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 ... -  《-》

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 ... -  《-》

Cordycepin Augments the Chemosensitivity of Human Glioma Cells to Temozolomide by Activating AMPK and Inhibiting the AKT Signaling Pathway.

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

Pharmacological inhibition of serine synthesis enhances temozolomide efficacy by decreasing O(6)-methylguanine DNA methyltransferase (MGMT) expression and reactive oxygen species (ROS)-mediated DNA damage in glioblastoma.

Glioblastoma (GBM) is the most malignant primary tumor in the central nervous system of adults. Temozolomide (TMZ), an alkylating agent, is the first-line chemotherapeutic agent for GBM patients. However, its efficacy is often limited by innate or acquired chemoresistance. Cancer cells can rewire their metabolic programming to support rapid growth and sustain cell survival against chemotherapies. An example is the de novo serine synthesis pathway (SSP), one of the main branches from glycolysis that is highly activated in multiple cancers in promoting cancer progression and inducing chemotherapy resistance. However, the roles of SSP in TMZ therapy for GBM patients remain unexplored. In this study, we employed NCT503, a highly selective inhibitor of phosphoglycerate dehydrogenase (PHGDH, the first rate-limiting enzyme of SSP), to study whether inhibition of SSP may enhance TMZ efficacy in MGMT-positive GBMs. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), flowcytometry and colony formation assays demonstrated that NCT503 worked synergistically with TMZ in suppressing GBM cell growth and inducing apoptosis in T98G and U118 cells in vitro. U118 and patient-derived GBM subcutaneous xenograft models showed that combined NCT503 and TMZ treatment inhibited GBM growth and promoted apoptosis more significantly than would each treatment alone in vivo. Mechanistically, we found that NCT503 treatment decreased MGMT expression possibly by modulating the Wnt/β-catenin pathway. Moreover, intracellular levels of reactive oxygen species were elevated especially when NCT503 and TMZ treatments were combined, and the synergistic effects could be partially negated by NAC, a classic scavenger of reactive oxygen species. Taken together, these results suggest that NCT503 may be a promising agent for augmenting TMZ efficacy in the treatment of GBM, especially in TMZ-resistant GBMs with high expression of MGMT.

Jin L ，Kiang KM ，Cheng SY ，Leung GK ... -  《-》

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 ... -  《-》