Background and Objectives: Breast cancer is among the most common cancer in women with 2.1 million new cases detected each year. Numerous studies have demonstrated a connection between body mass index (BMI) and cancer incidence, with obesity (BMI ≥ 30) being responsible for the development of at least 13 types of cancer, and 15% to 20% of total cancer-related mortality. The effects of extracellular vesicles (EVs) derived from the obese adipose tissue microenvironment on breast cancer have not yet been clearly elucidated.
Methods: EVs were obtained from media conditioned with human breast adipose tissue from reduction mammoplasty (n=31). Women were healthy at the time of surgery and had no history of breast cancer. Patient samples were stratified based on their body mass index (BMI), with a BMI < 25 considered healthy and a BMI ≥ 25 considered overweight/obese. Breast adipose tissue-derived EVs (AT-EVs) were characterized (Quantitative Mass Spectrometry) and used to treat human breast cancer cell lines, including the ER+ MCF7 and triple negative breast cancer (TNBC) MDA-MB-231. Effects on cell proliferation and migration in vitro, and on tumor growth in a mouse xenograft model, were examined after long-term education with EVs. RNA sequencing was performed to investigate potential reprogramming induced by AT-EVs.
Results: We found a positive correlation between protein amount per AT-EV and BMI. Quantitative proteomics of AT-EVs revealed 46 proteins that were significantly higher and 54 proteins that were significantly lower in specimens from women with a BMI ≥ 25 compared to women with a BMI < 25. AT-EVs from patients with a BMI ≥ 25 induced proliferation of MCF7 cells compared to AT-EVs from patients with a BMI < 25. Obese EVs induced a more aggressive phenotype in MDA-MB-231 cells, increasing their invasiveness in vitro. Obese EVs also increased the growth of MCF7 and MDA-MB-231 cells in vivo. Ingenuity pathway analysis of RNA-Seq data identified significant differences in mTOR signaling and canonical pathways associated with altered mitochondrial function.
Conclusion: Our studies identify a novel mechanism to explain the obesity-breast cancer link in older women. Namely, that in obesity, the breast microenvironment produces EVs capable of reprogramming breast cancer cells to grow faster and be more aggressive. Identifying which cargo in breast AT-EV mediates these effects may provide new targets for intervention.