Induction of cancer stem-like cells in A549 cells after exposure to carbon ions and X-rays

Cancer stem-like cells (CSCs) play a crucial role in the initiation, progression, and recurrence of cancer. Evidence indicates that the high linear energy transfer (LET) carbon ion beam is more effective against CSCs than the conventional X-ray beam. Carbon ion radiotherapy is considered as a promising cancer strategy, however, information about whether, or not, new CSCs are induced after carcinoma cells exposed to carbon ions is limited and incomplete. The selected A549 cells, derived from a single colony with low CD133 expression, were irradiated by high LET carbon ion beam or low LET X-ray, and then the cell clonal survival fraction, CD133+ expression subpopulations and soft agar colony formation potential were detected. The cell-killing ability of carbon ions was higher than that of X-rays. The fractions of CD133+ or Oct4+ high expression cells increased in a dose-dependent manner at 12 h after both X-ray and carbon ion exposure. Compared to that of carbon ion irradiation, the efficiency of transformation in a cell colony was higher in the X-ray irradiation group after 30 d; however, the amount of colonies with higher fractions of CD133+ expression cell subpopulation in the carbon ion irradiation group was more than that in X-ray irradiation treatment group after 30 and 50 d. Our results indicate that, although high-LET radiation kill more cells including cancer stem-like A549 cells, it may induce more stable stem cell-like colonies than low LET radiation.