Preparation and Optimization of PEGylated Nano Graphene Oxide-Based Delivery System for Drugs with Different Molecular Structures Using Design of Experiment (DoE)

Graphene oxide (GO), due to its 2D planar structure and favorable physical and chemical properties, has been used in different fields including drug delivery. This study aimed to investigate the impact of different process parameters on the average size of drug-loaded PEGylated nano graphene oxide (NGO-PEG) particles using design of experiment (DoE) and the loading of drugs with different molecular structures on an NGO-PEG-based delivery system. GO was prepared from graphite, processed using a sonication method, and functionalized using PEG 6000. Acetaminophen (AMP), diclofenac (DIC), and methotrexate (MTX) were loaded onto NGO-PEG particles. Drug-loaded NGO-PEG was then characterized using dynamic light scattering (DLS), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), XRD. The DLS data showed that the drug-loaded NGO-PEG suspensions were in the size range of 200 nm-1.3 µm. The sonication time and the stirring rate were found to be the major process parameters which affected the average size of the drug-loaded NGO-PEG. FTIR, DSC, XRD, and SEM demonstrated that the functionalization or coating of the NGO occurred through physical interaction using PEG 6000. Methotrexate (MTX), with the highest number of aromatic rings, showed the highest loading efficiency of 95.6% compared to drugs with fewer aromatic rings (diclofenac (DIC) 70.5% and acetaminophen (AMP) 65.5%). This study suggests that GO-based nano delivery systems can be used to deliver drugs with multiple aromatic rings with a low water solubility and targeted delivery (e.g., cancer).

Impact of polymer geometry on the interactions of protein-PEG conjugates

The conjugation of high molecular weight polyethylene glycol (PEG) to an active pharmaceutical ingredient (API) is an attractive strategy for the modification of biophysical and biodistribution properties of the API. Indeed, several therapeutic proteins conjugated to PEG have been safely administered in the clinic. While there have been studies on the configuration of these conjugates in solution, investigations on the impact of PEG geometry on protein-PEG conjugate interactions is limited. In this study, we use dynamic light scattering (DLS), rheology, and small-angle neutron scattering (SANS) to investigate the biophysical solution and interaction behavior of a 50kDa Fab protein attached to either a linear or tetrameric (branched) 40kDa PEG molecule. The hydrodynamic radii, diffusivity, viscosity and pair distance distribution function (PDDF) were obtained for the protein-PEG conjugates in solution. An analysis revealed that interactions between unconjugated proteins were quite attractive, however linear PEG-protein conjugates exhibited net repulsive interactions, similar to that of the unconjugated polymer. Tetramer PEG-protein conjugates on the other hand, exhibited a net weak attractive interaction, indicating a more balanced distribution of repulsive and attractive interaction states. Further analysis of the SANS data using geometric models consistent with the PDDF elucidated the conjugates' equilibrium configuration in solution. Insights gained from measurements and analysis used here can also be useful in predicting how conjugate geometries affect viscosity and aggregation behavior, which are important in determining suitable protein-polymer drug formulations.

An Unusual Coupling of Poly(Ethylene Glycol) to Tyrosine Residues in Epidermal Growth Factor

An unusual covalent binding of hydroxysuccinimidyl ester activated polyethylene glycol), PEG, was found in the modification of a genetic variant of mouse epidermal growth factor (EGF): PEG was bound not only to the amino groups of the polypeptide as expected, but to a tyrosine residue as well. This unexpected PEGylation is related to the tyrosine environment in the peptide which does not occur in human EGF; furthermore, it is related to PEG size since it was found to occur to a greater extent with the PEG 5,000 molecular weight, than with the more hindered PEG 10,000.

Synthesis of Mono-PEGylated Growth Hormone Releasing Peptide-2 and Investigation of its Biological Activity

The purpose of this study was to investigate an efficient synthetic route to the mono-PEGylated growth hormone releasing peptide-2 (GHRP-2) and its biological activity in vivo. The commercially available key PEGylating reagent, mPEG-NHS ester, was successfully utilized to the synthesis of mono-PEGylated GHRP-2, during which the PEGylation profiles of GHRP-2 were monitored by high-performance liquid chromatography (HPLC). The product was purified by cation exchange chromatography, and its biological activity was conducted in rats. The desired mono-PEGylated GHRP-2 as the major product was readily obtained in anhydrous aprotic solvent, such as dimethyl formamide (DMF) and dimethylsulfoxide (DMSO), when the molar ratio of mPEG-NHS ester to GHRP-2 was fixed to be 0.8:1. The products were characterized by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry. The evaluation of the biological activity for the products showed that the mono-PEGylated GHRP-2 gave a more stable activity than GHRP-2, suggesting that PEGylation led to the increase in the half-life of GHRP-2 in plasma without greatly impairing the biological activity. PEGylation of the GHRP-2 is a good choice for the development of the GHRP-2 applications.

Adenosine-associated delivery systems

Adenosine is a naturally occurring purine nucleoside in every cell. Many critical treatments such as modulating irregular heartbeat (arrhythmias), regulation of central nervous system (CNS) activity and inhibiting seizural episodes can be carried out using adenosine. Despite the significant potential therapeutic impact of adenosine and its derivatives, the severe side effects caused by their systemic administration have significantly limited their clinical use. In addition, due to adenosine's extremely short half-life in human blood (<10 s), there is an unmet need for sustained delivery systems to enhance efficacy and reduce side effects. In this article, various adenosine delivery techniques, including encapsulation into biodegradable polymers, cell-based delivery, implantable biomaterials and mechanical-based delivery systems, are critically reviewed and the existing challenges are highlighted.

Synthesis, characterization, in vitro and in vivo evaluation of PEGylated oridonin conjugates

Oridonin (ORI), a diterpenoid compound with promising antitumor activity, was proved to possess potent antileukemia efficacies in vitro and in vivo recently. However, the development and application of ORI was limited by its poor solubility and rapid plasma clearance. The purpose of this study was to solve these problems. PEGylated oridonin linked with succinic acid (SA) as spacer moiety (PEG-SA-ORI conjugate) was synthesized. mPEG amines with four specifications of molecular weight (MW) were utilized. All polymeric conjugates showed satisfactory aqueous solubility and in vitro studies implied that the drug solubility and release features of conjugates were relevant to PEGs. The drug solubility increased more when the MW of PEG was lower, while more significant sustained-release effect was shown with higher PEG MW. Moreover, the release behaviors of conjugates showed a pH-sensitive property. In vivo pharmacokinetic studies demonstrated that the elimination half-life was prolonged in comparison with ORI solution. PEGylation could be a promising method to obtain better efficacy in the field of drug delivery system.

Cell uptake survey of pegylated nanographene oxide

Graphene and more specifically, nanographene oxide (GO) has been proposed as a highly efficient antitumoral therapy agent. Nevertheless, its cell uptake kinetics, its influence in different types of cells and the possibility of controlling cellular internalization timing, is still a field that remains unexplored. Herein, different cell types have been cultured in vitro for several incubation periods in the presence of 0.075 mg ml(-1) pegylated GO solutions. GO uptake kinetics revealed differences in the agent's uptake amount and speed as a function of the type of cell involved. Osteoblast-like cells GO uptake is higher and faster without resulting in greater cell membrane damage. Moreover, the dependence on the commonly used PEG nature (number of branches) also influences the viability and cell uptake speed. These facts play an important role in the future definition of timing parameters and selective cell uptake control in order to achieve an effective therapy.

Stimuli-responsive star poly(ethylene glycol) drug conjugates for improved intracellular delivery of the drug in neuroinflammation

N-Acetyl cysteine (NAC) is a vital drug currently under clinical trials for the treatment of neuroinflammation in maternal-fetal applications. The free sulfhydryl groups in NAC lead to high plasma protein binding, resulting in low bioavailability. Preparation and activity of conjugates of NAC with thiol terminated multi-arm (6 and 8) poly(ethylene-glycol) (PEG) with disulfide linkages involving sulfhydryls of NAC are reported. Multiple copies (5 and 7) of NAC were conjugated on 6 and 8-arm-PEG respectively. Both the conjugates released 74% of NAC within 2h by thiol exchange reactions in the redox environment provided by glutathione (GSH) intracellularly (2-10mM). At physiological extracellular glutathione concentration (2 microM) both the conjugates were stable and did not release NAC. MTT assay showed comparable cell viability for unmodified PEGs and both the PEG-S-S-NAC conjugates. The conjugates were readily endocytosed by cells, as confirmed by flow cytometry and confocal microscopy. Efficacy of 6 and 8-arm-PEG-S-S-NAC conjugates was evaluated on activated microglial cells (the target cells, in vivo) by monitoring cytokine release in lipopolysaccharide (LPS) induced inflammatory response in microglial cells using the reactive oxygen species (ROS), free radical nitrile (NO), anti-inflammatory activity and GSH depletion. The conjugates showed significant increase in antioxidant activity (more than a factor of 2) compared to free drug as seen from the inhibition of LPS induced ROS, NO, GSH and tumor necrosis factor-alpha (TNF-alpha) release in microglial cells.

Protein-polymer conjugates for forming photopolymerizable biomimetic hydrogels for tissue engineering

Collagen, fibrin and albumin are popular proteins for making biological scaffolds for tissue engineering because of their biocompatibility, biodegradability, and availability. A major drawback of biological protein-based biomaterials is the limited control over their physical and biodegradation properties. Our laboratory has been developing new protein-based biomaterials with tunable properties without the use of cytotoxic protein cross-linking techniques. We describe the formation and assembly of photopolymerizable biomimetic hydrogel scaffolds made from protein-polymer conjugates of poly(ethylene glycol) (PEG) and collagen, fibrin or albumin. The conjugation of PEG to these proteins (PEGylation) was verified by SDS-PAGE and the polymerization reaction into a hydrogel network was confirmed by shear rheometry. The differences in rheology and swelling characteristics of the three hydrogel materials underscore the importance of the molecular relationship between the PEG and the protein constituent in this protein-polymer arrangement. The biofunctionality of the PEGylated collagen and fibrinogen hydrogels sustained both cell adhesion and proteolytic degradation that enabled 3-D cell spreading and migration within the hydrogel network. PEG-albumin hydrogels exhibited poor cell spreading and migration by virtue of the fact that the albumin backbone lacks any known cell adhesion sites. Despite differences in the biological and structural composition of the PEGylated fibrinogen and collagen hydrogels, the rate of cellular migration within each material was not significantly different.

Production of heparin-functionalized hydrogels for the development of responsive and controlled growth factor delivery systems

Methods to assemble polymeric hydrogels on the basis of noncovalent protein-glycosaminoglycan interactions have been previously demonstrated by us and others and hold promise in the development of receptor-responsive hydrogel materials; improvements in the mechanical properties of such systems would broaden their utility. Thus, in situ crosslinkable and degradable heparin-containing hydrogels were designed for the binding and controlled release of growth factors. Specifically, maleimide-functionalized high molecular weight heparin (HMWH) was synthesized via straightforward chemical methods that permitted facile and controllable modification of carboxylates in HMWH with maleimide groups via control of catalyst and reaction conditions, as assessed via 1H NMR spectroscopy. These modified heparins were crosslinked into hydrogels via reaction with various thiol-functionalized PEGs. The gelation times and elastic moduli of the gels, as assessed through oscillatory rheometry, could be tuned by controlling the functionality of HMWH, the concentration of the hydrogel, the identity of the PEG-based crosslinker, as well as the molar ratio between maleimide and thiol groups. The capability of the hydrogels to bind to growth factors was investigated with immunochemical assays. Preliminary studies indicate the controlled release of basic fibroblast growth factor (bFGF) from these materials and suggest their broader use in the design of responsive materials.

Well-defined protein–polymer conjugates—synthesis and potential applications

During the last decades, numerous studies have focused on combining the unique catalytic/functional properties and structural characteristics of proteins and enzymes with those of synthetic molecules and macromolecules. The aim of such multidisciplinary studies is to improve the properties of the natural component, combine them with those of the synthetic, and create novel biomaterials in the nanometer scale. The specific coupling of polymers onto the protein structures has proved to be one of the most straightforward and applicable approaches in that sense. In this article, we focus on the synthetic pathways that have or can be utilized to specifically couple proteins to polymers. The different categories of well-defined protein-polymer conjugates and the effect of the polymer on the protein function are discussed. Studies have shown that the specific conjugation of a synthetic polymer to a protein conveys its physico-chemical properties and, therefore, modifies the biodistribution and solubility of the protein, making it in certain cases soluble and active in organic solvents. An overview of the applications derived from such bioconjugates in the pharmaceutical industry, biocatalysis, and supramolecular nanobiotechnology is presented at the final part of the article.

Delivery of viral vectors to tumor cells: extracellular transport, systemic distribution, and strategies for improvement

It is a challenge to deliver therapeutic genes to tumor cells using viral vectors because (i) the size of these vectors are close to or larger than the space between fibers in extracellular matrix and (ii) viral proteins are potentially toxic in normal tissues. In general, gene delivery is hindered by various physiological barriers to virus transport from the site of injection to the nucleus of tumor cells and is limited by normal tissue tolerance of toxicity determined by local concentrations of transgene products and viral proteins. To illustrate the obstacles encountered in the delivery and yet limit the scope of discussion, this review focuses only on extracellular transport in solid tumors and distribution of viral vectors in normal organs after they are injected intravenously or intratumorally. This review also discusses current strategies for improving intratumoral transport and specificity of viral vectors.

Reproducible preparation and effective separation of PEGylated recombinant human granulocyte colony-stimulating factor with novel “PEG-pellet” PEGylation mode and ion-exchange chromatography

A novel preparation for polyethylene glycol (PEG) derivatives and chromatographic separation procedure of the PEGylated recombinant human granulocyte colony-stimulating factor (rhG-CSF) were designed to evaluate the reproducibility and scalability at large laboratory-scale level. The new "PEG-pellet" PEGylation mode was successfully applied to control the pH fluctuation during the conjugation reaction, a general problem in traditional liquid-phase conjugation mode. Moreover, two consecutive ion-exchange chromatography steps were successfully used to separate and purify the PEGylated rhG-CSF. Cation-exchange chromatography was firstly applied to separate PEGylated rhG-CSF from intact rhG-CSF, followed by anion-exchange chromatography to obtain individual PEG-rhG-CSF species (mono-, di- and tri-PEGylated rhG-CSF) and remove the excess free PEG. Furthermore, the molecular weight of individual PEGylated rhG-CSF was identified by matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry and SDS-PAGE, and cell proliferation activity in vitro was detected by MTT assay using NFS-60 cell.

Covalent polymer-drug conjugates

In this work, polymer-drugs conjugates used as drug delivery systems (DDS) are revised attending to their chemical conjugation. Namely, the classification of this type of DDS is based on the conjugation sites of the reactive groups (i.e., via end groups or pendant polymer groups). Advantages and limitations of these types of DDS are discussed through representative examples of polymer-drugs and polymer-proteins conjugates recently developed.

Immune reactions of lymphocytes and macrophages against PEG-grafted pancreatic islets

Graft rejection is the major limiting factor in islet transplantation and is closely related with the recruitment and activation of T cells and macrophages against the graft. To reduce the immunogenicity of islets, we have grafted biocompatible polyethylene glycol (PEG) onto the collagen capsule of islets without changing the morphology and function of islets. In this study, we evaluated whether the grafted PEG molecules on the collagen capsule of islet could prevent the activation of immune cells, and investigated factors that are mainly related to the immune reaction in vitro. During the co-culture with lymphocytes, the morphology and viability of PEG-grafted islets were not damaged, and the amounts of IL-2 and TNF-alpha secreted from lymphocytes co-cultured with PEG-grafted islets were significantly lower than that of free islets. However, when both kinds of islets were cultured with macrophages, there were no significant differences in morphology, viability and the secreted amounts of cytokines and nitric oxide. In conclusion, the grafted PEG could inhibit activation of lymphocytes, which are essential in initiating the graft rejection process. However, the grafted PEG molecules could not completely prevent the infiltration of cytotoxic molecules into the islets.

Effective drug delivery by PEGylated drug conjugates

The current review presents an update of drug delivery using poly(ethylene glycol) (PEG), that focuses on recent developments in both protein and organic drugs. Certainly the past 10 years has resulted in a renaissance of the field of PEG drug conjugates, initiated by the use of higher molecular weight PEGs (M(w)>20,000), especially 40,000 which is estimated to have a plasma circulating t(1/2) of approximately 10 h in mice. This recent resuscitation of small organic molecule delivery by high molecular weight PEG conjugates was founded on meaningful in vivo testing using established tumor models, and has led to a clinical candidate, PEG-camptothecin (PROTHECAN), an ester based prodrug currently in phase II trials. Additional applications of high molecular weight PEG prodrug strategies to amino containing drugs are presented: similar tripartate systems based on lower M(w) PEG and their use with proteins is expounded on. The modification of a benzyl elimination tripartate prodrug specific for mercaptans is presented, and its successful application to 6-mercaptopurine giving a water soluble formulation is discussed. Recent novel PEG oligonucleotides and immunoconjugates are also covered. Clinical results of FDA approved PEGylated proteins are also presented.

Chemistry for peptide and protein PEGylation

Poly(ethylene glycol) (PEG) is a highly investigated polymer for the covalent modification of biological macromolecules and surfaces for many pharmaceutical and biotechnical applications. In the modification of biological macromolecules, peptides and proteins are of extreme importance. Reasons for PEGylation (i.e. the covalent attachment of PEG) of peptides and proteins are numerous and include shielding of antigenic and immunogenic epitopes, shielding receptor-mediated uptake by the reticuloendothelial system (RES), and preventing recognition and degradation by proteolytic enzymes. PEG conjugation also increases the apparent size of the polypeptide, thus reducing the renal filtration and altering biodistribution. An important aspect of PEGylation is the incorporation of various PEG functional groups that are used to attach the PEG to the peptide or protein. In this paper, we review PEG chemistry and methods of preparation with a particular focus on new (second-generation) PEG derivatives, reversible conjugation and PEG structures.

Preparation and characterization of PEGylated adducts of recombinant human tumor necrosis factor-alpha from Escherichia coli

This study was conducted to get an insight into monomethoxypolyethylene glycol (MPEG) modified recombinant human TNF-alpha (rhTNF-alpha) derived from gene cloning and expression. The purification and modification processes were integrated together to make the scale-up production of PEG-modified rhTNF-alpha practical. Capillary electrophoresis was demonstrated to be a highly efficient tool in the biochemical characterization of the PEGylated products compared to slab electrophoresis. The cytotoxicity of MPEG-modified rhTNF-alpha was studied in vitro towards L929 cell line and found to decrease gradually along with the increase in the reaction ratio between the activated MPEG and the native rhTNF-alpha. The MPEG-modified rhTNF-alpha was more resistant to proteinase degradation in vitro than the native. When MPEG chains were released partially from the MPEG-modified rhTNF-alpha by alkaline pretreatment, the cytotoxicity of the MPEG-modified rhTNF-alpha was enhanced, which was in contrast to the native. These results would be helpful to explain the disagreement between the high bioavailability of MPEG-modified TNF-alpha in vivo and its decreased cytotoxicity in vitro.

Stimuli-responsive properties of conjugates of N-isopropylacrylamide-co-acrylic acid oligomers with alanine, glycine and serine mono-, di- and tri-peptides

A random oligomer of N-isopropylacrylamide (NIPAAm) and acrylic acid (AAc) with a AAc content of 3.1+/-0.19 mmol carboxylic acid groups per gram of the oligomer and with a number average molecular weight of 1400 was synthesised by a free radical polymerisation using AIBN in DMF. Then, mono-, di-, and tri-peptide conjugates of this oligomer were prepared by using carboxyl-ends-protected (with methyl ester hydrochloride) forms of alanine, glycine and serine, with a water-soluble carbodiimide. 95, 93, and 31% of the carboxylic acids were conjugated (loaded) at the first step (mono-peptides) with glycine, alanine and serine, respectively. At the second step, percentage of the conjugation of carboxylic acid groups with glycine, alanine and serine were between 99 and 80, 68 and 100, and 21 and 58%, respectively, while the third amino acids were attached to only 21-64% of the carboxylic acids available on the conjugate chains. A decrease was observed in the lower critical solution temperatures (LCSTs) of the amino acid conjugates at pH 4.0 compared with the unconjugated oligomer, which has LCST at 37.7 degrees C at the same pH. LCSTs of di- and tri-peptide conjugates at pH 4.0 were in the range of 38.4-43.3 degrees C, and 42.6-50.8 degrees C, respectively. At pH 7.4, LCSTs of the mono- and di-peptide conjugates were observed in the range of 41.6-43.9 degrees C, and 46.2-60.2 degrees C, respectively, while the co-oligomer at pH 7.4 did not show a LCST up to 60 degrees C. Tri-peptide conjugates did not display LCST at pH 7.4, except the one with glycine-alanine-serine sequence.

Peptide and protein PEGylation: a review of problems and solutions

The paper discusses general problems in using PEG for conjugation to high or low molecular weight molecules. Methods of binding PEG to different functional groups in macromolecules is reported together with their eventual limitations. Problems encountered in conjugation, such as the evaluation of the number of PEG chains bound, the localisation of the site of conjugation in polypeptides and the procedure to direct PEGylation to the desired site in the molecule are discussed. Finally, the paper reports on more specific methods regarding reversible PEGylation, cross-linking reagents with PEG arms, PEG for enzyme solubilization in organic solvent and new polymers as alternative to PEG.

Drug delivery systems employing 1,6-elimination: releasable poly(ethylene glycol) conjugates of proteins

Using lysozyme as a representative protein substrate that loses its activity when PEGylation takes place on the epsilon-amino group of lysine residues, various amounts of a novel releasable PEG linker (rPEG) were conjugated to the protein. rPEG-lysozyme conjugates were relatively stable in pH 7.4 buffer for over 24 h. However, regeneration of native protein from the rPEG conjugates occurred in a predictable manner during incubation in high pH buffer or rat plasma, as demonstrated by enzymatic activity and structural characterization. The rates of regeneration were also correlated with PEG number: native lysozyme was released more rapidly from the monosubstituted conjugate than from the disubstituted conjugate, suggesting possible steric hindrance to the approach of cleaving enzymes. Recovery of normal activity and structure for the regenerated native lysozyme was shown by a variety of assays.

B-Domain deleted recombinant coagulation factor VIII modified with monomethoxy polyethylene glycol

Recombinant coagulation factor VIII (r-VIII SQ) was chemically modified with monomethoxy poly(ethylene glycol) (mPEG). Three mPEG derivatives were used for coupling to the r-VIII SQ lysines, a mixed anhydride of monomethoxy poly(ethylene glycol) succinic acid (mPEG-SAH), monomethoxy poly(ethylene glycol) succinimidyl succinate (mPEG-SS), and monomethoxy poly(ethylene glycol) tresylate (mPEG-TRES). A consequence of the modification with all derivatives was a substantial reduction in coagulant activity, even at very low degrees of modification. A method was developed with the purpose of avoiding conjugation at certain important biological sites on the factor VIII and thereby producing conjugates with better retained activity. This was achieved by immobilizing the protein onto a solid matrix during the modification reaction. Characterization of conjugates by SDS-PAGE, western blots, interaction with von Willebrand factor (vWf), and thrombin activation/inactivation analyses was undertaken. The SDS-PAGE and western blots revealed coupling heterogeneity regarding degree of modification. The amount of factor VIII able to bind to vWf decreased with the conjugation. Thrombin activated the modified factor VIII to essentially the same extent as the reference preparation of r-VIII SQ. Inactivation of the modified factor VIII was, however, slower than inactivation of the unmodified protein. Finally, an in vitro study was performed to evaluate the influence of the mPEG modification on the protein stability in extract of porcine tissue. Despite that conjugates with low degrees of modification were included in the study, the coagulant activity was preserved to a significantly higher extent in all incubation mixtures containing conjugates compared to that with unmodified protein.