TF--a novel cell-permeable and selective inhibitor of human protein kinase CK2 induces apoptosis in the prostate cancer cell line LNCaP

Inhibition of CK2 Reduces NG2 Expression in Juvenile Angiofibroma

Juvenile angiofibroma (JA) is a rare fibrovascular neoplasm predominately found within the posterior nasal cavity of adolescent males. JA expresses the proteoglycan nerve–glial antigen (NG)2, which crucially determines the migratory capacity of distinct cancer cells. Moreover, it is known that the protein kinase CK2 regulates NG2 gene expression. Therefore, in the present study, we analyzed whether the inhibition of CK2 suppresses NG2-dependent JA cell proliferation and migration. For this purpose, we assessed the expression of NG2 and CK2 in patient-derived JA tissue samples, as well as in patient-derived JA cell cultures by Western blot, immunohistochemistry, flow cytometry and quantitative real-time PCR. The mitochondrial activity, proliferation and migratory capacity of the JA cells were determined by water-soluble tetrazolium (WST)-1, 5-bromo-2′-deoxyuridine (BrdU) and collagen sprouting assays. We found that NG2 and CK2 were expressed in both the JA tissue samples and cell cultures. The treatment of the JA cells with the two CK2 inhibitors, CX-4945 and SGC-CK2-1, significantly reduced NG2 gene and protein expression when compared to the vehicle-treated cells. In addition, the loss of CK2 activity suppressed the JA cell proliferation and migration. These findings indicate that the inhibition of CK2 may represent a promising therapeutic approach for the treatment of NG2-expressing JA.

Treatment of advanced cutaneous squamous cell carcinoma: a Mohs surgery and dermatologic oncology perspective

Locally advanced or metastatic cutaneous squamous cell carcinoma no longer amenable to surgical resection or primary radiation therapy requires an alternative approach to treatment. Until 2018, management consisted of limited systemic chemotherapies, which carried marginal clinical benefit. The introduction of immunotherapy with anti-PD-1 antibodies resulted in alternative treatment options for advanced cutaneous squamous cell carcinoma with substantial antitumor activity, durable response and acceptable safety profile. The field of immunotherapeutics continues to expand with adjuvant, neoadjuvant and intralesional studies currently in progress. Herein, the authors discuss their approach for the treatment of advanced cutaneous squamous cell carcinoma from the perspective of a Mohs surgeon and a dermatologic oncologist.

Okur-Chung neurodevelopmental syndrome-linked CK2α variants have reduced kinase activity

The Okur-Chung neurodevelopmental syndrome, or OCNDS, is a newly discovered rare neurodevelopmental disorder. It is characterized by developmental delay, intellectual disability, behavioral problems (hyperactivity, repetitive movements and social interaction deficits), hypotonia, epilepsy and language/verbalization deficits. OCNDS is linked to de novo mutations in CSNK2A1, that lead to missense or deletion/truncating variants in the encoded protein, the protein kinase CK2α. Eighteen different missense CK2α mutations have been identified to date; however, no biochemical or cell biological studies have yet been performed to clarify the functional impact of such mutations. Here, we show that 15 different missense CK2α mutations lead to varying degrees of loss of kinase activity as recombinant purified proteins and when mutants are ectopically expressed in mammalian cells. We further detect changes in the phosphoproteome of three patient-derived fibroblast lines and show that the subcellular localization of CK2α is altered for some of the OCNDS-linked variants and in patient-derived fibroblasts. Our data argue that reduced kinase activity and abnormal localization of CK2α may underlie the OCNDS phenotype.

Proposed Allosteric Inhibitors Bind to the ATP Site of CK2α

CK2α is a ubiquitous, well-studied kinase that is a target for small-molecule inhibition, for treatment of cancers. While many different classes of adenosine 5'-triphosphate (ATP)-competitive inhibitors have been described for CK2α, they tend to suffer from significant off-target activity and new approaches are needed. A series of inhibitors of CK2α has recently been described as allosteric, acting at a previously unidentified binding site. Given the similarity of these inhibitors to known ATP-competitive inhibitors, we have investigated them further. In our thorough structural and biophysical analyses, we have found no evidence that these inhibitors bind to the proposed allosteric site. Rather, we report crystal structures, competitive isothermal titration calorimetry (ITC) and NMR, hydrogen-deuterium exchange (HDX) mass spectrometry, and chemoinformatic analyses that all point to these compounds binding in the ATP pocket. Comparisons of our results and experimental approach with the data presented in the original report suggest that the primary reason for the disparity is nonspecific inhibition by aggregation.

Development of an in vitro screening assay for PIP5K1α lipid kinase and identification of potent inhibitors

The human phosphatidylinositol 4-phosphate 5-kinase type I α (hPIP5K1α) participates in the phosphoinositide-3-kinase/protein kinase B/mammalian target of rapamycin signaling pathway. Despite the evidence that hPIP5K1α plays a role in the development of prostate cancer (PCa), only one inhibitor is known to date. With the aim of identifying new inhibitors, a nonradiometric assay for measurement of the hPIP5K1α enzyme activity was developed. The assay is based on the separation of the fluorescently labeled substrate phosphatidylinositol-4-phosphate (PI(4)P) and the resulting product phosphatidylinositol-4,5-bisphosphate (PIP₂ ) by capillary electrophoresis (CE). Furthermore, an inactive mutant K261A of hPIP5K1α was generated by site-directed mutagenesis and used as a control. Michaelis-Menten analysis revealed a K_m value of 21.6 µm and V_max of 0.65 pmol·min^-1 for the cosubstrate ATP. The average Z' value was determined to be 0.86, indicating a high reliability of the assay. An in silico screening of an in-house compound library was performed employing the crystal structure of zebrafish PIP5K1α. By applying this strategy, three compounds with a 2-amino-3-cyano-4H-pyranobenzoquinone scaffold were identified and tested using the CE-based assay. These compounds inhibited hPIP5K1α to > 90% at a concentration of 50 µm. Subsequently, the inhibitory activity of all compounds with a pyranobenzoquinone scaffold (29) was tested on hPIP5K1α. Compound 4-(2-amino-3-cyano-6-hydroxy-5,8-dioxo-7-undecyl-5,8-dihydro-4H-chromen-4-yl)benzoic acid appeared to be the most potent inhibitor of hPIP5K1α identified so far with an IC₅₀ value of 1.55 µm, exhibiting a substrate-competitive mode of action. The effects of this compound on cell viability and the induction of apoptosis were investigated in LNCaP, DU145, and PC3 PCa cells.

Protein Kinase CK2-A Putative Target for the Therapy of Diabetes Mellitus?

Since diabetes is a global epidemic, the development of novel therapeutic strategies for the treatment of this disease is of major clinical interest. Diabetes is differentiated in two types: type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM). T1DM arises from an autoimmune destruction of insulin-producing β-cells whereas T2DM is characterized by an insulin resistance, an impaired insulin reaction of the target cells, and/or dysregulated insulin secretion. In the past, a growing number of studies have reported on the important role of the protein kinase CK2 in the regulation of the survival and endocrine function of pancreatic β-cells. In fact, inhibition of CK2 is capable of reducing cytokine-induced loss of β-cells and increases insulin expression as well as secretion by various pathways that are regulated by reversible phosphorylation of proteins. Moreover, CK2 inhibition modulates pathways that are involved in the development of diabetes and prevents signal transduction, leading to late complications such as diabetic retinopathy. Hence, targeting CK2 may represent a novel therapeutic strategy for the treatment of diabetes.

Involvement of endothelial CK2 in the radiation induced perivascular resistant niche (PVRN) and the induction of radioresistance for non-small cell lung cancer (NSCLC) cells

BACKGROUND

Tumor microenvironment (TME) plays a vital role in determining the outcomes of radiotherapy. As an important component of TME, vascular endothelial cells are involved in the perivascular resistance niche (PVRN), which is formed by inflammation or cytokine production induced by ionizing radiation (IR). Protein kinase CK2 is a constitutively active serine/threonine kinase which plays a vital role in cell proliferation and inflammation. In this study, we investigated the potential role of CK2 in PVRN after IR exposure.

RESULT

Specific CK2 inhibitors, Quinalizarin and CX-4945, were employed to effectively suppressed the kinase activity of CK2 in human umbilical vein endothelial cells (HUVECs) without affecting their viability. Results showing that conditioned medium from IR-exposed HUVECs increased cell viability of A549 and H460 cells, and the pretreatment of CK2 inhibitors slowed down such increment. The secretion of IL-8 and IL-6 in HUVECs was induced after exposure with IR, but significantly inhibited by the addition of CK2 inhibitors. Furthermore, IR exposure elevated the nuclear phosphorylated factor-κB (NF-κB) p65 expression in HUVECs, which was a master factor regulating cytokine production. But when pretreated with CK2 inhibitors, such elevation was significantly suppressed.

CONCLUSION

This study indicated that protein kinase CK2 is involved in the key process of the IR induced perivascular resistant niche, namely cytokine production, by endothelial cells, which finally led to radioresistance of non-small cell lung cancer cells. Thus, the inhibition of CK2 may be a promising way to improve the outcomes of radiation in non-small cell lung cancer 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.

Second-generation CK2α inhibitors targeting the αD pocket

CK2 is a critical cell cycle regulator that also promotes various anti-apoptotic mechanisms. Development of ATP-non-competitive inhibitors of CK2 is a very attractive strategy considering that the ATP binding site is highly conserved among other kinases. We have previously utilised a pocket outside the active site to develop a novel CK2 inhibitor, CAM4066. Whilst CAM4066 bound to this new pocket it was also interacting with the ATP site: herein, we describe an example of a CK2α inhibitor that binds completely outside the active site. This second generation αD-site binding inhibitor, compound CAM4712 (IC50 = 7 μM, GI50 = 10.0 ± 3.6 μM), has numerous advantages over the previously reported CAM4066, including a reduction in the number of rotatable bonds, the absence of amide groups susceptible to the action of proteases and improved cellular permeability. Unlike with CAM4066, there was no need to facilitate cellular uptake by making a prodrug. Moreover, CAM4712 displayed no drop off between its ability to inhibit the kinase in vitro (IC50) and the ability to inhibit cell proliferation (GI50).

A π-Halogen Bond of Dibenzofuranones with the Gatekeeper Phe113 in Human Protein Kinase CK2 Leads to Potent Tight Binding Inhibitors

Human protein kinase CK2 is an emerging target for neoplastic diseases. Potent lead structures for human CK2 inhibitors are derived from dibenzofuranones. Two new derivatives, 7,9-dichloro-1,2-dihydro-8-hydroxy-4-[(4-methoxyphenylamino)-methylene]dibenzo[b,d]furan-3(2H)-one (4a) and (E)-1,3-dichloro-6-[(4-methoxyphenylimino)-methyl]dibenzo[b,d]furan-2,7-diol (5) were tested for inhibition of CK2 and induction of apoptosis in LNCaP cells. Both turned out to be tight binding inhibitors, with IC₅₀ values of 7 nM (4a) and 5 nM (5) and an apparent K_i value of 0.4 nM for both. Compounds 4a and 5 reduced cellular CK2 activity, indicating cell permeability. Cell viability was substantially impaired in LNCaP cells, as well as apoptosis was induced, which was not appearing in non-neoplastic ARPE-19 cells. Co-crystallization of 4a and 5 revealed an unexpected π-halogen bond of the chloro substituent at C9 with the gatekeeper amino acid Phe113, leading to an inverted binding mode in comparison to parent compound 4b, with the Cl at C6 instead, which was co-crystallized as a control. This indicates that the position of the chloro substituent on ring A of the dibenzofuran scaffold is responsible for an inversion of the binding mode that enhances potency.

Evaluation of protein kinase CK2 as a therapeutic target for squamous cell carcinoma of cats

OBJECTIVE To investigate protein kinase CK2 (CK2) expression in squamous cell carcinoma (SCC) of cats and to examine effects of CK2 downregulation on in vitro apoptosis and viability in SCC. SAMPLE Biopsy specimens of oral mucosa and testis and blood samples from clinically normal cats, biopsy specimens of oral SCC from cats, and feline SCC (SCCF1) and mammary gland carcinoma (K12) cell lines. PROCEDURES Immunohistochemical labeling for CK2α was performed on biopsy specimens. Sequences of the CK2α subunit gene and CK2α' subunit gene in feline blood and feline cancer cell lines were determined by use of PCR and reverse-transcription PCR assays followed by direct Sanger sequencing. Specific small interfering RNAs (siRNAs) were developed for feline CK2α and CK2α'. The SCCF1 cells were treated with siRNA and assessed 72 hours later for CK2α and CK2α' expression and markers of apoptosis (via western blot analysis) and for viability (via 3-[4,5-dimethylthiazol-2-yl]-5-[3-carboxymethoxyphenyl]-2-[4-sulfophenyl]-2H-tetrazolium assays). RESULTS CK2α was expressed in all feline oral mucosa samples and 7 of 8 oral SCC samples. Expression of CK2α and CK2α' was successfully downregulated in SCCF1 cells by use of siRNAs, which resulted in decreased viability and induction of apoptosis. CONCLUSIONS AND CLINICAL RELEVANCE In this study, CK2 appeared to be a promising therapeutic target for SCCs of cats. A possible treatment strategy for SCCs of cats would be RNA interference that targets CK2.

Selected flavonoid compounds as promising inhibitors of protein kinase CK2α and CK2α', the catalytic subunits of CK2

CK2 is a ubiquitous protein kinase involved in many cell functions. During the last years it became an interesting target in cancer research. A series of flavonoid compounds was tested as inhibitors of protein kinase CK2. Several substances were found to be highly active against both catalytic subunits with IC₅₀ values below 1 μM in case of CK2α'. The most promising inhibitor we identified is chrysoeriol with IC₅₀ values of 250 and 34 nM for CK2α and CK2α', respectively.

CK2 in Cancer: Cellular and Biochemical Mechanisms and Potential Therapeutic Target

CK2 genes are overexpressed in many human cancers, and most often overexpression is associated with worse prognosis. Site-specific expression in mice leads to cancer development (e.g., breast, lymphoma) indicating the oncogenic nature of CK2. CK2 is involved in many key aspects of cancer including inhibition of apoptosis, modulation of signaling pathways, DNA damage response, and cell cycle regulation. A number of CK2 inhibitors are now available and have been shown to have activity against various cancers in vitro and in pre-clinical models. Some of these inhibitors are now undergoing exploration in clinical trials as well. In this review, we will examine some of the major cancers in which CK2 inhibition has promise based on in vitro and pre-clinical studies, the proposed cellular and signaling mechanisms of anti-cancer activity by CK2 inhibitors, and the current or recent clinical trials using CK2 inhibitors.

Specific inhibition of CK2α from an anchor outside the active site

The development of selective inhibitors of protein kinases is challenging because of the significant conservation of the ATP binding site. Here, we describe a new mechanism by which the protein kinase CK2α can be selectively inhibited using features outside the ATP site. We have identified a new binding site for small molecules on CK2α adjacent to the ATP site and behind the αD loop, termed the αD pocket. An elaborated fragment anchored in this site has been linked with a low affinity fragment binding in the ATP site, creating a novel and selective inhibitor (CAM4066) that binds CK2α with a Kd of 320 nM and shows significantly improved selectivity compared to other CK2α inhibitors. CAM4066 shows target engagement in several cell lines and similar potency to clinical trial candidate CX4945. Our data demonstrate that targeting a poorly conserved, cryptic pocket allows inhibition of CK2α via a novel mechanism, enabling the development of a new generation of selective CK2α inhibitors.

Site-Specific Labeling of Protein Kinase CK2: Combining Surface Display and Click Chemistry for Drug Discovery Applications

Human CK2 is a heterotetrameric constitutively active serine/threonine protein kinase and is an emerging target in current anti-cancer drug discovery. The kinase is composed of two catalytic CK2α subunits and two regulatory CK2β subunits. In order to establish an assay to identify protein-protein-interaction inhibitors (PPI) of the CK2α/CK2β interface, a bioorthogonal click reaction was used to modify the protein kinase α-subunit with a fluorophore. By expanding the genetic code, the unnatural amino acid para azidophenylalanine (pAzF) could be incorporated into CK2α. Performing the SPAAC click reaction (Strain-Promoted Azide-Alkyne Cycloaddition) by the use of a dibenzylcyclooctyne-fluorophore (DBCO-fluorophore) led to a specifically labeled human protein kinase CK2α. This site-specific labeling does not impair the phosphorylation activity of CK2, which was evaluated by capillary electrophoresis. Furthermore a dissociation constant (K_D) of 631 ± 86.2 nM was determined for the substrate α_S1-casein towards CK2α. This labeling strategy was also applied to CK2β subunit on Escherichia coli, indicating the site-specific modifications of proteins on the bacterial cell surface when displayed by Autodisplay.

Identification of a novel potent, selective and cell permeable inhibitor of protein kinase CK2 from the NIH/NCI Diversity Set Library

The anti-apoptotic protein kinase CK2 increasingly becomes an attractive target in cancer research with great therapeutic potential. Here, we have performed an in vitro screening of the Diversity Set III of the DTP program from the NCI/NIH, comprising 1600 compounds. We have identified 1,3-Dichloro-6-[(E)-((4-methoxyphenyl)imino)methyl] dibenzo(b,d) furan-2,7-diol (referred to as D11) to be a potent and selective inhibitor of protein kinase CK2. The D11 compound was tested against 354 eukaryotic protein kinases. By setting the threshold for inhibition to <2% remaining kinase activity, only DYRK1B, IRAK1 and PIM3 were inhibited to an extent as the tetrameric CK2 holoenzyme and its catalytic subunits α and α'. The IC50 values for the CK2α and CK2α' were on average 1-2 nM in comparison to the DYRK1B, IRAK1 and PIM3 kinases, which ranged from 18 to 49 nM. Cell permeability and efficacy of D11 were tested with cells in culture. In MIA PaCa-2 cells (human pancreatic carcinoma cell line), the phosphorylation of the CK2 biomarker CDC37 at S13 was almost completely inhibited in the presence of D11. This was observed both under normoxia and hypoxia. In the case of the human non-small cell lung carcinoma cell line, H1299, increasing amounts of D11 led to an inhibition of S380/T382/383 phosphorylation in PTEN, another biomarker for CK2 activity.

CK2-NCoR signaling cascade promotes prostate tumorigenesis

The aberrant expressions of casein kinase 2 (CK2) was found in prostate cancer patient and cell lines, but little is known of the detailed mechanisms implicated in prostate tumorigenesis. In this study, we report that both CK2 activity and CK2-mediated NCoR phosphorylation are significantly elevated in the androgen-independent prostate cancer cell line DU145 and PC-3 compared with RWPE1 and LNCaP cells. Increased phosphorylation inversely correlates with the mRNA level of the NCoR-regulated gene, interferon-γ-inducible protein 10 (IP-10). CK2 inhibition abrogated NCoR phosphorylation, IP-10 transcriptional repression, and the invasion activity of PC-3 cells. Inhibition of the CK2-NCoR network significantly reduced in vivo PC-3 cell tumorigenicity, likely due to transcriptional derepression of IP-10. Clinicopathological analyses revealed that increased CK2-mediated NCoR phosphorylation significantly correlates with poor survival among prostate cancer patients. These findings elucidate a CK2-modulated oncogenic cascade in prostate tumorigenesis.