Formulation of polylactide-co-glycolic acid nanospheres for encapsulation and sustained release of poly(ethylene imine)-poly(ethylene glycol) copolymers complexed to oligonucleotides

Development of erythromycin loaded PLGA nanoparticles for improved drug efficacy and sustained release against bacterial infections and biofilm formation

Bacterial infections are a common cause of sepsis, often leading to high patient mortality. Such infections are challenging to treat due to bacterial resistance to many existing drugs. Erythromycin (Ery) is a macrolide antibiotic used against bacterial infections with reported resistance. Recently, synthetic poly-lactide co-glycolic acid (PLGA) polymer nanoparticles (NPs) have displayed improved drug delivery characteristics and biocompatibility. In this study, PLGA-Ery NPs were synthesized by the o/w emulsion diffusion method, having a particle size of 159 ± 23 nm and displayed 71.89 % of encapsulation efficiency. The PLGA-Ery NPs showed 1.5, 2.1 and 1.5-fold improved MIC and antibacterial efficacy against E. coli, S. aureus, and P. aeruginosa, respectively than the pure drug. As illustrated by scanning electron microscopy, PLGA-Ery NPs caused damage to the bacterial cell walls. Furthermore, a surface coating with PLGA-Ery NPs on a glass surface showed efficient inhibition (>90 %) of the biofilm formation by P. aeruginosa, as determined by fluorescence microscopy and MTT assay. This study demonstrates that PLGA-Ery NPs can increase the efficiency of erythromycin and can suppress the growth and biofilm formation of P. aeruginosa. Such polymeric nanoparticles drug nanoformulations have potential as an antimicrobial and as a surface coating for medical devices.

Effect of mPEG-PLGA on Drug Crystallinity and Release of Long-Acting Injection Microspheres: In Vitro and In Vivo Perspectives

PURPOSE

Traditional progesterone (PRG) injections require long-term administration, leading to poor patient compliance. The emergence of long-acting injectable microspheres extends the release period to several days or even months. However, these microspheres often face challenges such as burst release and incomplete drug release. This study aims to regulate drug release by altering the crystallinity of the drug during the release process from the microspheres.

METHODS

This research incorporates methoxy poly(ethylene glycol)-b-poly(lactide-co-glycolide) (mPEG-PLGA) into poly(lactide-co-glycolide) (PLGA) microspheres to enhance their hydrophilicity, thus regulating the release rate and drug morphology during release. This modification aims to address the issues of burst and incomplete release in traditional PLGA microspheres. PRG was used as the model drug. PRG/mPEG-PLGA/PLGA microspheres (PmPPMs) were prepared via an emulsification-solvent evaporation method. Scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), and differential scanning calorimetry (DSC) were employed to investigate the presence of PRG in PmPPMs and its physical state changes during release.

RESULTS

The addition of mPEG-PLGA altered the crystallinity of the drug within the microspheres at different release stages. The crystallinity correlated positively with the amount of mPEG-PLGA incorporated; the greater the amount, the faster the drug release from the formulation. The bioavailability and muscular irritation of the long-acting injectable were assessed through pharmacokinetic and muscle irritation studies in Sprague-Dawley (SD) rats. The results indicated that PmPPMs containing mPEG-PLGA achieved low burst release and sustained release over 7 days, with minimal irritation and self-healing within this period. PmPPMs with 5% mPEG-PLGA showed a relative bioavailability (Frel) of 146.88%.

IN CONCLUSION

In summary, adding an appropriate amount of mPEG to PLGA microspheres can alter the drug release process and enhance bioavailability.

PLGA and PEG based porous microparticles as vehicles for pulmonary somatropin delivery

Breakthrough advances in protein therapeutics and sustained release systems continue to fuel innovation in novel, non-invasive polymeric platforms for delivery of biologicals. Despite the bench potential and proof-of-concept work, market analysis still shows biologicals to be predominantly injections. Characterized by insufficient secretion of growth hormone by the pituitary gland, growth hormone deficiency (GHD) is a rare disorder. Currently, chronic somatropin (r-hGH) replacement therapy is only available as subcutaneous injections administered several times a week. We aim to prepare large, porous, biodegradable and aerodynamically light microparticles as tunable carriers for pulmonary r-hGH delivery. We developed a range of microparticles using PLGA 5050 1Awith sizes between 5 μm and 13 μm, densities lower than 0.4 g/cc and aerodynamic diameters lower than 6 μm. Polyethylene glycol's multitude of advantages - plasticizing PLGA, improving the biocompatibility of the system and preventing protein burst release - have been extensively studied, making it our excipient (pore-former) of choice. Drug loading was characterized at pH 4.0 (acidic), 5.3 (pI) and pH 7.2 (neutral) and was a result of an interplay of electrostatic and hydrophobic interactions between the polymer and somatropin. Considering the physicochemical interactions, we observed some pH dependent protein unfolding characterized by reduction in intrinsic fluorescence of the Tryptophan 86 residue at 331 nm. The secondary ⍺-helix structure characterized by 2 negative minima at 209 nm and 222 nm in the circular dichroism spectra, was intact at all pH values. R-hGH was released over a period of seven days, and the release profile was a function of the microparticle porosity.

Use of Glycine to Augment Exon Skipping and Cell Therapies for Duchenne Muscular Dystrophy

Antisense oligonucleotide (AO)-based exon-skipping and cell therapies are the main therapeutic approaches for Duchenne muscular dystrophy (DMD). Insufficient systemic delivery leading to low therapeutic efficacy limits the former; low transplantation efficiency hampers the latter. Here we describe how glycine can address these issues by augmenting satellite proliferation and muscle regeneration, resulting in enhanced AO uptake in regenerating myofibers and cell transplantation efficiency in dystrophic mice. The dual functionality of glycine demonstrated in AO-based exon-skipping and cell therapies presents a simple and efficient method to augment AO potency and cell transplantation efficacy in DMD and other muscle diseases.

Nanomedicine for Treating Muscle Dystrophies: Opportunities, Challenges, and Future Perspectives

Muscular dystrophies are a group of genetic muscular diseases characterized by impaired muscle regeneration, which leads to pathological inflammation that drives muscle wasting and eventually results in weakness, functional dependency, and premature death. The most known causes of death include respiratory muscle failure due to diaphragm muscle decay. There is no definitive treatment for muscular dystrophies, and conventional therapies aim to ameliorate muscle wasting by promoting physiological muscle regeneration and growth. However, their effects on muscle function remain limited, illustrating the requirement for major advancements in novel approaches to treatments, such as nanomedicine. Nanomedicine is a rapidly evolving field that seeks to optimize drug delivery to target tissues by merging pharmaceutical and biomedical sciences. However, the therapeutic potential of nanomedicine in muscular dystrophies is poorly understood. This review highlights recent work in the application of nanomedicine in treating muscular dystrophies. First, we discuss the history and applications of nanomedicine from a broader perspective. Second, we address the use of nanoparticles for drug delivery, gene regulation, and editing to target Duchenne muscular dystrophy and myotonic dystrophy. Next, we highlight the potential hindrances and limitations of using nanomedicine in the context of cell culture and animal models. Finally, the future perspectives for using nanomedicine in clinics are summarized with relevance to muscular dystrophies.

Nanomedicine, a valuable tool for skeletal muscle disorders: Challenges, promises, and limitations

Muscular dystrophies are a group of rare genetic disorders characterized by progressive muscle weakness, which, in the most severe forms, leads to the patient's death due to cardiorespiratory problems. There is still no cure available for these diseases and significant effort is being placed into developing new strategies to either correct the genetic defect or to compensate muscle loss by stimulating skeletal muscle regeneration. However, the vast anatomical extension of the target tissue poses great challenges to these goals, highlighting the need for complementary strategies. Nanomedicine is an actively evolving field that merges nanotechnologies with biomedical and pharmaceutical sciences. It holds great potential in regenerative medicine, both in supporting tissue engineering and regeneration, and in optimizing drug and oligonucleotide delivery and gene therapy strategies. In this review, we will summarize the state‐of‐the‐art in the field of nanomedicine applied to skeletal muscle regeneration. We will discuss the recent work toward the development of nanopatterned scaffolds for tissue engineering, the efforts in the synthesis of organic and inorganic nanoparticles for gene therapy and drug delivery applications, as well as their use as immune modulators. Although nanomedicine holds great promise for muscle and other degenerative diseases, many challenges still need to be systematically addressed to assure a smooth transition from the bench to the bedside.

This article is categorized under:

Implantable Materials and Surgical Technologies > Nanotechnology in Tissue Repair and Replacement

Nanomedicine for Gene Delivery and Drug Repurposing in the Treatment of Muscular Dystrophies

Muscular Dystrophies (MDs) are a group of rare inherited genetic muscular pathologies encompassing a variety of clinical phenotypes, gene mutations and mechanisms of disease. MDs undergo progressive skeletal muscle degeneration causing severe health problems that lead to poor life quality, disability and premature death. There are no available therapies to counteract the causes of these diseases and conventional treatments are administered only to mitigate symptoms. Recent understanding on the pathogenetic mechanisms allowed the development of novel therapeutic strategies based on gene therapy, genome editing CRISPR/Cas9 and drug repurposing approaches. Despite the therapeutic potential of these treatments, once the actives are administered, their instability, susceptibility to degradation and toxicity limit their applications. In this frame, the design of delivery strategies based on nanomedicines holds great promise for MD treatments. This review focuses on nanomedicine approaches able to encapsulate therapeutic agents such as small chemical molecules and oligonucleotides to target the most common MDs such as Duchenne Muscular Dystrophy and the Myotonic Dystrophies. The challenge related to in vitro and in vivo testing of nanosystems in appropriate animal models is also addressed. Finally, the most promising nanomedicine-based strategies are highlighted and a critical view in future developments of nanomedicine for neuromuscular diseases is provided.

Lipid/polymer-based nanocomplexes in nucleic acid delivery as cancer vaccines

Cancer vaccines consist of nucleic acid derivatives such as plasmid DNA, small interfering RNA and mRNA, and can be customized according to the patient's needs. Nanomedicines have proven to be exceptionally good as miniaturized drug carriers, and thus they offer great advantages for delivering cancer vaccines. This review provides an overview of the literature on cancer vaccines, from their inception to current developments in the field.

Use of Glucose-Fructose to Enhance the Exon Skipping Efficacy

Exon-skipping antisense oligonucleotides (AOs) are promising treatments for muscle-related genetic ailments including Duchenne muscular dystrophy (DMD), but clinical translation is unfortunately hampered by insufficient systemic delivery. Here we describe that how one can employ a glucose-fructose injection mixture to improve muscle uptake and functional outcomes of DMD AOs in energy-deficient peripheral muscles of mdx mice. The potentiating effect of glucose-fructose on AOs in energy-deficient muscles offers a simple and economical method for enhancing AO potency, reducing screening costs for researchers and accelerating the translation of nucleic acid-based therapeutics in DMD and other muscular dystrophies.

Long-Term Morpholino Oligomers in Hexose Elicits Long-Lasting Therapeutic Improvements in mdx Mice

Approval of antisense oligonucleotide eteplirsen highlights the promise of exon-skipping therapeutics for Duchenne muscular dystrophy patients. However, the limited efficacy of eteplirsen underscores the importance to improve systemic delivery and efficacy. Recently, we demonstrated that a glucose and fructose (GF) delivery formulation effectively potentiates phosphorodiamidate morpholino oligomer (PMO). Considering the clinical potential of GF, it is important to determine the long-term compatibility and efficacy with PMO in mdx mice prior to clinical translation. Here, we report that yearlong administration of a clinically applicable PMO dose (50 mg/kg/week for 3 weeks followed by 50 mg/kg/month for 11 months) with GF elicited sustainably high levels of dystrophin expression in mdx mice, with up to 45% of the normal level of dystrophin restored in most peripheral muscles without any detectable toxicity. Importantly, PMO-GF resulted in phenotypical rescue and mitochondrial biogenesis with functional improvement. Carbohydrate metabolites measurements revealed improved metabolic and energetic conditions after PMO-GF treatment in mdx mice without metabolic anomaly. Collectively, our study shows PMO-GF’s ability to elicit long-lasting therapeutic effects with tolerable toxicity and represents a new treatment modality for Duchenne muscular dystrophy, and provides guidelines for antisense oligonucleotides with GF in clinical use.

Cyclic Peptides to Improve Delivery and Exon Skipping of Antisense Oligonucleotides in a Mouse Model for Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a severe, progressive muscle wasting disorder caused by reading frame disrupting mutations in the DMD gene. Exon skipping is a therapeutic approach for DMD. It employs antisense oligonucleotides (AONs) to restore the disrupted open reading frame, allowing the production of shorter, but partly functional dystrophin protein as seen in less severely affected Becker muscular dystrophy patients. To be effective, AONs need to be delivered and effectively taken up by the target cells, which can be accomplished by the conjugation of tissue-homing peptides. We performed phage display screens using a cyclic peptide library combined with next generation sequencing analyses to identify candidate muscle-homing peptides. Conjugation of the lead peptide to 2'-O-methyl phosphorothioate AONs enabled a significant, 2-fold increase in delivery and exon skipping in all analyzed skeletal and cardiac muscle of mdx mice and appeared well tolerated. While selected as a muscle-homing peptide, uptake was increased in liver and kidney as well. The homing capacity of the peptide may have been overruled by the natural biodistribution of the AON. Nonetheless, our results suggest that the identified peptide has the potential to facilitate delivery of AONs and perhaps other compounds to skeletal and cardiac muscle.

Ionizing radiation: a versatile tool for nanostructuring of polymers

Very high energies of particulate (accelerated electrons, swift heavy ions) or electromagnetic wave (γ-, X-rays) radiation can be used to initiate free radical based reactions in solids, liquids or gases. Because of non-selectivity of absorption of X-rays, γ rays and accelerated electrons in matter free radicals are generated homogeneously in the bulk material. These free radicals on the polymers or monomers are used extensively in the synthesis and modification of polymeric materials. The unique properties of ionizing radiation make it a very useful tool in the top-down and bottom-up synthesis of nanomaterials. In this article the utilization of ionizing radiation in the form of swift heavy ions, accelerated electrons, X- and γ rays will be described for development of advanced materials by radiation-induced grafting in nanoscale, synthesis of polymeric nanoparticles, radiation-assisted synthesis of nanogels and nanocomposites. The properties difficult to be attained by other techniques will be described by giving examples for the cases of ion track-etched membranes, fuel cell membranes, sensors, detectors, cell culture media, polymer thin films embedded with metal nanoparticles, polymer/clay nanocomposites with a prospect for the future outlook.

Linear polyethylenimine as (multi) functional initiator for organocatalytic l-lactide polymerization

The preparation of polyethylenimine (PEI)–polylactide (PLA) copolymer structures is promising as these materials may find use in gene and/or drug delivery applications.

Antisense mediated exon skipping therapy for duchenne muscular dystrophy (DMD)

Duchenne Muscular Dystrophy (DMD) is a lethal disease caused by mutations in the dystrophin gene (DMD) that result in the absence of essential muscle protein dystrophin. Among many different approaches for DMD treatment, exon skipping, mediated by antisense oligonucleotides, is one of the most promising methods for restoration of dystrophin expression. This approach has been tested extensively targeting different exons in numerous models both in vitro and in vivo. During the past 10 years, there has been a considerable progress by using DMD animal models involving three types of antisense oligonucleotides (2'-O-methyl phosphorothioate (2OME-PS), phosphorodiamidate morpholino oligomer (PMO)) and peptide nucleic acid (PNA).

Encapsulated microbubbles and echogenic liposomes for contrast ultrasound imaging and targeted drug delivery

Micron- to nanometer-sized ultrasound agents, like encapsulated microbubbles and echogenic liposomes, are being developed for diagnostic imaging and ultrasound mediated drug/gene delivery. This review provides an overview of the current state of the art of the mathematical models of the acoustic behavior of ultrasound contrast microbubbles. We also present a review of the in vitro experimental characterization of the acoustic properties of microbubble based contrast agents undertaken in our laboratory. The hierarchical two-pronged approach of modeling contrast agents we developed is demonstrated for a lipid coated (Sonazoid™) and a polymer shelled (poly D-L-lactic acid) contrast microbubbles. The acoustic and drug release properties of the newly developed echogenic liposomes are discussed for their use as simultaneous imaging and drug/gene delivery agents. Although echogenicity is conclusively demonstrated in experiments, its physical mechanisms remain uncertain. Addressing questions raised here will accelerate further development and eventual clinical approval of these novel technologies.

New developments in the use of gene therapy to treat Duchenne muscular dystrophy

INTRODUCTION

Duchenne muscular dystrophy (DMD) is a lethal X-linked inherited disorder characterised by progressive muscle weakness, wasting and degeneration. Although the gene affected in DMD was identified over 25 years ago, there is still no effective treatment.

AREAS COVERED

Here we review some of the genetic-based strategies aimed at amelioration of the DMD phenotype. A number of Phase II/III clinical trials of antisense oligonucleotide-induced exon skipping for restoration of the open reading frame (ORF) of the DMD gene have recently been completed. The potential strategies for overcoming the hurdles that appear to prevent exon skipping becoming an effective treatment for DMD currently are discussed.

EXPERT OPINION

The applicability of exon skipping as a therapy to DMD is restricted and the development of alternative strategies that are more encompassing is needed. The rapid pre-clinical advances that are being made in the field of adeno-associated virus (AAV)-based delivery of micro-dystrophin would address this. The obstacles to be faced with gene replacement strategies would include the need for high viral titres, efficient muscle targeting and avoidance of immune response to vector and transgene. The new emerging field of gene editing could potentially provide permanent correction of the DMD gene and the feasibility of such an approach to DMD is discussed.

Determination of the interfacial rheological properties of a poly(DL-lactic acid)-encapsulated contrast agent using in vitro attenuation and scattering

The stabilizing encapsulation of a microbubble-based ultrasound contrast agent (UCA) critically affects its acoustic properties. Polymers, which behave differently from materials commonly used (i.e., lipids or proteins) for monolayer encapsulation, have the potential for better stability and improved control of encapsulation properties. Air-filled microbubbles coated with poly(DL-lactic acid) (PLA) are characterized here using in vitro acoustic experiments and several models of encapsulation. The interfacial rheological properties of the encapsulation are determined according to each model using attenuation of ultrasound through a suspension of microbubbles. Then the model predictions are compared with scattered non-linear (sub- and second harmonic) responses. For this microbubble population (average diameter, 1.9 μm), the peak in attenuation measurement indicates a weighted-average resonance frequency of 2.5-3 MHz, which, in contrast to other encapsulated microbubbles, is lower than the resonance frequency of a free bubble of similar size (diameter, 1.9 μm). This apparently contradictory result stems from the extremely low surface dilational elasticity (around 0.01-0.07 N/m) and the reduced surface tension of the poly(DL-lactic acid) encapsulation, as well as the polydispersity of the bubble population. All models considered here are shown to behave similarly even in the non-linear regime because of the low surface dilational elasticity value. Pressure-dependent scattering measurements at two different excitation frequencies (2.25 and 3 MHz) revealed strongly non-linear behavior with 25-30 dB and 5-20 dB enhancements in fundamental and second-harmonic responses, respectively, for a contrast agent concentration of 1.33 μg/mL in the suspension. Sub-harmonic responses are registered above a relatively low generation threshold of 100-150 kPa, with up to 20 dB enhancement beyond that pressure. Numerical predictions from all models show good agreement with the experimentally measured fundamental response, but not with the experimental second-harmonic response. The characteristic features of sub-harmonic responses and the steady response beyond the threshold are matched well by model predictions. However, prediction of the threshold value depends on estimated properties and size distribution. The variation in size distribution from sample to sample leads to variation in estimates of encapsulation properties: the lowest estimated value for surface dilational viscosity better predicts the sub-harmonic threshold.

Genetic therapeutic approaches for Duchenne muscular dystrophy

Despite an expansive wealth of research following the discovery of the DMD gene 25 years ago, there is still no curative treatment for Duchenne muscular dystrophy. However, there are currently many promising lines of research, including cell-based therapies and pharmacological reagents to upregulate dystrophin via readthrough of nonsense mutations or by upregulation of the dystrophin homolog utrophin. Here we review genetic-based therapeutic strategies aimed at the amelioration of the DMD phenotype. These include the reintroduction of a copy of the DMD gene into an affected tissue by means of a viral vector; correction of the mutated DMD transcript by antisense oligonucleotide-induced exon skipping to restore the open reading frame; and direct modification of the DMD gene at a chromosomal level through genome editing. All these approaches are discussed in terms of the more recent advances, and the hurdles to be overcome if a comprehensive and effective treatment for DMD is to be found. These hurdles include the need to target all musculature of the body. Therefore any potential treatment would need to be administered systemically. In addition, any treatment needs to have a long-term effect, with the possibility of readministration, while avoiding any potentially detrimental immune response to the vector or transgene.

A novel hybrid delivery system: polymer-oil nanostructured carrier for controlled delivery of highly lipophilic drug all-trans-retinoic acid (ATRA)

Many recently developed drugs encounter delivery issues due to their high lipophilicity and poor aqueous solubility. This study reports the development of a novel hybrid nanocarrier known as polymer-oil nanostructured carrier (PONC), in which highly lipophilic drugs such as all-trans-retinoic acid (ATRA) and indomethacin pre-solubilized in oil phase were dispersed in a polymeric matrix of poly(D,L-lactic-co-glycolic acid) (PLGA). In comparison to the standard PLGA only nanoparticles, PONC substantially increased the encapsulation efficiency of ATRA and indomethacin by up to 259% and 124%, respectively. Differential scanning calorimetry analysis revealed that the inclusion of oil introduced nanostructure into the polymeric matrix of the carrier. This feature facilitated more uniform distribution of the drug molecules which subsequently led to improved drug release kinetics with significantly reduced burst release effects (p<0.05). PONC was lyophilizable, remained physically stable when stored at low temperatures, and demonstrated low non-specific carrier toxicity. Delivery of ATRA by PONC also significantly improved its anticancer activity over the standard PLGA only nanoparticles (p<0.05). Our findings have therefore validated a promising delivery system that integrates the advantages of lipid-based (e.g. efficient encapsulation of highly lipophilic drugs) and polymeric colloidal carriers (e.g. uniform size, good stability), plus potential therapeutic benefits for delivery of poorly water-soluble anticancer drugs like ATRA.

PLGA nanoparticle-mediated delivery of tumor antigenic peptides elicits effective immune responses

The peptide vaccine clinical trials encountered limited success because of difficulties associated with stability and delivery, resulting in inefficient antigen presentation and low response rates in patients with cancer. The purpose of this study was to develop a novel delivery approach for tumor antigenic peptides in order to elicit enhanced immune responses using poly(DL-lactide-co-glycolide) nanoparticles (PLGA-NPs) encapsulating tumor antigenic peptides. PLGA-NPs were made using the double emulsion-solvent evaporation method. Artificial antigen-presenting cells were generated by human dendritic cells (DCs) loaded with PLGA-NPs encapsulating tumor antigenic peptide(s). The efficiency of the antigen presentation was measured by interferon-γ ELISpot assay (Vector Laboratories, Burlingame, CA). Antigen-specific cytotoxic T lymphocytes (CTLs) were generated and evaluated by CytoTox 96^® Non-Radioactive Cytotoxicity Assay (Promega, Fitchburg, WI). The efficiency of the peptide delivery was compared between the methods of emulsification in incomplete Freund’s adjuvant and encapsulation in PLGA-NPs. Our results showed that most of the PLGA-NPs were from 150 nm to 500 nm in diameter, and were negatively charged at pH 7.4 with a mean zeta potential of −15.53 ± 0.71 mV; the PLGA-NPs could be colocalized in human DCs in 30 minutes of incubation. Human DCs loaded with PLGA-NPs encapsulating peptide induced significantly stronger CTL cytotoxicity than those pulsed with free peptide, while human DCs loaded with PLGA-NPs encapsulating a three-peptide cocktail induced a significantly greater CTL response than those encapsulating a two-peptide cocktail. Most importantly, the peptide dose encapsulated in PLGA-NPs was 63 times less than that emulsified in incomplete Freund’s adjuvant, but it induced a more powerful CTL response in vivo. These results demonstrate that the delivery of peptides encapsulated in PLGA-NPs is a promising approach to induce effective antitumor CTL responses in vivo.

Cytotoxicity and ion release of alloy nanoparticles

It is well-known that nanoparticles could cause toxic effects in cells. Alloy nanoparticles with yet unknown health risk may be released from cardiovascular implants made of Nickel-Titanium or Cobalt-Chromium due to abrasion or production failure. We show the bio-response of human primary endothelial and smooth muscle cells exposed to different concentrations of metal and alloy nanoparticles. Nanoparticles having primary particle sizes in the range of 5-250 nm were generated using laser ablation in three different solutions avoiding artificial chemical additives, and giving access to formulations containing nanoparticles only stabilized by biological ligands. Endothelial cells are found to be more sensitive to nanoparticle exposure than smooth muscle cells. Cobalt and Nickel nanoparticles caused the highest cytotoxicity. In contrast, Titanium, Nickel-Iron, and Nickel-Titanium nanoparticles had almost no influence on cells below a nanoparticle concentration of 10 μM. Nanoparticles in cysteine dissolved almost completely, whereas less ions are released when nanoparticles were stabilized in water or citrate solution. Nanoparticles stabilized by cysteine caused less inhibitory effects on cells suggesting cysteine to form metal complexes with bioactive ions in media.

PEG based hyperbranched polymeric hollow nanospheres

The synthesis of a new PEG based hyperbranched copolymer of poly(ethylene glycol) methyl ether methacrylate-co-ethylene glycol dimethacrylate (PEGMEMA-co-EGDMA) was achieved via a one-step in situ deactivation enhanced atom transfer radical polymerization (DE-ATRP). Then, hollow PEG based nanospheres were fabricated from this polymer using a solvent evaporation method and post-stabilisation strategy. Furthermore, the analysis using a cellular metabolic activity assay proved that the copolymer did not affect cellular metabolism, indicating that this PEG based polymeric nanosphere has potential for use in drug delivery applications.

Fabrication of PLGA nanoparticles with a fluidic nanoprecipitation system

Particle size is a key feature in determining performance of nanoparticles as drug carriers because it influences circulating half-life, cellular uptake and biodistribution. Because the size of particles has such a major impact on their performance, the uniformity of the particle population is also a significant factor. Particles comprised of the polymer poly(lactic-co-glycolic acid) (PLGA) are widely studied as therapeutic delivery vehicles because they are biodegradable and biocompatible. In fact, microparticles comprised of PLGA are already approved for drug delivery. Unfortunately, PLGA nanoparticles prepared by conventional methods usually lack uniformity. We developed a novel Fluidic NanoPrecipitation System (FNPS) to fabricate highly uniform PLGA particles. Several parameters can be fine-tuned to generate particles of various sizes.

RNA-targeted splice-correction therapy for neuromuscular disease

Splice-modulation therapy, whereby molecular manipulation of premessenger RNA splicing is engineered to yield genetic correction, is a promising novel therapy for genetic diseases of muscle and nerve-the prototypical example being Duchenne muscular dystrophy. Duchenne muscular dystrophy is the most common childhood genetic disease, affecting one in 3500 newborn boys, causing progressive muscle weakness, heart and respiratory failure and premature death. No cure exists for this disease and a number of promising new molecular therapies are being intensively studied. Duchenne muscular dystrophy arises due to mutations that disrupt the open-reading-frame in the DMD gene leading to the absence of the essential muscle protein dystrophin. Of all novel molecular interventions currently being investigated for Duchenne muscular dystrophy, perhaps the most promising method aiming to restore dystrophin expression to diseased cells is known as 'exon skipping' or splice-modulation, whereby antisense oligonucleotides eliminate the deleterious effects of DMD mutations by modulating dystrophin pre-messenger RNA splicing, such that functional dystrophin protein is produced. Recently this method was shown to be promising and safe in clinical trials both in The Netherlands and the UK. These trials studied direct antisense oligonucleotide injections into single peripheral lower limb muscles, whereas a viable therapy will need antisense oligonucleotides to be delivered systemically to all muscles, most critically to the heart, and ultimately to all other affected tissues including brain. There has also been considerable progress in understanding how such splice-correction methods could be applied to the treatment of related neuromuscular diseases, including spinal muscular atrophy and myotonic dystrophy, where defects of splicing or alternative splicing are closely related to the disease mechanism.

Emerging genetic therapies to treat Duchenne muscular dystrophy

PURPOSE OF REVIEW

Duchenne muscular dystrophy is a progressive muscle degenerative disease caused by dystrophin mutations. The purpose of this review is to highlight two emerging therapies designed to repair the primary genetic defect, called 'exon skipping' and 'nonsense codon suppression'.

RECENT FINDINGS

A drug, PTC124, was identified that suppresses nonsense codon translation termination. PTC124 can lead to restoration of some dystrophin expression in human Duchenne muscular dystrophy muscles with mutations resulting in premature stops. Two drugs developed for exon skipping, PRO051 and AVI-4658, result in the exclusion of exon 51 from mature mRNA. They can restore the translational reading frame to dystrophin transcripts from patients with a particular subset of dystrophin gene deletions and lead to some restoration of dystrophin expression in affected boys' muscle in vivo. Both approaches have concluded phase I trials with no serious adverse events.

SUMMARY

These novel therapies that act to correct the primary genetic defect of dystrophin deficiency are among the first generation of therapies tailored to correct specific mutations in humans. Thus, they represent paradigm forming approaches to personalized medicine with the potential to lead to life changing treatment for those affected by Duchenne muscular dystrophy.

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.