VEGF antagonists are now widely used cancer therapeutics, but predictive biomarkers of response or toxicity remain unavailable. In this study, we analyzed the effects of anti-VEGF therapy on tumor metabolism and therapeutic response by using an integrated set of imaging techniques, including bioluminescence metabolic imaging, 18-fluorodeoxyglucose positron emission tomography, and MRI imaging and spectroscopy. Our results revealed that anti-VEGF therapy caused a dramatic depletion of glucose and an exhaustion of ATP levels in tumors, although glucose uptake was maintained. These metabolic changes selectively accompanied the presence of large necrotic areas and partial tumor regression in highly glycolytic tumors. In addition, we found that the central metabolic protein kinase AMP-activated protein kinase (AMPK)-a cellular sensor of ATP levels that supports cell viability in response to energy stress-was activated by anti-VEGF therapy in experimental tumors. AMPK-a2 attenuation increased glucose consumption, tumor cell sensitivity to glucose starvation, and tumor necrosis following anti-VEGF therapy. Taken together, our findings reveal functional links between the Warburg effect and the AMPK pathway with therapeutic responses to VEGF neutralization in tumor xenograft models. Cancer Res; 71(12); 4214-25. Ó2011 AACR.

Ovarian serous carcinoma (OSC) is a fatal gynecologic malignancy usually presenting with bilateral localization and malignant peritoneal effusion. Programmed cell death 4 (PDCD4) is a tumor suppressor gene whose expression is directly controlled by microRNA-21 (miR-21). Exosomes are small cell-derived vesicles that participate in intercellular communication, delivering their cargo of molecules to specific cells. Exosomes are involved in several physiological and pathological processes including oncogenesis, immunomodulation, angiogenesis, and metastasis. The current study analyzed the expression of PDCD4 and miR-21 in resected OSC specimens and in cells and exosomes from OSC peritoneal effusions. PDCD4 was immunohistochemically examined in 14 normal ovaries, 14 serous cystadenoma (CA), and 14 OSC cases. Quantitative reverse transcriptase-polymerase chain reaction analysis of PDCD4 and miR-21 expression was performed in CA and OSC cases and in cells and exosomes obtained from 10 OSC and 10 nonneoplastic peritoneal effusions. miR-21 was also evaluated by in situ hybridization. Immunohistochemistry demonstrated a gradual PDCD4 loss from normal ovaries to CA and OSC specimens. Quantitative reverse transcriptase-polymerase chain reaction displayed higher PDCD4 messenger RNA levels in CA specimens compared with OSC cases and highlighted miR-21 overexpression in OSC specimens. In situ hybridization detected miR-21 only in OSC cells. This PDCD4 and miR-21 inverse expression was also noted in cells and exosomes from OSC peritoneal effusions compared with nonneoplastic effusions. PDCD4 and miR-21 are involved in OSC oncogenesis. The transfer of miR-21 by exosomes could promote oncogenic transformation in target cells distant from the primary tumor without direct colonization by cancer cells and could be used as a diagnostic tool