Abstract P1-04-01: Breast milk exosomes promote breast cancer progression

Abstract

Abstract Background: The stimulation of extant neoplastic cells vs. their inhibition during breast involution is a key concept in whether pregnancy and lactation decrease or increase breast cancer risk. The time of weaning, a period of breast involution and remodeling, appears critical to future breast cancer risk, as during involution the breast microenvironment becomes tumor promotional. Both matrix metalloproteinases (MMPs) and transforming growth factor (TGF)β isoforms have been implicated in this process. We previously reported that TGFβ2 (but not TGFβ1) expression was significantly higher in milk collected from the cancer containing (vs. matched clinically normal) breast of women diagnosed with cancer during lactation. Hypothesis: TGFβ2 in milk exosomes from healthy lactating women modulates the development and progression of breast cancer. Methods: Matched (early, mature and wean-early involution) milk samples were collected from 13 lactating women, exosomes isolated and the levels of five (MMP2, 3, 9; TGFβ1, 2) proteins measured. Based on the results, additional wean samples were analyzed for TGFβ2 expression and samples divided based on their TGFβ2 expression. The highest and lowest TGFβ2 expressing milk exosome samples were co-cultured with MCF-7 breast cancer cells grown in exosome-depleted media. Cell proliferation was measured after 24h. Confocal microscopy was performed after 72h to evaluate epithelial to mesenchymal transition (EMT) in the cells. A TGFβ2 neutralizing blocking antibody was applied after 72 h co-culture. Results: The greatest increase in expression (four-fold) at the time of involution was in TGFβ2. Confocal microscopy performed 24h after co-culture confirmed the uptake of the exosomes (both those expressing hi and lo TGFβ2) in the MCF-7 cells. There was a significant increase in cell proliferation compared to control (p<0.001) in cells treated with hi TGFβ2 milk exosomes. 72h after co-culture, bright field microscopy demonstrated that MCF-7 cells treated with hi TGFβ2 underwent EMT including the formation of filopodia, whereas those treated with low TGFβ2 did not. A TGFβ2 blocking antibody reversed the EMT phenotype and filopodia formation. Impact: Pregnancy has a lasting influence on breast cancer risk, and pregnancy associated breast cancers (PABCs) diagnosed after delivery are generally aggressive, with a poor prognosis. Part of the reason for the development of PABCs, and the aggressive nature of PABCs may be the influence of high-expressing TGFβ2 exosomes in the milk on the breast ductal epithelium. Citation Format: Sauter ER, Qin W, Dasgupta S. Breast milk exosomes promote breast cancer progression. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P1-04-01.