Intrinsic or acquired resistance to cisplatin (CDDP) is a problem for its use in cancer chemotherapy. This resistance has been reported to correlate with expression of the human copper transporter 1 and two copper export pumps, ATP7A and ATP7B. In the current study, we investigated the correlation between the expression of these transporters and sensitivity to CDDP using four cell lines derived from each of high invasive oral squamous cell carcinoma (OSCC) and low invasive OSCC. We found that the amount of CDDP accumulated in high invasive OSCC cell lines (Yamamoto-Kohama criteria: grade 4C and 4D) with strong intrinsic tolerance was lower than in low invasive OSCC cell lines (grade 3) with weak intrinsic tolerance. Additionally, overexpression of ATP7B mRNA in cell lines derived from high invasive OSCC conferred low sensitivity to CDDP. Furthermore, the accumulation and sensitivity of CDDP was higher in HOC313 cells transfected with the ATP7B siRNA than in cells transfected with the nonsense siRNA. These results suggest that the overexpression of ATP7B results in the export of and, therefore, resistance to CDDP. Furthermore, ATP7B may be a key determinant of the intrinsic resistance to CDDP.

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