The cellular pharmacology and cytotoxic activity of cisplatin are modulated by the copper transporter ATP7A

Cisplatin is a widely used platinum-containing chemotherapeutic agent whose effectiveness is limited due to frequent acquisition of resistance. Many studies have demonstrated that cisplatin resistance can be mediated in part by changes in cellular influx and/or efflux, and recent studies provide evidence that the copper transporters ATP7B and CTR1 modulate the cellular accumulation of and sensitivity to cisplatin. The overall goal of the experiments described in this dissertation was to determine whether the copper transporter ATP7A modulates the cellular pharmacology of cisplatin and mediates the sensitivity to the cytotoxic effect of this important chemotherapeutic agent. In order to explore this hypothesis, studies were performed in two cell models. The first consisted of a normal fibroblast cell line established from a patient with Menkes disease that does not express any ATP7A or ATP7B and sublines engineered to express ATP7A or ATP7B. The second model consisted of an ovarian carcinoma cell line that expressed basal levels of ATP7A and a subline engineered to express an incrementally greater amount of ATP7A. These cell lines were examined for drug sensitivity, whole cell platinum accumulation, DNA adduct formation, and accumulation of platinum in vesicles. The results demonstrated that ATP7A mediates resistance to cisplatin and the clinically important analogs carboplatin and oxaliplatin. This is accompanied by alterations in the cellular pharmacology of cisplatin consistent with increased sequestration into vesicles. Based on these results a study was undertaken of the expression of ATP7A in tumor samples obtained from ovarian carcinoma patients before and after platinum drug-based treatment. The results demonstrated that patients whose tumors became enriched for ATP7A-expressing cells had worse survival.; The investigations described in this dissertation provide additional evidence for the importance of copper homeostasis mechanisms in determining sensitivity to the platinum drugs. The results support the concept that ATP7A sequesters cisplatin into intracellular vesicular compartments thereby detoxifying the drug and protecting the cell from its cytotoxic effect. The results of tissue cultures studies of this mechanism appear to have direct clinical relevance. Thus, ATP7A is a potential target for the development of strategies aimed at preventing or overcoming resistance to the platinum drugs.