Ototoxicity Screening with Zebrafish: Using the Lateral Line Hair Cell Assay to Detect Drug-Induced Auditory Damage Early

Chemotherapeutic agents like cisplatin cause permanent hearing damage in 36% of adult patients and 40-60% of pediatric ones, although there are sources that escalate the incidence up to 75-100%. Hearing loss is one of the most frequent adverse effects of drug treatment, yet it is not routinely evaluated in preclinical development.

Zebrafish offer a practical, in vivo alternative to test ototoxicity in the preclinical setting. Their lateral line system contains mechanosensory hair cells that are structurally and functionally analogous to human inner ear hair cells, and they respond to the same ototoxic compounds. 

What Is Ototoxicity and Why Is It Underestimated in Preclinical Drug Safety

Ototoxicity is defined as the adverse reaction in the auditory system caused by drug or chemical exposure. The World Health Organization recognizes it as a significant global cause of hearing loss, yet it is not routinely evaluated in preclinical testing. 

Behavioral ototoxicity tests in rodents generate frequent false negatives: they can lose most of their high-frequency hearing and still respond to ambient sound. Auditory brainstem response (ABR) studies, the gold standard for preclinical hearing assessment, are expensive, time-consuming, and laborious. It requires specialized equipment, trained personnel, and considerable animal numbers, making them impractical to deploy at the hit-to-lead stages.

The result is ototoxicity entering the development process late, when candidates have already advanced through extensive in vitro and in vivo programs. At that point, identifying auditory liability means either accepting the risk, deprioritizing a compound that has already consumed significant resources, or starting optimization that could have been initiated much earlier.

The Zebrafish Lateral Line as a Predictive Model for Hair Cell Damage

The inner ear structure varies among vertebrates, but all species rely on hair cells to detect sensory stimulation. Zebrafish possess mechanosensory organs called neuromasts, arranged along the lateral line of the head, body, and tail. Each neuromast contains a cluster of sensory hair cells that are structurally and functionally homologous to the hair cells of the mammalian inner ear: they express conserved ion channels, undergo the same oxidative and apoptotic death pathways, and respond to ototoxic drugs in a dose-dependent manner.

In zebrafish larvae, these hair cells are placed on the body surface, which means drug exposure is achieved simply by immersion. Because larvae are also optically transparent, hair cells can be visualized directly in living animals using stable transgenic lines that express GFP specifically in hair cells, such as brn3c:GFP, or fluorescent vital dyes such as DASPEI (2-(4-(dimethylamino)styryl)-N-ethylpyridinium iodide). Hair cell number, morphology, or fluorescence intensity across the neuromasts can be quantified by automated image analysis. The output is a quantitative, dose-response dataset generated in living organisms within a few days. 

The lateral line and neuromasts in the zebrafish larva. (A) Low magnification view of a zebrafish larva under transmitted light. (B) Hair cells in the lateral line were labeled with the fluorescent vital dye DiAsp (bright orange). It shows the superficial distribution of neuromasts along the anterior (head) and posterior (trunk and tail) lateral-line systems. (C) Schematic representation of the distribution of the neuromasts in the lateral line of a zebrafish larva. Orange highlights the anterior neuromasts, green the posterior neuromasts, and blue the dorsal neuromasts. (D,E) High magnification confocal image of a frontal view of a posterior neuromast revealing the hair cells (blue), supporting cells (red and green). (F) Schematic representation of a neuromast viewed from the side, depicting every known cell, including the neurons. (G) High magnification side-view image of a mature neuromast labeled with the vital dye DiAsp. Scale bars are 10μm. Source: Pinto-Teixeira F, Muzzopappa M, Swoger J, Mineo A, Sharpe J, López-Schier H. Intravital imaging of hair-cell development and regeneration in the zebrafish. Front Neuroanat. 2013 Oct 11;7:33.

The biological validity of zebrafish for ototoxic and otoprotective assays has been well established since 2005. Ton and Parng ranked the ototoxicity of known drugs in zebrafish (aminoglycosides > cisplatin > vinblastine > quinine). The ranking mirrored the one observed in humans, where aminoglycosides and cisplatin are potent ototoxicity inducers, while vinblastine sulfate and quinine induce ototoxicity less frequently, and the damage can be reversible. They also studied antioxidant otoprotectants (glutathione, N-acetyl-L-cysteine, D-methionine) that protect against cisplatin-induced hair cell loss in mammalian models and revealed that they produce consistent protective effects in zebrafish, with comparable dose-response relationships. 

Cisplatin and Aminoglycoside Ototoxicity: How Zebrafish Models Replicate Drug-Induced Hearing Loss

The most clinically important ototoxic drug classes (aminoglycoside antibiotics and platinum-based chemotherapeutics) have been characterized in zebrafish with a level of translational fidelity that supports direct preclinical application.

Aminoglycosides enter hair cells primarily through mechanoelectrical transducer (MET) channels at the tips of the stereocilia. Once inside, they accumulate and trigger mitochondrial dysfunction and apoptosis. In zebrafish, fluorescently labeled aminoglycosides are visible inside lateral line hair cells within 3 minutes of exposure. Blocking MET channel entry prevents both drug accumulation and hair cell death, a mechanism confirmed in mammalian cochlear preparations by patch-clamp electrophysiology (Kitcher et al. 2019).

Cisplatin's mechanism is not fully understood, but various studies show that the MET channel may also be implicated. In zebrafish lateral line assays, it causes dose-dependent hair cell loss; in mouse cochlear cultures, it preferentially kills outer hair cells beginning at the basal high-frequency end of the cochlea, matching the pattern of high-frequency hearing loss seen in patients.

The compound ORC-13661 illustrates exactly zebrafish translatability. This compound is a high-affinity reversible blocker of the MET channel derived from PROTO-1, a molecule originally identified in a large-scale zebrafish screen. It protects zebrafish hair cells from gentamicin, neomycin, amikacin, and cisplatin; provides full protection of mammalian cochlear outer hair cells in vitro; and significantly reduces ABR threshold shifts in amikacin-treated rats at oral doses (Kitcher et al. 2019). 

ORC-13661 is now in a Phase II randomized controlled trial (NCT05730283), recruiting patients with non-tuberculous mycobacterial lung disease treated with intravenous amikacin. Its path from a zebrafish screen to a registrational clinical trial is one of the clearest demonstrations of the model's translational power.

Integrating Zebrafish Ototoxicity Screening Before Rodent ABR Studies: A Smarter Early-Stage Strategy

The evidence base supporting zebrafish as an ototoxicity model is well established. Thus, the next question should be: Where should we place this screening in the drug discovery and development pipeline?

The answer is before rodent ABR studies. Deploying the lateral line hair cell assay at the hit-to-lead stage generates quantitative ototoxicity data on multiple compounds simultaneously, within days, at a fraction of the cost of mammalian studies. Compounds with significant hair cell toxicity can be deprioritized or flagged for structural optimization before any rodent investment is made. On the other side, it can also be useful to identify and prioritize otoprotective compounds in the hit-finding stage. Those with promising profiles advance with greater confidence, reducing animal use, cutting timelines, and concentrating resources where they matter.

At ZeClinics, we have validated several drug-induced ototoxicity models based on exposure to cisplatin, gentamicin, or neomycin. These pharmacological models induce a marked and statistically significant reduction in lateral line hair cells, providing a robust effect window to screen and benchmark potential otoprotective compounds.

The assay leverages our automated VAST imaging platform, enabling high-throughput analysis, strong experimental robustness, and reliable quantification of ototoxic and otoprotective effects. Additionally, by screening candidates against a panel of different ototoxicants, it allows addressing the mechanism of action of your candidates or expanding their therapeutic range.

Whether you are assessing the auditory safety of a new compound, optimizing a structural series with known ototoxic liability, or exploring otoprotection as a co-treatment strategy, zebrafish lateral line screening provides the earliest, most cost-efficient path to an informed go/no-go decision.

If you are working on a program where ototoxicity is a concern, ZeClinics can help you.

Sources

Kitcher SR, Kirkwood NK, Camci ED, Wu P, Gibson RM, Redila VA, Simon JA, Rubel EW, Raible DW, Richardson GP, Kros CJ. ORC-13661 protects sensory hair cells from aminoglycoside and cisplatin ototoxicity. JCI Insight. 2019 Aug 8;4(15):e126764. doi: 10.1172/jci.insight.126764.

Oliveira Cunha E, de Athayde Saul D, Sander de Abreu M, Salgado Machado M, Dallegrave E. Studying ototoxicity in zebrafish. Environ Toxicol Chem. 2025 Oct 1;44(10):2744-2753. doi: 10.1093/etojnl/vgaf161.

Owens KN, Santos F, Roberts B, Linbo T, Coffin AB, Knisely AJ, Simon JA, Rubel EW, Raible DW. Identification of genetic and chemical modulators of zebrafish mechanosensory hair cell death. PLoS Genet. 2008 Feb 29;4(2):e1000020. doi: 10.1371/journal.pgen.1000020.

Pinto-Teixeira F, Muzzopappa M, Swoger J, Mineo A, Sharpe J, López-Schier H. Intravital imaging of hair-cell development and regeneration in the zebrafish. Front Neuroanat. 2013 Oct 11;7:33. doi: 10.3389/fnana.2013.00033.
Ton C, Parng C. The use of zebrafish for assessing ototoxic and otoprotective agents. Hear Res. 2005 Oct;208(1-2):79-88. doi: 10.1016/j.heares.2005.05.005.

Header image: A zebrafish larva at 5 days post fertilization. At this stage, both the inner ear and lateral line hair cell systems are functional. All hair cells are visualized via YFP fluorescence (Tg[myo6b:D3cpv]vo9). Scale bar: 500 µm. Credit: Sheets L, Holmgren M, Kindt KS. How Zebrafish Can Drive the Future of Genetic-based Hearing and Balance Research. J Assoc Res Otolaryngol. 2021 Jun;22(3):215-235.

By Javier Terriente

Javier is the co-founder of ZeClinics and ZeCardio Therapeutics, two biotech firms specializing in zebrafish-based preclinical drug discovery for cardiovascular, neural, and toxicology applications. He combines scientific leadership with business acumen, having successfully driven fundraising efforts and strategic partnerships.

Currently leading scientific efforts at ZeCardioTx (and formerly CSO at ZeClinics), Javier also serves on the Board of Directors of AseBio, where he advocates for industry collaboration. His academic background includes a PhD in Molecular Biology and a Marie Curie Fellowship. Recognized as an expert in zebrafish models, he has published extensively and has supervised five industrial PhD theses.