Positron emission tomography of human hepatocellular carcinoma xenografts in mice using copper (II)-64 chloride as a tracer with copper (II)-64 chloride

Targeting Copper in Cancer Imaging and Therapy: A New Theragnostic Agent

Copper is required for cancer cell proliferation and tumor angiogenesis. Copper-64 radionuclide (⁶⁴Cu), a form of copper chloride (⁶⁴CuCl₂), is rapidly emerging as a diagnostic PET/CT tracer in oncology. It may also represent an interesting alternative to gallium-68 (⁶⁸Ga) as a radionuclide precursor for labelling radiopharmaceuticals used to investigate neuroendocrine tumors and prostate cancer. This emerging interest is also related to the nuclear properties of ⁶⁴CuCl₂ that make it an ideal theragnostic nuclide. Indeed, ⁶⁴CuCl₂ emits β⁺ and β^- particles together with high-linear-energy-transfer Auger electrons, suggesting the therapeutic potential of ⁶⁴CuCl₂ for the radionuclide cancer therapy of copper-avid tumors. Recently, ⁶⁴CuCl₂ was successfully used to image prostate cancer, bladder cancer, glioblastoma multiforme (GBM), and non-small cell lung carcinoma in humans. Copper cancer uptake was related to the expression of human copper transport 1 (hCTR1) on the cancer cell surface. Biodistribution, toxicology and radiation safety studies showed its radiation and toxicology safety. Based on the findings from the preclinical research studies, ⁶⁴CuCl₂ PET/CT also holds potential for the diagnostic imaging of human hepatocellular carcinoma (HCC), malignant melanoma, and the detection of the intracranial metastasis of copper-avid tumors based on the low physiological background of radioactive copper uptake in the brain.

Non-invasive radionuclide imaging of trace metal trafficking in health and disease: "PET metallomics"

Several specific metallic elements must be present in the human body to maintain health and function. Maintaining the correct quantity (from trace to bulk) and location at the cell and tissue level is essential. The study of the biological role of metals has become known as metallomics. While quantities of metals in cells and tissues can be readily measured in biopsy and autopsy samples by destructive analytical techniques, their trafficking and its role in health and disease are poorly understood. Molecular imaging with radionuclides - positron emission tomography (PET) and single photon emission computed tomography (SPECT) - is emerging as a means to non-invasively study the acute trafficking of essential metals between organs, non-invasively and in real time, in health and disease. PET scanners are increasingly widely available in hospitals, and methods for producing radionuclides of some of the key essential metals are developing fast. This review summarises recent developments in radionuclide imaging technology that permit such investigations, describes the radiological and physicochemical properties of key radioisotopes of essential trace metals and useful analogues, and introduces current and potential future applications in preclinical and clinical investigations to study the biology of essential trace metals in health and disease.

Recent Advances in Cancer Imaging with 64CuCl2 PET/CT

Copper is required for cancer cell proliferation and tumor angiogenesis. Radioactive copper-64 chloride (⁶⁴CuCl₂) is a useful radiotracer for cancer imaging with position emission tomography (PET) based on increased cellular uptake of copper mediated by human copper transporter 1 (hCtr1) expressed on cancer cell membrane. Significant progress has been made in research of using ⁶⁴CuCl₂ as a radiotracer for cancer imaging with PET. Radiation dosimetry study in humans demonstrated radiation safety of ⁶⁴CuCl₂. Recently, ⁶⁴CuCl₂ was successfully used for PET imaging of prostate cancer, bladder cancer, glioblastoma multiforme (GBM), and non-small cell lung carcinoma in humans. Based on the findings from the preclinical research studies, ⁶⁴CuCl₂ PET/CT also holds potential for diagnostic imaging of human hepatocellular carcinoma (HCC), malignant melanoma, and detection of intracranial metastasis of copper-avid tumors based on low physiological background of radioactive copper uptake in the brain. Copper-64 radionuclide emits both β⁺ and β^- particles, suggesting therapeutic potential of ⁶⁴CuCl₂ for radionuclide cancer therapy of copper-avid tumors. Recent progress in production of therapeutic copper-67 radionuclide invites clinical research in use of theranostic pair of ⁶⁴CuCl₂ and ⁶⁷CuCl₂ for cancer imaging and radionuclide therapy.

Theranostics in Brain Tumors

Theranostic nuclear oncology, mainly in neuro-oncology (neurotheranostics), aims to combine cancer imaging and therapy using the same targeting molecule. This approach tries to identify patients who are most likely to benefit from tumor molecular radionuclide therapy. The ability of radioneurotheranostic agents to interact with cancer cells at the molecular level with high specificity can significantly improve the effectiveness of cancer therapy. A variety of biologic targets are under investigation for treating brain tumors. PET-based precision imaging can substantially improve the therapeutic efficacy of radiotheranostic approach in brain tumors.

Preclinical PET imaging study of lung cancer with 64CuCl2

OBJECTIVE

Human copper transporter 1 (CTR1) has been proven to be overexpressed in many types of cancer cells, and copper (II)-64 chloride (⁶⁴CuCl₂) has been used as an effective tracer for positron emission tomography (PET) imaging in tumor-bearing animal models. Thus, this study aimed to investigate the potential application of ⁶⁴CuCl₂ in PET imaging of lung cancer through targeting CTR1.

METHODS

The expression of CTR1 in a series of lung cancer cell lines was identified by quantitative real-time polymerase chain reaction (Q-PCR), western blot, enzyme-linked immunosorbnent assay (ELISA), and immunofluorescent staining. Then in vitro cell uptake assay of ⁶⁴CuCl₂ was investigated in human lung cancer cell lines with different levels of CTR1 expression. Small animal PET imaging and quantitative analysis were performed in human lung cancer tumor-bearing mice after intravenous injection of ⁶⁴CuCl₂, respectively.

RESULTS

The CTR1 expression in multiple human lung cancer cells was identified and confirmed, and H1299 cell lines with high CTR1 expression, H460 with moderate CTR1, and H1703 with low CTR1 were selected for further experiments. In vitro cellular uptake assay displayed that the ⁶⁴CuCl₂ uptake by these three kinds of cells was positively correlated with their CTR1 expressed levels. The blocking experiments testified the specificity of ⁶⁴CuCl₂ to target CTR1. Moreover, small animal PET imaging and quantitative results showed that ⁶⁴CuCl₂ accumulation in H1299, H460, and H1703 tumor-bearing mice were consistent with CTR1 levels and cell uptake experiments.

CONCLUSIONS

The expression of CTR1 in human lung cancer xenograft model could be successfully visualized by ⁶⁴CuCl₂ PET examination. With the expected growth of PET/CT examination to be an essential strategy in clinical lung cancer management, ⁶⁴CuCl₂ has the potential to be a promising PET imaging agent of lung cancer.

Hypoxia imaging and theranostic potential of [64Cu][Cu(ATSM)] and ionic Cu(II) salts: a review of current evidence and discussion of the retention mechanisms

Background

Tumor hypoxia (low tissue oxygenation) is an adverse condition of the solid tumor environment, associated with malignant progression, radiotherapy resistance, and poor prognosis. One method to detect tumor hypoxia is by positron emission tomography (PET) with the tracer [⁶⁴Cu][Cu-diacetyl-bis(N(4)-methylthiosemicarbazone)] ([⁶⁴Cu][Cu(ATSM)]), as demonstrated in both preclinical and clinical studies. In addition, emerging studies suggest using [⁶⁴Cu][Cu(ATSM)] for molecular radiotherapy, mainly due to the release of therapeutic Auger electrons from copper-64, making [⁶⁴Cu][Cu(ATSM)] a “theranostic” agent. However, the radiocopper retention based on a metal-ligand dissociation mechanism under hypoxia has long been controversial. Recent studies using ionic Cu(II) salts as tracers have raised further questions on the original mechanism and proposed a potential role of copper itself in the tracer uptake. We have reviewed the evidence of using the copper radiopharmaceuticals [^60/61/62/64Cu][Cu(ATSM)]/ionic copper salts for PET imaging of tumor hypoxia, their possible therapeutic applications, issues related to the metal-ligand dissociation mechanism, and possible explanations of copper trapping based on studies of the copper metabolism under hypoxia.

Results

We found that hypoxia selectivity of [⁶⁴Cu][Cu(ATSM)] has been clearly demonstrated in both preclinical and clinical studies. Preclinical therapeutic studies in mice have also demonstrated promising results, recently reporting significant tumor volume reductions and improved survival in a dose-dependent manner. Cu(II)-[Cu(ATSM)] appears to be accumulated in regions with substantially higher CD133⁺ expression, a marker for cancer stem cells. This, combined with the reported requirement of copper for activation of the hypoxia inducible factor 1 (HIF-1), provides a possible explanation for the therapeutic effects of [⁶⁴Cu][Cu(ATSM)]. Comparisons between [⁶⁴Cu][Cu(ATSM)] and ionic Cu(II) salts have showed similar results in both imaging and therapeutic studies, supporting the argument for the central role of copper itself in the retention mechanism.

Conclusions

We found promising evidence of using copper-64 radiopharmaceuticals for both PET imaging and treatment of hypoxic tumors. The Cu(II)-[Cu(ATSM)] retention mechanism remains controversial and future mechanistic studies should be focused on understanding the role of copper itself in the hypoxic tumor metabolism.

Bombesin functionalized 64Cu-copper sulfide nanoparticles for targeted imaging of orthotopic prostate cancer

Aim: To synthesize and evaluate the imaging potential of Bom-PEG-[64Cu]CuS nanoparticles (NPs) in orothotopic prostate tumor. Materials & methods: [64Cu]CuS NPs were synthesized in aqueous solution by 64CuCl2 and Na2S reaction. Then PEG linker with or without bombesin peptide were conjugated to the surface of [64Cu]CuS NPs to produce Bom-PEG-[64Cu]CuS and PEG-[64Cu]CuS NPs. These two kinds of NPs were used for testing specific uptake in prostate cancer cells in vitro and imaging of orthotopic prostate tumor in vivo. Results: Bom-PEG-[64Cu]CuS and PEG-[64Cu]CuS NPs were successfully synthesized with core diameter of approximately 5 nm. Radioactive cellular uptake revealed that Bom-PEG-[64Cu]CuS was able to specifically bind to prostate cancer cells, and the microPET-CT imaging indicated clear visualization of orthotopic prostate tumors. Conclusion: Radiolabeled Bom-PEG-[64Cu]CuS NPs have potential as an ideal agent for orthotopic prostate tumor imaging by microPET-CT.

Biokinetic and dosimetric aspects of 64CuCl2 in human prostate cancer: possible theranostic implications

BACKGROUND

The aim of the present study is to evaluate the kinetics and dosimetry of 64CuCl2 in human prostate cancer (PCa) lesions. We prospectively evaluated 50 PCa patients with biochemical relapse after surgery or external beam radiation therapy. All patients underwent 64CuCl2-PET/CT to detect PCa recurrence/metastases. Volumes of interest were manually drawn for each 64CuCl2 avid PCa lesion with a diameter > 1 cm on mpMRI in each patient. Time-activity curves for all lesions were obtained. The effective and biological half-life and the standard uptake values (SUVs) were calculated. Tumour/background ratio (TBR) curves as a function of time were considered. Finally, the absorbed dose per lesion was estimated.

RESULTS

The mean effective half-life of 64CuCl2 calculated in the lymph nodes (10.2 ± 1.7 h) was significantly higher than in local relapses (8.8 ± 1.1 h) and similar to that seen in bone metastases (9.0 ± 0.4 h). The mean 64CuCl2 SUVmax calculated 1 h after tracer injection was significantly higher in the lymph nodes (6.8 ± 4.3) and bone metastases (6.8 ± 2.9) than in local relapses (4.7 ± 2.4). TBR mean curve of 64CuCl2 revealed that the calculated TBRmax value was 5.0, 7.0, and 6.2 in local relapse and lymph node and bone metastases, respectively, and it was achieved about 1 h after 64CuCl2 injection. The mean absorbed dose of the PCa lesions per administrated activity was 6.00E-2 ± 4.74E-2mGy/MBq. Indeed, for an administered activity of 3.7 GBq, the mean dose absorbed by the lesion would be 0.22 Gy.

CONCLUSIONS

Dosimetry showed that the dose absorbed by PCa recurrences/metastases per administrated activity was low. The dosimetric study performed does not take into account the possible therapeutic effect of the Auger electrons. Clinical trials are needed to evaluate 64Cu internalization in the cell nucleus that seems related to the therapeutic effectiveness reported in preclinical studies.

Pilot Study of 64CuCl₂ for PET Imaging of Inflammation

Copper(II) ion (Cu²⁺) is the essential element for numerous pathophysiological processes in vivo. Copper transporter 1 (CTR1) is mainly responsible for maintaining Cu²⁺ accumulation in cells, which has been found to be over-expressed in inflammatory tissues. Therefore, we explored the potential application of ⁶⁴CuCl₂ for PET imaging of inflammation through targeting CTR1. The animal models of H₂O₂ induced muscle inflammation and lipopolysaccaharide induced lung inflammation were successfully established, then imaged by small animal PET (PET/CT) post-injection of ⁶⁴CuCl₂, and PET images were quantitatively analyzed. H&E and immunohistochemical (IHC) staining and western blot experiments were performed for evaluating CTR1 levels in the inflammatory and control tissues. Both inflammatory muscle and lungs can be clearly imaged by PET. PET image quantitative analysis revealed that the inflammatory muscle and lungs showed significantly higher ⁶⁴Cu accumulation than the controls, respectively (p < 0.05). Furthermore, IHC staining and western blot analysis demonstrated that compared with the controls, CTR1 expression was increased in both the inflammatory muscle and lungs, which was consistent with the levels of ⁶⁴Cu²⁺ accumulation in these tissues. ⁶⁴CuCl₂ can be used as a novel, simple, and highly promising PET tracer for CTR1 targeted imaging of inflammation.

Restrained management of copper level enhances the antineoplastic activity of imatinib in vitro and in vivo

The present study was designed to investigate if elevated copper level can be targeted to enhance the efficacy of a significant anticancer drug, imatinib (ITB). The antineoplastic activity of this drug was assessed in the HepG2, HEK-293, MCF-7 and MDA-MD-231 cells targeting elevated copper level as their common drug target. The cell lines were treated with the different doses of copper chloride (Cu II) and disulfiram (DSF) alone as well as in their combinations with the drug for 24 h in standard culture medium and conditions. The treated cells were subjected to various assays including MTT, PARP, p-53, caspase-7, caspase-3, LDH and single cell electrophoresis. The study shows that DSF and Cu (II) synergizes the anticancer activity of ITB to a significant extent in a dose-specific way as evidenced by the combinations treated groups. Furthermore, the same treatment strategy was employed in cancer-induced rats in which the combinations of ITB-DSF and ITB-Cu II showed enhanced antineoplastic activity as compared to ITB alone. However, DSF was more effective than Cu (II) as an adjuvant to the drug. Hence, restrained manipulation of copper level in tumor cells can orchestrate the redox and molecular dispositions inside the cells favoring the induction of apoptosis.

Studies of copper trafficking in a mouse model of Alzheimer's disease by positron emission tomography: comparison of 64Cu acetate and 64CuGTSM

Alzheimer's disease can involve brain copper dyshomeostasis. We aimed to determine the effect of AD-like pathology on 64Cu trafficking in mice, using positron emission tomography (PET imaging), during 24 hours after intravenous administration of ionic 64Cu (Cu(ii) acetate) and 64Cu-GTSM (GTSMH2 = glyoxalbis(thiosemicarbazone)). Copper trafficking was evaluated in 6-8-month-old and 13-15 month-old TASTPM transgenic and wild-type mice, by imaging 0-30 min and 24-25 h after intravenous administration of 64Cu tracer. Regional 64Cu distribution in brains was compared by ex vivo autoradiography to that of amyloid-β plaque. 64Cu-acetate showed uptake in, and excretion through, liver and kidneys. There was minimal uptake in other tissues by 30 minutes, and little further change after 24 h. Radioactivity within brain was focussed in and around the ventricles and was significantly greater in younger mice. 64CuGTSM was taken up in all tissues by 30 min, remaining high in brain but clearing substantially from other tissues by 24 h. Distribution in brain was not localised to specific regions. TASTPM mice showed no major changes in global or regional 64Cu brain uptake compared to wildtype after administration of 64Cu acetate (unlike 64Cu-GTSM) but efflux of 64Cu from brain by 24 h was slightly greater in 6-8 month-old TASTPM mice than in wildtype controls. Changes in copper trafficking associated with Alzheimer's-like pathology after administration of ionic 64Cu are minor compared to those observed after administration of 64Cu-GTSM. PET imaging with 64Cu could help understand changes in brain copper dynamics in AD and underpin new clinical diagnostic imaging methods.

Pilot Study of 64Cu(I) for PET Imaging of Melanoma

At present, ⁶⁴Cu(II) labeled tracers including ⁶⁴CuCl₂ have been widely applied in the research of molecular imaging and therapy. Human copper transporter 1 (hCTR1) is the major high affinity copper influx transporter in mammalian cells, and specially responsible for the transportation of Cu(I) not Cu(II). Thus, we investigated the feasible application of ⁶⁴Cu(I) for PET imaging. ⁶⁴Cu(II) was reduced to ⁶⁴Cu(I) with the existence of sodium L-ascorbate, DL-Dithiothreitol or cysteine. Cell uptake and efflux assay was investigated using B16F10 and A375 cell lines, respectively. Small animal PET and biodistribution studies were performed in both B16F10 and A375 tumor-bearing mice. Compared with ⁶⁴Cu(II), ⁶⁴Cu(I) exhibited higher cellular uptake by melanoma, which testified CTR1 specially influx of Cu(I). However, due to oxidation reaction in vivo, no significant difference between ⁶⁴Cu(I) and ⁶⁴Cu(II) was observed through PET images and biodistribution. Additionally, radiation absorbed doses for major tissues of human were calculated based on the mouse biodistribution. Radiodosimetry calculations for ^64/67Cu(I) and ^64/67Cu(II) were similar, which suggested that although melanoma were with high radiation absorbed doses, high radioactivity accumulation by liver and kidney should be noticed for the further application. Thus, ⁶⁴Cu(I) should be further studied to evaluate it as a PET imaging radiotracer.

Cyclam te1pa for64Cu PET imaging. Bioconjugation to antibody, radiolabeling and preclinical application in xenografted colorectal cancer

te1pa conjugated to an F6 antibody was confirmed to be an interesting alternative to dota for⁶⁴Cuin vivoPET imaging.

Cyclotron Production of High-Specific Activity 55Co and In Vivo Evaluation of the Stability of 55Co Metal-Chelate-Peptide Complexes

This work describes the production of high-specific activity 55Co and the evaluation of the stability of 55Co-metal-chelate-peptide complexes in vivo. 55Co was produced via the 58Ni(p,α)55Co reaction and purified using anion exchange chromatography with an average recovery of 92% and an average specific activity of 1.96 GBq/μmol. 55Co-DO3A and 55Co-NO2A peptide complexes were radiolabeled at 3.7 MBq/μg and injected into HCT-116 tumor xenografted mice. Positron emission tomography (PET) and biodistribution studies were performed at 24 and 48 hours postinjection and compared to those of 55CoCl2. Both 55Co-metal-chelate complexes demonstrated good in vivo stability by reducing the radiotracers' uptake in the liver by sixfold at 24 hours with ~ 1% ID/g and at 48 hours with ~ 0.5% ID/g and reducing uptake in the heart by fourfold at 24 hours with ~ 0.7% ID/g and sevenfold at 48 hours with ~ 0.35% ID/g. These results support the use of 55Co as a promising new radiotracer for PET imaging of cancer and other diseases.

Imaging of Brain Tumors with Copper-64 Chloride: Early Experience and Results

OBJECTIVES

To conduct the first investigational study that is aimed at evaluating the ability of the simple salt (64)CuCl2 to diagnose cerebral tumors in patients affected by glioblastoma multiforme (GBM).

METHODS

Nineteen patients with a documented history and radiologic evidence of brain tumors were enrolled in the study. Eighteen patients were diagnosed with GBM, and one patient was diagnosed with grade II astrocytoma. After initial cerebral magnetic resonance imaging (MRI), patients were administered with (64)CuCl2 (13 MBq/kg) and brain positron emission tomography (PET)/computed tomography (CT) imaging was performed at 1, 3, and 24 hours after administration. Standardized uptake values (SUVs) were calculated and used to figure out the pharmacokinetic profile of the tracer. Absorbed radiation doses were estimated using OLINDA/EXM.

RESULTS

Copper-64 chloride clearly visualized brain cancerous lesions within 1 hour after injection, with stable retention of radioactivity at 3 and 24 hours. Excellent agreement was found between PET/CT and MRI. No uptake of the tracer was observed in low-grade astrocytoma. The agent cleared rapidly from the blood and was mostly excreted through the liver, without significant kidney washout. Analysis of time variation of SUVmax values showed persistent uptake in malignant tissues with a slight increase of radioactive concentration at 24 hours.

CONCLUSIONS

Copper-64 chloride has favorable biological properties for brain imaging and warrants further investigation as a diagnostic tracer for GBM.

Molecular imaging and therapy targeting copper metabolism in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide. Significant efforts have been devoted to identify new biomarkers for molecular imaging and targeted therapy of HCC. Copper is a nutritional metal required for the function of numerous enzymatic molecules in the metabolic pathways of human cells. Emerging evidence suggests that copper plays a role in cell proliferation and angiogenesis. Increased accumulation of copper ions was detected in tissue samples of HCC and many other cancers in humans. Altered copper metabolism is a new biomarker for molecular cancer imaging with position emission tomography (PET) using radioactive copper as a tracer. It has been reported that extrahepatic mouse hepatoma or HCC xenografts can be localized with PET using copper-64 chloride as a tracer, suggesting that copper metabolism is a new biomarker for the detection of HCC metastasis in areas of low physiological copper uptake. In addition to copper modulation therapy with copper chelators, short-interference RNA specific for human copper transporter 1 (hCtr1) may be used to suppress growth of HCC by blocking increased copper uptake mediated by hCtr1. Furthermore, altered copper metabolism is a promising target for radionuclide therapy of HCC using therapeutic copper radionuclides. Copper metabolism has potential as a new theranostic biomarker for molecular imaging as well as targeted therapy of HCC.

Application of inhibitors of differentiation 2 and 3 for evaluation of chemotherapy efficacy in liver cancer

AIM: To explore the influence of surgery alone and in combination with postoperative adjuvant chemotherapy on tumor markers, inhibitor of differentiation 2 (ID2), ID3 and survival time in patients with liver cancer, analyze the influence of ID2 and ID3 on the invasion and metastasis of liver cancer, and explore the feasibility of detection of ID2 and ID3 expression in evaluating efficacy of postoperative adjuvant chemotherapy.

METHODS: This was a 1:1 matched case-control study. ELISA was used to detect the levels of tumor markers, ID2 and ID3 in the serum of patients. Western blot was used to detect the protein expression levels of ID2 and ID3 in tumor tissues and adjacent tissues. Transwell assay was used to detect the invasion and metastasis of liver cancer cells. The correlation between the content of AFP and the expression levels of ID2 and ID3 was statistically analyzed.

RESULTS: The tumor markers CEA, CA50, AFP, and CA242 as well as ID2 and ID3 in the serum decreased significantly and the survival time was longer in patients receiving surgery with postoperative adjuvant chemotherapy when compared with patients receiving surgery alone (P < 0.05). The protein expression levels of ID2 and ID3 were decreased in the adjacent normal tissues compared with the liver cancer tissues (P < 0.05). Transwell analysis indicated that ID2 and ID3 knockdown inhibited the invasion and metastasis ability of HepG2 cells while overexpression of ID2 and ID3 promoted the invasion and metastasis of HepG2 cells (P < 0.05). There was a positive correlation between the content of AFP and the expression levels of ID2 and ID3 (r_ID2 = 0.881, r_ID3 = 0.928, P < 0.05).

CONCLUSION: ID2 and ID3 have similar effects to liver tumor markers, and the increased expression of ID2 and ID3 indicates greater invasion and metastasis ability of HepG2 cells and shorter survival time in patients with liver cancer. ID2 and ID3 expression might be used for clinical evaluation of efficacy of postoperative adjuvant chemotherapy.

Assessment of Traumatic Brain Injury by Increased 64Cu Uptake on 64CuCl2 PET/CT

Copper is a nutritional trace element required for cell proliferation and wound repair.

METHODS

To explore increased copper uptake as a biomarker for noninvasive assessment of traumatic brain injury (TBI), experimental TBI in C57BL/6 mice was induced by controlled cortical impact, and (64)Cu uptake in the injured cortex was assessed with (64)CuCl2 PET/CT.

RESULTS

At 24 h after intravenous injection of the tracer, uptake was significantly higher in the injured cortex of TBI mice (1.15 ± 0.53 percentage injected dose per gram of tissue [%ID/g]) than in the uninjured cortex of mice without TBI (0.53 ± 0.07 %ID/g, P = 0.027) or the cortex of mice that received an intracortical injection of zymosan A (0.62 ± 0.22 %ID/g, P = 0.025). Furthermore, uptake in the traumatized cortex of untreated TBI mice (1.15 ± 0.53 %ID/g) did not significantly differ from that in minocycline-treated TBI mice (0.93 ± 0.30 %ID/g, P = 0.33).

CONCLUSION

Overall, the data suggest that increased (64)Cu uptake in traumatized brain tissues holds potential as a new biomarker for noninvasive assessment of TBI with (64)CuCl2 PET/CT.

Detection of increased 64Cu uptake by human copper transporter 1 gene overexpression using PET with 64CuCl2 in human breast cancer xenograft model

Copper is an essential cofactor for a variety of biochemical processes including oxidative phosphorylation, cellular antioxidant activity, and elimination of free radicals. The copper transporter 1 is known to be involved in cellular uptake of copper ions. In this study, we evaluated the utility of human copper transporter 1 (hCTR1) gene as a new reporter gene for (64)Cu PET imaging.

METHODS

Human breast cancer cells (MDA-MB-231) were infected with a lentiviral vector constitutively expressing the hCTR1 gene under super cytomegalovirus promoter, and positive clones (MDA-MB-231-hCTR1) were selected. The expression of hCTR1 gene in MDA-MB-231-hCTR1 cells was measured by reverse transcription polymerase chain reaction, Western blot, and (64)Cu uptake assay. To evaluate the cytotoxic effects induced by hCTR1 expression, the dose-dependent cell survival rate after treatment with cisplatin (Cis-diaminedichloroplatinum (II) [CDDP]) was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and trypan blue dye exclusion. Small-animal PET images were acquired in tumor-bearing mice from 2 to 48 h after an intravenous injection of (64)Cu.

RESULTS

The hCTR1 gene expression in MDA-MB-231-hCTR1 cells was confirmed at the RNA and protein expression and the cellular (64)Cu uptake level. MTT assay and trypan blue dye exclusion showed that the cell viability of MDA-MB-231-hCTR1 cells decreased more rapidly than that of MDA-MB-231 cells after treatment with CDDP for 96 or 72 h, respectively. Small-animal PET imaging revealed a higher accumulation of (64)Cu in MDA-MB-231-hCTR1 tumors than in MDA-MB-231 tumors. With respect to the biodistribution data, the percentage injected dose per gram of (64)Cu in the MDA-MB-231 tumors and MDA-MB-231-hCTR1 tumors at 48 h after (64)Cu injection was 2.581 ± 0.254 and 5.373 ± 1.098, respectively.

CONCLUSION

An increase in (64)Cu uptake induced by the expression of hCTR1 gene was demonstrated in vivo and in vitro, suggesting the potential use of hCTR1 gene as a new imaging reporter gene for PET with (64)CuCl2.

Reduced 64Cu uptake and tumor growth inhibition by knockdown of human copper transporter 1 in xenograft mouse model of prostate cancer

Copper is an element required for cell proliferation and angiogenesis. Human prostate cancer xenografts with increased (64)Cu radioactivity were visualized previously by PET using (64)CuCl2 as a radiotracer ((64)CuCl2 PET). This study aimed to determine whether the increased tumor (64)Cu radioactivity was due to increased cellular uptake of (64)Cu mediated by human copper transporter 1 (hCtr1) or simply due to nonspecific binding of ionic (64)CuCl2 to tumor tissue. In addition, the functional role of hCtr1 in proliferation of prostate cancer cells and tumor growth was also assessed.

METHODS

A lentiviral vector encoding short-hairpin RNA specific for hCtr1 (Lenti-hCtr1-shRNA) was constructed for RNA interference-mediated knockdown of hCtr1 expression in prostate cancer cells. The degree of hCtr1 knockdown was determined by Western blot, and the effect of hCtr1 knockdown on copper uptake and proliferation were examined in vitro by cellular (64)Cu uptake and cell proliferation assays. The effects of hCtr1 knockdown on tumor uptake of (64)Cu were determined by PET quantification and tissue radioactivity assay. The effects of hCtr1 knockdown on tumor growth were assessed by PET/CT and tumor size measurement with a caliper.

RESULTS

RNA interference-mediated knockdown of hCtr1 was associated with the reduced cellular uptake of (64)Cu and the suppression of prostate cancer cell proliferation in vitro. At 24 h after intravenous injection of the tracer (64)CuCl2, the (64)Cu uptake by the tumors with knockdown of hCtr1 (4.02 ± 0.31 percentage injected dose per gram [%ID/g] in Lenti-hCtr1-shRNA-PC-3 and 2.30 ± 0.59 %ID/g in Lenti-hCtr1-shRNA-DU-145) was significantly lower than the (64)Cu uptake by the control tumors without knockdown of hCtr1 (7.21 ± 1.48 %ID/g in Lenti-SCR-shRNA-PC-3 and 5.57 ± 1.20 %ID/g in Lenti-SCR-shRNA-DU-145, P < 0.001) by PET quantification. Moreover, the volumes of prostate cancer xenograft tumors with knockdown of hCtr1 (179 ± 111 mm(3) for Lenti-hCtr1-shRNA-PC-3 or 39 ± 22 mm(3) for Lenti-hCtr1-shRNA-DU-145) were significantly smaller than those without knockdown of hCtr1 (536 ± 191 mm(3) for Lenti- SCR-shRNA-PC-3 or 208 ± 104 mm(3) for Lenti-SCR-shRNA-DU-145, P < 0.01).

CONCLUSION

Overall, data indicated that hCtr1 is a promising theranostic target, which can be further developed for metabolic imaging of prostate cancer using (64)CuCl2 PET/CT and personalized cancer therapy targeting copper metabolism.

Positron emission tomography for measurement of copper fluxes in live organisms

Copper is an essential nutrient for the physiology of live organisms, but excessive copper can be harmful. Copper radioisotopes are used for measurement of copper fluxes in live organisms using a radioactivity assay of body fluids or whole-body positron emission tomography (PET). Hybrid positron emission tomography-computed tomography (PET/CT) is a versatile tool for real-time measurement of copper fluxes combining the high sensitivity and quantification capability of PET and the superior spatial resolution of CT for anatomic localization of radioactive tracer activity. Kinetic analysis of copper metabolism in the liver and extrahepatic tissues of Atp7b(-/-) knockout mice, a mouse model of Wilson's disease, demonstrated the feasibility of measuring copper fluxes in live organisms with PET/CT using copper-64 chloride ((64) CuCl2 ) as a radioactive tracer ((64) CuCl2 -PET/CT). (64) CuCl2 -PET/CT holds potential as a useful tool for the diagnosis of inherited and acquired human copper metabolism disorders and for monitoring the effects of copper-modulating therapy.

Theranostics of malignant melanoma with 64CuCl2

Human copper transporter 1 (CTR1) is overexpressed in a variety of cancers. This study aimed to evaluate the use of (64)CuCl2 as a theranostic agent for PET and radionuclide therapy of malignant melanoma.

METHODS

CTR1 expression levels were detected by Western blot analysis of a group of tumor cell lines. Two melanoma cell lines (B16F10 and A375M) that highly expressed CTR1 were then selected to study the uptake and efflux of (64)CuCl2. Mice bearing B16F10 or A375M tumors (n = 4 for each group) were subjected to 5 min of static whole-body PET scans at different time points after intravenous injection of (64)CuCl2. Dynamic scans were also obtained for B16F10 tumor-bearing mice. All mice were sacrificed at 72 h after injection of (64)CuCl2, and biodistribution studies were performed. Mice bearing B16F10 or A375M tumors were further subjected to (64)CuCl2 radionuclide therapy. Specifically, when the tumor size reached 0.5-0.8 cm in diameter, tumor-bearing mice were systemically administered (64)CuCl2 (74 MBq) or phosphate-buffered saline, and tumor sizes were monitored over the treatment period.

RESULTS

CTR1 was found to be overexpressed in the cancer cell lines tested at different levels, and high expression levels in melanoma cells and tissues were observed (melanotic B16F10 and amelanotic A375M). (64)CuCl2 displayed high and specific uptake in B16F10 and A375M cells. In vivo (64)CuCl2 PET imaging demonstrated that both B16F10 and A375M tumors were clearly visualized. Radionuclide treatment studies showed that the tumor growth in both the B16F10 and the A375M models under (64)CuCl2 treatment were much slower than that of the control group.

CONCLUSION

Both melanotic and amelanotic melanomas (B16F10 and A375M) tested were found to overexpress CTR1. The tumors can be successfully visualized by (64)CuCl2 PET and further treated by (64)CuCl2, highlighting the high potential of using (64)CuCl2 as a theranostic agent for the management of melanoma.

A comparison of the behavior of (64)Cu-acetate and (64)Cu-ATSM in vitro and in vivo

(64)Cu-diacetyl-bis(N(4)-methylthiosemicarbazonate), (64)Cu-ATSM, continues to be investigated clinically as a PET agent both for delineation of tumor hypoxia and as an effective indicator of patient prognosis, but there are still aspects of the mechanism of action that are not fully understood.

METHODS

The retention of radioactivity in tumors after administration of (64)Cu-ATSM in vivo is substantially higher for tumors with a significant hypoxic fraction. This hypoxia-dependent retention is believed to involve the reduction of Cu-ATSM, followed by the loss of copper to cellular copper processing. To shed light on a possible role of copper metabolism in hypoxia targeting, we have compared (64)Cu retention in vitro and in vivo in CaNT and EMT6 cells or cancers after the administration of (64)Cu-ATSM or (64)Cu-acetate.

RESULTS

In vivo in mice bearing CaNT or EMT6 tumors, biodistributions and dynamic PET data are broadly similar for (64)Cu-ATSM and (64)Cu-acetate. Copper retention in tumors at 15 min is higher after injection of (64)Cu-acetate than (64)Cu-ATSM, but similar values result at 2 and 16 h for both. Colocalization with hypoxia as measured by EF5 immunohistochemistry is evident for both at 16 h after administration but not at 15 min or 2 h. Interestingly, at 2 h tumor retention for (64)Cu-acetate and (64)Cu-ATSM, although not colocalizing with hypoxia, is reduced by similar amounts by increased tumor oxygenation due to inhalation of increased O2. In vitro, substantially less uptake is observed for (64)Cu-acetate, although this uptake had some hypoxia selectivity. Although (64)Cu-ATSM is stable in mouse serum alone, there is rapid disappearance of intact complex from the blood in vivo and comparable amounts of serum bound activity for both (64)Cu-ATSM and (64)Cu-acetate.

CONCLUSION

That in vivo, in the EMT6 and CaNT tumors studied, the distribution of radiocopper from (64)Cu-ATSM in tumors essentially mirrors that of (64)Cu-acetate suggests that copper metabolism may also play a role in the mechanism of selectivity of Cu-ATSM.

Knockdown of copper chaperone antioxidant-1 by RNA interference inhibits copper-stimulated proliferation of non-small cell lung carcinoma cells

Copper is required for cell proliferation and tumor angiogenesis. Cellular copper metabolism is regulated by a network of copper transporters and chaperones. Antioxidant-1 (ATOX1) is a cytosolic copper chaperone important for intracellular copper transport, which plays a role in the regulation of cell proliferation by functioning as a transcription factor in cell growth signal-transduction pathways. The present study aimed to explore the role of ATOX1 in the copper-related regulation of lung cancer cell proliferation by immunohistochemical (IHC) analysis of ATOX1 expression in non-small cell lung cancer (NSCLC) tissue samples and by assessing the effects of RNA interference (RNAi)-mediated knockdown of ATOX1 on copper-stimulated proliferation of NSCLC cells. Overexpression of ATOX1 was detected in NSCLC by IHC analysis of the tissue samples from patients diagnosed with NSCLC when compared with expression of ATOX1 in non-malignant lung tissue samples. Knockdown of ATOX1 in the NSCLC cells transduced by a lentiviral vector encoding short hairpin RNA (shRNA) specific for ATOX1 was associated with reduction in copper-stimulated cell proliferation. These findings suggest that ATOX1 plays an important role in copper-stimulated proliferation of NSCLC cells and ATOX1 holds potential as a therapeutic target for lung cancer therapy targeting copper metabolism.

High tumor uptake of (64)Cu: implications for molecular imaging of tumor characteristics with copper-based PET tracers

INTRODUCTION

The use of copper-based positron emission tomography (PET) tracers in cancer studies is increasing. However, as copper has previously been found in high concentrations in human tumor tissue in vivo, instability of PET tracers could result in tumor accumulation of non-tracer-bound radioactive copper that may influence PET measurements. Here we determine the degree of (64)Cu uptake in five commonly used human cancer xenograft models in mice. Additionally, we compare copper accumulation in tumor tissue to gene expression of human copper transporter 1 (CTR1).

METHODS

Small animal PET scans were performed on five different human cancer xenograft mice models 1h and 22h post injection (p.i.) of (64)CuCl2. Regions of interest (ROIs) were drawn on tumor tissue and sections of various organs on all images. Quantitative real-time PCR (qPCR) gene expression measurements of CTR1 were performed on tumor samples obtained after the 22h scan.

RESULTS

A relatively high tumor uptake of (64)Cu was seen in four out of five tumor types and an increase in (64)Cu accumulation was seen in three out of five tumor types between 1h and 22h p.i. No relationship was found between tumor uptake of (64)Cu and gene expression of CTR1.

CONCLUSIONS

The relatively high, time- and tumor type dependent (64)Cu uptake demonstrated here in five different human cancer xenograft models in mice, emphasizes the importance of validating tracer uptake and indicates that high in vivo stability of copper-based PET tracers is of particular importance because non-tracer-bound copper can accumulate in tumor tissue to a level that could potentially lead to misinterpretation of PET data.