Enhanced circulation half-life of site-specific PEGylated rhG-CSF: optimization of PEG molecular weight

Safety and efficacy of pegylated recombinant human granulocyte colony-stimulating factor during concurrent chemoradiotherapy for small-cell lung cancer: a retrospective, cohort-controlled trial

Objective

To investigate pegylated recombinant human granulocyte colony-stimulating factor (PEG-rhG-CSF) safety and efficacy in preventing hematological toxicity during concurrent chemoradiotherapy (CCRT) for small-cell lung cancer (SCLC).

Methods

We retrospectively assessed 80 SCLC patients treated with CCRT from January 2013 to December 2018 who received PEG-rhG-CSF within 48 hours after the end of chemotherapy, defined as prophylactic use, as the experimental group. An additional 80 patients who were not treated with PEG-rhG-CSF were matched 1:1 by the propensity score matching method and served as the control group. The main observations were differences in hematological toxicity, neutrophil changes, febrile neutropenia (FN) incidence and adverse reactions. Progression-free survival (PFS) and overall survival (OS) were analyzed with regular assessment and follow-up.

Results

The leukocyte, neutrophil, erythrocyte, and platelet counts and hemoglobin level decreased after CCRT, but the experimental group had slightly higher leukocyte and neutrophil counts than the control group (P < 0.05). The incidences of grade III-IV leukopenia (18.75% vs. 61.25%) and neutropenia (23.75% vs. 67.5%) in the experimental group were significantly lower than those in the control group (P < 0.05). The absolute neutrophil count was 4.17 ± 0.79 (× 10⁹/L) on day 1 and peaked 6.81 ± 2.37 (× 10⁹/L) on day 10 in the experimental group; the value in the control group was 2.81 ± 0.86 (× 10⁹/L) on day 1. It decreased significantly and reached the minimum 0.91 ± 0.53 (× 10⁹/L) on day 10 (P < 0.05). The experimental group had a lower FN incidence than the control group (P < 0.05). There was also no significant acute esophagitis or pulmonary toxicity. The treatment had no significant effect on PFS (11.4 months vs. 8.7 months, P = 0.958) or OS (23.9 months vs. 17.3 months, P = 0.325) over an 18.6-month median follow-up time.

Conclusion

PEG-rhG-CSF has good efficacy and safety in preventing hematological toxicity in SCLC patients during CCRT and has no significant effects on PFS or OS.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09644-8.

Process Development for the Production and Purification of PEGylated RhG-CSF Expressed in Escherichia coli

Background and objective:

Recombinant human granulocyte-colony stimulating factor (rhG-CSF) and its PEGylated form (PEG-GCSF) are used in the cancer therapy. Thus the development of a more cost-effectively method for expressing rhG-CSF and the PEGylation optimization of rhG-CSF by reaction engineering and subsequent the purification strategy is necessary.

Methods:

RhG-CSF expression in Escherichia coli BL21 (DE3) was carried out by auto-induction batch fermentation and improved for maximizing rhG-CSF productivity. After that, purified rhG-CSF was PEGylated using methoxy polyethylene glycol propionaldehydes (mPEG20-ALD). The various conditions effect of extraction and purification of rhG-CSF and PEG-GCSF were assayed.

Results:

The assessment results revealed that auto-induction batch cultivation strategy had maximum productivity and rhG-CSF purity was more than 99%. The obtained Data of rhG-CSF PEGylation displayed that the optimized conditions of rhG-CSF PEGylation and purification enhanced hemogenisity PEG-GCSF and managed reaction toward optimal yield of PEG-GCSF (70%) and purity of 99.9%. Findings from FTIR, CD, and fluorescence spectroscopy and bioassay revealed that PEGylation was executed exactly in the rhG-CSF N-terminus, and products maintained their conformation properties.

Conclusion:

Overall, the developed approach expanded strategies for high yield rhG-CSF by simplified auto-induction batch fermentation system and rhG-CSF PEGylation, which are simple and time-saving, economical and high efficiency.

Pegylated LyeTx I-b peptide is effective against carbapenem-resistant Acinetobacter baumannii in an in vivo model of pneumonia and shows reduced toxicity

The World Health Organization (WHO) has been warning about the importance of developing new drugs against superbugs. Antimicrobial peptides are an alternative in this context, most of them being involved in innate immunity, acting in various ways, and some even showing synergism with commercial antimicrobial agents. LyeTx I-b is a synthetic peptide derived from native LyeTx I, originally isolated from Lycosa erythrognatha spider venom. Although LyeTx I-b is active against several multidrug-resistant bacteria, it shows some hemolytic and cytotoxic effects. To overcome this hindrance, in the present study we PEGylated LyeTx I-b and evaluated its toxicity and in vitro and in vivo activities on pneumonia caused by multi-resistant Acinetobacter baumannii. PEGylated LyeTx I-b (LyeTx I-bPEG) maintained the same MIC value as the non- PEGylated peptide, showed anti-biofilm activity, synergistic effect with commercial antimicrobial agents, and did not induce resistance. Moreover, in vivo experiments showed its activity against pneumonia. Additionally, LyeTx I-bPEG reduced hemolysis up to 10 times, was approximately 2 times less cytotoxic to HEK-293 cells and 4 times less toxic to mice in acute toxicity models, compared to LyeTx I-b. Our results show LyeTx I-bPEG as a promising antimicrobial candidate, significantly active against pneumonia caused by multidrug-resistant A. baumannii.

A clinical study of pegylated recombinant human granulocyte colony stimulating factor (PEG-rhG-CSF) in preventing neutropenia during concurrent chemoradiotherapy of cervical cancer

Purpose

To evaluate the effectiveness and safety of pegylated recombinant human granulocyte colony stimulating factor (PEG-rhG-CSF) in preventing neutropenia during chemoradiotherapy in patients with cervical cancer.

Methods

From August 2018 to April 2020, 60 patients who were pathologically confirmed as cervical cancer were randomly divided into two groups at a ratio of 2:1: PEG-modified-rhG-CSF experimental group and control group. The primary endpoints were the incidence of grade 3–4 neutropenia. Secondary endpoints included the duration of grade 3–4 neutropenia, the incidence of grade 4 neutropenia, the incidence of febrile neutropenia (FN), delay rate of chemotherapy, prolonged time of chemotherapy, time to complete radiotherapy and safety.

Results

The incidence of grade 3–4 neutropenia in the experimental group was significantly lower than the control group (10% vs. 77.78%, P < 0.001). However, there was no statistical significance between the two groups in the duration of grade 3–4 neutropenia (3.75 days vs. 5.07 days, P = 0.871). The experimental group was better than the control group in the incidence of grade 4 neutropenia, the incidence of FN and delay rate of chemotherapy, and the difference was statistically significant (P < 0.05). Besides, the prolonged time of chemotherapy and the time to complete radiotherapy in the experimental group were less than those in the control group, but the difference was not statistically significant (P > 0.05). The incidence of adverse events in the experimental group and control group were 55.00 and 94.44%, respectively, and the difference was statistically significant (P = 0.003).

Conclusion

PEG-rhG-CSF preventive treatment used in the course of chemoradiotherapy for patients with cervical cancer can reduce the incidence of neutropenia and improve the incidence of delayed chemotherapy cycles.

Trial registration

ClinicalTrials.gov, NCT04542356. Registered 9 September 2020 - Retrospectively registered.

Development of Site-Specific PEGylated Granulocyte Colony Stimulating Factor With Prolonged Biological Activity

Currently, amino-terminal PEGylated human granulocyte colony stimulating factor (huG-CSF) is used to prevent and treat neutropenia. Although huG-CSF has been used as a drug for more than 20 years, it has three significant drawbacks: (i) it relies on PEG aldehyde for PEGylation of the alpha-amino group of the first amino acid, and this leads to non-specific PEGylation of the epsilon amino group of lysine residues within the G-CSF; (ii) longer-acting G-CSF variants are desirable to reduce the risk of chemotherapy-associated neutropenia; and (iii) G-CSF cannot be administered on the day of chemotherapy. In an attempt to overcome the above drawbacks, we engineered cysteine variants of G-CSF to facilitate the maleimide PEG-based site-specific PEGylation that leads to a highly homogenous PEGylated product. Importantly, we have demonstrated that 20 kDa thiol-reactive PEG conjugated by maleimide chemistry to the Cys2 G-CSF variant exhibits leukocyte proliferative activity similar to that of the commercially available G-CSF conjugated with aldehyde PEG in a neutropenia mice model. Moreover, we have demonstrated that PEGylation of the cysteine variant of huG-CSF with higher molecular weight PEGs, such as 30 kDa PEG and 40 kDa PEG, leads to significantly prolonged leukocyte proliferation activity compared to the variant conjugated with 20 kDa PEG. Importantly, even a half-dose of the engineered variant conjugated with 40 kDa PEG exhibited significantly longer biological activity than the commercially available 20 kDa PEGylated huG-CSF. Finally, we have demonstrated that administration of the engineered variant conjugated with 40 kDa PEG on the day of administration of cyclophosphamide for inducing neutropenia in mice can alleviate neutropenia through leukocyte proliferation. In summary, this study provides the design of site-specific PEGylated huG-CSF variants with improved therapeutic potential. It opens the possibility of long-acting and same-day prophylactic administration of G-CSF after chemotherapy drug regimens. These results may pave the way for the development of potential G-CSF derivatives possessing longer half-lives and favorable clinical attributes.

Process analytical technology application for protein PEGylation using near infrared spectroscopy: G-CSF as a case study

Conjugation of protein therapeutics with polymers like polyethylene glycol (PEG) has been shown to increase their therapeutic efficiency. However, manufacturing of PEGylated drugs requires an additional, carefully controlled reaction step after purifying the protein, followed by further purification of over- and under-PEGylated variants. In this work, we have used a combined spectroscopic and statistical approach for monitoring and control of the PEGylation reaction for G-CSF using near infrared spectroscopy (NIRS). An online NIRS probe deployed in the reaction vessel has been used to track conversion of G-CSF into monoPEGylated and multiPEGylated forms using calibrated partial least squares regression models on the NIRS spectra which are collected in real time every 3 s. A pH probe integrated with a peristaltic pump facilitates automated quenching of the reaction at the targeted time. The NIRS spectra have also been used to build a batch evolution model for the reaction from end-to-end, including the addition of the reactants to the reaction vessel, the progress of the reaction for 70 min, and the final quenching with Tris base. Online spectra are compared against the statistical process control charts of the batch evolution model in real time to detect deviations as soon as they occur. The system was demonstrated for four common deviations in the PEGylation process, namely: delayed quenching time, wrong concentration of reducing agent added, wrong PEG to G-CSF ratio, and wrong sequence of addition of reactants. The system was able to identify all four deviations in real time and alert the operator to take control actions. The PAT approach suggested here embraces the quality by design framework and can be generalized for manufacturing scale monitoring and control of different biotechnology reactions with spectroscopic signatures.

Metabolism of bioconjugate therapeutics: why, when, and how?

Bioconjugation of therapeutic agents has been used as a selective drug delivery platform for many therapeutic areas. Bioconjugates are prepared by the covalent linkage of active compounds (small or large molecule) to a carrier molecule (lipids, proteins, peptides, carbohydrates, and polymers) through a chemical linker. The linkage of the active component to a carrier molecule enhances the therapeutic window through a targeted delivery and by reducing toxicity. Bioconjugates also possess improved pharmacokinetic properties such as a long half-life, increased stability, and cleavage by intracellular enzymes/environment. However, premature cleavage of the bioconjugates and the resulting metabolites/catabolites may produce undesirable toxic effects and, hence, it is critical to understand cleavage mechanisms, metabolism of bioconjugates, and translatability to human in the discovery stages. This article provides a comprehensive overview of linker cleavage pathways and catabolism/metabolism of antibody-drug conjugates, glycoconjugates, polymer-drug conjugates, lipid-drug conjugates, folate-targeted small molecule-drug conjugates, and drug-drug conjugates.

Expression, Purification, and Polyethylene Glycol Site-Specific Modification of Recombinant Human Interleukin 24 in Escherichia coli

Interleukin 24 (IL-24) has a broad spectrum of specific antitumor activities without affecting normal cells. The recombinant human IL-24 (rhIL-24) expressed in E. coli has low biological activity due to lack of necessary glycosylation modification. In this study, based on the modification of the non-glycosylated IL-24 with polyethylene glycol (PEG), we aimed to improve the stability and prolong its half-life in vivo. Firstly, the recombinant plasmid containing the hIL-24 cDNA was prepared by the prokaryotic-expression plasmid pET-28a and transformed into E. coli BL21. After induced by isopropyl β-D-thiogalactoside (IPTG), the target protein rhIL-24 was expressed as insoluble inclusion body, which was solubilized and denatured by 6 M guanidine hydrochloride. The denatured rhIL-24 was diluted to refold in the optimized buffer overnight at the protein concentration of 0.1 mg/mL. The refolded rhIL-24 was mainly in the form of soluble aggregate, but high-purity monomer rhIL-24 was obtained through size exchange chromatography with the addition of SDS in elution buffer. The tertiary structure of rhIL-24 was confirmed by fluorescence spectroscopy. Western blot analysis showed that rhIL-24 could be site-specifically modified by mPEG5000-ALD. Methyl thiazolyl tetrazolium (MTT) assay showed no significant difference between mPEG5000-ALD-rhIL-24 and rhIL-24 in inhibiting the growth of melanoma cell line A375 in vitro. Pharmacokinetic studies showed that PEG modification could significantly improve the stability and prolong the half-life of rhIL-24 from 8.41 to 13.2 h. The data strongly suggested that mPEG-ALD 5000 could site-specifically modify rhIL-24 expressed in E. coli. The PEG modification significantly prolonged the half-life of rhIL-24 without reducing its antitumor activity in vitro.

Molecular insights into the improved clinical performance of PEGylated interferon therapeutics: a molecular dynamics perspective

PEGylation is a widely adopted process to covalently attach a polyethylene glycol (PEG) polymer to a protein drug for the purpose of optimizing drug clinical performance. While the outcomes of PEGylation in imparting pharmacological advantages have been examined through experimental studies, the underlying molecular mechanisms remain poorly understood. Using interferon (IFN) as a representative model system, we carried out comparative molecular dynamics (MD) simulations of free PEGx, apo-IFN, and PEGx-IFN (x = 50, 100, 200, 300) to characterize the molecular-level changes in IFN introduced by PEGylation. The simulations yielded molecular evidence directly linked to the improved protein stability, bioavailability, retention time, as well as the decrease in protein bioactivity with PEG conjugates. Our results indicate that there is a tradeoff between the benefits and costs of PEGylation. The optimal PEG chain length used in PEGylation needs to strike a good balance among the competing factors and maximizes the overall therapeutic efficacy of the protein drug. We anticipate the study will have a broad implication for protein drug design and development, and provide a unique computational approach in the context of optimizing PEGylated protein drug conjugates.

We discovered molecular evidence that links PEGylation to improved clinical performance, yet at the expense of decreased bioactivity. Our computational approach will facilitate PEGylated protein drug design and optimize its overall therapeutic efficacy.

Towards the next generation of biomedicines by site-selective conjugation

Bioconjugates represent an emerging class of medicines, which offer therapeutic opportunities overtaking those of the individual components. Many novel bioconjugates have been explored in order to address various emerging medical needs. The last decade has witnessed the exponential growth of new site-selective bioconjugation techniques, however very few methods have made the way into human clinical trials. Here we discuss various applications of site-selective conjugation in biomedicines, including half-life extension, antibody-drug conjugates, conjugate vaccines, bispecific antibodies and cell therapy. The review is intended to highlight both the progress and challenges, and identify a potential roadmap to address the gap.

Preparation and preliminary characterization of recombinant neurolysin for in vivo studies

The goal of this study was to produce milligram quantities of pure, catalytically active, endotoxin-free recombinant neurolysin (rNln) in standard laboratory conditions for use as a research tool. To this end, we transformed E. coli cells with a plasmid construct for polyhistidine-tagged rNln, selected a high-expressing clone and determined the optimal time-point for translation of rNln. rNln was purified to homogeneity from the soluble pool of the cell lysate using Ni-NTA affinity and size-exclusion chromatography, followed by removal of endotoxins. Using this protocol ∼3mg pure, catalytically active and nearly endotoxin-free (≈0.003EU/μg protein) rNln was reproducibly obtained from 1l of culture. Lack of cytotoxicity of rNln preparation was documented in cultured mouse cells, whereas stability in whole mouse blood. Intraperitonealy administered rNln in mice reached the systemic circulation in intact and enzymatically active form with Tmax of 1h and T1/2 of ∼30min. Administration of rNln (2 and 10mg/kg) did not alter arterial blood pressure, heart rate, body temperature and blood glucose levels in mice. These studies demonstrate that the rNln preparation is suitable for cell culture and in vivo studies and can serve as a research tool to investigate the (patho)physiological function of this peptidase.

PEGylation and its impact on the design of new protein-based medicines

PEGylation is the covalent conjugation of PEG to therapeutic molecules. Protein PEGylation is a clinically proven approach for extending the circulation half-life and reducing the immunogenicity of protein therapeutics. Most clinically used PEGylated proteins are heterogeneous mixtures of PEG positional isomers conjugated to different residues on the protein main chain. Current research is focused to reduce product heterogeneity and to preserve bioactivity. Recent advances and possible future directions in PEGylation are described in this review. So far protein PEGylation has yielded more than 10 marketed products and in view of the lack of equally successful alternatives to extend the circulation half-life of proteins, PEGylation will still play a major role in drug delivery for many years to come.

Local drug delivery for enhancing fracture healing in osteoporotic bone

Fragility fractures can cause significant morbidity and mortality in patients with osteoporosis and inflict a considerable medical and socioeconomic burden. Moreover, treatment of an osteoporotic fracture is challenging due to the decreased strength of the surrounding bone and suboptimal healing capacity, predisposing both to fixation failure and non-union. Whereas a systemic osteoporosis treatment acts slowly, local release of osteogenic agents in osteoporotic fracture would act rapidly to increase bone strength and quality, as well as to reduce the bone healing period and prevent development of a problematic non-union. The identification of agents with potential to stimulate bone formation and improve implant fixation strength in osteoporotic bone has raised hope for the fast augmentation of osteoporotic fractures. Stimulation of bone formation by local delivery of growth factors is an approach already in clinical use for the treatment of non-unions, and could be utilized for osteoporotic fractures as well. Small molecules have also gained ground as stable and inexpensive compounds to enhance bone formation and tackle osteoporosis. The aim of this paper is to present the state of the art on local drug delivery in osteoporotic fractures. Advantages, disadvantages and underlying molecular mechanisms of different active species for local bone healing in osteoporotic bone are discussed. This review also identifies promising new candidate molecules and innovative approaches for the local drug delivery in osteoporotic bone.

Establishment of the first international standard for PEGylated granulocyte colony stimulating factor (PEG-G-CSF): report of an international collaborative study

We assessed the feasibility of developing a suitable international reference standard for determination of in vitro biological activity of human sequence recombinant PEG-G-CSF products with a 20kD linear PEG linked to the N-terminal methionyl residue of G-CSF (INN Filgrastim), produced using a conjugation process and coupling chemistry similar to that employed for the lead PEGfilgrastim product. Based on initial data which showed that the current WHO 2nd international standard, IS for G-CSF (09/136) or alternatively, a PEG-G-CSF standard with a unitage traceable to the G-CSF IS may potentially serve as the IS for PEG-G-CSF products, two candidate preparations of PEG-G-CSF were formulated and lyophilized at NIBSC. These preparations were tested by 23 laboratories using in vitro bioassays in a multi-centre collaborative study. Results indicated that on the basis of parallelism, the current WHO 2nd IS for G-CSF or any of the PEG-G-CSF samples could be used as the international standard for PEG-G-CSF preparations. However, because of the variability in potency estimates seen when PEG-G-CSF preparations were compared with the current WHO 2nd IS for G-CSF, a candidate PEG-G-CSF was suitable as the WHO IS. The preparation 12/188 was judged suitable to serve as the WHO IS based on in vitro biological activity data. Therefore, the preparation coded 12/188 was established by the WHO Expert Committee on Biological Standardization (ECBS) in 2013 as the WHO 1st IS for human PEGylated G-CSF with an assigned in vitro bioactivity of 10,000IU per ampoule.

Bone marrow cell mobilization by the systemic use of granulocyte colony-stimulating factor (GCSF) improves wound bed preparation

Innovative approaches are needed to accelerate the healing of human chronic wounds not responding to conventional therapies. An evolving and promising treatment is the use of stem cells. Our group has previously described the use of expanded (in vitro) autologous stem cells aspirated from human bone marrow and applied topically in a fibrin spray to human acute and chronic wounds. More recently, we have sought ways to mobilize stem cells directly from the bone marrow, without in vitro expansion. In this report, we show that systemic injections of granulocyte colony-stimulating factor (GCSF) can mobilize stem cells from bone marrow into the peripheral blood and then to the wound site. Our objectives were to optimize parameters for this method by using mouse models and proof of principle in a human chronic wound situation. Mice were injected for 5 days with 2 different formulations of GCSF and compared to control saline. To monitor stem cell mobilization, flow cytometric measurements of Sca-1 and c-Kit and colony-forming cell assays were performed. Full-thickness tail wounds in mice were created and monitored for healing, and polyvinyl alcohol sponges were implanted dorsally to assess collagen accumulation. To determine bone marrow stem cell homing to the wound site, chimeric mice transplanted with Green Fluorescent Protein bone marrow cells were scanned by live imaging. Additionally, as proof of principle, we tested the systemic GCSF approach in a patient with a nonhealing venous ulcer. Our findings lay the ground work and indicate that the systemic administration of GCSF is effective in mobilizing bone marrow stem cells into the peripheral blood and to the wound site. These findings are associated with an increased accumulation of collagen and promising results in terms of wound bed preparation and healing.

PEGylated interferon beta-1a in the treatment of multiple sclerosis - an update

Current standard immunomodulatory therapy with interferons (IFNs) for relapsing-remitting multiple sclerosis (MS) exhibits proven, but limited, efficacy and increased side effects due to the need of frequent application of the drug. Therefore, there is a need for more effective and tolerable drugs. Due to their small size, optimization of therapy with IFNs in MS by PEGylation is feasible. PEGylation of an IFN means that at least one molecule of polyethylene glycol (PEG) is covalently added. This modification is a standard procedure to increase the stability, solubility, half-life, and efficacy of a drug, and is applied in several drugs and diseases. Currently, a therapy regimen applying PEG-IFN beta-1a in MS is being developed to achieve an optimized relationship between therapy-related side effects and pharmacokinetic/pharmacodynamic efficacy. Phase I studies demonstrated that subcutaneous PEG-IFN beta-1a at a dose of 125 μg every 2 or 4 weeks might be at least as efficient and safe as the current standard therapy with IFN beta-1a. A global Phase III clinical study is investigating the efficacy of PEG-IFN beta-1a in terms of reduction of the relapse rate in relapsing-remitting MS patients. The latest primary safety and efficacy analysis after 1 year has revealed a favorable risk-benefit profile with no significant difference between dosing regimens. Compared to placebo, the annualized relapse rate was reduced by about one-third and new or newly enlarging T2 brain lesions were reduced by about one-third when dosing every 4 weeks or by two-thirds when dosing every 2 weeks. This presents a significant effect of the dosing interval, favoring administration every 2 weeks. Chronic administration of PEGylated proteins mostly at toxic concentrations causes vacuolation of renal epithelium in animals, which - along with the issue of occurrence of anti-PEG antibodies - has to be addressed by Phase IV studies.

A new site-specific monoPEGylated filgrastim derivative prepared by enzymatic conjugation: Production and physicochemical characterization

We describe the preparation and characterization of a new monoPEGylated derivate of a recombinant form of filgrastim (methionyl human granulocite colony stimulating factor, rh-Met-G-CSF), BK0026, prepared by enzymatic site-specific 20kDa PEG conjugation to glutamine 135 residue by microbial transglutaminase catalyzed reaction. BK0026 was purified to a clinical grade by a single cation exchange chromatography step and characterized by using a panel of physicochemical analyses. NH(2)-terminal sequence and peptide mapping demonstrated no differences between the primary structure of BK0026 and the non-PEGylated filgrastim. The circular dichroism and fluorescence spectroscopy showed the preservation of high order protein structure. The single conjugation site on glutamine 135 was identified by endoproteinase Glu-C peptide mapping combined with mass spectrometry analysis and NH(2)-terminal sequence of the PEGylated peptides. BK0026 purity as well as product- and process-related contaminants was determined by several analytical methods, which showed that BK0026 is stable for more than 2 years when stored at 4-8°C. The advantages of enzymatic PEGylation of filgrastim are the absolute specificity of glutamine 135 conjugation combined with high PEGylation yields under very mild reaction conditions. The new site specific monoPEGylated filgrastim is a promising candidate for preclinical and clinical studies aimed at developing a long-lasting treatment of neutropenia in oncological patients under chemotherapy treatments.

Site-specific PEGylation at histidine tags

The efficacy of protein-based medicines can be compromised by their rapid clearance from the blood circulatory system. Achieving optimal pharmacokinetics is a key requirement for the successful development of safe protein-based medicines. Protein PEGylation is a clinically proven strategy to increase the circulation half-life of protein-based medicines. One limitation of PEGylation is that there are few strategies that achieve site-specific conjugation of PEG to the protein. Here, we describe the covalent conjugation of PEG site-specifically to a polyhistidine tag (His-tag) on a protein. His-tag site-specific PEGylation was achieved with a domain antibody (dAb) that had a 6-histidine His-tag on the C-terminus (dAb-His(6)) and interferon α-2a (IFN) that had an 8-histidine His-tag on the N-terminus (His(8)-IFN). The site of PEGylation at the His-tag for both dAb-His(6)-PEG and PEG-His(8)-IFN was confirmed by digestion, chromatographic, and mass-spectral studies. A methionine was also inserted directly after the N-terminal His-tag in IFN to give His(8)Met-IFN. Cyanogen bromide digestion studies of PEG-His(8)Met-IFN were also consistent with PEGylation at the His-tag. By using increased stoichiometries of the PEGylation reagent, it was possible to conjugate two separate PEG molecules to the His-tag of both the dAb and IFN proteins. Stability studies followed by in vitro evaluation confirmed that these PEGylated proteins retained their biological activity. In vivo PK studies showed that all of the His-tag PEGylated samples displayed extended circulation half-lives. Together, our results indicate that site-specific, covalent PEG conjugation at a His-tag can be achieved and biological activity maintained with therapeutically relevant proteins.

Role of tumor vascular architecture in drug delivery

Tumor targeted drug delivery has the potential to improve cancer care by reducing non-target toxicities and increasing the efficacy of a drug. Tumor targeted delivery of a drug from the systemic circulation, however, requires a thorough understanding of tumor pathophysiology. A growing or receding (under the impact of therapy) tumor represents a dynamic environment with changes in its angiogenic status, cell mass, and extracellular matrix composition. An appreciation of the salient characteristics of tumor vascular architecture and the unique biochemical markers that may be used for targeting drug therapy is important to overcome barriers to tumor drug therapy and to facilitate targeted drug delivery. This review discusses the unique aspects of tumor vascular architecture that need to be overcome or exploited for tumor targeted drug delivery.

In vivo anti-tumor activity of polypeptide HM-3 modified by different polyethylene glycols (PEG)

HM-3, designed by our laboratory, is a polypeptide composed of 18 amino acids. Pharmacodynamic studies in vivo and in vitro indicated that HM-3 could inhibit endothelial cell migration and angiogenesis, thereby inhibiting tumor growth. However, the half-life of HM-3 is short. In this study, we modified HM-3 with different polyethylene glycols (PEG) in order to reduce the plasma clearance rate, extend the half-life in the body, maintain a high concentration of HM-3 in the blood and increase the therapeutic efficiency. HM-3 was modified with four different types of PEG with different molecular weights (ALD-mPEG_5k, ALD-mPEG_10k, SC-mPEG_10k and SC-mPEG_20k), resulting in four modified products (ALD-mPEG_5k-HM-3, ALD-mPEG_10k-HM-3, SC-mPEG_10k-HM-3 and SC-mPEG_20k-HM-3, respectively). Anti-tumor activity of these four modified HM-3 was determined in BALB/c mice with Taxol as a positive control and normal saline as a negative control. Tumor weight inhibition rates of mice treated with Taxol, HM-3, ALD-mPEG_5k-HM-3, ALD-mPEG_10k-HM-3, SC-mPEG_10k-HM-3 and SC-mPEG_20k-HM-3 were 44.50%, 43.92%, 37.95%, 31.64%, 20.27% and 50.23%, respectively. Tumor inhibition rates in the Taxol, HM-3 and SC-mPEG_20k-HM-3 groups were significantly higher than that in the negative control group. The efficiency of tumor inhibition in the SC-mPEG_20k-HM-3 group (drug treatment frequency: once per two days) was better than that in the HM-3 group (drug treatment frequency: twice per day). In addition, tumor inhibition rate in the SC-mPEG_20k-HM-3 group was higher than that in the taxol group. We conclude that SC-mPEG_20k-HM-3 had a low plasma clearance rate and long half-life, resulting in high anti-tumor therapeutic efficacy in vivo. Therefore, SC-mPEG_20k-HM-3 could be potentially developed as new anti-tumor drugs.

Delivery of therapeutic proteins

The safety and efficacy of protein therapeutics are limited by three interrelated pharmaceutical issues, in vitro and in vivo instability, immunogenicity and shorter half-lives. Novel drug modifications for overcoming these issues are under investigation and include covalent attachment of poly(ethylene glycol) (PEG), polysialic acid, or glycolic acid, as well as developing new formulations containing nanoparticulate or colloidal systems (e.g., liposomes, polymeric microspheres, polymeric nanoparticles). Such strategies have the potential to develop as next generation protein therapeutics. This review includes a general discussion on these delivery approaches.