Drug delivery to the inner ear using gene therapy.

The last 10 years have seen the development of numerous strategies for the delivery of genes to the inner ear. Besides being a useful research tool,gene therapy has significant promise as a potential clinical treatment. The human inner ear is easily accessible through either the round window or the stapes footplate. It is now possible to choose a variety of vectors to target a variety of different tissues. Modification of promoters yields different expression patterns as well as differences in degree of expression. Several animal studies have also demonstrated that expression of exogenous genes in the cochlea does not result in loss of hearing function. A variety of potential clinical applications are already evident from these early studies. Protective strategies such as prevention of neuronal degeneration and protection of auditory hair cells from oxidative stress are potential examples where gene therapy may be useful. As the understanding of gene therapy improves, investigators will be able to move toward targeted single-gene replacement to treat disorders such as connexin mutations and applying gene therapy to sensory cell replacement.