Molecular Imaging and Preclinical Studies of Radiolabeled Long-Term RGD Peptides in U-87 MG Tumor-Bearing Mice.

The Arg-Gly-Asp (RGD) peptide shows a high affinity for αvß3 integrin, which is overexpressed in new tumor blood vessels and many types of tumor cells. The radiolabeled RGD peptide has been studied for cancer imaging and radionuclide therapy. We have developed a long-term tumor-targeting peptide DOTA-EB-cRGDfK, which combines a DOTA chelator, a truncated Evans blue dye (EB), a modified linker, and cRGDfK peptide. The aim of this study was to evaluate the potential of indium-111(111In) radiolabeled DOTA-EB-cRGDfK in αvß3 integrin-expressing tumors. The human glioblastoma cell line U-87 MG was used to determine the in vitro binding affinity of the radiolabeled peptide. The in vivo distribution of radiolabeled peptides in U-87 MG xenografts was investigated by biodistribution, nanoSPECT/CT, pharmacokinetic and excretion studies. The in vitro competition assay showed that 111In-DOTA-EB-cRGDfK had a significant binding affinity to U-87 MG cancer cells (IC50 = 71.7 nM). NanoSPECT/CT imaging showed 111In-DOTA-EB-cRGDfK has higher tumor uptake than control peptides (111In-DOTA-cRGDfK and 111In-DOTA-EB), and there is still a clear signal until 72 h after injection. The biodistribution results showed significant tumor accumulation (27.1 ± 2.7% ID/g) and the tumor to non-tumor ratio was 22.85 at 24 h after injection. In addition, the pharmacokinetics results indicated that the 111In-DOTA-EB-cRGDfK peptide has a long-term half-life (T1/2λz = 77.3 h) and that the calculated absorbed dose was safe for humans. We demonstrated that radiolabeled DOTA-EB-cRGDfK may be a promising agent for glioblastoma tumor imaging and has the potential as a theranostic radiopharmaceutical.

Measuring the Pancreatic ß Cell Mass in Vivo with Exendin SPECT during Hyperglycemia and Severe Insulitis.

OBJECTIVE: Targeting the glucagon-like peptide-1 receptor with radiolabeled exendin is a very promising method to noninvasively determine the ß cell mass in the pancreas, which is needed to unravel the pathophysiology of type 1 and type 2 diabetes. The present study aimed to explore the effects of both hyperglycemia and insulitis on the uptake of exendin in a spontaneous type 1 diabetes mouse model, nonobese diabetic (NOD) mice. METHODS: NOD mice (n = 75, 7-21 weeks old) were injected intravenously with [111In]In-DTPA-exendin-3, and single-photon emission computed tomography (SPECT) images were acquired 1 h pi. The pancreatic accumulation of [111In]In-DTPA-exendin-3 was quantified in vivo using SPECT and by ex vivo counting and correlated to the ß cell mass (BCM). The influence of insulitis and hyperglycemia on the exendin uptake was assessed. RESULTS: The pancreas could be visualized longitudinally using SPECT. A linear correlation was found between the BCM (%) and pancreatic uptake (%ID/g) as measured by ex vivo counting (Pearson r = 0.64, p < 0.001), which was not affected by either insulitis (Pearson r = 0.66, p = 0.83) or hyperglycemia (Pearson r = 0.57, p = 0.51). Biodistribution and ex vivo autoradiography revealed remaining [111In]In-DTPA-exendin-3 uptake in the pancreas despite total ablation of BCM. CONCLUSIONS: Despite hyperglycemia and severe insulitis, we have found a good correlation between BCM and pancreatic exendin uptake, even in a suboptimal model with relatively high background activity.

Imaging of atherosclerosis, targeting LFA-1 on inflammatory cells with 111In-DANBIRT.

BACKGROUND: 111In-DOTA-butylamino-NorBIRT (DANBIRT) is a novel radioligand which binds to Leukocyte Function-associated Antigen-1 (LFA-1), expressed on inflammatory cells. This study evaluated 111In-DANBIRT for the visualization of atherosclerotic plaque inflammation in mice. METHODS AND RESULTS: ApoE-/- mice, fed an atherogenic diet up to 20 weeks (n = 10), were imaged by SPECT/CT 3 hours post injection of 111In-DANBIRT (~ 200 pmol, ~ 40 MBq). Focal spots of 111In-DANBIRT were visible in the aortic arch of all animals, with an average Target-to-Background Ratio (TBR) of 1.7 ± 0.5. In vivo imaging results were validated by ex vivo SPECT/CT imaging, with a TBR up to 11.5 (range 2.6 to 11.5). Plaques, identified by Oil Red O lipid-staining on excised arteries, co-localized with 111In-DANBIRT uptake as determined by ex vivo autoradiography. Subsequent histological processing and in vitro autoradiography confirmed 111In-DANBIRT uptake at plaque areas containing CD68 expressing macrophages and LFA-1 expressing inflammatory cells. Ex vivo incubation of a human carotid endarterectomy specimen with 111In-DANBIRT (~ 950 nmol, ~ 190 MBq) for 2 hours showed heterogeneous plaque uptake on SPECT/CT, after which immunohistochemical analysis demonstrated co-localization of 111In-DANBIRT uptake and CD68 and LFA-1 expressing cells. CONCLUSIONS: Our results indicate the potential of radiolabeled DANBIRT as a relevant imaging radioligand for non-invasive evaluation of atherosclerotic inflammation.

Radiometal-Dependent Biological Profile of the Radiolabeled Gastrin-Releasing Peptide Receptor Antagonist SB3 in Cancer Theranostics: Metabolic and Biodistribution Patterns Defined by Neprilysin.

Recent advances in oncology involve the use of diagnostic/therapeutic radionuclide-carrier pairs that target cancer cells, offering exciting opportunities for personalized patient treatment. Theranostic gastrin-releasing peptide receptor (GRPR)-directed radiopeptides have been proposed for the management of GRPR-expressing prostate and breast cancers. We have recently introduced the PET tracer 68Ga-SB3 (SB3, DOTA- p-aminomethylaniline-diglycolic acid-DPhe-Gln-Trp-Ala-Val-Gly-His-Leu-NHEt), a receptor-radioantagonist that enables the visualization of GRPR-positive lesions in humans. Aiming to fully assess the theranostic potential of SB3, we herein report on the impact of switching 68Ga to 111In/177Lu-label on the biological properties of resulting radiopeptides. Notably, the bioavailability of 111In/177Lu-SB3 in mice drastically deteriorated compared with metabolically robust 68Ga-SB3, and as a result led to poorer 111In/177Lu-SB3 uptake in GRPR-positive PC-3 xenografts. The peptide cleavage sites were identified by chromatographic comparison of blood samples from mice intravenously receiving 111In/177Lu-SB3 with each of newly synthesized 111In/177Lu-SB3-fragments. Coinjection of the radioconjugates with the neprilysin (NEP)-inhibitor phosphoramidon led to full stabilization of 111In/177Lu-SB3 in peripheral mouse blood and resulted in markedly enhanced radiolabel uptake in the PC-3 tumors. In conclusion, in situ NEP-inhibition led to indistinguishable 68Ga/111In/177Lu-SB3 profiles in mice emphasizing the theranostic prospects of SB3 for clinical use.

Optimized Molecular Design of ADAPT-Based HER2-Imaging Probes Labeled with 111In and 68Ga.

Radionuclide molecular imaging is a promising tool for visualization of cancer associated molecular abnormalities in vivo and stratification of patients for specific therapies. ADAPT is a new type of small engineered proteins based on the scaffold of an albumin binding domain of protein G. ADAPTs have been utilized to select and develop high affinity binders to different proteinaceous targets. ADAPT6 binds to human epidermal growth factor 2 (HER2) with low nanomolar affinity and can be used for its in vivo visualization. Molecular design of 111In-labeled anti-HER2 ADAPT has been optimized in several earlier studies. In this study, we made a direct comparison of two of the most promising variants, having either a DEAVDANS or a (HE)3DANS sequence at the N-terminus, conjugated with a maleimido derivative of DOTA to a GSSC amino acids sequence at the C-terminus. The variants (designated DOTA-C59-DEAVDANS-ADAPT6-GSSC and DOTA-C61-(HE)3DANS-ADAPT6-GSSC) were stably labeled with 111In for SPECT and 68Ga for PET. Biodistribution of labeled ADAPT variants was evaluated in nude mice bearing human tumor xenografts with different levels of HER2 expression. Both variants enabled clear discrimination between tumors with high and low levels of HER2 expression. 111In-labeled ADAPT6 derivatives provided higher tumor-to-organ ratios compared to 68Ga-labeled counterparts. The best performing variant was DOTA-C61-(HE)3DANS-ADAPT6-GSSC, which provided tumor-to-blood ratios of 208 ± 36 and 109 ± 17 at 3 h for 111In and 68Ga labels, respectively.

Enzymatic degradation study of 111In-labeled minigastrin peptides using cathepsin B enzyme and AR42J cancer cell line for the development of neuroendocrine tumor imaging radiopharmaceuticals.

Neuroendocrine tumors (NET) are the rare tumors which often impose graveyard threat. These tumors are characterized by the over expression of various G-protein coupled receptors including cholecystokinin (CCK) receptors-1 and 2 (A or B). Minigastrin peptides are being investigated for theranostic purposes of CCK-2 receptor positive NET. The minigastrin analogue (APHO70) was modified by engineering enzyme susceptible tetrapeptide sequence into APHO70 peptide to reduce the random degradation by lysosome enzymes which pave the way to random trafficking in patient's body and dipeptide addition at c-terminus. All the four modified minigastrin peptides (MG-CL1-4) were investigated for lysosome cathepsin B (catB) enzyme susceptibility and fate into AR42J cancer cell line. The indium-111 labeled MG-CL1-4 peptides were also studied for target (tumor) and non-target saccumulation by using tumor induced mice. The RP-HPLC analysis result showed nonspecific cleavage of standard 111In-APH070 and 111In-MGCL1 while specific cleavage was noted in case of 111In-MGCL (2-4). The effect of specific and non-specific cleavage on biodistribution in tumor induced nude mice model indicates the promising accumulation of 111In-MGCL2, 111In-MGCL3, and 111In-MGCL4 radiotracers while 111In-MGCL1 showed less accumulation. 111In-MGCL2 and 111In-MGCL3 showed highest target-to-kidney ratio (T/K) i.e. 1.71 and 1.72, respectively whereas standard compound showed T/K 1.13. In conclusion, the two indium-111 labeled analogues i.e. 111In-MGCL2 and 111In-MGCL3 showed promising sensitivity for tumor andcould be tested for further investigation to reach pre-clinical studies.

Radiolabeled 111In-FGF-2 Is Suitable for In Vitro/Ex Vivo Evaluations and In Vivo Imaging.

Fibroblast growth factor-2 (FGF-2) is a potent modulator of cell growth and regulation, with improper FGF-2 signaling being involved in impaired responses to injury or even cancer. Therefore, the exploitation of FGF-2 as a therapeutic drives the prerequisite for effective insight into drug disposition kinetics. In this article, we present an 111In-radiolabeled FGF-2 derivative for noninvasive imaging in small animals deploying single photon emission tomography (SPECT). 111In-FGF-2 is equally well suitable for in vitro and ex vivo investigations as 125I-FGF-2. Furthermore, 111In-FGF-2 permits the performance of in vivo imaging, for example for the analysis of FGF-2 containing pharmaceutical formulations in developmental or preclinical stages. 111In-FGF-2 had affinity for the low-molecular-weight heparin enoxaparin identical to that of unlabeled FGF-2 (Kd: 0.6 ± 0.07 µM and 0.33 ± 0.03 µM, respectively) as assessed by isothermal titration calorimetry. The binding of 111In-FGF-2 to heparan sulfate proteoglycans (HPSGs) and the biological activity were comparable to those of unlabeled FGF-2, with EC50 values of 12 ± 2 pM and 25 ± 6 pM, respectively. In vivo biodistribution in healthy nude mice indicated a predominant accumulation of 111In-FGF-2 in filtering organs and minor uptake in the retina and the salivary and pituitary glands, which was confirmed by SPECT imaging. Therefore, 111In-FGF-2 is a valid tracer for future noninvasive animal imaging of FGF-2 in pharmaceutical development.

Nuclear imaging of thrombosis in small animal.

Thromboembolic disorders are a major cause of morbidity and mortality worldwide. The progress in noninvasive imaging techniques has led to the development of radionuclide imaging based on SPECT and PET approaches to observe molecular and cellular processes that may underlie the onset and progression of disease. The advantages of using normal and genetically modified small animal research have spurred the development of dedicated small animal imaging systems. Animal models of venous and arterial thrombosis are largely used and have improved our understanding of the etiology and pathogenesis of thrombosis. Here, we review the literature regarding nuclear imaging of thrombosis in mice and rats.

Antitumor efficacy of Auger electron emitter 111In delivered by modular nanotransporter into the nuclei of cells with folate receptor overexpression.

A new modular nanotransporter (MNT) for the delivery of anticancer agents into the nuclei of cells with folate receptor overexpression was created. An effective method for acceding labeling of this MNT with Auger electron emitter 111In has been developed. A significant therapeutic effect was observed after a single intratumoral injection of the new 111In-labeled MNT to mice grafted with human cervical carcinoma characterized by folate receptor overexpression.

Imaging a functional tumorigenic biomarker in the transformed epithelium.

Proteases responsible for the increased peritumoral proteolysis associated with cancer represent functional biomarkers for monitoring tumorigenesis. One attractive extracellular biomarker is the transmembrane serine protease matriptase. Found on the surface of epithelial cells, the activity of matriptase is regulated by its cognate inhibitor hepatocyte growth factor activator inhibitor-1 (HAI-1). Quantitative mass spectrometry allowed us to show that, in selected cancers, HAI-1 expression decreases, leading to active matriptase. A preclinical probe specific for the measurement of emergent active matriptase was developed. Using an active-site-specific, recombinant human antibody for matriptase, we found that the selective targeting of active matriptase can be used to visualize the tumorigenic epithelium. Live-cell fluorescence imaging validated the selectivity of the antibody in vitro by showing that the probe localized only to cancer cell lines with active matriptase on the surface. Immunofluorescence with the antibody documented significant levels of active matriptase in 68% of primary and metastatic colon cancer sections from tissue microarrays. Labeling of the active form of matriptase in vivo was measured in human colon cancer xenografts and in a patient-derived xenograft model using near-infrared and single-photon emission computed tomography imaging. Tumor uptake of the radiolabeled antibody, (111)In-A11, by active matriptase was high in xenografts (28% injected dose per gram) and was blocked in vivo by the addition of a matriptase-specific variant of ecotin. These findings suggest, through a HAI-1-dependent mechanism, that emergent active matriptase is a functional biomarker of the transformed epithelium and that its proteolytic activity can be exploited to noninvasively evaluate tumorigenesis in vivo.

Stereochemistry of amino acid spacers determines the pharmacokinetics of (111)In-DOTA-minigastrin analogues for targeting the CCK2/gastrin receptor.

The metabolic instability and high kidney retention of minigastrin (MG) analogues hamper their suitability for use in peptide-receptor radionuclide therapy of CCK2/gastrin receptor-expressing tumors. High kidney retention has been related to N-terminal glutamic acids and can be substantially reduced by coinjection of polyglutamic acids or gelofusine. The aim of the present study was to investigate the influence of the stereochemistry of the N-terminal amino acid spacer on the enzymatic stability and pharmacokinetics of (111)In-DOTA-(d-Glu)6-Ala-Tyr-Gly-Trp-Met-Asp-Phe-NH2 ((111)In-PP11-D) and (111)In-DOTA-(l-Glu)6-Ala-Tyr-Gly-Trp-Met-Asp-Phe-NH2 ((111)In-PP11-L). Using circular dichroism measurements, we demonstrate the important role of secondary structure on the pharmacokinetics of the two MG analogues. The higher in vitro serum stability together with the improved tumor-to-kidney ratio of the (d-Glu)6 congener indicates that this MG analogue might be a good candidate for further clinical study.

Use of 111-Indium-labeled autologous eosinophils to establish the in vivo kinetics of human eosinophils in healthy subjects.

Eosinophils are the major cellular effectors of allergic inflammation and represent an important therapeutic target. Although the genesis and activation of eosinophils have been extensively explored, little is known about their intravascular kinetics or physiological fate. This study was designed to determine the intravascular life span of eosinophils, their partitioning between circulating and marginated pools, and sites of disposal in healthy persons. Using autologous, minimally manipulated 111-Indium-labeled leukocytes with blood sampling, we measured the eosinophil intravascular residence time as 25.2 hours (compared with 10.3 hours for neutrophils) and demonstrated a substantial marginated eosinophil pool. γ camera imaging studies using purified eosinophils demonstrated initial retention in the lungs, with early redistribution to the liver and spleen, and evidence of recirculation from a hepatic pool. This work provides the first in vivo measurements of eosinophil kinetics in healthy volunteers and shows that 111-Indium-labeled eosinophils can be used to monitor the fate of eosinophils noninvasively.

Reduction of renal uptake of 111In-DOTA-labeled and A700-labeled RAFT-RGD during integrin αvß3 targeting using single photon emission computed tomography and optical imaging.

Integrin α(v)ß(3) expression is upregulated during tumor growth and invasion in newly formed endothelial cells in tumor neovasculature and in some tumor cells. A tetrameric RGD-based peptide, regioselectively addressable functionalized template-(cyclo-[RGDfK])4 (RAFT-RGD), specifically targets integrin α(v)ß(3) in vitro and in vivo. When labeled with indium-111, the RAFT-RGD is partially reabsorbed and trapped in the kidneys, limiting its use for further internal targeted radiotherapy and imaging investigations. We studied the effect of Gelofusine on RAFT-RGD renal retention in tumor-bearing mice. Mice were imaged using single photon emission computed tomography and optical imaging 1 and 24 h following tracer injection. Distribution of RAFT-RGD was further investigated by tissue removal and direct counting of the tracer. Kidney sections were analyzed by confocal microscopy. Gelofusine significantly induced a >50% reduction of the renal reabsorption of (111)In-DOTA-RAFT-RGD and A700-RAFT-RGD, without affecting tumor uptake. Injection of Gelofusine significantly reduced the renal retention of labeled RAFT-RGD, while increasing the tumor over healthy tissue ratio. These results will lead to the development of future therapeutic approaches.

Comprehensive evaluation of a somatostatin-based radiolabelled antagonist for diagnostic imaging and radionuclide therapy.

PURPOSE: Targeting of tumours positive for somatostatin receptors (sst) with radiolabelled peptides is of interest for tumour localization, staging, therapy follow-up and targeted radionuclide therapy. The peptides used clinically are exclusively agonists, but recently we have shown that the radiolabelled somatostatin-based antagonist (111)In-DOTA-sst2-ANT may be preferable to agonists. However, a comprehensive study of this radiolabelled antagonist to determine its significance was lacking. The present report describes the evaluation of this novel antagonist labelled with (111)In and (177)Lu in three different tumour models. METHODS: Radiopeptide binding, internalization and dissociation studies were performed using cells expressing HEK293-rsst(2). Biodistribution studies were performed in HEK293-rsst(2), HEK293-hsst(2) and HEK293-rsst(3) xenografted mice. RESULTS: Saturation binding analysis confirmed earlier IC(50) data for (111/nat)In-DOTA-sst2-ANT and showed similar affinity of (177/nat)Lu-DOTA-sst2-ANT for the sst(2). Only low internalization was found in cell culture (6.68 ± 0.06 % at 4 h), which was not unexpected for an antagonist, and this could be further reduced by the addition of sucrose. No internalization was observed in HEK293 cells not expressing sst. Both results indicate that the internalization was specific. (111)In-DOTA-sst2-ANT and (177)Lu-DOTA-sst2-ANT were shown to target tumour xenografts expressing the rat and the human sst(2) receptor with no differences in their uptake or pharmacokinetics. The uptake in rsst(2) and hsst(2) was high (about 30 %IA/g 4 h after injection) and surprisingly long-lasting (about 20-23 %IA/g 24 h after injection). Kidney uptake was blocked by approximately 50 % by lysine or Gelofusine. CONCLUSION: These results indicate that radiolabelled somatostatin-based antagonists may be superior to corresponding agonists. The long tumour retention time of (177)Lu-DOTA-sst2-ANT indicates that this new class of compounds is of relevance not only in diagnostic imaging but also in targeted radionuclide therapy of sst-positive tumours.

111In-Pentetreotide Uptake Due to COVID-19 Vaccination.

ABSTRACT: A 72-year-old woman was referred for whole-body 111In-pentetreotide scintigraphy with SPECT/CT. There was increased uptake of lymphadenopathy in the left axilla and left deltoid muscle. The patient's history revealed that the patient received the first dose of the COVID-19 vaccine 3 days before the 111In-pentetreotide scintigraphy with SPECT/CT. This case demonstrates that the COVID-19 vaccine can cause 111In-pentetreotide uptake in the lymph nodes and the deltoid muscle.

Quantification of neutrophil migration into the lungs of patients with chronic obstructive pulmonary disease.

OBJECTIVE: To quantify neutrophil migration into the lungs of patients with chronic pulmonary obstructive disease (COPD). METHODS: Neutrophil loss via airways was assessed by dedicated whole-body counting 45 min, 24 h and 2, 4, 7 and 10 days after injection of very small activities of (111)In-labelled neutrophils in 12 healthy nonsmokers, 5 healthy smokers, 16 patients with COPD (of whom 7 were ex-smokers) and 10 patients with bronchiectasis. Lung accumulation of (99m)Tc-labelled neutrophils was assessed by sequential SPECT and Patlak analysis in six COPD patients and three healthy nonsmoking subjects. RESULTS: Whole body (111)In counts, expressed as percentages of 24 h counts, decreased in all subjects. Losses at 7 days (mean ± SD) were similar in healthy nonsmoking subjects (5.5 ± 1.5%), smoking subjects (6.5 ± 4.4%) and ex-smoking COPD patients (5.8 ± 1.5%). In contrast, currently smoking COPD patients showed higher losses (8.0 ± 3.0%) than healthy nonsmokers (p = 0.03). Two bronchiectatic patients lost 25% and 26%, indicating active disease; mean loss in the remaining eight was 6.9 ± 2.5%. The rate of accumulation of (99m)Tc-neutrophils in the lungs, determined by sequential SPECT, was increased in COPD patients (0.030-0.073 min(-1)) compared with healthy nonsmokers (0-0.002 min(-1); p = 0.02). CONCLUSION: In patients with COPD, sequential SPECT showed increased lung accumulation of (99m)Tc-labelled neutrophils, while whole-body counting demonstrated subsequent higher losses of (111)In-labelled neutrophils in patients who continued to smoke. Sequential SPECT as a means of quantifying neutrophil migration deserves further evaluation.

High-resolution in vivo imaging of breast cancer by targeting the pro-invasive integrin alphavbeta6.

The integrin alphavbeta6 is expressed only on epithelia and then usually only during processes of tissue remodelling including cancer, where its high expression correlates with reduced survival. Thus, alphavbeta6 represents an important target for imaging and therapy of cancer and new molecular-specific targeting agents are required. We have developed A20FMDV2, a peptide derived from the VP1 coat protein of foot-and-mouth-disease virus that binds specifically and stably to alphavbeta6. Using a newly generated pair of isogenic human cell lines that differ only in alphavbeta6 expression, it was shown, using biodistribution and SPECT imaging, that indium-111-labelled A20FMDV2 locates specifically to alphavbeta6-expressing tissues in vivo, achieving at least seven-times higher retention in alphavbeta6-positive than in alphavbeta6-negative tumours. In further studies with MCF10.DCIS.COM and MCF10A.CA1a breast carcinoma cell lines, which express alphavbeta6 endogenously, the radiopeptide achieved similar levels of tumour retention and permitted excellent discriminatory imaging of tumours. Thus, A20FMDV2 can be used for molecular-specific targeting of alphavbeta6 for imaging in vivo the often more aggressive, alphavbeta6-positive cancers. In the future, A20FMDV2 could serve also to deliver therapy to these same cancers.

111In-Labeled White Blood Cell Uptake in the Urinary Bladder in Occult Urinary Tract Infection.

ABSTRACT: A 55-year-old woman with multiple medical problems, including anuric, dialysis-dependent, end-stage renal disease, presented with persistent fever of unknown origin. Despite extensive workup with cross-sectional imaging and panculture, the etiology was not found. Eventually, an 111In-labeled WBC scan was performed to evaluate for occult infection, which revealed intense heterogeneous uptake in the urinary bladder. Subsequent bladder catheterization showed pus and blood, which grew Klebsiella pneumoniae. The fevers resolved with adjustment of the therapy. Although urinary analysis and culture are standard practice in the workup of fever of unknown origin, anuria may obscure this common source of infection.

Red cell volume measurement - using indium as a replacement for chromium.

The withdrawal of Cr-chromate has meant that the technique commonly used for direct measurement of red cell volume has had to be replaced. Most centres moved to a Tc erythrocyte label, however, Tc is known to dissociate over time. We have investigated an alternative technique using an In-chloride and tropolone solution and tested this both in vitro and in vivo. Initial in-vitro and in-vivo work, which included a check of the stability of the radio-labelled product at one hour, demonstrated this label to be stable over this time period. To date, 20 patients have undergone this technique and results show that this technique is a viable alternative to Cr-chromate particularly for patients with splenomegaly who require late sampling. This procedure is now in routine use in our institution.

Association of glucagon-like peptide-1 receptor-targeted imaging probe with in vivo glucagon-like peptide-1 receptor agonist glucose-lowering effects.

AIMS/INTRODUCTION: Glucagon-like peptide-1 receptor agonists (GLP-1RA) are used for treatment of type 2 diabetes mellitus worldwide. However, some patients do not respond well to the therapy, and caution must be taken for certain patients, including those with reduced insulin secretory capacity. Thus, it is clinically important to predict the efficacy of GLP-1RA therapy. GLP-1R-targeted imaging has recently emerged to visualize and quantify ß-cells. We investigated whether GLP-1R-targeted imaging can predict the efficacy of GLP-1RA treatment. MATERIALS AND METHODS: We developed 111 Indium-labeled exendin-4 derivative (111 In-Ex4) as a GLP-1R-targeting probe. Diabetic mice were selected from NONcNZO10/LtJ male mice that were fed for different durations with 11% fat chow. After 3-week administration of dulaglutide as GLP-1RA therapy, mice with non-fasting blood glucose levels <300 mg/dL and >300 mg/dL were defined as responders and non-responders, respectively. In addition, ex vivo 111 In-Ex4 pancreatic accumulations (111 In-Ex4 pancreatic values) were examined. RESULTS: The non-fasting blood glucose levels after treatment were 172.5 ± 42.4 mg/dL in responders (n = 4) and 330.8 ± 20.7 mg/dL in non-responders (n = 5), respectively. Ex vivo 111 In-Ex4 pancreatic values showed significant correlations with post-treatment glycohemoglobin and glucose area under curve during an oral glucose tolerance test (R2  = 0.76 and 0.80; P < 0.01 and <0.01, respectively). The receiver operating characteristic area under curve for identifying responders by ex vivo 111 In-Ex4 pancreatic values was 1.00 (P < 0.01). CONCLUSION: Ex vivo 111 In-Ex4 pancreatic values reflected dulaglutide efficacy, suggesting clinical possibilities for expanding GLP-1R-targeted imaging applications.