Gene transfer with poly-melittin peptides

Endolysosomal trapping of therapeutics and endosomal escape strategies

Internalizing therapeutic molecules or genes into cells and safely delivering them to the target tissue where they can perform the intended tasks is one of the key characteristics of the smart gene/drug delivery vector. Despite much research in this field, endosomal escape continues to be a significant obstacle to the development of effective gene/drug delivery systems. In this review, we discuss in depth the several types of endocytic pathways involved in the endolysosomal trapping of therapeutic agents. In addition, we describe numerous mechanisms involved in nanoparticle endosomal escape. Furthermore, many other techniques are employed to increase endosomal escape to minimize entrapment of therapeutic compounds within endolysosomes, which have been reviewed at length in this study.

Melittin analog p5RHH enhances recombinant adeno-associated virus transduction efficiency

OBJECTIVE

Melittin and its derivative have been developed to support effective gene delivery systems. Their ability to facilitate endosomal release enhances the delivery of nanoparticle-based gene therapy. Nevertheless, its potential application in the context of viral vectors has not received much attention. Therefore, we would like to optimize the rAAV vector by Melittin analog to improve the transduction efficiency of rAAV in liver cancer cells and explore the mechanism of Melittin analog on rAAV.

METHODS

Various melittin-derived peptides were inserted into loop VIII of the capsid protein in recombinant adeno-associated virus vectors. These vectors carrying either gfp or fluc genes were subjected to quantitative polymerase chain reaction assays and transduction assays in human embryonic kidney 293 (HEK293T) cells to investigate the efficiency of vector production and gene delivery. In addition, the ability of a specific p5RHH-rAAV vector to deliver genes was examined through in vitro transduction of different cultured cells and in vivo tail vein administration to C57BL/6 mice. Finally, the intricate details of the vector-mediated transduction mechanisms were explored by using pharmacological inhibitors of every stage of the rAAV2 intracellular life cycle.

RESULTS

A total of 76 melittin-related peptides were identified from existing literature. Among them, CMA-3, p5RHH and aAR3 were found to significantly inhibit transduction of rAAV2 vector crude lysate. The p5RHH-rAAV2 vectors efficiently transduced not only rAAV-potent cell lines but also cell lines previously considered resistant to rAAV. Mechanistically, bafilomycin A1, a vacuolar endosome acidification inhibitor, completely inhibited the transgene expression mediated by the p5RHH-rAAV2 vectors. Most importantly, p5RHH-rAAV8 vectors also increased hepatic transduction in vivo in C57BL/6 mice.

CONCLUSION

The incorporation of melittin analogs into the rAAV capsids results in a significant improvement in rAAV-mediated transgene expression. While further modifications remain an area of interest, our studies have substantially broadened the pharmacological prospects of melittin in the context of viral vector-mediated gene delivery. Please cite this article as: Meng J, He Y, Yang H, Zhou L, Wang S, Feng X, Al-shargi OY, Yu X, Zhu L, Ling, C. Melittin analog p5RHH enhances recombinant adeno-associated virus transduction efficiency. J Integr Med. 2024; 22(1): 72-82.

Melittin-Based Nano-Delivery Systems for Cancer Therapy

Melittin (MEL) is a 26-amino acid polypeptide with a variety of pharmacological and toxicological effects, which include strong surface activity on cell lipid membranes, hemolytic activity, and potential anti-tumor properties. However, the clinical application of melittin is restricted due to its severe hemolytic activity. Different nanocarrier systems have been developed to achieve stable loading, side effects shielding, and tumor-targeted delivery, such as liposomes, cationic polymers, lipodisks, etc. In addition, MEL can be modified on nano drugs as a non-selective cytolytic peptide to enhance cellular uptake and endosomal/lysosomal escape. In this review, we discuss recent advances in MEL’s nano-delivery systems and MEL-modified nano drug carriers for cancer therapy.

The Reduced-Charge Melittin Analogue MelP5 Improves the Transfection of Non-Viral DNA Nanoparticles

Melittin is a 26 amino acid amphiphilic alpha-helical peptide derived from honeybee venom. Prior studies have incorporated melittin into non-viral delivery systems to effect endosomal escape of DNA nanoparticles and improve transfection efficiency. Recent advances have led to the development of two newer melittin analogues, MelP5 and Macrolittin 70, with improved pore formation in lipid bilayers while possessing fewer positive charges relative to natural melittin. Consequently, MelP5 and Macrolittin 70 were conjugated through a disulfide bond to a DNA binding polyacridine peptide. The resulting peptide conjugates were used to prepare DNA nanoparticles to compare their relative endosomolytic potency by transfection of HepG2 cells. Melittin and MelP5 conjugates were equally potent at mediating in vitro gene transfer, whereas PEGylation of DNA nanoparticles revealed improved transfection with MelP5 relative to melittin. The results demonstrate the ability to substitute a potent, reduced charge analogue of melittin to improve overall DNA nanoparticle biocompatibility needed for in vivo testing.

A Global Review on Short Peptides: Frontiers and Perspectives

Peptides are fragments of proteins that carry out biological functions. They act as signaling entities via all domains of life and interfere with protein-protein interactions, which are indispensable in bio-processes. Short peptides include fundamental molecular information for a prelude to the symphony of life. They have aroused considerable interest due to their unique features and great promise in innovative bio-therapies. This work focusing on the current state-of-the-art short peptide-based therapeutical developments is the first global review written by researchers from all continents, as a celebration of 100 years of peptide therapeutics since the commencement of insulin therapy in the 1920s. Peptide "drugs" initially played only the role of hormone analogs to balance disorders. Nowadays, they achieve numerous biomedical tasks, can cross membranes, or reach intracellular targets. The role of peptides in bio-processes can hardly be mimicked by other chemical substances. The article is divided into independent sections, which are related to either the progress in short peptide-based theranostics or the problems posing challenge to bio-medicine. In particular, the SWOT analysis of short peptides, their relevance in therapies of diverse diseases, improvements in (bio)synthesis platforms, advanced nano-supramolecular technologies, aptamers, altered peptide ligands and in silico methodologies to overcome peptide limitations, modern smart bio-functional materials, vaccines, and drug/gene-targeted delivery systems are discussed.

Peptides as a material platform for gene delivery: Emerging concepts and converging technologies

Successful gene therapies rely on methods that safely introduce DNA into target cells and enable subsequent expression of proteins. To that end, peptides are an attractive materials platform for DNA delivery, facilitating condensation into nanoparticles, delivery into cells, and subcellular release to enable protein expression. Peptides are programmable materials that can be designed to address biocompatibility, stability, and subcellular barriers that limit efficiency of non-viral gene delivery systems. This review focuses on fundamental structure-function relationships regarding peptide design and their impact on nanoparticle physical properties, biologic activity, and biocompatibility. Recent peptide technologies utilize multi-dimensional structures, non-natural chemistries, and combinations of peptides with lipids to achieve desired properties and efficient transfection. Advances in DNA cargo design are also presented to highlight further opportunities for peptide-based gene delivery. Modern DNA designs enable prolonged expression compared to traditional plasmids, providing an additional component that can be synergized with peptide carriers for improved transfection. Peptide transfection systems are poised to become a flexible and efficient platform incorporating new chemistries, functionalities, and improved DNA cargos to usher in a new era of gene therapy.

Antimicrobial peptide AR-23 derivatives with high endosomal disrupting ability enhance poly(l-lysine)-mediated gene transfer

Background

pH‐sensitive peptides are a relatively new strategy for conquering the poor endosomal release of cationic polymer‐mediated transfection. Modification of antimicrobial peptides by exchanging positively‐charged residues with negatively‐charged glutamic acid residues (Glu) greatly improves its lytic activity at the endosomal pH, which could improve cationic polymer‐mediated transfection.

Methods

In the present study, we investigated the effect of the number of Glu substituted for positively‐charged residues on the endosomal escape activity of AR‐23 and the ability of mutated AR‐23 with respect to enhancing cationic polymer‐mediated transfection. Three analogs were synthesized by replacing the positively‐charged residues in the AR‐23 sequence with Glu one‐by‐one.

Results

The pH‐sensitive lysis ability of the peptides, the effect of peptides on the physicochemical characteristics, the intracellular trafficking, the transfection efficiency and the cytotoxicity of the polyplexes were determined. Increased lytic activity of peptides was observed with the increased number of Glu replacement in the AR‐23 sequence at acidic pH. The number of Glu substituted for positively‐charged residues of AR‐23 dramatically affects its lysis ability at neutral pH. Triple‐Glu substitution in the AR‐23 sequence greatly improved poly(l‐lysine)‐mediated gene transfection efficiency at the same time as maintaining low cytotoxicity.

Conclusions

The results indicate that replacement of positively‐charged residues with sufficient Glu residues may be considered as a method for designing pH‐sensitive peptides, which could be applied as potential enhancers for improving cationic polymer‐mediated transfection.

Applications of RNA interference in the treatment of arthritis

RNA interference (RNAi) is a cellular mechanism for post-transcriptional gene regulation mediated by small interfering RNA (siRNA) and microRNA. siRNA-based therapy holds significant promise for the treatment of a wide-range of arthritic diseases. siRNA selectively suppresses the expression of a gene product and can thus achieve the specificity that is lacking in small molecule inhibitors. The potential use of siRNA-based therapy in arthritis, however, has not progressed to clinical trials despite ample evidence for efficacy in preclinical studies. One of the main challenges to clinical translation is the lack of a suitable delivery vehicle to efficiently and safely access diverse pathologies. Moreover, the ideal targets in treatment of arthritides remain elusive given the complexity and heterogeneity of these disease pathogeneses. Herein, we review recent preclinical studies that use RNAi-based drug delivery systems to mitigate inflammation in models of rheumatoid arthritis and osteoarthritis. We discuss a self-assembling peptide-based nanostructure that demonstrates the potential of overcoming many of the critical barriers preventing the translation of this technology to the clinic.

Bioresponsive polyplexes - chemically programmed for nucleic acid delivery

INTRODUCTION

The whole delivery process of nucleic acids is very challenging. Appropriate carrier systems are needed, which show extracellular stability and intracellular disassembly. Viruses have developed various strategies to meet these requirements, as they are optimized by biological evolution to transfer genetic information into host cells. Taking viruses as models, smart synthetic carriers can be designed, mimicking the efficient delivery process of viral infection. These 'synthetic viruses' are pre-programmed and respond to little differences in their microenvironment, caused by either exogenous or endogenous stimuli.

AREAS COVERED

This review deals with polymer-based, bioresponsive nanosystems (polyplexes) for the delivery of nucleic acids. Strategies utilizing pH-responsiveness, redox-responsiveness as well as sensitivity towards enzymes will be described more in detail. Systems, which respond to other endogenous triggers (i.e. reactive oxygen species, adenosine triphosphate, hypoxia), will be briefly illustrated. Moreover, some examples for combined bioresponsiveness will be presented.

EXPERT OPINION

Bioresponsive polyplexes are a smart way to facilitate programmed, timely delivery of nucleic acids to desired, specific sites. Nevertheless, further optimization is necessary to improve the still moderate transfection efficiency and specificity - also in regard to medical translation. For this purpose, precise carrier structures are desirable and stability issues of bioresponsive systems must be considered.

Chinese Medicine Protein and Peptide in Gene and Cell Therapy

The success of gene and cell therapy in clinic during the past two decades as well as our expanding ability to manipulate these biomaterials are leading to new therapeutic options for a wide range of inherited and acquired diseases. Combining conventional therapies with this emerging field is a promising strategy to treat those previously-thought untreatable diseases. Traditional Chinese medicine (TCM) has evolved for thousands of years in China and still plays an important role in human health. As part of the active ingredients of TCM, proteins and peptides have attracted long-term enthusiasm of researchers. More recently, they have been utilized in gene and cell therapy, resulting in promising novel strategies to treat both cancer and non-cancer diseases. This manuscript presents a critical review on this field, accompanied with perspectives on the challenges and new directions for future research in this emerging frontier.

Design of Poly-l-Glutamate-Based Complexes for pDNA Delivery

Due to the polyanionic nature of DNA, typically cationic or neutral delivery vehicles have been used for gene delivery. As a new approach, this study focuses on the design, development, and validation of nonviral polypeptide-based carriers for oligonucleotide delivery based on a negatively charged poly-l-glutamic acid (PGA) backbone partly derivatized with oligoaminoamide residues. To this end, PGA-derivatives modified with different pentameric succinyl tetraethylene pentamines (Stp₅ ) are designed. Optionally, histidines for modulation of endosomal buffer capacity and cysteines for pDNA complex stabilization are included, followed by characterization of biophysical properties and gene transfer efficiency in N2a neuroblastoma or 4T1 breast cancer cells.

Design of pH-sensitive peptides from natural antimicrobial peptides for enhancing polyethylenimine-mediated gene transfection

BACKGROUND

Poor endosomal release is a major barrier of polyplex-mediated gene transfection. Antimicrobial peptides (AMPs) are commonly used to improve polyethylenimine (PEI)-mediated gene transfection by increasing endosomal release. In the present study, we designed novel pH-sensitive peptides that highly enhance transfection efficiency compared to their parent peptides.

METHODS

Two analogues of melittin (Mel) and RV-23 (RV) were synthesized by replacing the positively-charged residues in their sequences with glutamic acid residues. The pH-sensitive lysis ability of the peptides, the effect of the peptides on physicochemical characteristics, the intracellular trafficking, the transfection efficiency, and the cytotoxicity of the polyplexes were determined.

RESULTS

The acidic peptides showed pH-sensitive lytic activity. The hemolytic activity of acidic peptides at pH 5.0 was higher than that at pH 7.4. The incorporation of acidic peptides did not affect the DNA binding ability of PEI but affected the physicochemical characteristics of the PEI/DNA polyplexes, which may be beneficial for endosomal release and gene transfection. The incorporation of acidic peptides into PEI/DNA polyplexes enhanced the PEI-mediated transfection efficiency corresponding to up to 42-fold higher luciferase activity compared to that of PEI alone.

CONCLUSIONS

The results of the present study indicate that replacement of positively-charged residues with glutamic acid residues in the AMP sequence yields pH-sensitive peptides, which enhance the transfection efficiency of PEI/DNA polyplexes in various cell lines.

Journey to the Center of the Cell: Current Nanocarrier Design Strategies Targeting Biopharmaceuticals to the Cytoplasm and Nucleus

New biopharmaceutical molecules, potentially able to provide more personalized and effective treatments, are being identified through the advent of advanced synthetic biology strategies, sophisticated chemical synthesis approaches, and new analytical methods to assess biological potency. However, translation of many of these structures has been significantly limited due to the need for more efficient strategies to deliver macromolecular therapeutics to desirable intracellular sites of action. Engineered nanocarriers that encapsulate peptides, proteins, or nucleic acids are generally internalized into target cells via one of several endocytic pathways. These nanostructures, entrapped within endosomes, must navigate the intracellular milieu to orchestrate delivery to the intended destination, typically the cytoplasm or nucleus. For therapeutics active in the cytoplasm, endosomal escape continues to represent a limiting step to effective treatment, since a majority of nanocarriers trapped within endosomes are ultimately marked for enzymatic degradation in lysosomes. Therapeutics active in the nucleus have the added challenges of reaching and penetrating the nuclear envelope, and nuclear delivery remains a preeminent challenge preventing clinical translation of gene therapy applications. Herein, we review cutting-edge peptide- and polymer-based design strategies with the potential to enable significant improvements in biopharmaceutical efficacy through improved intracellular targeting. These strategies often mimic the activities of pathogens, which have developed innate and highly effective mechanisms to penetrate plasma membranes and enter the nucleus of host cells. Understanding these mechanisms has enabled advances in synthetic peptide and polymer design that may ultimately improve intracellular trafficking and bioavailability, leading to increased access to new classes of biotherapeutics.

A role for peptides in overcoming endosomal entrapment in siRNA delivery - A focus on melittin

siRNA has the possibility to revolutionize medicine by enabling highly specific and efficient silencing of proteins involved in disease pathogenesis. Despite nearly 20 years of research dedicated to translating siRNA from a research tool into a clinically relevant therapeutic, minimal success has been had to date. Access to RNA interference machinery located in the cytoplasm is often overlooked, but must be considered when designing the next generation of siRNA delivery strategies. Peptide transduction domains (PTDs) have demonstrated moderate siRNA transfection, which is primarily limited by endosomal entrapment. Strategies aimed at overcoming endosomal entrapment associated with peptide vectors are reviewed here, including osmotic methods, lipid conjugation, and fusogenic peptides. As an alternative to traditional PTD, the hemolytic peptide melittin exhibits the native capacity for endosomal disruption but causes cytotoxicity. However, appropriate packaging and protection of melittin with activation and release in the endosomal compartment has allowed melittin-based strategies to demonstrate both in vitro and in vivo safety and efficacy. These data suggest that melittin's membrane disruptive properties can enable safe and effective endosomolysis, building a case for melittin as a key component in a new generation of siRNA therapeutics.

"Evolving nanoparticle gene delivery vectors for the liver: What has been learned in 30 years"

Nonviral gene delivery to the liver has been under evolution for nearly 30years. Early demonstrations established relatively simple nonviral vectors could mediate gene expression in HepG2 cells which understandably led to speculation that these same vectors would be immediately successful at transfecting primary hepatocytes in vivo. However, it was soon recognized that the properties of a nonviral vector resulting in efficient transfection in vitro were uncorrelated with those needed to achieve efficient nonviral transfection in vivo. The discovery of major barriers to liver gene transfer has set the field on a course to design biocompatible vectors that demonstrate increased DNA stability in the circulation with correlating expression in liver. The improved understanding of what limits nonviral vector gene transfer efficiency in vivo has resulted in more sophisticated, low molecular weight vectors that allow systematic optimization of nanoparticle size, charge and ligand presentation. While the field has evolved DNA nanoparticles that are stable in the circulation, target hepatocytes, and deliver DNA to the cytosol, breaching the nucleus remains the last major barrier to a fully successful nonviral gene transfer system for the liver. The lessons learned along the way are fundamentally important to the design of all systemically delivered nanoparticle nonviral gene delivery systems.

Polymers for nucleic acid transfer-an overview

For the last five decades cationic polymers have been used for nucleic acids transfection. Our understanding of polymer-nucleic acid interactions and their rational use in delivery has continuously increased. The great improvements in macromolecular chemistry and the recognition of distinct biological extra- and intracellular delivery hurdles triggered several breakthrough developments, including the discovery of natural and synthetic polycations for compaction of nucleic acids into stable nanoparticles termed polyplexes; the incorporation of targeting ligands and surface-shielding of polyplexes to enable receptor-mediated gene delivery into defined target tissues; and strongly improved intracellular transfer efficacy by better endosomal escape of vesicle-trapped polyplexes into the cytosol. These experiences triggered the development of second-generation polymers with more dynamic properties, such as endosomal pH-responsive release mechanisms, or biodegradable units for improved biocompatibility and intracellular release of the nucleic acid pay load. Despite a better biological understanding, significant challenges such as efficient nuclear delivery and persistence of gene expression persist. The therapeutic perspectives widened from pDNA-based gene therapy to application of novel therapeutic nucleic acids including mRNA, siRNA, and microRNA. The finding that different therapeutic pay loads require different tailor-made carriers complicates preclinical developments. Convincing evidence of medical efficacy still remains to be demonstrated. Bioinspired multifunctional polyplexes resembling "synthetic viruses" appear as attractive opportunity, but provide additional challenges: how to identify optimum combinations of functional delivery units, and how to prepare such polyplexes reproducibly in precise form? Design of sequence-defined polymers, screening of combinatorial polymer and polyplex libraries are tools for further chemical evolution of polyplexes.

riDOM, a cell penetrating peptide. Interaction with phospholipid bilayers

Melittin is an amphipathic peptide which has received much attention as a model peptide for peptide-membrane interactions. It is however not suited as a transfection agent due to its cytolytic and toxicological effects. Retro-inverso-melittin, when covalently linked to the lipid 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (riDOM), eliminates these shortcomings. The interaction of riDOM with phospholipid membranes was investigated with circular dichroism (CD) spectroscopy, dynamic light scattering, ζ-potential measurements, and high-sensitivity isothermal titration calorimetry. riDOM forms cationic nanoparticles with a diameter of ~13nm which are well soluble in water and bind with high affinity to DNA and lipid membranes. When dissolved in bilayer membranes, riDOM nanoparticles dissociate and form transient pores. riDOM-induced membrane leakiness is however much reduced compared to that of authentic melittin. The secondary structure of the ri-melittin is not changed when riDOM is transferred from water to the membrane and displays a large fraction of β-structure. The (31)P NMR spectrum of the nanoparticle is however transformed into a typical bilayer spectrum. The Gibbs free energy of riDOM binding to bilayer membranes is -8.0 to -10.0kcal/mol which corresponds to the partition energy of just one fatty acyl chain. Half of the hydrophobic surface of the riDOM lipid extension with its 2 oleic acyl chains is therefore involved in a lipid-peptide interaction. This packing arrangement guarantees a good solubility of riDOM both in the aqueous and in the membrane phase. The membrane binding enthalpy is small and riDOM binding is thus entropy-driven.

From rationally designed polymeric and peptidic systems to sophisticated gene delivery nano-vectors

Lack of safe, efficient and controllable methods for delivering therapeutic genes appears to be the most important factor preventing human gene therapy. Safety issues encountered with viral vectors have prompted substantial attention to in vivo investigations with non-viral vectors throughout the past decade. However, developing non-viral vectors with effectiveness comparable to viral ones has been a challenge. The strategy of designing multifunctional synthetic carriers targeting several extracellular and intracellular barriers in the gene transfer pathway has emerged as a promising approach to improving the efficacy of gene delivery systems. This review will explain how sophisticated synthetic vectors can be created by combining conventional polycationic vectors such as polyethylenimine and basic amino acid peptides with additional polymers and peptides that are designed to overcome potential barriers to the gene delivery process.

Opposing influence of intracellular and membrane thiols on the toxicity of reducible polycations

Toxicity of polycations has been recognized since their first use in gene delivery. Bioreducible polycations attract attention because of their improved safety due to selective intracellular degradation by glutathione (GSH). Here we present a systematic study of the toxicity of bioreducible poly(amido amine)s (PAA). PAA with increasing content of disulfide bonds were synthesized by Michael addition. Toxicity of PAA was evaluated in two cell lines with different innate levels of intracellular GSH. Increasing the content of disulfide bonds decreased the toxicity of PAA, with more significant decrease observed in cells with high GSH. Depleting intracellular GSH by diethyl maleate resulted in increased toxicity of bioreducible PAA. In contrast, increasing the GSH concentrations by growing cells in hypoxic conditions resulted in further decreased toxicity compared with cells grown in normoxic conditions. The presence of exofacial plasma membrane thiols selectively increased toxicity of bioreducible PAA while having no effect on non-degradable controls. These results improve our understanding of the cellular mechanisms of polycation toxicity. They also shed light on the opposing effects of different cellular thiol pools on the toxicity of bioreducible polycations.

A Convergent Synthesis of Homogeneous Reducible Polypeptides

The convergent syntheses of homogeneous disulfide cross-linked polypeptides are reported. Reducible polypeptides were synthesized containing four and eight dodecapeptides in two and three linear conjugation steps. Critical for the convergent methodology was the use of orthogonally protected cysteines as either acetamidomethyl (Acm) or Fmoc-thiazolidine (Thz). Both groups could be selectively deprotected with silver trifluoromethanesulfonate in the presence of internal disulfide bonds using TFA and aqueous conditions, respectively. This approach allows for large, reducible polypeptides to be synthesized in efficient yields and minimizes the number of conjugation steps, allowing the development and optimization of gene delivery polypeptides containing multiple peptide components necessary to overcome the numerous in vivo barriers for efficacious gene delivery.

Truncated peptides from melittin and its analog with high lytic activity at endosomal pH enhance branched polyethylenimine-mediated gene transfection

BACKGROUND

Melittin is a commonly used cell-penetrating peptide (CPP) for improving branched polyethylenimine (BPEI)-mediated gene transfection. However, its application is limited owing to the cytotoxicity generated by the lytic activity at neutral pH. In the present study, we report two truncated peptides from melittin and florae with improved transfection efficiency.

METHODS

Two truncated peptides consisting of 1-20 residues of melittin (MT20) and florae (FL20) were synthesized. Circular dichroism (CD) spectrometry was used to analyze the secondary structures of the peptides. The membrane-lytic activity of the peptides and their potency in enhancing cellular uptake of calcein were evaluated. The peptides and BPEI mixtures were mixed with plasmid DNA to prepare peptide/BPEI/DNA complexes. The physicochemical characters of complexes were measured and the effect of the peptides on BPEI-mediated transfection was determined.

RESULTS

CD analysis and structure observation showed that the truncated peptides have α-helical conformation, which was necessary for penetrating activity. The truncated peptides exhibited several advantages than their parent peptides: (i) they showed higher hemolytic potency in acidic pH but lower lytic activity than their parent peptides in neutral pH; (ii) enhanced calcein efficiently release from both early and late endosome; (iii) they did not affect the DNA-binding affinity of BPEI and the physicochemical characteristics of BPEI/DNA complexes. Moreover, the peptides could increase BPEI-mediated transfection efficiency in different cell lines (293FT, B16F10 and CHO-K1) by simply mixing with BPEI, without causing cytotoxicity.

CONCLUSIONS

The results obtained in the present study indicate that the truncated peptides with higher endosomal disrupting activity were better enhancers for increasing transfection efficiency.

Iterative Reducible Ligation to form Homogeneous Penicillamine Cross-linked Polypeptides

The syntheses of homogeneous penicillamine disulfide cross-linked polypeptides are reported. Dodecapeptides containing N-terminal, C-terminal, or N- and C-terminal Pen were serially ligated into 36 amino acid polypeptides linked through Cys-Pen, Pen-Cys or Pen-Pen disulfide bonds. Critical to the syntheses was the incorporation of thiazolidine masked Cys and Pen as the N-terminal residues and selective hydrolysis with silver trifluoromethanesulfonate in acidic aqueous conditions to generate a free thiol for subsequent ligation. This approach allows the synthesis of homogeneous disulfide cross-linked polypeptides that have different reductive stabilities and have application in gene delivery by undergoing a tempered reductive triggered release of DNA.

Noncovalently associated cell-penetrating peptides for gene delivery applications

The use of various cell-penetrating peptides (CPPs) to deliver genetic material for gene therapy applications has been a topic of interest for more than 20 years. The delivery of genetic material by using CPPs can be divided into two categories: covalently bound and electrostatically bound. Complexity of the synthesis procedure can be a significant barrier to translation when using a strategy requiring covalent binding of CPPs. In contrast, electrostatically complexing CPPs with genetic material or with a viral vector is relatively simple and has been demonstrated to improve gene delivery in both in vitro and in vivo studies. This review highlights gene therapy applications of complexes formed noncovalently between CPPs and genetic material or viruses.

Mechanistic and functional aspects of the interaction of AR-23 with mammalian cell membrane and improvement of branched polyethylenimine-mediated gene transfection

BACKGROUND

Previous studies have suggested that reducing the positive charge of melittin could increase endosomal release activity and improve branched polyethylenimine (BPEI)-mediated transfection. AR-23 is a melittin-related peptide from Rana tagoi, which shows 81% sequence identity with melittin but has less positively-charged residues than melittin. The present study aimed to investigate the mechanistic and functional aspects of the interaction of AR-23 with mammalian cells and thus improve BPEI-mediated gene transfection.

METHODS

AR23 and two AR-23 analogs (AR-20 without positively-charged residues and AR-26 with the same positively-charged residues as melittin) were analyzed. Circular dichroism (CD) spectrometry was used to analyze the secondary structures of the peptides. Peptide-induced depolarization of cell membrane, the membrane-lytic activity of the peptides, and their potency with respect to enhancing the cellular uptake of calcein were evaluated. The physicochemical characters of complexes were measured and the effect of the peptides on BPEI-mediated transfection was determined.

RESULTS

The CD spectra results indicated that a positive charge in AR-23 played a crucial role in maintaining the α-helical conformation, whereas an extra positive charge could not increase α-helical formation. AR-23 displayed a similar depolarization ability to melittin. However, AR-23 showed a lower membrane lytic activity under physiological conditions and a higher lytic activity at endosomal pH than melittin and AR-26, which possess more positive charges. Compared to melittin and AR-26, AR-23, with a higher endosomal escaping activity, resulted in a higher enhancement of BPEI-mediated gene transfection, as well as the maintainance of a lower cytotoxicity.

CONCLUSIONS

We suggest that AR-23 may be considered as a potential enhancer for improving the transfection efficiency of cationic polymers.

Synthesis of homogenous disulfide cross-linked polypeptides by iterative reducible ligation

A new method of directed solution phase synthesis of polypeptides linked through iterative formation of disulfide bonds is reported. Four dodecapeptides were successfully ligated into a single 48 amino acid polypeptide using an N-terminal Fmoc-thiazolidine and a novel acidic silver trifluoromethanesulfonate thiazolidine hydrolysis to achieve efficient ligation in the presence of internal disulfide bonds. The approach allows the synthesis of homogeneous disulfide cross-linked polypeptides that have application in gene delivery by undergoing a reductively triggered release of DNA.

Melittin-grafted HPMA-oligolysine based copolymers for gene delivery

Non-viral gene delivery systems capable of transfecting cells in the brain are critical in realizing the potential impact of nucleic acid therapeutics for diseases of the central nervous system. In this study, the membrane-lytic peptide melittin was incorporated into block copolymers synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. The first block, designed for melittin conjugation, was composed of N-(2-hydroxypropyl)methacrylamide (HPMA) and pyridyl disulfide methacrylamide (PDSMA) and the second block, designed for DNA binding, was composed of oligo-l-lysine (K10) and HPMA. Melittin modified with cysteine at the C-terminus was conjugated to the polymers through the pyridyl disulfide pendent groups via disulfide exchange. The resulting pHgMelbHK10 copolymers are more membrane-lytic than melittin-free control polymers, and efficiently condensed plasmid DNA into salt-stable particles (~100-200 nm). The melittin-modified polymers transfected both HeLa and neuron-like PC-12 cells more efficiently than melittin-free polymers although toxicity associated with the melittin peptide was observed. Optimized formulations containing the luciferase reporter gene were delivered to mouse brain by intraventricular brain injections. Melittin-containing polyplexes produced about 35-fold higher luciferase activity in the brain compared to polyplexes without melittin. Thus, the melittin-containing block copolymers described in this work are promising materials for gene delivery to the brain.

Polymers for siRNA delivery: inspired by viruses to be targeted, dynamic, and precise

Synthetic small interfering RNA (siRNA) presents an exciting novel medical opportunity. Although researchers agree that siRNA could have a great therapeutic impact, the required extracellular and intracellular delivery of these molecules into the disease-associated target cells presents the primary roadblock for the broader translation of these molecules into medicines. Thus, the design of adequate delivery technologies has utmost importance. Viruses are natural masterpieces of nucleic acid delivery and present chemists and drug delivery experts with a template for the design of artificial carriers for synthetic nucleic acids such as siRNA. They have been developed into gene vectors and have provided convincing successes in gene therapy. Optimized by biological evolution, viruses are programmed to be dynamic and bioresponsive as they enter living cells, and they carry out their functions in a precisely defined sequence. However, because they are synthesized within living cells and with naturally available nucleotides and amino acids, the chemistry of viruses is limited. With the use of diverse synthetic molecules and macromolecules, chemists can provide delivery solutions beyond the scope of the natural evolution of viruses. This Account describes the design and synthesis of "synthetic siRNA viruses." These structures contain elements that mimic the delivery functions of viral particles and surface domains that shield against undesired biological interactions and enable specific host cell receptor binding through the presentation of multiple targeting ligands. For example, cationic polymers can reversibly package one or more siRNA molecules into nanoparticle cores to protect them against a degradative bioenvironment. After internalization by receptor-mediated endocytosis into the acidifying endosomes of cells, synthetic siRNA can escape from these vesicles through the activation of membrane-disruption domains as viruses do and reach the cytoplasm, the location of RNA interference. This multistep task presents an attractive challenge for chemists. Similar to the design of prodrugs, the functional domains of these systems have to be activated in a dynamic mode, triggered by conformational changes or bond cleavages in the relevant microenvironment such as the acidic endosome or disulfide-reducing cytoplasm. These chemical analogues of viral domains are often synthetically simpler and more easily accessible molecules than viral proteins. Their precise assembly into multifunctional macromolecular and supramolecular structures is facilitated by improved analytical techniques, precise orthogonal conjugation chemistries, and sequence-defined polymer syntheses. The chemical evolution of microdomains using chemical libraries and macromolecular and supramolecular evolution could provide key strategies for optimizing siRNA carriers to selected medical indications.

Effect of cell membrane thiols and reduction-triggered disassembly on transfection activity of bioreducible polyplexes

Bioreducible polyplexes are promising vectors for delivery of nucleic acids due to low toxicity and favorable transfection activity. The often improved transfection is usually explained by enhanced intracellular reductive disassembly of the polyplexes. This study evaluated the effect of enhanced reductive disassembly on transfection activity of plasmid DNA and antisense oligonucleotide (AON) polyplexes based on a series of bioreducible poly(amido amine)s (PAA). We found that the presence of disulfide bonds in PAA had no effect on nucleic acid binding, hydrodynamic size and zeta potential of polyplexes. Increasing the disulfide content in PAA increased susceptibility to reduction-triggered DNA and AON release from the polyplexes. Increasing the disulfide content in PAA increased DNA transfection but had no effect on AON transfection. Plasma membrane protein thiols played a key role in the observed enhancement of DNA transfection. The presence of disulfide bonds in PAA had no significant effect on the rate of intracellular DNA clearance, suggesting that enhanced intracellular disassembly of the bioreducible polyplexes is not a major contributing factor to the improved transfection activity.

Reactive and bioactive cationic α-helical polypeptide template for nonviral gene delivery

Poly(γ-(4-vinylbenzyl)-l -glutamate) (PVBLG) served as a bioactive and reactive template for the generation of a library of cationic α-helical polypeptides for gene delivery. The top performing polymer outperformed 25-kDa polyethylenimine by 12-fold. Preliminary data indicates that helicity of these cationic polypeptides is essential for their improved performance, with enhanced membrane disruption a likely source of their transfection efficiency.

Delivery of intracellular-acting biologics in pro-apoptotic therapies

The recent elucidation of molecular regulators of apoptosis and their roles in cellular oncogenesis has motivated the development of biomacromolecular anticancer therapeutics that can activate intracellular apoptotic signaling pathways. Pharmaceutical scientists have employed a variety of classes of biologics toward this goal, including antisense oligodeoxynucleotides, small interfering RNA, proteins, antibodies, and peptides. However, stability in the in vivo environment, tumor-specific biodistribution, cell internalization, and localization to the intracellular microenvironment where the targeted molecule is localized pose significant challenges that limit the ability to directly apply intracellular-acting, pro-apoptotic biologics for therapeutic use. Thus, approaches to improve the pharmaceutical properties of therapeutic biomacromolecules are of great significance and have included chemically modifying the bioactive molecule itself or formulation with auxiliary compounds. Recently, promising advances in delivery of pro-apoptotic biomacromolecular agents have been made using tools such as peptide "stapling", cell penetrating peptides, fusogenic peptides, liposomes, nanoparticles, smart polymers, and synergistic combinations of these components. This review will discuss the molecular mediators of cellular apoptosis, the respective mechanisms by which these mediators are dysregulated in cellular oncogenesis, the history and development of both nucleic-acid and amino-acid based drugs, and techniques to achieve intracellular delivery of these biologics. Finally, recent applications where pro-apoptotic functionality has been achieved through delivery of intracellular-acting biomacromolecular drugs will be highlighted.

Synthesis and in vitro testing of new potent polyacridine-melittin gene delivery peptides

The combination of a polyacridine peptide modified with a melittin fusogenic peptide results in a potent gene transfer agent. Polyacridine peptides of the general formula (Acr-X)(n)-Cys were prepared by solid-phase peptide synthesis, where Acr is Lys modified on its epsilon-amine with acridine, X is Arg, Leu, or Lys and n is 2, 3, or 4 repeats. The Cys residue was modified by either a maleimide-melittin or a thiolpyridine-Cys-melittin fusogenic peptide resulting in reducible or non-reducible polyacridine-melittin peptides. Hemolysis assays established that polyacridine-melittin peptides retained their membrane lytic potency relative to melittin at pH 7.4 and 5. When combined with plasmid DNA, the membrane lytic potency of polyacridine-melittin peptides was neutralized. Gene transfer experiments in multiple cell lines established that polyacridine-melittin peptides mediate expression as efficiently as PEI. The expression was very dependent upon a disulfide bond linking polyacridine to melittin. The gene transfer was most efficient when X is Arg and n is 3 or 4 repeats. These studies establish polyacridine peptides as a novel DNA binding anchor peptide.

Engineered nanoscaled polyplex gene delivery systems

Improving the transfection efficiencies of nonviral gene delivery requires properly engineered nanoscaled delivery carriers that can overcome the multiple barriers associated with the delivery of oligonucleotides from the site of administration to the nucleus or cytoplasm of the target cell. This article reviews the current advantages and limitation of polyplex nonviral delivery systems, including the apparent barriers that limit gene expression efficiency compared to physical methods such as hydrodynamic dosing and electroporation. An emphasis is placed on engineered nanoscaled polyplexes (NSPs) of modular design that both self-assemble and systematically disassemble at the desired stage of delivery. It is suggested that NSPs of increasingly sophisticated designs are necessary to improve the efficiency of the rate limiting steps in gene delivery.

Delivery of nucleic acids via disulfide-based carrier systems

Nucleic acids are not only expected to assume a pivotal position as "drugs" in the treatment of genetic and acquired diseases, but could also act as molecular cues to control the microenvironment during tissue regeneration. Despite this promise, the efficient delivery of nucleic acids to their side of action is still the major hurdle. One among many prerequisites for a successful carrier system for nucleic acids is high stability in the extracellular environment, accompanied by an efficient release of the cargo in the intracellular compartment. A promising strategy to create such an interactive delivery system is to exploit the redox gradient between the extra- and intracellular compartments. In this review, emphasis is placed on the biological rationale for the synthesis of redox sensitive, disulfide-based carrier systems, as well as the extra- and intracellular processing of macromolecules containing disulfide bonds. Moreover, the basic synthetic approaches for introducing disulfide bonds into carrier molecules, together with examples that demonstrate the benefit of disulfides at the individual stages of nucleic acid delivery, will be presented.

Influence of the molecular weight of bioreducible oligoethylenimine conjugates on the polyplex transfection properties

The purpose of the present study was to investigate the influence of molecular weights on the chemical, biophysical, and biological properties of bioreducible oligoethylenimine conjugates. The cationic conjugates were synthesized by polyaddition between branched oligoethylenimine 800 Da (OEI) and the disulfide bond containing N,N'-cystamine bisacrylamide (CBA) linker. A correlation between the copolymer molecular weights and the polyplex transfection properties was found. The OEI-CBA copolymers differing in molecular weights (from 8.6 to 37 kDa) showed good plasmid DNA binding ability resulting in compact 90- to 150-nm-sized polyplexes. Colloidal stability of the polyplexes was lost in reductive environment. A low concentration of dithiothreitol of 5 microM was sufficient to render polyplexes unstable in size. Reducing conditions at physiological salt concentration triggered polyplex dissociation. The bioreducible polymers displayed much lower cytotoxicity (IC(50) approximately 100 microg/mL in cell culture) than branched polyethylenimine 25 kDa (BPEI) and linear polyethylenimine 22 kDa (LPEI). Reporter gene transfection experiments were done with CHO-K1 and B16-F10 cells. The largest (37 kDa) copolymer HC-6-8 demonstrated highest transfection levels among all the bioreducible copolymers, which was comparable with LPEI and much more effective than BPEI.

Nucleic acid delivery with chitosan and its derivatives

Chitosan is a naturally occurring cationic mucopolysaccharide. It is generally biocompatible, biodegradable, mucoadhesive, non-immunogenic and non-toxic. Although chitosan is able to condense nucleic acids (NA) (both DNA and RNA) and protect them from nuclease degradation, its poor water solubility and low transfection efficacy have impeded its use as an NA carrier. In order to overcome such limitations, a multitude of strategies for chitosan modification and formulation have been proposed. In this article, we will first give a brief overview of the physical and biological properties of chitosan. Then, with a special focus on plasmid DNA delivery, we will have a detailed discussion of the latest advances in chitosan-mediated NA transfer. For future research, the following three important areas will be discussed: chitosan-mediated therapeutic small RNA transfer, structure-activity relationships (SAR) in chitosan vector design, and chitosan-mediated oral/nasal NA therapy.

Peptide-assisted traffic engineering for nonviral gene therapy

Many of the challenges facing nonviral gene therapy, to make it as effective as the viral-based version, have yet to be overcome. The technology possesses sufficient biosafety advantages to make the construction of 'artificial viruses' a worthwhile undertaking. The impact of vehicle architecture on traffic regulation, and the convergence of several intracellular pathways in late endosomes, indicates that the particular intracellular route might be less relevant than formerly believed. Proper functional tuning of artificial viruses by the use of full proteins or protein stretches, and especially, the incorporation of membrane-active peptides, would improve transgene expression levels and convert artificial viruses into powerful tools for gene medicine.