Nanoscale monitoring of drug actions on cell membrane using atomic force microscopy

Abstract

Knowledge of the nanoscale changes that take place in individual cells in response to a drug is useful for understanding the drug action. However, due to the lack of adequate techniques, such knowledge was scarce until the advent of atomic force microscopy (AFM), which is a multifunctional tool for investigating cellular behavior with nanometer resolution under near-physiological conditions. In the past decade, researchers have applied AFM to monitor the morphological and mechanical dynamics of individual cells following drug stimulation, yielding considerable novel insight into how the drug molecules affect an individual cell at the nanoscale. In this article we summarize the representative applications of AFM in characterization of drug actions on cell membrane, including topographic imaging, elasticity measurements, molecular interaction quantification, native membrane protein imaging and manipulation, etc. The challenges that are hampering the further development of AFM for studies of cellular activities are aslo discussed.

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“…The first challenge is to improve the spatial resolution and temporal resolution of AFM [13]. Currently, high-resolution AFM imaging has been mainly limited to microbial cells which have well-defined and stiff cell envelope [56].…”

“…After the manipulations are finished, the operator controls AFM tip to another cell. This manualdependent process leads to a very low throughput (the time of handling one cell is often several minutes) [13,62,63]. In practice, in order to obtain statistically significant results, we need to perform experiments on many cells, and this will results in heavy workloads.…”

“…Performing measurements on representative cells will improve the experimental efficiency. If fully automated AFM measurements can be achieved, then they can be applied to drug screening (e.g., automatically monitoring the changes in cellular nanostructures and mechanical properties after drug stimulation) [13].…”

“…During the indentation process, force curves are recorded. By fitting the force curves with adequate theoretical models (the most commonly used models are Hertz model and Sneddon model [13]), the Young's modulus of cells is obtained. In our experiments, in order to make the results comparable, all force curves were recorded at the same loading rate (240 nN/s).…”

“…Besides imaging the surface topography of cells, AFM can acquire multiple parameters that reflect the physiological states of cells [12,13], e.g., cellular mechanics, molecular mechanics, energy dissipation, deformation, adhesion force, and molecular recognition. In the past decades, a large number of scholars have applied AFM to investigate related biological issues at the nanoscale, yielding a lot of novel insights into cell/molecular biology [14,15] and certain diseases such as cancer [16].…”