Effects of low-dose radiation on adaptive response in colon cancer stem cells.

PURPOSE: Biological effects of low-dose radiation (LDR) are distinguishable from those of high-dose radiation. Adaptive response is an important biological effect following low-dose radiation. Cancer stem cells (CSCs) have self-renewal and multidirectional differentiation potency which results in relapse and metastasis of cancer. In this study, we aimed to examine whether adaptive response could be induced in CSCs by LDR.

METHODS: Parental cells of three colon cancer cell lines (HRT18, HT29, and HCT116) and CSCs of these three cell lines were irradiated with LDR (i.e., D1) and then high-dose radiation (HDR) of X-rays (i.e., D1 + D2) or only HDR (D2 alone), followed by examination of adaptive response.

RESULTS: Adaptive response was not observed either in the three tumor parental cells lines or in three CSCs lines following LDR, due to the lack of resistance to subsequent D2-induced cell growth inhibition.

CONCLUSION: These results suggested that LDR may not induce adaptive response in colon cancer cells or colon CSCs under in vitro conditions. Our study provided experimental and clinical foundations for the application of LDR in the treatment of colon cancers.