Local recurrence in head and neck cancer: relationship to radiation resistance and signal transduction.

PURPOSE: Locoregional recurrence is the dominant form of treatment failure in head and neck (H&N) cancer. The epidermal growth factor receptor (EGFR) is frequently amplified in this disease (相似文献   

Overcoming resistance to gamma-rays in squamous carcinoma cells by poly-drug elevation of ceramide levels

Recent strategies to sensitize radioresistant tumours are based on combining gamma-irradiation with inducers of apoptosis. We report that the combination of three inhibitors of sphingolipid metabolism, DL-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol.HCl(DL-PDMP)+imipramine +/- D-erythro-2-(N-myristoylamino)-1-phenyl-1-propanol (D-MAPP), with 10-Gy irradiation triggers both mitotic and apoptotic killing in radioresistant SQ20B squamous carcinoma cells. In these cells, apoptosis is defective due to a lack of ceramide generation upstream, which cannot be explained by sphingomyelinase (neutral and acidic) deficiency or rapid derivation to the sphingolipid pathway. We present evidence of a functional transduction death pathway when ceramide generation is restored, which involves the mitochondrial-mediated pathway coupled to alterations in redox status and to executive caspases activation. The poly-drug treatment restored apoptosis to levels similar to those observed in radiosensitive SCC61 squamous carcinoma cells. Simultaneous exposure to gamma-irradiation and poly-drug treatment acted synergistically in SQ20B cells to produce a marked increase in both mitochondrial dysfunction and caspase cleavage, which led to a 7.8-fold increase in apoptosis within 48 h, relative to irradiated cells. Moreover, the results suggest that the ceramide released by irradiation or poly-drug treatment converges upon common cellular targets. Modulation of endogenous ceramide levels by inhibitors of sphingolipid metabolism may represent a new cellular target for the sensitization of radioresistant tumours to gamma-ray therapy.     

Antiproliferative effects of rapamycin as a single agent and in combination with carboplatin and paclitaxel in head and neck cancer cell lines

PURPOSE: Recent data suggested that combining targeted therapies with chemotherapy may counteract drug resistance. Activation of the PI3K/AKT/mTOR pathway downstream to kinase receptors, such as EGFR, was found in 57-81% of head and neck squamous cell carcinoma (HNSCC), and was eventually associated with a loss of PTEN function. mTOR was shown to modulate cell proliferation, apoptosis, invasion, and angiogenesis. This study aimed to evaluate molecular and cellular effects of rapamycin in a panel of cell lines either as single agent or in combination with cytotoxics commonly used in HNSCC. METHODS: Antiproliferative effects of rapamycin, carboplatin, and paclitaxel were evaluated in a panel of three HNSCC cell lines (SCC61, SQ20B and HEP2). Cells were exposed to rapamycin for 48 h, to carboplatin for 48 h, or to paclitaxel for 24 h. Antiproliferative effects of simultaneous and sequential rapamycin-based combinations were studied using MTT assay and median effect plot analysis. Cell cycle effects were analysed using flow cytometry. RESULTS: Rapamycin induced concentration dependent antiproliferative effects in HNSCC cell lines with IC(50) of 5 +/- 1, 12 +/- 2 and 20 +/- 2 microM in SCC61, SQ20B, and HEP2 cells, respectively. Higher antiproliferative effects were observed in SCC61 cells overexpressing NOXA and cyclin D1 than in HEP2 that overexpressed MDR1 and BCL2. In our panel, antiproliferative effects of rapamycin were associated with G0/G1 cell cycle accumulation and apoptosis induction, at concentrations ranging 3-30 microM. Combinations of rapamycin with paclitaxel and carboplatin displayed synergistic and additive effects. Synergistic effects were observed with paclitaxel in SQ20B and HEP2 cells and with carboplatin in SQ20B cells, when cells were exposed to cytotoxics prior to rapamycin. CONCLUSION: Our results show that rapamycin displays antiproliferative effects and induces apoptosis in HNSCC cell lines, cellular effects being more potent in cells that do not express BCL2 and MDR1. Additive and synergistic effects were observed when rapamycin was combined with carboplatin and paclitaxel.     

Radiosensitization of human vascular endothelial cells through Hsp90 inhibition with 17-N-allilamino-17-demethoxygeldanamycin

PURPOSE: In addition to invasive tumor cells, endothelial cells (ECs) of the tumor vasculature are an important target for anticancer radiotherapy. The purpose of the present work is to investigate how 17-N-allilamino-17-demethoxygeldanamycin (17AAG), known as an anticancer drug inhibiting heat shock protein 90 (Hsp90), modifies radiation responses of human vascular ECs. METHODS AND MATERIALS: The ECs cultured from human umbilical veins were exposed to gamma-irradiation, whereas some EC samples were pretreated with growth factors and/or 17AAG. Postirradiation cell death/survival and morphogenesis were assessed by means of terminal deoxynucleotidyl transferase biotin-deoxyuridine triphosphate nick end labeling or annexin V staining and clonogenic and tube-formation assays. The 17AAG-affected expression and phosphorylation of radioresistance-related proteins were probed by means of immunoblotting. Dominant negative or constitutively activated Akt was transiently expressed in ECs to manipulate Akt activity. RESULTS: It was found that nanomolar concentrations of 17AAG sensitize ECs to relatively low doses (2-6 Gy) of gamma-irradiation and abolish the radioprotective effects of vascular endothelial growth factor and basic fibroblast growth factor. The drug-induced radiosensitization of ECs seems to be caused by prevention of Hsp90-dependent phosphorylation (activation) of Akt that results in blocking the radioprotective phosphatidylinositol 3-kinase/Akt pathway. CONCLUSIONS: Clinically achievable concentrations of 17AAG can decrease the radioresistance intrinsic to vascular ECs and minimize the radioprotection conferred upon them by tumor-derived growth factors. These findings characterize 17AAG as a promising radiosensitizer for the tumor vasculature.     

HIV protease inhibitors block Akt signaling and radiosensitize tumor cells both in vitro and in vivo

In tumor cells with mutations in epidermal growth factor receptor (SQ20B), H-Ras (T24), or K-Ras (MIAPACA2 and A549), the inhibition of Akt phosphorylation increases radiation sensitivity in clonogenic assays, suggesting that Akt is a potential molecular target when combined with therapeutic radiation. Insulin resistance and diabetes are recognized side effects of HIV protease inhibitors (HPIs), suggesting that these agents may inhibit Akt signaling. Because activation of the phosphatidylinositol 3-kinase (PI3K)-Akt signaling pathway is common in human cancers, we hypothesized that HPIs can inhibit Akt activity resulting in increased tumor cell sensitivity to ionizing radiation-induced cell death. Five first-generation HPIs were subsequently tested and three of the five (amprenavir, nelfinavir, and saquinavir but not ritonavir or indinavir) inhibited Akt phosphorylation at Ser473 at serum concentrations routinely achieved in HIV patients. In both tumor cell colony formation assays and tumor regrowth delay experiments, combinations of drug and radiation exerted synergistic effects compared with either modality alone. In addition, in vivo, doses of amprenavir or nelfinavir comparable with the therapeutic levels achieved in HIV patients were sufficient to down-regulate phosphorylation of Akt in SQ20B and T24 xenografts. Finally, overexpression of active PI3K in cells without activation of Akt resulted in radiation resistance that could be inhibited with HPIs. Because there is abundant safety data on HPIs accumulated in thousands of HIV patients over the last 5 years, these agents are excellent candidates to be tested as radiation sensitizers in clinical trials.     

Prevention of phosphatidylinositol 3'-kinase-Akt survival signaling pathway during topotecan-induced apoptosis

The serine/threonine kinase Akt (also known as protein kinase B) is a downstream effector of phosphatidylinositol-3'-kinase [PI(3)K] that is recognized as the major mediator of survival signals that protect cells from undergoing apoptosis. In the course of examining the target molecules of the topoisomerase I inhibitor topotecan, we found that topotecan treatment promoted Akt dephosphorylation that led to the inactivation of Akt in human lung cancer A549 cells. Transfection of the constitutively active akt cDNA into A549 cells resulted in the reduction of the cytotoxic effect of topotecan, indicating that inhibition of the Akt pathway played an important role in exhibition of topotecan-mediated cytotoxic effects. Further analysis of Akt dephosphorylation revealed that topotecan treatment suppressed upstream kinases of Akt, 3-phosphoinositide-dependent protein kinase 1, and PI(3)K. Overall, the results demonstrate that topotecan exhibited its cytotoxic effects by down-regulating the PI(3)K-Akt survival signaling pathway in addition to inhibiting topoisomerase I.     

Phosphorous metabolite and cell cycle kinetic response of two human squamous cell carcinomas to radiation.

Phosphorous metabolism and cell cycle phase kinetics in response to radiation of two perfused human squamous cell carcinoma cell lines, SQ20B (radioresistant) and SQ38 (relatively radiosensitive), embedded in both basement membrane (Matrigel) and agarose gel threads were studied. The findings for these human cancer cells in response to 2- and 50-Gy irradiation are as follows. (a) Well perfused pure cancer cells (both SQ20B and SQ38) in both proliferative (cells embedded in Matrigel) and static (cells embedded in agarose threads) states did not show significant alteration in either phosphorous bioenergetics or membrane metabolites at 24 and 48 h after irradiation, although a large fraction of the population was clonogenically impaired. Previously reported, sensitively detected, metabolite alterations in response to radiation in rodent and human tumors in situ were not seen in these homogeneous cancer cell populations. (b) The radiosensitive squamous cell carcinoma cell lines SQ38 exhibited G1 block (from 54.38 +/- 1.40% in control to 73.93 +/- 1.01% after irradiation; mean +/ SD) in response to low-dose 2-Gy irradiation and G2 block (from 12.98 +/- 2.15% in control to 25.6 +/- 3.15% after irradiation) in response to high-dose 50-Gy irradiation, while the radioresistant cell line SQ20B showed only conventional G2 block in response to both doses. The differential cell cycle phase response may indicate the difference in radioresistance. (c) The membrane metabolites (including phosphomonoesters and phosphodiesters) and phosphocreatine gradually increased from the early passages to late passages, suggesting that cell proliferation rates were increasing as the cells adapted to tissue culture. The results suggest that the radiation-induced metabolite changes observed in solid tumors in situ may not be a direct response to interim changes within the cancer cells but, rather, a consequence of radiation damage either to the vasculature or to other host-mediated factors.     

Protective role of Hsp27 protein against gamma radiation-induced apoptosis and radiosensitization effects of Hsp27 gene silencing in different human tumor cells

PURPOSE: The ability of heat shock protein 27 (Hsp27) to protect cells from stressful stimuli and its increased levels in tumors resistant to anticancer therapeutics suggest that it may represent a target for sensitization to radiotherapy. In this study, we investigate the protective role of Hsp27 against radiation-induced apoptosis and the effect of its attenuation in highly expressing radioresistant cancer cell lines. METHODS AND MATERIALS: We examined clonogenic death and the kinetics of apoptotic events in different tumor cell lines overexpressing or underexpressing Hsp27 protein irradiated with photons. The radiosensitive Jurkat cell line, which does not express Hsp27 constitutively or in response to gamma-rays, was stably transfected with Hsp27 complementary DNA. Attenuation of Hsp27 expression was accomplished by antisense or RNAi (interfering RNA) strategies in SQ20B head-and-neck squamous carcinoma, PC3 prostate cancer, and U87 glioblastoma radioresistant cells. RESULTS: We measured concentration-dependent protection against the cytotoxic effects of radiation in Jurkat-Hsp27 cells, which led to a 50% decrease in apoptotic cells at 48 hours in the highest expressing cells. Underlying mechanisms leading to radiation resistance involved a significant increase in glutathione levels associated with detoxification of reactive oxygen species, a delay in mitochondrial collapse, and caspase activation. Conversely, attenuation of Hsp27 in SQ20B cells, characterized by their resistance to apoptosis, sensitizes cells to irradiation. This was emphasized by increased apoptosis, decreased glutathione basal level, and clonogenic cell death. Sensitization to irradiation was confirmed in PC3 and U87 radioresistant cells. CONCLUSION: Hsp27 gene therapy offers a potential adjuvant to radiation-based therapy of resistant tumors.     

Radiobiologic parameters and local effect model predictions for head-and-neck squamous cell carcinomas exposed to high linear energy transfer ions

PURPOSE: To establish the radiobiologic parameters of head-and-neck squamous cell carcinomas (HNSCC) in response to ion irradiation with various linear energy transfer (LET) values and to evaluate the relevance of the local effect model (LEM) in HNSCC. METHODS AND MATERIALS: Cell survival curves were established in radiosensitive SCC61 and radioresistant SQ20B cell lines irradiated with [33.6 and 184 keV/n] carbon, [302 keV/n] argon, and X-rays. The results of ion experiments were confronted to LEM predictions. RESULTS: The relative biologic efficiency ranged from 1.5 to 4.2 for SCC61 and 2.1 to 2.8 for SQ20B cells. Fixing an arbitrary D(0) parameter, which characterized survival to X-ray at high doses (>10 Gy), gave unsatisfying LEM predictions for both cell lines. For D(0) = 10 Gy, the error on survival fraction at 2 Gy amounted to a factor of 10 for [184 keV/n] carbon in SCC61 cells. We showed that the slope (s(max)) of the survival curve at high doses was much more reliable than D(0). Fitting s(max) to 2.5 Gy(-1) gave better predictions for both cell lines. Nevertheless, LEM could not predict the responses to fast and slow ions with the same accuracy. CONCLUSIONS: The LEM could predict the main trends of these experimental data with correct orders of magnitude while s(max) was optimized. Thus the efficiency of carbon ions cannot be simply extracted from the clinical response of a patient to X-rays. LEM should help to optimize planning for hadrontherapy if a set of experimental data is available for high-LET radiations in various types of tumors.     

Vascular responses to radiotherapy and androgen-deprivation therapy in experimental prostate cancer

Background

The phosphatidylinositol 3-kinase (PI3K)/Akt pathway is activated in tumor cells and promotes tumor cell survival after radiation-induced DNA damage. Because the pathway may not be completely inhibited after blockade of PI3K itself, due to feedback through mammalian target of rapamycin (mTOR), more effective inhibition might be expected by targeting both PI3K and mTOR inhibition.

Materials and methods

We investigated the effect of two dual PI3K/mTOR (both mTORC1 and mTORC2) inhibitors, NVP-BEZ235 and NVP-BGT226, on SQ20B laryngeal and FaDu hypopharyngeal cancer cells characterised by EGFR overexpression, on T24 bladder tumor cell lines with H-Ras mutation and on endothelial cells. Analysis of target protein phosphorylation, clonogenic survival, number of residual ??H2AX foci, cell cycle and apoptosis after radiation was performed in both tumor and endothelial cells. In vitro angiogenesis assays were conducted as well.

Results

Both compounds effectively inhibited phosphorylation of Akt, mTOR and S6 target proteins and reduced clonogenic survival in irradiated tumor cells. Persistence of DNA damage, as evidenced by increased number of ??H2AX foci, was detected after irradiation in the presence of PI3K/mTOR inhibition, together with enhanced G2 cell cycle delay. Treatment with one of the inhibitors, NVP-BEZ235, also resulted in decreased clonogenicity after irradiation of tumor cells under hypoxic conditions. In addition, NVP-BEZ235 blocked VEGF- and IR-induced Akt phosphorylation and increased radiation killing in human umbilical venous endothelial cells (HUVEC) and human dermal microvascular dermal cells (HDMVC). NVP-BEZ235 inhibited VEGF-induced cell migration and capillary tube formation in vitro and enhanced the antivascular effect of irradiation. Treatment with NVP-BEZ235 moderately increased apoptosis in SQ20B and HUVEC cells but not in FaDu cells, and increased necrosis in both tumor and endothelial all cells tumor.

Conclusions

The results of this study demonstrate that PI3K/mTOR inhibitors can enhance radiation-induced killing in tumor and endothelial cells and may be of benefit when combined with radiotherapy.     

Differential activation of the phosphatidylinositol 3'-kinase/Akt survival pathway by ionizing radiation in tumor and primary endothelial cells

Ionizing radiation induces an intracellular stress response via activation of the phosphatidylinositol 3'-kinase (PI3K)/Akt survival pathway. In tumor cells, the PI3K/Akt pathway is induced through activation of members of ErbB receptor tyrosine kinases. Here, we investigated the receptor dependence of radiation-induced PI3K/Akt activation in tumor cells and in endothelial cells. The integrity of both the ErbB and the vascular endothelial growth factor (VEGF) ligand-activated PI3K/Akt pathway in endothelial cells was demonstrated using specific ErbB and VEGF receptor tyrosine kinase inhibitors. Irradiation of endothelial cells resulted in protein kinase B (PKB)/Akt activation in a similar time course as observed in response to VEGF. More importantly, radiation-induced PKB/Akt phosphorylation in endothelial cells was strongly down-regulated by the VEGF receptor tyrosine kinase inhibitor, whereas the ErbB receptor tyrosine kinase inhibitor did not affect PKB/Akt stimulation in response to irradiation. An opposite receptor dependence for radiation-induced PKB/Akt phosphorylation was observed in ErbB receptor-overexpressing A431 tumor cells. Furthermore, direct VEGF receptor phosphorylation was detected after irradiation in endothelial cells in absence of VEGF, which was almost completely inhibited after irradiation in presence of the VEGF receptor tyrosine kinase inhibitor. These data demonstrate that ionizing radiation induces VEGF ligand-independent but VEGF receptor-dependent PKB/Akt activation in endothelial cells and that PI3K/Akt pathway activation by radiation occurs in a differential cell type and receptor-dependent pattern.     

Activation of PI3K-Akt signaling pathway promotes prostate cancer cell invasion

Activated phosphoinositide 3-kinase (PI3K) and its downstream target Akt/PKB are important signaling molecules and key survival factors involved in the control of cell proliferation, apoptosis and oncogenesis. We investigated the role of the PI3K-Akt signaling pathway in the invasion of prostate cancer cell lines and activation of this pathway in primary human prostate tumors. Treatment of human prostate cancer cells viz. LNCaP, PC-3 and DU145 with PI3K pharmacological inhibitor, LY294002, potentially suppressed the invasive properties in each of these cell lines. Restoration of the PTEN gene to highly invasive prostate cancer PC-3 cells or expression of a dominant negative version of the PI3K target, Akt also significantly inhibited invasion and downregulated protein expression of urokinase-type plasminogen activator (uPA) and matrix metalloproteinase (MMP)-9, markers for cell invasion, indicating a central role of the PI3K-Akt pathway in this process. Immunoblot analysis of PI3K and total/activated levels of Akt showed increased protein levels of catalytic (p110alpha/beta) and regulatory (p85) subunits of PI3K and constitutive Akt activation in high-grade tumors compared to low-grade tumor and benign tissue. Immunohistochemical analyses further confirmed a progressive increase in p-Akt (p-Ser473) levels but not of total-Akt (Akt1/2) in cancer tissues compared to benign specimens. A successive increase in p-Akt expression was further noted in specimens serially obtained from individuals with time-course disease progression. Taken together, these results suggest that aberrant activation of PI3K-Akt pathway may contribute to increased cell invasiveness and facilitate prostate cancer progression.     

Insulin-like growth factor I-mediated protection from rapamycin-induced apoptosis is independent of Ras-Erk1-Erk2 and phosphatidylinositol 3'-kinase-Akt signaling pathways

The mTOR inhibitor rapamycin induces G1 cell cycle accumulation and p53-independent apoptosis of the human rhabdomyosarcoma cell line Rh1. Insulin-like growth factor I (IGF-I) and insulin, but not epidermal growth factor or platelet-derived growth factor, completely prevented apoptosis of this cell line. Because the Ras-Erk1-Erk2 and phosphatidylinositol 3'-kinase (PI3K)-Akt pathways are implicated in the survival of various cancer cells, we determined whether protection from rapamycin-induced apoptosis by IGF-I requires one or both of these pathways. Despite the blocking of Ras-Erk signaling by the addition of PD 98059 (a MEK1 inhibitor) or by the overexpression of dominant-negative RasN17, IGF-I completely prevented rapamycin-induced death. Inhibition of Ras signaling did not prevent Akt activation by IGF-I. To determine the role of the PI3K-Akt pathway in rescuing cells from apoptosis caused by rapamycin, cells expressing dominant-negative Akt were tested. This mutant protein inhibited IGF-I-induced phosphorylation of Akt and blocked phosphorylation of glycogen synthase kinase 3. The prevention of rapamycin-induced apoptosis by IGF-I was not inhibited by expression of dominant-negative Akt either alone or under conditions in which LY 294002 inhibited PI3K signaling. Furthermore, IGF-I prevented rapamycin-induced apoptosis when the Ras-Erk1-Erk2 and PI3K-Akt pathways were blocked simultaneously. Similar experiments in a second rhabdomyosarcoma cell line, Rh30, using pharmacological inhibitors of PI3K or MEK1, alone or in combination, failed to block IGF-I rescue from rapamycin-induced apoptosis. Therefore, we conclude that a novel pathway(s) is responsible for the IGF-I-mediated protection against rapamycin-induced apoptosis in these rhabdomyosarcoma cells.     

PI3K-Akt信号通路阻断在乳腺癌治疗中的作用

分子靶向药物为肿瘤的治疗提供了新的方向。抑制信号通路中一些小分子的活性,从而阻断某些信号的转导,成为肿瘤治疗中的新的策略。在肿瘤的发生、发展过程中,经常伴有P13K信号通路的异常改变。过度激活P13K-Akt信号通路之后,可以引起一系列的反应,包括细胞的生长、增殖和转移,上皮细胞向间叶细胞的转变以及血管的生成。因此,这条信号通路成为人们比较感兴趣的分子治疗的靶标。另外,在一些实验中,过度表达P13K或者Akt,特别是当它们持续活化时,就足以引起细胞的恶性转变,并且能够使细胞产生耐药。当P13K-Akt信号通路被阻断之后,具有高水平Akt的细胞生长就会受到抑制,并且开始凋亡。由于某些肿瘤细胞的存活和生长对P13K-Akt信号通路的依赖,使分子靶向药物能够比较特异的杀死肿瘤细胞。在过去的几年中,人们已经找到了一些此信号通路的抑制剂。我们介绍了P13K-Akt信号通路以及阻断此信号通路在乳腺癌治疗中的应用,重点介绍pAkt和mTOR的分子抑制剂。     

Akt inhibitor shows anticancer and radiosensitizing effects in malignant glioma cells by inducing autophagy

Autophagy, or programmed cell death type II, is one of the responses of cancer cells to various therapies, including ionizing radiation. Recently, we have shown that radiation induces autophagy, but not apoptosis, in various malignant glioma cell lines. Autophagy is mainly regulated by the mammalian target of rapamycin (mTOR) pathway. The Akt/mTOR pathway also mediates oncogenesis and radioresistance. Thus, we hypothesized that inhibiting this pathway has both an anticancer and radiosensitizing effect by activating autophagy. The purpose of our study was therefore to determine whether and by which mechanisms an Akt inhibitor, 1L-6-hydroxymethyl-chiro-inositol 2(R)-2-O-methyl-3-O-octadecylcarbonate, had anticancer and radiosensitizing effects on malignant glioma U87-MG and radioresistant U87-MG cells with a consistitutively active form of epidermal growth factor receptor (U87-MGDeltaEGFR). Treatment with the Akt inhibitor successfully inhibited Akt activity and reduced cell viability in both cell lines. In terms of the mechanism, the Akt inhibitor decreased phosphorylated p70S6 kinase, a downstream target of Akt, and induced autophagy, but not apoptosis. Furthermore, the Akt inhibitor radiosensitized both U87-MG and U87-MGDeltaEGFR cells by enhancing autophagy. Specific inhibition of Akt using the dominant-negative Akt plasmid also resulted in enhanced radiation-induced autophagy. In conclusion, an Akt inhibitor showed anticancer and radiosensitizing effect on U87-MG and U87-MGDeltaEGFR cells by inducing autophagy. Thus, Akt inhibitors may represent a promising new therapy as a single treatment or used in combination with radiation for malignant gliomas, including radioresistant ones that express DeltaEGFR.     

VES对MDA-MB-453细胞PI3K/Akt信号通路的影响

目的：检测维生素E琥珀酸酯（vitamin E succinate,VES）对MDA-MB-453乳腺癌细胞PI3K/Akt信号通路中PI3K及Akt表达的影响。方法：不同浓度VES作用于人乳腺癌细胞MDA-MB-453（Her-2过表达株）24h和48h,VES的浓度分别为5、10和20μg/ml。RT-PCR法检测VES作用前后PI3K及Akt的mR-NA表达变化。结果：VES对MDA-MB-453乳腺癌细胞PI3 K/Akt信号通路中PI3 K有抑制作用（P〈0.05）,并呈时间-剂量依赖关系;而对Akt无明显的抑制作用（P〉0.05）。结论：VES可能是通过作用于PI3K/Akt信号通路而发挥其对MDA-MB-453乳腺癌细胞的抑制及凋亡作用。     

Combination treatment with 17-N-allylamino-17-demethoxy geldanamycin and acute irradiation produces supra-additive growth suppression in human prostate carcinoma spheroids

Failure to control localized prostate cancer can result not only in localized disease progression but also distant metastatic spread. Whereas significant advances in both surgical technique and radiation therapy have improved local control rates with decreased morbidity, consistent long-term control remains elusive. This study investigates the potential of 17-N-allylamino-17-demethoxy geldanamycin (17AAG), a geldanamycin derivative, to sensitize tumor cells to ionizing radiation, permitting a significant improvement to targeted radiotherapies of prostate carcinoma. As a monotherapeutic, 17AAG functions to modulate the action of heat shock protein 90, ultimately affecting a multitude of cellular signaling pathways. It is in Phase I trial and has shown promise in controlling prostate cancer progression. Human prostate tumor cells (LNCaP and CWR22Rv1) were grown as spheroids and incubated for 96 h with increasing doses of 17AAG immediately before and after 2 or 6 Gy low linear energy transfer (LET), high dose-rate irradiation (Cs-137 irradiator). Twelve or 24 spheroids (initial diameter, 150-200 microm) were used per experiment. Response was determined by spheroid volume measurements taken over at least 40 days, after treatment. Incubation of either cell line with 17AAG (相似文献   

Targeting fibroblast growth factor receptor 3 enhances radiosensitivity in human squamous cancer cells

Conventional therapies including radiation therapy cannot cure squamous cell carcinoma (SCC), and new treatments are clearly required. Our recent studies have shown that SCC cell lines exhibiting radioresistance show significant upregulation of the fibroblast growth factor receptor 3 (FGFR3) gene. We hypothesized that inhibiting FGFR3 would suppress tumor cell radioresistance and provide a new treatment approach for human SCCs. In the present study, we found that RNA interference-mediated FGFR3 depletion in HSC-2 cells, a radioresistant cell line, induced radiosensitivity and inhibited tumor growth. Use of an FGFR3 inhibitor (PD173074) obtained similar results with suppression of the autophosphorylation extracellular signal-regulated kinase pathway in HSC-2 cells and lung cancer cell lines. Moreover, the antitumor growth effect of the combination of PD173074 and radiation in vivo was also greater than that with either drug alone or radiation alone. Our results provided novel information on which to base further mechanistic study of radiosensitization by inhibiting FGFR3 in human SCC cells and for developing strategies to improve outcomes with concurrent radiotherapy.     

Radiation-enhanced hepatocellular carcinoma cell invasion with MMP-9 expression through PI3K/Akt/NF-kappaB signal transduction pathway

This study is to investigate the molecular mechanism of radiation-enhanced cell invasiveness of hepatocellular carcinoma (HCC) correlating with clinical patients undergoing radiotherapy and subsequently developing metastasis. Three HCC cell lines (HepG2, Hep3B and Huh7) and normal hepatocyte cell line (CL-48) were irradiated with different doses. The effect of radiation on cell invasiveness was determined using the Boyden chamber assay. Radiation-enhanced invasion capability was evident in HCC cells but not in normal hepatocytes. Invasion was observed in gelatin-coated but not fibronectin-coated or type I collagen-coated membranes. Radiation upregulated matrix metalloproteinase-9 (MMP-9) mRNA level, MMP-9 protein level and MMP-9 activity. MMP-9 antisense oligonucleotides inhibited radiation-induced MMP-9 expression and thereby significantly inhibited radiation-induced HCC invasion. Furthermore, phosphatidylinositol 3-kinase (PI3K)/Akt chemical inhibitors LY294002 and wortmannin suppressed radiation-induced MMP-9 mRNA expression. Transient transfection with dominant-negative Akt plasmid also showed that the PI3K/Akt-signaling pathway was involved in this radiation-induced MMP-9 expression. Moreover, nuclear factor-kappaB (NF-kappaB) decoy oligodeoxynucleotide suppressed radiation enhanced MMP-9 promoter activity completely. PI3K/Akt chemical inhibitors inhibited radiation-induced NF-kappaB-driven luciferase promoter activity. Taken together, our results indicated that sublethal dose of radiation could enhance HCC cell invasiveness by MMP-9 expression through the PI3K/Akt/NF-kappaB signal transduction pathway.     

microRNA-7 increases radiosensitivity of human cancer cells with activated EGFR-associated signaling

Many microRNAs (miRNAs) play crucial roles in regulating expression of oncogenes or tumor suppressor genes. The epidermal growth factor receptor (EGFR) is frequently overexpressed in a wide range of solid tumors and is an important therapeutic target; however, the therapeutic outcome of currently available anti-EGFR agents is often limited due to diverse molecular resistance mechanisms. In this study, we evaluated the potential of targeting miRNA-7 for overcoming radio-resistance of cancer cells with activated EGFR-associated signaling. A panel of human cancer cell lines with increased EGFR-PI3K-Akt signaling was transfected with pre-miR-7 or control miRNA. Ectopic overexpression of miR-7 attenuated EGFR and Akt expression and radiosensitized SQ20B squamous cell carcinoma of the larynx, MDA-MB-468 breast cancer cells, A549 lung carcinoma cells, and U251 and U87 malignant glioma cells. In contrast, antisense-mediated inhibition of mature miR-7 expression led up-regulation of EGFR and its downstream effectors, and increased radio-resistance of U251 glioma cells. Overexpression of miR-7 prolonged radiation-induced γH2AX foci formation and downregulation of DNA-dependent protein kinases (DNA-PKcs). miR-7 may be a useful therapeutic target for overcoming the radio-resistance of human cancers with activated EGFR-PI3K-AKT signaling.