Progression to advanced stage metastatic disease, resistance to endocrine therapies, and failure of drug combinations remain major barriers in the breast cancer therapy. Tumor microenvironments play an important role in progression from non-invasive to invasive disease as well as in response to therapies. Development of physiologically relevant, three-dimensional (3D) controlled microenvironments that can reliably recapitulate tumor progression from the early non-invasive to advanced metastatic stage will contribute to our understanding of disease biology and serve as a tool for screening of drug regimens targeting different disease stages. We have recently engineered physicochemical microenvironments by precisely controlling the size of 3D microtumors of non-invasive T47D breast cancer cells. We hypothesized that the precise control over physiochemical microenvironments will generate unique molecular signatures in size-controlled microtumors (small 150 μm vs large 600 μm) leading to differential phenotypic features and drug responses. The results indicated that large (600 μm) T47D microtumors exhibited traits of clinically advanced tumors such as hypoxia, reactive oxygen species, mesenchymal marker upregulation and collective cell migration unlike non-hypoxic, non-migratory small microtumors (150 μm). Interestingly, large microtumors also lost estrogen receptor alpha (ER-α) protein, consequently showing resistance to 4-hydroxytamoxifen (4-OHT). On the other hand, large microtumors showed upregulation of pro-angiogenic marker, vascular endothelial growth factor (VEGF), and hence were more responsive than small microtumors to the growth inhibition by anti-VEGF antibody. Surprisingly, both small and large microtumors exhibited comparable levels of phosphorylated epidermal growth factor receptor (pEGFR) and downstream signaling molecules such as AKT. As a consequence, both small and large microtumors showed comparable growth inhibition in response to gefitinib (inhibitor preferentially targeting EGFR) independent of microtumor size. Thus, precise control over the microenvironmental factors successfully recapitulated molecular characteristics underlying early vs advanced stage disease using the same non-invasive T47D cells. Such unique molecular signatures further resulted in differential response of small and large microtumors to anti-estrogen, and anti-VEGF treatments with comparable response to the EGFR-targeted therapies, underlining the importance of such stage-specific disease progression models in cancer drug discovery.
Keywords: EGFR/VEGF targeted therapy; breast cancer progression; endocrine resistance; in vitro drug screening; size-controlled microtumor model; three-dimensional in vitro models.