Lipase is essential for the study of in vitro release kinetics from organogels.

In vitro drug release studies remain indispensable in the development of drug delivery systems, even if correlations between in vitro and in vivo results are often imperfect. In this work, an improved in vitro analysis method for studying in situ-forming lipid-based implants was developed. More specifically, lipase was found to be an essential additive for evidencing differences in drug release kinetics from organogels of different amino acid-based organogelators, organogelator concentrations, drug loadings, and volumes. Lipases are thought to participate in the degradation of and release from amino acid-based organogel implants in vivo. Our experimental conditions allowed for the rapid and reliable screening of in vitro parameters that may be optimized to slow or accelerate drug release, once preliminary in vivo data are available.

pH-sensitive vesicles, polymeric micelles, and nanospheres prepared with polycarboxylates.

Titratable polyanions, and more particularly polymers bearing carboxylate groups, have been used in recent years to produce a variety of pH-sensitive colloids. These polymers undergo a coil-to-globule conformational change upon a variation in pH of the surrounding environment. This conformational change can be exploited to trigger the release of a drug from a drug delivery system in a pH-dependent fashion. This review describes the current status of pH-sensitive vesicles, polymeric micelles, and nanospheres prepared with polycarboxylates and their performance as nano-scale drug delivery systems, with emphasis on our recent contribution to this field.

Preparation of polyion complex micelles from poly(ethylene glycol)-block-polyions.

Polyion complex micelles (PICMs) arise from the spontaneous self-assembly of ionic polymers of opposite charges to form a condensate that is dispersed in aqueous media by a hydrophilic segment, usually poly(ethylene glycol) (PEG), present on at least one of the two ionic polymers. PICMs are used for many applications, especially drug delivery. This protocol paper describes the preparation by atom transfer radical polymerization (ATRP) of diblock copolymers of PEG bearing either positive or negative charges, both of which have been shown to form PICMs. Furthermore, methods of preparation and characterization of PICMs loaded with nucleic acid drugs are presented.

Characterization of polyion complex micelles designed to address the challenges of oligonucleotide delivery.

PURPOSE: To optimize oligonucleotide (ODN)-based polyion complex micelles (PICMs) by studying the effects of polymer composition and length on their properties. METHODS: Atom transfer radical polymerization was used to synthesize copolymers with increasing hydrophilic nonionic and cationic block lengths. PICMs were prepared by mixing the copolymers and ODN at various nitrogen-to-phosphate (N/P) ratios and characterized by gel electrophoresis and dynamic light scattering. The stability of the complexes towards dissociation was tested using a competitive assay with heparin. Finally, protection of the incorporated ODN against DNAse I degradation was evaluated. RESULTS: A library of copolymers composed of poly(ethylene glycol) (PEG) and poly(aminoethyl methacrylate) (PAEMA) and/or poly((dimethylamino)ethylmethacrylate) (PDMAEMA) was synthesized. All polymers efficiently interacted with the ODN at N/P ratios approaching 1.5. Narrowly distributed but easily dissociable PICMs were obtained using PEG 5000 and short DMAEMA chains. Shortening the PEG block to 2000, increasing the number of cationic units and using AEMA produced more stable complexes but at the cost of colloidal properties. All polymers were able to protect the ODN from nuclease degradation. CONCLUSIONS: PEG 3000-based PICMs possess good colloidal properties, intermediate stability towards dissociation and adjustable buffering capacity, making them potentially useful for the delivery of nucleic acid drugs.

Proton-actuated membrane-destabilizing polyion complex micelles.

The efficiency of nucleic acid-based drugs is usually hampered by the fact that, following their uptake by the cell, these drugs end up in acidic organelles (i.e., endosomes/lysosomes) from which they barely escape. This work relates to the preparation and characterization of polyion complex micelles (PICM) formed by the self-assembly of three polyelectrolytes: a diblock cationic copolymer; a membranolytic, methacrylic acid copolymer; and an oligonucleotide. It is demonstrated that a synthetic membrane-active polyanion can be successfully integrated within the structure of PICM to yield well-defined, narrowly distributed micelles (30 nm) with a core/shell architecture. Besides their ability to protect the oligonucleotide against nuclease degradation, PICM partly dissociate under mildly acidic conditions, releasing chain clusters that destabilize bilayer membranes. This association/dissociation behavior illustrates the potential of these pH-sensitive PICM for the transport and efficient delivery of polyionic drugs.

Block copolymer micelles: preparation, characterization and application in drug delivery.

Block copolymer micelles are generally formed by the self-assembly of either amphiphilic or oppositely charged copolymers in aqueous medium. The hydrophilic and hydrophobic blocks form the corona and the core of the micelles, respectively. The presence of a nonionic water-soluble shell as well as the scale (10-100 nm) of polymeric micelles are expected to restrict their uptake by the mononuclear phagocyte system and allow for passive targeting of cancerous or inflamed tissues through the enhanced permeation and retention effect. Research in the field has been increasingly focused on achieving enhanced stability of the micellar assembly, prolonged circulation times and controlled release of the drug for optimal targeting. With that in mind, our group has developed a range of block copolymers for various applications, including amphiphilic micelles for passive targeting of chemotherapeutic agents and environment-sensitive micelles for the oral delivery of poorly bioavailable compounds. Here, we propose to review the innovations in block copolymer synthesis, polymeric micelle preparation and characterization, as well as the relevance of these developments to the field of biomedical research.

Thiol-functionalized polymeric micelles: from molecular recognition to improved mucoadhesion.

Surface-modified colloids which can selectively interact with biological species or surfaces show promise as drug delivery systems. However, the preparation of such targeted devices remains challenging, especially when considering polyion complex micelles for which side reactions with the ionic core components (typically carboxylic acid or amino groups) can occur. To solve this issue, an innovative synthetic strategy is proposed and used to prepare an asymmetric poly(ethylene glycol)-block-poly(2-(N,N-dimethylamino)ethyl methacrylate) copolymer presenting a thiol group at the end of the poly(ethylene glycol) chain. Thiol groups are highly appealing given that they react almost exclusively and quantitatively with maleimides under physiological conditions, thereby facilitating the chemical functionalization of the copolymer. The simplicity of the derivatization procedure is illustrated by preparing model biotin-capped copolymers. The biotinylated copolymers are shown to self-assemble with an oligonucleotide in aqueous media to form polyion complex micelles with biotin groups at their outer surface. These micelles are capable of molecular recognition toward streptavidin. Alternatively, thiol-decorated (nonderivatized) micelles are prepared and show improved mucoadhesion through the formation of disulfide bonds with mucin. Finally, intermicellar disulfide bonds are generated under oxidative conditions to promote the formation of stimuli-responsive micellar networks.

A novel one-step drug-loading procedure for water-soluble amphiphilic nanocarriers.

PURPOSE: The lack of water-solubility hampers the use of many potent pharmaceuticals. Polymeric micelles are self-assembled nanocarriers with versatile properties that can be engineered to solubilize, target, and release hydrophobic drugs in a controlled-release fashion. Unfortunately, their large-scale use is limited by the incorporation methods available, especially when sterile dosage forms are sought. METHODS: In this manuscript, we describe a straightforward, economical, and innovative drug-loading procedure that consists in dissolving both the drug and an amphiphilic diblock copolymer in a water/tert-butanol mixture that is subsequently freeze-dried. RESULTS: We demonstrate that monodisperse 20-60 nm-sized drug-loaded polymeric micelles are produced directly and spontaneously upon rehydration of the freeze-dried cake. To establish the proof-of-principle, two hydrophobic taxane derivatives were solubilized in the micelles, and their partition coefficient was determined. CONCLUSIONS: This approach is efficient yet astonishingly simple and may be of great interest for scientists working in nanotechnology and pharmaceutical sciences.

Study of the micellization behavior of different order amino block copolymers with heparin.

PURPOSE: The purpose of this study was to prepare and characterize copolymers presenting different pendant amino groups and to study their ability to form polyelectrolyte complexes with heparin. The responsiveness of the complexes to variations in pH and ionic strength was correlated to the nature of the copolymers. METHODS: Copolymers composed of different aminoethyl methacrylate monomers were synthesized by atom transfer radical polymerization (ATRP) from a poly(ethylene glycol) macroinitiator. Copolymers were characterized by gel permeation chromatography and nuclear magnetic resonance spectroscopy. Micellization properties were assessed by atomic force microscopy, multiangle static light scattering, and dynamic light scattering on complexes formed from the addition of heparin to a solution of polymer. RESULTS: Primary, tertiary, and quaternary amine-based diblock copolymers with molecular weights ranging from 4900 to 7400 and low polydispersity indexes were prepared. The synthesis of a copolymer bearing primary amines was achieved for the first time by ATRP. Micellization was found to be pH- and polymer-dependent. All polymers interacted with heparin at acidic pH to yield monodisperse assemblies of less than 30 nm. Complexes dissociated in response to increases in ionic strength. CONCLUSIONS: Electrostatic interactions between the amino copolymers and heparin triggered the formation of small, monodisperse, and stable complexes that present great potential as oral drug delivery systems.