CELLULAR PHARMACOLOGY OF DICHLORO(ETHYLENEDIAMINE) PLATINUM(II) IN CISPLATIN-SENSITIVE AND RESISTANT HUMAN OVARIAN-CARCINOMA CELLS

The cellular pharmacology of the tritium-labeled cisplatin analogue di chloro(ethylenediamine)platinum(II) ([H-3]DEP) was compared in cisplat in-sensitive 2008 and resistant 2008/C135.25 human ovarian carcinoma cells. The cellular content of total [H-3], ultrafiltrable [H-3], and free native [H-3]DEP was measured during and following incubation with 5 mu M [H-3]DEP. While the rate constant for [H-3]DEP uptake in the r esistant cells was reduced to 25% of that in the sensitive cells, DNA intrastrand adduct formation was reduced even further to 11%, indicati ng the presence of defects in both uptake and the ability of intracell ular drug to access or react with DNA. The latter could not be account ed for by enhanced repair. Together, these defects were sufficient to account for the 11-fold level of resistance. At steady state, the intr acellular to extracellular concentration ratio for native [H-3]DEP was 7.7 in the sensitive cells and 11.7 in the resistant cells, suggestin g the presence of a trapping or concentrative mechanism. Thus, despite the slower initial influx, the resistant cells eventually accumulated more free [H-3]DEP than the sensitive cells. We conclude that the res istant phenotype in these cells is accounted for primarily by impaired uptake and decreased reaction of [H-3]DEP with DNA rather than by cha nges in efflux or DNA repair.