Reducing the immunogenicity and improving the in vivo activity of trichosanthin by site-directed pegylation

Use of mPEG-PLGA nanoparticles to improve bioactivity and hemocompatibility of streptokinase: In-vitro and in-vivo studies

Streptokinase, a clot-dissolving agent, is widely used in treatment of cardiovascular diseases such as blood clots and deep thrombosis. Streptokinase is a cost-effective drug with a short biological half-life (i.e. 15 to 30 min). In addition, due to its prokaryotic source, the immune response quickly reacts to the drug. Despite these limitations, streptokinase is still the first choice for diseases associated with thrombosis. In this work, streptokinase was encapsulated in mPEG-PLGA nanoparticles to improve its pharmacokinetic properties. The nanoparticles containing the enzyme were prepared by coaxial electrospray and their physicochemical properties, blood compatibility, circulation time and cell toxicity were evaluated. The results showed that the use of mPEG-PLGA nanoparticles to encapsulate the enzyme resulted in prolonged circulation time (up to 120 min) with a slight decrease in its activity. In vivo studies also showed that the nanoparticles containing streptokinase did not have adverse effect on blood biochemistry parameters as well as liver and kidney tissues. As a result, the mPEG-PLGA nanoparticles showed the potential for increasing the biological activity of streptokinase with no important adverse effect.

Engineering of Ribosome-inactivating Proteins for Improving Pharmacological Properties

Ribosome-inactivating proteins (RIPs) are N-glycosidases, which depurinate a specific adenine residue in the conserved α-sarcin/ricin loop (α-SRL) of rRNA. This loop is important for anchoring elongation factor (EF-G for prokaryote or eEF2 for eukaryote) in mRNA translocation. Translation is inhibited after the attack. RIPs therefore may have been applied for anti-cancer, and anti-virus and other therapeutic applications. The main obstacles of treatment with RIPs include short plasma half-life, non-selective cytotoxicity and antigenicity. This review focuses on the strategies used to improve the pharmacological properties of RIPs on human immunodeficiency virus (HIV) and cancers. Coupling with polyethylene glycol (PEG) increases plasma time and reduces antigenicity. RIPs conjugated with antibodies to form immunotoxins increase the selective toxicity to target cells. The prospects for future development on the engineering of RIPs for improving their pharmacological properties are also discussed.

Preparation of PEG-grafted chitosan/streptokinase nanoparticles to improve biological half-life and reduce immunogenicity of the enzyme

Streptokinase, as a thrombolytic drug, is widely used in treatment of cardiovascular disorders and deep vein thrombosis. Streptokinase is immunogenic due to its prokaryotic source, having short biological half-life (i.e. 15 to 30 min) that is not enough for an efficient therapy. In this study, nanoparticles (NPs) of chitosan/streptokinase and polyethylene glycol (PEG)-grafted chitosan/streptokinase were prepared by polyelectrolyte complex method. Particle size of chitosan and PEG-grafted chitosan NPs were 154 ± 42 and 211 ± 47 nm, respectively. Results showed that using PEG in preparation of nanoparticles leads to ~24% decrease in encapsulation efficiency. Encapsulation of streptokinase in the NPs also resulted in a slight reduction in enzymatic activity. However, in vivo findings indicated that response of the immune system was delayed for 20 days and blood circulation time of the enzyme increased up to 120 min by using PEG. Biological half-life of the drug also increased up to twice in PEG-grafted chitosan. In conclusion, PEG-grafted chitosan NPs could be an alternative for delivery of streptokinase to reduce its clinical limitations.

Clinical Use of Toxic Proteins and Peptides from Tian Hua Fen and Scorpion Venom

Traditional Chinese Medicine (TCM) has been practiced in China for thousands of years. As a complementary and alternative treatment, herbal medicines that are frequently used in the TCM are the most accepted in the Western world. However, animal materials, which are equally important in the TCM practice, are not well-known in other countries. On the other hand, the Chinese doctors had documented the toxic profiles of hundreds of animals and plants thousand years ago. Furthermore, they saw the potential benefits of these materials and used their toxic properties to treat a wide variety of diseases, such as heavy pain and cancer. Since the 50s of the last century, efforts of the Chinese government and societies to modernize TCM have achieved tremendous scientific results in both laboratory and clinic. A number of toxic proteins have been isolated and their functions identified. Although most of the literature was written in Chinese, this review provide a summary, in English, regarding our knowledge of the clinical use of the toxic proteins isolated from a plant, Tian Hua Fen, and an animal, scorpion, both of which are famous toxic prescriptions in TCM.

Polymer-Doxorubicin Prodrug with Biocompatibility, pH Response, and Main Chain Breakability Prepared by Catalyst-Free Click Reaction

Click chemistry has increasing applications of the development of polymer materials and modification of drug carriers. The amino-yne click polymerization reacts quickly at room temperature without catalyst, and the enamine bond (-ena-) gained from the reaction is sensitive to acid and can be used to prepare stimulus-responsive polymeric prodrugs. Herein, we report an alkynyl-terminated polymer containing alternately distributed low molecular weight polyethylene glycol (PEG) and hexamethylenediamino (HMDA) linked by enamine bonds, abbreviated as A-P(PEG-alt-HMDA)-A, which was synthesized within 3 h at 35 °C without catalyst. The polymer was verified to have good water solubility, biocompatibility, and acid-sensitive fracturing. Then, a pH-responsive polymeric prodrug (DOX-ena-PPEG-ena-DOX) was further prepared through the amino-yne click reaction between the alkynyl groups of A-P(PEG-alt-HMDA)-A and the amino group of doxorubicin hydrochloride (DOX·HCl). The resulting prodrug can self-assemble into nanoparticles (NPs) in aqueous solution. The pH responsiveness of the prodrug NPs was demonstrated by a stability experiment of NPs and in vitro drug release behavior measurement. The accumulative release of doxorubicin (DOX) was tested with different pH media, which confirmed that the prodrug NPs could effectively dissociate and release drug under a weak acid microenvironment of lysosome/endosome. Subsequently, we investigated cell cytotoxicity and intracellular uptake of the prodrug. It turned out that the prodrug nanoparticles could be internalized into HeLa cells, release original DOX, and efficiently inhibit the proliferation of cancer cells. These results show that the pH-responsive DOX-ena-PPEG-ena-DOX has the potential for use in cancer therapy.

Medical Options for the Adjuvant Treatment and Management of Pediatric Melanoma

Although melanoma is a rare diagnosis in the pediatric population, advances in the management of adults with melanoma offer the prospect of promising therapeutic options for children. At this time, medical management is not considered curative but may reduce the risk of recurrence or prolong survival. Surgical management remains the mainstay of treatment. Medical therapy of pediatric melanoma is not thought to have a role for in situ, early-stage, or localized disease, but adjuvant therapy may have a role in improving the prognosis of patients with positive sentinel lymph node biopsy (SLNB), spread beyond the regional lymph node basin, metastatic disease, or recurrent disease. Medical treatment options include immunotherapies, particularly checkpoint inhibitors, and targeted therapies, which have provided improved toxicity profiles compared with traditional chemotherapy regimens in the setting of advanced disease. There is a growing body of pediatric-specific data relevant to the use of adjuvant therapies for advanced melanoma in children.

Antibacterial Peptides in Dermatology-Strategies for Evaluation of Allergic Potential

During recent decades, the market for peptide-based drugs, including antimicrobial peptides, has vastly extended and evolved. These drugs can be useful in treatment of various types of disorders, e.g., cancer, autoimmune diseases, infections, and non-healing wounds. Although peptides are less immunogenic than other biologic therapeutics, they can still induce immune responses and cause allergies. It is important to evaluate the immunogenic and allergic potential of peptides before they are forwarded to the expensive stages of clinical trials. The process of the evaluation of immunogenicity and cytotoxicity is complicated, as in vitro models and bioinformatics tools cannot fully simulate situations in the clinic. Nevertheless, several potentially promising tests for the preclinical evaluation of peptide drugs have been implemented (e.g., cytotoxicity assays, the basophil activation test, and lymphocyte activation assays). In this review, we focus on strategies for evaluation of the allergic potential of peptide-based therapeutics.

Strategies to Improve the Clinical Utility of Saporin-Based Targeted Toxins

Plant Ribosome-inactivating proteins (RIPs) including the type I RIP Saporin have been used for the construction of Immunotoxins (ITxs) obtained via chemical conjugation of the toxic domain to whole antibodies or by generating genetic fusions to antibody fragments/targeting domains able to direct the chimeric toxin against a desired sub-population of cancer cells. The high enzymatic activity, stability and resistance to conjugation procedures and especially the possibility to express recombinant fusions in yeast, make Saporin a well-suited tool for anti-cancer therapy approaches. Previous clinical work on RIPs-based Immunotoxins (including Saporin) has shown that several critical issues must be taken into deeper consideration to fully exploit their therapeutic potential. This review focuses on possible combinatorial strategies (chemical and genetic) to augment Saporin-targeted toxin efficacy. Combinatorial approaches may facilitate RIP escape into the cytosolic compartment (where target ribosomes are), while genetic manipulations may minimize potential adverse effects such as vascular-leak syndrome or may identify T/B cell epitopes in order to decrease the immunogenicity following similar strategies as those used in the case of bacterial toxins such as Pseudomonas Exotoxin A or as for Type I RIP Bouganin. This review will further focus on strategies to improve recombinant production of Saporin-based chimeric toxins.

Glioma Dual-Targeting Nanohybrid Protein Toxin Constructed by Intein-Mediated Site-Specific Ligation for Multistage Booster Delivery

Malignant glioma is one of the most untreatable cancers because of the formidable blood-brain barrier (BBB), through which few therapeutics can penetrate and reach the tumors. Biologics have been booming in cancer therapy in the past two decades, but their application in brain tumor has long been ignored due to the impermeable nature of BBB against effective delivery of biologics. Indeed, it is a long unsolved problem for brain delivery of macromolecular drugs, which becomes the Holy Grail in medical and pharmaceutical sciences. Even assisting by targeting ligands, protein brain delivery still remains challenging because of the synthesis difficulties of ligand-modified proteins. Herein, we propose a rocket-like, multistage booster delivery system of a protein toxin, trichosanthin (TCS), for antiglioma treatment. TCS is a ribosome-inactivating protein with the potent activity against various solid tumors but lack of specific action and cell penetration ability. To overcome the challenge of its poor druggability and site-specific modification, intein-mediated ligation was applied, by which a gelatinase-cleavable peptide and cell-penetrating peptide (CPP)-fused recombinant TCS toxin can be site-specifically conjugated to lactoferrin (LF), thus constructing a BBB-penetrating, gelatinase-activatable cell-penetrating nanohybrid TCS toxin. This nanohybrid TCS system is featured by the multistage booster strategy for glioma dual-targeting delivery. First, LF can target to the BBB-overexpressing low-density lipoprotein receptor-related protein-1 (LRP-1), and assist with BBB penetration. Second, once reaching the tumor site, the gelatinase-cleavable peptide acts as a separator responsive to the glioma-associated matrix metalloproteinases (MMPs), thus releasing to the CPP-fused toxin. Third, CPP mediates intratumoral and intracellular penetration of TCS toxin, thereby enhancing its antitumor activity. The BBB penetration and MMP-2-activability of this delivery system were demonstrated. The antiglioma activity was evaluated in the subcutaneous and orthotopic animal models. Our work provides a useful protocol for improving the druggability of such class of protein toxins and promoting their in-vivo application for targeted cancer therapy.

Conjugate of an IgG Binding Domain with Botulinum Neurotoxin A Lacking the Acceptor Moiety Targets Its SNARE Protease into TrkA-Expressing Cells When Coupled to Anti-TrkA IgG or Fc-βNGF

Numerous naturally occurring toxins can perturb biological systems when they invade susceptible cells. Coupling of pertinent targeting ligands to the active domains of such proteins provides a strategy for directing these to particular cellular populations implicated in disease. A novel approach described herein involved fusion of one mutated immunoglobulin G (IgG) binding moiety of staphylococcal protein A to the SNARE protease and translocation domain of botulinum neurotoxin A (BoNT/A). This chimera could be monovalently coupled to IgG or via its Fc region to recombinant targeting ligands. The utility of the resulting conjugates is demonstrated by the delivery of a SNARE protease into a cell line expressing tropomyosin receptor kinase A (TrkA) through coupling to anti-TrkA IgG or a fusion of Fc and nerve-growth factor. Thus, this is a versitile and innovative technology for conjugating toxins to diverse ligands for retargeted cell delivery of potential therapeutics.

Novel purification method and antibiotic activity of recombinant Momordica charantia MAP30

Ribosome-inactivating proteins (RIPs) are a group of enzymes originally isolated from plants that possess the ability to damage ribosomes in an irreversible manner, leading to inhibition of protein synthesis in eukaryotic cells. In this study, we aimed to purify recombinant RIPs, investigate their function in the treatment of bacterial infection, and determine their toxicity in mice. We employed a pMAL protein fusion and purification system using E. coli transformed with a plasmid containing MBP-tagged MAP30 cDNA. MBP-tagged MAP30 was purified using a modified novel protocol to effectively produce highly active MAP30 of high purity. In an acute toxicity study in mice, no mortality occurred at doses lower than 1.25 mg/kg. MAP30 at both 0.42 and 0.14 mg/kg induced anti-MAP30 IgG, which reached a maximum titer at week 3. In conclusion, recombinant MAP30 prepared using our purification method possesses bioactivity, and has a synergistic bacteria-killing effect that can significantly reduce the required dosages of chloramphenicol and erythromycin. Therefore, when MAP30 is used in combination with chloramphenicol or erythromycin, it may of benefit in terms of reducing the side effects of the antibiotics, as lower concentrations of antibiotics are required.

High frequency of antidrug antibodies and association of random drug levels with efficacy in certolizumab pegol-treated patients with rheumatoid arthritis: results from the BRAGGSS cohort

OBJECTIVES

To evaluate (i) the association between random certolizumab drug levels, antidrug antibodies (ADAbs) and treatment response in patients with rheumatoid arthritis (RA); (ii) longitudinal factors associated with ADAbs and certolizumab drug levels.

METHODS

This prospective cohort included 115 patients with RA treated with certolizumab. Serum samples were collected at 3, 6 and 12 months following treatment initiation. Drug levels and ADAbs were measured using ELISA and radioimmunoassay, respectively, at 3, 6 and 12 months. Disease Activity Score in 28 joints (DAS28) were measured at each visit and 12 months European League Against Rheumatism (EULAR) response was calculated. Patient self-reported adherence was collected longitudinally. Ordinal logistic regression and generalised estimating equation were used to test the association: (i) between drug levels, from serum sampled and treatment response; (ii) between ADAbs and drug levels; (iii) patient-centred factors and drug levels.

RESULTS

ADAbs were detected in 37% (42/112 patients by 12 months). The presence of ADAbs were significantly associated with lower drug levels over 12 months (β=-0.037, 95% CI -0.055 to 0.018, p<0.0001) but not independently with 12 months EULAR response (β=0.0013 (95% CI -0.0032 to 0.00061), p=0.18). Drug level was associated with 12 months EULAR response (β=0.032 (95% CI 0.0011 to 0.063), p=0.042). In the multivariate model, ADAb level and adherence were significantly associated with drug concentrations.

CONCLUSIONS

This is the first study to demonstrate that higher certolizumab drug levels are associated with better 12 months EULAR response. ADAbs in certolizumab-treated patients with RA were detected at higher levels than previous studies and help determine the aetiology of a low drug level.

Intein-mediated site-specific synthesis of tumor-targeting protein delivery system: Turning PEG dilemma into prodrug-like feature

Poor tumor-targeted and cytoplasmic delivery is a bottleneck for protein toxin-based cancer therapy. Ideally, a protein toxin drug should remain stealthy in circulation for prolonged half-life and reduced side toxicity, but turn activated at tumor. PEGylation is a solution to achieve the first goal, but creates a hurdle for the second because PEG rejects interaction between the drugs and tumor cells therein. Such PEG dilemma is an unsolved problem in protein delivery. Herein proposed is a concept of turning PEG dilemma into prodrug-like feature. A site-selectively PEGylated, gelatinase-triggered cell-penetrating trichosanthin protein delivery system is developed with three specific aims. The first is to develop an intein-based ligation method for achieving site-specific modification of protein toxins. The second is to develop a prodrug feature that renders protein toxins remaining stealthy in blood for reduced side toxicity and improved EPR effect. The third is to develop a gelatinase activatable cell-penetration strategy for enhanced tumor targeting and cytoplasmic delivery. Of note, site-specific modification is a big challenge in protein drug research, especially for such a complicated, multifunctional protein delivery system. We successfully develop a protocol for constructing a macromolecular prodrug system with intein-mediated ligation synthesis. With an on-column process of purification and intein-mediated cleavage, the site-specific PEGylation then can be readily achieved by conjugation with the activated C-terminus, thus constructing a PEG-capped, cell-penetrating trichosanthin system with a gelatinase-cleavable linker that enables tumor-specific activation of cytoplasmic delivery. It provides a promising method to address the PEG dilemma for enhanced protein drug delivery, and importantly, a facile protocol for site-specific modification of such a class of protein drugs for improving their druggability and industrial translation.

Improvement of the Pharmacological Properties of Maize RIP by Cysteine-Specific PEGylation

To improve the pharmacological properties of maize ribosome-inactivating protein (maize RIP) for targeting HIV-infected cells, the previously engineered TAT-fused active form of maize RIP (MOD) was further engineered for cysteine-directed PEGylation. In this work, two potential antigenic sites, namely Lys-78 and Lys-264, were identified. They were mutated to cysteine residue and conjugated with PEG_5k or PEG_20k. The resultant PEG derivatives of MOD variants were examined for ribosome-inactivating activity, circulating half-life and immunogenicity. Our results showed that MOD-PEG conjugates had two- to five-fold lower biological activity compared to the wild-type. Mutation of the two sites respectively did not decrease the anti-MOD IgG and IgE level in mice, but the conjugation of PEG did dramatically reduce the antigenicity. Furthermore, pharmacokinetics studies demonstrated that attachment of PEG_20k prolonged the plasma half-life by five-fold for MOD-K78C and 17-fold for MOD-K264C, respectively. The site-specific mutation together with PEGylation therefore generated MOD derivatives with improved pharmacological properties.

Small sized EGFR1 and HER2 specific bifunctional antibody for targeted cancer therapy

Targeting tumors using miniature antibodies is a novel and attractive therapeutic approach, as these biomolecules exhibit low immunogenicity, rapid clearance, and high targeting specificity. However, most of the small-sized antibodies in existence do not exhibit marked anti-tumor effects, which limit their use in targeted cancer immunotherapy. To overcome this difficulty in targeting multiple biomarkers by combination therapies, we designed a new bifunctional antibody, named MaAbNA (multivalent antibody comprised of nanobody and affibody moieties), capable of targeting EGFR1 and HER2, which are widely overexpressed in a variety of tumor types. The small-sized (29 kDa) MaAbNA, which was expressed in E.coli, consists of one anti-EGFR1 nanobody and two anti-HER2 affibodies, and possesses high affinity (KD) for EGFR1 (~4.1 nM) and HER2 (~4.7 nM). In order to enhance its anti-tumor activity, MaAbNA was conjugated with adriamycin (ADM) using a PEG2000 linker, forming a new complex anticancer drug, MaAbNA-PEG2000-ADM. MaAbNA exhibited high inhibitory effects on tumor cells over-expressing both EGFR1 and HER2, but displayed minimal cytotoxicity in cells expressing low levels of EGFR1 and HER2. Moreover, MaAbNA-PEG2000-ADM displayed increased tumoricidal effects than ADM or MaAbNA alone, as well exhibited greater antitumor efficacy than EGFR1 (Cetuximab) and HER2 (Herceptin) antibody drugs. The ability of MaAbNA to regulate expression of downstream oncogenes c-jun, c-fos, c-myc, as well as AEG-1 for therapeutic potential was evaluated by qPCR and western-blot analyses. The antitumor efficacy of MaAbNA and its derivative MaAbNA-PEG2000-ADM were validated in vivo, highlighting the potential for use of MaAbNA as a highly tumor-specific dual molecular imaging probe and targeted cancer therapeutic.

PEGylation alleviates the non-specific toxicities of Alpha-Momorcharin and preserves its antitumor efficacy in vivo

Alpha-Momorcharin (α-MMC) is a ribosome inactivating protein from Momordica charantia with anti-tumor activity. Previously, we had observed that modification of α-MMC with polyethylene glycol (PEG) could reduce toxicity, but it also reduces its anti-tumor activity in vitro. This study aims to investigate whether the metabolism-extended properties of α-MMC resulting from PEGylation could preserve its anti-tumor efficacy in vivo through pharmacokinetics and antitumor experiments. The pharmacokinetics experiments were conducted in rats using the TCA (Trichloroacetic Acid) method. Antitumor activity in vivo was investigated in murine mammary carcinoma (EMT-6) and human mammary carcinoma (MDA-MB-231) transplanted tumor mouse models. The results showed that PEGylation increased the plasma half-life of α-MMC in rats from 6.2-7.5 h to 52-87 h. When administered at 1 mg/kg, α-MMC-PEG and α-MMC showed similar anti-tumor activities in vivo, with a T/C% of 38.56% for α-MMC versus 35.43% for α-MMC-PEG in the EMT-6 tumor model and 36.30% for α-MMC versus 39.88% for α-MMC-PEG in the MDA-MB-231 tumor model (p > 0.05). Importantly, at the dose of 3 mg/kg, all the animals treated with α-MMC died while the animals treated with α-MMC-PEG exhibited only moderate toxic reactions, and α-MMC-PEG exhibited improved anti-tumor efficacy with a T/C% (relative tumor growth rate) of 25.18% and 21.07% in the EMT-6 and MDA-MB-231 tumor models, respectively. The present study demonstrates that PEGylation extends the half-life of α-MMC and alleviates non-specific toxicity, thereby preserving its antitumor efficacy in vivo, and a higher lever of dosage can be used to achieve better therapeutic efficacy.

Peginterferon-α2b and ribavirin

Hepatitis C virus infection is among the leading causes of chronic liver disease in the USA and has a worldwide prevalence of approximately 300 million people. Chronic hepatitis C virus is the most common indication for liver transplantation in the USA. Due to the chronic nature of hepatitis C virus infection, these numbers are expected to grow fourfold in the next decade. Interferon-alpha(2b) monotherapy followed by combination therapy with ribavirin have been used to treat chronic hepatitis C virus with limited success. The development of pegylated interferon-alpha(2b), (Peg-intron, Schering-Plough) instituted the next chapter in hepatitis C virus therapy. The demonstration of its safety and efficacy led to a major trial studying coadministration with ribavirin for compensated chronic hepatitis C virus infection. Pegylated interferon combination therapy has improved efficacy over standard interferon combination therapy without an increase in adverse effects. This article reviews the data regarding pegylated interferon-alpha(2b) with ribavirin therapy. The pharmacokinetics and pharmacodynamics of combination therapy will be presented along with clinical trial data. The efficacy and ease of usage of Pegintron and ribavirin support its use for chronic hepatitis C virus infection.

Mutations for decreasing the immunogenicity and maintaining the function of core streptavidin

The defining property of core streptavidin (cSA) is not only its high binding affinity for biotin but also its pronounced thermal and chemical stability. Although potential applications of these properties including therapeutic methods have prompted much biological research, the high immunogenicity of this bacterial protein is a key obstacle to its clinical use. To this end, we have successfully constructed hypoimmunogenic cSA muteins in a previous report. However, the effects of these mutations on the physicochemical properties of muteins were still unclear. These mutations retained the similar electrostatic charges to those of wild-type (WT) cSA, and functional moieties with similar hydrogen bond pattern. Herein, we performed isothermal titration calorimetry, differential scanning calorimetry, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis to gain insight into the physicochemical properties and functions of these modified versions of cSA. The results indicated that the hypoimmunogenic muteins retained the biotin-binding function and the tetramer structure of WT cSA. In addition, we discuss the potential mechanisms underlying the success of these mutations in achieving both immune evasion and retention of function; these mechanisms might be incorporated into a new strategy for constructing hypoimmunogenic proteins.

Effects of receptor binding on plasma half-life of bifunctional transferrin fusion proteins

In contrast to the wide applications of recombinant bifunctional fusion proteins in clinical usage, the systematic study for the pharmacokinetics (PK) of bifunctional fusion proteins is left blank. In this report, recombinant fusion proteins consisting of transferrin (Tf) and growth hormone (GH) or granulocyte colony-stimulating factor (G-CSF) have been constructed as a model for studying the PK of bifunctional fusion proteins. The results showed that the insertion of different linkers between the two protein domains altered the binding affinities of the fusion proteins to both domain receptors, and that the fusion proteins' plasma half-lives were greatly affected. A strong correlation between GH receptor binding affinity and plasma half-life of GH-Tf fusion proteins was observed. In addition, we demonstrated that the intracellular processing after receptor binding plays an important role in determining the half-life of fusion proteins. While the binding of the GH domain to the GH receptor will lead to endocytosis and lysosomal degradation in target cells, binding of the Tf domain to the Tf receptor may recycle the fusion protein and prolong its plasma half-life. To further confirm the effects of receptor binding on plasma half-life, G-CSF-Tf bifunctional fusion proteins with the same three linkers as GH-Tf were evaluated. While the 3 fusion proteins showed a similar G-CSF receptor binding affinity, the G-CSF-Tf fusion protein with the higher Tf receptor binding affinity exhibited longer plasma half-life. The linker insertion further demonstrated the involvement of Tf in recycling and prolonging plasma half-life. Based on our results, a model was developed to summarize the factors in determining the PK of bifunctional fusion proteins. Our findings are useful for predicting the plasma half-lives, as well as for improving the pharmacokinetic profiles of therapeutic bifunctional fusion proteins by applying linker technology.

Purification of singly PEGylated α-lactalbumin using charged ultrafiltration membranes

One of the challenges in producing a PEGylated therapeutic protein is that the PEGylation reaction typically generates a mixture of both singly and multiply PEGylated species. The objective of this study was to examine the feasibility of using ultrafiltration for the purification of a singly PEGylated protein from the multiply PEGylated conjugates. Data were obtained with α-lactalbumin that was PEGylated with a 20 kDa activated PEG, with the ultrafiltration performed over a range of pH and ionic strength using both unmodified and negatively charged composite regenerated cellulose membranes. Purification of the singly PEGylated α-lactalbumin from the multiply PEGylated species was accomplished using a diafiltration process with a negatively charged membrane at pH 5 and an ionic strength of 0.4 mM, conditions that maximized the electrostatic exclusion of the multiply PEGylated species from the charged membrane. The diafiltration process provided more than 97% yield with greater than 20-fold purification between the singly and doubly PEGylated proteins and nearly complete removal of the more heavily PEGylated species. The singly PEGylated α-lactalbumin was recovered as a dilute filtrate solution, although this dilution could be eliminated using a cascade filtration or the final product could be re-concentrated in a second ultrafiltration as part of the final formulation. These results demonstrate the feasibility of using ultrafiltration for the purification of singly PEGylated protein therapeutics.

Quantitative determination of pegylated consensus interferon in rhesus monkey serum using a competitive enzyme-linked immunosorbent assay

A competitive enzyme-linked immunosorbent assay (ELISA) with generated mouse anti-consensus interferon (CIFN) antibody was developed for quantitative determination of pegylated consensus interferon (PEG-CIFN) in rhesus monkey serum. The operational concentrations of the original assay were determined using the chessboard method. ELISA working range was 10-5000 ng/ml, corresponding to a limit of quantification of 8.4 ng/ml in rhesus monkey serum. In a precision test, intra-assay CV ranged 1.8-9.6% and inter-assay CV ranged 3.5-12.7%. Relative recovery rate of this ELISA assay ranged from 102.65-115.77%, with RSD values ranging from 2.26-5.44%. Three groups of rhesus monkeys received 1250 microg/kg, 300 microg/kg, 150 microg/kg PEG-CIFN by subcutaneous administration, and blood samples were drawn via the femoral vein at the specified time points. PEG-CIFN in rhesus monkey serum was determined using the competitive ELISA, and the results were compared with antiviral activity assay. In conclusion, the competitive ELISA assay we developed has sufficient sensitivity, precision, and accuracy for the analysis of a rhesus monkey serum sample.

PEGylation of bacterial cocaine esterase for protection against protease digestion and immunogenicity

Enhancing cocaine metabolism by administration of cocaine esterase (CocE) has been considered as a promising treatment strategy for cocaine overdose and addiction, as CocE is the most efficient native enzyme yet identified for metabolizing the naturally occurring cocaine. A major obstacle to the clinical application of CocE, however, lies in its thermo-instability, rapid degradation by circulating proteases, and potential immunogenicity. PEGylation, namely by modifying a protein or peptide compound via attachment of polyethylene glycol (PEG) chains, has been proven to overcome such problems and was therefore exploited in this CocE investigation. The PEG-CocE conjugates prepared in this study showed a purity of greater than 93.5%. Attachment of PEG to CocE apparently inhibited the binding of anti-CocE antibodies to the conjugate, as demonstrated by the enzyme-linked immunosorbent assay (ELISA) assay. In addition, PEGylation yielded protection to CocE against thermal degradation and protease digestion. Furthermore, preliminary in vivo results suggested that, similarly to native CocE, the PEG-CocE conjugates were able to protect animals from cocaine-induced toxic effects. Overall, this study provides evidence that the PEGylation may serve as a tool to prolong CocE functionality in the circulation and reduce its potential immunogenicity.

A recombinant polypeptide extends the in vivo half-life of peptides and proteins in a tunable manner

Increasing the in vivo residence times of protein therapeutics could decrease their dosing frequencies. We show that genetic fusion of an unstructured recombinant polypeptide of 864 amino acids, called XTEN, to a peptide or protein provides an apparently generic approach to extend plasma half-life. Allometric scaling suggests that a fusion of XTEN to the exenatide peptide should increase exenatide half-life in humans from 2.4 h to a projected time of 139 h. We confirmed the biological activity of the exenatide-XTEN fusion in mice. As extended stability might exacerbate undesirable side effects in some cases, we show that truncating the XTEN sequence can regulate plasma half-life. XTEN lacks hydrophobic amino acid residues that often contribute to immunogenicity and complicate manufacture. Based on data on XTEN fusions to exenatide, glucagon, GFP and human growth hormone, we expect that XTEN will enable dosing of otherwise rapidly cleared protein drugs at up to monthly intervals in humans.

Novel peptide therapeutics for treatment of infections

As antibiotic resistance increases worldwide, there is an increasing pressure to develop novel classes of antimicrobial compounds to fight infectious disease. Peptide therapeutics represent a novel class of therapeutic agents. Some, such as cationic antimicrobial peptides and peptidoglycan recognition proteins, have been identified from studies of innate immune effector mechanisms, while others are completely novel compounds generated in biological systems. Currently, only selected cationic antimicrobial peptides have been licensed, and only for topical applications. However, research using new approaches to identify novel antimicrobial peptide therapeutics, and new approaches to delivery and improving stability, will result in an increased range of peptide therapeutics available in the clinic for broader applications.

Immunogenicity of biologically-derived therapeutics: assessment and interpretation of nonclinical safety studies

An evaluation of potential antibody formation to biologic therapeutics during the course of nonclinical safety studies and its impact on the toxicity profile is expected under current regulatory guidance and is accepted standard practice. However, approaches for incorporating this information in the interpretation of nonclinical safety studies are not clearly established. Described here are the immunological basis of anti-drug antibody formation to biopharmaceuticals (immunogenicity) in laboratory animals, and approaches for generating and interpreting immunogenicity data from nonclinical safety studies of biotechnology-derived therapeutics to support their progression to clinical evaluation. We subscribe that immunogenicity testing strategies should be adapted to the specific needs of each therapeutic development program, and data generated from such analyses should be integrated with available clinical and anatomic pathology, pharmacokinetic, and pharmacodynamic data to properly interpret nonclinical studies.

Safety of peginterferon in the treatment of chronic hepatitis C

BACKGROUND

Combination of 'pegylated' interferons (IFNs) plus ribavirin, the standard treatment of chronic hepatitis C (CHC), is frequently associated with side effects. Anticipation, recognition and proper management of these side effects are important to ensure compliance with therapy and achievement of sustained virologic response.

OBJECTIVE

To illustrate the side effect profile of pegIFN-alpha in the treatment of CHC.

METHODS

Studies and abstracts were identified through a computerized, English language literature search. Key search terms included peginterferon and CHC. Information available only in abstract form was retrieved from national and international hepatology associations.

RESULTS

Most adverse events occurring with combination therapy can be anticipated and managed appropriately; therefore, premature discontinuation of therapy owing to side effects is not required in most patients.

Bioreversibly crosslinked polyplexes of PEI and high molecular weight PEG show extended circulation times in vivo

Copolymers consisting of branched PEI 25 kDa grafted with high molecular weight PEG at a low degree of substitution were successfully synthesized using a simple two-step procedure. The resulting AB-type and ABA-type copolymers were tested for cytotoxicity and DNA condensation and complexation properties. Their polyplexes with plasmid DNA were characterized in terms of DNA size and surface charge, transfection efficiency and blood compatibility. Pharmacokinetic profiles of the complexes containing (32)P-labeled plasmid were assessed before and after surface crosslinking. A set of four copolymers containing one or two PEG 20 kDa or PEG 30 kDa chains was obtained. The cytotoxicity of PEI was strongly reduced after copolymerization. The copolymer polyplexes showed hydrodynamic diameters of less than 200 nm, comparable to PEI 25. Similarly, no reduction in DNA condensation and complexation properties was found. In fact, PEI-PEG(30 k) copolymers exhibited better condensation and complexation properties than PEI 25. The transfection efficiency of copolymer polyplexes was increased 10-fold compared to PEI 25 control and the hemolytic activity was markedly reduced. After intravenous injection into mice, plasmids complexed to PEI-PEG(30 k) copolymers resulted in significantly increased circulation times. After stabilizing the polyplexes with a redox sensitive, biodegradable crosslinker, blood levels of plasmid could be further increased up to 125% compared to PEI. These results demonstrate that polyplexes prepared using a combined strategy of surface crosslinking and PEGylation seem to provide promising properties as stable, long circulating vectors.

Purification and modification by polyethylene glycol of a new human basic fibroblast growth factor mutant-hbFGF(Ser25,87,92)

The mutant of human basic fibroblast growth factor (hbFGF), hbFGF(Ser25,87,92), which was constructed by replacing the cysteine residues at the positions of the 25th, the 87th and the 92nd with serine residues, was coupled to polyethylene glycol (PEG) with a molecular size of 20 kDa (20K) (PEG(20K)) to obtain hbFGF derivative, PEG(20K)-hbFGF(Ser25,87,92). The optimal modified reaction was conducted at 12 degrees C for 12h with the molar ratio of PEG(20K) to hbFGF(Ser25,87,92) of 30:1. The result of sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed that the modification rate was up to 60%. The PEGylated product retained binding affinity to heparin and could be purified by heparin affinity chromatography. Compared to hbFGF mutant, purified PEG(20K)-hbFGF(Ser25,87,92) retained about 34% of mitogenic activity. Heat-stability assay indicated that the modified product was more stable than the native protein at the temperature of 37 degrees C.

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.

Therapeutic peptides: technological advances driving peptides into development

As potential therapeutics, peptides offer several advantages over small molecules (increased specificity) and antibodies (small size). Nevertheless, a number of key issues have hampered their use as drug candidates. A series of new technologies have recently been developed that allow peptides to be viable drug candidates in areas usually restricted to protein therapeutics, such as monoclonal antibodies. These include the development of various types of peptide-conjugates that have lower rates of clearance and hence the potential to increase the exposure of peptide drug candidates in chronic diseases. Structural additions have also been made to peptides, including the use of unnatural amino acids, mainchain modifications and other novel substitutions, which have helped to improve peptide stability and further their therapeutic potential.

Y55 and D78 are crucial amino acid residues of a new IgE epitope on trichosanthin

Trichosanthin (TCS) possesses many biological and pharmaceutical activities, but its strong immunogenicity limits its clinical application. To reduce the immunogenicity of TCS, we modified the reported method for the prediction of antigenic site and identified two crucial amino acid residues (Y55 and D78) for a new epitope. We mutated these two residues into glycine and serine, respectively, and obtained three mutants, Y55G, D78S, and Y55G/D78S. These mutants induced less amount of Ig and IgG antibodies in C57BL/6J mice than wild-type TCS (wTCS) (p<0.01) and almost lost the ability to induce IgE antibody production. The mutants stimulated fewer TCS-specific B cells in C57BL/6J mice than wTCS (p<0.01). Compared with wTCS, Y55G, D78S, and Y55G/D78S lost 26.9%, 17.9%, and 98.7% specific binding ability to anti-TCS monoclonal antibody TCS4E9, respectively. These mutants still retained RNA N-glycosidase activity. In conclusion, Y55 and D78 are two crucial amino acid residues of a new IgE epitope on TCS, and their mutation reduces the immunogenicity of TCS, but still retained the enzymatic activity.

Trichosanthin suppresses the elevation of p38 MAPK, and Bcl-2 induced by HSV-1 infection in Vero cells

Trichosanthin (TCS) is a type 1 ribosome-inactivating protein (RIP) effective against HIV-1 and HSV-1 replication. The mechanism of its antiviral activity is not clear. Many believe that it is related to ribosome inactivation. Some RIPs and viral infection affect the phosphorylation of MAPK and Bcl-2 and these proteins may be the common element linking RIP and viral infection. This study investigated the effect of HSV-1 infection on p38 MAPK and Bcl-2 as well as possible interference by TCS. Results showed that HSV-1 infection induced an elevation of phosphorylated p38 and Bcl-2 in Vero cells, which could be partially blocked by TCS. At the same time, both viral replication and host cells viability were lowered. Viral replication, Vero cell viability, p38 MAPK and Bcl-2 were further reduced with the addition of a p38 MAPK inhibitor (SB203580). This suggested that TCS may interfere with MAPK and Bcl-2 signals generated by infection leading to inhibition of viral replication. In summary, our results demonstrated that HSV-1 infection in Vero cells induced an elevation of p38 MAPK and Bcl-2. TCS suppressed this rise and reduced viral replication. The MAPK family may play a role in the antiviral mechanism of TCS.

Strategies to improve plasma half life time of peptide and protein drugs

Due to the obvious advantages of long-acting peptide and protein drugs, strategies to prolong plasma half life time of such compounds are highly on demand. Short plasma half life times are commonly due to fast renal clearance as well as to enzymatic degradation occurring during systemic circulation. Modifications of the peptide/protein can lead to prolonged plasma half life times. By shortening the overall amino acid amount of somatostatin and replacing L: -analogue amino acids with D: -amino acids, plasma half life time of the derivate octreotide was 1.5 hours in comparison to only few minutes of somatostatin. A PEG(2,40 K) conjugate of INF-alpha-2b exhibited a 330-fold prolonged plasma half life time compared to the native protein. It was the aim of this review to provide an overview of possible strategies to prolong plasma half life time such as modification of N- and C-terminus or PEGylation as well as methods to evaluate the effectiveness of drug modifications. Furthermore, fundamental data about most important proteolytic enzymes of human blood, liver and kidney as well as their cleavage specificity and inhibitors for them are provided in order to predict enzymatic cleavage of peptide and protein drugs during systemic circulation.

Enhanced apoptotic action of trichosanthin in HIV-1 infected cells

Trichosanthin (TCS) is a type 1 ribosome-inactivating protein (RIP) effective against HIV-1 replication. The mechanism is not clear. Present results suggested that the antiviral action may be partly mediated through enhanced apoptosis on infected cells. TCS induced apoptosis in normal H9 cells and this action was more potent in those infected with HIV-1. In flow cytometry study, TCS induced larger population of apoptotic H9 cells chronically infected with HIV-1 in a dose-dependent manner. At TCS concentration of 25 microg/ml, 8.4% of normal H9 cells were found to be apoptotic whereas the same concentration induced 24.5% in HIV-1 chronically infected cells. Such difference was not found in the control experiments without TCS treatment. Two other studies supported this action. Cytotoxic study showed that cell viability was always lower in HIV-1 infected cells after TCS treatment, and DNA fragmentation study confirmed more laddering in infected cells. The mechanism of TCS induced apoptosis in normal or infected H9 cells is not clear. Results in this study demonstrated that TCS is more effective in inducing apoptosis in HIV-1 infected cells. This may explain in part the antiviral action of TCS.

Role of blood transfusion in trichosanthin-induced anaphylaxis

Trichosanthin (TCS) is a type 1 ribosome inactivating protein extracted from Chinese medicinal herb. It possesses various biological functions such as abortifacient, anti-tumor and anti-viral activities. Clinical trial of this compound against human immunodeficiency virus (HIV) had been conducted. However, its use is limited by its high immunogenicity that elicits hypersensitivity reaction. This may lead to fatal anaphylactic response. The study described an approach of using blood transfusion to reduce TCS induced anaphylaxis in rats using a cross-circulation model. A TCS-sensitized Sprague Dawley rat was connected to a normal rat via the femoral vessels in a cross-circulation circuit before antigenic challenge. The donor rat served as a blood exchange basin to lower the level of the blood-borne components responsible for the anaphylactic reaction in the sensitized rat. Our results showed that cross-circulation shortened the duration of circulatory hypotension and reduced mortality of TCS induced anaphylaxis. The control group not undergoing cross-circulation had a mortality of 50% at 2h post-TCS challenge and there was no mortality in the cross-circulation group. This demonstrated that prior blood transfusion can be one of the alternatives to reduce anaphylactic response of TCS.

Recent advances in trichosanthin, a ribosome-inactivating protein with multiple pharmacological properties

Trichosanthin (TCS), a ribosome-inactivating protein extracted from the root tuber of Chinese medicinal herb Trichosanthes kirilowii Maximowicz, has multiple pharmacological properties including abortifacient, anti-tumor and anti-HIV. It is traditionally used to induce abortion but its antigenicity and short plasma half-life have limited the repeated clinical administration. In this review, work to locating antigenic sites and prolonging plasma half-life are discussed. Studies on structure-function relationship and mechanism of cell entry are also covered. Recently, TCS has been found to induce apoptosis, enhance the action of chemokines and inhibit HIV-1 integrase. These findings give new insights on the pharmacological properties of TCS and other members of ribosome-inactivating proteins.

Protein carboxyl amidation increases the potential extent of protein polyethylene glycol conjugation

Chemical coupling of polyethylene glycol (PEG) to therapeutic proteins reduces their immunogenicity and prolongs their circulating half-life. The limitation of this approach is the number and distribution of sites on proteins available for PEGylation (the N terminus and the -amino group of lysines). To increase the extent of PEGylation, we have developed a method to increase the number of PEGylation sites in a model protein, recombinant methionine alpha,gamma-lyase (recombinant methioninase; rMETase), an enzyme cancer therapeutic cloned from Pseudomonas putida. rMETase was first PEGylated with methoxypolyethylene glycol succinimidyl glutarate-5000 with a molar ratio of PEG:rMETase of 15:1. The carboxyl groups of the initially PEGylated protein were then conjugated with diaminobutane, resulting in carboxyl amidation. This reaction was catalyzed by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide, a water-soluble carbodiimide. The steric hindrance provided by the PEG chains already coupled to the protein prevented cross-linking between rMETase molecules during the carboxyl amidation reaction. The carboxyl-amidated PEGylated rMETase was hyper-PEGylated at a molar ratio of PEG to PEG-rMETase of 60:1. Biochemical analysis indicated that 13 PEG chains were coupled to each subunit of rMETase after hyper-PEGylation compared with 6-8 PEG chains attached to the non-carboxyl-amidated PEG-rMETase. Approximately 15-20% of the non-PEGylated rMETase activity was retained in the hyper-PEGylated molecule. Immunogenicity of the hyper-PEG-rMETase was significantly reduced relative to PEG-rMETase and rMETase. Initial results suggest that hyper-PEGylation may become a new strategy for PEGylation of protein biologics.