Influence of treatment temperature on the genotoxic effects of cisplatin in CHO cells: cytotoxicity, mutagenicity and induction of lesions in DNA

Abstract

In cells exposed in vitro to the cytotoxic and mutagenic antitumor drug cisplatin ( cis-Pt(NH 3) 2Cl 2), various adducts with nuclear DNA are formed. A comparative study was made of the influence of temperature variation during treatment of cultured Chinese hamster ovary (CHO) cells with cisplatin on cytotoxicity, mutation induction and Pt-DNA adduct formation. Before and after treatment (1 h at 32, 37 or 40°C) cells were kept at 37°C. Cytotoxicity increased with temperature; D 0 values were 29.6 ± 1.6, 21.1 ± 1.2 and 11.4 ± 0.6 μM at 32, 37 and 40°C, respectively. PtDNA binding to DNA at 40°C was 2.0 (±0.3) times as high as at 32°C. This factor remained practically constant 24-h post-treatment incubation of the cells, during which about 60% of DNA-bound Pt were removed the increase in cytotoxicity between 32 and 40°C was roughly in proportion to that in Pt binding, no substantial changes in the spectrum of adducts appeared to occur. The induction of DNA interstrand cross-linkss, studied at 32 and 40°C, varied linearly with dose. Influence of temperature on cross-link formation was comparable to that on total Pt binding. Amounts of cross-links highly increased during 24 h after treatment. Plots of cross-links against survival after treatments at 32 and 40°C almost coincided. Induction of 6-thioguanine-resistant (HGPRT) mutants at various cisplatin concentrations did not show a clear temperature dependency. Consequently, equitoxic treatments were significantly more mutagenic at 32°C than at 40°C, the opposite of what has been reported for E. coli.