Protection of oligonucleotides against enzymatic degradation by pegylated and nonpegylated branched polyethyleneimine

Nucleic acid degradation as barrier to gene delivery: a guide to understand and overcome nuclease activity

Gene therapy is on its way to revolutionize the treatment of both inherited and acquired diseases, by transferring nucleic acids to correct a disease-causing gene in the target cells of patients. In the fight against infectious diseases, mRNA-based therapeutics have proven to be a viable strategy in the recent Covid-19 pandemic. Although a growing number of gene therapies have been approved, the success rate is limited when compared to the large number of preclinical and clinical trials that have been/are being performed. In this review, we highlight some of the hurdles which gene therapies encounter after administration into the human body, with a focus on nucleic acid degradation by nucleases that are extremely abundant in mammalian organs, biological fluids as well as in subcellular compartments. We overview the available strategies to reduce the biodegradation of gene therapeutics after administration, including chemical modifications of the nucleic acids, encapsulation into vectors and co-administration with nuclease inhibitors and discuss which strategies are applied for clinically approved nucleic acid therapeutics. In the final part, we discuss the currently available methods and techniques to qualify and quantify the integrity of nucleic acids, with their own strengths and limitations.

Effect of Polyplex Size on Penetration into Tumor Spheroids

Ovarian cancer is one of the most lethal gynecological cancers in the world. In recent years, nucleic acid (NA)-based formulations have been shown to be promising treatments for ovarian cancer, including tumor nodules. However, gene therapy is not that far advanced in clinical reality due to unfavorable physicochemical properties of the NAs, such as high molecular weight, poor cellular uptake, rapid degradation by nucleases, etc. One of the strategies used to overcome these drawbacks is the complexation of anionic NAs via electrostatic interactions with cationic polymers, resulting in the formation of so-called polyplexes. In this work, the role of the size of pDNA and siRNA polyplexes on their penetration into ovarian-cancer-based tumor spheroids was investigated. For this, a methoxypoly(ethylene glycol) poly(2-(dimethylamino)ethyl methacrylate) (mPEG-pDMAEMA) diblock copolymer was synthesized as a polymeric carrier for NA binding and condensation with either plasmid DNA (pDNA) or short interfering RNA (siRNA). When prepared in HEPES buffer (10 mM, pH 7.4) at a nitrogen/phosphate (N/P) charge ratio of 5 and pDNA polyplexes were formed with a size of 162 ± 11 nm, while siRNA-based polyplexes displayed a size of 25 ± 2 nm. The polyplexes had a slightly positive zeta potential of +7-8 mV in the same buffer. SiRNA and pDNA polyplexes were tracked in vitro into tumor spheroids, resembling in vivo avascular ovarian tumor nodules. For this purpose, reproducible spheroids were obtained by coculturing ovarian carcinoma cells with primary mouse embryonic fibroblasts in different ratios (5:2, 1:1, and 2:5). Penetration studies revealed that after 24 h of incubation, siRNA polyplexes were able to penetrate deeper into the homospheroids (composed of only cancer cells) and heterospheroids (cancer cells cocultured with fibroblasts) compared to pDNA polyplexes which were mainly located in the rim. The penetration of the polyplexes was slowed when increasing the fraction of fibroblasts present in the spheroids. Furthermore, in the presence of serum siRNA polyplexes encoding for luciferase showed a high cellular uptake in 2D cells resulting in ∼50% silencing of luciferase expression. Taken together, these findings show that self-assembled small siRNA polyplexes have good potential as a platform to test ovarian tumor nodulus penetration..

3D Printed Gene-Activated Sodium Alginate Hydrogel Scaffolds

Gene therapy is one of the most promising approaches in regenerative medicine to restore damaged tissues of various types. However, the ability to control the dose of bioactive molecules in the injection site can be challenging. The combination of genetic constructs, bioresorbable material, and the 3D printing technique can help to overcome these difficulties and not only serve as a microenvironment for cell infiltration but also provide localized gene release in a more sustainable way to induce effective cell differentiation. Herein, the cell transfection with plasmid DNA directly incorporated into sodium alginate prior to 3D printing was investigated both in vitro and in vivo. The 3D cryoprinting ensures pDNA structure integrity and safety. 3D printed gene-activated scaffolds (GAS) mediated HEK293 transfection in vitro and effective synthesis of model EGFP protein in vivo, thereby allowing the implementation of the developed GAS in future tissue engineering applications.

Local release of siRNA using polyplex-loaded thermosensitive hydrogels

One of the challenges for the clinical translation of RNA interference (RNAi)-based therapies concerns the deposition of therapeutically effective doses of the nucleic acids, like siRNA, at a local tissue level without severe off-target effects. To address this issue, hydrogels can be used as matrices for the local and sustained release of the siRNA cargo. In this study, the formation of polyplexes based on siRNA and poly(2-dimethylaminoethyl methacrylate) (PDMAEMA)-based polymers was investigated, followed by their loading in a thermosensitive hydrogel to promote local siRNA release. A multifunctional NPD triblock copolymer consisting of a thermosensitive poly(N-isopropylacrylamide) (PNIPAM, N), a hydrophilic poly(ethylene glycol) (PEG, P), and a cationic PDMAEMA (D) block was used to study the binding properties with siRNA taking the non-thermosensitive PD polymer as control. For both polymers, small polyplexes with sizes ranging from 10-20 nm were formed in aqueous solution (HBS buffer, 20 mM HEPES, 150 mM NaCl, pH 7.4) when prepared at a N/P charge ratio of 5 or higher. Formulating the siRNA into NPD or PD polyplexes before loading into the thermosensitive PNIPAM-PEG-PNIPAM hydrogel resulted in a more controlled and sustained release compared to free siRNA release from the hydrogel. The polyplexes were released for 128 hours in HBS, when changing the release medium twice a day, while free siRNA was completely released within 50 hours with already 40% being released after changing the release medium just once. The release of the polyplexes was dependent on the dissolution rate of the hydrogel matrix. Moreover, intact polyplexes were released from the hydrogels with a similar size as before loading, suggesting that the hydrogel material did not compromise the polyplex stability. Finally, it was shown that the released polyplexes were still biologically active and transfected FaDu cells, which was observed by siRNA-induced luciferase silencing in vitro. This study shows the development of an injectable thermosensitive hydrogel to promote local and sustained release of siRNA, which can potentially be used to deliver siRNA for various applications, such as the treatment of tumors.

Tumor microenvironment-induced structure changing drug/gene delivery system for overcoming delivery-associated challenges

Nano-drug/gene delivery systems (DDS) are powerful weapons for the targeted delivery of various therapeutic molecules in treatment of tumors. Nano systems are being extensively investigated for drug and gene delivery applications because of their exceptional ability to protect the payload from degradation in vivo, prolong circulation of the nanoparticles (NPs), realize controlled release of the contents, reduce side effects, and enhance targeted delivery among others. However, the specific properties required for a DDS vary at different phase of the complex delivery process, and these requirements are often conflicting, including the surface charge, particle size, and stability of DDS, which severely reduces the efficiency of the drug/gene delivery. Therefore, researchers have attempted to fabricate structure, size, or charge changeable DDS by introducing various tumor microenvironment (TME) stimuli-responsive elements into the DDS to meet the varying requirements at different phases of the delivery process, thus improving drug/gene delivery efficiency. This paper summarizes the most recent developments in TME stimuli-responsive DDS and addresses the aforementioned challenges.

Fluorescence-Based Quantification of Messenger RNA and Plasmid DNA Decay Kinetics in Extracellular Biological Fluids and Cell Extracts

Extracellular and intracellular degradation of nucleic acids remains an issue in non-viral gene therapy. Understanding biodegradation is critical for the rational design of gene therapeutics in order to maintain stability and functionality at the target site. However, there are only limited methods available that allow determining the stability of genetic materials in biological environments. In this context, the decay kinetics of fluorescently labeled plasmid DNA (pDNA) and messenger RNA (mRNA) in undiluted biological samples (i.e., human serum, human ascites, bovine vitreous) and cell extracts is studied using fluorescence correlation spectroscopy (FCS) and single particle tracking (SPT). It is demonstrated that FCS is suitable to follow mRNA degradation, while SPT is better suited to investigate pDNA integrity. The half-life of mRNA and pDNA is ≈1-2 min and 1-4 h in biological samples, respectively. The resistance against biodegradation drastically improves by complexation with lipid-based carriers. Taken together, FCS and SPT are able to quantify the integrity of mRNA and pDNA, respectively, as a function of time, both in the extracellular biological fluids and cell extracts. This in turn allows to focus on the important but less understood issue of nucleic acids degradation in more detail and to rationally optimize gene delivery system as therapeutics.

Fluorescence Correlation Spectroscopy to find the critical balance between extracellular association and intracellular dissociation of mRNA complexes

Fluorescence Correlation Spectroscopy (FCS) is a promising tool to study interactions on a single molecule level. The diffusion of fluorescent molecules in and out of the excitation volume of a confocal microscope leads to the fluorescence fluctuations that give information on the average number of fluorescent molecules present in the excitation volume and their diffusion coefficients. In this context, we complexed mRNA into lipoplexes and polyplexes and explored the association/dissociation degree of complexes by using gel electrophoresis and FCS. FCS enabled us to measure the association and dissociation degree of mRNA-based complexes both in buffer and protein-rich biological fluids such as human serum and ascitic fluid, which is a clear advantage over gel electrophoresis that was only applicable in protein-free buffer solutions. Furthermore, following the complex stability in buffer and biological fluids by FCS assisted to understand how complex characteristics, such as charge ratio and strength of mRNA binding, correlated to the transfection efficiency. We found that linear polyethyleneimine prevented efficient translation of mRNA, most likely due to a too strong mRNA binding, whereas the lipid based carrier Lipofectamine® messengerMAX did succeed in efficient release and subsequent translation of mRNA in the cytoplasm of the cells. Overall, FCS is a reliable tool for the in depth characterization of mRNA complexes and can help us to find the critical balance keeping mRNA bound in complexes in the extracellular environment and efficient intracellular mRNA release leading to protein production.

STATEMENT OF SIGNIFICANCE

The delivery of messenger RNA (mRNA) to cells is promising to treat a variety of diseases. Therefore, the mRNA is typically packed in small lipid particles or polymer particles that help the mRNA to reach the cytoplasm of the cells. These particles should bind and carry the mRNA in the extracellular environment (e.g. blood, peritoneal fluid, …), but should release the mRNA again in the intracellular environment. In this paper, we evaluated a method (Fluorescence Correlation Spectroscopy) that allows for the in depth characterization of mRNA complexes and can help us to find the critical balance keeping mRNA bound in complexes in the extracellular environment and efficient intracellular mRNA release leading to protein production.

Specific targeting of human epidermal growth factor receptor 2 (HER2) overexpressing breast cancer cells by polyethylene glycol-grafted polyethyleneimine modified with anti-HER2 single-domain antibody

Polyethyleneimine is one of the most efficient non-viral gene delivery agents. However, some limitations such as non-specific cell binding, interactions with blood components, and relatively high cytotoxicity restrict its in vivo applications. In order to improve the properties of this molecule as a gene transfection vector, in this study, we developed a nano-carrier system based on polyethyleneimine derivatives synthesized by grafting bi-functional polyethylene glycol molecules (MAL-PEG3500-NHS) to 25 kDa branched polyethyleneimine polymer at three different molar ratios of 10, 20, and 30 (polyethylene glycol:polyethyleneimine). Variable domain of heavy-chain antibody against human epidermal growth factor receptor 2 as targeting agent was conjugated to polyethylene glycol–polyethyleneimine copolymer. In order to find the most effective resultant conjugate, the effect of these modifications on physicochemical properties, cytotoxicity, cellular uptake, and gene transfection efficiency of polyethyleneimine polymer was evaluated. According to the findings of this study and compared to unconjugated polyethyleneimine, PEGylated polyethyleneimine copolymers exhibit lower in vitro cytotoxicity. Polyethylene glycol–polyethyleneimine copolymer conjugated at a molar ratio of 10:1 (polyethylene glycol:polyethyleneimine) demonstrated a low cytotoxicity effect and desirable physicochemical properties. Anti-human epidermal growth factor receptor 2 variable domain of heavy-chain antibody conjugation further reduced the cytotoxicity of unmodified polyethyleneimine in all cell lines studied by 1.5- to 2-folds and also resulted in higher cellular uptake and transfection ability of this copolymer in human epidermal growth factor receptor 2 overexpressing breast cancer cell lines versus normal breast cells or human epidermal growth factor receptor 2 negative cell lines. Altogether, our data suggested that variable domain of heavy-chain antibody–polyethylene glycol–polyethyleneimine copolymers might be an efficient nano-carrier system for specific targeting of human epidermal growth factor receptor 2 expressing tumors.

Multifunctional Magnetoliposomes for Sequential Controlled Release

The simultaneous or sequential delivery of multiple therapeutic active principles to a specific target is one of the main challenges of nanomedicine. This goal requires the construction of complex devices often extremely time and cost consuming. Supramolecular self-assemblies, with building blocks of different nature, each providing a specific function to the final construct, can combine a facile synthetic route with a high tunability and structural control. In this study we provide the proof-of-principle of a drug delivery system, DDS, constituted of (i) liposomes, providing a fully biocompatible lipid scaffold suitable to host both hydrophobic and hydrophilic drugs; (ii) a double-stranded DNA conjugated with a cholesteryl unit that spontaneously inserts into the lipid membrane; and (iii) hydrophobic and hydrophilic superparamagnetic iron oxide nanoparticles (SPIONs) embedded inside the lipid membrane of liposomes or connected to the DNA, respectively. Upon application of an alternating magnetic field, the SPIONs can trigger, through thermal activation, the release of a DNA strand or of the liposomal payload, depending on the frequency and the application time of the field, as proved by both steady-state and time-resolved fluorescence studies. This feature is due to the different localization of the two kinds of SPIONS within the construct and demonstrates the feasibility of a multifunctional DDS, built up from self-assembly of biocompatible building blocks.

Stealth monoolein-based nanocarriers for delivery of siRNA to cancer cells

While the delivery of small interfering RNAs (siRNAs) is an attractive strategy to treat several clinical conditions, siRNA-nanocarriers' stability after intravenous administration is still a major obstacle for the development of RNA-interference based therapies. But, although the need for stability is well recognized, the notion that strong stabilization can decrease nanocarriers' efficiency is sometimes neglected. In this work we evaluated two stealth functionalization strategies to stabilize the previously validated dioctadecyldimethylammonium bromide (DODAB):monoolein (MO) siRNA-lipoplexes. The nanocarriers were pre- and post-pegylated, forming vectors with different stabilities in biological fluids. The stealth nanocarriers' behavior was tested under biological mimetic conditions, as the production of stable siRNA-lipoplexes is determinant to achieve efficient intravenous siRNA delivery to cancer cells. Upon incubation in human serum for 2h, by fluorescence Single Particle Tracking microscopy, PEG-coated lipoplexes were found to have better colloidal stability as they could maintain a relatively stable size. In addition, using fluorescence fluctuation spectroscopy, post-pegylation also proved to avoid siRNA dissociation from the nanocarriers in human serum. Concomitantly it was found that PEG-coated lipoplexes improved cellular uptake and transfection efficiency in H1299 cells, and had the ability to silence BCR-ABL, affecting the survival of K562 cells. Based on an efficient cellular internalization, good silencing effect, good siRNA retention and good colloidal stability in human serum, DODAB:MO (2:1) siRNA-lipoplexes coated with PEG-Cer are considered promising nanocarriers for further in vivo validation.

STATEMENT OF SIGNIFICANCE

This work describes two stealth functionalization strategies for the stabilization of the previously validated dioctadecyldimethylammonium bromide (DODAB):monoolein (MO) siRNA-lipoplexes. These nanocarriers are capable of efficiently incorporating and delivering siRNA molecules to cells in order to silence genes whose expression is implicated in a pathological condition. The main objective was to functionalize these nanocarriers with a coating conferring protection to siRNA in blood without compromising its efficient delivery to cancer cells, validating the potential of DODAB:MO (2:1) siRNA-lipoplexes as therapeutic vectors. We show that the stealth strategy is determinant to achieve a stable and efficient nanocarrier, and that DODAB:MO mixtures have a very promising potential for systemic siRNA delivery to leukemic cells.

Diol glycidyl ether-bridged low molecular weight PEI as potential gene delivery vehicles

PEI 600-based polymers were synthesized via ring-opening polymerization and exhibited much better transfection efficiency and biocompatibility than PEI 25 kDa.

Realizing the potential of gene-based molecular therapies in bone repair

A better understanding of osteogenesis at genetic and biochemical levels is yielding new molecular entities that can modulate bone regeneration and potentially act as novel therapies in a clinical setting. These new entities are motivating alternative approaches for bone repair by utilizing DNA-derived expression systems, as well as RNA-based regulatory molecules controlling the fate of cells involved in osteogenesis. These sophisticated mediators of osteogenesis, however, pose unique delivery challenges that are not obvious in deployment of conventional therapeutic agents. Viral and nonviral delivery systems are actively pursued in preclinical animal models to realize the potential of the gene-based medicines. This article will summarize promising bone-inducing molecular agents on the horizon as well as provide a critical review of delivery systems employed for their administration. Special attention was paid to synthetic (nonviral) delivery systems because they are more likely to be adopted for clinical testing because of safety considerations. We present a comparative analysis of dose-response relationships, as well as pharmacokinetic and pharmacodynamic features of various approaches, with the purpose of clearly defining the current frontier in the field. We conclude with the authors' perspective on the future of gene-based therapy of bone defects, articulating promising research avenues to advance the field of clinical bone repair.

Gelatin coating to stabilize the transfection ability of nucleic acid polyplexes

Amphiphilic polymers are effective in complexing and delivering therapeutic nucleic acids, such as plasmid DNA (pDNA) and short interfering RNA (siRNA). However, long-term stability of the complexes is not desirable, as it may have an impact on the transfection efficiency in vivo. To develop a method to preserve complex stability we first showed that pDNA complexes formed with the amphiphilic polymer linoleic acid-substituted polyethylenimine (PEI-LA) and incubated at 37°C lost ~90% of their transfection efficiency after only 24h of complex formation. Polyethyleneglycol modification of complexes to control the increase in complex size and incubation in scaffolds used for implantation did not preserve the transfection ability of the complexes. Among a variety of approaches explored, gelatin coating of complexes was found to be the best at maintaining the original transfection efficiency. Mechanistic studies suggested that improved complex uptake, not size stability, was responsible for retention of the transfection efficiency. Similarly to the results with pDNA, gelatin coating also prevented the decreases in uptake and silencing efficiency of siRNA complexes observed following incubation at 37°C. Gelatin-stabilized complexes were, furthermore, effective in vivo and led to subcutaneous transgene expression with a low pDNA dose that was otherwise ineffective. We conclude that a simple gelatin coating approach offers an efficient means to preserve the transfection efficiency of polyplexes.

Designing PEGylated therapeutic molecules: advantages in ADMET properties

BACKGROUND

PEGylation, association of poly(ethylene glycol) (PEG) to drug molecules or drug-bearing particles, is one of the most promising techniques on the way to improve the pharmacokinetic features of a drug which, in turn, leads to pharmacodynamic improvements.

OBJECTIVE

The aim of this review is to describe PEGylation as a procedure for alteration of drug molecular structure with the main emphasis on its pharmacokinetic consequences.

METHODS

After a brief but concise overview of the history and chemistry of PEGylation, the boundary of this literature survey is confined to the findings and reports on the impact of PEGylation on biodistribution and bioelimination of therapeutic molecules.

CONCLUSION

It is concluded, based on the whole body of the data in literature, that the main results of PEGylation on pharmacokinetic properties of the drug include prolongation of lifespan in circulation, alterations in drug elimination pathway(s) and changes in drug biodistribution profile, among others, which all are derived from the structural changes that occur in the drug molecule, mainly reversible attachment of a large polymeric moiety to parent drug.

Specific effects of PEGylation on gene delivery efficacy of polyethylenimine: interplay between PEG substitution and N/P ratio

While an effective non-viral gene carrier, 25 kDa branched polyethylenimine (PEI) is cytotoxic, and decreasing its toxicity while maintaining its functionality is vital. Conjugation of carriers with polyethylene glycol (PEG) is a common approach to decreasing toxicity and improving biodistribution; however, the effect of PEGylation on PEI transfection efficacy is contradictory at present. The aim of this work was to reveal the details of this dependence. Polymers were synthesized by grafting 2 kDa PEG to 25 kDa PEI at multiple ratios. Unlike typical investigations, parallel studies based on either total polymer weight or PEI-backbone weight were employed at the same time for accurate investigation into the specific effects of PEGylation. Polymers were assessed for toxicity and plasmid DNA (pDNA) binding, while polyplexes were formed at various polymer/pDNA weight ratios and monitored by dynamic light scattering (DLS) in the presence of serum. The efficacy of the polyplexes for pDNA delivery and transgene expression in HEK293 cells was assessed by flow cytometry. This approach unexpectedly revealed that increased PEG substitution caused lower toxicity and pDNA-binding on a per total polymer weight basis, but not on a per PEI-backbone weight basis. DLS indicated that high PEGylation prevents an increase in polyplex size in the presence of serum. Plasmid uptake and transgene expression were found to have a complex relationship with PEG substitution, dependent on the polymer/plasmid-DNA weight ratio. PEGylation generally decreased the transfection efficacy of PEI, but under ideal conditions of PEG substitution and polymer/pDNA ratio, PEGylation provided more effective carrier formulations than the native PEI itself.

Intracellular nucleic acid interactions facilitated by quantum dots: conceptualizing theranostics

The concept of theranostics arises from the unification of both diagnostic and therapeutic applications into a single package. The implementation of nanoparticles, such as semiconductor quantum dots (QDs), to achieve theranostic applications, offers great potential for development of methods that are suitable for personalized medicine. Researchers have taken advantage of the physiochemical properties of QDs to elicit novel bioconjugation techniques that enable the attachment of multifunctional moieties on the surface of QDs. In this review, the diagnostic and therapeutic applications of QDs that feature the use of nucleic acids are highlighted with a particular emphasis on the possibility of combinatorial applications. Nucleic acid research is of particular interest for gene therapy, and is relevant to the understanding of gene regulation pathways and gene expression dynamics. Recent toxicity studies featuring multifunctional QDs are also examined. Future perspectives discussing the expected development of this field conclude the article.

Stabilization and photochemical regulation of antisense agents through PEGylation

Oligonucleotides are effective tools for the regulation of gene expression in cell culture and model organisms, most importantly through antisense mechanisms. Due to the inherent instability of DNA antisense agents, various modifications have been introduced to increase the efficacy of oligonucleotides, including phosphorothioate DNA, locked nucleic acids, peptide nucleic acids, and others. Here, we present antisense agent stabilization through conjugation of a poly(ethylene glycol) (PEG) group to a DNA oligonucleotide. By employing a photocleavable linker between the PEG group and the antisense agent, we were able to achieve light-induced deactivation of antisense activity. The bioconjugated PEG group provides stability to the DNA antisense agent without affecting its native function of silencing gene expression via RNase H-catalyzed mRNA degradation. Once irradiated with UV light of 365 nm, the PEG group is cleaved from the antisense agent leaving the DNA unprotected and open for degradation by endogenous nucleases, thereby restoring gene expression. By using a photocleavable PEG group (PhotoPEG), antisense activity can be regulated with high spatial and temporal resolution, paving the way for precise regulation of gene expression in biological systems.

Polyplex-microbubble hybrids for ultrasound-guided plasmid DNA delivery to solid tumors

Microbubble ultrasound contrast agents are being developed as image-guided gene carriers for targeted delivery in vivo. In this study, novel polyplex-microbubbles were synthesized, characterized and evaluated for systemic circulation and tumor transfection. Branched polyethylenimine (PEI; 25 kDa) was modified with polyethylene glycol (PEG; 5 kDa), thiolated and covalently attached to maleimide groups on lipid-coated microbubbles. The PEI-microbubbles demonstrated increasingly positive surface charge and DNA loading capacity with increasing maleimide content. The in vivo ultrasound contrast persistence of PEI-microbubbles was measured in the healthy mouse kidney, and a two-compartment pharmacokinetic model accounting for free and adherent microbubbles was developed to describe the anomalous time-intensity curves. The model suggested that PEI loading dramatically reduced free circulation and increased nonspecific adhesion to the vasculature. However, DNA loading to form polyplex-microbubbles increased circulation in the bloodstream and decreased nonspecific adhesion. PEI-microbubbles coupled to a luciferase bioluminescence reporter plasmid DNA were shown to transfect tumors implanted in the mouse kidney. Site-specific delivery was achieved using ultrasound applied over the tumor area following bolus injection of the DNA/PEI-microbubbles. In vivo imaging showed over 10-fold higher bioluminescence from the tumor region compared to untreated tissue. Ex vivo analysis of excised tumors showed greater than 40-fold higher expression in tumor tissue than non-sonicated control (heart) tissue. These results suggest that the polyplex-microbubble platform offers improved control of DNA loading and packaging suitable for ultrasound-guided tissue transfection.

In vitro and in vivo mRNA delivery using lipid-enveloped pH-responsive polymer nanoparticles

Biodegradable core--shell structured nanoparticles with a poly(β-amino ester) (PBAE) core enveloped by a phospholipid bilayer shell were developed for in vivo mRNA delivery with a view toward delivery of mRNA-based vaccines. The pH-responsive PBAE component was chosen to promote endosome disruption, while the lipid surface layer was selected to minimize toxicity of the polycation core. Messenger RNA was efficiently adsorbed via electrostatic interactions onto the surface of these net positively charged nanoparticles. In vitro, mRNA-loaded particle uptake by dendritic cells led to mRNA delivery into the cytosol with low cytotoxicity, followed by translation of the encoded protein in these difficult-to-transfect cells at a frequency of ~30%. Particles loaded with mRNA administered intranasally (i.n.) in mice led to the expression of the reporter protein luciferase in vivo as soon as 6 h after administration, a time point when naked mRNA given i.n. showed no expression. At later time points, luciferase expression was detected in naked mRNA-treated mice, but this group showed a wide variation in levels of transfection, compared to particle-treated mice. This system may thus be promising for noninvasive delivery of mRNA-based vaccines.

Modification of curcumin with polyethylene glycol enhances the delivery of curcumin in preadipocytes and its antiadipogenic property

Conjugation of curcumin (CCM) by polyethylene glycol (PEG) has been previously developed to improve water solubility of the natural form of CCM and its antiproliferative role in some human cancer cell lines. This study examined the cellular uptake kinetics of the natural form of CCM and CCM-PEG. Their cytotoxic effect in proliferating preadipocytes and antiadipogenic property in differentiating preadipocytes had also been investigated. CCM and CCM-PEG were found to be differently absorbed in 3T3-L1 preadipocytes and adipocytes with a limited amount of CCM-PEG absorption in the cell. The improved water solubility of CCM-PEG was correlated with increased cellular retention of CCM in 3T3-L1 cells, particularly in preadipocytes. Consequently, CCM-PEG treatment sensitized proliferating preadipocytes to CCM-induced cell toxicity. Furthermore, incubation of differentiating 3T3-L1 cells with CCM-PEG resulted in improvement of the inhibitory role of CCM in adipocyte differentiation with no toxic effect. These results suggest that pegylation-improved water solubility and cellular retention of CCM may be uniquely useful for improving the delivery of CCM in preadipocytes and its antiadipogenic ability.

Oligonucleotide delivery in cancer therapy

IMPORTANCE OF THE FIELD

Cancer is frequently caused by altered protein expression. Oligonucleotides (ONs) are short synthetic nucleic acid fragments, able to selectively correct protein expression into cells by different mechanisms. However, biological barriers hamper the therapeutic use of ONs without suitable delivery strategies.

AREAS COVERED IN THIS REVIEW

This review summarizes the most meaningful non-viral strategies for ON delivery, including the chemical modifications of the ON backbone and non-viral delivery systems.

WHAT THE READER WILL GAIN

The reader will gain an update of the main strategies for ON delivery in cancer. Advantages and limits of each approach are underlined. Emphasis is given to the delivery strategies that contributed to bringing ONs into clinical trials.

TAKE HOME MESSAGE

In the long story of ONs for cancer therapy, the development of delivery strategies has led, in the last few years, to different opportunities to use the high therapeutic potential of these molecules in humans.

Polyethylenimine-PEG coated albumin nanoparticles for BMP-2 delivery

Bone Morphogenetic Protein-2 (BMP-2) plays an important role in stimulating new bone formation, and has been utilized in clinical bone repair by implantation. In this study, we report a nanoparticulate (NP) system for BMP-2 delivery based on bovine serum albumin (BSA) NPs stabilized with a poly(ethylene glycol) modified polyethylenimine (PEI-PEG) coating. PEI-PEG with different PEG substitutions were synthesized, and the cell viability assay showed PEG substitution greatly reduced the cytotoxicity of the native PEI. Furthermore, PEI-PEG coated BSA NPs demonstrated smaller size and decreased zeta potential compared to PEI-coated NPs. The bioactivity of the encapsulated BMP-2 and the toxicity of PEI-PEG coated NPs were examined by the alkaline phosphatase (ALP) induction assay and the MTT assay, respectively, using human C2C12 cells. The results indicated that BMP-2 remained bioactive in NPs and PEI-PEG coating was advantageous in reducing the NP toxicity as compared to PEI. A 7-day pharmacokinetics study showed the BMP-2 retention in PEI-PEG coated NPs was similar to the uncoated NPs, but lower than that of the PEI-coated NPs. The osteoinductivity of BMP-2 delivered in NPs was determined by subcutaneous implantation in rats, and the results revealed that PEI-PEG coated BSA NPs induced significant de novo bone formation after implantation, while PEI-coated NPs demonstrated much less bone formation. We conclude that BMP-2 delivered by PEGylated PEI-coated BSA NPs displays favorable biocompatibility and promotes new bone formation after implantation.

Nano and microtechnologies for the delivery of oligonucleotides with gene silencing properties

Oligonucleotides (ONs) are synthetic fragments of nucleic acid designed to modulate the expression of target proteins. DNA-based ONs (antisense, antigene, aptamer or decoy) and more recently a new class of RNA-based ONs, the small interfering RNAs (siRNAs), have gained great attention for the treatment of different disease states, such as viral infections, inflammation, diabetes, and cancer. However, the development of therapeutic strategies based on ONs is hampered by their low bioavailability, poor intracellular uptake and rapid degradation in biological fluids. The use of a non-viral carrier can be a powerful tool to overcome these drawbacks. Lipid or polymer-based nanotechnologies can improve biological stability and cellular uptake of ONs, with possibility of tissue and/or cellular targeting. The use of polymeric devices can also produce a prolonged release of the ON, thus reducing the need of frequent administrations. This review summarizes advantages and issues related to the main non-viral vectors used for ON delivery.

Simultaneous Non-invasive Analysis of DNA Condensation and Stability by Two-step QD-FRET

Nanoscale vectors comprised of cationic polymers that condense DNA to form nanocomplexes are promising options for gene transfer. The rational design of more efficient nonviral gene carriers will be possible only with better mechanistic understanding of the critical rate-limiting steps, such as nanocomplex unpacking to release DNA and degradation by nucleases. We present a two-step quantum dot fluorescence resonance energy transfer (two-step QD-FRET) approach to simultaneously and non-invasively analyze DNA condensation and stability. Plasmid DNA, double-labeled with QD (525 nm emission) and nucleic acid dyes, were complexed with Cy5-labeled cationic gene carriers. The QD donor drives energy transfer stepwise through the intermediate nucleic acid dye to the final acceptor Cy5. At least three distinct states of DNA condensation and integrity were distinguished in single particle manner and within cells by quantitative ratiometric analysis of energy transfer efficiencies. This novel two-step QD-FRET method allows for more detailed assessment of the onset of DNA release and degradation simultaneously.

Opsonized erythrocyte ghosts for liver-targeted delivery of antisense oligodeoxynucleotides

The use of antisense oligodeoxynucleotides (AS-ODNs) in therapeutic applications requires the development of appropriate analysis and delivery systems. Here, we report a quantitation method and a carrier-mediated AS-ODN delivery system. AS-ODN levels were quantitated using an enzyme-linked immunosorbent assay (ELISA) in which biotinylated AS-ODNs bound to streptavidin-coated plates were detected by binding of a complementary, dinitrophenol-labeled detector ODN. The ELISA-based assay could detect AS-ODNs at the femtomole level. AS-ODN delivery systems based on opsinized erythrocyte ghosts (EGs) were developed using various combinations of hypotonic solution and resealing buffer to optimize AS-ODN encapsulation efficiencies. AS-ODN and polyethyleneimine (PEI) complex formation did not affect encapsulation into EGs. The ELISA-based assay showed that the pharmacokinetics of AS-ODNs differed significantly among the various delivery methods. Opsonized EG-encapsulated AS-ODNs exhibited a mean residence time (MRT) significantly shorter than AS-ODN encapsulated in EGs. The biodistribution of EG-loaded AS-ODNs depended on opsonization, with opsonized EG carriers producing 4.5-fold higher levels of AS-ODN in the liver compared with unopsonized EGs. These results indicate that opsonized EGs can be used for liver-targeted delivery of AS-ODN and suggest that an ELISA-based method may be useful for studying the in vivo fate of AS-ODNs.

Cytosolic delivery of membrane-impermeable molecules in dendritic cells using pH-responsive core-shell nanoparticles

Polycations that absorb protons in response to the acidification of endosomes can theoretically disrupt these vesicles via the "proton sponge" effect. To exploit this mechanism, we created nanoparticles with a segregated core-shell structure for efficient, noncytotoxic intracellular drug delivery. Cross-linked polymer nanoparticles were synthesized with a pH-responsive core and hydrophilic charged shell designed to disrupt endosomes and mediate drug/cell binding, respectively. By sequestering the relatively hydrophobic pH-responsive core component within a more hydrophilic pH-insensitive shell, nontoxic delivery of small molecules and proteins to the cytosol was achieved in dendritic cells, a key cell type of interest in the context of vaccines and immunotherapy.

Paclitaxel-Functionalized Gold Nanoparticles

Here we describe the first example of 2 nm gold nanoparticles (Au NPs) covalently functionalized with a chemotherapeutic drug, paclitaxel. The synthetic strategy involves the attachment of a flexible hexaethylene glycol linker at the C-7 position of paclitaxel followed by coupling of the resulting linear analogue to phenol-terminated gold nanocrystals. The reaction proceeds under mild esterification conditions and yields the product with a high molecular weight, while exhibiting an extremely low polydispersity index (1.02, relative to linear polystyrene standards). TGA analysis of the hybrid nanoparticles reveals the content of the covalently attached organic shell as nearly 67% by weight, which corresponds to approximately 70 molecules of paclitaxel per 1 nanoparticle. The presence of a paclitaxel shell with a high grafting density renders the product soluble in organic solvents and allows for detailed (1)H NMR analysis and, therefore, definitive confirmation of its chemical structure. High-resolution TEM was employed for direct visualization of the inorganic core of hybrid nanoparticles, which were found to retain their average size, shape, and high crystallinity after multiple synthetic steps and purifications. The interparticle distance substantially increases after the attachment of paclitaxel as revealed by low-magnification TEM, suggesting the presence of a larger organic shell. The method described here demonstrates that organic molecules with exceedingly complex structures can be covalently attached to gold nanocrystals in a controlled manner and fully characterized by traditional analytical techniques. In addition, this approach gives a rare opportunity to prepare hybrid particles with a well-defined amount of drug and offers a new alternative for the design of nanosized drug-delivery systems.