Current Gene Therapy - Volume 21, Issue 5, 2021

Glaucoma leads to irreversible vision loss and current therapeutic strategies are often insufficient to prevent the progression of the disease and consequent blindness. Elevated intraocular pressure is an important risk factor, but not required for the progression of glaucomatous neurodegeneration. The demise of retinal ganglion cells represents the final common pathway of glaucomatous vision loss. Still, lifelong control of intraocular pressure is the only current treatment to prevent severe vision loss, although it frequently fails despite best practices. This scenario calls for the development of neuroprotective and pro-regenerative therapies targeting the retinal ganglion cells as well as the optic nerve. Several experimental studies have shown the potential of gene modulation as a tool for neuroprotection and regeneration. In this context, gene therapy represents an attractive approach as a persistent treatment for glaucoma. Viral vectors engineered to promote overexpression of a broad range of cellular factors have been shown to protect retinal ganglion cells and/or promote axonal regeneration in experimental models. Here, we review the mechanisms involved in glaucomatous neurodegeneration and regeneration in the central nervous system. Then, we point out the current limitations of gene therapy platforms and review a myriad of studies that use viral vectors to manipulate genes in retinal ganglion cells, as a strategy to promote neuroprotection and regeneration. Finally, we address the potential of combining neuroprotective and regenerative gene therapies as an approach to glaucomatous neurodegeneration.

The Mesenchymal stromal cells (MSCs) are a diverse subset of adult multipotent precursors, known for their potential therapeutic properties in regenerative medicine mainly sustained by paracrine effects through secretion of a variety of biologically active molecules. MSC secretome includes a wide range of soluble protein factors, composed of growth factors and cytokines, and vesicular components, which transfer proteins and genetic material modulating the host microenvironment. In particular, MSC-derived secretome mediates the different steps of the angiogenic process, inducing endothelial cell functions in vitro and promoting angiogenesis in vivo. As a result, MSCs have been widely explored as a promising cell-based therapy in diseases caused by insufficient angiogenesis. Numerous studies of myocardial infarction, ischemic stroke, and critical limb ischemia in animals have shown that human MSCs can enhance angiogenesis and accelerate tissue regeneration. This extensive preclinical work encouraged the study of these remarkable cells for the treatment of these disorders in human clinical settings. The present review provides a comprehensive overview of the pro-angiogenic potential of MSCs and paracrine effectors of their secretome. In addition, bioengineering strategies, including ex vivo preconditioning and genetic modification approaches, to enhance MSC innate angiogenic properties, and thereby therapeutic potency, will be presented. Finally, an update on completed preclinical and clinical studies with MSCs for the treatment of ischemia-related diseases will be discussed.

Gene therapy is a technique that aims at the delivery of nucleic acids to cells, to obtain a therapeutic effect. In situ gene therapy consists of the administration of the gene product to a specific site. It possesses several advantages, such as the reduction in potential side effects, the need for a lower vector dose, and, as a consequence, reduced costs, compared to intravenous administration. Different vectors, administration routes and doses involving in situ gene transfer have been tested both in animal models and humans, with in situ gene therapy drugs already approved in the market. In this review, we present applications of in situ gene therapy for different diseases, ranging from monogenic to multifactorial diseases, focusing mainly on therapies designed for the intra-articular and intraocular compartments, as well as gene therapies for the central nervous system (CNS) and for tumors. Gene therapy finally seems to blossom as a viable therapeutic approach. The growth in the number of clinical protocols shown here is evident, and the positive outcomes observed in several clinical trials indicate that more products based on in situ gene therapy should reach the market in the next years.

Background: Gene delivery is a promising technology for treating diseases linked to abnormal gene expression. Since nucleic acids are the therapeutic entities in such approach, a transfecting vector is required because the macromolecules are not able to efficiently enter the cells by themselves. Viral vectors have been evidenced to be highly effective in this context; however, they suffer from fundamental drawbacks, such as the ability to stimulate immune responses. The development of synthetic vectors has accordingly emerged as an alternative. Objectives: Gene delivery by using non-viral vectors is a multi-step process that poses many challenges, either regarding the extracellular or intracellular media. We explore the delivery pathway and afterwards, we review the main classes of non-viral gene delivery vectors. We further focus on the progresses concerning polyethylenimine-based polymer-nucleic acid polyplexes, which have emerged as one of the most efficient systems for delivering genetic material inside the cells. Discussion: The complexity of the whole transfection pathway, along with a lack of fundamental understanding, particularly regarding the intracellular trafficking of nucleic acids complexed to non-viral vectors, probably justifies the current (beginning of 2021) limited number of formulations that have progressed to clinical trials. Truly, successful medical developments still require a lot of basic research. Conclusion: Advances in macromolecular chemistry and high-resolution imaging techniques will be useful to understand fundamental aspects towards further optimizations and future applications. More investigations concerning the dynamics, thermodynamics and structural parameters of polyplexes would be valuable since they can be connected to the different levels of transfection efficiency hitherto evidenced.

Gliomas are primary brain tumors originating from glial cells, representing 30% of all Central Nervous System (CNS) neoplasia. Among them, the astrocytoma grade IV (glioblastoma multiforme) is the most common, presenting an invasive and aggressive profile, with an estimated life expectancy of about 15 months after diagnosis even after treatment with radiation, surgical resection, and chemotherapy. This poor prognosis is related to the presence of the blood-brain barrier (BBB) and multidrug resistance mechanisms that prevent the uptake and retention of chemotherapeutics inside the brain. Gene therapy has been a promising strategy to overcome these treatment limitations since it has the ability to modify the defective genetic information in tumor cells, being able to induce cellular apoptosis and silence the genes responsible for multidrug resistance. Lipidbased nanoparticles, non-viral vectors, have been investigated to deliver genes across the BBB to reach the glioma cell target. Besides, their low immunogenicity, easy production, ability to incorporate ligands to specific target cells, and capacity to carry higher size genes have made the gene therapy based on non-viral vectors a promising glioma treatment. In this context, this review addresses the most common non-viral vectors based on lipid-based nanoparticles used for glioma gene therapy, such as liposomes, solid lipid nanoparticles, nanostructured lipid carriers, and nanoemulsions.

Background: Mucopolysaccharidosis type I (MPS I) is an inherited disorder caused by α-L-iduronidase (IDUA) deficiency. The available treatments are not effective in improving all signs and symptoms of the disease. Objective: In the present study, we evaluated the transfection efficiency of repeated intravenous administrations of cationic nanoemulsions associated with the plasmid pIDUA (containing IDUA gene). Methods: Cationic nanoemulsions were composed of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-(amino[polyethylene glycol]- 2000) (DSPE-PEG), 1,2-dioleoyl-sn-glycero-3-trimethylammonium propane (DOTAP), medium- chain triglycerides, glycerol, and water and were prepared by high-pressure homogenization and were repeatedly administered to MPS I mice for IDUA production and gene expression. Results: A significant increase in IDUA expression was observed in all organs analyzed, and IDUA activity tended to increase with repeated administrations when compared to our previous report when mice received a single administration of the same dose. In addition, GAGs were partially cleared from organs, as assessed through biochemical and histological analyzes. There was no presence of inflammatory infiltrate, necrosis, or signs of an increase in apoptosis. Furthermore, immunohistochemistry for CD68 showed a reduced presence of macrophage cells in treated than in untreated MPS I mice. Conclusion: These sets of results suggest that repeated administrations can improve transfection efficiency of cationic complexes without a significant increase in toxicity in the MPS I murine model.