Interrogating the Electromechanical Regulation of Cellular Volume at the Single-Cell Level

Detection of the mesenchymal-to-epithelial transition of invasive non-small cell lung cancer cells by their membrane undulation spectra

A cancer cell changes its state from being epithelial- to mesenchymal-like in a dynamic manner during tumor progression. For example, it is well known that mesenchymal-to-epithelial transition (MET) is essential for cancer cells to regain the capability of seeding on and then invading secondary/tertiary regions. However, there is no fast yet reliable method for detecting this transition. Here, we showed that membrane undulation of invasive cancer cells could be used as a novel marker for MET detection, both in invasive model cell lines and repopulated circulating tumor cells (rCTCs) from non-small cell lung cancer (NSCLC) patients. Specifically, using atomic force microscopy (AFM), it was found that the surface oscillation spectra of different cancer cells, after undergoing MET, all exhibited two distinct peaks from 0.001 to 0.007 Hz that are absent in the spectra before MET. In addition, by adopting the long short-term memory (LSTM) based recurrent neural network learning algorithm, we showed that the positions of recorded membrane undulation peaks can be used to predict the occurrence of MET in invasive NSCLC cells with high accuracy (>90% for model cell lines and >80% for rCTCs when benchmarking against the conventional bio-marker vimentin). These findings demonstrate the potential of our approach in achieving rapid MET detection with a much reduced cell sample size as well as quantifying changes in the mesenchymal level of tumor cells.

Quantitative screening of the effects of hyper-osmotic stress on cancer cells cultured in 2- or 3-dimensional settings

The maintenance of precise cell volume is critical for cell survival. Changes in extracellular osmolarity affect cell volume and may impact various cellular processes such as mitosis, mitochondrial functions, DNA repair as well as cell migration and proliferation. Much of what we know about the mechanisms of cell osmoregulation comes from in vitro two-dimensional (2D) assays that are less physiologically relevant than three-dimensional (3D) in vitro or in vivo settings. Here, we developed a microfluidic model to study the impact of hyper-osmotic stress on the migration, proliferation and ion channel/transporter expression changes of three metastatic cell lines (MDA-MB-231, A549, T24) in 2D versus 3D environments. We observed a global decrease in cell migration and proliferation upon hyper-osmotic stress treatment, with similar responses between 2D and 3D conditions. Specific ion channels/aquaporins are over-expressed in metastatic cells and play a central role during osmo-regulation. Therefore, the effects of hyper-osmotic stress on two transporters, aquaporin 5 (AQP5) and the transient receptor potential cation channel (TRPV4), was investigated. While hyper-osmotic stress had no major impact on the transporters of cells cultured in 2D, cells embedded in collagen gel (3D) decreased their AQP5 expression and exhibited a reduction in intra-cellular translocation of TRPV4. Furthermore, cell dispersion from T24 aggregates embedded in 3D collagen gel decreased with higher levels of hyper-osmotic stress. In conclusion, this study provides evidence on the impact of hyper-osmotic stress on various aspects of metastatic cell progression and highlights the importance of having a 3D cell culture platform in investigating molecular players involved in cancer cell migration.