Comparison of lipid content, surface membrane fluidity, and temperature dependence of cis-diamminedichloroplatinum(II) accumulation in sensitive and resistant human ovarian carcinoma cells.

We conducted studies to determine whether the cisplatin (DDP)-resistant human ovarian carcinoma cell line designated 2008/DDP has membrane changes which could slow the passive diffusion of the drug into cells, thereby accounting for the observed reduction in DDP accumulation in 2008/DDP cells compared to the sensitive parental 2008 cells. To this end, we compared three indicators of membrane lipid composition and fluidity in the resistant and sensitive cells. In a comparison of major membrane lipid classes, the resistant line had a 17% increase in phosphatidyl choline, and an 11% increase in phosphatidyl ethanolamine relative to the sensitive line. There were no differences in the other major phospholipids or in the free cholesterol content of the cell lines. Secondly, results of fluorescence polarization measurements on whole cells of each line using the plasma membrane specific probe trimethylammonium diphenylhexatriene revealed no difference between the cell lines at both 28 degrees C and 37 degrees C. Finally, an examination of the temperature-dependence of DDP accumulation over 1 h produced Arrhenius plots of similar shape in 2008 and 2008/DDP cells. Both plots were linear from 40 degrees C down to a break point between 4 degrees C and 12 degrees C. The Q10's for DDP accumulation from 30 degrees C to 40 degrees C were greater than 2 in each cell line and were not significantly different. Results of these 3 comparisons point to substantial similarity in the bulk membrane lipid composition and fluidity of the two cell lines. We conclude that decreased DDP accumulation in our resistant cells is not due to membrane changes that would be expected to retard passive diffusion of the drug into the cells.