Hepatocyte growth factor mimetic protects lateral line hair cells from aminoglycoside exposure.

Phillip M. Uribe,Leen H. Kawas,Joseph W. Harding,Allison B. Coffin

doi:10.3389/fncel.2015.00003

Abstract

Loss of sensory hair cells from exposure to certain licit drugs (e.g., aminoglycoside antibiotics, platinum-based chemotherapy agents) can result in permanent hearing loss. Here we ask if allosteric activation of the hepatocyte growth factor (HGF) cascade via Dihexa, a small molecule drug candidate, can protect hair cells from aminoglycoside toxicity. Unlike native HGF, Dihexa is chemically stable and blood-brain barrier permeable. As a synthetic HGF mimetic, it forms a functional ligand by dimerizing with endogenous HGF to activate the HGF receptor and downstream signaling cascades. To evaluate Dihexa as a potential hair cell protectant, we used the larval zebrafish lateral line, which possesses hair cells that are homologous to mammalian inner ear hair cells and show similar responses to toxins. A dose-response relationship for Dihexa protection was established using two ototoxins, neomycin and gentamicin. We found that a Dihexa concentration of 1 μM confers optimal protection from acute treatment with either ototoxin. Pretreatment with Dihexa does not affect the amount of fluorescently tagged gentamicin that enters hair cells, indicating that Dihexa’s protection is likely mediated by intracellular events and not by inhibiting aminoglycoside entry. Dihexa-mediated protection is attenuated by co-treatment with the HGF antagonist 6-AH, further evidence that HGF activation is a component of the observed protection. Additionally, Dihexa’s robust protection is partially attenuated by co-treatment with inhibitors of the downstream HGF targets Akt, TOR and MEK. Addition of an amino group to the N-terminal of Dihexa also attenuates the protective response, suggesting that even small substitutions greatly alter the specificity of Dihexa for its target. Our data suggest that Dihexa confers protection of hair cells through an HGF-mediated mechanism and that Dihexa holds clinical potential for mitigating chemical ototoxicity.

Highlights

Hearing loss and vestibular dysfunction are some of the most prevalent and debilitating disorders due to social isolation resulting from sensory deprivation
We demonstrate that Dihexa protects lateral line hair cells from aminoglycoside ototoxicity
Direct hair cell counts were obtained from Brn3c:mGFP fish, further demonstrating that Dihexa robustly protects hair cells from neomycin damage (Figure 3).These results indicate that Dihexa only modulates targets responsible for the acute phase of aminoglycoside ototoxicity

Summary

INTRODUCTION

Hearing loss and vestibular dysfunction are some of the most prevalent and debilitating disorders due to social isolation resulting from sensory deprivation. Hearing loss can result from excessive exposure to loud noise, genetic factors, or exposure to certain licit drugs, termed ototoxins, such as aminoglycoside antibiotics and platinumbased chemotherapeutics like cisplatin (Fee, 1980; Rybak et al, 2009). Due to their high efficacy, many ototoxins are still used despite the risk of hearing loss. Previous drug discovery work in the larval zebrafish lateral line identified the novel compound PROTO-1 that prevents aminoglycoside-induced hair cell toxicity in rodent models in vivo, demonstrating that otoprotective drug discovery in zebrafish translates to mammalian systems (Owens et al, 2008; Rubel et al, 2011). This work demonstrates the potential clinical utility of Dihexa as a co-administered protectant to prevent aminoglycoside ototoxicity

MATERIALS AND METHODS

RESULTS

Findings

DISCUSSION