Response of cancer stem-like cells and non-stem cancer cells to proton and γ-ray irradiation

Ionizing radiation is a widely used therapy for solid tumors. Compelling evidence indicates cancer stem-like cells (CSCs) exist in solid tumors, which is on the top of hierarchically organization and suggested to be involved in carcinogenesis, tumor invasion, recurrence and resistance to various forms of therapies. Understanding the response of CSCs to irradiation is of great importance to improve cancer curability. In present study, the response to proton and γ-ray irradiation of these cells, including DNA damage and apoptosis were investigated experimentally. The results show that CSCs have higher resistance than non-stem cancer cells (NSCCs) to either proton or γ-ray irradiation. In addition, compared with γ-ray, proton irradiation is more efficient to kill CSCs at the same dose with lower survival as well as higher DNA damages. The results suggest that proton irradiation may have greater capability of eliminating CSCs for cancer radiotherapy than γ-ray at the same dose, which in turn makes radiotherapy more efficient.