No abstract

Micellization of poly(oxyethylene-6-oxypropylene-6-oxyethylene) triblock copolymers (Pluronic polymers F68, P85, and F108) in aqueous solutions was studied, and critical micellization concentrations (cmc) were determined using surface tension measurements and fluorescent probes (pyrene, l,6-diphenyl-l,3,5-hexatriene). The dependence of cmc on temperature was observed, and critical micellization temperatures characterizing temperature-dependent transitions of Pluronic unimers to multimolecular micelles were measured. The molecular characteristics of P85 and F108 micelles including their dimensions, molecular masses and surfactant aggregation numbers were determined using lightscattering and ultracentrifugation techniques. Depending on the type of Pluronic, the micelles had an average hydrodynamic diameter ranging from about 15 to about 35 nm, a molecular mass of about 200 kDa and aggregation numbers ranging from one to several dozens. The partitioning of fluorescent probes between aqueous and micellar phases was analyzed within the frame of a pseudophase model, and the partitioning coefficients were determined using the fluorescence data. The results are compared with previous reports and are discussed in relationship to the application of block copolymer micelles as microcontainers for drug delivery.

Block polyelectrolyte micelles formed by poly(styrene-5-sodium acrylate) in aqueous solutions were characterized by static light scattering (SLS). Initially, the solutions contained gel-like particles; the kinetics of disentanglement of these particles were measured from the intensity of the scattered light at different angles as a function of heating time at 100 °C. It was found that after ca. 50 h of heating no further changes occurred in the scattered intensity. The effect of different sodium chloride concentrations on the aggregation numbers (N), radii of gyration (Rg), and second virial coefficients (A2) of the resulting micellar solutions was determined for two block copolymers, PS(6)-5-PANa(180) and PS( 23)-6-PANa-(300). It was found that N increased as a function of salt concentration at low salt contents, but the values remained constant above ca. 0.10 M NaCl. A range of samples with PS block lengths ranging from 6 to 71 units and PANa block lengths ranging from 44 to 780 units was measured in 2.5 M NaCl. As expected, the length of the insoluble block had a much greater effect on the aggregation numbers than that of the soluble block. The data were examined according to the scaling predictions of the star model and several mean-field models. Comparison with several of the models showed good agreement with experimental values of N, calculated core radius CRc), and Rg as a function of block lengths. The core radii values of the micelles agreed very well with those determined independently for similar samples measured in the solid state by small-angle X-ray scattering (SAXS). From this result, it was concluded that the micelles in 2.5 M NaCl exist singly, i.e., that no supermicellar aggregates are present and that the core is solvent free.

Critical micelle concentrations (cmcs) of block polyelectrolyte micelles formed from poly-(styrene-6-sodium acrylate) in aqueous and NaCl salt solutions were investigated by fluorescence measurements of solubilized pyrene. The measurements were made for a range of PS block lengths (6 to 110 units) and of PANa block lengths (15-2400 units). For the series consisting of 11 and 23 units of PS, which had been prepared with a wide range of PANa lengths, the cmc was found to pass through a maximum as a function of the soluble (PANa) block length. It was observed that as the length of the PS block increased, the dependence of the log cmc versus the PANa block length decreased. For all samples except the PS(6) series at low salt concentrations, the log cmc values were found to decrease linearly as a function of the square root of the NaCl concentration (VCa) which was varied from 0.10-2.5 M. The shape of the gradient d(log cmc)/d(VCa) versus the log of the number of PANa units was found to follow a curve of the same shape for the block polyelectrolyte micelles consisting of 6, 11, and 23 units of PS. The behavior of the curve was explained on the basis of polyelectrolyte conformations.

Stent coating with cRGD may be useful for reducing in-stent restenosis by accelerating endothelialization.

Though stents are deployed in diseased arteries drug distribution has only been quantified in intact, non-diseased vessels. We correlated steady-state arterial drug distribution with tissue ultrastructure and composition, in abdominal aortae from atherosclerotic human autopsy specimens and rabbits with lesions induced by dietary manipulation and controlled injury. Paclitaxel, everolimus, and sirolimus deposition in human aortae was maximal in the media and scaled inversely with lipid content. Net tissue paclitaxel and everolimus levels were indistinguishable in mildly injured rabbit arteries independent of diet. Yet, serial sectioning of cryopreserved arterial segments demonstrated a differential transmural deposition pattern that was amplified with disease and correlated with expression of their intracellular targets, tubulin and FKBP-12. Tubulin distribution and paclitaxel binding increased with vascular injury and macrophage infiltration, and were reduced with lipid content. Sirolimus analogues and their specific binding target FKBP-12 were less sensitive to alterations of diet in mildly injured arteries, presumably reflecting a faster transient response of FKBP-12 to injury. The data demonstrate that disease-induced changes in the distribution of drug binding proteins and interstitial lipid alter the distribution of these drugs, forcing one to consider how disease might affect the evaluation and efficacy of local release of these and like compounds.

A new method for mammalian cell transformation is proposed which is based on incorporation of plasmids into interpolyelectrolyte complexes (IPECs) with carbon chain polycations. The method is illustrated by examples of pRSV CAT and p beta-Gal plasmid IPECs with poly(N-ethyl-4-vinylpyridinium bromide) (C2PVP) and poly(N-ethyl-4-vinylpyridinium)-poly(N-cetyl-4-vinylpyridinium+ ++) bromides random copolymer (C16PVP). These IPECs are produced spontaneously due to formation of a cooperative system of interchain electrostatic bonds after mixing DNA and polycation solutions. The interaction of IPEC with normal mouse fibroblasts NIH 3T3, human T-lymphoma "Jurkat", and Mardin Darby canine kidney cells has been studied. The data obtained has revealed that plasmid incorporation into IPECs significantly enhances both DNA adsorption on the plasma membrane and DNA uptake into a cell. The in vitro transformation of NIH 3T3 cells was monitored by a standard cloramphenicol acetyltransferase (CAT) assay (pRSV CAT plasmid) and by detection of beta-galactosidase (beta-Gal) expression using 4-methylumbeliferril beta-D-galactopyranoside as a substrate (p beta-Gal plasmid). In both cases it has been proved that IPEC-incorporated plasmids possess an ability for efficient cell transformation. The transforming activity of IPECs depends on their composition and polycation chemical structure. Under optimal conditions the efficiency of cell transformation with IPECs is several fold higher than that observed during standard calcium phosphate precipitation. The mechanism of the phenomenon observed is discussed.(ABSTRACT TRUNCATED AT 250 WORDS)

Polyelectrolyte complexes formed between DNA and poly(N-ethyl-4-vinylpyridinium) cations were shown to effectively transfect mammalian ceils [7]. This work suggests that the polycation-mediated uptake of the plasmid DNA and cell transfection are significantly enhanced when these complexes are administered simultaneously with a poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) copolymer, Pluronic P85. The uptake studies were performed using radioactively labeled pRSV CAT plasmid on NIH 3T3, MDCK, and Jurkat cell lines. The transfection was investigated by ehloramphenicol acetyltransferase assay using 3T3 cells as a model. The effects reported may be useful for the enhancement of the polycation-mediated cell transfection.cytic compartments in the cytoplasm and nucleus of cells [1 3]. Further, due to charge neutralization these complexes are often unstable in aqueous solutions and precipitate, thereby hindering their application in gene delivery [3 8]. One approach recently advanced for drug delivery of water insoluble compounds involves the use of micelles of Pluronic block copolymers [9,10]. Recent work on these systems suggests that they enhance the transport of charged molecules across cell membranes [11,12]. This paper reports a significant increase in cell uptake and transfection of mammalian cells using a combination of DNA-PEVP complexes and micelles of Pluronic P85 block copolymer.