Abstract 446: Differential effects of folate depletion on metabolic reprogramming and oxidative stress in nonmetastatic and metastatic claudin-low breast cancer cells

Folate coenzymes play an important role in biosynthesis and methylation reactions. Aberrant folate metabolism has been implicated in the development of several cancer types, though mechanisms underlying folate metabolism and cancer development remain unclear. We previously showed that a folate-restricted diet can exert differential effects on metastatic versus nonmetastatic murine claudin-low breast cancer cells in vivo. Specifically, folate restriction increased growth and invasion of orthotopically transplanted M-Wnt (nonmetastatic) tumor cells, but decreased growth and lung metastases of transplanted metM-Wnt cells, a metastatic subclone of M-Wnt cells. The current study set out to explore the underlying mechanism. To examine the effect of long-term folate depletion (LFD) on M-Wnt and metM-Wnt cell metabolism, oxidative stress and autophagic flux in vitro, the two cell lines were grown in standard and folate-depleted media for 14 days. metM-Wnt cells showed higher oxidative stress, as measured by ROS staining and Nrf2 expression, and phosphorylation of the key nutrient sensor, AMPK, compared to M-Wnt cells when grown in standard growth medium. LFD M-Wnt cells showed an increased dependence on glycolysis compared to those cultured in standard medium. Both M-Wnt and metM-Wnt cells displayed a high autophagy level in LFD, measured by LC3B cleavage, and AMPK phosphorylation. However, LFD metM-Wnt cells showed low viability, increased apoptosis and loss of redox defense, as measured by cleaved-caspase 3 and Nrf2 expressions. These results suggest that non-metastatic M-Wnt cells undergo metabolic reprogramming, including a shift from oxidative phosphorylation to glycolysis that may fuel cell growth and proliferation. Further, an elevated autophagic flux may mitigate nutrient stress induced by folate depletion, which allows them to withstand LFD and which may contribute to a more invasive primary tumor in response to folate restriction. In contrast, metM-Wnt cells are unable to undergo this metabolic adaptation, and display increased oxidative stress and cell death in response to LFD, preventing the development of metastatic lesions in vitro. This study highlights different responses of primary and metastatic breast cancer cells to folate depletion. The results provide additional rationale for targeting folate metabolism as a potential strategy for treating metastatic breast cancer. Citation Format: Xuewen Chen, Ciara H. O9Flanagan, Stephen D. Hursting. Differential effects of folate depletion on metabolic reprogramming and oxidative stress in nonmetastatic and metastatic claudin-low breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 446. doi:10.1158/1538-7445.AM2017-446