text: Many foods are currently fortified with folic acid (FA), a synthetic folate (Vitamin B9). Folate deficiency causes many human health defects, most notably anemia and neural tube defects. The effects of excess supplementation on human health have to date been understudied. The rise in obesity in the last three decades further complicates this issue, with the combined effects of excess or insufficient folic acid intake and an obese phenotype being unknown. Obesity is associated with a number of cancers, including triple negative breast cancer (TNBC). TNBC comprises 16% of all breast cancers, is highly aggressive and more likely to recur and metastasize than other breast cancers. Unlike other subtypes, TNBC does not respond to hormone-targeted therapies and treatment options are limited to cytotoxic chemotherapy. Here, we examined the effects of FA supplementation and deficiency on tumor growth, metastasis and metabolism in obesity-responsive models of primary (M-Wnt) and metastatic (metM-Wnt; MDA-MB-231) TNBC. FA supplementation and deficiency significantly enhanced primary tumor growth and invasiveness in lean mice, while no difference in tumor size was detected in obese groups. FA supplementation reduced while deficiency increased survival and reduced lung tumor metastasis incidence in lean, but not obese mice. Liver and tumor metabolomic profiling revealed that modulation of dietary FA caused systemic and tumor-specific metabolic reprogramming, altering pathways involved in fatty acid, purine, amino acid, glutathione and energy metabolism. Short term in vitro FA withdrawal resulted in reduced proliferation, migration and invasion and energy production in all cell lines, as well as significant changes in gene expression profile, particularly of many metabolic pathways. In contrast, chronic in vitro FA depletion resulted in heightened oxidative stress, autophagy and apoptosis in metastatic TNBC cells, with nonmetastatic TNBC cells being able to adapt to and withstand the nutrient stress via the pentose phosphate pathway and glutathione redox signaling. Taken together, these results suggest that modulation of dietary folic acid in lean (but not obese) individuals causes systemic and tumor-specific metabolic reprogramming, which may confer a growth advantage in nonmetastatic cells and from which metastatic TNBC cells cannot recover. Moreover, obesity and FA excess cause similar metabolic and procancer effects and in combination, are not synergistic.
  Citation Format: Ciara H. O'Flanagan, Xuewen Chen, Zahra Ashkavand, Sergey A. Krupenko, Stephen D. Hursting. Nutrient stress via folic acid modulation causes systemic and cancer-specific metabolic reprogramming and differential effects on primary and metastatic mammary tumor growth in lean and obese mice [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 247. doi:10.1158/1538-7445.AM2017-247