Cells generate mechanical force to organize the extracellular matrix (ECM) and drive important developmental and reparative processes. Likewise, tumor cells invading into three-dimensional (3D) matrices remodel the ECM microenvironment. Importantly, we previously reported a distinct radial reorganization of the collagen matrix surrounding tumors that facilitates local invasion. Here we describe a mechanism by which cells utilize contractility events to reorganize the ECM to provide contact guidance that facilitates 3D migration. Using novel assays to differentially organize the collagen matrix we show that alignment of collagen perpendicular to the tumor-explant boundary promotes local invasion of both human and mouse mammary epithelial cells. In contrast, organizing the collagen matrix to mimic the ECM organization associated with noninvading regions of tumors suppresses 3D migration/invasion. Moreover, we demonstrate that matrix reorganization is contractility-dependent and that the Rho/Rho kinase pathway is necessary for collagen alignment to provide contact guidance. Yet, if matrices are prealigned, inhibiting neither Rho nor Rho kinase inhibits 3D migration, which supports our conclusion that Rho-mediated matrix alignment is an early step in the invasion process, preceding and subsequently facilitating 3D migration.

Interest in constructing a reliable 3-dimensional (3D) collagen culture platform in microfabricated systems is increasing as researchers strive to investigate reciprocal interaction between extra cellular matrix (ECM) and cells under various conditions. However, in comparison to conventional 2-dimensional (2D) cell culture research, relatively little work has been reported about the polymerization of collagen type I matrix in microsystems. We, thus, present a study of 3D collagen polymerization to achieve reproducible 3D cell culture in microfluidic devices. Array-based microchannels are employed to efficiently examine various polymerization conditions, providing more replicates with less sample volume than conventional means. Collagen fibers assembled in microchannels were almost two-times thinner than those in conventional gels prepared under similar conditions, and the fiber thickness difference influenced viability and morphology of embedded human mammary fibroblast (HMF) cells. HMF cells contained more actin stress fibers and showed increased viability in 3D collagen matrix composed of thicker collagen fibers. Relatively low pH of the collagen solution within a physiological pH range (6.5~8.5) and pre-incubation at low temperature (~ 4 °C) before polymerization at 37 °C allow sufficient time for molecular assembly, generating thicker collagen fibers and enhancing HMF cell viability. The results provide the basis for improved process control and reproducibility of 3D collagen matrix culture in microchannels, allowing predictable modifications to provide optimum conditions for specific cell types. In addition, the presented method lays the foundation for high throughput 3D cellular screening.

Multiphoton laser scanning microscopy (MPLSM) utilizing techniques such as multiphoton excitation (MPE), second harmonic generation (SHG), and multiphoton fluorescence lifetime imaging and spectral lifetime imaging (FLIM and SLIM, respectively) are greatly expanding the degree of information obtainable with optical imaging in biomedical research. The application of these nonlinear optical approaches to the study of breast cancer holds particular promise. These noninvasive, multidimensional techniques are well suited to image exogenous fluorophores that allow relevant questions regarding protein localization and signaling to be addressed both in vivo and in vitro. Furthermore, MPLSM imaging of endogenous signals from collagen and fluorophores such as nicotinamide adenine dinucleotide (NADH) or flavin adenine dinucleotide (FAD), address important questions regarding the tumor-stromal interaction and the physiologic state of the cell. We demonstrate the utility of multimodal MPE/SHG/FLIM for imaging both exogenous and/or endogenous fluorophores in mammary tumors or relevant 3-D systems. Using SLIM, we present a method for imaging and differentiating signals from multiple fluorophores that can have overlapping spectra via SLIM Plotter-a computational tool for visualizing and analyzing large spectral-lifetime data sets.