Characterization of Radioprotective, Radiomitigative and Bystander Signaling Modulating Effects of Endogenous Metabolites Phenylacetate, Ursodeoxycholate and Tauroursodeoxycholate on HCT116 Human Colon Carcinoma Cell Line

Exposures to ionizing radiation can cause depletion in stem cell reservoirs and lead to chronic injury processes that exacerbate carcinogenic and inflammatory responses. Therefore, radioprotective measures, against both acute and chronic biological effects of radiation, require frequent intake of nontoxic natural products, which have practical oral administration. The goal of this study was to characterize the radioprotective, radiomitigative and radiation-induced bystander effect-inhibiting properties of endogenous metabolites: phenylacetate, ursodeoxycholate and tauroursodeoxycholate. Compounds were administered pre- and postirradiation as well as in donor and recipient bystander flasks to analyze whether these might adequately protect against radiation injury as well as facilitate recovery from the exposures. The clonogenic HCT116 p53 wild-type cancer cell line in this study shares characteristics of stem cells, such as high reproductive viability, which is an effective marker to demonstrate compound effectiveness. Clonogenic assays were therefore used to characterize radioprotective, radiomitigative and bystander inhibiting properties of treatment compounds whereby cellular responses to radiation were quantified with macroscopic colony counts to measure cell survival in flasks. The results were statistically significant for phenylacetate and tauroursodeoxycholate when administered preirradiation, conferring radioprotection up to 2 Gy, whereas administration postirradiation and in bystander experiments did not confer radioprotection in vitro. These findings suggest that phenylacetate and tauroursodeoxycholate might be effective radioprotectors, although they possess no radiomitigative properties.