Otosclerosis is a disease of the otic capsule that is among the most common causes of acquired hearing loss. During the last fifteen years, our laboratory has focused on elucidating the molecular pathology of otosclerosis with the long-term goal of developing better forms of therapy. These studies have led us to a new and innovative treatment strategy: the inner ear delivery of bisphosphonates via a drug-eluting polymer. We have begun to develop and test a drug formulation for use in humans, and have developed an animal model to test it. Since most patients with otosclerosis receive stapes prosthesis, we will integrate the polymer into the prosthesis for intracochlear delivery. We will also integrate the polymer into a wafer for delivery via the round window membrane. The otic capsule is unique in that it normally exhibits little or no bone remodeling. Otosclerosis is characterized by an abnormal remodeling of the otic capsule. Some bisphosphonate compounds are potent inhibitors of bone remodeling, but potentially serious side effects can occur with systemic administration in humans such as inhibition of all skeletal remodeling and osteonecrosis of the jaw. Intracochlear and intratympanic administration should bypass these systemic problems and ensure that the drugs reach cochlear tissues and the otic capsule in the form and concentration desired. We have identified an animal model, the OPG-/- (knockout) mouse, which exhibits foci of active remodeling within the otic capsule, similar to otosclerosis. These mice also develop progressive hearing loss, similar to cases of advanced otosclerosis. We have shown that bisphosphonates are highly effective in halting the pathologic remodeling and hearing loss in OPG-/- mice. We will now investigate effects of direct intracochlear and intratympanic delivery of risedronate, a potent bisphosphonate. We have chosen risedronate because of its high potency and availability of a fluorescein conjugated form of the drug that allows its quantification and localization. These experiments will guide the development of a bisphosphonate formulation for inner ear delivery in humans. If successful, these studies will lead quickly to clinical trials in humans with progressive sensorineural hearing loss from cochlear otosclerosis using a bisphosphonate-eluting stapes prosthesis, an intratympanic bisphosphonate formulation, or both. The development of this technology will also be valuable for other inner ear disorders that may benefit from direct drug delivery.
If successful, these studies will lead directly to clinical trials in humans with progressive sensorineural hearing loss from cochlear otosclerosis using a bisphosphonate-eluting stapes prosthesis, an intratympanic bisphosphonate formulation, or both, using safe and well-established techniques of middle ear surgery. The development of this technology will also be valuable for other inner ear disorders that may benefit from direct drug delivery.
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