Stanislav Rangelov

Polymeric nanoparticle engineering: from temperature-responsive polymer mesoglobules to gene delivery systems.

A novel approach for the preparation of nano- and microcapsules in aqueous solutions by using thermoresponsive polymer (TRP) templates (mesoglobules) is described. The method comprised three steps: formation of mesoglobules, coating the templates by seeded radical copolymerization, followed by core dissolution and core removal upon cooling. When mesoglobule entraps biomacromolecules during the process of their formation, it makes it possible to load a controlled amount of bioactive compounds without covalent attachment. Special attention is paid to the mesoglobule dissolution upon cooling, as well as their loading efficiency. Details on the outer shell formation and the possibilities for targeting ligands incorporation and control of the shell porosity are discussed. Finally, the seeded radical copolymerization was used for covering DNA complexes with cationic copolymers bearing TRP blocks. This Review is an attempt to convince researchers of the promising perspectives for using mesoglobules as potential reservoirs, carriers, and transferring agents for biologically active substances.

Polymorph dispersed particles from the bicontinuous cubic phase of glycerol monooleate stabilized by PEG-copolymers with lipid-mimetic hydrophobic anchors

Four unique nonionic block‐copolymers have been tested as dispersants and stabilizers for dispersed particles from the bicontinuous cubic phase of glycerol monooleate, GMO. The polymers have hydrophilic blocks composed of PEO with 52 to 136 EO units. These are linked via ether bonds to lipid mimetic hydrophobic anchor groups, bearing between two and eight dodecyl chains. The polymer with the longest PEO block is a triblock polymer, with hydrophobic anchors at both ends. The polymers are taken up by the cubic phase of GMO, and their effect on the swelling of this phase in water was investigated. The excess aqueous solution above the cubic phase was found to contain dispersed particles in varying amounts, depending on polymer type and concentration. The structure and morphology of these colloidal particles were investigated by cryogenic transmission electron microscopy (cryoTEM). Besides dispersed particles of the cubic phase, various types of vesicles and particles with disordered interior were observed, as well as in some systems more peculiar structures, e.g, a honeycomb structure. Particle dispersions were also prepared via a precursor dispersion of the GMO‐polymer mixtures in glycerol. The particles resulting from a dilution of this precursor dispersion in a ten‐fold excess of water were examined with cryoTEM. Using low proportions of the polymers, dispersed cubic particles were obtained, although only occasionally shaped as small cubes. Usually the particles were very polydisperse in both size, shape, and morphology. In some systems large amounts of particles with a disordered interior, reminiscent of particles from a sponge phase, were observed. At higher concentrations of the polymers, vesicles of various morphologies were most abundant, and at highest concentrations of the most hydrophobic polymers, band‐shaped micellar structures appeared together with vesicles. Since these polymers were sparingly soluble in water, the band‐shaped micelles are probably mixed micelles containing GMO and the polymer. The packing of the polymers and their effects as steric stabilizers are discussed and related to the Flory measure of their size.

Curcumin loaded pH-sensitive hybrid lipid/block copolymer nanosized drug delivery systems.

Curcumin is a perspective drug candidate with pleiotropic antineoplastic activity, whose exceptionally low aqueous solubility and poor pharmacokinetic properties have hampered its development beyond the preclinical level. A possible approach to overcome these limitations is the encapsulation of curcumin into nano-carriers, incl. liposomes. The present contribution is focused on feasibility of using hybrid pH-sensitive liposomes, whereby curcumin is entrapped as a free drug and as a water soluble inclusion complex with PEGylated tert-butylcalix[4]arene, which allows the drug to occupy both the phospholipid membranes and the aqueous core of liposomes. The inclusion complexes were encapsulated in dipalmithoylphosphathydilcholine:cholesterol liposomes, whose membranes were grafted with a poly(isoprene-b-acrylic acid) diblock copolymer to confer pH-sensitivity. The liposomes were characterized by DLS, ζ-potential measurements, cryo-TEM, curcumin encapsulation efficacy, loading capacity, and in vitro release as a function of pH. Free and formulated curcumin were further investigated for cytotoxicity, apoptosis-induction and caspase-8, and 9 activation in chemosensitive HL-60 and its resistant sublines HL-60/Dox and HL-60/CDDP. Formulated curcumin was superior cytotoxic and apoptogenic agent vs. the free drug. The mechanistic assay demonstrated that the potent proapoptotic effects of pH-sensitive liposomal curcumin presumably mediated via recruitment of both extrinsic and intrinsic apoptotic pathways in both HL-60 and HL-60/CDDP cells.

Rheology of Aqueous Solutions of Polyglycidol-Based Analogues to Pluronic Block Copolymers

The aqueous solution properties of a series of polyglycidol-poly(propylene oxide)-polyglycidol (PG-PPO-PG) block copolymers were investigated by means of rheology. The copolymers are considered as analogues to the commercially available Pluronic, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO), block copolymers in which the flanking PEO blocks are substituted by blocks of structurally similar PG bearing a hydroxyl group in each repeating monomer unit. In the dilute regime, the samples normally behave as Newtonian fluids. Shear thinning was observed only for the solutions of LGP65 (the copolymer of 50 wt % PG content) as well as at concentrations well above the critical micellization concentration for the rest of the copolymers. The zero shear viscosities exhibited pronounced maxima at PG content of 50 wt % and were found to decrease with increasing temperature. The concentrated solutions were investigated using oscillatory measurements. Large hystereses were observed during the temperature sweeps 15-70-15 degrees C. The evolutions of the loss and storage moduli with frequency, PG content, and temperature displayed transitions from a non-elastic to elastic behavior of the solutions. A phase diagram showing areas of predominant elasticity or fluidity was constructed.

Synthesis and polymerization of novel oxirane bearing an aliphatic double chain moiety

Abstract A novel epoxide monomer, 1,3-didodecyloxy-2-glycidyl-glycerol (DDGG), bearing an aliphatic double chain was prepared. DDGG was anionically homopolymerized and block copolymerized with ethylene oxide (EO). The polymers were characterized by 1 H nuclear magnetic resonance spectroscopy, gel permeation chromatography, vapor pressure osmometry, and differential scanning calorimetry. The decrease in transmittance of the aqueous solutions of the copolymer, denoted EO 115 DDGG 2 , with raising temperature and/or concentration was attributed to the presence of aggregates. An anomalous increase in the transmittance at 35°C was noted as well. A dye solubilization method was used to demonstrate the ability of EO 115 DDGG 2 to associate in aqueous solution. The associative interactions gave rise to a sharp increase in viscosity.

DNA encapsulation via nanotemplates from cationic block copolymer micelles

We report on a method for the encapsulation of DNA into polymeric nanocapsules. The encapsulation procedure involves three steps: formation of polyplexes between DNA and cationic polymeric micelles; coating of polyplexes with a cross-linked shell; dissociation of polyplexes. In the first step copolymer micelles were obtained by self-assembly of an amphiphilic polystyrene-b-poly(quaternized 2-vinylpyridine) (PS-b-PQ2VP) block copolymer in aqueous solution. Nanosized polyplexes (Dh = 190 nm and ζ = −21 mV) were formed upon the addition of DNA to the micellar solution at a phosphate/amine group ratio of 3 : 1. In the second step the complexes were coated with a cross-linked shell formed by seeded radical polymerization of N-isopropylacrylamide which resulted in a slight shift of ζ potential of the particles to a less negative value. The dissociation of polyplexes and removal of PS-b-PQ2VP were achieved by addition of salt and solvent exchange. Following rehydration viadialysis against water, polymeric nanocapsules with entrapped DNA were obtained. The nanocapsules were visualized by transmission electron microscopy; they exhibited smaller dimensions compared to the initial polyplexes and ζ potential very close to that of the pristine DNA.

Hybrid liposomal PEGylated calix[4]arene systems as drug delivery platforms for curcumin

The tremendous therapeutic potential of curcumin as a chemopreventive, antineoplastic and chemosensitizing agent has failed to progress towards clinical development and commercialization due to its unfavorable physicochemical properties, low aqueous solubility, chemical instability, and pharmacokinetics. The present contribution is focused on the feasibility of using PEGylated calixarene, in particular polyoxyethylene-derivatized tert-butylcalix[4]arene, to prepare various platforms for delivery of curcumin such as inclusion complex, supramolecular aggregates, and hybrid liposomal systems. The inclusion complex is characterized by UV-vis and FT-IR spectroscopy as well as thermal gravimetrical analysis and differential scanning calorimetry. At concentrations exceeding the critical micellization concentration of PEGylated calixarene, the tremendous solubility enhancement of curcumin is attributed to additional solubilization and hydrophobic non-covalent interactions of the drug with supramolecular aggregates. A hybrid liposomal system is created via encapsulation of the inclusion complex in dipalmitoylphosphatidylcholine:cholesterol liposomes. Bare and liposomal curcumin:BEC-X inclusion complexes, as well as free curcumin were additionally investigated for cytotoxicity and apoptogenic activity against human tumor cell lines.

THE INFLUENCE OF POLYMERIZATION CONDITIONS ON THE STRUCTURE AND PROPERTIES OF HIGH MOLECULAR WEIGHT POLYETHYLENE OBTAINED ON SUPPORTED VANADIUM CATALYST SYSTEM

Abstract During a slurry polymerization of ethylene, the influence of the molar ratio of the catalyst components and the pressure on the activity of an amorphous SiO 2 -supported vanadium containing catalyst system is investigated. (C 2 H 5 ) 2 AlCl is used as a first co-catalyst and (C 4 H 9 ) 1.5 (C 8 H 17 ) 0.5 Mg as a second one. It is shown that using only the first co-catalyst the polymers obtained have a uniform structure consisting of compact angular particles. When both co-catalysts are used the polymers have a heterogeneous structure—spherulitic aggregates are also observed. Based on the differences established in the morphology of the polyethylenes an explanation is given for the influence of the second co-catalyst on the catalytic activity as well as for the peculiarities of the synthesized polymers in comparison with the commercial products.

Enhanced Gene Expression Promoted by Hybrid Magnetic/Cationic Block Copolymer Micelles

We report on novel gene delivery vector systems based on hybrid polymer-magnetic micelles. The hybrid micelles were prepared by codissolution of hydrophobically surface modified iron oxide and amphiphilic polystyrene-b-poly(quaternized 2-vinylpyridine) block copolymer (PS-b-P2QVP) in organic solvent. After extensive dialysis against water, micelles with positively charged hydrophilic corona of PQVP and hydrophobic PS core were prepared, in which magnetic nanoparticles were randomly distributed. The hybrid micelles were used to form complexes with linear (salmon sperm, 2000 bp, corresponding to M(w) of 1.32 × 10(6) Da) and plasmid (pEGFP-N1, 4730 bp, corresponding to M(w) of 3.12 × 10(6) Da) DNA. The resulting magnetopolyplexes of phosphate:amine (P/N) ratios in the 0.05-20 range were characterized by light scattering, ζ-potential measurements, and transmission electron microscopy as well as cytotoxicity and gel retardation assays. The investigated systems displayed a narrow size distribution, particle dimensions below 360 nm, whereas their ζ-potential values varied from positive to negative depending of the P/N ratio. The resulting vector nanosystems exhibited low toxicity. They were able to introduce pEGFP-N1 molecules into the cells. The application of a magnetic field markedly boosted the transgene expression efficiency of the magnetopolyplexes, which was even superior to those of commercial transfectants such as Lipofectamine and dendritic polyethylenimine.

Physicochemical and biopharmaceutical characterization of dipalmitoyl phosphatidylcholine liposomes sterically stabilized by copolymers bearing short blocks of lipid-mimetic units

Amphiphilic block copolymers were used to provide steric stabilization of dipalmitoyl phosphatidylcholine (DPPC) liposomes. The copolymers are based on poly(ethylene glycol) (PEG), but unlike the commercial PEG-lipids, bear short blocks of lipid-mimetic units. The liposomes were prepared by the lipid film hydration method and extrusion which yielded liposomes in the range of 140–170 nm in diameter as revealed by dynamic light scattering. The cryogenic transmission electron microscopy study documented unilamellar, spherical, well-separated and predominantly intact liposomes, even at copolymer contents as high as 10 mol%. The leakage of 5(6)-carboxyfluorescein was typically reduced compared to the plain liposomes. Some differences in the leakage profiles and membrane permeability were discussed in terms of shapes of the macromolecules and phase propensity of the copolymers studied. The pharmacokinetic parameters showed that the liposomes modified by a copolymer bearing four lipid-mimetic anchors exhibit superior longevity in vivo and two times lower accumulation in the liver compared to the plain liposomes and liposomes stabilized by commercial PEG-lipid. The cellular interactions were evaluated by means of fluorescence microscopy. Both the plain and the sterically stabilized liposomes were found to adhere to the membrane of MGH-U1 cells thus showing potential of serving as containers for sustained release of cytostatics. By using an ammonium transmembrane gradient method, mitoxantrone was loaded into liposomes with efficiency greater than 96%. The presence of a stabilizing copolymer did not compromise the drug loading efficacy. The liposomal mitoxantrone showed pronounced cytotoxicity towards an HL-60/Dox, which is of clinical importance as far as by-passing of multi-drug resistance is concerned.