The role of p53 in the trafficking of copper-64 to tumor cell nuclei

Copper-64 (T-1/2 = 12.7 h; beta(+): 17.8%, beta(-): 41%) has applications in both positron emission tomography (PET) imaging and targeted radiotherapy of cancer. Copper-64 radiopharmaceuticals have shown tumor growth inhibition with a relatively low radiation dose in animal models; however, the mechanism of cytotoxicity has not been fully elucidated. Here, we report an investigation on the potential role of the tumor suppressor protein p53 in trafficking Cu-64 to tumor cell nuclei. Two EGFR expressing human colorectal cell lines (HCT 116 (+)/(+) and HCT 116 (-)/(-)) that are positive or negative for p53 expression respectively, were used to compare internalization and nuclear localization of [Cu-64] copper acetate and of Cu-64-DOTA-cetuximab, a monoclonal anti-EGFR antibody. [Cu-64] copper acetate uptake into cells was similar between the two cell lines during a 24 h time course. In contrast, the uptake of [Cu-64] copper acetate in the nuclei of HCT 116 +/+ cells was significantly higher than in HCT 116 (-)/(-) cells (p < 0.0001) at 24 h. There was no difference in receptor binding, receptor-mediated internalization, and efflux of Cu-64-DOTA-cetuximab between the two HCT 116 cells lines. However, nuclear localization of Cu-64-DOTA-cetuximab showed increased uptake in the nuclei of HCT 116 +/+ cells as early as 4 h. These data demonstrate that Cu-64 is delivered to tumor cell nuclei in a p53 positive cell line in significantly greater amounts than in p53 negative cells by both non-specific and receptor-mediated uptake mechanisms.