Short-term cis-diamminedichloroplatinum(II) accumulation in sensitive and resistant human ovarian carcinoma cells

We examined the short-term accumulation of cisplatin (DDP) in sensitive 2008 human ovarian carcinoma cells and in a 2- to 3-fold DDP-resistant and accumulation-deficient variant. During the 1st min of exposure to 500 microM DDP, sensitive cells accumulated platinum at a rate of 187 +/- 63 pmol/mg protein per min, whereas resistant cells accumulated platinum at 123 +/- 85 pmol/mg protein per min, a rate that was 66% that of sensitive cells. From 2-10 min of exposure, sensitive and resistant cells accumulated the drug at rates of 51.4 +/- 21.5 and 34.0 +/- 9.70 pmol/mg protein per min, respectively. In resistant cells, this rate again represented 66% that of sensitive cells. For each cell line, the DDP accumulation was 3.6 times faster during the 1st min than it was over 2-10 min. Initial DDP accumulation was linear with drug concentration in each cell line. Efflux measurements were made over a 50-min period after a 10-min load in 500 microM DDP. The loss of platinum was biphasic in each cell line, with an initial, rapidly effluxing component being lost within 10 min in each cell line. The rate constant for loss of platinum from this rapidly effluxing pool, measured after a 10-min loading period in 500 microM DDP, was 0.67 +/- 0.09 s-1 in sensitive cells and 1.03 +/- 0.15 s-1 (a 53% increase) in resistant cells. Between 5 and 50 min of an accumulation time course in 500 microM DDP, the size of the rapidly effluxing platinum pool remained relatively constant in each cell line, with the major contribution to the increase in total platinum over time coming from growth of the slowly effluxing platinum pool. We conclude that diminished retention of platinum in the rapidly effluxing pool of resistant cells is a major determinant of decreased DDP accumulation in these cells.