Abstract
Abstract
While, normal cells primarily rely on mitochondrial oxidative phosporylation (OXPHOS), cancer cells are known to preferentially take up glucose to produce energy using aerobic glycolysis pathway, described as the ‘Warburg effect’. Recently, this view that all cancer cells are dependent on glycolysis is being challenged. We examined the bioenergetic characteristics of a panel of 10 human ovarian cancer cell lines and 2 immortalized ovarian surface epithelial cell lines, using the Seahorse XF Extracellular Flux analyzer to measure glycolysis and mitochondrial respiration in real time using the outputs of extracellular acidification rate (ECAR) and oxygen consumption rate (OCR) respectively. The mitochondrial bioenergetics was read by taking baseline OCR following sequential addition of oligomycin, FCCP and rotenone/antimycin, which inhibit mitochondrial ATP synthase, uncouple mitochondrial OXPHOS and induce maximal respiration respectively. Glycolytic profile (ECAR) was generated after keeping the cells glucose free followed by sequential addition of glucose to induce glycolysis, oligomycin and 2-deoxy glucose to inhibit glycolysis. The OCR profile showed ovarian cancer cells lines to have diverse mitochondrial bioenergetics and diverse ability to use glycolysis. The OCR:ECAR ratio showed varied bioenergetic organization, with some cells relying heavily on glycolysis or OXPHOS, but most using both pathways equally. A significant positive correlation (correlation coefficient 0.7705; p=0.003) was observed between mitochondrial respiration and glycolysis, confirming that glycolysis dependent cells have lower ATP-linked respiration rates. A similar diversity was observed in the mRNA expression of glycolytic (Glut1 and LDH) and mitochondrial (PGC-1α and CoxVb) genes. These findings highlight the actuality of extreme heterogeneity observed in cancer cells. A unique observation was the distinctive behavior of chemosensitive and resistant cell line pairs. Our panel contained a set of (i) cisplatin sensitive A2780 and resistant C200 cell lines and (ii) taxol sensitive PEO1 and resistant PEO4 cell lines. The resistant cells (C200 and PEO4) displayed higher ECAR and OCR profile compared to the sensitive cells (A2780 and PEO1), indicating an increased utilization of both energy pathways. The OCR:ECAR ratio suggested the sensitive cell lines to be glycolytic and the resistant cell lines to be highly metabolically active. This was further supported by increased mitochondrial function in the resistant cells, measured in terms of augmented fatty acid oxidation and mitochondrial potential in the resistant cells. On inhibition of glycolysis, the resistant cells were able to increase OX-PHOS and maintain their growth, whereas sensitive cells could not increase OX-PHOS and ceased growth. This led us to a novel hypothesis that chemo-resistant ovarian cancer cells exhibit greater plasticity than normal and sensitive cells, making them more adaptable to rearrange their metabolic phenotype according to microenvironment changes and stress, giving them a selective advantage to overcome adverse conditions. Thus, the metabolic diversity could be a means of selecting resilient chemo-resistant cells over a period of cytotoxic insults.
Citation Format: J. Chhina, S. Dar, M. Deshpande, S. Giri, A. Munkarah, R. Rattan. Bioenergetic adaptations in chemoresistant ovarian cancer cells [abstract]. In: Proceedings of the 10th Biennial Ovarian Cancer Research Symposium; Sep 8-9, 2014; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(16 Suppl):Abstract nr POSTER-BIOL-1307.