Radiation protection by cysteamine against the lethal effects of intracellularly localized Auger electron, alpha- and beta-particle emitting radionuclides

The mechanisms by which DNA-incorporated radionuclides impart lethal damage to mammalian cells were investigated by examining the capacity of cysteami ne (MEA) to protect against lethal damage to V79 cells caused by unbound tr itium (3H(2)O), DNA-incorporated I-131/125-iododeoxyuridine (IdU) and the a lpha -particle emitter Po-210-citrate. Radiolabeled cells were maintained a t 10.5 degreesC for 72 h in the absence or presence of MEA (0.65-2.6 mM) an d the surviving fraction was determined. Protection against lethal damage c aused by 3H(2)O, (131)IdU or (125)IdU and Po-210-citrate depended on the co ncentration of MEA with maximum protection at 1.3-1.9 mM. The dose modifica tion factors obtained at 1.3 mM for the radiochemicals were 2.5 +/- 0.3, 1. 8 +/- 0.2, 1.7 +/- 0.1 and 1.4 +/- 0.1, respectively. MEA provides more pro tection against indirect than direct effects of ionizing radiation, and ind irect effects play a role in the radiotoxicity of Auger electron emitters i ncorporated into the DNA of mammalian cells.