Malignant Progression Impacts Small Extracellular Vesicle (sEV) Interstitial Transport and Spatial Distribution
From 2000 to 2015, 97% of clinical trials in oncology failed, in part, due to an incomplete understanding of the dynamic tumor microenvironment (TME). The interplay between the developing neoplasm, resident immune and stromal cells, the extracellular matrix, and signaling molecules results in a complex balance that can promote or prevent tumor progression. An improved understanding of the relationship between these features will facilitate the development of novel cancer therapeutics.The primary goal of this thesis is to characterize how cancer cell-secreted small extracellular vesicles (sEV) are transported and distributed within the interstitial space of the TME. sEVs influence cancer progression through interactions with a range of cell populations in the TME. However, how sEVs are physically distributed within the interstitial matrix, and how this distribution is altered over the course of malignant cancer progression is poorly defined. To assess sEV interstitial transport, sEVs were isolated from the MCF10 series—a model human cell line of breast cancer progression. sEV characterization demonstrated increasing presence of laminin-binding integrins α3β1 and α6β1 on sEVs as the malignant potential of the MCF10 cells increased. Diffusion experiments using fluorescence recovery after photobleaching (FRAP) provided quantitative characterization of diffusion and kinetic binding parameters between bulk sEVs and a laminin-rich ECM, and demonstrated increased accumulation of bound sEVs in the matrix as the malignancy of the parent cell increased. In silico finite element models illustrated sEV accumulation in the matrix resulting in higher bound interstitial sEV concentrations as well as the formation of a transient spatial gradient. Subsequent in vitro microfluidic device convective flow experiments confirmed enhanced concentration of sEVs in the matrix and the formation of interstitial concentration gradients mediated by integrin interactions with laminin-rich ECM. Taken together, these studies demonstrate that sEV interstitial transport, concentration, and spatial distribution are partially dependent on integrin binding to laminin, and evolves with cancer cell malignancy.