Iwamaru, A 1; Kondo, Y 1; Iwado, E 1; Aoki, H 1; Fujiwara, K 1; Yokoyama, T 1; Mills, G B 2; Kondo, S 1,3,4

(1)Department of Neurosurgery, The University of Texas MD Anderson Cancer Center, Houston, TX, USA; (2)Department of Molecular Therapeutics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA; (3)The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, TX, USA and (4)Department of Neurosurgery, The Baylor College of Medicine, Houston, TX, USA

Silencing mammalian target of rapamycin signaling by small interfering RNA enhances rapamycin-induced autophagy in malignant glioma cells.[Article]

Oncogene. 26(13):1840-1851, March 22, 2007.

中文摘要(林中客翻译)

    哺乳动物雷帕霉素靶位(mTOR )在调节恶性胶质瘤细胞增殖中起着核心作用,并且mTOR 特异抑制剂比如雷帕霉素类似物被认为对于恶性胶质瘤治疗是有前景的。然而在治疗恶性胶质瘤病人mTOR 抑制剂的效能只能是适度的,可能因为这些因子仅仅起mTOR 活化酶抑制剂作用，而不是阻碍mTOR /raptor (mTOR 的调节相关蛋白)复合物的功能，从而没有扰乱所有mTOR 功能。此研究目的是确定在恶性胶质瘤细胞mTOR 分子的全面抑制是否可以增加雷帕霉素的抗癌作用。我们结果显示：雷帕霉素诱导自噬,而且通过指向对抗自噬相关基因Beclin 1的小干扰RNA (siRNA )的自噬抑制减弱雷帕霉素敏感的肿瘤细胞中雷帕霉素的细胞毒性,表明自噬是雷帕霉素抗癌作用的主要介体而不是保护反应。用其活化酶活性干扰mTOR 突变物的外原性表达显著增加雷帕霉素诱导的自噬的发生率。另外用siRNA沉默mTOR 通过刺激自噬可以增强雷帕霉素对肿瘤细胞活力的抑制效果。更重要的是，通过mTOR siRNA，不仅PTEN 突变的雷帕霉素敏感恶性胶质瘤细胞，而且野生型PTEN的雷帕霉素抵抗的恶性胶质瘤细胞都对雷帕霉素变得敏感。这些结果表明雷帕霉素诱导的自噬是抗癌作用的原因，而且沉默或者抑制mTOR 活化酶活性可以增加雷帕霉素的作用。

The mammalian target of rapamycin (mTOR) plays a central role in regulating the proliferation of malignant glioma cells, and mTOR-specific inhibitors such as rapamycin analogs are considered as promising therapy for malignant gliomas. However, the efficacy of mTOR inhibitors alone in the treatment of patients with malignant gliomas is only modest, potentially because these agents rather than acting as mTOR kinase inhibitors instead interfere with the function of only mTOR/raptor (regulatory-associated protein of mTOR) complex and thus do not perturb all mTOR functions. The purpose of this study was to determine whether global inhibition of the mTOR molecule enhances the antitumor effect of rapamycin on malignant glioma cells. We showed that rapamycin induced autophagy and that inhibition of autophagy by small interfering RNA (siRNA) directed against autophagy-related gene Beclin 1 attenuated the cytotoxicity of rapamycin in rapamycin-sensitive tumor cells, indicating that the autophagy was a primary mediator of rapamycin's antitumor effect rather than a protective response. Exogenous expression of an mTOR mutant interfering with its kinase activity markedly enhanced the incidence of rapamycin-induced autophagy. Moreover, silencing of mTOR with siRNA augmented the inhibitory effect of rapamycin on tumor cell viability by stimulating autophagy. Importantly, not only rapamycin-sensitive malignant glioma cells with PTEN mutations but also rapamycin-resistant malignant glioma cells with wild-type PTEN were sensitized to rapamycin by mTOR siRNA. These results indicate that rapamycin-induced autophagy is one of the agent's antitumor effects and that silencing or inhibiting mTOR kinase activity could enhance the effectiveness of rapamycin.