The formation and repair of cisplatin-DNA adducts in wild-type and cisplatin-resistant L1210 cells: comparison of immunocytochemical determination with detection in isolated DNA

We have studied the formation and repair of cisplatin-DNA adducts in wild-type mouse leukemia L1210/0 cells and in the sublines L1210/2 and L1210/5, which differ in cisplatin sensitivity. In a colony-formation assay these sublines were 9- and 22-fold more resistant compared to L1210/0, respectively. Cisplatin-induced DNA modification was studied at the cellular level by immunocytochemistry with antiserum NKI-A59 raised against cisplatin-treated DNA. Levels of nuclear staining immediately after a 1-h treatment were similar to those seen after a 23-h post-incubation In drug-free medium. Clear differences in DNA platination were found between the cell lines: immediately after exposure? L1210/2 and L1210/5 showed only 32 and 14%, respective, of the nuclear staining observed in L1210/0, and 48 and 13% after 24 h. In these experiments. adduct-specific nuclear staining was quantified as the area under the adduct versus concentration curves (AUG). The formation and repair in these cell lines of the bifunctional adducts cis-Pt(NH3)(2)d(pGpG) (Pt-GG), cis-Pt(NH3)(2)d(pApG) (Pt-AG) and cis-Pt(NH3)(2)(dGMP)(2) (G-Pt-G) were studied with an enzyme-linked immunosorbent assay (ELISA). No relation between repair and resistance was observed. The results suggest that differences in induced DNA platination levels, rather than in repair, are responsible--at least in part--for the differences in cisplatin resistance. A mechanism such as an increased tolerance of the resistant cells to platinum-DNA damage may also be involved. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.