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Increased Expression of the Copper Efflux Transporter ATP7A Mediates Resistance to Cisplatin, Carboplatin, and Oxaliplatin in Ovarian Cancer Cells

¹ Department of Medicine, the Rebecca and John Moores University of California San Diego Cancer Center and the Biomedical Sciences Graduate Program, ² Department of Chemistry, University of California San Diego, La Jolla, California, and ³ Globomax Service Group, Hanover, Maryland

ABSTRACT

Purpose: The goal of this study was to determine the effect of small changes in ATP7A expression on the pharmacodynamics of cisplatin, carboplatin, and oxaliplatin in human ovarian carcinoma cells.

Experimental Design: Drug sensitivity and cellular pharmacology parameters were determined in human 2008 ovarian carcinoma cells and a subline transfected with an ATP7A-expression vector ATP7A (2008/MNK). Drug sensitivity was determined by clonogenic assay, platinum (Pt) levels were measured by inductively coupled plasma mass spectroscopy, copper (Cu) accumulation was quantified with ⁶⁴Cu, and the subcellular distribution of ATP7A was assessed by confocal digital microscopy.

Results: The 1.5-fold higher expression of ATP7A in the 2008/MNK cells was sufficient to alter Cu cellular pharmacokinetics but not confer Cu resistance. In contrast, it was sufficient to render the 2008/MNK cells resistant to cisplatin, carboplatin, and oxaliplatin. Resistance was associated with increased rather than decreased whole-cell Pt drug accumulation and increased sequestration of Pt into the vesicular fraction. Cu triggered relocalization of ATP7A away from the perinuclear region, whereas at equitoxic concentrations the Pt drugs did not.

Conclusions: A small increase in ATP7A expression produced resistance to all three of the clinically available Pt drugs. Whereas increased expression of ATP7A reduced Cu accumulation, it did not reduce accumulation of the Pt drugs. Under conditions where Cu triggered ATP7A relocalization, the Pt drugs did not. Thus, although ATP7A is an important determinant of sensitivity to the Pt drugs, there are substantial differences between Cu and the Pt drugs with respect to how they interact with ATP7A and the mechanism by which ATP7A protects the cell.

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