BKM120 sensitizes C6 glioma cells to temozolomide via suppression of the PI3K/Akt/NF-κB/MGMT signaling pathway

Transcriptomic analysis identifies the neuropeptide cortistatin (CORT) as an inhibitor of temozolomide (TMZ) resistance by suppressing the NF-κB-MGMT signaling axis in human glioma

Glioma is a common tumor originating in the brain that has a high mortality rate. Temozolomide (TMZ) is the first-line treatment for high-grade gliomas. However, a large proportion of gliomas are resistant to TMZ, posing a great challenge to their treatment. In the study, the specific functions and mechanism(s) by which cortistatin (CORT) regulates TMZ resistance and glioma progression were evaluated. The decreased expression of CORT was detected in glioma tissues, and highly expressed CORT was associated with a better survival rate in patients with glioma. CORT overexpression notably decreased the capacity of glioma cells to proliferate and migrate in vitro and to form tumors in vivo. CORT overexpression also markedly suppressed the viability and enhanced the apoptosis of TMZ-resistant U251 cells by regulating MGMT, p21, and Puma expression. Importantly, CORT overexpression reduced the resistance of gliomas to TMZ in vivo. CORT expression was negatively correlated with MGMT expression in both glioma tissues and cells, and it was found that CORT inhibited NF-κB pathway activation in glioma cells, thereby inhibiting MGMT expression. In conclusion, CORT regulates glioma cell growth, migration, apoptosis, and TMZ resistance by weakening the activity of NF-κB/p65 and thereby regulating MGMT expression. The CORT/NF-κB/MGMT axis might be regarded as a molecular mechanism contributing to the resistance of glioma to TMZ. Our data also suggest that CORT regulates the viability and metastatic potential of glioma cells, independent of its effects on TMZ resistance, providing evidence of novel therapeutic targets for glioma that should be evaluated in further studies.

Enhancing temozolomide antiglioma response by inhibiting O6-methylguanine-DNA methyltransferase with selected phytochemicals: in silico and in vitro approach

The aim of our study was to investigate the potential of rutin, catechin, dehydrozingerone, naringenin, and quercetin, both alone and in combination with temozolomide, to inhibit the expression of O6-methylguanine-DNA methyltransferase (MGMT) in glioma cells. MGMT has been shown to be a major cause of temozolomide resistance in glioma. Our study used both in silico and in vitro methods to assess the inhibitory activity of these phytochemicals on MGMT, with the goal of identifying the most effective combination of compounds for reducing temozolomide resistance. After conducting an initial in silico screening of natural compounds against MGMT protein, five phytochemicals were chosen based on their high docking scores and favorable binding energies. From the molecular docking and simulation studies, we found that quercetin showed a good inhibitory effect of MGMT with its high binding affinity. C6 glioma cells showed increased cytotoxicity when treated with the temozolomide and quercetin combination. It was understood from the isobologram and combination index plot that the drug combination showed a synergistic effect at the lowest dose. Quercetin when combined with temozolomide significantly decreased the MGMT levels in C6 cells in comparison with the other drugs as estimated by ELISA. The percentage of apoptotic cells increased significantly in the temozolomide-quercetin group indicating the potency of quercetin in decreasing the resistance of temozolomide as confirmed by acridine orange/ethidium bromide staining. Our experiment hence suggests that temozolomide resistance can be reduced by combining the drug with quercetin which will serve as an effective therapeutic target for glioblastoma treatment.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03821-7.

The first evidence of biological activity for free Hypusine, an enigmatic amino acid discovered in the '70s

Hypusine amino acid [N^ε-(4-amino-2-hydroxybutyl)-lysine] was first isolated in 1971 from bovine brain extracts. Hypusine originates from a post-translational modification at the eukaryotic translation initiation factor 5A (eIF5A), a protein produced by archaebacteria and eukaryotes. The eIF5A protein is the only one described containing the hypusine residue, which is essential for its activity. Hypusine as a free amino acid is a consequence of proteolytic degradation of eIF5A. Herein, we showed, for the first time, evidence of biological activity for the free hypusine. C6 rat glioma cells were treated with hypusine, and different cellular parameters were evaluated. Hypusine treatment significantly reduced C6 cell proliferation and potently suppressed their clonogenic capacity without leading to apoptosis. Hypusine also decreased the Eif5A transcript content and the global protein synthesis profile that may occur due to negative feedback in response to high hypusine concentration, controlling the content of newly synthesized eIF5A, which can affect the translation process. Besides, hypusine treatment also altered cellular metabolism by changing the pathways for energy production, reducing cellular respiration coupled with oxidative phosphorylation, and increasing the anaerobic metabolism. These observed results and the relationship between eIF5A and tumor processes led us to test the combination of hypusine with the chemotherapeutic drug temozolomide. Combining temozolomide with hypusine reduced the MTT conversion to the same levels as those observed using double temozolomide dosage alone, demonstrating a synergetic action between the compounds. Thus, since 1971, this is the first study showing evidence of biological activity for hypusine not associated with being an essential component of the eiF5A protein. Finding out the molecular targets of hypusine are the following efforts to completely characterize its biological activity.

Tau Protein as Therapeutic Target for Cancer? Focus on Glioblastoma

Despite being extensively studied for several decades, the microtubule-associated protein Tau has not finished revealing its secrets. For long, Tau has been known for its ability to promote microtubule assembly. A less known feature of Tau is its capability to bind to cancer-related protein kinases, suggesting a possible role of Tau in modulating microtubule-independent cellular pathways that are associated with oncogenesis. With the intention of finding new therapeutic targets for cancer, it appears essential to examine the interaction of Tau with these kinases and their consequences. This review aims at collecting the literature data supporting the relationship between Tau and cancer with a particular focus on glioblastoma tumors in which the pathological significance of Tau remains largely unexplored. We will first treat this subject from a mechanistic point of view showing the pivotal role of Tau in oncogenic processes. Then, we will discuss the involvement of Tau in dysregulating critical pathways in glioblastoma. Finally, we will outline promising strategies to target Tau protein for the therapy of glioblastoma.

Modification Patterns of DNA Methylation-Related lncRNAs Regulating Genomic Instability for Improving the Clinical Outcomes and Tumour Microenvironment Characterisation of Lower-Grade Gliomas

Background: DNA methylation is an important epigenetic modification that affects genomic instability and regulates gene expression. Long non-coding RNAs (lncRNAs) modulate gene expression by interacting with chromosomal modifications or remodelling factors. It is urgently needed to evaluate the effects of DNA methylation-related lncRNAs (DMlncRNAs) on genome instability and further investigate the mechanism of action of DMlncRNAs in mediating the progression of lower-grade gliomas (LGGs) and their impact on the immune microenvironment.

Methods: LGG transcriptome data, somatic mutation profiles and clinical features analysed in the present study were obtained from the CGGA, GEO and TCGA databases. Univariate, multivariate Cox and Lasso regression analyses were performed to establish a DMlncRNA signature. The KEGG and GO analyses were performed to screen for pathways and biological functions associated with key genes. The ESTIMATE and CIBERSORT algorithms were used to determine the level of immune cells in LGGs and the immune microenvironment fraction. In addition, DMlncRNAs were assessed using survival analysis, ROC curves, correlation analysis, external validation, independent prognostic analysis, clinical stratification analysis and qRT-PCR.

Results: We identified five DMlncRNAs with prognostic value for LGGs and established a prognostic signature using them. The Kaplan–Meier analysis revealed 10-years survival rate of 10.10% [95% confidence interval (CI): 3.27–31.40%] in high-risk patients and 57.28% (95% CI: 43.17–76.00%) in low-risk patients. The hazard ratio (HR) and 95% CI of risk scores were 1.013 and 1.009–1.017 (p < 0.001), respectively, based on the univariate Cox regression analysis and 1.009 and 1.004–1.013 (p < 0.001), respectively, based on the multivariate Cox regression analysis. Therefore, the five-lncRNAs were identified as independent prognostic markers for patients with LGGs. Furthermore, GO and KEGG analyses revealed that these lncRNAs are involved in the prognosis and tumorigenesis of LGGs by regulating cancer pathways and DNA methylation.

Conclusion: The findings of the study provide key information regarding the functions of lncRNAs in DNA methylation and reveal that DNA methylation can regulate tumour progression through modulation of the immune microenvironment and genomic instability. The identified prognostic lncRNAs have high potential for clinical grouping of patients with LGGs to ensure effective treatment and management.

The function and mechanism of the JARID2/CCND1 axis in modulating glioma cell growth and sensitivity to temozolomide (TMZ)

A maximal surgical resection followed by radiotherapy and chemotherapy with temozolomide (TMZ) as the representative agent is the standard therapy for gliomas. However, tumor cell resistance to radiotherapy and chemotherapy leads to poor prognosis and high mortality in patients with glioma. In the present study, we demonstrated that JARID2 was downregulated and CCND1 was upregulated within glioma tissues of different grades and glioma cells. In tissue samples, JARID2 was negatively correlated with CCND1. JARID2 overexpression significantly inhibited glioma cell viability, promoted glioma cell apoptosis upon TMZ treatment, and increased p21, cleaved-PARP, and cleaved-caspase3 in TMZ-treated glioma cells. JASPAR tool predicted the possible binding sites between JARID2 and CCND1 promoter regions; through direct binding to CCND1 promoter region, JARID2 negatively regulated CCND1 expression. Under TMZ treatment, JARID2 overexpression inhibited CCND1 expression, promoted glioma cell apoptosis, and increased p21, cleaved-PARP, and cleaved-caspase3 in glioma cells treated with TMZ; meanwhile, CCND1 overexpression exerted opposite effects on glioma cells treated with TMZ and partially reversed the effects of JARID2 overexpression. In conclusion, JARID2 targets and inhibits CCND1. The JARID2/CCND1 axis modulates glioma cell growth and glioma cell sensitivity to TMZ.

Research update on the anticancer effects of buparlisib

Buparlisib is a highly efficient and selective PI3K inhibitor and a member of the 2,6-dimorpholinopyrimidine-derived family of compounds. It selectively inhibits four isomers of PI3K, PI3Kα, PI3Kβ, PI3Kγ and PI3Kδ, by competitively binding the lipid kinase domain on adenosine 5'-triphosphate (ATP), and serves an important role in inhibiting proliferation, promoting apoptosis and blocking angiogenesis, predominantly by antagonizing the PI3K/AKT pathway. Buparlisib has been confirmed to have a clinical effect in patients with solid tumors and hematological malignancies. A global, phase II clinical trial with buparlisib and paclitaxel in head and neck squamous cell carcinoma has now been completed, with a manageable safety profile. Buparlisib currently has fast-track status with the United States Food and Drug Administration. The present review examined the biochemical structure, pharmacokinetic characteristics, preclinical data and ongoing clinical studies of buparlisib. The various mechanisms of influence of buparlisib in tumors, particularly in preclinical research, were summarized, providing a theoretical basis and direction for basic research on and clinical treatment with buparlisib.

TRIM31 enhances chemoresistance in glioblastoma through activation of the PI3K/Akt signaling pathway

Temozolomide (TMZ) resistance is a complication of treatment of glioma, and new strategies are urgently required to overcome chemoresistance in glioma cells. In the present study, it was demonstrated that tripartite motif-containing 31 (TRIM31) was abnormally upregulated in glioma tissues and cell lines compared with normal samples. Furthermore, the role of TRIM31 was assessed by overexpressing and knocking down its expression. Overexpression of TRIM31 increased cell viability, increased TMZ IC₅₀ values and inhibited apoptosis in A172 and U251 cells; whereas overexpression of TRIM31 decreased the expression of the apoptosis-associated protein p53. Knockdown of TRIM31 increased apoptosis in cells treated with TMZ. Additionally, the mechanisms by which TRIM31 affected glioma cells treated with TMZ were determined. Overexpression of TRIM31 increased phosphorylation of AKT and inhibiting the PI3K/AKT signaling pathway abolished the increase in cell viability and decreased phospho-Akt protein expression in TRIM31 overexpressing A172 cells treated with TMZ. Together, the findings suggest that TRIM31 may be a potentially novel target for glioma chemotherapy.

A steroidal saponin form Paris vietnamensis (Takht.) reverses temozolomide resistance in glioblastoma cells via inducing apoptosis through ROS/PI3K/Akt pathway

Glioblastoma is one of the most difficult cancers to treat with a 5-year overall survival rate less than 5%. Temozolomide (TMZ) is an effective drug for prolonging the overall survival time of patients, while drug-resistance is an important clinical problem at present. Pennogenin-3-α-L-rhamnopyranosyl-(1→4)-[α-Lrhamno-pyranosyl-(1→2)]- β-D-glucopyranoside (N45), a steroidal saponin, was isolated from the rhizomes of Paris vietnamensis (Takht.), which is used as a Traditional Chinese Medicine and has been reported to possess preclinical anticancer efficacy in various cancer types. However, the mechanism of the inhibition of N45 on glioblastoma cells and its possible application in the treatment of chemotherapy-resistant glioblastoma cells are still unknown. In this study, we use cellular methodological experiments including cell counting kit-8 (CCK-8) assay, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining assay, flow cytometry assay, transmission electron microscopy (TEM) and Western blot. The results show that N45 significantly suppresses the proliferation of glioblastoma cells and TMZ-resistant glioblastoma cells (U87R) by inducing mitochondrial apoptosis through reactive oxygen species (ROS)/phosphoinositide 3-kinase (PI3K)/Akt signal pathway, and the N-acetyl-L-cysteine (NAC) combined with N45 effectively reduced N45-mediated apoptosis and reversed the inhibition of PI3K/Akt signal pathway. In addition, N45 decreased the drug-resistance by down-regulation of nuclear factor kappa-B p65 (NF-κB p65) to attenuate O⁶-methylguanine-DNA methyltransferase (MGMT) in TMZ-resistant glioblastoma cells (U87R). Our findings proved that N45 might be a potential therapeutic agent against glioblastoma and TMZ-resistant glioblastoma, promising to be a potential agent to reduce drug resistance.

Polyphyllin VII Promotes Apoptosis and Autophagic Cell Death via ROS-Inhibited AKT Activity, and Sensitizes Glioma Cells to Temozolomide

The high recurrence frequency of gliomas but deficiency of effective treatment and prevalent chemoresistance have elicited interests in exploring and developing new agents. Paris polyphyllins are monomers extracted from rhizome of Paris polyphylla var. yunnanensis. Here, we first reported that polyphyllin VII (PP7) exhibited cytotoxic effect on glioma cells. PP7 significantly suppressed the viability and induced cell death of U87-MG and U251 cells after 24 h, with the IC50 values 4.24 ± 0.87 μM and 2.17 ± 0.14 μM, respectively. Both apoptotic and autophagic processes were involved in the cytotoxic effect of PP7, as PP7 activated the Bcl2/Bax pathway and the inhibition of autophagy partly rescued the toxicity of PP7 in glioma cells. In addition, an inhibition of AKT/mTORC1 activity was found after PP7 administration, and it seemed that the overproduction of reactive oxygen species (ROS) was responsible for this effect. Namely, the removal of ROS by NAC treatment mitigated PP7-induced cell death, autophagy, and its effect on the AKT/mTORC1 signaling. Additionally, a combination assay of PP7 with temozolomide (TMZ), the most used chemotherapy for glioma patients, was performed resulting in synergism, while PP7 reduced TMZ resistance through inhibition of MGMT expression. Thus, our study reports PP7 as a potential agent for glioma treatment and reveals its underlying mechanisms of action.

The reversal of MRP1 expression induced by low-frequency and low-intensity ultrasound and curcumin mediated by VEGF in brain glioma

Purpose: To explore the effect of curcumin and low-frequency and low-intensity ultrasound (LFLIU) on C6 and U87 cell, and whether LFLIU could inhibit multidrug resistance protein 1 (MRP1) by increasing the sensitivity of curcumin via vascular epithelial growth factor (VEGF)/PI3K/Akt signaling pathway targeting.

Methods: C6 and U87 cells were treated with various doses of curcumin and/or different intensities of LFLIU for 60 s. After 24 hrs, the effects of curcumin and/or LFLIU on the proliferation of C6 and U87 cells were examined. Real-time PCR and western blot analysis were used to detect the expression of VEGF and MRP1 at both mRNA and protein levels. The expression of MRP1 in C6 and U87 cells was also determined following stimulation with recombinant human VEGF and/or LY294002.

Results: Curcumin and LFLIU inhibited the proliferation of glioma cells in an intensity- or dose-dependent manner. Furthermore, survivin was significant after combined treatment compares with that of curcumin or LFLIU treatment alone. VEGF and MRP1 were highly expressed in C6 and U87 cells, curcumin and LFLIU alone or in combination could decrease the expression of both VEGF and MRP1. MRP1 expression was down-regulated following LY294002 treatment, which blocked after exposure to VEGF.

Conclusion: The synergistic effects, such as a higher inhibition rate, and lower expressions of MRP1 and VEGF, of combined curcumin and LFLIU against glioma was much better than that of a single treatment. The down-regulation of MRP1 may be related with the VEGF/PI3K/Akt pathway in glioma.

Combined targeting of PI3K and MEK effector pathways via CED for DIPG therapy

BACKGROUND

Midline gliomas like diffuse intrinsic pontine glioma (DIPG) carry poor prognosis and lack effective treatment options. Studies have implicated amplifications in the phosphatidylinositol 3-kinase (PI3K) signaling pathway in tumorigenesis; compensatory activation of parallel pathways (eg, mitogen-activated protein kinase [MEK]) may underlie the resistance to PI3K inhibition observed in the clinic.

METHODS

Three patient-derived cell lines (SU-DIPG-IV, SU-DIPG-XIII, and SF8628) and a mouse-derived brainstem glioma cell line were treated with PI3K (ZSTK474) and MEK (trametinib) inhibitors, alone or in combination. Synergy was analyzed using Chou-Talalay combination index (CI). These agents were also used alone or in combination in a subcutaneous SU-DIPG-XIII tumor model and in an intracranial genetic mouse model of DIPG, given via convection-enhanced delivery (CED).

RESULTS

We found that these agents abrogate cell proliferation in a dose-dependent manner. Combination treatments were found to be synergistic (CI < 1) across cell lines tested. They also showed significant tumor suppression when given systemically against a subcutaneous DIPG model (alone or in combination) or when given via direct intracranial injection (CED) in a intracranial DIPG mouse model (combination only, median survival 47 vs 35 days post-induction, P = .038). No significant short- or long-term neurotoxicity of ZSTK474 and trametinib delivered via CED was observed.

CONCLUSIONS

Our data indicate that ZSTK474 and trametinib combinatorial treatment inhibits malignant growth of DIPG cells in vitro and in vivo, prolonging survival. These results suggest a promising new combinatorial approach using CED for DIPG therapy, which warrants further investigation.

Bufalin Induces Apoptosis and Improves the Sensitivity of Human Glioma Stem-Like Cells to Temozolamide

Glioma is the most common malignant tumor of the central nervous system, and it is characterized by high relapse and fatality rates and poor prognosis. Bufalin is one of the main ingredients of Chan-su, a traditional Chinese medicine (TCM) extracted from toad venom. Previous studies revealed that bufalin exerted inhibitory effects on a variety of tumor cells. To demonstrate the inhibitory effect of bufalin on glioma cells and glioma stem-like cells (GSCs) and discuss the underlying mechanism, the proliferation of glioma cells was detected by MTT and colony formation assays following treatment with bufalin. In addition, we investigated whether bufalin inhibits or kills GSCs using flow cytometry, Western blotting, and reverse transcription polymerase chain reaction analysis (RT-PCR). Finally, we investigated whether bufalin could improve the therapeutic effect of temozolomide (TMZ) and discussed the underlying mechanism. Taken together, our data demonstrated that bufalin inhibits glioma cell growth and proliferation, inhibits GSC proliferation, and kills GSCs. Bufalin was found to induce the apoptosis of GSCs by upregulating the expression of the apoptotic proteins cleaved caspase 3 and poly(ADP-ribose) polymerase (PARP) and by downregulating the expression of human telomerase reverse transcriptase, which is a marker of telomerase activity. Bufalin also improved the inhibitory effect of TMZ on GSCs by activating the mitochondrial apoptotic pathway. These results suggest that bufalin damages GSCs, induces apoptosis, and enhances the sensitivity of GSCs to TMZ.

Down-regulation of ABCE1 inhibits temozolomide resistance in glioma through the PI3K/Akt/NF-κB signaling pathway

The ATP binding cassette (ABC) E1 (ABCE1), a member of the ABC family, was originally described as the RNase L inhibitor. Through forming a heterodimer with RNase L, ABCE1 participates in the negative regulation of the 2-5A/RNase L system and thus mediates a wide range of biological functions. Recent evidence has shown the new roles of ABCE1 in tumorigenesis. However, there have been no investigations on the specific effect of ABCE1 on glioma. In the present study, we examined the expression pattern and possible role of ABCE1 in glioma. Our study demonstrated that ABCE1 was up-regulated in glioma tissues and cell lines. Down-regulation of ABCE1 inhibited temozolomide (TMZ) resistance of glioma cells in vitro and in vivo In addition, we found that the PI3K/Akt/NF-κB pathway was involved in ABCE1-mediated chemoresistance of glioma cells. Taken together, our study suggested ABCE1 as a promising target for glioma chemotherapy.

Novel approach to temozolomide resistance in malignant glioma: connexin43-directed therapeutics

Resistance of malignant glioma, including glioblastoma (GBM), to the chemotherapeutic temozolomide (TMZ) remains a key obstacle in treatment strategies. The gap junction protein connexin43 (Cx43) has complex roles in the establishment, progression, and persistence of malignant glioma. Recent findings demonstrate that connexins play an important role in the microenvironment of malignant glioma and that Cx43 is capable of conferring chemotherapeutic resistance to GBM cells. Carboxyl-terminal Cx43 peptidomimetics show therapeutic promise in overcoming TMZ resistance via mechanisms that may include modulating junctional activity between tumor cells and peritumoral cells and/or downstream molecular signaling events mediated by Cx43 protein binding. High levels of intra-tumor and inter-tumor heterogeneity make it difficult to clearly define specific populations for Cx43-targeted therapy; hence, development of in vitro models that better mimic the microenvironment of malignant glioma, and the incorporation of patient-derived stem cells, could provide opportunities for patient-specific drug screening. This review summarizes recent advances in understanding the roles of Cx43 in malignant glioma, with a special focus on tumor microenvironment, TMZ resistance, and therapeutic opportunity offered by Cx43 peptidomimetics.