Skp2 modulates proliferation, senescence and tumorigenesis of glioma

The ubiquitin-proteasome system in the regulation of tumor dormancy and recurrence

Tumor recurrence is a mechanism triggered in sparse populations of cancer cells that usually remain in a quiescent state after strict stress and/or therapeutic factors, which is affected by a variety of autocrine and microenvironmental cues. Despite thorough investigations, the biology of dormant and/or cancer stem cells is still not fully elucidated, as for the mechanisms of their reawakening, while only the major molecular patterns driving the relapse process have been identified to date. These molecular patterns profoundly interfere with the elements of cellular proteostasis systems that support the efficiency of the recurrence process. As a major proteostasis machinery, we review the role of the ubiquitin-proteasome system (UPS) in tumor cell dormancy and reawakening, devoting particular attention to the functions of its components, E3 ligases, deubiquitinating enzymes and proteasomes in cancer recurrence. We demonstrate how UPS components functionally or mechanistically interact with the pivotal proteins implicated in the recurrence program and reveal that modulators of the UPS hold promise to become an efficient adjuvant therapy for eradicating refractory tumor cells to impede tumor relapse.

Targeting of S-phase kinase associated protein 2 stabilized tumor suppressors leading to apoptotic cell death in squamous skin cancer cells

S-phase kinase-associated protein 2 (Skp2) is an F-box protein overexpressed in human cancers and linked with poor prognosis. It triggers cancer pathogenesis, including stemness and drug resistance. In this study, we have explored the potential role of Skp2 targeting in restoring the expression of tumor suppressors in human cutaneous squamous cell carcinoma (cSCC) cells. Our results showed that genetic and pharmacological Skp2 targeting markedly suppressed cSCC cell proliferation, colony growth, spheroid formation, and enhanced sensitization to chemotherapeutic drugs. Further, western blot results demonstrated restoration of tumor suppressor (KLF4) and CDKI (p21) and suppression of vimentin and survivin in Skp2-knocked-down cSCC cells. Importantly, we also explored that Skp2 targeting potentiates apoptosis of cSCC cells through MAPK signaling. Moreover, co-targeting of Skp2 and PI3K/AKT resulted in increased cancer cell death. Interestingly, curcumin, a well-known naturally derived anticancer agent, also inhibits Skp2 expression with concomitant CDKI upregulation. In line, curcumin suppressed cSCC cell growth through ROS-mediated apoptosis, while the use of N-acetyl cysteine (NAC) reversed curcumin-induced cell death. Curcumin treatment also sensitized cSCC cells to conventional anticancer drugs, such as cisplatin and doxorubicin. Altogether, these data suggest that Skp2 targeting restores the functioning of tumor suppressors, inhibits the expression of genes associated with cell proliferation and stemness, and sensitizes cancer cells to anticancer drugs. Thus, genetic, and pharmacological ablation of Skp2 can be an important strategy for attenuating cancer pathogenesis and associated complications in skin squamous cell carcinoma.

SKP2 promotes the metastasis of pancreatic ductal adenocarcinoma by suppressing TRIM21-mediated PSPC1 degradation

Despite significant advances in diagnostic techniques and treatment approaches, the prognosis of pancreatic ductal adenocarcinoma (PDAC) is still poor. Previous studies have reported that S-phase kinase-associated protein 2 (SKP2), a subunit of the SCF E3 ubiquitin ligase complex, is engaged in the malignant biological behavior of some tumor entities. However, SKP2 has not been fully investigated in PDAC. In the present study, it was observed that high expression of SKP2 significantly correlates with decreased survival time. Further experiments suggested that SKP2 promotes metastasis by interacting with the putative transcription factor paraspeckle component 1 (PSPC1). According to the results of coimmunoprecipitation and ubiquitination assays, SKP2 depletion resulted in the polyubiquitination of PSPC1, followed by its degradation. Furthermore, the SKP2-mediated ubiquitination of PSPC1 partially depended on the activity of the E3 ligase TRIM21. In addition, inhibition of the SKP2/PSPC1 axis by SMIP004, a traditional inhibitor of SKP2, impaired the migration of PDAC cells. In summary, this study provides novel insight into the mechanisms involved in PDAC malignant progression. Targeting the SKP2/PSPC1 axis is a promising strategy for the treatment of PDAC.

Skp2: A critical molecule for ubiquitination and its role in cancer

The ubiquitin-proteasome system (UPS) is a multi-step process that serves as the primary pathway for protein degradation within cells. UPS activity also plays a crucial role in regulating various life processes, including the cell cycle, signal transduction, DNA repair, and others. The F-box protein Skp2, a crucial member of the UPS, plays a central role in the development of various diseases. Skp2 controls cancer cell growth and drug resistance by ubiquitinating modifications to a variety of proteins. This review emphasizes the multifaceted role of Skp2 in a wide range of cancers and the mechanisms involved, highlighting the potential of Skp2 as a therapeutic target in cancer. Additionally, we describe the impactful influence exerted by Skp2 in various other diseases beyond cancer.

Identification of a miRNA multi-targeting therapeutic strategy in glioblastoma

Glioblastoma (GBM) is a deadly and the most common primary brain tumor in adults. Due to their regulation of a high number of mRNA transcripts, microRNAs (miRNAs) are key molecules in the control of biological processes and are thereby promising therapeutic targets for GBM patients. In this regard, we recently reported miRNAs as strong modulators of GBM aggressiveness. Here, using an integrative and comprehensive analysis of the TCGA database and the transcriptome of GBM biopsies, we identified three critical and clinically relevant miRNAs for GBM, miR-17-3p, miR-222, and miR-340. In addition, we showed that the combinatorial modulation of three of these miRNAs efficiently inhibited several biological processes in patient-derived GBM cells of all these three GBM subtypes (Mesenchymal, Proneural, Classical), induced cell death, and delayed tumor growth in a mouse tumor model. Finally, in a doxycycline-inducible model, we observed a significant inhibition of GBM stem cell viability and a significant delay of orthotopic tumor growth. Collectively, our results reveal, for the first time, the potential of miR-17-3p, miR-222 and miR-340 multi-targeting as a promising therapeutic strategy for GBM patients.

Cellular senescence in glioma

INTRODUCTION

Glioma is the most common primary brain tumor and is often associated with treatment resistance and poor prognosis. Standard treatment typically involves radiotherapy and temozolomide-based chemotherapy, both of which induce cellular senescence-a tumor suppression mechanism.

DISCUSSION

Gliomas employ various mechanisms to bypass or escape senescence and remain in a proliferative state. Importantly, senescent cells remain viable and secrete a large number of factors collectively known as the senescence-associated secretory phenotype (SASP) that, paradoxically, also have pro-tumorigenic effects. Furthermore, senescent cells may represent one form of tumor dormancy and play a role in glioma recurrence and progression.

CONCLUSION

In this article, we delineate an overview of senescence in the context of gliomas, including the mechanisms that lead to senescence induction, bypass, and escape. Furthermore, we examine the role of senescent cells in the tumor microenvironment and their role in tumor progression and recurrence. Additionally, we highlight potential therapeutic opportunities for targeting senescence in glioma.

Platycodin D suppresses proliferation, migration, and invasion of human glioblastoma cells through regulation of Skp2

BACKGROUND

Platycodin D (PD) is a major bioactive component of Platycodon grandiflorum, a medicinal herb that is widely used in China, and is effective against various human cancers, including glioblastoma multiforme (GBM). S phase kinase-related protein 2 (Skp2) is oncogenic and overexpressed in various human tumors. It is highly expressed in GBM and its expression is correlated with tumor growth, drug resistance and poor prognosis. In this study, we investigated whether inhibition of glioma progression by PD is mediated by decreasing expression of Skp2.

METHODS

Cell Counting Kit-8 (CCK-8) and Transwell assays were used to determine the effects of PD on GBM cell proliferation, migration, and invasion in vitro. mRNA and protein expression were determined by real time polymerase chain reaction (RT-PCR) and western blotting, respectively. The U87 xenograft model was used to verify the anti-glioma effect of PD in vivo. Expression levels of Skp2 protein were analyzed by immunofluorescence staining.

RESULTS

PD suppressed proliferation and motility of GBM cells in vitro. The expression of Skp2 in U87 and U251 cells was significantly reduced by PD. PD mainly decreased the cytoplasmic expression of Skp2 in glioma cells. Skp2 protein expression was downregulated by PD, resulting in upregulation of its downstream targets, p21and p27. The inhibitory effect of PD was enhanced by Skp2 knockdown in GBM cells and reversed in cells with Skp2 overexpression.

CONCLUSION

PD suppresses glioma development by regulation of Skp2 in GBM cells.

A Review of the Regulatory Mechanisms of N-Myc on Cell Cycle

Neuroblastoma has obvious heterogeneity. It is one of the few undifferentiated malignant tumors that can spontaneously degenerate into completely benign tumors. However, for its high-risk type, even with various intensive treatment options, the prognosis is still unsatisfactory. At the same time, a large number of research data show that the abnormal amplification and high-level expression of the MYCN gene are positively correlated with the malignant progression, poor prognosis, and mortality of neuroblastoma. In this context, this article explores the role of the N-Myc, MYCN gene expression product on its target genes related to the cell cycle and reveals its regulatory network in promoting tumor proliferation and malignant progression. We hope it can provide ideas and direction for the research and development of drugs targeting N-Myc and its downstream target genes.

Small-molecule compounds inhibiting S-phase kinase-associated protein 2: A review

S-phase kinase-associated protein 2 (Skp2) is a substrate-specific adaptor in Skp1-CUL1-ROC1-F-box E3 ubiquitin ligases and widely regarded as an oncogene. Therefore, Skp2 has remained as an active anticancer research topic since its discovery. Accordingly, the structure of Skp2 has been solved and numerous Skp2 inhibiting compounds have been identified. In this review, we would describe the structural features of Skp2, introduce the ubiquitination function of SCF^Skp2, and summarize the diverse natural and synthetic Skp2 inhibiting compounds reported to date. The IC₅₀ data of the Skp2 inhibitors or inhibiting compounds in various kinds of tumors at cellular levels implied that the cancer type, stage and pathological mechanisms should be taken into consideration when selecting Skp2-inhibiting compound for cancer treatment.

Echinacoside (ECH) suppresses proliferation, migration, and invasion of human glioblastoma cells by inhibiting Skp2-triggered epithelial-mesenchymal transition (EMT)

BACKGROUND

Echinacoside (ECH) is a phenylethanoid extracted from the stems of Cistanches salsa, an herb used in Chinese medicine formulations, and is effective against glioblastoma multiforme (GBM). Epithelial-mesenchymal transition (EMT) is the cornerstone of tumorigenesis and metastasis, and increases the malignant behavior of GBM cells. The S phase kinase-related protein 2 (skp2), an oncoprotein associated with EMT, is highly expressed in GBM and significantly associated with drug resistance, tumor grade and dismal prognosis. The aim of this study was to explore the inhibitory effects of ECH against GBM development and skp2-induced EMT.

METHODS

CCK-8, EdU incorporation, transwell, colony formation and sphere formation assays were used to determine the effects of ECH on GBM cell viability, proliferation, migration and invasion in vitro. The in vivo anti-glioma effects of ECH were examined using a U87 xenograft model. The expression levels of skp2 protein, EMT-associated markers (vimentin and snail) and stemness markers (Nestin and sox2) were analyzed by immunohistochemistry, immunofluorescence staining and western blotting experiments.

RESULTS

ECH suppressed the proliferation, invasiveness and migration of GBM cells in vitro, as well as the growth of U87 xenograft in vivo. In addition, ECH downregulated the skp2 protein, EMT-related markers (vimentin and snail) and stemness markers (sox2 and Nestin). The inhibitory effects of ECH were augmented in the skp2-knockdown GBM cells, and reversed in cells with ectopic expression of skp2.

CONCLUSION

ECH inhibits glioma development by suppressing skp2-induced EMT of GBM cells.

Driver mutations in ADGRL3 are involved in the evolution of ependymoma

Although there have been recent advances in the molecular pathology of ependymomas, little is known about the underlying molecular evolution during its development. Here, we assessed the clinical, pathological and molecular evolutionary process of ependymoma recurrence in a 9-year-old patient who had seven recurrences of supratentorial ependymoma and died from intracranial multiregional recurrences at the age of 19 years old. Whole-genome sequencing (WGS) of 7 tumor samples (1 primary and 6 subsequent recurrent tumors) was performed to elucidate the mutation landscape and identify potential driver mutations for tumor evolution. The genetic profiles of the seven tumor specimens showed significant heterogeneity and suggested a highly branched evolutionary pattern. The mutational signatures and chromothripsis changed with treatments. Strikingly, adhesion G protein-coupled receptor L3 (ADGRL3, also known as Latrophilins 3, LPNH3) was found to be consistently mutated during the entire disease process. However, Sanger sequencing of other 78 ependymoma patients who underwent surgery at our institution showed no genetic alteration of ADGRL3, as found in the present case. The mRNA levels of ADGRL3 were significantly lower in ependymomas (n = 36), as compared with normal brain tissue (n = 3). Grade III ependymomas had the lowest ADGRL3 expression. Moreover, ependymomas with lower mRNA level of ADGRL3 had shorter overall survival. Our findings, therefore, demonstrate a rare evolutionary process of ependymoma involving ADGRL3.

Andrographolide, a diterpene lactone from the Traditional Chinese Medicine Andrographis paniculate, induces senescence in human lung adenocarcinoma via p53/p21 and Skp2/p27

BACKGROUND

Senescence leads to permanent cell-cycle arrest and is a potential target for cancer therapy. Andrographolide (AD) is a diterpene lactone isolated from Traditional Chinese Medicine (TCM) Andrographis paniculate, which has been used as an anti-inflammatory drug in clinical practice with the potential to target senescence in recalcitrant lung cancer.

PURPOSE

To determine whether AD can induce senescence in human lung adenocarcinoma in vitro and in vivo and to elucidate the underlying mechanisms.

METHODS

SA-β-Gal staining was used to detect the expression of senescence-associated β-galactosidase (SA-β-Gal) in human lung adenocarcinoma cells A549 and NCI-H1795. DNA damage was examined by the detection of γH2AX foci. Cell cycle was analyzed by flow cytometry. Cancer cell proliferation was determined by ATPlite assay and clonogenic survival assay in vitro. Tumor growth was determined in a mouse model of A549. The expression level of proteins and mRNA was estimated by Western blotting and Quantitative RT-PCR, respectively. Small interfering RNA (siRNA) was used to knock down p21, p27 and p53 to explore the potential mechanism of AD-induced senescence in human lung adenocarcinoma cells.

RESULTS

AD-induced A549 and NCI-H1795 cell senescence determined by increased cell size, flattened morphology, DNA damage, cell cycle arrest as well as the increased expression of β-galactosidase. AD inhibited cell proliferation in lung cells in vitro and lung cells xenograft growth in nude mice. p21 and p27, the major cell cycle regulators and mediators of senescence, were upregulated at the protein level in AD-treated A549 lung adenocarcinoma in vitro and in vivo. Further studies demonstrated that AD induced cell senescence via p53/p21 and Skp2/p27.

CONCLUSION

In the present study, we found that the primary anti-inflammatory drug AD could have a potential antitumor effect in lung cancer. We demonstrated that AD induced lung adenocarcinoma senescence in vitro and in vivo via p53/p21 and Skp2/p27 for the first time. AD is therefore a promising senescence-inducing therapeutic for recalcitrant human lung adenocarcinoma.

SPDL1 Is an Independent Predictor of Patient Outcome in Colorectal Cancer

Spindle Apparatus Coiled-Coil Protein 1 (SPDL1) is a relatively recently identified coiled-coil domain containing protein and an important determinant of DNA fidelity by ensuring faithful mitosis. Hence, SPDL1 is suspected to underlie genomic (in-)stability in human cancers, yet its exact roles in these diseases remain largely underexplored. Given that genomic instability (GIN) is a crucial feature in colorectal cancer (CRC), we primarily asked whether the expression of this protein may account for differences in clinicopathological features and survival rates of CRC patients. Protein expression was evaluated by immunohistochemistry in the institutional tissue microarray (TMA), and gene expression by the analysis of publicly available datasets. To place the prognostic relevance in a predicted biological context, gene co-expression set around SPDL1 identified by public data mining was annotated and assessed for enrichment in gene ontology (GO) categories, BRITE hierarchies, and Reactome pathways. The comparison with adjacent normal tissue revealed a high expression of SPDL1 protein in a subset of tumor cases (48.84%), and these had better prognosis than the SPDL1-low expression counterpart even after adjustment for multiple confounders. SPDL1-high expression within tumors was associated with a median 56-month survival advantage, but not with any clinicopathological characteristics of our cohort. In the TCGA cohort, SPDL1 was overexpressed in tumor tissue and positively associated with improved survival, chromosome instability phenotype, and various GIN markers. In addition to the genes critically involved in the cell cycle and mitosis, a gene set co-expressed with SPDL1 contained checkpoint members of both chromosome segregation and DNA replication, as well as those associated with defective DNA repair, and retrograde vesicle-mediated transport. In conclusion, SPDL1 is an independent predictor of CRC patient survival in a possible connection with chromosomal instability.

Exploring the potential biomarkers for prognosis of glioblastoma via weighted gene co-expression network analysis

BACKGROUND

Glioblastoma (GBM) is the most common malignant tumor in the central system with a poor prognosis. Due to the complexity of its molecular mechanism, the recurrence rate and mortality rate of GBM patients are still high. Therefore, there is an urgent need to screen GBM biomarkers to prove the therapeutic effect and improve the prognosis.

RESULTS

We extracted data from GBM patients from the Gene Expression Integration Database (GEO), analyzed differentially expressed genes in GEO and identified key modules by weighted gene co-expression network analysis (WGCNA). GSE145128 data was obtained from the GEO database, and the darkturquoise module was determined to be the most relevant to the GBM prognosis by WGCNA (r =  - 0.62, p = 0.01). We performed enrichment analysis of Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) to reveal the interaction activity in the selected modules. Then Kaplan-Meier survival curve analysis was used to extract genes closely related to GBM prognosis. We used Kaplan-Meier survival curves to analyze the 139 genes in the darkturquoise module, identified four genes (DARS/GDI2/P4HA2/TRUB1) associated with prognostic GBM. Low expression of DARS/GDI2/TRUB1 and high expression of P4HA2 had a poor prognosis. Finally, we used tumor genome map (TCGA) data, verified the characteristics of hub genes through Co-expression analysis, Drug sensitivity analysis, TIMER database analysis and GSVA analysis. We downloaded the data of GBM from the TCGA database, the results of co-expression analysis showed that DARS/GDI2/P4HA2/TRUB1 could regulate the development of GBM by affecting genes such as CDC73/CDC123/B4GALT1/CUL2. Drug sensitivity analysis showed that genes are involved in many classic Cancer-related pathways including TSC/mTOR, RAS/MAPK.TIMER database analysis showed DARS expression is positively correlated with tumor purity (cor = 0.125, p = 1.07e-02)), P4HA2 expression is negatively correlated with tumor purity (cor =-0.279, p = 6.06e-09). Finally, GSVA analysis found that DARS/GDI2/P4HA2/TRUB1 gene sets are closely related to the occurrence of cancer.

CONCLUSION

We used two public databases to identify four valuable biomarkers for GBM prognosis, namely DARS/GDI2/P4HA2/TRUB1, which have potential clinical application value and can be used as prognostic markers for GBM.

Effects of Lovastatin on Brain Cancer Cells

Although brain tumors occur less frequently than other forms of cancer, they have one of the bleakest prognoses with low survival rates. The conventional treatment for brain tumors includes surgery, radiotherapy, and chemotherapy. However, resistance to treatment remains a problem with recurrence shortly following. The resistance to treatment may be caused by cancer stem cells (CSCs), a subset of brain tumor cells with the affinity for self-renewal and differentiation into multiple cell lineages. An emerging approach to targeting CSCs in brain tumors is through repurposing the lipid-lowering medication, lovastatin. Lovastatin is a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor that impacts the mevalonate pathway. The inhibition of intermediates in the mevalonate pathway affects signaling cascades and oncogenes associated with brain tumor stem cells (BTSC). In this review, we show the possible mechanisms where lovastatin can target BTSC for different varieties of malignant brain tumors.

PI3K/AKT/mTOR Signaling Pathway Is Required for JCPyV Infection in Primary Astrocytes

Astrocytes are a main target of JC polyomavirus (JCPyV) in the central nervous system (CNS), where the destruction of these cells, along with oligodendrocytes, leads to the fatal disease progressive multifocal leukoencephalopathy (PML). There is no cure currently available for PML, so it is essential to discover antivirals for this aggressive disease. Additionally, the lack of a tractable in vivo models for studying JCPyV infection makes primary cells an accurate alternative for elucidating mechanisms of viral infection in the CNS. This research to better understand the signaling pathways activated in response to JCPyV infection reveals and establishes the importance of the PI3K/AKT/mTOR signaling pathway in JCPyV infection in primary human astrocytes compared to transformed cell lines. Using RNA sequencing and chemical inhibitors to target PI3K, AKT, and mTOR, we have demonstrated the importance of this signaling pathway in JCPyV infection of primary astrocytes not observed in transformed cells. Collectively, these findings illuminate the potential for repurposing drugs that are involved with inhibition of the PI3K/AKT/mTOR signaling pathway and cancer treatment as potential therapeutics for PML, caused by this neuroinvasive virus.

Hypoxia-Related lncRNA Correlates With Prognosis and Immune Microenvironment in Lower-Grade Glioma

Background

Hypoxia-related genes are demonstrated to correlate with the prognosis of various cancers. However, the role of hypoxia-related long non-coding RNAs (HRLs) in lower-grade glioma (LGG) remains unclear.

Methods

A total of 700 LGG samples were extracted from TCGA and CGGA databases. Pearson correlation analysis was used to identify HRLs. Lasso analysis was adopted to construct the HRL signature. TIDE algorithm was used to predict responses to immune checkpoint inhibitors. Cell proliferation was estimated by cell counting kit-8 assay, colony formation assay, and EdU assay.

Results

We identified 340 HRLs and constructed a novel risk signature composed of 19 HRLs. The risk score exhibited potent value in predicting the prognosis of LGG patients and was significantly associated with the prognosis of LGG patients. Moreover, HRL signature could distinguish patients with similar expression levels of immune checkpoints and might predict the efficacy of immune checkpoint inhibitors. Additionally, hypoxia-related pathways and immune pathways were enriched in high-risk group, and high risk score indicated low tumor purity and high immune infiltration. Two major HRLs, LINC00941 and BASP1-AS1, could significantly affect the proliferation of glioma cells.

Conclusions

Our study constructed a novel HRL signature that could predict the prognosis and immunotherapy response of LGG patients. HRLs could be novel biomarkers to predict the prognosis of LGG patients and potential targets for LGG treatment.

Antitumoral Activities of Curcumin and Recent Advances to ImProve Its Oral Bioavailability

Curcumin, a main bioactive component of the Curcuma longa L. rhizome, is a phenolic compound that exerts a wide range of beneficial effects, acting as an antimicrobial, antioxidant, anti-inflammatory and anticancer agent. This review summarizes recent data on curcumin's ability to interfere with the multiple cell signaling pathways involved in cell cycle regulation, apoptosis and the migration of several cancer cell types. However, although curcumin displays anticancer potential, its clinical application is limited by its low absorption, rapid metabolism and poor bioavailability. To overcome these limitations, several curcumin-based derivatives/analogues and different drug delivery approaches have been developed. Here, we also report the anticancer mechanisms and pharmacokinetic characteristics of some derivatives/analogues and the delivery systems used. These strategies, although encouraging, require additional in vivo studies to support curcumin clinical applications.

RIOK2 Inhibitor NSC139021 Exerts Anti-Tumor Effects on Glioblastoma via Inducing Skp2-Mediated Cell Cycle Arrest and Apoptosis

Up to now, the chemotherapy approaches for glioblastoma were limited. 1-[2-Thiazolylazo]-2-naphthol (named as NSC139021) was shown to significantly inhibit the proliferation of prostate cancer cells by targeting the atypical protein kinase RIOK2. It is documented that RIOK2 overexpressed in glioblastoma. However, whether NSC139021 can inhibit the growth of glioblastoma cells and be a potential drug for glioblastoma treatment need to be clarified. In this study, we investigated the effects of NSC139021 on human U118MG, LN-18, and mouse GL261 glioblastoma cells and the mouse models of glioblastoma. We verified that NSC139021 effectively inhibited glioblastoma cells proliferation, but it is independent of RIOK2. Our data showed that NSC139021 induced cell cycle arrest at G0/G1 phase via the Skp2-p27/p21-Cyclin E/CDK2-pRb signaling pathway in G1/S checkpoint regulation. In addition, NSC139021 also increased the apoptosis of glioblastoma cells by activating the p53 signaling pathway and increasing the levels of Bax and cleaved caspase 3. Furthermore, intraperitoneal administration of 150 mg/kg NSC139021 significantly suppressed the growth of human and mouse glioblastoma in vivo. Our study suggests that NSC139021 may be a potential chemotherapy drug for the treatment of glioblastoma by targeting the Skp2-p27/p21-Cyclin E/CDK2-pRb signaling pathway.

The multifaceted NF-kB: are there still prospects of its inhibition for clinical intervention in pediatric central nervous system tumors?

Despite advances in the understanding of the molecular mechanisms underlying the basic biology and pathogenesis of pediatric central nervous system (CNS) malignancies, patients still have an extremely unfavorable prognosis. Over the years, a plethora of natural and synthetic compounds has emerged for the pharmacologic intervention of the NF-kB pathway, one of the most frequently dysregulated signaling cascades in human cancer with key roles in cell growth, survival, and therapy resistance. Here, we provide a review about the state-of-the-art concerning the dysregulation of this hub transcription factor in the most prevalent pediatric CNS tumors: glioma, medulloblastoma, and ependymoma. Moreover, we compile the available literature on the anti-proliferative effects of varied NF-kB inhibitors acting alone or in combination with other therapies in vitro, in vivo, and clinical trials. As the wealth of basic research data continues to accumulate, recognizing NF-kB as a therapeutic target may provide important insights to treat these diseases, hopefully contributing to increase cure rates and lower side effects related to therapy.

The Paradoxical Role of Cellular Senescence in Cancer

Cellular senescence occurs in proliferating cells as a consequence of various triggers including telomere shortening, DNA damage, and inappropriate expression of oncogenes. The senescent state is accompanied by failure to reenter the cell cycle under mitotic stimulation, resistance to cell death and enhanced secretory phenotype. A growing number of studies have convincingly demonstrated a paradoxical role for spontaneous senescence and therapy-induced senescence (TIS), that senescence may involve both cancer prevention and cancer aggressiveness. Cellular senescence was initially described as a physiological suppressor mechanism of tumor cells, because cancer development requires cell proliferation. However, there is growing evidence that senescent cells may contribute to oncogenesis, partly in a senescence-associated secretory phenotype (SASP)-dependent manner. On the one hand, SASP prevents cell division and promotes immune clearance of damaged cells, thereby avoiding tumor development. On the other hand, SASP contributes to tumor progression and relapse through creating an immunosuppressive environment. In this review, we performed a review to summarize both bright and dark sides of senescence in cancer, and the strategies to handle senescence in cancer therapy were also discussed.

F-box proteins in cancer stemness: An emerging prognostic and therapeutic target

Cancer is a complex heterogenic disease with significant therapeutic challenges. The presence of cancer stem cells (CSCs) in cancer tissue orchestrates tumor growth, progression, and metastasis, the tumor heterogeneity, disease relapse, and therapeutic resistance. Hence, it is imperative to explore how progenitor or cancer-initiating cells acquire stemness features and reprogram different biological mechanisms to maintain their sustained oncogenicity. Interestingly, deregulation of F-box proteins (FBPs) is crucial for cancer stemness features, including drug resistance and disease relapse. In this review, we highlight recent updates on the clinical significance of targeting FBPs in cancer therapy, with emphasis on eliminating CSCs and associated therapeutic challenges. Moreover, we also discuss novel strategies for the selective elimination of CSCs by targeting FBPs.

Small molecule-mediated modulation of ubiquitination and neddylation improves HSC function ex vivo

Hematopoietic stem cells (HSCs) are particularly characterized by their quiescence and self-renewal. Cell cycle regulators tightly control quiescence and self-renewal capacity. Studies suggest that modulation of ubiquitination and neddylation could contribute to HSC function via cyclin-dependent kinase inhibitors (CDKIs). S-phase kinase-associated protein 2 (SKP2) is responsible for ubiquitin-mediated proteolysis of CDKIs. Here, we modulated overall neddylation and SKP2-associated ubiquitination in HSCs by using SKP2-C25, an SKP2 inhibitor, and MLN4924 (Pevonedistat) as an inhibitor of the NEDD8 system. Treatments of SKP2-C25 and MLN4924 increased both murine and human stem and progenitor cell (HSPC) compartments. This is associated with the improved quiescence of murine HSC by upregulation of p27 and p57 CDKIs. A colony-forming unit assay showed an enhanced in vitro self-renewal potential post inhibition of ubiquitination and neddylation. In addition, MLN4924 triggered the mobilization of bone marrow HSPCs to peripheral blood. Intriguingly, MLN4924 treatment could decrease the proliferation of murine bone marrow mesenchymal stem cells or endothelial cells. These findings shed light on the contribution of SKP2, and associated ubiquitination and neddylation in HSC maintenance, self-renewal, and expansion.

An Alternative Pipeline for Glioblastoma Therapeutics: A Systematic Review of Drug Repurposing in Glioblastoma

Simple Summary

Glioblastoma is a devastating malignancy that has continued to prove resistant to a variety of therapeutics. No new systemic therapy has been approved for use against glioblastoma in almost two decades. This observation is particularly disturbing given the amount of money invested in identifying novel therapies for this disease. A relatively rapid and economical pipeline for identification of novel agents is drug repurposing. Here, a comprehensive review detailing the state of drug repurposing in glioblastoma is provided. We reveal details on studies that have examined agents in vitro, in animal models and in patients. While most agents have not progressed beyond the initial stages, several drugs, from a variety of classes, have demonstrated promising results in early phase clinical trials.

Abstract

The treatment of glioblastoma (GBM) remains a significant challenge, with outcome for most pa-tients remaining poor. Although novel therapies have been developed, several obstacles restrict the incentive of drug developers to continue these efforts including the exorbitant cost, high failure rate and relatively small patient population. Repositioning drugs that have well-characterized mechanistic and safety profiles is an attractive alternative for drug development in GBM. In ad-dition, the relative ease with which repurposed agents can be transitioned to the clinic further supports their potential for examination in patients. Here, a systematic analysis of the literature and clinical trials provides a comprehensive review of primary articles and unpublished trials that use repurposed drugs for the treatment of GBM. The findings demonstrate that numerous drug classes that have a range of initial indications have efficacy against preclinical GBM models and that certain agents have shown significant potential for clinical benefit. With examination in randomized, placebo-controlled trials and the targeting of particular GBM subgroups, it is pos-sible that repurposing can be a cost-effective approach to identify agents for use in multimodal anti-GBM strategies.

Recent insight into the role of RING-finger E3 ligases in glioma

The ubiquitin proteasome system (UPS) serves as the major posttranslational modification system for the maintenance of protein homeostasis. The ubiquitin ligases (E3s) are responsible for the recognition and recruitment of specific substrate proteins for polyubiquitination. Really interesting new gene (RING) finger E3s account for the majority of E3s. The human genome encodes more than 600 RING E3s, which are divided into three subclasses: single polypeptide E3s, cullin-RING ligases (CRLs) and other multisubunit E3s. The abnormal regulation of RING E3s has been reported to disrupt normal biological processes and induce the occurrence of many human malignancies. Glioma is the most common type of malignant primary brain tumor. In the last few decades, patient prognosis has improved as novel targeted therapeutic agents have developed. In this review, we will summarize the current knowledge about the dysregulation of RING E3s and the altered stability of their substrates in glioma. We will further introduce and discuss the current status and future perspectives of the application of small inhibitors and proteolysis-targeting chimeric molecules (PROTACs) interfering with RING E3s as potential anticancer agents for glioma.

Antitumor Activity of Curcumin in Glioblastoma

Current standard-of-care treatment for glioblastoma, the most common malignant primary central nervous system (CNS) tumor, consists of surgical resection followed by adjuvant chemotherapy and radiation (Stupp protocol), providing an overall median survival of 15 months. With additional treatment using tumor-treating fields (Optune^® therapy, Novocure Ltd., Haifa, Israel), survival can be extended up to 20 months. In spite of significant progress in our understanding of the molecular pathogenesis, the prognosis for patients with malignant gliomas remains poor and additional treatment modalities are critically needed. Curcumin is a bright yellow pigment found in the rhizome of the widely utilized spice, turmeric (Curcuma longa). It has long been used in South Asian traditional medicines and has been demonstrated to have in vitro antioxidant, anti-inflammatory, and antiproliferative effects. Curcumin has been demonstrated to induce multiple cytotoxic effects in tumor cells including cell cycle arrest, apoptosis, autophagy, changes in gene expression, and disruption of molecular signaling. Additionally, curcumin has been shown to potentiate the effect of radiation on cancer cells, while exhibiting a protective effect on normal tissue. Curcumin’s positive safety profile and widespread availability make it a promising compound for future clinical trials for high-grade gliomas.

Targeting the Ubiquitin System in Glioblastoma

Glioblastoma is the most common primary brain tumor in adults with poor overall outcome and 5-year survival of less than 5%. Treatment has not changed much in the last decade or so, with surgical resection and radio/chemotherapy being the main options. Glioblastoma is highly heterogeneous and frequently becomes treatment-resistant due to the ability of glioblastoma cells to adopt stem cell states facilitating tumor recurrence. Therefore, there is an urgent need for novel therapeutic strategies. The ubiquitin system, in particular E3 ubiquitin ligases and deubiquitinating enzymes, have emerged as a promising source of novel drug targets. In addition to conventional small molecule drug discovery approaches aimed at modulating enzyme activity, several new and exciting strategies are also being explored. Among these, PROteolysis TArgeting Chimeras (PROTACs) aim to harness the endogenous protein turnover machinery to direct therapeutically relevant targets, including previously considered "undruggable" ones, for proteasomal degradation. PROTAC and other strategies targeting the ubiquitin proteasome system offer new therapeutic avenues which will expand the drug development toolboxes for glioblastoma. This review will provide a comprehensive overview of E3 ubiquitin ligases and deubiquitinating enzymes in the context of glioblastoma and their involvement in core signaling pathways including EGFR, TGF-β, p53 and stemness-related pathways. Finally, we offer new insights into how these ubiquitin-dependent mechanisms could be exploited therapeutically for glioblastoma.

The long noncoding RNA FTX promotes a malignant phenotype in bone marrow mesenchymal stem cells via the miR-186/c-Met axis

Gliomas are the most common and aggressive primary tumours of the central nervous system in adults. Bone marrow-derived mesenchymal stem cells (BMSCs) are an important component of the glioma microenvironment. Our previous study indicated that BMSCs in the glioma microenvironment could be induced to malignantly transform by glioma stem cells (GSCs). The malignant transformation of BMSCs is closely related to glioma progression; however, the underlying mechanism of this transformation has not been fully clarified. In this study, we found that compared with the levels in normal BMSCs, the levels of the long noncoding RNA FTX transcript XIST regulator (lncRNA-FTX) were increased in malignantly transformed BMSCs (tBMSCs), which was associated with the proliferation, migration and invasion of tBMSCs. Next, by using a luciferase reporter assay and an RNA pull-down assay, we found that lncRNA-FTX acted as a sponge for miR-186 in tBMSCs. Further research revealed that miR-186 could bind to the 3'-UTR (untranslated region) of c-Met, which acts as an oncogene in gliomas. Through functional assays, we showed that lncRNA-FTX could regulate c-Met expression in tBMSCs in a miR-186-dependent manner. Based on these data, we concluded that lncRNA-FTX plays a key role in the GSC-mediated malignant transformation of BMSCs in the glioma microenvironment, which is of great significance for further understanding the pathogenesis of glioma.