Casein kinases as potential therapeutic targets

CK2: The master regulator in tumor immune-microenvironment - A crucial target in oncotherapy

A constitutively active serine/threonine kinase, casein kinase 2 (CK2) is involved in several physiological functions, such as DNA repair, apoptosis, and cell cycle control. New research emphasizes how critical CK2 is to the immune system's dysregulation in the tumor immune-microenvironment (TIME). The inhibition of immunological responses, including the downregulation of immune effector cells and the elevation of immunosuppressive proteins that aid in the development of tumor and immune evasion, has been linked to CK2 overexpression. CK2 maintains an immunosuppressive milieu that impedes anti-tumor immunity by encouraging the expressions and activities of immune checkpoint markers, regulating cytokines release, and boosting immune-suppressive cells such as regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs) to maintain immune evasion. It is a promising target for cancer treatment due to its complex role in immune regulation and oncogenic pathways. In this study, we address the therapeutic perspectives of targeting CK2 in oncotherapy and investigate the mechanisms by which it controls immunological responses in the TME. This review, comprehending the function of CK2 in immune suppression can facilitate the creation of innovative treatment approaches aimed at augmenting anti-tumor immunity and enhancing immunotherapy effectiveness.

Subunit specific altered expression and activity of casein kinase 2 in the brain tissues resected from mesial temporal lobe epilepsy with hippocampal sclerosis patients & rodent temporal lobe epilepsy model

INTRODUCTION

Mesial temporal lobe epilepsy (MTLE), is associated with dysregulated excitatory-inhibitory balance in the brain. Numerous enzymes, protein kinases, that are modulated through phosphorylation, have been linked with key processes involved in the pathogenesis of epilepsy. Therefore, in this study, we determined the subunit specific expression and activity of multi-subunit casein Kinase 2 (CK2) which influences NMDARs through phosphorylation events, in MTS patients as well as pilocarpine model of TLE.

METHODS

mRNA expression of CK2 (α, α', β) & NR2B was measured by real time PCR andprotein expression of CK2 (α, α', β), NR2B, and NR2B Ser1480 were evaluated using western blotting and immunohistochemistry in experimental models of TLE and MTS patients. CK2 α and α' activity was measured by kinase assay.

RESULTS

Significant increase in CK2α', CK2β, and NR2B mRNA expression were noted in chronic TLE rat model. Similarly, MTS patients displayed upregulated CK2α' and CK2β expressions, but NR2B mRNA remained unchanged. CK2α', CK2β, and NR2B Ser1480 protein expressions were higher in chronic TLE and MTS patients in relation to controls (p < 0.05), as was kinase activity (p < 0.05). In acute TLE rats, only NR2B protein expression was upregulated (p < 0.05).

CONCLUSION

Our research demonstrated for the first time the upregulation of CK2α' subunit and its increased kinase activityin resected brain samples from MTS patients as well as pilocarpine model of TLE. Altered expression and higher activity of CK2 α' highlights subunit specific contribution, suggesting the modulation of NMDA receptors by Casein Kinase 2 may contribute to hyperexcitability in MTLE.

Cold Atmospheric Plasma Jet Promotes Wound Healing through CK2-coordinated PI3K/AKT and MAPK Signaling Pathways

The promising role of cold atmospheric plasma jet (CAPJ) treatment in promoting wound healing has been widely documented in therapeutic implications. However, the fact that not all subjects respond equally to CAPJ necessitates the investigation of the underlying cellular mechanisms, which have been rarely understood so far. Given that wound healing is a complex and prolonged process, post-plasma-activated medium (PAM) treated keratinocytes were collected at two time points, 2 hours (receiving) and 24 hours (recovery), for (phospho)proteomic analysis to systematically dissect the molecular basis of CAPJ-promoted wound healing. The receiving (phospho)proteomics datasets, referred to the time point of 2 hours, revealed an apparent increase in the phosphorylation of CK2 and its-mediated PI3K/AKT and MAPK signaling pathways, accompanied by a prompted downstream physiological response of cell migration. Additionally, incorporating the network analysis of predicted kinases and their direct interactors, we reiterated that CAPJ influenced cell growth and migration, thereby paving the way for its role in subsequent wound healing processes. Further determining the proteome profiles at recovery phase, which is the time point of 24 hours, displayed a totally different view from the receiving proteome which had almost no change. The up-regulation of ROBOs/SLITs expression and vesicle trafficking and fusion-related proteins, along with the abundant presence of 14-3-3 family proteins, indicated that the persistent effect of PAM on the wound healing process could potentially promote keratinocyte-fibroblast crosstalk and stimulate extracellular matrix (ECM) synthesis upon epithelialization. Consistent with proteome patterns, CAPJ-treated wound tissues indeed showed a denser and well-organized ECM architecture, implying hastened epithelialization during wound healing. Collectively, we delineated the molecular basis of CAPJ-accelerated wound healing at early and late responses, providing valuable insights for treatment selection and the development of therapeutic strategies to achieve better outcomes.

FAM20C: A key protein kinase in multiple diseases

Family with sequence similarity 20 C (FAM20C) is a Golgi protein kinase that phosphorylates the serine residue in the S-x-E/pS motif of target proteins. FAM20C phosphorylates most secreted proteins, which play important roles in multiple biological processes, including cancer progression, biomineralization, and lipid homeostasis. Numerous studies have documented the potential contribution of FAM20C to the growth, invasion, and metastasis of glioma, breast cancer, and other cancers, as well as to the mineralization process of teeth and bone. In addition, FAM20C has been found to be associated with the occurrence and development of certain cardiovascular diseases and endocrine metabolism disorders. It raises hopes that understanding the disease-specific mechanisms of FAM20C may hold the key to developing new strategies for these diseases. This review comprehensively covers the existing literature to provide a summary of the structure and biological functions of FAM20C, with a particular focus on its roles in the disease context.

Advances in pyrazolo[1,5-a]pyrimidines: synthesis and their role as protein kinase inhibitors in cancer treatment

Pyrazolo[1,5-a]pyrimidines are a notable class of heterocyclic compounds with potent protein kinase inhibitor (PKI) activity, playing a critical role in targeted cancer therapy. Protein kinases, key regulators in cellular signalling, are frequently disrupted in cancers, making them important targets for small-molecule inhibitors. This review explores recent advances in pyrazolo[1,5-a]pyrimidine synthesis and their application as PKIs, with emphasis on inhibiting kinases such as CK2, EGFR, B-Raf, MEK, PDE4, BCL6, DRAK1, CDK1 and CDK2, Pim-1, among others. Several synthetic strategies have been developed for the efficient synthesis of pyrazolo[1,5-a]pyrimidines, including cyclization, condensation, three-component reactions, microwave-assisted methods, and green chemistry approaches. Palladium-catalyzed cross-coupling and click chemistry have enabled the introduction of diverse functional groups, enhancing the biological activity and structural diversity of these compounds. Structure-activity relationship (SAR) studies highlight the influence of substituent patterns on their pharmacological properties. Pyrazolo[1,5-a]pyrimidines act as ATP-competitive and allosteric inhibitors of protein kinases, with EGFR-targeting derivatives showing promise in non-small cell lung cancer (NSCLC) treatment. Their inhibitory effects on B-Raf and MEK kinases are particularly relevant in melanoma. Biological evaluations, including in vitro and in vivo studies, have demonstrated their cytotoxicity, kinase selectivity, and antiproliferative effects. Despite these advances, challenges such as drug resistance, off-target effects, and toxicity persist. Future research will focus on optimizing synthetic approaches, improving drug selectivity, and enhancing bioavailability to increase clinical efficacy.

CK1δ/ε kinases regulate TDP-43 phosphorylation and are therapeutic targets for ALS-related TDP-43 hyperphosphorylation

Hyperphosphorylated TAR DNA-binding protein 43 (TDP-43) aggregates in the cytoplasm of neurons is the neuropathological hallmark of amyotrophic lateral sclerosis (ALS) and a group of neurodegenerative diseases collectively referred to as TDP-43 proteinopathies that includes frontotemporal dementia, Alzheimer's disease, and limbic onset age-related TDP-43 encephalopathy. The mechanism of TDP-43 phosphorylation is poorly understood. Previously we reported casein kinase 1 epsilon gene (CSNK1E gene encoding CK1ε protein) as being tightly correlated with phosphorylated TDP-43 (pTDP-43) pathology. Here we pursued studies to investigate in cellular models and in vitro how CK1ε and CK1δ (a closely related family sub-member) mediate TDP-43 phosphorylation in disease. We first validated the binding interaction between TDP-43 and either CK1δ and CK1ε using kinase activity assays and predictive bioinformatic database. We utilized novel inducible cellular models that generated translocated phosphorylated TDP-43 (pTDP-43) and cytoplasmic aggregation. Reducing CK1 kinase activity with siRNA or small molecule chemical inhibitors resulted in significant reduction of pTDP-43, in both soluble and insoluble protein fractions. We also established CK1δ and CK1ε are the primary kinases that phosphorylate TDP-43 compared to CK2α, CDC7, ERK1/2, p38α/MAPK14, and TTBK1, other identified kinases that have been implicated in TDP-43 phosphorylation. Throughout our studies, we were careful to examine both the soluble and insoluble TDP-43 protein fractions, the critical protein fractions related to protein aggregation diseases. These results identify CK1s as critical kinases involved in TDP-43 hyperphosphorylation and aggregation in cellular models and in vitro, and in turn are potential therapeutic targets by way of CK1δ/ε inhibitors.

Fuzzy interactions between the auto-phosphorylated C-terminus and the kinase domain of CK1δ inhibits activation of TAp63α

The p53 family member TAp63α plays an important role in maintaining the genetic integrity in oocytes. DNA damage, in particular DNA double strand breaks, lead to the transformation of the inhibited, only dimeric conformation into the active tetrameric one that results in the initiation of an apoptotic program. Activation requires phosphorylation by the kinase CK1 which phosphorylates TAp63α at four positions. The third phosphorylation event is the decisive step that transforms TAp63α into the active state. This third phosphorylation, however, is ~ 20 times slower than the first two phosphorylation events. This difference in the phosphorylation kinetics constitutes a safety mechanism that allows oocytes with a low degree of DNA damage to survive. So far these kinetic investigations of the phosphorylation steps have been performed with the isolated CK1 kinase domain. However, all CK1 enzymes contain C-terminal extensions that become auto-phosphorylated and inhibit the activity of the kinase. Here we have investigated the effect of auto-phosphorylation of the C-terminus in the kinase CK1δ and show that it slows down phosphorylation of the first two sites in TAp63α but basically inhibits the phosphorylation of the third site. We have identified up to ten auto-phosphorylation sites in the CK1δ C-terminal domain and show that all of them interact with the kinase domain in a "fuzzy" way in which not a single site is particularly important. Through mutation analysis we further show that hydrophobic amino acids following the phosphorylation site are important for a substrate to be able to successfully compete with the auto-inhibitory effect of the C-terminal domain. This auto-phosphorylation adds a new layer to the regulation of apoptosis in oocytes.

Inhibition of CK2α accelerates skin wound healing by promoting endothelial cell proliferation through the Hedgehog signaling pathway

Diabetes is a chronic disease characterized by perturbed glucose and lipid metabolism, resulting in high blood glucose levels. Many complications induced by endothelial dysfunction can cause disability and even death of diabetic patients. Here, we found that the protein level of casein kinase 2α (CK2α) was increased in the endothelium of mice with type I diabetes (T1D) induced by streptozotocin (STZ) injection. Although a potential correlation between the protein level of CK2α and endothelial dysfunction in diabetes was established, the contribution of CK2α to the progression of endothelial dysfunction in diabetes remained largely unknown. By using CX4945 (a selective CK2α antagonist) and Si-csnk2a1 (small interfering RNA targeting CK2α), we found that inhibition of CK2α accelerated skin wound healing in T1D mice by promoting proliferation of endothelial cells. Administration of CX4945 or Si-csnk2a1 rescued the impaired Hedgehog signaling pathway in high glucose-treated human umbilical vein endothelial cells (HUVECs). Exploration of the underlying molecular mechanism revealed that the protective effect of CK2α inhibition on angiogenesis, which contributes to skin wound healing in diabetic mice, was blocked by administration of GANT61 (an inhibitor targeting the Hedgehog signaling pathway). Our findings establish CK2α as a regulator of endothelial dysfunction in diabetes and demonstrate that inhibition of CK2α accelerates skin wound healing in T1D mice by promoting endothelial cell proliferation via the Hedgehog signaling pathway.

2-Aminobenzothiazoles in anticancer drug design and discovery

Cancer is one of the major causes of mortality and morbidity worldwide. Substantial research efforts have been made to develop new chemical entities with improved anticancer efficacy. 2-Aminobenzothiazole is an important class of heterocycles containing one sulfur and two nitrogen atoms, which is associated with a broad spectrum of medical and pharmacological activities, including antitumor, antibacterial, antimalarial, anti-inflammatory, and antiviral activities. In recent years, an extraordinary collection of potent and low-toxicity 2-aminobenzothiazole compounds have been discovered as new anticancer agents. Herein, we provide a comprehensive review of this class of compounds based on their activities against tumor-related proteins, including tyrosine kinases (CSF1R, EGFR, VEGFR-2, FAK, and MET), serine/threonine kinases (Aurora, CDK, CK, RAF, and DYRK2), PI3K kinase, BCL-XL, HSP90, mutant p53 protein, DNA topoisomerase, HDAC, NSD1, LSD1, FTO, mPGES-1, SCD, hCA IX/XII, and CXCR. In addition, the anticancer potentials of 2-aminobenzothiazole-derived chelators and metal complexes are also described here. Moreover, the design strategies, mechanism of actions, structure-activity relationships (SAR) and more advanced stages of pre-clinical development of 2-aminobenzothiazoles as new anticancer agents are extensively reviewed in this article. Finally, the examples that 2-aminobenzothiazoles showcase an advantage over other heterocyclic systems are also highlighted.

Potential Role of Protein Kinase FAM20C on the Brain in Raine Syndrome, an In Silico Analysis

FAM20C (family with sequence similarity 20, member C) is a serine/threonine-specific protein kinase that is ubiquitously expressed and mainly associated with biomineralization and phosphatemia regulation. It is mostly known due to pathogenic variants causing its deficiency, which results in Raine syndrome (RNS), a sclerosing bone dysplasia with hypophosphatemia. The phenotype is recognized by the skeletal features, which are related to hypophosphorylation of different FAM20C bone-target proteins. However, FAM20C has many targets, including brain proteins and the cerebrospinal fluid phosphoproteome. Individuals with RNS can have developmental delay, intellectual disability, seizures, and structural brain defects, but little is known about FAM20C brain-target-protein dysregulation or about a potential pathogenesis associated with neurologic features. In order to identify the potential FAM20C actions on the brain, an in silico analysis was conducted. Structural and functional defects reported in RNS were described; FAM20C targets and interactors were identified, including their brain expression. Gene ontology of molecular processes, function, and components was completed for these targets, as well as for potential involved signaling pathways and diseases. The BioGRID and Human Protein Atlas databases, the Gorilla tool, and the PANTHER and DisGeNET databases were used. Results show that genes with high expression in the brain are involved in cholesterol and lipoprotein processes, plus axo-dendritic transport and the neuron part. These results could highlight some proteins involved in the neurologic pathogenesis of RNS.

Triazole-fused pyrimidines in target-based anticancer drug discovery

In recent decades, the development of targeted drugs has featured prominently in the treatment of cancer, which is among the major causes of mortality globally. Triazole-fused pyrimidines, a widely-used class of heterocycles in medicinal chemistry, have attracted considerable interest as potential anticancer agents that target various cancer-associated targets in recent years, demonstrating them as valuable templates for discovering novel anticancer candidates. The current review concentrates on the latest advancements of triazole-pyrimidines as target-based anticancer agents, including works published between 2007 and the present (2007-2022). The structure-activity relationships (SARs) and multiple pathways are also reviewed to shed light on the development of more effective and biotargeted anticancer candidates.

Silmitasertib, a casein kinase 2 inhibitor, induces massive lipid droplet accumulation and nonapoptotic cell death in head and neck cancer cells

BACKGROUND

Accumulating evidence shows that high expression of casein kinase 2 (CK2) and phosphorylated acetyl CoA carboxylase (pACC) in patients with squamous cell carcinoma of the head and neck (SCCHN) correlates with decreased survival rates. Computational analysis has shown that ACC is a potential substrate for CK2, and its inhibition can suppress ACC phosphorylation in vitro. CX-4945, also known as silmitasertib, is an orally administered, highly specific, ATP-competitive inhibitor of CK2 and is under clinical investigation as a treatment for malignancies. We hypothesize that inhibition of CK2 by CX-4945 can reduce CK2-downstream phosphorylation of ACC as a therapeutic strategy against SCCHN.

METHODS

Three aggressive SCCHN cell lines (OSC-19, FaDu and HN31) were cultured to investigate the anticancer mechanism of the CK2 inhibitor, CX-4945. Cell cycle analysis, Annexin V/PI staining, and cleavage of PARP were performed to detect apoptosis. Western blot, electron microscopy and analysis of acidic vesicular organelle development were used to detect autophagy. Interference with cellular metabolism by CX-4945 treatment was determined by Seahorse XF24 Extracellular Flux Analyzer and mass spectrometry.

RESULTS

Cellular metabolism was impeded by CX-4945 in aggressive SCCHN cells by Seahorse XF24 Extracellular Flux Analyzer and mass spectrometry, and consequently time- and dose-dependent lipid droplet accumulation and non-apoptotic cell death were observed. The lipogenic enzyme ACC was demonstrated to be associated with CK2, and its repressive phosphorylation could be removed by the CK2 inhibitor CX-4945. Overexpression of ACC resulted in impaired cell survival following transient transfection.

CONCLUSION

The findings demonstrate that CK2 inhibition impairs normal cellular energy metabolism and may be an attractive therapy for treating aggressive SCCHN.

Protein Kinase CK2 and Epstein-Barr Virus

Protein kinase CK2 is a pleiotropic protein kinase, which phosphorylates a number of cellular and viral proteins. Thereby, this kinase is implicated in the regulation of cellular signaling, controlling of cell proliferation, apoptosis, angiogenesis, immune response, migration and invasion. In general, viruses use host signaling mechanisms for the replication of their genome as well as for cell transformation leading to cancer. Therefore, it is not surprising that CK2 also plays a role in controlling viral infection and the generation of cancer cells. Epstein-Barr virus (EBV) lytically infects epithelial cells of the oropharynx and B cells. These latently infected B cells subsequently become resting memory B cells when passing the germinal center. Importantly, EBV is responsible for the generation of tumors such as Burkitt's lymphoma. EBV was one of the first human viruses, which was connected to CK2 in the early nineties of the last century. The present review shows that protein kinase CK2 phosphorylates EBV encoded proteins as well as cellular proteins, which are implicated in the lytic and persistent infection and in EBV-induced neoplastic transformation. EBV-encoded and CK2-phosphorylated proteins together with CK2-phosphorylated cellular signaling proteins have the potential to provide efficient virus replication and cell transformation. Since there are powerful inhibitors known for CK2 kinase activity, CK2 might become an attractive target for the inhibition of EBV replication and cell transformation.

6-(Tetrazol-5-yl)-7-aminoazolo[1,5-a]pyrimidines as Novel Potent CK2 Inhibitors

In this work, we describe the design, synthesis, and structure-activity relationship of 6-(tetrazol-5-yl)-7-aminoazolo[1,5-a]pyrimidines as inhibitors of Casein kinase 2 (CK2). At first, we optimized the reaction conditions for the azide-nitrile cycloaddition in the series of 6-cyano-7-aminoazolopyridimines and sodium azide. The regioselectivity of this process has been shown, as the cyano group of the pyrimidine cycle was converted to tetrazole while the nitrile of the azole fragment did not react. The desired tetrazolyl-azolopyrimidines were obtained in a moderate to excellent yields (42−95%) and converted further to water soluble sodium salts by the action of sodium bicarbonate. The obtained 6-(tetrazol-5-yl)-7-aminopyrazolo[1,5-a]pyrimidines 2a−k and their sodium salts 3a−c, 3g−k showed nano to low micromolar range of CK2 inhibition while corresponding [1,2,4]triazolopyrimidines 10a−k were less active (IC50 > 10 µM). The leader compound 3-phenyl-6-(tetrazol-5-yl)-7-aminopyrazolo[1,5-a]pyrimidine 2i as CK2 inhibitor showed IC50 45 nM.

CK2 and protein kinases of the CK1 superfamily as targets for neurodegenerative disorders

Casein kinases are involved in a variety of signaling pathways, and also in inflammation, cancer, and neurological diseases. Therefore, they are regarded as potential therapeutic targets for drug design. Recent studies have highlighted the importance of the casein kinase 1 superfamily as well as protein kinase CK2 in the development of several neurodegenerative pathologies, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. CK1 kinases and their closely related tau tubulin kinases as well as CK2 are found to be overexpressed in the mammalian brain. Numerous substrates have been detected which play crucial roles in neuronal and synaptic network functions and activities. The development of new substances for the treatment of these pathologies is in high demand. The impact of these kinases in the progress of neurodegenerative disorders, their bona fide substrates, and numerous natural and synthetic compounds which are able to inhibit CK1, TTBK, and CK2 are discussed in this review.

Exploring the Activity of Fungal Phenalenone Derivatives as Potential CK2 Inhibitors Using Computational Methods

Cancer represents one of the most prevalent causes of global death. CK2 (casein kinase 2) activation boosted cancer proliferation and progression. Therefore, CK2 inhibition can have a crucial role in prohibiting cancer progression and enhancing apoptosis. Fungi have gained vast interest as a wealthy pool of anticancer metabolites that could particularly target various cancer progression-linked signaling pathways. Phenalenones are a unique class of secondary metabolites that possess diverse bioactivities. In the current work, the CK2 inhibitory capacity of 33 fungal phenalenones was explored using computational studies. After evaluating the usefulness of the compounds as enzyme inhibitors by ADMET prediction, the compounds were prepared for molecular docking in the CK2-α1 crystal structure (PDB: 7BU4). Molecular dynamic simulation was performed on the top two scoring compounds to evaluate their binding affinity and protein stability through a simulated physiological environment. Compound 19 had a superior binding affinity to the co-crystallized ligand (Y49). The improved affinity can be attributed to the fact that the aliphatic chain makes additional contact with Asp120 in a pocket distant from the active site.

Epidrugs in Amyotrophic Lateral Sclerosis/Frontotemporal Dementia: Contextualizing a Role for Histone Kinase Inhibition in Neurodegenerative Disease

Breakthroughs in understanding the epigenetic mechanisms involved in neurodegenerative disease have highlighted "epidrugs" as a potential avenue for therapeutic development. Here, we expand on the future of epidrugs against neurodegeneration and discuss promising novel targets underexploited thus far: histone kinases.

Fam20C in Human Diseases: Emerging Biological Functions and Therapeutic Implications

Fam20C, a typical member of Fam20 family, has been well-known as a Golgi casein kinase, which is closely associated with Raine Syndrome (RS). It can phosphorylate many secreted proteins and multiple substrates, and thereby plays a crucial role in biological functions. More importantly, Fam20C has also been found to enhance the metastasis of several types of human cancers, such as breast cancer, indicating that Fam20C may be a promising therapeutic target. Accordingly, some small-molecule inhibitors of Fam20C have been reported in cancer. Taken together, these inspiring findings would shed new light on exploiting Fam20C as a potential therapeutic target and inhibiting Fam20C with small-molecule compounds would provide a clue on discovery of more candidate small-molecule drugs for fighting with human diseases.

CHMP2B regulates TDP-43 phosphorylation and cytotoxicity independent of autophagy via CK1

The ESCRT protein CHMP2B and the RNA-binding protein TDP-43 are both associated with ALS and FTD. The pathogenicity of CHMP2B has mainly been considered a consequence of autophagy–endolysosomal dysfunction, whereas protein inclusions containing phosphorylated TDP-43 are a pathological hallmark of ALS and FTD. Intriguingly, TDP-43 pathology has not been associated with the FTD-causing CHMP2B^Intron5 mutation. In this study, we identify CHMP2B as a modifier of TDP-43–mediated neurodegeneration in a Drosophila screen. Down-regulation of CHMP2B reduces TDP-43 phosphorylation and toxicity in flies and mammalian cells. Surprisingly, although CHMP2B^Intron5 causes dramatic autophagy dysfunction, disturbance of autophagy does not alter TDP-43 phosphorylation levels. Instead, we find that inhibition of CK1, but not TTBK1/2 (all of which are kinases phosphorylating TDP-43), abolishes the modifying effect of CHMP2B on TDP-43 phosphorylation. Finally, we uncover that CHMP2B modulates CK1 protein levels by negatively regulating ubiquitination and the proteasome-mediated turnover of CK1. Together, our findings propose an autophagy-independent role and mechanism of CHMP2B in regulating CK1 abundance and TDP-43 phosphorylation.

SGC-CK2-1 Is an Efficient Inducer of Insulin Production and Secretion in Pancreatic β-Cells

The pyrazolopyrimidine based compound SGC-CK2-1 is a potent and highly specific CK2 inhibitor and a new tool to study the biological functions of protein kinase CK2 irrespective from off-target effects. We used this compound in comparison with the well-established CK2 inhibitor CX-4945 to analyze the importance of CK2 for insulin production and secretion from pancreatic β-cells. Both inhibitors affected the proliferation and viability of MIN6 cells only marginally and downregulated the endogenous CK2 activity to a similar level. Furthermore, both inhibitors increased the message for insulin and boosted the secretion of insulin from storage vesicles. Thus, regarding the high specificity of SGC-CK2-1, we can clearly attribute the observed effects to biological functions of protein kinase CK2.

Imidazo[1,2-b]pyridazine as privileged scaffold in medicinal chemistry: An extensive review

Imidazo[1,2-b]pyridazine scaffold represents an important class of heterocyclic nucleus which provides various bioactives molecules. Among them, the successful kinase inhibitor ponatinib led to a resurgence of interest in exploring new imidazo[1,2-b]pyridazine-containing derivatives for their putative therapeutic applications in medicine. This present review intends to provide a state-of-the-art of this framework in medicinal chemistry from 1966 to nowadays, unveiling different aspects of its structure-activity relationships (SAR). This extensive literature surveil may guide medicinal chemists for the quest of novel imidazo[1,2-b]pyridazine compounds with enhanced pharmacokinetics profile and efficiency.

Stress-activated kinases as therapeutic targets in pancreatic cancer

Pancreatic cancer is a dismal disease with high incidence and poor survival rates. With the aim to improve overall survival of pancreatic cancer patients, new therapeutic approaches are urgently needed. Protein kinases are key regulatory players in basically all stages of development, maintaining physiologic functions but also being involved in pathogenic processes. c-Jun N-terminal kinases (JNK) and p38 kinases, representatives of the mitogen-activated protein kinases, as well as the casein kinase 1 (CK1) family of protein kinases are important mediators of adequate response to cellular stress following inflammatory and metabolic stressors, DNA damage, and others. In their physiologic roles, they are responsible for the regulation of cell cycle progression, cell proliferation and differentiation, and apoptosis. Dysregulation of the underlying pathways consequently has been identified in various cancer types, including pancreatic cancer. Pharmacological targeting of those pathways has been the field of interest for several years. While success in earlier studies was limited due to lacking specificity and off-target effects, more recent improvements in small molecule inhibitor design against stress-activated protein kinases and their use in combination therapies have shown promising in vitro results. Consequently, targeting of JNK, p38, and CK1 protein kinase family members may actually be of particular interest in the field of precision medicine in patients with highly deregulated kinase pathways related to these kinases. However, further studies are warranted, especially involving in vivo investigation and clinical trials, in order to advance inhibition of stress-activated kinases to the field of translational medicine.

FAM20C Overview: Classic and Novel Targets, Pathogenic Variants and Raine Syndrome Phenotypes

FAM20C is a gene coding for a protein kinase that targets S-X-E/pS motifs on different phosphoproteins belonging to diverse tissues. Pathogenic variants of FAM20C are responsible for Raine syndrome (RS), initially described as a lethal and congenital osteosclerotic dysplasia characterized by generalized atherosclerosis with periosteal bone formation, characteristic facial dysmorphisms and intracerebral calcifications. The aim of this review is to give an overview of targets and variants of FAM20C as well as RS aspects. We performed a wide phenotypic review focusing on clinical aspects and differences between all lethal (LRS) and non-lethal (NLRS) reported cases, besides the FAM20C pathogenic variant description for each. As new targets of FAM20C kinase have been identified, we reviewed FAM20C targets and their functions in bone and other tissues, with emphasis on novel targets not previously considered. We found the classic lethal and milder non-lethal phenotypes. The milder phenotype is defined by a large spectrum ranging from osteonecrosis to osteosclerosis with additional congenital defects or intellectual disability in some cases. We discuss our current understanding of FAM20C deficiency, its mechanism in RS through classic FAM20C targets in bone tissue and its potential biological relevance through novel targets in non-bone tissues.

Natural Compounds Isolated from Stachybotrys chartarum Are Potent Inhibitors of Human Protein Kinase CK2

A large number of secondary metabolites have been isolated from the filamentous fungus Stachybotrys chartarum and have been described before. Fourteen of these natural compounds were evaluated in vitro in the present study for their inhibitory activity towards the cancer target CK2. Among these compounds, stachybotrychromene C, stachybotrydial acetate and acetoxystachybotrydial acetate turned out to be potent inhibitors with IC₅₀ values of 0.32 µM, 0.69 µM and 1.86 µM, respectively. The effects of these three compounds on cell proliferation, growth and viability of MCF7 cells, representing human breast adenocarcinoma as well as A427 (human lung carcinoma) and A431 (human epidermoid carcinoma) cells, were tested using EdU assay, IncuCyte^® live-cell imaging and MTT assay. The most active compound in inhibiting MCF7 cell proliferation was acetoxystachybotrydial acetate with an EC₅₀ value of 0.39 µM. In addition, acetoxystachybotrydial acetate turned out to inhibit the growth of all three cell lines completely at a concentration of 1 µM. In contrast, cell viability was impaired only moderately, to 37%, 14% and 23% in MCF7, A427 and A431 cells, respectively.

In Silico and In Vitro Studies of Natural Compounds as Human CK2 Inhibitors

BACKGROUND

Casein Kinase 2 (CK2) is a ubiquitous cellular serine-threonine kinase with broad spectrum of substrates. This enzyme is widely expressed in eukaryotic cells and is overexpressed in different human cancers. Thus, the inhibition of CK2 can induce the physiological process of apoptosis leading to tumor cell death.

OBJECTIVES

Selecting natural inhibitors toward the target enzyme using database mining.

METHODS

With our continuous effort to discover new compounds with CK2 inhibitory effect, several commercial natural databases were searched using molecular modeling approach and the selected compounds were evaluated in vitro.

RESULTS

Three compounds were selected as candidates and evaluated in vitro using CK2 holoenzyme, their effect on three cancer cell lines was determined. The selected candidates were weak inhibitors toward the target enzyme, only one compound showed moderate effect on cell viability.

CONCLUSION

Several natural databases were screened, compounds were selected and tested in vitro. Despite the unexpected low inhibitory activity of the tested compounds, this study can help in directing the search of potent CK2 inhibitors and better understand the binding requirements of the ATP competitive inhibitors.

Protein kinase CK2: a potential therapeutic target for diverse human diseases

CK2 is a constitutively active Ser/Thr protein kinase, which phosphorylates hundreds of substrates, controls several signaling pathways, and is implicated in a plethora of human diseases. Its best documented role is in cancer, where it regulates practically all malignant hallmarks. Other well-known functions of CK2 are in human infections; in particular, several viruses exploit host cell CK2 for their life cycle. Very recently, also SARS-CoV-2, the virus responsible for the COVID-19 pandemic, has been found to enhance CK2 activity and to induce the phosphorylation of several CK2 substrates (either viral and host proteins). CK2 is also considered an emerging target for neurological diseases, inflammation and autoimmune disorders, diverse ophthalmic pathologies, diabetes, and obesity. In addition, CK2 activity has been associated with cardiovascular diseases, as cardiac ischemia-reperfusion injury, atherosclerosis, and cardiac hypertrophy. The hypothesis of considering CK2 inhibition for cystic fibrosis therapies has been also entertained for many years. Moreover, psychiatric disorders and syndromes due to CK2 mutations have been recently identified. On these bases, CK2 is emerging as an increasingly attractive target in various fields of human medicine, with the advantage that several very specific and effective inhibitors are already available. Here, we review the literature on CK2 implication in different human pathologies and evaluate its potential as a pharmacological target in the light of the most recent findings.

Leishmania Protein Kinases: Important Regulators of the Parasite Life Cycle and Molecular Targets for Treating Leishmaniasis

Leishmania is a protozoan parasite of the trypanosomatid family, causing a wide range of diseases with different clinical manifestations including cutaneous, mucocutaneous and visceral leishmaniasis. According to WHO, one billion people are at risk of Leishmania infection as they live in endemic areas while there are 12 million infected people worldwide. Annually, 0.9-1.6 million new infections are reported and 20-50 thousand deaths occur due to Leishmania infection. As current chemotherapy for treating leishmaniasis exhibits numerous drawbacks and due to the lack of effective human vaccine, there is an urgent need to develop new antileishmanial therapy treatment. To this end, eukaryotic protein kinases can be ideal target candidates for rational drug design against leishmaniasis. Eukaryotic protein kinases mediate signal transduction through protein phosphorylation and their inhibition is anticipated to be disease modifying as they regulate all essential processes for Leishmania viability and completion of the parasitic life cycle including cell-cycle progression, differentiation and virulence. This review highlights existing knowledge concerning the exploitation of Leishmania protein kinases as molecular targets to treat leishmaniasis and the current knowledge of their role in the biology of Leishmania spp. and in the regulation of signalling events that promote parasite survival in the insect vector or the mammalian host.

Exogenous bacterial DnaK increases protein kinases activity in human cancer cell lines

BACKGROUND

Studies of molecular mechanisms underlying tumor cell signaling highlighted a critical role for kinases in carcinogenesis and cancer progression. To this regard, protein kinases regulates a number of critical cellular pathways by adding phosphate groups to specific substrates. For this reason, their involvement in the complex interactions between the human microbiota and cancer cells to determine therapy and tumor progression outcome is becoming increasingly relevant. Mycoplasmas are components of the normal human microbiota, and several species have also been associated to human diseases, including certain cancers. It is also important to note that Mycoplasmas and their proteins are a component of the common tumor microenvironment. In addition, several epidemiological, in vivo and in vitro studies indicate a close involvement of Mycoplasmas in cellular transformation and cancer progression.

METHODS

In this study, we investigate the effect of exogenous Mycoplasma DnaK on kinases activity by treating in vitro four different eukaryotic cancer cell lines, namely lung and prostate cancer, colon adenocarcinoma, and neuroblastoma. Phosphorylation of kinases and specific substrates was measured at 20 and 60 min.

RESULTS

Kinome analysis of our data indicates that Mycoplasma DnaK promotes the dysregulation of the activity of specific kinases and their substrates, with a known involvement in carcinogenesis and cancer progression.

CONCLUSIONS

Given the similarity in structure and amino acid composition of this protein with other bacterial DnaKs we provide a novel mechanism whereby components of the human microbiota and present in the tumor microenvironment are able to deregulate phosphorylation events occurring during carcinogenesis and cancer progression.

Cooperative Blockade of CK2 and ATM Kinases Drives Apoptosis in VHL-Deficient Renal Carcinoma Cells through ROS Overproduction

Simple Summary

Renal cell carcinoma (RCC) is the eighth leading malignancy in the world, accounting for 4% of all cancers with poor outcome when metastatic. Protein kinases are highly druggable proteins, which are often aberrantly activated in cancers. The aim of our study was to identify candidate targets for metastatic clear cell renal cell carcinoma therapy, using chemo-genomic-based high-throughput screening. We found that the combined inhibition of the CK2 and ATM kinases in renal tumor cells and patient-derived tumor samples induces synthetic lethality. Mechanistic investigations unveil that this drug combination triggers apoptosis through HIF-2α-(Hypoxic inducible factor HIF-2α) dependent reactive oxygen species (ROS) overproduction, giving a new option for patient care in metastatic RCC.

Abstract

Kinase-targeted agents demonstrate antitumor activity in advanced metastatic clear cell renal cell carcinoma (ccRCC), which remains largely incurable. Integration of genomic approaches through small-molecules and genetically based high-throughput screening holds the promise of improved discovery of candidate targets for cancer therapy. The 786-O cell line represents a model for most ccRCC that have a loss of functional pVHL (von Hippel-Lindau). A multiplexed assay was used to study the cellular fitness of a panel of engineered ccRCC isogenic 786-O VHL⁻ cell lines in response to a collection of targeted cancer therapeutics including kinase inhibitors, allowing the interrogation of over 2880 drug–gene pairs. Among diverse patterns of drug sensitivities, investigation of the mechanistic effect of one selected drug combination on tumor spheroids and ex vivo renal tumor slice cultures showed that VHL-defective ccRCC cells were more vulnerable to the combined inhibition of the CK2 and ATM kinases than wild-type VHL cells. Importantly, we found that HIF-2α acts as a key mediator that potentiates the response to combined CK2/ATM inhibition by triggering ROS-dependent apoptosis. Importantly, our findings reveal a selective killing of VHL-deficient renal carcinoma cells and provide a rationale for a mechanism-based use of combined CK2/ATM inhibitors for improved patient care in metastatic VHL-ccRCC.

Comparing the efficacy and selectivity of Ck2 inhibitors. A phosphoproteomics approach

CK2 (an acronym derived from the misnomer "casein kinase 2") denotes a ubiquitous, highly pleiotropic protein kinase which has been implicated in global human pathologies, with special reference to cancer. A large spectrum of fairly selective, cell permeable CK2 inhibitors are available, one of which, CX4945 is already in clinical trials for the treatment of neoplasia. Another recently developed CK2 inhibitor, GO289, displays in vitro potency and selectivity comparable to CX4945. Here the cellular efficiency of these two inhibitors has been evaluated by treating C2C12 myoblasts for 5 h with each of them at 4 μM concentration and running a quantitative phosphoproteomics analysis of phosphosites affected by the two compounds. A small but significant proportion of the quantified phosphosites is decreased by treatment with CX4945 and, even more with GO289. This figure substantially increases if a subset of quantified phosphosites conforming to the CK2 consensus (pS/pT-x-x-D/E/pS/pT) is considered. Also in this case GO289 is more effective than CX4945. By adopting stringent criteria two shortlists of 70 and 35 sites whose phosphorylation is decreased >50% by GO289 and CX4945, respectively, have been generated. All these phosphosites conform to the consensus of CK2 with just sporadic exceptions. Their WebLogos are indistinguishable from that of bona fide CK2 phosphosites and their Two-Sample Logos rule out any significant contribution of Pro-directed and basophilic protein kinases to their generation. To sum up, we can conclude that by treating C2C12 cells for 5 h with either CX4945 or GO289 off-target effects are negligible since almost all the phosphosites undergoing a substantial reduction are attributable to CK2, with a higher inhibitory efficacy displayed by GO289. CX4945 and GO289 provide highly selective tools to control the CK2-dependent phosphoproteome compared with previously developed CK2 inhibitors.

Myeloid Cell CK2 Regulates Inflammation and Resistance to Bacterial Infection

Kinase activity plays an essential role in the regulation of immune cell defenses against pathogens. The protein kinase CK2 (formerly casein kinase II) is an evolutionarily conserved kinase with hundreds of identified substrates. CK2 is ubiquitously expressed in somatic and immune cells, but the roles of CK2 in regulation of immune cell function remain largely elusive. This reflects the essential role of CK2 in organismal development and limited prior work with conditional CK2 mutant murine models. Here, we generated mice with a conditional (floxed) allele of Csnk2a, which encodes the catalytic CK2α subunit of CK2. When crossed to Lyz2-cre mice, excision of Csnk2a sequence impaired CK2α expression in myeloid cells but failed to detectably alter myeloid cell development. By contrast, deficiency for CK2α increased inflammatory myeloid cell recruitment, activation, and resistance following systemic Listeria monocytogenes (Lm) infection. Results from mixed chimera experiments indicated that CK2α deficiency in only a subset of myeloid cells was not sufficient to reduce bacterial burdens. Nor did cell-intrinsic deficiency for CK2α suffice to alter accumulation or activation of monocytes and neutrophils in infected tissues. These data suggest that CK2α expression by Lyz2-expressing cells promotes inflammatory and anti-bacterial responses through effects in trans. Our results highlight previously undescribed suppressive effects of CK2 activity on inflammatory myeloid cell responses and illustrate that cell-extrinsic effects of CK2 can shape inflammatory and protective innate immune responses.

Targeting Casein Kinase 1 (CK1) in Hematological Cancers

The casein kinase 1 enzymes (CK1) form a family of serine/threonine kinases with seven CK1 isoforms identified in humans. The most important substrates of CK1 kinases are proteins that act in the regulatory nodes essential for tumorigenesis of hematological malignancies. Among those, the most important are the functions of CK1s in the regulation of Wnt pathways, cell proliferation, apoptosis and autophagy. In this review we summarize the recent developments in the understanding of biology and therapeutic potential of the inhibition of CK1 isoforms in the pathogenesis of chronic lymphocytic leukemia (CLL), other non-Hodgkin lymphomas (NHL), myelodysplastic syndrome (MDS), acute myeloid leukemia (AML) and multiple myeloma (MM). CK1δ/ε inhibitors block CLL development in preclinical models via inhibition of WNT-5A/ROR1-driven non-canonical Wnt pathway. While no selective CK1 inhibitors have reached clinical stage to date, one dual PI3Kδ and CK1ε inhibitor, umbralisib, is currently in clinical trials for CLL and NHL patients. In MDS, AML and MM, inhibition of CK1α, acting via activation of p53 pathway, showed promising preclinical activities and the first CK1α inhibitor has now entered the clinical trials.

Winter is coming: Regulation of cellular metabolism by enzyme polymerization in dormancy and disease

Metabolism feeds growth. Accordingly, metabolism is regulated by nutrient-sensing pathways that converge growth promoting signals into biosynthesis by regulating the activity of metabolic enzymes. When the environment does not support growth, organisms invest in survival. For cells, this entails transitioning into a dormant, quiescent state (G0). In dormancy, the activity of biosynthetic pathways is dampened, and catabolic metabolism and stress tolerance pathways are activated. Recent work in yeast has demonstrated that dormancy is associated with alterations in the physicochemical properties of the cytoplasm, including changes in pH, viscosity and macromolecular crowding. Accompanying these changes, numerous metabolic enzymes transition from soluble to polymerized assemblies. These large-scale self-assemblies are dynamic and depolymerize when cells resume growth. Here we review how enzyme polymerization enables metabolic plasticity by tuning carbohydrate, nucleic acid, amino acid and lipid metabolic pathways, with particular focus on its potential adaptive value in cellular dormancy.

Clinically Precedented Protein Kinases: Rationale for Their Use in Neurodegenerative Disease

Kinases are an intensively studied drug target class in current pharmacological research as evidenced by the large number of kinase inhibitors being assessed in clinical trials. Kinase-targeted therapies have potential for treatment of a broad array of indications including central nervous system (CNS) disorders. In addition to the many variables which contribute to identification of a successful therapeutic molecule, drug discovery for CNS-related disorders also requires significant consideration of access to the target organ and specifically crossing the blood-brain barrier (BBB). To date, only a small number of kinase inhibitors have been reported that are specifically designed to be BBB permeable, which nonetheless demonstrates the potential for success. This review considers the potential for kinase inhibitors in the context of unmet medical need for neurodegenerative disease. A subset of kinases that have been the focus of clinical investigations over a 10-year period have been identified and discussed individually. For each kinase target, the data underpinning the validity of each in the context of neurodegenerative disease is critically evaluated. Selected molecules for each kinase are identified with information on modality, binding site and CNS penetrance, if known. Current clinical development in neurodegenerative disease are summarized. Collectively, the review indicates that kinase targets with sufficient rationale warrant careful design approaches with an emphasis on improving brain penetrance and selectivity.

"Janus" efficacy of CX-5011: CK2 inhibition and methuosis induction by independent mechanisms

Methuosis has been described as a distinctive form of cell death characterized by the displacement of large fluid-filled vacuoles derived from uncontrolled macropinocytosis. Its induction has been proposed as a new strategy against cancer cells. Small molecules, such as indole-based calchones, have been identified as methuosis inducers and, recently, the CK2 inhibitor CX-4945 has been shown to have a similar effect on different cell types. However, the contribution of protein kinase CK2 to methuosis signalling is still controversial. Here we show that methuosis is not related to CK2 activity since it is not affected by structurally unrelated CK2 inhibitors and genetic reduction/ablation of CK2 subunits. Interestingly, CX-5011, a CK2 inhibitor related to CX-4945, behaves as a CK2-independent methuosis inducer, four times more powerful than its parental compound and capable to promote the formation on enlarged cytosolic vacuoles at low micromolar concentrations. We show that pharmacological inhibition of the small GTPase Rac-1, its downregulation by siRNA treatment, or the over-expression of the dominant-negative mutated form of Rac-1 (Rac-1 T17N), impairs CX-5011 ability to induce methuosis. Furthermore, cell treatment with CX-5011 induces a durable activation of Rac-1 that persists for at least 24 h. Worthy of note, CX-5011 is able to promote macropinocytosis not only in mammalian cells, but also in an in-vivo zebrafish model. Based on these evidences, CX-5011 is, therefore, proposed as a potential promising compound for cancer therapies for its dual efficacy as an inhibitor of the pro-survival kinase CK2 and inducer of methuosis.

Exploring Kinase Inhibition Properties of 9H-pyrimido[5,4-b]- and [4,5-b]indol-4-amine Derivatives

We previously highlighted the interest in 6,5,6-fused tricyclic analogues of 4-aminoquinazolines as kinase inhibitors in the micromolar to the nanomolar range of IC₅₀ values. For the generation of chemical libraries, the formamide-mediated cyclization of the cyanoamidine precursors was carried out under microwave irradiation in an eco-friendly approach. In order to explore more in-depth the pharmacological interest in such tricyclic skeletons, the central five member ring, i.e., thiophène or furan, was replaced by a pyrrole to afford 9H-pyrimido[5,4-b]- and [4,5-b]indol-4-amine derivatives inspired from harmine. The inhibitory potency of the final products was determined against four protein kinases (CDK5/p25, CK1δ/ε, GSK3α/β, and DYRK1A). As a result, we have identified promising compounds targeting CK1δ/ε and DYRK1A and displaying micromolar and submicromolar IC₅₀ values.

Motor neuron preservation and decrease of in vivo TDP-43 phosphorylation by protein CK-1δ kinase inhibitor treatment

Pathogenesis of amyotrophic lateral sclerosis (ALS), a devastating disease where no treatment exists, involves the compartmentalization of the nuclear protein TDP-43 (TAR DNA-binding protein 43) in the cytoplasm which is promoted by its aberrant phosphorylation and others posttranslational modifications. Recently, it was reported that CK-1δ (protein casein kinase-1δ) is able to phosphorylate TDP-43. Here, the preclinical efficacy of a benzothiazole-based CK-1δ inhibitor IGS-2.7, both in a TDP-43 (A315T) transgenic mouse and in a human cell-based model of ALS, is shown. Treatment with IGS-2.7 produces a significant preservation of motor neurons in the anterior horn at lumbar level, a decrease in both astroglial and microglial reactivity in this area, and in TDP-43 phosphorylation in spinal cord samples. Furthermore, the recovery of TDP-43 homeostasis (phosphorylation and localization) in a human-based cell model from ALS patients after treatment with IGS-2.7 is also reported. Moreover, we have shown a trend to increase in CK-1δ mRNA in spinal cord and significantly in frontal cortex of sALS cases. All these data show for the first time the in vivo modulation of TDP-43 toxicity by CK-1δ inhibition with IGS-2.7, which may explain the benefits in the preservation of spinal motor neurons and point to the relevance of CK-1δ inhibitors in a future disease-modifying treatment for ALS.

Two Novel FAM20C Variants in A Family with Raine Syndrome

Two siblings from a Mexican family who carried lethal Raine syndrome are presented. A newborn term male (case 1) and his 21 gestational week brother (case 2), with a similar osteosclerotic pattern: generalized osteosclerosis, which is more evident in facial bones and cranial base. Prenatal findings at 21 weeks and histopathological features for case 2 are described. A novel combination of biallelic FAM20C pathogenic variants were detected, a maternal cytosine duplication at position 456 and a paternal deletion of a cytosine in position 474 in exon 1, which change the reading frame with a premature termination at codon 207 and 185 respectively. These changes are in concordance with a negative detection of the protein in liver and kidney as shown in case 2. Necropsy showed absence of pancreatic Langerhans Islets, which are reported here for the first time. Corpus callosum absence is added to the few reported cases of brain defects in Raine syndrome. This report shows two new FAM20C variants not described previously, and negative protein detection in the liver and the kidney. We highlight that lethal Raine syndrome is well defined as early as 21 weeks, including mineralization defects and craniofacial features. Pancreas and brain defects found here in FAM20C deficiency extend the functional spectrum of this protein to previously unknown organs.

Recent Advances in the Discovery of CK2 Allosteric Inhibitors: From Traditional Screening to Structure-Based Design

Protein kinase (CK2) has emerged as an attractive cancer therapeutic target and recent efforts have been made to develop its inhibitors. However, the development of selective inhibitors remains challenging because of the highly conserved ATP-binding pocket (orthosteric site) of kinase family. As an alternative strategy, allosteric inhibitors, by targeting the much more diversified allosteric site relative to the conserved ATP-binding site, achieve better pharmacological advantages than orthosteric inhibitors. Traditional serendipitous screening and structure-based design are robust tools for the discovery of CK2 allosteric inhibitors. In this review, we summarize the recent advances in the identification of CK2 allosteric inhibitors. Firstly, we briefly present the CK2 allosteric sites. Then, the allosteric inhibitors targeting the well-elucidated allosteric sites (α/β interface, αD pocket and interface between the Glycine-rich loop and αC-helix) are highlighted in the discovery process and possible binding modes with the allosteric sites are described. This study is expected to provide valuable clues for the design of CK2 allosteric inhibitors.

Identification and Biological Evaluation of CK2 Allosteric Fragments through Structure-Based Virtual Screening

Casein kinase II (CK2) is considered as an attractive cancer therapeutic target, and recent efforts have been made to develop its ATP-competitive inhibitors. However, achieving selectivity with respect to related kinases remains challenging due to the highly conserved ATP-binding pocket of kinases. Allosteric inhibitors, by targeting the much more diversified allosteric site relative to the highly conserved ATP-binding pocket, might be a promising strategy with the enhanced selectivity and reduced toxicity than ATP-competitive inhibitors. The previous studies have highlighted the traditional serendipitousity of discovering allosteric inhibitors owing to the complicate allosteric modulation. In this current study, we identified the novel allosteric inhibitors of CK2α by combing structure-based virtual screening and biological evaluation methods. The structure-based pharmacophore model was built based on the crystal structure of CK2α-compound 15 complex. The ChemBridge fragment library was searched by evaluating the fit values of these molecules with the optimized pharmacophore model, as well as the binding affinity of the CK2α-ligand complexes predicted by Alloscore web server. Six hits forming the holistic interaction mechanism with the αD pocket were retained after pharmacophore- and Alloscore-based screening for biological test. Compound 3 was found to be the most potent non-ATP competitive CK2α inhibitor (IC50 = 13.0 μM) with the anti-proliferative activity on A549 cancer cells (IC50 = 23.1 μM). Our results provide new clues for further development of CK2 allosteric inhibitors as anti-cancer hits.

Kinase and GPCR polypharmacological approach for the identification of efficient anticancer medicines

Discovery of an anticancer medicine using a single target protein has often been unsuccessful due to the complexity of pathogenic mechanisms as well as the presence of redundant signaling pathways. In this work, we attempted to find promising anticancer drug candidates by simultaneously targeting casein kinase 1 delta (CK1δ) and muscarinic acetylcholine receptor M3 (M3R). Through the structure-based virtual screening and de novo design with the modified potential function for protein-ligand binding, a series of benzo[4,5]imidazo[1,2-a][1,3,5]triazine-2-amine (BITA) derivatives were identified as CK1δ inhibitors and also as M3R antagonists. The biochemical potencies of these bifunctional molecules reached the nanomolar and low-micromolar levels with respect to CK1δ and M3R, respectively. A common interaction feature in the calculated CK1δ-inhibitor and M3R-antagonist complexes is that the BITA moiety is well-stabilized in the orthosteric site of M3R and the hinge region of CK1δ through the establishment of the three hydrogen bonds and the hydrophobic contacts in the vicinity. The computational and experimental results found in this work exemplify the efficiency of kinase and GPCR polypharmacology in developing anticancer medicines.

The protein kinase CK2 contributes to the malignant phenotype of cholangiocarcinoma cells

Cholangiocarcinoma (CCA) is a particularly aggressive hepatobiliary malignancy, for which the molecular mechanisms underlying the malignant phenotype are still poorly understood, and novel and effective therapeutic strategies are limited. The pro-survival protein kinase CK2 is frequently overexpressed in cancer and is receiving increasing interest as an anti-tumor drug target. Its precise role in CCA biology is still largely unknown. Here we show that expression of the CK2α and α' catalytic subunits and of the β regulatory subunit is increased in human CCA samples. Increased expression of CK2 subunits was shown in CCA cell lines compared to non-transformed cholangiocytes. We used chemical inhibition of CK2 and genetic modification by CRISPR/Cas9 to explore the contribution of CK2 to the malignant phenotype of CCA cells. Disruption of CK2 activity results in cell death through apoptosis, reduced invasion and migration potential, and G0/G1 cell cycle arrest. Importantly, CCA cells with a reduced CK2 activity are more sensitive to chemotherapy. Altogether, our results demonstrate that CK2 significantly contributes to increased proliferative potential and augmented growth of CCA cells and indicate the rationale for its targeting as a promising pharmacologic strategy for cholangiocarcinoma.

A Journey through the Cytoskeleton with Protein Kinase CK2

Substrate pleiotropicity, a very acidic phosphorylation consensus sequence, and an apparent uncontrolled activity, are the main features of CK2, a Ser/Thr protein kinase that is required for a plethora of cell functions. Not surprisingly, CK2 appears to affect cytoskeletal structures and correlated functions such as cell shape, mechanical integrity, cell movement and division. This review outlines our current knowledge of how CK2 regulates cytoskeletal structures, and discusses involved pathways and molecular mechanisms.

Role of protein kinase CK2 in antitumor drug resistance

Drug resistance represents the major reason of pharmacological treatment failure. It is supported by a broad spectrum of mechanisms, whose molecular bases have been frequently correlated to aberrant protein phosphorylation. CK2 is a constitutively active protein kinase which phosphorylates hundreds of substrates; it is expressed in all cells, but its level is commonly found higher in cancer cells, where it plays anti-apoptotic, pro-migration and pro-proliferation functions. Several evidences support a role for CK2 in processes directly responsible of drug resistance, such as drug efflux and DNA repair; moreover, CK2 intervenes in signaling pathways which are crucial to evade drug response (as PI3K/AKT/PTEN, NF-κB, β-catenin, hedgehog signaling, p53), and controls the activity of chaperone machineries fundamental in resistant cells. Interestingly, a panel of specific and effective inhibitors of CK2 is available, and several examples are known of their efficacy in resistant cells, with synergistic effect when used in combination with conventional drugs, also in vivo. Here we analyze and discuss evidences supporting the hypothesis that CK2 targeting represents a valuable strategy to overcome drug resistance.

CK2 Pro-Survival Role in Prostate Cancer Is Mediated via Maintenance and Promotion of Androgen Receptor and NFκB p65 Expression

The prosurvival protein kinase CK2, androgen receptor (AR), and nuclear factor kappa B (NFκB) interact in the function of prostate cells, and there is evidence of crosstalk between these signals in the pathobiology of prostate cancer (PCa). As CK2 is elevated in PCa, and AR and NFκB are involved in the development and progression of prostate cancer, we investigated their interaction in benign and malignant prostate cells in the presence of altered CK2 expression. Our results show that elevation of CK2 levels caused increased levels of AR and NFκB p65 in prostate cells of different phenotypes. Analysis of TCGA PCa data indicated that AR and CK2α RNA expression are strongly correlated. Small molecule inhibition or molecular down-regulation of CK2 caused reduction in AR mRNA expression and protein levels in PCa cells and in orthotopic xenograft tumors by various pathways. Among these, regulation of AR protein stability plays a unifying role in CK2 maintenance of AR protein levels. Our results show induction of various endoplasmic reticulum stress signals after CK2 inhibition, which may play a role in the PCa cell death response. Of note, CK2 inhibition caused loss of cell viability in both parental and enzalutamide-resistant castrate-resistant PCa cells. The present work elucidates the specific link of CK2 to the pathogenesis of PCa in association with AR and NFκB expression; further, the observation that inhibition of CK2 can exert a growth inhibitory effect on therapy-resistant PCa cells emphasizes the potential utility of CK2 inhibition in patients who are on enzalutamide treatment for advanced cancer.