Direct Synthesis of Biotinylated Stimuli-Responsive Polymer and Diblock Copolymer by RAFT Polymerization Using Biotinylated Trithiocarbonate as RAFT Agent

Biotin-decorated all-HPMA polymeric micelles for paclitaxel delivery

To avoid poly(ethylene glycol)-related issues of nanomedicines such as accelerated blood clearance, fully N-2-hydroxypropyl methacrylamide (HPMAm)-based polymeric micelles decorated with biotin for drug delivery were designed. To this end, a biotin-functionalized chain transfer agent (CTA), 4-cyano-4-[(dodecylsulfanylthiocarbonyl)-sulfanyl]pentanoic acid (biotin-CDTPA), was synthesized for reversible addition-fragmentation chain-transfer (RAFT) polymerization. Amphiphilic poly(N-2-hydroxypropyl methacrylamide)-block-poly(N-2-benzoyloxypropyl methacrylamide) (p(HPMAm)-b-p(HPMAm-Bz)) with molecular weights ranging from 8 to 24 kDa were synthesized using CDTPA or biotin-CDTPA as CTA and 2,2'-azobis(2-methylpropionitrile) as initiator. The copolymers self-assembled in aqueous media into micelles with sizes of 40-90 nm which positively correlated to the chain length of the hydrophobic block in the polymers, whereas the critical micelle concentrations decreased with increasing hydrophobic block length. The polymer with a molecular weight of 22.1 kDa was used to prepare paclitaxel-loaded micelles which had sizes between 61 and 70 nm, and a maximum loading capacity of around 10 wt%. A549 lung cancer cells overexpressing the biotin receptor, internalized the biotin-decorated micelles more efficiently than non-targeted micelles, while very low internalization of both types of micelles by HEK293 human embryonic kidney cells lacking the biotin receptor was observed. As a consequence, the paclitaxel-loaded micelles with biotin decoration exhibited stronger cytotoxicity in A549 cells than non-targeted micelles. Overall, a synthetic pathway to obtain actively targeted poly(ethylene glycol)-free micelles fully based on a poly(HPMAm) backbone was established. These polymeric micelles are promising systems for the delivery of hydrophobic anticancer drugs.

Preparation of Biomolecule-Polymer Conjugates by Grafting-From Using ATRP, RAFT, or ROMP

Biomolecule-polymer conjugates are constructs that take advantage of the functional or otherwise beneficial traits inherent to biomolecules and combine them with synthetic polymers possessing specially tailored properties. The rapid development of novel biomolecule-polymer conjugates based on proteins, peptides, or nucleic acids has ushered in a variety of unique materials, which exhibit functional attributes including thermo-responsiveness, exceptional stability, and specialized specificity. Key to the synthesis of new biomolecule-polymer hybrids is the use of controlled polymerization techniques coupled with either grafting-from, grafting-to, or grafting-through methodology, each of which exhibit distinct advantages and/or disadvantages. In this review, we present recent progress in the development of biomolecule-polymer conjugates with a focus on works that have detailed the use of grafting-from methods employing ATRP, RAFT, or ROMP.

Carborane RAFT agents as tunable and functional molecular probes for polymer materials

Carborane RAFT agents are introduced as tunable multi-purpose tools acting as ¹H NMR spectroscopic handles, Raman probes, and recognition units.

RAFT polymer cross-coupling with boronic acids

The ability to modify the thiocarbonylthio end-groups of RAFT polymers is important for applications where an inert or highly functionalised material is required. Here we report a copper promoted cross-coupling reaction between RAFT polymer end-groups and aryl boronic acids. This method gives high conversion to the modified polymers, and is compatible with a wide variety of functional molecules.

Cyclic Peptide-Polymer Nanotubes as Efficient and Highly Potent Drug Delivery Systems for Organometallic Anticancer Complexes

Functional drug carrier systems have potential for increasing solubility and potency of drugs while reducing side effects. Complex polymeric materials, particularly anisotropic structures, are especially attractive due to their long circulation times. Here, we have conjugated cyclic peptides to the biocompatible polymer poly(2-hydroxypropyl methacrylamide) (pHPMA). The resulting conjugates were functionalized with organoiridium anticancer complexes. Small angle neutron scattering and static light scattering confirmed their self-assembly and elongated cylindrical shape. Drug-loaded nanotubes exhibited more potent antiproliferative activity toward human cancer cells than either free drug or the drug-loaded polymers, while the nanotubes themselves were nontoxic. Cellular accumulation studies revealed that the increased potency of the conjugate appears to be related to a more efficient mode of action rather than a higher cellular accumulation of iridium.

Acrylamides with hydrolytically labile carbonate ester side chains as versatile building blocks for well-defined block copolymer micelles via RAFT polymerization

Hydrophobic modification of N-(2-hydroxyethyl)acrylamide yields a class of building blocks that is attractive for biomaterial synthesis.

Well-defined polyurethane-graft-poly(N,N-dimethylacrylamide) copolymer with a controlled graft density and grafted chain length: synthesis and its application as a Pickering emulsion

Well-defined PU-g-PDMA graft copolymers with controlled graft densities and grafted chain lengths could be facilely synthesized by combining the polyaddition reaction with the RAFT polymerization.

Micelle-forming HPMA copolymer conjugates of ritonavir bound via a pH-sensitive spacer with improved cellular uptake designed for enhanced tumor accumulation

We describe design, synthesis, physico-chemical characterization and preliminary biological evaluation of micelle-forming polymer drug conjugates with controlled drug release intended for tumor treatment.

Folate-decorated hydrophilic three-arm star-block terpolymer as a novel nanovehicle for targeted co-delivery of doxorubicin and Bcl-2 siRNA in breast cancer therapy

To minimize the side effects and enhance the efficiency of chemotherapy, a novel folate-decorated hydrophilic cationic star-block terpolymer, [poly(l-glutamic acid γ-hydrazide)-b-poly(N,N-dimethylaminopropyl methacrylamide)]3-g-poly(ethylene glycol) ((PGAH-b-PDMAPMA)3-g-PEG), with disulfide linkages between the PEG and PDMAPMA blocks, was developed for targeted co-delivery of doxorubicin and Bcl-2 small interfering RNA (siRNA) into breast cancer cells. The terpolymer was synthesized by a combination of ring-opening polymerization, reversible addition-fragmentation chain transfer polymerization, PEGylation and hydrazinolysis. The chemical structures of the polymers were confirmed by (1)H-NMR analysis. The terpolymer could conjugate doxorubicin via an acid-labile hydrazone linkage and simultaneously efficiently complex siRNA through electrostatic interaction at N/P ratios of ⩾4:1 to form "two-in-one" nanomicelleplexes, which displayed a spherical shape and had an average size of 101.3 nm. The doxorubicin loading efficiency and content were 61.0 and 13.23%, respectively. The cytotoxicity, drug release profile, targeting ability, cellular uptake and intracellular distribution of the nanomicelleplexes were evaluated in vitro. We found that the release behaviors of doxorubicin and siRNA had a pH/reduction dual dependency. They were released faster under reductive acidic conditions (pH 5.0, glutathione: 10mM) than under physiological conditions (pH 7.4). The folate-decorated nanomicelleplexes could deliver doxorubicin and Bcl-2 siRNA more efficiently into the same MCF-7 cell and exhibited a higher cytotoxicity than non-targeted nanomicelleplexes. These results indicate that the terpolymer could act as an efficient vehicle for targeted intracellular co-delivery of doxorubicin and therapeutic siRNA in cancer therapy.

Co-delivery of doxorubicin and P-glycoprotein siRNA by multifunctional triblock copolymers for enhanced anticancer efficacy in breast cancer cells

Combined treatment of chemotherapeutics and small interfering RNAs (siRNAs) is a promising therapy strategy for breast carcinoma via their synergetic effects. In this study, to improve the therapeutic effect of doxorubicin (DOX), novel triblock copolymers, folate/methoxy-poly(ethylene glycol)-block-poly(l-glutamate-hydrazide)-block-poly(N,N-dimethylaminopropyl methacrylamide) (FA/m-PEG-b-P(LG-Hyd)-b-PDMAPMA), were synthesized and used as a vehicle for the co-delivery of DOX and P-glycoprotein (P-gp) siRNA into breast cancer cells. The triblock copolymers were synthesized by a combination of ring-opening polymerization of γ-benzyl-l-glutamate-N-carboxyanhydride using cystamine-terminated heterotelechelic PEG derivatives possessing folate or methoxy end groups (FA/m-PEG-Cys) as initiators and reversible addition-fragmentation chain transfer polymerization of N,N-dimethylaminopropyl methacrylamide followed by hydrazinolysis. The successful synthesis of the copolymers was confirmed by ¹H NMR and gel permeation chromatography. DOX was covalently conjugated onto the poly(l-glutamate-hydrazide) blocks via a pH-labile hydrazone linkage, and the DOX-conjugated triblock copolymers could self-assemble into nanoparticles in aqueous solutions. P-glycoprotein (P-gp) siRNA was then bound to the cationic poly(N,N-dimethylaminopropyl methacrylamide) (PDMAPMA) blocks through an electrostatic interaction, resulting in the formation of spherical nanocomplexes with an average diameter of 196.8 nm and a zeta potential of +28.3 mV. The in vitro release behaviors of DOX and siRNA from the nanocomplexes were pH- and reduction-dependent, and the release rates were much faster under a reductive acidic condition (pH 5.0, glutathione: 10 mM) simulating the intracellular endo-lysosomal environment of cancer cells compared to physiological conditions. The fast payload release rates were closely related to both the glutathione-triggered detachment of PEG blocks from the nanocomplex surface and the pH-sensitive cleavage of hydrazone linkages. FA-decorated nanocomplexes showed higher cellular uptake efficiency and cytotoxicity against MCF-7 cells than FA-free nanocomplexes, as confirmed by confocal laser scanning microscopy, transmission electron microscopy, MTT and flow cytometry analyses. Our results demonstrated that the multifunctional triblock copolymer-mediated co-delivery of DOX and P-gp siRNA might be a new promising therapeutic strategy for breast cancer treatment.

Poly(styrene-alt-maleic anhydride)-based diblock copolymer micelles exhibit versatile hydrophobic drug loading, drug-dependent release, and internalization by multidrug resistant ovarian cancer cells

Amphiphilic diblock copolymers of poly(styrene-alt-maleic anhydride)-b-poly(styrene) (PSMA-b-PS) and poly(styrene-alt-maleic anhydride)-b-poly(butyl acrylate) (PSMA-b-PBA) were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerizations. Polymers were well-controlled with respect to molecular weight evolution and polydispersity indices (PDI < 1.2). Additionally, RAFT allowed for control of diblock compositions (i.e., ratio of hydrophilic PSMA blocks to hydrophobic PS/PBA blocks) and overall molecular weight, which resulted in reproducible self-assembly of diblocks into micelle nanoparticles with diameters of 20-100 nm. Parthenolide (PTL), a hydrophobic anticancer drug, was loaded and released from the micelles. The highest loading and prolonged release of PTL was observed from predominantly hydrophobic PSMA-b-PS micelles (e.g., PSMA100-b-PS258), which exhibited the most ordered hydrophobic environment for more favorable core-drug interactions. PSMA100-b-PS258 micelles were further loaded with doxorubicin (DOX), as well as two hydrophobic fluorescent probes, nile red and IR-780. While PTL released quantitatively within 24 h, DOX, IR-780, and nile red showed release over 1 week, suggesting stronger drug-core interactions and/or hindrance due to less favorable drug-solvent interactions. Finally, uptake and intracellular localization of PSMA100-b-PS258 micelles by multidrug resistant (MDR) ovarian cancer cells was observed by transmission electron microscopy (TEM). Additionally, in vitro analyses showed DOX-loaded PSMA-b-PS micelles exhibited greater cytotoxicity to NCI/ADR RES cells than equivalent free DOX doses (75% reduction in cell viability by DOX-loaded micelles compared to 40% reduction in viability by free DOX at 10 μM DOX), likely due to avoidance of MDR mechanisms that limit free hydrophobic drug accumulation. The ability of micelles to achieve intracellular delivery via avoidance of MDR mechanisms, along with the versatility of chemical constituents and drug loading and release rates, offer many advantages for a variety of drug delivery applications.

Nanocrystalline cellulose grafted random copolymers of N-isopropylacrylamide and acrylic acid synthesized by RAFT polymerization: effect of different acrylic acid contents on LCST behavior

NCC-attached dual-sensitive copolymers of N-isopropylacrylamide and acrylic acid (AA) with different contents of AA were synthesized by RAFT polymerization. Effect of NCC, AA content, and pH on LCST was evaluated.

Reversible Addition-Fragmentation Chain Transfer Synthesis of a Micelle-Forming, Structure Reversible Thermosensitive Diblock Copolymer Based on the N-(2-Hydroxy propyl) Methacrylamide Backbone

A diblock copolymer composed of N-(2-hydroxy propyl) methacrylamide (HPMAm) as hydrophilic block and N-(2-hydroxy propyl) methacrylamide dilactate (HPMAm-Lac₂) as thermosensitive block was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. To this end, HPMAm was first polymerized with 4-cyano-4-[(dodecylsulfanylthiocarbonyl)-sulfanyl]pentanoic acid as the chain transfer agent and azobisisobutyronitrile (AIBN) as the initiator. The polymerization showed a linear increase in M_n as a function of monomer conversion. The living p(HPMAm) chain (7 kDa) was subsequently extended with HPMAm-Lac₂ yielding a diblock copolymer (total M_n of 22 kDa). The copolymer showed reversible thermosensitivity in aqueous solution and self-assembled into micelles with a size of 58 nm (PDI 0.13) above its critical micelle temperature (CMT, 2.1 °C) and concentration (CMC, 0.044 mg/mL) and was soluble below the CMT. Paclitaxel, a hydrophobic chemotherapeutic drug, was encapsulated in the micelles with a loading capacity of 16.1 ± 1.2%. Hydrolysis of the dilactate side groups of the p(HPMAm-Lac₂) block converted the copolymer to the fully hydrophilic p(HPMAm) homopolymer, resulting in dissociation of the micelles. In conclusion, the livingness and versatility of RAFT polymerization provide possibilities to synthesize block copolymers with HPMAm and derivatives thereof.

Temperature- and pH-sensitive Polymeric Micelles for Drug Encapsulation, Release and Targeting

More than 50% of the drugs in the market and 70% of the new candidates are poorly water soluble according to the Biopharmaceutic Classification System (BCS(. Poor aqueous solubility and physico-chemical stability of drugs in biological fluids remain key limitations in oral, parenteral and transdermal administration and contribute to an increase the drug attrition rate. Motivated by the outbreak of nanotechnology, different nanocarriers made of lipids and polymers have been designed and developed to address these limitations. Moreover, robust platforms were exploited to achieve the temporal and spatial release of drugs, thus constraining the systemic exposure to toxic agents and the appearance of severe adverse effects and improving the safety ratio. Owing to unique features such as (i( great chemical flexibility, (ii( capacity to host, solubilize and physico-chemically stabilize poorly water soluble drugs, (iii( ability to accumulate selectively in highly vascularized solid tumors and (iv( ability of single amphiphile molecules (unimers( to inhibit the activity of different pumps of the ATP-binding cassette superfamily (ABCs(, polymeric micelles have emerged as one of the most versatile nanotechnologies. Despite their diverse applications to improve the therapeutic outcomes, polymeric micelles remain clinically uncapitalized. The present chapter overviews the most recent applications of temperature- and pH-responsive polymeric micelles for the encapsulation, release and targeting of drugs and discusses the perspectives for these unique nanocarriers in the near future.

Synthesis of biotinylated aldehyde polymers for biomolecule conjugation

Biotinylated polymers with side-chain aldehydes were prepared for use as multifunctional scaffolds. Two different biotin-containing chain transfer agents (CTAs) and an aldehyde-containing monomer, 6-oxohexyl acrylate (6OHA), are synthesized. Poly(ethylene glycol) methyl ether acrylate (PEGA) and 6OHA are copolymerized by reversible addition-fragmentation chain transfer (RAFT) polymerization in the presence of the biotinylated CTAs. The resulting polymers are analyzed by GPC and(1) H NMR spectroscopy. The polymer end groups contained a disulfide bond, which could be readily reduced in solution to remove the biotin. Reactivity of the aldehyde side chains is demonstrated by oxime and hydrazone formation at the polymer side chains, and conjugate formation of fluorescently labeled polymers with streptavidin is investigated by gel electrophoresis.

Spiropyran-based hyperbranched star copolymer: synthesis, phototropy, FRET, and bioapplication

Photo- and pH-responsive amphiphilic hyperbranched star copolymers, poly(6-O-methacryloyl-1,2;3,4-di-O-isopropylidene-d-galactopyranose)[poly(2-(N,N-dimethylaminoethyl) methacrylate)-co-poly(1'-(2-methacryloxyethyl)-3',3'-dimethyl-6-nitro-spiro(2H-1-benzo-pyran-2,2'-indoline))](n)s [HPMAlpGP(PDMAEMA-co-PSPMA)(n)], were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization of the DMAEMA and the SPMA using hyperbranched PMAlpGP as a macro RAFT agent. In aqueous solution, the copolymers self-assembled to form core-shell micelles with HPMAlpGP core and PDMAEMA-co-PSPMA shell. The hydrophobic fluorescent dye nitrobenzoxadiazolyl derivative (NBD) was loaded into the spiropyran-containing micelles. The obtained micelles not only have the photochromic properties, but also modulate the fluorescence of NBD through fluorescence resonance energy transfer (FRET), which was also observed in living cells. Slight fluorescence intensity decrease of the spiropyran in merocyanine (ME) form was observed after five UV-visible light irradiation cycles. The cytotoxicity of the HPMAlpGP(PDMAEMA-co-PSPMA)(n) micelles was lower than that of 25k PEI. All the results revealed that these photoresponsive nanoparticles are a good candidate for cell imaging and may find broad applications in biological areas such as biological diagnosis, imaging, and detection.

Biological stimuli and biomolecules in the assembly and manipulation of nanoscale polymeric particles

Living systems are replete with complex, stimuli-responsive nanoscale materials and molecular self-assemblies. There is an ever increasing and intense interest within the chemical sciences to understand, mimic and interface with these biological systems utilizing synthetic and/or semi-synthetic tools. Our aim in this review is to give perspective on this emerging field of research by highlighting examples of polymeric nanoparticles and micelles that are prepared utilizing biopolymers together with synthetic polymers for the purpose of developing nanomaterials capable of interacting and responding to biologically relevant stimuli. It is expected that with the merging of evolved biological molecules with synthetic materials, will come the ability to prepare complex, functional devices. A variety of applications will become accessible including self-healing materials, self-replicating systems, biodiagnostic tools, drug targeting materials and autonomous, adaptive sensors. Most importantly, the success of this type of strategy will impact how biomolecules are stabilized and incorporated into synthetic devices and at the same time, will influence how synthetic materials are utilized within biomedical applications.

Synthesis of fullerene-containing poly(ethylene oxide)-block-polystyrene as model shape amphiphiles with variable composition, diverse architecture, and high fullerene functionality

Click chemistry provides a precise and effective approach towards construction of fullerene-containing block polymers with diverse architecture, and high fullerene functionality.

Surface Functionalization Methods to Enhance Bioconjugation in Metal-Labeled Polystyrene Particles

Lanthanide-encoded polystyrene particles synthesized by dispersion polymerization are excellent candidates for mass cytometry based immunoassays, however they have previously lacked the ability to conjugate biomolecules to the particle surface. We present here three approaches to post-functionalize these particles, enabling the covalent attachment of proteins. Our first approach used partially hydrolyzed poly(N-vinylpyrrolidone) as a dispersion polymerization stabilizer to synthesize particles with high concentration of -COOH groups on the particle surface. In an alternative strategy to provide -COOH functionality to the lanthanide-encoded particles, we employed seeded emulsion polymerization to graft poly(methacrylic acid) (PMAA) chains onto the surface of these particles. However, these two approaches gave little to no improvement in the extent of bioconjugation. In our third approach, seeded emulsion polymerization was subsequently used as a method to grow a functional polymer shell (in this case, poly(glycidyl methacrylate) (PGMA)) onto the surface of these particles, which proved highly successful. The epoxide-rich PGMA shell permitted extensive surface bioconjugation of NeutrAvidin, as probed by an Lu-labeled biotin reporter (ca. 7 × 10(5) binding events per particle with a very low amount of non-specific binding) and analyzed by mass cytometry. It was shown that coupling agents such as EDC were not needed, such was the reactivity of the particle surface. These particles were stable and the addition of a polymeric shell was shown did not affect the narrow lanthanide ion distribution within the particle interior as analyzed by mass cytometry. These particles represent the most promising candidates for the development of a highly multiplexed bioassay based on lanthanide-labeled particles to date.

Anti-CD22 antibody targeting of pH-responsive micelles enhances small interfering RNA delivery and gene silencing in lymphoma cells

The application of small interfering RNA (siRNA) for cancer treatment is a promising strategy currently being explored in early phase clinical trials. However, efficient systemic delivery limits clinical implementation. We developed and tested a novel delivery system comprised of (i) an internalizing streptavidin-conjugated monoclonal antibody (mAb-SA) directed against CD22 and (ii) a biotinylated diblock copolymer containing both a positively charged siRNA condensing block and a pH-responsive block to facilitate endosome release. The modular design of the carrier facilitates the exchange of different targeting moieties and siRNAs to permit its usage in a variety of tumor types. The polymer was synthesized using the reversible addition fragmentation chain transfer (RAFT) technique and formed micelles capable of binding siRNA and mAb-SA. A hemolysis assay confirmed the predicted membrane destabilizing activity of the polymer under acidic conditions typical of the endosomal compartment. Enhanced siRNA uptake was demonstrated in DoHH2 lymphoma and transduced HeLa-R cells expressing CD22 but not in CD22 negative HeLa-R cells. Gene knockdown was significantly improved with CD22-targeted vs. nontargeted polymeric micelles. Treatment of DoHH2 cells with CD22-targeted polymeric micelles containing 15 nmol/l siRNA produced 70% reduction of gene expression. This CD22-targeted polymer carrier may be useful for siRNA delivery to lymphoma cells.

Biomimetic smart interface materials for biological applications

Controlling the surface chemical and physical properties of materials and modulating the interfacial behaviors of biological entities, e.g., cells and biomolecules, are central tasks in the study of biomaterials. In this context, smart polymer interface materials have recently attracted much interest in biorelated applications and have broad prospects due to the excellent controllability of their surface properties by external stimuli. Among such materials, poly(N-isopropylacrylamide) and its copolymer films are especially attractive due to their reversible hydrogen-bonding-mediated reversible phase transition, which mimics natural biological processes. This platform is promising for tuning surface properties or to introduce novel biofunctionalities via copolymerization with various functional units and/or combination with other materials. Important progress in this field in recent years is highlighted.

Synthesis and characterization of a naphthalimide–dye end-labeled copolymer by reversible addition–fragmentation chain transfer (RAFT) polymerization

We describe the synthesis of an end-functionalized copolymer of N-(2-hydroxypropyl)methacrylamide (HPMA) and N-hydroxysuccinimide methacrylate (NMS) by reversible addition–fragmentation chain transfer (RAFT) polymerization. To control the polymer composition, the faster reacting monomer (NMS) was added slowly to the reaction mixture beginning 30 min after initating the polymerization (ca. 16% HPMA conversion). One RAFT agent, based on azocyanopentanoic acid, introduced a –COOH group to the chain at one end. Use of a different RAFT agent containing a 4-amino-1,8-naphthalimide dye introduced a UV–vis absorbing and fluorescent group at this chain end. The polymers obtained had molecular weights of 30 000 and 20 000, respectively, and contained about 30 mol% NMS active ester groups.

Biohybrid block copolymers: towards functional micelles and vesicles

This critical review covers the elaboration of micelles and vesicles made from block copolymers containing peptide or oligonucleotide blocks with a focus on recent developments toward responsive and functional assemblies (166 references).