Radiobiological characteristics of cancer stem cells from esophageal cancer cell lines

AIM:To study the cancer stem cell population in esophageal cancer cell lines KYSE-150 and TE-1 and identify whether the resulting stem-like spheroid cells display cancer stem cells and radiation resistance characteristics.METHODS:A serum-free medium(SFM)suspension was used to culture esophageal cancer stem cell lines and enrich the esophageal stem-like spheres.A reverse transcription polymerase chain reaction assay was used to detect stem cell gene expression in the spheroid cells.Radiosensitivity of stem-like spheres and parental cells were evaluated by clonogenic assays.Furthermore,different cells after different doses of irradiation were tested to evaluate the change in sphere formation,cell cycle and CD44+CD271+expression of tumor stem-like spheroid cells using flow cytometry beforeand after irradiation.RESULTS:The cells were observed to generate an increased number of spheres in SFM with increasing cell passage.Radiation increased the rate of generation of stem-like spheres in both types of cells.The average survival fraction(SF2)of the cultured KYSE-150compared with TE-1 stem-like spheres after 2 Gy of radiation was 0.81±0.03 vs 0.87±0.01(P<0.05),while the average SF2 of KYSE-150 compared with TE-1 parental cells was 0.69±0.04 vs 0.80±0.03,P<0.05.In the esophageal parental cells,irradiation dose-dependently induced G2 arrest.Stem-like esophageal spheres were resistant to irradiation-induced G2arrest without significant changes in the percentage population of irradiated stem-like cells.Under irradiation at 0,4,and 8 Gy,the CD44+CD271+cell percentage for KYSE150 parental cells was 1.08%±0.03%vs1.29%±0.07%vs 1.11%±0.09%,respectively;the CD44+CD271+cell percentage for TE1 parental cells was 1.16%±0.11%vs 0.97%±0.08%vs 1.45%±0.35%,respectively.The differences were not statistically significant.Under irradiation at 0,4,and 8 Gy,the CD44+CD271+cell percentage for KYSE-150 stemlike spheres was 35.83%±1.23%vs 44.9%±1.67%vs 57.77%±1.88%,respectively;the CD44+CD271+cell percentage for TE1 stem-like spheres was 16.07%±0.91%vs 22.67%±1.12%,16.07%±0.91%vs33.27%±1.07%,respectively.The 4 and 8 Gy irradiated KYSE-150 and TE-1 stem-like spheres were compared with the 0 Gy irradiated group,and the differences were statistically significant(P<0.05).CONCLUSION:The KYSE-150 and TE-1 stem-like spheres are more radioresistant than their parental cells which may suggest that cancer stem cells are related to radioresistance.