Ototoxicity is a dose-limiting side effect of chemotherapeutic treatment with cisplatin. In a series of experiments on neonatal rat cochlear organotypic cultures, the extent of damage induced by a broad range of cisplatin treatment concentrations was examined. Paradoxically, it was found that hair cell loss was greater following 48 h exposure to low (10, 50 and 100 μM) versus high (400 and 1000 μM) concentrations of cisplatin; these findings indicate that hair cells possess intrinsic resistance to high levels of extracellular cisplatin. Using cisplatin conjugated to Alexa Fluor 488, it was found that cisplatin is readily taken up by hair cells at low concentrations, but is largely excluded at high concentrations. Recent studies indicate that the major influx of cisplatin into hair cells occurs via the copper transporter, Ctr1, whereas ATP7A and ATP7B are copper pumps responsible for cisplatin sequestration and efflux. Using immunolabeling procedures for these copper trafficking proteins, it was found that Ctr1 and ATP7B were localized in the hair cells, whereas ATP7A showed extensive labeling in the pillar cells in the organ of Corti. Additional experiments confirmed the protective effect of copper sulfate and cimetidine in attenuating cisplatin-induced hair cell loss. However, because neither copper sulfate nor cimetidine provided complete protection against cisplatin, and high levels of copper sulfate itself were found to be ototoxic, it is suggested that future therapeutic efforts may benefit from a combination of pharmacological treatments which seek to not only limit the uptake of cisplatin into cochlear cells but also increase its efflux.
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