Fractionated radiotherapy might induce epithelial‐mesenchymal transition and radioresistance in a cellular context manner

Abstract

Despite the fact that radiotherapy is a main therapeutic modality in cancer treatment, recent evidence suggests that fractionated radiotherapy (FR) might confer radioresistance through epithelial‐mesenchymal transition (EMT). Nevertheless, the effects of FR on EMT phenotype and the potential link between EMT induction and radioresistance development yet to be clarified. The aim of this study was to assess whether FR could promote EMT, and to elucidate if induction of EMT contributes to the acquisition of radioresistance. To this end, two human cancer cell lines (A549 and HT‐29) were irradiated (2 Gy/day) and analyzed using wound healing, transwell migration and invasion assays, real‐time polymerase chain reaction (for E‐cadherin, N‐cadherin, Vimentin, CD44, CD133, Snail, and Twist), clonogenic assay, Annexin V/PI, and 3‐[4,5‐dimethylthiazol‐2‐yl]‐2,5 diphenyl tetrazolium bromide (MTT) assay. Irradiation of A549 (for 5 or 10 consecutive days) resulted in morphological changes including elongation of cytoplasm and nuclei and pleomorphic nuclei. Also, irradiation‐enhanced migratory and invasive potential of A549. These phenotypic changes were in agreement with decreased expression of the epithelial marker (E‐cadherin), enhanced expression of mesenchymal markers (N‐cadherin, Vimentin, Snail, and Twist) and increased stemness factors (CD44 and CD133). Moreover, induction of EMT phenotype was accompanied with enhanced radioresistance and proliferation of irradiated A549. However, FR (for 5 consecutive days) did not increase HT‐29 motility. Furthermore, molecular alterations did not resemble EMT phenotype (downregulation of E‐cadherin, Vimentin, ALDH, CD44, CD133, and Snail). Eventually, FR led to enhanced radiosensitivity and decreased proliferation of HT‐29. Altogether, our findings suggest that FR might induce EMT and confer radioresistance in a cell context‐dependent manner.

Investigation the Effect of Low, Medium and High Dose of X-Radiation on the Expression of E-cadherin in Colorectal Cancer Cell Line

“…Although our data show no significant changes in the expression of E-cadherin, it does not necessarily mean that radiation does not promote invasiveness and metastatic potential in cancer cells, due to the fact that the change of E-cadherin gene is not the just activator of cell migration and invasion. Moreover, according to Ikeguch et al, and Akimoto et al, there is a complex process behind the expression of Ecadherin in metastatic foci of colorectal cancer cells, which might lead to E-cadherin overexpression with negative function [17][18][19][20][21][22][23][24][25][26][27]. In addition, according to molecular studies, Wnt/ βcatenin, STAT3 and ZEB1 are reported as the most important signaling pathways associated with E-cadherin expression in colorectal cancer cells [12,28].…”

“…Radiotherapy is one of the most important modalities for cancer treatment. However, according to recent clinical and experimental studies, ionizing radiation might induce invasion and enhance metastasis potential in cancer cells [3,8,19,20,23,24]. Moreover, recent studies have demonstrated that changes undergoing in cell-cell adhesion and cell-extracellular matrix interaction in post-irradiated tumor cells might cause them to loss their epithelial characters and acquire mesenchymal morphology which lead to enhanced potential for migration, invasion and metastasis [9,18,22].…”

“…Regarding the two different irradiation regimens used in the two studies, different changes in E-cadherin gene expression in HT-29 cell line, may be explained. We irradiated the cells with single doses of 0.1, 2.5, 5, and 10 Gy, while, they applied fractionated irradiation regimen (cumulative doses of 10 and 20 Gy with 2 Gy/day fractions) [19]. There are more evidence that fractionated radiation has rendered reduced expression of E-cadherin gene.…”

Potential role of exosomes in cancer therapy

“…Radiotherapy is an essential modality that can be implemented at various phases in the cancer treatment process; 59 approximately 50% of cancer patients annually receive radiotherapy either alone or in combination with other modalities. 60 Radioresistance in cancer cells causes recurrence of diseases and treatment failure, which is a major clinical obstacle for the treatment by radiotherapy. 61,62 Exosomes modulate the radioresistance of head and neck cancer cells, as indicated by higher overall survival and accelerated DNA repair in cells treated with exosomes isolated from irradiated cells.…”

“…Radiotherapy is an essential modality that can be implemented at various phases in the cancer treatment process; approximately 50% of cancer patients annually receive radiotherapy either alone or in combination with other modalities . Radioresistance in cancer cells causes recurrence of diseases and treatment failure, which is a major clinical obstacle for the treatment by radiotherapy .…”