Molecular PET/CT Profiling of ACE2 Expression In Vivo: Implications for Infection and Outcome from SARS-CoV-2

Rapid progress has been made to identify and study the causative agent leading to coronavirus disease 2019 (COVID-19) but many questions including who is most susceptible and what determines severity remain unanswered. Angiotensin-converting enzyme 2 (ACE2) is a key factor in the infection process of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). In this study, molecularly specific positron emission tomography imaging agents for targeting ACE2 are first developed, and these novel agents are evaluated in vitro, in preclinical model systems, and in a first-in-human translational ACE2 imaging of healthy volunteers and a SARS-CoV-2 recovered patient (NCT04422457). ACE2 expression levels in different organs in live subjects are quantitatively delineated and observable differences are measured in the patient recovered from COVID-19. Surprising sites of uptake in the breast, reproductive system and very low uptake in pulmonary tissues are reported. This novel method can add a unique tool to facilitate SARS-CoV-2 related research and improve understanding of this enigmatic disease. Molecular imaging provides quantitative annotation of ACE2, the SARS-CoV-2 entry receptor, to noninvasively monitor organs impacted by the COVID-19.

Evaluation of glucagon-like peptide-1 receptor expression in nondiabetic and diabetic atherosclerotic mice using PET tracer 68Ga-NODAGA-exendin-4

Cardiovascular effects of glucagon-like peptide-1 receptor (GLP-1R) agonist therapies are potentially mediated by anti-inflammatory effects on atherosclerosis. Our study demonstrates that ⁶⁸Ga-NODAGA-exendin-4, a radioligand specifically targeting GLP-1R, detects GLP-1R expression in inflamed atherosclerotic lesions in nondiabetic and diabetic hypercholesterolemic mice. Immunofluorescence staining suggests that GLP-1R is primarily localized in M2 macrophages in lesions. This study describes a new potential tool that may have translational relevance for studies of pharmacological modification of GLP-1R signaling in atherosclerosis.

Early differences in dynamic uptake of 68Ga-PSMA-11 in primary prostate cancer: A test-retest study

INTRODUCTION

Dynamic PET/CT allows visualization of pharmacokinetics over the time, in contrast to static whole body PET/CT. The objective of this study was to assess 68Ga-PSMA-11 uptake in pathological lesions and benign tissue, within 30 minutes after injection in primary prostate cancer (PCa) patients in test-retest setting.

MATERIALS AND METHODS

Five patients, with biopsy proven PCa, were scanned dynamically in list mode for 30 minutes on a digital PET/CT-scanner directly after an intravenous bolus injection of 100 MBq 68Ga-PSMA-11. Approximately 45 minutes after injection a static whole body scan was acquired, followed by a one bed position scan of the pelvic region. The scans were repeated approximately four weeks later, without any intervention in between. Semi-quantitative assessment was performed using regions-of-interest in the prostate tumor, bladder, gluteal muscle and iliac artery. Time-activity curves were extracted from the counts in these regions and the intra-patient variability between both scans was assessed.

RESULTS

The uptake of the iliac artery and gluteal muscle reached a plateau after 5 and 3 minutes, respectively. The population fell apart in two groups with respect to tumor uptake: in some patients the tumor uptake reached a plateau after 5 minutes, whereas in other patients the uptake kept increasing, which correlated with larger tumor volumes on PET/CT scan. Median intra-patient variation between both scans was 12.2% for artery, 9.7% for tumor, 32.7% for the bladder and 14.1% for the gluteal muscle.

CONCLUSION

Dynamic 68Ga-PSMA-11 PET/CT scans, with a time interval of four weeks, are reproducible with a 10% variation in uptake in the primary prostate tumor. An uptake plateau was reached for the iliac artery and gluteal muscle within 5 minutes post-injection. A larger tumor volume seems to be related to continued tumor uptake. This information might be relevant for both response monitoring and PSMA-based radionuclide therapies.

Can SUVmax of 68Ga-labeled PSMA Ligand and 18F-choline PET/CT Be Used to Predict the Radiation Dose in Prostate Cancer Patients?

Gallium-68 (Ga)-PSMA and F-Choline are two radionuclides that have already shown high potential for the detection of prostate cancer. The comparison between these two radionuclides has several advantages in radiation protection. The aim of this prospective study was to identify which of these two radionuclides can help in predicting the equivalent dose using the maximum standard uptake value (SUVmax) of normal organs, the kidneys. Two groups of 40 patients (total n = 80) who underwent PET/CT using Ga or F for diagnosis of prostate cancer between April 2018 and December 2018 at the American University of Beirut Medical Center were included. First, the dose rates were measured after 1 h of radionuclide uptake at 1 m distance with background of 0.015 μSv h. Then, SUVmax for kidneys were determined from images obtained with PET/CT 1 h after injection of both radionuclides. The ratios of the equivalent doses to the SUVmax for kidneys were compared for both Ga-PSMA and F-Choline. There is a positive moderate relationship between the SUVmax for kidneys and the Ga dose rate after 1 h of injection at 1 m distance from the abdomen (p-value = 0.023 < 0.05). This relationship is statistically significant. However, there is a very low negative relationship between the SUVmax kidney and F dose rate after 1 h of injection at 1 m distance from the abdomen (p-value = 0.93 > 0.05). This relationship is not statistically significant. This leads to the suggestion that we can predict the equivalent dose due to Ga by indicating the SUVmax from the PET/CT images.

Evaluation of Met-Val-Lys as a Renal Brush Border Enzyme-Cleavable Linker to Reduce Kidney Uptake of 68Ga-Labeled DOTA-Conjugated Peptides and Peptidomimetics

High kidney uptake is a common feature of peptide-based radiopharmaceuticals, leading to reduced detection sensitivity for lesions adjacent to kidneys and lower maximum tolerated therapeutic dose. In this study, we evaluated if the Met-Val-Lys (MVK) linker could be used to lower kidney uptake of ⁶⁸Ga-labeled DOTA-conjugated peptides and peptidomimetics. A model compound, [⁶⁸Ga]Ga-DOTA-AmBz-MVK(Ac)-OH (AmBz: aminomethylbenzoyl), and its derivative, [⁶⁸Ga]Ga-DOTA-AmBz-MVK(HTK01166)-OH, coupled with the PSMA (prostate-specific membrane antigen)-targeting motif of the previously reported HTK01166 were synthesized and evaluated to determine if they could be recognized and cleaved by the renal brush border enzymes. Additionally, positron emission tomography (PET) imaging, ex vivo biodistribution and in vivo stability studies were conducted in mice to evaluate their pharmacokinetics. [⁶⁸Ga]Ga-DOTA-AmBz-MVK(Ac)-OH was effectively cleaved specifically by neutral endopeptidase (NEP) of renal brush border enzymes at the Met-Val amide bond, and the radio-metabolite [⁶⁸Ga]Ga-DOTA-AmBz-Met-OH was rapidly excreted via the renal pathway with minimal kidney retention. [⁶⁸Ga]Ga-DOTA-AmBz-MVK(HTK01166)-OH retained its PSMA-targeting capability and was also cleaved by NEP, although less effectively when compared to [⁶⁸Ga]Ga-DOTA-AmBz-MVK(Ac)-OH. The kidney uptake of [⁶⁸Ga]Ga-DOTA-AmBz-MVK(HTK01166)-OH was 30% less compared to that of [⁶⁸Ga]Ga-HTK01166. Our data demonstrated that derivatives of [⁶⁸Ga]Ga-DOTA-AmBz-MVK-OH can be cleaved specifically by NEP, and therefore, MVK can be a promising cleavable linker for use to reduce kidney uptake of radiolabeled DOTA-conjugated peptides and peptidomimetics.

Preclinical Evaluation of NHS-Activated Gold Nanoparticles Functionalized with Bombesin or Neurotensin-Like Peptides for Targeting Colon and Prostate Tumours

Recent advances and large-scale use of hybrid imaging modalities like PET-CT have led to the necessity of improving nano-drug carriers that can facilitate both functional and metabolic screening in nuclear medicine applications. In this study, we focused on the evaluation of four potential imaging nanoparticle structures labelled with the 68Ga positron emitter. For this purpose, we functionalized NHS-activated PEG-gold nanoparticles with 68Ga-DOTA-Neuromedin B, 68Ga-DOTA-PEG(4)-BBN(7-14), 68Ga-DOTA-NT and 68Ga-DOTA-Neuromedin N. In vitro binding kinetics and specific binding to human HT-29 colon carcinoma cells and DU-145 prostate carcinoma cells respectively were assessed, over 75% retention being obtained in the case of 68Ga-DOTA-PEG(4)-BBN(7-14)-AuNP in prostate tumour cells and over 50% in colon carcinoma cells. Biodistribution in NU/J mice highlighted a three-fold uptake increase in tumours at 30 min post-injection of 68Ga-DOTA-NT-AuNP and 68Ga-DOTA-PEG(4)-BBN(7-14)-AuNP compared to 68Ga-DOTA-NT and 68Ga-DOTA-PEG(4)-BBN(7-14) respectively, therewith fast distribution in prostate and colon tumours and minimum accumulation in non-targeted tissues.

Preparation, Characterization, and Radiolabeling of [68Ga]Ga-NODAGA-Pamidronic Acid: A Potential PET Bone Imaging Agent

Early diagnosis of bone metastases is crucial to prevent skeletal-related events, and for that, the non-invasive techniques to diagnose bone metastases that make use of image-guided radiopharmaceuticals are being employed as an alternative to traditional biopsies. Hence, in the present work, we tested the efficacy of a gallium-68 (⁶⁸Ga)-based compound as a radiopharmaceutical agent towards the bone imaging in positron emitting tomography (PET). For that, we prepared, thoroughly characterized, and radiolabeled [⁶⁸Ga]Ga-NODAGA-pamidronic acid radiopharmaceutical, a ⁶⁸Ga precursor for PET bone cancer imaging applications. The preparation of NODAGA-pamidronic acid was performed via the N-Hydroxysuccinimide (NHS) ester strategy and was characterized using liquid chromatography-mass spectrometry (LC-MS) and tandem mass spectrometry (MSⁿ). The unreacted NODAGA chelator was separated using the ion-suppression reverse phase-high performance liquid chromatography (RP-HPLC) method, and the freeze-dried NODAGA-pamidronic acid was radiolabeled with ⁶⁸Ga. The radiolabeling condition was found to be most optimum at a pH ranging from 4 to 4.5 and a temperature of above 60 °C. From previous work, we found that the pamidronic acid itself has a good bone binding affinity. Moreover, from the analysis of the results, the ionic structure of radiolabeled [⁶⁸Ga]Ga-NODAGA-pamidronic acid has the ability to improve the blood clearance and may exert good renal excretion, enhance the bone-to-background ratio, and consequently the final image quality. This was reflected by both the in vitro bone binding assay and in vivo animal biodistribution presented in this research.

In vivo biodistribution of calcium phosphate nanoparticles after intravascular, intramuscular, intratumoral, and soft tissue administration in mice investigated by small animal PET/CT

Calcium phosphate nanoparticles were covalently surface-functionalized with the ligand DOTA and loaded with the radioisotope ⁶⁸Ga. The biodistribution of such ⁶⁸Ga-labelled nanoparticles was followed in vivo in mice by positron emission tomography in combination with computer tomography (PET-CT). The biodistribution of ⁶⁸Ga-labelled nanoparticles was compared for different application routes: intravenous, intramuscular, intratumoral, and into soft tissue. The particle distribution was measured in vivo by PET-CT after 5 min, 15 min, 30 min, 1 h, 2 h, and 4 h, and ex vivo after 5 h. After intravenous injection (tail vein), the nanoparticles rapidly entered the lungs with later redistribution into liver and spleen. The nanoparticles remained mostly at the injection site following intramuscular, intratumoral, or soft tissue application, with less than 10 percent being mobilized into the blood stream. STATEMENT OF SIGNIFICANCE: The in vivo biodistribution of DOTA-terminated calcium phosphate nanoparticles was followed by PET/CT. To our knowledge, this is the first study of this kind. Four different application routes of clinical relevance were pursued: Intravascular, intramuscular, intratumoral, and into soft tissue. Given the high importance of calcium phosphate as biomaterial and for nanoparticular drug delivery and immunization, this is most important to assess the biofate of calcium phosphate nanoparticles for therapeutic application and also judge biodistribution of nanoscopic calcium phosphate ceramics, including debris from endoprostheses and related implants.

Methods to Enhance the Metabolic Stability of Peptide-Based PET Radiopharmaceuticals

The high affinity and specificity of peptides towards biological targets, in addition to their favorable pharmacological properties, has encouraged the development of many peptide-based pharmaceuticals, including peptide-based positron emission tomography (PET) radiopharmaceuticals. However, the poor in vivo stability of unmodified peptides against proteolysis is a major challenge that must be overcome, as it can result in an impractically short in vivo biological half-life and a subsequently poor bioavailability when used in imaging and therapeutic applications. Consequently, many biologically and pharmacologically interesting peptide-based drugs may never see application. A potential way to overcome this is using peptide analogues designed to mimic the pharmacophore of a native peptide while also containing unnatural modifications that act to maintain or improve the pharmacological properties. This review explores strategies that have been developed to increase the metabolic stability of peptide-based pharmaceuticals. It includes modifications of the C- and/or N-termini, introduction of d- or other unnatural amino acids, backbone modification, PEGylation and alkyl chain incorporation, cyclization and peptide bond substitution, and where those strategies have been, or could be, applied to PET peptide-based radiopharmaceuticals.

Imaging and biodistribution of radiolabeled SP90 peptide in BT-483 tumor bearing mice

The objective of this study was to evaluate radiolabeled DOTA-SP90 as a radiotracer for breast cancer. The in vitro competition assay showed that radiolabeled DOTA-SP90 had significant binding affinity to BT-483 cancer cells. Biodistribution, nanoSPECT/CT and nanoPET/CT imaging results indicated that radiolabeled DOTA-SP90 can accumulate in tumors. In addition, radiolabeled DOTA-SP90 peptides can also detect metastatic tumors. Therefore, radiolabeled SP90 peptide may provide the potential capability as diagnostic agent for breast cancer patients.

A nanobody-based nuclear imaging tracer targeting dipeptidyl peptidase 6 to determine the mass of human beta cell grafts in mice

AIMS/HYPOTHESIS

Type 1 diabetes is characterised by a progressive decline in beta cell mass. This is also observed following implantation of pancreatic islet allografts, but there is no reliable information regarding the time course of beta cell loss. This is due to the limited availability of non-invasive pancreatic islet imaging techniques. We have previously described that dipeptidyl peptidase 6 (DPP6) is an alpha and beta cell-specific biomarker, and developed a camelid antibody (nanobody '4hD29') against it. We demonstrated the possibility to detect DPP6-expressing cells by single-photon emission computed tomography (SPECT)/ computed tomography (CT), but the correlation between the number of cells grafted and the SPECT signal was not assessed. Here, we investigate whether the 4hD29 nanobody allows us to detect different amounts of human pancreatic islets implanted into immune-deficient mice. In addition, we also describe the adaptation of the probe for use with positron emission tomography (PET).

METHODS

DPP6 expression was assessed in human samples using tissue arrays and immunohistochemistry. The effect of the 4hD29 nanobody on cell death and glucose-stimulated insulin secretion was measured in EndoC-βH1 cells and in human islets using Hoechst/propidium iodide staining and an anti-insulin ELISA, respectively. We performed in vivo SPECT imaging on severe combined immunodeficient (SCID) mice transplanted with different amounts of EndoC-βH1 cells (2 × 10⁶, 5 × 10⁶ and 10 × 10⁶ cells), human islets (1000 and 3000) or pancreatic exocrine tissue using ^99mTc-labelled 4hD29 nanobody. This DPP6 nanobody was also conjugated to N-chlorosuccinimide (NCS)-1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA), radiolabelled with either ⁶⁷Ga (SPECT) or ⁶⁸Ga (PET) and used in a proof-of-principle experiment to detect DPP6-expressing cells (Kelly neuroblastoma) grafted in SCID mice.

RESULTS

The DPP6 protein is mainly expressed in pancreatic islets. Importantly, the anti-DPP6 nanobody 4hD29 allows non-invasive detection of high amounts of EndoC-βH1 cells or human islets grafted in immunodeficient mice. This suggests that the probe must be further improved to detect lower numbers of islet cells. The 4hD29 nanobody neither affected beta cell viability nor altered insulin secretion in EndoC-βH1 cells and human islets. The conversion of 4hD29 nanobody into a PET probe was successful and did not alter its specificity.

CONCLUSIONS/INTERPRETATION

These findings suggest that the anti-DPP6 4hD29 nanobody may become a useful tool for the quantification of human islet grafts in mice and, pending future development, islet mass in individuals with diabetes.

Preparation, radiolabeling with 99mTc and 67Ga and biodistribution studies of albumin nanoparticles covered with polymers

OBJECTIVE

To optimize radiolabeling with ^99mTc and ⁶⁷Ga of albumin nanoparticles coated with 4 differents synthetic polymers and to evaluate their stability in vivo and in vitro, as well as their biodistribution in vivo after intravenous administration.

MATERIAL AND METHODS

The nanoparticles were prepared using albumin and NOTA-modified albumin by the desolvation method and coated with 4 different polymers; HPMC, GMN2, GPM2 and GTM2. They were purified, lyophilized and characterized. Radiolabelling with ^99mTc was perfomed with 74 MBq of ^99mTc sodium pertechnetate, previously reduced with and acid solution of tin chloride at different concentrations (0.003, 0.005, 0.007, 0.01, 0.05 and 0.1mg/ml) and at different times (5, 10, 15, 30 and 60minutes) and temperatures (room temperature, 40°C and 60°C). Radiolabelling with ⁶⁷Ga was perfomed by incubation of the nanoparticles with 37 MBq of ⁶⁷Gallium chloride (obtained from commercial gallium-⁶⁷ citrate) at different times (10 and 30minutes) and temperatures (room temperature, 30°C and 60°C), and posterior purification with microconcentrators. The radiochemical purity was evaluated by TLC. Stability studies of radiolabeled nanoparticles in physiological serum and blood plasma were perfomed. Biodistribution studies of nanoparticles coated with GPM2 polymer were carried out in Wistar rats after intravenous administration of the nanoparticles. Control animals were carried out with ^99mTc sodium pertechnetate and ⁶⁷Ga chloride. To do so, the animals were killed and activity in organs was measured in a gamma counter.

RESULTS

^99mTc labeling was carried out optimally with a tin concentration of 0.007mg/ ml for the GPM2 nanoparticles and 0.005mg / ml for the rest of the formulations, with a radiolabelling time of 10minutes at room temperature. In the case of ⁶⁷Ga the label was optimized at 30° C temperature and 30minutes of incubation. In both cases the radiochemical purity obtained was greater than 97%. The nanoparticles showed high stability in vitro after 48hours of labeling (70% nanoparticles labeled with ^99mTc and 90% those labeled with ⁶⁷Ga). Biodistribution studies of nanoparticles ^99mTc -GPM2 and ⁶⁷Ga -NOTA-GPM2 showed a high accumulation of activity in the liver at 2 and 24hours after intravenous administration.

CONCLUSION

The labeling procedure with ^99mTc and ⁶⁷Ga of albumin and albumin modified with NOTA nanoparticles allows obtaining nanoparticles with high labeling yields and adequate in vitro stability, allowing their use for in vivo studies.

Lower 68 Ga-DOTATOC uptake in nonfunctioning pituitary neuroendocrine tumours compared to normal pituitary gland-A proof-of-concept study

OBJECTIVES

⁶⁸  Ga-DOTATOC PET targets somatostatin receptors (SSTRs) and is well established for the detection of SSTR-expressing tumors, such as gastrointestinal neuroendocrine tumors. Pituitary adenomas, recently designated as pituitary neuroendocrine tumors (PitNETs), also express SSTRs, but there has been no previous evaluations of ⁶⁸  Ga-DOTATOC PET in PitNET patients. The aim of this pilot study was to evaluate the diagnostic properties of ⁶⁸  Ga-DOTATOC PET in the most common PitNET, ie non-functioning (NF)-PitNET.

DESIGN/PATIENTS

NF-PitNET patients (n = 9) and controls (n = 13) were examined preoperatively with ⁶⁸  Ga-DOTATOC PET for 45 min after tracer injection in dynamic list mode. Tumor specimens were collected during surgery in patients. MRI and PET images were co-registered using PMOD software. The maximum standard uptake value (SUV_max ) was analyzed in manually outlined regions of interest (ROI) around the tumor in patients and around the pituitary gland in controls. Immunohistochemical analyses were conducted on tumor specimens for assessment of tumor cell type and SSTR expression.

RESULTS

Median SUV_max (IQR) was lower in patients than in controls (3.9 [3.4-8.5] vs 14.1 [12.5-15.9]; P < .01]. In ROC analysis, the area under the curve was 0.87 (P < .01) for SUV_max , with 78% sensitivity and 92% specificity. Immunohistochemical analysis showed NF-PitNETs were of gonadotroph (n = 7) and corticotroph (n = 2) origin. SSTR expression was high for SSTR3, low-to-moderate for SSTR2, and low for SSTR1 and SSTR5.

CONCLUSIONS

This proof-of-concept study shows that ⁶⁸ Ga-DOTATOC PET can be used to differentiate between normal pituitary tissue and NF-PitNET.

Manipulating the In Vivo Behaviour of 68Ga with Tris(Hydroxypyridinone) Chelators: Pretargeting and Blood Clearance

Pretargeting is widely explored in immunoPET as a strategy to reduce radiation exposure of non-target organs and allow the use of short-lived radionuclides that would not otherwise be compatible with the slow pharmacokinetic profiles of antibodies. Here we investigate a pretargeting strategy based on gallium-68 and the chelator THPMe as a high-affinity pair capable of combining in vivo. After confirming the ability of THPMe to bind 68Ga in vivo at low concentrations, the bifunctional THPMe-NCS was conjugated to a humanised huA33 antibody targeting the A33 glycoprotein. Imaging experiments performed in nude mice bearing A33-positive SW1222 colorectal cancer xenografts compared pretargeting (100 μg of THPMe-NCS-huA33, followed after 24 h by 8-10 MBq of 68Ga3+) with both a directly labelled radioimmunoconjugate (89Zr-DFO-NCS-huA33, 88 μg, 7 MBq) and a 68Ga-only negative control (8-10 MBq of 68Ga3+). Imaging was performed 25 h after antibody administration (1 h after 68Ga3+ administration for negative control). No difference between pretargeting and the negative control was observed, suggesting that pretargeting via metal chelation is not feasible using this model. However, significant accumulation of "unchelated" 68Ga3+ in the tumour was found (12.9 %ID/g) even without prior administration of THPMe-NCS-huA33, though tumour-to-background contrast was impaired by residual activity in the blood. Therefore, the 68Ga-only experiment was repeated using THPMe (20 μg, 1 h after 68Ga3+ administration) to clear circulating 68Ga3+, producing a three-fold improvement of the tumour-to-blood activity concentration ratio. Although preliminary, these results highlight the potential of THPMe as a 68Ga clearing agent in imaging applications with gallium citrate.

Comparison of the binding of the gastrin-releasing peptide receptor (GRP-R) antagonist 68Ga-RM2 and 18F-FDG in breast cancer samples

The Gastrin-Releasing Peptide Receptor (GRPR) is over-expressed in estrogen receptor (ER) positive breast tumors and related metastatic lymph nodes offering the opportunity of imaging and therapy of luminal tumors. ⁶⁸Ga-RM2 binding and ¹⁸F-FDG binding in tumoral zones were measured and compared using tissue micro-imaging with a beta imager on 14 breast cancer samples (10 primaries and 4 associated metastatic lymph nodes). Results were then assessed against ER expression, progesterone receptor (PR) expression, HER2 over-expression or not and Ki-67 expression. GRPR immunohistochemistry (IHC) was also performed on all samples. We also retrospectively compared ⁶⁸Ga-RM2 and ¹⁸F-FDG bindings to ¹⁸F-FDG SUV_max on the pre-therapeutic PET/CT examination, if available. ⁶⁸Ga-RM2 binding was significantly higher in tumors expressing GRPR on IHC than in GRPR-negative tumors (P = 0.022). In ER⁺ tumors, binding of ⁶⁸Ga-RM2 was significantly higher than ¹⁸F-FDG (P = 0.015). In tumors with low Ki-67, ⁶⁸Ga-RM2 binding was also significantly increased compared to ¹⁸F-FDG (P = 0.029). Overall, the binding of ⁶⁸Ga-RM2 and ¹⁸F-FDG displayed an opposite pattern in tumor samples and ⁶⁸Ga-RM2 binding was significantly higher in tumors that had low ¹⁸F-FDG binding (P = 0.021). This inverse correlation was also documented in the few patients in whom a ¹⁸F-FDG PET/CT examination before surgery was available. Findings from this in vitro study suggest that GRPR targeting can be an alternative to ¹⁸F-FDG imaging in ER⁺ breast tumors. Moreover, because GRPR antagonists can also be labeled with lutetium-177 this opens new avenues for targeted radionuclide therapy in the subset of patients with progressive metastatic disease following conventional treatments.

Multiple endocrine neoplasia type 2A syndrome (MEN2A) and usefulness of 68Ga-DOTATATE PET/CT in this syndrome

AIM

The aim of this study was to evaluate a new imaging method 68Ga-DOTATATE PET/CT as an alternative method to diagnose evidence of neuroendocrine tumors or their metastasis (if any) in patient with MEN 2A.

METHODS

Three patients( 2F, 1M; age 28,46 and 50 years) with MEN 2A syndrome who underwent 68Ga-DOTATATE PET/CT scan were prospectively evaluated. PET/CT images were analyzed with measurement of maximum standardized uptake value (SUVmax).

RESULTS

All patients had adrenal masses with increased uptake of 68Ga-DOTATATE (first case adrenal mass SUVmax: 9,1, second case adrenal mass SUVmax: 32,4(right), 30,3(left) and third case SUVmax:12,4). All of the patients had medullary thyroid carcinoma with increased uptake of 68Ga-DOTATATE (first case SUVmax: 3,3 second case SUVmax:7,7 and third case SUVmax: left thyroid nodule: 19,4, right thyroid nodule: 21,2). Third case has a parathyroid adenoma with SUVmax: 2,8.

CONCLUSIONS

New imaging method 68Ga-DOTATATE PET/CT may be an alternative method to diagnose MEN 2A patients. 68Ga-DOTATATE PET/CT can give a great opportunity to detecting the multiple neoplasia like MEN 2A with only one session.

KEY WORDS

MEN 2A syndrome, 68Ga-DOTATATE PET/CT, Neuroendocrine tumors.

Monosodium Glutamate Reduces 68Ga-PSMA-11 Uptake in Salivary Glands and Kidneys in a Preclinical Prostate Cancer Model

We evaluated the ability of monosodium glutamate (MSG) to reduce salivary and kidney uptake of a prostate-specific membrane antigen (PSMA) radioligand without affecting tumor uptake. Methods: LNCaP tumor-bearing mice were intraperitoneally injected with MSG (657, 329, or 164 mg/kg) or phosphate-buffered saline (PBS). Fifteen minutes later, the mice were intravenously administered 68Ga-PSMA-11. PET/CT imaging and biodistribution studies were performed 1 h after administration. Results: Tumor uptake (percentage injected dose per gram [%ID]) was not statistically different between groups, at 8.42 ± 1.40 %ID in the 657 mg/kg group, 7.19 ± 0.86 %ID in the 329 mg/kg group, 8.20 ± 2.44 %ID in the 164 mg/kg group, and 8.67 ± 1.97 %ID in the PBS group. Kidney uptake was significantly lower in the 657 mg/kg group (85.8 ± 24.2 %ID) than in the 329 mg/kg (159 ± 26.2 %ID), 164 mg/kg (211 ± 27.4 %ID), and PBS groups (182 ± 33.5 %ID) (P < 0.001). Salivary gland uptake was lower in the 657 mg/kg (3.72 ± 2.12 %ID) and 329 mg/kg (5.74 ± 0.62 %ID) groups than in the PBS group (10.04 ± 2.52 %ID) (P < 0.01). Conclusion: MSG decreased salivary and kidney uptake of 68Ga-PSMA-11 in a dose-dependent manner, whereas tumor uptake was unaffected.

Biodistribution and Tumor Uptake of 67Ga-Nimotuzumab in a Malignant Pleural Mesothelioma Xenograft

Malignant pleural mesothelioma (MPM) is the most common tumor of the pulmonary pleura. It is a rare and aggressive malignancy, generally associated with continuous occupational exposure to asbestos. Only a multimodal-approach to treatment, based on surgical resection, chemotherapy and/or radiation, has shown some benefits. However, the survival rate remains low. Nimotuzumab (h-R3), an anti-EGFR (epidermal growth factor receptor) humanized antibody, is proposed as a promising agent for the treatment of MPM. The aim of this research was to implement a procedure for nimotuzumab radiolabeling to evaluate its biodistribution and affinity for EGF (epidermal growth factor) receptors present in a mesothelioma xenograft. Nimotuzumab was radiolabeled with 67Ga; radiolabel efficiency, radiochemical purity, serum stability, and biodistribution were evaluated. Biodistribution and tumor uptake imaging studies by microSPECT/CT in mesothelioma xenografts revealed constant nimotuzumab uptake at the tumor site during the first 48 h after drug administration. In vivo studies using MPM xenografts showed a significant uptake of this radioimmunoconjugate, which illustrates its potential as a biomarker that could promote its theranostic use in patients with MPM.

68Ga-DOTA-GGNle-CycMSHhex targets the melanocortin-1 receptor for melanoma imaging

Melanocortin-1 receptor (MC1R) is a molecular target for melanoma imaging and therapy because of its overexpression on rodent and human melanoma cells. Here, we evaluated the MC1R targeting and specificity of 68Ga-DOTA-GGNle-CycMSHhex and Cy5.5-GGNle-CycMSHhex using murine and human melanoma cells, and murine and xenografted tumors. 68Ga-DOTA-GGNle-CycMSHhex was used first in human as an imaging probe to evaluate the possibility of radionuclide therapy in patients with advanced-stage melanoma. 68Ga-DOTA-GGNle-CycMSHhex and Cy5.5-GGNle-CycMSHhex displayed MC1R-specific targeting properties in murine and human melanoma cells, as well as in murine melanoma and human melanoma-xenografted tumors. Both B16/F10 and M21 melanoma lesions could be easily imaged by positron emission tomography using 68Ga-DOTA-GGNle-CycMSHhex The first-in-human images of melanoma brain metastases in patients demonstrated the clinical relevance of MC1R as a molecular target for melanoma imaging, highlighting the potential of 68Ga-DOTA-GGNle-CycMSHhex as an MC1R-targeting melanoma imaging probe and underscoring the need to develop MC1R-targeting therapeutic agents for treating patients with metastatic melanoma.

Gallium-67 as a Tumor-seeking Agent in Lymphomas - a Review

Background

At present 67Ga can be considered one of the most widely used viability radiotracers. There is general consensus in the literature that 67Ga has the highest clinical value in the management of lymphoma patients.

Methods

We critically discuss the role of gallium scintigraphy in lymphoma patients on the basis of the experience of the Nuclear Medicine Division at the National Cancer Institute of Milan.

Results and Conclusions

The sensitivity of gallium scan is very high (80-90%) in the staging and follow-up of Hodgkin's disease, and the method is also of great importance in the follow-up of lymphoma patients. We recommend scintigraphy to study the residual mediastinal mass after treatment. Our experiences during the follow-up of 189 lymphoma patients clearly showed the superior performance of gallium scan compared to MRI in the study of the mediastinal region after treatment. Sensitivity and specificity were both very high (90% and 96.9% vs 88.7% and 89.2%, respectively). Gallium scintigraphy can also be used to study the disease-free interval, posttreatment survival, early signs of recurrence and treatment response times. Comparison of the survival curves of 33 patients with diffuse large cell Non-Hodgkin's lymphoma examined at the National Cancer Institute showed a statistically significant difference (logrank test, P=0.0125) between patients with positive and those with negative gallium scan after 4-6 cycles of chemotherapy.

Enhancing PET Signal at Target Tissue in Vivo: Dendritic and Multimeric Tris(hydroxypyridinone) Conjugates for Molecular Imaging of αvβ3 Integrin Expression with Gallium-68

Tris(hydroxypyridinone) chelators conjugated to peptides can rapidly complex the positron-emitting isotope gallium-68 (68Ga) under mild conditions, and the resulting radiotracers can delineate peptide receptor expression at sites of diseased tissue in vivo. We have synthesized a dendritic bifunctional chelator containing nine 1,6-dimethyl-3-hydroxypyridin-4-one groups (SCN-HP9) that can coordinate up to three Ga3+ ions. This derivative has been conjugated to a trimeric peptide (RGD3) containing three peptide groups that target the αvβ3 integrin receptor. The resulting dendritic compound, HP9-RGD3, can be radiolabeled in 97% radiochemical yield at a 3-fold higher specific activity than its homologues HP3-RGD and HP3-RGD3 that contain only a single metal binding site. PET scanning and biodistribution studies show that [68Ga(HP9-RGD3)] demonstrates higher receptor-mediated tumor uptake in animals bearing U87MG tumors that overexpress αvβ3 integrin than [68Ga(HP3-RGD)] and [68Ga(HP3-RGD3)]. However, concomitant nontarget organ retention of [68Ga(HP9-RGD3)] results in low tumor to nontarget organ contrast in PET images. On the other hand, the trimeric peptide homologue containing a single tris(hydroxypyridinone) chelator, [68Ga(HP3-RGD3)], clears nontarget organs and exhibits receptor-mediated uptake in mice bearing tumors and in mice with induced rheumatoid arthritis. PET imaging with [68Ga(HP3-RGD3)] enables clear delineation of αvβ3 integrin receptor expression in vivo.

Radioiodinated Exendin-4 Is Superior to the Radiometal-Labelled Glucagon-Like Peptide-1 Receptor Probes Overcoming Their High Kidney Uptake

GLP-1 receptors are ideal targets for preoperative imaging of benign insulinoma and for quantifying the beta cell mass. The existing clinical tracers targeting GLP-1R are all agonists with low specific activity and very high kidney uptake. In order to solve those issues we evaluated GLP-1R agonist Ex-4 and antagonist Ex(9-39) radioiodinated at Tyr40 side by side with [Nle14,Lys40(Ahx-DOTA-68Ga)NH2]Ex-4 (68Ga-Ex-4) used in the clinic. The Kd, Bmax, internalization and binding kinetics of [Nle14,125I-Tyr40-NH2]Ex-4 and [Nle14,125I-Tyr40-NH2]Ex(9-39) were studied in vitro using Ins-1E cells. Biodistribution and imaging studies were performed in nude mice bearing Ins-1E xenografts. In vitro evaluation demonstrated high affinity binding of the [Nle14,125I-Tyr40-NH2]Ex-4 agonist to the Ins-1E cells with fast internalization kinetics reaching a plateau after 30 min. The antagonist [Nle14,125I-Tyr40-NH2]Ex(9-39) did not internalize and had a 4-fold higher Kd value compared to the agonist. In contrast to [Nle14,125I-Tyr40-NH2]Ex(9-39), which showed low and transient tumor uptake, [Nle14,125I-Tyr40-NH2]Ex-4 demonstrated excellent in vivo binding properties with tumor uptake identical to that of 68Ga-Ex-4, but substantially lower kidney uptake resulting in a tumor-to-kidney ratio of 9.7 at 1 h compared to 0.3 with 68Ga-Ex-4. Accumulation of activity in thyroid and stomach for both peptides, which was effectively blocked by irenat, confirms that in vivo deiodination is the mechanism behind the low kidney retention of iodinated peptides. The 124I congener of [Nle14,125I-Tyr40-NH2]Ex-4 demonstrated a similar favourable biodistribution profile in the PET imaging studies in contrast to the typical biodistribution pattern of [Nle14,Lys40(Ahx-DOTA-68Ga)NH2]Ex-4. Our results demonstrate that iodinated Ex-4 is a very promising tracer for imaging of benign insulinomas. It solves the problem of high kidney uptake of the radiometal-labelled tracers by improving the tumor-to-kidney ratio measured for [Nle14,Lys40(Ahx-DOTA-68Ga)NH2]Ex-4 by 32 fold.

Synthesis and evaluation of a (68)Ga labeled folic acid derivative for targeting folate receptors

Present work evaluates the potential of a newly synthesized (68)Ga-NOTA-folic acid conjugate for PET imaging of tumors over-expressing folate receptors (FRs). NOTA-folic acid conjugate was synthesized and characterized. It was radiolabeled with (68)Ga in ≥ 95% radiolabeling yields. In vitro cell binding studies showed a maximum cell uptake of 1.7±0.4% per million KB cells which was completely blocked on addition of cold folic acid showing specificity towards the FRs. However, further studies in tumor xenografts are warranted in order to assess the potential of (68)Ga-folic acid complex for imaging tumors over-expressing FRs.

Current knowledge on the sensitivity of the (68)Ga-somatostatin receptor positron emission tomography and the SUVmax reference range for management of pancreatic neuroendocrine tumours

Physiologically increased pancreatic uptake at the head/uncinate process is observed in more than one-third of patients after injection of one of the three ⁶⁸Ga-labelled octreotide-based peptides used for somatostatin (sst) receptor (r) imaging. There are minor differences between these ⁶⁸Ga-sstr-binding peptides in the imaging setting. On ⁶⁸Ga-sstr-imaging the physiological uptake can be diffuse or focal and usually remains stable over time. Differences in the maximal standardised uptake values (SUV_max) reported for the normal pancreas as well as for pancreatic neuroendocrine tumour (PNET) lesions may be related to several factors, including (a) differences in the peptide binding affinities as well as differences in sstr subtype expression of pancreatic α- and β-cells, and heterogeneity / density of tumour cells, (b) differences in scanner resolution, image reconstruction techniques and acquisition protocols, (c) mostly retrospective study designs, (d) mixed patient populations, or (e) interference with medications such as treatment with long-acting sst analogues. The major limitation in most of the studies lies in the lack of histopathological confirmation of abnormal findings. There is a significant overlap between the calculated SUV_max-values for physiological pancreas and PNET-lesions of the head/uncinate process that do not favour the use of quantitative parameters in the clinical setting. Anecdotal long-term follow-up studies have even indicated that increased uptake in the head/uncinate process still can turn out to be malignant over years of follow up. SUV_max-data for the pancreatic body and tail are limited. Therefore, any visible focal tracer uptake in the pancreas must be considered as suspicious for malignancy irrespective of quantitative parameters. In general, sstr-PET/CT has significant implications for the management of NET patients leading to a change in treatment decision in about one-third of patients. Therefore, follow-up with ⁶⁸Ga-sstr-PET/CT is mandatory in the clinical setting if uptake in the head/uncinate process is observed.

New Tris(hydroxypyridinone) Bifunctional Chelators Containing Isothiocyanate Groups Provide a Versatile Platform for Rapid One-Step Labeling and PET Imaging with (68)Ga(3.)

Two new bifunctional tris(hydroxypyridinone) (THP) chelators designed specifically for rapid labeling with (68)Ga have been synthesized, each with pendant isothiocyanate groups and three 1,6-dimethyl-3-hydroxypyridin-4-one groups. Both compounds have been conjugated with the primary amine group of a cyclic integrin targeting peptide, RGD. Each conjugate can be radiolabeled and formulated by treatment with generator-produced (68)Ga(3+) in over 95% radiochemical yield under ambient conditions in less than 5 min, with specific activities of 60-80 MBq nmol(-1). Competitive binding assays and in vivo biodistribution in mice bearing U87MG tumors demonstrate that the new (68)Ga(3+)-labeled THP peptide conjugates retain affinity for the αvβ3 integrin receptor, clear within 1-2 h from circulation, and undergo receptor-mediated tumor uptake in vivo. We conclude that bifunctional THP chelators can be used for simple, efficient labeling of (68)Ga biomolecules under mild conditions suitable for peptides and proteins.

Microwave gallium-68 radiochemistry for kinetically stable bis(thiosemicarbazone) complexes: structural investigations and cellular uptake under hypoxia

We report the microwave synthesis of several bis(thiosemicarbazones) and the rapid gallium-68 incorporation to give the corresponding metal complexes. These proved kinetically stable under 'cold' and 'hot' biological assays and were investigated using laser scanning confocal microscopy, flow cytometry and radioactive cell retention studies under normoxia and hypoxia. (68)Ga complex retention was found to be 34% higher in hypoxic cells than in normoxic cells over 30 min, further increasing to 53% at 120 min. Our data suggests that this class of gallium complexes show hypoxia selectivity suitable for imaging in living cells and in vivo tests by microPET in nude athymic mice showed that they are excreted within 1 h of their administration.

FDG and Beyond

Although many PET tracers are in use, FDG still is the most widely used in clinical oncology practice. FDG therefore deserves an in-depth discussion, which is even more interesting because of the huge increase in the molecular biology of glucose metabolism. Obviously, other tracers are of increasing importance as well, and these will be discussed in short.

Improved quantification for local regions of interest in preclinical PET imaging

In Positron Emission Tomography, there are several causes of quantitative inaccuracy, such as partial volume or spillover effects. The impact of these effects is greater when using radionuclides that have a large positron range, e.g. (68)Ga and (124)I, which have been increasingly used in the clinic. We have implemented and evaluated a local projection algorithm (LPA), originally evaluated for SPECT, to compensate for both partial-volume and spillover effects in PET. This method is based on the use of a high-resolution CT or MR image, co-registered with a PET image, which permits a high-resolution segmentation of a few tissues within a volume of interest (VOI) centered on a region within which tissue-activity values need to be estimated. The additional boundary information is used to obtain improved activity estimates for each tissue within the VOI, by solving a simple inversion problem. We implemented this algorithm for the preclinical Argus PET/CT scanner and assessed its performance using the radionuclides (18)F, (68)Ga and (124)I. We also evaluated and compared the results obtained when it was applied during the iterative reconstruction, as well as after the reconstruction as a postprocessing procedure. In addition, we studied how LPA can help to reduce the 'spillover contamination', which causes inaccurate quantification of lesions in the immediate neighborhood of large, 'hot' sources. Quantification was significantly improved by using LPA, which provided more accurate ratios of lesion-to-background activity concentration for hot and cold regions. For (18)F, the contrast was improved from 3.0 to 4.0 in hot lesions (when the true ratio was 4.0) and from 0.16 to 0.06 in cold lesions (true ratio  =  0.0), when using the LPA postprocessing. Furthermore, activity values estimated within the VOI using LPA during reconstruction were slightly more accurate than those obtained by post-processing, while also visually improving the image contrast and uniformity within the VOI.

Dimeric [(68)Ga]DOTA-RGD peptide targeting αvβ 3 integrin reveals extracellular matrix alterations after myocardial infarction

PURPOSE

We evaluated a dimeric RGD-peptide, [(68)Ga]DOTA-E-[c(RGDfK)]2, for positron emission tomography (PET) imaging of myocardial integrin expression associated with extracellular matrix remodeling after myocardial infarction (MI) in rat.

PROCEDURES

Male Sprague-Dawley rats were studied at 7 days and 4 weeks after MI induced by permanent ligation of the left coronary artery and compared with sham-operated controls.

RESULTS

In vivo imaging revealed higher tracer uptake in the infarcted area than in the remote non-infarcted myocardium of the same rats both at 7 days (MI/remote ratio, 2.25 ± 0.24) and 4 weeks (MI/remote ratio, 2.13 ± 0.37) post-MI. Compared with sham-operated rats, tracer uptake was higher also in the remote, non-infarcted myocardium of MI rats both at 7 days and 4 weeks where it coincided with an increased interstitial fibrosis. Standardized uptake values correlated well with the results of tracer kinetic modeling. Autoradiography confirmed the imaging results showing 5.1 times higher tracer uptake in the infarcted than remote area. Tracer uptake correlated with the amount of β3 integrin subunits in the infarcted area.

CONCLUSIONS

Our results show that integrin-targeting [(68)Ga]DOTA-E-[c(RGDfK)]2 is a potential tracer for monitoring of myocardial extracellular matrix remodeling after MI using PET.

Application and Dosimetric Requirements for Gallium-68-labeled Somatostatin Analogues in Targeted Radionuclide Therapy for Gastroenteropancreatic Neuroendocrine Tumors

Neuroendocrine tumors (NETs) are associated with variable prognosis, with grade 1 and 2 NETs having more favorable outcomes than grade 3. Patients with gastroenteropancreatic (GEP)-NET need individualized interdisciplinary evaluations and treatment. New treatment options have become available with significant improvements in progression-free survival. Peptide receptor radionuclide therapy (PRRT) using (90)Y or (177)Lu-labeled somatostatin analogues (SSTa) has also shown promise in the treatment of advanced progressive NETs. (68)Ga-1,4,7,10-tetraazacyclodecane-1,4,7,10-tetraacetic acid (DOTA)-SSTa can be used as companion imaging agents to assist in radionuclide therapy selection. (68)Ga-DOTA-SSTa PET/computed tomography might also provide information for prognosis, tumor response assessment to PRRT, and internal dosimetry.

(68)Ga-DOTANOC PET/CT detection of multiple extracranial localizations in a patient with anaplastic meningioma

We report herein a case of a 65-year-old male with intracranial recurrence of atypical meningioma initially treated with a combination of surgical resection and gamma knife radiotherapy. Afterwards, he underwent a (68)Ga-DOTANOC PET/CT scan in order to evaluate the feasibility of peptide receptor radionuclide therapy (PRRT). The scan identified multiple pulmonary, pleural and lymph node localizations. Histological diagnosis was consistent with intracranial atypical meningioma with diffuse metastatic spread. In our case, we have shown that meningioma with extracranial locations may present high uptake of somatostatin receptor analogues. Among other radionuclides, we believe that (68)Ga-DOTANOC PET/CT may be particularly useful for staging, detection of recurrence, evaluation of disease extension and alternative therapeutic approaches.

In vivo monitoring of parathyroid hormone treatment after myocardial infarction in mice with [68Ga]annexin A5 and [18F]fluorodeoxyglucose positron emission tomography

[68Ga]Annexin A5 positron emission tomography (PET) reveals the externalization of phosphatidylserine as a surrogate marker for apoptosis. We tested this technique for therapy monitoring in a murine model of myocardial infarction (MI) including parathyroid hormone (PTH) treatment. MI was induced in mice, and they were assigned to the saline or the PTH group. On day 2, they received [68Ga]annexin A5 PET or histofluorescence TUNEL staining. Mice had 2-deoxy-2-[18F]fluoro-d-glucose (FDG)-PET examinations on days 6 and 30 for calculation of the left ventricular ejection fraction and infarct area. [68Ga]Annexin A5 uptake was 7.4 ± 1.3 %ID/g within the infarction for the controls and 4.5 ± 1.9 %ID/g for the PTH group (p  =  .013). TUNEL staining revealed significantly more apoptotic cells in the infarct area on day 2 in the controls (64 ± 9%) compared to the treatment group (52 ± 4%; p  =  .045). FDG-PET revealed a significant decrease in infarct size in the treatment group and an increase in the controls. Examinations of left ventricular ejection fraction on days 6 and 30 did not reveal treatment effects. [68Ga]Annexin A5 PET can detect the effects of PTH treatment as a marker of apoptosis 2 days after MI; ex vivo examination confirmed significant rescue of myocardiocytes. FDG-PET showed a small but significant reduction in infarct size but no functional improvement.

Positron emission tomographic imaging of copper 64- and gallium 68-labeled chelator conjugates of the somatostatin agonist tyr3-octreotate

The bifunctional chelator and radiometal have been shown to have a direct effect on the pharmacokinetics of somatostatin receptor (SSTR)-targeted imaging agents. We evaluated three Y3-TATE analogues conjugated to NOTA-based chelators for radiolabeling with 64Cu and 68Ga for small-animal positron emission tomographic/computed tomographic (PET/CT) imaging. Two commercially available NOTA analogues, p-SCN-Bn-NOTA and NODAGA, were evaluated. The p-SCN-Bn-NOTA analogues were conjugated to Y3-TATE through β-Ala and PEG8 linkages. The NODAGA chelator was directly conjugated to Y3-TATE. The analogues labeled with 64Cu or 68Ga were analyzed in vitro for binding affinity and internalization and in vivo by PET/CT imaging, biodistribution, and Cerenkov imaging (68Ga analogues). We evaluated the effects of the radiometals, chelators, and linkers on the performance of the SSTR subtype 2--targeted imaging agents and also compared them to a previously reported agent, 64Cu-CB-TE2A-Y3-TATE. We found that the method of conjugation, particularly the length of the linkage between the chelator and the peptide, significantly impacted tumor and nontarget tissue uptake and clearance. Among the 64Cu- and 68Ga-labeled NOTA analogues, NODAGA-Y3-TATE had the most optimal in vivo behavior and was comparable to 64Cu-CB-TE2A-Y3-TATE. An advantage of NODAGA-Y3-TATE is that it allows labeling with 64Cu and 68Ga, providing a versatile PET probe for imaging SSTr subtype 2-positive tumors.

Development and pre-clinical evaluation of new 68Ga-NOTA-folate conjugates for PET imaging of folate receptor-positive tumors

In an attempt to develop new folate radiotracers with favorable biochemical properties for detecting folate receptor-positive cancers, we synthesized 68Ga-NOTA- and 68Ga-NOTAM-folate conjugates using a straightforward and a one-step simple reaction. Radiochemical yields were greater than 95% (decay-corrected) with total synthesis time of less than 20 min. Radiochemical purities were always greater than 98% without high-performance liquid chromatography (HPLC) purification. These synthetic approaches hold considerable promise as a rapid and simple method for 68Ga-folate conjugate preparation with high radiochemical yield in a short synthesis time. In vitro tests on the KB cell line showed that significant amounts of the radioconjugates were associated with cell fractions. Biodistribution studies in nude mice bearing human KB xenografts, demonstrated a significant tumor uptake and favorable biodistribution profile for 68Ga-NOTA-folate over the 68Ga-NOTAM-folate conjugate. The uptake in the tumors was blocked by excess injection of folic acid, suggesting a receptor-mediated process. These results demonstrate that the 68Ga-NOTA-folate conjugate may be useful as a molecular probe for detection and staging of folate receptor-positive cancers, such as ovarian cancer and their metastasis, as well as monitoring tumor response to treatment.

PET and PET/CT with 68gallium-labeled somatostatin analogues in Non GEP-NETs Tumors

Somatostatin (SST) is a 28-amino-acid cyclic neuropeptide mainly secreted by neurons and endocrine cells. A major interest for SST receptors (SSTR) as target for in vivo diagnostic and therapeutic purposes was born since a series of stable synthetic SST-analouges PET became available, being the native somatostatin non feasible for clinical use due to the very low metabolic stability. The rationale for the employment of SST-analogues to image cancer is both based on the expression of SSTR by tumor and on the high affinity of these compounds for SSTR. The primary indication of SST-analogues imaging is for neuroendocrine tumors (NETs), which usually express a high density of SSTR, so they can be effectively targeted and visualized with radiolabeled SST-analogues in vivo. Particularly, SST-analogues imaging has been widely employed in gastroenteropancreatic (GEP) NETs. Nevertheless, a variety of tumors other than NETs expresses SSTR thus SST-analogues imaging can also be used in these tumors, particularly if treatment with radiolabeled therapeutic SST-analouges PET is being considered. The aim of this paper is to provide a concise overview of the role of positron emission tomography/computed tomography (PET/CT) with (68)Ga-radiolabeled SST-analouges PET in tumors other than GEP-NETs.

Multimodality imaging probe for positron emission tomography and fluorescence imaging studies

Our goal is to develop multimodality imaging agents for use in cell tracking studies by positron emission tomography (PET) and optical imaging (OI). For this purpose, bovine serum albumin (BSA) was complexed with biotin (histologic studies), 5(6)-carboxyfluorescein, succinimidyl ester (FAM SE) (OI studies), and diethylenetriamine pentaacetic acid (DTPA) for chelating gallium 68 (PET studies). For synthesis of BSA-biotin-FAM-DTPA, BSA was coupled to (+)-biotin N-hydroxysuccinimide ester (biotin-NHSI). BSA-biotin was treated with DTPA-anhydride and biotin-BSA-DTPA was reacted with FAM. The biotin-BSA-DTPA-FAM was reacted with gallium chloride 3 to 5 mCi eluted from the generator using 0.1 N HCl and was passed through basic resin (AG 11 A8) and 150 μCi (100 μL, pH 7-8) was incubated with 0.1 mg of FAM conjugate (100 μL) at room temperature for 15 minutes to give 68Ga-BSA-biotin-DTPA-FAM. A shaved C57 black mouse was injected with FAM conjugate (50 μL) at one flank and FAM-68Ga (50 μL, 30 μCi) at the other. Immediately after injection, the mouse was placed in a fluorescence imaging system (Kodak In-Vivo F, Bruker Biospin Co., Woodbridge, CT) and imaged (λex: 465 nm, λem: 535 nm, time: 8 seconds, Xenon Light Source, Kodak). The same mouse was then placed under an Inveon microPET scanner (Siemens Medical Solutions, Knoxville, TN) injected (intravenously) with 25 μCi of 18F and after a half-hour (to allow sufficient bone uptake) was imaged for 30 minutes. Molecular weight determined using matrix-associated laser desorption ionization (MALDI) for the BSA sample was 66,485 Da and for biotin-BSA was 67,116 Da, indicating two biotin moieties per BSA molecule; for biotin-BSA-DTPA was 81,584 Da, indicating an average of 30 DTPA moieties per BSA molecule; and for FAM conjugate was 82,383 Da, indicating an average of 1.7 fluorescent moieties per BSA molecule. Fluorescence imaging clearly showed localization of FAM conjugate and FAM-68Ga at respective flanks of the mouse, whereas only a hot spot at the expected flank (FAM-68Ga injection site) was observed in microPET imaging. Our results suggest that BSA-biotin-DTPA-FAM may function as a multiprobe for PET and fluorescence imaging. Experiments are currently in progress to demonstrate cell tracking using both optical and nuclear imaging.

High uptake of (68)Ga-DOTATOC in spleen as compared to splenosis: measurement by PET/CT

AIM

The aim of this study is to ascertain the high somatostatin receptor (SSTR) uptake in spleen and to compare the uptake in spleen and splenosis using SSTR PET/CT using( 68)Ga-DOTATOC.

MATERIALS AND METHODS

SUV(max) of spleen on (68)Ga-DOTATOC SSTR PET/CT (acquired for initial staging) in 10 patients with known neuroendocrine neoplasm of pancreatic tail was analyzed. All patients underwent left pancreatectomy and splenectomy. Diagnosis of splenosis was confirmed on CT, and SUV(max) was noted on follow-up SSTR PET/CT.

RESULTS

SUV(max)was 28.8 ± 12.5 in normal spleen and 10.5 ± 4.3 in splenosis.

CONCLUSION

The high uptake of( 68)Ga-DOTATOC (which has a high affinity to SSTR 2) in the spleen as compared to splenosis, which has a different histology, suggests white pulp as the probable site of high SSTR 2 expression.

In vitro and in vivo characterization of three 68Ga- and 111In-labeled peptides for cholecystokinin receptor imaging

Cholecystokinin (CCK) receptors are overexpressed in several human tumor types, such as medullary thyroid carcinomas and small cell lung cancers. Several ligands for the CCK2 receptor (CCK2R) have been developed for radionuclide targeting of these tumors. In this study, we evaluated whether radiolabeled DOTA-sCCK8 and its stabilized derivative, DOTA-sCCK8[Phe(2)(p-CH2SO3H), Nle(3,6)], are suitable for imaging of CCK2R-positive tumors, using DOTA-MG0 as a reference. In vivo targeting of CCK2R-positive tumors with DOTA-sCCK8, DOTA-sCCK8[Phe(2)(p-CH2SO3H), Nle(3,6)], and DOTA-MG0, labeled with (111)In or (68)Ga, was evaluated in BALB/c nude mice with a subcutaneous A431-CCK2R tumor. Biodistribution studies and single-photon emission computed tomography (SPECT) and positron emission tomography (PET) were performed at 1 hour postinjection. All peptides specifically accreted in the CCK2R-expressing tumors. Both (111)In-DOTA-sCCK8 and (111)In-DOTA-sCCK8[Phe(2)(p-CH2SO3H), Nle(3,6)] showed good tumor retention (4.65% ID/g and 5.44% ID/g, respectively, at 4 hours postinjection). On PET/computed tomographic (CT) and SPECT/CT scans, subcutaneous A431-CCK2R tumors were clearly visualized with low uptake of sCCK8 peptides in the intestines. Whereas radiolabeled DOTA-MG0 showed high kidney uptake (70% ID/g), the sCCK8 peptides showed low uptake in the kidneys. Sulfated CCK8 analogues combined high tumor uptake with low retention in the kidney and are therefore promising tracers for imaging of CCK2R-positive tumors.

Long-circulating non-toxic blood pool imaging agent based on hyperbranched polyglycerols

PURPOSE

Currently, in vivo or in vitro(99m)Tc-radiolabelled red blood cells are the standard blood pool imaging agents. Due to risks associated with handling of blood and the problems with the current (99m)Tc shortage, we were interested in a long-circulating biocompatible synthetic macromolecule that would be simple to prepare and could also be used for PET imaging.

METHODS

A high molecular weight hyperbranched polyglycerol (HPG) of 500 kDa was derivatized to coordinate radioactive gallium and to establish its labelling efficiency, stability and pharmacokinetics.

RESULTS

The resulting radiopharmaceutical in kit form was labelled rapidly within a couple of minutes at room temperature, was stable in transferrin and EDTA challenge tests, and was non-toxic in both cell viability and different hemocompatibility assays. A pharmacokinetic biodistribution study showed that the (67)Ga-HPGN was confined to the blood compartment with a biological half life of 50.7h.

CONCLUSION

(67)Ga-HPGN is thus a simple to prepare blood pool imaging agent for applications where a long biological half-life is essential, i.e., the diagnosis of internal bleeding. Since radiolabelling of the same kit with (68)Ga was also confirmed, we plan to evaluate it shortly as a PET blood pool imaging agent for cardiac applications.

68Ga-chloride PET reveals human pancreatic adenocarcinoma xenografts in rats--comparison with FDG

PURPOSE

The aim of the study was to compare (68)Ga-chloride with 2-[(18)F]fluoro-2-deoxy-D: -glucose (FDG) for the imaging of pancreatic xenografts.

PROCEDURES

Rats with subcutaneous human pancreatic adenocarcinoma xenografts were evaluated in vivo by dynamic positron emission tomography (PET) and ex vivo by measuring radioactivity of excised tissues and by digital autoradiography of tumor cryosections.

RESULTS

Both tracers were capable of delineating all subcutaneous tumors from surrounding tissues by PET. The standardized uptake values of tumors by PET were 0.9 +/- 0.3 (mean +/- SD) for (68)Ga-chloride (n = 13) and 1.8 +/- 1.2 for FDG (n = 11). Ex vivo studies showed tumor-to-muscle ratio of 4.0 +/- 0.3 for (68)Ga-chloride (n = 4) and 7.9 +/- 3.2 for FDG (n = 4).

CONCLUSIONS

(68)Ga-chloride delineated subcutaneously implanted pancreatic adenocarcinoma xenografts by PET, but the uptake was lower than FDG. Further studies to clarify the value of (68)Ga-chloride for PET imaging of tumors are warranted.

Somatostatin-receptor-based imaging and therapy of gastroenteropancreatic neuroendocrine tumors

Somatostatin receptor imaging (SRI) with [(111)In-DTPA(0)]octreotide has proven its role in the diagnosis and staging of gastroenteropancreatic neuroendocrine tumors (GEPNETs). Newer radiolabeled somatostatin analogs which can be used in positron emission tomography (PET) imaging, and which have a higher affinity for the somatostatin receptor, especially receptor subtype-2, have been developed. It would be desirable, however, if one radiolabeled analog became the new standard for PET imaging, because the current application of a multitude of analogs implies a fragmented knowledge on the interpretation of the images that are obtained in clinical practice. In our view, the most likely candidates for such a universal PET tracer for SRI are [(68)Ga-DOTA(0),Tyr(3)]octreotate or [(68)Ga-DOTA(0),Tyr(3)]octreotide. Treatment with radiolabeled somatostatin analogs is a promising new tool in the management of patients with inoperable or metastasized neuroendocrine tumors. Symptomatic improvement may occur with all (111)In-, (90)Y-, or (177)Lu-labeled somatostatin analogs that have been used for peptide receptor radionuclide therapy (PRRT). The results that were obtained with [(90)Y-DOTA(0),Tyr(3)]octreotide and [(177)Lu-DOTA(0),Tyr(3)]octreotate are very encouraging in terms of tumor regression. Also, if kidney protective agents are used, the side effects of this therapy are few and mild, and the median duration of the therapy response for these radiopharmaceuticals is 30 and 40 months respectively. The patients' self-assessed quality of life increases significantly after treatment with [(177)Lu-DOTA(0),Tyr(3)]octreotate. Lastly, compared to historical controls, there is a benefit in overall survival of several years from the time of diagnosis in patients treated with [(177)Lu-DOTA(0),Tyr(3)]octreotate. These data compare favorably with the limited number of alternative treatment approaches. If more widespread use of PRRT can be guaranteed, such therapy may well become the therapy of first choice in patients with metastasized or inoperable GEPNETs.

Preliminary experience with (68)Ga-DOTA-lanreotide positron emission tomography

AIM

Positron emission tomography (PET) of (68)Ga-radiolabelled (SST) somatostatin receptor (R) binding peptides has recently been evaluated in SSTR positive tumor patients. First promising results in lung and thyroid tumor patients with (111)In-DOTA-Lanreotide (DOTA-LAN) scintigraphy have been described. We report our first experience with (68)Ga-labeled DOTA-LAN.

METHODS

Eleven patients (3 non small cell lung cancer [NSCLC], 3 small cell lung cancer [SCLC], 3 radioiodine negative thyroid cancer, 2 medullary thyroid cancer [MTC]) were investigated. After intravenous injection of 75-150 MBq (68)Ga-DOTA-LAN dynamic studies were acquired over the tumor site for the first 40 min with a dedicated PET scanner in 3 patients, and 2 partial body scans were acquired at 20 and 50 min p.i. in 2 patients. Whole body acquisitions at 90 min after injection were acquired in all 11 patients. Image reconstruction was performed by iterative reconstruction utilizing additional transmission scans for attenuation correction. Vital parameters were recorded during the PET study and up to 24 h p.i. Blood and urinary sampling was done up to 4 hr after tracer injection in 8 patients. PET results were compared to conventional imaging techniques (CIT), i.e. computed tomography (CT) and/or magnetic resonance imaging (MRI). In 5 patients, (68)Ga-DOTA-LAN was compared with 2-[(18)F]fluoro-2-deoxy-D-glucose ((18)F-FDG).

RESULTS

After intravenous (i.v.) injection of (68)Ga-DOTA-LAN the radioactivity in the blood rapidly decreased to less then 20% of the injected dose (ID) within the first 20 min and further decreased to less than 9% ID after 4 h. A cumulative urinary excretion of (68)Ga-DOTA-LAN up to 29.2 + or - 13.2% ID at 4 h was found. No acute side effects were observed. Tumor sites were visualized already during the first min after injection. Comparison of positron emission tomography (PET) and CIT showed concordant results in 3/8 patients and partial concordant results in 5/8 patients with matched results for the primary/recurrent tumor, mediastinal lymph nodes, or adrenal gland metastases. Partial concordant results were seen for the lung, bone, liver and cervical lymph node metastases. Micronodular metastases of the lung and the cerebrum were not visualized by (68)Ga-DOTA-LAN PET. The maximal standardized uptake values of the lung and bone tumor lesions ranged from 6 to 8 g/ml at 90 min p.i..

CONCLUSIONS

(68)Ga-DOTA-LAN visualized the majority of tumor lesions. Further studies are required to assess the clinical value, and to obtain the best imaging protocol of this new PET SSTR tracer.

Sarcoidosis involving the lacrimal, submandibular, and parotid glands with panda sign

Sarcoidosis is a granulomatous inflammation of unknown origin that varies in severity and distribution. We present a case of sarcoidosis with involvement of the skin, lacrimal, parotid, and submandibular glands. The patient had been previously misdiagnosed as having angioedema and allergic contact dermatitis; he had the rare finding of panda sign on gallium scintigraphy.

68Ga-DOTA-Tyr3-Octreotide PET in Neuroendocrine Tumors: Comparison with Somatostatin Receptor Scintigraphy and CT

The aim of this study was to evaluate the diagnostic value of a new somatostatin analog, (68)Ga-labeled 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid-d-Phe(1)-Tyr(3)-octreotide ((68)Ga-DOTA-TOC), for PET in patients with known or suspected neuroendocrine tumors. PET was compared with conventional scintigraphy and dedicated CT.

METHODS

Eighty-four patients (48 men, 36 women; age range, 28-79 y; mean age +/- SD, 58.2 +/- 12.2 y) were prospectively studied. For analysis, patients were divided into 3 groups: detection of unknown primary tumor in the presence of clinical or biochemical suspicion of neuroendocrine malignancy (n = 13 patients), initial tumor staging (n = 36 patients), and follow-up after therapy (n = 35 patients). Each patient received 100-150 MBq (68)Ga-DOTA-TOC. Imaging results of PET were compared with (99m)Tc-labeled hydrazinonicotinyl-Tyr(3)-octreotide ((99m)Tc-HYNIC-TOC) and (111)In-DOTA-TOC. CT was also performed on every patient using a multidetector scanner. Each imaging modality was interpreted separately by observers who were unaware of imaging findings before comparison with PET. The gold standard for defining true-positive (TP), true-negative (TN), false-positive (FP), and false-negative (FN) results was based on all available histologic, imaging, and follow-up findings.

RESULTS

PET was TP in 69 patients, TN in 12 patients, FP in 1 patient, and FN in 2 patients, indicating a sensitivity of 97%, a specificity of 92%, and an accuracy of 96%. The FP finding was caused by enhanced tracer accumulation in the pancreatic head, and the FN results were obtained in patients with a tumor of the gastrointestinal tract displaying liver metastases. (68)Ga-DOTA-TOC showed higher diagnostic efficacy compared with SPECT (TP in 37 patients, TN in 12 patients, FP in 1 patient, and FN in 34 patients) and diagnostic CT (TP in 41 patients, TN in 12 patients, FP in 5 patients, and FN in 26 patients). This difference was of statistical significance (P < 0.001). However, the combined use of PET and CT showed the highest overall accuracy.

CONCLUSION

(68)Ga-DOTA-TOC PET shows a significantly higher detection rate compared with conventional somatostatin receptor scintigraphy and diagnostic CT with clinical impact in a considerable number of patients.

Are radiogallium-labelled DOTA-conjugated somatostatin analogues superior to those labelled with other radiometals?

PURPOSE

Gallium-68 is a metallic positron emitter with a half-life of 68 min that is ideal for the in vivo use of small molecules, such as [68Ga-DOTA,Tyr3]octreotide, in the diagnostic imaging of somatostatin receptor-positive tumours. In preclinical studies it has shown a striking superiority over its 111In-labelled congener. The purpose of this study was to evaluate whether third-generation somatostatin-based, radiogallium-labelled peptides show the same superiority.

METHODS

Peptides were synthesised on solid phase. The receptor affinity was determined by in vitro receptor autoradiography. The internalisation rate was studied in AR4-2J and hsst-HEK-transfected cell lines. The pharmacokinetics was studied in a rat xenograft tumour model, AR4-2J.

RESULTS

All peptides showed high affinities on hsst2, with the highest affinity for the Ga(III)-complexed peptides. On hsst3 the situation was reversed, with a trend towards lower affinity of the Ga(III) peptides. A significantly increased internalisation rate was found in sst2-expressing cells for all 67Ga-labelled peptides. Internalisation into HEK-sst3 was usually faster for the 111In-labelled peptides. No internalisation was found into sst5. Biodistribution studies employing [67Ga-DOTA,1-Nal3]octreotide in comparison to [111In-DOTA,1-Nal3]octreotide and [67Ga-DOTA,Tyr3]octreotide showed a significantly higher and receptor-mediated uptake of the two 67Ga-labelled peptides in the tumour and somatostatin receptor-positive tissues. A patient study illustrated the potential advantage of a broad receptor subtype profile radiopeptide over a high-affinity sst2-selective radiopeptide.

CONCLUSION

This study demonstrates that 67/68Ga-DOTA-octapeptides show distinctly better preclinical, pharmacological performances than the 111In-labelled peptides, especially on sst2-expressing cells and the corresponding animal models. They may be excellent candidates for further development for clinical studies.

Gallium-67 scintigraphy in polymyalgia rheumatica

A patient with atypical presentation of polymyalgia rheumatica is presented. Her major symptoms were mild weakness, pain on passive movement of the shoulder and hip girdles, with mild tenderness but no joint stiffness. Muscle enzymes were within the normal range. The diagnostic work-up included gallium-67 scintigraphy, which showed intense uptake in both shoulders, with remarkable improvement following steroid treatment. A prospective study may delineate the possible role of this imaging modality in establishing a diagnosis of polymyalgia rheumatica.

Evaluation of [67Ga]-insulin for insulin receptor imaging

BACKGROUND

Radiolabelled human recombinant insulin can be used for the imaging of insulin receptors in some tumours where FDG has natural uptake and diminishes the value of its imaging.

MATERIAL AND METHODS

Insulin was successively labelled with [(67)Ga]-gallium chloride after conjugation with freshly prepared cyclic DTPA-dianhydride (HPLC radiochemical purity assay > 96%) followed by biodistribution studies in normal rats, white blood cell labelling and preliminary SPECT studies.

RESULTS

In vitro studies demonstrated the retention of radiolabelled insulin receptor affinity using freshly prepared human white blood cells at different blood sugar conditions. Preliminary in vivo studies in a normal rat model was performed to determine the biodistribution of the radioimmunoconjugate at up to 44 h. SPECT images revealed high uptake of the liver.

CONCLUSION

Radiolabelled insulin is stable enough to be used in biological studies in order to image insulin receptors in diabetic conditions as well as possible tumour imaging applications. The data was consistent with other radiolabelled insulin studies.

Extravascular lung water to blood volume ratios as measures of permeability in sepsis-induced ALI/ARDS

OBJECTIVE

We studied the relationship, and the effect of fluid loading on this, between the ratio of extravascular lung water (EVLW) to intrathoracic/pulmonary blood volumes (ITBV, PBV) and the radionuclide pulmonary leak index (PLI) to protein during sepsis-induced acute lung injury/acute respiratory distress syndrome (ALI/ARDS).

DESIGN AND SETTING

A prospective observational study, in the intensive care unit of a university hospital.

PATIENTS

Twenty-two consecutive mechanically ventilated patients with sepsis-related ALI/ARDS from pneumonia (n = 12) or extrapulmonary sources (n = 10), without elevated cardiac filling pressures.

INTERVENTION

Crystalloid (1700-1800 ml) or colloid (1000-1800 ml) fluid loading until target filling pressures.

MEASUREMENTS AND RESULTS

Protein permeability was assessed noninvasively over the lungs with help of 67Ga-labeled transferrin and 99mTc-labeled red blood cells (Pulmonary leak index, upper limit normal 14.1 x 10(-3)/min) and EVLW and blood volumes by the thermal-dye transpulmonary dilution technique before and after fluid loading. Prior to fluids the pulmonary leak index related to the ratio of EVLW/ITBV and EVLW/PBV (r(s) = 0.46) particularly when the pulmonary leak index was below 100 x 10(-3)/min and in extrapulmonary sepsis (PLI vs. EVLW/PBV r(s) = 0.71). Fluid loading did not alter EVLW, EVLW/ITBV, or EVLW/PBV or the relationship to PLI.

CONCLUSION

The data demonstrate that EVLW/ITBV or EVLW/PBV are imperfect measures of increased protein permeability in mechanically ventilated patients with sepsis-induced ALI/ARDS particularly when the PLI is severely increased and during pneumonia, independent of fluid status.