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We developed mitochondrial (MT) scoring system based on MT ultrastructural findings in association with response to chemotherapy in ovarian cancer (OC). Ultrathin sections of MT prepared from 28 OC patients before chemotherapy were examined by electron microscopy. Platinum-sensitive ovarian carcinoma cell line 2008 and its resistant variant C13 were used as control cells. Seven independent MT features including, diameter, pattern of cresta structure, electron density, distribution-density and -pattern, ratio of minimal/maximal diameter and MT architecture were examined and were assigned a score between 0 and 2. Twenty-eight cases were primary advanced OC, including 4 recurrent cases. Nine cases were chemosensitive while 19 were resistant. Univariate and multivariate analysis in each factor showed good correlation to chemosensitivity for 2 factors of electron density, distribution pattern. Total score of these 2 factors in 9 sensitive cells was 1.44+/-0.41 (M +/- SE) and was 3.58+/-0.18 in 19 resistant cells (P<0.001). Receptor operative characteristics (ROC) analysis revealed that total 'cut-off' score was 3 point (P<0.05; AUC=0.84). In conclusion, this MT scoring system was excellently correlated to response regardless of histopathologic findings and this strongly suggests that the system is deemed to be of great value as biomarker for the chemosensitivity in OC.

Paclitaxel (PX) binds to and stabilizes tubulin, preventing depolymerization, and resulting in cell death. Based on a previous report showing the activity of phosphatidylinositol kinase (PIK) on tubulin, we investigated the effect of the PI4K inhibitor orobol and the PI3K activator platelet derived growth factor (PDGF) on PX sensitivity. Drug sensitivity was examined by classical colony forming assay. Tubulin isotype expression was determined by semi-quantitative RT-PCR. Microtubule texture was observed by laser confocal microscope using anti-beta-tubulin antibody. Apoptotic activity was estimated by frequency of condensed nuclear chromatin with Hoechst 33342 stain. Orobol enhanced PX sensitivity of human ovarian carcinoma 2008 cells by 18.9+/-1.2-fold (N=3; P<0.01). In contrast, pretreatment with PDGF rendered cells resistant to PX by 2.3+/-0.4-fold (N=3; P<0.01). Neither orobol nor PDGF showed any effect on cell growth. Orobol produced a 2.5-fold sensitization in cisplatin-resistant 2008/C13*5.25 (C13) cells, and PDGF rendered the cells 2.3-fold resistant to PX. Orobol suppressed the beta 4a-tubulin isotype expression by 85% and other isotypes by 20%. In contrast, PDGF induced beta 4a-tubulin isotype expression by 1.3-fold, while it supressed all the other isotypes by 20-40%. Orobol produced thick microtubules and PDGF generated ring condensed microtubules. Orobol promoted PX-induced apoptosis, while PDGF caused 50% reduction of apoptosis. These results indicate that orobol and PDGF regulate PX sensitivity by reciprocally altering the proportion of tubulin isotype expression and PX-induced apoptotic signaling.

One of the mechanisms of cisplatin cell cytotoxicity is the mitochondria-associated induction of apoptosis. The morphological or functional change of mitochondria in cisplatin-resistant cells has already been reported. Herein we present additional data describing the mitochondrial genomic and functional changes in cisplatin- resistant cells. Cisplatin increased the level of apoptotic cells in cisplatin-sensitive human ovarian carcinoma OV 2008 and C13 cells by 3.90+/-1.01 (SD; N=3) (p<0.01)-fold and 2.03+/-0.20 (SD; N=3) (p<0.01)-fold compared to the basal apoptotic level. This indicates a lower level induction of apoptosis by 50% in cisplatin-resistant OV 2008/C13 *5.25 variant (C13) cells. In both cell types, cisplatin cytotoxicity is mostly inhibited by the caspase-9 inhibitor as well as the caspase-3 inhibitor, Ac-DEVD-CHO, suggesting that the mitochondrial downstream event was functioning well in both the C13 cells and in OV 2008 cells. Mitochondrial transmembrane potential (DeltaPsim) determined by flow cytometry using DiOC6-stained cells revealed a significant depolarization of C13 cells as compared to OV 2008 cells. Treatment of these cells with cisplatin or hydrogen peroxide induces complete mitochondrial DNA damage in OV 2008 cells, while only partial DNA-destruction is observed in C13 cells, strongly suggesting that mitochondria are resistant to cisplatin and oxidative stress response. Continuous oxygen consumption of these cells monitored by a multi-channel dissolved oxygen meter is 1.70-fold higher in OV 2008 cells than C13 cells and the oxygen consumption was decreased by 30% in C13 cells, suggesting mitochondrial respiratory malfunction in these cells. The hypothesis generated here is that mitochondrial DNA resistance to cisplatin and oxidative stress response might be one of the main characteristics concerning the lower level of apoptosis induced by cisplatin. However, the mechanism by which the mitochondrial DNA encoded molecule is involved in cisplatin resistance remains to be determined.