Impact of genomic methylation on radiation sensitivity of colorectal carcinoma

SUMO1 Modification Stabilizes TET3 Protein and Increases Colorectal Cancer Radiation Therapy Sensitivity

PURPOSE

The aim of this work was to explore the role and mechanism of active DNA demethylase in colorectal cancer (CRC) radiation sensitization and better understand the function of DNA demethylation in tumor radiosensitization.

METHODS AND MATERIALS

Tested the effect of ten-eleven translocation 3 (TET3) overexpression on the sensitivity of CRC to radiation therapy through G2/M arrest, apoptosis, and clonogenic suppression. TET3 knockdown HCT 116 and TET3 knockdown LS 180 cell lines were constructed by siRNA technology, and the effect of exogenous knockdown of TET3 on radiation-induced apoptosis, cell cycle arrest, DNA damage, and clone formation in CRC cells were detected. The co-localization of TET3 and small ubiquitin-like modifier 1 (SUMO1), SUMO2/3 was detected by immunofluorescence and cytoplasmic-nuclear extraction, and the interaction between TET3 and SUMO1, SUMO2/3 was detected by a coimmunoprecipitation assay.

RESULTS

The malignant phenotype and radiosensitivity of CRC cell lines were favorably linked with TET3 protein and mRNA expression. TET3 is upregulated in 23 of the 27 tumor types investigated, including colon cancer. TET3 was shown to correlate with the CRC pathologic malignancy grade positively. Overexpression of TET3 in CRC cell lines increased radiation-induced apoptosis, G2/M phase arrest, DNA damage, and clonal suppression in vitro. The binding region of TET3 and SUMO2/3 was located at 833-1795 AA except for K1012, K1188, K1397, and K1623. SUMOylation of TET3 increased the stability of the TET3 protein without changing its nuclear localization.

CONCLUSIONS

We report the sensitizing role of TET3 protein in the radiation of CRC cells, depending on SUMO1 modification of TET3 at the lysine sites (K479, K758, K1012, K1188, K1397, K1623), in turn stabilizing TET3 expression in the nucleus and subsequently increasing the sensitivity of CRC to radiation therapy. Together, this study highlights the potentially critical role of TET3 SUMOylation in radiation regulation, which may contribute to an enhanced understanding of the relationship between DNA demethylation and radiation therapy.

Radioresistance in rhabdomyosarcomas: Much more than a question of dose

Management of rhabdomyosarcoma (RMS), the most common soft tissue sarcoma in children, frequently accounting the genitourinary tract is complex and requires a multimodal therapy. In particular, as a consequence of the advancement in dose conformity technology, radiation therapy (RT) has now become the standard therapeutic option for patients with RMS. In the clinical practice, dose and timing of RT are adjusted on the basis of patients' risk stratification to reduce late toxicity and side effects on normal tissues. However, despite the substantial improvement in cure rates, local failure and recurrence frequently occur. In this review, we summarize the general principles of the treatment of RMS, focusing on RT, and the main molecular pathways and specific proteins involved into radioresistance in RMS tumors. Specifically, we focused on DNA damage/repair, reactive oxygen species, cancer stem cells, and epigenetic modifications that have been reported in the context of RMS neoplasia in both in vitro and in vivo studies. The precise elucidation of the radioresistance-related molecular mechanisms is of pivotal importance to set up new more effective and tolerable combined therapeutic approaches that can radiosensitize cancer cells to finally ameliorate the overall survival of patients with RMS, especially for the most aggressive subtypes.

DAB2IP predicts treatment response and prognosis of ESCC patients and modulates its radiosensitivity through enhancing IR-induced activation of the ASK1-JNK pathway

Background

Disabled homolog 2 interacting protein (DAB2IP) plays a tumor-suppressive role in several types of human cancers. However, the molecular status and function of the DAB2IP gene in esophageal squamous cell carcinoma (ESCC) patients who received definitive chemoradiotherapy is rarely reported.

Methods

We examined the expression dynamics of DAB2IP by immunohistochemistry (IHC) in 140 ESCC patients treated with definitive chemoradiotherapy. A series of in vivo and in vitro experiments were performed to elucidate the effect of DAB2IP on the chemoradiotherapy (CRT) response and its underlying mechanisms in ESCC.

Results

Decreased expression of DAB2IP in ESCCs correlated positively with ESCC resistance to CRT and was a strong and independent predictor for short disease-specific survival (DSS) of ESCC patients. Furthermore, the therapeutic sensitivity of CRT was substantially increased by ectopic overexpression of DAB2IP in ESCC cells. In addition, knockdown of DAB2IP dramatically enhanced resistance to CRT in ESCC. Finally, we demonstrated that DAB2IP regulates ESCC cell radiosensitivity through enhancing ionizing radiation (IR)-induced activation of the ASK1-JNK signaling pathway.

Conclusions

Our data highlight the molecular etiology and clinical significance of DAB2IP in ESCC, which may represent a new therapeutic strategy to improve therapy and survival for ESCC patients.

Enhancement of Radiosensitivity by DNA Hypomethylating Drugs through Apoptosis and Autophagy in Human Sarcoma Cells

The targeting of DNA methylation in cancer using DNA hypomethylating drugs has been well known to sensitize cancer cells to chemotherapy and immunotherapy by affecting multiple pathways. Herein, we investigated the combinational effects of DNA hypomethylating drugs and ionizing radiation (IR) in human sarcoma cell lines both in vitro and in vivo. Clonogenic assays were performed to determine the radiosensitizing properties of two DNA hypomethylating drugs on sarcoma cell lines we tested in this study with multiple doses of IR. We analyzed the effects of 5-aza-dC or SGI-110, as DNA hypomethylating drugs, in combination with IR in vitro on the proliferation, apoptosis, caspase-3/7 activity, migration/invasion, and Western blotting using apoptosis- or autophagy-related factors. To confirm the combined effect of DNA hypomethylating drugs and IR in our in vitro experiment, we generated the sarcoma cells in nude mouse xenograft models. Here, we found that the combination of DNA hypomethylating drugs and IR improved anticancer effects by inhibiting cell proliferation and by promoting synergistic cell death that is associated with both apoptosis and autophagy in vitro and in vivo. Our data demonstrated that the combination effects of DNA hypomethylating drugs with radiation exhibited greater cellular effects than the use of a single agent treatment, thus suggesting that the combination of DNA hypomethylating drugs and radiation may become a new radiotherapy to improve therapeutic efficacy for cancer treatment.

Investigation of the Effect of 5-Aza-2'-Deoxycytidine in Comparison to and in Combination with Trichostatin A on p16INK4a, p14ARF, p15INK4b Gene Expression, Cell Growth Inhibition and Apoptosis Induction in Colon Cancer Caco-2 Cell Line

Background

The cell cycle is divided into four phases, G1, G2, S, and M phase. The mammalian cell cycle is controlled and governed by the kinase complexes including cyclin and the cyclin-dependent kinase (CDK), cyclin-CDK complexes. The activity of the complexes is regulated by cyclin-dependent kinase inhibitors (CDKIs), the INK4, and the CDK interacting protein/kinase inhibitory protein (CIP/KIP) families. Promoter hypermethylation and histone deacetylation of CDKIs have been reported in several cancers. These changes can be reversed by DNA demethylating agents, such as decitabine, 5-Aza-2'-deoxycytidine (5-Aza-CdR), and histone deacetylase inhibitors (HDACIs), such as trichostatin A. Previously, we reported the effect of 5-Aza-CdR and trichostatin A (TSA) on hepatocellular carcinoma (HCC). The present study aimed to investigate the effect of 5-Aza-CdR in comparison to and in combination with trichostatin A on p16INK4a, p14ARF, p15INK4b genes expression, cell growth inhibition and apoptosis induction in colon cancer Caco-2 cell line.

Methods

The Caco-2 cells were cultured and treated with 5-Aza-CdR and TSA (alone and combined). The cell viability, apoptosis, and relative gene expression were determined by MTT assay, flow cytometry, and real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR), respectively.

Results

Both compounds inhibited cell growth, induced apoptosis, and up-regulated the p16INK4a, p14ARF, p15INK4b gene significantly. The TSA had a more significant effect in comparison to 5-Aza-CdR. Furthermore, maximal apoptosis and up-regulation were observed with combined treatment.

Conclusions

our finding indicated that 5-Aza-CdR and TSA can epigenetically re-activate the p16INK4a, p14ARF, p15INK4b gene resulting in cell growth inhibition and apoptosis induction in colon cancer.

Role of epigenetic mechanisms in propagating off-targeted effects following radiation based therapies - A review

Despite being an important diagnostic and treatment modality, ionizing radiation (IR) is also known to cause genotoxicity and multiple side effects leading to secondary carcinogenesis. While modern cancer radiation therapy has improved patient recovery and enhanced survival rates, the risk of radiation-related adverse effects has become a growing challenge. It is now well-accepted that IR-induced side effects are not exclusively restricted to exposed cells but also spread to distant 'bystander' cells and even to the unexposed progeny of the irradiated cells. These 'off-targeted' effects involve a plethora of molecular events depending on the type of radiation and tumor tissue background. While the mechanisms by which off-targeted effects arise remain obscure, emerging evidence based on the non-mendelian inheritance of various manifestations of them as well as their persistence for longer periods supports a contribution of epigenetic factors. This review focuses on the major epigenetic phenomena including DNA methylation, histone modifications, and small RNA mediated silencing and their versatile role in the manifestation of IR induced off-targeted effects. As short- and long-range communication vehicles respectively, the role of gap junctions and exosomes in spreading these epigenetic-alteration driven off-targeted effects is also discussed. Furthermore, this review emphasizes the possible therapeutic potentials of these epigenetic mechanisms and how beneficial outcomes could potentially be achieved by targeting various signaling molecules involved in these mechanisms.

The methylation status of the embryonic limb skeletal progenitors determines their cell fate in chicken

Digits shape is sculpted by interdigital programmed cell death during limb development. Here, we show that DNA breakage in the periphery of 5-methylcytosine nuclei foci of interdigital precursors precedes cell death. These cells showed higher genome instability than the digit-forming precursors when exposed to X-ray irradiation or local bone morphogenetic protein (BMP) treatments. Regional but not global DNA methylation differences were found between both progenitors. DNA-Methyl-Transferases (DNMTs) including DNMT1, DNMT3B and, to a lesser extent, DNMT3A, exhibited well-defined expression patterns in regions destined to degenerate, as the interdigital tissue and the prospective joint regions. Dnmt3b functional experiments revealed an inverse regulation of cell death and cartilage differentiation, by transcriptional regulation of key genes including Sox9, Scleraxis, p21 and Bak1, via differential methylation of CpG islands across their promoters. Our findings point to a regulation of cell death versus chondrogenesis of limb skeletal precursors based on epigenetic mechanisms.

Esophageal 3D organoids of MPV17-/- mouse model of mitochondrial DNA depletion show epithelial cell plasticity and telomere attrition

Esophageal squamous cell carcinoma (ESCC) is an aggressive cancer with late-stage detection and poor prognosis. This emphasizes the need to identify new markers for early diagnosis and treatment. Altered mitochondrial genome (mtDNA) content in primary tumors correlates with poor patient prognosis. Here we used three-dimensional (3D) organoids of esophageal epithelial cells (EECs) from the MPV17-/- mouse model of mtDNA depletion to investigate the contribution of reduced mtDNA content in ESCC oncogenicity. To test if mtDNA defects are a contributing factor in ESCC, we used oncogenic stimuli such as ESCC carcinogen 4-nitroquinoline oxide (4-NQO) treatment, or expressing p53R175H oncogenic driver mutation. We observed that EECs and 3D-organoids with mtDNA depletion had cellular, morphological and genetic alterations typical of an oncogenic transition. Furthermore, mitochondrial dysfunction induced cellular transformation is accompanied by elevated mitochondrial fission protein, DRP1 and pharmacologic inhibition of mitochondrial fission by mDivi-1 in the MPV17-/- organoids reversed the phenotype to that of normal EEC organoids. Our studies show that mtDNA copy number depletion, activates a mitochondrial retrograde response, potentiates telomere defects, and increases the oncogenic susceptibility towards ESCC. Furthermore, mtDNA depletion driven cellular plasticity is mediated via altered mitochondrial fission-fusion dynamics.

DNA methylation changes following DNA damage in prostate cancer cells

Many cancer therapies operate by inducing double-strand breaks (DSBs) in cancer cells, however treatment-resistant cells rapidly initiate mechanisms to repair damage enabling survival. While the DNA repair mechanisms responsible for cancer cell survival following DNA damaging treatments are becoming better understood, less is known about the role of the epigenome in this process. Using prostate cancer cell lines with differing sensitivities to radiation treatment, we analysed the DNA methylation profiles prior to and following a single dose of radiotherapy (RT) using the Illumina Infinium HumanMethylation450 BeadChip platform. DSB formation and repair, in the absence and presence of the DNA hypomethylating agent, 5-azacytidine (5-AzaC), were also investigated using γH2A.X immunofluorescence staining. Here we demonstrate that DNA methylation is generally stable following a single dose of RT; however, a small number of CpG sites are stably altered up to 14 d following exposure. While the radioresistant and radiosensitive cells displayed distinct basal DNA methylation profiles, their susceptibility to DNA damage appeared similar demonstrating that basal DNA methylation has a limited influence on DSB induction at the regions examined. Recovery from DSB induction was also similar between these cells. Treatment with 5-AzaC did not sensitize resistant cells to DNA damage, but rather delayed recruitment of phosphorylated BRCA1 (S1423) and repair of DSBs. These results highlight that stable epigenetic changes are possible following a single dose of RT and may have significant clinical implications for cancer treatment involving recurrent or fractionated dosing regimens.

Radiation biology and oncology in the genomic era

Radiobiology research is building the foundation for applying genomics in precision radiation oncology. Advances in high-throughput approaches will underpin increased understanding of radiosensitivity and the development of future predictive assays for clinical application. There is an established contribution of genetics as a risk factor for radiotherapy side effects. An individual's radiosensitivity is an inherited polygenic trait with an architecture that includes rare mutations in a few genes that confer large effects and common variants in many genes with small effects. Current thinking is that some will be tissue specific, and future tests will be tailored to the normal tissues at risk. The relationship between normal and tumor cell radiosensitivity is poorly understood. Data are emerging suggesting interplay between germline genetic variation and epigenetic modification with growing evidence that changes in DNA methylation regulate the radiosensitivity of cancer cells and histone acetyltransferase inhibitors have radiosensitizing effects. Changes in histone methylation can also impair DNA damage response signaling and alter radiosensitivity. An important effort to advance radiobiology in the genomic era was establishment of the Radiogenomics Consortium to enable the creation of the large radiotherapy cohorts required to exploit advances in genomics. To address challenges in harmonizing data from multiple cohorts, the consortium established the REQUITE project to collect standardized data and genotyping for ~5,000 patients. The collection of detailed dosimetric data is important to produce validated multivariable models. Continued efforts will identify new genes that impact on radiosensitivity to generate new knowledge on toxicity pathogenesis and tests to incorporate into the clinical decision-making process.

A novel DNA methylation panel accurately detects colorectal cancer independently of molecular pathway

Background

Colorectal cancer (CRC) is one of the most incident cancers, associated with significant morbidity and mortality, and usually classified into three main molecular pathways: chromosomal instability, microsatellite instability (MSI) and CpG island methylator phenotype (CIMP). Currently, available screening methods are either costly or of limited specificity, impairing global implementation. More cost-effective strategies, including DNA methylation-based tests, might prove advantageous. Although some are already available, its performance is suboptimal, entailing the need for better candidate biomarkers. Herein, we tested whether combined use of APC, IGF2, MGMT, RASSF1A, and SEPT9 promoter methylation might accurately detect CRC irrespective of molecular subtype.

Methods

Selected genes were validated using formalin-fixed paraffin-embedded tissues from 214 CRC and 50 non-malignant colorectal mucosae (CRN). Promoter methylation levels were assessed using real-time quantitative methylation-specific PCR. MSI and CIMP status were determined. Molecular data were correlated with standard clinicopathological features. Diagnostic and prognostic performances were evaluated by receiver operator characteristics curve and survival analyses, respectively.

Results

Except for IGF2, promoter methylation levels were significantly higher in CRC compared to CRN. A three-gene panel (MGMT, RASSF1A, SEPT9) identified malignancy with 96.6% sensitivity, 74.0% specificity and 91.5 positive predictive value (area under the curve: 0.97), independently of tumor location, stage, and molecular pathway.

Conclusions

Combined promoter methylation analysis of MGMT/RASSF1A/SEPT9 displays a better performance than currently available epigenetic-based biomarkers for CRC, providing the basis for the development of a non-invasive assay to detect CRC irrespective of the molecular pathway.

Electronic supplementary material

The online version of this article (10.1186/s12967-018-1415-9) contains supplementary material, which is available to authorized users.

Methylation of promoter of RBL1 enhances the radioresistance of three dimensional cultured carcinoma cells

Three dimensional (3D) culture in vitro is a new cell culture model that more closely mimics the physiology features of the in vivo environment and is being used widely in the field of medical and biological research. It has been demonstrated that cancer cells cultured in 3D matrices are more radioresistant compared with cells in monolayer (2D). However, the mechanisms causing this difference remain largely unclear. Here we found that the cell cycle distribution and expression of cell cycle regulation genes in 3D A549 cells are different from the 2D. The higher levels of the promotor methylation of cell cycle regulation genes such as RBL1 were observed in 3D A549 cells compared with cells in 2D. The treatments of irradiation or 5-Aza-CdR activated the demethylation of RBL1 promotor and resulted in the increased expression of RBL1 only in 3D A549 cells. Inhibition of RBL1 enhanced the radioresistance and decreased the G2/M phase arrest induced by irradiation in 2D A549 and MCF7 cells. Overexpression of RBL1 sensitized 3D cultured A549 and MCF7 cells to irradiation. Taken together, to our knowledge, it is the first time to revealthat the low expression of RBL1 due to itself promotor methylation in 3D cells enhances the radioresistance. Our finding sheds a new light on understanding the features of the 3D cultured cell model and its application in basic research into cancer radiotherapy and medcine development.

Impact of DNA and RNA Methylation on Radiobiology and Cancer Progression

Radiotherapy is a well-established regimen for nearly half the cancer patients worldwide. However, not all cancer patients respond to irradiation treatment, and radioresistance is highly associated with poor prognosis and risk of recurrence. Elucidation of the biological characteristics of radioresistance and development of effective prognostic markers to guide clinical decision making clearly remain an urgent medical requirement. In tumorigenic and radioresistant cancer cell populations, phenotypic switch is observed during the course of irradiation treatment, which is associated with both stable genetic and epigenetic changes. While the importance of epigenetic changes is widely accepted, the irradiation-triggered specific epigenetic alterations at the molecular level are incompletely defined. The present review provides a summary of current studies on the molecular functions of DNA and RNA m⁶A methylation, the key epigenetic mechanisms involved in regulating the expression of genetic information, in resistance to irradiation and cancer progression. We additionally discuss the effects of DNA methylation and RNA N⁶-methyladenosine (m⁶A) of specific genes in cancer progression, recurrence, and radioresistance. As epigenetic alterations could be reversed by drug treatment or inhibition of specific genes, they are also considered potential targets for anticancer therapy and/or radiotherapy sensitizers. The mechanisms of irradiation-induced alterations in DNA and RNA m⁶A methylation, and ways in which this understanding can be applied clinically, including utilization of methylation patterns as prognostic markers for cancer radiotherapy and their manipulation for anticancer therapy or use as radiotherapy sensitizers, have been further discussed.

The clinical value of aberrant epigenetic changes of DNA damage repair genes in human cancer

The stability and integrity of the human genome are maintained by the DNA damage repair (DDR) system. Unrepaired DNA damage is a major source of potentially mutagenic lesions that drive carcinogenesis. In addition to gene mutation, DNA methylation occurs more frequently in DDR genes in human cancer. Thus, DNA methylation may play more important roles in DNA damage repair genes to drive carcinogenesis. Aberrant methylation patterns in DNA damage repair genes may serve as predictive, diagnostic, prognostic and chemosensitive markers of human cancer. MGMT methylation is a marker for poor prognosis in human glioma, while, MGMT methylation is a sensitive marker of glioma cells to alkylating agents. Aberrant epigenetic changes in DNA damage repair genes may serve as therapeutic targets. Treatment of MLH1-methylated colon cancer cell lines with the demethylating agent 5′-aza-2′-deoxycytidine induces the expression of MLH1 and sensitizes cancer cells to 5-fluorouracil. Synthetic lethality is a more exciting approach in patients with DDR defects. PARP inhibitors are the most effective anticancer reagents in BRCA-deficient cancer cells.

DNA Methylation in Radiation-Induced Carcinogenesis: Experimental Evidence and Clinical Perspectives

Ionizing radiation is a valuable tool in many spheres of human life. At the same time, it is a genotoxic agent with a well-established carcinogenic potential. Progress achieved in the last two decades has demonstrated convincingly that ionizing radiation can also target the cellular epigenome. Epigenetics is defined as heritable changes in the expression of genes that are not due to alterations of DNA sequence but consist of specific covalent modifications of chromatin components, such as methylation of DNA, histone modifications, and control performed by non-coding RNAs. Accumulating evidence suggests that DNA methylation, a key epigenetic mechanism involved in the control of expression of genetic information, may serve as one of the driving mechanisms of radiation-induced carcinogenesis. Here, we review the literature on the effects of ionizing radiation on DNA methylation in various biological systems, discuss the role of DNA methylation in radiation carcinogenesis, and provide our opinion on the potential utilization of this knowledge in radiation oncology.

Effects of ionizing radiation on DNA methylation: from experimental biology to clinical applications

PURPOSE

Ionizing radiation (IR) is a ubiquitous environmental stressor with genotoxic and epigenotoxic capabilities. Terrestrial IR, predominantly a low-linear energy transfer (LET) radiation, is being widely utilized in medicine, as well as in multiple industrial applications. Additionally, an interest in understanding the effects of high-LET irradiation is emerging due to the potential of exposure during space missions and the growing utilization of high-LET radiation in medicine.

CONCLUSIONS

In this review, we summarize the current knowledge of the effects of IR on DNA methylation, a key epigenetic mechanism regulating the expression of genetic information. We discuss global, repetitive elements and gene-specific DNA methylation in light of exposure to high and low doses of high- or low-LET IR, fractionated IR exposure, and bystander effects. Finally, we describe the mechanisms of IR-induced alterations to DNA methylation and discuss ways in which that understanding can be applied clinically, including utilization of DNA methylation as a predictor of response to radiotherapy and in the manipulation of DNA methylation patterns for tumor radiosensitization.

Analysis of DNA methylation and gene expression in radiation-resistant head and neck tumors

Resistance to radiation therapy constitutes a significant challenge in the treatment of head and neck squamous cell cancer (HNSCC). Alteration in DNA methylation is thought to play a role in this resistance. Here, we analyzed DNA methylation changes in a matched model of radiation resistance for HNSCC using the Illumina HumanMethylation450 BeadChip. Our results show that compared to radiation-sensitive cells (SCC-61), radiation-resistant cells (rSCC-61) had a significant increase in DNA methylation. After combining these results with microarray gene expression data, we identified 84 differentially methylated and expressed genes between these 2 cell lines. Ingenuity Pathway Analysis revealed ILK signaling, glucocorticoid receptor signaling, fatty acid α-oxidation, and cell cycle regulation as top canonical pathways associated with radiation resistance. Validation studies focused on CCND2, a protein involved in cell cycle regulation, which was identified as hypermethylated in the promoter region and downregulated in rSCC-61 relative to SCC-61 cells. Treatment of rSCC-61 and SCC-61 with the DNA hypomethylating agent 5-aza-2'deoxycitidine increased CCND2 levels only in rSCC-61 cells, while treatment with the control reagent cytosine arabinoside did not influence the expression of this gene. Further analysis of HNSCC data from The Cancer Genome Atlas found increased methylation in radiation-resistant tumors, consistent with the cell culture data. Our findings point to global DNA methylation status as a biomarker of radiation resistance in HNSCC, and suggest a need for targeted manipulation of DNA methylation to increase radiation response in HNSCC.

A comprehensive analysis of radiosensitization targets; functional inhibition of DNA methyltransferase 3B radiosensitizes by disrupting DNA damage regulation

A comprehensive genome-wide screen of radiosensitization targets in HeLa cells was performed using a shRNA-library/functional cluster analysis and DNMT3B was identified as a candidate target. DNMT3B RNAi increased the sensitivity of HeLa, A549 and HCT116 cells to both γ-irradiation and carbon-ion beam irradiation. DNMT3B RNAi reduced the activation of DNA damage responses induced by γ-irradiation, including HP1β-, γH2AX- and Rad51-foci formation. DNMT3B RNAi impaired damage-dependent H2AX accumulation and showed a reduced level of γH2AX induction after γ-irradiation. DNMT3B interacted with HP1β in non-irradiated conditions, whereas irradiation abrogated the DNMT3B/HP1β complex but induced interaction between DNMT3B and H2AX. Consistent with radiosensitization, TP63, BAX, PUMA and NOXA expression was induced after γ-irradiation in DNMT3B knockdown cells. Together with the observation that H2AX overexpression canceled radiosensitization by DNMT3B RNAi, these results suggest that DNMT3B RNAi induced radiosensitization through impairment of damage-dependent HP1β foci formation and efficient γH2AX-induction mechanisms including H2AX accumulation. Enhanced radiosensitivity by DNMT3B RNAi was also observed in a tumor xenograft model. Taken together, the current study implies that comprehensive screening accompanied by a cluster analysis enabled the identification of radiosensitization targets. Downregulation of DNMT3B, one of the targets identified using this method, radiosensitizes cancer cells by disturbing multiple DNA damage responses.

DNA methylome analysis identifies epigenetic silencing of FHIT as a determining factor for radiosensitivity in oral cancer: an outcome-predicting and treatment-implicating study

Radioresistance is still an emerging problem for radiotherapy of oral cancer. Aberrant epigenetic alterations play an important role in cancer development, yet the role of such alterations in radioresistance of oral cancer is not fully explored. Using a methylation microarray, we identified promoter hypermethylation of FHIT (fragile histidine triad) in radioresistant OML1-R cells, established from hypo-fractionated irradiation of parental OML1 radiosensitive oral cancer cells. Further analysis confirmed that transcriptional repression of FHIT was due to promoter hypermethylation, H3K27me3 and overexpression of methyltransferase EZH2 in OML1-R cells. Epigenetic interventions or depletion of EZH2 restored FHIT expression. Ectopic expression of FHIT inhibited tumor growth in both in vitro and in vivo models, while also resensitizing radioresistant cancer cells to irradiation, by restoring Chk2 phosphorylation and G2/M arrest. Clinically, promoter hypermethylation of FHIT inversely correlated with its expression and independently predicted both locoregional control and overall survival in 40 match-paired oral cancer patient samples. Further in vivo therapeutic experiments confirmed that inhibition of DNA methylation significantly resensitized radioresistant oral cancer cell xenograft tumors. These results show that epigenetic silencing of FHIT contributes partially to radioresistance and predicts clinical outcomes in irradiated oral cancer. The radiosensitizing effect of epigenetic interventions warrants further clinical investigation.

Potential of DNA methylation in rectal cancer as diagnostic and prognostic biomarkers

Background:

Aberrant DNA methylation is more prominent in proximal compared with distal colorectal cancers. Although a number of methylation markers were identified for colon cancer, yet few are available for rectal cancer.

Methods:

DNA methylation differences were assessed by a targeted DNA microarray for 360 marker candidates between 22 fresh frozen rectal tumour samples and 8 controls and validated by microfluidic high-throughput and methylation-sensitive qPCR in fresh frozen and formalin-fixed paraffin-embedded (FFPE) samples, respectively. The CpG island methylator phenotype (CIMP) was assessed by MethyLight in FFPE material from 78 patients with pT2 and pT3 rectal adenocarcinoma.

Results:

We identified and confirmed two novel three-gene signatures in fresh frozen samples that can distinguish tumours from adjacent tissue as well as from blood with a high sensitivity and specificity of up to 1 and an AUC of 1. In addition, methylation of individual CIMP markers was associated with specific clinical parameters such as tumour stage, therapy or patients' age. Methylation of CDKN2A was a negative prognostic factor for overall survival of patients.

Conclusions:

The newly defined methylation markers will be suitable for early disease detection and monitoring of rectal cancer.

Epigenetic DNA methylation in radiation biology: on the field or on the sidelines?

DNA methylation has been studied with regard to chemotherapeutics for a number of years. The radiation field has just begun to look at this in the context of radiotherapy or radiation exposure. So far, the data suggest that radiation induces epigenetic reprogramming which indicates a purposeful response that influences the cell fate or alters the response to future exposure. Further studies may result in discovery of biomarkers for radiotherapy outcome or prediction of the degree of radiation resistance. Past and ongoing development of DNMT1 inhibitors that lead to DNA hypomethylation appear to sensitize many tumor types to radiation and may be an area with long term clinical implications.

Review of the development of DNA methylation as a marker of response to neoadjuvant therapy and outcomes in rectal cancer

There is much debate around the preoperative treatment of colorectal cancer and, in particular, neoadjuvant chemoradiotherapy in locally advanced rectal cancer. This treatment carries a significant risk of harmful side effects and has a highly variable response rate. Predictive biomarkers have been the subject of a great deal of study with the aim of pretreatment risk stratification in order to more accurately determine which patients will derive the most benefit and least harm from these treatments. The study of epigenetics in colorectal cancer is relatively recent, and distinct patterns of aberrant DNA methylation, in particular the cytosine-phosphate-guanine (CpG) island methylator phenotype (CIMP), have been demonstrated in colorectal cancer, and their characterisation and significance are under debate, particularly in rectal cancer. These patterns of DNA methylation have been associated with differences in response to therapy and treatment outcomes and therefore have the potential to be used as biomarkers in tailored therapy regimes for patients with rectal cancer. This review aims to summarise the current state of the art in rectal cancer, with particular regard to the determination of DNA methylation patterns, the CpG island methylator phenotype and its potential as a novel biomarker in rectal cancer treatment and prediction of outcomes and response after neoadjuvant chemoradiotherapy.

Targeting chromatin to improve radiation response

Chromatin, the structure formed by the wrapping of approximately 146 base pairs of DNA around an octamer of histones, has a profound impact on numerous DNA-based processes. Chromatin modifications and chromatin remodellers have recently been implicated in important aspects of the DNA damage response including facilitating the initial sensing of the damage as well as subsequent recruitment of repair factors. Radiation is an effective cancer therapy for a large number of tumours, and there is considerable interest in finding approaches that might further increase the efficacy of radiotherapy. The use of radiation leads to the generation of DNA damage and, therefore, agents that can affect the sensing and repair of DNA damage may have an impact on overall radiation efficacy. The chromatin modifications as well as chromatin modifiers that have been associated with the DNA damage response will be summarized in this review. An emphasis will be placed on those processes that can be pharmacologically manipulated with currently available inhibitors. The rationale for the use of these inhibitors in combination with radiation will also be described.

Identification of radiation-induced aberrant hypomethylation in colon cancer

Background

Exposure to ionizing radiation (IR) results in the simultaneous activation or downregulation of multiple signaling pathways that play critical roles in cell type-specific control of survival or death. IR is a well-known genotoxic agent and human carcinogen that induces cellular damage through direct and indirect mechanisms. However, its impact on epigenetic mechanisms has not been elucidated, and more specifically, little information is available regarding genome-wide DNA methylation changes in cancer cells after IR exposure. Recently, genome-wide DNA methylation profiling technology using the Illumina HumanMethylation450K platform has emerged that allows us to query >450,000 loci within the genome. This improved technology is capable of identifying genome-wide DNA methylation changes in CpG islands and other CpG island-associated regions.

Results

In this study, we employed this technology to test the hypothesis that exposure to IR not only induces differential DNA methylation patterns at a genome-wide level, but also results in locus- and gene-specific DNA methylation changes. We screened for differential DNA methylation changes in colorectal cancer cells after IR exposure with 2 and 5 Gy. Twenty-nine genes showed radiation-induced hypomethylation in colon cancer cells, and of those, seven genes showed a corresponding increase in gene expression by reverse transcriptase polymerase chain reaction (RT-PCR). In addition, we performed chromatin immunoprecipitation (ChIP) to confirm that the DNA-methyltransferase 1 (DNMT1) level associated with the promoter regions of these genes correlated with their methylation level and gene expression changes. Finally, we used a gene ontology (GO) database to show that a handful of hypomethylated genes induced by IR are associated with a variety of biological pathways related to cancer.

Conclusion

We identified alterations in global DNA methylation patterns and hypomethylation at specific cancer-related genes following IR exposure, which suggests that radiation exposure plays a critical role in conferring epigenetic alterations in cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1229-6) contains supplementary material, which is available to authorized users.

Combination effect of epigenetic regulation and ionizing radiation in colorectal cancer cells

Exposure of cells to ionizing radiation (IR) induces, not only, activation of multiple signaling pathways that play critical roles in cell fate determination, but also alteration of molecular pathways involved in cell death or survival. Recently, DNA methylation has been established as a critical epigenetic process involved in the regulation of gene expression in cancer cells, suggesting that DNA methylation inhibition may be an effective cancer treatment strategy. Because alterations of gene expression by DNA methylation have been considered to influence radioresponsiveness, we investigated the effect of a DNA methyltransferase inhibitor, 5-aza-2'-deoxycytidine (5-aza-dC), on radiosensitivity. In addition, we investigated the underlying cellular mechanisms of combination treatments of ionizing irradiation (IR) and 5-aza-dC in human colon cancer cells. Colon cancer cell lines were initially tested for radiation sensitivity by IR in vitro and were treated with two different doses of 5-aza-dC. Survival of these cell lines was measured using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) and clonogenic assays. The effects of 5-aza-dC along with irradiation on cell growth, cell cycle distribution, apoptosis, and apoptosis-related gene expression were examined. Combination irradiation treatment with 5-aza-dC significantly decreased growth activity compared with irradiation treatment alone or with 5-aza-dC treatment alone. The percentage of HCT116 cells in the sub-G1 phase and their apoptotic rate was increased when cells were treated with irradiation in combination with 5-aza-dC compared with either treatment alone. These observations were strongly supported by increased caspase activity, increased comet tails using comet assays, and increased protein levels of apoptosis-associated molecules (caspase 3/9, cleaved PARP). Our data demonstrated that 5-aza-dC enhanced radiosensitivity in colon cancer cells, and the combination effects of 5-aza-dC with radiation showed greater cellular effects than that of single treatment, suggesting that the combination of 5-aza-dC and radiation has the potential to become a clinical strategy for the treatment of cancer.

Epigenetics in radiation-induced fibrosis

Radiotherapy is a major cancer treatment option but dose-limiting side effects such as late-onset fibrosis in the irradiated tissue severely impair quality of life in cancer survivors. Efforts to explain radiation-induced fibrosis, for example, by genetic variation remained largely inconclusive. Recently published molecular analyses on radiation response and fibrogenesis showed a prominent role of epigenetic gene regulation. This review summarizes the current knowledge on epigenetic modifications in fibrotic disease and radiation response, and it points out the important role for epigenetic mechanisms such as DNA methylation, microRNAs and histone modifications in the development of this disease. The synopsis illustrates the complexity of radiation-induced fibrosis and reveals the need for investigations to further unravel its molecular mechanisms. Importantly, epigenetic changes are long-term determinants of gene expression and can therefore support those mechanisms that induce and perpetuate fibrogenesis even in the absence of the initial damaging stimulus. Future work must comprise the interconnection of acute radiation response and long-lasting epigenetic effects in order to assess their role in late-onset radiation fibrosis. An improved understanding of the underlying biology is fundamental to better comprehend the origin of this disease and to improve both preventive and therapeutic strategies.

5-Azacytidine enhances the radiosensitivity of CNE2 and SUNE1 cells in vitro and in vivo possibly by altering DNA methylation

The radioresistance of tumor cells remains a major cause of treatment failure in nasopharyngeal carcinoma (NPC). Recently, several reports have highlighted the importance of epigenetic changes in radiation-induced responses. Here, we investigated whether the demethylating agent 5-azacytidine (5-azaC) enhances the radiosensitivity of NPC cells. The NPC cell lines CNE2 and SUNE1 were treated with 1 μmol/L 5-azaC for 24 h before irradiation (IR); clonogenic survival was then assessed. Tumor growth was investigated in a mouse xenograft model in vivo. The apoptosis, cell cycle progression and DNA damage repair were examined using flow cytometry, immunofluorescent staining and western blotting. Promoter methylation and the expression of four genes epigenetically silenced during the development of NPC were evaluated by pyrosequencing and real-time PCR. We found that pretreatment with 5-azaC significantly decreased clonogenic survival after IR compared to IR alone; the sensitivity-enhancement ratio of 5-azaC was 1.4 and 1.2 for CNE2 and SUNE1 cells, respectively. The combined administration of 5-azaC and IR significantly inhibited tumor growth in the mouse xenograft model, and enhanced radiation-induced apoptosis in vitro compared to 5-azaC alone or IR alone. 5-AzaC also decreased promoter methylation and upregulated the expression of genes which are epigenetically silenced both in vitro and in vivo in NPC. Thus, 5-azaC enhance the radiosensitivity of both the CNE2 and SUNE1 cell lines, possibly by altering DNA methylation levels and increasing the ability of irradiated cells to undergo apoptosis. The use of 5-azaC combined with IR maybe represent an attractive strategy for the treatment of NPC.

Gene methylation in rectal cancer: predictive marker of response to chemoradiotherapy?

Although numerous studies have focused on the link between CpG island methylator phenotypes and the development of colorectal cancer, few studies have dealt specifically with methylation profiling in rectal cancer and its role in predicting response to neoadjuvant chemoradiotherapy (NCRT). We characterized methylation profiles in normal and neoplastic tissue samples from patients with rectal cancer and assessed the role of this molecular profile in predicting chemoradioactivity. We evaluated 74 pretreatment tumor samples and 16 apparently normal tissue biopsies from rectal cancer patients submitted to NCRT. The methylation profile of 24 different tumor suppressor genes was analyzed from FFPE samples by methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA). Methylation status was studied in relation to tissue type and clinical pathological parameters, in particular, pathological response evaluated by tumor regression grade (TRG). ESR1, CDH13, RARB, IGSF4, and APC genes showed high methylation levels in tumor samples (range 18.92-49.77) with respect to normal tissue. Methylation levels of the remaining genes were low and similar in both normal (range 1.91-14.56) and tumor tissue (range 1.84-11). Analysis of the association between methylation and response to therapy in tumor samples showed that only TIMP3 methylation status differed significantly within the four TRG classes (ANOVA, P < 0.05). Results from the present explorative study suggest that quantitative epigenetic classification of rectal cancer by MS-MLPA clearly distinguishes tumor tissue from apparently normal mucosa. Conversely, with the exception of TIMP3 gene, the methylation of selected genes does not seem to correlate with response to NCRT.

Role of DNA methylation in long-term low-dose γ-rays induced adaptive response in human B lymphoblast cells

PURPOSE

With widespread use of ionizing radiation, more attention has been attracted to low-dose radiation (LDR); however, the mechanisms of long-term LDR-induced bio-effects are unclear. Here, we applied human B lymphoblast cell line HMy2.CIR to monitor the effects of long-term LDR and the potential involvement of DNA methylation.

MATERIALS AND METHODS

HMy2.CIR cells were irradiated with 0.032 Gy γ-rays three times per week for 1-4 weeks. Some of these primed cells were further challenged with 2 Gy γ-rays. Cell proliferation, micronuclei formation, gene expression of DNA methyltransferases (DNMT), levels of global genomic DNA methylation and protein expression of methyl CpG binding protein 2 (MeCP2) and heterochromatin protein-1 (HP1) were measured.

RESULTS

Long-term LDR enhanced cell proliferation and clonogenicity and triggered a cellular adaptive response (AR). Furthermore, global genomic DNA methylation was increased in HMy2.CIR cells after long-term LDR, accompanied with an increase of gene expression of DNMT1 and protein expression of MeCP2 and HP1. After treatment with 5-aza-2'-deoxycytidine (5-aza-dC), a DNA methyltransferase inhibitor, the long-term LDR-induced global genomic DNA hypermethylation was decreased and the AR was eliminated.

CONCLUSION

Global genomic DNA hypermethylation accompanied with increases of DNMT1 and MeCP2 expression and heterochromatin formation might be involved in long-term LDR-induced adaptive response.

Epigenetics meets radiation biology as a new approach in cancer treatment

Cancer is a disease that results from both genetic and epigenetic changes. In recent decades, a number of people have investigated the disparities in gene expression resulting from variable DNA methylation alteration and chromatin structure modification in response to the environment. Especially, colon cancer is a great model system for investigating the epigenetic mechanism for aberrant gene expression alteration. Ionizing radiation (IR) could affect a variety of processes within exposed cells and, in particular, cause changes in gene expression, disruption of cell cycle arrest, and apoptotic cell death. Even though there is growing evidence on the importance of epigenetics and biological processes induced by radiation exposure in various cancer types including colon cancer, specific epigenetic alterations induced by radiation at the molecular level are incompletely defined. This review focuses on discussing possible IR-mediated changes of DNA methylation and histone modification in cancer.

Radiation-induced epigenetic DNA methylation modification of radiation-response pathways

DNA methylation can regulate gene expression and has been shown to modulate cancer cell biology and chemotherapy resistance. Therapeutic radiation results in a biological response to counter the subsequent DNA damage and genomic stress in order to avoid cell death. In this study, we analyzed DNA methylation changes at>450,000 loci to determine a potential epigenetic response to ionizing radiation in MDA-MB-231 cells. Cells were irradiated at 2 and 6 Gy and analyzed at 7 time points from 1-72 h. Significantly differentially methylated genes were enriched in gene ontology categories relating to cell cycle, DNA repair, and apoptosis pathways. The degree of differential methylation of these pathways varied with radiation dose and time post-irradiation in a manner consistent with classical biological responses to radiation. A cell cycle arrest was observed 24 h post-irradiation and DNA damage, as measured by γH2AX, resolved at 24 h. In addition, cells showed low levels of apoptosis 2-48 h post-6 Gy and cellular senescence became significant at 72 h post-irradiation. These DNA methylation changes suggest an epigenetic role in the cellular response to radiation.

PITX2: a promising predictive biomarker of patients' prognosis and chemoradioresistance in esophageal squamous cell carcinoma

The paired-like homeodomain transcription factor 2 (PITX2), a downstream effector of wnt/β-catenin signaling, is well known to play critical role during normal embryonic development. However, the possible involvement of PITX2 in human tumorigenesis remains unclear. In this study, we extend its function in human esophageal squamous cell carcinoma (ESCC). The real-time PCR, Western blotting and immunohistochemistry (IHC) methods were applied to examine expression pattern of PITX2 in two different cohorts of ESCC cases treated with definitive chemoradiotherapy (CRT). Receiver operating characteristic (ROC) curve analysis was used to determine the cutoff point for PITX2 high expression in the training cohort. The ROC-derived cutoff point was then subjected to analyze the association of PITX2 expression with patients' survival and clinical characteristics in training and validation cohort, respectively. The expression level of PITX2 was significantly higher in ESCCs than that in normal esophageal mucosa. There was a positive correlation between PITX2 expression and clinical aggressiveness of ESCC. Importantly, high expression of PITX2 was observed more frequently in CRT resistant group than that in CRT effective group (p < 0.05). Furthermore, high expression of PITX2 was associated with poor disease-specific survival (p < 0.05) in ESCC. Then, the MTS, clonogenic survival fraction and cell apoptosis experiments showed that knockdown of PITX2 substantially increased ESCC cells sensitivity to ionizing radiation (IR) or cisplatin in vitro. Thus, the expression of PITX2, as detected by IHC, may be a useful tool for predicting CRT resistance and serves as an independent molecular marker for poor prognosis of ESCC patients treated with definite CRT.

DNMT (DNA methyltransferase) inhibitors radiosensitize human cancer cells by suppressing DNA repair activity

BACKGROUND

Histone modifications and DNA methylation are two major factors in epigenetic phenomenon. Unlike the histone deacetylase inhibitors, which are known to exert radiosensitizing effects, there have only been a few studies thus far concerning the role of DNA methyltransferase (DNMT) inhibitors as radiosensitizers. The principal objective of this study was to evaluate the effects of DNMT inhibitors on the radiosensitivity of human cancer cell lines, and to elucidate the mechanisms relevant to that process.

METHODS

A549 (lung cancer) and U373MG (glioblastoma) cells were exposed to radiation with or without six DNMT inhibitors (5-azacytidine, 5-aza-2'-deoxycytidine, zebularine, hydralazine, epigallocatechin gallate, and psammaplin A) for 18 hours prior to radiation, after which cell survival was evaluated via clonogenic assays. Cell cycle and apoptosis were analyzed via flow cytometry. Expressions of DNMT1, 3A/3B, and cleaved caspase-3 were detected via Western blotting. Expression of γH2AX, a marker of radiation-induced DNA double-strand break, was examined by immunocytochemistry.

RESULTS

Pretreatment with psammaplin A, 5-aza-2'-deoxycytidine, and zebularine radiosensitized both A549 and U373MG cells. Pretreatment with psammaplin A increased the sub-G1 fraction of A549 cells, as compared to cells exposed to radiation alone. Prolongation of γH2AX expression was observed in the cells treated with DNMT inhibitors prior to radiation as compared with those treated by radiation alone.

CONCLUSIONS

Psammaplin A, 5-aza-2'-deoxycytidine, and zebularine induce radiosensitivity in both A549 and U373MG cell lines, and suggest that this effect might be associated with the inhibition of DNA repair.

Epigenetics in ovarian cancer

Ovarian cancer is the most lethal gynecological cancer. Due to few early symptoms and a lack of early detection strategies, most patients are diagnosed with advanced-stage disease. Most of these patients, although initially responsive, eventually develop drug resistance. In this chapter, epigenetic changes in ovarian cancer are described. Various epigenetic changes including CpG island methylation and histone modification have been identified in ovarian cancer. These aberrations are associated with distinct disease subtypes and present in circulating serum of ovarian cancer patients. Several epigenetic changes have shown promise for their diagnostic, prognostic, and predictive capacity but still need further validation.In contrast to DNA mutations and deletions, epigenetic modifications are potentially reversible by epigenetic therapies. Promising preclinical studies show epigenetic drugs to enhance gene re-expression and drug sensitivity in ovarian cancer cell lines and animal models.

CD44 is a biomarker associated with human prostate cancer radiation sensitivity

CD44 plays an important role in cancer metastasis, chemotherapy, and radiation resistance. The present study investigated the relationship of CD44 expression and radioresistance, and the potential mechanisms of CD44 in radiosensitivity using prostate cancer (CaP) cell lines. CD44 was knocked down in three CaP cell lines (PC-3, PC-3M-luc, and LNCaP) using small interfering RNA (siRNA) and clonogenic survival fractions after single dose irradiation were compared before and after CD44 knocking down (KD). The effect of radiation on cell cycle distribution was examined by flow cytometry and the cell cycle-related protein levels of phospho-Chk1 and phospho-Chk2 were ascertained by Western blotting. The expression of the DNA double strand break (DSB) marker-γH2AX was also quantified by immunofluorescence staining. Our results indicate that the down-regulation of CD44 enhanced radiosensitivity in PC-3, PC-3M-luc, and LNCaP CaP cells, the sensitizing enhancement ratio for these cell lines was 2.3, 1.3, and 1.5, respectively and that the delay of DNA DSB repair in low CD44-expressing KD CaP cells correlated with ineffective cell cycle arrest and the delayed phosphorylation of Chk1 and Chk2. These findings suggest that CD44 may be a valuable biomarker and a predictor of radiosensitivity in CaP treatment.

Continuous and low-energy 125I seed irradiation changes DNA methyltransferases expression patterns and inhibits pancreatic cancer tumor growth

BACKGROUND

Iodine 125 (125I) seed irradiation is an effective treatment for unresectable pancreatic cancers. However, the radiobiological mechanisms underlying brachytherapy remain unclear. Therefore, we investigated the influence of continuous and low-energy 125I irradiation on apoptosis, expression of DNA methyltransferases (DNMTs) and cell growth in pancreatic cancers.

MATERIALS AND METHODS

For in vitro 125I seed irradiation, SW-1990 cells were divided into three groups: control (0 Gy), 2 Gy, and 4 Gy. To create an animal model of pancreatic cancer, the SW 1990 cells were surgically implanted into the mouse pancreas. At 10 d post-implantation, the 30 mice with pancreatic cancer underwent 125I seed implantation and were separated into three groups: 0 Gy, 2 Gy, and 4 Gy group. At 48 or 72 h after irradiation, apoptosis was detected by flow cytometry; changes in DNMTs mRNA and protein expression were assessed by real-time PCR and western blotting analysis, respectively. At 28 d after 125I seed implantation, in vivo apoptosis was evaluated with TUNEL staining, while DNMTs protein expression was detected with immunohistochemical staining. The tumor volume was measured 0 and 28 d after 125I seed implantation.

RESULTS

125I seed irradiation induced significant apoptosis, especially at 4 Gy. DNMT1 and DNMT3b mRNA and protein expression were substantially higher in the 2 Gy group than in the control group. Conversely, the 4 Gy cell group exhibited significantly decreased DNMT3b mRNA and protein expression relative to the control group. There were substantially more TUNEL positive in the 125I seed implantation treatment group than in the control group, especially at 4 Gy. The 4 Gy seed implantation group showed weaker staining for DNMT1 and DNMT3b protein relative to the control group. Consequently, 125I seed implantation inhibited cancer growth and reduced cancer volume.

CONCLUSION

125I seed implantation kills pancreatic cancer cells, especially at 4 Gy. 125I-induced apoptosis and changes in DNMT1 and DNMT3b expression suggest potential mechanisms underlying effective brachytherapy.