The conjugation of proteins with polyethylene glycol and other polymers

The Effect of PEGylation on Drugs' Pharmacokinetic Parameters; from Absorption to Excretion

Until the drugs enter humans life, they may face problems in transportation, drug delivery, and metabolism. These problems can cause reducing drug's therapeutic effect and even increase its side effects. Together, these cases can reduce the patient's compliance with the treatment and complicate the treatment process. Much work has been done to solve or at least reduce these problems. For example, using different forms of a single drug molecule (like Citalopram and Escitalopram); slight changes in the drug's molecule like Meperidine and α-Prodine, and using carriers (like Tigerase®). PEGylation is a recently presented method that can use for many targets. Poly Ethylene Glycol or PEG is a polymer that can attach to drugs by using different methods and resulting sustained release, controlled metabolism, targeted delivery, and other cases. Although they will not necessarily lead to an increase in the effect of the drug, they will lead to the improvement of the treatment process in certain ways. In this article, the team of authors has tried to collect and carefully review the best cases based on the PEGylation of drugs that can help the readers of this article.

Methacrylated Fibrinogen Hydrogels for 3D Cell Culture and Delivery

Methacrylation was performed on fibrinogen to design a new biomedical hydrogel for 3D cell culture or as a biodegradable delivery matrix for in vivo implantation. The methacrylation of denatured fibrinogen in solution was performed using methacrylic anhydride (MAA). The extent of fibrinogen methacrylation was quantified by proton NMR and controlled using stochiometric quantities of MAA during the reaction. The methacrylated fibrinogen (FibMA) hydrogels were formed by light-activated free-radical polymerization in the presence of macromolecular cross-linking polymers made from acrylated poly(ethylene glycol) (PEG). The biocompatibility and biodegradability of the FibMA hydrogels were characterized by in vitro assays and in vivo implantation experiments using quantitative magnetic resonance imaging (MRI) of the implant volume. The FibMA supported the growth and metabolic activity of human dermal fibroblasts in both 2D and 3D cultures. The methacrylation did not alter important biological attributes of the fibrinogen, including the ability to support cell adhesion and 3D cell culture, as well as to undergo proteolysis. Animal experiments confirmed the biodegradability of the FibMA for potential use as a scaffold in tissue engineering, as a bioink for 3D printing, or as a biodegradable matrix for in vivo sustained delivery of bioactive factors. STATEMENT OF SIGNIFICANCE: : This paper describes methacrylated fibrinogen (FibMA) and the formation of a biomedical hydrogel from FibMA for cell culture and other biomedical applications. Inspired from methacrylated gelatin (GelMA), the FibMA is made from blood-derived fibrinogen which is more suitable for clinical use. Sharing similar properties to other hydrogels made from methacrylated proteins, the FibMA has yet to be reported in the literature. In this manuscript, we provide the methodology to produce the FibMA hydrogels, we document the mechanical versatility of this new biomaterial, and we show the biocompatibility using 3D cell culture studies and in vivo implantations.

Effects of Vitamin A (Retinol) Release from Calcium Phosphate Matrices and Porous 3D Printed Scaffolds on Bone Cell Proliferation and Maturation

Vitamin A is a fat-soluble compound widely known for vision health. Highly variable reports on its effects on bone health have necessitated further research to truly understand its role on bone cell proliferation. Retinol, one bioactive form of vitamin A, is incorporated into synthetic bone graft scaffolds for low load-bearing clinical bone treatment. The objective of this work is to understand the effects of retinol on osteoblast and osteoclast cells when embedded within calcium phosphate matrices, including interconnected porous 3D printed tricalcium phosphate scaffolds. Results show that hydrophobic retinol can be released from bone scaffolds when a combination of biodegradable polymers, polycaprolactone and polyethylene glycol, are employed as drug carriers. The release of retinol in vitro can support a 20 ± 1% increase in osteoblast (bone-forming) cell proliferation with proper cell adhesion and filopodial extensions. Osteoclast cell morphology is necrosed and torn with a reduction in proliferation at approximately 6 ± 1% when retinol is present. In addition, inhibition of osteoclastic resorption pit bays is noted using scanning electron microscopy. With the scaffolds' round pore interconnectivity facilitating retinol release, this system can provide an alternative to traditional bone grafts while additionally supporting bone healing through enhanced osteoblast cell proliferation and inhibition of osteoclast resorption activity.

Physiological and Pathological Factors Affecting Drug Delivery to the Brain by Nanoparticles

The prevalence of neurological/neurodegenerative diseases, such as Alzheimer's disease is known to be increasing due to an aging population and is anticipated to further grow in the decades ahead. The treatment of brain diseases is challenging partly due to the inaccessibility of therapeutic agents to the brain. An increasingly important observation is that the physiology of the brain alters during many brain diseases, and aging adds even more to the complexity of the disease. There is a notion that the permeability of the blood-brain barrier (BBB) increases with aging or disease, however, the body has a defense mechanism that still retains the separation of the brain from harmful chemicals in the blood. This makes drug delivery to the diseased brain, even more challenging and complex task. Here, the physiological changes to the diseased brain and aged brain are covered in the context of drug delivery to the brain using nanoparticles. Also, recent and novel approaches are discussed for the delivery of therapeutic agents to the diseased brain using nanoparticle based or magnetic resonance imaging guided systems. Furthermore, the complement activation, toxicity, and immunogenicity of brain targeting nanoparticles as well as novel in vitro BBB models are discussed.

Mechanistic Understanding From Molecular Dynamics Simulation in Pharmaceutical Research 1: Drug Delivery

In this review, we outline the growing role that molecular dynamics simulation is able to play as a design tool in drug delivery. We cover both the pharmaceutical and computational backgrounds, in a pedagogical fashion, as this review is designed to be equally accessible to pharmaceutical researchers interested in what this new computational tool is capable of and experts in molecular modeling who wish to pursue pharmaceutical applications as a context for their research. The field has become too broad for us to concisely describe all work that has been carried out; many comprehensive reviews on subtopics of this area are cited. We discuss the insight molecular dynamics modeling has provided in dissolution and solubility, however, the majority of the discussion is focused on nanomedicine: the development of nanoscale drug delivery vehicles. Here we focus on three areas where molecular dynamics modeling has had a particularly strong impact: (1) behavior in the bloodstream and protective polymer corona, (2) Drug loading and controlled release, and (3) Nanoparticle interaction with both model and biological membranes. We conclude with some thoughts on the role that molecular dynamics simulation can grow to play in the development of new drug delivery systems.

Rapid synthesis of PEGylated multiblock polymers by sequence-controlled polymerization in H2O

Multiblock polymers with a poly(ethylene glycol) (PEG) block are attractive candidates for biomedical applications because of their favorable properties regarding biocompatibility and hydrophilicity.

Conjugation of Amine-Functionalized Polyesters With Dimethylcasein Using Microbial Transglutaminase

Protein-polymer conjugates have been used as therapeutics because they exhibit frequently higher stability, prolonged in vivo half-life, and lower immunogenicity compared with native proteins. The first part of this report describes the enzymatic synthesis of poly(glycerol adipate) (PGA(M)) by transesterification between glycerol and dimethyl adipate using lipase B from Candida antarctica. PGA(M) is a hydrophilic, biodegradable but water insoluble polyester. By acylation, PGA(M) is modified with 6-(Fmoc-amino)hexanoic acid and with hydrophilic poly(ethylene glycol) side chains (mPEG12) rendering the polymer highly water soluble. This is followed by the removal of protecting groups, fluorenylmethyloxycarbonyl, to generate polyester with primary amine groups, namely PGA(M)-g-NH₂-g-mPEG12. ¹H NMR spectroscopy, FTIR spectroscopy, and gel permeation chromatography have been used to determine the chemical structure and polydispersity index of PGA(M) before and after modification. In the second part, we discuss the microbial transglutaminase-mediated conjugation of the model protein dimethylcasein with PGA(M)-g-NH₂-g-mPEG12 under mild reaction conditions. SDS-PAGE proves the protein-polyester conjugation.

Synthesis and Aggregation of Polymer-Amyloid β Conjugates

Modulating the assembly of medically relevant peptides and proteins via macromolecular engineering is an important step in modifying their overall pathological effects. The synthesis of polymer-peptide conjugates composed of the amyloidogenic Alzheimer peptide, Aβ_1-40 , and poly(oligo(ethylene glycol)_m acrylates) (m = 2,3) with different molecular weights (M_n = 1400-6600 g mol^-1 ) is presented here. The challenging conjugation of a synthetic polymer to an in situ aggregating protein is established via two different coupling strategies, only successful for polymers with molecular weights not exceeding 6600 g mol^-1 , relying on resin-based synthesis or solution-based coupling chemistries. The conjugates are characterized by high-performance liquid chromatography and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. The aggregation of these polymer-Aβ_1-40 conjugates, as monitored via thioflavine-T (ThT)-fluorescence spectroscopy, is accelerated mainly upon attaching the polymers. However, the appearance of the observed fibrils is different from those composed of native Aβ_1-40, specifically with respect to length and morphology of the obtained aggregates. Instead of long, unbranched fibrils characteristic for Aβ_1-40 , bundles of short aggregates are observed for the conjugates. Finally, the ThT kinetics and morphologies of Aβ_1-40 fibrils formed in the presence of the conjugates give some mechanistic insights.

Site-specific PEGylation of micro-plasmin for improved thrombolytic therapy through engineering enhanced resistance against serpin mediated inhibition

The relatively rapid inhibition of microplasmin by α₂-AP leads to short functional half-life of the molecule in vivo, causing inefficient clot dissolution, even after site-specific, local catheter-based delivery. Here, we describe a PEGylation approach for improving the therapeutic potential via improving the survival of microplasmin in presence of its cognate inhibitor, α₂-AP, wherein a series of strategically designed cysteine analogs of micro-plasminogen were prepared and expressed in E. coli, and further modified by covalent grafting in vitro with PEG groups of different molecular sizes so as to select single or double PEG chains that increase the molecular weight and hydrodynamic radii of the conjugates, but with a minimal discernible effect on intrinsic plasmin activity and structural framework, as explored by amidolytic activity and CD-spectroscopy, respectively. Interestingly, some of the purified PEG-coupled proteins after conversion to their corresponding proteolytically active forms were found to exhibit significantly reduced inhibition rates (up to 2-fold) by α₂-AP relative to that observed with wild-type microplasmin. These results indicate an interesting, and not often observed, effect of PEG groups through reduced/altered dynamics between protease and inhibitor, likely through a steric hindrance mechanism. Thus, the present study successfully identifies single- and double-site PEGylated muteins of microplasmin with significantly enhanced functional half-life through enhanced resistance to inactivation by its in vivo plasma inhibitor. Such an increased survival of bioactivity in situ, holds unmistakable potential for therapeutic exploitation, especially in ischemic strokes where a direct, catheter-based deposition within the cranium has been shown to be promising, but is currently limited by the very short in vivo bioactive half-life of the fibrin dissolving agent/s.

Comparison of expression optimization of new derivative of staphylokinase (SAK-2RGD-TTI) with the rSAK

Staphylokinase (SAK) is a promising thrombolytic agent for the treatment of patients suffering from blood-clotting disorders. To increase the potency of SAK and to minimize vessel reocclusion, a new construct bearing SAK motif fused to tsetse thrombin inhibitor (TTI) via a 20-amino acid linker with 2 RGD (2 × arginine-glycine-aspartic acid inhibiting platelet aggregation via attachment to integrin receptors of platelet) was codon optimized and expressed comparatively in Pichia pastoris GS115 as a Mut⁺ strain and KM71H as a Mut^s strain. Fusion protein was optimized in terms of best expression condition and fibrinolytic activity and compared with the rSAK. Expression level of the designed construct reached up to 175 mg/L of the culture medium after 72-hr stimulation with 2.5% methanol and remained steady for 3-4 days. The highest expression was obtained at the range of 2-3% methanol. The SAK-2RGD-TT (relative activity >82%) was more active at 25-37 °C than rSAK (relative activity of 93%). Further, it showed relative activity >80% at pH ranges of 7-9. Western blot analysis showed two bands of nearly 27 and 24 kDa at ratio of 5 to 3, respectively. The specific fibrinolytic activity of the SAK-2RGD-TTI was measured as 8,269 U/mg, and 19,616 U/mg for the nonpurified and purified proteins, respectively. Deglycosylation by using tunicamycin in culture medium resulted in higher fibrinolytic activity of SAK-2RGD-TTI (2.2 fold). Consequently, compared to the rSAK, at the same equimolar proportion, addition of RGD and TTI fragments could increase fibrinolytic activity. Also, P. pastoris can be considered as an efficient host for overexpression of the soluble SAK-2RGD-TTI with high activity without requiring a complicated purification procedure.

Impact of Polymer Bioconjugation on Protein Stability and Activity Investigated with Discrete Conjugates: Alternatives to PEGylation

Covalent attachment of synthetic polymers to proteins, known as protein-polymer conjugation, is currently one of the main approaches for improving the physicochemical properties of these biomolecules. The most commonly employed polymer is polyethylene glycol (PEG), as evidenced by extensive research and clinical track records for its use in biopharmaceuticals. However, the occurrence of allergic reactions or hypersensitivity and the discovery of PEG antibodies, on the one hand, and the rise of controlled polymerization techniques and novel monomers, on the other hand, have been driving the search for alternative polymers for bioconjugation. The present study describes the synthesis, purification, and properties of conjugates of lysozyme with poly( N-acryloylmorpholine) (PNAM) and poly(oligoethylene glycol methyl ether methacrylate) (POEGMA). Particularly, conjugate species with distinct conjugation degrees are investigated for their residual activity, aggregation behavior, and solubility, by using a high-throughput screening approach. Our study showcases the importance of evaluating conjugates obtained by nonsite-specific modification through isolated species with discrete degrees of conjugation rather than on the batch level. Monovalent conjugates with relatively low molar mass polymers displayed equal or even higher activity than the native protein, while all conjugates showed an improved protein solubility. To achieve a comparable effect on solubility as with PEG, PNAM and POEGMA of higher molar masses were required.

Block copolymer crystalsomes with an ultrathin shell to extend blood circulation time

In water, amphiphilic block copolymers (BCPs) can self-assemble into various micelle structures depicting curved liquid/liquid interface. Crystallization, which is incommensurate with this curved space, often leads to defect accumulation and renders the structures leaky, undermining their potential biomedical applications. Herein we report using an emulsion-solution crystallization method to control the crystallization of an amphiphilic BCP, poly (l-lactide acid)-b-poly (ethylene glycol) (PLLA-b-PEG), at curved liquid/liquid interface. The resultant BCP crystalsomes (BCCs) structurally mimic the classical polymersomes and liposomes yet mechanically are more robust thanks to the single crystal-like crystalline PLLA shell. In blood circulation and biodistribution experiments, fluorophore-loaded BCCs show a 24 h circulation half-life and a 8% particle retention in the blood even at 96 h post injection. We further demonstrate that this good performance can be attributed to controlled polymer crystallization and the unique BCC nanostructure.

In block copolymer vesicles, crystallization often leads to defects and renders the structures leaky that undermines their potential biomedical application. Here the authors use an emulsion solution method to control the crystallization of an amphiphilic block copolymer at the curved liquid/liquid interface to improve the blood circulation time.

Improving the catalytic, kinetic and thermodynamic properties of Bacillus subtilis KU710517 milk clotting enzyme via conjugation with polyethylene glycol

Milk clotting enzyme (MCE) produced by Bacillus subtilis KU710517 was conjugated to several activated polysaccharides. Among all the conjugates, the enzyme conjugated with polyethylene glycol (PEG) exhibited the highest retained activity (551U/mg protein) with a recovered activity of 95.3%. The activation energy of PEG-conjugated enzyme was calculated as 24.56kJ·mol^-1which was lower than that of the native one (29.27kJ·mol^-1) however, the temperature quotient (Q₁₀) was about 1.08 for the two forms of the enzyme. The calculated half-life times of PEG-conjugated enzyme at 55 and 60°C were 317.78 and 128.6min respectively, whereas at the same temperatures the native enzyme had lower half-life times (53 and 19.6min respectively). The data of thermodynamic analysis for substrate catalysis including the specificity constant (V_max/K_m), turnover number (k_cat), catalytic efficiency (k_cat/K_m), enthalpy of activation (ΔH*), free energy of activation (ΔG*), free energy for transition state formation ΔG*_E-T and free energy of substrate binding ΔG*_E-S were determined for both native and PEG-conjugated enzyme. In addition, the thermodynamic parameters for irreversible inactivation (ΔH, ΔG, ΔS) were evaluated. The calculated results indicated that the catalytic properties after the PEG-conjugation were significantly improved.

Antiobesity and emetic effects of a short-length peptide YY analog and its PEGylated and alkylated derivatives

Neuropeptide Y2 receptor (Y2R) agonism is an important anorectic signal and a target of antiobesity drug discovery. Recently, we synthesized a short-length Y2R agonist, PYY-1119 (4-imidazolecarbonyl-[d-Hyp²⁴,Iva²⁵,Pya(4)²⁶,Cha^27,36,γMeLeu²⁸,Lys³⁰,Aib³¹]PYY(23-36), 1) as an antiobesity drug candidate. Compound 1 induced marked body weight loss in diet-induced obese (DIO) mice; however, 1 also induced severe vomiting in dogs at a lower dose than the minimum effective dose administered to DIO mice. The rapid absorption of 1 after subcutaneous administration caused the severe vomiting. Polyethylene glycol (PEG)- and alkyl-modified derivatives of 1 were synthesized to develop Y2R agonists with improved pharmacokinetic profiles, i.e., lower maximum plasma concentration (C_max) and longer time at maximum concentration (T_max). Compounds 5 and 10, modified with 20 kDa PEG at the N-terminus and eicosanedioic acid at the Lys³⁰ side chain of 1, respectively, showed high Y2R binding affinity and induced significant body weight reduction upon once-daily administration to DIO mice. Compounds 5 and 10, with their relatively low C_max and long T_max, partially attenuated emesis in dogs compared with 1. These results indicate that optimization of pharmacokinetic properties of Y2R agonists is an effective strategy to alleviate emesis induced by Y2R agonism.

Calprotectin Pegylation Enhanced Its Physical and Structural Properties

Calprotectin is member of the S-100 protein family with a wide plethora of intra-and extracellular functions. Anticancer activities, antimicrobial effects and being a qualified disease marker are among the compelling features of this protein to be used as a pharmaceutical agent. However, there are several impediments to applications of protein pharmaceuticals including: proteolytic degradation, short circulating half-life, low solubility and immunogenicity. Pegylation is a common bioconjugation polymer capable of overcoming these drawbacks. Recombinant expression and purification of calprotectin along with its pegylation would result in enhanced pharmaco-dynamic and pharmacokinetic properties. Our florescence spectroscopy and far Ultraviolet-optical density results indicate that pegylation altered the physical and structural properties of the calprotectin to become in a more stable and functionally active state. Due to enhanced pharmacodynamic and pharmacokinetic properties of the calprotectin via pegylation, this study would pave the way for better in vitro and in vivo validations of calprotectin applications in medical practice.

In vitro antiviral activity of Lactobacillus casei and Bifidobacterium adolescentis against rotavirus infection monitored by NSP4 protein production

AIMS

The aim of this study was to determine the antiviral activity of four probiotic metabolites (Lactobacillus and Bifidobacetrium species) against rotavirus in vitro infection monitored by the NSP4 protein production and Ca(2+) release.

METHODS AND RESULTS

The antiviral effect of the metabolites was performed due a comparison between a blocking model and an intracelullar model on MA104 cells, with the response of NSP4 production and Ca(2+) liberation measured by flow cytometry. Significant results were obtained with the metabolites of Lactobacillus casei, and Bifidobacterium adolescentis in the reduction of the protein production (P = 0·04 and P = 0·014) and Ca(2+) liberation (P = 0·094 and P = 0·020) in the intracellular model, which suggests a successful antiviral activity against RV infection.

CONCLUSIONS

This study demonstrates that probiotic metabolites were able to interfere with the final amount of intracellular NSP4 protein and a successful Ca(2+) regulation, which suggests a new approach to the mechanism exerted by probiotics against the rotavirus infection.

SIGNIFICANCE AND IMPACT OF THE STUDY

A novel anti-rotaviral effect exerted by probiotic metabolites monitored by the NSP4 protein during the RV in vitro infection and the effect on the Ca(2+) release is reported; suggesting a reduction on the impact of the infection by decreasing the damage of the cells preventing the electrolyte loss.

Imaging of Poly(N-Isopropyl Acrylamide-Co-Acrylic Acid)–Amino Acid Conjugates with Scanning Tunnelling Microscopy

A copolymer of N-isopropyl acrylamide (NIPAAm) and acrylic acid (AAc), Mw 1,400, AAc content of 3.1 mmol carboxylic acid groups per gram of the copolymer, was synthesised by a free radical polymerisation. Mono-, di-, and tripeptide conjugates of this copolymer were prepared by using the carboxylprotected alanine, glycine and serine, with a water-soluble carbodiimide. Scanning tunnelling microscope images of the conjugates were taken after each synthesis step. The average length and width of the copolymer with no amino acid were measured as 17 and 2.5 nm, respectively. The lengths of the mono-, di-, and tri-peptide conjugates were similar to the length of the copolymer chain while the widths were in the range of 3.0–3.2, 3.5–4.0 and 4.2–4.4 nm, respectively.

Cytotoxicity and Anticancer Activity of Macromolecular Prodrugs of 5-Fluorouracil

Polymeric conjugates of 5-fluorouracil (5-FU) were synthesized by covalent attachment of tetrapeptide chains with 2-(5-fluorouracil-1-yl)glycine ethyl ester [Gly(FU)OEt] as the C-terminus, to poly(ethylene glycol) (PEG) and dextran (Dex). Cytotoxicity of these conjugates was compared with free 5-FU against the murine colorectal carcinoma cell line C26. All the conjugates displayed lower cytotoxicity than 5-FU. The chemical structure and the configuration of the tetrapeptide chains influenced the activity of the conjugates. Materials containing the tetrapeptide Gly-Phe-Gly-Gly(FU)OEt (l,d), with Dex-based conjugates were more cytotoxic than the analogue PEG-based conjugate. PEG-Gly-Phe-Gly-Gly(FU)OEt (l,d) administered to mice at doses of 150 and 250 mg 5-FU equivalent/kg, following by inoculation of C26 tumor cells, mediated much less toxicity than equivalent doses of free 5-FU. The anticancer activity achieved using free and polymer-bound drugs were comparable, although decreased toxicity of the conjugate should facilitate administration of increased doses with improved efficacy.

Poly(Ethylene Glycol)-Bovine Serum Albumin Hydrogel as a Matrix for Enzyme Immobilization. In Vitro Biochemical Characterization

Arginase, isolated from beef liver, apyrase and glutaminase, isolated from Escherichia coli, were immobilized during the synthesis of a hydrogel matrix made from poly(ethylene glycol) (PEG) and bovine serum albumin (BSA). After synthesis, a one- to three-fold increase in the K m values was observed for the enzymes. The apparent K m were 30 mM of arginine, 6.5 mM of glutamine, and 52 μM of ATP for immobilized arginase, glutaminase, and apyrase, respectively. In general, immobilization allowed the enzymes to retain most of their initial activity; after incubating for 1 month at 37°C in the presence of the respective substrates, more than 95% of the initial activity was found. The optimal temperatures varied from 40 to 60°C for all enzyme preparations. The immobilized arginase, glutaminase, and apyrase had optimal activity over a larger pH range which was due to the matrix effect. Surface modification of arginase with 5,000 Mw methoxy-PEG increased the stability for up to 24 days (incubated at 37°C) compared to eight days for the native enzyme tested under the same conditions. However, this modification did not affect the stability of glutaminase.

Improved Pharmacological Properties for Superoxide Dismutase Modified with Carboxymethycellulose

Superoxide dismutase (SOD) was chemically modified with carboxymethylcellulose through two different synthetic procedures: Reductive alkylation with the periodate-oxidized polymer (SOD-CMCox), and the formation of amide linkages through a carbodiimide catalyzed reaction (SODCMCedac). The SOD-CMCox and SOD-CMCedac conjugates contained about 1.8–1.2mol of polymer per mol of protein, and retained 68–78% of the initial catalytic activity, respectively. The glycosidated enzymes were more resistant to inactivation with H2O2 and their plasma half-life times were prolonged to 34.7h – 6.6h when compared with 4.8min for native SOD. The anti-inflammatory activity of the enzyme was 2–2.4 times increased after conjugation with the polymer.

PEG Modified Anticancer Drugs: Synthesis and Biological Activity

Three well known anticancer drugs, doxorubicin, methotrexate and paclitaxel (taxol), have been modified by the permanent attachment of poly(ethylene glycol)(PEG) and evaluated for in vitro cytotoxic activity against murine leukemias P388 and L1210. The relative potencies of the PEG derivatives suggest that modification of antitumor agents with this type of polymer yields compounds that are highly water soluble but less cytotoxic.

New Bioartificial Polymeric Material: Poly(ethylene glycol) Cross-Linked with Albumin. I. Synthesis and Swelling Properties

A new family of translucide hydrogels obtained by cross-linking of bifunctionalized poly(ethylene glycol) (PEG) of various molecular masses (M, 2,000 to 35,000) with an albumin protein, namely bovine serum albumin (BSA), is described. The composition and the structure of these hydrogels have been investigated on the basis of the molar ratio of reagents, and through measurements of PEG and BSA released during washing and swelling steps. It appears that an excess of activated PEG is required in the reaction mixture to allow the gel formation with PEG of molecular mass ranging from 3,350 to 10,000. Above these Mr of PEG, smaller amounts of PEG are needed to carry out the gel formation. Experimental results suggest that the cross-link density decreases when the molecular mass of PEG increases. These hydrogels are characterized by a very high swelling ability with equilibrium water contents (EWC) ranging from 96.6 to 97.5% in distilled water containing NaN3 at 0.02% (w/v). The swelling factors (SF) ranged from 14 to 40 according to the incuba tion medium and to the PEG molecular mass involved. The swelling rates increased with increasing PEG molecular mass used to synthesize the hy drogel. This family of hydrogels possesses a good porosity since diffusion of bovine serum albumin out of the hydrogel network was observed in a long-term period.

Preservation of Thrombolytic Activity of Urokinase Modified with Monomethoxypoly(ethylene glycol

A method is described to modify urokinase by covalent binding of monomethoxypoly(ethylene glycol) (mPEG) without impairing its catalytic ac tivity towards high molecular weight substrates. The urokinase active site is protected by an inhibitor, benzamidine, bound to Sepharose during the mPEG modification in order to avoid binding mPEG chains to the active site or to the surrounding area. The mPEG modified urokinase had increased activity towards small molecular weight substrates (acetyl-Gly-methyl ester) as com pared to the unmodified enzyme, while the activity towards the high molecular weight plasminogen and the insoluble substrate fibrin clot was preserved. This did not occur when the enzyme was modified in the absence of active site pro tection. The polymer modification increased the enzyme's thermostability and the stability in plasma in vitro and prolonged in vivo retention after in travenous injection in rats.

Conjugates of Semitelechelic Poly[N-(2-Hydroxypropyl)Methacrylamide] with Enzymes for Protein Delivery

The semitelechelic poly[N-(2-hydroxypropyl)methacrylamide] [poly(HPMA)] with a carboxyl end group was prepared with 3-mercaptopropionic acid as a chain transfer agent. Bovine seminal ribonuclease (BSR) and α-chymotrypsin (ChT) were modified with various molecular weights of active poly(HPMA) succinimidyl ester by the reaction with the amino groups of the respective enzyme. The modification of ChT did not significantly change the activity or the substrate specificity of the conjugates towards low-molecular-weight tripeptidic substrates. However, modified ChT activity towards the corresponding poly(ethylene glycol)-based synthetic substrate was significant. The activity decreased as a result of the elevated steric hindrance to the active site of the polymer-modified enzyme. Similarly, the ChT conjugates completely lost their proteolytic activity toward native bovine serum albumin. The autolytic stability of ChT conjugates was improved and the proteolytic stability of the ChT and BSR conjugates substantially increased compared with the free enzymes. The modification of ChT with poly(HPMA) significantly decreased the immunogenicity of ChT conjugates depending on the molecular weight of the poly(HPMA) and the degree of enzyme substitution.

Physico-Chemical and Biological Properties of Monofunctional Hydroxy Teriminating Poly(N-Vinylpyrrolidone) Conjugated Superoxide Dismutase

Monofunctional hydroxy-terminated poly( N-vinylpyrrolidone) was obtained by radical polymerization in the presence of isopropoxyethanol for protein surface modification. Superoxide dismutase was modified to various degrees by reaction with PVP-OH activated by 4-nitrophenyl chloroformate with high retention of enzymatic activity. All the polymer-enzyme conjugates showed increased body residence time after intravenous injection in rats with respect to the native enzyme. The residence time depended upon the number of bound polymer chains. PVP was found to affect the pharmacokinetic properties of the enzyme after subcutaneous, intramuscular and intraperitoneal administration. The antigenicity of superoxide dismutase was reduced to one third following modification, while its immunogenicity after intravenous, subcutaneous and intraperitoneal injection totally disappeared. The conjugates exhibited increased solubility in organic solvents and increased stability towards thermal denaturation, whereas changes in the structural properties were observed by circular dichroism measurements.

Polymer–protein hybrid scaffolds as carriers for CORM-3: platforms for the delivery of carbon monoxide (CO)

The carbon monoxide releasing molecule, CORM-3, was grafted onto a polymer–protein conjugate thereby improving its half-life and release characteristics.

Evaluation of in vitro cytotoxic activity of mono-PEGylated StAP3 (Solanum tuberosum aspartic protease 3) forms

StAP3 is a plant aspartic protease with cytotoxic activity toward a broad spectrum of pathogens, including potato and human pathogen microorganisms, and cancer cells, but not against human T cells, human red blood cells or plant cells. For this reason, StAP3 could be a promising and potential drug candidate for future therapies. In this work, the improvement of the performance of StAP3 was achieved by means of a modification with PEG. The separation of a mono-PEGylated StAP3 fraction was easily performed by gel filtration chromatography. The mono-PEGylated StAP3 fraction was studied in terms of in vitro antimicrobial activity, exhibiting higher antimicrobial activity against Fusarium solani spores and Bacillus cereus, but slightly lower activity against Escherichia coli than native protein. Such increase in antifungal activity has not been reported previously for a PEGylated plant protein. In addition, PEGylation did not affect the selective cytotoxicity of StAP3, since no hemolytic activity was observed.

Encapsidated atom-transfer radical polymerization in Qβ virus-like nanoparticles

Virus-like particles (VLPs) are unique macromolecular structures that hold great promise in biomedical and biomaterial applications. The interior of the 30 nm-diameter Qβ VLP was functionalized by a three-step process: (1) hydrolytic removal of endogenously packaged RNA, (2) covalent attachment of initiator molecules to unnatural amino acid residues located on the interior capsid surface, and (3) atom-transfer radical polymerization of tertiary amine-bearing methacrylate monomers. The resulting polymer-containing particles were moderately expanded in size; however, biotin-derivatized polymer strands were only very weakly accessible to avidin, suggesting that most of the polymer was confined within the protein shell. The polymer-containing particles were also found to exhibit physical and chemical properties characteristic of positively charged nanostructures, including the ability to easily enter mammalian cells and deliver functional small interfering RNA.

Protective effect of chemically modified SOD on lipid peroxidation and antioxidant status in diabetic rats

Reactive oxygen species mediated oxidative stress play an important role on the injury of tissue damage and increased attention has been focused on the role of free radicals in diabetes mellitus (DM). In the present study firstly superoxide dismutase (SOD) enzyme was chemically modified with two different polymer and physicochemical properties of these conjugates clearly analyzed. Then, the stability of carboxymethylcellulose-SOD (CMC-SOD) and poly methyl vinyl ether-co-maleic anhydride-SOD (PMVE/MA-SOD) conjugates was investigated against temperature and externally added H2O2. Moreover, we investigated the effect of chemically modified SOD enzyme on lipid peroxidation and antioxidant status in streptozotocin (STZ)-induced diabetic rats. PMVE/MA-SOD conjugate treatment significantly reduced MDA level compared with the control groups, native and CMC-SOD conjugate treated groups in brain, kidney and liver tissue. GSH and SOD enzyme activity in diabetic groups was significantly increased by treatment of CMC-SOD and PMVE/MA-SOD conjugates. The protective effects on degenerative changes in diabetic rats were also further confirmed by histopathological examination. This study provides the preventative activity of SOD-polymer conjugates against complication of oxidative stress in experimentally induced diabetic rats. These results suggest that chemically modified SOD is effective on the oxidative stress-associated disease and offer a therapeutic advantage in clinical use.

Glycoengineering of interferon-β 1a improves its biophysical and pharmacokinetic properties

The purpose of this study was to develop a biobetter version of recombinant human interferon-β 1a (rhIFN-β 1a) to improve its biophysical properties, such as aggregation, production and stability, and pharmacokinetic properties without jeopardizing its activity. To achieve this, we introduced additional glycosylation into rhIFN-β 1a via site-directed mutagenesis. Glycoengineering of rhIFN-β 1a resulted in a new molecular entity, termed R27T, which was defined as a rhIFN-β mutein with two N-glycosylation sites at 80^th (original site) and at an additional 25^th amino acid due to a mutation of Thr for Arg at position 27^th of rhIFN-β 1a. Glycoengineering had no effect on rhIFN-β ligand-receptor binding, as no loss of specific activity was observed. R27T showed improved stability and had a reduced propensity for aggregation and an increased half-life. Therefore, hyperglycosylated rhIFN-β could be a biobetter version of rhIFN-β 1a with a potential for use as a drug against multiple sclerosis.

Synthesis, characterization and biodistribution studies of (125)I-radioiodinated di-PEGylated bone targeting salmon calcitonin analogue in healthy rats

PURPOSE

The objective of this study was to prepare a bisphosphonate (BP) mediated bone targeting di-PEGylated salmon calcitonin analogue sCT-2(PEG-BP) as a novel bone targeting pharmaceutical.

METHODS

HPLC was used for isolation of sCT-2(PEG-BP) from the reaction mixture, followed by determination of possible PEGylation sites by trypsin digestion. Stability of the compound over time, bone mineral affinity using hydroxyapatite, and biodistribution in normal rats after radiolabeling of sCT-2(PEG-BP) or control sCT with (125)I was evaluated.

RESULTS

PEGylated sCT analogues were synthesized, and sCT-2(PEG-BP) was isolated by HPLC and confirmed by MALDI-TOF and ICP-MS. MALDI-TOF analysis of trypsinized fragments suggested Cys(1) (or Lys(11)) and Lys(18) to be the two PEGylation sites. Bone mineral affinity test showed sCT-2(PEG-BP) or (125)I-sCT-2(PEG-BP) exhibited significantly increased bone mineral affinity over sCT or (125)I-sCT, respectively. sCT-2(PEG-BP) remained stable for at least 1 month. In vivo biodistribution study showed significantly increased bone retention and prolonged plasma circulation time for sCT-2(PEG-BP) compared to the control sCT.

CONCLUSION

Those results support sCT-2(PEG-BP) as a promising new drug candidate for the treatment of resorptive and/or maladaptive bone conditions, such as Osteoporosis, Osteoarthritis, Rheumatoid Arthritis, Paget's disease and bone cancers.

Bio-inspired liposomal thrombomodulin conjugate through bio-orthogonal chemistry

We report the synthesis of bioinspired liposomal thrombomodulin (TM) conjugates by chemoselective and site-specific liposomal conjugation of recombinant TM at C-terminus. TM is an endothelial cell membrane protein that acts as a major cofactor in the protein C anticoagulant pathway. To closely mimic membrane protein structural features of TM, we proposed membrane-mimetic re-expression of recombinant TM onto liposome. A recombinant TM containing the EGF-like 456 domains and an azidohomoalanine at C-terminus was expressed in E. coli. Conjugation of the recombinant TM onto liposome via Staudinger ligation and copper-free click chemistry were investigated as an optimal platform for exploring membrane protein TM's activity, respectively. The bioinspired liposomal TM conjugates were confirmed with Western blotting and protein C activation activity. The recombinant TM-liposome conjugates showed a 2-fold higher k(cat)/K(m) value for protein C activation than that of the recombinant TM alone, which indicated that the lipid membrane has a beneficiary effect on the recombinant TM's activity. The reported liposomal protein conjugate approach provides a rational design strategy for both studying membrane protein TM's functions and generating a membrane protein TM-based anticoagulant agent.