Reduced Cationic Nanoparticle Cytotoxicity Based on Serum Masking of Surface Potential.

Functionalization of nanoparticles with cationic moieties, such as polyethyleneimine (PEI), enhances binding to the cell membrane; however, it also disrupts the integrity of the cell's plasma and vesicular membranes, leading to cell death. Primary fibroblasts were found to display high surface affinity for cationic iron oxide nanoparticles and greater sensitivity than their immortalized counterparts. Treatment of cells with cationic nanoparticles in the presence of incremental increases in serum led to a corresponding linear decrease in cell death. The surface potential of the nanoparticles also decreased linearly as serum increased and this was strongly and inversely correlated with cell death. While low doses of nanoparticles were rendered non-toxic in 25% serum, large doses overcame the toxic threshold. Serum did not reduce nanoparticle association with primary fibroblasts, indicating that the decrease in nanoparticle cytotoxicity was based on serum masking of the PEI surface, rather than decreased exposure. Primary endothelial cells were likewise more sensitive to the cytotoxic effects of cationic nanoparticles than their immortalized counterparts, and this held true for cellular responses to cationic microparticles despite the much lower toxicity of microparticles compared to nanoparticles.

A New Imaging Platform for Visualizing Biological Effects of Non-Invasive Radiofrequency Electric-Field Cancer Hyperthermia.

Herein, we present a novel imaging platform to study the biological effects of non-invasive radiofrequency (RF) electric field cancer hyperthermia. This system allows for real-time in vivo intravital microscopy (IVM) imaging of radiofrequency-induced biological alterations such as changes in vessel structure and drug perfusion. Our results indicate that the IVM system is able to handle exposure to high-power electric-fields without inducing significant hardware damage or imaging artifacts. Furthermore, short durations of low-power (< 200 W) radiofrequency exposure increased transport and perfusion of fluorescent tracers into the tumors at temperatures below 41°C. Vessel deformations and blood coagulation were seen for tumor temperatures around 44°C. These results highlight the use of our integrated IVM-RF imaging platform as a powerful new tool to visualize the dynamics and interplay between radiofrequency energy and biological tissues, organs, and tumors.

Analysis of the influence of cell heterogeneity on nanoparticle dose response.

Understanding the effect of variability in the interaction of individual cells with nanoparticles on the overall response of the cell population to a nanoagent is a fundamental challenge in bionanotechnology. Here, we show that the technique of time-resolved, high-throughput microscopy can be used in this endeavor. Mass measurement with single-cell resolution provides statistically robust assessments of cell heterogeneity, while the addition of a temporal element allows assessment of separate processes leading to deconvolution of the effects of particle supply and biological response. We provide a specific demonstration of the approach, in vitro, through time-resolved measurement of fibroblast cell (HFF-1) death caused by exposure to cationic nanoparticles. The results show that heterogeneity in cell area is the major source of variability with area-dependent nanoparticle capture rates determining the time of cell death and hence the form of the exposure­response characteristic. Moreover, due to the particulate nature of the nanoparticle suspension, there is a reduction in the particle concentration over the course of the experiment, eventually causing saturation in the level of measured biological outcome. A generalized mathematical description of the system is proposed, based on a simple model of particle depletion from a finite supply reservoir. This captures the essential aspects of the nanoparticle­cell interaction dynamics and accurately predicts the population exposure­response curves from individual cell heterogeneity distributions.

Inter-endothelial transport of microvectors using cellular shuttles and tunneling nanotubes.

New insights into the intra- and intercellular trafficking of drug delivery particles challenges the dogma of particles as static intracellular depots for sustained drug release. Recent discoveries in the cell-to-cell transfer of cellular constituents, including proteins, organelles, and microparticles sheds light on new ways to propagate signals and therapeutics. While beneficial for the dispersion of therapeutics at sites of pathologies, propagation of biological entities advancing disease states is less desirable. Mechanisms are presented for the transfer of porous silicon microparticles between cells. Direct cell-to-cell transfer of microparticles by means of membrane adhesion or using membrane extensions known as tunneling nanotubes is presented. Cellular relays, or shuttle cells, are also shown to mediate the transfer of microparticles between cells. These microparticle-transfer events appear to be stimulated by environmental cues, introducing a new paradigm of environmentally triggered propagation of cellular signals and rapid dispersion of particle-delivered therapeutics. The opportunity to use microparticles to study cellular transfer events and biological triggers that induce these events may aid in the discovery of therapeutics that limit the spread of disease.