Nanoparticle Mediated Gene Therapy: A Trailblazer Armament to Fight CNS Disorders

Central nervous system (CNS) disorders account for boundless socioeconomic burdens with devastating effects among the population, especially the elderly. The major symptoms of these disorders are neurodegeneration, neuroinflammation, and cognitive dysfunction caused by inherited genetic mutations or by genetic and epigenetic changes due to injury, environmental factors, and disease-related events. Currently available clinical treatments for CNS diseases, i.e., Alzheimer's disease, Parkinson's disease, stroke, and brain tumor, have significant side effects and are largely unable to halt the clinical progression. So gene therapy displays a new paradigm in the treatment of these disorders with some modalities, varying from the suppression of endogenous genes to the expression of exogenous genes. Both viral and non-viral vectors are commonly used for gene therapy. Viral vectors are quite effective but associated with severe side effects, like immunogenicity and carcinogenicity, and poor target cell specificity. Thus, non-viral vectors, mainly nanotherapeutics like nanoparticles (NPs), turn out to be a realistic approach in gene therapy, achieving higher efficacy. NPs demonstrate a new avenue in pharmacotherapy for the delivery of drugs or genes to their selective cells or tissue, thus providing concentrated and constant drug delivery to targeted tissues, minimizing systemic toxicity and side effects. The current review will emphasize the role of NPs in mediating gene therapy for CNS disorders treatment. Moreover, the challenges and perspectives of NPs in gene therapy will be summarized.

Cell therapy in Huntington's disease: Taking stock of past studies to move the field forward

Huntington's disease (HD) is a rare inherited neurodegenerative disease that manifests mostly in adulthood with progressive cognitive, behavioral, and motor dysfunction. Neuronal loss occurs predominantly in the striatum but also extends to other brain regions, notably the cortex. Most patients die around 20 years after motor onset, although there is variability in the rate of progression and some phenotypic heterogeneity. The most advanced experimental therapies currently are huntingtin-lowering strategies, some of which are in stage 3 clinical trials. However, even if these approaches are successful, it is unlikely that they will be applicable to all patients or will completely halt continued loss of neural cells in all cases. On the other hand, cellular therapies have the potential to restore atrophied tissues and may therefore provide an important complementary therapeutic avenue. Pilot studies of fetal cell grafts in the 2000s reported the most dramatic clinical improvements yet achieved for this disease, but subsequent studies have so far failed to identify methodology to reliably reproduce these results. Moving forward, a major challenge will be to generate suitable donor cells from (nonfetal) cell sources, but in parallel there are a host of procedural and trial design issues that will be important for improving reliability of transplants and so urgently need attention. Here, we consider findings that have emerged from clinical transplant studies in HD to date, in particular new findings emerging from the recent multicenter intracerebral transplant HD study, and consider how these data may be used to inform future cell therapy trials.

Growth Factor Therapy for Parkinson's Disease: Alternative Delivery Systems

Despite decades of research and billions in global investment, there remains no preventative or curative treatment for any neurodegenerative condition, including Parkinson's disease (PD). Arguably, the most promising approach for neuroprotection and neurorestoration in PD is using growth factors which can promote the growth and survival of degenerating neurons. However, although neurotrophin therapy may seem like the ideal approach for neurodegenerative disease, the use of growth factors as drugs presents major challenges because of their protein structure which creates serious hurdles related to accessing the brain and specific targeting of affected brain regions. To address these challenges, several different delivery systems have been developed, and two major approaches-direct infusion of the growth factor protein into the target brain region and in vivo gene therapy-have progressed to clinical trials in patients with PD. In addition to these clinically evaluated approaches, a range of other delivery methods are in various degrees of development, each with their own unique potential. This review will give a short overview of some of these alternative delivery systems, with a focus on ex vivo gene therapy and biomaterial-aided protein and gene delivery, and will provide some perspectives on their potential for clinical development and translation.

Polylysine-modified polyethylenimine (PEI-PLL) mediated VEGF gene delivery protects dopaminergic neurons in cell culture and in rat models of Parkinson's Disease (PD)

Parkinson's Disease (PD) is a chronic neurodegenerative disorder characterized by motor deficits which result from the progressive loss of dopaminergic neurons. Gene therapy using growth factors such as VEGF seems to be a viable approach for potential therapeutic treatment of PD. In this study, we utilized a novel non-viral gene carrier designated as PEI-PLL synthesized by our laboratory to deliver VEGF gene to study its effect by using both cell culture as well as animal models of PD. For cell culture experiments, we utilized 6-hydroxydopamine (6-OHDA) mediated cell death model of MN9D cells following transfection with either a control plasmid or VEGF expressing plasmid. As compared to control transfected cells, PEI-PLL mediated VEGF gene delivery to MN9D cells resulted in increased cell viability, increase in the number of Tyrosine hydroxylase (TH) positive cells and decreased apoptosis following 6-OHDA insult. Next, we studied the therapeutic potential of PEI-PLL mediated VEGF gene delivery in SNPc by using unilateral 6-OHDA Medial forebrain bundle (MFB) lesion model of PD in rats. VEGF administration prevented the loss of motor functions induced by 6-OHDA as determined by behavior analysis. Similarly, VEGF inhibited the 6-OHDA mediated loss of DA neurons in Substantia Nigra Pars Compacta (SNPc) as well as DA nerve fibers in striatum as determined by TH immunostaining. In addition, PEI-PLL mediated VEGF gene delivery also prevented apoptosis and microglial activation in PD rat models. Together, these results clearly demonstrated the beneficial effects of PEI-PLL mediated VEGF gene delivery on dopaminergic system in both cell culture and animal models of PD.

STATEMENT OF SIGNIFICANCE

In this report, we exploited the potential of PEI-PLL to deliver VEGF gene for the potential therapeutic treatment of PD by using both cell culture and animal models of PD. To the best of our knowledge, this is the first report describing the use of novel polymeric gene carriers for the delivery of VEGF gene to DA neurons with improved transfection efficiency. Finally, the study will lead to a significant advancement in the field of non-viral PD gene therapy treatment.

Non-viral xylosyltransferase-1 siRNA delivery as an effective alternative to chondroitinase in an in vitro model of reactive astrocytes

Reactive astrocytosis and the subsequent glial scar is ubiquitous to injuries of the central nervous system, especially spinal cord injury (SCI) and primarily serves to protect against further damage, but is also a prominent inhibitor of regeneration. Manipulating the glial scar by targeting chondroitin sulfate proteoglycans (CSPGs) has been the focus of much study as a means to improve axon regeneration and subsequently functional recovery. In this study we investigate the ability of small interfering RNA (siRNA) delivered by a non-viral polymer vector to silence the rate-limiting enzyme involved in CSPG synthesis. Gene expression of this enzyme, xylosyltransferase-1, was silenced by 65% in Neu7 astrocytes which conferred a reduced expression of CSPGs. Furthermore, conditioned medium taken from treated Neu7s, or co-culture experiments with dorsal root ganglia (DRG) showed that siRNA treatment resulted in a more permissive environment for DRG neurite outgrowth than treatment with chondroitinase ABC alone. These results indicate that there is a role for targeted siRNA therapy using polymeric vectors to facilitate regeneration of injured axons following central nervous system injury.

Single Cell Transfection through Precise Microinjection with Quantitatively Controlled Injection Volumes

Cell transfection is a technique wherein foreign genetic molecules are delivered into cells. To elucidate distinct responses during cell genetic modification, methods to achieve transfection at the single-cell level are of great value. Herein, we developed an automated micropipette-based quantitative microinjection technology that can deliver precise amounts of materials into cells. The developed microinjection system achieved precise single-cell microinjection by pre-patterning cells in an array and controlling the amount of substance delivered based on injection pressure and time. The precision of the proposed injection technique was examined by comparing the fluorescence intensities of fluorescent dye droplets with a standard concentration and water droplets with a known injection amount of the dye in oil. Injection of synthetic modified mRNA (modRNA) encoding green fluorescence proteins or a cocktail of plasmids encoding green and red fluorescence proteins into human foreskin fibroblast cells demonstrated that the resulting green fluorescence intensity or green/red fluorescence intensity ratio were well correlated with the amount of genetic material injected into the cells. Single-cell transfection via the developed microinjection technique will be of particular use in cases where cell transfection is challenging and genetically modified of selected cells are desired.

Synthesis of ROS scavenging microspheres from a dopamine containing poly(β-amino ester) for applications for neurodegenerative disorders

Parkinson's disease (PD) is a common neurodegenerative disease characterized by a substantial decrease of dopaminergic neurons in the substantia nigra pars compacta. The neurological deterioration during PD can be, in part, attributed to elevated levels of reactive oxygen species (ROS). Radical scavengers have previously been shown to protect dopaminergic cells from toxic effects in vitro. Hence, new approaches need to be investigated to improve the administration of antioxidants in order to provide neuroprotection. Polymers exhibiting catechol structures offer one such approach due to their interesting physicochemical properties. In the present study a photocrosslinkable dopamine-containing poly(β-amino ester) (DPAE) was synthesized from poly(ethylene glycol) diacrylate (PEGDA) and dopamine hydrochloride using Michael type addition. A water-in-oil emulsion technique was used to photo-crosslink the polymer into spherical microparticles. DPAE microspheres featured excellent scavenging properties towards 1,1-Diphenyl-2-picryl-hydrazyl (DPPH) radicals in a dose dependent manner and could even reduce the dissolved oxygen content of physiological solution. Furthermore, the concentrations required for radical scavenging were shown to be non-toxic towards dopaminergic SH-SY5Y cells as well as primary astrocytes and primary embryonic rat ventral midbrain cultures.

A hyperbranched dopamine-containing PEG-based polymer for the inhibition of α-synuclein fibrillation

Aggregation of α-synuclein is believed to play an important role in Parkinson's disease and in other neurodegenerative maladies. Small molecule inhibitors of this process are among the most promising drug candidates for neurodegenerative diseases. Dendrimers have also been studied for anti-fibrillation applications but they can be difficult and expensive to synthetize. Here we show that RAFT polymerization can be used to produce a hyperbranched polyethylene glycol structure via a one-pot reaction. This polymer included a dopamine moiety, a known inhibitor of α-synuclein fibril formation. Dopamine within the polymer structure was capable of aggregation inhibition, although not to the same degree as free dopamine. This result opens up new avenues for the use of controlled radical polymerizations as a means of preparing hyperbranched polymers for anti-fibrillation activity, but shows that the incorporation of functional groups from known small molecules within polymers may alter their biological activity.

Tackling Cell Transplantation Anoikis: An Injectable, Shape Memory Cryogel Microcarrier Platform Material for Stem Cell and Neuronal Cell Growth

Highly macroporous semisynthetic cryogel microcarriers can be synthesized for culturing stem cells and neuronal type cells. Growth factors loaded to heparin-containing microcarriers show near zero-order release kinetics and cell-loaded microcarriers can be injected through a fine gauge cannula without negative effect on the cells. These carriers can be applied for cell transplantation applications.

Liposomes in tissue engineering and regenerative medicine

Liposomes are vesicular structures made of lipids that are formed in aqueous solutions. Structurally, they resemble the lipid membrane of living cells. Therefore, they have been widely investigated, since the 1960s, as models to study the cell membrane, and as carriers for protection and/or delivery of bioactive agents. They have been used in different areas of research including vaccines, imaging, applications in cosmetics and tissue engineering. Tissue engineering is defined as a strategy for promoting the regeneration of tissues for the human body. This strategy may involve the coordinated application of defined cell types with structured biomaterial scaffolds to produce living structures. To create a new tissue, based on this strategy, a controlled stimulation of cultured cells is needed, through a systematic combination of bioactive agents and mechanical signals. In this review, we highlight the potential role of liposomes as a platform for the sustained and local delivery of bioactive agents for tissue engineering and regenerative medicine approaches.

Untying a nanoscale knotted polymer structure to linear chains for efficient gene delivery in vitro and to the brain

The purpose of this study was to develop a platform transfection technology, for applications in the brain, which could transfect astrocytes without requiring cell specific functionalization and without the common cause of toxicity through high charge density. Here we show that a simple and scalable preparation technique can be used to produce a "knot" structured cationic polymer, where single growing chains can crosslink together via disulphide intramolecular crosslinks (internal cyclizations). This well-defined knot structure can thus "untie" under reducing conditions, showing a more favorable transfection profile for astrocytes compared to 25 kDa-PEI (48-fold), SuperFect® (39-fold) and Lipofectamine®2000 (18-fold) whilst maintaining neural cell viability at over 80% after four days of culture. The high transfection/lack of toxicity of this knot structured polymer in vitro, combined with its ability to mediate luciferase transgene expression in the adult rat brain, demonstrates its use as a platform transfection technology which should be investigated further for neurodegenerative disease therapies.

Synthesis of cholic acid-core poly(ε-caprolactone-ran-lactide)-b-poly(ethylene glycol) 1000 random copolymer as a chemotherapeutic nanocarrier for liver cancer treatment

DTX-loaded CA-(PCL-ran-PLA)-b-PEG_1k NPs were prepared and shown great potential as drug delivery nanocarriers for cancer therapy.