Julie Thevenot

Doxorubicin Loaded Magnetic Polymersomes: Theranostic Nanocarriers for MR Imaging and Magneto-Chemotherapy

Hydrophobically modified maghemite (γ-Fe(2)O(3)) nanoparticles were encapsulated within the membrane of poly(trimethylene carbonate)-b-poly(l-glutamic acid) (PTMC-b-PGA) block copolymer vesicles using a nanoprecipitation process. This formation method gives simple access to highly magnetic nanoparticles (MNPs) (loaded up to 70 wt %) together with good control over the vesicles size (100-400 nm). The simultaneous loading of maghemite nanoparticles and doxorubicin was also achieved by nanoprecipitation. The deformation of the vesicle membrane under an applied magnetic field has been evidenced by small angle neutron scattering. These superparamagnetic hybrid self-assemblies display enhanced contrast properties that open potential applications for magnetic resonance imaging. They can also be guided in a magnetic field gradient. The feasibility of controlled drug release by radio frequency magnetic hyperthermia was demonstrated in the case of encapsulated doxorubicin molecules, showing the viability of the concept of magneto-chemotherapy. These magnetic polymersomes can be used as efficient multifunctional nanocarriers for combined therapy and imaging.

A simple method to achieve high doxorubicin loading in biodegradable polymersomes.

Doxorubicin (Dox), an anthracycline anticancer drug, was successfully incorporated into block copolymer vesicles of poly(trimethylene carbonate)-b-poly(L-glutamic acid) (PTMC-b-PGA) by a solvent-displacement (nanoprecipitation) method. pH conditions were shown to have a strong influence on loading capacity and release profiles. Substantial drug loading (47% w/w) was achieved at pH 10.5. After pH neutralization, aqueous dispersions of drug-loaded vesicles were found stable for a prolonged period of time (at least 6months) without vesicle disruption or drug precipitation. Dox-loaded vesicles exhibited in vitro pH and temperature-dependent drug release profiles: release kinetics fastened in acid conditions or by increasing temperature. These features strongly support the interest of developing PTMC-b-PGA polymersomes as carriers for the controlled delivery of Dox.

Self-Assembly of Thermally Responsive Amphiphilic Diblock Copolypeptides into Spherical Micellar Nanoparticles†

As structure–property relationships for protein self-assembly have been elucidated, advances in chemistry and structural biology have facilitated the development of biologically inspired polypeptides through chemical and biosynthetic schemes that have afforded novel protein-based films, fibers, micelles, and gels. In a number of instances, reversible protein self-assembly has been driven by welldefined conformational changes of peptide units induced in response to an external stimulus. Indeed, designed molecular assembly of stimuli-responsive peptides has emerged as a “bottom-up” approach for creating complex, but ordered, hierarchical structures from simple amino acid building blocks. As illustrated by the design of diand triblock polypeptides, microand nanoscale features can be tuned by control of the amino acid sequence, molecular weight, and secondary structure of the peptide. In particular, amphiphilic block copolypeptides can self-assemble into a variety of diverse structures, including rods, cylinders, spheres, and vesicles. Although diblock copolymers consisting of chemically and conformationally distinctive individual polypeptide blocks have been produced by chemical and biosynthetic schemes, to date, relatively few recombinant amphiphilic diblock polypeptides have been synthesized. Given the capacity to incorporate targeting ligands, cell membrane fusion sequences, receptor activating peptides, fluorescent or chelating groups, as well as the ability to tailor pharmacokinetics, biodistribution, and peptide stability, significant opportunities exist for micelles or vesicles produced from recombinant protein block copolymers. Elastin-mimetic polypeptides based on the pentameric repeat sequence (Val-Pro-Gly-Xaa-Gly) undergo thermal and pH-responsive self-assembly in aqueous solution. Spontaneous phase separation of the polypeptide coincides with a conformational rearrangement of local secondary structure above a unique transition temperature (Tt) determined by the chemical identity of the fourth amino acid (Xaa) in the pentapeptide repeat. Recent studies have demonstrated the potential of engineered materials derived from elastin in a broad range of biomedical and biotechnological applications and, in particular, drug delivery. 8] Characteristically, elastin-mimetic blocks that contain hydrophobic amino acids in the fourth amino acid position, such as tyrosine, display a conformational transition from random coil to repetitive type II b turns at temperatures well below 37 8C, whereas blocks that contain a charged amino acid in this position, such as glutamic acid, persist as a random coil throughout the physiologic temperature range. Thus, we postulated that amphiphilic diblock copolymers bearing glutamic acid and tyrosine residues in Nand C-terminal blocks, respectively, would promote micelle formation by temperature-induced self-assembly with a core–shell structure. Moreover, we speculated that at a sufficiently high density of glutamic acid units, charge repulsion would limit the association of the hydrophilic blocks andminimize micelle aggregation. Micelles stabilized by self-assembly alone are typically unstable in a complex environment containing naturally occurring amphiphiles, such as plasma proteins, glycolipids, and lipopeptides. Therefore, by positioning cysteine residues between blocks, we hypothesized that highmolecular-weight protein aggregation or uncontrolled micelle–micelle association would be avoided by nanoparticle stabilization through disulfide cross-linking. These studies represent the first report of thermally responsive and crosslink stabilized protein micelles produced through the tailored design of recombinant amphiphilic diblock copolymers. Two amphiphilic diblock polypeptides (ADP1 and ADP2) were synthesized and self-assembled into micellar structures with consecutive cysteine residues incorporated at the core– shell interface (Scheme 1). Expression of the diblock synthetic genes in E. coli expression strain, BL21(DE3), afforded recombinant protein polymers in high yield after immobilized-metal-affinity chromatography (IMAC) purification from the cell lysate. Mass spectrometry confirmed a correspondence between the observed and expected masses of the respective diblocks with consistent sequence composition by amino acid analysis. The presence of cysteine residues within the polypeptide chain was characterized by the use of a thiolreactive fluorescent dye (see the Supporting Information). Differential scanning calorimetry (DSC) demonstrated an endothermic transition at around 10 8C for both diblock copolymers, which conforms to the established relationship between the position of the transition temperature and the mole fraction of tyrosine in elastin-mimetic protein poly[*] Dr. W. Kim, Dr. E. L. Chaikof Emory University Departments of Biomedical Engineering and Surgery Georgia Institute of Technology, School of Chemical Engineering 101 Woodruff Circle, Rm 5105, Atlanta, GA 30322 (USA) Fax: (+1)404-727-3667 E-mail: echaiko@emory.edu

Magnetic responsive polymer composite materials

Magnetic responsive materials are the topic of intense research due to their potential breakthrough applications in the biomedical, coatings, microfluidics and microelectronics fields. By merging magnetic and polymer materials one can obtain composites with exceptional magnetic responsive features. Magnetic actuation provides unique capabilities as it can be spatially and temporally controlled, and can additionally be operated externally to the system, providing a non-invasive approach to remote control. We identified three classes of magnetic responsive composite materials, according to their activation mode and intended applications, which can be defined by the following aspects. (A) Their ability to be deformed (stretching, bending, rotation) upon exposure to a magnetic field. (B) The possibility of remotely dragging them to a targeted area, called magnetic guidance, which is particularly interesting for biomedical applications, including cell and biomolecule guidance and separation

Magnetic field triggered drug release from polymersomes for cancer therapeutics.

Local and temporal control of drug release has for long been a main focus in the development of novel drug carriers. Polymersomes, which can load both hydrophilic and hydrophobic species and, at the same time, be tailored to respond to a desired stimulus, have drawn much attention over the last decade. Here we describe polymersomes able to encapsulate up to 6% (w/w) of doxorubicin (DOX) together with 30% (w/w) of superparamagnetic iron oxide nanoparticles (USPIO; γ-Fe2O3). Upon internalization in HeLa cells and when a high frequency AC magnetic field (14mT at 750kHz) was applied, the developed delivery system elicited an 18% increase in cell toxicity, associated with augmented DOX release kinetics. In order to ensure that the observed cytotoxicity arose from the increased doxorubicin release and not from a pure magnetic hyperthermia effect, polymersomes loaded with magnetic nanoparticles alone were also tested. In this case, no increased toxicity was observed. We hypothesize that the magnetic field is inducing a very local hyperthermia effect at the level of the polymersome membrane, increasing drug release. This approach opens new perspectives in the development of smart delivery systems able to release drug upon demand and therefore, improving treatment control.

Smart polymersomes for therapy and diagnosis: fast progress toward multifunctional biomimetic nanomedicines

Rising from the shortcomings of modern day therapeutics there is a need for a controlled approach in carrier-mediated drug delivery. Polymeric vesicles, also called polymersomes, are powerful tools to address issues of efficacy, specificity, and controlled release of drugs to diseased tissues. These recent, biomimetic structures are able to overcome the bodys natural defences, remaining stable for extended time in circulation, have tuneable membrane properties, allowing the control of membrane permeability and therefore of drug release, and have the potential to be functionalized for active targeting of specific tissues, reducing undesirable side effects. Extensive work has been carried out in order to attain multifunctional polymeric vesicles that respond to precise triggers (e.g., temperature, pH, redox, magnetic field, etc) with a spatial and temporal monitoring what may enable unprecedented control of drug release in the body. These versatile structures can be loaded with different type of (bio)molecules and nanoparticles, from drugs to contrast agents for medical imaging, and are able to accommodate them in different subcompartments of the vesicle (i.e., hydrophobic membrane and hydrophilic core). Multimodal targeted delivery system could be obtained from this unique platform, with abilities in both drug delivery and medical imaging contrast enhancement, widening the perspectives toward theranostics. Polymersomes offer a promising route toward more effective treatments with fewer side effects and superior outcomes.

Antibody-functionalized magnetic polymersomes: in vivo targeting and imaging of bone metastases using high resolution MRI.

Multifunctional polymersomes loaded with maghemite nanoparticles and grafted with an antibody, directed against human endothelial receptor 2, are developed as novel MRI contrast agents for bone metastasis imaging. Upon administration in mice bearing bone tumor grown from human breast cancer cells, MR images show targeting and enhanced retention of antibody-labeled polymersomes at the tumor site.

Polymeric micelles and vesicles: biological behavior evaluation using radiolabeling techniques

Abstract The application of combined diagnosis and therapy through nanotechnology applications is attracting increasing attention worldwide. Polymeric self-assembled nanoparticles (NPs) have been studied for this purpose. Micelles and vesicles with or without a magnetic core can efficiently carry diagnostic and/or therapeutic agents to a desired target. The biological behavior of these NPs has been evaluated in this study, after radiolabeling with 99mTc. In vitro stability, in media that mimic the environment of the living body, was better for vesicles than for micelles at 1 h and decreased for both as time passed. After administration to healthy animals, all NPs presented major uptake at liver and spleen as expected. Biodistribution and imaging studies confirmed the higher uptake in these organs for the hybrid NPs and at higher extent for the ones with larger size, indicating that the magnetic load and size play an important role on in vivo distribution.

Polymersomes for theranostics

In spite of the clear potential of personalized medicine, its pace of implementation has not yet fulfilled initial hopes. Polymeric vesicles, also named polymersomes, are presented as versatile systems able to address issues of efficacy, specificity and controlled release of drugs in a wide range of pathological scenarios that might show the way to novel therapies. Extensive work has endowed these biomimetic structures with the ability to overcome the bodys natural defences, remain stable for an extended time in circulation, tuneable membrane properties for controlled drug release, and the ability to be functionalized for active targeting and therefore reducing undesirable side effects. Additionally, this unique platform has the ability to integrate both drug delivery and medical imaging capabilities, widening the perspectives towards theranostics. Polymersomes hold promise for more effective treatments with both fewer side effects and superior outcomes.