Abstract 1020: Autophagy forms part of a metabolic switch during epithelial-to-mesenchymal transition and metastasis in a murine claudin-low breast cancer model
Authors: O’Flanagan Ciara H. , Rossi Emily L. , Hursting Stephen D. 
Published: July 2016

Epithelial-to-mesenchymal transition (EMT), the process through which epithelial cells gain mesenchymal characteristics including reduced adhesion and enhanced invasion, is a critical step in progression of cancer cells toward metastasis. However, the molecular mechanisms governing this process remain poorly understood. Furthermore, though metastasis is the cause of 90% of cancer deaths, no targeted therapy is currently available for metastatic disease. Metabolic reprogramming is a key feature of most cancer cells, with oxidative phosphorylation often being switched off in favor of glycolytic and synthetic pathways. Autophagy is a catabolic process in which protein complexes, damaged organelles and other macromolecules are lysosomally degraded. Autophagy can promote cancer cell survival, providing protein, lipid, nucleic acid and membrane precursors as well as auxiliary energy during periods of energy stress. The role of metabolism in EMT and metastasis has not been well studied. We hypothesized that the transition to metastasis involves metabolic alterations, including activation of autophagy.

Previously, we derived (from a spontaneous mammary tumor in an MMTV-Wnt transgenic mouse) epithelial-like (E-Wnt) and mesenchymal-like (M-Wnt) cell lines, which recapitulate basal-like and claudin-low and breast tumors, respectively. Here, a metastatic derivative of M-Wnt cells was generated from lung metastases following serial passages in a severe combined immunodeficient (SCID) mouse. metM-Wnt cells were more proliferative, invasive and formed more colonies in soft agar than their parental M-Wnt cell line. Tail vein injection or mammary fat pad orthotopic implantation of metM-Wnt cells resulted in metastatic tumor formation in either the lungs or liver as detected by IVIS imaging and histological analysis. metM-Wnt cells displayed higher rates of glycolysis and oxidative phosphorylation, indicating that these cells are highly energetic. Furthermore, M-Wnt and metM-Wnt cells and tumors were found to have increased autophagic flux, as measured by LC3B expression and cleavage compared to E-Wnt cells and tumors. metM-Wnt cells were more sensitive to autophagy inhibition (either via chloroquine treatment or knockout of Atg5, a key component of the autophagic machinery) than M-Wnt or E-Wnt cells. Conversely, metM-Wnt cells were resistant to treatment with rapamycin, concomitant with sustained activation of mTOR, which controls many metabolic pathways including autophagy and protein synthesis. These results indicate that metabolic alteration is a feature of EMT in claudin-low breast cancer, including increased glycolysis, oxidative phosphorylation and autophagy. Furthermore, metastatic breast cancer cells may be more reliant on autophagy than non-metastatic cells, and autophagy may therefore be a therapeutic target in which to treat metastatic breast cancers.

Citation Format: Ciara H. O’Flanagan, Emily L. Rossi, Stephen D. Hursting. Autophagy forms part of a metabolic switch during epithelial-to-mesenchymal transition and metastasis in a murine claudin-low breast cancer model. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1020.