Acquired resistance to cisplatin (CDDP) is an issue in cancer chemotherapy. This resistance has been reported to be correlated with the expression of the Cu influx copper transporter 1 (CTR1) and two copper efflux transporters (ATP7A, ATP7B). We investigated the correlation between the expression of these transporters and the sensitivity to CDDP using three pairs of parent cell lines and resistant cell lines derived from various types of invasive oral squamous cell carcinoma (OSCC). Using multiple steps, each of the CDDP-resistant cell lines, HSC-4-R, OSC-19-R, HOC313-R, was selected from HSC-4 cells derived from a cancer with medium invasiveness, OSC-19 cells derived from a cancer with high invasiveness and HOC313 cells derived from a cancer with the highest invasiveness. Resistant cell lines had a stronger expression of ATP7B in conjunction with the acquisition of CDDP-resistance than parent cell lines. Furthermore, OSC-19-R cells transfected with the ATP7B siRNA had a 10.6-fold higher sensitivity to CDDP compared to OSC-19-R cells transfected with a nonsense siRNA. These results suggest that each of the resistant cell lines had acquired resistance to CDDP due to the overexpression of ATP7B. On the other hand, the expression of CTR1 was the same between sensitive cell lines and resistant cell lines and ATP7A mRNA expression was barely noted. We conclude that ATP7B is correlated with the acquisition of CDDP resistance more closely than either CTR1 or ATP7A. ATP7B may be a key determinant in the acquired resistance to CDDP in OSCC.

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