雷帕霉素单独及联合化疗药物应用对胃癌细胞生长的影响

目的:研究mTOR抑制剂雷帕霉素对SGC-7901胃癌细胞增殖的影响及其可能的机制,并探讨其与传统化疗药物的联合作用。方法:体外培养胃癌SGC-7901细胞,取对数生长期的细胞进行试验,用不同浓度的mTOR抑制剂雷帕霉素以及长春新碱分别作用于胃癌SGC-7901细胞24、48、72小时,用MTT法检测雷帕霉素单独以及联合化疗药物对其生长的影响。用流式细胞术检测mTOR抑制剂雷帕霉素、长春新碱单独以及联合应用对胃癌SGC-7901细胞周期的影响。结果:MTT法结果显示:雷帕霉素单独能够显著抑制胃癌SGC-7901细胞的增殖,其作用随着药物浓度以及作用时间的增加而增加,呈现时间-剂量效应关系;与化疗药物长春新碱联合应用其抑制效应明显增强。流式细胞术检测结果显示:雷帕霉素、长春新碱单独作用胃癌细胞将细胞周期主要阻滞在G0/G1期,而联合给药时G0/G1期比例增加。结论:mTOR抑制剂雷帕霉素能够显著抑制胃癌SGC-7901细胞的增殖,其机制可能与通过阻滞细胞周期在G0/G1期相关;并且雷帕霉素可提高传统化疗药物长春新碱对胃癌细胞的敏感性。     

mTOR通路与胃癌的研究进展

哺乳动物雷帕霉素靶蛋白(mTOR)信号转导通路在肿瘤的形成和发展中扮演着非常重要的角色,并参与肿瘤的侵袭和转移。此信号通路于胃癌中高度激活,调控细胞增殖、凋亡、转录、翻译、代谢等细胞生物学过程。本文对mTOR信号传导通路、在胃癌发生发展中的作用及mTOR抑制剂在胃癌治疗中的最新进展进行综述。     

哺乳动物雷帕霉素靶蛋白抑制剂依维莫司抗肿瘤作用的研究进展

 哺乳动物雷帕霉素靶蛋白（mTOR）是一种丝氨酸／苏氨酸蛋白激酶,广泛存在于细胞内,已被证实为肿瘤治疗的一个可靠靶点。依维莫司是一种口服mTOR抑制剂,是雷帕霉素衍生物中的一种,其改善了既往雷帕霉素药物特性,主要抑制哺乳动物肿瘤细胞生长和分化有关的mTOR。2009年3月,依维莫司被美国食品药品监督局（FDA）批准用于治疗晚期肾癌。目前其在乳腺癌、肺癌、胃癌等多种肿瘤中的临床研究也取得了一定的进展。     

mTOR信号通路与胃癌的研究进展

哺乳动物雷帕霉素靶蛋白（mTOR）及其信号通路调控蛋白质的合成,细胞生长、迁移、凋亡以及血管形成等,该信号通路在胃癌中常被高度激活,并与胃癌的复发、转移等临床病理特性密切相关。雷帕霉素及其衍生物通过阻断mTOR通路的信号传递,抑制胃癌细胞生长,促进肿瘤坏死,并与其他化疗药物产生协同作用,有望为胃癌预防和治疗提供有效的方法。     

哺乳动物雷帕霉素靶蛋白及其信号通路在胃癌中的研究进展

哺乳动物雷帕霉素靶蛋白(mTOR)及其信号通路控制着蛋白质合成、细胞的生长和代谢以及血管的生成等.其信号通路在胃癌中常被高度激活,与胃癌进展及预后密切相关.雷帕霉素及其衍生物可通过阻断mTOR通路的信号传递,抑制胃癌细胞生长,促进肿瘤坏死,并能与其他化疗药物产生协同作用,有望为胃癌预防和治疗提供有效的方法.     

哺乳动物雷帕霉素靶蛋白及其信号通路在胃癌中的研究进展

哺乳动物雷帕霉素靶蛋白(mTOR)及其信号通路控制着蛋白质合成、细胞的生长和代谢以及血管的生成等.其信号通路在胃癌中常被高度激活,与胃癌进展及预后密切相关.雷帕霉素及其衍生物可通过阻断mTOR通路的信号传递,抑制胃癌细胞生长,促进肿瘤坏死,并能与其他化疗药物产生协同作用,有望为胃癌预防和治疗提供有效的方法.     

哺乳动物雷帕霉素靶蛋白及其与胃癌的关系

哺乳动物雷帕霉素靶蛋白（mTOR）信号途径在多种恶性肿瘤中存在异常激活或变异,该途径激活可以调控肿瘤细胞的增殖、存活以及转移能力,进而导致恶性肿瘤发生发展。雷帕霉素及其衍生物通过阻断mTOR通路的信号传递,抑制胃癌细胞生长,促进肿瘤坏死,并能与其他化疗药物产生协同作用,有望为胃癌预防和治疗提供有效的方法。     

雷帕霉素靶蛋白与白血病治疗

雷帕霉素靶蛋白（mTOR）广泛存在于各种生物细胞中,近年来研究发现mTOR信号通路的活化与肿瘤的发生、发展密切相关,并参与包括血液系统恶性肿瘤在内的许多肿瘤细胞的增生和分化。研究表明其抑制剂雷帕霉素及其衍生物等均有抗肿瘤作用。现就mTOR的结构功能、信号通路,在白血病发病机制中的主要上游调节因子及其抑制剂在白血病中的应用进行简述。     

mTOR功能及其抑制剂研究进展

哺乳动物雷帕霉素靶蛋白（mammalian target of rapamycin mTOR）是一种丝／苏氨酸蛋白激酶，mTOR在肿瘤细胞生长、增殖过程中起重要作用，mTOR信号通路活动异常与肿瘤的发生有密切关系，mTOR足肿瘤药物治疗作用的理想靶点，目前新的mTOR抑制剂不断出现。本文对mTOR蛋白的结构、功能和mTOR信号通路及其抑制剂进行了综述。     

mTOR信号通路与消化系统肿瘤

哺乳动物雷帕霉素靶蛋白(mTOR)信号途径的异常与肿瘤密切相关.经典和新型的mTOR抑制剂在消化系统肿瘤的临床前和临床研究显示了该类药物具有抗肿瘤作用,并且能够增强肿瘤细胞对现有化疗药物的敏感性.     

Differential effects of rapamycin on mammalian target of rapamycin signaling functions in mammalian cells

Rapamycin and its analogues have shown promising anticancer activities in preclinical and clinical studies. However, the mechanism whereby rapamycin inhibits signaling through the mammalian target of rapamycin (mTOR) remains poorly understood. Here, we show that the FKBP12/rapamycin complex is an essentially irreversible inhibitor of mTOR kinase activity in vitro. However, we observe no suppression of mTOR catalytic activity after immunoprecipitation from rapamycin-treated cells. These results suggest either that rapamycin acts as a reversible kinase inhibitor in intact cells or that the cellular effects of rapamycin are not mediated through global suppression in mTOR kinase activity. To better understand the cellular pharmacology of rapamycin, we compared the individual and combined effects of rapamycin and kinase-inactive mTOR expression on a panel of mTOR-dependent cellular responses. These studies identified glycolytic activity, amino acid transporter trafficking, and Akt kinase activity as novel, mTOR-modulated functions in mammalian cells. Whereas kinase-inactive mTOR did not enhance the decreases in cell size and glycolysis induced by rapamycin, expression of this mTOR mutant significantly enhanced the inhibitory effects of rapamycin on cell proliferation, 4EBP1 phosphorylation, and Akt activity. Unexpectedly, amino acid transporter trafficking was perturbed by kinase-inactive mTOR but not by rapamycin, indicating that this process is rapamycin insensitive. These results indicate that rapamycin exerts variable inhibitory actions on mTOR signaling functions and suggest that direct inhibitors of the mTOR kinase domain will display substantially broader anticancer activities than rapamycin.     

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

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.     

A retroinhibition approach reveals a tumor cell-autonomous response to rapamycin in head and neck cancer

Emerging evidence supporting the activation of the Akt-mammalian target of rapamycin (mTOR) signaling network in head and neck squamous cell carcinoma (HNSCC) progression has provided the rationale for exploring the therapeutic potential of inhibiting this pathway for HNSCC treatment. Indeed, rapamycin, a clinically relevant mTOR inhibitor, promotes the rapid regression of HNSCC-tumor xenografts in mice. However, rapamycin does not affect the growth of HNSCC cells in vitro, thus raising the possibility that, as for other cancer types, rapamycin may not target cancer cells directly but may instead act on a component of the tumor microenvironment, such as tumor-associated vasculature. Here, we used a retroinhibition approach to assess the contribution of cancer cell-autonomous actions of rapamycin to its antitumor activity in HNSCC. A rapamycin-resistant form of mTOR (mTOR-RR) was expressed in HNSCC cells while retaining the wild-type (rapamycin-sensitive) mTOR (mTOR-WT) alleles in host-derived endothelial and stromal cells. Expression of mTOR-RR prevented the decrease in phospho-S6 levels caused by rapamycin through mTOR in HNSCC cells but not in stromal cells, and rendered HNSCC xenografts completely resistant to the antitumoral activity of rapamycin. This reverse pharmacology strategy also enabled monitoring the direct consequences of inhibiting mTOR in cancer cells within the complex tumor microenvironment, which revealed that mTOR controls the accumulation of hypoxia-inducible factor-1 alpha (HIF-1 alpha) and the consequent expression of vascular endothelial growth factor and a glucose transporter, Glut-1, in HNSCC cells. These findings indicate that HNSCC cells are the primary target of rapamycin in vivo, and provide evidence that its antiangiogenic effects may represent a downstream consequence of mTOR inhibition in HNSCC cells.     

mTOR kinase inhibitors as potential cancer therapeutic drugs

The mammalian target of rapamycin (mTOR) plays a critical role in the positive regulation of cell growth and survival primarily through direct interaction with raptor (forming mTORC complex 1; mTORC1) or rictor (forming mTOR complex 2; mTORC2). The mTOR axis is often activated in many types of cancer and thus has become an attractive cancer therapeutic target. The modest clinical anticancer activity of conventional mTOR allosteric inhibitors, rapamycin and its analogs (rapalogs), which preferentially inhibit mTORC1, in most types of cancer, has encouraged great efforts to develop mTOR kinase inhibitors (TORKinibs) that inhibit both mTORC1 and mTORC2, in the hope of developing a novel generation of mTOR inhibitors with better therapeutic efficacy than rapalogs. Several TORKinibs have been developed and actively studied pre-clinically and clinically. This review will highlight recent advances in the development and research of TORKinibs and discuss some potential issues or challenges in this area.     

Dysregulation of mTOR activity through LKB1 inactivation

Mammalian target of rapamycin (mTOR) is aberrantly activated in many cancer types, and two rapamycin derivatives are currently approved by the Food and Drug Administration (FDA) of the United States fo...     

Synergistic augmentation of rapamycin-induced autophagy in malignant glioma cells by phosphatidylinositol 3-kinase/protein kinase B inhibitors

The mammalian target of rapamycin (mTOR) is a downstream effector of the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) signaling pathway and a central modulator of cell proliferation in malignant gliomas. Therefore, the targeting of mTOR signaling is considered a promising therapy for malignant gliomas. However, the mechanisms underlying the cytotoxic effects of a selective mTOR inhibitor, rapamycin, on malignant glioma cells are poorly understood. The purpose of this study was thus to elucidate how rapamycin exerts its cytotoxic effects on malignant glioma cells. We showed that rapamycin induced autophagy but not apoptosis in rapamycin-sensitive malignant glioma U87-MG and T98G cells by inhibiting the function of mTOR. In contrast, in rapamycin-resistant U373-MG cells, the inhibitory effect of rapamycin was minor, although the phosphorylation of p70S6 kinase, a molecule downstream of mTOR, was remarkably inhibited. Interestingly, a PI3K inhibitor, LY294002, and an Akt inhibitor, UCN-01 (7-hydroxystaurosporine), both synergistically sensitized U87-MG and T98G cells as well as U373-MG cells to rapamycin by stimulating the induction of autophagy. Enforced expression of active Akt in tumor cells suppressed the combined effects of LY294002 or UCN-01, whereas dominant-negative Akt expression was sufficient to increase the sensitivity of tumor cells to rapamycin. These results indicate that rapamycin exerts its antitumor effect on malignant glioma cells by inducing autophagy and suggest that in malignant glioma cells a disruption of the PI3K/Akt signaling pathway could greatly enhance the effectiveness of mTOR inhibitors.     

Simultaneous targeting of EGFR and mTOR inhibits the growth of colorectal carcinoma cells

Epidermal growth factor receptor (EGFR) is highly expressed in colorectal carcinomas and, as a result, it leads to the activation of downstream mammalian target of rapamycin (mTOR) kinase pathways for cancer growth and progression. Clinical and preclinical studies, however, have shown that inhibition of epidermal growth factor receptor (EGFR) and mammalian target of rapamycin (mTOR) alone is not sufficient to treat colorectal carcinomas. In search of effective combination therapies, we show here that simultaneous targeting of EGFR with its inhibitor, erlotinib and mTOR with its inhibitor, rapamycin inhibits the phosphorylation and activation of downstream phosphatidylinositol 3-kinase (PI3K), Akt, mTOR and extracellular-signal-regulated kinase 1/2 (Erk1/2) pathways, resulting in the inhibition of cell cycle progression and the growth of both KRAS wild-type and mutated colorectal carcinoma cells. This study has demonstrated the principle that the combination of erlotinib and rapamycin may provide an effective therapy for colorectal carcinomas.     

哺乳动物雷帕霉素靶蛋白抑制剂与肿瘤治疗

 哺乳类动物雷帕霉素靶蛋白（mTOR）抑制剂的抗肿瘤作用已被熟知，传统的mTOR抑制剂包括雷帕霉素及其衍生物，早期已应用于临床。目前mTOR小分子抑制剂如磷脂酰肌醇激酶3 激酶（PI3K）/mTOR双重抑制剂、Torin1等陆续被发现在肿瘤治疗中有着独特的作用。     

Activation of Akt and eIF4E survival pathways by rapamycin-mediated mammalian target of rapamycin inhibition

The mammalian target of rapamycin (mTOR) has emerged as an important cancer therapeutic target. Rapamycin and its derivatives that specifically inhibit mTOR are now being actively evaluated in clinical trials. Recently, the inhibition of mTOR has been shown to reverse Akt-dependent prostate intraepithelial neoplasia. However, many cancer cells are resistant to rapamycin and its derivatives. The mechanism of this resistance remains a subject of major therapeutic significance. Here we report that the inhibition of mTOR by rapamycin triggers the activation of two survival signaling pathways that may contribute to drug resistance. Treatment of human lung cancer cells with rapamycin suppressed the phosphorylation of p70S6 kinase and 4E-BP1, indicating an inhibition of mTOR signaling. Paradoxically, rapamycin also concurrently increased the phosphorylation of both Akt and eIF4E. The rapamycin-induced phosphorylation of Akt and eIF4E was suppressed by the phosphatidylinositol-3 kinase (PI3K) inhibitor LY294002, suggesting the requirement of PI3K in this process. The activated Akt and eIF4E seem to attenuate rapamycin's growth-inhibitory effects, serving as a negative feedback mechanism. In support of this model, rapamycin combined with LY294002 exhibited enhanced inhibitory effects on the growth and colony formation of cancer cells. Thus, our study provides a mechanistic basis for enhancing mTOR-targeted cancer therapy by combining an mTOR inhibitor with a PI3K or Akt inhibitor.