Department of Neurosurgery, New York Medical College, Valhalla, NY 10595, USA.
Oncol Rep. 2013 Oct;30(4):1645-50. doi: 10.3892/or.2013.2625. Epub 2013 Jul 18.
Glioblastoma multiforme (GBM), the most aggressive primary brain tumor, portends a poor prognosis despite current treatment modalities. Recurrence of tumor growth is attributed to the presence of treatment-resistant cancer stem cells (CSCs). The targeting of these CSCs is therefore essential in the treatment of this disease. Mechanistic target of rapamycin (mTOR) forms two multiprotein complexes, mTORC1 and mTORC2, which regulate proliferation and migration, respectively. Aberrant function of mTOR has been shown to be present in GBM CSCs. All-trans retinoic acid (ATRA), a derivative of retinol, causes differentiation of CSCs as well as normal neural progenitor cells. The purpose of this investigation was to delineate the role of mTOR in CSC maintenance, and to establish the mechanism of targeting GBM CSCs using differentiating agents along with inhibitors of the mTOR pathways. The results demonstrated that ATRA caused differentiation of CSCs, as demonstrated by the loss of the stem cell marker Nestin. These observations were confirmed by western blotting, which demonstrated a time-dependent decrease in Nestin expression following ATRA treatment. This effect occurred despite combination with mTOR (rapamycin), PI3K (LY294002) and MEK1/2 (U0126) inhibitors. Expression of activated extracellular signal-regulated kinase 1/2 (pERK1/2) was enhanced following treatment with ATRA, independent of mTOR pathway inhibitors. Proliferation of CSCs, determined by neurosphere diameter, was decreased following treatment with ATRA alone and in combination with rapamycin. The motility of GBM cells was mitigated by treatment with ATRA, rapamycin and LY29002 alone. However, combination treatment augmented the inhibitory effect on migration suggesting synergism. These findings indicate that ATRA-induced differentiation is mediated via the ERK1/2 pathway, and underscores the significance of including differentiating agents along with inhibitors of mTOR pathways in the treatment of GBM.
多形性胶质母细胞瘤（GBM）是最具侵袭性的原发性脑肿瘤，尽管目前有多种治疗方法，但预后仍然很差。肿瘤生长的复发归因于存在治疗耐药性的癌症干细胞（CSC）。因此，针对这些 CSC 是治疗这种疾病的关键。雷帕霉素（mTOR）的作用机制形成两个多蛋白复合物，mTORC1 和 mTORC2，分别调节增殖和迁移。已经表明，mTOR 的异常功能存在于 GBM CSC 中。全反式视黄酸（ATRA），视黄醇的衍生物，可引起 CSC 以及正常神经祖细胞的分化。本研究旨在阐明 mTOR 在 CSC 维持中的作用，并利用分化剂以及 mTOR 通路抑制剂来确定靶向 GBM CSC 的机制。结果表明，ATRA 引起 CSC 分化，这表现为干细胞标志物巢蛋白（Nestin）的丧失。Western blot 进一步证实了这一观察结果，显示 ATRA 处理后巢蛋白表达随时间下降。这种作用的发生与 mTOR（雷帕霉素）、PI3K（LY294002）和 MEK1/2（U0126）抑制剂的组合无关。在 ATRA 处理后，细胞外信号调节激酶 1/2（pERK1/2）的激活表达增强，与 mTOR 通路抑制剂无关。CSC 的增殖通过神经球直径确定，单独用 ATRA 处理以及与雷帕霉素联合处理后均降低。单独用 ATRA、雷帕霉素和 LY29002 处理可减轻 GBM 细胞的迁移，但联合治疗增强了对迁移的抑制作用，提示协同作用。这些发现表明，ATRA 诱导的分化是通过 ERK1/2 通路介导的，这突出了在 GBM 治疗中包含分化剂以及 mTOR 通路抑制剂的重要性。
