Magnetite-Arginine Nanoparticles as a Multifunctional Biomedical Tool

Abstract

Iron oxide nanoparticles are a promising platform for biomedical applications, both in terms of diagnostics and therapeutics. In addition, arginine-rich polypeptides are known to penetrate across cell membranes. Here, we thus introduce a system based on magnetite nanoparticles and the polypeptide poly-l-arginine (polyR-Fe₃O₄). We show that the hybrid nanoparticles exhibit a low cytotoxicity that is comparable to Resovist^®, a commercially available drug. PolyR-Fe₃O₄ particles perform very well in diagnostic applications, such as magnetic particle imaging (1.7 and 1.35 higher signal respectively for the 3rd and 11th harmonic when compared to Resovist^®), or as contrast agents for magnetic resonance imaging (R2/R1 ratio of 17 as compared to 11 at 0.94 T for Resovist^®). Moreover, these novel particles can also be used for therapeutic purposes such as hyperthermia, achieving a specific heating power ratio of 208 W/g as compared to 83 W/g for Feridex^®, another commercially available product. Therefore, we envision such materials to play a role in the future theranostic applications, where the arginine ability to deliver cargo into the cell can be coupled to the magnetite imaging properties and cancer fighting activity.

Keywords: MRI; hyperthermia; iron oxide; nanoparticle; theranostics.

Figure 1

(a) STEM image of polyR-Fe₃O₄ nanoparticles. (b) Image of vial with colloidal stable polyR-Fe₃O₄ nanoparticles solution one year after synthesis.

Figure 2

Intensity-weighted log-normal distribution of the hydrodynamic diameter of polyR-Fe₃O₄ at different time points after synthesis. The mean hydrodynamic diameter $\overline{d}$ is displayed for comparison.

Figure 3

Biological effects of polyR-Fe₃O₄ particles on endothelial cells grown in static conditions analyzed by real-time cell analysis. HUVECs were seeded 24 h before nanoparticle application. After the initial 24 h, particles at different concentrations were added and cell index was monitored for up to 72 h post application. Cell Index is displayed as x-fold of untreated controls. Data are expressed as mean ± SEM of n = 3 experiments performed in hexaplicate, *** p < 0.001 vs. corresponding control (One-way Anova).

Figure 4

Live-cell microscopy of HUVECs treated with polyR-Fe₃O₄: Phase contrast images of HUVECs were taken after 72 h post particle addition. (a) Untreated control HUVECs, (b) HUVECs treated with 50 µg mL⁻¹, (c) HUVECs treated with 100 µg mL⁻¹ and (d) HUVECs treated with 200 µg mL⁻¹ polyR-Fe₃O₄. Representative images of n = 3 experiments and hexaplicate samples are shown.

Figure 5

Effects of circulating polyR-Fe₃O₄ on enthodelial cell grown under flow conditions. HUVECs were grown in bifurcating slides until confluence and perfused with polyR-Fe₃O₄-containing medium for 18 h. The representative laminar and non-uniform regions are shown after fluorescent staining. Nuclei are visualized using a Hoechst 33342 (blue) staining, whereas F-actin is visualized with Alexa 488-conjugated phalloidin (green). Representative images of n = 3 experiments are shown. (Scale bars: 50 μm).

Figure 6

Relationship of the iron concentration c(Fe) in [mM] and the reciprocal of the relaxation time 1/T_1,2 in [1/s]. The relaxivities R1 and R2 were calculated using the slope of the obtained linear equation.

Figure 7

MPS measurement of polyR-Fe₃O₄ particles (pink) and Resovist^® (black) as comparison.