Solid tumours are typically first diagnosed by palpation, revealing increased stiffness, while cancer cells are usually reported to be softer. The mechanical characteristics are not universal and depend on the cell type and the stage of development. Current techniques are usually point or 2D measurement techniques that lack depth penetration in 3D samples. We are developing optical coherence mechano-microscopy integrated with a confocal fluorescence microscope as a platform to investigate the mechanical phenotypes of 3D cancer models, mimicking the conditions in the native tumour microenvironment. This platform enables unique measurement of the 3D elasticity (i.e. Young’s modulus) of metastatic and non-metastatic breast cancer cell spheroids embedded in GelMAl, presenting the extracellular matrix, co-registered with fluorescence images. Our findings show that cells at the centre of non-metastatic cancer cell spheroids are softer (5.8 kPa) than the cells at the periphery (12.7 kPa). In contrast, migrating cells at the periphery of the metastatic cancer cell spheroids are softer (5.7 kPa) than the less motile cells at the centre of these spheroids (8.0 kPa).
Multicellular tumour spheroids have recently become important tools to investigate different stages of cancer development due to their 3D nature. We propose dynamic optical coherence microscopy (OCM) as a label-free low coherence interferometric technique for 3D characterization of morphology and cell motility during cell migration in multicellular cancer cell spheroids. We integrate dynamic OCM with confocal fluorescence microscopy (CFM) to validate and co-register the subcellular-scale endogenous contrast generated by dynamic OCM signal with sub-cellular features such as cell nucleus and membrane. We apply dynamic OCM integrated with CFM to scan metastatic and non-metastatic breast cancer cell spheroids embedded in gelatin-methacryloyl (GelMA) hydrogel and demonstrate that dynamic OCM provides high-contrast morphological imaging equivalent to that of confocal fluorescence in cancer cell spheroids. We use dynamic OCM to visualize different phases of cell migration such as invadopodia formation, cells breaking off from the primary tumour model, and migrating cells presenting a spindle-like shape, and to characterize cell motility at different stages.
Multicellular spheroids are a powerful model to study biochemical and biophysical interactions between cancer cells during growth and progression. However, little is known about how the biomechanics of the three-dimensional (3-D) microenvironment control cancer cell behaviors due to the lack of enabling technologies that can measure 3-D subcellular-scale elasticity and co-register it with the morphology and function of cells in a 3-D microenvironment. Here, we propose a multimodal imaging system that integrates an optical coherence microscopy-based subcellular mechano-microscopy system with a multi-channel confocal fluorescence microscopy system. Using this multimodal imaging system, we scan non-metastatic MCF7 breast cancer cell spheroids encapsulated in gelatin methacryloyl (GelMA) hydrogels and co-register 3-D intra-spheroid elasticity with subcellular structures, such as nuclei and cell membranes.
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