Short PEG Research Articles

Multifunctional Stable and pH-Responsive Polymer Vesicles Formed by Heterofunctional Triblock Copolymer for Targeted Anticancer Drug Delivery and Ultrasensitive MR Imaging

A multifunctional stable and pH-responsive polymer vesicle nanocarrier system was developed for combined tumor-targeted delivery of an anticancer drug and superparamagnetic iron oxide (SPIO) nanoparticles (NPs). These multifunctional polymer vesicles were formed by heterofunctional amphiphilic triblock copolymers, that is, R (folate (FA) or methoxy)-poly(ethylene glycol)(M(w):5000)-poly(glutamate hydrozone doxorubicin)-poly(ethylene glycol) (M(w):2000)-acrylate (i.e., R (FA or methoxy)-PEG(114)-P(Glu-Hyd-DOX)-PEG(46)-acrylate). The amphiphilic triblock copolymers can self-assemble into stable vesicles in aqueous solution. It was found that the long PEG segments were mostly segregated into the outer hydrophilic PEG layers of the vesicles, thereby providing active tumor targeting via FA, while the short PEG segments were mostly segregated into the inner hydrophilic PEG layer of the vesicles, thereby making it possible to cross-link the inner PEG layer via the acrylate groups for enhanced in vivo stability. The therapeutic drug, DOX, was conjugated onto the polyglutamate segment, which formed the hydrophobic membrane of the vesicles using a pH-sensitive hydrazone bond to achieve pH-responsive drug release, while the hydrophilic SPIO NPs were encapsulated into the aqueous core of the stable vesicles, allowing for ultrasensitive magnetic resonance imaging (MRI) detection. The SPIO/DOX-loaded vesicles demonstrated a much higher r(2) relaxivity value than Feridex, a commercially available SPIO-based T(2) contrast agent, which was attributed to the high SPIO NPs loading level and the SPIO clustering effect in the aqueous core of the vesicles. Results from flow cytometry and confocal laser scanning microscopy (CLSM) analysis showed that FA-conjugated vesicles exhibited higher cellular uptake than FA-free vesicles which also led to higher cytotoxicity. Thus, these tumor-targeting multifunctional SPIO/DOX-loaded vesicles will provide excellent in vivo stability, pH-controlled drug release, as well as enhanced MRI contrast, thereby making targeted cancer therapy and diagnosis possible.

Multifunctional SPIO/DOX-loaded wormlike polymer vesicles for cancer therapy and MR imaging

Stable and tumor-targeting multifunctional wormlike polymer vesicles simultaneously loaded with superparamagnetic iron oxide (SPIO) nanoparticles (NPs) as magnetic resonance imaging (MRI) contrast agent and anticancer drug doxorubicin (DOX) were developed for targeted cancer therapy and ultrasensitive MR imaging. These multifunctional wormlike polymer vesicles were formed by heterobifunctional amphiphilic triblock copolymers R (R = methoxy or folate (FA))-PEG 114-PLA x -PEG 46-acrylate using a double emulsion method. The long PEG segments bearing methoxy/folate groups (CH 3O/FA-PEG 114) were mostly segregated to the outer hydrophilic PEG layers of the wormlike vesicles thereby providing active tumor-targeting ability, while the short PEG segments bearing acrylate groups (PEG 46-acrylate) were mostly segregated onto the inner hydrophilic PEG layers of the wormlike vesicles thereby allowing the inner PEG layers to be crosslinked via free radical polymerization for enhanced in vivo stability. The hydrophobic anticancer drug, DOX, was loaded into the hydrophobic membrane of the wormlike vesicles. Meanwhile, a cluster of hydrophilic SPIO NPs was encapsulated into the aqueous cores of the stable wormlike vesicles with crosslinked inner PEG layers for ultrasensitive MRI detection. Cellular uptake of the FA-conjugated wormlike vesicles facilitated by the folate receptor-mediated endocytosis process was higher than that of the FA-free vesicles thereby leading to high cytotoxicity against the HeLa human cervical tumor cell line. Moreover, the SPIO/DOX-loaded wormlike vesicles with crosslinked inner PEG layers demonstrated a much higher r 2 relaxivity value than Feridex ®, a commercially available T 2 agent, which can be attributed to the high SPIO NPs loading level as well as the SPIO clustering effect. These unique stable and tumor-targeting multifunctional SPIO/DOX-loaded wormlike polymer vesicles would make targeted cancer theranostics possible thereby paving the road for personalized medicine.

Development of Worm-like Polymeric Drug Carriers with Multiple Ligands for Targeting Heterogeneous Breast Cancer Cells

In this study, wormorm-like polymeric micelles were construted from poly(L-lactic acid)-b-poly(ethyelen glycol) (PLLA-b-PEG) block copolymers via worm-like (or cylindrical) self- assembly that consisted of a relatively long PLLA block (<TEX>$M_n$</TEX> 7K Daltons) at the core and a relatively short PEG block (<TEX>$M_n$</TEX> 2K Daltons) as the shell. Several cancer-targeting moieties (such as folate, cobalamin, and cyclic arginine-glycine-aspartic (RGD) peptide) were chemically coupled with the succinylated or maleimided PEG block of PLLA-b-PEG to act as a cancer cell-specific targeting ligand for breast cancer. The worm-like micelles with muplite cancer cell-specific ligands proved to be successful in recognizing different breast cancer cells at once. This has the potential to aid in cancer-specific drug delivery and to be used as an effective treatment for breast cancer.

Effects of Monomer Composition on CO2−Selective Polymer Brush Membranes

Membranes that contain a high fraction of amorphous poly(ethylene glycol) (PEG) are attractive for selective removal of CO2 from H2 streams, but crystallization of PEG chains restricts both flux and selectivity. The high thickness of solution-cast membranes also limits flux. This study demonstrates the formation of composite, PEG-containing membranes through atom transfer radical polymerization of poly(ethylene glycol methyl ether methacrylate) from initiator-modified, porous substrates. The resulting membrane skins are only 50−500 nm thick, and copolymers that contain a mixture of short and long PEG side chains do not readily crystallize. The smaller PEG chains (8−9 ethylene oxide units) prevent crystallization, while the presence of longer side chains (23−24 ethylene oxide units) allows the membranes to maintain a CO2/H2 selectivity of 12 at room temperature. This work examines the effect of side-chain length on polymerization rate as well as the permeability, selectivity, and crystallinity of copolymer...

Cruciate-retaining TKA Using a Third-generation System with a Four-pegged Tibial Component: A Minimum 10-year Followup Note

A third-generation TKA system was designed to address problems encountered with earlier designs including a high rate of patellofemoral complications. At a minimum of 5 years, we previously reported survivorship of 98.7% using revision for any reason as the endpoint for a cohort that includes the patients described in this report. That cohort was unique in that a tibial component that uses four short pegs for fixation was used in a subset of patients undergoing cruciate-retaining TKA and the tibial and femoral components were precoated with polymethylmethacrylate. We now report the survival rate, postoperative function, complications, radiographic loosening, and osteolysis at a minimum of 10 years postoperatively. We retrospectively reviewed 161 patients who underwent 179 TKAs. The patella was resurfaced in all cases and all components were cemented. Patients were evaluated clinically and radiographically for evidence of component loosening and osteolysis. Forty of the 161 patients (with 44 TKAs) had died and eight patients (nine knees) were lost to followup. For the remaining 113 patients (126 knees), the minimum followup was 10 years (mean, 11.7 years; range, 10.0-13.9 years). Survivorship at a minimum of 10 years postoperatively using revision for any reason and revision for aseptic loosening were 97.7% and 100%, respectively. Three knees were revised: one for infection, one for periprosthetic fracture, and one for postoperative arthrofibrosis. There were no reoperations for patellar component maltracking, wear or loosening, tibiofemoral polyethylene wear, osteolysis, or aseptic loosening. Hospital for Special Surgery scores improved from a mean of 47.7 (range, 23-78) preoperatively to 85.4 (range, 33-100). This cruciate-retaining design had a low risk of implant failure or revision and the design changes eliminated the patellar failures seen with earlier iterations at up to 10 years. Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Abstract 2438: Efficacious therapies of two human pancreatic cancer xenografts and an aggressive human lymphoma xenograft with redesigned antibody-SN-38 conjugates

Abstract Antibody (MAb) conjugates of the potent topoisomerase I inhibitor, SN-38, have been previously shown by our groups to be efficacious in the targeted therapies of human cancer xenografts in nude mice. The conjugates have since been redesigned with a new bifunctional SN-38, ‘CL2A-SN-38’ (maleimido-[x]-Lys-PABOCO-20-O-SN-38, where PAB is p-aminobenzyl and ‘x’ contains a short PEG), without a cleavable dipeptide, to simplify process and improve quality. CL2A-SN-38 was conjugated to humanized MAbs, hRS7 (anti-EGP-1), hPAM4 (anti-mucin), hMN-14 (anti-CEACAM5), hLL2 (anti-CD22), and hA20 (anti-CD20). The conjugates, with a mean SN-38/MAb substitution of ∼ 6, were evaluated in the Capan-1 and BxPC-3 pancreatic human tumor xenografts and the Ramos human NHL tumor xenograft grown s.c. in female athymic nude mice. When the starting tumor sizes in animals reached 0.2 to 0.3 cm3, specific and non-targeting control conjugates were administered i.p. in a twice-weekly × 4 weeks schedule using 0.39 mg/kg (protocol-1) or 0.20 mg/kg (protocol-2) or 0.08 mg/kg (protocol 3) of SN-38 equivalent. Saline controls were included. In the therapy of Capan-1 xenograft (protocol 2; n = 10), specific targeting by SN-38 conjugates of hRS7, hPAM4, and hMN-14 produced significant tumor growth control versus control hA20-SN-38 conjugate on day 35 (AUC, P &amp;lt; 0.034), but there was no difference among the specific conjugates. Median survival time (MST) for untreated was 35 days, while MST was not reached on day 56 for treatments with all the three specific conjugates (protocol 2). In therapy in the BxPC-3 model (protocol 1; n = 10), MST for treatment with specific hRS7-SN-38 was significantly better than that for untreated or treatment with control hA20-SN-38 (P &amp;lt; 0.0006) or treatment with hMN-14-SN-38 (P &amp;lt; 0.0046). In the Ramos lymphoma model (n = 5), MST in untreated animals was only 7 days owing to rapid tumor growth, while MST was not reached on day 35 with the specific hLL2-SN-38 treatment (protocol 2). Moreover, combination of hA20 immunotherapy and hLL2-SN-38 immunoconjugate therapy (protocol 3) extended MST significantly versus conjugate treatment alone (P &amp;lt; 0.015). A dose of up to 47 mg/kg of SN-38 equivalent [240 mg/kg human equivalent protein dose of the conjugate], examined thus far, was very well tolerated in normal mice, as determined by blood counts and serum chemistries, which indicated an excellent therapeutic window. The redesigned conjugates, without the cathepsin B cleavable peptide, retained the efficacies of the CL2-SN-38-based conjugates, were monomeric, and were amenable to scale-up. These features, together with very favorable safety profiles, portend well for the clinical development of these immunoconjugates for different cancer indications. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2438.

Abstract 2439: Cross-linker evaluation in the design of antibody-SN-38 conjugates for cancer therapy

Abstract Antibody (MAb) conjugates of the potent topoisomerase I inhibitor, SN-38, prepared using the bifunctional derivative, ‘CL2-SN-38’ (maleimido-[x]-Phe-Lys-PABOCO-20-O-SN-38), were previously shown to produce significant and selective therapeutic efficacies of human tumor xenografts in nude mice. With a view to examining alternative linkers for possible improvement, we prepared a variant, namely maleimido-[x]-Lys-PABOCO-20-O-SN-38 (‘CL2A-SN-38’), and two other derivatives with cross-linker attachment at the 10-position of SN-38 instead of the 20-position: maleimido-[x]-Phe-Lys-N(Me)-(CH2)2-N(Me)-CO-10-O-SN-38 (‘CL2D-SN-38’) and maleimido-[x]-Phe-Lys-PABOCO-N(Me)-(CH2)2-N(Me)-CO-10-O-SN-38 (‘CL2E-SN-38’). In these, PAB is p-aminobenzyl moiety and ‘x’ contains a short PEG group to increase solubility. Conjugates of the humanized anti-CEACAM5 MAb, hMN-14 (labetuzumab), were prepared by reacting the maleimide-appended SN-38 derivatives with mildly reduced hMN-14. The SN-38/MAb molar substitutions were in the range of 5.9 to 6.3. In vitro studies showed a similarity in the stabilities, in mouse serum, of CL2 and CL2A-based linkers, but an order of magnitude greater stability for conjugates with linker at the 10-position; however, CL2D-SN-38 linker was inert to dipeptide cleavage by cathepsin B at the lysosomal pH of ∼ 5. The latter finding was also reflected in the loss of cytotoxicity due to hMN-14-CL2D-SN-38 conjugate in the LS174T colon cancer cell line in vitro. All conjugates were also evaluated in an exploratory preclinical therapy experiment in nude mice with aggressive s.c. LS174T human colon cancer xenografts. Conjugates were administered i.p. in groups of tumor-bearing animals (n = 10) at a schedule of 0.39 mg/kg of SN-38 equivalent twice weekly × 2 weeks. Untreated animals received saline. Mean tumor volumes (cm3) of animals in various treatment groups, on day 18, were: 0.073 ± 0.035 for the hMN-14-CL2-SN-38 positive control group; 0.055 ± 0.032 for the hMN-14-CL2A-SN-38 group; 0.518 ± 0.239 for the hMN-14-CL2D-SN-38 group; 0.490 ± 0.224 for the hMN-14-CL2E-SN-38 group; and 1.09 ± 0.88 for the untreated group. Median survival times (days) were 54.5, 55, 30, 25, and 26.5 for these groups, respectively. These results showed that a cleavable peptide was not necessary in the SN-38 conjugate design, as hMN-14-CL2A-SN-38 was equivalent to hMN-14-CL2-SN-38 in efficacy, and that hMN-14-CL2E-SN-38 was surprisingly much less efficacious than the CL2 and CL2A-based conjugates despite its higher relative stability. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2439.

Mutual enhancement of the complexing properties of components in tertiary systems containing copper nanoparticles, poly(acrylic acid), and poly(ethylene glycol)

It is shown that nonstoichiometric interpolymer complexes composed of high-molecular-mass poly( acrylic acid) and PEG of various molecular masses are more efficient stabilizers of copper sols than each component of the complex taken separately. This conclusion is based on comparison of dimensions of copper nanoparticles in sols formed via reduction of copper(II) ions in solutions of poly (acrylic acid), PEG, and their blends and on the enhanced stability of sols protected by the interpolymer complex against aggregation and oxidation of metal particles. Much shorter PEG chains than those necessary for formation of corresponding interpolymer complexes in the absence of nanoparticles can be involved in formation of tertiary complexes including copper nanoparticles, poly(acrylic acid), and PEG. On the basis of the experimental data, it is inferred that the mutual enhancement of the complexing behavior of components occurs in tertiary complexes containing copper nanoparticles and both polymers.

Mono-amine Functionalized Phthalocyanines: Microwave-Assisted Solid-Phase Synthesis and Bioconjugation Strategies

Phthalocyanines (Pcs) are excellent candidates for use as fluors for near-infrared (near-IR) fluorescent tagging of biomolecules for a wide variety of bioanalytical applications. Monofunctionalized Pcs, having two different types of peripheral substitutents, one for covalent conjugation of the Pc to biomolecules and others to improve the solubility of the macrocycle, are ideally suited for the desired applications. To date, difficulties faced during the purification of monofunctionalized Pcs limited their usage in various types of applications. Herein are reported a new synthetic method for rapid synthesis of the target Pcs and bioconjugation techniques for labeling of the oligonucleotides with the near-IR fluors. A novel synthetic route was developed utilizing a hydrophilic, poly(ethylene glycol) (PEG)-based support with an acid-labile Rink Amide linker. The Pcs were functionalized with an amine group for covalent conjugation purposes and were decorated with short PEG chains, serving as solubilizing groups. Microwave-assisted solid-phase synthetic method was successfully applied to obtain pure asymmetrically substituted monoamine functionalized Pcs in a short period of time. Three different bioconjugation techniques, reductive amination, amidation, and Huisgen cycloaddition, were employed for covalent conjugation of Pcs to oligonucleotides. The described microwave-assisted bioconjugation methods give an opportunity to synthesize and isolate the Pc-oligonucleotide conjugate in a few hours.

PEGylated Dendritic Unimolecular Micelles as Versatile Carriers for Ligands of G Protein-Coupled Receptors

Despite its widespread application in nanomedicine, poly(ethylene glycol) (PEG) is seldom used for covalent modification of ligands for G protein-coupled receptors (GPCRs) due to potential steric complications. In order to study the influence of PEG chains on the biological activity of GPCR ligands bound to a common macromolecular carrier, we prepared a series of G3 polyamidoamine (PAMAM) dendrimers derivatized with Alexa Fluor 488, varying numbers of PEG(550)/PEG(750)/PEG(2000), and nucleoside moieties derived from the A(2A) adenosine receptor (AR) agonist CGS21680 (2-[4-(2-carboxylethyl)phenylethylamino]-5'-N-ethylcarboxamidoadenosine). These dendrimer conjugates were purified by size exclusion chromatography and characterized by (1)H NMR and MALDI MS. In radioligand binding assays, some PAMAM-PEG conjugates showed enhanced subtype-selectivity at the human A(2A) AR compared to monomeric ligands of comparable affinity. The functional potency was measured in the A(2A) AR-mediated activation of adenylate cyclase and inhibition of ADP-induced platelet aggregation. Interestingly, the dendrimer conjugate 10c bearing 11 PEG(750) chains (out of theoretical 32 amino end groups) and 14 nucleoside moieties was 5-fold more potent in A(2A) AR-mediated stimulation of cyclic AMP formation than 10d with 4 PEG(2000) chains and 21 nucleosides, although the binding affinities of these 2 compounds were similar. Thus, a relatively small (≤10 nm) multivalent ligand 10c modified for water solubility maintained high potency and displayed increased A(2A) AR binding selectivity over the monomeric nucleosides. The current study demonstrates the feasibility of using short PEG chains in the design of carriers that target ligand-receptor interactions.

Molecular dynamics study of the structure and interparticle interactions of polyethylene glycol-conjugated PAMAM dendrimers.

We performed molecular dynamics (MD) simulations of one or two copies of polyethylene glycol of molecular weight 550 (PEG550) and 5000 (PEG5000) daltons, conjugated to generation 3 (G3) to 5 (G5) polyamidoamine (PAMAM) dendrimers with explicit water using a coarse-grained model. We found the radii of gyration of these dendrimer-PEG molecules to be close to those measured in experiments by Hedden and Bauer (Hedden , R. C. ; Bauer , B. J. Macromolecules 2003 , 36 , 1829.). Densely grafted PEG ligands (>50% of the dendrimer surface) extend like brushes, with layer thickness in agreement with theory for starlike polymers. Two dendrimer-PEG complexes in the box drift away from each other, indicating that no aggregation is induced by either short or long PEG chains, conflicting with a recent view that the cytotoxicity of some PEGylated particles might be due to particle aggregation for long PEG lengths.

Encapsulation of diclofenac sodium with acidic copolymer hydrogels based on PEG/poly(N‐isopropylacrylamide‐co‐2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid) semi‐interpenetrating network using in situ loading technique

AbstractA pH‐ and temperature‐responsive semi‐interpenetrating copolymer PEG6000/poly(NIPA‐co‐AMPS) (PEG/AMPS‐co‐NIPA SIPN), for short PEG SIPN, was made by ammonium persulfate‐initiated suspension copolymerization of N‐isopropylacrylamide, 2‐acrylamido‐2‐methylpropanesulphonic acid, and N,N′‐methylene‐bis‐acrylamide (MBAA; crosslinker) in the presence of PEG6000. The PEG SIPN copolymer matrices containing nanostructures made in the high‐temperature copolymerization resulted in channels for PEG and facile migration of drugs. In drug encapsulation or drug‐loading process, one can easily ignore or pay less attention to the interaction between a drug and its encapsulation materials; however, the ignored interactions may induce problems in drug properties or the release behavior in use. Sodium diclofenac (DFNa) precipitates as the carboxylic acid form in an acidic environment, and it is challenging to encapsulate sodium diclofenac in such an acidic matrix without precipitation of the sparingly soluble acid form of DFNa on the surface of the polymer substrate. To avoid bulky precipitation in drug loading, an in situ loading technique was developed for producing gel spheres with DFNa uniformly distributed in the polymer matrix. The technique is based on fast polymerization of spherical droplets of a pregel solution in which the drug is dissolved. Diffusion‐loading prodrugs were made in comparison with in situ loading prodrugs in thermal, release kinetics, and release behavior. Drug release profiles (in pH 7.4 phosphate buffer) show that the new drug loading technique gives controlled release during a period of about 7 days at 37°C. By contrast, gel spheres loaded with sodium diclofenac using the conventional diffusion technique produced almost total release of the drug within about 24 h. The thermal stability of sodium diclofenac, the PEG/AMPS‐co‐NIPA SIPN, and the prodrugs made with the SIPN and sodium diclofenac was studied. A near zero‐order release kinetics was found in the in vitro release of sodium diclofenac with in situ loading PEG SIPN prodrug. We have, for the first time, studied sodium diclofenac release behavior from the PEG SIPN hydrogel systems. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

PNA-PEG Modified Silicon Platforms as Functional Bio-Interfaces for Applications in DNA Microarrays and Biosensors

The synthesis and characterization of two types of silicon-based biofunctional interfaces are reported; each interface bonds a dense layer of poly(ethylene glycol) (PEG(n)) and peptide nucleic acid (PNA) probes. Phosphonate self-assembled monolayers were derivatized with PNA using a maleimido-terminated PEG(45). Similarly, siloxane monolayers were functionalized with PNA using a maleimido-terminated PEG(45) spacer and were subsequently modified with a shorter methoxy-terminated PEG(12) ("back-filling"). The long PEG(45) spacer was used to distance the PNA probe from the surface and to minimize undesirable nonspecific adsorption of DNA analyte. The short PEG(12) "back-filler" was used to provide additional passivation of the surface against nonspecific DNA adsorption. X-ray photoelectron spectroscopic (XPS) analysis near the C 1s and N 1s ionization edges was done to characterize chemical groups formed in the near-surface region, which confirmed binding of PEG and PNA to the phosphonate and silane films. XPS also indicated that additional PEG chains were tethered to the surface during the back-filling process. Fluorescence hybridization experiments were carried out with complementary and noncDNA strands; both phosphonate and siloxane biofunctional surfaces were effective for hybridization of cDNA strands and significantly reduced nonspecific adsorption of the analyte. Spatial patterns were prepared by polydimethylsiloxane (PDMS) micromolding on the PNA-functionalized surfaces; selective hybridization of fluorescently labeled DNA was shown at the PNA functionalized regions, and physisorption at the probe-less PEG-functionalized regions was dramatically reduced. These results show that PNA-PEG derivatized phosphonate monolayers hold promise for the smooth integration of device surface chemistry with semiconductor technology for the fabrication of DNA biosensors. In addition, our results confirm that PNA-PEG derivatized self-assembled carboxyalkylsiloxane films are promising substrates for DNA microarray applications.

Improvement of Co3O4 Nanoparticle Synthesis in Apoferritin Cavity by Outer Surface PEGylation

Abstract The outer surface of horse spleen apoferritin (HsAFr) was chemically modified by poly(ethylene glycol) (PEG) to prevent bulk precipitation during artificial biomineralization of the cobalt-oxide core (Co3O4) in its cavity. Two kinds of PEGs, with average molecular weights of 2000 and 5000 were covalently attached (PEGylation) on the outer surface of HsAFr and suppressed the bulk precipitation drastically, whereas neither free PEGs nor short PEG (N-{2-[2-(2-methoxyethoxy)ethoxy]ethanoyloxy}succinimide) performed such suppression. The PEGylated HsAFr accommodated fully developed Co3O4 cores and achieved a high yield of homogeneous Co3O4 nanoparticles. Investigation of the early biomineralization stage suggested that [CoIIIO] complex ions were accumulated around the negatively charged outer surface of HsAFr.

PH-dependent swelling of hydrogels containing highly branched polyamine macromonomers

We examine the pH-dependent swelling of end-linked hydrogels containing high concentrations of amine-functional macromonomers. Gels are formed by end-linking of epoxide-terminated, linear poly(ethylene glycol) (PEG) to either amine-terminated poly(amidoamine) (PAMAM) dendrimers or highly branched poly(ethyleneimine) (PEI). After extraction in neutral water, the hydrogels are swollen in aqueous solutions of HCl or NH4OH to vary the external pH. Equilibrium volume swelling ratios (Qs) pass through a maximum value (Qmax) at an external pH denoted as pH∗ which is approximately 4–5 for the gels studied. The swelling behavior is modeled using Donnan equilibrium theory to describe the ion swelling pressure, with the Flory–Rehner phantom network expression representing the elastic and mixing contributions to the free energy. The model accurately predicts the maximum in swelling near pH=4–5, but overestimates Qmax for several of the gels due to neglecting the finite extensibility of the short linear PEG chains.

Modification of Antimicrobial Peptide with Low Molar Mass Poly(ethylene glycol)

PEGylation of peptide drugs prolongs their circulating lifetimes in plasma. However, PEGylation can produce a decrease in the in vitro bioactivity. Longer poly(ethylene glycol) (PEG) chains are favourable for circulating lifetimes but unfavourable for in vitro bioactivities. In order to circumvent the conflicting effects of PEG length, a hydrophobic peptide, using an antimicrobial peptide as a model, was PEGylated with short PEG chains. The PEGylated peptides self-assembled in aqueous solution into micelles with PEG shell and peptide core. In these micelles, the core peptides were protected by the shell, thus reducing proteolytic degradation. Meanwhile, most of the in vitro antimicrobial activities still remained due to the short PEG chain attached. The stabilities of the PEGylated peptides were much higher than that of the unPEGylated peptides in the presence of chymotrypsin and serum. The antimicrobial activities of the PEGylated peptides in the presence of serum, an ex vivo assay, were much higher than that of the unPEGylated peptide.

Thermothickening modification of the poly(ethylene glycol) and amino acid ester grafted polyphosphazenes by monomethyl end-capped poly(ethylene glycol) addition

To control physical properties of the temperature-responsive biomedical materials for targeted applications in easy and safe way biocompatible additives are tried. Systematic controls are studied to obtain effectively controlled results in molecular interaction viewpoint. Thermothickening behaviors of the polyphosphazenes grafted with poly(ethylene glycol) (PEG) and amino acid ester are uniquely modified by physical mixing with another PEG molecules. Depending on the length of the added PEGs and the type of the subtituents of the polyphosphazenes, there are characteristic changes in the maximum viscosity ( η max) and the phase transition temperature ( T max) reflecting peculiar molecular interactions. For the short chain PEG addition, hydrophobic co-association of the end-capped methyl group of the added PEGs seems to play an important role while for the longer chain PEG additions the interaction between the added and the substituted PEGs seems to be dominating, which changes the η max and T max in a unique way. Longer PEG substituted polyphosphazene is not much affected by the type of the PEGs added probably because of more effective intra-molecular self-interaction than interaction with added ones. For the less hydrophobic amino acid ester substituted polyphosphazene the interaction between the substituted and the added PEGs dominates the de-hydration, which leads to the changes in the phase transition temperature sensitive to the length of the added PEGs. This unique thermothickening modification of the thermosenstitive and biocompatible polyphosphazenes is proposed to be contributed to the special and competitive hydrogen bonding between PEG–water and PEG–PEG molecules, which changes under different conditions like concentration, molecular weight and temperature.

Synthesis of Bifunctional Integrin‐Binding Peptides Containing PEG Spacers of Defined Length for Non‐Viral Gene Delivery

AbstractImproving the buffer and serum stability of non‐viral gene delivery vectors, and increasing their circulation time in vivo, is an important focus of current research in gene therapy. The most successful strategies to date have involved shielding the complexes with large polydisperse PEG adducts. However, this approach is accompanied by a fall in transfection efficiency. In this paper we describe the solid‐phase synthesis of a series of bifunctional peptides bearing short PEG spacers of defined structure as components of lipopolyplex gene delivery vectors. Short, high‐yielding routes to a series of PEG‐amino acids are described: these PEG‐amino acids can be used in varying combinations to afford bifunctional peptides with varying lengths of PEG spacers by using standard solid‐phase synthesis techniques. A series of lipopolyplexes were formulated using these bifunctional peptides, and their transfection properties assessed. Dynamic light scattering measurements on the complex with the best transfection properties showed that in phosphate‐buffered saline this complex was considerably more stable, and aggregated more slowly, than a complex formulated using a similar peptide lacking the short PEG spacer.(© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2008)

Synthesis and self-assembly of reactive H-shaped block copolymers

The H-shaped block copolymers (PTMSPMA)2-PEG(PMPSTMSPMA)2 with two compositions, (EG)91-b-(TMSPMA)92 and (EG)455-b-(TMSPMA)176 have been successfully synthesized by atom transfer radical polymerization (ATRP) of tri(methoxylsilyl)propyl methacrylate (TMSPMA) at room temperature in methanol. The initiation system applied was composed of 2,2-bis(methylene α-bromoisobutyrate)propionyl terminated poly(ethylene glycol) (Br2PEGBr2) with M n = 4000 or 2000, CuBr and 2,2′-bipyridine. The macroinitiator, Br2PEGBr2, was prepared by the reaction of two hydroxyl groups terminated PEG with 2,2-bis(methylene α-bromoisobutyrate)propionyl chloride. The NMR spectroscopy and GPC measurements were used to characterize the structure and molecular weight and molecular weight distribution of the resultant copolymers. The H-shaped block copolymers Sam 1 and Sam 2 were self-assembled in DMF/water mixtures and then the trimethoxysilyl groups in PTMSPMA were cross-linked by condensation reaction in the presence of triethylamine. Stable large-compound vesicles with 10 nm diameter of cavities were formed for Sam 1 which contains a short PEG chain. However, the self-assembling of the Sam 2 in the selective solvents resulted in big vesicles aggregates. These two different morphologies of aggregates are attributed to their relative chain length of water soluble PEG. The vesicles formed from Sam1 with short PEG chains have big surface energy which will lead them to self-assemble further, forming large-compound vesicles.

Syntheses and Properties of a Series of Cationic Water-Soluble Phthalocyanines

A series of symmetrical cationic phthalocyanines (Pcs) with either Zn(II) or Si(IV) metal ions and two bulky axial ligands on the silicon complexes was synthesized in high yields. The photophysical (absorption, emission, fluorescence, and singlet oxygen quantum yields) and cellular (uptake, toxicity, and subcellular localization) properties of this series of Pcs were investigated. The Si(IV)-Pcs exist mainly as monomers in aqueous media and have higher fluorescent quantum yields in protic solvents (methanol and water) than the Zn(II)-Pcs. The presence of eight short PEG groups at the periphery of a Zn(II)-Pc significantly increases its solubility in protic solvents, but a centrally chelated silicon ion and associated bulky axial ligands were more efficient in preventing aggregation of the Pc macrocycles. The singlet oxygen quantum yields for this series of Pcs in DMSO are in the range 0.09-0.15. All Pcs were readily taken up by human HEp2 cells, and the extent of their accumulation within cells depends on their hydrophobic character. Intracellularly, all Pcs localized preferentially within the cell lysosomes. The Zn(II)-Pc 11 and Si(IV)-Pcs 12 and 14 were found to be the most phototoxic (IC50 = 2.2 microM at a 1 J cm(-2) light dose) of this series of compounds.