Protection against cisplatin-induced ototoxicity by adeno-associated virus-mediated delivery of the X-linked inhibitor of apoptosis protein is not dependent on caspase inhibition.
OBJECTIVE
Gene therapy with an adeno-associated viral (AAV) vector encoding the X-linked inhibitor of apoptosis protein (XIAP) in an animal model of cisplatin-induced ototoxicity can elucidate apoptotic pathways in the inner ear.


BACKGROUND
Cisplatin is limited clinically by ototoxicity associated with apoptosis in the inner ear. The relevant intracellular apoptotic pathways, however, are unknown. XIAP is an antiapoptotic protein that both inhibits caspases and reciprocally regulates the proapoptotic Smac/Omi proteins. AAV-mediated delivery of various XIAP mutants could distinguish between these antiapoptotic pathways in the ear and further the development of specific reagents for gene therapy- mediated prevention of cisplatin-induced ototoxicity.


METHODS
We administered unilaterally through the round-window AAV-harboring genes encoding wild-type dXIAP, yellow fluorescent protein, or either of two dXIAP point mutants-one deficient in caspase inhibition (dXIAP-d) and the other additionally deficient in the binding of Smac/Omi (dXIAP-t). All rats received a 3-day systemic course of cisplatin. Functional hearing loss was measured by shifts in auditory brainstem response (ABR) thresholds after cisplatin treatment, and hair-cell loss was assessed by whole-mount phalloidin staining of cochlear turns.


RESULTS
Uninjected ears universally displayed high-frequency-specific hair-cell loss and ABR threshold shifts upon cisplatin treatment. Although yellow fluorescent protein had no effect, ears injected with dXIAP exhibited 68% less ABR threshold shift at 32 kHz and 50% less basal-turn outer-hair-cell loss compared with contralateral untreated ears. This protection was maintained in ears injected with dXIAP-d but was abolished in those expressing dXIAP-t, which is incapable of blocking Smac/Omi.


CONCLUSIONS
Hair-cell apoptosis induced by cisplatin involves the Smac/Omi pathway. Thus, gene therapy with either wild-type dXIAP or Smac/Omi-selective dXIAP-d may be effective to protect against cisplatin-mediated ototoxicity.
Chan
Dylan K
DK
Weill Medical College, Cornell University, New York, New York 10021, USA.
Lieberman
David M
DM
Musatov
Sergei
S
Goldfein
Joshua A
JA
Selesnick
Samuel H
SH
Kaplitt
Michael G
MG
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D061945:Caspase Inhibitors; D002945:Cisplatin / Q000009:adverse effects*; D000229:Dependovirus / Q000235:genetics*; D007758:Ear, Inner / Q000187:drug effects* / Q000503:physiopathology*; D016057:Evoked Potentials, Auditory, Brain Stem; D015316:Genetic Therapy / Q000379:methods*; D006198:Hair Cells, Auditory / Q000187:drug effects / Q000473:pathology; D006311:Hearing Disorders / Q000139:chemically induced* / Q000175:diagnosis / Q000517:prevention & control*; D008297:Male; D050505:Mutant Proteins / Q000235:genetics / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000008:administration & dosage / Q000494:pharmacology*
D061945:Caspase Inhibitors; D050505:Mutant Proteins; D051636:X-Linked Inhibitor of Apoptosis Protein; D002945:Cisplatin