Abstract 1092: AMPK alpha 2 promotes tumor cell survival in models of breast cancer dormancy.

Breast cancer can recur after standard of care treatment, even after many years. As a result, there is a need to identify new ways to treat metastatic recurrence, and to understand the mechanisms behind long-term cancer cell dormancy. AMP-dependent kinase (AMPK) has been implicated in tumor cell survival pathways and is under investigation as a potential target for breast cancer treatment. A defining characteristic of dormant tumor cells has been shown to be a reduction in mitogenic ERK1/2 signaling with a concomitant activation of stress-induced p38MAPK signaling. This study aimed to investigate the role of AMPKα2 in establishing and/or maintaining a dormant state. Two estrogen-dependent human breast cancer cell lines that express different levels of AMPKα2 were used. MCF-7 cells, with little to no AMPKα2 expression, were transfected to express GFP control or AMPKα2, while ZR-75-1 cells, with high AMPKα2 expression, were transduced with lentiviral shAMPKα2 or shGFP control particles. Stable cell lines were plated into mammospheres and were exposed to stress conditions such as hypoxia, depletion of essential growth factors, or low glucose. These mammospheres were evaluated by direct cell count, size, and immunofluoresence. In addition, single cell suspensions were mixed with matrigel and injected into athymic nude mice containing slow-release estradiol cholesterol pellets. Estradiol pellets were removed one week after implantation, and re-introduced six weeks later. Matrigel plugs and tumors were harvested and analyzed for cell survival by histological analysis, as well as immunofluorescent analysis of the tumor cells for ERK/p38 activation, epithelial cadherin, differentiation proteins, and autophagy markers. In order to investigate the survival of MCF-7 cells with and without AMPKα2, the amount of cells remaining after prolonged estrogen deprivation was evaluated. There were twice as many viable AMPKα2 expressing cells as GFP cells. Re-exposure of these animals to estradiol resulted in a rapid expansion of the remaining GFP and AMPKα2 tumor cells. Notably, AMPKα2 tumors maintained a significant growth advantage and were double the size of the GFP control tumors at harvest. Evaluation of the p38MAPK pathway by immunoblot revealed that those cells expressing increased amounts of AMPKα2 exhibited high levels of phospho-p38MAPK. Furthermore, those cells that expressed AMPKα2 also expressed increased amounts of LC3-II and autophagosome formation, standard autophagy markers. In conclusion, AMPK promotes breast cancer cell survival under stress in models of tumor dormancy potentially through promotion of the p38MAPK pathway with concomitant reduction in MAPK signaling, and/or autophagy pathways. This study suggests that AMPKα2 contributes to breast cancer recurrence by promotion of tumor cell dormancy and may be a novel therapeutic target. Citation Format: Katie L. Sullivan, Kathryn N. Phoenix, Melissa M. Fox, Stavros Kopsiaftis, Kevin P. Claffey. AMPK alpha 2 promotes tumor cell survival in models of breast cancer dormancy. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1092. doi:10.1158/1538-7445.AM2013-1092