Further investigations into the nature of the trigger of increased radioresistance: The effect of {sup 14}C and {sup 3}H thymidine on low-dose hypersensitivity

In this study, the authors have shown that the hypersensitive region of the low dose survival curve is diminished in {sup 14}C and {sup 3}H thymidine-labeled cells. This implies that such cells are relatively radioresistant at very low doses of x-rays, presumably due to induced radioprotection, which has been proposed to be via induced repair, or increased time for repair. If this is true, then caution must be exercised when comparing results from labeled cells (e.g. studies of DNA damage) and unlabeled cells (e.g. survival studies), as the labeled cells may be already turned on by the radioactivity. This result, while possibly the first using survival in mammalian cells as an endpoint, is perhaps not surprising in that it agrees with earlier studies on the adaptive response using other endpoints. However, given the clinical relevance of the doses in these studies, it is important to note that various insults may lead to radioresistance.