The main threat and the reason for most cancer deaths are metastases. During the metastasis, invasion of cancer cells plays an important role that leads to the development of malignancy. To understand the specific patterns of tumor invasion and migration, as well as the relationship between cells, extracellular matrix (ECM) and substrate, engineered surfaces that not only can control the mechanical properties of the ECM structural but also can regulate cell adhesion, morphology, migration and other processes germane to cancer metastasis.
Thus, this study aims to establish both experimental and computation model for three-dimensional (3D) multicellular tumor spheroids (MCTS) invasive hydrogel platform for studying cell migration at matrix-substrate interface (MSI). This platform can be used to understand the specific patterns of tumor invasion and migration, as well as the relationship between cells and ECM and substrate.
Several cancer cell lines were grown into MCTS prior to embedding into collagen type I with concentration 2 mg/ml. Glass coverslip and a series of polydimethylsiloxane (PDMS) substrate membrane with different base/curing agent mass ratios were used to explore the effect substrate stiffness on MCTS invasion process, whose base/agent mass ratios were 10:1 and 30:1 (w:w). Besides, to investigate the effect of matrix-substrate interfacial adhesion strength (MSIAS), the MCTS-collagen mixture was then put onto PDMS (10:1) substrate, where the surface modification was performed using Poly-D-Lysine (PDL), glutaraldehyde (GA) and pluronic. Blebbistatin 10 µM and PD166793 10 µM were used to inhibit myosin II and matrix metalloproteinase (MMPs), respectively, after 3 hours of embedded MCTS into collagen. Migration of MTS invading ECM at MSI was observed for 24 hours through time-lapse imaging.
After examining the behavior and migration of several MCTSs formed from different cell lines on a non-coating glass substrate, MDA-MB-231 MTCS has the most obvious different character compared to other MTCS. Therefore, the investigation on the effect of matrix-substrate adhesion strength in the metastatic pattern of MCTS invasion at the heterogeneous interfaces in this study would be focused on the breast cancer cell line MDA-MB-231.
The MDA-MB-231 MCTSs had a movement speed on a stiff surface that was faster than a soft surface. MCTS tended to move in collective mode and spread according to the mechanism which was that the cells at the border of the MCTS that sensed the stiffness and movement dragged the cells at the core and became a conical spreading with a hollow bottom.
The differences in the extent of the spread, the invasion, and the migration mode of the MDA-MB-231 MCTSs were significantly different between the coatings. MCTSs were more invasive where MSIS is lower, and conversely, the rate of spreading is slower than where MSIS is high. In the case that has no influence on the substrate surface (pluronic coating), the metastatic behavior of MCTS is made easier because many single cells separate and move further.
Myosin II and MMPs are two important factors that help cells move in ECM. However, the results showed that MDA-MB-231 MCTS movement in ECM is mainly due to the contraction activity of myosin II.
By establishing this experimental and computational model, this study has the opportunity to identify salient patterns for this type of matrix-interface migration for cancer. The mechanics view may shed light on prevention of early metastasis.

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