Abstract 1104: Malignant stroma regulates luminal breast cancer-cell growth versus basal breast cancer cell migration through different growth factor pathways.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC The stromal microenvironment plays an important role in growth and aggressiveness of breast cancers. We have generated a reactive mouse mammary stromal cell line called BJ3Z that is tumorigenic in nude mice. In mixed-cell xenografts, BJ3Z cells enhance growth and angiogenesis of solid tumors established from MCF-7 human breast cancer cells. To minimize extensive dependence on in vivo studies, we have developed Matrigel-based 3D colony co-culture assays to analyze the role of the stromal microenvironment on epithelial-cell derived breast cancers in vitro. First, to define the properties of reactive BJ3Z cells, they were contrasted to normal mouse mammary gland fibroblasts (NMF), both grown in 3D. Expression profiling showed that Transforming Growth Factor-β1 (TGF-β1) and Platelet-Derived Growth Factor ligands A and B (PDGF-A & PDGF-B) are upregulated in BJ3Z cells. Next, we contrasted effects of BJ3Z and NMF cells on the three major breast cancer subtypes: Luminal MCF-7 cells; HER2 amplified BT-474 cells; Basal-like MDA-MB-231 and BT-20 cells. We find that malignant stroma has differential effects depending on the breast cancer subtype. 1. With regard to PDGF: Reactive stroma generated by BJ3Z cells in 3D, increases the growth of Luminal and HER2-amplified breast cancer cells as measured by BrdU incorporation. In contrast, BJ3Z cells suppress growth of Basal-like breast cancer cells. Similar results were obtained using BJ3Z-conditioned media. This suggests that the effects of BJ3Z cells on Luminal tumor-cell growth involve soluble factors. In that regard, use of Imatinib Mesylate (IM) a tyrosine kinase inhibitor against PDGF receptors completely blocks the rise in MCF-7 cell proliferation caused by BJ3Z-cell co-culture, or by BJ3Z cell-conditioned medium. In order to demonstrate that this is not due to a mouse-specific factor we showed that recombinant human PDGF-BB enhances 3D growth of MCF-7 cells. Parenthetically, BJ3Z-conditioned medium also enhances an in vitro angiogenesis model by a PDGF-dependent pathway that can be inhibited by IM. 2. With regard to TGF-β this pathway is not involved in Luminal tumor-cell growth. Rather in Basal-like cancer cells, BJ3Z or their conditioned medium use TGF-β pathway-dependent Smad 2/3 phosphorylation to enhance cell migration. This effect can be blocked by a TGF-βR1 inhibitor. We conclude that the stromal microenvironment uses the PDGF pathway to regulate Luminal tumor-cell growth and angiogenesis; the TGF-β pathway to regulate Basal tumor-cell aggressiveness. Citation Format: Mauricio P. Pinto, Britta M. Jacobsen, Kathryn B. Horwitz. Malignant stroma regulates luminal breast cancer-cell growth versus basal breast cancer cell migration through different growth factor pathways. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1104. doi:10.1158/1538-7445.AM2013-1104