The conjugation of proteins with polyethylene glycol and other polymers

Site-specific PEGylated Exendin-4 modified with a high molecular weight trimeric PEG reduces steric hindrance and increases type 2 antidiabetic therapeutic effects

The purpose of this study was to optimize an Exendin-4 (Ex4-Cys) site-specific PEGylation method with a high-molecular-weight trimeric PEG. Here, we describe the preparation of C-terminal specific PEGylated Ex4-Cys (C40-tPEG-Ex4-Cys), which was performed using cysteine and amine residue specific coupling reactions between Ex4-Cys and activated trimeric PEG. The C40-PEG-Ex4-Cys was obtained at high yields (~83%) and characterized by MALDI-TOF mass spectrometry. The receptor binding affinity of C40-PEG(5K)-Ex4-Cys was 3.5-fold higher than that of N-terminal PEGylated Ex4-Cys (N(ter)-PEG(5K)-Ex4-Cys), and receptor binding by the trimeric PEG (tPEG; 23, 50 kDa) adduct was much higher than that of branched PEG (20 kDa). Furthermore, C40-tPEG(50K)-Ex4-Cys was found to have greater blood circulating t(1/2) and AUC(inf) values than native Ex4-Cys by 7.53- and 45.61-fold, respectively. Accordingly, its hypoglycemic duration was much greater at 59.2 h than that of native Ex4-Cys at 7.3 h, with a dose of 25 nM/kg. The results of this study show that C-terminal specific PEGylation using trimeric PEG is effective when applied to Ex4-Cys and suggest that C40-tPEG(50K)-Ex4-Cys has considerable potential as a type 2 antidiabetic agent.

PEGylation of bacteriophages increases blood circulation time and reduces T-helper type 1 immune response

The increasing occurrence of antibiotic-resistant pathogens is of growing concern, and must be counteracted by alternative antimicrobial treatments. Bacteriophages represent the natural enemies of bacteria. However, the strong immune response following application of phages and rapid clearance from the blood stream are hurdles which need to be overcome. Towards our goal to render phages less immunogenic and prolong blood circulation time, we have chemically modified intact bacteriophages by conjugation of the non-immunogenic polymer monomethoxy-polyethylene glycol (mPEG) to virus proteins. As a proof of concept, we have used two different polyvalent and strictly virulent phages of the Myoviridae, representing typical candidates for therapeutical approaches: Felix-O1 (infects Salmonella) and A511 (infects Listeria). Loss of phage infectivity after PEGylation was found to be proportional to the degree of modification, and could be conveniently controlled by adjusting the PEG concentration. When injected into naïve mice, PEGylated phages showed a strong increase in circulation half-life, whereas challenge of immunized mice did not reveal a significant difference. Our results suggest that the prolonged half-life is due to decreased susceptibility to innate immunity as well as avoidance of cellular defence mechanisms. PEGylated viruses elicited significantly reduced levels of T-helper type 1-associated cytokine release (IFN-γ and IL-6), in both naïve and immunized mice. This is the first study demonstrating that PEGylation can increases survival of infective phage by delaying immune responses, and indicates that this approach can increase efficacy of bacteriophage therapy.

Effect of poly(ethylene glycol) (PEG) spacers on the conformational properties of small peptides: a molecular dynamics study

Poly(ethylene glycol) (PEG) is used as an inert spacer in a wide range of biotechnological applications such as to display peptides and proteins on surfaces for diagnostic purposes. In such applications it is critical that the peptide is accessible to solvent and that the PEG does not affect the conformational properties of the peptide to which it is attached. Using molecular dynamics (MD) simulation techniques, we have investigated the influence of a commonly used PEG spacer on the conformation properties of a series of five peptides with differing physical-chemical properties (YGSLPQ, VFVVFV, GSGGSG, EEGEEG, and KKGKKG). The conformational properties of the peptides were compared (a) free in solution, (b) attached to a PEG-11 spacer in solution, and (c) constrained to a two-dimensional lattice via a (PEG-11)(3) spacer, mimicking a peptide displayed on a surface as used in microarray techniques. The simulations suggest that the PEG spacer has little effect on the conformational properties of small neutral peptides but has a significant effect on the conformational properties of small highly charged peptides. When constrained to a two-dimensional surface at peptide densities similar to those used experimentally, it was found that the peptides, in particular the polar and nonpolar peptides, aggregated strongly. The peptides also partitioned into the PEG layer. Potentially, this means that at high packing densities only a small fraction of the peptide attached to the surface would in fact be accessible to a potential interaction partner.

Protein modification with amphiphilic block copoly(2-oxazoline)s as a new platform for enhanced cellular delivery

Several homopolymers, random copolymers and block copolymers based on poly(2-oxazoline)s (POx) were synthesized and conjugated to horseradish peroxidase (HRP) using biodegradable and nonbiodegradable linkers. These conjugates were characterized by amino group titration, polyacrylamide gel electrophoresis (PAGE), isoelectric focusing, enzymatic activity assay and conformation analysis. The conjugates contained on average from about one to two polymer chains per enzyme. From 70% to 90% of enzymatic activity was retained in most cases. Circular dichroism (CD) analysis revealed that HRP modification affected the secondary structure of the apoprotein but did not affect the tertiary structure and heme environment. Enhanced cellular uptake was found in the conjugates of two block copolymers using both MDCK cells and Caco-2 cells, but not in the conjugates of random copolymer and homopolymer. Conjugation with a block copolymer of 2-methyl-2-oxazoline and 2-butyl-2-oxazoline led to the highest cellular uptake as compared to other conjugates. Our data indicates that modification with amphiphilic POx has the potential to modulate and enhance cellular delivery of proteins.

Pharmacokinetics of125I-radiolabelled PEG-hemoglobin SB1

PEG-hemoglobin SB1 (SB1) is a polyethylene glycol (PEG)-modified hemoglobin-based oxygen carrier, intended for use as resuscitation fluid for brain stroke and as a blood substitute. An intravenous pharmacokinetics (PK) studies with SB1 was investigated in male albino Sprague-Dawley (SD) rats and male beagle dogs at doses of 5 and 12.5 ml/kg for rats and 10 ml/kg for dogs. Total hemoglobin in plasma and whole blood was determined by gamma scintillation counter-detecting 125I-radiolabelled SB1. In the 5 ml/kg rats (n = 9), the Cmax, t1/2, AUCt and Tmax were 9.055 mg equivalents/ml, 9.6 hr, 79.6 mg equivalents.hr/ml and 0.20 hr in the plasma and 4.954 mg equivalents/ml, 9.7 hr, 37.6 mg equivalents.hr/ml and 0.11 hr in the whole blood, respectively. Those parameters in the 12.5 ml/Kg of rats (n = 9) were 19.00 mg equivalents/ml, 10.6 hr, 223.5 mg equivalents.hr/ml and 0.33 hr in the plasma and 10.58 mg equivalents/ml, 16.1 hr, 99.0 mg equivalents.hr/ml and 0.33 hr in the whole blood, respectively. An increase in the dose level from 5 to 12.5 ml/kg resulted in the increase in both Cmax and AUC24, and the increases in these parameters appeared to be in proportion to the dose increment. Thus, following the 2.5-fold increase in administered dose, Cmax was increased by a factor of 2.1 in both plasma and whole blood, while AUC24 was increased by a factor of 2.8 for plasma and 2.6 for whole blood. In the dogs receiving 10 ml/kg (n = 3), the Cmax, t1/2, AUC168 and Tmax were 12.70 mg equivalents/ml, 47.2 hr, 425.7 mg equivalents.hr/ml and 0.083 hr in the plasma and 8.372 mg equivalents/ml, 50.3 hr, 241.3 mg equivalents.hr/ml and 1.003 hr in the whole blood, respectively. The present work provides an insight into the pharmacological behavior of a PEG-modified hemoglobin.

Systematic investigation of preparing biocompatible, single, and small ZnS-Capped CdSe quantum dots with amphiphilic polymers

The successful transfer of nanoparticles between solvents is critical for many applications. We evaluated the impact of amphiphilic polymer composition on the size, transfer efficiency, and biocompatibility of tri-n-octylphosphine oxide/hexadecylamine-stabilized semiconductor ZnS-capped CdSe and CdS-capped CdTe(x)Se(1-x) quantum dots (QDs). We also investigated the adsorption of various proteins onto the surface of these QDs and studied the effect of surface chemistry on non-specific protein binding. The results from these studies will have implications in the design of QDs and other nanoparticles for biological and biomedical applications.

Protein conjugation with amphiphilic block copolymers for enhanced cellular delivery

Modification of a model protein, horseradish peroxidase (HRP), with amphiphilic block copolymer poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (Pluronic), was previously shown to enhance the transport of this protein across the blood-brain barrier in vivo and brain microvessel endothelial cells in vitro. This work develops procedures for synthesis and characterization of HRP with Pluronic copolymers, having different lengths of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) blocks. Four monoamine Pluronic derivatives (L81, P85, L121, P123) were synthesized and successfully conjugated to a model protein, HRP, via biodegradable or nondegradable linkers (dithiobis(succinimidyl propionate) (DSP), dimethyl 3,3'-dithiobispropionimidate (DTBP), and disuccinimidyl propionate (DSS)). The conjugation was confirmed by HRP amino group titration, matrix-assisted laser desorption/ionization-time of flight spectroscopy, and cation-exchange chromatography. HRP conjugates containing an average of one to two Pluronic moieties and retaining in most cases over 70% of the activity were synthesized. Increased cellular uptake of these conjugates was demonstrated using the Mardin-Derby canine kidney cell line and primary bovine brain microvessel endothelial cells. The optimal modifications included Pluronic L81 and P85. These copolymers have shorter PPO chains compared to Pluronic P123 and L121, which were less efficient. There was little if any dependence of the uptake on the length of the hydrophilic PEO block for the optimal modifications. The proposed modifications may be used to increase cellular uptake of other proteins.

Reversible pegylation of insulin facilitates its prolonged action in vivo

We attempted to engineer a novel long-acting insulin based on the following properties: (i) action as a prodrug to preclude supraphysiological concentrations shortly after injection; (ii) maintenance of low-circulating level of biologically active insulin for prolonged period; and (iii) high solubility in aqueous solution. A spontaneously hydrolyzable prodrug was thus designed and prepared by conjugating insulin through its amino side chains to a 40kDa polyethylene glycol containing sulfhydryl moiety (PEG(40)-SH), employing recently developed hetero-bifunctional spacer 9-hydroxymethyl-7(amino-3-maleimidopropionate)-fluorene-N-hydroxysucinimide (MAL-Fmoc-0Su). A conjugate trapped in the circulatory system and capable of releasing insulin by spontaneous chemical hydrolysis has been created. PEG(40)-Fmoc-insulin is a water-soluble, reactivatable prodrug with low biological activity. Upon incubation at physiological conditions, the covalently linked insulin undergoes spontaneous hydrolysis at a slow rate and in a linear fashion, releasing the nonmodified immunologically and biologically active insulin with a t(1/2) value of 30h. A single subcutaneous administration of PEG(40)-Fmoc-insulin to healthy and diabetic rodents facilitates prolonged glucose-lowering effects 4- to 7-fold greater than similar doses of the native hormone. The beneficial pharmacological features endowed by PEGylation are thus preserved. In contrast, nonreversible, "conventional" pegylation of insulin led to inactivation of the hormone.

Dynamic imaging of lymphatic vessels and lymph nodes using a bimodal nanoparticulate contrast agent

BACKGROUND

Evaluation of lymphedema and lymph node metastasis in humans has relied primarily on invasive or radioactive modalities. While noninvasive technologies such as magnetic resonance imaging (MRI) offer the potential for true three-dimensional imaging of lymphatic structures, invasive modalities, such as optical fluorescence microscopy, provide higher resolution and clearer delineation of both lymph nodes and lymphatic vessels. Thus, contrast agents that image lymphatic vessels and lymph nodes by both fluorescence and MRI may further enhance our understanding of the structure and function of the lymphatic system. Recent applications of bimodal (fluorescence and MR) contrast agents in mice have not achieved clear visualization of lymphatic vessels and nodes. Here the authors describe the development of a nanoparticulate contrast agent that is taken up by lymphatic vessels to draining lymph nodes and detected by both modalities.

METHODS

A unique nanoparticulate contrast agent composed of a polyamidoamine dendrimer core conjugated to paramagnetic contrast agents and fluorescent probes was synthesized. Anesthetized mice were injected with the nanoparticulates in the hind footpads and imaged by MR and fluorescence microscopy. High resolution MR and fluorescence images were obtained and compared to traditional techniques for lymphatic visualization using Evans blue dye.

RESULTS

Lymph nodes and lymphatic vessels were clearly observed by both MRI and fluorescence microscopy using the bimodal nanoparticulate contrast agent. Characteristic tail-lymphatics were also visualized by both modalities. Contrast imaging yielded a higher resolution than the traditional method employing Evans blue dye. MR data correlated with fluorescence and Evans blue dye imaging.

CONCLUSION

A bimodal nanoparticulate contrast agent facilitates the visualization of lymphatic vessels and lymph nodes by both fluorescence microscopy and MRI with strong correlation between the two modalities. This agent may translate to applications such as the assessment of malignancy and lymphedema in humans and the evaluation of lymphatic vessel function and morphology in animal models.

Plasma clearance of bacteriophage Qbeta particles as a function of surface charge

Self-assembled protein capsids have gained attention as a promising class of nanoparticles for biomedical applications due to their monodisperse nature and versatile genetic and chemical tailorability. To determine the plasma clearance and tissue distribution in mice of the versatile capsid of bacteriophage Qbeta, the particles were decorated with gadolinium complexes using the CuI-mediated azide-alkyne cycloaddition reaction. Interior surface labeling was engineered by the introduction of an azide-containing unnatural amino acid into the coat protein for the first time. Clearance rates were conveniently monitored by quantitative detection of Gd using inductively coupled plasma optical emission spectroscopy and were found to be inversely proportional to the number of complexes attached to the exterior surface of the particle. This phenomenon was correlated to changes in exterior surface charge brought about by acylation of surface-exposed amine groups in the initial step of the bioconjugation protocol. When primary amine groups were reintroduced by azide-alkyne coupling, the circulation time increased accordingly. These results show that nanoparticle trafficking may be tailored in predictable ways by chemical and genetic modifications that modulate surface charge.

PEGylation of cyanovirin-N, an entry inhibitor of HIV

Cyanovirin-N (CV-N) is a potent inhibitor of human immunodeficiency virus and many other viruses. It has a high potential for use as a systemic compound to control viral load or in the development of microbicides to prevent primary viral infection. Due to its cyanobacterial origin it is likely to show the typical drawbacks associated with pharmaceutical use of foreign proteins such as short plasma half-life, proteolysis and immunogenicity. Several strategies were used to covalently bond poly(ethylene glycol) (PEGylate) to CV-N. Random PEGylation at lysine residues resulted in poor retention of antiviral activity. Many site-directed mutants were made to test site-specific PEGylation. One mutant, where glutamine 62 was replaced with cysteine (CV-N(Q62C)) and PEGylated with maleimide activated PEG, retained significant anti-HIV activity in vitro.

Nanosystems for simultaneous imaging and drug delivery to T cells

The T-cell response defines the pathogenesis of many common chronic disease states, including diabetes, rheumatoid arthritis, and transplant rejection. Therefore, a diagnostic strategy that visualizes this response can potentially lead to early therapeutic intervention, avoiding catastrophic organ failure or prolonged sickness. In addition, the means to deliver a drug dose to those cells in situ with the same specificity used to image those cells would provide for a powerful therapeutic alternative for many disease states involving T cells. In this report, we review emerging nanosystems that can be used for simultaneous tracking and drug delivery to those cells. Because of their versatility, these systems--which combine specific receptor targeting with an imaging agent and drug delivery--are suited to both basic science and applications, from developing therapeutic strategies for autoimmune and alloimmune diseases, to noninvasive tracking of pathogenic T-cell migration.

A nanoscopic multivalent antigen-presenting carrier for sensitive detection and drug delivery to T cells

Both monoclonal T cell-specific antibodies and multivalent major histocompatibility complex proteins are used as diagnostic reagents for T cell-mediated diseases. However, their widespread use as vehicles for drug delivery has been hindered by the lack of versatile methods that couple the targeting potential of these reagents with drugs of clinical relevance. To address this problem, we engineered a multivalent nanoscopic drug carrier that flexibly tethers to a variety of T-cell antigens. Our carriers bound their target T cells specifically and with enhanced sensitivities as compared with free antigen. Additionally, they consistently inhibited the proliferation of the target T cells in vitro and in vivo, whereas drug-free constructs elicited strong stimulation of the target populations. As a result of the flexibility of incorporating multivalent antigen and drug, these carriers have wide potential use as sensitive T-cell detection reagents as well as promising immunostimulatory or immunosuppressive tools.

Depth profiling of poly(L-lactic acid)/triblock copolymer blends with time-of-flight secondary ion mass spectrometry

Time-of-flight secondary ion mass spectrometry employing an SF5+ polyatomic primary ion source was utilized to obtain a series of in-depth profiles from PLLA/Pluronic-P104 (poly(ethylene oxide-co-propylene oxide) triblock copolymer) blends in attempts to quantify the in-depth surface segregated Pluronic region. The resultant in-depth profiles were consistent with theoretical models describing the surface segregated region in polymeric blends and copolymer systems, with a surface enriched Pluronic-P104 region, followed by a P104 depletion layer, and finally a constant composition bulk region. These results were consistent over a range of concentrations (1-25%). The depth profiles obtained using cluster SIMS were compared to information obtained using X-ray photoelectron spectroscopy. The results demonstrate that, with cluster primary ion bombardment, we are for the first time able to quantify the polymeric composition as a function of depth within certain multicomponent polymer blends. This success can be attributed to the sputter characteristics of polyatomic primary ion bombardment (SF5+) as compared to monatomic primary ion beams.

Pharmacokinetic consequences of pegylation

Pegylation, generally described as the molecular attachment of polyethylene glycols (PEGs) with different molecular weights to active drug molecules or surface treatment of drug-bearing particles with PEGs, is one of the most promising and extensively studied strategies with the goal of improving the pharmacokinetic behavior of the therapeutic drugs. A variety of PEGs, both linear and branched, with different molecular weights have been exploited successfully for use in this procedure in the form of reactive PEG species. Both reversible and irreversible PEG-drug conjugates have been prepared with relative advantages/disadvantages. The main pharmacokinetic outcomes of pegylation are summarized as changes occurring in overall circulation life-span, tissue distribution pattern, and elimination pathway of the parent drug/particle. Based on these favorable pharmacokinetic consequences leading to desired pharmacodynamic outcomes, a variety of proteins/peptides as well as small molecule drugs have been pegylated and evaluated successfully. Also a number of corresponding products have been approved by the U.S. FDA for specific clinical indications and some others are underway. In this article, the chemistry, rationale, strategies, pharmacokinetic outcomes, and therapeutic possibilities of pegylated drugs are reviewed with pharmacokinetic aspects presented with more details.

Pegylated protein encapsulated multivesicular liposomes: a novel approach for sustained release of interferon alpha

Hepatitis C viral chemotherapy suffers from a relatively short half-life of the interferon alpha-2a (IFN alpha). To address this issue, we investigated the effects of polyethylene glycol modification and their subsequent encapsulation in multivesicular liposomes (MVLs), on the release properties of IFN alpha. In the present study, interferon-alpha was conjugated with methoxy-polyethylene glycol (mPEG, MW 5000). Prepared IFN alpha-mPEG5000 conjugate (IFN alpha-mPEG5000) was purified with size exclusion chromatography. The relative in vitro anti-viral activity of pegylated interferon alpha-2a was found to 87.9% of the unmodified IFN alpha. Pegylated IFN alpha encapsulated multivesicular liposomes were prepared by double emulsification technique followed by evaporation of organic solvents from chloroform ether spherules suspended in water. Prepared MVLs were then characterized for shape, size, vesicle count, encapsulation efficiency, and in vitro release rate. In process stability studies of pegylated IFN alpha protein exhibited better stability when exposed to chloroform: diethyl ether (1:1 ratio) mixture as well as variable vortexing time as compared to native IFN alpha. Relatively high percentage of encapsulation of protein ( approximately 75%) was achieved. In vitro release profile of pegylated IFN alpha-mPEG5000 containing MVLs in the PBS showed lower initial burst release with sustained and incomplete release over a period of 1 week. In contrast, native IFN alpha entrapped MVLs were observed as higher initial burst release, i.e., nearly 35% followed by almost complete release. The results confirmed the possibility of multivesicular liposomes as a long-acting or sustained-release delivery system using a combination of pegylation and encapsulation technique for controlled delivery of interferon alpha.

High-yield production of biologically active mono-PEGylated salmon calcitonin by site-specific PEGylation

The purpose of this study was to develop and optimize a unique one-pot, two-step site-specific PEGylation method suitable for the high-yield production of mono-PEGylated (Lys(18)) salmon calcitonin (Lys(18)-PEG-sCT), which was previously demonstrated to have superior pharmaceutical properties to other conjugates. For the site-specific PEGylation, this study used the sCT derivative (FMOC(1,11)-sCT), which was FMOC protected at Cys(1)- and Lys(11)-amines among three PEGylation sites including Lys(18)-amine. This PEGylation process was achieved by the consecutive one-pot, two-step reaction: (i) the PEG conjugation to FMOC(1,11)-sCT; and (ii) the subsequent deprotection of FMOC group from the PEGylated FMOC(1,11)-sCT. The optimized reaction resulted in the high production yield of Lys(18)-PEG-sCT (about 86%), compared with that from conventional non-specific PEGylation (about 18%). The prepared Lys(18)-PEG-sCT conjugate showed improved biological stability without the loss in the in vitro and in vivo biological activity by PEGylation. Consequently, this site-specific PEGylation using an FMOC protection/deprotection strategy showed great usefulness in the production of the most promising Lys(18)-PEG-sCT conjugate with a high yield.

Synthetic Biodegradable Ionomers that Engulf, Store, and Deliver Intact Proteins

Telechelic anionic and cationic biodegradable ionomers capable of loading, storing, and releasing proteins are presented. Two different ionomers have been synthesized with either anionic or cationic end groups. The reaction was done quantitatively as shown by (1)H NMR. The swelling properties of the hydrophobic poly(trimethylene carbonate) polymer are contributed to the ionic end groups that display hydrophilic properties. Depending on the molecular weight of the ionomer, and also on the ionic charge, the materials swell differently in water, from approximately 50% for M(w) = 12 000 g/mol to approximately 500% when dealing with 2000 g/mol. The high swelling led us to believe that it would be possible to load and release proteins preferably in a still active form. As models, two different proteins were chosen: hemoglobin and cytochrome c. The swelling and release study shows that both ionomers possess the capability to adsorb and later release the proteins with retained structure. Release measurements from both the swollen and dried states have been evaluated with similar results, showing that the dried state seems to release a little bit less than the swollen one. These kinds of materials should be interesting for a wide variety of applications where drug and protein release is wanted, as well as in applications such as protein separation media.

Pharmacokinetics and Stability Properties of Catalase Modified with Water-Soluble Polysaccharides

Bovine liver catalase (EC 1.11.1.6) was chemically modified with mannan, carboxymethylcellulose, and carboxymethylchitin. The enzyme retained about 48-97% of the initial specific activity after glycosidation with the polysaccharides. The prepared neoglycoenzyme was 1.9-5.7 fold more stable against the thermal inactivation processes at 55 degrees C, in comparison with the native counterpart. Also, the modified enzyme was more resistant to proteolytic degradation with trypsin. Pharmacokinetics studies revealed higher plasma half-life time for all the enzyme-polymer preparations, but better results were achieved for the enzyme modified with the anionic macromolecules.

GlycoPEGylation of recombinant therapeutic proteins produced in Escherichia coli

Covalent attachment of polyethylene glycol, PEGylation, has been shown to prolong the half-life and enhance the pharmacodynamics of therapeutic proteins. Current methods for PEGylation, which rely on chemical conjugation through reactive groups on amino acids, often generate isoforms in which PEG is attached at sites that interfere with bioactivity. Here, we present a novel strategy for site-directed PEGylation using glycosyltransferases to attach PEG to O-glycans. The process involves enzymatic GalNAc glycosylation at specific serine and threonine residues in proteins expressed without glycosylation in Escherichia coli, followed by enzymatic transfer of sialic acid conjugated with PEG to the introduced GalNAc residues. The strategy was applied to three therapeutic polypeptides, granulocyte colony stimulating factor (G-CSF), interferon-alpha2b (IFN-alpha2b), and granulocyte/macrophage colony stimulating factor (GM-CSF), which are currently in clinical use.

Transglutaminase-catalyzed site-specific glycosidation of catalase with aminated dextran

An enzymatic approach, based on a transglutaminase-catalyzed coupling reaction, was investigated to modify bovine liver catalase with an end-group aminated dextran derivative. We demonstrated that catalase activity increased after enzymatic glycosidation and that the conjugate was 3.8-fold more stable to thermal inactivation at 55 degrees C and 2-fold more resistant to proteolytic degradation by trypsin. Moreover, the transglutaminase-mediated modification also improved the pharmacokinetics behavior of catalase, increasing 2.5-fold its plasma half-life time and reducing 3-fold the total clearance after its i.v. administration in rats.

Long-acting interferon-alpha 2a modified with a trimer-structured polyethylene glycol: preparation, in vitro bioactivity, in vivo stability and pharmacokinetics

The proper selection of size and shape for polyethylene glycol (PEG) is one of the most important points in PEGylation technology. Therefore, PEGs of various sizes and shapes have been widely developed to endow specific properties. In this study, a unique, trimer-structured, 43 kDa PEG was conjugated to interferon-alpha 2a (IFN) by forming an amide bond to improve the pharmacokinetic properties and minimize the loss of IFN bioactivity. Mono-PEGylated IFN (PEG(3)-IFN) prepared by utilizing this unique PEG was purified and characterized by cation-exchange chromatography and MALDI-TOF mass spectrometry. The in vitro bioactivity, in vivo stability, and pharmacokinetics of PEG(3)-IFN were examined and compared to those of native IFN. PEG(3)-IFN exhibited comparable in vitro bioactivities to native IFN and an excellent stability of the conjugation linkage in rat serum and various organs following subcutaneous injection. Furthermore, it showed slow absorption and markedly reduced clearance in rats, thereby increasing the biological half-life by about 40-fold compared to that of native IFN. This is the first report on the application of unique, trimer-structured PEG to bioactive proteins. The results suggest that unique, trimer-structured 43 kDa PEG can provide some advantages to improve the pharmacokinetic properties and to maintain the bioactivity of therapeutic proteins in clinical use.

Characterization of EGF coupling to aminated silicone rubber surfaces

Tethering of growth factors to biomaterial substrates via a polyethylene glycol (PEG) spacer has been established as a means of controlling dosage and conformation of the protein at the material surface, while retaining biological activity. However, the extent of modification through a comparison of bound versus unbound protein has not generally been characterized. In this work, covalent tethering of epidermal growth factor (EGF) to allylamine plasma modified polydimethylsiloxane (PDMS) substrates is characterized to determine the nature of the bound growth factor and to optimize the conditions for the reaction. Tethering is achieved via conjugation of EGF with homobifunctional N-hydroxysuccinimide (NHS) ester of PEG-butanoic acid (SBA2-PEG) in solution, followed by exposure of the pegylated EGF to the aminated surfaces (solution first reaction). SDS-PAGE analysis indicates that a low ratio of EGF:PEG is required to maximize the yield of the EGF-PEG reaction; a relatively short reaction time is needed to limit hydrolysis of the NHS ester. With increasing amounts of PEG and a higher reaction time, a higher fraction of the EGF can be covalently tethered to the surfaces, as shown by binding of 125I-labeled EGF and subsequent washing with sodium dodecyl sulfate (SDS) to remove adsorbed protein. However, even under the optimal reaction conditions established by the SDS-PAGE analysis, higher molecular weight EGF-PEG complexes are observed by SDS-PAGE and matrix-assisted laser desorption/ionization (MALDI). The presence of these complexes, as well as unreacted growth factor, can lead to a surface of heterogeneous composition. While these surfaces were found to have biological activity, stimulating the adhesion and growth of corneal epithelial cells versus PDMS controls, further optimization of reaction conditions, including the use of a homobifunctional PEG linker and possibly separation of reaction species are required to achieve a uniformly active and well-defined biomaterial surface.