Significance of Na+, K(+)-ATPase on intracellular accumulation of cis-diamminedichloroplatinum(II) in human non-small-cell but not in small-cell lung cancer cell lines.

cis-Diamminedichloroplatinum(II) (CDDP) is the most active anticancer agent. It has been reported that intracellular accumulation of CDDP is an important step as a determinant for resistance to CDDP, which may be modulated by Na+, K(+)-ATPase activity. In this study, the significance of membrane Na+, K(+)-ATPase activity in the intracellular accumulation of CDDP were evaluated using human lung cancer cell lines. Na+, K(+)-ATPase was active in each cell line, not only non-small-cell lung cancer (NSCLC) but also in small-cell lung cancer (SCLC) cell lines. In NSCLC cell lines, there were significant correlations between Na+, K(+)-ATPase activities and intracellular accumulation of CDDP and the accumulation significantly decreased by ouabain, an inhibitor of Na+, K(+)-ATPase in each cell line. However, the correlation between enzyme activity and intracellular accumulation of CDDP were not significant in SCLC cell lines where sensitivity to CDDP was better than in NSCLC cell lines. These results suggest Na+, K(+)-ATPase are active in both NSCLC and SCLC cells, however, the importance of the enzyme as an active transporter of CDDP may be limited only to NSCLC cells. The mechanisms of intracellular accumulation may not be so important as a determinant of sensitivity to CDDP in SCLC cells.