Transport of platinum-based anticancer drugs by recombinant human copper ATPases (ATP7A/B)

ATP7A and ATP7B are members of the P1B-ATPase subfamily of the P-type ATPases, and catalyze the ATP-dependent copper transport across cellular membranes via a process involving formation of a phosphoenzyme intermediate. Numerous physiological processes depend on adequate and timely copper transport by these proteins. Inactivation of either ATP7A or ATP7B is associated with severe metabolic disorders, known as Menkes (ATP7A) and Wilson (ATP7B) diseases. Platinum-based anticancer drugs, e.g. cisplatin, carboplatin and oxaliplatin, are used to treat various types of tumors. As with most anticancer drugs, the efficacy of treatment is limited by intrinsic and acquired resistance of tumor cells. Recently, experimental evidence indicated that Cu-ATPases mediate resistance to platinum anticancer drugs. However, the mechanism by which Cu-ATPases mediate resistance to such drugs is not fully understood. The present study aims at investigating the mechanism of interaction of platinum drugs with recombinant human ATP7A/B, obtained by heterologous expression in COS-1 cells. We performed ATP concentration jumps on microsomes containing ATP7A or ATP7B adsorbed on a solid supported membrane. The ATP jump induces a current transient in the presence of platinum-based drugs. We suggest that the observed current transient is due to movement of platinum through ATP7A/B upon ATP utilization (formation of the phosphoenzyme intermediate required). We also found that copper interferes with platinum transport and viceversa. A mechanism for the electrogenic platinum transport by ATP7A/B is proposed. This work was supported by the Italian Ministry of Education, University and Research, the Universities of Florence and Bari, the Ente Cassa di Risparmio di Firenze and EU (COST Actions CM0902 and CM1105).