Adipose-mimetic granular hydrogels uncover biophysical cues driving breast cancer invasion
1.Breast cancer cells invade mammary adipose tissue during initial stages of metastasis but how the physical properties of adipose tissue regulate this process remains unclear. Here, we combined single cell mechanical characterization of primary adipocytes with microfluidic hydrogel fabrication, quantitative multiparametric imaging, Discrete Element Method (DEM) simulations, and in vivo experiments to elucidate these connections. First, we quantified the heterogeneous size and stiffness of primary adipocytes, and replicated these properties by fabricating adipocyte-sized polyacrylamide (PAAm) beads with tunable elasticity. Subsequently, we embedded these beads into type I collagen, the primary fibrillar extracellular matrix (ECM) component of breast adipose tissue, to form 3D granular hydrogels mimicking aspects of native adipose tissue architecture. Granular hydrogels embedded with beads demonstrated increased breast cancer cell invasion relative to bead-free controls, an effect that was more pronounced with soft versus stiff beads and correlated with increased collagen fiber alignment and hierarchical organization. In addition, live cell imaging and DEM simulations revealed that soft beads promoted invasion relative to stiff beads by deforming in response to confined cancer cell migration. Fiber alignment and adipocyte deformation trends were validated in vivo via intravital imaging of cancer cell migration in mammary fat pads of mice, and suggest that adipocyte mechanics regulate breast cancer invasion by coordinating both ECM architecture and cellular confinement. Ultimately, this work highlights the utility of tunable PAAm bead-collagen composites as micromechanical models to study the effect of adipose tissue structure on cancer cell invasion. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=106 SRC="FIGDIR/small/684224v1_ufig1.gif" ALT="Figure 1"> View larger version (56K): org.highwire.dtl.DTLVardef@d3ce0org.highwire.dtl.DTLVardef@117abb1org.highwire.dtl.DTLVardef@10917faorg.highwire.dtl.DTLVardef@55f3e_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGraphical Abstract:C_FLOATNO Polyacrylamide bead granular hydrogels recapitulate adipose tissue structure and alter cancer cell invasion in a stiffness-dependent manner. The invasion of primary breast cancer cells through mammary adipose is influenced by the heterogeneous mechanical properties of native stromal components, namely adipocytes and extracellular matrix (left). Customizable granular hydrogels provide insight into the physical regulation of breast cancer progression by mimicking adipose tissue extracellular matrix structure (collagen I, i.) and stromal cell mechanics (polyacrylamide bead, ii.), whereby the inclusion of soft beads and/or dilute matrix promotes cancer cell migration compared to stiffer hydrogels (right). C_FIG