Signal Transducers and Activators of Transcription (STAT) are a group of transcription factors that are known to play a major role in cancer progression. In ovarian cancer, increased STAT3 leads to cancer proliferation in response to cytokines and confers resistance to chemotherapy-induced apoptosis in epithelial malignancies. STAT3 is constitutively activated in patient derived ovarian cancer cells, and increased STAT3 expression is a predictor of poor prognosis. Apart from its function as a transcription factor, recently STAT3 has been shown to modulate mitochondrial function to promote carcinogenesis. The aim of our study was to investigate if STAT3 activation can modulate cellular metabolism of ovarian cancer cells. Stable clones expressing STAT3 were generated in A2780 ovarian cancer cells, along with empty vector clones. Ectopic expression of STAT3 in A2780 ovarian cancer cell line resulted in increased proliferation (p\u3c0.01) and colony formation ability (p\u3c0.001) in vitro and led to large ovarian tumors (p\u3c0.01) compared to parental and vector controls in xenograft mouse model. Bioenergetics profiling showed higher mitochondrial respiration (OCR) and glycolysis (ECAR) in STAT3 clones compared to parental and vector clones. Ratio of ECAR/OCR in the STAT3 overexpressing cells placed them in the \u27metabolically active\u27 phenotype, while parental A2780 and vector clones were in \u27metabolically less active\u27 phenotype. A selective inhibitor of STAT3, STATTIC, inhibited the STAT3 mediated growth of A2780 cells both in vitro (p\u3c0.01) and in vivo (p\u3c0.01). In addition, STATTIC treatments reversed the \u27metabolically active\u27 state of STAT3 overexpressing clones to a \u27lower metabolic state\u27, placing them in the same category as the control cells. In addition, STATTIC inhibited the cell proliferation and modulated bioenergetic phenotype of other ovarian cancer cells lines (PEO4, C200 and OVCAR3) that display a \u27metabolically active\u27 phenotype. Overall, STAT3 can induce metabolic changes in ovarian cancer cells, maybe as survival mechanism and enhances the cellular fitness of the ovarian cancer cell resulting in increased oncogenic abilities
