A methylation is one of the important approaches for regulation of gene expression. It plays a role in tumor development and progression and is closely associated with the radiosensitivity of cancer cells. The aberrant DNA methylation in cancer cells can provide biomarkers for early diagnosis of cancer. Moreover, it can contribute to the evaluation of the efficacy of radiotherapy, radiosensitivity enhancement, prognostic assessment, and disease monitoring. In order to provide a theoretical basis for further investigation of the epigenetic mechanisms for radioresistance of cancer cells, this paper reviews the relationship between DNA methylation and radiosensitivity and the potential value of DNA methylation in radiotherapy.

Objective To investigate the role of cancer stem cells in radiation resistance of esophageal cancer and its molecular mechanism, and to provide a theoretical basis for radiotherapy for esophageal cancer.Methods Esophageal cancer cell line TE1 was treated with 8 Gy of radiation. Esophageal cancer cell line with resistance to radiation, TE1-res, was established and screened.Cell counting was used to evaluate cell proliferation.Flow cytometry was used to determine the expression of CD44 (high) CD24(-) CD133(+) and apoptosis in cells.The colony formation assay was used to determine the colony-forming rate and cell survival curve.Bisulfite sequencing PCR was used to determine the methylation status of cancer suppressor genes.Comparison of the data was made by group t test or analysis of variance. Results Compared with TE1 cells, TE1-res cells had significantly enhanced proliferation, a significantly higher proportion of CD44( high) CD24(-) CD133(+) cells, and significantly enhanced resistance to apoptosis (mean value 20.84×105 vs.4.46×105/day, P=0.008;(38.0±2.9)%vs.(10.1±1.3)%, P=0.001;mean value 33.23% vs.10.50%, P=0.003 ) .After treatment with 8 Gy of radiation, TE1-res cells had significantly higher colony-forming rate and D0 value than TE1 cells ((14.3±2.6)%vs.(0.9±0.3)%, P=0.011;3.28 vs.2.19 Gy, P=0.125 ) .Moreover, the promoter methylation in cancer suppressor genes including SPINT2, CDKN1B, DKK1, TP53, and PPP2R1B was significantly enhanced in TE1-res cells than in TE1 cells ((89.7±4.9)%vs.(5.0±0.5)%, P=0.001;(92.3±4.7)%vs.(10.4±0.7)%, P=0.001;(90.7±3.7)%vs.(7.9±0.4)%, P=0.001;(83.4±5.7)%vs.(17.2±1.2)%, P=0.002;(90.2±
6.7)%vs.(4.4±1.2)%, P=0.002).Conclusions Cancer stem cells play an important role in radiation resistance of esophageal cancer. The resistance to radiation is closely associated with promoter hypermethylation in cancer suppressor genes including SPINT2, CDKN1B, DKK1, TP53, and PPP2R1B.

Objective To establish a radioresistant esophageal squamous cancer cell line,and to identify the radioresistant genes and mechanisms.Methods The radioresistant KYSE410-res cell line was established by repeated exposure of cell line KYSE410 to radiation.The proliferation and apoptosis of esophageal squamous cancer cells were evaluated before and after radiation.The changes in gene expression of the esophageal squamous cancer cells after radiation were determined by gene microarray and analyzed by group t test.The genes with significant difference in expression after radiation were validated.Results The KYSE410-res cells had significantly enhanced proliferation and anti-apoptosis than the KYSE410 cells (all P＜0.05).The result of gene microarray showed that compared with the KYSE410 cells,the KYSE410-res cells had the expression of 463 and 251 genes upregulated and downregulated by no less than 4 folds,respectively.Those genes with different expression levels after radiation were mainly responsible for cell proliferation,adhesion,signal transduction,angiogenesis,reactive oxygen metabolism,cell damage repair,and the MAPK/ERK signaling pathway.OAS2 and UBD were key proteins in the network.In the KYSE410-res cells,the expression of HLA-DQBI,MMP1,NCAM1,ZNF521,GPC6,SELENBP1,LCN15,and TFPI-2 genes measured by real-time PCR was consistent with that measured by gene microarray.Conclusions Abnormal activation of the MAPK/ERK signaling pathway,upregulated expression of OAS2 and UBD,downregulated expression of TFPI-2,and upregulated expression of MMPs may play a role in radioresistance of esophageal cancer cells.

To establish an injectable hydrogel containing Prussian blue (PB) nanospheres for photothermal therapy against cancer, PB nanospheres were prepared by one-pot synthesis and the thermosensitive Pluronic F127 was used as the hydrogel matrix. The PB nanospheres and the hydrogel were characterized by shape, particle size, serum stability, photothermal performance upon repeated 808 nm laser irradiation, as well as the rheological features. The effect of the PB nanospheres and the hydrogel were evaluated qualitatively and quantitatively in 4T1 mouse breast cancer cells. The retention, photothermal efficacy, therapeutic effects and systemic toxicity of the hydrogel were assessed in a tumor-bearing mouse model. The PB nanospheres had a diameter of about 150 nm and exhibited satisfactory serum stability, photo-heat convert ability and repeated laser exposure stability. The hydrogel encapsulation did not negatively influence the above features of the photothermal agent. The nanosphere-containing hydrogel showed a phase transition at body temperature and, as a result, a long retention time . The photothermal agent-embedded hydrogel displayed promising photothermal therapeutic effects in the tumor-bearing mouse model with little-to-no systemic toxicity after peritumoral administration.