Alterations in DNA repair efficiency are involved in the radioresistance of esophageal adenocarcinoma

Low-dose non-targeted radiation effects in human esophageal adenocarcinoma cell lines

PURPOSE

To investigate non-targeted radiation effects in esophageal adenocarcinoma cell lines (OE19 and OE33) using human keratinocyte and colorectal cancer cell reporters following γ-ray exposure.

MATERIALS AND METHODS

Both clonogenic assays and ratiometric calcium endpoints were used to check for the occurrence of bystander signals in reporter cells.

RESULTS

We report data suggesting that γ-irradiation increases cell killing over the expected linear quadratic (LQ) model levels in the OE19 cell line exposed to doses below 1 Gy, i.e. which may be suggestive to be a low hyper-radiosensitive (HRS) response to direct irradiation. Both EAC cell lines (OE19 and OE33) have the ability to produce bystander signals when irradiated cell conditioned medium (ICCM) is placed onto human keratinocyte reporters, but do not seem to be capable of responding to bystander signals when placed on their autologous reporters. Further work with human keratinocyte reporter models showed statistically significant intracellular calcium fluxes following exposure of the reporters to ICCM harvested from both EAC cell lines exposed to 0.5 Gy.

CONCLUSION

These experiments suggest that the OE19 and OE33 cell lines produce bystander signals in human keratinocyte reporter cells. However, the radiosensitivity of the EAC cell lines used in this study cannot be enhanced by the bystander response since both cell lines could not respond to bystander signals.

Intricate Macrophage-Colorectal Cancer Cell Communication in Response to Radiation

Both cancer and tumour-associated host cells are exposed to ionizing radiation when a tumour is subjected to radiotherapy. Macrophages frequently constitute the most abundant tumour-associated immune population, playing a role in tumour progression and response to therapy. The present work aimed to evaluate the importance of macrophage-cancer cell communication in the cellular response to radiation. To address this question, we established monocultures and indirect co-cultures of human monocyte-derived macrophages with RKO or SW1463 colorectal cancer cells, which exhibit higher and lower radiation sensitivity, respectively. Mono- and co-cultures were then irradiated with 5 cumulative doses, in a similar fractionated scheme to that used during cancer patients' treatment (2 Gy/fraction/day). Our results demonstrated that macrophages sensitize RKO to radiation-induced apoptosis, while protecting SW1463 cells. Additionally, the co-culture with macrophages increased the mRNA expression of metabolism- and survival-related genes more in SW1463 than in RKO. The presence of macrophages also upregulated glucose transporter 1 expression in irradiated SW1463, but not in RKO cells. In addition, the influence of cancer cells on the expression of pro- and anti-inflammatory macrophage markers, upon radiation exposure, was also evaluated. In the presence of RKO or SW1463, irradiated macrophages exhibit higher levels of pro-inflammatory TNF, IL6, CCL2 and CCR7, and of anti-inflammatory CCL18. However, RKO cells induce an increase of macrophage pro-inflammatory IL1B, while SW1463 cells promote higher pro-inflammatory CXCL8 and CD80, and also anti-inflammatory VCAN and IL10 levels. Thus, our data demonstrated that macrophages and cancer cells mutually influence their response to radiation. Notably, conditioned medium from irradiated co-cultures increased non-irradiated RKO cell migration and invasion and did not impact on angiogenesis in a chicken embryo chorioallantoic membrane assay. Overall, the establishment of primary human macrophage-cancer cell co-cultures revealed an intricate cell communication in response to ionizing radiation, which should be considered when developing therapies adjuvant to radiotherapy.

MicroRNAs and Their Impact on Radiotherapy for Cancer

Resistance to radiation is considered to be an important reason for local failure after radiotherapy and tumor recurrence. However, the exact mechanisms of tumor resistance remain poorly understood. Current investigations of microRNAs as potential diagnostic and therapeutic tools for cancer treatment have shown promising results. With respect to radiotherapy resistance and response, there is now emerging evidence that microRNAs modulate key cellular pathways that mediate response to radiation. These data suggest that microRNAs might have significant potential as targets for the development of new therapeutic strategies to overcome radioresistance in cancer. This review summarizes the current literature pertinent to the influence of microRNAs in the response to radiotherapy for cancer treatment, with an emphasis on microRNAs as novel diagnostic and prognostic markers, as well as their potential to alter radiosensitivity.

Low miR-187 expression promotes resistance to chemoradiation therapy in vitro and correlates with treatment failure in patients with esophageal adenocarcinoma

Esophageal adenocarcinoma (EAC) has a poor prognosis and is increasing in incidence in many western populations. Neoadjuvant chemoradiation therapy (CRT) followed by surgery is increasingly the standard of care for locally advanced EAC; however, resistance to treatment is a significant clinical problem. The identification of both novel biomarkers predicting response to treatment and novel therapeutic targets to enhance the efficacy of CRT are key to improving survival rates in EAC. In this study we performed global microRNA (miRNA) profiling of pre-treatment EAC biopsies and identified 67 miRNA significantly altered in patients who are resistant to CRT. One of these miRNA, miR-187, was significantly decreased in pre-treatment EAC tumors from patients having a poor response to neoadjuvant CRT, highlighting downregulation of miR-187 as a potential mechanism of treatment resistance in EAC. In vitro, miR-187 was demonstrated to play a functional role in modulating sensitivity to X-ray radiation and cisplatin in EAC and its dysregulation was demonstrated to be due to chromosomal alterations. In vitro, miR-187 altered expression of a diverse array of pathways, including the immune regulator complement component 3 (C3), serum levels of which we have previously demonstrated to predict patient response to CRT. In vivo, expression of C3 was significantly increased in tumors from patients having a poor response to CRT. This study highlights for the first time a role for miR-187 as a novel biomarker of response to CRT and a potential therapeutic target for enhancing the efficacy of CRT in EAC.

MicroRNA-145 Modulates Tumor Sensitivity to Radiation in Prostate Cancer

Radiation therapy prior to surgery has increasingly become the standard of care for locally advanced prostate cancer, however tumor radioresistance remains a major clinical problem. While restoration of microRNA-145 (miR-145) expression reduces chemoradioresistance in glioblastoma and suppress prostate cancer proliferation, migration and invasion, the role of miR-145 in response to radiation therapy for prostate cancer is still unknown. The aim of this study was to investigate the role of miR-145 in determining the tumor response to radiation treatment in prostate cancer. Human prostate cancer cells LNCAP and PC3 were transfected with miR-145 mimic. Clonogenic assay was used to determine whether overexpression of miR-145 could alter radiation response in vitro. Immunofluorescence of γ-H2AX and flow cytometric analysis of phosphorylated histone H3 were performed to investigate the potential mechanisms contributing to the enhanced radiation-induced cell killing induced by miR-145. In addition, a qPCR-based array was used to detect the possible miR-145-mediated regulated genes involved. Tumor growth delay assays and survival curves were then analyzed in an animal model to investigate whether miR-145 induced radiosensitivity in vivo. Furthermore, miR-145 expression was assessed in 30 prostate tumor tissue biopsies taken prior to neoadjuvant radiotherapy using miRNA arrays. Our current study suggested that ectopic expression of miR-145 significantly sensitized prostate cancer cells to radiation and we used γ-H2AX phosphorylation as a surrogate marker of radiotherapy response versus miR-145 expression levels. We observed significantly more foci per cell in the group treated with miR-145 and radiation. In addition, mitotic catastrophe was significantly increased in cells receiving miR-145 and radiation. The above results suggest that miR-145 appears to reduced the efficiency of the repair of radiation-induced DNA double-strand breaks in cells. A detailed examination of the involvement of the DNA repair pathway showed that miR-145 reduced the expression of 10 genes involved in DNA repair according to a qPCR-based array data. Irradiation of subcutaneous PC3 tumors in mice treated with R11-miR-145 (a cellular permeable peptide, previously reported) resulted in an increase in radiation-induced tumor growth delay and lived the longest after combination treatment. Moreover, miR-145 expression was significantly increased in patients demonstrating good response (PSA < 2.0 ng/ml/year) to neoadjuvant radiotherapy, while expression of the miR-145-regulated DNA repair genes was significantly decreased. In conclusion, these data suggest a possible mechanism for miR-145 radiosensitivity, potentially through down regulating of DNA repair. This novel study shows a role for miR-145 in modulating radiosensitivity in vivo and highlights the need for further study investigating the potential role of miR-145 as both a predictive marker of response and a novel therapeutic agent with which to enhance the efficacy of radiation therapy.

Visceral obesity stimulates anaphase bridge formation and spindle assembly checkpoint dysregulation in radioresistant oesophageal adenocarcinoma

PURPOSE

Oesophageal adenocarcinoma is an exemplar model of obesity-associated cancer. Locally advanced disease is treated with neoadjuvant chemoradiotherapy, and survival rates are highest in patients demonstrating a pathological response following neoadjuvant therapy. Given that 55 % of oesophageal adenocarcinoma patients are obese, uncovering the effect of adipose tissue on radioresponse is clinically relevant. This study investigates if adipose tissue activates genomic instability events in radioresponsive (OE33P) and radioresistant (OE33R) oesophageal cancer cell lines and tumour samples.

METHODS

OE33R and OE33P were cultured with adipose-conditioned media derived from oesophageal adenocarcinoma patients (n = 10). Anaphase bridges, a marker of genomic instability, were enumerated in both cell lines following treatment with adipose media, and normalised to cell number. Genomic instability is regulated by the spindle assembly complex. Expression of two spindle assembly complex genes (MAD2L2, BUB1B) was assessed using qPCR, and validated in patient tumour specimens from viscerally obese (n = 46) and nonobese patients (n = 41).

RESULTS

Adipose-conditioned media increased anaphase bridging in OE33R (p < 0.0001), with a threefold increase in OE33R compared to OE33P (p < 0.01). Levels of anaphase bridges in OE33R cells correlated with visceral obesity status as measured by waist circumference (R = 0.709, p = 0.03) and visceral fat area (R = 0.794, p = 0.006). Adipose tissue altered expression of MAD2L2 in vitro. In vivo, MAD2L2 expression was higher in viscerally obese oesophageal adenocarcinoma patients compared with nonobese patients (p < 0.05).

CONCLUSIONS

Anaphase bridge levels are influenced by obesity and radiosensitivity status in oesophageal adenocarcinoma. Furthermore, visceral adipose-conditioned media stimulates dysregulation of the spindle assembly complex in oesophageal adenocarcinoma patients.

MicroRNA-330-5p as a Putative Modulator of Neoadjuvant Chemoradiotherapy Sensitivity in Oesophageal Adenocarcinoma

Oesophageal adenocarcinoma (OAC) is the sixth most common cause of cancer deaths worldwide, and the 5-year survival rate for patients diagnosed with the disease is approximately 17%. The standard of care for locally advanced disease is neoadjuvant chemotherapy or, more commonly, combined neoadjuvant chemoradiation therapy (neo-CRT) prior to surgery. Unfortunately, ~60-70% of patients will fail to respond to neo-CRT. Therefore, the identification of biomarkers indicative of patient response to treatment has significant clinical implications in the stratification of patient treatment. Furthermore, understanding the molecular mechanisms underpinning tumour response and resistance to neo-CRT will contribute towards the identification of novel therapeutic targets for enhancing OAC sensitivity to CRT. MicroRNAs (miRNA/miR) function to regulate gene and protein expression and play a causal role in cancer development and progression. MiRNAs have also been identified as modulators of key cellular pathways associated with resistance to CRT. Here, to identify miRNAs associated with resistance to CRT, pre-treatment diagnostic biopsy specimens from patients with OAC were analysed using miRNA-profiling arrays. In pre-treatment biopsies miR-330-5p was the most downregulated miRNA in patients who subsequently failed to respond to neo-CRT. The role of miR-330 as a potential modulator of tumour response and sensitivity to CRT in OAC was further investigated in vitro. Through vector-based overexpression the E2F1/p-AKT survival pathway, as previously described, was confirmed as a target of miR-330 regulation. However, miR-330-mediated alterations to the E2F1/p-AKT pathway were insufficient to significantly alter cellular sensitivity to chemotherapy (cisplatin and 5-flurouracil). In contrast, silencing of miR-330-5p enhanced, albeit subtly, cellular resistance to clinically relevant doses of radiation. This study highlights the need for further investigation into the potential of miR-330-5p as a predictive biomarker of patient sensitivity to neo-CRT and as a novel therapeutic target for manipulating cellular sensitivity to neo-CRT in patients with OAC.

Translational research on esophageal adenocarcinoma: from cell line to clinic

Human esophageal adenocarcinoma (EAC) cell lines have made a substantial contribution to elucidating mechanisms of carcinogenesis and drug discovery. Model research on EAC relies almost entirely on a relatively small set of established tumor cell lines because appropriate animal models are lacking. Nowadays, more than 20% of all fundamental translational research studies regarding EAC are partially or entirely based on these cell lines. The ready availability of these cell lines to investigators worldwide have resulted in more than 250 publications, including many examples of important biomedical discoveries. The high genomic similarities (but certainly not completely identical) between the EAC cell lines and their original tumors provide rational for their use. Recently, in a collaborative effort all available EAC cell lines have been verified resulting in the establishment of a reliable panel of 10 EAC cell lines. It could be expected that the value of these cell lines increases as unlimited source of tumor material because new biomedical techniques require more tumor cells and the supply of viable tumor cells is diminishing because of neoadjuvant chemo(radio)therapy of patients with EAC. Here, we review the history of the EAC cell lines and their utility in translational research and biomedical discovery.

Heterochromatin domain number correlates with X-ray and carbon-ion radiation resistance in cancer cells

Although it is known that cancer cells can develop radiation resistance after repeated exposures to X rays, the underlying mechanisms and characteristics of this radiation-induced resistance of cancer cells are not well understood. Additionally, it is not known whether cells that develop X-ray resistance also would develop resistance to other types of radiation such as heavy-ions including carbon ions (C-ion). In this study, we established X-ray resistant cancer cell lines by delivering repeated exposures to X rays, and then assessed whether the cells were resistant to carbon ions. The mouse squamous cell carcinoma cell line, NR-S1, was X irradiated six times with 10 Gy, and the X-ray resistant cancer cells named X60 and ten subclones were established. Significant X-ray resistance was induced in four of the subclones (X60, X60-H2, X60-A3 and X60-B12). The X60 cells and all of the subclones were resistant to carbon ions. The correlation analysis between radioresistance and morphological characteristics of these cells showed that X-ray (R=0.74) and C-ion (R=0.79) resistance correlated strongly with the number of heterochromatin domains. Moreover, the numbers of γ-H2AX foci remaining in irradiated X60 cells and radioresistant subclones X60-A3 and X60-H2 were lower than in the NR-S1 cells after X-ray or C-ion irradiation, indicating that X60 cells and the radioresistant subclones rapidly repaired the DNA double-strand breaks compared with NR-S1 cells. Our findings suggest that the underlying causal mechanisms of X-ray and C-ion radiation resistance may overlap, and that an increase in heterochromatin domain number may be an indicator of X-ray and C-ion resistance.

Altered mitochondrial function and energy metabolism is associated with a radioresistant phenotype in oesophageal adenocarcinoma

Neoadjuvant chemoradiation therapy (CRT) is increasingly the standard of care for locally advanced oesophageal cancer. A complete pathological response to CRT is associated with a favourable outcome. Radiation therapy is important for local tumour control, however, radioresistance remains a substantial clinical problem. We hypothesise that alterations in mitochondrial function and energy metabolism are involved in the radioresistance of oesophageal adenocarcinoma (OAC). To investigate this, we used an established isogenic cell line model of radioresistant OAC. Radioresistant cells (OE33 R) demonstrated significantly increased levels of random mitochondrial mutations, which were coupled with alterations in mitochondrial function, size, morphology and gene expression, supporting a role for mitochondrial dysfunction in the radioresistance of this model. OE33 R cells also demonstrated altered bioenergetics, demonstrating significantly increased intracellular ATP levels, which was attributed to enhanced mitochondrial respiration. Radioresistant cells also demonstrated metabolic plasticity, efficiently switching between the glycolysis and oxidative phosphorylation energy metabolism pathways, which were accompanied by enhanced clonogenic survival. This data was supported in vivo, in pre-treatment OAC tumour tissue. Tumour ATP5B expression, a marker of oxidative phosphorylation, was significantly increased in patients who subsequently had a poor pathological response to neoadjuvant CRT. This suggests for the first time, a role for specific mitochondrial alterations and metabolic remodelling in the radioresistance of OAC.

Development of TRAIL resistance by radiation-induced hypermethylation of DR4 CpG island in recurrent laryngeal squamous cell carcinoma

PURPOSE

There are limited therapeutic options for patients with recurrent head and neck cancer after radiation therapy failure. To assess the use of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) as a salvage chemotherapeutic agent for recurrent cancer after radiation failure, we investigated the effect of clinically relevant cumulative irradiation on TRAIL-induced apoptosis.

METHODS AND MATERIALS

Using a previously established HN3 cell line from a laryngeal carcinoma patient, we generated a chronically irradiated HN3R isogenic cell line. Viability and apoptosis in HN3 and HN3R cells treated with TRAIL were analyzed with MTS and PI/annexin V-FITC assays. Western blotting and flow cytometry were used to determine the underlying mechanism of TRAIL resistance. DR4 expression was semiquantitatively scored in a tissue microarray with 107 laryngeal cancer specimens. Methylation-specific polymerase chain reaction and bisulfite sequencing for DR4 were performed for genomic DNA isolated from each cell line.

RESULTS

HN3R cells were more resistant than HN3 cells to TRAIL-induced apoptosis because of significantly reduced levels of the DR4 receptor. The DR4 staining score in 37 salvage surgical specimens after radiation failure was lower in 70 surgical specimens without radiation treatment (3.03 ± 2.75 vs 5.46 ± 3.30, respectively; P<.001). HN3R cells had a methylated DR4 CpG island that was partially demethylated by the DNA demethylating agent 5-aza-2'-deoxycytidine.

CONCLUSION

Epigenetic silencing of the TRAIL receptor by hypermethylation of a DR4 CpG island might be an underlying mechanism for TRAIL resistance in recurrent laryngeal carcinoma treated with radiation.

Isogenic radiation resistant cell lines: development and validation strategies

PURPOSE

The comparison of cell lines with differing radiosensitivities and their molecular response to radiation exposure has been used in a number of human cancer models to study the molecular response to radiation. This review proposes to analyze and compare the protocols used by investigators for the development and validation of these isogenic models of radioresistance.

CONCLUSION

There is large variability in the strategies used to generate and validate isogenic models of radioresistance. Further characterization of these models is required.

A hormone-DNA repair circuit governs the response to genotoxic insult

Alterations in DNA repair promote tumor development, but the impact on tumor progression is poorly understood. Here, discovery of a biochemical circuit linking hormone signaling to DNA repair and therapeutic resistance is reported. Findings show that androgen receptor (AR) activity is induced by DNA damage and promotes expression and activation of a gene expression program governing DNA repair. Subsequent investigation revealed that activated AR promotes resolution of double-strand breaks and resistance to DNA damage both in vitro and in vivo. Mechanistically, DNA-dependent protein kinase catalytic subunit (DNAPKcs) was identified as a key target of AR after damage, controlling AR-mediated DNA repair and cell survival after genotoxic insult. Finally, DNAPKcs was shown to potentiate AR function, consistent with a dual role in both DNA repair and transcriptional regulation. Combined, these studies identify the AR-DNAPKcs circuit as a major effector of DNA repair and therapeutic resistance and establish a new node for therapeutic intervention in advanced disease.

SIGNIFICANCE

The present study identifies for the fi rst time a positive feedback circuit linking hormone action to the DNA damage response and shows the significant impact of this process on tumor progression and therapeutic response. These provocative findings provide the foundation for development of novel nodes of therapeutic intervention for advanced disease.

miR-506 regulates epithelial mesenchymal transition in breast cancer cell lines

Epithelial-mesenchymal transition (EMT) is an important parameter related to breast cancer survival. Among several microRNAs predicted to target EMT-related genes, miR-506 is a novel miRNA found to be significantly related to breast cancer patient survival in a meta-analysis. miR-506 suppressed the expression of mesenchymal genes such as Vimentin, Snai2, and CD151 in MDA-MB-231 human breast cancer cell line. Moreover, NF-κB bound to the upstream promoter region of miR-506 to suppress transcription. Overexpression of miR-506 inhibited TGFβ-induced EMT and suppressed adhesion, invasion, and migration of MDA-MB-231 cells. From these results, we concluded that miR-506 plays a key role in the process of EMT through posttranslational control of EMT-related genes.

Development and characterization of an isogenic cell line with a radioresistant phenotype

INTRODUCTION

Radiation resistance is a major cause of death in cancer patients. Cancer cells react during radiotherapy by re-programming specific cell functions that may confer resistance to radiation. The understanding of this complex process is hindered due to the lack of appropriate study models. We describe an experimental development of a radioresistant isogenic cancer cell line, and its molecular characterization.

MATERIALS AND METHODS

A431-cultured cells were irradiated for 7 month until 85 Gy. Then, a selected single cell was left to grow as stable A431-R cell line. Clonogenic assay was used to determine cell survival, the α and β parameters of the LQ model, and the mean inactivation dose. The DNA repair ability of cells was evaluated by pulsed-field electrophoresis method. Differential effect of fractionated radiation was ultimately tested in xenografts. Furthermore, we used a wound healing assay, Western blot for EGFR, AKT and ERK1/2 and ELISA test for vascular endothelial growth factor (VEGF) secretion. Finally we explored CD44 marker and cell cycle distribution.

RESULTS

The established A431-R cell line showed radiation resistance in clonogenic assays, repair of radiation-induced DNA fragmentation and xenografted tumours. The radiation resistance was associated with in vitro higher cell growth and migration, increased levels of former oncoproteins, and secretion of VEGF.

CONCLUSIONS

In this model, the emergence of radiation resistance was associated with the acquisition of biological traits that support more aggressive behaviour of cancer cells. We have generated a model that will be useful for mechanistic studies and development of rational treatments against radiation resistance in cancer.

MicroRNA-31 modulates tumour sensitivity to radiation in oesophageal adenocarcinoma

Chemoradiation therapy (CRT) prior to surgery is increasingly the standard of care for locally advanced oesophageal cancer. Radiation therapy is important for local tumour control; however, tumour resistance to radiation is a substantial clinical problem. The mechanism(s) of radioresistance are still poorly understood, however, mounting evidence supports a role for microRNA (miRNA) in modulating key cellular pathways mediating response to radiation. Global miRNA profiling of an established isogenic model of radioresistance in oesophageal adenocarcinoma demonstrated a significant downregulation of miR-31 in radioresistant cells, both basally and in response to radiation. Ectopic re-expression of miR-31 significantly re-sensitised radioresistant cells to radiation. miR-31 was demonstrated to alter the expression of 13 genes involved in DNA repair, which is a critical cellular defence against radiation-induced DNA damage. In oesophageal tumours, miR-31 expression was significantly reduced in patients demonstrating poor histomorphologic response to neoadjuvant CRT, whilst expression of the miR-31-regulated DNA repair genes was significantly increased. Our data suggest a possible mechanism for resistance to CRT, potentially via enhanced DNA repair. This study demonstrates, for the first time, a role for miR-31 in modulating radioresistance and highlights the need for further study investigating the potential role of miR-31 as both a predictive marker of response and a novel therapeutic agent with which to enhance the efficacy of radiation therapy.