Loss of cw-Diamminedichloroplatinum(H) Resistance in Human Ovarian Carcinoma Cells Selected for Rhodamine 123 Resistance1

Cisplatin (DDP)-resistant 2008 human ovarian carcinoma cells (C13*) have an elevated mitochondria! membrane potential that confers hypersensitivity to lipophilic cations. We have addressed whether this change was directly linked to the DDP-resistant phenotype or was a random alteration, unrelated to resistance. The elevated mitochondria! membrane potential and ensuing rhodamine 123 (Rhl23) hypersensitivity of C13* cells provided a positive selection rationale. Cells with low mitochondria! membrane potential will have a survival advantage over those with a high mitochondria! membrane potential, when exposed to Rhl23. We there fore used Rhl23 to isolate revertants (RH4) from the 12-fold DDPresistant C13* cell line that had a low mitochondrial membrane potential. RH4 cells had parental (2008) mitochondrial membrane potential levels as shown by flow cytometry analysis of Rhl23 stained cells and by tetraphenylphosphonium cation uptake. The RH4 cells lost a substantial portion of their DDP resistance such that they were only 2to 3-fold resistant to DDP. Despite this major loss of resistance, they retained a number of the phenotypic changes related to DDP resistance, observed in C13* cells. RH4 cells displayed the same DDP accumulation defect, 2-fold elevated glutathione levels and 2-fold resistance to ( d( I. as C13* cells. We conclude that although the biochemical mechanism by which an elevated mitochondrial membrane potential elicits DDP resistance is unknown, these mitochondrial changes are central to the expression of DDP resistance in C13* cells.