Self-complementary adeno-associated viral vectors for gene therapy of hemophilia B: progress and challenges

Viral-based animal models in polyglutamine disorders

Polyglutamine disorders are a complex group of incurable neurodegenerative disorders caused by an abnormal expansion in the trinucleotide cytosine-adenine-guanine tract of the affected gene. To better understand these disorders, our dependence on animal models persists, primarily relying on transgenic models. In an effort to complement and deepen our knowledge, researchers have also developed animal models of polyglutamine disorders employing viral vectors. Viral vectors have been extensively used to deliver genes to the brain, not only for therapeutic purposes but also for the development of animal models, given their remarkable flexibility. In a time- and cost-effective manner, it is possible to use different transgenes, at varying doses, in diverse targeted tissues, at different ages, and in different species, to recreate polyglutamine pathology. This paper aims to showcase the utility of viral vectors in disease modelling, share essential considerations for developing animal models with viral vectors, and provide a comprehensive review of existing viral-based animal models for polyglutamine disorders.

Self-complementary AAV vector therapy for treating corneal cloudiness of mucopolysaccharidosis type VII (MPS VII)

PURPOSE

To design a novel efficacious scAAV-Gusb viral vector for treating Mucopolysaccharidosis Type VII (MPS VII) caused by a mutation in the β-Glu gene (Gusb allele).

METHODS

β-Glu expression of single-stranded AAV-Gusb (ssAAV-Gusb) and self-complementary AAV (scAAV-Gusb) vectors are tested with cultured murine Gusb fibroblasts. The scAAV-Gusb vector was chosen in further studies to prolong the life span and treat corneal pathology of Gusb mice via intrahepatic injection of neonates and intrastromal injection in adults, respectively. Corneal pathology was studied using HRT2 in vivo confocal microscope and histochemistry in mice corneas.

RESULTS

Both ssAAV-Gusb and scAAV-Gusb vectors expressed murine β-Glu in cultured Gusb fibroblasts. The scAAV-Gusb vector had higher transduction efficiency than the ssAAV-Gusb vector. To prolong the life span of Gusb mice, neonates (3 days old) were administered with scAAV-Gusb virus via intrahepatic injection. The treatment improves the survival rate of Gusb mice, prolonging the median survival rate from 22.5 weeks (untreated) to 50 weeks (treated). Thereafter, we determined the efficacy of the scAAV-Gusb virus in ameliorating corneal cloudiness observed in aged Gusb mice. Both corneal cloudiness and stroma thickness decreased, and there was the presence of β-Glu enzyme activity in the Gusb corneas receiving scAAV-Gusb virus associated with morphology change of amoeboid stromal cells in untreated to characteristic dendritic keratocytes morphology after 4-12 weeks of scAAV-Gusb virus injection.

CONCLUSION

Intrahepatic injection of scAAV-Gusb is efficacious in prolonging the life span of Gusb mice, and intrastromal injection can ameliorate corneal phenotypes. Both strategies can be adapted for treating other MPS.

Potential Therapeutic Approach using Aromatic l-amino Acid Decarboxylase and Glial-derived Neurotrophic Factor Therapy Targeting Putamen in Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative illness characterized by specific loss of dopaminergic neurons, resulting in impaired motor movement. Its prevalence is twice as compared to the previous 25 years and affects more than 10 million individuals. Lack of treatment still uses levodopa and other options as disease management measures. Treatment shifts to gene therapy (GT), which utilizes direct delivery of specific genes at the targeted area. Therefore, the use of aromatic L-amino acid decarboxylase (AADC) and glial-derived neurotrophic factor (GDNF) therapy achieves an effective control to treat PD. Patients diagnosed with PD may experience improved therapeutic outcomes by reducing the frequency of drug administration while utilizing provasin and AADC as dopaminergic protective therapy. Enhancing the enzymatic activity of tyrosine hydroxylase (TH), glucocorticoid hormone (GCH), and AADC in the striatum would be useful for external L-DOPA to restore the dopamine (DA) level. Increased expression of glutamic acid decarboxylase (GAD) in the subthalamic nucleus (STN) may also be beneficial in PD. Targeting GDNF therapy specifically to the putaminal region is clinically sound and beneficial in protecting the dopaminergic neurons. Furthermore, preclinical and clinical studies supported the role of GDNF in exhibiting its neuroprotective effect in neurological disorders. Another Ret receptor, which belongs to the tyrosine kinase family, is expressed in dopaminergic neurons and sounds to play a vital role in inhibiting the advancement of PD. GDNF binding on those receptors results in the formation of a receptor-ligand complex. On the other hand, venous delivery of recombinant GDNF by liposome-based and encapsulated cellular approaches enables the secure and effective distribution of neurotrophic factors into the putamen and parenchyma. The current review emphasized the rate of GT target GDNF and AADC therapy, along with the corresponding empirical evidence.

Gene therapy with bidridistrogene xeboparvovec for limb-girdle muscular dystrophy type 2E/R4: phase 1/2 trial results

Limb-girdle muscular dystrophy 2E/R4 is caused by mutations in the β-sarcoglycan (SGCB) gene, leading to SGCB deficiency and consequent muscle loss. We developed a gene therapy approach based on functional replacement of the deficient SCB protein. Here we report interim results from a first-in-human, open-label, nonrandomized, phase 1/2 trial evaluating the safety and efficacy of bidridistrogene xeboparvovec, an adeno-associated virus-based gene therapy containing a codon-optimized, full-length human SGCB transgene. Patients aged 4-15 years with confirmed SGCB mutations at both alleles received one intravenous infusion of either 1.85 × 1013 vector genome copies kg-1 (Cohort 1, n = 3) or 7.41 × 1013 vector gene copies kg-1 (Cohort 2, n = 3). Primary endpoint was safety, and secondary endpoint was change in SGCB expression in skeletal muscle from baseline to Day 60. We report interim Year 2 results (trial ongoing). The most frequent treatment-related adverse events were vomiting (four of six patients) and gamma-glutamyl transferase increase (three of six patients). Serious adverse events resolved with standard therapies. Robust SGCB expression was observed: Day 60 mean (s.d.) percentage of normal expression 36.2% (2.7%) in Cohort 1 and 62.1% (8.7%) in Cohort 2. Post hoc exploratory analysis showed preliminary motor improvements using the North Star Assessment for Limb-girdle Type Muscular Dystrophies maintained through Year 2. The 2-year safety and efficacy of bidridistrogene xeboparvovec support clinical development advancement. Further studies are necessary to confirm the long-term safety and efficacy of this gene therapy. ClinicalTrials.gov registration: NCT03652259 .

scAAV2-Mediated Expression of Thioredoxin 2 and C3 Transferase Prevents Retinal Ganglion Cell Death and Lowers Intraocular Pressure in a Mouse Model of Glaucoma

Elevated intraocular pressure (IOP) in glaucoma causes retinal ganglion cell (RGC) loss and damage to the optic nerve. Although IOP is controlled pharmacologically, no treatment is available to restore retinal and optic nerve function. In this paper, we aimed to develop a novel gene therapy for glaucoma using an AAV2-based thioredoxin 2 (Trx2)-exoenzyme C3 transferase (C3) fusion protein expression vector (scAAV2-Trx2-C3). We evaluated the therapeutic effects of this vector in vitro and in vivo using dexamethasone (DEX)-induced glaucoma models. We found that scAAV2-Trx2-C3-treated HeLa cells had significantly reduced GTP-bound active RhoA and increased phosphor-cofilin Ser3 protein expression levels. scAAV2-Trx2-C3 was also shown to inhibit oxidative stress, fibronectin expression, and alpha-SMA expression in DEX-treated HeLa cells. NeuN immunostaining and TUNEL assay in mouse retinal tissues was performed to evaluate its neuroprotective effect upon RGCs, whereas changes in mouse IOP were monitored via rebound tonometer. The present study showed that scAAV2-Trx2-C3 can protect RGCs from degeneration and reduce IOP in a DEX-induced mouse model of glaucoma, while immunohistochemistry revealed that the expression of fibronectin and alpha-SMA was decreased after the transduction of scAAV2-Trx2-C3 in murine eye tissues. Our results suggest that AAV2-Trx2-C3 modulates the outflow resistance of the trabecular meshwork, protects retinal and other ocular tissues from oxidative damage, and may lead to the development of a gene therapeutic for glaucoma.

Emerging Perspectives on Gene Therapy Delivery for Neurodegenerative and Neuromuscular Disorders

Neurodegenerative disorders (NDDs), such as Alzheimer's disease (AD) and Parkinson's Disease (PD), are a group of heterogeneous diseases that mainly affect central nervous system (CNS) functions. A subset of NDDs exhibit CNS dysfunction and muscle degeneration, as observed in Gangliosidosis 1 (GM1) and late stages of PD. Neuromuscular disorders (NMDs) are a group of diseases in which patients show primary progressive muscle weaknesses, including Duchenne Muscular Dystrophy (DMD), Pompe disease, and Spinal Muscular Atrophy (SMA). NDDs and NMDs typically have a genetic component, which affects the physiological functioning of critical cellular processes, leading to pathogenesis. Currently, there is no cure or efficient treatment for most of these diseases. More than 200 clinical trials have been completed or are currently underway in order to establish safety, tolerability, and efficacy of promising gene therapy approaches. Thus, gene therapy-based therapeutics, including viral or non-viral delivery, are very appealing for the treatment of NDDs and NMDs. In particular, adeno-associated viral vectors (AAV) are an attractive option for gene therapy for NDDs and NMDs. However, limitations have been identified after systemic delivery, including the suboptimal capacity of these therapies to traverse the blood-brain barrier (BBB), degradation of the particles during the delivery, high reactivity of the patient's immune system during the treatment, and the potential need for redosing. To circumvent these limitations, several preclinical and clinical studies have suggested intrathecal (IT) delivery to target the CNS and peripheral organs via cerebrospinal fluid (CSF). CSF administration can vastly improve the delivery of small molecules and drugs to the brain and spinal cord as compared to systemic delivery. Here, we review AAV biology and vector design elements, different therapeutic routes of administration, and highlight CSF delivery as an attractive route of administration. We discuss the different aspects of neuromuscular and neurodegenerative diseases, such as pathogenesis, the landscape of mutations, and the biological processes associated with the disease. We also describe the hallmarks of NDDs and NMDs as well as discuss current therapeutic approaches and clinical progress in viral and non-viral gene therapy and enzyme replacement strategies for those diseases.

Gene Therapy Advances: A Meta-Analysis of AAV Usage in Clinical Settings

Adeno-associated viruses (AAVs) are the safest and most effective gene delivery vehicles to drive long-term transgene expression in gene therapy. While animal studies have shown promising results, the translatability of AAVs into clinical settings has been partly limited due to their restricted gene packaging capacities, off-target transduction, and immunogenicity. In this study, we analysed over two decades of AAV applications, in 136 clinical trials. This meta-analysis aims to provide an up-to-date overview of the use and successes of AAVs in clinical trials, while evaluating the approaches used to address the above challenges. First, this study reveals that the speed of novel AAV development has varied between therapeutic areas, with particular room for improvement in Central Nervous System disorders, where development has been slow. Second, the lack of dose-dependent toxicity and efficacy data indicates that optimal dosing regimes remain elusive. Third, more clinical data on the effectiveness of various immune-modulation strategies and gene editing approaches are required to direct future research and to accelerate the translation of AAV-mediated gene therapy into human applications.

Capsid-Engineering for Central Nervous System-Directed Gene Therapy with Adeno-Associated Virus Vectors

Closing the gap in knowledge on the cause of neurodegenerative disorders is paving the way toward innovative treatment strategies, among which gene therapy has emerged as a top candidate. Both conventional gene therapy and genome editing approaches are being developed, and a great number of human clinical trials are ongoing. Already 2 years ago, the first gene therapy for a neurodegenerative disease, spinal muscular atrophy type 1 (SMA1), obtained market approval. To realize such innovative strategies, gene therapy delivery tools are key assets. Here, we focus on recombinant adeno-associated virus (AAV) vectors and report on strategies to improve first-generation vectors. Current efforts focus on the viral capsid to modify the host-vector interaction aiming at increasing the efficacy of target cell transduction, at simplifying vector administration, and at reducing the risk of vector dose-related side effects.

Combinations of Single Chain Variable Fragments From HIV Broadly Neutralizing Antibodies Demonstrate High Potency and Breadth

Broadly neutralizing antibodies (bNAbs) are currently being assessed in clinical trials for their ability to prevent HIV infection. Single chain variable fragments (scFv) of bNAbs have advantages over full antibodies as their smaller size permits improved diffusion into mucosal tissues and facilitates vector-driven gene expression. We have previously shown that scFv of bNAbs individually retain significant breadth and potency. Here we tested combinations of five scFv derived from bNAbs CAP256-VRC26.25 (V2-apex), PGT121 (N332-supersite), 3BNC117 (CD4bs), 8ANC195 (gp120-gp41 interface) and 10E8v4 (MPER). Either two or three scFv were combined in equimolar amounts and tested in the TZM-bl neutralization assay against a multiclade panel of 17 viruses. Experimental IC50 and IC80 data were compared to predicted neutralization titers based on single scFv titers using the Loewe additive and the Bliss-Hill model. Like full-sized antibodies, combinations of scFv showed significantly improved potency and breadth compared to single scFv. Combinations of two or three scFv generally followed an independent action model for breadth and potency with no significant synergy or antagonism observed overall although some exceptions were noted. The Loewe model underestimated potency for some dual and triple combinations while the Bliss-Hill model was better at predicting IC80 titers of triple combinations. Given this, we used the Bliss-Hill model to predict the coverage of scFv against a 45-virus panel at concentrations that correlated with protection in the AMP trials. Using IC80 titers and concentrations of 1μg/mL, there was 93% coverage for one dual scFv combination (3BNC117+10E8v4), and 96% coverage for two of the triple combinations (CAP256.25+3BNC117+10E8v4 and PGT121+3BNC117+10E8v4). Combinations of scFv, therefore, show significantly improved breadth and potency over individual scFv and given their size advantage, have potential for use in passive immunization.

Genome-based therapeutic interventions for β-type hemoglobinopathies

For decades, various strategies have been proposed to solve the enigma of hemoglobinopathies, especially severe cases. However, most of them seem to be lagging in terms of effectiveness and safety. So far, the most prevalent and promising treatment options for patients with β-types hemoglobinopathies, among others, predominantly include drug treatment and gene therapy. Despite the significant improvements of such interventions to the patient's quality of life, a variable response has been demonstrated among different groups of patients and populations. This is essentially due to the complexity of the disease and other genetic factors. In recent years, a more in-depth understanding of the molecular basis of the β-type hemoglobinopathies has led to significant upgrades to the current technologies, as well as the addition of new ones attempting to elucidate these barriers. Therefore, the purpose of this article is to shed light on pharmacogenomics, gene addition, and genome editing technologies, and consequently, their potential use as direct and indirect genome-based interventions, in different strategies, referring to drug and gene therapy. Furthermore, all the latest progress, updates, and scientific achievements for patients with β-type hemoglobinopathies will be described in detail.

Etranacogene dezaparvovec for hemophilia B gene therapy

The treatment landscape for hemophilia has been rapidly changing with introduction of novel therapies. Gene therapy for hemophilia is a promising therapeutic option for sustained endogenous factor production to mitigate the need for prophylactic treatment to prevent spontaneous and traumatic bleeding. Etranacogene dezaparvovec is an investigational factor IX (FIX) gene transfer product that utilizes the adeno-associated virus (AAV) 5 vector with a liver-specific promoter and a hyperactive FIX transgene. Here, the development of etranacogene dezaparvovec and available efficacy and safety data from clinical trials are reviewed. Overall, etranacogene dezaparvovec provides sustained FIX expression for more than 2 years and allows for a bleed and infusion-free life in the majority of patients. Safety, efficacy, and quality-of-life data will inform shared decision-making for patients who are considering gene therapy. Long-term follow-up regarding duration of expression and safety are crucial.

Liver induced transgene tolerance with AAV vectors

Immune tolerance is a vital component of immunity, as persistent activation of immune cells causes significant tissue damage and loss of tolerance leads to autoimmunity. Likewise, unwanted immune responses can occur in inherited disorders, such as hemophilia and Pompe disease, in which patients lack any expression of protein, during treatment with enzyme replacement therapy, or gene therapy. While the liver has long been known as being tolerogenic, it was only recently appreciated in the last decade that liver directed adeno-associated virus (AAV) gene therapy can induce systemic tolerance to a transgene. In this review, we look at the mechanisms behind liver induced tolerance, discuss different factors influencing successful tolerance induction with AAV, and applications where AAV mediated tolerance may be helpful.

Clinical advances in gene therapy updates on clinical trials of gene therapy in haemophilia

Gene therapy is rapidly becoming a new therapeutic strategy for haemophilia A and B treatment. In the 1990s, studies in animal models showed that adeno-associated vectors (AAV) exhibited an efficient expression of factor IX (FIX). In the first clinical trial in patients with haemophilia B, therapeutic levels of FIX were documented but the expression remained only for few weeks. Subsequently, improvements in vector design, such as the use of different AAV serotypes, the development of the self-complementary vector, the engineering of the transgene with codon optimization and liver-specific expression cassette resulted in circulating FIX level between 2% and 5% for long-lasting period. Recently, a natural gain of function FIX variant (Padua) inserted in the F9 cDNA improved the expression of FIX achieving a level of more than 30% resulting in cessation of infusions and in a greatly reduction of bleeding events. Encouraging clinical progresses have been also obtained from trials of gene therapy for haemophilia A. Transgene expression persisted for three years with circulating FVIII activity levels of 52.3% in patients treated with AAV vector containing a codon-optimized F8 cDNA. A complication, reported in both clinical trials for haemophilia A and B, was the elevation of liver enzymes, which resolved with steroid treatment in a large group of patients. However, to date, the pathophysiological mechanism for the liver toxicity remains still unclear. Clinical trials with adeno-associated vectors have documented a significant success for haemophilia gene therapy demonstrating potential to transform haemophilia treatment offering hope for a long-term expression.

Basic Concepts in Viral Vector-Mediated Gene Therapy

Today any researcher with the desire can easily purchase a viral vector. However, despite the availability of viral vectors themselves, the requisite knowledge that is absolutely essential to conducting a gene therapy experiment remains somewhat obscure and esoteric. To utilize viral vectors to their full potential, a large number of decisions must be made, in some instances prior to even obtaining the vector itself. For example, critical decisions include selection of the proper virus, selection of the proper expression cassette, whether to produce or purchase a viral vector, proper viral handling and storage, the most appropriate delivery method, selecting the proper controls, how to ensure your virus is expressing properly, and many other complex decisions that are essential to performing a successful gene therapy experiment. The need to make so many important decisions can be overwhelming and potentially prohibitive, especially to the novice gene therapist. In order to aid in this challenging process, here we provide an overview of basic gene therapy modalities and a decision tree that can be used to make oneself aware of the options available to the beginning gene therapist. This information can be used as a road map to help navigate the complex and perhaps confusing process of designing a successful gene therapy experiment.

Adeno-associated Virus Genome Population Sequencing Achieves Full Vector Genome Resolution and Reveals Human-Vector Chimeras

Recombinant adeno-associated virus (rAAV)-based gene therapy has entered a phase of clinical translation and commercialization. Despite this progress, vector integrity following production is often overlooked. Compromised vectors may negatively impact therapeutic efficacy and safety. Using single molecule, real-time (SMRT) sequencing, we can comprehensively profile packaged genomes as a single intact molecule and directly assess vector integrity without extensive preparation. We have exploited this methodology to profile all heterogeneic populations of self-complementary AAV genomes via bioinformatics pipelines and have coined this approach AAV-genome population sequencing (AAV-GPseq). The approach can reveal the relative distribution of truncated genomes versus full-length genomes in vector preparations. Preparations that seemingly show high genome homogeneity by gel electrophoresis are revealed to consist of less than 50% full-length species. With AAV-GPseq, we can also detect many reverse-packaged genomes that encompass sequences originating from plasmid backbone, as well as sequences from packaging and helper plasmids. Finally, we detect host-cell genomic sequences that are chimeric with inverted terminal repeat (ITR)-containing vector sequences. We show that vector populations can contain between 1.3% and 2.3% of this type of undesirable genome. These discoveries redefine quality control standards for viral vector preparations and highlight the degree of foreign products in rAAV-based therapeutic vectors.

Gene therapy for hemophilia

Hemophilia is an X-linked inherited bleeding disorder consisting of two classifications, hemophilia A and hemophilia B, depending on the underlying mutation. Although the disease is currently treatable with intravenous delivery of replacement recombinant clotting factor, this approach represents a significant cost both monetarily and in terms of quality of life. Gene therapy is an attractive alternative approach to the treatment of hemophilia that would ideally provide life-long correction of clotting activity with a single injection. In this review, we will discuss the multitude of approaches that have been explored for the treatment of both hemophilia A and B, including both in vivo and ex vivo approaches with viral and nonviral delivery vectors.

Immune responses to intramuscular administration of alipogene tiparvovec (AAV1-LPL(S447X)) in a phase II clinical trial of lipoprotein lipase deficiency gene therapy

Cellular immune responses to adeno-associated viral (AAV) vectors used for gene therapy have been linked to attenuated transgene expression and loss of efficacy. The impact of such cellular immune responses on the clinical efficacy of alipogene tiparvovec (Glybera; AAV1-LPL(S447X); uniQure), a gene therapy consisting of intramuscular administration of a recombinant AAV1 mediating muscle-directed expression of lipoprotein lipase (LPL), was investigated. Five subjects with LPL deficiency (LPLD) were administered intramuscularly with a dose of 1 × 10(12) gc/kg alipogene tiparvovec. All subjects were treated with immune suppression starting shortly before administration of alipogene tiparvovec and maintained until 12 weeks after administration. Systemic antibody and T cell responses against AAV1 and LPL(S447X), as well as local cellular immune responses in the injected muscle, were investigated in five LPLD subjects. Long-term transgene expression was demonstrated despite a transient systemic cellular response and a stable humoral immune response against the AAV1 capsid protein. Cellular infiltrates were found in four of the five subjects but were not associated with adverse clinical events or elevation of inflammation markers. Consistent herewith, CD8+ T cells in the infiltrates lacked cytotoxic potential. Furthermore, FoxP3+/CD4+ T cells were found in the infiltrates, suggesting that multiple mechanisms contribute to local tolerance. Systemic and local immune responses induced by intramuscular injection of alipogene tiparvovec did not appear to have an impact on safety and did not prevent LPL transgene expression. These findings support the use of alipogene tiparvovec in individuals with LPLD and indicate that muscle-directed AAV-based gene therapy remains a promising approach for the treatment of human diseases.

Role of the vector genome and underlying factor IX mutation in immune responses to AAV gene therapy for hemophilia B

Background

Self-complementary adeno-associated virus (scAAV) vectors have become a desirable vector for therapeutic gene transfer due to their ability to produce greater levels of transgene than single-stranded AAV (ssAAV). However, recent reports have suggested that scAAV vectors are more immunogenic than ssAAV. In this study, we investigated the effects of a self-complementary genome during gene therapy with a therapeutic protein, human factor IX (hF.IX).

Methods

Hemophilia B mice were injected intramuscularly with ss or scAAV1 vectors expressing hF.IX. The outcome of gene transfer was assessed, including transgene expression as well as antibody and CD8⁺ T cell responses to hF.IX.

Results

Self-complementary AAV1 vectors induced similar antibody responses (which eliminated systemic hF.IX expression) but stronger CD8⁺ T cell responses to hF.IX relative to ssAAV1 in mice with F9 gene deletion. As a result, hF.IX-expressing muscle fibers were effectively eliminated in scAAV-treated mice. In contrast, mice with F9 nonsense mutation (late stop codon) lacked antibody or T cell responses, thus showing long-term expression regardless of the vector genome.

Conclusions

The nature of the AAV genome can impact the CD8⁺ T cell response to the therapeutic transgene product. In mice with endogenous hF.IX expression, however, this enhanced immunogenicity did not break tolerance to hF.IX, suggesting that the underlying mutation is a more important risk factor for transgene-specific immunity than the molecular form of the AAV genome.

Development of gene therapy for blood disorders: an update

This review addresses the current status of gene therapy for immunodeficiencies, chronic granulomatous disease, suicide gene therapy for graft-versus-host disease, viral infections, malignant hematologic disorders, hemophilia, and the hemoglobin disorders. New developments in vector design have fostered improved expression as well as enhanced safety, particularly of integrating retroviral vectors. Several immunodeficiencies have been treated successfully by stem cell-targeted, retroviral-mediated gene transfer with reconstitution of the immune system following infusion of the transduced cells. In a trial for hemophilia B, long-term expression of human FIX has been observed following adeno-associated viral vector-mediated gene transfer into the liver. This approach should be successful in treating any disorder in which liver production of a specific protein is therapeutic.

Acceleration of gene transfection efficiency in neuroblastoma cells through polyethyleneimine/poly(methyl methacrylate) core-shell magnetic nanoparticles

Background

The purpose of this study was to demonstrate the potential of magnetic poly(methyl methacrylate) (PMMA) core/polyethyleneimine (PEI) shell (mag-PEI) nanoparticles, which possess high saturation magnetization for gene delivery. By using mag-PEI nanoparticles as a gene carrier, this study focused on evaluation of transfection efficiency under magnetic induction. The potential role of this newly synthesized nanosphere for therapeutic delivery of the tryptophan hydroxylase-2 (TPH-2) gene was also investigated in cultured neuronal LAN-5 cells.

Methods

The mag-PEI nanoparticles were prepared by one-step emulsifier-free emulsion polymerization, generating highly loaded and monodispersed magnetic polymeric nanoparticles bearing an amine group. The physicochemical properties of the mag-PEI nanoparticles and DNA-bound mag-PEI nanoparticles were investigated using the gel retardation assay, atomic force microscopy, and zeta size measurements. The gene transfection efficiencies of mag-PEI nanoparticles were evaluated at different transfection times. Confocal laser scanning microscopy confirmed intracellular uptake of the magnetoplex. The optimal conditions for transfection of TPH-2 were selected for therapeutic gene transfection. We isolated the TPH-2 gene from the total RNA of the human medulla oblongata and cloned it into an expression vector. The plasmid containing TPH-2 was subsequently bound onto the surfaces of the mag-PEI nanoparticles via electrostatic interaction. Finally, the mag-PEI nanoparticle magnetoplex was delivered into LAN-5 cells. Reverse-transcriptase polymerase chain reaction was performed to evaluate TPH-2 expression in a quantitative manner.

Results

The study demonstrated the role of newly synthesized high-magnetization mag-PEI nanoparticles for gene transfection in vitro. The expression signals of a model gene, luciferase, and a therapeutic gene, TPH-2, were enhanced under magnetic-assisted transfection. An in vitro study in neuronal cells confirmed that using mag-PEI nanoparticles as a DNA carrier for gene delivery provided high transfection efficiency with low cytotoxicity.

Conclusion

The mag-PEI nanoparticle is a promising alternative gene transfection reagent due to its ease of use, effectiveness, and low cellular toxicity. The mag-PEI nanoparticle is not only practical for gene transfection in cultured neuronal cells but may also be suitable for transfection in other cells as well.