Induction and removal of cisplatin-DNA adducts in human cells in vivo and in vitro as measured by immunochemical techniques

Abstract

The same spectrum of cisplatin adducts was detected in DNA isolated from white blood cells of a cisplatin-treated cancer patient as had been found in cisplatin-treated DNA in vitro. The adducts were quantified in femtomole amounts by competitive enzyme-linked immunosorbent assay (ELISA) with three antisera raised against synthetic cisplatin-containing (oligo)nucleotides. For this assay, DNA samples digested with nucleases were fractionated by ion-exchange chromatography; the fractions were used as inhibitors of antibody binding. Determinations of the main adduct formed, cis-Pt(NH3)2d(pGpG), in patients immediately after a first treatment with equal doses of cisplatin showed interindividual differences in the platination levels of the white blood cells. These differences were found to correlate with those found after in-vitro exposure to cisplatin of blood samples taken from patients before treatment. In vivo, about 75% of the adducts formed after the first treatment were removed within 24 h. During a five-day course, the amounts of the main adduct increased after the first three administrations; no increase was seen on day 4 or 5. By day 6, considerable removal of adducts had occurred. Analysis of the formation and repair of the cis-Pt(NH3)2d(pGpG) adducts in cultured cells, i.e., human fibroblasts with different DNA repair capacities and one bladder and two testicular human cancer cell lines, indicated that both the amounts of adducts formed and the ability of the cells to repair the adducts can differ. These differences appear to determine the susceptibility of the cells for the cytotoxic action of cisplatin.