Abstract B10: Soluble lung-derived factors mediate breast cancer cell migration and growth via CD44 receptor-ligand interactions

Abstract

Abstract Background: The majority of breast cancer deaths occur due to metastatic disease. Clinical studies have identified a specific pattern for the metastatic spread of breast cancer, where preferential secondary sites include the lymph node, lung, liver, bone, and brain. However, it is not clear whether properties of the cancer cells (the “seeds”); properties of the organ microenvironment (the “soil”), or a combination of both are responsible for this observed organ tropism of breast cancer. It has been proposed that small subsets of stem-like tumor cells are responsible for tumor initiation and progression. In breast cancer, these cells are identified by their high aldehyde dehydrogenase (ALDH) activity and/or CD44+CD24- phenotype. We have previously shown that ALDHhiCD44+ breast cancer cells exhibit key metastatic behaviors in vitro and in vivo. However, the mechanisms underlying the organ-specific metastatic capacity of these cells requires further elucidation. Hypothesis: Breast cancer cells exhibit differential growth and migration patterns in specific organ microenvironments; and ALDHhiCD44+ breast cancer cells exhibit increased organ-specific migration and growth (1) preferentially in the lung microenvironment and (2) compared to their ALDHlowCD44- counterparts. Methods: A novel ex vivo model system comprised of organ-conditioned media generated from athymic nude mice was used to test organotropic migration/growth of whole populations of MDA-MB-231, MDA-MB-468, SUM149, and SUM159 human breast cancer cell lines, and ALDHhiCD44+ and ALDHlowCD44- populations isolated from the MDA-MB-231 cell line. Protein arrays were used to interrogate lung-conditioned media and identify soluble factors of interest. Bead-based immunodepletion of target proteins was performed on lung-conditioned media. The migration/growth response of MDA-MB-231 breast cancer cells was then assessed following exposure to depleted vs. non-depleted lung-conditioned media. Results: Whole populations of all 4 human breast cancer cell lines examined responded via cell line specific patterns of migration towards organ-conditioned media. Notably, all lines demonstrated increased migration towards lung-conditioned media (p<0.05). These observations closely mirror previously observed patterns of in vivo metastatic behavior, providing validation for our ex vivo model system. ALDHhiCD44+ cells responded in a chemotactic manner towards organ-conditioned media in a similar pattern to whole population results. Notably, ALDHhiCD44+ cells showed preferential migration towards lung-conditioned media relative to all other organ-conditioned media tested (p<0.05). Several CD44 ligands including osteopontin (OPN) and E-, L-, and P-selectin were identified by protein array analysis of lung-conditioned media. Immunodepletion of L-selectin or OPN from lung-conditioned media resulted in decreased migration of MDA-MB-231 cells, however only depletion of OPN also resulted in decreased growth relative to non-depleted media. These effects could be abrogated by pre-treatment with a functional CD44 receptor blocking antibody (p<0.05). Conclusions: Our data suggest an important role for CD44 receptor-ligand interactions in mediating lung-specific breast cancer cell migration and growth. To the best of our knowledge, this is the first study to undertake ex vivo investigation of the role of the microenvironment in metastatic organ tropism in the context of the cancer stem cell hypothesis. Citation Format: Ying Xia, Jenny E. Chu, Benjamin Chin-Yee, David Goodale, Alysha K. Croker, Alison L. Allan. Soluble lung-derived factors mediate breast cancer cell migration and growth via CD44 receptor-ligand interactions. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Invasion and Metastasis; Jan 20-23, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;73(3 Suppl):Abstract nr B10.