| Popis: |
Ovarian cancer is the fourth leading cause of cancer-related death in women and the leading cause of gynecologic cancer death. Moreover, it is regarded as a therapy resistant tumor, because it shows the formation of more aggressive recurrence of the primary tumor as a result of chemotherapy. This chemo-resistance is thought to be related to the presence of the Cancer Stem Cells (CSC). Tumor cells are characterized by a high glycolytic metabolism even in the presence of oxygen, the so-called Warburg effect; however, it is unclear whether this condition is also shared by CSC. We identified ovarian CSC, according to their co-expression of CD44 and CD117 markers, in 40 samples of ascitic effusions from ovarian cancer-bearing patients. We have analyzed phenotipic characteristics by investigating stemness marker expression by flow-cytometry, spheroid formation assay, tumorigenicity in vivo and gene expression in RT-PCR. For the analysis of metabolic characteristics, ovarian cancer cells were FACS-sorted in to CD44+CD117+ and CD44+CD117- cell populations and analyzed through specific metabolic gene-cards. Results were confirmed also through Western Blot for specific metabolic enzymes and functional assay of mitochondrial activity. We have demonstrated that CD44+CD117+ EOC cells presented high tumorigenicity and expressed stemness-associated markers and multidrug resistance pumps. Moreover, the CD44+CD117+ cell population overexpressed genes associated with glucose uptake, oxidative phosphorylation (OXPHOS), and fatty acid -oxidation, indicating higher ability to direct pyruvate towards the Krebs cycle. Consistent with a metabolic profile dominated by OXPHOS, the CD44+CD117+ cells showed higher mitochondrial reactive oxygen species (ROS) production and elevated membrane potential, and underwent apoptosis upon inhibition of the mitochondrial respiratory chain. The CSC also had a high rate of pentose phosphate pathway (PPP) activity, which is not typical of cells privileging OXPHOS over glycolysis, and may rather reflect the PPP role in recharging scavenging enzymes. Furthermore, CSC resisted in vitro and in vivo glucose deprivation, while maintaining their CSC phenotype and OXPHOS profile. In this study, we show that a subpopulation of CD44+CD117+ EOC cells fulfilling the canonical properties of CSC does not preferentially exploit a glycolytic metabolism, privileging instead the mitochondrial respiratory pathway. These observations could explain the CSC resistance to anti-angiogenic therapies, and indicate this peculiar metabolic profile as a possible target of novel treatment strategies. |
