Expression of Tumor Suppressors PTEN and TP53 in Isogenic Glioblastoma U-251MG Cells Affects Cellular Mechanical Properties — An AFM-Based Quantitative Investigation

Alexandre Berquand,Jan Mollenhauer,Petra Kioschis,Hella-Monika Kuhn,Andreas Holloschi

doi:10.7567/jjapcp.1.011002

Abstract

Glioblastoma is the most common and malign form of brain cancer that is highly resistant to therapy and particularly hard to cure since the blood-barrier is not very permeable to drugs. Moreover, a surgery is always highly risky. Thus, there is a real need to develop technique enabling accurate identification of potentially tumor cells at an early stage. It is getting well established that cancer cells are usually softer than their normal homologues and Atomic Force Microscopy (AFM) has proven itself over the last decade to be a tool of choice to characterize cells mechanical properties. Among the various AFM techniques, Force Spectroscopy (FS), especially Force Volume (FV) is the most commonly used. In the present study, AFM has been used to successfully characterize malignant and modified less malignant forms of glioblastoma U-251MG isogenic cells, using FV and Peak Force Tapping (PFT), a newly released AFM mode. Although both modes are quantitative and easy to use, PFT appears as the most relevant. Benefits and drawbacks of both techniques are discussed.

Highlights

Force Spectroscopy (FS) is by far the most widely used Atomic Force Microscopy (AFM) mode to extract the samples’ mechanical properties
We have shown that, combining the isogenic glioblastoma cell model and quantitative AFM measurements, significant changes in elasticity and deformation could be monitored which allowed us to discriminate between cells expressing tumor-related genes and tumor control cells
With both AFM techniques we have proven that U-251MG glioblastoma cells are about 3 times softer and 2 times more deformable in contrast to their recombinant counterparts

Summary

Introduction

Force Spectroscopy (FS) is by far the most widely used Atomic Force Microscopy (AFM) mode to extract the samples’ mechanical properties. Different states of cancer progression for esophageal cells have successfully been correlated to characteristic mechanical properties: normal squamous cells are stiffer than metaplastic cells, and themselves stiffer than their dysplastic homologues [13] This change in stiffness can be directly associated to a decrease in the actin level in the cell cytoskeleton [28]. All those studies tend to prompt that AFM might become a diagnosis tool for cancer detection [29] and are for the vast majority based on force volume experiments. The present study aims at showing that a new AFM-based technique called Peak Force Tapping (PFT) can be applied for quantitative measurements of living glioblastoma U-251MG cells for determining the effect of tumor-related genes on biomechanical properties. We hereby report an AFM-based study where FV and PFT have been quantitatively used to examine the impact of genetic modifications on mechanical properties of isogenic glioblastoma cell lines, and to test the potential of this method to discriminate between cells with different tumorigenic behaviour

Material and Methods

Results

Conclusion