Expression of an activated mammalian target of rapamycin in adenocarcinoma of the cervix: A potential biomarker and molecular target therapy

Alterations of the Akt/mTOR pathway have been observed in numerous types of cancer, thus this pathway represents an exciting new target for molecular therapeutics. We investigated the expression of activated Akt (p-Akt) and mTOR (p-mTOR) in patients with adenocarcinoma of the cervix and the involvement of the p-Akt/p-mTOR pathway in response to combination of inhibitor agents, rapamycin and LY294002, with conventional therapy, cisplatin, in vitro. Immunohistochemistry analysis of p-Akt and p-mTOR was conducted in 26 patients with adenocarcinoma of the cervix. Western blot analysis was performed to determine the protein expression involved in response to chemotherapy in cervical cancer cell lines. The results showed that p-Akt and p-mTOR were identified in 50% and 53.8% of adenocarcinoma of the cervix. The expression of p-mTOR was a significant independent marker for prognosis. A significant correlation between p-Akt and p-mTOR was observed. There was no correlation between their expressions with any of clinicopathological factors. In the in vitro study, cisplatin at CPI(50) targets both the apoptosis and survival pathway by activating the caspase-cascade; inhibiting Akt, mTOR, p70S6K, and 4EBP1. Combination of rapamycin with cisplatin induced synergistic interaction. On the other hand, combination with LY294002 resulted in either synergistic or antagonistic effect depending on the doses given. Rapamycin pretreatment potentiated cisplatin-induced apoptosis cell death and enhanced blocking of the survival pathway. Overall, the expression of p-mTOR is a significant prognostic marker of adenocarcinoma of the cervix and a potential molecular target for the treatment of cervical cancer. Inhibition of the mTOR pathway contributes to cisplatin-induced apoptosis in cervical cancer cell lines.     

三七皂苷R1调控PI3K/AKT/mTOR信号通路诱导人下咽鳞状细胞癌FaDu细胞凋亡和自噬北大核心

目的:探讨三七皂苷R1(notoginsenoside R1,NGR1)对人下咽鳞状细胞癌(hypopharyngeal squamous cell carcinoma,HSCC)FaDu细胞凋亡以及自噬的影响,并对其涉及的信号通路进行研究。方法:75μmol/L、150μmol/L、300μmol/L NGR1作用于FaDu细胞24 h后,采用MTT检测细胞增殖能力;流式细胞术检测细胞凋亡;自噬双标腺病毒检测自噬流;Western blot检测自噬相关蛋白LC3Ⅱ/LC3Ⅰ以及PI3K/AKT/mTOR信号通路相关蛋白表达水平。结果:NGR1能够抑制FaDu细胞的增殖并促进细胞凋亡;NGR1可诱导FaDu细胞自噬,并呈一定浓度依赖性;Western blot结果显示,NGR1作用于Fa Du细胞24 h后,LC3Ⅱ表达明显增加,而p-PI3K、p-AKT、p-m TOR表达相较于Control组明显下降。结论:NGR1可抑制Fa Du细胞增殖,诱导细胞凋亡与自噬,其机制可能与抑制PI3K/AKT/m TOR信号通路有关。     

氟奋乃静通过自噬诱导U87胶质瘤细胞死亡及其机制探讨

目的：观察氟奋乃静（FPZ）通过自噬诱导U87胶质瘤细胞死亡的机制。方法体外培养U87胶质瘤细胞并经FPZ处理,采用细胞活力和集落形成方法分析细胞的生存率,采用Western blot检测自噬相关蛋白及PI3K/AKT/mTOR通路蛋白的表达。结果 FPZ处理后,U87胶质瘤细胞活力显著降低（P﹤0.05）,菌落数显著降低（P﹤0.05）;微管相关蛋白1轻链3-Ⅱ型（LC3-Ⅱ）显著增加,并呈时间和剂量依赖性;p-AKT水平及其下游p-mTOR水平显著下降,并呈时间依赖性。采用PI3K抑制剂LY294002处理U87胶质瘤细胞后,LC3-Ⅱ生成明显增加。结论 FPZ可通过抑制PI3K/AKT/mTOR通路调节自噬,发挥细胞毒性作用。     

Resveratrol-induced apoptosis is enhanced by inhibition of autophagy in esophageal squamous cell carcinoma

The anti-cancer activity of resveratrol in human esophageal squamous cell carcinoma (ESCC) was investigated focusing on the role of autophagy and its effects on apoptotic cell death. We demonstrated that resveratrol inhibits ESCC cell growth in a dose-dependent manner by inducing cell cycle arrest at the sub-G1 phase and resulting in subsequent apoptosis. Mechanistically, resveratrol-induced autophagy in the ESCC cells is AMPK/mTOR pathway independent. Since both pharmacological and genetic inhibition of autophagy enhanced the resveratrol-induced cytotoxicity to the ESCC cells, this provided a novel strategy in potentiating the anti-cancer effects of resveratrol and other chemotherapeutic reagents in ESCC cancer treatment.     

Monepantel induces autophagy in human ovarian cancer cells through disruption of the mTOR/p70S6K signalling pathway

We have recently shown that the novel anthelmintic drug monepantel (MPL) inhibits growth, proliferation and colony formation, arrests the cell cycle and induces cleavage of PARP-1 in ovarian cancer cell lines. Here we report on the mechanism behind the anticancer properties of MPL. The cytotoxic effect of MPL on ovarian cancer cells (OVCAR-3 and A2780) was investigated employing a panel of tests used for the detection of apoptosis and autophagy. Apoptosis and autophagy were defined by caspase activity, DNA-laddering, Annexin-V and acridine orange (AO) staining. Autophagy markers such as LC3B, SQSTM1/p62 and mammalian target of rapamycin (mTOR) pathway related proteins were assessed by western blotting and ELISA techniques. MPL did not activate caspases 3 or 8, nor did it alter the percentage of Annexin V positive stained cells. Failure to cause DNA laddering and the inability of z-VAD-fmk to block the MPL antiproliferative effects led to the ruling out of apoptosis as the mechanism behind MPL-induced cell death. On the other hand, accumulation of acidic vacuoles with distinct chromatin morphology and an increase in punctuate localization of green fluorescent protein-LC3B, and MPL-induced changes in the expression of SQSTM1/p62 were all indicative of MPL-induced autophagy. Consistent with this, we found inhibition of mTOR phosphorylation leading to suppression of the mTOR/p70S6K signalling pathway. Our findings provide the first evidence to show that MPL triggers autophagy through the deactivation of mTOR/p70S6K signalling pathway.     

XPA serves as an autophagy and apoptosis inducer by suppressing hepatocellular carcinoma in a PI3K/Akt/mTOR dependent manner

BackgroundTo explore the potential biological function of XPA (Xeroderma pigmentosum group A) in hepatic neoplasms and the underlying molecular mechanisms.MethodsLiver cells were used as experimental models to establish HCC (hepatocellular carcinoma) in vitro. Protein extractions were subjected to Western blotting to detect the proteins expression. The lentivirus transfection efficiency was confirmed by Western blot and RT-qPCR, Tunnel staining was used to detect apoptosis, and Transwell assays were used to observe cell migration and invasion. Cell proliferation was detected with colony formation and CCK-8 (cell counting kit-8) assays.ResultsXPA expression was obviously lower in HCC tissue and liver cancer cell lines. XPA overexpression induced autophagy and apoptosis by increasing LC3B II/I, Beclin1, cleaved-caspase-3, and Bax expression and decreasing p62 and Bcl2 protein levels. XPA also suppressed HCC EMT (Epithelial-Mesenchymal Transition) by increasing E-cadherin and decreasing N-cadherin and vimentin protein expression. Cell proliferation, migration and invasion in vivo were significantly inhibited by the overexpression of XPA, and p-PI3K, p-Akt, and p-mTOR expression were decreased in LV-XPA cells. In general, XPA inhibited HCC by inducing autophagy and apoptosis and by modulating the expression of PI3K/Akt/mTOR proteins.ConclusionsXPA overexpression was found to suppress HCC by inducing autophagy and apoptosis and repressing EMT and proliferation. Each of these effects may be involved in modulating the PI3K/Akt/mTOR signaling pathway.     

Molecular effects of the phosphatidylinositol-3-kinase inhibitor NVP-BKM120 on T and B-cell acute lymphoblastic leukaemia

BackgroundConstitutive activation of the PI3K pathway in T cell acute lymphoblastic leukaemia (T-ALL) has been reported and in a mouse model, PI3K activation, together with MYC, cooperates in Burkitt lymphoma (BL) pathogenesis. We investigated the effects of NVP-BKM120, a potent pan-class I PI3K inhibitor, in lymphoblastic leukaemia cell lines.MethodsEffects of NVP-BKM120 on cell viability, clonogenicity, apoptosis, cell cycle, cell signalling and autophagy were assessed in vitro on T-ALL (Jurkat and MOLT-4) and BL (Daudi and NAMALWA) cell lines.ResultsNVP-BKM120 treatment decreased cell viability and clonogenic growth in all tested cells. Moreover, the drug arrested cell cycling in association with a decrease in Cyclin B1 protein levels, and increased apoptosis. Immunoblotting analysis of cells treated with the drug revealed decreased phosphorylation, in a dose-dependent manner, of AKT, mTOR, P70S6K and 4EBP1, with stable total protein levels. Additionally, we observed a dose-dependent decrease in BAD phosphorylation, in association with augmented BAX:BCL2 ratio. Quantification of autophagy showed a dose-dependent increase in acidic vesicular organelles in all cells tested.ConclusionIn summary, our present study establishes that NVP-BKM120 presents an effective antitumour activity against T-ALL and BL cell lines.     

Activity of the novel mTOR inhibitor Torin-2 in B-precursor acute lymphoblastic leukemia and its therapeutic potential to prevent Akt reactivation

The PI3K/Akt/mTOR signaling cascade is a key regulatory pathway controlling cell growth and survival, and its dysregulation is a reported feature of B-precursor acute lymphoblastic leukemia (B-pre ALL).Torin-2 is a novel, second-generation ATP-competitive inhibitor that is potent and selective for mTOR with a superior pharmacokinetic profile to previous inhibitors. It has been shown that Torin-2 displayed dramatic antiproliferative activity across a panel of cancer cell lines.To investigate if Torin-2 could represent a new option for the treatment of B-pre ALL, we tested its activity on a panel of B-pre ALL cell lines. In all of them Torin-2 showed a powerful cytotoxic activity, inhibiting the growth of each cell line in a dose-dependent manner, with an IC₅₀ in the nanomolar range. Torin-2 caused both apoptosis and autophagy, induced cell cycle arrest in G₀/G₁ phase and affected both mTORC1 and mTORC2 activities as assessed by their specific substrate dephosphorylation.Torin-2 alone suppressed feedback activation of PI3K/Akt, whereas the mTORC1 inhibitor RAD001 required the addition of the Akt inhibitor MK-2206 to achieve the same effect. These pharmacological strategies targeting PI3K/Akt/mTOR at different points of the signaling pathway cascade might represent a new promising therapeutic strategy for treatment of B-pre ALL patients.     

Autophagy limits the cytotoxic effects of the AKT inhibitor AZ7328 in human bladder cancer cells

Background: Mutations that activate the PI3K/AKT/mTOR pathway are relatively common in urothelial (bladder) cancers, but how these pathway mutations affect AKT dependency is not known. We characterized the relationship between AKT pathway mutational status and sensitivity to the effects of the selective AKT kinase inhibitor AZ7328 using a panel of 12 well-characterized human bladder cancer cell lines.Methods: Sequenome DNA sequencing was performed to identify mutations in a panel of 12 urothelial cancer cell lines. Drug-induced proliferative inhibition and apoptosis were quantified using MTT assays and propidium iodide staining with FACS analyses. Protein activation via phosphorylation was measured by immunoblotting. Autophagy was measured by LC3 immunofluorescence and immunoblotting.Results: AZ7328 inhibited proliferation and AKT substrate phosphorylation in a concentration-dependent manner but had minimal effects on apoptosis. Proliferative inhibition correlated loosely with the presence of activating PIK3CA mutations and was strengthened in combination with the mTOR inhibitor rapamycin. AZ7328 induced autophagy in some of the lines, and in the cells exposed to a combination of AZ7328 and chemical autophagy inhibitors apoptosis was induced.Conclusions: The cytostatic effects of AZ7328 correlate with PIK3CA mutations and are greatly enhanced by dual pathway inhibition using an mTOR inhibitor. Furthermore, AZ7328 can interact with autophagy inhibitors to induce apoptosis in some cell lines. Overall, our results support the further evaluation of combinations of PI3K/AKT/mTOR pathway and autophagy inhibitors in pre-clinical in vivo models and ultimately in patients with PIK3CA mutant bladder cancers.     

马鞭草总黄酮通过AKT/mTOR信号通路调控自噬抑制肝癌细胞增殖

目的:分析马鞭草总黄酮(total flavonoids of verbena officinalis L.,TFV)对肝癌细胞自噬和增殖的影响,并探讨其机制。方法:MDC染色法检测自噬泡水平,Western印迹检测自噬相关蛋白水平,运用3-甲基腺嘌呤(3-MA)、雷帕霉素(RAPA)研究TFV对自噬、细胞增殖的影响,MTT法检测细胞存活率。裸鼠成瘤实验验证TFV对裸鼠体内瘤体的瘤重、瘤体积及自噬相关蛋白水平的影响。结果:TFV能增加HepG2、Huh-7细胞中MDC染色标记的荧光颗粒,并伴随浓度的上调明显增加,促进HepG2、Huh-7细胞中自噬蛋白Beclin-1、LC3 II/LC3 I水平表达,降低p-AKT/AKT、p-mTOR/mTOR水平(P<0.05)。与TFV组比较,TFV+3-MA组抑制率、LC3 II/LC3 I明显降低,p-mTOR/mTOR明显增加(P<0.05);与TFV组比较,TFV+RAPA组抑制率、LC3 II/LC3 I明显增加,p-mTOR/mTOR明显降低(P<0.05);与TFV组比较,TFV+3-MA组裸鼠瘤体LC3 II/...     

CircLASP1 silence strengthens the therapeutic effects of MK-2206 on nasopharyngeal cancer through upregulating miR-625

Therapeutic effects of MK-2206 are largely limited due to the complexity of the pathogenesis of nasopharyngeal cancer (NPC). Here, we aimed to investigate whether and how circLASP1 is involved in the therapeutic effects of MK-2206 on NPC. We showed circLASP1 was increased while miR-625 was decreased in NPC tissues and cell lines. CircLASP1 silence strengthened the therapeutic effects of MK-2206 via suppressing NPC cell proliferation and inducing autophagy and apoptosis in vitro. In mechanism analyses, we found that circLASP1 indirectly released AKT by directly binding to miR-625 in NPC cells, and miR-625 acted as a tumor suppressor in NPC and activated cell autophagy through inhibiting the AKT/mTOR pathway. Most importantly, knockdown of circLASP1 was revealed to enhance the therapeutic effects of MK-2206 on NPC in vivo. Our results suggest that the circLASP1/miR-625 axis is involved the therapeutic effects of MK-2206 on NPC by regulating autophagy, proliferation, and apoptosis through the AKT/mTOR pathway. miR-625 is involved in NPC tumorigenesis.     

Plumbagin induces apoptotic and autophagic cell death through inhibition of the PI3K/Akt/mTOR pathway in human non-small cell lung cancer cells

Plumbagin (PLB) has shown anti-cancer activity but the mechanism is unclear. This study has found that PLB has a potent pro-apoptotic and pro-autophagic effect on A549 and H23 cells. PLB arrests cells in G2/M phase, and increases the intracellular level of reactive oxygen species in both cell lines. PLB dose-dependently induces autophagy through inhibition of PI3K/Akt/mTOR pathway as indicated by reduced phosphorylation of Akt and mTOR. Inhibition or induction of autophagy enhances PLB-induced apoptosis. There is crosstalk between PLB-induced apoptosis and autophagy. These findings indicate that PLB initiates both apoptosis and autophagy in NSCLC cells through coordinated pathways.     

Inhibition of induced autophagy increases apoptosis of Nara-H cells

Inhibition of the mTOR signaling pathway promotes initiation of autophagy. However, recent studies indicate that autophagy is a self-defense mechanism of cancer cells that are subjected to anti-tumor agents and that blocking autophagy can trigger apoptosis. Here, we examined the effects of an mTOR inhibitor, temsirolimus, on a malignant fibrous histiocytoma (MFH) cell line, Nara-H cells, and the effect of suppressing autophagy on the induction of apoptosis in these MFH cells. In Nara-H cells, we examined the effects of temsirolimus treatment on cell proliferation using the CellTiter 96? AQueous One Solution Cell Proliferation Assay and on phosphorylation of mTOR pathway components and autophagy using Western blot-based assays. Furthermore, we examined the effects of temsirolimus with or without 3-methyladenine (3-MA) on induction of apoptosis using fluorescent microscopic analysis. In Nara-H cells, temsirolimus treatment inhibited cell proliferation, suppressed phosphorylation of mTOR pathway components, and induced autophagy as assessed by LC-3 II expression. Moreover, treatment with a combination of temsirolimus and 3-MA induced apoptosis in Nara-H cells. Apparently, simultaneous inhibition of autophagy and mTOR induced apoptosis in Nara-H cells because inhibition of autophagy prevented the cells from protecting themselves from the effects of the inhibition of mTOR. Therefore, a combination therapy that includes an mTOR inhibitor and an autophagy inhibitor (temsirolimus and 3-MA, respectively) may effectively treat MFH by inducing apoptosis in tumor cells.     

Increased activation of PI3K/AKT signaling pathway is associated with cholangiocarcinoma metastasis and PI3K/mTOR inhibition presents a possible therapeutic strategy

Phosphatidylinositol 3-kinase (PI3K) signaling plays a critical role in cholangiocarcinoma (CCA), as well as anti-cancer drug resistance and autophagy, the type II program cell death regulation. In this work, we aimed to: (1) determine the expression levels of several key components of PI3K signaling and (2) evaluate whether NVP-BEZ235, a novel dual PI3K/mTOR inhibitor, could inhibit CCA cell growth. Immunohistochemistry for p85α, p110α, AKT, p-AKT (T308), mTOR, p-mTOR (S2448), GSK-3β, p-GSK-3β (S9), PTEN, and p-PTEN (S380, T382/383) was performed in 30 CCA patients. Western blotting was used to analyze PTEN and p-PTEN expression in the cell lines (KKU-OCA17, KKU-100, KKU-M055, KKU-M139, KKU-M156, KKU-M213, and KKU-M214). The effects of NVP-BEZ235 on CCA cells were evaluated using a growth inhibition assay, flow cytometer and migration assay. Increased activation of PI3K/AKT signaling was reproducibly observed in the CCA tissues. The expression of p85α, mTOR, and GSK-3β was significantly correlated with metastasis. Interestingly, PTEN suppression by loss of expression or inactivation by phosphorylation was observed in the majority of patients. Furthermore, NVP-BEZ235 effectively inhibited CCA cell growth and migration through reduced AKT and mTOR phosphorylation and significantly induced G1 arrest without apoptosis induction, although increase autophagy response was observed. In conclusion, the constitutive activation of PI3K/AKT pathway in CCA is mainly due to PTEN inactivation by either loss of expression or phosphorylation along with an increased expression in its pathway components heralding a poor prognosis for CCA patients. This work also indicates that inhibition of PI3K and mTOR activity by the inhibitor NVP-BEZ235 has anti-cancer activity against CCA cells which might be further tested for CCA treatment.     

mTOR通路对神经母细胞瘤SH-SY5 Y细胞自噬作用的影响

目的：研究雷帕霉素靶蛋白（ mammalian target of rapamycin,mTOR）通路对神经母细胞瘤SH-SY5Y细胞自体吞噬作用的影响。方法：应用不同浓度的雷帕霉素作用于神经母细胞瘤细胞,采用实时荧光定量PCR检测雷帕霉素作用前后神经母细胞瘤细胞株的mTOR、LC3及Beclin 1 mRNA表达情况。结果：雷帕霉素能抑制mTOR表达且呈现量效依赖关系,不同浓度的雷帕霉素分别对SH-SY5Y细胞作用72h后,mTOR mR-NA的表达随浓度增加逐渐下降。而LC3及Beclin 1 mRNA的表达随浓度增加逐渐上升,神经母细胞瘤中mTOR与LC3及Beclin 1的表达呈负相关。结论：雷帕霉素通过抑制mTOR信号通路促进神经母细胞瘤的自体吞噬作用,动态观察mTOR可作为神经母细胞瘤治疗效果监测的指标之一。     

芹菜素诱导胃癌SGC-7901细胞自噬及其对凋亡 的影响

目的：探讨芹菜素（API）是否诱导胃癌SGC-7901细胞发生自噬及其对细胞凋亡的影响。方法：采用不同浓度（0、20、40、60、80 μmol/L）的API处理胃癌SGC-7901细胞24 h,MTT法检测API对细胞生长的抑制情况。分别采用不同浓度（0、20、40、60、80 μmol/L）API处理细胞24 h,及60 μmol/L的API处理不同时间（0、12、24、36、48 h）,Western blot检测自噬标志蛋白微管相关蛋白l轻链3（LC3）、Beclin-1和磷脂酰肌醇-3-激酶（PI3K）/Akt/mTOR信号通路中关键分子p-Akt、p-mTOR的表达;电子显微镜下观察细胞自噬情况。细胞经自噬抑制剂氯喹（CQ）或3-甲基腺苷（3-MA）预处理后再加入API,Western blot检测聚二磷酸腺苷-核糖体聚合酶（PARP）的表达;流式细胞术流检测细胞凋亡率。结果：API对胃癌SGC-7901细胞生长具有明显抑制作用并呈剂量-效应关系。随着API浓度和作用时间的增加,SGC-7901细胞LC3Ⅱ与Beclin-1蛋白表达均增加,各剂量组与对照组相比较差异均具有统计学意义（P < 0.05）;API处理后的细胞逐渐出现自噬囊泡和自噬溶酶体;p-Akt、p-mTOR蛋白表达降低。采用自噬抑制剂抑制细胞自噬后,除API组LC3Ⅱ与Beclin-1蛋白表达明显高于对照组外（P < 0.05）,各组蛋白表达无显著差异。API+CQ组和API+3-MA组的PARP蛋白剪切片段表达及凋亡率均高于对照组和API组（P < 0.05）。结论：API可以诱导胃癌SGC-7901细胞发生自噬,其机制可能与抑制PI3K/Akt/mTOR信号通路关键分子p-Akt、p-mTOR活性有关;抑制API诱导的自噬能够增强API的凋亡诱导效应,从而增强对胃癌SGC-7901细胞的杀伤作用。     

mTOR inhibitors show promising in vitro activity in bladder cancer and head and neck squamous cell carcinoma

Bladder cancer and head and neck squamous cell carcinoma (HNSCC) are frequent but lack efficient therapies especially in advanced disease. Almost no studies on mTOR function and inhibition in these tumor entities have been reported. We examined the gene and protein expression levels of mTOR and its activated form (pmTOR) in three human bladder carcinoma cell lines (RT-4, T24, EJ28) and three HNSCC cell lines (PCI-1, PCI-13, BHY). Furthermore, the consequences of mTOR inhibition by mTOR-specific siRNAs and the mTOR inhibitor temsirolimus were analysed in vitro using immunohistochemical Ki-67 staining, mTOR and pmTOR western blot analysis, MTT assay, as well as cell cycle analysis with flow cytometry. Especially pmTOR protein expression levels showed marked differences between cell lines. siRNA transfection was associated with dose-dependent target protein reduction but not proliferation inhibition or apoptosis. On the contrary, temsirolimus significantly reduced cell viability and induced apoptosis and cell cycle arrest. According to these data, bladder cancer and HNSCC are promising tumor entities for mTOR inhibition with temsirolimus.     

Inhibition of mammalian target of rapamycin or apoptotic pathway induces autophagy and radiosensitizes PTEN null prostate cancer cells

The phosphatidylinositol 3-kinase/Akt pathway plays a critical role in oncogenesis, and dysregulation of this pathway through loss of PTEN suppression is a particularly common phenomenon in aggressive prostate cancers. The mammalian target of rapamycin (mTOR) is a downstream signaling kinase in this pathway, exerting prosurvival influence on cells through the activation of factors involved in protein synthesis. The mTOR inhibitor rapamycin and its derivatives are cytotoxic to a number of cell lines. Recently, mTOR inhibition has also been shown to radiosensitize endothelial and breast cancer cells in vitro. Because radiation is an important modality in the treatment of prostate cancer, we tested the ability of the mTOR inhibitor RAD001 (everolimus) to enhance the cytotoxic effects of radiation on two prostate cancer cell lines, PC-3 and DU145. We found that both cell lines became more vulnerable to irradiation after treatment with RAD001, with the PTEN-deficient PC-3 cell line showing the greater sensitivity. This increased susceptibility to radiation is associated with induction of autophagy. Furthermore, we show that blocking apoptosis with caspase inhibition and Bax/Bak small interfering RNA in these cell lines enhances radiation-induced mortality and induces autophagy. Together, these data highlight the emerging importance of mTOR as a molecular target for therapeutic intervention, and lend support to the idea that nonapoptotic modes of cell death may play a crucial role in improving tumor cell kill.     

Dual inhibition of EGFR and mTOR pathways in small cell lung cancer

Background:

In this report we investigated the combination of epidermal growth factor receptor (EGFR) and mammalian target of rapamycin (mTOR) pathway inhibition as a possible new therapeutic strategy for small cell lung cancer (SCLC).

Methods:

EGFR, p-AKT, p-ERK, p-mTOR and p-p70s6K protein expressions were studied by immunohistochemistry in 107 small cell lung carcinomas and correlated with clinicopathological parameters. Cells of SCLC were treated with erlotinib±RAD001 and analysed for cell viability, proliferation, autophagy, and pathway regulation.

Results:

Epidermal growth factor receptor, p-AKT, p-ERK, p-mTOR, and p-p70s6K were expressed in 37, 24, 13, 55 and 91% of the tumour specimens of all SCLC patients, respectively, and were not associated with disease-free or overall survival. The expression of EGFR was lower in neoadjuvant-treated patients (P=0.038); mTOR pathway activation was higher in the early stages of disease (P=0.048). Coexpression of EGFR/p-mTOR/p-p70s6K was observed in 28% of all patients . EGFR immunoreactivity was associated with p-ERK and p-mTOR expression (P=0.02 and P=0.0001); p-mTOR immunoreactivity was associated with p-p70s6K expression (P=0.001). Tumour cells comprised a functional EGFR, no activating mutations in exons 18–21, and resistance to RAD001 monotherapy. We found synergistic effects of erlotinib and RAD001 combination therapy on the molecular level, cell viability, proliferation and autophagy.

Conclusions:

The combined inhibition of EGFR/mTOR pathways could be a promising approach to treat SCLC.