Mannose inhibits proliferation and promotes apoptosis to enhance sensitivity of glioma cells to temozolomide through Wnt/β-catenin signaling pathway.

Temozolomide (TMZ) is generally applied for glioma treatment, while drug resistance of TMZ limits its therapeutic efficacy. Mannose exerts evident anti-tumor effect. We intended to investigate whether mannose enhanced TMZ sensitivity to glioma and examined the underlying mechanism. MTT and clone formation assays were performed to detect cell viability and proliferation. Cell apoptosis was measured by flow cytometry. The protein and gene expression levels were detected by Western blot and qRT-PCR assays. Xenograft glioma model was established to explore the influence of mannose in vivo. Mannose inhibited glioma cell growth, which was facilitated by knockdown of phosphomannose isomerase (PMI) while reversed by overexpression of PMI. Mannose enhanced the sensitivity of glioma cells to TMZ, indicated by the further inhibited cell viability and colony formation and the aggravated cell apoptosis, which was reversed by overexpression of O6-methylguanine DNA methyltransferase (MGMT). Furthermore, mannose and TMZ inhibited MGMT expression and Wnt/β-catenin activation. Moreover, activating Wnt/β-catenin pathway blocked anti-proliferative effect induced by mannose and TMZ, which was further suppressed by overexpressed MGMT. Mannose inhibited glioma growth, suppressed Ki67 and downregulated MGMT and β-catenin in vivo. Mannose inhibited MGMT to enhance sensitivity of glioma cells to TMZ, with Wnt/β-catenin pathway involvement. Our data suggested that mannose could be an innovative agent to improve glioma treatment, particularly in TMZ-resistant glioma with high MGMT.

Fei YQ ，Shi RT ，Zhou YF ，Wu JZ ，Song Z ... -  《-》

β-catenin contributes to cordycepin-induced MGMT inhibition and reduction of temozolomide resistance in glioma cells by increasing intracellular reactive oxygen species.

Glioblastoma multiforme (GBM) is one of the most aggressive human tumors, and it has a poor prognosis. Temozolomide (TMZ) is the primary alkylating agent used to treat GBM. Nevertheless, a number of GBM patients are resistant to TMZ. Therefore, there is an urgent need for more effective therapeutic options. Cordycepin (COR) is a natural chemical with anti-tumor effects, although its mechanism of action is poorly understood. Several lines of evidence suggest that O6-methylguanine DNA methyltransferase (MGMT) repairs damaged DNA and contributes to drug resistance to TMZ in gliomas. The Wnt/β-catenin pathway regulates MGMT gene expression. However, whether cordycepin inhibits MGMT expression by downregulating the β catenin pathway and augmenting chemosensitivity to TMZ in glioma cells remains unclear. In the present study, we found that cordycepin inhibited the viability of glioma cells and induced apoptosis, cell cycle arrest, overproduction of reactive oxygen species (ROS) and reduction of glutathione (GSH) in vitro. Moreover, cordycepin significantly reduced tumor volume and prolonged median survival of tumor-bearing rats in vivo. We also found that cordycepin inhibited MGMT expression and augmented chemosensitivity to TMZ in glioma cells in vitro and in vivo, accompanied by downregulation of p-GSK-3β and β-catenin. Moreover, overexpression of MGMT reversed the synergistic effect of cordycepin and TMZ. Pharmacological inhibition of GSK-3β with CHIR-99021 or overexpression of β-catenin reversed cordycepin-induced reduction of cell viability, downregulation of β-catenin and MGMT, increase of apoptosis and reduction of TMZ resistance. Furthermore, we found that β-catenin regulated cordycepin-induced overproduction of ROS by decreasing GSH. Inhibition of ROS production with N-acetyl-l-cysteine (NAC) not only rescued the reduction of cell viability but also eliminated β-catenin and MGMT inhibition, prevented glioma cells apoptosis and reversed the synergistic effect of cordycepin and TMZ. Taken together, we demonstrated that β-catenin contributed to cordycepin-induced MGMT inhibition and reduction of TMZ resistance in glioma cells via increasing intracellular ROS. These results indicate that cordycepin may be a novel agent to improve GBM treatment, especially in TMZ-resistant GBM with high MGMT expression.

Bi Y ，Li H ，Yi D ，Bai Y ，Zhong S ，Liu Q ，Chen Y ，Zhao G ... -  《-》

Resveratrol restores sensitivity of glioma cells to temozolamide through inhibiting the activation of Wnt signaling pathway.

Malignant gliomas are aggressive primary neoplasms that originate in the glial cells of the brain or the spine with notable resistance to standard treatment options. We carried out the study with the aim to shed light on the sensitization of resveratrol to temozolomide (TMZ) against glioma through the Wnt signaling pathway. Initially, glioma cell lines with strong resistance to TMZ were selected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Then, the glioma cells were subjected to resveratrol, TMZ, Wnt signaling pathway inhibitors, and activators. Cell survival rate and inhibitory concentration at half maximum value were detected by MTT, apoptosis by flow cytometry, and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining, in vitro proliferation by hanging drop method and β-catenin translocation into nuclei by TOP/FOP-FLASH assay. The expressions of the Wnt signaling pathway-related and apoptosis-related factors were determined by western blot analysis. Nude mice with glioma xenograft were established to detect tumorigenic ability. Glioma cell lines T98G and U138 which were highly resistant to TMZ were selected for subsequent experiments. Resveratrol increased the efficacy of TMZ by restraining cell proliferation, tumor growth, and promoting cell apoptosis in glioma cells. Resveratrol inhibited Wnt2 and β-catenin expressions yet elevated GSK-3β expression. Moreover, the Wnt signaling pathway participates in the sensitivity enhancing of resveratrol to TMZ via regulating O 6 -methylguanine-DNA methyltransferase (MGMT) expression. Resveratrol sensitized TMZ-induced glioma cell apoptosis by repressing the activation of the Wnt signaling pathway and downregulating MGMT expression, which may confer new thoughts to the chemotherapy of glioma.

Yang HC ，Wang JY ，Bu XY ，Yang B ，Wang BQ ，Hu S ，Yan ZY ，Gao YS ，Han SY ，Qu MQ ... -  《-》

20(S)-ginsenoside-Rg3 reverses temozolomide resistance and restrains epithelial-mesenchymal transition progression in glioblastoma.

Glioblastoma multiforme (GBM) is one of the most malignant human intracranial tumors. Temozolomide (TMZ) is the primary alkylating agent for GBM patients. However, many GBM patients are resistant to TMZ. Therefore, patients with GBM urgently need more effective therapeutic options. 20(S)-ginsenoside-Rg3 (20(S)-Rg3) is a natural chemical with anti-tumor effects, but at present there is little understanding of its functional mechanism. Several research reports have demonstrated that O6 -methylguanine DNA-methyltransferase (MGMT) repairs damaged DNA and contributes to TMZ resistance in gliomas. In addition, recent studies have shown that MGMT gene expression could be regulated by the Wnt/β-catenin pathway. However, whether 20(S)-Rg3 inhibits MGMT expression and augments chemosensitivity to Temozolomide (TMZ) in glioma cells remains unclear. In this study, we explored the modulating effects of 20(S)-Rg3 on MGMT. We used glioma cell lines, primary cell strain (including T98G, U118 and GBM-XX; all of them are MGMT-positive glioma cell lines) and xenograft glioma models to examine whether 20(S)-Rg3 increased the sensitivity to TMZ and to reveal the underlying mechanisms. We found that the MGMT expression was effectively downregulated by 20(S)-Rg3 via the Wnt/β-catenin pathway in glioma cell lines, and TMZ resistance was significantly reversed by 20(S)-Rg3. Meanwhile, 20(S)-Rg3 shows no obvious cytotoxicity at its effective dose and is well tolerated in vivo. In addition, we found that 20(S)-Rg3 significantly restrains the epithelial-mesenchymal transition (EMT) progression of glioma cells. Taken together, these results indicate that 20(S)-Rg3 may be a novel agent to use in treatment of GBM, especially in TMZ-resistant GBM with high MGMT expression.

Chen Z ，Wei X ，Shen L ，Zhu H ，Zheng X ... -  《-》

A positive feedback loop of lncRNA-RMRP/ZNRF3 axis and Wnt/β-catenin signaling regulates the progression and temozolomide resistance in glioma.

Drug resistance strikingly limits the therapeutic effect of temozolomide (TMZ) (a common drug for glioma). Long non-coding RNA (lncRNA) RMRP has been found to be implicated in glioma progression. However, the effect of RMRP on TMZ resistance along with related molecular mechanisms is poorly defined in glioma. In the present study, RMRP, ZNRF3, and IGF2BP3 were screened out by bioinformatics analysis. The expression levels of lncRNAs and mRNAs were measured by RT-qPCR assay. Protein levels of genes were detected by western blot and immunofluorescence assays. ZNRF3 mRNA stability was analyzed using Actinomycin D assay. Cell proliferative ability and survival rate were determined by CCK-8 assay. Cell apoptotic pattern was estimated by flow cytometry. The effect of RMRP knockdown on the growth of TMZ-treated glioma xenograft tumors was explored in vivo. The relationships of IGF2BP3, RMRP, and ZNRF3 were explored by bioinformatics prediction analysis, RNA immunoprecipitation, luciferase, and RNA pull-down, and chromatin immunoprecipitation assays. The results showed that RMRP was highly expressed in glioma. RMRP knockdown curbed cell proliferation, facilitated cell apoptosis and reduced TMZ resistance in glioma cells, and hindered the growth of TMZ-treated glioma xenograft tumors. RMRP exerted its functions by down-regulating ZNRF3 in glioma cells. IGF2BP3 interacted with RMRP and ZNRF3 mRNA. IGF2BP3 knockdown weakened the interaction of Argonaute 2 (Ago2) and ZNRF3. RMRP reduced ZNRF3 expression and mRNA stability by IGF2BP3. RMRP knockdown inhibited β-catenin expression by up-regulating ZNRF3. The inhibition of Wnt/β-catenin signaling pathway by XAV-939 weakened RMRP-mediated TMZ resistance in glioma cells. β-catenin promoted RMRP expression by TCF4 in glioma cells. In conclusion, RMRP/ZNRF3 axis and Wnt/β-catenin signaling formed a positive feedback loop to regulate TMZ resistance in glioma. The sustained activation of Wnt/β-catenin signaling by RMRP might contribute to the better management of cancers.

Liu T ，Hu J ，Han B ，Tan S ，Jia W ，Xin Y ... -  《Cell Death & Disease》