Influence of chronic low-dose/dose-rate high-LET irradiation from radium-226 in a human colorectal carcinoma cell line.

PURPOSE

To evaluate potential damages of chronic environmentally relevant low-dose/dose-rate high-LET irradiation from a naturally occurring alpha-emitting radionuclide (radium-226, Ra) on a human colorectal carcinoma HCT116 p53 cell line.

METHODS

Clonogenic survival assays and mitochondrial membrane potential (MMP) measurement with a sensitive fluorescent MMP probe JC-1 were performed in HCT116 p53 cells chronically exposure to low doses/dose rates of Ra with high-LET. Comparisons were made with the human non-transformed keratinocyte HaCaT cell line and acute low-dose direct low-LET gamma radiation.

RESULTS AND CONCLUSION

The chronic low-dose/dose-rate alpha radiation (CLD/DRAR) did not reduce the clonogenic survival of HCT116 p53 cells over the period of 70 days of exposure. Only one significant reduction in the HCT116 p53 cells' clonogenic survival was when cells were grown with 10,000mBq/mL Ra for 40 days and progeny cells were clonogenically assessed in the presence of 10,000mBq/mL Ra. The cumulative doses that cells received during this period ranged from 0.05 to 46.2mGy. The mitochondrial membrane potential (MMP) dropped initially in both HCT116 p53 and HaCaT cells in response to CLD/DRAR. The MMP in HCT116 p53 cells recovered more quickly at all dose points than and that in HaCaT cells until the end of the exposure period. The highest dose rate of 0.66mGy/day depolarized the HaCaT's mitochondria more consistently during the exposure period. The faster recovery status of the MMP in HCT116 p53 cells than that in HaCaT cells was also observed after exposure to acute low-dose gamma rays. Overall, it was found that CLD/DRAR had little impact on the MMP of human colorectal cancer and keratinocyte cell lines.