64CuCl2 PET/CT in Prostate Cancer Relapse

Incidental Detection of Second Primary Thyroid Malignancy in Patients of Metastatic Castration-Resistant Prostate Carcinoma: Documentation on 68Ga-PSMA-11 and 64CuCl2 PET/CT

ABSTRACT

Second primary tumors are being increasingly detected owing to and in proportion to the use of advanced imaging modalities including PET/CT. Patients suffering from prostate cancer have been reported to have increased second primary cancers of gastrointestinal tract, urinary bladder, and thyroid. We herein describe incidental detection of thyroid carcinoma, in 2 patients of mCRPC (metastatic castration-resistant prostate carcinoma) undergoing preradioligand therapy workup, on 68Ga-prostate-specific membrane antigen PET/CT initially, subsequently also observed on multitracer PET/CT (64CuCl2 and 18F-FDG). Thus, the potential of PET/CT for early in vivo second primary detection in mCRPC setting is illustrated in the aforementioned 2 patients.

Unveiling the promising anticancer effect of copper-based compounds: a comprehensive review

Copper is a necessary micronutrient for maintaining the well-being of the human body. The biological activity of organic ligands, especially their anticancer activity, is often enhanced when they coordinate with copper(I) and (II) ions. Copper and its compounds are capable of inducing tumor cell death through various mechanisms of action, including activation of apoptosis signaling pathways by reactive oxygen species (ROS), inhibition of angiogenesis, induction of cuproptosis, and paraptosis. Some of the copper complexes are currently being evaluated in clinical trials for their ability to map tumor hypoxia in various cancers, including locally advanced rectal cancer and bulky tumors. Several studies have shown that copper nanoparticles can be used as effective agents in chemodynamic therapy, phototherapy, hyperthermia, and immunotherapy. Despite the promising anticancer activity of copper-based compounds, their use in clinical trials is subject to certain limitations. Elevated copper concentrations may promote tumor growth, angiogenesis, and metastasis by affecting cellular processes.

Cuproptosis: Harnessing Transition Metal for Cancer Therapy

Transition metal elements, such as copper, play diverse and pivotal roles in oncology. They act as constituents of metalloenzymes involved in cellular metabolism, function as signaling molecules to regulate the proliferation and metastasis of tumors, and are integral components of metal-based anticancer drugs. Notably, recent research reveals that excessive copper can also modulate the occurrence of programmed cell death (PCD), known as cuprotosis, in cancer cells. This modulation occurs through the disruption of tumor cell metabolism and the induction of proteotoxic stress. This discovery uncovers a mode of interaction between transition metals and proteins, emphasizing the intricate link between copper homeostasis and tumor metabolism. Moreover, they provide innovative therapeutic strategies for the precise diagnosis and treatment of malignant tumors. At the crossroads of chemistry and oncology, we undertake a comprehensive review of copper homeostasis in tumors, elucidating the molecular mechanisms underpinning cuproptosis. Additionally, we summarize current nanotherapeutic approaches that target cuproptosis and provide an overview of the available laboratory and clinical methods for monitoring this process. In the context of emerging concepts, challenges, and opportunities, we emphasize the significant potential of nanotechnology in the advancement of this field.

Exploratory analysis of 64 CuCl 2 PET-CT imaging in carcinoma prostate and its comparison with 68 Ga-PSMA-11 and 18 F-FDG PET-CT

AIM

Exploratory analysis of 64 CuCl 2 PET-CT imaging in patients of carcinoma prostate and its head-to-head comparison with 68 Ga-PSMA-11 and 18 F-FDG PET-CT.

METHODS

In this prospective study, 50 patients of biopsy-proven carcinoma prostate belonging to the entire spectrum of disease were evaluated, out of which 21 patients were for initial staging and 29 were for restaging/response evaluation. Both 64 CuCl 2 (early and delayed) and 68 Ga-PSMA-11 PET-CT were undertaken in all patients and 18 F-FDG PET-CT was done in patients whenever possible. All scans were done within a period of 2 weeks, without any interim therapeutic intervention. 64 CuCl 2 PET-CT was acquired at 1 and 3 h. We evaluated the physiological uptake of 64 CuCl 2 , correlated the uptake in primary with disease parameters like Gleason score and serum PSA levels, and compared the detection rates for primary and metastatic disease with 68 Ga-PSMA-11 and 18 F-FDG PET-CT.

RESULTS

The detection rates of primary disease were same for both 64 CuCl 2 and 68 Ga-PSMA-11 PET-CT and both agents performed similarly in detecting extra-prostatic disease. There was no statistically significant correlation observed between the uptake of 64 CuCl 2 in the primary lesion with disease parameters. With regard to the evaluation of metastatic disease, the detection rate of 64 CuCl 2 PET-CT was 86% for lymph nodes, 77.3% for skeletal metastases and 80.6% for soft tissue metastases while 68 Ga-PSMA-11 PET-CT performed better with detection rates were 98%, 99% and 85.4%, respectively. In 17 patients where 18 F-FDG PET-CT was available, 64 CuCl 2 PET-CT detected more metastatic disease than 18 F-FDG PET-CT.

CONCLUSION

64 CuCl 2 PET-CT did not show any additional advantage over 68 Ga-PSMA-11 PET-CT in evaluation of local disease or for the assessment of metastatic disease. When compared to 68 Ga-PSMA-11 PET-CT, the absence of urinary bladder and ureteric activity allows better contrast for evaluating local disease, but it does not translate into increased disease detection.

Emerging Role of Nuclear Medicine in Prostate Cancer: Current State and Future Perspectives

Prostate cancer is the most frequent epithelial neoplasia after skin cancer in men starting from 50 years and prostate-specific antigen (PSA) dosage can be used as an early screening tool. Prostate cancer imaging includes several radiological modalities, ranging from ultrasonography, computed tomography (CT), and magnetic resonance to nuclear medicine hybrid techniques such as single-photon emission computed tomography (SPECT)/CT and positron emission tomography (PET)/CT. Innovation in radiopharmaceutical compounds has introduced specific tracers with diagnostic and therapeutic indications, opening the horizons to targeted and very effective clinical care for patients with prostate cancer. The aim of the present review is to illustrate the current knowledge and future perspectives of nuclear medicine, including stand-alone diagnostic techniques and theragnostic approaches, in the clinical management of patients with prostate cancer from initial staging to advanced disease.

Functional Imaging of Hypoxia: PET and MRI

Molecular and functional imaging have critical roles in cancer care. Existing evidence suggests that noninvasive detection of hypoxia within a particular type of cancer can provide new information regarding the relationship between hypoxia, cancer aggressiveness and altered therapeutic responses. Following the identification of hypoxia inducible factor (HIF), significant progress in understanding the regulation of hypoxia-induced genes has been made. These advances have provided the ability to therapeutically target HIF and tumor-associated hypoxia. Therefore, by utilizing the molecular basis of hypoxia, hypoxia-based theranostic strategies are in the process of being developed which will further personalize care for cancer patients. The aim of this review is to provide an overview of the significance of tumor hypoxia and its relevance in cancer management as well as to lay out the role of imaging in detecting hypoxia within the context of cancer.

Diagnostic and Dosimetry Features of [64Cu]CuCl2 in High-Grade Paediatric Infiltrative Gliomas

PURPOSE OF THE REPORT

Paediatric diffuse high-grade gliomas (PDHGG) are rare central nervous system neoplasms lacking effective therapeutic options. Molecular imaging of tumour metabolism might identify novel diagnostic/therapeutic targets. In this study, we evaluated the distribution and the dosimetry aspects of [⁶⁴Cu]CuCl₂ in PDHGG subjects, as copper is a key element in cellular metabolism whose turnover may be increased in tumour cells.

MATERIAL AND METHODS

Paediatric patients with PDHGG were prospectively recruited. [⁶⁴Cu]CuCl₂ PET/CT was performed 1 h after tracer injection; if the scan was positive, it was repeated 24 and 72 h later. Lesion standardised uptake value (SUV) and target-to-background ratio (TBR) were calculated. Tumour and organ dosimetry were computed using the MIRD algorithm. Each patient underwent an MRI scan, including FLAIR, T2-weighted and post-contrast T1-weighted imaging.

RESULTS

Ten patients were enrolled (median age 9, range 6-16 years, 6 females). Diagnoses were diffuse midline gliomas (n = 8, 5 of which with H3K27 alterations) and diffuse hemispheric gliomas (n = 2). Six patients had visible tracer uptake (SUV: 1.0 ± 0.6 TBR: 5 ± 3.1). [⁶⁴Cu]CuCl₂ accumulation was always concordant with MRI contrast enhancement and was higher in the presence of radiological signs of necrosis. SUV and TBR progressively increased on the 24- and 72-h acquisitions (p < 0.05 and p < 0.01, respectively). The liver and the abdominal organs received the highest non-target dose.

CONCLUSIONS

[⁶⁴Cu]CuCl₂ is a well-tolerated radiotracer with reasonably favourable dosimetric properties, showing selective uptake in tumour areas with visible contrast enhancement and necrosis, thus suggesting that blood-brain barrier damage is a pre-requisite for its distribution to the intracranial structures. Moreover, tracer uptake showed an accumulating trend over time. These characteristics could deserve further analysis, to determine whether this radiopharmaceutical might have a possible therapeutic role as well.

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.

Theragnostic Radionuclide Pairs for Prostate Cancer Management: 64Cu/67Cu, Can Be a Budding Hot Duo

Prostate cancer (PCa) is one of the preeminent causes of mortality in men worldwide. Theragnostic, a combination of therapy and diagnostic, using radionuclide pairs to diagnose and treat disease, has been shown to be a promising approach for combating PCa. In PCa patients, bone is one of the most common sites of metastases, and about 90% of patients develop bone metastases. This review focuses on (i) clinically translated theragnostic radionuclide pairs for the management of PCa, (ii) radionuclide therapy of bone metastases in PCa, and (iii) a special emphasis on emerging theragnostic radionuclide pair, Copper-64/Copper-67 (64Cu/67Cu) for managing the disease.

Synergism of 64Cu-Labeled RGD with Anti-PD-L1 Immunotherapy for the Long-Acting Antitumor Effect

We put forward a novel targeting-triggering-therapy (TTT) scheme that combines ⁶⁴Cu-based targeted radionuclide therapy (TRT) with programmed death-ligand 1 (PD-L1)-based immunotherapy for enhancing therapeutic efficacy. The α_vβ₃ integrin-targeted ⁶⁴Cu-DOTA-EB-cRGDfK (⁶⁴Cu-DER) was synthesized. Flow cytometry, immunofluorescence staining, and RT-qPCR were performed to verify PD-L1 upregulation after irradiation with ⁶⁴Cu-DER. Positron emission tomography imaging was performed to investigate the prominent tumor retention property of ⁶⁴Cu-DER. In the MC38 tumor model, anti-PD-L1 antibody (αPD-L1 mAb) was delivered in a concurrent or sequential manner after ⁶⁴Cu-DER was injected, followed by the testing of changes in tumor microenvironment (TME). PD-L1 was upregulated in a time- and dose-dependent manner after being induced by ⁶⁴Cu-DER. The combination of ⁶⁴Cu-DER TRT (925 MBq/kg) and αPD-L1 mAb (10 mg/kg) resulted in significant delay in tumor growth and protected against tumor rechallenge. Blockade of PD-L1 at 4 h after ⁶⁴Cu-DER TRT (⁶⁴Cu-DER + αPD-L1 mAb @ 4 h combination group) was able to achieve 100% survival rate, prevent tumor relapse, and evidently prolong the survival of mice. In summary, the combination of ⁶⁴Cu-DER and αPD-L1 mAb in a time-dependent manner could be a promising approach to improve therapeutic efficacy. Understandably, this strategy has the potential to extend the scope of ⁶⁴Cu-based TTT and merits translation into clinical practice for the better management of immune checkpoint blockade immunotherapy.

64CuCl2 PET Imaging of 4T1-Related Allograft of Triple-Negative Breast Cancer in Mice

⁶⁴CuCl₂ is an economic radiotracer for oncologic PET investigations. In the present study, we characterized the uptake of ⁶⁴CuCl₂ in vivo by µPET/CT in an allograft 4T1-related mouse model (BALB/c) of advanced breast cancer. ¹⁸F-FDG was used as a comparator. Twenty-two animals were imaged 7–9 days following 4T1-cell implantation inside mammary glands. Dynamic ⁶⁴CuCl₂ µPET/CT acquisition or iterative static images up to 8 h p.i. were performed. Animal biodistribution and tumor uptake were first evaluated in vivo by µPET analysis and then assessed on tissue specimens. Concerning ¹⁸F-FDG µPET, a static acquisition was performed at 15 min and 60 min p.i. Tumor ⁶⁴CuCl₂ accumulation increased from 5 min to 4 h p.i., reaching a maximum value of 5.0 ± 0.20 %ID/g. Liver, brain, and muscle ⁶⁴CuCl₂ accumulation was stable over time. The tumor-to-muscle ratio remained stable from 1 to 8 h p.i., ranging from 3.0 to 3.7. Ex vivo data were consistent with in vivo estimations. The ¹⁸F-FDG tumor accumulation was 8.82 ± 1.03 %ID/g, and the tumor-to-muscle ratio was 4.54 ± 1.11. ⁶⁴CuCl₂ PET/CT provides good characterization of the 4T1-related breast cancer model and allows for exploration of non-glycolytic cellular pathways potentially of interest for theragnostic strategies.

The pathophysiology of Wilson's disease visualized: A human 64 Cu PET study

BACKGROUND AND AIMS

Wilson's disease (WD) is a genetic disease with systemic accumulation of copper that leads to symptoms from the liver and brain. However, the underlying defects in copper transport kinetics are only partly understood. We sought to quantify hepatic copper turnover in patients with WD compared with heterozygote and control subjects using PET with copper-64 (64 Cu) as a tracer. Furthermore, we assessed the diagnostic potential of the method.

APPROACH AND RESULTS

Nine patients with WD, 5 healthy heterozygote subjects, and 8 healthy controls were injected with an i.v. bolus of 64 Cu followed by a 90-min dynamic PET scan of the liver and static whole-body PET/CT scans after 1.5, 6, and 20 h. Blood 64 Cu concentrations were measured in parallel. Hepatic copper retention and redistribution were evaluated by standardized uptake values (SUVs). At 90 min, hepatic SUVs were similar in the three groups. In contrast, at 20 h postinjection, the SUV in WD patients (mean ± SEM, 31 ± 4) was higher than in heterozygotes (24 ± 3) and controls (21 ± 4; p < 0.001). An SUV-ratio of hepatic 64 Cu concentration at 20 and 1.5 h completely discriminated between WD patients and control groups (p < 0.0001; ANOVA). By Patlak analysis of the initial 90 min of the PET scan, the steady-state hepatic clearance of 64 Cu was estimated to be slightly lower in patients with WD than in controls (p = 0.04).

CONCLUSIONS

64 Cu PET imaging enables visualization and quantification of the hepatic copper retention characteristic for WD patients. This method represents a valuable tool for future studies of WD pathophysiology, and may assist the development of therapies, and accurate diagnosis.

Emerging roles of the copper-CTR1 axis in tumorigenesis

Physiological roles of copper in metabolic homeostasis have been well established, however, whether and how copper is dysregulated in tumors and contributes to tumorigenesis are not recapitulated. Here, we comprehensively summarize the potential origins of copper accumulation in diseases especially in cancers by dysregulating copper transporter 1 (CTR1) or ATPase copper transporting alpha/beta (ATP7A/B) and further demonstrate the underlying mechanism of copper contributing to tumorigenesis. Specifically, in addition to modulating reactive oxygen species (ROS), angiogenesis, immune response, and metabolic homeostasis, copper recently has drawn more attention by directly binding to oncoproteins such as MEK, ULK, Memo, and PDK1 to activate distinct oncogenic signals and account for tumorigenesis. In the end, we disclose the emerging applications of copper in cancer diagnosis and highlight the promising strategies to target the copper-CTR1 axis for cancer therapies.

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.

Prospective clinical trial of disulfiram plus copper in men with metastatic castration-resistant prostate cancer

BACKGROUND

In preclinical models of prostate cancer (PC), disulfiram (DSF) reduced tumor growth only when co-administered with copper (Cu), and Cu uptake in tumors is partially regulated by androgen-receptor signaling. However, prior trials of DSF in PC used DSF as monotherapy.

OBJECTIVE

To assess the safety and efficacy of concurrent administration of DSF with Cu, we conducted a phase 1b clinical trial of patients with metastatic castration-resistant prostate cancer (mCRPC) receiving Cu with DSF.

DESIGN, SETTING, AND PARTICIPANTS

Patients with mCRPC were treated in two cohorts: mCRPC with nonliver/peritoneal metastases (A), and mCRPC with liver and/or peritoneal metastases (B). Baseline Cu avidity was measured by 64 CuCl2 PET scan. Intravenous (IV) CuCl2 was given weekly for three doses with oral daily DSF followed by daily oral Cu gluconate and DSF until disease progression. DSF and metabolite diethyldithiocarbamic acid methyl ester (Me-DDC) levels in plasma were measured. DSF and Me-DDC were then assessed for cytotoxicity in vitro.

RESULTS

We treated nine patients with mCRPC (six on cohort A and three on cohort B). Bone and nodal metastases showed differential and heterogeneous Cu uptake on 64 CuCl2 PET scans. No confirmed PSA declines or radiographic responses were observed. Median PFS was 2.8 months and median OS was 8.3 months. Common adverse events included fatigue and psychomotor depression; no Grade 4/5 AEs were observed. Me-DDC was measurable in all samples (LOQ = 0.512 ng/ml), whereas DSF was not (LOQ = 0.032 ng/ml, LOD = 0.01 ng/ml); Me-DDC was not cytotoxic in vitro.

CONCLUSIONS

Oral DSF is not an effective treatment for mCRPC due to rapid metabolism into an inactive metabolite, Me-DDC. This trial has stopped enrollment and further work is needed to identify a stable DSF formulation for treatment of mCRPC.

A feasibility study of the therapeutic application of a mixture of 67/64 Cu radioisotopes produced by cyclotrons with proton irradiation

PURPOSE

64 Cu and 67 Cu radioisotopes have nuclear characteristics suitable for nuclear medicine applications. The production of 64 Cu is already well established. However, the production of 67 Cu in quantities suitable to conduct clinical trials is more challenging as it leads to the coproduction of other Cu isotopes, in particular 64 Cu. The aim of this study is to investigate the possibility of using a CuCl2 solution with a mixture of 67/64 Cu radioisotopes for therapeutic purposes, providing an alternative solution for the cyclotron production problem.

METHODS

Copper radioisotopes activities were calculated by considering proton beam irradiation of the following targets: (i) 70 Zn in the energy range 70-45 MeV; (ii) 68 Zn in the energy range 70-35 MeV; (iii) a combination of 70 Zn (70-55 MeV) and 68 Zn (55-35 MeV). The contribution of each copper radioisotope to the human-absorbed dose was estimated with OLINDA/EXM software using the biokinetic model for CuCl2 published by ICRP 53. The total absorbed dose generated by the 67/64 CuCl2 mixture, obtained through different production routes, was calculated at different times after the end of the bombardment (EOB). A simple spherical model was used to simulate tumors of different sizes containing uniformly distributed 67/64 Cu mixture and to calculate the absorbed dose of self-irradiation. The biological damage produced by 67 Cu and 64 Cu was also evaluated through cellular dosimetry and cell surviving fraction assessment using the MIRDcell code, considering two prostate cancer cell lines with different radiosensitivity.

RESULTS

The absorbed dose to healthy organs and the effective dose (ED) per unit of administered activity of 67 CuCl2 are higher than those of 64 CuCl2 . Absorbed dose values per unit of administered activity of 67/64 CuCl2 mixture increase with time after the EOB because the amount of 67 Cu in the mixture increases. Survival data showed that the biological damage caused per each decay of 67 Cu is greater than that of 64 Cu, assuming that radionuclides remain accumulated in the cell cytoplasm. Sphere model calculations demonstrated that 64 Cu administered activity must be about five times higher than that of 67 Cu to obtain the same absorbed dose for tumor mass between 0.01 and 10 g and about 10 times higher for very small spheres. Consequently, the 64 CuCl2 -absorbed dose to healthy organs will reach higher values than those of 67 CuCl2 . The supplemental activity of the 67/64 CuCl2 mixture, required to get the same tumor-absorbed dose produced by 67 CuCl2 , triggers a dose increment (DI) in healthy organs. The waiting time post-EOB necessary to keep this DI below 10% (t10% ) depends on the irradiation methods employed for the production of the 67/64 CuCl2 mixture.

CONCLUSIONS

A mixture of cyclotron produced 67/64 Cu radioisotopes proved to be an alternative solution for the therapeutic use of CuCl2 with minimal DI to healthy organs compared with pure 67 Cu. Irradiation of a 70 Zn+68 Zn target in the 70-35 MeV proton energy range for 185 h appears to be the best option from among all the production routes investigated, as it gives the maximum amount of activity, the shortest t10% (10 h), and less than 1% of 61 Cu and 60 Cu impurities.

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.

Connecting copper and cancer: from transition metal signalling to metalloplasia

Copper is an essential nutrient whose redox properties make it both beneficial and toxic to the cell. Recent progress in studying transition metal signalling has forged new links between researchers of different disciplines that can help translate basic research in the chemistry and biology of copper into clinical therapies and diagnostics to exploit copper-dependent disease vulnerabilities. This concept is particularly relevant in cancer, as tumour growth and metastasis have a heightened requirement for this metal nutrient. Indeed, the traditional view of copper as solely an active site metabolic cofactor has been challenged by emerging evidence that copper is also a dynamic signalling metal and metalloallosteric regulator, such as for copper-dependent phosphodiesterase 3B (PDE3B) in lipolysis, mitogen-activated protein kinase kinase 1 (MEK1) and MEK2 in cell growth and proliferation and the kinases ULK1 and ULK2 in autophagy. In this Perspective, we summarize our current understanding of the connection between copper and cancer and explore how challenges in the field could be addressed by using the framework of cuproplasia, which is defined as regulated copper-dependent cell proliferation and is a representative example of a broad range of metalloplasias. Cuproplasia is linked to a diverse array of cellular processes, including mitochondrial respiration, antioxidant defence, redox signalling, kinase signalling, autophagy and protein quality control. Identifying and characterizing new modes of copper-dependent signalling offers translational opportunities that leverage disease vulnerabilities to this metal nutrient.

Copper-64-Labeled 1C1m-Fc, a New Tool for TEM-1 PET Imaging and Prediction of Lutetium-177-Labeled 1C1m-Fc Therapy Efficacy and Safety

Simple Summary

The prevalence of TEM-1 in the vasculature and the stroma of solid tumors and in malignant cells of sarcomas suggests that targeting TEM-1 could have therapeutic benefit. In this context, an anti-TEM-1 companion diagnostic may assist in the personalized medicine approach, whereby TEM-1 expression is exploited as a biomarker to select patients that would most benefit from a treatment directed toward the TEM-1 antigen. In our previous works, we have selected 1C1m-Fc, a fusion protein antibody, radiolabeled it with ¹⁷⁷Lu and demonstrated that [¹⁷⁷Lu]Lu-1C1m-Fc has interesting therapeutic performance. To define a suitable radiopharmaceutical companion for theranostic applications, ⁶⁴Cu was chosen to radiolabel the fusion protein antibody. The aim of this work was thus to determine if [⁶⁴Cu]Cu-1C1m-Fc can be considered for TEM-1 PET imaging and to predict the dosimetry of the [¹⁷⁷Lu]Lu-1C1m-Fc companion therapy.

Abstract

1C1m-Fc, a promising anti-TEM-1 DOTA conjugate, was labeled with ⁶⁴Cu to target cancer cells for PET imaging and predicting the efficacy and safety of a previously studied [¹⁷⁷Lu]Lu-1C1m-Fc companion therapy. DOTA-conjugated 1C1m-Fc was characterized by mass spectrometry, thin layer chromatography and immunoreactivity assessment. PET/CT and biodistribution studies were performed in human neuroblastoma xenografted mice. Absorbed doses were assessed from biodistribution results and extrapolated to ¹⁷⁷Lu based on the [⁶⁴Cu]Cu-1C1m-Fc data. The immunoreactivity was ≥ 70% after 48 h of incubation in serum, and the specificity of [⁶⁴Cu]Cu-1C1m-Fc for the target was validated. High-resolution PET/CT images were obtained, with the best tumor-to-organ ratios reached at 24 or 48 h and correlated with results of the biodistribution study. Healthy organs receiving the highest doses were the liver, the kidneys and the uterus. [⁶⁴Cu]Cu-1C1m-Fc could be of interest to give an indication of ¹⁷⁷Lu dosimetry for parenchymal organs. In the uterus and the tumor, characterized by specific TEM-1 expression, the ¹⁷⁷Lu-extrapolated absorbed doses are overestimated because of the lack of later measurement time points. Nevertheless, 1C1m-Fc radiolabeled with ⁶⁴Cu for imaging would appear as an interesting radionuclide companion for therapeutic application with [¹⁷⁷Lu]Lu-1C1m-Fc.

A Prospective Study Assessing the Post-Prostatectomy Detection Rate of a Presumed Local Failure at mpMR with Either 64CuCl2 or 64CuPSMA PET/CT

Simple Summary

The role of PET/CT with two novel tracers was investigated in prostate cancer patients with both a biochemical failure after surgery and a presumed local failure at multiparametric MR. Overall, both PET tracers detected only about 50% of local failures. Therefore, multiparametric MR remains the exam of choice to investigate the prostatic fossa in patients who fail surgery.

Abstract

Background: We aimed assess the detection rate (DR) of positron emission tomography/computed tomography with two novel tracers in patients referred for salvage radiotherapy (sRT) with a presumed local recurrence at multiparametric magnetic resonance (mpMR) after radical prostatectomy (RP). Methods: The present prospective study was conducted at a single institution between August 2017 and June 2020. Eligibility criteria were undetectable PSA after RP; subsequent biochemical recurrence (two consecutive PSA rises to 0.2 ng/mL or greater); a presumed local failure at mpMR; no distant metastases at ¹⁸F-fluorocholine PET/CT (CH/PET); no previous history of androgen deprivation therapy. Patients were offered both ⁶⁴CuCl₂ PET/CT (CU/PET) and ⁶⁴Cu-PSMA PET/CT (PSMA/PET) before sRT. After image co-registration, PET findings were compared to mpMR ones in terms of DR and independent predictors of DR investigated at logistic regression. Results: A total of 62 patients with 72 nodules at mpMR were accrued. Compared to mpMR (DR = 100%, 95%CI: 94.9–100%), DRs were 47.2% (95%CI: 36.1–58.6%) and 54.4% (95%CI: 42.7–65.7%) for CU/PET and PSMA/PET, respectively (p < 0.001 for both). Both experimental PET/CT performed particularly poorly at PSA levels consistent with early sRT. Conclusions: The two novel radiotracers are inferior to mpMR in restaging the prostatic fossa for sRT planning purposes, particularly in the context of early salvage radiotherapy.

Imaging of Tumor Hypoxia With Radionuclide-Labeled Tracers for PET

The hypoxic state in a solid tumor refers to the internal hypoxic environment that appears as the tumor volume increases (the maximum radius exceeds 180-200 microns). This state can promote angiogenesis, destroy the balance of the cell’s internal environment, and lead to resistance to radiotherapy and chemotherapy, as well as poor prognostic factors such as metastasis and recurrence. Therefore, accurate quantification, mapping, and monitoring of hypoxia, targeted therapy, and improvement of tumor hypoxia are of great significance for tumor treatment and improving patient survival. Despite many years of development, PET-based hypoxia imaging is still the most widely used evaluation method. This article provides a comprehensive overview of tumor hypoxia imaging using radionuclide-labeled PET tracers. We introduced the mechanism of tumor hypoxia and the reasons leading to the poor prognosis, and more comprehensively included the past, recent and ongoing studies of PET radiotracers for tumor hypoxia imaging. At the same time, the advantages and disadvantages of mainstream methods for detecting tumor hypoxia are summarized.

Production of copper-64 using a hospital cyclotron: targetry, purification and quality analysis

OBJECTIVES

To construct and evaluate a 64Cu production system that minimises the amount of costly 64Ni, radionuclidic impurities and nonradioactive metal contamination and maximises radiochemical and radionuclidic purity and molar activity; and to report analytical and quality control methods that can be used within typical PET radiochemistry production facilities to measure metal ion concentrations and radiometal molar activities.

METHODS

Low volume was ensured by dissolving the irradiated nickel in a low volume of hydrochloric acid (<1 mL) using the concave gold target backing as a reaction vessel in a custom-built target holder. Removal of contaminating 55Co and nonradioactive trace metals was ensured by adding an intermediate hydrochloric acid concentration step during the conventional ion-exchange elution process. The radionuclidic purity of the product was determined by half-life measurements, gamma spectroscopy and ion radiochromatography. Trace metal contamination and molar activity were determined by ion chromatography.

RESULTS AND CONCLUSIONS

On a small scale, suitable for preclinical research, the process produced typically 3.2 GBq 64Cu in 2 mL solution from 9.4 ± 2.1 mg nickel-64 electroplated onto a gold target backing. The product had high molar activity (121.5 GBq/µmol), was free of trace metal contamination detectable by ion chromatography and has been used for many preclinical and clinical PET imaging applications.

Incorporating PSMA-Targeting Theranostics Into Personalized Prostate Cancer Treatment: a Multidisciplinary Perspective

Recent developments in prostate-specific membrane antigen (PSMA) targeted diagnostic imaging and therapeutics (theranostics) promise to advance the management of primary, biochemically recurrent, and metastatic prostate cancer. In order to maximize the clinical impact of PSMA-targeted theranostics, a coordinated approach between the clinical stakeholders involved in prostate cancer management is required. Here, we present a vision for multidisciplinary use of PSMA theranostics from the viewpoints of nuclear radiology, medical oncology, urology, and radiation oncology. We review the currently available and forthcoming PSMA-based imaging and therapeutics and examine current and potential impacts on prostate cancer management from early localized disease to advanced treatment-refractory disease. Finally, we highlight the clinical and research opportunities related to PSMA-targeted theranostics and describe the importance of multidisciplinary collaboration in this space.

Efficacy and Safety of the 64Cu(II)Cl2 PET/CT for Urological Malignancies: Phase IIa Clinical Study

PURPOSE OF THE REPORT

The aim of this study was to evaluate safety and efficacy of copper-64(II)dichloride (64Cu(II)Cl2) as a new PET tracer for urological malignancies (UMs).

METHODS

Patients with UM were enrolled in a prospective study. All patients were staged with preoperative CT and 64Cu(II)Cl2 PET/CT. Patient characteristics, anatomical and functional imaging, and final histopathology were recorded. Surgical specimens for histopathological examination were collected. To determine time-activity curves for 64Cu(II)Cl2 uptake in UM and normal tissues, SUVs were calculated. The safety of 64Cu(II)Cl2 was assessed.

RESULTS

Twenty-three patients were included. An administered activity of 174.7 MBq (4.72 mCi) for 64Cu(II)Cl2 was equal to 9.80 mSv of the effective dose. The median SUVmax values were 5.7, 0.9, 1.8, and 9.8 for the prostate, bladder, penis, and kidney, respectively. Median SUVmax values were higher in organs with a malignancy in comparison with healthy tissue (prostate [11.5 vs 5.3, P < 0.001], bladder [6.2 vs 0.9, P = 0.007], and penis [3.9 vs 1.3, P = 0.027]), but not in the kidneys (5.0 vs 10.4, P = 0.998). The highest area under the curve (AUC) was reported for prostate cancer (AUC, 0.978), and the lowest for penile cancer (AUC, 0.775). The detection rates based on the best suggested cutoff according to the SUVmax were 85.7% (6/7) for prostate and bladder and 83.3% (5/6) for penile cancer. Neither drug-related effects nor physiologic responses occurred, nor adverse reactions.

CONCLUSIONS

64Cu(II)Cl2 is an effective and well-tolerated tracer in patients with UM. Our results show higher SUVmax in cancer patients than in healthy subjects. Our findings suggest that 64Cu(II)Cl2 PET/CT is useful in patients affected by prostate, bladder, and penis cancer.

Management of Prostate Cancer with Systemic Therapy: A Prostate Cancer Unit Perspective

The scenario of systemic therapy for prostate cancer is rapidly evolving, with new drugs and new treatment options. To update the background knowledge of shared uro-oncologic practice, we reviewed current statements and landmarks in systemic therapy. A number of new agents are under investigation in non-metastatic and metastatic disease. Similarly, new target imaging technologies are under development to improve the detection rate of true non-metastatic and true metastatic patient. Five new drugs have shown to be effective on progression-free and overall survival in metastatìc prostate cancer. However, the optimal sequencing of these treatments requires further investigation. The tolerability and side effects of the new drugs are also crucial issues to be discussed, as well as their activity against the disease. The uro-oncologic team has to stay updated about new medical therapies in order to be confident in debating with other professionals involved in prostate cancer decision making. Different points of view and nuances should be shared during multidisciplinary group discussions to achieve a balanced decision in disease management.

Radiolabelling of nanomaterials for medical imaging and therapy

Nanomaterials offer unique physical, chemical and biological properties of interest for medical imaging and therapy. Over the last two decades, there has been an increasing effort to translate nanomaterial-based medicinal products (so-called nanomedicines) into clinical practice and, although multiple nanoparticle-based formulations are clinically available, there is still a disparity between the number of pre-clinical products and those that reach clinical approval. To facilitate the efficient clinical translation of nanomedicinal-drugs, it is important to study their whole-body biodistribution and pharmacokinetics from the early stages of their development. Integrating this knowledge with that of their therapeutic profile and/or toxicity should provide a powerful combination to efficiently inform nanomedicine trials and allow early selection of the most promising candidates. In this context, radiolabelling nanomaterials allows whole-body and non-invasive in vivo tracking by the sensitive clinical imaging techniques positron emission tomography (PET), and single photon emission computed tomography (SPECT). Furthermore, certain radionuclides with specific nuclear emissions can elicit therapeutic effects by themselves, leading to radionuclide-based therapy. To ensure robust information during the development of nanomaterials for PET/SPECT imaging and/or radionuclide therapy, selection of the most appropriate radiolabelling method and knowledge of its limitations are critical. Different radiolabelling strategies are available depending on the type of material, the radionuclide and/or the final application. In this review we describe the different radiolabelling strategies currently available, with a critical vision over their advantages and disadvantages. The final aim is to review the most relevant and up-to-date knowledge available in this field, and support the efficient clinical translation of future nanomedicinal products for in vivo imaging and/or therapy.

Copper-64 Chloride Exhibits Therapeutic Potential in Three-Dimensional Cellular Models of Prostate Cancer

Prostate cancer (PCa) is the second most common cancer type in men, and in advanced metastatic stages is considerable incurable. This justifies the need for efficient early diagnostic methods and novel therapies, particularly radiopharmaceuticals with the potential for simultaneous diagnosis and therapy (theranostics). We have previously demonstrated, using monolayer-cultured cells, that copper-64 chloride, a promising theranostic agent for PCa, has the potential to induce significant damage in cancer cells while having minimal side effects in healthy tissues. Here, we further explored this compound for its theranostic applications using more advanced PCa cellular models, specifically multicellular spheroids. Namely, we evaluated the cellular uptake of ⁶⁴CuCl₂ in three human PCa spheroids (derived from 22RV1, DU145, and LNCaP cells), and characterized the growth profile and viability of those spheroids as well as the clonogenic capacity of spheroid-derived cells after exposure to ⁶⁴CuCl₂. Furthermore, the populations of cancer stem cells (CSCs), known to be important for cancer resistance and recurrence, present in the spheroid models were also evaluated using two different markers (CD44 and CD117). ⁶⁴CuCl₂ was found to have significant detrimental effects in spheroids and spheroid-derived cells, being able to reduce their growth and impair the viability and reproductive ability of spheroids from both castration-resistant (22RV1 and DU145) and hormone-naïve PCa (LNCaP). Interestingly, resistance to ⁶⁴CuCl₂ treatment seemed to be related with the presence of a CSC population, since the most resistant spheroids, derived from the DU145 cell line, had the highest initial percentage of CSCs among the three cell lines under study. Altogether, these results clearly highlight the theranostic potential of ⁶⁴CuCl₂.

Copper, PET/CT and prostate cancer: a systematic review of the literature

Copper is an essential element that plays an important role in both cancer development and growth. Indeed, high levels of copper have been found in prostate cancer (PCa), and this finding have paved the way for the use of this element as a target for positron emission tomography (PET) imaging. Copper64 (64Cu) can be used alone, as 64CuCl2, and also as a precursor for the in-vitro radio-labelling of specific carriers for PET imaging in PCa, (e.g. associated to prostate-specific membrane antigen: PSMA). The use of 64Cu-PSMA can yield late acquisitions in which PET images are characterized by a higher target-to-background ratio. At the same time, the shorter positron range of 64Cu provides high spatial resolution, which leads to better detection of small lesions. In this context, the aim of this review was to systematically review studies evaluating the identification of PCa in humans by means of 64CuCl2 and other PET tracers radio-labelled with 64Cu.

Diagnostic value of retrospectively fused 64CuCl2 PET/MRI in biochemical relapse of prostate cancer: comparison with fused 18F-Choline PET/MRI, 64CuCl2 PET/CT, 18F-Choline PET/CT, and mpMRI

PURPOSE

To assess the diagnostic value of retrospectively fused PET/MRI by comparing the detection rates (DRs) of fused ⁶⁴CuCl₂ PET/MRI vs. fused ¹⁸F-Choline PET/MRI in patients with suspected prostatic cancer (PCa) recurrence. The secondary objective was to compare the DRs of fused PET/MRI vs. those of the separate imaging modalities.

METHODS

We retrospectively evaluated 50 PCa patients with biochemical relapse after radical prostatectomy (RP) or radiotherapy (RT). All patients underwent ⁶⁴CuCl₂ PET/CT, ¹⁸F-Choline PET/CT, and multiparametric magnetic resonance imaging (mpMRI) within 15 days. Fused ⁶⁴CuCl₂-PET/MRI and fused ¹⁸F-Choline PET/MRI images were obtained by retrospective co-registration of MRI and PET images. Experienced readers interpreted the images, and the DRs of each imaging modality were assessed.

RESULTS

In the patient-based analysis, overall DRs of fused ⁶⁴CuCl₂ PET/MRI, fused ¹⁸F-Choline PET/MRI, ⁶⁴CuCl₂ PET/CT, ¹⁸F-Choline PET/CT, and mpMRI were 88%, 68%, 82%, 56%, and 74%, respectively. In the lesion-based analysis, overall DRs of fused ⁶⁴CuCl₂ PET/MRI, fused ¹⁸F-Choline PET/MRI, ⁶⁴CuCl₂ PET/CT, ¹⁸ F-Choline PET/CT, and mpMRI were 95%, 66%, 87%, 58%, and 71%, respectively.

CONCLUSIONS

Retrospectively fused PET/MRI is able to overcome the limitations of the separate interpretation of the individual imaging modalities. Fused ⁶⁴CuCl₂ PET/MRI provided the highest diagnostic performance in the detection of PCa local relapse.

L-Cysteine-mediated modulation of copper trafficking in prostate cancer cells: an in vitro and in vivo investigation with 64Cu and 64Cu-PET

Copper imbalance is implicated in many diseases, including cancer. Copper in blood is mainly transported by carrier proteins but a small fraction is bound to low molecular weight species, possibly amino acids. Their roles in cellular copper delivery are unknown. Our aim was to test whether accumulation of 64Cu into cancer-derived cells can be influenced by copper-binding serum amino acids. In vitro cellular accumulation of 64Cu was measured in Hank's Balanced Salt Solution in the presence of 100 μM l-histidine, l-methionine, l-cysteine and l-threonine. l-Cysteine markedly increased 64Cu accumulation and retention in DU145, PC3 and SK-OV-3 cells, while some other cell lines did not show an effect. This effect was not due to 64Cu delivery in the form of a 64Cu-cysteine complex, nor to reduction of 64Cu(ii) to 64Cu(i) by l-cysteine. Pre-incubation of cells with l-cysteine increased 64Cu accumulation, even if l-cysteine was removed from HBSS before 64Cu was added. The effect of l-cysteine on 64Cu accumulation was not mediated by increased glutathione synthesis. Despite the demonstrable in vitro effect, pre-injection of l-cysteine precursor N-acetyl-cysteine (NAC) in vivo did not enhance 64Cu delivery to DU145 xenografts in mice. Instead, it decreased 64Cu accumulation in the DU145 tumour and in brain, as assessed by PET imaging. We conclude that 64Cu is not delivered to DU145 cancer cells in vitro as a complex with amino acids but its cellular accumulation is enhanced by l-cysteine or NAC influx to cells. The latter effect was not demonstrable in vivo in the DU145 xenograft.

Reactor produced [64Cu]CuCl2 as a PET radiopharmaceutical for cancer imaging: from radiochemistry laboratory to nuclear medicine clinic

OBJECTIVE

Copper-64 is a useful theranostic radioisotope that is attracting renewed interest from the nuclear medicine community in the recent times. This study aims to demonstrate the utility of research reactors to produce clinical-grade ⁶⁴Cu via ⁶³Cu(n,γ)⁶⁴Cu reaction and use it in the form of [⁶⁴Cu]CuCl₂ as a radiopharmaceutical for PET imaging of cancer in human patients.

METHODS

Copper-64 was produced by irradiation of natural CuO target in a medium flux research reactor. The irradiated target was radiochemically processed and detailed quality control analyses were carried out. Sub-acute toxicity studies were carried out with different doses of Cu in Wistar rats. The biological efficacy of the radiopharmaceutical was established in preclinical setting by biodistribution studies in melanoma tumor bearing mice. After getting regulatory approvals, [⁶⁴Cu]CuCl₂ formulation was clinically used for PET imaging of prostate cancer and glioblastoma patients.

RESULTS

Large-scale (~ 30 GBq) production of ⁶⁴Cu could be achieved in a typical batch and it was adequate for formulation of clinical doses for multiple patients. The radiopharmaceutical met all the purity requirements for administration in human subjects. Studies carried out in animal model showed that the toxicity due to "cold" Cu in clinical dose of [⁶⁴Cu]CuCl₂ for PET scans would be negligible. Clinical PET scans showed satisfactory uptake of the radiopharmaceutical in the primary cancer and its metastatic sites.

CONCLUSIONS

To the best of our knowledge, this is the first study on use of reactor produced [⁶⁴Cu]CuCl₂ for PET imaging of cancer in human patients. It is envisaged that this route of production of ⁶⁴Cu would aid towards affordable availability of this radioisotope for widespread clinical use in countries with limited cyclotron facilities.

The emerging value of 64Cu for molecular imaging and therapy

Along with other novel metallic radionuclides, copper-64 (⁶⁴Cu) is currently being investigated as an alternative option to the gallium-68 (⁶⁸Ga) and lutetium-177 (¹⁷⁷Lu) radiopharmaceuticals widely used for targeting somatostatin receptors, expressed by neuroendocrine tumors (NETs), and recently prostate specific membrane antigen (PSMA), expressed by prostate cancer cells. This interest is mostly driven by the peculiar nuclear properties of ⁶⁴Cu that make it an almost ideal example of theranostic radionuclide. In fact, ⁶⁴Cu emits both low-energy positrons, β^- particles and a swarm of Auger electrons. This combination of different emissions may allow to collect high-resolution PET images, but also to use the same radiopharmaceutical for eliciting a therapeutic effect. Another unique behavior of ⁶⁴Cu originates from the fundamental biological role played in organisms by the ionic forms of the copper element, which is naturally involved in a multitude of cellular processes including cell replication. These intrinsic biological characteristics has led to the discovery that ⁶⁴Cu, under its simplest dicationic form Cu²⁺, is able to specifically target a variety of cancerous cells and to detect the onset of a metastatic process in its initial stage. This short review reports an outline of the status of ⁶⁴Cu radiopharmaceuticals and of the most relevant results that are constantly disclosed by preclinical and investigational clinical studies.

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.

Intravenous and oral copper kinetics, biodistribution and dosimetry in healthy humans studied by [64Cu]copper PET/CT

Purpose

Copper is essential for enzymatic processes throughout the body. [⁶⁴Cu]copper (⁶⁴Cu) positron emission tomography (PET) has been investigated as a diagnostic tool for certain malignancies, but has not yet been used to study copper homeostasis in humans. In this study, we determined the hepatic removal kinetics, biodistribution and radiation dosimetry of ⁶⁴Cu in healthy humans by both intravenous and oral administration.

Methods

Six healthy participants underwent PET/CT studies with intravenous or oral administration of ⁶⁴Cu. A 90 min dynamic PET/CT scan of the liver was followed by three whole-body PET/CT scans at 1.5, 6, and 20 h after tracer administration. PET data were used for estimation of hepatic kinetics, biodistribution, effective doses, and absorbed doses for critical organs.

Results

After intravenous administration, ⁶⁴Cu uptake was highest in the liver, intestinal walls and pancreas; the gender-averaged effective dose was 62 ± 5 μSv/MBq (mean ± SD). After oral administration, ⁶⁴Cu was almost exclusively taken up by the liver while leaving a significant amount of radiotracer in the gastrointestinal lumen, resulting in an effective dose of 113 ± 1 μSv/MBq. Excretion of ⁶⁴Cu in urine and faeces after intravenous administration was negligible. Hepatic removal kinetics showed that the clearance of ⁶⁴Cu from blood was 0.10 ± 0.02 mL blood/min/mL liver tissue, and the rate constant for excretion into bile or blood was 0.003 ± 0.002 min^− 1.

Conclusion

⁶⁴Cu biodistribution and radiation dosimetry are influenced by the manner of tracer administration with high uptake by the liver, intestinal walls, and pancreas after intravenous administration, while after oral administration, ⁶⁴Cu is rapidly absorbed from the gastrointestinal tract and deposited primarily in the liver. Administration of 50 MBq ⁶⁴Cu yielded images of high quality for both administration forms with radiation doses of approximately 3.1 and 5.7 mSv, respectively, allowing for sequential studies in humans.

Trial registration number

EudraCT no. 2016–001975-59. Registration date: 19/09/2016.

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.

Dithiocarbamate prodrugs activated by prostate specific antigen to target prostate cancer

Disulfiram in conjunction with copper has been shown to be a potent anticancer agent. However, disulfiram's therapeutic potential in prostate cancer is hindered by off-target effects due to its reactive and nucleophilic thiol-containing component, diethyldithiocarbamate (DTC). To minimize undesirable reactivity, we have strategically blocked the thiol moiety in DTC with a cleavable p-aminobenzyl (pAB) group linked to peptide substrates recognized by prostate specific antigen (PSA). Here we report the synthesis and evaluation in cancer cell models of two PSA-activatable prodrugs: HPD (Ac-HSSKLQL-pAB-DTC and RPD (RSSYYSL-pAB-DTC). In vitro exposure to PSA was found to trigger activation of HPD and RPD to release diethyldithiocarbamate, and both prodrugs were found to induce toxicity in prostate cancer cells, with HPD showing the most promising selectivity. With copper supplementation, the IC₅₀ of HPD was 1.4 µM in PSA-expressing LNCaP cells, and 11 µM in PC3 cells that do not express PSA. These studies demonstrate the utility of using peptide recognition handles to direct the activity of dithiocarbamate prodrugs for selective cytotoxicity of cancer cells.

64CuCl2 PET/CT as a potential new imaging method in prostate cancer: illusion or reality?

Copper (Cu) is an essential element for many cellular functions, including proliferation and angiogenesis. High serum Cu levels have been demonstrated in patients with neoplasia as well as high intra-tumoral Cu levels have been reported. Preclinical and clinical evidences suggest its use, in the form of ⁶⁴Copper chloride (⁶⁴CuCl<inf>2</inf>), as metabolic PET tracer in cancer diagnosis and therapy. Specifically, the use of ⁶⁴CuCl<inf>2</inf> in human prostate cancer (PCa) evidenced a high uptake of ⁶⁴CuCl<inf>2</inf> in tumoral prostate and involved regional lymph nodes in a staging setting and high sensitivity for local recurrence and lymph nodes detection in restaging, indicating its great potential. However, further and more solid clinical evidences are needed. On the other hand, ⁶⁴CuCl<inf>2</inf> seems to be a promising radiometabolic drug with great cytotoxic abilities on PCa cells. We have collected the most recent and relevant findings on its potential uses and limitations for the study and treatment of PCa, together with its possible translation in daily clinical practice.

Development of Novel PSMA Ligands for Imaging and Therapy with Copper Isotopes

Prostate-specific membrane antigen (PSMA)-binding tracers have been shown to be promising agents for the specific targeting of prostate tumors. On labeling with the short-lived isotopes ¹⁸F and ⁶⁸Ga, excellent molecular imaging performance is achieved. This potential could be further exploited using long-lived isotopes. Because of the favorable half-life of ⁶⁴Cu, tracers labeled with this PET nuclide could solve logistic problems. Moreover, this isotope provides a theranostic pair with the therapeutic copper isotope ⁶⁷Cu. Hence, 9 novel tracers that combine dedicated copper chelators with the PSMA-specific urea-based binding motif were developed. Methods: The precursors were obtained by solid-phase synthesis. The purity and molecular weight of the PSMA ligands were confirmed by high-performance liquid chromatography and liquid chromatography-mass spectrometry. The compounds were labeled with ⁶⁴Cu, with a radiolabeling yield of more than 99%. Competitive cell binding assays and internalization assays were performed with C4-2 cells, a subline of the PSMA-positive cell line LNCaP (human lymph node carcinoma of the prostate). In vitro serum stability, the stability of ⁶⁴Cu-CA003 in blood, and the in vivo fate of neat ⁶⁴Cu-chloride or ⁶⁴Cu-CA003 were determined to prove whether the stability of the radiolabeled compounds is sufficient to ensure no significant loss of copper during the targeting process. For PET imaging and biodistribution studies, a C4-2 tumor-bearing mouse model was used. Results: The radiolabeled ⁶⁴Cu-PSMA ligands showed high serum stability. All PSMA ligands showed high inhibition potencies, with equilibrium inhibition constants in the low nanomolar range. ⁶⁴Cu-CA003 and ⁶⁴Cu-CA005 showed high internalization ratios (34.6% ± 2.8 and 18.6% ± 4.4, respectively). Both the in vitro serum stability determination and the in vivo characterization of the main radiolabeled compounds confirmed that, except for ⁶⁴Cu-PSMA-617, all compounds showed high serum stability within the observation period of 24 h. Small-animal PET imaging demonstrated high tumor uptake within 20 min. Organ distribution studies confirmed high specific uptake in the tumor, with 30.8 ± 12.6 percentage injected dose (%ID)/g at 1 h after injection. Rapid clearance from the kidneys was observed-a decrease from 67.0 ± 20.9 %ID/g at 1 h after injection to 7.5 ± 8.51 %ID/g at 24 h after injection (in the case of CA003). The performance of CA003, the compound with the best preclinical properties, was assessed in a first patient. In line with its preclinical data, PET imaging resulted in clear visualization of the cancer lesions, with high contrast. Conclusion: The ⁶⁴Cu-labeled PSMA ligands are promising agents to target PSMA and visualize PSMA-positive tumor lesions as shown in preclinical evaluation by small-animal PET studies, organ distribution, and a patient application. Most importantly, the images obtained at 20 h enabled delineation of unclear lesions, showing that the compounds fulfill the prerequisite for dosimetry in the course of therapy planning with ⁶⁷Cu. Thus, we suggest clinical use of copper-labeled CA003 for diagnostics and radiotherapy of prostate cancer.

Dual-time-point 64 Cu-PSMA-617-PET/CT in patients suffering from prostate cancer

Regardless of its high positron energy, ⁶⁸ Ga-labeled PSMA ligands have become standard of care in metabolic prostate cancer imaging. ⁶⁴ Cu, a radionuclide with a much longer half-life (12.7 h), is available for PSMA labeling allowing imaging much later than ⁶⁸ Ga. In this study, the diagnostic performance of ⁶⁴ Cu-labeled PSMA was compared between early and late scans. Sixteen men (median age: 70 y) with prostate cancer in different stages underwent ⁶⁴ Cu-PSMA-617-PET/CT 2 and 22 hours post tracer injection. Pathologic and physiologic uptakes were analyzed for both points of time. Pathologic tracer accumulations occurred in 12 patients. Five patients presented with pathologic uptake in 17 different lymph nodes, two patients showed pathologic bone uptake in nine lesions, and seven patients had pathologic PSMA uptake in eight prostatic lesions. Physiologic uptake of the renal parenchyma, urine bladder, and salivary glands decreased over time, while the physiologic uptake of liver and bowel increased. In the present study, ⁶⁴ Cu-PSMA-617-PET demonstrated to be feasible for imaging prostate cancer for both the primary tumor site and metastases. Later imaging showed no additional, clinically relevant benefit compared with the early scans. At least the investigated time points we chose did not vindicate the additional expenditure.

64Cu-based Radiopharmaceuticals in Molecular Imaging

Copper-64 (T_1/2 = 12.7 hours; β⁺: 19%, β^-: 38%) has a unique decay profile and can be used for positron emission tomography imaging and radionuclide therapy. The well-established coordination chemistry of copper allows for its reaction with different types of chelator systems. It can be linked to antibodies, proteins, peptides, and other biologically relevant small molecules. Two potential ways to produce copper-64 radioisotopes concern the use of the cyclotron or the reactor. This review summarized several commonly used biomarkers of copper-64 radionuclide.

Nuclear imaging of liposomal drug delivery systems: A critical review of radiolabelling methods and applications in nanomedicine

The integration of nuclear imaging with nanomedicine is a powerful tool for efficient development and clinical translation of liposomal drug delivery systems. Furthermore, it may allow highly efficient imaging-guided personalised treatments. In this article, we critically review methods available for radiolabelling liposomes. We discuss the influence that the radiolabelling methods can have on their biodistribution and highlight the often-overlooked possibility of misinterpretation of results due to decomposition in vivo. We stress the need for knowing the biodistribution/pharmacokinetics of both the radiolabelled liposomal components and free radionuclides in order to confidently evaluate the images, as they often share excretion pathways with intact liposomes (e.g. phospholipids, metallic radionuclides) and even show significant tumour uptake by themselves (e.g. some radionuclides). Finally, we describe preclinical and clinical studies using radiolabelled liposomes and discuss their impact in supporting liposomal drug development and clinical translation in several diseases, including personalised nanomedicine approaches.

Radiobiological Characterization of 64CuCl₂ as a Simple Tool for Prostate Cancer Theranostics

⁶⁴CuCl₂ has recently been proposed as a promising agent for prostate cancer (PCa) theranostics, based on preclinical studies in cellular and animal models, and on the increasing number of human studies documenting its use for PCa diagnosis. Nevertheless, the use of ⁶⁴CuCl₂ raises important radiobiological questions that have yet to be addressed. In this work, using a panel of PCa cell lines in comparison with a non-tumoral prostate cell line, we combined cytogenetic approaches with radiocytotoxicity assays to obtain significant insights into the cellular consequences of exposure to ⁶⁴CuCl₂. PCa cells were found to exhibit increased ⁶⁴CuCl₂ uptake, which could not be attributed to increased expression of the main copper cellular importer, hCtr1, as had been previously suggested. Early DNA damage and genomic instability were also higher in PCa cells, with the tumoral cell lines exhibiting deficient DNA-damage repair upon exposure to ⁶⁴CuCl₂. This was corroborated by the observation that ⁶⁴CuCl₂ was more cytotoxic in PCa cells than in non-tumoral cells. Overall, we showed for the first time that PCa cells had a higher sensitivity to ⁶⁴CuCl₂ than healthy cells, supporting the idea that this compound deserved to be further evaluated as a theranostic agent in PCa.

Leveraging γ-Glutamyl Transferase To Direct Cytotoxicity of Copper Dithiocarbamates against Prostate Cancer Cells

A prodrug approach is presented to direct copper-dependent cytotoxicity to prostate cancer cells. The prochelator GGTDTC requires activation by γ-glutamyl transferase (GGT) to release the metal chelator diethyldithiocarbamate from a linker that masks its thiol reactivity and metal binding properties. In vitro studies demonstrated successful masking of copper binding as well as clean liberation of the chelator by GGT. GGTDTC was stable to non-specific degradation when incubated with a series of prostate cancer and normal cell lines, with selective release of diethyldithiocarbamate only occurring in cells with measurable GGT activity. The antiproliferative efficacy of the prochelator correlated with cellular GGT activity, with 24 h inhibitory concentrations ranging from 800 nm in prostate cancer lines 22Rv1 and LNCaP to over 15 μm in normal prostate PWR-1E cells. These findings underscore a new strategy to leverage the amplified copper metabolism of prostate cancer by conditional activation of a metal-binding pharmacophore.

Insights into Trace Metal Metabolism in Health and Disease from PET: "PET Metallomics"

Essential trace metals such as copper, zinc, iron, and manganese perform critical functions in cellular and physiologic processes including catalytic, regulatory, and signaling roles. Disturbed metal homeostasis is associated with the pathogenesis of diseases such as dementia, cancer, and inherited metabolic abnormalities. Intracellular pathways involving essential metals have been extensively studied but whole-body fluxes and transport between different compartments remain poorly understood. The growing availability of PET scanners and positron-emitting isotopes of key essential metals, particularly 64Cu, 63Zn, and 52Mn, provide new tools with which to study these processes in vivo. This review highlights opportunities that now present themselves, exemplified by studies of copper metabolism that are in the vanguard of a new research front in molecular imaging: "PET metallomics."