Abstract A23: Reversible metabolic changes in human melanoma cells enable distant metastasis
Authors: Piskounova Elena , Agathocleous Michalis , Mann Sara , DeBerardinis Ralph , Morrison Sean J. 
Published: May 2016

Metastasis is a complex multistep process: cancer cells have to detach from the bulk of the primary tumor, intravasate into the blood, survive anoikis and high shear forces in the blood stream while existing as single cells, extravasate into a distal site, and finally proliferate to form metastatic nodules. Currently our understanding of the mechanisms that govern the metastatic cascade is very limited. Our laboratory has developed a model of melanoma metastasis using patient-derived xenografts in immunocompromised NOD/SCID gamma (NSG) mice. This model is predictive of the clinical outcome in patients: stage III melanomas that metastasize efficiently in NSG mice also form distant metastases in patients, whereas melanomas that metastasize inefficiently in mice do not readily metastasize in patients. Using this model we have isolated melanoma cells from primary subcutaneous tumors, peripheral blood, and metastatic nodules from visceral organs, and tested their capacity to form tumors at different sites. The blood and distant sites were hostile environments that prevented efficient tumorigenesis, compared to the primary site. Cells from metastatic nodules formed tumors at higher frequency than cells from the blood or primary subcutaneous tumors, when transplanted directly into visceral organs. To examine the mechanism underlying the ability of metastatic cells to grow in visceral organs, we have performed metabolomic profiling of these cell populations and discovered that compared to cells from primary subcutaneous tumors, both circulating tumor cells (CTCs) as well as cells from metastatic nodules have a low Glutathione (GSH)/oxidized glutathione (GSSG) ratio as well as high levels of reactive oxygen species (ROS). These data strongly indicate that melanoma cells experience high levels of oxidative stress in the blood and in visceral organs, suggesting this might be the reason why solid cancers are highly inefficient at forming distant metastases. Furthermore, chronic treatment of mice with antioxidants such as N-acetylcysteine had no effect on the growth of the primary subcutaneous tumors but caused a significant increase in circulating tumor cell frequency and the overall metastatic burden in distant organs. These data suggest that the ability of the cells to detoxify ROS may be directly linked to their ability to metastasize. We found that reversible metabolic changes in efficiently metastasizing melanomas increased their capacity to withstand oxidative stress. Depletion of NADPH-producing enzymes in the folate pathway had a detrimental effect on both circulating tumor cell frequency as well as overall metastatic burden. Thus, oxidative stress limits distant metastasis by melanoma cells in vivo, and successful metastasizers rely on upregulation of antioxidant mechanisms particularly through the folate pathway. This work provides insight into the metabolism of metastasis and suggests that specific folate pathway enzymes may represent potential novel therapeutic targets.

Citation Format: Elena Piskounova, Michalis Agathocleous, Sara Mann, Ralph DeBerardinis, Sean J. Morrison. Reversible metabolic changes in human melanoma cells enable distant metastasis. [abstract]. In: Proceedings of the AACR Special Conference: Metabolism and Cancer; Jun 7-10, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(1_Suppl):Abstract nr A23.