Removable nanocoatings for siRNA polyplexes.

To assist in overcoming the inherent instability of nucleic acid-containing polyplexes in physiological solutions, we have here set out to develop removable nanocoatings for modifying the surface of siRNA-based nanoparticles. Here, N-(2-hydroxypropyl)methacrylamide (HPMA) based copolymers containing carbonylthiazolidine-2-thione (TT) reactive groups in their side chains bound via disulfide spacers to the polymeric backbone were synthesized, and these copolymers were used to coat the surface of polyplexes formed by the self-assembly of anti-Luciferase siRNA with the polycations polyethylene imine (PEI) and poly(HPMA)-grafted poly(l-lysine) (GPL). The coating process was monitored by analyzing changes in the weight-average molecular weight (M(w)), the hydrodynamic radius (R(h)), and the zeta-potential (ζ) of the polyplexes, using both static (SLS) and dynamic (DLS) light scattering methods. The outlined methods resulted in the attachment of, on average, 28 polymer molecules to the surface of the polyplexes, forming a ∼5-nm-thick hydrophilic stealth coating. Initial efforts to develop RGD-targeted coated polyplexes are also described. Atomic force microscopy (AFM) showed an angular polyplex structure and confirmed the narrow size distribution of the coated nanoparticles. The stability of the polymer-coated and uncoated polyplexes was evaluated by gel electrophoresis and by turbidity measurements, and it was found that modifying the surface of the siRNA-containing polyplexes substantially improved their stability in physiological solutions. Using polymer-coated GPL-based polyplexes containing anti-Luciferase siRNA, we finally also obtained some initial proof-of-principle for time- and concentration-dependent target-specific gene silencing, suggesting that these systems hold significant potential for further in vitro and in vivo evaluation.

pH sensitive polymer nanoparticles: effect of hydrophobicity on self-assembly.

The influence of hydrophobicity on formation, stability, and size of pH-responsive methacryloylated oligopeptide-based polymer nanoparticles has been studied by dynamic light scattering (DLS), transmission electron microscopy (Cryo-TEM), and NMR. Different polyanions/surfactant systems have been studied at constant polymer concentration and within a broad range of surfactant concentrations. The two newly synthesized pH-sensitive hydrophobic polyanions, poly(N(ω)-methacryloyl glycyl-L-leucine) and poly(N(ω)-methacryloyl glycyl-L-phenylalanyl-L-leucinyl-glycine), and three nonionic surfactants (Brij97, Brij98, and Brij700) have been investigated. The surfactants were different in the length of hydrophilic poly(ethylene oxide) (PEO) chain. In surfactant-free solution at basic pH, the polyanions form hydrophobic domains. In the presence of a surfactant, our results prove the complex formation at high pH between the nonionic surfactant and the polyelectrolyte; a pearl-necklace structure is formed. At low pH below critical pH (pH(tr)), reversible nanoscale structures occur in solutions for all systems. The detailed mechanism of the formation of pH-sensitive nanoparticles from polymer-surfactant complex with varying pH is established. Our results suggest that the polymer hydrophobicity is of primary importance in pretransitional behavior of the complex. Once preliminary nanoparticle nuclei are formed, the hydrophobicity of the polymer plays a minor role on further behavior of formed nanostructures. The subsequent transformation of nanoparticles is determined by the surfactant hydrophilicity, the length of hydrophilic tail that prevents further aggregation due to steric repulsions.

Chemical conjugation of cowpea mosaic viruses with reactive HPMA-based polymers.

N-(2-Hydroxypropyl)methacrylamide (HPMA) co-polymers containing disulfide and carbonyl thiazolidine-2-thione (TT) reactive groups in their side-chains (pHPMA-TT) were used as reductively removable chemical modification of the surface of cowpea mosaic viruses (CPMV). CPMV was used in this study as a model particle for viral gene delivery. The co-polymer reaction with CPMV surfaces carried out in aqueous solution was evaluated by monitoring the changes in the weight-average molecular weight and hydrodynamic size of the viruses using light scattering methods. The reaction conditions were optimized. The surface modification of CPMV with pHPMA-TT under selected conditions (concentrations of a coating polymer (c(p)) and NaCl) has not influenced the size distribution of the viral particles. The uncharged polymers bound to the viral surface via biodegradable S-S bonds can be fully removed by the exchange reaction with reductive dithiothreitol. To achieve optimal covering of viral surfaces, the positively charged reactive polymers (with or without biodegradable S-S bonds) should be applied at low concentrations (c(p)=0.1-0.5 mg/ml) and in presence of NaCl (0.15 M).

Effect of hydrophobic interactions on properties and stability of DNA-polyelectrolyte complexes.

Polyplexes are polyelectrolyte complexes of DNA and polycations, designed for potential gene delivery. We investigated the properties of new polyplexes formed from cholesterol-modified polycations and DNA. Three complexes were tested; their cholesterol contents were 1.4, 6.3, and 8.7 mol %. UV spectroscopy and fluorescence assay using ethidium bromide proved the formation of polyplexes. The kinetics of turbidity of polyplexes solutions in physiological solution showed that the colloid stability of polyplexes increases with increasing content of cholesterol in polycations. Dynamic, static, and electrophoretic light scattering, small-angle X-ray scattering, and atomic force microscopy were used for characterization of polyplexes. The observed hydrodynamic radii of polyplexes were in the range of 30-60 nm; they were related to the polycation/DNA ratio and hydrophobicity of the used polycations (the cholesterol content). The properties of polyplex particles depend, in addition to polycation structure, on the rate of polycation addition to DNA solutions.

Molecular weight and polydispersity of calf-thymus DNA: static light-scattering and size-exclusion chromatography with dual detection.

Plausible calf-thymus DNA molecular weight distribution can be obtained by size-exclusion chromatography with dual low-angle light scattering/refractometric detection at sufficiently low flow rate. The distribution extends over three decades of molecular weight and is characterized by weight average molecular weight M(w) = 8418000 and polydispersity index M(w)/M(n) = 5.2. After strongly scattering impurities had been removed from the sample using adsorption properties of the 3 mum mixed-cellulose-ester filter membranes, static light-scattering measurement in flow injection mode was feasible and gave M(w) = 8580000, corroborating the veracity of SEC results.

Thermoresponsive, hydrolytically degradable polymer micelles intended for radionuclide delivery.

Novel polymer micelles, prepared by self-assembling thermoresponsive poly(N-isopropylacrylamide)-graft-poly[N-(2-hydroxypropyl)methacrylamide] copolymers with hydrolytically degradable N-glycosylamine groups between the polymer blocks are proposed for delivery of diagnostic and therapeutic radionuclides into solid tumors. The micelles are formed by fast heating of an aqueous solution of the copolymer to 37 degrees C. They have a hydrodynamic diameter of 128 nm (measured using dynamic light scattering) and slowly degrade during incubation in aqueous buffer at pH = 7.4. Labeling with both (131)I and (90)Y proceeds with high yields (>85%). The unlabeled polymers are not cytotoxic for any of the tested murine and human cell lines.

Novel pH-responsive nanoparticles.

In this work we report a new type of pH-responsive micelle-like nanoparticle. Reversible nanoscale structures are formed in solutions of a pH-sensitive hydrophobic polyelectrolyte, poly( N-methacryloyl- l-valine) or poly( N-methacryloyl- l-phenylalanine), and nonionic surfactant (Brij 98) in the presence of hydrochloric acid. The influence of composition and pH on particles size and shape was investigated by a variety of methods. An entity's size and polydispersity could be varied in a broad range making them a perspective candidate as a drug carrier. Unlike the case of typical micelles, our results indicate the presence of cavities in the formed particles. A hypothetical model of a nanoparticle and mechanism of formation are proposed.

Coating of vesicles with hydrophilic reactive polymers.

Vesicles bearing either cationic (amino) groups or zwitterionic (amino acid) groups on the surface were coated with a reactive multivalent hydrophilic N-(2-hydroxypropyl)methacrylamide polymer (PHPMA) and its positively charged analogue (3 mol % quaternary ammonium groups), both having reactive thiazolidine-2-thione (TT) groups randomly distributed along the polymer chain. The vesicles were dispersed in water at a concentration of 1 mg/mL. The effect of surface charges of model vesicles on the surface coating efficiency was evaluated. The changes in the weight-average molecular weight, in the hydrodynamic size, and in the zeta-potential of model vesicles were tested using light scattering methods. The most effective coating of vesicles was observed for the zwitterionic vesicles coated with the positively charged hydrophilic PHPMA-TT copolymer at a concentration of reactive polymer cp = 2 mg/mL. The coating efficiency was more than 1 order of magnitude higher than that obtained for positively charged vesicles coated by the uncharged hydrophilic polymer at the same cp.

Dynamic light scattering study of self-assembly of HPMA hybrid graft copolymers.

The time course of self-assembly of a hybrid hydrogel system was investigated using dynamic light scattering (DLS) techniques. The self-assembling system consisted of a hydrophilic synthetic N-(2-hydroxypropyl)methacrylamide (HPMA) polymer backbone and a pair of oppositely charged peptide grafts (CCE and CCK). These two distinct pentaheptad peptides were anticipated to act as physical cross-linkers by the formation of antiparallel coiled-coil heterodimers. Equimolar mixture of HPMA graft copolymers CCE-P and CCK-P solutions (where P is the HPMA copolymer backbone) with total concentration from 1.25 to 10 mg/mL were measured at a scattering angle 90 degrees and room temperature. A critical extension of average relaxation time was observed with increasing concentration and incubation time. To reveal the role of coiled-coil grafts in the self-assembly process, a pair of modified random coil peptides, CCEw and CCKy, was designed. The DLS evaluation of HPMA copolymer conjugates (CCEw-P and CCKy-P) at total concentration of 10 mg/mL demonstrated that no association occurred after 28 h of incubation. Moreover, addition of a competing peptide (CCK) or a denaturant (guanidium chloride, GndHCl) to the self-assembled CCE-P/CCK-P hydrogels resulted in partial disassembly or collapse of the hydrogel clusters. These results correlated to changes in the secondary structure of peptides (grafts) as measured by circular dichroism spectroscopy (CD). These investigations supported the hypothesis that the self-assembly of CCE-P/CCK-P into hybrid hydrogels is mediated by the formation of coiled-coil heterodimers.

New bioerodable thermoresponsive polymers for possible radiotherapeutic applications.

A new thermoresponsive system designed for local radiotherapy has been developed. In this system a radionuclide complex is entrapped in a thermoresponsive polymer locally precipitated at body temperature after injection of a polymer-complex solution into the tissue where a therapeutic effect is required. The lifetime of the system is controlled by the rate of polymer hydrolysis, its dissolution and elimination from the body. The thermoresponsive polymer with the cloud temperature (CT) below body temperature is based on copolymers of N-isopropylmethacrylamide with a methacrylamide-type comonomer containing hydrophobic n-alkyls of three different sizes (C(3), C(6) and C(12)) bonded by a hydrolytically labile hydrazone bond. Hydrolysis of hydrazone bond results in a copolymer soluble at body temperature. The copolymer containing 27.5 mole% of the comonomer with the C(6) moiety, which was chosen for further study, has the CT 22 degrees C and its phase separation is complete at 34 degrees C. Polymer dissolution is complete within 48 h at both pH 5.0 or 7.4. The model therapeutic radionuclide, (64)Cu, in the form of its hydrophobic chelate bis(quinolin-8-olato-N,O) [(64)Cu]copper, is efficiently kept hydrophobically entrapped in the phase-separated polymer until the dissolution by hydrolytic degradation is completed.

Thermoresponsive self-assembly of short elastin-like polypentapeptides and their poly(ethylene glycol) derivatives.

Short polypeptides with four pentad repeats, (VPGVG)(4) and (VPAVG)(4), were synthesised by manual fluorenylmethoxycarbonyl/tert-butyl (Fmoc/t-Bu) solid phase peptide synthesis using a convergent approach. In the next step, the peptides were coupled via their N-terminus with activated semi-telechelic poly(ethylene glycol) O-(N-Fmoc-2-aminoethyl)-O'-(2-carboxyethyl)undeca(ethylene glycol) (Fmoc-PEG-COOH) to yield monodisperse Fmoc-PEG-peptide diblock copolymer. Both the presence of the terminal hydrophobic Fmoc group and the hydrophilic PEG chain in the copolymers were shown to play a crucial role in their self-associative behaviour, leading to reversible formation of supramolecular thermoresponsive assemblies. The peptides and their PEG derivatives were characterised by HPLC, NMR and MALDI-TOF MS. The associative behaviour of the peptides and their PEG derivatives was studied by dynamic light scattering, MAS NMR and phase contrast microscopy. [image: see text]

Properties of HPMA copolymer-doxorubicin conjugates with pH-controlled activation: effect of polymer chain modification.

Various conjugates of anticancer drug doxorubicin (DOX) covalently attached via hydrolytically degradable hydrazone bond to water-soluble N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer drug carriers were synthesized. Three types of precursors containing either positively or negatively charged groups or a hydrophobic substituent were employed. In vitro incubation of the conjugates in buffers showed relative stability at pH 7.4 (modelling blood) and a fast DOX release at pH 5 (modelling intracellular environment). The presence of carboxylic groups in the copolymer structure resulted in an increase in the DOX release rate of 15-20% while no effect of the introduction of positively charged groups was observed if compared with the unmodified conjugate. Self-assembling of the oleoyl groups-containing conjugate led into formation of polymeric micelles with high apparent molecular weight (M(w)=170,000) in aqueous solution and resulted in a decrease in the DOX release rate of approximately 20%. The cytostatic activity of the conjugates tested on several cancer cell lines was comparable with that of free DOX.HCl, depending on the sensitivity of a particular cell line to DOX. All the conjugates showed a much higher antitumour activity in vivo than the free drug tested in mice bearing EL4 T-cell lymphoma and treated using the therapeutic regime of drug administration. The highest activity (100% long-term survivors) exhibited polymer-DOX conjugate containing negatively charged GFLG sequences.

Coating of DNA/poly(L-lysine) complexes by covalent attachment of poly[N-(2-hydroxypropyl)methacrylamide].

N-(2-Hydroxypropyl)methacrylamide (HPMA) copolymers (pHPMA) containing 4-nitrophenyl ester (ONp) or thiazolidine-2-thione (TT) reactive groups in side chains and telechelic/semitelechelic pHPMA with TT groups were designed as highly hydrophilic biocompatible polymers suitable for chemical coating of polyelectrolyte-based DNA-containing nanoparticles bearing amino groups on the surface. The course of the coating reaction carried out in aqueous solution was evaluated on model self-assembling polyelectrolyte DNA/poly(L-lysine) (DNA/PLL) complexes either by monitoring the amount of residual polymer reactive groups by UV spectroscopy or by monitoring changes in the weight-average molecular weight and hydrodynamic size of the complexes using light scattering methods. Physicochemical stability of the coated complexes in buffered saline solution was also investigated. Contrary to uncoated particles, the coated complexes showed remarkable stability to aggregate in 0.15 M NaCl. Coating with pHPMA had practically no effect on the size distribution of the most stable complexes prepared by complexation of DNA with high-molecular-weight PLL (M(w) = 134 000) as shown by dynamic light scattering. The coating reaction was faster and more efficient with multivalent HPMA copolymers containing TT reactive groups than that with HPMA copolymers containing ONp groups.

Astatination of nanoparticles containing silver as possible carriers of 211At.

The alpha emitter 211At is a prospective radionuclide for the therapy of smaller tumours and metastases. However, the chemical properties of 211At together with the fact that it is available only in trace amounts, makes the labelling of prospective astatine carriers rather complicated. In this context we have studied a new class of possible astatine carriers--nanoparticle systems, which tend to concentrate themselves in some types of tumours by means of the EPR effect. Additionally, such nanoparticles have the advantage that they may be chemically modified by the attachment of a tumour-seeking agent, and also directly applied to the target site. In order to reach high labelling yields, and in order to protect the nanoparticles from rapid degradation by the immune system, silver-containing particles covalently coated by poly(ethylene oxide) were developed and tested. The effect of the different reducing and oxidizing agents on the labelling yield was also determined. It was found that labelling yields were almost quantitative and well reproducible under reducing conditions, while under oxidizing conditions they dropped to ca. 50%. In the absence of any reducing or oxidizing agent, the labelling yields were randomly distributed between a range of 50% and 97%. The labelled nanoparticles were stable even in a large surplus of competing chloride ions.

Interaction of DNA/polycation complexes with phospholipids: stabilizing strategy for gene delivery.

The interaction between negatively charged lipid vesicles and positively charged DNA/polylysine complexes was studied. The interaction does not lead to release of DNA from the initial complexes. The particles formed are easy to prepare, they have slight negative charge, small dimensions and show good stability in physiological NaCl solution. Such properties might indicate that stabilization of the particles by lipid coating might be a potent strategy, alternative to PEGylation of DNA/polycation complexes. Interaction of DNA/polycation complex particles with lipid vesicles.

Polymeric micellar pH-sensitive drug delivery system for doxorubicin.

A novel polymeric micellar pH-sensitive system for delivery of doxorubicin (DOX) is described. Polymeric micelles were prepared by self-assembly of amphiphilic diblock copolymers in aqueous solutions. The copolymers consist of a biocompatible hydrophilic poly(ethylene oxide) (PEO) block and a hydrophobic block containing covalently bound anthracycline antibiotic DOX. The starting block copolymers poly(ethylene oxide)-block-poly(allyl glycidyl ether) (PEO-PAGE) with a very narrow molecular weight distribution (Mw/Mn ca. 1.05) were prepared by anionic ring opening polymerization using sodium salt of poly(ethylene oxide) monomethyl ether as macroinitiator and allyl glycidyl ether as functional monomer. The copolymers were covalently modified via reactive double bonds by the addition of methyl sulfanylacetate. The resulting ester subsequently reacted with hydrazine hydrate yielding polymer hydrazide. The hydrazide was coupled with DOX yielding pH-sensitive hydrazone bonds between the drug and carrier. The resulting conjugate containing ca. 3 wt.% DOX forms micelles with Rh(a)=104 nm in phosphate-buffered saline. After incubation in buffers at 37 degrees C DOX was released faster at pH 5.0 (close to pH in endosomes; 43% DOX released within 24 h) than at pH 7.4 (pH of blood plasma; 16% DOX released within 24 h). Cleavage of hydrazone bonds between DOX and carrier continues even after plateau in the DOX release from micelles incubated in aqueous solutions is reached.

(1)H NMR and small-angle neutron scattering investigation of the structure and solubilization behavior of three-layer nanoparticles.

Three-layer nanoparticles were prepared by radiation-induced polymerization of 1-10 g/L of methyl methacrylate dissolved in a 0.1 wt % D(2)O solution of polystyrene-poly(methacrylic acid) (PS-PMA) micelles. According to NMR and small-angle neutron scattering (SANS), most of the poly(methyl methacrylate) (PMMA) is adsorbed at the core-shell interface of the particles. A small fraction of shorter PMMA probably sticks to outer parts of the PMA chains. The absorption kinetics and equilibria of benzene and chloroform were studied by NMR and SANS time-resolved experiments. The diffusion front in the PS core is very narrow but quite broad in the PMMA sheet suggesting, thus, a less compact state of PMMA. According to SANS, the diffusion kinetics is almost independent of the PMMA sheet thickness. In contrast to it, the absorption capacity, reflected by both SANS and NMR, increases markedly with the PMMA content in the particle. The maximum amount of solubilized compound depends on its positive interaction with PMMA (expressed by the chi parameter) but is restricted by the growing interface tension between swollen PMMA and D(2)O. In accordance with this conclusion, a particle saturated with benzene can absorb chloroform only at the expense of a part of benzene expelled into the surrounding medium and vice versa. Starting with 10 g PMMA/L (10 times the weight of the original micelles), the particles become unstable when being swollen with a good solvent.

Physical properties and in vitro transfection efficiency of gene delivery vectors based on complexes of DNA with synthetic polycations.

Biophysical properties of polycation/DNA complexes designed for gene delivery were studied with respect to the conditions of their preparation, chemical structure and molecular weight of the polycations involved. The polycations used included a variety of cationic polymers and copolymers containing primary and tertiary amino or quaternary ammonium groups. It was found that the molecular weight and the size of these polyelectrolyte complexes (PECs) increase with increasing temperature and pH of the buffer. By decreasing the molecular weight of polycations used for PEC formation, the complexes become unstable towards coagulation in aqueous solution at lower pH. The self-assembly of DNA with low-molecular-weight polycations in water provides PECs with the lowest molecular weight, smallest size and the lowest density but their stability in NaCl solutions is very poor. Despite the complexity of the multistep transfection process, a direct correlation between the transfection efficiency in vitro and the stability of the complexes in NaCl solutions and coagulation in 0.15 M NaCl solution was found. DNA complexes with polycations containing primary amino groups showed the best stability in saline solutions and also the best transfection activity. PECs formed by polycations with quaternary ammonium groups were the least resistant to destruction by the added salt and provided the lowest activity in transfection assays. The highest transfection activity was found for DNA complexes formed with a statistical copolymer containing primary and tertiary amines.