lacking. This study examines the effects of chloroquine on hair cells using two common 31 experimental models: the zebrafish lateral line and neonatal mouse cochlear cultures. 32
Zebrafish larvae were exposed to varying concentrations of chloroquine phosphate or 33 hydroxychloroquine for 1 hr or 24 hr, and hair cells assessed by antibody staining. A 34 significant, dose-dependent reduction in the number of surviving hair cells was seen 35 across conditions for both exposure periods. Hydroxycholroquine showed similar toxicity. 36
In mouse cochlear cultures, chloroquine damage was specific to outer hair cells in tissue 37 from the cochlear basal turn, consistent with susceptibility to other ototoxic agents. As hydroxychloroquine is often used to replace chloroquine in clinical settings, 183 these two drugs were compared for relative hair cell toxicity. Both drugs showed dose-184 dependent hair cell loss ( Figure 2 ). Hydroxychloroquine showed slightly more toxicity than 185 chloroquine (F=4.774, p=0.03; two-way ANOVA). These results demonstrate that both 186 clinically-relevant chloroquine drugs show hair cell toxicity in the zebrafish model. 187
Previous work has demonstrated that quinoline drugs, including chloroquine, can 188 inhibit aminoglycoside ototoxicity by partially blocking mechanotransduction-dependent 189 toxin uptake (Ou et al., 2012) . We reasoned that the asymptotic nature of the chloroquine 190 dose-response function might be due to its ability to block its own uptake. We implying that chloroquine uptake is rapid and affects hair cells soon after they are exposed. 