Uribe Phillip M, Kawas Leen H, Harding Joseph W, Coffin Allison B
Department of Integrative Physiology and Neuroscience, Washington State University Pullman, WA, USA.
Department of Integrative Physiology and Neuroscience, Washington State University Pullman, WA, USA ; M3 Biotechnology, Inc. Seattle, WA, USA.
Front Cell Neurosci. 2015 Jan 28;9:3. doi: 10.3389/fncel.2015.00003. eCollection 2015.
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.
接触某些合法药物（如氨基糖苷类抗生素、铂类化疗药物）导致感觉毛细胞丧失会造成永久性听力损失。在此，我们探究一种小分子候选药物二己环肽（Dihexa）通过变构激活肝细胞生长因子（HGF）级联反应能否保护毛细胞免受氨基糖苷类毒性的影响。与天然HGF不同，二己环肽化学性质稳定且可透过血脑屏障。作为一种合成的HGF模拟物，它通过与内源性HGF二聚化形成功能性配体，从而激活HGF受体及下游信号级联反应。为了评估二己环肽作为一种潜在的毛细胞保护剂，我们使用了斑马鱼幼体侧线，其拥有与哺乳动物内耳毛细胞同源且对毒素有相似反应的毛细胞。使用两种耳毒素新霉素和庆大霉素建立了二己环肽保护作用的剂量反应关系。我们发现1μM的二己环肽浓度能为两种耳毒素的急性处理提供最佳保护。用二己环肽预处理并不影响进入毛细胞的荧光标记庆大霉素的量，这表明二己环肽的保护作用可能是由细胞内事件介导的，而非通过抑制氨基糖苷类的进入。与HGF拮抗剂6 - AH共同处理会减弱二己环肽介导的保护作用，这进一步证明HGF激活是观察到的保护作用的一个组成部分。此外，与下游HGF靶点Akt、TOR和MEK的抑制剂共同处理会部分减弱二己环肽的强大保护作用。在二己环肽的N端添加一个氨基也会减弱保护反应，这表明即使是微小的取代也会极大地改变二己环肽对其靶点的特异性。我们的数据表明，二己环肽通过HGF介导的机制赋予毛细胞保护作用，并且二己环肽在减轻化学性耳毒性方面具有临床潜力。
