Positron Emission Tomography of Human Hepatocellular Carcinoma Xenografts in Mice Using Copper (II)-64 Chloride as a Tracer with Copper (II)-64 Chloride

Rationale and Objectives: The aim of this study was to assess copper metabolism of human hepatocellular carcinoma (HCC) with positron emission tomographic (PET) imaging using copper (II)-64 chloride ( ⁶⁴CuCl ₂) as a tracer. Materials and Methods: PET imaging of athymic mice (n = 5) bearing extrahepatic HCC xenografts was performed 24 hours after the intravenous injection of ⁶⁴CuCl ₂, followed by ex vivo tissue radioactivity assay. Expression of human copper transporter 1 (hCTR1) in HCC cells and tissues was examined by real-time reverse transcription polymerase chain reaction and immunohistochemistry analysis, respectively. Results: The extrahepatic HCC xenografts in mice with increased uptake of ⁶⁴Cu radionuclide were visualized on the micro-PET images obtained 24 hours after the intravenous injection of ⁶⁴CuCl ₂. PET quantitative analysis revealed increased ⁶⁴Cu radioactivity in tumor tissues (2.7 ± 0.6 %ID/g) compared to that in the soft tissue of the left shoulder opposite to the tumor site (0.6 ± 0.2 %ID/g) and the brain (0.7 ± 0.1 %ID/g) but lower than that of the liver (16.6 ± 1.3 %ID/g). Expression of hCTR1 in the HCC cells and xenograft tumor tissues was demonstrated by real-time reverse transcription polymerase chain reaction and immunohistochemistry analysis, respectively. The expression level of hCTR1 in the Hep3B HCC xenograft tissues was lower than that detected in the normal hepatic tissues and the tissue samples of well-differentiated primary HCC. Variable expression of hCTR1 was detected in the tissue samples of moderately differentiated primary HCC. Conclusions: Extrahepatic human HCC xenografts in mice could be localized with ⁶⁴CuCl ₂ PET imaging, which might be useful for the localization and quantitative assessment of copper metabolism in extrahepatic metastases of HCC in humans.