Fariya Sahadat, MPH

 Introduction. In the United States, breast cancer accounts for 30% of all new cancers in women and kills about 41,000 each year.^1,2 Women with Triple Negative Breast Cancer (TNBC) experience poorer outcomes due to TNBC’s aggressive nature and refractoriness to treatment.³ Unlike receptor positive breast cancers, TNBC lacks estrogen receptors, progesterone receptors and human epidermal growth factor 2 receptors.³ Many chemotherapies that target the glycolytic pathway have been ineffective in treating TNBC.⁴ Studies suggest that women who are obese or have excessive fat intake experience worse outcomes.⁵ This suggests that TNBC utilizes other metabolic processes for energy production outside the Warburg Effect.⁴ This effects posits that cancer cells rely on aerobic glycolysis over oxidative phosphorylation for energy production.⁶ Methods. TNBC cell lines that were resistant to glutaminase inhibition by CB-839 were analyzed using RNA-Seq to find differentially expressed genes.⁴ Cybrids and microarray, were used on resistant TNBC cells to show alterations in the Src oncogenic pathway.⁷ Glutamine was blocked to look at its effect on Src.⁷ Then, FAO was blocked using the CPT1 inhibitor, etoximir, to examine its impacts on Src and TNBC metastasis.⁷ miRNA microarray analysis and qRT-PCR were used to determine which miRNAs were differentially expressed in TNBC cells. miR34a was administered to TNBC cell lines to examine its effect on tumorigenesis.⁸ The MDA-MB-231 cell line treated with miR34a was injected into mice to examine its impact on Src and mouse survival.⁸ Results. In resistant TNBC, inhibition of glycolysis did not decrease ATP production.⁴ However, genes involved in trafficking fatty acids (FA) into the mitochondria, including CPT1, were upregulated.⁴ In these cells, there was an increase in phosphorylation of the Src Y419 domain.⁷ While blocking FAO with etoximir downregulated Src, blocking glycolysis had no effect on Src.⁷ Treatment of TNBC cells with miR34a downregulated Src and decreased both colony formation and cell invasion.⁸ Mouse models treated with miR34a showed increased survival due to reduced tumor progression.⁸ Conclusion. These studies illustrate that both FAO and Src are upregulated in TNBC, even in the presence of glycolytic inhibitors; illustrating that the Warburg Effect does not apply in this type of breast cancer.⁴ Rather, in TNBC, FAO increases autophosphorylation of Src which in-turn activates electron transport chain proteins to generate ATP.⁸ miR34a blocks Src directly, reducing tumorigenesis and increasing survival in mouse models.⁸ Consequently, blocking FAO or downstream Src may prove to be effective targets against TNBC. Targeting modifiable risk factors like diet and exercise could also have therapeutic potential since they decrease the FA substrates required for FAO.

1. Sun YS, Zhao Z, Yang ZN, et al. Risk Factors and Preventions of Breast Cancer. Int J Biol Sci. 2017;13(11):1387–1397. Published 2017 Nov 1. doi:10.7150/ijbs.21635
2. Centers for Disease Control and Prevention. Breast Cancer Statistics. US Department of Health and Human Services. Published 2019 May 28. Website: https://www.cdc.gov/cancer/breast/statistics/index.htm
3. Bianchini G, Balko J, Mayer I, et al.Triple-Negative Breast Cancer: Challenges and Opportunities of a Heterogeneous Disease. Nat Rev Clin Oncol. 2016;13:674–690. Published 2016 May 17. doi: https://doi.org/10.1038/nrclinonc.2016.66
4. Reis LMD, Adamoski D, Souza ROO, et al. Dual inhibition of glutaminase and carnitine palmitoyltransferase decreases growth and migration of glutaminase inhibition–resistant triple-negative breast cancer cells. Journal of Biological Chemistry. 2019;294(24):9342-9357. doi:10.1074/jbc.ra119.008180.
5. Balaban S, Shearer RF, Lee LS. et al.Adipocyte Lipolysis Links Obesity to Breast Cancer Growth: Adipocyte-derived Fatty Acids Drive Breast Cancer Cell Proliferation and Migration. Cancer Metab. 2017;5(1). Published 2017 Jan 13. doi: https://doi.org/10.1186/s40170-016-0163-7
6. Liberti MV, Locasale JW. The Warburg Effect: How Does it Benefit Cancer Cells? [published correction appears in Trends Biochem Sci. 2016 Mar;41(3):287] [published correction appears in Trends Biochem Sci. 2016 Mar;41(3):287]. Trends Biochem Sci. 2016;41(3):211‐ doi:10.1016/j.tibs.2015.12.001
7. Park JH, Vithayathil S, Kumar S, et al. Fatty Acid Oxidation-Driven Src Links Mitochondrial Energy Reprogramming and Oncogenic Properties in Triple-Negative Breast Cancer. Cell Rep. 2016;14(9):2154–2165. doi:10.1016/j.celrep.2016.02.004
8. Adams BD, Wali VB, Cheng CJ, et al. miR-34a Silences c-SRC to Attenuate Tumor Growth in Triple-Negative Breast Cancer. Cancer Research. 2015;76(4):927-939. doi:10.1158/0008-5472.can-15-2321.