Body copper homeostasis is regulated by the liver, which removes excess copper via bile. In Wilson's disease (WD), this function is disrupted due to inactivation of the copper transporter ATP7B resulting in hepatic copper overload. High urinary copper is a diagnostic feature of WD linked to liver malfunction; the mechanism behind urinary copper elevation is not fully understood. Using Positron Emission Tomography-Computed Tomography (PET-CT) imaging of live Atp7b−/− mice at different stages of disease, a longitudinal metal analysis, and characterization of copper-binding molecules, we show that urinary copper elevation is a specific regulatory process mediated by distinct molecules. PET-CT and atomic absorption spectroscopy directly demonstrate an age-dependent decrease in the capacity of Atp7b−/− livers to accumulate copper, concomitant with an increase in urinary copper. This reciprocal relationship is specific for copper, indicating that cell necrosis is not the primary cause for the initial phase of metal elevation in the urine. Instead, the urinary copper increase is associated with the down-regulation of the copper-transporter Ctr1 in the liver and appearance of a 2 kDa Small Copper Carrier, SCC, in the urine. SCC is also elevated in the urine of the liver-specific Ctr1 −/− knockouts, which have normal ATP7B function, suggesting that SCC is a normal metabolite carrying copper in the serum. In agreement with this hypothesis, partially purified SCC-Cu competes with free copper for uptake by Ctr1. Thus, hepatic down-regulation of Ctr1 allows switching to an SCC-mediated removal of copper via kidney when liver function is impaired. These results demonstrate that the body regulates copper export through more than one mechanism; better understanding of urinary copper excretion may contribute to an improved diagnosis and monitoring of WD.

Recent research suggests that copper could be used as a novel selective target for cancer therapies. Copper is a co-factor essential for tumor angiogenesis processes and high levels of copper have been found in many types of human cancers, including prostate, breast and brain. We have reported that organic copper-containing compounds, such as 8-hydroxyquinoline-copper(II), are a novel class of proteasome inhibitors and tumor cell apoptosis inducers (Daniel et al., Biochem Pharmacol. 2004;67:1139-51). Most recently, we have found that when complexed with copper, the known antioxidant pyrrolidine dithiocarbamate (PDTC) forms a potent proteasome inhibitor in human breast cancer, but not normal cells (Daniel, Chen, et al., submitted). In the current study, we investigate whether the PDTC-copper complex can play similar roles in inhibiting the proteasomal activity and consequently inducing apoptosis in human prostate cancer cells. We used tetrathiomolybdate (TM), a strong copper chelator currently being tested in clinical trials, as a control. We report here that after binding to copper, PDTC, but not TM, can inhibit the proteasomal chymotrypsin-like activity, suppress proliferation, induce apoptotic cell death, and inhibit uptake of radiopharmaceutical 2-[18F]Fluoro-2-deoxy-D-glucose in cultured human prostate cancer cells. In contrast, PDTC, TM or copper alone or a TM-copper mixture had no such effects. Our study suggests that high copper levels in human prostate cancer in vivo can be targeted by a ligand such as PDTC, resulting in formation of an active proteasome inhibitor and apoptosis inducer specifically in prostate tumor, but not normal cells.

Purpose This study aims to determine feasibility and utility of copper-64(II) chloride (64CuCl2) as a tracer for positron emission tomography (PET) of copper metabolism imbalance in human Wilson’s disease (WD). Procedures Atp7b−/− mice, a mouse model of human WD, were injected with 64CuCl2 intravenously and subjected to PET scanning using a hybrid PET-CT (computerized tomography) scanner, with the wild-type C57BL mice as a normal control. Quantitative PET analysis was performed to determine biodistribution of 64Cu radioactivity and radiation dosimetry estimates of 64Cu were calculated for PET of copper metabolism in humans. Results Dynamic PET analysis revealed increased accumulation and markedly reduced clearance of 64Cu from the liver of the Atp7b−/− mice, compared to hepatic uptake and clearance of 64Cu in the wild-type C57BL mice. Kinetics of copper clearance and retention was also altered for kidneys, heart, and lungs in the Atp7b−/− mice. Based on biodistribution of 64Cu in wild-type C57BL mice, radiation dosimetry estimates of 64Cu in normal human subjects were obtained, showing an effective dose (ED) of 32.2 μ (micro)Sv/MBq (weighted dose over 22 organs) and the small intestine as the critical organ for radiation dose (61 μGy/MBq for males and 69 μGy/MBq for females). Radiation dosimetry estimates for the patients with WD, based on biodistribution of 64Cu in the Atp7b−/− mice, showed a similar ED of 32.8 μ (micro)Sv/MBq (p= 0.53), with the liver as the critical organ for radiation dose (120 μSv/MBq for male and 161 μSv/MBq for female). Conclusions Quantitative PET analysis demonstrates abnormal copper metabolism in the mouse model of WD with improved time–resolution. Human radiation dosimetry estimates obtained in this preclinical study encourage direct radiation dosimetry of 64CuCl2 in human subjects. The results suggest feasibility of utilizing 64CuCl2 as a tracer for noninvasive assessment of copper metabolism in WD with PET.