Abstract P3-06-51: Atomic force microscopy of triple negative breast cancer cells: A predictive value of mechanical phenotype
Authors: Osmulski Pawel A , Gaczynska Maria 
Published: May 2015

Abstract
We applied Quantitative Nanomechanical Measurements with Atomic Force Microscopy (QNM-AFM) to test a response of triple negative breast cancer (TNBC) cells to treatment with inhibitors of proteasome. Genetic screens identified TNBCs as addicted to the activity of ubiquitin-proteasome pathway, the major intracellular venue of regulated protein degradation, served by the essential protease, the proteasome. Here we tested the effects of treatment of two proteasome inhibitors on the canonical triple-negative cell line, MDA-MB-231. The inhibitors represent two very distinct types of mechanism. Bortezomib (Velcade®) is a competitive inhibitor that targets active sites of the enzyme. On the other hand, B1 is a novel noncompetitive allosteric drug lead that interferes with interactions between the subcomplexes of proteasome, the 20S catalytic core and the 19S regulatory particle ("cap"). In a search for test to predict the putative value of inhibitors we turned to a mechanical phenotype. Mechanical properties of cells constitute a sensitive indicator of physiological status of cells. The best-known and most explored mechanical parameters are elasticity ("softness") represented by the Young modulus, and surface adhesiveness ("stickiness"). It has been well established that cancer cell are much softer and less sticky than the healthy counterparts. These changes in physical phenotype of cancer cells are usually linked to remodeling of their cytoskeleton and altered expression of membrane proteins. Such remodeling may be a very early indicator of the cells’ response to a drug, a less explored but potentially very useful feature. Indeed, it has been shown that often treatment of cancer cells with anticancer drugs at least partially reverses their mechanical phenotype resembling healthy cells. Here we found that 24-hrs exposure of the cells to 10 nM bortezomib increased their stiffness and adhesiveness about two times. Even more striking, a treatment of the cells with 10 nM B1 induced almost threefold increase of stiffness with twofold increase in adhesion. Strikingly, treatments with such concentrations of the inhibitors alone did not significantly influence the viability of the cells, whereas their combination reduced the population of live cells to 50% or less of the control values. The strong effects of the inhibitor treatment on the mechanical phenotype are in stark contrast with little or no effects on cell viability. The results point at extraordinary sensitivity of the mechanical phenotype in detection of cell response to anticancer drugs. We are exploring the potential predictive value of AFM-based cell surface studies in a search for effective drugs or drug combinations.
Citation Format: Pawel A Osmulski, Maria Gaczynska. Atomic force microscopy of triple negative breast cancer cells: A predictive value of mechanical phenotype [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P3-06-51.