Determinants of cisplatin sensitivity in non-malignant non-drug-selected human T cell lines.

We have studied molecular mechanisms of cisplatin sensitivity and resistance in 3 non-malignant, non-drug-selected human T lymphocyte cell lines. HuT 78, H9, and MOLT-4 cells were assessed for sensitivity to cisplatin, DNA damage levels following defined drug exposures, drug accumulation, and DNA repair efficiency as measured by adduct removal from cellular DNA and by host-cell reactivation of cisplatin-modified plasmid DNA. Based on 3-day continuous drug exposures, the IC50 values for the cell lines were: HuT 78, 0.83 microM; H9, 0.45 microM; and MOLT-4, 0.33 microM. These cells retained this order with respect to DNA repair capability, whether measured by platinum-DNA adduct removal from cellular DNA or by host-cell reactivation assays. DNA repair values measured by these two assays were directly related to one another with a linear correlation coefficient of 0.993. At sublethal cisplatin doses the more resistant cells showed the highest levels of drug uptake. When drug uptake levels were 'corrected' for drug-induced cell kill, there were equal levels of DNA repair efficiency for a given level of drug uptake. Absolute levels of cisplatin-DNA adduct repair increased with increasing drug dose. However, at supralethal doses of drug, efficient DNA repair could be overcome in all 3 cell lines with percentage-adduct-removal dropping from a 60-80% range to a less than 30% range. We conclude that in non-malignant non-drug-selected human T cells, DNA repair appears to be the primary determinant of cisplatin sensitivity/resistance and that enhanced DNA repair may be a biologic compensatory mechanism for cells that cannot prevent cellular uptake of DNA-damaging agents.