Microbubbles and ultrasound increase intraventricular polyplex gene transfer to the brain

Abstract

Neurons in the brain can be damaged or lost from neurodegenerative disease, stroke, or traumatic injury. Although neurogenesis occurs in mammalian adult brains, the levels of natural neurogenesis are insufficient to restore function in these cases. Gene therapy has been pursued as a promising strategy to induce differentiation of neural progenitor cells into functional neurons. Non-viral vectors are a preferred method of gene transfer due to potential safety and manufacturing benefits but suffer from lower delivery efficiencies compared to viral vectors. Since the neural stem and progenitor cells reside in the subventricular zone of the brain, intraventricular injection has been used as an administration route for gene transfer to these cells. However, the choroid plexus epithelium remains an obstacle to delivery. Recently, transient disruption of the blood-brain barrier by microbubble-enhanced ultrasound has been used to successfully improve drug delivery to the brain after intravenous injection. In this work, we demonstrate that microbubble-enhanced ultrasound can similarly improve gene transfer to the subventricular zone after intraventricular injection. Microbubbles of different surface charges (neutral, slightly cationic, and cationic) were prepared, characterized by acoustic flow cytometry, and evaluated for their ability to increase the permeability of immortalized choroid plexus epithelium monolayers in vitro. Based on these results, slightly cationic microbubbles were evaluated for microbubble and ultrasound-mediated enhancement of non-viral gene transfer in vivo. When coupled with our previously reported gene delivery vehicles, the slightly cationic microbubbles significantly increased ultrasound-mediated transfection of the murine brain when compared to commercially available Definity® microbubbles. Temporary disruption of the choroid plexus by microbubble-enhanced ultrasound is therefore a viable way of enhancing gene delivery to the brain and merits further research.

Microbubbles and Nanobubbles with Ultrasound for Systemic Gene Delivery

“…Based on these reasons, extremely high amounts of nucleic acids are required when administered systemically. In regard to the issue of nucleic acids stability in vivo, it has been reported that nanoparticles of nucleic acids and polymers, such as polyethyleneimine or poly(lactic- co -glycolic acid), could increase their transfection efficiencies with ultrasound and microbubbles, via systemic injections [ 31 , 32 , 33 ]. The formation of nanoparticles with these cationic polymers reduced the risk of the degradation by nuclease and the removal from circulation.…”

Nucleic Acid-Based Therapy: Development of a Nonviral-Based Delivery Approach

“…These methods are used in combination with other methods, such as lipofection, to protect nucleic acid against degradation by nucleases. To increase gene delivery efficiency of sonoporation, microbubbles were shown to be effective [43] and applied for delivery to cancer cells [44,45] and the central nervous system [46,47]. Clinical trials in phases I and II have been reported for the treatment of melanoma [48][49][50] and solid tumors [51].…”

Destination Brain: the Past, Present, and Future of Therapeutic Gene Delivery

“…AD) are diagnosed and treated in older patients, improved gene delivery older mice will be more relevant. Disruption of BBB to enhance delivery has been explored via microbubbles, ultrasound (Tan et al, 2016) and chemicals ( e.g. mannitol) (Kwon et al., 2010; Gray et al, 2011); but the clinical implications of such approaches are not known.…”