Benoit Louage

Dual pH- and temperature-responsive RAFT-based block co-polymer micelles and polymer–protein conjugates with transient solubility

Via a smart combination of temperature-responsive and acid labile acetal monomers, copolymers are obtained with a la carte lower critical solution temperature behavior. RAFT copolymerization of these monomers using, respectively, a PEG-functionalized or amine-reactive NHS-functionalized chain transfer agent allows designing of micelles and polymer–protein conjugates with transient solubility properties within a physiologically relevant window.

Magnetically Engineered Microcapsules as Intracellular Anchors for Remote Control Over Cellular Mobility

Living cells are anchored with magnetic microcapsules that allow in vitro manipulation via a magnetic field.

Degradable ketal-based block copolymer nanoparticles for anticancer drug delivery: a systematic evaluation.

Low solubility of potent (anticancer) drugs is a major driving force for the development of noncytotoxic, stimuli-responsive nanocarriers, including systems based on amphiphilic block copolymers. In this regard, we investigated the potential of block copolymers based on 2-hydroxyethyl acrylate (HEA) and the acid-sensitive ketal-containing monomer (2,2-dimethyl-1,3-dioxolane-4-yl)methyl acrylate (DMDMA) to form responsive drug nanocarriers. Block copolymers were successfully synthesized by sequential reversible addition-fragmentation chain transfer (RAFT) polymerization, in which we combined a hydrophilic poly(HEA)x block with a (responsive) hydrophobic poly(HEAm-co-DMDMAn)y copolymer block. The DMDMA content of the hydrophobic block was systematically varied to investigate the influence of polymer design on physicochemical properties and in vitro biological performance. We found that a DMDMA content higher than 11 mol % is required for self-assembly behavior in aqueous medium. All particles showed colloidal stability in PBS at 37 °C for at least 4 days, with sizes ranging from 23 to 338 nm, proportional to the block copolymer DMDMA content. Under acidic conditions, the nanoparticles decomposed into soluble unimers, of which the decomposition rate was inversely proportional to the block copolymer DMDMA content. Flow cytometry and confocal microscopy showed dose-dependent, active in vitro cellular uptake of the particles loaded with hydrophobic octadecyl rhodamine B chloride (R18). The block copolymers showed no intrinsic in vitro cytotoxicity, while loaded with paclitaxel (PTX), a significant decrease in cell viability was observed comparable or better than the two commercial PTX nanoformulations Abraxane and Genexol-PM at equal PTX dose. This systematic approach evaluated and showed the potential of these block copolymers as nanocarriers for hydrophobic drugs.

Polymer-protein conjugation via a ‘grafting to’ approach – a comparative study of the performance of protein-reactive RAFT chain transfer agents

Efficient polymer-protein conjugation is a crucial step in the design of many therapeutic protein formulations including nanoscopic vaccine formulations, antibody-drug conjugates and to enhance the in vivo behaviour of proteins. Here we aimed at preparing well-defined polymers for conjugation to proteins by reversible addition–fragmentation chain transfer (RAFT) polymerization of both acrylates and methacrylamides with protein-reactive chain transfer agents (CTAs). These RAFT agents contain either a N-hydroxysuccinimide (NHS) or pentafluorophenyl (PFP) ester moiety that can be conjugated to lysine residues, and alternatively a maleimide (MAL) or pyridyl disulfide (PDS) moiety that can be conjugated to cysteine residues. Efficiency of the bioconjugation of these polymers to bovine and avian serum albumin was investigated as a function of stoichiometry, polymer molecular weight and the presence of reducing agents. A large molar excess of polymer was required to obtain an acceptable degree of protein conjugation. However, protein modification with N-succinimidyl-S-acetylthiopropionate (SATP) to introduce sulfhydryl groups onto primary amines, significantly increased conjugation efficiency with MAL- and PDS-containing polymers.

Thermoresponsive hyaluronic acid nanogels as hydrophobic drug carrier to macrophages

Delivery systems for macrophages are particularly attractive since these phagocytic cells play a important role in immunological and inflammatory responses, also acting as host cells for microorganisms that are involved in deadly infectious diseases, such as leishmaniasis. Hyaluronic acid (HA) is specifically recognized by macrophages that are known to express HA receptors. Therefore, in this study, we focused on HA-based nanogels as drug carriers for these cells. The drug delivery was validated in an in vivo study on mice using intravital two-photon laser scanning microscopy. HA derivatives were modified with a biocompatible oligo(ethylene glycol)-based thermoresponsive polymer to form nanogels. These HA conjugates were readily prepared by varying the molar mass of initial HA and the degree of substitution via radical-mediated thiol-ene chemistry in aqueous solution. The derivatives were shown to self-assemble into spherical gel particles with diameters ranging from 150 to 214 nm above 37 °C. A poorly water-soluble two-photon dye was successfully loaded into the nanogels during this self-assembly process. In vitro cellular uptake tests using a RAW 264.7 murine macrophage cell line showed successful intracellular delivery of the hydrophobic dye. After intravenous injection in mice, the nanogels circulated freely in the blood but were rapidly phagocytized within 13 min by circulating macrophages and stored in the liver and spleen, as observed by two-photon microscopy. Benefit can be thus expected in using such a delivery system for the liver and spleen macrophage-associated diseases.

pH-Degradable Mannosylated Nanogels for Dendritic Cell Targeting

We report on the design of glycosylated nanogels via core-cross-linking of amphiphilic non-water-soluble block copolymers composed of an acetylated glycosylated block and a pentafluorophenyl (PFP) activated ester block prepared by reversible addition-fragmentation (RAFT) polymerization. Self-assembly, pH-sensitive core-cross-linking, and removal of remaining PFP esters and protecting groups are achieved in one pot and yield fully hydrated sub-100 nm nanogels. Using cell subsets that exhibit high and low expression of the mannose receptor (MR) under conditions that suppress active endocytosis, we show that mannosylated but not galactosylated nanogels can efficiently target the MR that is expressed on the cell surface of primary dendritic cells (DCs). These nanogels hold promise for immunological applications involving DCs and macrophage subsets.

Acid‐Labile Thermoresponsive Copolymers That Combine Fast pH‐Triggered Hydrolysis and High Stability under Neutral Conditions

Biodegradable polymeric materials are intensively used in biomedical applications. Of particular interest for drug-delivery applications are polymers that are stable at pH 7.4, that is, in the blood stream, but rapidly hydrolyze under acidic conditions, such as those encountered in the endo/lysosome or the tumor microenvironment. However, an increase in the acidic-degradation rate of acid-labile groups goes hand in hand with higher instability of the polymer at pH 7.4 or during storage, thus posing an intrinsic limitation on fast degradation under acidic conditions. Herein, we report that a combination of acid-labile dimethyldioxolane side chains and hydroxyethyl side chains leads to acid-degradable thermoresponsive polymers that are quickly hydrolyzed under slightly acidic conditions but stable at pH 7.4 or during storage. We ascribe these properties to high hydration of the hydroxy-containing collapsed polymer globules in conjunction with autocatalytic acceleration of the hydrolysis reactions by the hydroxy groups.

Transiently Responsive Block Copolymer Micelles Based on N-(2-Hydroxypropyl)methacrylamide Engineered with Hydrolyzable Ethylcarbonate Side Chains

The lack of selectivity and low solubility of many chemotherapeutics impels the development of different biocompatible nanosized drug carriers. Amphiphilic block copolymers, composed of a hydrophilic and hydrophobic domain, show great potential because of their small size, large solubilizing power and loading capacity. In this paper, we introduce a new class of degradable temperature-responsive block copolymers based on the modification of N-(2-hydroxypropyl)methacrylamide (HPMA) with an ethyl group via a hydrolytically sensitive carbonate ester, polymerized by radical polymerization using a PEG-based macroinitiatior. The micellization and temperature-responsive behavior of the PEG-poly(HPMA-EC) block copolymer were investigated by dynamic light scattering (DLS). We observed that the polymer exhibits lower critical solution temperature (LCST) behavior and that above the cloud point (cp) of 17 °C the block copolymer self-assembles in micelles with a diameter of 40 nm. Flow cytometry analysis and confocal microscopy show a dose-dependent cellular uptake of the micelles loaded with a hydrophobic dye. The block copolymer nanoparticles were capable of delivering the hydrophobic payload into cancer cells in both 2D and 3D in vitro cultures. The block copolymer has excellent cytocompatibility, whereas loading the particles with the hydrophobic anticancer drug paclitaxel results in a dose-dependent decrease in cell viability.

Amphiphilic Ferrocene-Containing PEG Block Copolymers as Micellar Nanocarriers and Smart Surfactants

An important and usually the only function of most surfactants in heterophase systems is stabilizing one phase in another, for example, droplets or particles in water. Surfactants with additional chemical or physical handles are promising in controlling the colloidal properties by external stimuli. The redox stimulus is an attractive feature; however, to date only a few ionic redox-responsive surfactants have been reported. Herein, the first nonionic and noncytotoxic ferrocene-containing block copolymers are prepared, carrying a hydrophilic poly(ethylene glycol) (PEG) chain and multiple ferrocenes in the hydrophobic segment. These amphiphiles were studied as redox-sensitive surfactants that destabilize particles as obtained in miniemulsion polymerization. Because of the nonionic nature of such PEG-based copolymers, they can stabilize nanoparticles even after the addition of ions, whereas particles stabilized with ionic surfactants would be destabilized by the addition of salt. The redox-active surfactants were prepared by the anionic ring-opening polymerization of ferrocenyl glycidyl ether, with PEG monomethyl ether as the macroinitiator. The resultant block copolymers with molecular weights (Mn) between 3600 and 8600 g mol-1 and narrow molecular weight distributions (Mw/Mn = 1.04-1.10) were investigated via 1H nuclear magnetic resonance and diffusion ordered spectroscopy, size exclusion chromatography, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Furthermore, the block copolymers were used as building blocks for redox-responsive micelles and as redox-responsive surfactants in radical polymerization in miniemulsion to stabilize model polystyrene nanoparticles. Oxidation of iron to the ferrocenium species converted the amphiphilic block copolymers into double hydrophilic macromolecules, which led to the destabilization of the nanoparticles. This destabilization of nanoparticle dispersions may be useful for the formation of coatings and the recovery of surfactants.

Developments and future clinical outlook of taxane nanomedicines

Taxanes are highly valuable drugs for cancer treatment. Low water-solubility however puts a major challenge in obtaining formulations that are stable and easy-to-use in clinical practice. Initially, solubilization and lowering toxicity of taxanes has been the main research focus. However, emerging passive and active targeting strategies, especially in the field of nanomedicine, have been capital incentives to further broaden therapeutic index by improving efficacy. This review provides an up-to-date clinical track record of taxane nanomedicines in view of the current state-of-the-art in anti-cancer drug delivery. Additionally, the clinical status of taxane nanomedicines is discussed and considerations are provided for improving future clinical translation.