Chemical modification of 5-[ 125 I]iodo-2'-deoxyuridine toxicity in mammalian cells in vitro

Abstract

Purpose : To address the cytotoxic effects of DNA-incorporated 125 I in Chinese hamster V79 lung fibroblasts under various scavenging conditions. Methods : The toxic effects of DNA-incorporated 5-[ 125 I]iodo-2'-deoxyuridine (125 IdUrd) were assessed by the colony-forming assay with cells incubated in medium containing serum and/or dimethyl sulphoxide (DMSO). Experiments were carried out at 0.3 or -135°C. Results : When 125 I decays were accumulated at 0.3°C in 10% serum 0, 5 or 10% DMSO, no radioprotection was afforded by 5% DMSO, while the dose modification factor (DMF) for 10% DMSO was 2.0. For cells accumulating decays at 135°C in the presence of 5 or 10% serum, DMSO was radioprotective (DMF= 1.8-1.9). D 0 obtained at each serum concentration correlated strongly (R =0.999) with the scavenging capacity of DMSO. Under these experimental conditions, 10% serum is ~3.6 times more protective than 5% serum. Conclusions : The contribution of indirect mechanisms to the toxicity of 125 I decaying within mammalian cell nuclear DNA can be demonstrated not only with DMSO, but also with the hydroxy radical scavengers present in serum.