Abstract B090: Collagen organization implicated in tumor dormancy

It is known that tumor cells can reside in a dormant state for decades. Data from numerous studies strongly suggest that extracellular matrix (ECM) proteins can impart a dormant phenotype, however little is known regarding how ECM regulates tumor cell dormancy. Given the technical difficulties in studying tumor cell dormancy in the context of secondary lesions (i.e., the searching for a needle in a haystack problem), here we use tumor suppression at the primary site as a model to investigate the role of ECM in breast cancer dormancy. Specifically, we hypothesize that insight into tumor dormancy can be obtained by studying the response of the mammary ECM to tamoxifen treatment and parity, two conditions that protect the mammary epithelium from tumorigenesis. Utilizing breast cancer cell lines capable of transitioning from indolent to proliferative/invasive states, we demonstrate that ECM isolated from tamoxifen treated or parous rat mammary glands decreases tumor growth and impedes invasive phenotypes compared to nulliparous mammary matrix, using both in vitro and in vivo models. Collagen stained tissues and proteomic analysis identified increased abundance of collagen I in tamoxifen treated and parous mammary stroma, an observation extended to breast tissue of parous women. These results are unexpected given the known pro-tumorigenic attributes of fibrillar collagen. Second harmonic generation imaging and atomic force microscopy reveals that the abundant collagen observed in the mammary glands of parous rats is less linearized and has decreased stromal stiffness compared to nulliparous mammary glands. These data implicate collagen organization rather than density in tumor suppression. Using 3D cell culture models, we demonstrate that linearized fibrillar collagen I induces an invasive phenotype in mammary tumor cells through a mechanism dependent on β1 integrin endocytic recycling. Conversely, high density, non-fibrillar collagen I decreases β1 endocytic integrin recycling, increases junctional E-cadherin staining, upregulates adherens and tight junction genes, and downregulates EMT transcription factors and metalloproteinase genes, all attributes consistent with tumor suppression. These data show that collagen organization, rather than collagen density, is a key contributor to the tumor cell invasive phenotype. In conclusion, we demonstrate that collagen | organization is dominant over density in driving tumor cell invasion, an observation that may have implications in understanding how mammographic breast density determines breast cancer risk, as well as how collagen organization contributes to tumor cell dormancy at distant sites. Citation Format: Ori Maller, Kirk C. Hansen, Valerie Weaver, Rytis Prekeris, Pepper Schedin. Collagen organization implicated in tumor dormancy. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; Oct 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2013;11(10 Suppl):Abstract nr B090.