Analysis of trajectories for targeting of magnetic nanoparticles in blood vessels.

The technique of magnetic drug targeting deals with binding drugs or genetic material to superparamagnetic nanoparticles and accumulating these complexes via an external magnetic field in a target region. For a successful approach, it is necessary to know the required magnetic setup as well as the physical properties of the complexes. With the help of computational methods, the complex accumulation and behavior can be predicted. We present a model for vascular targeting with a full three-dimensional analysis of the magnetic and fluidic forces and a subsequent evaluation of the resulting trajectories of the complexes. These trajectories were calculated with respect to the physiological boundary conditions, the magnetic properties of both the external field and the particles as well as the hydrodynamics of the fluid. We paid special regard to modeling input parameters like flow velocity as well as the distribution functions of the hydrodynamic size and magnetic moment of the nanoparticle complexes. We are able to estimate the amount of complexes, as well as the spatial distribution of those complexes. Additionally, we examine the development of the trapping rate for multiple passages of the complexes and compare the influence of several input parameters. Finally, we provide experimental data of an ex vivo flow-loop system which serves as a model for large vessel targeting. In this model, we achieve a deposition of lentivirus/magnetic nanoparticle complexes in a murine aorta and compare our simulation with the experimental results gained by a non-heme-iron assay.

Magnetized aerosols comprising superparamagnetic iron oxide nanoparticles improve targeted drug and gene delivery to the lung.

PURPOSE: Targeted delivery of aerosols could not only improve efficacy of inhaled drugs but also reduce side effects resulting from their accumulation in healthy tissue. Here we investigated the impact of magnetized aerosols on model drug accumulation and transgene expression in magnetically targeted lung regions of unanesthetized mice. METHODS: Solutions containing superparamagnetic iron oxide nanoparticles (SPIONs) and model drugs (fluorescein or complexed plasmid DNA) were nebulized to unanesthetized mice under the influence of an external magnetic gradient directed to the lungs. Drug accumulation and transgene expression was subsequently measured at different time points. RESULTS: We could demonstrate 2-3 fold higher accumulation of the model drug fluorescein and specific transgene expression in lung regions of mice which had been exposed to an external magnetic gradient during nebulization compared to the control mice without any exposure to magnetic gradient. CONCLUSIONS: Magnetized aerosols present themselves as an efficient approach for targeted pulmonary delivery of drugs and gene therapeutic agents in order to treat localized diseases of the deeper airways.

Local gene targeting and cell positioning using magnetic nanoparticles and magnetic tips: comparison of mathematical simulations with experiments.

PURPOSE: Magnetic nanoparticles (MNPs) and magnets can be used to enhance gene transfer or cell attachment but gene or cell delivery to confined areas has not been addressed. We therefore searched for an optimal method to simulate and perform local gene targeting and cell delivery in vitro. METHODS: Localized gene transfer or cell positioning was achieved using permanent magnets with newly designed soft iron tips and MNP/lentivirus complexes or MNP-loaded cells, respectively. Their distribution was simulated with a mathematical model calculating magnetic flux density gradients and particle trajectories. RESULTS: Soft iron tips generated strong confined magnetic fields and could be reliably used for local (~500 µm diameter) gene targeting and positioning of bone marrow cells or cardiomyocytes. The calculated distribution of MNP/lentivirus complexes and MNP-loaded cells concurred very well with the experimental results of local gene expression and cell attachment, respectively. CONCLUSION: MNP-based gene targeting and cell positioning can be reliably performed in vitro using magnetic soft iron tips, and computer simulations are effective methods to predict and optimize experimental results.

Local anti-angiogenic therapy by magnet-assisted downregulation of SHP2 phosphatase.

Anti-angiogenic therapies are promising options for diseases with enhanced vessel formation such as tumors or retinopathies. In most cases, a site-specific local effect on vessel growth is required, while the current focus on systemic distribution of angiogenesis inhibitors may cause severe unwanted side-effects. Therefore, in the current study we have developed an approach for the local inhibition of vascularization, using complexes of lentivirus and magnetic nanoparticles in combination with magnetic fields. Using this strategy in the murine embryonic stem cell (ESC) system, we were able to site-specifically downregulate the protein tyrosine phosphatase SHP2 by RNAi technology in areas with active vessel formation. This resulted in a reduction of vessel development, as shown by reduced vascular tube length, branching points and vascular loops. The anti-angiogenic effect could also be recapitulated in the dorsal skinfold chamber of mice in vivo. Here, site-specific downregulation of SHP2 reduced re-vascularization after wound induction. Thus, we have developed a magnet-assisted, RNAi-based strategy for the efficient local inhibition of angiogenesis in ESCs in vitro and also in vivo.

Improved heart repair upon myocardial infarction: Combination of magnetic nanoparticles and tailored magnets strongly increases engraftment of myocytes.

Cell replacement in the heart is considered a promising strategy for the treatment of post-infarct heart failure. Direct intramyocardial injection of cells proved to be the most effective application route, however, engraftment rates are very low (<5%) strongly hampering its efficacy. Herein we combine magnetic nanoparticle (MNP) loading of EGFP labeled embryonic cardiomyocytes (eCM) and embryonic stem cell-derived cardiomyocytes (ES-CM) with application of custom designed magnets to enhance their short and long-term engraftment. To optimize cellular MNP uptake and magnetic force within the infarct area, first numerical simulations and experiments were performed in vitro. All tested cell types could be loaded efficiently with SOMag5-MNP (200 pg/cell) without toxic side effects. Application of a 1.3 T magnet at 5 mm distance from the heart for 10 min enhanced engraftment of both eCM and ES-CM by approximately 7 fold at 2 weeks and 3.4 fold (eCM) at 8 weeks after treatment respectively and also strongly improved left ventricular function at all time points. As underlying mechanisms we found that application of the magnetic field prevented the initial dramatic loss of cells via the injection channel. In addition, grafted eCM displayed higher proliferation and lower apoptosis rates. Electron microscopy revealed better differentiation of engrafted eCM, formation of cell to cell contacts and more physiological matrix formation in magnet-treated grafts. These results were corroborated by gene expression data. Thus, combination of MNP-loaded cells and magnet-application strongly increases long-term engraftment of cells addressing a major shortcoming of cardiomyoplasty.

Frequency-dependent drug screening using optogenetic stimulation of human iPSC-derived cardiomyocytes.

Side effects on cardiac ion channels are one major reason for new drugs to fail during preclinical evaluation. Herein we propose a simple optogenetic screening tool measuring extracellular field potentials (FP) from paced cardiomyocytes to identify drug effects over the whole physiological heart range, which is essential given the rate-dependency of ion channel function and drug action. Human induced pluripotent stem cell-derived cardiomyocytes were transduced with an adeno-associated virus to express Channelrhodopsin2 and plated on micro-electrode arrays. Global pulsed illumination (470 nm, 1 ms, 0.9 mW/mm2) was applied at frequencies from 1 to 2.5 Hz, which evoked FP simultaneously in all cardiomyocytes. This synchronized activation allowed averaging of FP from all electrodes resulting in one robust FP signal for analysis. Field potential duration (FPD) was ~25% shorter at 2.5 Hz compared to 1 Hz. Inhibition of hERG channels prolonged FPD only at low heart rates whereas Ca2+ channel block shortened FPD at all heart rates. Optogenetic pacing also allowed analysis of the maximum downstroke velocity of the FP to detect drug effects on Na+ channel availability. In principle, the presented method is well scalable for high content cardiac toxicity screening or personalized medicine for inherited cardiac channelopathies.

Targeting of Magnetic Nanoparticle-coated Microbubbles to the Vascular Wall Empowers Site-specific Lentiviral Gene Delivery in vivo.

In the field of vascular gene therapy, targeting systems are promising advancements to improve site-specificity of gene delivery. Here, we studied whether incorporation of magnetic nanoparticles (MNP) with different magnetic properties into ultrasound sensitive microbubbles may represent an efficient way to enable gene targeting in the vascular system after systemic application. Thus, we associated novel silicon oxide-coated magnetic nanoparticle containing microbubbles (SO-Mag MMB) with lentiviral particles carrying therapeutic genes and determined their physico-chemical as well as biological properties compared to MMB coated with polyethylenimine-coated magnetic nanoparticles (PEI-Mag MMB). While there were no differences between both MMB types concerning size and lentivirus binding, SO-Mag MMB exhibited superior characteristics regarding magnetic moment, magnetizability as well as transduction efficiency under static and flow conditions in vitro. Focal disruption of lentiviral SO-Mag MMB by ultrasound within isolated vessels exposed to an external magnetic field decisively improved localized VEGF expression in aortic endothelium ex vivo and enhanced the angiogenic response. Using the same system in vivo, we achieved a highly effective, site-specific lentiviral transgene expression in microvessels of the mouse dorsal skin after arterial injection. Thus, we established a novel lentiviral MMB technique, which has great potential towards site-directed vascular gene therapy.

Improvement of vascular function by magnetic nanoparticle-assisted circumferential gene transfer into the native endothelium.

Gene therapy is a promising approach for chronic disorders that require continuous treatment such as cardiovascular disease. Overexpression of vasoprotective genes has generated encouraging results in animal models, but not in clinical trials. One major problem in humans is the delivery of sufficient amounts of genetic vectors to the endothelium which is impeded by blood flow, whereas prolonged stop-flow conditions impose the risk of ischemia. In the current study we have therefore developed a strategy for the efficient circumferential lentiviral gene transfer in the native endothelium under constant flow conditions. For that purpose we perfused vessels that were exposed to specially designed magnetic fields with complexes of lentivirus and magnetic nanoparticles thereby enabling overexpression of therapeutic genes such as endothelial nitric oxide synthase (eNOS) and vascular endothelial growth factor (VEGF). This treatment enhanced NO and VEGF production in the transduced endothelium and resulted in a reduction of vascular tone and increased angiogenesis. Thus, the combination of MNPs with magnetic fields is an innovative strategy for site-specific and efficient vascular gene therapy.

Vascular Repair by Circumferential Cell Therapy Using Magnetic Nanoparticles and Tailored Magnets.

Cardiovascular disease is often caused by endothelial cell (EC) dysfunction and atherosclerotic plaque formation at predilection sites. Also surgical procedures of plaque removal cause irreversible damage to the EC layer, inducing impairment of vascular function and restenosis. In the current study we have examined a potentially curative approach by radially symmetric re-endothelialization of vessels after their mechanical denudation. For this purpose a combination of nanotechnology with gene and cell therapy was applied to site-specifically re-endothelialize and restore vascular function. We have used complexes of lentiviral vectors and magnetic nanoparticles (MNPs) to overexpress the vasoprotective gene endothelial nitric oxide synthase (eNOS) in ECs. The MNP-loaded and eNOS-overexpressing cells were magnetic, and by magnetic fields they could be positioned at the vascular wall in a radially symmetric fashion even under flow conditions. We demonstrate that the treated vessels displayed enhanced eNOS expression and activity. Moreover, isometric force measurements revealed that EC replacement with eNOS-overexpressing cells restored endothelial function after vascular injury in eNOS(-/-) mice ex and in vivo. Thus, the combination of MNP-based gene and cell therapy with custom-made magnetic fields enables circumferential re-endothelialization of vessels and improvement of vascular function.