Role of the Copper Transporter, CTR1, in Platinum-Induced Ototoxicity

Abstract

The goal of this study was to determine the role of an influx copper transporter, CTR1, in the ototoxicity induced by cisplatin, a potent anticancer platinum analog used in the treatment of a variety of solid tumors. As determined through reverse transcriptase-PCR (RT-PCR), quantitative RT-PCR, Western blot, and immunohistochemistry, mouse CTR1 (Ctr1) was found to be abundantly expressed and highly localized at the primary sites of cisplatin toxicity in the inner ear, mainly outer hair cells (OHCs), inner hair cells, stria vascularis, spiral ganglia, and surrounding nerves in the mouse cochlea. A CTR1 substrate, copper sulfate, decreased the uptake and cytotoxicity of cisplatin in HEI-OC1, a cell line that expresses many molecular markers reminiscent of OHCs. Small interfering RNA-mediated knockdown of Ctr1 in this cell line caused a corresponding decrease in cisplatin uptake. In mice, intratympanic administration of copper sulfate 30 min before intraperitoneal administration of cisplatin was found to prevent hearing loss at click stimulus and 8, 16, and 32 kHz frequencies. To date, the utility of cisplatin remains severely limited because of its ototoxic effects. The studies described in this report suggest that cisplatin-induced ototoxicity and cochlear uptake can be modulated by administration of a CTR1 inhibitor, copper sulfate. The possibility of local administration of CTR1 inhibitors during cisplatin therapy as a means of otoprotection is thereby raised.

Detection of Increased 64Cu Uptake by Human Copper Transporter 1 Gene Overexpression Using PET with 64CuCl2 in Human Breast Cancer Xenograft Model

“…Because hCTR1 can transport platinumcontaining drugs such as CDDP and CDDP-like drugs, hCTR1 overexpression was associated with favorable therapeutic effects of a CDDP-based cancer chemotherapy (27). As shown in Figure 3, our results are in accordance with aforementioned reports.…”

Sound preconditioning therapy inhibits ototoxic hearing loss in mice

“…Previous models relied on a single injection of high-dose cisplatin, resulting in high toxicity and little reduction in hearing sensitivity (8)(9)(10). We developed a new mouse model of cisplatin ototoxicity that approximates the pattern of multiple cycles of cisplatin administration in humans (11)(12)(13).…”

Molecular mechanisms of cisplatin resistance

“…Ctr1 À/À mouse embryonic fibroblasts accumulate much less cisplatin than their wild-type counterparts, and are indeed two-to threefold more resistant to its cytotoxic effects (Ishida et al, 2002;Katano et al, 2002;. Accordingly, cells pre-treated with copper (the main CTR1 substrate) are protected from cisplatin cytotoxicity (More et al, 2010), whereas copper chelators result in Figure 1 Modes of action of cisplatin. Because of the relatively low (compared with the extracellular microenvironment) concentration of chloride ions, intracellular cisplatin quickly becomes aquated and hence highly reactive.…”