The effects of DFMO on polyamine metabolism in the inner ear.

Difluoromethylornithine (DFMO) is a novel antineoplastic agent that was associated with an unexpected hearing loss in Phase II clinical trials. DFMO interferes with polyamine synthesis by inhibition of the enzyme ornithine decarboxylase (ODC). The objective of the current study was to establish a methodology to determine the effect of DFMO on polyamine levels and ODC activity in the cochlea. Guinea pigs received DFMO in their drinking water and were tested for auditory brainstem response threshold shifts. The organ of Corti, the lateral wall, and the acoustic nerve were assayed for both ODC activity and polyamine levels. In DFMO treated animals there was an inhibition of ODC activity in cochlear tissues as well as in intestinal mucosa. In addition, a significant depletion of cochlear polyamines was observed in the treatment animals. This study suggests that systemically administered DFMO inhibits ODC activity and interferes with polyamine synthesis in the cochlea.