Biomechanics in tumor cell membrane repairing, cancer metastasis, and T cell activation

Abstract

During cancer metastasis, tumor cells need to go through narrow blood vessels or tight endothelial junctions on the vascular wall. These physical barriers will inevitably cause large deformations as well as membrane damages of the cell. Therefore, it is commonly believed that the deformability and damage response of cancer cells are closely related to their invasiveness. Along this line of reasoning, many attempts have been made to measure the mechanical response of tumor cells, using state-of-art characterization techniques such as atomic force microscope and magnetic tweezer, and then examine its possible correlation with their pathological state. However, it is hard to achieve high-throughput with these single cell measurement methods and most of existing studies only focused on the elastic or viscoelastic properties of the cell while the capability of tumor cells to undergo irreversible (i.e. plastic) deformations has seldom been examined. In addition, the question of how tumor cells recover from membrane damage remains largely unclear. Aiming to address these outstanding issues, we developed a microfluidic system capable of imposing precisely controlled cyclic deformation on cells and therefore probing their plastic characteristics. It was found that significant plastic strain can accumulate rapidly in highly invasive cancer cell lines and circulating tumor cells (CTCs) from late-stage lung cancer patients with a characteristic time of a few seconds. In comparison, very little irreversible deformation was observed in the less invasive cell lines and CTCs from early-stage lung cancer patients, highlighting the potential of using the plastic response of cells as a novel marker in future cancer study. Next, we showed that micron-sized membrane pores, induced by puncturing by a cylindrical atomic force microscope probe, resealed significantly (~ 1.3-1.5 times) faster in drug-resistant non-small cell lung cancer (NSCLC) cell lines than in their drug-sensitive counterparts. The enhanced membrane repairing ability is found to be caused by the overexpression of annexin in drug-resistant NSCLC cells. In addition, it was also observed that the membrane resealing time was further decreased by almost 50% (i.e. from ~23s to ~13s) by epithelial-mesenchymal-transition, demonstrating the superb survival capability of highly invasive tumor cells.

Finally, the influence of extracellular ligand nano-geometry on T cell activation was also investigated. Interestingly, we found that large aspect ratio (AR) of gold nanorods conjugated on cell culture substrate enhancing both murine and human T cell activation through the nanoscale anisotropic presentation of stimulatory ligands (anti-CD3(αCD3) and anti-CD28(αCD28) antibodies). Specifically, nanorods with large AR bearing αCD3 and αCD28 antibodies significantly promote T cell expansion and key cytokine secretion, indicating the possibility of improving immunotherapeutic outcomes via the manipulation of the geometry of extracellular ligands.