Radioprotection against Lethal Damage Caused by Chronic Irradiation with Radionuclides In Vitro

To examine the capacity of chemical protectors to mitigate damage caused by chronic irradiation by incorporated radionuclides in vitro, cells must be maintained in the presence of the protector during the course of the irradiation. Such long exposures to chemical protectors at concentrations high enough to afford protection usually results in extreme chemotoxicity. To overcome this problem, experimental conditions were developed to allow Chinese hamster V79 cells to be maintained in 5% DMSO for prolonged periods (up to 72 h) with no observable chemotoxicity. Under these conditions, the capacity of DMSO to protect against damage to V79 cells caused by unbound ³² P and ³ H₂ O and DNA-incorporated ${}^{131}{\rm IdU}$, [³ H] dThd and ${}^{125}{\rm IdU}$ was examined. The dose modification factors for ³² P, ³ H₂ O, ${}^{131}{\rm IdU}$, [³ H] dThd and ${}^{125}{\rm IdU}$ were 2.6 ± 0.5, 2.3 ± 0.3, 1.0 ± 0.1, 1.16 ± 0.07 and 1.07 ± 0.02, respectively. These results show that 5% DMSO is capable of protecting cultured V79 cells against lethal damage caused by β particles emitted by unbound ³² P and ³ H₂ O, whereas little or no protection is afforded against damage caused by β particles emitted by DNA-incorporated ¹³¹ I and ³ H or low-energy Auger electrons emitted by DNA-incorporated ¹²⁵ I.