Subjective tinnitus is the perception of a phantom sound, which negatively impacts the quality of life for millions of people worldwide. Despite the great demand for remedy, there are no FDA-approved drugs to prevent or treat tinnitus. Possible causes of tinnitus are complicated. The current view is that hyperactivity in the central auditory nervous system contributes to the majority of tinnitus cases. This abnormal electrical activity, including an increase in delta-band activity, may be the direct result of an increase in T-type calcium channel activity. Other studies suggest that inflammatory responses within the brain may be involved in the development and persistence of tinnitus; therefore, drug candidates targeting both inflammatory and calcium signaling pathways may act synergistically to prevent and treat tinnitus. Tetrandrine (TET), an approved drug used in China, exhibits both anti-inflammatory and calcium channel-blocking properties. Using a new tinnitus detection method in mice, we have shown that both salicylate-induced and noise-induced tinnitus can be effectively treated by TET in a dose-dependent manner. Our hypothesis is that TET or its chemical analogs can be developed as drugs to prevent and treat tinnitus. In our proposed experiments, we have two parallel goals: (1) obtain investigational new drug (IND)-enabling toxicity and pharmacokinetics data for TET (Aim 1) and (2) optimize second-generation products with structure-activity relationship studies of TET and its chemical analogs (Aim 2). Successful accomplishment of Aim 1 will enable TET to advance into clinical development. In addition, the studies of Aim 2 will enable us to identify additional candidates in case TET fails at clinical stages. By targeting multiple cellular signaling pathways that impinge upon tinnitus, our study will open new areas for the treatment and prevention of tinnitus. The extensive body of data publicly available for TET and its analogs will help us significantly reduce development time and costs.
The market for a specific tinnitus relief drug is enormous and will grow in the future. This project, focusing on drug repurposing targeting multiple signaling pathways, will lead to the development of a new pharmacological agent against tinnitus.