Effects of selenium on radiation responses of tumor cells and tissue.

PURPOSE

This review summarizes information about modulation of radiation effects in tumor cells and tissues by selenium.

RESULTS

In vitro, clonogenic survival to ionizing radiation was found to be reduced, depending on selenite concentration and duration of administration, by a factor of 1.5-4.4. In experimental animal tumors, a positive effect of selenium was observed with chemotherapy. The only available study in combination with irradiation did not show any benefit of selenium with clinically relevant radiotherapy protocols in R1H tumors. None of the investigations demonstrated a negative effect on the tumor response to therapy.

CONCLUSION

The only study with fractionated irradiation was performed in a rat R1H tumor, which does not show accelerated repopulation. Therefore, interaction of selenium with such repopulation processes, potentially resulting in increased tumor tolerance, could not be detected. For local administration of normal tissues with selenium, potential tumor effects may be of less importance, but these may be relevant for systemic administration. Therefore, well-designed studies with relevant tumor models and endpoints, and with clinically relevant fractionation protocols are recommended.