Mitochondria in platinum resistant cells.

Based on the previous report showing that mitochondrial (MT) alteration is associated with platinum (Pt) resistance, we have determined how the alternative MT function is involved in Pt cell cytotoxicity particularly in relation to the apoptosis. MT membrane potential (delta psi m) semi-quantitatively assessed by rhodamin 123 (Rh) sensitivity was significantly elevated in acquired Pt-resistant 2008/C13*5.25 cells (C13) established from its parental 2008 cells or known intrinsic Pt-resistant JHOC cells established from ovarian clear cell adenocarcinoma. Laser confocal microscopy of these cells stained with Rh revealed that MT in Pt-resistant cells were distributed in whole cytoplasm with relatively higher fluorescent intensity whereas MT in Pt-sensitive cells were localized in perinuclear space with lower fluorescent intensity. Electron microscopy showed the predominantly condensed MT in which crestal structure was not observed clearly in Pt-resistant cells. Western blot analysis using murine monoclonal anti-Bcl-2 antibody showed more than 5-fold Bcl-2 overexpression in Pt-resistant cells in response to cisplatin treatment. Cytochrome C (CytC) in MT was released from MT into cytoplasm in response to cisplatin treatment in Pt-sensitive cells, whereas up-regulation of CytC level in MT rather than CytC release from MT was observed in Pt-resistant cells. These data are strongly suggesting that changes at MT level would impact on the relative resistance of malignant cells to undergo drug-induced apoptosis.