Kinetics of DNA cross-linking in normal and neoplastic mouse tissues following treatment with cis-diamminedichloroplatinum(II) in vivo

Abstract

The formation and repair of cis-diamminedichloroplatinum(II) (cis-DDP)-induced DNA cross-links in cells from a number of different mouse tissues, both normal and neoplastic, were compared in three different populations of animals, tumor-free mice and mice bearing a transplanted fibrosarcoma (either FSa or NFSa) in their thighs. Groups of mice were given i.v. injections of 4-12-mg/kg doses of cis-DDP, and the amount of cis-DDP-induced DNA cross-linking was determined at different times after injection using an adaptation of the alkaline elution technique. The degree of cross-linking in each tissue was linearly related to the dose of cis-DDP at either 6 or 24 h after injection and varied significantly among the different tissues, with FSa, NFSa, kidney, and liver showing the highest level of cross-linking of the tissues studied. The relative contributions of DNA-interstrand and DNA-protein cross-links to the elution profiles were estimated by proteinase K (PK) digestion. At either 6 or 24 h after injection with cis-DDP, the rate of elution of the DNA was substantially increased by PK, indicating a large contribution of DNA-protein cross-links. This effect was observed in all tissues studied, although the proportion of PK-resistant lesions appeared to vary from tissue to tissue, liver and spleen showing a significantly lower proportion of DNA-interstrand to total cross-links than either of the tumors. For liver, virtually no interstrand cross-links could be detected after PK treatment. The kinetics of the repair of cis-DDP-induced DNA cross-linking in these tissues were also compared. In cells from tumor-free animals, the amount of total (DNA-interstrand plus DNA-protein) cross-linking increased gradually, reaching a maximum after about 6 h; however, little evidence of repair of these lesions was observed in any of these normal tissues. In fact, the degree of cross-linking tended to increase somewhat between 6 and 24 h after injection. The kinetics of cross-linking in cells isolated from the FSa tumor were very different; while there was an initial increase in cross-linking up to 6 h, these lesions were subsequently repaired, although at a somewhat slower rate than has been reported for cultured mammalian cells.(ABSTRACT TRUNCATED AT 400 WORDS)