Blockage of Epidermal Growth Factor Receptor-Phosphatidylinositol 3-Kinase-AKT Signaling Increases Radiosensitivity of K-RAS Mutated Human Tumor Cells In vitro by Affecting DNA Repair

[Effect and mechanism of gefitinib inhibition on non-small cell lung cancer radiosensitivity of HCC827 and H358 cell lines]

背景与目的

表皮生长因子受体（epidermal growth factor receptor, EGFR）是决定放疗效应的一个重要因素，其过表达或是下游通路的激活与包括非小细胞肺癌在内的肿瘤的放疗抵抗相关，因而阻断EGFR的信号通路可能会增强放疗敏感性。本研究旨在探讨小分子EGFR酪氨酸激酶抑制剂吉非替尼能否增加肺癌细胞株HCC827和H358的放疗敏感性及其可能的机制。

方法

选取HCC827和H358这两个非小细胞肺癌细胞株，分为单纯X线组和X线+吉非替尼两组。单纯X线组采用单纯X线照射，X线+吉非替尼组经1 μmol/L吉非替尼作用24 h后再行X线照射。克隆形成实验比较两株细胞中不同分组细胞放射敏感性，免疫荧光激光共聚焦显微镜观察X线照射后各时间点细胞核中的磷酸化H2AX（γ-H2AX）及EGFR焦点在细胞中的定位情况，Western blot法检测放疗后胞质胞核蛋白中EGFR的表达。

结果

克隆形成实验中，H358细胞实验组与对照组在各放疗剂量点的SF2值分别为0.355和0.433；HCC827细胞实验组与对照组在各放疗剂量点的SF2值分别为0.223和0.242，差别不明显。激光共聚焦显微镜观察照射4 Gy后各时间段实验组H358细胞核中g-H2AX斑点相比对照组要多，且持续时间更长。而对照组和实验组的HCC827细胞g-H2AX斑点在各时间段并无明显差异；激光共聚焦显微镜观察照射4 Gy后对照组H358的EGFR蛋白在1 h内入核，而经吉非替尼处理后EGFR蛋白几乎不入核；实验组及对照组HCC827细胞的EGFR表达位置均在细胞质中，胞核中很少或者没有，可以认为并无入核现象；Western blot结果显示，H358细胞在经4 Gy放射处理后有入核现象，而预先经吉非替尼处理后，EGFR蛋白几乎不在核内表达而仍位于细胞浆内。对于HCC827细胞，实验组及对照组的EGFR蛋白均在细胞质中表达，胞核中很少或没有，且两组并无明显差异。

结论

吉非替尼可增加肺癌细胞株H358的放射敏感性，这可能与其阻止放疗后EGFR入核、影响放疗后双链断裂（double strand break, DSB）修复有关；而对HCC827细胞无影响，可能与其放疗后EGFR不入核相关。

Role of DNA-dependent protein kinase catalytic subunit in cancer development and treatment

DNA-dependent protein kinase catalytic subunit (DNA-PKcs), a key component of the non-homologous end-joining (NHEJ) pathway, is involved in DNA double-strand break repair, immunocompetence, genomic integrity, and epidermal growth factor receptor signaling. Clinical studies indicate that expression and activity of DNA-PKcs is correlated with cancer progression and response to treatment. Various anti-DNA-PKcs strategies have been developed and tested in preclinical studies to exploit the benefit of DNA-PKcs inhibition in sensitization of radiotherapy and in combined modality therapy with other antitumor agents. In this article, we review the association between DNA-PKcs and cancer development and discuss current approaches and mechanisms for inhibition of DNA-PKcs. The future challenges are to understand how DNA-PKcs activity is correlated with cancer susceptibility and to identify those patients who would most benefit from DNA-PKcs inhibition.

Akt promotes post-irradiation survival of human tumor cells through initiation, progression, and termination of DNA-PKcs-dependent DNA double-strand break repair

Akt phosphorylation has previously been described to be involved in mediating DNA damage repair through the nonhomologous end-joining (NHEJ) repair pathway. Yet the mechanism how Akt stimulates DNA-protein kinase catalytic subunit (DNA-PKcs)-dependent DNA double-strand break (DNA-DSB) repair has not been described so far. In the present study, we investigated the mechanism by which Akt can interact with DNA-PKcs and promote its function during the NHEJ repair process. The results obtained indicate a prominent role of Akt, especially Akt1 in the regulation of NHEJ mechanism for DNA-DSB repair. As shown by pull-down assay of DNA-PKcs, Akt1 through its C-terminal domain interacts with DNA-PKcs. After exposure of cells to ionizing radiation (IR), Akt1 and DNA-PKcs form a functional complex in a first initiating step of DNA-DSB repair. Thereafter, Akt plays a pivotal role in the recruitment of AKT1/DNA-PKcs complex to DNA duplex ends marked by Ku dimers. Moreover, in the formed complex, Akt1 promotes DNA-PKcs kinase activity, which is the necessary step for progression of DNA-DSB repair. Akt1-dependent DNA-PKcs kinase activity stimulates autophosphorylation of DNA-PKcs at S2056 that is needed for efficient DNA-DSB repair and the release of DNA-PKcs from the damage site. Thus, targeting of Akt results in radiosensitization of DNA-PKcs and Ku80 expressing, but not of cells deficient for, either of these proteins. The data showed indicate for the first time that Akt through an immediate complex formation with DNA-PKcs can stimulate the accumulation of DNA-PKcs at DNA-DSBs and promote DNA-PKcs activity for efficient NHEJ DNA-DSB repair.

Houttuyninum, an active constituent of Chinese herbal medicine, inhibits phosphorylation of HER2/neu receptor tyrosine kinase and the tumor growth of HER2/neu-overexpressing cancer cells

AIMS

The overexpression of HER2/neu receptor plays a key role in tumorigenesis and tumor progression. Small molecules targeting HER2/neu have therapeutic value in cancers that overexpress HER2. In this present study, the effect of houttuyninum, a component in the Chinese herbal medicine Houttuynia cordata Thunb, on HER2/neu tyrosine phosphorylation and its in vivo antitumour activity was investigated.

MAIN METHODS

The phosphorylation and expression of proteins were determined by Western blot analysis. The MTT assay was employed to examine the inhibition of cell proliferation in vitro. Xenografts were established in nude mice for evaluating the antitumour activity of houttuyninum in vivo.

KEY FINDINGS

Houttuyninum inhibited phosphorylation of HER2 in a dose-dependent manner with an IC50 of 5.52 μg/ml without reducing HER2/neu protein expression in MDA-MB-453 cells. Houttuyninum also inhibited the activation of ERK1/2 and AKT, downstream molecules in the HER2/neu-mediated signal transduction pathway. In contrast, tyrosine phosphorylation of EGFR was unaffected when the concentration of houttuyninum was increased to 40 μg/ml in both A431 cells and MDA-MB-468 cells. Additionally, houttuyninum preferentially inhibited the growth of MDA-MB-453 cells that overexpressed HER2/neu; the MDA-MB-468 cells that overexpress EGFR remained unaffected. Administration of houttuyninum in vivo resulted in a significant reduction of phosphorylated HER2 levels and in tumor volumes of the BT474 and N87 xenografts, which both overexpress HER2/neu.

SIGNIFICANCE

Our findings showed that houttuyninum can inhibit the HER2/neu signalling pathway and the tumor growth of cancer cells that overexpress HER2/neu. This drug may provide therapeutic value in the treatment of cancers that involve overexpression of HER2/neu.

Akt: a double-edged sword in cell proliferation and genome stability

The Akt family of serine/threonine protein kinases are key regulators of multiple aspects of cell behaviour, including proliferation, survival, metabolism, and tumorigenesis. Growth-factor-activated Akt signalling promotes progression through normal, unperturbed cell cycles by acting on diverse downstream factors involved in controlling the G1/S and G2/M transitions. Remarkably, several recent studies have also implicated Akt in modulating DNA damage responses and genome stability. High Akt activity can suppress ATR/Chk1 signalling and homologous recombination repair (HRR) via direct phosphorylation of Chk1 or TopBP1 or, indirectly, by inhibiting recruitment of double-strand break (DSB) resection factors, such as RPA, Brca1, and Rad51, to sites of damage. Loss of checkpoint and/or HRR proficiency is therefore a potential cause of genomic instability in tumor cells with high Akt. Conversely, Akt is activated by DNA double-strand breaks (DSBs) in a DNA-PK- or ATM/ATR-dependent manner and in some circumstances can contribute to radioresistance by stimulating DNA repair by nonhomologous end joining (NHEJ). Akt therefore modifies both the response to and repair of genotoxic damage in complex ways that are likely to have important consequences for the therapy of tumors with deregulation of the PI3K-Akt-PTEN pathway.

Radiosensitizing effect of epothilone B on human epithelial cancer cells

BACKGROUND

A combined modality treatment employing radiation and chemotherapy plays a central role in the management of solid tumors. In our study, we examined the cytotoxic and radiosensitive effect of the microtubule stabilizer epothilone B on two human epithelial tumor cell lines in vitro and its influence on the microtubule assembly.

METHODS

Cancer cells were treated with epothilone B in proliferation assays and in combination with radiation in colony-forming assays. For the analysis of ionizing radiation-induced DNA damage and the influence of the drug on its repair a γH2AX foci assay was used. To determine the effect of epothilone B on the microtubule assembly in cells and on purified tubulin, immunofluorescence staining and tubulin polymerization assay, respectively, were conducted.

RESULTS

Epothilone B induced a concentration- and application-dependent antiproliferative effect on the cells, with IC(50) values in the low nanomolar range. Colony forming assays showed a synergistic radiosensitive effect on both cell lines which was dependent on incubation time and applied concentration of epothilone B. The γH2AX assays demonstrated that ionizing radiation combined with the drug resulted in a concentration-dependent increase in the number of double-strand breaks and suggested a reduction in DNA repair capacity. Epothilone B produced enhanced microtubule bundling and abnormal spindle formation as revealed by immunofluorescence microscopy and caused microtubule formation from purified tubulin.

CONCLUSION

The results of this study showed that epothilone B displays cytotoxic antitumor activity at low nanomolar concentrations and also enhances the radiation response in the tumor cells tested; this may be induced by a reduced DNA repair capacity triggered by epothilone B. It was also demonstrated that epothilone B in fact targets microtubules in a more effective manner than paclitaxel.

Cooperative interaction between reactive oxygen species and Ca2+ signals contributes to angiotensin II-induced hypertrophy in adult rat cardiomyocytes

Reactive oxygen species (ROS) and Ca(2+) signals are closely associated with the pathogenesis of cardiac hypertrophy. However, the cause and effect of the two signals in cardiac hypertrophy remain to be clarified. We extend our recent report by investigating a potential interaction between ROS and Ca(2+) signals utilizing in vitro and in vivo angiotensin II (ANG II)-induced cardiac hypertrophy models. ANG II-induced initial Ca(2+) transients mediated by inositol trisphosphate (IP(3)) triggered initial ROS production in adult rat cardiomyocytes. The ROS generated by activation of the NAD(P)H oxidase complex via Rac1 in concert with Ca(2+) activates ADP-ribosyl cyclase to generate cyclic ADP-ribose (cADPR). This messenger-mediated Ca(2+) signal further augments ROS production, since 2,2'-dihydroxyazobenzene, an ADP-ribosyl cyclase inhibitor, or 8-Br-cADPR, an antagonistic analog of cADPR, abolished further ROS production. Data from short hairpin RNA (shRNA)-mediated knockdown of Akt1 and p47(phox) demonstrated that Akt1 is the upstream key molecule responsible for the initiation of Ca(2+) signal that activates p47(phox) to generate ROS in cardiomyocytes. Nuclear translocation of nuclear factor of activated T-cell in cardiomyocytes was significantly suppressed by treatment with NAD(P)H oxidase inhibitors as well as by shRNA against Akt1 and p47(phox). Our results suggest that in cardiomyocytes Ca(2+) and ROS messengers generated by ANG II amplify the initial signals in a cooperative manner, thereby leading to cardiac hypertrophy.

Combined hyperthermia and radiotherapy for the treatment of cancer

Radiotherapy is used to treat approximately 50% of all cancer patients, with varying success. Radiation therapy has become an integral part of modern treatment strategies for many types of cancer in recent decades, but is associated with a risk of long-term adverse effects. Of these side effects, cardiac complications are particularly relevant since they not only adversely affect quality of life but can also be potentially life-threatening. The dose of ionizing radiation that can be given to the tumor is determined by the sensitivity of the surrounding normal tissues. Strategies to improve radiotherapy therefore aim to increase the effect on the tumor or to decrease the effects on normal tissues, which must be achieved without sensitizing the normal tissues in the first approach and without protecting the tumor in the second approach. Hyperthermia is a potent sensitizer of cell killing by ionizing radiation (IR), which can be attributed to the fact that heat is a pleiotropic damaging agent, affecting multiple cell components to varying degrees by altering protein structures, thus influencing the DNA damage response. Hyperthermia induces heat shock protein 70 (Hsp70; HSPA1A) synthesis and enhances telomerase activity. HSPA1A expression is associated with radioresistance. Inactivation of HSPA1A and telomerase increases residual DNA DSBs post IR exposure, which correlates with increased cell killing, supporting the role of HSPA1A and telomerase in IR-induced DNA damage repair. Thus, hyperthermia influences several molecular parameters involved in sensitizing tumor cells to radiation and can enhance the potential of targeted radiotherapy. Therapy-inducible vectors are useful for conditional expression of therapeutic genes in gene therapy, which is based on the control of gene expression by conventional treatment modalities. The understanding of the molecular response of cells and tissues to ionizing radiation has lead to a new appreciation of the exploitable genetic alterations in tumors and the development of treatments combining pharmacological interventions with ionizing radiation that more specifically target either tumor or normal tissue, leading to improvements in efficacy.

Insulin-like growth factor-type 1 receptor inhibitor NVP-AEW541 enhances radiosensitivity of PTEN wild-type but not PTEN-deficient human prostate cancer cells

PURPOSE

During the past decade, many clinical trials with both monoclonal antibodies and small molecules that target the insulin-like growth factor-type 1 receptor (IGF-1R) have been launched. Despite the important role of IGF-1R signaling in radioresistance, studies of such agents in combination with radiotherapy are lagging behind. Therefore, the aim of this study was to investigate the effect of the small molecule IGF-1R kinase inhibitor NVP-AEW541 on the intrinsic radioresistance of prostate cancer cells.

METHODS AND MATERIALS

The effect of NVP-AEW541 on cell proliferation, cell viability, IGF-1R signaling, radiosensitivity, cell cycle distribution, and double strand break repair was determined in three human prostate cancer cell lines (PC3, DU145, 22Rv1). Moreover, the importance of the PTEN pathway status was explored by means of transfection experiments with constitutively active Akt or inactive kinase-dead Akt.

RESULTS

NVP-AEW541 inhibited cell proliferation and decreased cell viability in a time-and dose-dependent manner in all three cell lines. Radiosensitization was observed in the PTEN wild-type cell lines DU145 and 22Rv1 but not in the PTEN-deficient PC3 cell line. NVP-AEW541-induced radiosensitization coincided with downregulation of phospho-Akt levels and high levels of residual double strand breaks. The importance of PTEN status in the radiosensitization effect was confirmed by transfection experiments with constitutively active Akt or inactive kinase-dead Akt.

CONCLUSIONS

NVP-AEW541 enhances the effect of ionizing radiation in PTEN wild-type, but not in PTEN-deficient, prostate cancer cells. Proper patient selection based on the PTEN status of the tumor will be critical to the achievement of optimal results in clinical trials in which the combination of radiotherapy and this IGF-1R inhibitor is being explored.

[Targeted therapies and radiation therapy in non-small cell lung cancer]

Lung cancer is the leading cause of cancer-related death. Between 80-85% of lung cancers are non-small cell lung carcinomas. One third of the patients are diagnosed with locally advanced stage. In this condition, concomitant radio-chemotherapy is the standard treatment for patients with good performance status. Despite important improvements in the last years, non-small cell lung carcinoma prognosis remains poor, with high rates of both local recurrences and metastases. The heterogeneity of molecular characteristics of non-small cell lung carcinoma cells and a better knowledge of potential targets offer promising developments for new pharmacologic agents. Hereafter we will review the currently most studied pathways and the most promising ones for the treatment of locally advanced unresectable non-small cell lung carcinoma. Two of the most attractive pathways where new agents have been developed and assessed in combination with thoracic radiotherapy or radiochemotherapy are the EGFR pathway (either with the use of monoclonal antibodies or tyrosine kinase inhibitors) and the angiogenesis inhibition. The development of targeted agents could lead to individualized therapeutic combinations taking into account the intrinsic characteristics of tumor cells. Pharmacological modulation of tumour cells radiosensitivity by targeted therapies is only starting, but yet offers promising perspectives.

Unexpected effect of the monoclonal antibody Panitumumab on human cancer cells with different KRAS status

Panitumumab is the first fully human monoclonal antibody targeting the epidermal growth factor receptor whose clinical use is limited to patients with a non-mutated KRAS status. The aim of this in vitro study was to evaluate whether the KRAS status might influence the cytotoxic and radiosensitizing efficacy of Panitumumab. Exponentially growing cancer cells (HT-29: KRAS wild-type, A549: KRAS mutant) were either treated with the monoclonal antibody alone in growth and proliferation assays or in combination with radiation in metabolic and colony-forming assays. For the assessment of ionizing radiation-induced DNA damage and to evaluate Panitumumab's influence on DNA damage repair, the γH2AX foci assay was performed. Treatment with Panitumumab resulted in a concentration-independent growth inhibition as well as a cytotoxic effect only in the KRAS-mutated cell line A549. BrdU assay confirmed an antiproliferative influence of Panitumumab. When combined with irradiation, incubation with the antibody was found to result in an enhanced radiosensitivity. Contrary to expectations, Panitumumab had no influence on the cell growth, LDH release or clonogenic survival of KRAS wild-type cells HT-29. Our results suggest that response to Panitumumab treatment is not only controlled by the KRAS status but may also be essentially influenced by other regulating factors.

MEK/ERK inhibitor U0126 increases the radiosensitivity of rhabdomyosarcoma cells in vitro and in vivo by downregulating growth and DNA repair signals

Multimodal treatment has improved the outcome of many solid tumors, and in some cases the use of radiosensitizers has significantly contributed to this gain. Activation of the extracellular signaling kinase pathway (MEK/ERK) generally results in stimulation of cell growth and confers a survival advantage playing the major role in human cancer. The potential involvement of this pathway in cellular radiosensitivity remains unclear. We previously reported that the disruption of c-Myc through MEK/ERK inhibition blocks the expression of the transformed phenotype; affects in vitro and in vivo growth and angiogenic signaling; and induces myogenic differentiation in the embryonal rhabdomyosarcoma (ERMS) cell lines (RD). This study was designed to examine whether the ERK pathway affects intrinsic radiosensitivity of rhabdomyosarcoma cancer cells. Exponentially growing human ERMS, RD, xenograft-derived RD-M1, and TE671 cell lines were used. The specific MEK/ERK inhibitor, U0126, reduced the clonogenic potential of the three cell lines, and was affected by radiation. U0126 inhibited phospho-active ERK1/2 and reduced DNA protein kinase catalytic subunit (DNA-PKcs) suggesting that ERKs and DNA-PKcs cooperate in radioprotection of rhabdomyosarcoma cells. The TE671 cell line xenotransplanted in mice showed a reduction in tumor mass and increase in the time of tumor progression with U0126 treatment associated with reduced DNA-PKcs, an effect enhanced by radiotherapy. Thus, our results show that MEK/ERK inhibition enhances radiosensitivity of rhabdomyosarcoma cells suggesting a rational approach in combination with radiotherapy.

Function of erbB receptors and DNA-PKcs on phosphorylation of cytoplasmic and nuclear Akt at S473 induced by erbB1 ligand and ionizing radiation

BACKGROUND AND PURPOSE

In the present study effect of erbB2 as well as DNA-PKcs on ionizing radiation (IR)- and erbB1 ligand-induced phosphorylation of Akt at S473 in cytoplasmic and nuclear fractions was investigated.

MATERIALS AND METHODS

DNA-PKcs proficient and deficient syngeneic colon carcinoma sublines of HCT116 and the glioblastoma cell lines MO59K and MO59J as well as the lung carcinoma cell line A549 were used. Akt-S473 phosphorylation was investigated in cells pre-treated with pharmacological inhibitors or transfected with siRNA by immunoprecipitation, Western blotting and confocal microscopy after different stimuli, i.e., ligands and IR.

RESULTS

IR-induced phosphorylation of Akt in both MO59K and MO59J cell lines but not in HCT116 cells was DNA-PKcs dependent. In A549 cells, IR-induced phosphorylation of nuclear Akt-S473 was dependent on erbB1, erbB2, and DNA-PKcs. EGF induced phosphorylation of nuclear Akt-S473 in a DNA-PKcs and erbB2 independent manner.

CONCLUSION

Data indicate that the function of DNA-PKcs on IR-induced Akt-S473 phosphorylation is cell line specific. IR-induced, but not EGF-induced phosphorylation of cytoplasmic and/or nuclear Akt-S473 is erbB2 dependent.

Lovastatin sensitizes lung cancer cells to ionizing radiation: modulation of molecular pathways of radioresistance and tumor suppression

INTRODUCTION

In this study, we investigated the effect of the 3-hydroxy-3-methylgutaryl-CoA reductase inhibitor lovastatin, as a sensitizer of lung cancer cells to ionizing radiation (IR).

METHODS

A549 lung adenocarcinoma cells were treated with 0 to 50 μM lovastatin alone or in combination with 0 to 8 Gy IR and subjected to clonogenic survival and proliferation assays. To assess the mechanism of drug action, we examined the effects of lovastatin and IR on the epidermal growth factor (EGF) receptor and AMP-activated kinase (AMPK) pathways and on apoptotic markers and the cell cycle.

RESULTS

Lovastatin inhibited basal clonogenic survival and proliferation of A549 cells and sensitized them to IR. This was reversed by mevalonate, the product of 3-hydroxy-3-methylgutaryl-CoA reductase. Lovastatin attenuated selectively EGF-induced phosphorylation of EGF receptor and Akt, and IR-induced Akt phosphorylation, in a mevalonate-sensitive fashion, without inhibition on extracellular signal-regulated kinase 1/2 phosphorylation by either stimulus. IR phosphorylated and activated the metabolic sensor and tumor suppressor AMPK, but lovastatin enhanced basal and IR-induced AMPK phosphorylation. The drug inhibited IR-induced expression of p53 and the cyclin-dependent kinase inhibitors p21(cip1) and p27(kip1), but caused a redistribution of cells from G1-S phase (control and radiated cells) and G2-M phase (radiated cells) of cell cycle into apoptosis. The latter was also evident by induction of nuclear fragmentation and cleavage of caspase 3 by lovastatin in both control and radiated cells.

CONCLUSIONS

We suggest that lovastatin inhibits survival and induces radiosensitization of lung cancer cells through induction of apoptosis, which may be mediated by a simultaneous inhibition of the Akt and activation of the AMPK signaling pathways.

Diverse effects of combined radiotherapy and EGFR inhibition with antibodies or TK inhibitors on local tumour control and correlation with EGFR gene expression

PURPOSE

To compare functional effects of combined irradiation and EGFR inhibition in different HNSCC tumour models in vivo with the results of molecular evaluations, aiming to set a basis for the development of potential biomarkers for local tumour control.

MATERIAL AND METHODS

In five HNSCC tumour models, all wild-type for EGFR and KRAS, the effect of radiotherapy alone (30 fractions/6 weeks) and with simultaneous cetuximab or erlotinib treatment on local tumour control were evaluated and compared with molecular data on western blot, immunohistochemistry and fluorescence-in situ-hybridisation (FISH).

RESULTS

Erlotinib and cetuximab alone significantly prolonged tumour growth time in 4/5 tumour models. Combined irradiation and cetuximab treatment significantly improved local tumour control in 3/5 tumour models, whereas erlotinib did not alter local tumour control in any of the tumour models. The amount of the cetuximab-effect on local tumour control significantly correlated with the EGFR/CEP-7 ratios obtained by FISH.

CONCLUSION

Both drugs prolonged growth time in most tumour models, but only application of cetuximab during irradiation significantly improved local tumour control in 3/5 tumour models. The significant correlation of this curative effect with the genetic EGFR expression measured by FISH will be further validated in preclinical and clinical studies.

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.

Strategies to improve radiotherapy with targeted drugs

Radiotherapy is used to treat approximately 50% of all cancer patients, with varying success. The dose of ionizing radiation that can be given to the tumour is determined by the sensitivity of the surrounding normal tissues. Strategies to improve radiotherapy therefore aim to increase the effect on the tumour or to decrease the effects on normal tissues. These aims must be achieved without sensitizing the normal tissues in the first approach and without protecting the tumour in the second approach. Two factors have made such approaches feasible: namely, an improved understanding of the molecular response of cells and tissues to ionizing radiation and a new appreciation of the exploitable genetic alterations in tumours. These have led to the development of treatments combining pharmacological interventions with ionizing radiation that more specifically target either tumour or normal tissue, leading to improvements in efficacy.

Impact of oncogenic K-RAS on YB-1 phosphorylation induced by ionizing radiation

Introduction

Expression of Y-box binding protein-1 (YB-1) is associated with tumor progression and drug resistance. Phosphorylation of YB-1 at serine residue 102 (S102) in response to growth factors is required for its transcriptional activity and is thought to be regulated by cytoplasmic signaling phosphatidylinositol 3-kinase (PI3K)/Akt and mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathways. These pathways can be activated by growth factors and by exposure to ionizing radiation (IR). So far, however, no studies have been conducted on IR-induced YB-1 phosphorylation.

Methods

IR-induced YB-1 phosphorylation in K-RAS wild-type (K-RAS_wt) and K-RAS-mutated (K-RAS_mt) breast cancer cell lines was investigated. Using pharmacological inhibitors, small interfering RNA (siRNA) and plasmid-based overexpression approaches, we analyzed pathways involved in YB-1 phosphorylation by IR. Using γ-H2AX foci and standard colony formation assays, we investigated the function of YB-1 in repair of IR-induced DNA double-stranded breaks (DNA-DSB) and postirradiation survival was investigated.

Results

The average level of phosphorylation of YB-1 in the breast cancer cell lines SKBr3, MCF-7, HBL100 and MDA-MB-231 was significantly higher than that in normal cells. Exposure to IR and stimulation with erbB1 ligands resulted in phosphorylation of YB-1 in K-RAS_wt SKBr3, MCF-7 and HBL100 cells, which was shown to be K-Ras-independent. In contrast, lack of YB-1 phosphorylation after stimulation with either IR or erbB1 ligands was observed in K-RAS_mt MDA-MB-231 cells. Similarly to MDA-MB-231 cells, YB-1 became constitutively phosphorylated in K-RAS_wt cells following the overexpression of mutated K-RAS, and its phosphorylation was not further enhanced by IR. Phosphorylation of YB-1 as a result of irradiation or K-RAS mutation was dependent on erbB1 and its downstream pathways, PI3K and MAPK/ERK. In K-RAS_mt cells K-RAS siRNA as well as YB-1 siRNA blocked repair of DNA-DSB. Likewise, YB-1 siRNA increased radiation sensitivity.

Conclusions

IR induces YB-1 phosphorylation. YB-1 phosphorylation induced by oncogenic K-Ras or IR enhances repair of DNA-DSB and postirradiation survival via erbB1 downstream PI3K/Akt and MAPK/ERK signaling pathways.

Effect of sunitinib combined with ionizing radiation on endothelial cells

The aims of present study were to evaluate the efficacy of combining sunitinib with ionizing radiation (IR) on endothelial cells in vitro and in vivo. Human umbilical vein endothelial cells (HUVECs) were exposed to IR with or without sunitinib pretreatment. Apoptosis assay and cell cycle distribution were analyzed by flow cytometry. Clonogenic survival assay at 3 Gy dose with or without sunitinib was performed. The activity of phosphatidylinositol 3-kinase (PI3K)/Akt signal pathway was detected by Western immunoblot. Lewis lung carcinoma mouse model was built to examine the effect of combination therapy on endothelial cells in vivo. Microvasculature changes were detected by immunohistochemistry using anti-CD31 antibody. Our results showed combination therapy of sunitinib and IR significantly increased apoptosis of endothelial cells and inhibited colony formation compared to sunitinib or radiotherapy alone. It also resulted in cell cycle redistribution (decreasing cells in S phase and increasing cells in G2/M phase). The activity of PI3K/Akt signal pathway was inhibited, which could be the potential mechanisms that account for the enhanced radiation response induced by sunitinib. In vivo analysis showed that combination therapy significantly decreased microvasculature formation. The results demonstrated that combination therapy of sunitinib and IR has the potential to increase the cytotoxic effects on endothelial cells.

新型分子靶向药物联合放疗在肺癌中的应用

非小细胞肺癌（non-small cell lung cancer, NSCLC）约占肺癌总病例数的80%-85%，对于Ⅲ期患者来说，NSCLC约占肺癌总病例数的40%。不可切除Ⅲ期NSCLC的治疗为以铂类为基础的化疗联合胸部放疗。本文将综述正在研发中且有可能用于联合治疗的新型靶向制剂。其中最具前景的策略之一为表皮生长因子受体（epidermal growth factor receptor, EGFR）通路的抑制。放疗可激活EGFR信号，通过诱导细胞增殖并增强DNA修复而导致放疗抵抗。几项临床前模型研究表明西妥昔单抗与放疗联合具有协同效应。几项Ⅱ期试验评估了西妥昔单抗与放疗同步使用的安全性与疗效，结果喜人。吉非替尼对多种细胞系具有放疗增敏作用，其与放疗的联合已被试验用于不可切除Ⅲ期NSCLC的治疗。然而，放化疗后使用吉非替尼作为维持治疗的结果不容乐观。一项Ⅰ期试验评估了厄洛替尼与放化疗联合的疗效。放疗可通过损伤细胞膜、DNA以及微血管内皮细胞而诱导肿瘤死亡，而这反过来可增加促血管生成生长因子的产生。抗血管生长制剂可降低血管密度，但可改善肿瘤的含氧量。应用血管内皮生长因子受体（vascular endothelial growth factor receptor, VEGFR）抑制剂可通过阻断亚致死量辐射损伤的修复而增强放疗对人NSCLC的疗效。厄洛替尼、贝伐珠单抗与胸部放疗联合试验正在进行中。该三种药物联合治疗的新策略尚需制订。由于放疗可增强HSP90分子伴侣的功能从而引起肺癌细胞的放疗抵抗，此通路的阻断剂可通过抑制HIF-1α和VEGF的表达进而抑制肺癌细胞的生存和血管生成，因而可能用于减少放疗抵抗。在NSCLC和间皮瘤的临床前模型中，Aurora激酶抑制剂似乎对放疗具有增效作用。

Phase I clinical trial of the anti-EGFR monoclonal antibody nimotuzumab with concurrent external thoracic radiotherapy in Canadian patients diagnosed with stage IIb, III or IV non-small cell lung cancer unsuitable for radical therapy

PURPOSE

Many patients with non-small cell lung cancer (NSCLC) are eligible only for palliative radiation (RT) at presentation. This study was designed to assess the feasibility of adding the anti-EGFR monoclonal antibody nimotuzumab to palliative thoracic RT.

METHODS

Patients with stage IIB, III or IV NSCLC considered unsuitable for radical radiation or chemo-radiation received nimotuzumab weekly 8× (100, 200 or 400 mg) with radiation (30 or 36 Gy in 3 Gy fractions). If response or disease stability was observed, nimotuzumab was continued every other week starting from week 10 until progression or toxicity.

RESULTS

Eighteen patients were enrolled: 6 at 100 mg, 7 at 200 mg, 5 at 400 mg nimotuzumab. Patient characteristics included median age 69 years, 11 males, 17 smokers, 17 Caucasians, stage IIIA/IIIB/IV 2/7/9, 5 Eastern Cooperative Oncology Group performance status (PS) 2; 9 adenocarcinoma. The most commonly reported adverse events were fatigue, anorexia, chills, pain and hypophosphatemia (grades 1 to 2 in most patients). No severe skin or allergic toxicity was noted. No dose-limiting toxicity was encountered. Objective response rate and disease control rate inside the radiation field were 66 and 94.0%, respectively.

CONCLUSION

Nimotuzumab administered concurrently with palliative thoracic radiation is well tolerated at each of the three doses investigated in NSCLC patients unsuitable for radical treatment. The low toxicity and absence of rash make this combination therapeutically attractive for frail patients with other co-morbidities and poor performance status. These results support further testing of this regimen in the phase II setting.

New molecular targeted therapies integrated with radiation therapy in lung cancer

Non-small-cell lung cancer (NSCLC) accounts for approximately 80%-85% of all cases of lung cancer; for patients with stage III disease, it accounts for approximately 40% of all cases. The treatment for unresectable stage III NSCLC is the combination of platinum-based chemotherapy and thoracic radiation. In this article, new targeted agents under investigation for possible integration into the combined therapy are reviewed. One of the most promising strategies is the inhibition of the epidermal growth factor receptor (EGFR) pathway. Radiation activates EGFR signaling, leading to radio-resistance by inducing cell proliferation and enhanced DNA repair. Several preclinical models have shown synergistic activity when cetuximab was combined with radiation therapy. Some phase II trials have evaluated the safety and efficacy of synchronous cetuximab and radiation therapy with promising results. Gefitinib has a radiosensitizing effect on cell lines and has been investigated in combination with radiation therapy for unresectable stage III NSCLC. However, disappointing results were observed in the maintenance treatment with gefitinib after chemoradiation therapy. Erlotinib has been tested in a phase I trial with chemoradiation therapy. Radiation induces tumor death by damaging cell membranes, DNA, and microvascular endothelial cells, which in response increase proangiogenic growth factors. Antiangiogenic agents reduce vascular density but improve tumor oxygenation. Use of vascular endothelial growth factor receptor (VEGFR) inhibitors enhances the therapeutic efficacy of irradiation in human NSCLC by hindering the repair of sublethal radiation damage. Trials combining erlotinib and bevacizumab with thoracic radiation are ongoing. New strategies must be developed for the integration of this triple-combination treatment. As radiation therapy enhances HSP90 chaperone function, causing radio-resistant lung cancer cells, therapeutic agents that block this path are likely candidates for decreasing radio-resistance by suppressing HIF-1alpha and VEGF expression and thus inhibiting the survival and angiogenic potential of lung cancer cells. Aurora kinase inhibitors with radiation therapy seem to have an additive effect in preclinical models in NSCLC and mesothelioma.

Effects of irradiation on tumor cell survival, invasion and angiogenesis

Ionizing irradiation is a widely applied therapeutic method for the majority of solid malignant neoplasms, including brain tumors where, depending on localization, this might often be the only feasible primary intervention.Without doubt, it has been proved to be a fundamental tool available in the battlefield against cancer, offering a clear survival benefit in most cases. However, numerous studies have associated tumor irradiation with enhanced aggressive phenotype of the remaining cancer cells. A cell population manages to survive after the exposure, either because it receives sublethal doses and/or because it successfully utilizes the repair mechanisms. The biology of irradiated cells is altered leading to up-regulation of genes that favor cell survival, invasion and angiogenesis. In addition, hypoxia within the tumor mass limits the cytotoxicity of irradiation, whereas irradiation itself may worsen hypoxic conditions, which also contribute to the generation of resistant cells. Activation of cell surface receptors, such as the epidermal growth factor receptor, utilization of signaling pathways, and over-expression of cytokines, proteases and growth factors, for example the matrix metalloproteinases and vascular endothelial growth factor, protect tumor and non-tumor cells from apoptosis, increase their ability to invade to adjacent or distant areas, and trigger angiogenesis. This review will try to unfold the various molecular events and interactions that control tumor cell survival, invasion and angiogenesis and which are elicited or influenced by irradiation of the tumor mass, and to emphasize the importance of combining irradiation therapy with molecular targeting.

ErbB2 expression through heterodimerization with erbB1 is necessary for ionizing radiation- but not EGF-induced activation of Akt survival pathway

PURPOSE

ErbB1-dependent Akt phosphorylation improves post-irradiation cellular survival. In the present study, we investigated the contribution of erbB2 as a heterodimerization partner of erbB1 in activation of Akt survival signaling after irradiation or EGF treatment.

MATERIALS AND METHODS

Pattern of receptor dimerization and protein phosphorylation were investigated by Western and immunoblotting as well as immunoprecipitation techniques. Residual DNA double-strand breaks (DNA-DSB) and clonogenic activity were analyzed by γH2AX and standard clonogenic assay. To knocked erbB2 expression siRNA was used.

RESULTS

In lung carcinoma cell lines A549 and H661, the erbB1-tyrosine kinase (TK) inhibitor erlotinib blocked EGF as well as ionizing radiation (IR)-induced Akt and DNA-PKcs phosphorylation. Targeting Akt and erbB1 induced cellular radiation sensitivity while, the erbB2-TK inhibitor AG825 neither affected phosphorylation of Akt and DNA-PKcs nor induced radiosensitization. ErbB2-siRNA and the anti-erbB2 antibody trastuzumab blocked IR-induced, but not EGF-stimulated Akt phosphorylation and impaired the repair of DNA-DSB. Likewise, IR but not EGF enhanced erbB1/erbB2 heterodimerization and resulted in the release of phosphorylated erbB2 cleavage products p135 and p95. Trastuzumab prevented radiation-induced formation of an active erbB1/erbB2 heterodimer and increased cellular radiation sensitivity. ErbB1- but not erbB2-TK inhibition stabilized erbB2 (p185) through preventing its cleavage.

CONCLUSIONS

The data indicates that ErbB2 through heterodimerization with erbB1 is necessary for the activation of Akt signaling following irradiation but not following EGF treatment.

Caffeine confers radiosensitization of PTEN-deficient malignant glioma cells by enhancing ionizing radiation-induced G1 arrest and negatively regulating Akt phosphorylation

PTEN mutations are frequently found in malignant glioma and can result in activated phosphatidylinositol-3-kinase/Akt survival signaling associated with resistance to radiotherapy. Strategies to interfere with aberrant PI3K/Akt activity are therefore being developed to improve the therapeutic efficacy of radiotherapy in patients with malignant glioma. The methylxanthine caffeine has been described as a PI3K inhibitor and is also known to sensitize cells to ionizing radiation. However, a direct association between these two caffeine-mediated effects has not been reported yet. Therefore, we asked whether caffeine or its derivative pentoxifylline differentially affect the radiosensitivity of malignant gliomas with different PTEN status. As models, we used the radiosensitive EA14 malignant glioma cell line containing wild-type PTEN and the radioresistant U87MG malignant glioma cell line harboring mutant PTEN. Our study revealed that caffeine and pentoxifylline radiosensitized PTEN-deficient but not PTEN-proficient glioma cells. Radiosensitization of PTEN-deficient U87MG cells by caffeine was significantly correlated with the activation of the G(1) DNA damage checkpoint that occurred independently of de novo synthesis of p53 and p21. The p53 independency was also confirmed by a significant caffeine-mediated radiosensitization of the glioma cell lines T98G and U373MG that are deficient for both PTEN and p53. Furthermore, caffeine-mediated radiosensitization was associated with the inhibition of Akt hyperphosphorylation in PTEN-deficient cells to a level comparable with PTEN-proficient cells. Our data suggest that the methylxanthine caffeine or its derivative pentoxifylline are promising candidate drugs for the radiosensitization of glioma cells particularly with PTEN mutations.

Nuclear EGFR as novel therapeutic target: insights into nuclear translocation and function

Emerging evidence suggests the existence of a new mode of epidermal growth factor receptor (EGFR) signaling in which activated EGFR undergoes nuclear translocation following treatment with ionizing radiation. The authors provide evidence that the nuclear EGFR transport is a stress-specific cellular reaction, which is linked to src-dependent EGFR internalization into caveolae. These flask-shaped pits can fuse with endoplasmic reticulum and the EGFR is sorted into a perinuclear localization. This compartment may serve as a reservoir for nuclear EGFR transport which is regulated by PKCepsilon (protein kinase Cepsilon). Nuclear EGFR is able to induce transcription of genes essential for cell proliferation and cell-cycle regulation. Moreover, nuclear EGFR has physical contact with compounds of the DNA repair machinery and is involved in removal of DNA damage. Anti-EGFR strategies target radiation-associated EGFR nuclear translocation in different manners. EGFR-inhibitory antibodies, i.e., cetuximab (Erbitux((R))), can block nuclear translocation by EGFR immobilization within the cytosol in responder cell lines, whereas tyrosine kinase inhibitors rather target nuclear kinase activity of EGFR linked with cytosolic or nuclear functions. However, both strategies can inhibit DNA repair following irradiation.

Radiocontrast media affect radiation-induced DNA damage repair in vitro and in vivo by affecting Akt signalling

PURPOSE

The study was performed to investigate cytogenetic effects of ionic and non-ionic radiocontrast media (RCM) meglumine, iohexol alone and in combination with irradiation in mouse bone marrow cells in vivo and in vitro.

MATERIALS AND METHODS

Micronuclei assay was performed in bone marrow cells (BMC) of Balb/C mice intraperitoneally injected with RCM in the presence or absence of whole-body irradiation of 50 mGy. DNA repair (NHEJ) signalling and efficiency were analyzed by Western blot and gammaH2AX-foci assay in normal fibroblast HSF-7 and HUVEC cells.

RESULTS

Both compounds reduced proliferation of BMC significantly. Concentrations of 0.5, 1 and 2 ml/kg meglumine or iohexol significantly enhanced the frequency of micronucleated polychromatic erythrocytes (MnPCEs) at all doses of meglumine (p<0.01) and 2 ml/kg of iohexol (p<0.05). Combined with irradiation meglumine at 0.5 and 1 ml/kg led to a higher frequency of MnPCEs than iohexol/IR (p<0.05). Meglumine induced DNA-double strand breaks (DNA-DSB) in non-irradiated HSF and strongly increased residual DNA-DSB within 10 min to 24h after irradiation with 200 or 400 mGy (p<0.001). Iohexol did not induce DNA-DSB but blocked repair of radiation-induced DNA-DSB significantly (p<0.05). Meglumine blocked IR-induced Akt phosphorylation, phosphorylation of DNA-PKcs (S2056, T2609) and ATM (S1981). Iohexol only blocked phosphorylation of Akt and DNA-PKcs at S2056.

CONCLUSION

RCM result in clastogenic effects through interference intracellular signalling cascades involved in the regulation of non-homologous end-joining repair of DNA-DSB.

Dose-dependent effect of radiation on angiogenic and angiostatic CXC chemokine expression in human endothelial cells

Blood vessel growth is regulated by angiogenic and angiostatic CXC chemokines, and radiation is a vasculogenic stimulus. We investigated the effect of radiation on endothelial cell chemokine signaling, receptor expression, and migration and apoptosis. Human umbilical vein endothelial cells were exposed to a single fraction of 0, 5, or 20 Gy of ionizing radiation (IR). All vasculogenic chemokines (CXCL1-3/5-8) increased 3-13-fold after 5 or 20 Gy IR. 20 Gy induced a marked increase (1.6-4-fold) in angiostatic CXC chemokines. CXCR4 expression increased 3.5 and 7-fold at 48 h after 5 and 20 Gy, respectively. Bone marrow progenitor cell chemotaxis was augmented by conditioned media from cells treated with 5 Gy IR. Whereas 5 Gy markedly decreased intrinsic cell apoptosis (0 Gy=16%+/-3.6 vs. 5 Gy=4.5%+/-0.3), 20 Gy increased it (21.4%+/-1.2); a reflection of pro-survival angiogenic chemokine expression. Radiation induces a dose-dependent increase in pro-angiogenic CXC chemokines and CXCR4. In contrast, angiostatic chemokines and apoptosis were induced at higher (20 Gy) radiation doses. Cell migration improved significantly following 5 Gy, but not 20 Gy IR. Collectively, these data suggest that lower doses of IR induce an angiogenic cascade while higher doses produce an angiostatic profile.

The pyridinylfuranopyrimidine inhibitor, PI-103, chemosensitizes glioblastoma cells for apoptosis by inhibiting DNA repair

The failure of conventional therapies in glioblastoma (GBM) is largely due to an aberrant activity of survival cascades, such as PI3 kinase (PI3K)/Akt-mediated signaling. This study is the first to show that the class I PI3K inhibitor, PI-103, enhances chemotherapy-induced cell death of GBM cells. Concurrent treatment with PI-103 and DNA-damaging drugs, in particular doxorubicin, significantly increases apoptosis and reduces colony formation compared with chemotherapy treatment alone. The underlying molecular mechanism for this chemosensitization was shown by two independent approaches, that is, pharmacological and genetic inhibition of PI3K, DNA-PK and mTOR, to involve inhibition of DNA-PK-mediated DNA repair. Accordingly, blockage of PI3K or DNA-PK, but not of mTOR, significantly delays the resolution of doxorubicin-induced DNA damage and concomitantly increases apoptosis. Importantly, not only are several GBM cell lines chemosensitized by PI-103 but also GBM stem cells. Clinical relevance was further confirmed by the use of primary cultured GBM cells, which also exhibit increased cell death and reduced colony formation on combined treatment with PI-103 and doxorubicin. By identifying class I PI3K inhibitors as powerful agents in enhancing the lethality of DNA-damaging drugs, to which GBMs are usually considered unresponsive, our findings have important implications for the design of rational combination regimens in overcoming the frequent chemoresistance of GBM.

Receptor signaling as a regulatory mechanism of DNA repair

Radiotherapy plays a crucial role in the treatment of many malignancies; however, locoregional disease progression remains a critical problem. This has stimulated laboratory research into understanding the basis for tumor cell resistance to radiation and the development of strategies for overcoming such resistance. We know that some cell signaling pathways that respond to normal growth factors are abnormally activated in human cancer and that these pathways also invoke cell survival mechanisms that lead to resistance to radiation. For example, abnormal activation of the epidermal growth factor receptor (EGFR) promotes unregulated growth and is believed to contribute to clinical radiation resistance. Molecular blockade of EGFR signaling is an attractive strategy for enhancing the cytotoxic effects of radiotherapy and, as shown in numerous reports, the radiosensitizing effects of EGFR antagonists correlate with a suppression of the ability of the cells to repair radiation-induced DNA double strand breaks (DSBs). The molecular connection between the EGFR and its governance of DNA repair capacity appears to be mediated by one or more signaling pathways downstream of this receptor. The purpose of this review is to highlight what is currently known regarding EGFR signaling and the processes responsible for repairing radiation-induced DNA lesions that would explain the radiosensitizing effects of EGFR antagonists.

2-Methoxyestradiol-induced radiosensitization is independent of SOD but depends on inhibition of Akt and DNA-PKcs activities

BACKGROUND AND PURPOSE

2-Methoxyestradiol (2-ME) is described as an inhibitor of the superoxide dismutase (SOD) enzyme activity. However, it attenuates PI3K/Akt pathway and induces radiosensitization in human tumor cells as well. Since the activation of catalytic subunit of DNA-protein kinase (DNA-PKcs) is partially regulated by Akt activity, in the present study we investigated whether 2-ME-induced radiosensitization is dependent on inhibition of Akt and DNA-PKcs activities or on SOD targeting.

MATERIALS AND METHODS

This study was performed using the lung carcinoma cell line A549. Ionizing radiation-induced SOD activity was analyzed by superoxide dismutase activity assay. Applying Western blotting, the pattern of radiation-induced SOD expression and activation of Akt as well as DNA-PKcs was analyzed. Colony formation assay and gammaH2AX foci assay were performed to measure radiosensitization and DNA-double strand break (DNA-DSB) repair. To downregulate SOD expression small interfering RNA (siRNA) was used.

RESULTS

Irradiation with 4Gy stimulated SOD enzyme activity as early as 1min after radiation exposure. Expression of Cu/Zn-SOD (SOD1) as well as Mn-SOD (SOD2) was increased by single doses of 1-4Gy within 24-36h. 2-ME blocked radiation-induced SOD enzyme activity but not protein expression and enhanced radiation sensitivity. Pretreatment with 2-ME blocked IR-induced Akt as well as DNA-PKcs phosphorylation and impaired the repair of DNA-DSB. SiRNA targeting of SOD1 and SOD2 affected neither DNA-PKcs phosphorylation nor post-irradiation survival while inhibition of Akt by specific inhibitor abrogated 2-ME-induced radiosensitization.

CONCLUSION

These results may indicate that 2-ME-induced radiosensitization is independent of SOD inhibition but mainly depends on inhibition of Akt and DNA-PKcs activities.

EGFRvIII and DNA double-strand break repair: a molecular mechanism for radioresistance in glioblastoma

Glioblastoma multiforme (GBM) is the most lethal of brain tumors and is highly resistant to ionizing radiation (IR) and chemotherapy. Here, we report on a molecular mechanism by which a key glioma-specific mutation, epidermal growth factor receptor variant III (EGFRvIII), confers radiation resistance. Using Ink4a/Arf-deficient primary mouse astrocytes, primary astrocytes immortalized by p53/Rb suppression, as well as human U87 glioma cells, we show that EGFRvIII expression enhances clonogenic survival following IR. This enhanced radioresistance is due to accelerated repair of DNA double-strand breaks (DSB), the most lethal lesion inflicted by IR. The EGFR inhibitor gefitinib (Iressa) and the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 attenuate the rate of DSB repair. Importantly, expression of constitutively active, myristylated Akt-1 accelerates repair, implicating the PI3K/Akt-1 pathway in radioresistance. Most notably, EGFRvIII-expressing U87 glioma cells show elevated activation of a key DSB repair enzyme, DNA-dependent protein kinase catalytic subunit (DNA-PKcs). Enhanced radioresistance is abrogated by the DNA-PKcs-specific inhibitor NU7026, and EGFRvIII fails to confer radioresistance in DNA-PKcs-deficient cells. In vivo, orthotopic U87-EGFRvIII-derived tumors display faster rates of DSB repair following whole-brain radiotherapy compared with U87-derived tumors. Consequently, EGFRvIII-expressing tumors are radioresistant and continue to grow following whole-brain radiotherapy with little effect on overall survival. These in vitro and in vivo data support our hypothesis that EGFRvIII expression promotes DNA-PKcs activation and DSB repair, perhaps as a consequence of hyperactivated PI3K/Akt-1 signaling. Taken together, our results raise the possibility that EGFR and/or DNA-PKcs inhibition concurrent with radiation may be an effective therapeutic strategy for radiosensitizing high-grade gliomas.

Radioactive EGFR antibody cetuximab in multimodal cancer treatment: stability and synergistic effects with radiotherapy

PURPOSE

Systemic therapies when added to whole brain radiotherapy have failed to improve the survival of patients with multiple brain metastases. The epidermal growth factor receptor antibody cetuximab is an attractive option, if it is able to cross the blood-brain barrier. This might be proven with molecular imaging if the radiolabeled antibody is stable long enough to be effective. This study investigated the stability of radiolabeled cetuximab (Erbitux) ((131)I-Erbi) and potential synergistic effects with radiotherapy in vitro.

METHODS AND MATERIALS

Two cell lines were investigated, A431 with numerous epidermal growth factor receptors, and JIMT without epidermal growth factor receptors. We labeled 0.4 mg cetuximab with 50 MBq of [(131)I] iodide. Stability was determined for 72 h. The cell cultures were incubated with (131)I-Erbi or cold cetuximab for 72 h. Uptake and cell proliferation were measured every 24 h after no radiotherapy or irradiation with 2, 4, or 10 Gy.

RESULTS

The radiolabeling yield of (131)I-Erbi was always >80%. The radiochemical purity was still 93.6% after 72 h. A431 cells showed a (131)I-Erbi uptake about 100-fold greater than the JIMT controls. After 48 h, the A431 cultures showed significantly decreased proliferation. At 72 h after irradiation, (131)I-Erbi resulted in more pronounced inhibition of cell proliferation than the cold antibody in all radiation dose groups.

CONCLUSION

(131)I-Erbi was stable for <or=72 h. Radiotherapy led to increased tumor cell uptake of (131)I-Erbi. Radiotherapy and (131)I-Erbi synergistically inhibited tumor cell proliferation. These results provide the prerequisite data for a planned in vivo study of whole brain radiotherapy plus cetuximab for brain metastases.

Absence of GAPDH regulation in tumor-cells of different origin under hypoxic conditions in - vitro

Background

Gene expression studies related to cancer diagnosis and treatment are important. In order to conduct such experiment accurately, absolutely reliable housekeeping genes are essential to normalize cancer related gene expression. The most important characteristics of such genes are their presence in all cells and their expression levels remain relatively constant under different experimental conditions. However, no single gene of this group of genes manifests always stable expression levels under all experimental conditions. Incorrect choice of housekeeping genes leads to interpretation errors of experimental results including evaluation and quantification of pathological gene expression. Here, we examined (a) the degree of GAPDH expression regulation in Hep-1-6 mouse hepatoma and Hep-3-B and HepG2 human hepatocellular carcinoma cell lines as well as in human lung adenocarcinoma epithelial cell line (A-549) in addition to both HT-29, and HCT-116 colon cancer cell lines, under hypoxic conditions in vitro in comparison to other housekeeping genes like β-actin, serving as experimental loading controls, (b) the potential use of GAPDH as a target for tumor therapeutic approaches was comparatively examined in vitro on both protein and mRNA level, by western blot and semi quantitative RT-PCR, respectively.

Findings

No hypoxia-induced regulatory effect on GAPDH expression was observed in the cell lines studied in vitro that were; Hep-1-6 mouse hepatoma and Hep-3-B and HepG2 human hepatocellular carcinoma cell lines, Human lung adenocarcinoma epithelial cell line (A-549), both colon cancer cell lines HT-29, and HCT-116.

Conclusion

As it is the case for human hepatocellular carcinoma, mouse hepatoma, human colon cancer, and human lung adenocarcinoma, GAPDH represents an optimal choice of a housekeeping gene and/(or) loading control to determine the expression of hypoxia induced genes in tumors of different origin. The results confirm our previous findings in human glioblastoma that this gene is not an attractive target for tumor therapeutic approaches because of the lack of GAPDH regulation under hypoxia.