Influence of common dietary supplements (curcumin, andrographolide, and d-limonene) on the radiobiological responses of p53-competent colonic cancer epithelial cells.

PURPOSE

The main goal of the research was to determine whether commercially available common dietary phytochemical supplements (curcumin, andrographolide, and d-limonene) have radiomodulatory effects on p53-competent human colonic epithelial cells.

METHODS

Clonogenic survival assays were used to characterize effects of the phytochemicals on cultured colonic epithelial cells (HCT116 p53) in direct irradiation or upon receipt of irradiated-cell conditioned media (for bystander effects). In direct irradiation, feeding regimen experiments included compound administration pre- and post-irradiation, which was used as a basis to define effects as radioprotective and radiomitigative, respectively. In the bystander effect experiments, either donor or recipient cell cultures were fed with the phytochemicals and bystander-induced clonogenic cell death was quantitatively evaluated. Dose challenge was in the range of 0.5 - 5 Gy using the gamma source (Cs-137).

RESULTS

Curcumin, andrographolide, and d-limonene appeared to not exhibit radioprotective and radiomitigative properties in HCT116 p53 cells. D-limonene was found to induce radiosensitization in post-irradiation administration. All three compounds appeared not to modulate the radiation-induced bystander signal production and response in HCT116 p53 cells.

CONCLUSIONS

Curcumin, andrographolide, and d-limonene are known to have many chemoprotective benefits. This work shows that they, however, did not protect colonic epithelial HCT116 p53 cells from radiation killing. As HCT116 p53 cells are tumourigenic in nature, this finding implies that these three dietary compounds would not reduce the killing efficacy of radiation in gastrointestinal tumorigenesis. The post-irradiation radiosensitizing effect of d-limonene was an intriguing observation worth further investigation.