Caging metal ions with visible light-responsive nanopolymersomes.

Polymersomes are bilayer vesicles that self-assemble from amphiphilic diblock copolymers, and provide an attractive system for the delivery of biological and nonbiological molecules due to their environmental compatibility, mechanical stability, synthetic tunability, large aqueous core, and hyperthick hydrophobic membrane. Herein, we report a nanoscale photoresponsive polymersome system featuring a meso-to-meso ethyne-bridged bis[(porphinato)zinc] (PZn2) fluorophore hydrophobic membrane solute and dextran in the aqueous core. Upon 488 nm irradiation in solution or in microinjected zebrafish embryos, the polymersomes underwent deformation, as monitored by a characteristic red-shifted PZn2 emission spectrum and confirmed by cryo-TEM. The versatility of this system was demonstrated through the encapsulation and photorelease of a fluorophore (FITC), as well as two different metal ions, Zn(2+) and Ca(2+).

Spherical micelles assembled from variants of recombinant oleosin.

An emerging field in biomaterials is the creation and engineering of protein surfactants made by recombinant biotechnology. Protein surfactants made by recombinant biotechnology allow for complete control of the molecular weight and chemical sequence of the surfactant. The proteins are monodisperse in molecular weight, and functionalization with bioactive amino acid sequences is straightforwardly achieved through genetic engineering. We modified the naturally occurring amphiphilic plant protein oleosin by truncating a large portion of its central hydrophobic block, creating a soluble triblock surfactant. Additional variants were constructed to eliminate secondary structure and create ionic surfactants. Variants of oleosin self-assembled into spherical micelles with a diameter of ∼21 nm at concentrations above the critical micelle concentration (cmc). We found that the cmc could be manipulated through changes in the protein backbone and was correlated with changes in the protein secondary structure. Micelle size and shape are characterized with dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and cryogenic transmission electron microscopy (cryo-TEM). Micelles were functionalized with the integrin-binding domain, RGDS, leading to a 2.9-fold increase in uptake in Ovcar-5 cells after 12 h. Oleosin surfactants present a promising platform for micellar assembly because of the ability to precisely modify the protein backbone through molecular biology, allowing for the control over the cmc and the addition of functional domains into the material.

Biodegradable Polymersomes for the Delivery of Gemcitabine to Panc-1 Cells.

Traditional anticancer chemotherapy often displays toxic side effects, poor bioavailability, and a low therapeutic index. Targeting and controlled release of a chemotherapeutic agent can increase drug bioavailability, mitigate undesirable side effects, and increase the therapeutic index. Here we report a polymersome-based system to deliver gemcitabine to Panc-1 cells in vitro. The polymersomes were self-assembled from a biocompatible and completely biodegradable polymer, poly(ethylene oxide)-poly(caprolactone), PEO-PCL. We showed that we can encapsulate gemcitabine within stable 200 nm vesicles with a 10% loading efficiency. These vesicles displayed a controlled release of gemcitabine with 60% release after 2 days at physiological pH. Upon treatment of Panc-1 cells in vitro, vesicles were internalized as verified with fluorescently labeled polymersomes. Clonogenic assays to determine cell survival were performed by treating Panc-1 cells with varying concentrations of unencapsulated gemcitabine (FreeGem) and polymersome-encapsulated gemcitabine (PolyGem) for 48 hours. 1 µM PolyGem was equivalent in tumor cell toxicity to 1 µM FreeGem, with a one log cell kill observed. These studies suggest that further investigation on polymersome-based drug formulations is warranted for chemotherapy of pancreatic cancer.

Combinatorial evaluation of cations, pH-sensitive and hydrophobic moieties for polymeric vector design.

Three combinatorial libraries of polymeric vectors were evaluated to investigate the functional roles of molecular weight (MW), cations, pH-sensitive moieties, and hydrophobic derivitization in polymer-mediated gene delivery. Four cationic and pH-sensitive moieties (imidazole, primary, secondary, and tertiary amino) and three hydrophobic residues (C4 butyl, C6 hexyl, and C8 octyl) were assessed in single and serially incremented, binary combinations. Three MWs were evaluated-10, 30, and 50 kDa. The highest levels of transfection, comparable to branched PEI (25 kDa), were achieved by 30 kDa and 50 kDa formulations containing primary amino and imidazole groups. Primary amino groups offered superior charge-neutralizing and size-condensing capacity, while imidazole groups appeared to bind with DNA via nonelectrostatically mediated interactions to produce stable polyplexes that were resistant to premature dissociation. Eight of the 10 highest-transfecting polymers possessed IC(50) values greater than the maximum concentration of free polymers exposed to cells (200 microg/ml). The results herein have identified highly efficient polymeric formulations with superb toxicity profiles and have revealed the functional roles that the investigated pendant groups play in the transfection process. The reported polymeric system offers a versatile and robust platform upon which future structure-function studies may be based to create safer and more efficient polymeric vectors.