Electric field focusing gene electrotransfer for cochlear DNA therapeutics

Applications for gene therapy that depend upon localization and control of gene expression are challenged by the mode for gene delivery. Viral vectors inherently suffer off-target spread of the viral particles, as do liposome-based gene transfer approaches. In contrast, conventional “open-field” electroporation (OFE) achieves gene electrotransfer of naked plasmid DNA injected generally into the target tissue by means of a brief train of high-voltage electrical pulses creating a quasi-uniform electric field. The targeting of the gene transfer with OFE can be controlled to some extent by the placement of the electrodes in the tissue and the volume of injected DNA. In this chapter, the application of electric field focusing gene electrotransfer (EFF-GET) is described, where a gene delivery probe is used as an “electro-lens” for highly localized and controlled gene electrotransfer. EFF-GET arose from use of cochlear implant electrode arrays, designed for spatially constrained electrical stimulation of the primary auditory neurons in the cochlea, where the array was reconfigured to provide electric field focusing that produces electric field strengths sufficient for gene delivery in the domain close to the bionic array using charge transfer considerably below that normally required for conventional electroporation. EFF-GET efficiency was found to be greatly enhanced by integrating fluidics-delivery of nonconductive sucrose-vehicle which reduced local conductivity and biased the local current to the polyanionic DNA species (defined as “conductivity-clamped” EFF-GET). EFF-GET has proved to be a highly robust and efficient means to target small tissue regions (hundreds of μm3—to several mm3) for efficient delivery of plasmid and fully synthetic DNA within the tunable pulsed electric field, by configuring the electric field shape around the bionic EFF-GET array; affording near “dial-up” control of DNA payload delivery by varying the pulse parameters. Application of the EFF-GET platform for delivery of plasmid and synthetic DNAs encoding neurotrophins to the cochlea in deafened animal models established proof of principle for gene augmentation in the cochlea to regenerate primary auditory neuron dendrites improving cochlear implant performance for hearing. The enhanced efficiency of conductivity-clamped EFF-GET enabled a first-in-human clinical trial to “close the neural gap” in cochlear implant patients. Conductivity-clamped EFF-GET has evidently broad application for vector-free targeted gene delivery, where the minimal charge transfer provides an optimal safety profile, critical for applications such as focal DNA/RNA therapeutics in the brain, and enables painless and efficient wireless single pulse delivery, for example, in DNA vaccine applications.