(64)Cu-NODAGA-c(RGDyK) Is a Promising New Angiogenesis PET Tracer: Correlation between Tumor Uptake and Integrin α(V)β(3) Expression in Human Neuroendocrine Tumor Xenografts

Dosimetry of [64Cu]FBP8: a fibrin-binding PET probe

Purpose

This study presents the biodistribution, clearance and dosimetry estimates of [64Cu]Fibrin Binding Probe #8 ([64Cu]FBP8) in healthy subjects.

Procedures

This prospective study included 8 healthy subjects to evaluate biodistribution, safety and dosimetry estimates of [64Cu]FBP8, a fibrin-binding positron emission tomography (PET) probe. All subjects underwent up to 3 sessions of PET/Magnetic Resonance Imaging (PET/MRI) 0-2 hours, 4h and 24h post injection. Dosimetry estimates were obtained using OLINDA 2.2 software.

Results

Subjects were injected with ~400 MBq of [64Cu]FBP8. Subjects did not experience adverse effects due to the injection of the probe. [64Cu]FBP8 PET images demonstrated fast blood clearance (half-life = 67 min) and renal excretion of the probe, showing low background signal across the body. The organs with the higher doses were: the urinary bladder (0.075 vs. 0.091 mGy/MBq for males and females, respectively); the kidneys (0.050 vs. 0.056 mGy/MBq respectively); and the liver (0.027 vs. 0.035 mGy/MBq respectively). The combined mean effective dose for males and females was 0.016 ± 0.0029 mSv/MBq, lower than the widely used [18F]fluorodeoxyglucose ([18F]FDG, 0.020mSv/MBq).

Conclusions

This study demonstrates the following properties of the [64Cu]FBP8 probe: low dosimetry estimates; fast blood clearance and renal excretion; low background signal; and whole-body acquisition within 20 minutes in a single session. These properties provide the basis for [64Cu]FBP8 to be an excellent candidate for whole-body non-invasive imaging of fibrin, an important driver/feature in many cardiovascular, oncological and neurological conditions.

Copper-containing chitosan-based hydrogels enabled 3D-printed scaffolds to accelerate bone repair and eliminate MRSA-related infection

Bone defect combined with drug-resistant bacteria-related infection is a thorny challenge in clinic. Herein, 3D-printed polyhydroxyalkanoates/β-tricalcium phosphate (PHA/β-TCP, PT) scaffolds were prepared by fused deposition modeling. Then copper-containing carboxymethyl chitosan/alginate (CA/Cu) hydrogels were integrated with the scaffolds via a facile and low-cost chemical crosslinking method. The resultant PT/CA/Cu scaffolds could not only promote proliferation but also osteogenic differentiation of preosteoblasts in vitro. Moreover, PT/CA/Cu scaffolds exhibited a strong antibacterial activity towards a broad-spectrum of bacteria including methicillin-resistant Staphylococcus aureus (MRSA) through inducing the intercellular generation of reactive oxygen species. In vivo experiments further demonstrated that PT/CA/Cu scaffolds significantly accelerated bone repair of cranial defects and efficiently eliminated MRSA-related infection, showing potential for application in infected bone defect therapy.

First-in-Human Study of [68Ga]Ga-NODAGA-E[c(RGDyK)]2 PET for Integrin αvβ3 Imaging in Patients with Breast Cancer and Neuroendocrine Neoplasms: Safety, Dosimetry and Tumor Imaging Ability

Arginine-Glycine-Aspartate (RGD)-recognizing cell surface integrins are involved in tumor growth, invasiveness/metastases, and angiogenesis, and are therefore an attractive treatment target in cancers. The subtype integrin α_vβ₃ is upregulated on endothelial cells during angiogenesis and on tumor cells. In vivo assessment of integrin α_vβ₃ is possible with positron emission tomography (PET). Preclinical data on radiochemical properties, tumor uptake and radiation exposure identified [⁶⁸Ga]Ga-NODAGA-E[c(RGDyK)]₂ as a promising candidate for clinical translation. In this first-in-human phase I study, we evaluate [⁶⁸Ga]Ga-NODAGA-E[c(RGDyK)]₂ PET in patients with neuroendocrine neoplasms (NEN) and breast cancer (BC). The aim was to investigate safety, biodistribution and dosimetry as well as tracer uptake in tumor lesions. A total of 10 patients (5 breast cancer, 5 neuroendocrine neoplasm) received a single intravenous dose of approximately 200 MBq [⁶⁸Ga]Ga-NODAGA-E[c(RGDyK)]₂. Biodistribution profile and dosimetry were assessed by whole-body PET/CT performed at 10 min, 1 h and 2 h after injection. Safety assessment with vital parameters, electrocardiograms and blood tests were performed before and after injection. In vivo stability of [⁶⁸Ga]Ga-NODAGA-E[c(RGDyK)]₂ was determined by analysis of blood and urine. PET images were analyzed for tracer uptake in tumors and background organs. No adverse events or pharmacologic effects were observed in the 10 patients. [⁶⁸Ga]Ga-NODAGA-E[c(RGDyK)]₂ exhibited good in vivo stability and fast clearance, primarily by renal excretion. The effective dose was 0.022 mSv/MBq, equaling a radiation exposure of 4.4 mSv at an injected activity of 200 MBq. The tracer demonstrated stable tumor retention and good image contrast. In conclusion, this first-in-human phase I trial demonstrated safe use of [⁶⁸Ga]Ga-NODAGA-E[c(RGDyK)]₂ for integrin α_vβ₃ imaging in cancer patients, low radiation exposure and favorable uptake in tumors. Further studies are warranted to establish whether [⁶⁸Ga]Ga-NODAGA-E[c(RGDyK)]₂ may become a tool for early identification of patients eligible for treatments targeting integrin α_vβ₃ and for risk stratification of patients.

[68Ga]Ga-NODAGA-E[(cRGDyK)]2 Angiogenesis PET/MR in a Porcine Model of Chronic Myocardial Infarction

Angiogenesis is crucial in tissue repair and prevents scar tissue formation following an ischemic event such as myocardial infarction. The ischemia induces formation of new capillaries, which have high expression of integrin α_vβ₃. [⁶⁸Ga]Ga-NODAGA-E[(cRGDyK)]₂ ([⁶⁸Ga]Ga-RGD) is a promising PET-radiotracer reflecting angiogenesis by binding to integrin α_vβ₃. A Göttingen mini-pig underwent transient catheter-induced left anterior descending artery (LAD) occlusion for 120 min, and after 8 weeks was imaged on a Siemens mMR 3T PET/MR system. A large antero-septal infarction was evident by late gadolinium enhancement (LGE) on the short axis and 2–4 chamber views. The infarcted area corresponded to the area with high [⁶⁸Ga]Ga-RGD uptake on the fused PET/MR images, with no uptake in the healthy myocardium. To support the hypothesis that [⁶⁸Ga]Ga-RGD uptake reflects angiogenesis, biopsies were sampled from the infarct border and healthy myocardium. Expression of α_vβ₃ was evaluated using immunohistochemistry. The staining showed higher α_vβ₃ expression in the capillaries of the infarct border compared to those in the healthy myocardium. These initial data confirm in vivo detection of angiogenesis using [⁶⁸Ga]Ga-RGD PET in a translational model, which overall support the method applicability when evaluating novel cardio-protective therapies.

[68Ga]Ga-DFO-c(RGDyK): Synthesis and Evaluation of Its Potential for Tumor Imaging in Mice

Angiogenesis has a pivotal role in tumor growth and the metastatic process. Molecular imaging was shown to be useful for imaging of tumor-induced angiogenesis. A great variety of radiolabeled peptides have been developed to target αvβ3 integrin, a target structure involved in the tumor-induced angiogenic process. The presented study aimed to synthesize deferoxamine (DFO)-based c(RGD) peptide conjugate for radiolabeling with gallium-68 and perform its basic preclinical characterization including testing of its tumor-imaging potential. DFO-c(RGDyK) was labeled with gallium-68 with high radiochemical purity. In vitro characterization including stability, partition coefficient, protein binding determination, tumor cell uptake assays, and ex vivo biodistribution as well as PET/CT imaging was performed. [⁶⁸Ga]Ga-DFO-c(RGDyK) showed hydrophilic properties, high stability in PBS and human serum, and specific uptake in U-87 MG and M21 tumor cell lines in vitro and in vivo. We have shown here that [⁶⁸Ga]Ga-DFO-c(RGDyK) can be used for αvβ3 integrin targeting, allowing imaging of tumor-induced angiogenesis by positron emission tomography.

Copper-based biomaterials for bone and cartilage tissue engineering

Backgroud

Tissue engineering using cells, scaffolds, and bioactive molecules can promote the repair and regeneration of injured tissues. Copper is an essential element for the human body that is involved in many physiological activities and in recent years, copper has been used increasingly in tissue engineering.

Methods

The current advances of copper-based biomaterial for bone and cartilage tissue engineering were searched on PubMed and Web of Science.

Results

Various forms of copper-based biomaterials, including pure copper, copper ions, copper nanoparticles, copper oxides, and copper alloy are introduced. The incorporation of copper into base materials provides unique properties, resulting in tuneable porosity, mechanical strength, degradation, and crosslinking of scaffolds. Copper also shows promising biological performance in cell migration, cell adhesion, osteogenesis, chondrogenesis, angiogenesis, and antibacterial activities. In vivo applications of copper for bone and cartilage tissue engineering are discussed.

Conclusion

This review focuses on copper’s physiochemical and biological effects, and its applications in bone and cartilage tissue engineering. The potential limitations and future perspectives are also discussed.

Translational potential of this article

This review introduces the recent advances in copper-based biomaterial for bone and cartilage tissue engineering. This revie could guide researchers to apply copper in biomaterials, improving the generation of bone and cartilages, decrease the possibility of infection and shorten the recovery time so as to decrease medical costs.

Development of a ghrelin receptor inverse agonist for positron emission tomography

Imaging of Ghrelin receptors in vivo provides unique potential to gain deeper understanding on Ghrelin and its receptors in health and disease, in particular, in cancer. Ghrelin, an octanoylated 28-mer peptide hormone activates the constitutively active growth hormone secretagogue receptor type 1a (GHS-R1a) with nanomolar activity. We developed novel compounds, derived from the potent inverse agonist K-(D-1-Nal)-FwLL-NH₂ but structurally varied by lysine conjugation with 1,4,7-triazacyclononane,1-glutaric acid-4,7-acetic acid (NODAGA), palmitic acid and/or diethylene glycol (PEG2) to allow radiolabeling and improve pharmacokinetics, respectively. All compounds were tested for receptor binding, potency and efficacy in vitro, for biodistribution and -kinetics in rats and in preclinical prostate cancer models on mice. Radiolabeling with Cu-64 and Ga-68 was successfully achieved. The Cu-64- or Ga-68-NODAGA-NH-K-K-(D-1-NaI)-F-w-L-L-NH₂ radiotracer were specifically accumulated by the GHS-R1a in xenotransplanted human prostate tumor models (PC-3, DU-145) in mice. The tumors were clearly delineated by PET. The radiotracer uptake was also partially blocked by K-(D-1-Nal)-FwLL-NH₂ in stomach and thyroid. The presence of the GHS-R1a was also confirmed by immunohistology. In the arterial rat blood plasma, only the original compounds were found. The Cu-64 or Ga-68-NODAGA-NH-K-K-(D-1-NaI)-F-w-L-L-NH₂ radiolabeled inverse agonists turned out to be potent and safe. Due to their easy synthesis, high affinity, medium potency, metabolic stability, and the suitable pharmacokinetic profiles, they are excellent tools for imaging and quantitation of GHS-R1a expression in normal and cancer tissues by PET. These compounds can be used as novel biomarkers of the Ghrelin system in precision medicine.

[68Ga]Ga-NODAGA-E[(cRGDyK)]2 PET and hyperpolarized [1-13C] pyruvate MRSI (hyperPET) in canine cancer patients: simultaneous imaging of angiogenesis and the Warburg effect

PURPOSE

Cancer has a multitude of phenotypic expressions and identifying these are important for correct diagnosis and treatment selection. Clinical molecular imaging such as positron emission tomography can access several of these hallmarks of cancer non-invasively. Recently, hyperpolarized magnetic resonance spectroscopy with [1-13C] pyruvate has shown great potential to probe metabolic pathways. Here, we investigate simultaneous dual modality clinical molecular imaging of angiogenesis and deregulated energy metabolism in canine cancer patients.

METHODS

Canine cancer patients (n = 11) underwent simultaneous [68Ga]Ga-NODAGA-E[(cRGDyK)]2 (RGD) PET and hyperpolarized [1-13C]pyruvate-MRSI (hyperPET). Standardized uptake values and [1-13C]lactate to total 13C ratio were quantified and compared generally and voxel-wise.

RESULTS

Ten out of 11 patients showed clear tumor uptake of [68Ga]Ga-NODAGA-RGD at both 20 and 60 min after injection, with an average SUVmean of 1.36 ± 0.23 g/mL and 1.13 ± 0.21 g/mL, respectively. A similar pattern was seen for SUVmax values, which were 2.74 ± 0.41 g/mL and 2.37 ± 0.45 g/mL. The [1-13C]lactate generation followed patterns previously reported. We found no obvious pattern or consistent correlation between the two modalities. Voxel-wise tumor values of RGD uptake and lactate generation analysis revealed a tendency for each canine cancer patient to cluster in separated groups.

CONCLUSION

We demonstrated combined imaging of [68Ga]Ga-NODAGA-RGD-PET for angiogenesis and hyperpolarized [1-13C]pyruvate-MRSI for probing energy metabolism. The results suggest that [68Ga]Ga-NODAGA-RGD-PET and [1-13C]pyruvate-MRSI may provide complementary information, indicating that hyperPET imaging of angiogenesis and energy metabolism is able to aid in cancer phenotyping, leading to improved therapy planning.

The Distribution Volume of 18F-Albumin as a Potential Biomarker of Antiangiogenic Treatment Efficacy

Objective: 18F-albumin, a vascular imaging agent, may have potential to assess tumor responses to anti-angiogenic therapies. In these studies tumor distribution volume of 18F-albumin were first determined in various human tumor xenografts from biodistribtuion measurments and then one of the tumor type was used to evaluate changes in 18F-albumin uptake in anti-angiognic tumor model. Method: 18F-albumin was synthesized via conjugation of 6-[18F]fluoronicotinic acid-2,3,5,6-tetrafluorophenyl ester, [18F]F-Py-TFP, with rat albumin. From the biodistribution of 18F-albumin in various human tumor xenografts tumor distribution volumes (DVs; tumor%ID/g:blood%ID/g) were first determined at various time points. Then, the ability of 18F-albumin to detect tumor angiogenic inhibition in one of these tumor types (U87MG) following treatment with sunitinib was evaluated by position emission tomography (PET) imaging at 0, 7, 14, and 21 days post treatment. Caliper measurements of tumor dimensions were also made at these same times. At Day 21, following imaging, biodistributions, autoradiography of tumor tissues and tumor blood vessel counts (CD31 IHC) were performed. Results: 18F-albumin retention in various tumors steadily increased over time with U87MG tumor exhibiting the highest uptake (DV) at all times. Significant decreases in 18F-albumin DVs were observed one week post-treatement (-39%) vs. controls whereas tumor caliper volumes were not significantly decreased until days 14 and 21. At day 21 the significant decrease in DVs in the treatment group (-44%) paralleled biodistribution DV measurements and was consistent with autoradiography and CD31 IHC findings. Conclusion: These data suggest that 18F-albumin DVs obtained by imaging may serve as an early biomarker of the effectiveness of anti-angiogenic therapy and thus aid in patient management and treatment planning.

Innovative Magnetic Nanoparticles for PET/MRI Bimodal Imaging

Superparamagnetic iron oxide nanoparticles were developed as positron emission tomography (PET) and magnetic resonance imaging (MRI) bimodal imaging agents. These nanoparticles (NPs), with a specific nanoflower morphology, were first synthesized and simultaneously functionalized with 3,4-dihydroxy-l-phenylalanine (LDOPA) under continuous hydrothermal conditions. The resulting NPs exhibited a low hydrodynamic size of 90 ± 2 nm. The functional groups of LDOPA (-NH₂ and -COOH) were successfully used for the grafting of molecules of interest in a second step. The nanostructures were modified by poly(ethylene glycol) (PEG) and a new macrocyclic chelator MANOTA for further ⁶⁴Cu radiolabeling for PET imaging. The functionalized NPs showed promising bimodal (PET and MRI) imaging capability with high r ₂ and r ₂* (T ₂ and T ₂* relaxivities) values and good stability. They were mainly uptaken from liver and kidneys. No cytotoxicity effect was observed. These NPs appear as a good candidate for bimodal tracers in PET/MRI.

Molecular imaging in neuroendocrine tumors: recent advances, controversies, unresolved issues, and roles in management

PURPOSE OF REVIEW

The purpose is to review recent advances in molecular imaging of neuroendocrine tumors (NETs), discuss unresolved issues, and review how these advances are affecting clinical management.

RECENT FINDINGS

Molecular imaging of NETs underwent a number of important changes in the last few years, leading to some controversies, unresolved issues, and significant changes in clinical management. The most recent changes are reviewed in this article. Particularly important is the rapid replacement in somatostatin receptor scintigraphy of In-diethylenetriamine penta-acetic acid-single-photon emission computed tomography/computed tomography (CT) by Ga-fluorodopa(F-D)PA), 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-peptide-PET/CT imaging, which is now approved in many countries including the USA. Numerous studies in many different types of NETs demonstrate the greater sensitivity of Ga-DOTA-peptide PET/CT, its high specificity, and its impact on management. Other important developments in somatostatin receptor scintigraphy/molecular imaging include demonstrating the prognostic value of both Ga-DOTA-peptide PET/CT and F-fluoro-deoxyglucose PET/CT; how their use can be complementary; comparing the sensitivities and usefulness of Ga-DOTA-peptide PET/CT and F-FDOPA PET/CT; introducing new linkers and radiolabeled ligands such as Cu-DOTA-peptides with a long half-life, enhancing utility; and the introduction of somatostatin receptor antagonists which show enhanced uptake by NETs. In addition, novel ligands which interact with other receptors (GLP-1, bombesin, cholecystokinin, gastric inhibitory polpeptide, integrin, chemokines) are described, which show promise in the imaging of both NETs and other tumors.

SUMMARY

Molecular imaging is now required for all aspects of the management of patients with NETs. Its results are essential not only for the proper diagnostic management of the patient, but also for assessing whether the patient is a candidate for peptide receptor radionuclide therapy with Lu and also for providing prognostic value.

MANOTA: a promising bifunctional chelating agent for copper-64 immunoPET

A comparison of four bifunctional chelating agents showed superior behaviour of a new NOTA derivative for ⁶⁴Cu labelling of antibody fragments.

68Ga 'vacuum elution approach' for direct radiolabelling of DOTA-conjugated and NODAGA-conjugated peptides

BACKGROUND/OBJECTIVES

The Ge/Ga generator is of increasing interest for clinical PET. The arrival on the market of the pharmaceutical-grade generator, which provides an eluate with chemical and radiochemical purities in conformity with the European Pharmacopeia specifications, makes the direct labelling of vectors possible. The kit formulation strategies using single vial productions can improve the access of hospitals and imaging centres that are not equipped with costly automated synthesis modules to the Ga-radiopharmaceutical production. The manual radiosynthesis of Ga requires handling of a relatively high amount of radioactivity, resulting in a high radiation dose to the hand. Moreover, the elution of the Ga/Ge generator with 5 ml of HCl as recommended by the manufacturer leads to a low Ga concentration, which can decrease the efficiency of the labelling procedure. The aim of our approach is to circumvent these disadvantages and to offer an alternative to the hand elution and labelling for a routine production of Ga-radiopharmaceuticals.

METHODS

A mixture of buffer and peptide was first transferred to an evacuated collection vial. Fixed volume of HCl was adapted to the inlet line of the generator. The elution was then performed by the action of vacuum and the labeling occurs at RT or 95°C.

RESULTS AND CONCLUSION

The 'vacuum elution approach' developed in this work enables the elution of 95% of the available generator activity with 2.5 ml of eluent, the direct labelling of DOTA-conjugated and NODAGA-conjugated peptides with high radiochemical (>97% for all cases) and radionuclidic (100%) purities without exposure of the hand to radiation during the preparation steps.

(68)Ga-DOTATOC PET and gene expression profile in patients with neuroendocrine carcinomas: strong correlation between PET tracer uptake and gene expression of somatostatin receptor subtype 2

Somatostatin receptor expression on both protein and gene expression level was compared with in vivo (68)Ga-DOTATOC PET/CT in patients with neuroendocrine carcinomas (NEC). Twenty-one patients with verified NEC who underwent a (68)Ga-DOTATOC PET/CT between November 2012 and May 2014, were retrospectively included. By real-time polymerase chain reaction, we quantitatively determined the gene expression of several genes and compared with (68)Ga-DOTATOC PET uptake. By immunohistochemistry we qualitatively studied the expression of assorted proteins in NEC. The median age at diagnosis was 68 years (range 41-84) years. All patients had WHO performance status 0-1. Median Ki67 index was 50% (range 20-100%). Gene expression of somatostatin receptor subtype (SSTR) 2 and Ki67 were both positively correlated to the (68)Ga-DOTATOC uptake (r=0.89; p<0.0001 and r=0.5; p=0.021, respectively). Furthermore, SSTR2 and SSTR5 gene expression were strongly and positively correlated (r=0.57; p=0.006). This study as the first verifies a positive and close correlation of (68)Ga-DOTATOC uptake and gene expression of SSTR2 in NEC. SSTR2 gene expression has a stronger correlation to (68)Ga-DOTATOC uptake than SSTR5. In addition, the results indicate that the gene expression levels of SSTR2 and SSTR5 at large follow one another.

Selection of suitable reference genes for normalization of genes of interest in canine soft tissue sarcomas using quantitative real-time polymerase chain reaction

Quantitative real-time reverse transcription polymerase chain reaction (RT-qPCR) is a sensitive technique for quantifying gene expression. Stably expressed reference genes are necessary for normalization of RT-qPCR data. Only a few articles have been published on reference genes in canine tumours. The objective of this study was to demonstrate how to identify suitable reference genes for normalization of genes of interest in canine soft tissue sarcomas using RT-qPCR. Primer pairs for 17 potential reference genes were designed and tested in archival tumour biopsies from six dogs. The geNorm algorithm was used to analyse the most suitable reference genes. Eight potential reference genes were excluded from this final analysis because of their dissociation curves. β-Glucuronidase (GUSB) and proteasome subunit, beta type, 6 (PSMB6) were most stably expressed with an M value of 0.154 and a CV of 0.053 describing their average stability. We suggest that choice of reference genes should be based on specific testing in every new experimental set-up.

PET/CT in therapy evaluation of patients with lung cancer

FDG-PET/CT is a well documented and widespread used imaging modality for the diagnosis and staging of patient with lung cancer. FDG-PET/CT is increasingly used for the assessment of treatment effects during and after chemotherapy. However, PET is not an accepted surrogate end-point for assessment of response rate in clinical trials. The aim of this review is to present current evidence on the use of PET in response evaluation of patients with lung cancer and to introduce the pearls and pitfalls of the PET-technology relating to response assessment. Based on this and relating to validation criteria, including stable technology, standardization, reproducibility and broad availability, the review discusses why, despite numerous studies on response assessment indicating a possible role for FDG-PET/CT, PET still has no place in guidelines relating to response evaluation in lung cancer.

Comparison of two new angiogenesis PET tracers 68Ga-NODAGA-E[c(RGDyK)]2 and (64)Cu-NODAGA-E[c(RGDyK)]2; in vivo imaging studies in human xenograft tumors

INTRODUCTION

The aim of this study was to synthesize and perform a side-by-side comparison of two new tumor-angiogenesis PET tracers (68)Ga-NODAGA-E[c(RGDyK)](2) and (64)Cu-NODAGA-E[c(RGDyK)](2) in vivo using human xenograft tumors in mice. Human radiation burden was estimated to evaluate potential for future use as clinical PET tracers for imaging of neo-angiogenesis.

METHODS

A (68)Ge/(68)Ga generator was used for the synthesis of (68)Ga-NODAGA-E[c(RGDyK)](2). (68)Ga and (64)Cu labeled NODAGA-E[c(RGDyK)](2) tracers were administrated in nude mice bearing either human glioblastoma (U87MG) or human neuroendocrine (H727) xenograft tumors. PET/CT scans at 3 time points were used for calculating the tracer uptake in tumors (%ID/g), integrin αVβ3 target specificity was shown by blocking with cold NODAGA-E[c(RGDyK)](2), and biodistribution in normal organs were also examined. From biodistribution data in mice human radiation-absorbed doses were estimated using OLINDA/EXM software.

RESULTS

(68)Ga-NODAGA-E[c(RGDyK)](2) was synthesized with a radiochemical purity of 89%-99% and a specific activity (SA) of 16-153 MBq/nmol. (64)Cu-NODAGA-E[c(RGDyK)](2) had a purity of 92%-99% and an SA of 64-78 MBq/nmol. Both tracers showed similar uptake in xenograft tumors 1h after injection (U87MG: 2.23 vs. 2.31%ID/g; H727: 1.53 vs. 1.48%ID/g). Both RGD dimers showed similar tracer uptake in non-tumoral tissues and a human radiation burden of less than 10 mSv with an administered dose of 200 MBq was estimated.

CONCLUSION

(68)Ga-NODAGA-E[c(RGDyK)](2) and (64)Cu-NODAGA-E[c(RGDyK)](2) can be easily synthesized and are both promising candidates for PET imaging of integrin αVβ3 positive tumor cells. (68)Ga-NODAGA-E[c(RGDyK)](2) showed slightly more stable tumor retention. With the advantage of in-house commercially (68)Ge/(68)Ga generators, (68)Ga-NODAGA-E[c(RGDyK)](2) may be the best choice for future clinical PET imaging in humans.

Positron emission tomography of the vulnerable atherosclerotic plaque in man--a contemporary review

Atherosclerosis is the primary underlying cause of cardiovascular disease (CVD). It is the leading cause of morbidity and mortality in the Western world today and is set to become the prevailing disease and major cause of death worldwide by 2020. In the 1950s surgical intervention was introduced to treat symptomatic patients with high-grade carotid artery stenosis due to atherosclerosis – a procedure known as carotid endarterectomy (CEA). By removing the atherosclerotic plaque from the affected carotid artery of these patients, CEA is beneficial by preventing subsequent ipsilateral ischemic stroke. However, it is known that patients with low to intermediate artery stenosis may still experience ischemic events, leading clinicians to consider plaque composition as an important feature of atherosclerosis. Today molecular imaging can be used for characterization, visualization and quantification of cellular and subcellular physiological processes as they take place in vivo; using this technology we can obtain valuable information on atherosclerostic plaque composition. Applying molecular imaging clinically to atherosclerotic disease therefore has the potential to identify atherosclerotic plaques vulnerable to rupture. This could prove to be an important tool for the selection of patients for CEA surgery in a health system increasingly focused on individualized treatment. This review focuses on current advances and future developments of in vivo atherosclerosis PET imaging in man.

(18)F-FDG imaging of human atherosclerotic carotid plaques reflects gene expression of the key hypoxia marker HIF-1α

To investigate the association between gene expression of key molecular markers of hypoxia and inflammation in atherosclerotic carotid lesions with 2-deoxy-2-[(18)F]fluoro-D-glucose ((18)F-FDG) uptake as determined clinically by positron emission tomography (PET). Studies using PET have demonstrated (18)F-FDG-uptake in patients with confirmed plaques of the carotid artery. Inflammatory active or "vulnerable" plaques progressively increase in bulk, develop necrotic cores, poor vessel-wall vascularization and become prone to hypoxia. We used quantitative polymerase-chain reaction (qPCR) to determine gene expression of hypoxia-inducible factor 1α (HIF-1α) and cluster of differentiation 68 (CD68) on plaques recovered by carotid endarterectomy (CEA) in 18 patients. Gene expression was compared with (18)F-FDG-uptake quantified as the maximum standardized uptake value (SUVmax) on co-registered PET/computed tomography (CT) scans performed the day before CEA. Immunohistochemistry was used to validate target-gene protein expression. In univariate linear regression analysis HIF-1α was significantly correlated with (18)F-FDG-uptake (SUVmax) as was CD68. A two-tailed Pearson regression model demonstrated that HIF-1α and CD68 gene expression co-variated and accordingly when entering the variables into multivariate linear regression models with SUV-values as dependent variables, HIF-1α was eliminated in the final models. (18)F-FDG-uptake (SUVmax) is correlated with HIF-1α gene expression indicating an association between hypoxia and glucose metabolism in vivo. The marker of inflammation CD68 is also associated with (18)F-FDG-uptake (SUVmax). As CD68 and HIF-1α gene expression co-variate their information is overlapping.