HSV amplicon-mediated neurotrophin-3 expression protects murine spiral ganglion neurons from cisplatin-induced damage

Ototoxicity is a major dose-limiting side effect of cisplatin (DDP) adminis tration due to its propensity to induce destruction of hair cells and neuro ns in the auditory system. Previous studies demonstrated that TrkC-expressi ng spiral ganglion neurons (SGN) are protected from the cytotoxic effects o f DDP by localized delivery of the trophic factor neurotrophin-3 (NT-3). Su ccessful in vivo implementation of such a therapy requires the development of an efficient gene delivery vehicle for expression of NT-3 within the coc hlea. To this end, we constructed a herpes simplex virus (HSV) amplicon vec tor that expressed a c-Myc-tagged NT-3 chimera (HSVnt-3myc). Helper virus-f ree vector stocks were initially evaluated in vitro for their capacity to d irect expression of NT-3 mRNA and protein. Transduction of cultured murine cochlear explants with HSVnt-3myc resulted in production of NT-3 mRNA and p rotein up to 3 ng/ml as measured over a 48-h period in culture supernatants . To determine whether NT-3 overexpression could abrogate DDP toxicity, coc hlear explants were transduced with HSVnt-3myc or a murine intestinal alkal ine phosphatase-expressing control vector, HSVmiap, and then exposed to cis platin. HSVnt-3myc-transduced cochlear explants harbored significantly grea ter numbers of surviving SGNs than those infected with control virus. These data demonstrate that amplicon-mediated NT-3 transduction can attenuate th e ototoxic action of DDP on organotypic culture. The potency of NT-3 in pro tecting spiral ganglion neurons from degeneration suggests that in vivo neu rotrophin-based gene therapy may be useful for the prevention and/or treatm ent of hearing disorders.