Radioresistant Patients Research Articles

Fast and Binary Assay for Predicting Radiosensitivity Based on the Theory of ATM Nucleo-Shuttling: Development, Validation, and Performance

To examine the possibility of predicting clinical radiosensitivity by quantifying the nuclear forms of autophosphorylated ATM protein (pATM) via a specific enzyme-linked immunosorbent assay (ELISA). This study was performed on 30 skin fibroblasts from 9 radioresistant patients and 21 patients with adverse tissue reaction events. Patients were divided into 2 groups: radioresistant (toxicity grade <2) and radiosensitive (toxicity grade ≥2). The quantity of nuclear pATM molecules was assessed by the ELISA method at 10minutes and 1hour after 2Gy and compared with pATM immunofluorescence data. The pATM ELISA data were in quantitative agreement with the immunofluorescence data. A receiver operating characteristic analysis was applied first to 2 data sets (a training set [n=14] and a validating [n=16] set) and thereafter to all the data with a 2-fold cross-validation method. The assay showed an area under the curve value higher than 0.8, a sensitivity of 0.8, and a specificity ranging from 0.75 to 1, which strongly documents the predictive power of the pATM ELISA. This study showed that the assessment of nuclear pATM quantity after 2Gy via an ELISA technique can be the basis of a predictive assay with the highest statistical performance among the available predictive approaches.

Cofilin-1 and phosphoglycerate kinase 1 as promising indicators for glioma radiosensibility and prognosis.

Glioma is a primary malignancy in central nervous system. Radiotherapy has been used as one of the standard treatments for glioma for decades. Since radioresistance can reduce the curative efficacy of radiotherapy in glioma, investigating the cause of radioresistance and predicting the tumour radiosensibility appeared particularly important. We previously reported that CFL1 and PGK1 are over-expressed in radioresistant U251 glioma cells. In this study, the level of CFL1 and PGK1 of 113 glioma tissues were measured by ELISA method. The relevance of the expression of these two proteins to radiosensibility was analyzed by mean test and multivariate logistic regression. The survival analysis was carried out in 85 irradiated patients and 105 followed-up patients respectively. The relationship between protein expression and clinical parameters was explored in overall 113 patients, and the correlation between CFL1 and PGK1 were determined as well. Our results showed that the expression of CFL1 and PGK1 were significantly higher (P < 0.001) in radioresistant patients than others. The multivariate Logistic regression demonstrated that the expression of CFL1 (p < 0.001) and PGK1 (p < 0.001) were associated with radioresistance in glioma. The multivariate Cox regression in overall survival suggested that CFL1 level or PGK1 level could be the independent prognosis factor for poor prognosis in 113 glioma patients. In addition, CFL1 expression was positively correlated with PGK1 expression in glioma. The results suggested that as promising indicators, CFL1 and PGK1 could be used to evaluate glioma radiosensibility and prognosis. These two proteins could also be the potential therapeutic targets of glioma.

Prognostic value of phosphorylated Raf kinase inhibitory protein at serine 153 and its predictive effect on the clinical response to radiotherapy in nasopharyngeal carcinoma.

BackgroundRadiation is an effective treatment against nasopharyngeal carcinoma (NPC). However, radioresistance-induced locoregional recurrence remains as a major cause of treatment failure. Therefore, radiosensitivity indicators prior to treatment should be developed to screen radioresistant patients. Previous studies revealed that RKIP (Raf kinase inhibitor protein) is associated with NPC prognosis and radiosensitivity. However, the relationship of p-Ser153 RKIP (RKIP in a phosphorylated form at residue serine153) expression with the effect of radiation and prognosis of NPC patients is not elucidated. Thus, these clinical implication of the phosphorylated RKIP in NPC has yet to be described.MethodsThe effect of p-Ser153 RKIP on locoregional relapse-free survival (LRRFS) was first analyzed in a retrospective cohort of NPC patients without distant metastasis at initial diagnosis. They received radical intensity-modulated radiotherapy alone. Of 180 patients were enrolled in the ongoing matched pair study. The patients were re-classified into radioresistant group or radiosensitive group on the basis of the specified criteria. Patients in the two groups were matched in terms of radiosensitivity-related factors. p-Ser153 RKIP was examined by immunohistochemical staining on a NPC tissue microarray before radiotherapy. The relationship between the expression of p-Ser153 RKIP and the effect of radiotherapy was also analyzed.ResultsIn this study, a retrospective cohort with 733 cases who received radical radiotherapy alone was established. Using the cohort, we validated that the p-Ser153 RKIP expression observed through immunohistochemical staining in a pretreatment NPC tissue microarray was an independent prognostic factor of LRRFS and OS; we also confirmed that endemic patients with a positive p-Ser153 RKIP expression benefited from irradiation alone in terms of locoregional relapse-free survival. A total of 180 patients were enrolled in a matched pair study. Both groups were well matched in terms of radiosensitivity-related factors. On the basis of the p-Ser153 RKIP expression, we predicted the following data: 80.0 % sensitivity, 73.3 % specificity, 76.7 % accuracy, 75.0 % positive predictive value, and 78.6 % negative predictive value.ConclusionsOur results revealed for the first time that positive p-Ser153 RKIP expression was a favorable prognostic factor. It was also positively correlated with the radiosensitivity of NPC. p-Ser153 RKIP could also be used as a biomolecular marker with good availability and authenticity to preliminarily screen NPC-related clinical radiosensitivity.Electronic supplementary materialThe online version of this article (doi:10.1186/s13014-016-0696-5) contains supplementary material, which is available to authorized users.

Re-sensitization of radiation resistant colorectal cancer cells to radiation through inhibition of AMPK pathway.

Radiotherapy (RT) is commonly used to treat multi-tumors to attenuate the risk of recurrence. Despite impressive initial clinical responses, a large proportion of patients experience resistance to RT. Therefore, identification of functionally relevant biomarkers would be beneficial for radioresistant patients. Adenosine monophosphate-activated kinase (AMPK) is recognized as a mediator of tumor suppressor gene function. In the present study, radio-sensitive and -resistant colon cancer patient samples were compared and the AMPK pathway was observed to be highly activated in radioresistant patients. In addition, the protein and mRNA levels of AMPK were upregulated in radioresistant colon cancer cells in comparison to radiosensitive colon cancer cells. The present study provides evidence that activation of AMPK by metformin contributes to radioresistance. Inhibition of AMPK by either small interfering RNA or Compound C, which is a specific inhibitor of AMPK, re-sensitized radiation resistant cells. The data presented indicates a synergistic effect on radiation resistant cancer cells by the combination of Compound C and radiation. In summary, the present study proposes that inhibition of the AMPK pathway is a potential strategy for reversing radiation resistance and may contribute to the development of therapeutic anticancer drugs.

Development of triple-negative breast cancer radiosensitive gene signature and validation based on transcriptome analysis.

Triple-negative breast cancer (TNBC) is a heterogeneous disease with highest loco-regional recurrence among breast cancer subtypes. Radiotherapy is indispensable for TNBC loco-regional control. However, intrinsic radiosensitivity differences exist in TNBC patients and RT is still prescribed mainly based on conventional clinicopathologic features of patients without considering the differences. The purpose of the present study is to develop and validate a TNBC radiosensitive gene signature (RSGS) and to guide therapeutic decisions. In this study, we compared transcriptome profiles of 12 locally recurrent TNBCs to 20 non-locally recurrent TNBCs treated with surgery radio-chemotherapy and developed a seven-gene RSGS and a simplified three-gene RSGS by using pathway analysis, univariate Cox proportional hazards regression model and rank-based linear algorithm. They were validated by using transcriptome profiles of 166 TNBC patients. Two gene signatures specifically identified a radiosensitive population that had an improved recurrence-free survival in patients treated with surgery radio-chemotherapy (Radiosensitive patients vs radioresistant patients, for seven-gene RSGS: P = 0.024, HR = 0.35, 95 %CI 0.14–0.87 and for three-gene RSGS: P = 0.035, HR = 0.38, 95 %CI 0.15–0.94). In contrast, there was no significant difference in outcome between predicted radiosensitive and radioresistant patients that treated with other treatment modality. RSGSs provide a useful tool for identification of radiosensitive/radioresistant TNBC patients and they could lead to a better selection of patients for RT protocols.

A five-variable signature predicts radioresistance and prognosis in nasopharyngeal carcinoma patients receiving radical radiotherapy.

Radioresistance poses a major challenge in nasopharyngeal carcinoma (NPC) treatment. Clinical tumor-node-metastasis (TNM) staging has limited accuracy in predicting NPC radioresponse and determining its therapeutic regimens. To construct a risk score model for predicting NPC radioresistance, immunohistochemistry was used to assess the expression of four proteins (14-3-3σ, Maspin, RKIP, and GRP78) in 149 NPC samples with different radiosensitivity. Sequentially, a logistic regression analysis was performed to identify independent predictors of NPC radioresistance and establish a risk score model. As a result, a risk score model, Z = -3.189 - 1.478 (14-3-3σ) - 1.082 (Maspin) - 1.666 (RKIP) + 2.499 (GRP78) + 2.597 (TNM stage), was constructed, and a patient's risk score was estimated by the formula: e (Z)/(e (Z) + 1) × 100, where "e" is the base of natural logarithm. High-risk score was closely associated with NPC radioresistance, and was observed more frequently in the radioresistant patients than that in the radiosensitive patients. The sensitivity, specificity, and accuracy of the risk score model for predicting NPC radioresistance was 88.00, 86.48, and 87.25%, respectively, which was clearly superior to each individual protein and TNM stage. Furthermore, Kaplan-Meier survival analysis showed that high-risk score correlated with the markedly reduced overall survival (OS) and disease-free survival (DFS) of the patients, and Cox regression analysis showed that the risk score model was an independent predictor for OS and DFS. This study constructs a risk score model for predicting NPC radioresistance and patient survival, and it may serve as a complement to current radioresistance risk stratification approaches.

Radiosensitivity index predicts for survival with adjuvant radiation in resectable pancreatic cancer

Background and purposeAdjuvant radiation therapy for resectable pancreatic cancer remains controversial. Sub-populations of radiosensitive tumors might exist given the genetic heterogeneity of pancreatic cancers. We evaluated whether RSI is predictive of survival in pancreatic cancer treated with radiation. Materials and methodsWe identified 73 genomically-profiled pancreas cancer patients treated with upfront surgery between 2000 and 2011 (48 radiation, 25 no radiation). Briefly, RSI score is derived from the expression of 10 specific genes and a linear regression algorithm modeled on SF2 of 48 cancer cells. The primary endpoint was to assess the association of RSI with overall survival. ResultsMedian follow-up was 67months for surviving patients. On multivariate analysis, patients with radioresistant tumors had a trend toward worse survival (Hazard ratio [HR] 2.1 [95% CI 1.0–4.3], p=0.054). Among high-risk, irradiated patients (positive margins, positive lymph nodes, or a post-operative CA19-9 >90; n=31), radiosensitive patients had significantly improved survival compared with radioresistant patients (median 31.2 vs. 13.2months; HR 0.42 [0.19, 0.94], p=0.04). Among irradiated patients (n=48), low-risk patients lived longer than both high-risk patients with radiosensitive tumors and radioresistant tumors (HR 2.7 [1.0, 7.2], p=0.04 and HR 6.3 [2.3, 17.0], p<0.001, respectively). ConclusionsIntegrating RSI with standard high-risk variables has the potential to refine the classification of high-risk resected pancreatic cancer patients treated with radiation therapy.

MicroRNA-18a enhances the radiosensitivity of cervical cancer cells by promoting radiation-induced apoptosis.

Evidence has demonstrated that microRNAs (miRNAs) are important in the regulation of cellular radiosensitivity of various types of human cancer. The aim of this study was to examine the role of miR-18a in regulating the radiosensitivity of cervical cancer, in order to understand the underlying mechanism and to assess the potential of miR-18a as a biomarker for predicting radiosensitivity. The expression of miR-18a was investigated in 48 cervical cancer patients. The results revealed that miR-18a expression was significantly higher in radiosensitive patients than in radioresistant patients by RT-qPCR (P<0.05). Transient transfection experiments showed that miR-18a was upregulated by the miR-18a mimic and downregulated by the miR-18a inhibitor in the SiHa and HeLa cells. Without irradiation treatment, a similar growth was observed in the cells with or without transfection of miR-18a. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) and Hoechst staining assays showed that miR-18a had no effect on the proliferation and apoptosis of cervical cancer cells after transfection. However, the upregulation of miR-18a suppressed the level of ataxia-telangiectasia mutated and attenuated DNA double-strand break repair after irradiation, which re-sensitized the cervical cancer cells to radiotherapy by promoting apoptosis. Taken together, these results demonstrated that miR-18a is a potential molecule predictor of radiosensitivity in cervical cancer patients and played an important role in the response to radiotherapy.

RNA-seq profiling of a radiation resistant and radiation sensitive prostate cancer cell line highlights opposing regulation of DNA repair and targets for radiosensitization.

BackgroundRadiotherapy is a chosen treatment option for prostate cancer patients and while some tumours respond well, up to 50% of patients may experience tumour recurrence. Identification of functionally relevant predictive biomarkers for radioresponse in prostate cancer would enable radioresistant patients to be directed to more appropriate treatment options, avoiding the side-effects of radiotherapy.MethodsUsing an in vitro model to screen for novel biomarkers of radioresistance, transcriptome analysis of a radioresistant (PC-3) and radiosensitive (LNCaP) prostate cancer cell line was performed. Following pathway analysis candidate genes were validated using qRT-PCR. The DNA repair pathway in radioresistant PC-3 cells was then targeted for radiation sensitization using the PARP inhibitor, niacinimide.ResultsOpposing regulation of a DNA repair and replication pathway was observed between PC-3 and LNCaP cells from RNA-seq analysis. Candidate genes BRCA1, RAD51, FANCG, MCM7, CDC6 and ORC1 were identified as being significantly differentially regulated post-irradiation. qRT-PCR validation confirmed BRCA1, RAD51 and FANCG as being significantly differentially regulated at 24 hours post radiotherapy (p-value =0.003, 0.045 and 0.003 respectively). While the radiosensitive LNCaP cells down-regulated BRCA1, FANCG and RAD51, the radioresistant PC-3 cell line up-regulated these candidates to promote cell survival post-radiotherapy and a similar trend was observed for MCM7, CDC6 and ORC1. Inhibition of DNA repair using niacinamide sensitised the radioresistant cells to irradiation, reducing cell survival at 2 Gy from 66% to 44.3% (p-value =0.02).ConclusionsThese findings suggest that the DNA repair candidates identified via RNA-seq hold potential as both targets for radiation sensitization and predictive biomarkers in prostate cancer.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2407-14-808) contains supplementary material, which is available to authorized users.

Supervised Learning Methods for the Prediction of Tumor Radiosensivity to Preoperative Radiochemotherapy

Disclosed is a gene expression panel that can predict radiation sensitivity (radiosensitivity) of a tumor in a subject. A method of predicting radiation sensitivity is provided that is based on cellular clonogenic survival after 2 Gy (SF2) for 48 cell lines. Gene expression is used as the basis of the prediction model. The radiosensitivity cell-based prediction model is validated using clinical patient data from rectal and esophagus cancer patients that received RT before surgery. The radiosensitivity genomic-based prediction model identifies patients with rectal cancer that may benefit from RT treatment by assigning higher values of SF2 to radio-resistant patients and lower values of SF2 to radio-sensitive patients.

A radiosensitivity gene signature in predicting glioma prognostic via EMT pathway.

A 31-gene signature derived by integrating four different microarray experiments, has been found to have a potential for predicting radiosensitivity of cancer cells, but it was seldom validated in clinical cancer samples. We proposed that the gene signature may serve as a predictive biomarker for estimating the overall survival of radiation-treated patients. The significance of gene signature was tested in two previously published datasets from Gene Expression Omnibus (GEO) and The Cancer Genome Altas (TCGA), respectively. In GEO data set, patients predicted to be radiosensitive(RS) had an improved overall survival when compared with radioresistant(RR) patients in either radiotherapy(RT)-treated or non radiotherapy(RT)-treated subgroups(p<0.0001 in the RT-treated group). Multivariate Cox regression analysis showed that the gene signature is the strongest predictor(p=0.0093) in the RT-treated subgroup of patients. However, it does not remain significant (p=0.7668) in non radiotherapy-treated group when adjusting for age and Karnofsky performance score (KPS) as covariates. Similarly, in the TCGA data set, radiotherapy-treated glioblastoma multiforme(GBM) patients assigned to RS group had an improved overall survival compared with RR group(p<0.0001). Geneset enrichment analysis(GSEA) analysis revealed that enrichment of epithelial mesenchymal transition(EMT) pathway was observed with radioresistant phenotype. These results suggest that the signature is a predictive biomarker for radiation-treated glioma patients' prognostic.

Individual radiosensitivity in a breast cancer collective is changed with the patients’ age

BackgroundIndividual radiosensitivity has a crucial impact on radiotherapy related side effects. Our aim was to study a breast cancer collective for its variation of individual radiosensitivity depending on the patients’ age.Materials and methodsPeripheral blood samples were obtained from 129 individuals. Individual radiosensitivity in 67 breast cancer patients and 62 healthy individuals was estimated by 3-color fluorescence in situ hybridization.ResultsBreast cancer patients were distinctly more radiosensitive compared to healthy controls. A subgroup of 9 rather radiosensitive and 9 rather radio-resistant patients was identified. A subgroup of patients aged between 40 and 50 was distinctly more radiosensitive than younger or older patients.ConclusionsIn the breast cancer collective a distinct resistant and sensitive subgroup is identified, which could be subject for treatment adjustment. Preliminary results indicate that especially in the range of age 40 to 50 patients with an increased radiosensitivity are more frequent and may have an increased risk to suffer from therapy related side effects.

Knock-down of glutaminase 2 expression decreases glutathione, NADH, and sensitizes cervical cancer to ionizing radiation

Phosphate-activated mitochondrial glutaminase (GLS2) is suggested to be linked with elevated glutamine metabolism. It plays an important role in catalyzing the hydrolysis of glutamine to glutamate. The present study was to investigate the potent effect of GLS2 on radioresistance of cervical carcinoma. GLS2 was examined in 144 cases of human cervical cancer specimens (58 radioresistant specimens, 86 radiosensitive specimens) and 15 adjacent normal cervical specimens with immunohistochemistry. HeLa cells were treated with a cumulative dose of 50Gy X-rays, over 6months, yielding the resistant sub-line HeLaR. The expressions of GLS2 were measured by Western blot. Radioresistance was tested by colony survival assay. Apoptosis was determined by flow cytometry. The levels of glutathione (GSH), reactive oxygen species (ROS), NAD+/NADH ratio and NADP+/NADPH ratio were detected by quantization assay kit. Xenografts were used to confirm the effect of GLS2 on radioresistance in vivo. The expressions of GLS2 were significantly enhanced in tumor tissues of radioresistant patients compared with that in radiosensitive patients. In vitro, the radioresistant cell line HeLaR exhibited significantly increased GLS2 levels than its parental cell line HeLa. GLS2 silenced radioresistant cell HeLaR shows substantially enhanced radiosensitivity with lower colony survival and higher apoptosis in response to radiation. In vivo, xenografts with GLS2 silenced HeLaR were more sensitive to radiation. At the molecular level, knock-down of GLS2 increased the intracellular ROS levels of HeLaR exposed to irradiation by decreasing the productions of antioxidant GSH, NADH and NADPH. GLS2 may have an important role in radioresistance in cervical cancer patients.

MiR-99b-targeted mTOR induction contributes to irradiation resistance in pancreatic cancer

BackgroundRadiation exerts direct antitumor effects and is widely used in clinics, but the efficacy is severely compromised by tumor resistance. Therefore uncovering the mechanism of radioresistance might promote the development of new strategies to overcome radioresistance by manipulating activity of the key molecules.MethodsImmunohistochemistry were used to find whether mTOR were over-activated in radioresistant patients’ biopsies. Then Western blot, real-time PCR and transfection were used to find whether radiotherapy regulates the expression and activity of mTOR by modulating its targeting microRNA in human pancreatic cancer cell lines PANC-1, Capan-2 and BxPC-3. Finally efficacy of radiation combined with mTOR dual inhibitor AZD8055 was assessed in vitro and in vivo.ResultsIonizing radiation promoted mTOR expression and activation in pancreatic cancer cells through reducing miR-99b expression, which negatively regulated mTOR. Novel mTOR inhibitor, AZD8055 (10 nM, 100 nM, 500 nM) synergistically promoted radiation (0–10 Gy) induced cell growth inhibition and apoptosis. In human pancreatic cancer xenografts, fractionated radiation combined with AZD8055 treatment further increased the anti-tumor effect, the tumor volume was shrinked to 278 mm3 after combination treatment for 3 weeks compared with single radiation (678 mm3) or AZD8055 (708 mm3) treatment (P < 0.01).ConclusionsOur data provide a rationale for overcoming radio-resistance by combined with mTOR inhibitor AZD8055 in pancreatic cancer therapy.

Telomere Profiling: Toward Glioblastoma Personalized Medicine

Despite a standard of care combining surgery, radiotherapy (RT), and temozolomide chemotherapy, the average overall survival (OS) of glioblastoma patients is only 15 months, and even far lower when the patient cannot benefit from this combination. Therefore, there is a strong need for new treatments, such as new irradiation techniques. Against this background, carbon ion hadrontherapy, a new kind of irradiation, leads to a greater biological response of the tumor, while minimizing adverse effects on healthy tissues in comparison with RT. As carbon ion hadrontherapy is restricted to RT-resistant patients, photon irradiation resistance biomarkers are needed. Long telomeres and high telomerase activity have been widely associated with photon radioresistance in other cancers. Moreover, telomere protection, telomere function, and telomere length (TL) also depend on the shelterin protein complex (TRF1, TRF2, TPP1, POT1, TIN2, and hRAP1). We thus decided to evaluate an enlarged telomeric status (TL, telomerase catalytic subunit, and the shelterin component expression level) as a potential radioresistance biomarker in vitro using cellular models and ex vivo using patient tumor biopsies. In addition, nothing was known about the role of telomeres in carbon ion response. We thus evaluated telomeric status after both types of irradiation. We report here a significant correlation between TL and the basal POT1 expression level and photon radioresistance, in vitro, and a significant increase in the OS of patients with long telomeres or a high POT1 level, in vivo. POT1 expression was predictive of patient response irrespective of the TL. Strikingly, these correlations were lost, in vitro, when considering carbon irradiation. We thus propose (1) a model of the implications of telomeric damage in the cell response to both types of irradiation and (2) assessment of the POT1 expression level and TL using patient tumor biopsies to identify radioresistant patients who could benefit from carbon hadrontherapy.

Validation of a Radiosensitivity Molecular Signature in Breast Cancer

Previously, we developed a radiosensitivity molecular signature [radiosensitivity index (RSI)] that was clinically validated in 3 independent datasets (rectal, esophageal, and head and neck) in 118 patients. Here, we test RSI in radiotherapy (RT)-treated breast cancer patients. RSI was tested in 2 previously published breast cancer datasets. Patients were treated at the Karolinska University Hospital (n = 159) and Erasmus Medical Center (n = 344). RSI was applied as previously described. We tested RSI in RT-treated patients (Karolinska). Patients predicted to be radiosensitive (RS) had an improved 5-year relapse-free survival when compared with radioresistant (RR) patients (95% vs. 75%, P = 0.0212), but there was no difference between RS/RR patients treated without RT (71% vs. 77%, P = 0.6744), consistent with RSI being RT-specific (interaction term RSI × RT, P = 0.05). Similarly, in the Erasmus dataset, RT-treated RS patients had an improved 5-year distant metastasis-free survival over RR patients (77% vs. 64%, P = 0.0409), but no difference was observed in patients treated without RT (RS vs. RR, 80% vs. 81%, P = 0.9425). Multivariable analysis showed RSI is the strongest variable in RT-treated patients (Karolinska, HR = 5.53, P = 0.0987, Erasmus, HR = 1.64, P = 0.0758) and in backward selection (removal α of 0.10), RSI was the only variable remaining in the final model. Finally, RSI is an independent predictor of outcome in RT-treated ER(+) patients (Erasmus, multivariable analysis, HR = 2.64, P = 0.0085). RSI is validated in 2 independent breast cancer datasets totaling 503 patients. Including prior data, RSI is validated in 5 independent cohorts (621 patients) and represents, to our knowledge, the most extensively validated molecular signature in radiation oncology.

αV integrin induces multicellular radioresistance in human nasopharyngeal carcinoma via activating SAPK/JNK pathway.

BackgroundTumor cells acquire the capacity of resistance to chemotherapy or radiotherapy via cell–matrix and cell–cell crosstalk. Integrins are the most important cell adhesion molecules, in which αV integrin mainly mediating the tight contact between tumor cells.Methodology/Principal FindingsTo investigate the role of αV integrin in multi-cellular radioresistance (MCR) of human nasopharyngeal carcinoma (NPC), we performed immunohistochemistry and Western blotting to find that the expression of αV integrin in the tumor tissue of radioresistant patients is much higher than that in radiosensitive patients. In vitro, we cultured human NPC cell line CNE-2 cells as multi-cellular spheroids (MCSs) or as monolayer cells (MCs), and found that the expression of αV integrin in MCSs is significantly higher than that in MCs. MTT, flow cytometry and clonogenic suvival assays showed that MCSs are less sensitive to X-ray irradiation than MCs while blocking of αV integrin in MCSs dramatically reversed their radioresistance. Furthermore, as detected by Western blotting, MCSs displayed sustained activation of the stress-activated protein kinase/c-Jun NH2-terminal kinase (SAPK/JNK) pathway in presence of irradiation. Blocking of αV integrin in MCSs decreased the expression of phosphorylated JNK. Additionally, blocking of SAPK/JNK signaling pathway synergistically induced apoptosis of MCSs exposed to irradiation by increasing the expression of cleaved caspase-3. In vivo, we found that irradiation combined with αV integrin blocking treatment significantly enhanced the radiosensitivity of NPC xenografts. ConclusionsOur results indicate a novel role of αV integrin in multi-cellular radioresistance of NPCs.

Po‐Poster ‐ 29: Radiation‐induced apoptosis of lymphocytes to predict late toxicity from radiotherapy

An important challenge arises in radiotherapy when certain individuals present with abnormal radiosensitivities. Radiosensitive individuals may not tolerate normal therapy and encounter complications whereas radioresistant patients may not respond adequately to standard treatments regimes because of intrinsic cellular resistance. It has been shown (Crompton et al. IJROBP 2003; 45:707–714 and IJROBP 2001; 49:547–554) that late normal tissue toxicity was correlated to low level apoptosis in CD4 and CD8 lymphocytes. The assay developed by this group used a simple flow cytometry based assay. Our group has researched the sensitivity of alternative apoptosis assays (DiOC6, Caspase‐3, Annexin‐V, PI, 7AAD and Comet), and have shown that both the Annexin V‐FITC and the DiOC6 assay have the greatest suitability in clinical use with respect to speed, simplicity and sensitivity. In our present study, 80 prostate cancer patients will be tested for radiosensitivity using lymphocyte apoptosis assays. These patients were formerly enrolled in a randomized dose‐escalation study (Sathya et al. JCO 2005; 45:1192–1199). Toxicity was recorded prospectively. The aim of this study is to determine a correlation between the proportion of T‐lymphocytes undergoing apoptosis when irradiated (2, 4 and 8Gy) and the occurrence of late toxicity (Grade II and above). We will present our current results showing a large inter‐individual variation within our patient cohort. Data obtained using the Annexin Assay measuring CD4 lymphocyte apoptosis receiving 8Gy show a wide range of responses (mean = 34% apoptosis, σ = 8.2) with z‐scores ranging from −1.5 to 2.4.