Less is more: Investigating the influence of cellular nanoparticle load on transfection outcomes in neural cells

Genetic engineering of cell transplant populations offers potential for delivery of neurotherapeutic factors to modify the regenerative microenvironment of the injured spinal cord. The use of magnetic nanoparticle (MNP)-based vectors has reduced the traditional reliance on viral methods and their associated obstacles in terms of scale up and safety. Studies utilizing magnetic assistive platforms for MNP-mediated gene delivery have found transfection efficiency in astrocytes (a major transplant and homeostatic neural cell type) to be both frequency- and amplitude-dependent. It is widely assumed that increased intracellular particle load will enhance transfection efficiency in a cell population. Therefore, we tested repeat delivery of MNP:plasmid complexes in conjunction with oscillating magnetic field parameters-a process termed "magneto-multifection"-in astrocytes of primary origin in an attempt to enhance transfection levels. We show (a) levels of transfection using magneto-multifection equal that seen with viral methods; (b) reporter protein expression using two reporter plasmids shows a diverse profile of single/dual transfected cells with implications for delivery of a "cocktail" of neurotherapeutic proteins; and (c) contrary to expectation, an inverse relationship exists between particle load and reporter protein expression.

Part II: Functional delivery of a neurotherapeutic gene to neural stem cells using minicircle DNA and nanoparticles: Translational advantages for regenerative neurology

Both neurotrophin-based therapy and neural stem cell (NSC)-based strategies have progressed to clinical trials for treatment of neurological diseases and injuries. Brain-derived neurotrophic factor (BDNF) in particular can confer neuroprotective and neuro-regenerative effects in preclinical studies, complementing the cell replacement benefits of NSCs. Therefore, combining both approaches by genetically-engineering NSCs to express BDNF is an attractive approach to achieve combinatorial therapy for complex neural injuries. Current genetic engineering approaches almost exclusively employ viral vectors for gene delivery to NSCs though safety and scalability pose major concerns for clinical translation and applicability. Magnetofection, a non-viral gene transfer approach deploying magnetic nanoparticles and DNA with magnetic fields offers a safe alternative but significant improvements are required to enhance its clinical application for delivery of large sized therapeutic plasmids. Here, we demonstrate for the first time the feasibility of using minicircles with magnetofection technology to safely engineer NSCs to overexpress BDNF. Primary mouse NSCs overexpressing BDNF generated increased daughter neuronal cell numbers post-differentiation, with accelerated maturation over a four-week period. Based on our findings we highlight the clinical potential of minicircle/magnetofection technology for therapeutic delivery of key neurotrophic agents.