Polymer-Grafted, Nonfouling, Magnetic Nanoparticles Designed to Selectively Store and Release Molecules via Ionic Interactions

Surface functionalization of superparamagnetic iron oxide nanoparticles (IONPs) was achieved by exploiting a grafting “onto” approach simultaneously with an in situ modification of the graft block copolymer. Terminal phosphonic-acid-bearing block copolymers composed of pendant-activated ester moieties, that is, poly­(pentafluorophenyl acrylate) (P­(PFPA)) and poly­(oligoethylene glycol acrylate) (P­(OEGA)), were synthesized and assembled on IONP surfaces. The assembly was performed in the presence of different primary amines to introduce different functionality to the grafted chains, followed by subsequent thiol–ene Michael additions with acrylates or maleimides to decorate the IONP surface. The aim of this “double”-click chemistry on the polymer-coated nanoparticles was to generate a library of IONPs consisting of an internal layer of functionalized polyacrylamides and an outer shell of antifouling P­(OEGA) decorated with fluorescent ligands. The resultant multifunctionalized IONPs were characterized using ATR-FTIR, XPS and TGA, proving the presence of modified polymers on the IONP surfaces. The functionalized nanoparticles proved to be stable in both water and phosphate buffer containing bovine serum albumin. Zeta potentials of the functionalized nanoparticles could be tuned by the judicious choice of functional groups introduced by the primary amines, for example, spermine, 3-(dimethylamino)-1-propylamine, l-lysine, l-histidine, l-arginine, β-alanine, and taurine. Depending on the pH of IONP dispersions, the charge induced by functional groups within the polymer shell was used to encapsulate ionic dyes (methyl blue and rhodamine 6G in cationic and anionic layers, respectively), serving as models for drug loading via ionic complexation. The attachment of fluorophore through thiol–ene Michael addition was demonstrated by conjugating fluorescein-<i>O</i>-acrylate, as monitored by fluorescence spectroscopy. Cytotoxicity studies revealed that multifunctionalized IONPs were nontoxic to normal human lung fibroblast cell lines. Fluorescence lifetime imaging microscopy was employed to demonstrate the complexation and release of rhodamine 6G dye from l-lysine-functionalized IONPs

Dextran-Based Doxorubicin Nanocarriers with Improved Tumor Penetration

Drug delivery systems with improved tumor penetration are valuable assets as anticancer agents. A dextran-based nanocarrier system with aldehyde functionalities capable of forming an acid labile linkage with the chemotherapy drug doxorubicin was developed. Aldehyde dextran nanocarriers (ald-dex-dox) demonstrated efficacy as delivery vehicles with an IC₅₀ of ∼300 nM against two-dimensional (2D) SK-N-BE(2) monolayers. Confocal imaging showed that the ald-dex-dox nanocarriers were rapidly internalized by SK-N-BE(2) cells. Fluorescence lifetime imaging microscopy (FLIM) analysis indicated that ald-dex-dox particles were internalized as intact complexes with the majority of the doxorubicin released from the particle four hours post uptake. Accumulation of the ald-dex-dox particles was significantly enhanced by ∼30% in the absence of glucose indicating a role for glucose and its receptors in their endocytosis. However, inhibition of clathrin dependent and independent endocytosis and macropinocytosis as well as membrane cholesterol depletion had no effect on ald-dex-dox particle accumulation. In three-dimensional (3D) SK-N-BE(2) tumor spheroids, which more closely resemble a solid tumor, the ald-dex-dox nanoparticles showed a significant improvement in efficacy over free doxorubicin, as evidenced by decreased spheroid outgrowth. Drug penetration studies in 3D demonstrated the ability of the ald-dex-dox nanocarriers to fully penetrate into a SK-N-BE(2) tumor spheroids, while doxorubicin only penetrates to a maximum distance of 50 μM. The ald-dex-dox nanocarriers represent a promising therapeutic delivery system for the treatment of solid tumors due to their unique enhanced penetration ability combined with their improved efficacy over the parent drug in 3D

Functionalizing Biodegradable Dextran Scaffolds Using Living Radical Polymerization: New Versatile Nanoparticles for the Delivery of Therapeutic Molecules

Conferring biodegradability to nanoparticles is vitally important when nanomedicine applications are being targeted, as this prevents potential problems with bioaccumulation of byproducts after delivery. In this work, dextran has been modified (and rendered hydrophobic) by partial acetalation. A solid state NMR method was first developed to fully characterize the acetalated polymers. In a subsequent synthetic step, RAFT functionality was attached via residual unmodified hydroxyl groups. The RAFT groups were then used in a living free radical polymerization reaction to control the growth of hydrophilic PEG-methacrylate chains, thereby generating amphiphilic comblike polymers. The amphiphilic polymers were then self-assembled in water to form various morphologies, including small vesicles, wormlike rods, and micellar structures, with PEG at the periphery acting as a nonfouling biocompatible polymer layer. The acetalated dextran nanoparticles were designed for potential doxorubicin (DOX) delivery application based on the premise that in the cell compartments (endosome, lysozome) the acetalated dextran would hydrolyze, destroying the nanoparticle structure, releasing the encapsulated DOX. <i>In-vitro</i> studies confirmed minimal cytotoxicity of the (unloaded) nanoparticles, even after 3 days, proving that the hydrolysis products from the acetal groups (methanol and acetone) had no observable cytotoxic effect. An intriguing initial result is reported that <i>in vitro</i> studies of DOX-loaded dextran-nanoparticles (compared to free DOX) revealed an increased differential toxicity toward a cancer cell line when compared to a normal cell line. Efficient accumulation of DOX in a human neuroblastoma cell line (SY-5Y) was confirmed by both confocal microscopy and flow cytometry measurements. Furthermore, the time dependent release of DOX was monitored using fluorescence lifetime imaging microscopy (FLIM) in SY-5Y live cells. FLIM revealed bimodal lifetime distributions, showing the accumulation of both DOX-loaded dextran-nanoparticles and subsequent release of DOX in the living cells. From FLIM data analysis, the amount of DOX released in SY-5Y cells was found to increase from 35% to 55% when the incubation time increased from 3 h to 24 h