Recent studies have shown that the mammalian high-affinity copper transporter encoded by Ctr1 is involved in the uptake of cisplatin. However, the roles of hCtr1 in cisplatin-sensitive and cisplatin-resistant mammalian cells have not been investigated. Here, we show that, of five cisplatin- resistant cell lines, only one (SR2) exhibited substantial reduction in hCtr1 expression as compared with that in its sensitive small cell lung cancer cell line (SCLC), whereas copper efflux transporter ATP7A and ATP7B were not significantly altered. SR2 exhibited cross-resistance to carboplatin but not to oxaliplatin. Transfection of expression hemagglutinin-tagged hCtr1 cDNA recombinant into SCLC and SR2 cells enhanced uptakes of cisplatin, carboplatin, and oxaliplatin, suggesting that hCtr1 transporter can transport these platinum-based drugs. Whereas increased sensitivities to all these platinum drugs were observed in hCtr1-transfected-SCLC cells, increased sensitivities to cisplatin and carboplatin but not to oxaliplatin were observed in hCtr1-transfected SR2 cells. These results suggest that SR2 acquired an additional unique intracellular resistance mechanism to oxaliplatin. Finally, using hCtr1 deletion mutants, we showed that the NH2-terminal domain of hCtr1 was involved in transporting all these platinum-based antitumor agents. These results collectively show the importance of hCtr1 in the transport of platinum-based antitumor agents in cisplatin-sensitive and cisplatin-resistant variants.
[Proc Amer Assoc Cancer Res, Volume 46, 2005]