Introduction: Children are at high risk for iatrogenic ototoxicity from therapeutics such as aminoglycoside antibiotics and platinum-based antineoplastic agents. Due in part to a lack of available translational biomarkers, there are no clinical strategies or therapeutics to prevent iatrogenic ototoxicity. Here, we present progress towards developing a biomarker system to evaluate the dose and time relationship between systemically administered aminoglycosides and cochlear accumulation. We further demonstrate that uptake can be modulated with ORC-13661, a hearing protection drug under clinical investigation.
Methods: Neonatal mice (P5) and juvenile mice with mature hearing (P25-30) were given systemic injections of a gentamicin analogue conjugated with Texas Red (G418-TR) either alone or in conjunction with ORC-13661 pretreatment. Dosage, injection schedules, and survival times of both drugs were systematically varied. At specified endpoints tissue was collected for whole mount preparations and cryostat sections. Tissue was immunolabeled with anti-myosin7a and/or Phalloidin and imaged with confocal microscopy.
Results: Neonatal and juvenile mice demonstrate dose-dependent hair cell uptake and accumulation of systemically administered G418-TR. Over time, we find that systemically administered G418-TR is retained in hair cells for 72 hours. Non-sensory tissues such the stria vascularis, pillar supporting cells, and spiral ganglia neurons do not retain G418-TR. Finally, we demonstrate that pretreatment with ORC-13661 is effective at blocking the uptake of G418-TR in mammalian hair cells in vivo.
Conclusion: Murine hair cells accumulate systemically administered G418-TR in a dose- and time-dependent manner. When evaluating uptake and retention within the neonatal cochlea, we find that aminoglycosides are selectively retained in the mechanosensory hair cells, s, suggesting that both ototoxin uptake and retention may contribute to ototoxicity. Finally, we demonstrate that ORC-13661 pretreatment blocks accumulation of aminoglycosides in vivo. We believe that this preparation can serve as a valuable translational tool to better understand mechanisms of ototoxicity and as a rapid model to assess biologic characteristics of therapeutic strategies designed to mitigate ototoxicity.