Department of Neurosurgery, The First Hospital of Jilin University, Changchun, China.
Department of Respiratory Medicine, The Second Hospital of Jilin University, Changchun, China.
Cancer Lett. 2018 Oct 28;435:66-79. doi: 10.1016/j.canlet.2018.07.040. Epub 2018 Aug 4.
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 O-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.
多形性胶质母细胞瘤（GBM）是最具侵袭性的人类肿瘤之一，预后较差。替莫唑胺（TMZ）是治疗 GBM 的主要烷化剂。然而，许多 GBM 患者对 TMZ 耐药。因此，迫切需要更有效的治疗选择。虫草素（COR）是一种具有抗肿瘤作用的天然化学物质，尽管其作用机制尚不清楚。有几条证据表明，O-甲基鸟嘌呤 DNA 甲基转移酶（MGMT）修复受损的 DNA，并有助于胶质母细胞瘤对 TMZ 的耐药性。Wnt/β-catenin 通路调节 MGMT 基因表达。然而，虫草素是否通过下调β-catenin 通路和增强胶质母细胞瘤细胞对 TMZ 的化疗敏感性来抑制 MGMT 表达仍不清楚。在本研究中，我们发现虫草素在体外抑制神经胶质瘤细胞的活力并诱导其凋亡、细胞周期停滞、活性氧（ROS）的过度产生和谷胱甘肽（GSH）的减少。此外，虫草素在体内显著减少荷瘤大鼠的肿瘤体积并延长其中位生存期。我们还发现，虫草素在体外和体内均抑制 MGMT 表达并增强 TMZ 对神经胶质瘤细胞的化疗敏感性，同时下调 p-GSK-3β 和β-catenin。此外，MGMT 的过表达逆转了虫草素和 TMZ 的协同作用。用 CHIR-99021 抑制 GSK-3β 或过表达β-catenin 可逆转虫草素诱导的细胞活力降低、β-catenin 和 MGMT 下调、凋亡增加和 TMZ 耐药性降低。此外，我们发现β-catenin 通过减少 GSH 调节虫草素诱导的 ROS 过度产生。用 N-乙酰-L-半胱氨酸（NAC）抑制 ROS 产生不仅挽救了细胞活力的降低，而且消除了β-catenin 和 MGMT 抑制，防止了神经胶质瘤细胞凋亡，并逆转了虫草素和 TMZ 的协同作用。总之，我们证明β-catenin 通过增加细胞内 ROS 促进虫草素诱导的 MGMT 抑制和 TMZ 耐药性降低在神经胶质瘤细胞中起作用。这些结果表明，虫草素可能是改善 GBM 治疗的一种新方法，特别是在 MGMT 表达高的 TMZ 耐药性 GBM 中。
