Introduction <p>Triple negative breast cancer (TNBC) has significantly worse outcomes compared to other subtypes. Strains in the tumor microenvironment (TME) generated by cancer-associated fibroblasts (CAFs) can regulate TNBC progression. Recent studies suggest that expression of VEGFR-2 on TNBC is linked to decreased survival, while our prior studies show strains activate VEGFR-2 to drive angiogenesis. We hypothesized that VEGFR-2 on TNBC can be mechanically activated to alter migration and proliferation.</p> Methods <p>We utilized MDA-MB-231 TNBC cells loaded into the center chamber of a multi-microtissue TME model; opposing side chambers were loaded with CAFs or normal breast fibroblasts (NBFs). A second series of studies utilized magnetic beads to generate strains in the model without secretion of growth factors. Microtissues were analyzed for TNBC migration and proliferation via Ki67 staining.</p> Results <p>TNBC cells migrated significantly more towards CAFs compared to NBFs (5×); TME models with magnetic beads showed a 2× increase in migration compared to no strain controls. TNBC cells treated with shRNA against VEGFR-2 demonstrated decreased overall migration but still significantly more towards CAFs vs. NBFs (2×). Proliferation analyses showed strain significantly increased Ki67 in control cells (10%+ vs. 28%+) but not in shVEGFR-2 TNBC (~ 10% all conditions).</p> Discussion <p>These studies demonstrate that strain in the TME drives increased migration and proliferation of TNBC. Loss of VEGFR-2 suppresses migration and growth, even with mechanical stimulation. Therefore, our results suggest that mechanosignaling via VEGFR-2 on TNBC may regulate disease progression and potentially explain failure of anti-VEGFR-2 drugs in breast cancer patients.</p>