MicroRNA-125b inhibitor sensitizes human primary glioblastoma cells to chemotherapeutic drug temozolomide on invasion

MicroRNAs as the pivotal regulators of Temozolomide resistance in glioblastoma

Glioblastoma (GBM) is an aggressive nervous system tumor with a poor prognosis. Although, surgery, radiation therapy, and chemotherapy are the current standard protocol for GBM patients, there is still a poor prognosis in these patients. Temozolomide (TMZ) as a first-line therapeutic agent in GBM can easily cross from the blood-brain barrier to inhibit tumor cell proliferation. However, there is a high rate of TMZ resistance in GBM patients. Since, there are limited therapeutic choices for GBM patients who develop TMZ resistance; it is required to clarify the molecular mechanisms of chemo resistance to introduce the novel therapeutic targets. MicroRNAs (miRNAs) regulate chemo resistance through regulation of drug metabolism, absorption, DNA repair, apoptosis, and cell cycle. In the present review we discussed the role of miRNAs in TMZ response of GBM cells. It has been reported that miRNAs mainly induced TMZ sensitivity by regulation of signaling pathways and autophagy in GBM cells. Therefore, miRNAs can be used as the reliable diagnostic/prognostic markers in GBM patients. They can also be used as the therapeutic targets to improve the TMZ response in GBM cells.

Multiple therapeutic approaches of glioblastoma multiforme: From terminal to therapy

Glioblastoma multiforme (GBM) is an aggressive brain cancer showing poor prognosis. Currently, treatment methods of GBM are limited with adverse outcomes and low survival rate. Thus, advancements in the treatment of GBM are of utmost importance, which can be achieved in recent decades. However, despite aggressive initial treatment, most patients develop recurrent diseases, and the overall survival rate of patients is impossible to achieve. Currently, researchers across the globe target signaling events along with tumor microenvironment (TME) through different drug molecules to inhibit the progression of GBM, but clinically they failed to demonstrate much success. Herein, we discuss the therapeutic targets and signaling cascades along with the role of the organoids model in GBM research. Moreover, we systematically review the traditional and emerging therapeutic strategies in GBM. In addition, we discuss the implications of nanotechnologies, AI, and combinatorial approach to enhance GBM therapeutics.

Therapeutic Targeting of the Notch Pathway in Glioblastoma Multiforme

BACKGROUND

Glioblastoma (GBM) is the most common and deadly form of brain tumor. After standard treatment of resection, radiotherapy, and chemotherapy, the 5-year survival is <5%. In recent years, research has uncovered several potential targets within the Notch signaling pathway, which may lead to improved patient outcomes.

METHODS

A literature search was performed for articles containing the terms "Glioblastoma" and "Receptors, Notch" between 2003 and July 2015. Of the 62 articles retrieved, 46 met our criteria and were included in our review. Nine articles were identified from other sources and were subsequently included, leaving 55 articles reviewed.

RESULTS

Of the 55 articles reviewed, 47 used established human GBM cell lines. Seventeen articles used human GBM surgical samples. Forty-five of 48 articles that assessed Notch activity showed increased expression in GBM cell lines. Targeting the Notch pathway was carried out through Notch knockdown and overexpression and targeting δ-like ligand, Jagged, γ-secretase, ADAM10, ADAM17, and Mastermindlike protein 1. Arsenic trioxide, microRNAs, and several other compounds were shown to have an effect on the Notch pathway in GBM. Notch activity in GBM was also shown to be associated with hypoxia and certain cancer-related molecular pathways such as PI3K/AKT/mTOR and ERK/MAPK. Most articles concluded that Notch activity amplifies malignant characteristics in GBM and targeting this pathway can bring about amelioration of these effects.

CONCLUSIONS

Recent literature suggests targeting the Notch pathway has great potential for future therapies for GBM.

MiR-29b inhibits the growth of glioma via MYCN dependent way

MiR-29b is widely involved in diverse cancers. We plan to study its role in glioma. The expression of miR-29b was detected by real-time polymerase chain reaction (PCR) and we found the expression of miR-29b was decreased in glioma. Cell proliferation was evaluated by cell counting kit (CCK8) and 5-Ethynyl-2'- deoxyuridine (EdU) and cell apoptosis was assayed with flow cytometry assay (FCA), which indicated miR-29b can inhibit the proliferation and promote the apoptosis of glioma cells. The target of miR-29b was predicted using miRanda, TargetScan and PicTar sofeware and we also found MYCN was a direct target of miR-29b in glioma cells and miR-29b inhibited the proliferation of glioma cells via MYCN dependent way. Subcutaneous xenotransplantation model was designed to investigate the affection of miR-29b on glioma growth. The effectiveness of miR-29b for glioma prediction was also performed and we determined miR-29b can stably exist and may act as a biomarker for the diagnosis of glioma. As a conclusion, miR-29b inhibits the growth of glioma via MYCN dependent way and can be a biomarker for the diagnosis of glioma.

The functional mechanism of miR-125b in gastric cancer and its effect on the chemosensitivity of cisplatin

Numerous studies have shown drug resistance of gastric cancer cells could be modulated by abnormal expression of microRNAs. Cisplatin (DDP) is one of the most commonly used drugs for chemotherapy of gastric cancer. In this study, the potential function of miR-125b on DDP resistance in gastric cancer cells was investigated. Sixteen miRNAs significantly differential expressed in gastric tumor tissues and adjacent tissues were characterized and their corresponding putative target genes were also screened. MiR-125b was selected as our focus for its evident down-regulated expression among candidate genes. Real-time polymerase chain reaction assay indicated that miR-125b was significantly down-regulated in gastric cancer tissues and various cell lines. HER2 was identified as a target gene of miR-125b by dual luciferase reporter assay and Western blot. Moreover, miR-125b overexpression inhibited not only the proliferation, migration, and invasion abilities of HGC-27 and MGC-803 cells, but also in vivo tumor growth of MGC-803 cells by an intratumoral delivery approach. Notably, we observed up-regulated miR-125b contributed to the chemosensitivity of DDP in HGC-27 and MGC-803 cells at different concentrations and also possessed sensibilization for DDP at different times. MiR-125b expression was found to be related to lymph node metastasis, HER2 expression and overall survival of patients through correlation analysis. Collectively, these results indicate miR-125b may regulate DDP resistance as a promising therapeutic target for gastric cancer treatment in future.

Demethoxycurcumin was superior to temozolomide in the inhibition of the growth of glioblastoma stem cells in vivo

Temozolomide (TMZ) is widely used in the treatment of glioblastoma multiforme (GBM) as it can effectively inhibit the growth of GBM for some months; however, this cancer type is still incurable. The existence of glioma stem cells (GSCs) is thought to be responsible for the invariable recurrence of GBM after treatment, but GSCs are insensitive to TMZ. Our recent research showed that demethoxycurcumin (DMC), a component of curcumin, was superior to TMZ in its ability to inhibit proliferation and induce apoptosis of GSCs in vitro. In addition, the combined treatment of TMZ + DMC induced more obvious anti-GSC effects. However, in this study, no obvious synergistic anti-GSC effects of TMZ + DMC were found in vivo, while DMC was still superior to TMZ with respect to growth inhibition of GSCs in vivo. Furthermore, immunohistochemistry for proliferating cell nuclear antigen (PCNA) showed that such inhibitory effects were mainly related to the inhibition of cell proliferation rather than to apoptosis. However, a high concentration of DMC (50 mg/kg) alone or combined with TMZ could also induce approximately 10 % of the cells to undergo apoptosis according to a terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. Finally, an investigation of the underlying mechanism revealed that the Janus kinase (JAK)/signal transducers and activators of transcription (STAT) 3 signaling pathway played an important role in the anti-GSC effects. When the JAK inhibitor AG490 was applied, the anti-GSC effects of DMC were enhanced. Taken together, the present work reveals that DMC is superior to TMZ with respect to its anti-GSC effects in vivo, which are mediated through the inhibition of the activation of the JAK/STAT3 pathway; however, DMC demonstrated no synergistic effects with TMZ.

miR-155 Regulates Glioma Cells Invasion and Chemosensitivity by p38 Isforms In Vitro

The critical role of microRNAs in cancer development has been extensively described. miRNAs are both specific markers and putative therapy targets. miR-155 has been identified to be an oncomiRNA and is highly expressed in several solid cancers, including glioblastoma. In this study, we found that miR-155 is a good potential therapy target. Knockdown of miR-155 sensitizes glioma cells to the chemotherapy of temozolomide (TMZ) by targeting the p38 isoforms mitogen-activated protein kinase 13 [MAPK13, also known as p38 MAPKδ or stress-activated protein kinase 4 (SAPK4)] and MAPK14 (also known as p38 MAPKα). As tumor suppressor genes, MAPK13 and MAPK14 play important roles in lowering the accumulation of reactive oxygen species (ROS), inducing cell apoptosis, and slowing the progression of cancer. Knockdown of miR-155 enhanced the anticancer effect of TMZ on glioma by targeting the MAPK13 and MAPK14-mediated oxidative stress and apoptosis, but did not affect the secretion of MMP2 and MMP9.

Regulation of expression of O6-methylguanine-DNA methyltransferase and the treatment of glioblastoma (Review)

O-6-methylguanine-DNA methyltransferase (MGMT) is an abundantly expressed nuclear protein dealkylating O⁶-methylguanine (O⁶-MG) DNA residue, thus correcting the mismatches of O⁶-MG with a thymine residue during DNA replication. The dealkylating effect of MGMT is relevant not only in repairing DNA mismatches produced by environmental alkylating agents promoting tumor pathogenesis, but also when alkylating molecules are applied in the chemotherapy of different cancers, including glioma, the most common primary tumor of the central nervous system. Elevated MGMT gene expression is known to confer resistance to the treatment with the alkylating drug temozolomide in patients affected by gliomas and, on the contrary, methylation of MGMT gene promoter, which causes reduction of MGMT protein expression, is known to predict a favourable response to temozolomide. Thus, detecting expression levels of MGMT gene is crucial to indicate the option of alkylating agents or to select patients directly for a second line targeted therapy. Further study is required to gain insights into MGMT expression regulation, that has attracted growing interest recently in MGMT promoter methylation, histone acetylation and microRNAs expression. The review will focus on the epigenetic regulation of MGMT gene, with translational applications to the identification of biomarkers predicting response to therapy and prognosis.

Decreased Expression of miR-15b in Human Gliomas is Associated with Poor Prognosis

MicroRNA-15b (miR-15b) has been demonstrated to suppress proliferation by arresting cell cycle progression and inducing apoptosis in glioma cells. However, the prognostic value of miR-15b expression in human gliomas remains unclear. In the present study, the authors examined the expression profile in glioma specimens and the prognostic value of miR-15b in patients with gliomas. Real-time polymerase chain reaction assay was employed to detect the expression levels of miR-15b in 92 glioma tissues categorized by World Health Organization (WHO) histopathological grades. However, the prognostic value of miR-15b in human glioma has not been evaluated yet. MiR-15b expression in human glioma tissues was distinctly lower than in normal brain tissues. Furthermore, the expression of miR-15b notably decreased with the ascending histopathological grade of gliomas. Additionally, Kaplan-Meier survival analysis showed that low miR-15b expression was associated with poor overall survival in patients with gliomas. Similarly, miR-15b reduction occurred with increasing frequency in glioma patients with lower Karnofsky performance scale (KPS) scores than in those with higher KPS scores. No significant difference was observed between miR-15b expression and gender, age, and tumor location. These findings revealed that a lower expression level of miR-15b was closely related to a shorter overall survival, suggesting that miR-15b could be an intrinsic factor that plays an important role in the malignant progression of gliomas.

MicroRNA expression signatures and their correlation with clinicopathological features in glioblastoma multiforme

The increasing interest in identifying molecular biomarkers to determine patient prognosis in glioblastoma multiforme (GBM) has resulted in several microRNA (miRNA)-based signatures able to predict progression-free and overall survival. However, the coherency between these signatures is small, and correlations to clinicopathological features other than survival are seldom seen. The aim of this study was to identify any significant relationship between miRNA signatures and clinicopathological data by combining pathological features with miRNA and mRNA analysis in fourteen GBM patients. In total, 161 miRNAs were shown to cluster the GBM tumor samples into long- and short-term-surviving patients. Many of these miRNAs were associated with differential expression in GBM, including a number of miRNAs shown to confer risk or protection with respect to clinical outcome and to modulate the mesenchymal mode of migration and invasion. An inverse relationship between miR-125b and nestin expression was identified and correlated with overall survival in GBM patients, eloquently illustrating how clinicopathological findings and molecular profiling may be a relevant combination to predict patient outcome. The intriguing finding that many of the differentially expressed miRNAs contained exosome-packaging motifs in their mature sequences suggests that we must expand our view to encompass the complex intercellular communication in order to identify molecular prognostic biomarkers and to increase our knowledge in the field of GBM pathogenesis.