Effect of intracellular chloride on the cellular pharmacodynamics of cis-diamminedichloroplatinum(II).

cis-Diamminedichloroplatinum(II) (DDP) is activated by aquation to species that are much more reactive with nucleophiles. The dichloro form of the drug predominates at the high CI- concentrations found outside the cell (approximately 108 mM), whereas the reactive aquated forms predominate at low CI-. Lower CI- levels inside cells are presumed to facilitate cellular platination reactions, but little actual data are available to support this general belief. We therefore determined intracellular CI- in tumor cell lines and assessed the effect of modulation of CI- levels on the sensitivity to DDP and the platination of DNA. Basal CI- levels were 22.7 +/- 1.5 mM (N = 4) in 2008 human ovarian carcinoma cells and 12.2 +/- 2.3 mM (N = 4) in the resistant subline C13*. Intracellular CI- concentrations in 2008 and C13* cells dropped to < 8% of basal levels within 30 min after exposure to medium in which CI- had been replaced by NO3-. Lowering the intracellular CI- level should shift the equilibrium to the aquated form of the drug and thereby enhance cytotoxicity. Exposure of cells to DDP in equiosmolar CI(-)-deficient medium, however, did not change cytoxicity as measured by colony-forming assay. Accumulation experiments at 1 hr confirmed that the same amount of platinum was entering the 2008 and C13* cells in normal or CI(-)-deficient media. Plantination of cellular DNA was also determined under normal and CI(-)-depleted conditions, but again no difference was found.(ABSTRACT TRUNCATED AT 250 WORDS)