Quantitative Assessment of Binding Affinities for Nanoparticles Targeted to Vulnerable Plaque

Abstract

Recent successes in targeted immune and cell-based therapies have driven new directions for pharmaceutical research. With the rise of these new therapies there is an unfilled need for companion diagnostics to assess patients’ potential for therapeutic response. Targeted nanomaterials have been widely investigated to fill this niche; however, in contrast to small molecule or peptide-based targeted agents, binding affinities are not reported for nanomaterials, and to date there has been no standard, quantitative measure for the interaction of targeted nanoparticle agents with their targets. Without a standard measure, accurate comparisons between systems and optimization of targeting behavior are challenging. Here, we demonstrate a method for quantitative assessment of the binding affinity for targeted nanoparticles to cell surface receptors in living systems and apply it to optimize the development of a novel targeted nanoprobe for imaging vulnerable atherosclerotic plaques. In this work, we developed sulfated dextran-coated iron oxide nanoparticles with specific targeting to macrophages, a cell type whose density strongly correlates with plaque vulnerability. Detailed quantitative, in vitro characterizations of 111In3+ radiolabeled probes show high-affinity binding to the macrophage scavenger receptor A (SR-A). Cell uptake studies illustrate that higher surface sulfation levels result in much higher uptake efficiency by macrophages. We use a modified Scatchard analysis to quantitatively describe nanoparticle binding to targeted receptors. This characterization represents a potential new standard metric for targeted nanomaterials.

In VivoMRI of Functionalized Iron Oxide Nanoparticles for Brain Inflammation

“…The synthesis and physical characterization of both DIO and SDIO were reported in a previous article [ 30 ]. The properties of the materials synthesized for the current studies were confirmed to match to our published results.…”

“…dextran sulfate) is widely known as one of the ligands for SR-A with a K d of 3 nM [ 29 ]. In our previous study, we have confirmed that the sulfation of dextran coating significantly improved the cellular binding and uptake of these nanoparticles by macrophages and the uptake efficiency enhances with higher level of surface sulfation [ 30 ]. The sulfated dextran-coated iron oxide nanoparticles have a similar binding affinity to the SR-A, compared with dextran sulfate itself.…”

“…Human TNF- α was purchased from PeproTech Inc. (Rocky Hill, NJ). Sulfated dextran-coated iron oxide was synthesized as described in our previous paper [ 30 ]. Lipopolysaccharides were purchased from Sigma-Aldrich (St. Louis, MO).…”

“…Nanoparticles were synthesized and characterized as previously described in detail [ 30 ]. Briefly, dextran-coated iron oxide (DIO) nanoparticles were synthesized by coprecipitation of iron salts and reduced dextran with the addition of ammonium hydroxide.…”

“…Thus, we hypothesize that these particles will also serve as promising imaging probes to visualize activated microglia in vivo . From the series of nanoparticles that we reported in previous work, SDIO-DO3A-10 had the highest surface sulfation level and best uptake efficiency [ 30 ]. SDIO-DO3A-10 and the nonsulfated analog DIO-DO3A are used in this study and referred to as SDIO and DIO, respectively.…”