Recent advances in the pharmacology of neurological gene therapy

Novel therapeutic interventions for combating Parkinson's disease and prospects of Nose-to-Brain drug delivery

Parkinson disease (PD) is a progressive neurodegenerative disorder prevalent mainly in geriatric population. While, L-DOPA remains one of the major choices for the therapeutic management of PD, various motor and non-motor manifestations complicate the management of PD. In the last two decades, exhaustive research has been carried out to explore novel therapeutic approaches for mitigating motor and non-motor symptoms of PD. These approaches majorly include receptor-based, anti-inflammatory, stem-cell and nucleic acid based. The major limitations of existing therapeutic interventions (of commonly oral route) are low efficacy due to low brain bioavailability and associated side effects. Nanotechnology has been exploited and has gained wide attention in the recent years as an approach for enhancement of bioavailability of various small molecule drugs in the brain. To address the challenges associated with PD therapy, nose-to-brain delivery utilizing nanomedicine-based approaches has been found to be encouraging in published evidence. Therefore, the present work summarises the major challenges and limitations with antiparkinsonian drugs, novel therapeutic interventions, and scope of nanomedicine-based nose-to-brain delivery in addressing the current challenges of antiparkinsonian therapy. The manuscript tries to sensitize the researchers for designing brain-targeted nanomedicine loaded with natural/synthetic scaffolds, biosimilars, and nucleic acids that can bypass the first-pass effect for the effective management of PD.

Gene Therapy Tools for Brain Diseases

Neurological disorders affecting the central nervous system (CNS) are still incompletely understood. Many of these disorders lack a cure and are seeking more specific and effective treatments. In fact, in spite of advancements in knowledge of the CNS function, the treatment of neurological disorders with modern medical and surgical approaches remains difficult for many reasons, such as the complexity of the CNS, the limited regenerative capacity of the tissue, and the difficulty in conveying conventional drugs to the organ due to the blood-brain barrier. Gene therapy, allowing the delivery of genetic materials that encodes potential therapeutic molecules, represents an attractive option. Gene therapy can result in a stable or inducible expression of transgene(s), and can allow a nearly specific expression in target cells. In this review, we will discuss the most commonly used tools for the delivery of genetic material in the CNS, including viral and non-viral vectors; their main applications; their advantages and disadvantages. We will discuss mechanisms of genetic regulation through cell-specific and inducible promoters, which allow to express gene products only in specific cells and to control their transcriptional activation. In addition, we will describe the applications to CNS diseases of post-transcriptional regulation systems (RNA interference); of systems allowing spatial or temporal control of expression [optogenetics and Designer Receptors Exclusively Activated by Designer Drugs (DREADDs)]; and of gene editing technologies (CRISPR/Cas9, Zinc finger proteins). Particular attention will be reserved to viral vectors derived from herpes simplex type 1, a potential tool for the delivery and expression of multiple transgene cassettes simultaneously.

Single vs. combination immunotherapeutic strategies for glioma

INTRODUCTION

Malignant gliomas are highly invasive tumors, associated with a dismal survival rate despite standard of care, which includes surgical resection, radiotherapy and chemotherapy with temozolomide (TMZ). Precision immunotherapies or combinations of immunotherapies that target unique tumor-specific features may substantially improve upon existing treatments. Areas covered: Clinical trials of single immunotherapies have shown therapeutic potential in high-grade glioma patients, and emerging preclinical studies indicate that combinations of immunotherapies may be more effective than monotherapies. In this review, the authors discuss emerging combinations of immunotherapies and compare efficacy of single vs. combined therapies tested in preclinical brain tumor models. Expert opinion: Malignant gliomas are characterized by a number of factors which may limit the success of single immunotherapies including inter-tumor and intra-tumor heterogeneity, intrinsic resistance to traditional therapies, immunosuppression, and immune selection for tumor cells with low antigenicity. Combination of therapies which target multiple aspects of tumor physiology are likely to be more effective than single therapies. While a limited number of combination immunotherapies are described which are currently being tested in preclinical and clinical studies, the field is expanding at an astounding rate, and endless combinations remain open for exploration.

Safety profile of gutless adenovirus vectors delivered into the normal brain parenchyma: implications for a glioma phase 1 clinical trial

Adenoviral vectors (Ads) have been evaluated in clinical trials for glioma. However, systemic immunity against the vectors can hamper therapeutic efficacy. We demonstrated that combined immunostimulation and cytotoxic gene therapy provides long-term survival in preclinical glioma models. Because helper-dependent high-capacity Ads (HC-Ads) elicit sustained transgene expression, in the presence of antiadenoviral immunity, we engineered HC-Ads encoding conditional cytotoxic herpes simplex type 1 thymidine kinase and immunostimulatory cytokine Fms-like tyrosine kinase ligand-3 under the control of the TetOn system. Escalating doses of combined HC-Ads (1×10(8), 1×10(9), and 1×10(10) viral particles [VP]) were delivered into the rat brain. We assessed neuropathology, biodistribution, transgene expression, systemic toxicity, and behavioral impact at acute and chronic time points after vector delivery. Histopathological analysis did not reveal any evidence of toxicity or long-term inflammation at the lower doses tested. Vector genomes were restricted to the injection site. Serum chemistry did not uncover adverse systemic side effects at any of the doses tested. Taken together, our data indicate that doses of up to 1×10(9) VP of each HC-Ad can be safely administered into the normal brain. This comprehensive toxicity and biodistribution study will lay the foundations for implementation of a phase 1 clinical trial for GBM using HC-Ads.

Gene-based approaches in the study of pathological pain

Chronic pathological pain is characterized by extensive plasticity of the systems involved in pain signal transmission and modulation and tissue remodeling in several CNS structures. These long-lasting alterations are mediated by, or associated with, changes in the production of key molecules of nociceptive processing. Gene-based approaches offer the unique possibility of using local or even cell-type specific interventions to correct the abnormal production of some of these proteins, modulate the activity of signal transduction pathways, or overproduce various therapeutic secreted proteins. We showed that certain viral-derived vectors are particularly suitable for mediating gene transfer highly preferential for instance into the primary sensory neurons or into the spinal cord glial cells that represent particularly pertinent targets in the search for new therapeutic strategies of pathological pain.

Development of a suspension serum-free helper-dependent adenovirus production system and assessment of co-infection conditions

Helper-dependent adenovirus (HDAd), deleted in all viral protein-coding sequences has been designed to reduce immune response and favor long-term expression of therapeutic genes in clinical programs. Its production requires co-infection of E1-complementing cells with helper adenovirus (HAd). Significant progresses have been made in the molecular design of HDAd, but large scale production remains a challenge. In this work, a scalable system for HDAd production is designed and evaluated focusing on the co-infection step. A human embryo kidney 293 (293) derived cell line, the 293SF/FLPe was generated to produce efficiently HDAd while restricting the packaging of HAd. This cell line was adapted to grow in suspension and in serum-free medium. Multiplicity of infection (MOI) of HDAd ranging from 0.1 to 50 was evaluated in presence of HAd at a MOI of 5. Optimal MOIs for HDAd amplification were found in the range of 5-10. HAd contamination was only 1%. These results were validated in a 3 L bioreactor under controlled operating conditions where a higher HDAd yield of 2.6 x 10(9) viral particles (VP)/mL or 3.5 x 10(8) infectious units (IU)/mL of HDAd was obtained.

Efficacy of nonviral gene transfer in the canine brain

OBJECT

The purpose of this study was to evaluate the gene transfer capability and tolerability of plasmid DNA/polyethylenimine (PEI) complexes in comparison with adenovirus and naked plasmid DNA in the canine brain.

METHODS

Plasmid or adenoviral vectors encoding firefly luciferase were injected directly into the cerebral parenchyma of five adult dogs at varying doses and volumes. Serial physical and neurological examinations, as well as blood and cerebrospinal fluid (CSF) analyses, were conducted before and after the surgery for 3 days. Three days after gene delivery, a luciferase activity assay and immunofluorescence analysis were used to test the brain tissue for gene expression.

RESULTS

Injection into the brain parenchyma resulted in gene transfer throughout the cerebrum with every vector tested. Luciferase expression was highest when adenovirus vectors were used. Injection of plasmid DNA/PEI complexes and naked DNA resulted in similar levels of luciferase expression, which were on average 0.5 to 1.5% of the expression achieved with adenovirus vectors. Immunofluorescent microscopy analysis revealed that plasmid DNA/PEI complexes transduced mainly neurons, whereas adenovirus transduced mainly astrocytes. No significant acute side effects or neurological complications were observed in any of the dogs. Mononuclear cell counts significantly increased in the CSF after adenovirus injection and modestly increased after injection of plasmid DNA/PEI complexes, suggesting that a mild, acute inflammatory response occurred in the central nervous system (CNS).

CONCLUSIONS

Compared with rodent models that are limited by very small brains, the dog is an excellent preclinical model in which to assess the distribution and safety of emerging gene transfer technologies. In this study, short-term gene transfer was evaluated as a prelude to long-term expression and safety studies. The authors conclude that the viral and nonviral vectors tested were well tolerated and effective at mediating gene transfer throughout a large portion of the canine brain. The nonviral plasmid vectors were less effective than adenovirus, yet they still achieved appreciable gene expression levels. Due to reduced gene transfer efficiency relative to viral vectors, nonviral vectors may be most useful when the expressed protein is secreted or exerts a bystander effect. Nonviral vectors offer an alternative means to genetically modify cells within the CNS of large mammals.

Novel liposomal formulation for targeted gene delivery

PURPOSE

Development of a polyethylene glycol (PEG)-stabilized immunoliposome (PSIL) formulation with high DNA content suitable for in vivo intravenous administration and targeted gene delivery.

MATERIALS AND METHODS

Plasmid DNA was condensed using 40% ethanol and packaged into neutral PSILs targeted to the mouse transferrin receptor using monoclonal antibodies (MAbs; clones RI7 and 8D3) attached to their PEG maleimide moieties. PSILs size was measured by quasi-elastic light scattering. The targeting capacity of the formulation was determined by transfection of mouse neuroblastoma Neuro 2A (N2A) cells with PSIL-DNA complexes conjugated with either RI7 or 8D3 MAbs.

RESULTS

DNA encapsulation and MAb conjugation efficiencies averaged 71 +/- 14% and 69 +/- 5% (mean +/- SD), respectively. No alteration in mean particle size (< 100 nm) or DNA leakage were found after 48 h storage in a physiological buffer, and the in vivo terminal half-life reached 23.9 h, indicating that the PSIL-DNA formulation was stable. Addition of free RI7 MAbs prevented transfection of N2A cells with PSIL-DNA complexes conjugated with either RI7 or 8D3 MAbs, confirming that the transfection was transferrin receptor-dependent.

CONCLUSIONS

The present data suggest that our new PSIL formulation combines molecular features required for targeted gene therapy including high DNA encapsulation efficiencies and vector-specific transient transfection capacity.

Regulatable gene expression systems for gene therapy

It is feasible to restrict transgene expression to a tissue or region in need of therapy by using promoters that respond to focusable physical stimuli. The most extensively investigated promoters of this type are radiation-inducible promoters and heat shock protein gene promoters that can be activated by directed, transient heat. Temporal regulation of transgenes can be achieved by various two- or three-component gene switches that are triggered by an appropriate small molecule inducer. The most commonly considered gene switches that are reviewed herein are based on small molecule-responsive transactivators derived from bacterial tetracycline repressor, insect or mammalian steroid receptors, or mammalian FKBP12/FRAP. A new generation of gene switches combines a heat shock protein gene promoter and a small molecule-responsive gene switch and can provide for both spatial and temporal regulation of transgene activity.

Polycation-mediated delivery of siRNAs for prophylaxis and treatment of influenza virus infection

Influenza A virus causes one of the most prevalent infections in humans. In a typical year, 10-20% of the population of the US is infected by influenza virus, resulting in up to 40,000 deaths and 200,000 hospitalisations. Vaccination is the most effective preventative measure that can protect 70-90% of healthy adults aged < 65; however, the protection rate is much lower in those most susceptible to infection, namely infants, the elderly and individuals with weakened immune systems. Although four drugs have been approved by the FDA for use as prophylaxis and/or treatment of influenza, concerns about their side effects and the emergence of drug-resistant viruses persist. RNA interference (RNAi), an emerging method of post transcriptional gene silencing, appears ideal for the prevention and treatment of influenza. RNAi in mammals can be mediated by short interfering RNAs (siRNAs) of approximately 21-27 nucleotides in length. The authors have previously shown that siRNAs specific for conserved regions of the influenza virus genome are potent inhibitors of influenza virus replication in both cell lines and chicken embryos. This review discusses the recent progress in the in vivo inhibition of influenza virus by the delivery of siRNAs mediated by non-viral vectors, and the prospects of this strategy for prophylaxis and treatment of influenza infection in humans.

Human gene therapy and imaging in neurological diseases

Molecular imaging aims to assess non-invasively disease-specific biological and molecular processes in animal models and humans in vivo. Apart from precise anatomical localisation and quantification, the most intriguing advantage of such imaging is the opportunity it provides to investigate the time course (dynamics) of disease-specific molecular events in the intact organism. Further, molecular imaging can be used to address basic scientific questions, e.g. transcriptional regulation, signal transduction or protein/protein interaction, and will be essential in developing treatment strategies based on gene therapy. Most importantly, molecular imaging is a key technology in translational research, helping to develop experimental protocols which may later be applied to human patients. Over the past 20 years, imaging based on positron emission tomography (PET) and magnetic resonance imaging (MRI) has been employed for the assessment and "phenotyping" of various neurological diseases, including cerebral ischaemia, neurodegeneration and brain gliomas. While in the past neuro-anatomical studies had to be performed post mortem, molecular imaging has ushered in the era of in vivo functional neuro-anatomy by allowing neuroscience to image structure, function, metabolism and molecular processes of the central nervous system in vivo in both health and disease. Recently, PET and MRI have been successfully utilised together in the non-invasive assessment of gene transfer and gene therapy in humans. To assess the efficiency of gene transfer, the same markers are being used in animals and humans, and have been applied for phenotyping human disease. Here, we review the imaging hallmarks of focal and disseminated neurological diseases, such as cerebral ischaemia, neurodegeneration and glioblastoma multiforme, as well as the attempts to translate gene therapy's experimental knowledge into clinical applications and the way in which this process is being promoted through the use of novel imaging approaches.

Regulatable gene expression systems for gene therapy applications: progress and future challenges

Gene therapy aims to revert diseased phenotypes by the use of both viral and nonviral gene delivery systems. Substantial progress has been made in making gene transfer vehicles more efficient, less toxic, and nonimmunogenic and in allowing long-term transgene expression. One of the key issues in successfully implementing gene therapies in the clinical setting is to be able to regulate gene expression very tightly and consistently as and when it is needed. The regulation ought to be achievable using a compound that should be nontoxic, be able to penetrate into the desired target tissue or organ, and have a half-life of a few hours (as opposed to minutes or days) so that when withdrawn or added (depending on the regulatable system used) gene expression can be turned "on" or "off" quickly and effectively. Also, the genetic switches employed should ideally be nonimmunogenic in the host. The ability to switch transgenes on and off would be of paramount importance not only when the therapy is no longer needed, but also in the case of the development of adverse side effects to the therapy. Many regulatable systems are currently under development and some, i.e., the tetracycline-dependent transcriptional switch, have been used successfully for in vivo preclinical applications. Despite this, there are no examples of switches that have been employed in a human clinical trial. In this review, we aim to highlight the main regulatable systems currently under development, the gene transfer systems employed for their expression, and also the preclinical models in which they have been used successfully. We also discuss the substantial challenges that still remain before these regulatable switches can be employed in the clinical setting.

Full deacylation of polyethylenimine dramatically boosts its gene delivery efficiency and specificity to mouse lung

High-molecular-mass polyethylenimines (PEIs) are widely used vectors for nucleic acid delivery. We found that removal of the residual N-acyl moieties from commercial linear 25-kDa PEI enhanced its plasmid DNA delivery efficiency 21 times in vitro, as well as 10,000 times in mice with a concomitant 1,500-fold enhancement in lung specificity. Several additional linear PEIs were synthesized by acid-catalyzed hydrolysis of poly(2-ethyl-2-oxazoline), yielding the pure polycations. PEI87 and PEI217 exhibited the highest efficiency in vitro: 115-fold and 6-fold above those of the commercial and deacylated PEI25s, respectively; moreover, PEI87 delivered DNA to mouse lung as efficiently as the pure PEI25 but at a lower concentration and with a 200-fold lung specificity. These improvements stem from an increase in the number of protonatable nitrogens, which presumably results in a tighter condensation of plasmid DNA and a better endosomal escape of the PEI/DNA complexes. As a validation of the potential of such linear, fully deacylated PEIs in gene therapy for lung diseases, systemic delivery in mice of the complexes of a short interfering RNA (siRNA) against a model gene, firefly luciferase, and PEI25 or PEI87 afforded a 77% and 93% suppression of the gene expression in the lungs, respectively. Furthermore, a polyplex of a siRNA against the influenza viral nucleocapsid protein gene and PEI87 resulted in a 94% drop of virus titers in the lungs of influenza-infected animals.