Screening of Ototoxicity and Otoprotective Drugs

Definition, scope & rationale of ototoxicity screening

• Ototoxicity — permanent or transient impairment of cochlear (hearing) and/or vestibular (balance) function caused by therapeutic drugs or other exogenous insults; the two agents that most reliably injure the human ear — and around which the validated models are built — are the aminoglycoside antibiotics and the platinum chemotherapeutics.
• Two mirror-image experimental questions — an assay that reliably induces a graded, reproducible hair-cell lesion can both rank the toxicity of new candidates (ototoxicity screening) and test the efficacy of putative protective agents co-administered against a standard insult (otoprotection screening).
• Clinical signature the models reproduce — aminoglycoside injury affects high frequencies first and progresses to lower frequencies — a base-to-apex cochlear gradient the validated models deliberately mirror.
• Two-tier screening logic (in-vitro → in-vivo) — the organotypic organ-of-Corti explant gives a rapid, sensitive first pass; promising protectants are then confirmed in an intact-animal model (guinea pig for aminoglycosides). A protective effect is considered compelling only when it reproduces in a different in-vivo species — cross-model, cross-species concordance is the standard of evidence.
• Unifying mechanism = oxidative stress — aminoglycoside, noise and ageing injury are attributed largely to reactive-oxygen-species / free-radical production in hair cells, which is why the benchmark otoprotectant class in every model is the antioxidants.
• Insults modelled — the assay families cover drug-induced (aminoglycoside, cisplatin) inner-ear damage, noise-induced hearing loss (NIHL) and age-related hearing loss (ARHL / presbycusis); noise and ageing are distinct yet interrelated and share the oxidative mechanism, so their models overlap heavily in endpoints.