Association of protein kinase CK2 inhibition with cellular radiosensitivity of non-small cell lung cancer

Identification of potential inhibitors of casein kinase 2 alpha of Plasmodium falciparum with potent in vitro activity

Drug resistance to commercially available antimalarials is a major obstacle in malaria control and elimination, creating the need to find new antiparasitic compounds with novel mechanisms of action. The success of kinase inhibitors for oncological treatments has paved the way for the exploitation of protein kinases as drug targets in various diseases, including malaria. Casein kinases are ubiquitous serine/threonine kinases involved in a wide range of cellular processes such as mitotic checkpoint signaling, DNA damage response, and circadian rhythm. In Plasmodium, it is suggested that these protein kinases are essential for both asexual and sexual blood-stage parasites, reinforcing their potential as targets for multi-stage antimalarials. To identify new putative PfCK2α inhibitors, we utilized an in silico chemogenomic strategy involving virtual screening with docking simulations and quantitative structure-activity relationship predictions. Our investigation resulted in the discovery of a new quinazoline molecule (542), which exhibited potent activity against asexual blood stages and a high selectivity index (>100). Subsequently, we conducted chemical-genetic interaction analysis on yeasts with mutations in casein kinases. Our chemical-genetic interaction results are consistent with the hypothesis that 542 inhibits yeast Cka1, which has a hinge region with high similarity to PfCK2α. This finding is in agreement with our in silico results suggesting that 542 inhibits PfCK2α via hinge region interaction.

Strategies of Targeting CK2 in Drug Discovery: Challenges, Opportunities, and Emerging Prospects

CK2 (casein kinase 2) is a serine/threonine protein kinase that is ubiquitous in eukaryotic cells and plays important roles in a variety of cellular functions, including cell growth, apoptosis, circadian rhythms, DNA damage repair, transcription, and translation. CK2 is involved in cancer pathogenesis and the occurrence of many diseases. Therefore, targeting CK2 is a promising therapeutic strategy. Although many CK2-specific small-molecule inhibitors have been developed, only CX-4945 has progressed to clinical trials. In recent years, novel CK2 inhibitors have gradually become a research hotspot, which is expected to overcome the limitations of traditional inhibitors. Herein, we summarize the structure, biological functions, and disease relevance of CK2 and emphatically analyze the structure-activity relationship (SAR) and binding modes of small-molecule CK2 inhibitors. We also discuss the latest progress of novel strategies, providing insights into new drugs targeting CK2 for clinical practice.

CIGB-300 Anticancer Peptide Differentially Interacts with CK2 Subunits and Regulates Specific Signaling Mediators in a Highly Sensitive Large Cell Lung Carcinoma Cell Model

Large cell lung carcinoma (LCLC) is one form of NSCLC that spreads more aggressively than some other forms, and it represents an unmet medical need. Here, we investigated for the first time the effect of the anti-CK2 CIGB-300 peptide in NCI-H460 cells as an LCLC model. NCI-H460 cells were highly sensitive toward CIGB-300 cytotoxicity, reaching a peak of apoptosis at 6 h. Moreover, CIGB-300 slightly impaired the cell cycle of NCI-H460 cells. The CIGB-300 interactomics profile revealed in more than 300 proteins that many of them participated in biological processes relevant in cancer. Interrogation of the CK2 subunits targeting by CIGB-300 indicated the higher binding of the peptide to the CK2α' catalytic subunit by in vivo pull-down assays plus immunoblotting analysis and confocal microscopy. The down-regulation of both phosphorylation and protein levels of the ribonuclear protein S6 (RPS6) was observed 48 h post treatment. Altogether, we have found that NCI-H460 cells are the most CIGB-300-sensitive solid tumor cell line described so far, and also, the findings we provide here uncover novel features linked to CK2 targeting by the CIGB-300 anticancer peptide.

Circadian clock-based therapeutics in chronic pulmonary diseases

The circadian clock is the biochemical oscillator that orchestrates the observable circadian rhythms in physiology and behavior. Disruption of the circadian clock in the lungs during chronic pulmonary diseases is considered one of the key etiological risk factors that drive pathobiology. Preclinical studies support that pharmacological manipulation of the circadian clock is a conceivable approach for the development of novel clock-based therapeutics. Despite recent advances, no effort has been undertaken to integrate novel findings for the treatment and management of chronic lung diseases. We, therefore, recognize the need to discuss the candidate clock genes that can be potentially targeted for therapeutic intervention. Here, we aim to create the first roadmap that will advance the development of circadian- clock-based therapeutics that may provide better outcomes in treating chronic pulmonary diseases.

Targeting CK2 in cancer: a valuable strategy or a waste of time?

CK2 is a protein kinase involved in several human diseases (ranging from neurological and cardiovascular diseases to autoimmune disorders, diabetes, and infections, including COVID-19), but its best-known implications are in cancer, where it is considered a pharmacological target. Several CK2 inhibitors are available and clinical trials are underway in different cancer types. Recently, the suitability of CK2 as a broad anticancer target has been questioned by the finding that a newly developed compound, named SGC-CK2-1, which is more selective than any other known CK2 inhibitor, is poorly effective in reducing cell growth in different cancer lines, prompting the conclusion that the anticancer efficacy of CX-4945, the commonly used clinical-grade CK2 inhibitor, is to be attributed to its off-target effects. Here we perform a detailed scrutiny of published studies on CK2 targeting and a more in-depth analysis of the available data on SGC-CK2-1 vs. CX-4945 efficacy, providing a different perspective about the actual reliance of cancer cells on CK2. Collectively taken, our arguments would indicate that the pretended dispensability of CK2 in cancer is far from having been proved and warn against premature conclusions, which could discourage ongoing investigations on a potentially valuable drug target.

Pink1/PARK2/mROS-Dependent Mitophagy Initiates the Sensitization of Cancer Cells to Radiation

Autophagy plays a double-edged sword for cancer; particularly, mitophagy plays important roles in the selective degradation of damaged mitochondria. However, whether mitophagy is involved in killing effects of tumor cells by ionizing radiation (IR) and its underlying mechanism remain elusive. The purpose is to evaluate the effects of mitochondrial ROS (mROS) on autophagy after IR; furthermore, we hypothesized that KillerRed (KR) targeting mitochondria could induce mROS generation, subsequent mitochondrial depolarization, accumulation of Pink1, and recruitment of PARK2 to promote the mitophagy. Thereby, we would achieve a new strategy to enhance mROS accumulation and clarify the roles and mechanisms of radiosensitization by KR and IR. Our data demonstrated that IR might cause autophagy of both MCF-7 and HeLa cells, which is related to mitochondria and mROS, and the ROS scavenger N-acetylcysteine (NAC) could reduce the effects. Based on the theory, mitochondrial targeting vector sterile α- and HEAT/armadillo motif-containing protein 1- (Sarm1-) mtKR has been successfully constructed, and we found that ROS levels have significantly increased after light exposure. Furthermore, mitochondrial depolarization of HeLa cells was triggered, such as the decrease of Na⁺K⁺ ATPase, Ca²⁺Mg²⁺ ATPase, and mitochondrial respiratory complex I and III activities, and mitochondrial membrane potential (MMP) has significantly decreased, and voltage-dependent anion channel 1 (VDAC1) protein has significantly increased in the mitochondria. Additionally, HeLa cell proliferation was obviously inhibited, and the cell autophagic rates dramatically increased, which referred to the regulation of the Pink1/PARK2 pathway. These results indicated that mitophagy induced by mROS can initiate the sensitization of cancer cells to IR and might be regulated by the Pink1/PARK2 pathway.

In Vivo Evaluation of Combined CK2 Inhibition and Irradiation in Human WiDr Tumours

BACKGROUND/AIM

Casein kinase 2 (CK2) which sustains multiple pro-survival functions in cellular DNA-damage response, is strictly regulated in normal cells but elevated in cancer. CK2 is considered as a potential therapeutic target, and its inhibition has been associated with radiosensitization in mammalian cells in vitro. Here, we investigated potential radiosensitization by CK2 inhibition in vivo.

MATERIALS AND METHODS

The effect of CK2 inhibition in vivo was investigated in human WiDr-xenograft tumours grown subcutaneously on BALB/c nu/nu mice with and without fractionated irradiation. CK2 inhibition was performed using the specific inhibitor tetra-bromobenzotriazole (TBB). Histological examinations included staining for apoptosis and double-strand breaks.

RESULTS

Both TBB treatment alone and radiation alone significantly reduced tumour growth, which was reflected by increased apoptosis rates. However, TBB treatment did not boost radiation-induced tumour growth suppression in combined treatment, although the apoptosis rate increased and repair of double-strand breaks was reduced. This was in stark contrast to previous data on in vitro radiosensitization.

CONCLUSION

The absence of radiosensitization by CK2 inhibition should be investigated in different tumour models.

MicroRNA-499 serves as a sensitizer for lung cancer cells to radiotherapy by inhibition of CK2α-mediated phosphorylation of p65

The present study aimed to define the tumor-suppressive role of microRNA-499 (miR-499) in lung cancer cells and its underlying mechanism. First, qRT-PCR analysis revealed poor expression of miR-499 in clinical samples and cell lines of lung cancer. Next, we performed loss- and gain-of-function experiments for the expression of miR-499 in lung cancer cells exposed to irradiation (IR) to determine the effect of miR-499 expression on cell viability and apoptosis as well as tumor growth. Results showed that overexpression of miR-499 inhibited cell viability, enhanced the radiosensitivity of lung cancer cells, and promoted cell apoptosis under IR. Furthermore, CK2α was verified to be a target of miR-499, and miR-499 was identified to repress p65 phosphorylation by downregulating CK2α expression, which ultimately diminished the survival rate of lung cancer cells under IR. Collectively, the key findings of the study illustrate the tumor-inhibiting function of miR-499 and confirmed that miR-499-mediated CK2α inhibition and altered p65 phosphorylation enhances the sensitivity of lung cancer cells to IR.

Genome Profiling for Aflatoxin B1 Resistance in Saccharomyces cerevisiae Reveals a Role for the CSM2/SHU Complex in Tolerance of Aflatoxin B1-Associated DNA Damage

Exposure to the mycotoxin aflatoxin B1 (AFB₁) strongly correlates with hepatocellular carcinoma (HCC). P450 enzymes convert AFB₁ into a highly reactive epoxide that forms unstable 8,9-dihydro-8-(N7-guanyl)-9-hydroxyaflatoxin B1 (AFB₁-N ⁷-Gua) DNA adducts, which convert to stable mutagenic AFB₁ formamidopyrimidine (FAPY) DNA adducts. In CYP1A2-expressing budding yeast, AFB₁ is a weak mutagen but a potent recombinagen. However, few genes have been identified that confer AFB₁ resistance. Here, we profiled the yeast genome for AFB₁ resistance. We introduced the human CYP1A2 into ∼90% of the diploid deletion library, and pooled samples from CYP1A2-expressing libraries and the original library were exposed to 50 μM AFB₁ for 20 hs. By using next generation sequencing (NGS) to count molecular barcodes, we initially identified 86 genes from the CYP1A2-expressing libraries, of which 79 were confirmed to confer AFB₁ resistance. While functionally diverse genes, including those that function in proteolysis, actin reorganization, and tRNA modification, were identified, those that function in postreplication DNA repair and encode proteins that bind to DNA damage were over-represented, compared to the yeast genome, at large. DNA metabolism genes also included those functioning in checkpoint recovery and replication fork maintenance, emphasizing the potency of the mycotoxin to trigger replication stress. Among genes involved in postreplication repair, we observed that CSM2, a member of the CSM2 (SHU) complex, functioned in AFB₁-associated sister chromatid recombination while suppressing AFB₁-associated mutations. These studies thus broaden the number of AFB₁ resistance genes and have elucidated a mechanism of error-free bypass of AFB₁-associated DNA adducts.

Litopenaeus vannamei CK2 is involved in shrimp innate immunity by modulating hemocytes apoptosis

Protein kinase CK2 (CK2) is a ubiquitous serine/threonine kinase with multiple cellular functions in vertebrates including apoptosis, differentiation, proliferation, survival, tumorigenesis, signal transduction, immune regulation and inflammation. In the current study, the catalytic and regulatory subunit homologs of Litopenaeus vannamei protein kinase CK2 (LvCK2α and LvCK2β) were cloned and characterized. LvCK2α has a full-length cDNA sequence of 1764 bp with a 1053 bp open reading frame (ORF) encoding a putative protein of 351 amino acids, which contains a typical serine/threonine kinase domain. On the other hand, LvCK2β has a 1394 bp full-length cDNA with an ORF of 663 bp encoding a protein with 221 amino acids, which contains a Casein kinase II regulatory subunit domain. Sequence and phylogenetic analysis revealed that LvCK2 was evolutionary related with the CK2 of invertebrates. Quantitative reverse transcription PCR (RT-qPCR) analysis showed that LvCK2α and LvCK2β transcripts were widely expressed in all shrimp tissues tested, and were both induced in hemocytes and hepatopancreas upon challenge with Vibrio parahaemolyticus, Streptoccocus iniae, lipopolysaccharide (LPS), and white spot syndrome virus (WSSV), suggesting their involvement in shrimp immune response. Moreover, RNA interference (RNAi) of LvCK2α resulted in increased hemocytes apoptosis, shown by high caspase 3/7 activity, increased number of apoptotic cells, coupled with an elevation in transcript levels of pro-apoptotic LvCaspase3 and LvCytochrome C, and a reduction in mRNA levels of pro-survival LvBcl2, LvIAP1, and LvIAP2. In addition, LvCK2α knockdown followed by V. parahaemolyticus challenge resulted in higher cumulative mortality of shrimp. Taken together, our current findings suggest that LvCK2 modulates shrimp hemocytes apoptosis as part of the innate immune response to pathogens.

The effect of ionizing radiation on the subcellular localization and kinase activity of protein kinase CK2 in human non-small cell lung cancer cells

Protein kinase CK2 is a ubiquitously expressed kinase in eukaryotes, which is known to phosphorylate many protein substrates. Because CK2 is involved in the regulation of various signaling pathways, we wondered whether CK2 participated in the regulation of ionizing radiation (IR) induced biological process. In this study, we investigated the effect of IR on the subcellular localization and kinase activity in human non-small cell lung cancer (NSCLC) cells. Immunofluorescent results showed that CK2 subunits shuttle into the nucleus mostly beginning 1 h after IR and lasting more than 6 h. We also conducted in vitro kinase assay and observed an increase in CK2 kinase activity at 6 h after IR. Furthermore, an increase in S phase was observed at 6 h after IR. Colony formation assay results demonstrated that CK2 inhibitor CX-4945 significantly enhanced the effect of irradiation in NSCLC cells. These results indicated that CK2 may be implicated in the regulation of IR-induced biological process.

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.

Quinalizarin, a specific CK2 inhibitor, can reduce icotinib resistance in human lung adenocarcinoma cell lines

The abnormal activation of the downstream signaling pathways of epidermal growth factor receptor (EGFR) that are independent of EGFR, contribute to the acquisition of EGFR-tyrosine kinase inhibitor (TKI) resistance in non-small cell lung cancer (NSCLC). The serine/threonine protein kinase casein kinase II (CK2) phosphorylates and modulates several members of the EGFR downstream signaling pathways. Thus, the purpose of the current study was to investigate the effects of the addition of quinalizarin (a specific CK2 inhibitor) to icotinib (an EGFR-TKI) on the proliferation and apoptosis of four NSCLC cell lines and its underlying mechanisms. The human lung adenocarcinoma cell lines HCC827, A549, H1650 and H1975 were employed to represent the EGFR-TKI-sensitive EGFR (EGFR-sensitive) mutation, wild-type EGFR and the EGFR-TKI-resistant EGFR (EGFR-resistant) mutations. The cell viability was determined by the MTT assay. Cell apoptosis was detected by flow cytom-etry using the Annexin V-enhanced green fluorescent protein Apoptosis Detection kit. The level of proteins in the EGFR downstream pathway was observed using a western blot assay. The results showed that the cells with the EGFR-sensitive mutation (HCC827, EGFR E716-A750del) were more sensitive to icotinib compared with those possessing the EGFR wild-type (A549) and the EGFR-resistant mutations (H1650, EGFR E716-A750del and PTEN lost; H1975, EGFR L858R+T790M). Quinalizarin inhibited proliferation and promoted apoptosis in the cells with the EGFR wild-type and resistant mutations, and the addition of quinalizarin to icotinib partially restored their sensitivity to icotinib. Quinalizarin and/or icotinib increased the apoptotic rates in the EGFR-TKI resistant cells, and the combination of these reduced the level of protein downstream of EGFR, including phosphorylated (p-AKT) and p-(ERK). In conclusion, quinalizarin may partially sensitize cells to icotinib by inhibiting proliferation and promoting apoptosis mediated by AKT and ERK in EGFR-TKI resistant NSCLC cell lines.

DNA‑PKcs inhibitor increases the sensitivity of gastric cancer cells to radiotherapy

Gastric cancer (GC) is a severe public health problem worldwide, particularly in China. Radiotherapy is the main locoregional treatment for various types of unresectable tumor, including GC. However, many patients fail to respond to radiotherapy due to the intrinsic radioresistance of cancer cells. This study was designed to investigate the effects and potential mechanism of radiosensitization associated with DNA-dependent protein kinase catalytic subunit (DNA-PKcs) inhibitor in human GC cell lines in vitro. Among the six GC cell lines (SGC7901, HGC-27, MKN45, MKN74, BGC823 and MGC803) that were exposed to increasing doses of IR (0, 2, 4, 6 and 8 Gy), the mean lethal dose and quasi-threshold dose measurements indicated that BGC823 and MGC803 were relatively insensitive to ionizing radiation (IR). IR induced significant elevation of γ H2A histone family member X (γH2AX) in MKN45 cells compared with BGC823 cells. DNA-PKcs and phospho-DNA-PKcs protein levels were increased in BGC823 and MGC803 cells compared with other GC cell lines (SGC7901, HGC-27, MKN45 and MKN74). DNA-PKcs inhibition led to increased sensitivity of BGC823 and MGC803 cells to IR. NU7441 increased γH2AX expression in the nuclei of BGC823 cells following IR. Combination of DNA-PKcs and CK2 inhibition further increased the sensitivity of GC cells to IR. The combination of NU7441 and CX4945 increased γH2AX expression in the nucleus of BGC823 cells following IR compared with treatment with NU7441 alone. Taken together, the findings suggest that DNA-PKcs inhibitor increased the sensitivity of radioresistant BGC823 and MGC803 cells to radiotherapy through the cleaved-caspase3/γH2AX signaling pathway, thus presenting a potential treatment method for GC.

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.

Mitochondrial Dysfunctions Regulated Radioresistance through Mitochondria-to-Nucleus Retrograde Signaling Pathway of NF-κB/PI3K/AKT2/mTOR

We investigated the relationship between significantly different genes of the mitochondria-to-nucleus retrograde signaling pathway (RTG) in H1299 ρ⁰ cells (mtDNA depleted cell) and compared their radiosensitivity to that of parental ρ⁺ cells, to determine the possible intervention targets of radiosensitization. ρ⁰ cells were depleted of mitochondrial DNA by chronic culturing in ethidium bromide at low concentration. Radiosensitivity was analyzed using clonogenic assay. Western blot was used to analyze the cell cycle-related proteins, serine/threonine kinase ataxia telangiectasia mutant (ATM), ataxia telangiectasia and Rad3-related protein (ATR) and cyclin B1 (CCNB1). The γ-H2AX foci were detected using confocal fluorescence microscopy. RNA samples were hybridized using the Agilent human genome expression microarray. The Kyoto Encyclopedia of Genes and Genomes (KEGG) database was used for Gene Ontology (GO) Consortium and pathway annotations of differentially expressed genes, respectively. The H1299 ρ⁰ cells were found to be more radioresistant than ρ⁺ cells. The ATP production of H1299 ρ⁰ cells was lower than that of the ρ⁺ cells before or after irradiation. Both H1299 ρ⁰ and ρ⁺ cells had higher ROS levels after irradiation, however, the radiation-induced ROS production in ρ⁰ cells was significantly lower than in ρ⁺ cells. In addition, the percentage of apoptosis in H1299 ρ⁰ cells was lower than in ρ⁺ cells after 6 Gy irradiation. As for the cell cycle and DNA damage response-related proteins ATM, ATR and CCNB1, the expression levels in ρ⁰ cells were significantly higher than in ρ⁺ cells, and there were less γ-H2AX foci in the ρ⁰ than ρ⁺ cells after irradiation. Furthermore, the results of the human genome expression microarray demonstrated that the phosphorylated protein levels of the NF-κB/PI3K/AKT2/mTOR signaling pathway were increased after 6 Gy irradiation and were decreased after treatment with the AKT2-specific inhibitor MK-2206 combined with radiation in H1299 ρ⁰ cells. MK-2206 treatment also led to an increase in pro-apoptotic proteins. In conclusion, these results demonstrate that mtDNA depletion might activate the mitochondria-to-nucleus retrograde signaling pathway of NF-κB/PI3K/AKT2/mTOR and induce radioresistance in H1299 ρ⁰ cells by evoking mitochondrial dysfunctions.