Abstract 560: Mesenchymal stem cells promote mammosphere formation in normal and malignant breast cells

Abstract

Abstract Purpose: Normal and malignant breast tissue contains a rare population of cells with the capacity to self-renew, referred to as stem cells, or tumor initiating cells (TIC) in the case of tumors. These cells can be enriched by growth as “mammospheres” in three-dimensional cultures. We tested the hypothesis that mesenchymal stem cells (MSC), which are known to support tumor growth and metastasis, increase mammosphere formation. Materials and Methods: Normal human mammary epithelial cells (HMEC), and breast cancer cells (MCF-7, SUM149 and IBC3) were grown as mammospheres, plated at low density in serum-free growth factor supplemented suspension cultures. MSC were added as an increasing percentage of total cells plated (0, 2, 5 and 10%). MSC-conditioned media was generated by growing MSC as spheroids for 5 days. Results: MSC integrated into mammospheres, resulting in a dose-dependent increase in the number of mammospheres formed. Normal mammary epithelial cells formed 1.6 to 2.4 to 2.7-fold (p< 0.001) more mammospheres in the presence of 2, 5 and 10% MSC. Similarly, the number of MCF-7 derived mammospheres increased 5.9 to 8.5 to14.8-fold (p = ≤ 0.001) in the presence of 2, 5 and 10% MSC. A similar dose-dependent increase in sphere formation was seen for SUM149 cells and inflammatory breast cancer cells in short-term culture derived from pleural effusions. This effect was found to be mediated by secreted factors as MSC-conditioned media also increased sphere formation. SUM149 cells formed 6.4 to 14.2 to 13.7-fold more mammospheres when incubated for 5 days in 5, 25 and 50% MSC conditioned-media (p <0.0001). HMEC derived mammospheres had higher levels of expression of N-cadherin and RhoC and lower levels of expression of E-cadherin and Notch when formed in the presence of MSC conditioned media. Conclusions: Mesenchymal stem cells increase mammosphere formation of normal breast epithelial cells, established cancer cell lines (MCF-7 and SUM149) and short term primary breast cancer cells (IBC3). This effect is mediated by MSC secreted factors and results in cadherin switching, which may promote breast cancer progression and resistance to therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 560.