Efficient GLP-1 gene delivery using two-step transcription amplification plasmid system with a secretion signal peptide and arginine-grafted bioreducible polymer

Progress in arginine-based gene delivery systems

Arginine based gene delivery systems with enhanced membrane penetration and lower cytotoxicity greatly enrich the gene vectors library and outline a new development direction of gene delivery.

Functional polymers of gene delivery for treatment of myocardial infarct

Ischemic heart disease is rapidly growing as the common cause of death in the world. It is a disease that occurs as a result of coronary artery stenosis and is caused by the lack of oxygen within cardiac muscles due to an imbalance between oxygen supply and demand. The conventional medical therapy is focused on the use of drug eluting stents, coronary-artery bypass graft surgery and anti-thrombosis. Gene therapy provides great opportunities for treatment of cardiovascular disease. In order for gene therapy to be successful, the development of proper gene delivery systems and hypoxia-regulated gene expression vectors is the most important factors. Several non-viral gene transfer methods have been developed to overcome the safety problems of viral transduction. Some of which include plasmids that regulate gene expression that is controlled by environment specific promoters in the transcriptional or the translational level. This review explores polymeric gene carriers that target the myocardium and hypoxia-inducible vectors, which regulate gene expression in response to hypoxia, and their application in animal myocardial infarction models.

Bioreducible polymers for therapeutic gene delivery

Most currently available cationic polymers have significant acute toxicity concerns such as cellular toxicity, aggregation of erythrocytes, and entrapment in the lung capillary bed, largely due to their poor biocompatibility and non-degradability under physiological conditions. To develop more intelligent polymers, disulfide bonds are introduced in the design of biodegradable polymers. Herein, the sustained innovations of biomimetic nano-sized constructs with bioreducible poly(disulfide amine)s demonstrate a viable clinical tool for the treatment of cardiovascular disease, anemia, diabetes, and cancer.

Enhanced Incretin Effects of Exendin-4 Expressing Chimeric Plasmid Based On Two-Step Transcription Amplification System with Dendritic Bioreducible Polymer for the Treatment of Type 2 Diabetes

Glucagon-like peptide 1 (GLP-1) agonist, exenxdin-4, is currently being advanced as a promising diabetes remedy via a variety of incretin actions similar with GLP-1. In this study, we investigated an effective anti-diabetic therapy via exendin-4 expressing chimeric plasmid based on two-step transcription amplification (TSTA) system with dendrimer-type bioreducible polymer for more improved incretin-based gene therapy. Arginine-grafted poly (cystaminebisacrylamide-diaminohexane) (ABP)-conjugated poly (amido amine) (PAMAM) dendrimer (PAM-ABP) was used as gene carrier. PAM-ABP/chimeric DNA polyplex was markedly elevated exendin-4 expression in ectopic cells as well as increased insulin production through an enhanced activation of protein kinase K (PKA) induced by up-regulation of exendin-4-stimulated cyclic adenosine monophosphate (cAMP) in pancreatic β-cell. Consistent with these results, intravenous administration of PAM-ABP/chimeric DNA polyplex improved glucoregulotory effects, as well as increased insulin secretion by high expression of exendin-4 in blood in type 2 diabetic mice with no any toxicity. Our exendin-4 system can be attributed to provide a potential diabetes therapeutic agent for improved incretin gene therapy.

Recent advances in chitosan-based nanoparticles for oral delivery of macromolecules

Chitosan (CS), a cationic polysaccharide, is widely regarded as a safe and efficient intestinal absorption enhancer of therapeutic macromolecules, owing to its inherent mucoadhesive feature and ability to modulate the integrity of epithelial tight junctions reversibly. By using CS-based nanoparticles, many studies have attempted to protect the loaded macromolecules against acidic denaturation and enzymatic degradation, prolong their intestinal residence time, and increase their absorption by the intestinal epithelium. Derivatives of CS such as quaternized CS, thiolated CS and carboxylated CS have also been examined to further enhance its effectiveness in oral absorption of macromolecular drugs. This review article describes the synthesis of these CS derivatives and their characteristics, as well as their potential transport mechanisms of macromolecular therapeutics across the intestinal biological membrane. Recent advances in using CS and its derivatives as carriers for oral delivery of hydrophilic macromolecules and their effects on drug transport are also reviewed.

Therapeutic targeting of chitosan-PEG-folate-complexed oncolytic adenovirus for active and systemic cancer gene therapy

Adenovirus (Ad)-based cancer therapies have shown much promise. However, until now, Ad has only been delivered directly to primary tumors because the therapeutic efficacy of systemic delivery is limited by the immune response of the host, short blood circulation times, and non-specific liver uptake of Ad. In order to circumvent the issues regarding systemic delivery and to increase the safety and efficacy of Ad therapies, the surface of oncolytic Ad was coated with cationic polymer chitosan via ionic crosslinking (Ad/chitosan), after which polyethylene glycol (PEG) and/or folic acid (FA) was chemically conjugated onto the surface of Ad/chitosan, generating Ad/chitosan-FA, Ad/chitosan-PEG, and Ad/chitosan-PEG-FA nanocomplex. The FA-coordinated Ad nanocomplexes (Ad/chitosan-FA & Ad/chitosan-PEG-FA) elicited folate receptor (FR)-selective cancer cell killing efficacy. In vivo administration of Ad/chitosan-PEG or Ad/chitosan-PEG-FA into mice demonstrated that PEGylation greatly increased blood circulation time, resulting in 9.0-fold and 48.9-fold increases at 24h after injection compared with naked Ad, respectively. In addition, generation of Ad-specific neutralizing antibodies in mice treated with Ad/chitosan-PEG-FA was markedly decreased by 75.3% compared with naked Ad. The quantitative polymerase chain reaction assay results showed a 285.0-fold increase in tumor tissues and a 378-fold reduction of Ad/chitosan-PEG-FA in liver tissues compared with naked Ad. Bioluminescence imaging study further supported the enhanced tumor-to-liver ratio of Ad/chitosan-PEG-FA. Consequently, systemic delivery of Ad/chitosan-PEG-FA significantly inhibited the growth of FR-positive tumor, decreasing 52.8% compared to the naked Ad-treated group. Importantly, PEGylated oncolytic Ad nanocomplexes showed no elevation of both alanine transaminase and aspartate transaminase levels, demonstrating that systemically delivered Ad-related hepatic damage can be completely eliminated with PEG conjugation. In sum, these results demonstrate that conjugation of chitosan-PEG-FA to oncolytic Ad significantly improves antitumor efficacy and safety profiles, suggesting that Ad/chitosan-PEG-FA has potential as a therapeutic agent to target FR-positive cancer via systemic administration.

Delivery of two-step transcription amplification exendin-4 plasmid system with arginine-grafted bioreducible polymer in type 2 diabetes animal model

Exendin-4, glucagon-like peptide 1 (GLP-1) receptor agonist, is an exocrine hormone, which has potent insulinotropic actions similar to GLP-1 such as stimulating insulin biosynthesis, facilitating glucose concentration dependent insulin secretion, slowing gastric emptying, reducing food intake and stimulating β-cell proliferation. Exendin-4, also, has a longer half-life than GLP-1, due to its resistance to degradation by dipeptidyl peptidase-IV (DPP-IV). In spite of its many advantages as a therapeutic agent for diabetes, its clinical application is still restricted. Thus, to improve the activity of exendin-4 in vivo, gene therapy system was developed as an alternative method. An exendin-4 expression system was constructed using the two-step transcription amplification (TSTA) system, which is composed of pβ-Gal4-p65 and pUAS-SP-exendin-4 with combining the advantages of signal peptide (SP) in order to facilitate its secretion in ectopic cells or tissue. Arginine-grafted cyctaminebisacrylamide-diaminohexane polymer (ABP) was used as a gene carrier. Increased expression of exendin-4, glucose dependent insulin secretion in NIT-1 insulinoma cells, and high insulin expression in the presence of DPP-IV were evaluated in vitro after delivery of ABP/TSTA-SP-exendin-4. Blood glucose levels in diabetic mice were decreased dramatically from the third day for experimental period after single intravenous administration with ABP/TSTA-SP-exendin-4. The highest insulinotropic effect of exendin-4 was also observed in the ABP/TSTA/SP-exendin-4-treated mice groups, compared with the others groups from the 3rd day after injection. TSTA exendin-4 expression system with SP and ABP polymer has a potential gene therapy for the treatment of type 2 diabetes.

Polymer-based delivery of glucagon-like Peptide-1 for the treatment of diabetes

The incretin hormones, glucagon-like peptide-1 (GLP-1) and its receptor agonist (exendin-4), are well known for glucose homeostasis, insulinotropic effect, and effects on weight loss and food intake. However, due to the rapid degradation of GLP-1 by dipeptidylpeptidase-IV (DPP-IV) enzyme and renal elimination of exendin-4, their clinical applications have been restricted. Although exendin-4 has longer half-life than GLP-1, it still requires frequent injections to maintain efficacy for the treatment of diabetes. In recent decades, various polymeric delivery systems have been developed for the delivery of GLP-1 and exendin-4 genes or peptides for their long-term action and the extra production in ectopic tissues. Herein, we discuss the modification of the expression cassettes and peptides for long-term production and secretion of the native peptides. In addition, the characteristics of nonviral or viral system used for a delivery of a modified GLP-1 or exendin-4 are described. Furthermore, recent efforts to improve the biological half-life of GLP-1 or exendin-4 peptide via chemical conjugation with various smart polymers via chemical conjugation compared with native peptide are discussed.

Post-translational regulated and hypoxia-responsible VEGF plasmid for efficient secretion

Gene therapy using angiogenic genes has emerged as a potentially viable alternative treatment strategy for myocardial ischemia. Non-specific expression of angiogenic genes, however, may result in side effects, including the growth of occult tumors. Regulation of gene expression may help to avoid the occurrence of these side effects. In this study, a plasmid expressing vascular endothelial growth factor (VEGF) was constructed with an oxygen dependent degradation (ODD) domain and a secretion signal peptide (SP) in order to stabilize the VEGF protein and facilitate the secretion of VEGF protein, specifically under hypoxic conditions. We found that this plasmid, pβ-SP-ODD-VEGF, expresses the SP-ODD-VEGF protein at increased levels under hypoxic conditions compared to normoxic conditions. Since the size of the ODD domain is almost the same as that of VEGF, the ODD-VEGF fusion protein may have lower secretion efficiency. To address this issue, a furin recognition site was located between the ODD domain and the VEGF site to facilitate elimination of the SP-ODD domain from the fusion protein before its secretion. This optimizes the likelihood that the VEGF secreted from the target cells will be wild-type VEGF. Treatment with a furin inhibitor reduced the secretion efficiency of the VEGF, indicating that furin digestion increases the secretion of VEGF. The secreted wild-type VEGF facilitated the growth of endothelial cells more efficiently under hypoxic conditions than normoxic conditions. These results suggest that this plasmid, pβ-SP-ODD-VEGF, warrants further study as a more efficient form of hypoxia-inducible gene therapy for the treatment of myocardial ischemia.