Conjugation of staphylokinase with the arabinogalactan-PEG conjugate: Study on the immunogenicity, in vitro bioactivity and pharmacokinetics

Extracellular DNA Traps: Origin, Function and Implications for Anti-Cancer Therapies

Extracellular DNA may serve as marker in liquid biopsies to determine individual diagnosis and prognosis in cancer patients. Cell death or active release from various cell types, including immune cells can result in the release of DNA into the extracellular milieu. Neutrophils are important components of the innate immune system, controlling pathogens through phagocytosis and/or the release of neutrophil extracellular traps (NETs). NETs also promote tumor progression and metastasis, by modulating angiogenesis, anti-tumor immunity, blood clotting and inflammation and providing a supportive niche for metastasizing cancer cells. Besides neutrophils, other immune cells such as eosinophils, dendritic cells, monocytes/macrophages, mast cells, basophils and lymphocytes can also form extracellular traps (ETs) during cancer progression, indicating possible multiple origins of extracellular DNA in cancer. In this review, we summarize the pathomechanisms of ET formation generated by different cell types, and analyze these processes in the context of cancer. We also critically discuss potential ET-inhibiting agents, which may open new therapeutic strategies for cancer prevention and treatment.

PEGylation and antioxidant effects of a human glutathione peroxidase 1 mutant

Human glutathione peroxidase1 (hGPx1) is a good antioxidant and potential drug, but the limited availability and poor stability of hGPx1 have affected its development and application. To solve this problem, we prepared a hGPx1 mutant (GPx1M) with high activity in an Escherichia coli BL21(DE3)cys auxotrophic strain using a single protein production (SPP) system. In this study, the GPx1M was conjugated with methoxypolyethylene glycol-succinimidyl succinate (SS-mPEG, M_w = 5 kDa) chains to enhance its stability. SS-mPEG-GPx1M and GPx1M exhibited similar enzymatic activity and stability toward pH and temperature change, and in a few cases, SS-mPEG-GPx1M was discovered to widen the range of pH stability and increase the temperature stability. Lys 38 was confirmed as PEGylated site by liquid-mass spectrometry. H9c2 cardiomyoblast cells and Sprague-Dawley (SD) rats were used to evaluate the effects of GPx1M and SS-mPEG-GPx1M on preventing or alleviating adriamycin (ADR)-mediated cardiotoxicity, respectively. The results indicated that GPx1M and SS-mPEG-GPx1M had good antioxidant effects in vitro and in vivo, and the effect of SS-mPEG-GPx1M is more prominent than GPx1M in vivo. Thus, PEGylation might be a promising method for the application of GPx1M as an important antioxidant and potential drug.

Conjugation with inulin improves the environmental stability of haloalkane dehalogenase DhaA

Haloalkane dehalogenase DhaA catalyzes the hydrolytic cleavage of carbon-halogen bonds and produces alcohol, a proton and a halide. However, DhaA suffers from the poor environmental stability, such as sensitivity to high temperature, low pH, hypersaline and organic solvent. In order to improve the environmental stability of DhaA, DhaA was covalently conjugated with inulin, a hydrophilic polysaccharide in the present study. Each DhaA was averagely conjugated with 7∼8 inulin molecules. The conjugated inulin could form a hydration layer around DhaA, which increased the conformational rigidity and decreased the entropy of the enzyme. Conjugation of inulin maintained 75.5 % of the enzymatic activity of DhaA and slightly altered the structure of DhaA. As compared with DhaA, the conjugate (inu-DhaA) showed slightly different kinetic parameters (K_m of 2.9 μmol/L and K_cat of 1.0 s^-1). Inulin conjugation could delay the structural unfolding and/or slow the protonation process of DhaA under undesirable environment, including the long-term storage, low pH, hypersaline and organic solvent stability. As a result, the environmental stability of DhaA was markedly increased upon conjugation with inulin. Thus, inulin conjugation was an effective approach to enhance the environmental stability of DhaA.

Construction of a novel Staphylokinase (SAK) mutant with low immunogenicity and its evaluation in rhesus monkey

The heterologous nature of SAK, a thrombolytic drug, elicits high titers of neutralizing antibodies, which limits its clinical use. Here, we aim to establish a SAK mutant with equivalent activity to the wild type but reduced antigenicity, which may allow for multiple injections. Biosun software was used to predict SAK antigenic epitopes, and several main epitopes were modified by gene deletion and mutation. Ten SAK mutants were constructed, and their thrombolytic activity and immunogenicity were analyzed in vitro. SAK6, with a high expression level (45%), similar thrombolytic activity, and lower antibody reaction, was chosen for in vivo analysis in rhesus monkey. In the nearly 8-month experimental period, the antibody level of the SAK6 group was significantly lower than that of the SAK group. Moreover, only 5% of SAK activity was retained, whereas 75.6% of SAK6 activity was retained after incubating with respective antiserum. Overall, these results demonstrated that SAK6, established through comprehensive site-directed mutagenesis program, had identical thrombolytic activity to SAK, low immunogenicity, and less side effects, demonstrating its efficient clinical potential for thrombus disease.

The Importance of Poly(ethylene glycol) Alternatives for Overcoming PEG Immunogenicity in Drug Delivery and Bioconjugation

Poly(ethylene glycol) (PEG) is widely used as a gold standard in bioconjugation and nanomedicine to prolong blood circulation time and improve drug efficacy. The conjugation of PEG to proteins, peptides, oligonucleotides (DNA, small interfering RNA (siRNA), microRNA (miRNA)) and nanoparticles is a well-established technique known as PEGylation, with PEGylated products have been using in clinics for the last few decades. However, it is increasingly recognized that treating patients with PEGylated drugs can lead to the formation of antibodies that specifically recognize and bind to PEG (i.e., anti-PEG antibodies). Anti-PEG antibodies are also found in patients who have never been treated with PEGylated drugs but have consumed products containing PEG. Consequently, treating patients who have acquired anti-PEG antibodies with PEGylated drugs results in accelerated blood clearance, low drug efficacy, hypersensitivity, and, in some cases, life-threatening side effects. In this succinct review, we collate recent literature to draw the attention of polymer chemists to the issue of PEG immunogenicity in drug delivery and bioconjugation, thereby highlighting the importance of developing alternative polymers to replace PEG. Several promising yet imperfect alternatives to PEG are also discussed. To achieve asatisfactory alternative, further joint efforts of polymer chemists and scientists in related fields are urgently needed to design, synthesize and evaluate new alternatives to PEG.

Antibodies against polyethylene glycol in human blood: A literature review

Polyethylene glycol (PEG) conjugation, i.e. PEGylation, is a successful strategy to improve the pharmacokinetics and pharmacodynamics of biopharmaceuticals. In the past few decades, PEGylation technology has developed tremendously, and >15 PEGylated therapeutics have been brought to market, with more in development. However, the widely accepted assumption that PEG would have no antigenicity or immunogenicity is increasingly challenged with popularization of PEGylation technique. Although PEGylation indeed reduces the immunogenicities of the modified molecules, and even appears to completely eliminate their immunogenicities, yet emerging clinical evidence of anti-PEG antibodies (including both pre-existing and PEGylated therapeutics-treatment induced anti-PEG antibodies) have been attracted more and more attention. Anti-PEG antibodies were detected in not only patients treated with PEGylated therapeutics but also PEGylated drugs treatment-naïve individuals with a prevalence from <1% to 72%. In patients, the existing anti-PEG antibodies may attenuate therapeutic efficacy of PEGylated drugs and increase adverse effects. Although there is no golden standard avenue, several types of methods, including passive hemagglutination, Western Blot, enzyme linked immunosorbent assay, flow cytometry, Meso Scale Discovery technology, Acoustic Membrane Microparticle assay, and surface plasmon resonace technique, were established and used to screen, confirm and quantitatively detect anti-PEG antibodies. Herein, we focused on reviewing the prevalence of anti-PEG antibodies in healthy and PEGylated therapeutics-treated patients, and highlighting the detection methods for pre-screening and quantitative detection of anti-PEG antibodies.