Accumulation efficiency of cancer stem-like cells post γ-ray and proton irradiation

Ionizing radiation (IR) has been proven to be a powerful medical treatment in cancer therapy. Rational and effective use of its killing power depends on understanding IR-mediated responses at the molecular, cellular and tissue levels. Increasing evidence supports that cancer stem-like cells (CSCs) play an important role in tumor regrowth and spread post radiotherapy, for they are resistant to various therapy methods including radiation. Presently, SW620 colon carcinoma monolayer culture cells were irradiated with γ-rays and protons of 2 Gy. Then apoptosis, clonogenic survival and the expression of CD133+ protein were examined. The results showed that there was no significantly difference either on long-term clonogenic survival or on short-term apoptosis ratio. However, compared with γ-rays, irradiation with protons was less efficient to accumulate CSCs at the same dose, although both protons and γ-rays can significantly accumulate the CD133+ CSCs subpopulation. In addition, the results of sphere formation assay also confirmed that proton irradiation is less efficient in CSCs accumulation, suggesting proton irradiation might have higher efficiency in CSCs elimination for cancer radiotherapy.