Discovery of 5-(3-Chlorophenylamino)benzo[c][2,6]naphthyridine Derivatives as Highly Selective CK2 Inhibitors with Potent Cancer Cell Stemness Inhibition

Discovery of 2,4-dianilinopyrimidine derivatives as novel p90 ribosomal S6 protein kinase (RSK) inhibitors

RSK, or p90 ribosomal S6 kinase, plays a crucial role in tumor cell proliferation and survival, making it an appealing target for cancer therapies. With the aim to explore novel RSK inhibitors as anticancer agents, a series of 2,4-dianilinopyrimidine derivatives 2b-2n and 3a-3n have been designed and synthesized. Among them, compound 3e displayed substantial kinase inhibitory activity against RSK2 (IC50 = 37.89 ± 3.08 nM) and a potent antiproliferative effect against a range of cell lines, including HeLa, MIA PaCa-2, U937, SW620, HT-29, AGS, and two kinds of EGFR mutant cells (IC50s = 0.189-0.572 μM). Additionally, compound 3e exhibited a high affinity for RSK and effectively inhibited RSK activity in HeLa cells. It triggered significant apoptosis and caused cell cycle arrest in the G2/M phase. Moreover, 3e displayed considerable in vivo anticancer activity while maintaining an acceptable safety profile. These findings imply that compound 3e, featuring a 2,4-dianilinopyrimidine scaffold, could serve as a promising RSK inhibitor for cancer treatment.

CK2α-mediated phosphorylation of DUB3 promotes YAP1 stability and oncogenic functions

The aberrant upregulation of Yes-associated protein 1 (YAP1) in a variety of solid cancers contributes to tumor progression and poor clinical outcomes, rendering it an appealing therapeutic target. However, effective therapies to directly target YAP1 remain challenging. In this study, we perform a high-throughput screening and identify Casein kinase II (CK2) as an uncharacterized upstream regulator of YAP1 turnover in cancer cells of ovarian cancer and several other cancer types. Pharmacological inhibition of Casein kinase II by Silmitasertib or genetic depletion of the catalytic subunit of Casein kinase II (CK2α) markedly destabilizes YAP1 and consequently suppresses its oncogenic functions in vitro and in vivo. Moreover, we reveal that DUB3 as a bona fide deubiquitinase of YAP1, which functionally links CK2 and YAP1 stability in a variety of human cancers. Mechanistically, CK2α directly phosphorylates DUB3 at Thr495, thereby facilitating DUB3-mediated deubiquitination process of YAP1. On the contrary, the loss of Thr495 phosphorylation by the phosphorylation-defective mutant DUB3 T495A, the cancer-related mutant DUB3 D496H and CK2 inhibition failed to deubiquitinate and stabilize YAP1 effectively. Notably, upregulated expressions of CK2α and DUB3 in ovarian cancer positively correlate with YAP1 overexpression. Collectively, our findings demonstrate the functional significance of the CK2α-DUB3 axis in YAP1 stabilization and YAP1-driven tumor progression, highlighting that strategies to target this axis might be of benefit in the clinical management of ovarian cancer and several other lethal cancers with aberrantly upregulated YAP1.

Novel Pt(IV) complexes containing salvigenin ligand reverse cisplatin-induced resistance by inhibiting Rap1b-mediated cancer cell stemness in esophageal squamous cell carcinoma treatments

Esophageal squamous cell carcinoma (ESCC) is a malignant tumor that is highly susceptible to metastasis, recurrence and resistance, and few therapeutic targets have been identified and proven effective. Herein, we demonstrated for the first time that Rap1b can positively regulate ESCC cell stemness, as well as designed and synthesized a novel class of Pt(IV) complexes that can effectively inhibit Raplb. In vitro biological studies showed that complex-1 exhibited stronger cytotoxicity than cisplatin and oxaliplatin against a variety of ESCC cells, and effectively reversed cisplatin-induced resistance of TE6 cells by increasing cellular accumulation of platinum and inhibiting cancer cell stemness. Significantly, complex-1 also exhibited strong ability to reversal cisplatin-induced cancer cell resistance and inhibit tumor growth in TE6/cDDP xenograft mice models, with a tumor growth inhibition rate of 73.3 % at 13 mg/kg and did not show significant systemic toxicity. Overall, Rap1b is a promising target to be developed as an effective treatment for ESCC. Complex-1, as the first Pt(IV) complex that can strongly inhibit Rap1b, is also worthy of further in-depth study.

Recent Advances in the Discovery of CK2 Inhibitors

CK2 is a vital enzyme that phosphorylates a large number of substrates and thereby controls many processes in the body. Its upregulation was reported in many cancer types. Inhibitors of CK2 might have anticancer activity, and two compounds are currently under clinical trials. However, both compounds are ATP-competitive inhibitors that may have off-target side effects. The development of allosteric and dual inhibitors can overcome this drawback. These inhibitors showed higher selectivity and specificity for the CK2 enzyme compared to the ATP-competitive inhibitors. The present review summarizes the efforts exerted in the last five years in the design of CK2 inhibitors.

CK2α-mediated phosphorylation of GRP94 facilitates the metastatic cascade in triple-negative breast cancer

Distant metastasis is a significant hallmark affecting to the high death rate of patients with triple-negative breast cancer (TNBC). Thus, it is crucial to identify and develop new therapeutic strategies to hinder cancer metastasis. While emerging studies have hinted a pivotal role of glucose-regulated protein 94 (GRP94) in tumorigenesis, the exact biological functions and molecular mechanisms of GRP94 in modulating cancer metastasis remain to be elucidated. Our study demonstrated an increased expression of GRP94 in TNBC correlated with metastatic progression and unfavorable prognosis in patients. Functionally, we identified that GRP94 depletion significantly diminished TNBC tumorigenesis and subsequent lung metastasis. In contrast, GRP94 overexpression exacerbated the invasiveness, migration, and lung metastasis of non-TNBC cells. Mechanistically, we found that casein kinase 2 alpha (CK2α) active in advanced breast cancer phosphorylated GRP94 at a conserved serine 306 (S306) residue. This phosphorylation increased the stability of GRP94 and enhanced its interaction with LRP6, leading to activation of canonical Wnt signaling. From a therapeutic standpoint, we found that benzamidine, a novel CK2α inhibitor, effectively suppressed GRP94 phosphorylation, LRP6 stabilization, and metastasis of TNBC. Our results point to the critical role of CK2α-mediated GRP94 phosphorylation in TNBC metastasis through activation of Wnt signaling, highlighting GRP94 as a therapeutic target to impede TNBC metastasis.

1H-1,2,3-triazolyl-1,6-naphthyridin-7(6H)-ones as Potential Fluorescent Nucleoside Analogues: Synthesis and Optical Properties

In this article, we present the synthesis and the optical properties of three original molecules as potential fluorescent ribonucleoside analogues incorporating a 1,6-naphthyridin-7(6H)-one scaffold as a fluorescent nucleobase and a 1,2,3-triazole as a linkage. The nucleosides were prepared via a Cu alkyne-azide cycloaddition (CuAAC) reaction between a ribofuranosyl azide and a 4-ethynylpyridine partner. Construction of substituted 1,6-naphthyridin-7(6H)-ones was achieved through two additional steps. Optical property studies were investigated on nucleoside analogues. Powerful fluorescence properties have been evidenced with a remarkable change of emissivity depending on the polarity of the solvent, making these molecules suitable as a new class of artificial fluorescent nucleosides for investigating enzyme binding sites as well as probing nucleic acids. In addition, we are convinced that such analogues could be of great interest in the search for new antiviral or antitumoral drugs based on nucleosides.

Blockade of chemo-resistance to 5-FU by a CK2-targeted combination via attenuating AhR-TLS-promoted genomic instability in human colon cancer cells

As highly expressed in several human cancers, Casein Kinase 2 (CK2) is involved in chemotherapy-induced resistance. As a new potent CK2 inhibitor, DN701 is used to overcome chemoresistance through its synergistic antitumor effect with 5-fluorouracil (5-FU). Translesion DNA synthesis (TLS) has drawn our attention because it is associated with the development of chemo-resistance and tumor recurrence. The in vitro biological properties of 5-FU-resistant colon cancer cells revealed that DN701 combined with 5-FU could overcome chemo-resistance via blocking CK2-mediated aryl hydrocarbon receptor (AhR) and TLS-induced DNA damage repair (DDR). Moreover, pharmacologic and genetic inhibitions of AhR potently reduced TLS-promoted genomic instability. The mechanistic studies showed that combined DN701 with 5-FU was investigated to inhibit CK2 expression level and AhR-TLS-REV1 pathway. Meanwhile, DN701 combined with 5-FU could reduce CK2-AhR-TLS genomic instability, thus leading to superior in vivo antitumor effect. The insights provide a rationale for combining DN701 with 5-FU as a therapeutic strategy for patients with colon cancer.

Circumventing drug resistance through a CK2-targeted combination via attenuating endogenous ahr-TLS-promoted genomic instability in human colorectal cancer cells

As anchoring Casein Kinase 2 (CK2) in several human tumors, DN701 as a novel CK2 inhibitor was applied to reverse chemo-resistance via its antitumor effect synergized with oxaliplatin. Recently, translesion DNA synthesis (TLS) has attracted our attention for its association with chemo-resistance, as demonstrated by previous clinical data. The in vitro cell-based properties supported that oxaliplatin combined with DN701 could reverse drug resistance via blockading CK2-mediated aryl hydrocarbon receptor (AhR) and translesion DNA synthesis (TLS)-induced DNA damage repair. Moreover, pharmacologic or genetic inhibition on REV3L (Protein reversion less 3-like) greatly impaired TLS-induced genomic instability. Mechanistically, combination of oxaliplatin with DN701 was found to inhibit CK2 expression and AhR-TLS-REV3L axis signaling, implying the potential decrease of genomic instability. In addition, the combination of oxaliplatin with DN701 could reduce CK2-AhR-TLS-related genomic instability, leading to potent antitumor effects in vivo. Our study presents an underlying mechanism that DN701 could attenuate tumoral chemo-resistance via decaying CK2-mediated AhR and TLS genomic instability, suggesting a potential cancer chemotherapeutic modality to prolong survival in chemo-resistant patients.

A platinum(II) complex HY1-Pt overcomes cisplatin-induced resistance and attenuates metastasis of epithelial ovarian cancer by cancer cell stemness inhibition

Tumor recurrence, acquired resistance and metastasis have severely limited the effect of clinical treatments for epithelial ovarian cancer. Recent researches reveal that cancer stem cells play important roles in the process of cisplatin-induced resistance and cancer cell metastasis. A platinum(II) complex (HY1-Pt) owning casein kinase 2 specificity reported in our recent research was herein applied to treat cisplatin-sensitive and cisplatin-resistant epithelial ovarian cancers, respectively, anticipating to achieve high anti-tumor efficacy. HY1-Pt showed highly efficient anti-tumor effect with low toxicity for either cisplatin-sensitive or cisplatin-resistant epithelial ovarian cancer both in vitro and in vivo. Biological studies indicated that HY1-Pt as a casein kinase 2 inhibitor could effectively overcome cisplatin resistance through the signaling pathway of Wnt/β-catenin by inhibiting expression of the signature genes of cancer stemness cells in A2780/CDDP cells. Moreover, HY1-Pt could suppress tumor migration and invasion in vitro and in vivo, further proving that HY1-Pt can be a potent novel platinum(II) agent for cisplatin-resistant epithelial ovarian cancer treatment.

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.

Design, synthesis and biological evaluation of chromone derivatives as novel protein kinase CK2 inhibitors

Protein kinase CK2 is a potential target for the discovery of anticancer drugs. Flavonoids are reported to be effective CK2 inhibitors. Herein, based on structural trimming of flavonoids, a series of chromone-2-aminothiazole derivatives (1a-d, 2a-g, 4a-j, 5a-k) were designed and synthesized by hybridizing the chromone skeleton with 2-aminothiazole scaffold. Among these compounds, compound 5i was the most effective CK2 inhibitor (IC₅₀ = 0.08 μM) and possessed potent anti-proliferative activity against HL-60 tumor cells (IC₅₀ = 0.25 μM). Cellular thermal shift assay (CESTA) confirmed that 5i directly bound to the CK2, and the possible binding mode of 5i toward CK2 was also simulated. Further studies showed that 5i induced the apoptosis of HL-60 cells and arrested the cell cycle. Finally, western-blot analysis showed that 5i could inhibit the downstream of CK2, including α-catenin/Akt pathway and PARP/Survivin pathway.

Discovery of Novel Dual-Target Inhibitor of Bromodomain-Containing Protein 4/Casein Kinase 2 Inducing Apoptosis and Autophagy-Associated Cell Death for Triple-Negative Breast Cancer Therapy

Bromodomain-containing protein 4 (BRD4) is an attractive epigenetic target in human cancers. Inhibiting the phosphorylation of BRD4 by casein kinase 2 (CK2) is a potential strategy to overcome drug resistance in cancer therapy. The present study describes the synthesis of multiple BRD4-CK2 dual inhibitors based on rational drug design, structure-activity relationship, and in vitro and in vivo evaluations, and 44e was identified to possess potent and balanced activities against BRD4 (IC₅₀ = 180 nM) and CK2 (IC₅₀ = 230 nM). In vitro experiments show that 44e could inhibit the proliferation and induce apoptosis and autophagy-associated cell death of MDA-MB-231 and MDA-MB-468 cells. In two in vivo xenograft mouse models, 44e displays potent anticancer activity without obvious toxicities. Taken together, we successfully synthesized the first highly effective BRD4-CK2 dual inhibitor, which is expected to be an attractive therapeutic strategy for triple-negative breast cancer (TNBC).

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.

Conjugates Derived from Lapatinib Derivatives with Cancer Cell Stemness Inhibitors Effectively Reversed Drug Resistance in Triple-Negative Breast Cancer

Increasing evidence indicates that the cancer stem cell (CSC) subpopulation contributes to the therapeutic resistance and metastasis of tumors, leading to patient recurrence and death. Herein, we designed and synthesized several compounds by conjugating lapatinib derivatives with different CSC inhibitors to treat with lapatinib-induced MDA-MB-231 drug-resistant cells. In vitro biological studies indicated that 3a showed strong cytotoxicity and EGFR enzyme inhibitory activity and effectively reversed lapatinib-mediated resistance of MDA-MB-231 cells via inhibiting triple-negative breast cancer (TNBC) cell stemness and the AKT/ERK signaling pathway. In addition, 3a was capable of strongly suppressing the invasion and migration of TNBC cells by inhibiting the Wnt/β-catenin signaling pathway and MMP-2 and MMP-9 protein expression. In vivo tumorigenicity tests showed that 3a could inhibit the occurrence of TNBC by inhibiting BCSCs, proving 3a is a potential EGFR and CSC dual inhibitor for TNBC treatment.