteins involved in multiple biological processes and signaling pathways, most of these perturbations can be explain by direct CK2 inhibition rather than off-target effects. Furthermore, CK2 substrates regulated by CX-4945 are mainly related to mRNA processing, translation, DNA repair, and cell cycle. Overall, we evidenced that CK2 inhibitor CX-4945 impinge on mediators of signaling pathways and biological processes essential for primary AML cells survival and chemosensitivity, reinforcing the rationale behind the pharmacologic blockade of protein kinase CK2 for AML targeted therapy.

Protein kinase CK2 inhibition as a pharmacological strategy

CK2 is a constitutively active Ser/Thr protein kinase which phosphorylates hundreds of substrates. Since they are primarily related to survival and proliferation pathways, the best-known pathological roles of CK2 are in cancer, where its targeting is currently being considered as a possible therapy. However, CK2 activity has been found instrumental in many other human pathologies, and its inhibition will expectably be extended to different purposes in the near future. Here, after a description of CK2 features and implications in diseases, we analyze the different inhibitors and strategies available to target CK2, and update the results so far obtained by their in vivo application.

Protein Kinase CK2 Controls CaV2.1-Dependent Calcium Currents and Insulin Release in Pancreatic β-Cells

The regulation of insulin biosynthesis and secretion in pancreatic β-cells is essential for glucose homeostasis in humans. Previous findings point to the highly conserved, ubiquitously expressed serine/threonine kinase CK2 as having a negative regulatory impact on this regulation. In the cell culture model of rat pancreatic β-cells INS-1, insulin secretion is enhanced after CK2 inhibition. This enhancement is preceded by a rise in the cytosolic Ca²⁺ concentration. Here, we identified the serine residues S₂₃₆₂ and S₂₃₆₄ of the voltage-dependent calcium channel Ca_V2.1 as targets of CK2 phosphorylation. Furthermore, co-immunoprecipitation experiments revealed that Ca_V2.1 binds to CK2 in vitro and in vivo. Ca_V2.1 knockdown experiments showed that the increase in the intracellular Ca²⁺ concentration, followed by an enhanced insulin secretion upon CK2 inhibition, is due to a Ca²⁺ influx through Ca_V2.1 channels. In summary, our results point to a modulating role of CK2 in the Ca_V2.1-mediated exocytosis of insulin.

LC-MS/MS method for quantitation of the CK2 inhibitor silmitasertib (CX-4945) in human plasma, CSF, and brain tissue, and application to a clinical pharmacokinetic study in children with brain tumors

Silmitasertib (CX-4945) as a potent and selective inhibitor of CK2 exhibited promising in vitro and in vivo anti-cancer activity. An assay employing cation-exchange solid phase extraction (SPE) followed by LC-MS/MS analysis was successfully developed and validated for the quantitation of silmitasertib in human plasma, brain tissue, and human cerebrospinal fluid (CSF). Reverse phase chromatographic separation was achieved using Synergi™ hydro-RP column (4 μm, 75 × 2.0 mm) and gradient elution with 5 mM ammonium formate aqueous solution (pH 6.5) as mobile phase A and 0.1% formic acid in acetonitrile as mobile phase B. Multiple reaction monitoring (MRM) transition of m/z 350.2 → 223.2 and m/z 316.2 → 223.2 were chosen for detection of silmitasertib and internal standard (CX-4786) respectively. Since silmitasertib concentration in patient plasma is expected to be in a wide range due to the study design, two calibration curves with range 0.2-125 ng/ml and 32-20,000 ng/ml were established. A different curve ranging from 2 to 40 ng/g was used for measurement of silmitasertib in brain tissue, while another calibration curve ranging from 0.2 to 20 ng/ml was established for CSF. All these calibration curves corresponding to different matrices showed good linearity (R² > 0.99) over the concentration range. This assay demonstrated excellent precision below 15% and accuracies between 85% and 115% within-day and between-day for all the concentration levels in each matrix. This assay was also validated for each matrix for selectivity, sensitivity, matrix effects, recovery, and stability. We applied the validated method to the analysis of plasma silmitasertib for a clinical study.

Casein kinase 2 modulates the spindle assembly checkpoint to orchestrate porcine oocyte meiotic progression

Background

CK2 (casein kinase 2) is a serine/threonine-selective protein kinase that has been involved in a variety of cellular processes such as DNA repair, cell cycle control and circadian rhythm regulation. However, its functional roles in oocyte meiosis have not been fully determined.

Results

We report that CK2 is essential for porcine oocyte meiotic maturation by regulating spindle assembly checkpoint (SAC). Immunostaining and immunoblotting analysis showed that CK2 was constantly expressed and located on the chromosomes during the entire oocyte meiotic maturation. Inhibition of CK2 activity by its selective inhibitor CX-4945 impaired the first polar body extrusion and arrested oocytes at M I stage, accompanied by the presence of BubR1 at kinetochores, indicative of activated SAC. In addition, we found that spindle/chromosome structure was disrupted in CK2-inhibited oocytes due to the weakened microtubule stability, which is a major cause resulting in the activation of SAC. Last, we found that the level DNA damage as assessed by γH2A.X staining was considerably elevated when CK2 was inhibited, suggesting that DNA damage might be another critical factor leading to the SAC activation and meiotic failure of oocytes.

Conclusions

Our findings demonstrate that CK2 promotes the porcine oocyte maturation by ensuring normal spindle assembly and DNA damage repair.

Influence of Casein kinase II inhibitor CX-4945 on BCL6-mediated apoptotic signaling in B-ALL in vitro and in vivo

Background

Casein kinase II (CK2) is involved in multiple tumor-relevant signaling pathways affecting proliferation and apoptosis. CK2 is frequently upregulated in acute B-lymphoblastic leukemia (B-ALL) and can be targeted by the ATP-competitive CK2 inhibitor CX-4945. While reduced proliferation of tumor entities including B-ALL after CX-4945 incubation has been shown in vitro and in vivo, the detailed way of action is unknown. Here, we investigated the influence on the PI3K/AKT and apoptosis cascades in vivo and in vitro for further clarification.

Methods

A B-ALL xenograft model in NSG mice was used to perform in vivo longitudinal bioluminescence imaging during six day CX-4945 treatment. CX-4945 serum levels were determined at various time points. Flow cytometry of bone marrow and spleen cells was performed to analyze CX-4945-induced effects on tumor cell proliferation and distribution in B-ALL engrafted mice. ALL cells were enriched and characterized by targeted RNA sequencing. In vitro, B-ALL cell lines SEM, RS4;11 and NALM-6 were incubated with CX-4945 and gene expression of apoptosis regulators BCL6 and BACH2 was determined.

Results

In B-ALL-engrafted mice, overall tumor cell proliferation and distribution was not significantly influenced by CK2 inhibition. CX-4945 was detectable in serum during therapy and serum levels declined rapidly after cessation of CX-4945. While overall proliferation was not affected, early bone marrow and spleen blast frequencies seemed reduced after CK2 inhibition. Gene expression analyses revealed reduced expression of anti-apoptotic oncogene BCL6 in bone marrow blasts of CX-4945-treated animals. Further, BCL6 protein expression decreased in B-ALL cell lines exposed to CX-4945 in vitro. Surprisingly, levels of BCL6 opponent and tumor suppressor BACH2 also declined after prolonged incubation. Simultaneously, increased phosphorylation of direct CK2 target and tumor initiator AKT was detected at respective time points, even in initially pAKT-negative cell line NALM-6.

Conclusions

The CK2 inhibitor CX-4945 has limited clinical effects in an in vivo B-ALL xenograft model when applied as a single drug over a six day period. However, gene expression in B-ALL cells was altered and suggested effects on apoptosis via downregulation of BCL6. Unexpectedly, the BCL6 opponent BACH2 was also reduced. Interactions and regulation loops have to be further evaluated.

Role of CK2 inhibitor CX-4945 in anti-cancer combination therapy - potential clinical relevance

BACKGROUND

Protein kinase CK2 inhibition has long been considered as an attractive anti-cancer strategy based on the following considerations: CK2 is a pro-survival kinase, it is frequently over-expressed in human tumours and its over-expression correlates with a worse prognosis. Preclinical evidence strongly supports the feasibility of this target and, although dozens of CK2 inhibitors have been described in the literature so far, CX-4945 (silmitasertib) was the first that entered into clinical trials for the treatment of both human haematological and solid tumours. However, kinase inhibitor monotherapies turned out to be effective only in a limited number of malignancies, probably due to the multifaceted causes that underlie them, supporting the emerging view that multi-targeted approaches to treat human tumours could be more effective.

CONCLUSIONS

In this review, we will address combined anti-cancer therapeutic strategies described so far which involve the use of CX-4945. Data from preclinical studies clearly show the ability of CX-4945 to synergistically cooperate with different classes of anti-neoplastic agents, thereby contributing to an orchestrated anti-tumour action against multiple targets. Overall, these promising outcomes support the translation of CX-4945 combined therapies into clinical anti-cancer applications.

Simultaneous Inhibition of Protein Kinase CK2 and Dihydrofolate Reductase Results in Synergistic Effect on Acute Lymphoblastic Leukemia Cells

BACKGROUND/AIM

Recently, we demonstrated the ability of inhibitors of protein kinase 2 (casein kinase II; CK2) to enhance the efficacy of 5-fluorouracil, a thymidylate synthase (TYMS)-directed drug for anticancer treatment. The present study aimed to investigate the antileukemic effect of simultaneous inhibition of dihydrofolate reductase (DHFR), another enzyme involved in the thymidylate biosynthesis cycle, and CK2 in CCRF-CEM acute lymphoblastic leukemia cells.

MATERIALS AND METHODS

The influence of combined treatment on apoptosis and cell-cycle progression, as well as the endocellular level of DHFR protein and inhibition of CK2 were determined using flow cytometry and western blot analysis, respectively. Real-time quantitative polymerase chain reaction was used to examine the influence of silmitasertib (CX-4945), a selective inhibitor of CK2 on the expression of DHFR and TYMS genes.

RESULTS

The synergistic effect was correlated with the increase of annexin V-binding cell fraction, caspase 3/7 activation and a significant reduce in the activity of CK2. An increase of DHFR protein level was observed in CCRF-CEM cells after CX-4945 treatment, with the mRNA level remaining relatively constant.

CONCLUSION

The obtained results demonstrate a possibility to improve methotrexate-based anti-leukemia therapy by simultaneous inhibition of CK2. The effect of CK2 inhibition on DHFR expression suggests the important regulatory role of CK2-mediated phosphorylation of DHFR inside cells.

Protein Kinase CK2, a Potential Therapeutic Target in Carcinoma Management

The Protein kinase CK2 (formerly known as casein kinase 2) is a highly conserved serine/ threonine kinase overexpressed in various human carcinomas and its high expression often correlates with poor prognosis. CK2 protein is localized in the nucleus of many tumor cells and correlates with clinical features in many cases. Increased expression of CK2 in mice results in the development of various types of carcinomas (both solids and blood related tumors, such as (breast carcinoma, lymphoma, etc), which reveals its carcinogenic properties. CK2 plays essential roles in many key biological processes related to carcinoma, including cell apoptosis, DNA damage responses and cell cycle regulation. CK2 has become a potential anti-carcinoma target. Various CK2 inhibitors have been developed with anti-neoplastic properties against a variety of carcinomas. Some CK2 inhibitors have showed good results in in vitro and pre-clinical models, and have even entered in clinical trials. This article will review effects of CK2 and its inhibitors on common carcinomas in in vitro and pre-clinical studies.

Regulation of MLL/COMPASS stability through its proteolytic cleavage by taspase1 as a possible approach for clinical therapy of leukemia

In this study, Zhao et al. investigated the biological significance of MLL1 cleavage by the endopeptidase taspase1. They demonstrate that taspase1-dependent cleavage of MLL1 results in the destabilization of MLL, and thus their findings provide insights into the direct regulation of the stability of MLL1 through its cleavage by taspase1.

Chromosomal translocations of the Mixed-lineage leukemia 1 (MLL1) gene generate MLL chimeras that drive the pathogenesis of acute myeloid and lymphoid leukemia. The untranslocated MLL1 is a substrate for proteolytic cleavage by the endopeptidase threonine aspartase 1 (taspase1); however, the biological significance of MLL1 cleavage by this endopeptidase remains unclear. Here, we demonstrate that taspase1-dependent cleavage of MLL1 results in the destabilization of MLL. Upon loss of taspase1, MLL1 association with chromatin is markedly increased due to the stabilization of its unprocessed version, and this stabilization of the uncleaved MLL1 can result in the displacement of MLL chimeras from chromatin in leukemic cells. Casein kinase II (CKII) phosphorylates MLL1 proximal to the taspase1 cleavage site, facilitating its cleavage, and pharmacological inhibition of CKII blocks taspase1-dependent MLL1 processing, increases MLL1 stability, and results in the displacement of the MLL chimeras from chromatin. Accordingly, inhibition of CKII in a MLL-AF9 mouse model of leukemia delayed leukemic progression in vivo. This study provides insights into the direct regulation of the stability of MLL1 through its cleavage by taspase1, which can be harnessed for targeted therapeutic approaches for the treatment of aggressive leukemia as the result of MLL translocations.

Chemically induced degradation of CK2 by proteolysis targeting chimeras based on a ubiquitin-proteasome pathway

As a ubiquitous, highly pleiotropic and constitutively active serine/threonine protein kinase, casein kinase 2 (CK2) is closely associated with tumorigenesis by its overexpression in cancer cells. Here we report several proteolysis targeting chimeras (PROTACs) via "click reaction" to connect a CK2 inhibitor (CX-4945) and pomalidomide for degradation of CK2 protein. Among them, compound 2 degraded CK2 in a dose and time-dependent manner, and kept CK2 at a low basal level by recruiting ubiquitin-proteasome system. The degradation of CK2 resulted in the reduced phosphorylation of Akt and the up-regulation of p53. As a CK2 protein degrader, 2 showed the analogous cytotoxicity to CX-4945 but with a quite different mechanism of action from the CK2 inhibitor, hinting that degradation of CK2 proteins by PROTACs is a potential way for cancer treatments.

CX-4945 Induces Methuosis in Cholangiocarcinoma Cell Lines by a CK2-Independent Mechanism

Cholangiocarcinoma is a disease with a poor prognosis and increasing incidence and hence there is a pressing unmet clinical need for new adjuvant treatments. Protein kinase CK2 (previously casein kinase II) is a ubiquitously expressed protein kinase that is up-regulated in multiple cancer cell types. The inhibition of CK2 activity using CX-4945 (Silmitasertib) has been proposed as a novel treatment in multiple disease settings including cholangiocarcinoma. Here, we show that CX-4945 inhibited the proliferation of cholangiocarcinoma cell lines in vitro. Moreover, CX-4945 treatment induced the formation of cytosolic vacuoles in cholangiocarcinoma cell lines and other cancer cell lines. The vacuoles contained extracellular fluid and had neutral pH, features characteristic of methuosis. In contrast, simultaneous knockdown of both the α and α' catalytic subunits of protein kinase CK2 using small interfering RNA (siRNA) had little or no effect on the proliferation of cholangiocarcinoma cell lines and failed to induce the vacuole formation. Surprisingly, low doses of CX-4945 increased the invasive properties of cholangiocarcinoma cells due to an upregulation of matrix metallopeptidase 7 (MMP-7), while the knockdown of CK2 inhibited cell invasion. Our data suggest that CX-4945 inhibits cell proliferation and induces cell death via CK2-independent pathways. Moreover, the increase in cell invasion brought about by CX-4945 treatment suggests that this drug might increase tumor invasion in clinical settings.

Effect of Simultaneous Inhibition of Protein Kinase CK2 and Thymidylate Synthase in Leukemia and Breast Cancer Cells

BACKGROUND/AIM

Protein kinase CK2 was recently identified as a promising therapeutic target for combination therapy. Our study aims to investigate the anticancer effect of a simultaneous inhibition of thymidylate synthase (TS) and CK2 in MCF-7 breast cancer and CCRF-CEM leukemia cells.

MATERIALS AND METHODS

The type of interaction between CK2 inhibitors: CX-4945, 4,5,6,7-tetrabromo-1H-benzimidazole (TBBi), or recently obtained 4,5,6,7-tetrabromo-2-methyl-1H-benzimidazol-1-yl)acetonitrile (2b) and TS-directed anticancer drug, 5-fluorouracil (5-FU) was determined using the MTT assay and a combination index method. The influence of the combined treatment on apoptosis in leukemia cells, as well as on cell-cycle progression and the levels of TS, CK2α and P-Ser529-p65 were determined in both cell lines, using flow cytometry and western blot analysis, respectively.

RESULTS

The best synergistic effect was observed in CCRF-CEM cell line with the combination of 5-FU and 2b which correlated with a decrease in the endocellular CK2 activity and enhancement of the pro-apoptotic effect.

CONCLUSION

The obtained results demonstrate the ability of CK2 inhibitors to enhance the efficacy of 5-FU in anticancer treatment, indicating a different molecular mechanism of the studied CK2 inhibitors interaction with 5-FU.

Nuclear localization of the CK2α-subunit correlates with poor prognosis in clear cell renal cell carcinoma

Protein kinase CK2α, one of the two catalytic isoforms of the protein kinase CK2 has been shown to contribute to tumor development, tumor proliferation and suppression of apoptosis in various malignancies. We conducted this study to investigate CK2 expression in different subtypes of Renal Cell Carcinoma (RCC) and in the benign oncocytoma. qRT-PCR, immunohistochemistry and Western blot analyses revealed that CK2α expression was significantly increased at the mRNA and protein levels in clear cell RCC (ccRCC). Also the kinase activity of CK2 was significantly increased in ccRCC compared to normal renal cortex. Nuclear protein expression of CK2α correlated in univariate analysis with poor Progression Free Survival (HR = 8.11, p = 0.016). Functional analyses (cell proliferation assay) revealed an inhibitory effect of Caki-2 cell growth following CK2 inhibition with CX-4945. Our results suggest that CK2α promotes migration and invasion of ccRCC and therefore could serve as a novel prognostic biomarker and molecular therapeutic target in this type of cancer.

Casein Kinase II (CK2) as a Therapeutic Target for Hematological Malignancies

BACKGROUND

Casein kinase II (CK2) is a pro-oncogenic protein, which is emerging as a promising therapeutic target in cancer. Recent studies have revealed an important role for CK2 in tumorigenesis. High levels of CK2 are noted in many malignancies including leukemia. Use of CK2 inhibitors in various malignancies including breast, prostate, and lung cancer are being tested. Although many CK2 inhibitors exist, only a few have emerged as selective inhibitors that are potent and effective. CX-4945 is a selective, orallybioavailable small molecule inhibitor, which has shown encouraging results in pre-clinical models of leukemia.

METHODS

In this review we will elaborate on the structure and physiological function of the CK2 protein as well as its role in cancer. We will review, in depth, the role of CK2 in leukemia and its mechanisms of tumorigenesis via phosphorylation of the tumor suppressor protein Ikaros. We will discuss both the importance of Ikaros in leukemia suppression and the restoration of Ikaros' tumor suppressor function after CK2 inhibition by CX-4945 (a CK2-specific inhibitor).

RESULTS

CK2 is an oncogene that is overexpressed in hematological malignancies. In high risk Pre-B ALL, CK2 phosphorylates Ikaros tumor suppressor and promotes leukemogenesis. Inhibition of CK2 using CX4945 restores Ikaros function and leads to anti leukemic effects in vitro and in pre-clinical leukemia models.

CONCLUSION

CK2 is an attractive target in treatment of various cancers. Currently only a few specific CK2 inhibitors are available. Preclinical studies using CK2 inhibitor, CX4945 in high risk pediatric leukemias have shown promising results and warrants further testing in other types of leukemia.

Identification of Candidate Casein Kinase 2 Substrates in Mitosis by Quantitative Phosphoproteomics

Protein phosphorylation is a crucial regulatory mechanism that controls many aspects of cellular signaling. Casein kinase 2 (CK2), a constitutively expressed and active kinase, plays key roles in an array of cellular events including transcription and translation, ribosome biogenesis, cell cycle progression, and apoptosis. CK2 is implicated in cancerous transformation and is a therapeutic target in anti-cancer therapy. The specific and selective CK2 ATP competitive inhibitor, CX-4945 (silmitaseratib), is currently in phase 2 clinical trials. While many substrates and interactors of CK2 have been identified, less is known about CK2 substrates in mitosis. In the present work, we utilize CX-4945 and quantitative phosphoproteomics to inhibit CK2 activity in mitotically arrested HeLa cells and determine candidate CK2 substrates. We identify 330 phosphorylation sites on 202 proteins as significantly decreased in abundance upon inhibition of CK2 activity. Motif analysis of decreased sites reveals a linear kinase motif with aspartic and glutamic amino acids downstream of the phosphorylated residues, which is consistent with known substrate preferences for CK2. To validate specific candidate CK2 substrates, we perform in vitro kinase assays using purified components. Furthermore, we identified CK2 interacting proteins by affinity purification-mass spectrometry (AP-MS). To investigate the biological processes regulated by CK2 in mitosis, we perform network analysis and identify an enrichment of proteins involved in chromosome condensation, chromatin organization, and RNA processing. We demonstrate that overexpression of CK2 in HeLa cells affects proper chromosome condensation. Previously, we found that phosphoprotein phosphatase 6 (PP6), but not phosphoprotein phosphatase 2A (PP2A), opposes CK2 phosphorylation of the condensin I complex, which is essential for chromosome condensation. Here, we extend this observation and demonstrate that PP6 opposition of CK2 is a more general cellular regulatory mechanism.

CX-4945: the protein kinase CK2 inhibitor and anti-cancer drug shows anti-fungal activity

CX-4945 is a selective inhibitor of protein kinase CK2 exhibiting clinical significance. Its antitumor properties arise from the abrogation of CK2-mediated pro-survival cellular pathways. The presented data reveal the influence of CX-4945 on the growth of yeast cells showing variable potency against Saccharomyces cerevisiae deletion strains with different contents of CK2 subunits. The catalytic subunit CK2α appears to sensitize yeast to the CX-4945 action. Moreover, the compound suppresses hyphal growth and cell adhesion of Candida albicans, thereby abolishing some hallmarks of invasiveness of the pathogen. It is known that cancer patients are more prone to fungal infections. Our data unveil the dual-activity of CX-4945; when used in anti-cancer therapy, it may simultaneously prevent cancer-associated candidiasis.

NS5ATP13 Promotes Liver Fibrogenesis Via Activation of Hepatic Stellate Cells

Liver fibrosis is a reversible wound-healing response to any etiology of chronic hepatic injuries. Activation of hepatic stellate cells (HSCs) is the key event in liver fibrogenesis. Generally, persistent activation and proliferation of HSCs results in liver fibrosis progression, while primary mechanisms of liver fibrosis resolution are apoptosis and reversion to a quiescent phenotype of activated HSCs. NS5ATP13 (HCV NS5A-transactivated protein 13) is involved in nucleologenesis and tumorigenesis, but its role in liver fibrosis and HSC activation remains unclear. This study found that NS5ATP13 was upregulated in both fibrotic liver tissues and activated human HSCs induced by TGF-β1. Moreover, NS5ATP13 enhanced extracellular matrix (ECM) production and HSC activation, with or without TGF-β1 treatment, likely involving the TGF-β1/Smad3 signaling pathway. Additionally, NS5ATP13 boosted HSC proliferation by inhibiting cell apoptosis. Furthermore, HCV NS5A promoted the profibrogenic effect of NS5ATP13 partly through TGF-β1 and NF-κB p65 (RelA) upregulation. Meanwhile, NS5ATP13 was required for the pro-fibrogenic effect of NF-κB. Moreover, NS5ATP13 and NF-κB phosphorylation as well as HSC activation were reduced by CX-4945, a CK2 specific inhibitor. These findings indicated that NS5ATP13 acts as a profibrogenic factor, providing a potential target for antifibrotic therapies. J. Cell. Biochem. 118: 2463-2473, 2017. © 2017 Wiley Periodicals, Inc.

Targeting Protein Kinase CK2: Evaluating CX-4945 Potential for GL261 Glioblastoma Therapy in Immunocompetent Mice

Glioblastoma (GBM) causes poor survival in patients even with aggressive treatment. Temozolomide (TMZ) is the standard chemotherapeutic choice for GBM treatment but resistance always ensues. Protein kinase CK2 (CK2) contributes to tumour development and proliferation in cancer, and it is overexpressed in human GBM. Accordingly, targeting CK2 in GBM may benefit patients. Our goal has been to evaluate whether CK2 inhibitors (iCK2s) could increase survival in an immunocompetent preclinical GBM model. Cultured GL261 cells were treated with different iCK2s including CX-4945, and target effects evaluated in vitro. CX-4945 was found to decrease CK2 activity and Akt(S129) phosphorylation in GL261 cells. Longitudinal in vivo studies with CX-4945 alone or in combination with TMZ were performed in tumour-bearing mice. Increase in survival (p < 0.05) was found with combined CX-4945 and TMZ metronomic treatment (54.7 ± 11.9 days, n = 6) when compared to individual metronomic treatments (CX-4945: 24.5 ± 2.0 and TMZ: 38.7 ± 2.7, n = 6) and controls (22.5 ± 1.2, n = 6). Despite this, CX-4945 did not improve mice outcome when administered on every/alternate days, either alone or in combination with 3-cycle TMZ. The highest survival rate was obtained with the metronomic combined TMZ+CX-4945 every 6 days, pointing to the participation of the immune system or other ancillary mechanism in therapy response.

A chemical with proven clinical safety rescues Down-syndrome-related phenotypes in through DYRK1A inhibition

DYRK1A is important in neuronal development and function, and its excessive activity is considered a significant pathogenic factor in Down syndrome and Alzheimer's disease. Thus, inhibition of DYRK1A has been suggested to be a new strategy to modify the disease. Very few compounds, however, have been reported to act as inhibitors, and their potential clinical uses require further evaluation. Here, we newly identify CX-4945, the safety of which has been already proven in the clinical setting, as a potent inhibitor of DYRK1A that acts in an ATP-competitive manner. The inhibitory potency of CX-4945 on DYRK1A (IC₅₀=6.8 nM) in vitro was higher than that of harmine, INDY or proINDY, which are well-known potent inhibitors of DYRK1A. CX-4945 effectively reverses the aberrant phosphorylation of Tau, amyloid precursor protein (APP) and presenilin 1 (PS1) in mammalian cells. To our surprise, feeding with CX-4945 significantly restored the neurological and phenotypic defects induced by the overexpression of minibrain, an ortholog of human DYRK1A, in the Drosophila model. Moreover, oral administration of CX-4945 acutely suppressed Tau hyperphosphorylation in the hippocampus of DYRK1A-overexpressing mice. Our research results demonstrate that CX-4945 is a potent DYRK1A inhibitor and also suggest that it has therapeutic potential for DYRK1A-associated diseases.

Editors' choice:In vivo validation of a potent DYRK1A inhibitor, with proven clinical safety, using Down-syndrome- and Alzheimer's-disease-like models.

Protein kinase CK2 is widely expressed in follicular, Burkitt and diffuse large B-cell lymphomas and propels malignant B-cell growth

Serine-threonine kinase CK2 is highly expressed and pivotal for survival and proliferation in multiple myeloma, chronic lymphocytic leukemia and mantle cell lymphoma. Here, we investigated the expression of α catalytic and β regulatory CK2 subunits by immunohistochemistry in 57 follicular (FL), 18 Burkitt (BL), 52 diffuse large B-cell (DLBCL) non-Hodgkin lymphomas (NHL) and in normal reactive follicles. In silico evaluation of available Gene Expression Profile (GEP) data sets from patients and Western blot (WB) analysis in NHL cell-lines were also performed. Moreover, the novel, clinical-grade, ATP-competitive CK2-inhibitor CX-4945 (Silmitasertib) was assayed on lymphoma cells. CK2 was detected in 98.4% of cases with a trend towards a stronger CK2α immunostain in BL compared to FL and DLBCL. No significant differences were observed between Germinal Center B (GCB) and non-GCB DLBCL types. GEP data and WB confirmed elevated CK2 mRNA and protein levels as well as active phosphorylation of specific targets in NHL cells. CX-4945 caused a dose-dependent growth-arresting effect on GCB, non-GCB DLBCL and BL cell-lines and it efficiently shut off phosphorylation of NF-κB RelA and CDC37 on CK2 target sites. Thus, CK2 is highly expressed and could represent a suitable therapeutic target in BL, FL and DLBCL NHL.

The casein kinase 2 inhibitor, CX-4945, as an anti-cancer drug in treatment of human hematological malignancies

The casein kinase 2 (CK2) protein kinase is a pro-survival kinase and therapeutic target in treatment of various human cancers. CK2 overexpression has been demonstrated in hematological malignancies, including chronic lymphocytic leukemia, chronic myeloid leukemia, acute lymphoblastic leukemia, acute myeloid leukemia, and multiple myeloma. CX-4945, also known as Silmitasertib, is an orally administered, highly specific, ATP-competitive inhibitor of CK2. CX-4945 induces cytotoxicity and apoptosis and is currently being evaluated in clinical trials for treatment of many cancer types. In the past 2 years, the focus on the therapeutic potential of CX-4945 has shifted from solid tumors to hematological malignancies. CX-4945 exerts anti-proliferative effects in hematological tumors by downregulating CK2 expression and suppressing activation of CK2-mediated PI3K/Akt/mTOR signaling pathways. Furthermore, combination of CX-4945 with other inhibitors yielded synergistic effects in cell death induction. These new findings demonstrate that CK2 overexpression contributes to blood cancer cell survival and resistance to chemotherapy. Combinatorial use of CX-4945 is a promising therapeutic tool for treatment of hematological malignancies.

MEK inhibitor PD-0325901 overcomes resistance to CK2 inhibitor CX-4945 and exhibits anti-tumor activity in head and neck cancer

The serine-threonine kinase CK2 exhibits genomic alterations and aberrant overexpression in human head and neck squamous cell carcinomas (HNSCC). Here, we investigated the effects of CK2 inhibitor CX-4945 in human HNSCC cell lines and xenograft models. The IC_50's of CX-4945 for 9 UM-SCC cell lines measured by MTT assay ranged from 3.4-11.9 μM. CX-4945 induced cell cycle arrest and cell death measured by DNA flow cytometry, and inhibited prosurvival mediators phospho-AKT and p-S6 in UM-SCC1 and UM-SCC46 cells. CX-4945 decreased NF-κB and Bcl-XL reporter gene activities in both cell lines, but upregulated proapoptotic TP53 and p21 reporter activities, and induced phospho-ERK, AP-1, and IL-8 activity in UM-SCC1 cells. CX-4945 exhibited modest anti-tumor activity in UM-SCC1 xenografts. Tumor immunostaining revealed significant inhibition of PI3K-Akt-mTOR pathway and increased apoptosis marker TUNEL, but also induced p-ERK, c-JUN, JUNB, FOSL1 and proliferation (Ki67) markers, as a possible resistance mechanism. To overcome the drug resistance, we tested MEK inhibitor PD-0325901 (PD-901), which inhibited ERK-AP-1 activation alone and in combination with CX-4945. PD-901 alone displayed significant anti-tumor effects in vivo, and the combination of PD-901 and CX-4945 slightly enhanced anti-tumor activity when compared with PD-901 alone. Immunostaining of tumor specimens after treatment revealed inhibition of p-AKT S129 and p-AKT T308 by CX-4945, and inhibition of p-ERK T202/204 and AP-1 family member FOSL-1 by PD-901. Our study reveals a drug resistance mechanism mediated by the MEK-ERK-AP-1 pathway in HNSCC. MEK inhibitor PD-0325901 is active in HNSCC resistant to CX-4945, meriting further clinical investigation.

CK2 inhibitor CX4945 induces sequential inactivation of proteins in the signaling pathways related with cell migration and suppresses metastasis of A549 human lung cancer cells

Casein kinase 2 (CK2) is known to be involved in various cellular processes such as cell cycle, apoptosis and proliferation. It has been reported that the inhibition of CK2 induced by recently developed small molecule CX4945 shows anti-cancer effects including anti-proliferation and anti-angiogenesis in several different cancers including prostate cancer. Here we report that migration and invasion of A549 human lung cancer cells are suppressed by the inhibition of CK2 induced by CX4945. We found that CX4945 sequentially attenuates the proteins in PI3K/Akt and MAPK pathways, two signaling pathways related with cell migration. This sequential control of signal pathways inhibits the expression of membrane type 1-matrix metalloproteinase and this leads to the selective attenuation of one of the gelatinases, MMP-2, which can degrade components of extracellular matrix, and metastasis of A549 human lung cancer cell.