The copper export pump ATP7B modulates the cellular pharmacology of carboplatin in ovarian carcinoma cells

Human tumor cells lines with acquired resistance to cisplatin (DDP) and carboplatin (CBDCA) are often cross-resistant to copper and vice versa, and some DDP-resistant cells overexpress the copper export pump ATP7B. We sought to demonstrate that ATP7B directly mediates resistance to DDP and CBDCA by stably transfecting human carcinoma cells with a vector designed to express ATP7B. Increased expression of ATP7B rendered all three cell lines tested more resistant to a 1-h exposure to DDP (1.6-2.6-fold), CBDCA (1.5-1.6-fold), and copper (1.2-1.4-fold). The effect of ATP7B on the cellular pharmacology of Cu-64 and [C-14] CBDCA was investigated in more detail using one cell pair ( 2008 cells transfected with an empty vector or an ATP7B-expressing vector). In the 2008/ATP7B subline, steady-state copper levels were decreased under both basal and copper-supplemented conditions, as was steadystate CBDCA content upon exposure to 50 muM [C-14] CBDCA. Over the first 5 min, the average rate of accumulation of copper and CBCDA in the 2008/ATP7B cells was reduced by 37 and 61%, respectively. Efflux was more rapid from 2008/ATP7B cells for both copper and CBDCA. Two-compartment modeling indicated that the second phase of efflux was increased by a factor of 3.9-fold for CBCDA and to an even greater extent for copper. We conclude that expression of ATP7B regulates sensitivity to CBDCA as well as to DDP and copper and that a transporter that normally mediates copper homeostasis modulates the cellular pharmacology of CBDCA.