Pancreatic cancer metastasis: Adhesion and stiffness

Abstract

Pancreatic ductal adenocarcinoma (PDAC) cells undergo a semi-epithelial to mesenchymal transition. They express Cadherin proteins characteristic of both normal (E-cadherin) and cancer (N-cadherin) cells. Cadherins are involved in cell-cell adhesion. Additionally, cells must adjust their mechanical properties to undergo metastasis. We use Atomic Force Microscopy (AFM) to characterise the mechanical properties of PDAC cell lines from the primary tumour sites (PANC1, PL45) and from liver (CFPAC1) and lymph node (Hs766T) metastases. AFM measures forces using the optical lever system. To measure their stiffness, cells were probed using a rectangular cantilever with a three-sided pyramidal tip. The Hertz contact model was used to calculate Apparent Young's modulus (E) from the approach curve. The structural damping model was used to calculate the power-law exponent (α) from force curves with logarithmically oscillating contact part. To probe the adhesive properties of the cells, a single cell was attached to functionalised triangular tipless cantilevers, and then pressed against a confluent layer of cells. When the cell-cantilever is retracted, the contact of the attached cell with the cell layer is broken. The detachment exerts force on the cantilever, and this signal is also recorded by and analysed from the retract curve. PANC1 and PL45 cells are stiffer in a confluent layer as compared to single cells. CFPAC1 cells soften in confluent layers, and have lesser adhesion between them as compared to PANC1. CFPAC1 cells also have reduced cell-cell interaction with endothelial cells (EA.hy926) after inhibiting N-cadherin. Thus, N-cadherin inhibition can increase liver metastatic cell lines’ self-interaction and decrease interaction with endothelial cells. While primary tumour cell lines experience mixed mechanical response to surrounding cells, liver metastasis cells are softer and more viscous.