When Mechanical Stress Matters: Generation of Polyploid Giant Cancer Cells in Tumor-like Microcapsules

In this work, we studied the generation and rising of polyploid cancer cells as a product of mechanical stress. To this purpose, MCF7 breast cancer cells were cultured on 2D ( i.e . flasks, or flat hydrogels), and in 3D milieus ( i.e . Spheroids, or immobilized within alginate-gelatin microbeads, named in this work as tumor-like microcapsules), and further analyzed by biophysical and genetic methods (i.e. single-cell Traction Force Microscopy and RNA-seq respectively). Our results show that MCF7 cells preconditioned onto 2D surfaces exhibit a low number of polynucleated cells, while their culture in 3D environments triggered their progressive generation with time. Genetic studies enabled us to determine that polyploid cells found in tumor-like microcapsules are likely originated by cell-cell fusion and disrupted cytokinesis, showing most of the genetic markers for Polyploid Giant Cancer Cell, while cells cultured as spheroids seem to be likely generated by other mechanisms, such as cell cannibalisms, entosis, or emperipolesis. Our outcomes strongly suggest that both mechanical stress and confinement are required to stimulate cell polyploidy, which can be easily addressed by the immobilization of breast cancer cells in tumor-like microcapsules.