Prevention of aminoglycoside antibiotic-induced ototoxicity of auditory hair cells via block of mechano-electrical transducer channels or intracellular mechanisms

This thesis addresses the pressing concern of clinical drug-induced hearing loss (ototoxicity). Described herein is the mechanism by which ototoxicity emerges following drug administration both in a clinical setting and in an in vitro model assay system used for its investigation, through use of mouse cochlear cultures. The predominant nature of this research concerns the identification of novel otoprotectants - compounds that when co-administered alongside clinical drug treatments can prevent the unfortunate ototoxic side-effect from occurring. Here I present my research, focussing on the identification of a number of novel compounds that have the potential to be taken forward to in vivo screening and, ultimately, clinical trials. Moreover, for each identified compound I present my investigation of their mechanism of protection – which could arise either by preventing the entry of the ototoxicity-inducing drugs into the sensory hair cells of the inner ear, or prevent their induction of apoptosis once inside the cell. To investigate their protective mechanism I employed a variety of methods, including: electrophysiology, fluorescent imaging and mitochondrial respirometry. Conclusively, I have identified at least five novel otoprotectants with the potential for clinical use. I show that three of these compounds likely block the entry of the damaging drugs into sensory hair cells, whereas the remaining two are thought to work intracellularly. Moreover, the two most effective compounds that I have identified seemingly work intracellularly, suggesting this to be the most viable mechanism of otoprotection for further investigation. I also show the potential for compound modification based on their mechanism of protection as a way of improving a compound’s otoprotective profile. Lastly, I devised an assay for the screening of clinical drug effects on mitochondria and employ this as a new avenue of screening for otoprotection.