(111)In-trastuzumab scintigraphy in HER2-positive metastatic breast cancer patients remains feasible during trastuzumab treatment

Human epidermal growth factor receptor (HER)2 imaging with radiolabeled trastuzumab might support HER2-targeted therapy. It is, however, frequently questioned whether HER2 imaging is also possible during trastuzumab treatment as the receptor might be saturated. We studied the effect of trastuzumab treatment on 111In-trastuzumab uptake. Patients received trastuzumab weekly and paclitaxel once every 3 weeks. 111In-trastuzumab was injected on day 1 of cycle 1 and day 15 of cycle 4. Whole-body planar scintigraphy was acquired at different time points postinjection. Tumor uptake and organ distribution between the first and repeated scan series were calculated via residence times. Twenty-five tumor lesions in 12 patients were visualized on both scintigraphy series. Tumor uptake decreased (19.6%; p  =  .03). The residence times of normal organs remained similar except for the cardiac blood pool (+ 16.3%; p  =  .014). Trastuzumab treatment decreases tumor 111In-trastuzumab uptake around 20%. HER2 imaging is feasible during trastuzumab treatment.

Precise fusion of MRI and dual energy 111In WBC/99mTc HDP SPECT/CT in the diabetic foot using companion CT: an example of SPECT/MRI imaging

AIM

The purpose of our study was to correctly fuse MRI and SPECT ¹¹¹In WBC and ⁹⁹m Tc HDP images using companion CT images. The fused images could be used to assess proper surgical approach in treatment of the diabetic foot.

METHODS

Nine patients who had dual energy ¹¹¹In WBC/ ⁹⁹m Tc HDP SPECT/CT and MRI studies within a week were investigated in an ongoing project. A GE Infinia SPECT/CT camera and Siemens MAGNETOM 1.5T MR system were used in this study. First, the MRI and corresponding CT images were coregistrated using a transformation based on normalized mutual information. The transformation was saved and used for MRI and ¹¹¹In WBC/ ⁹⁹m Tc HDP SPECT fusion. A Jaszczak phantom study was also performed in order to estimate accuracy of MRI/ SPECT fusion.

RESULTS

The Jaszczak phantom study with 3.7 MBq ¹¹¹In hot sphere showed that MRI/SPECT alignment using the approach described above produced registration with 0.7 ± 0.4 mm accuracy in all three dimensions (3D). The nine clinical cases were visually evaluated and showed 1-2 mm 3D fusion accuracy. MRI provides almost perfect anatomy of soft tissue and bony structures but it may exaggerate the extent of infection. ¹¹¹In WBC/⁹⁹m Tc HDP SPECT imaging is more accurate for infection detection but lacks anatomical reference. Combination of these images proved an essential adjunct to diagnosis. A clinical utility of the approach is illustrated in two clinical examples.

CONCLUSION

The CT in dual energy ¹¹¹In WBC/⁹⁹m Tc HDP SPECT/CT studies can be used to accurately fuse and compare ¹¹¹In WBC/⁹⁹m Tc HDP SPECT and MRI images of the diabetic foot. This can significantly help in conservative treatment planning and limb salvage procedures in treatment of diabetic foot infections.

Evaluation and comparison of a new DOTA and DTPA-bombesin agonist in vitro and in vivo in low and high GRPR expressing prostate and breast tumor models

We evaluated and compared a new bombesin analog [Tyr-Gly5, Nle(14)]-BBN(6-14) conjugated to DOTA or DTPA and radiolabeled with In-111 in low and high GRPR expressing tumor models. Both peptides were radiolabeled with high radiochemical purity and specific activity. In vitro assays on T-47D, LNCaP and PC-3 cells showed that the affinity of peptides is similar and a higher binding and internalization of DOTA-peptide to PC-3 cells was observed. Both peptides could target PC-3 and LNCaP tumors in vivo and both tumor types could be visualized by microSPECT/CT.

Inside the pancreas: progress and challenges of human beta cell mass quantification

The accurate quantification of beta cell mass in humans is one of the key challenges in understanding the role of beta cell loss and dysfunction in the pathogenesis of diabetes mellitus. Autopsy studies indicate that beta cell loss is not only a hallmark of autoimmune diabetes but also plays a pivotal role in type 2 diabetes, owing to the toxic effects of lipids, glucose and cytokines. Thus, there is an urgent need for non-invasive clinical techniques for beta cell mass quantification, which should be optimally integrated into standard diagnostic equipment in hospitals. In this issue of Diabetologia (Brom et al DOI 10.1007/s00125-014-3166-3) it is reported that single photon emission computed tomography (SPECT) data with (111)indium-labelled glucagon-like peptide-1 (GLP-1) receptor agonist exendin-3 correlate with the morphometric analysis of beta cell mass in a rat model of alloxan-induced diabetes. With this validation, the authors were able to demonstrate a significant loss of beta cell mass in C-peptide-negative type 1 diabetic patients. Thus, (111)indium-labelled exendin-3 could serve as a model tracer for future studies of larger cohorts of diabetic patients to monitor the dynamics of beta cell loss and regeneration. Despite the recent progress from SPECT imaging data there remain open questions that await clarification in the near future such as variations in GLP-1 receptor density and physiological variation of beta cell mass in relation to beta cell function. The use of GLP-1-based tracer analysis may open new clinical avenues for non-invasive quantification of beta cell mass in patients with newly diagnosed type 1 diabetes and prediabetic individuals with high titres of autoantibodies.

Non-invasive quantification of the beta cell mass by SPECT with ¹¹¹In-labelled exendin

AIMS/HYPOTHESIS

A reliable method for in vivo quantification of pancreatic beta cell mass (BCM) could lead to further insight into the pathophysiology of diabetes. The glucagon-like peptide 1 receptor, abundantly expressed on beta cells, may be a suitable target for imaging. We investigated the potential of radiotracer imaging with the GLP-1 analogue exendin labelled with indium-111 for determination of BCM in vivo in a rodent model of beta cell loss and in patients with type 1 diabetes and healthy individuals.

METHODS

The targeting of (111)In-labelled exendin was examined in a rat model of alloxan-induced beta cell loss. Rats were injected with 15 MBq (111)In-labelled exendin and single photon emission computed tomography (SPECT) acquisition was performed 1 h post injection, followed by dissection, biodistribution and ex vivo autoradiography studies of pancreatic sections. BCM was determined by morphometric analysis after staining with an anti-insulin antibody. For clinical evaluation SPECT was acquired 4, 24 and 48 h after injection of 150 MBq (111)In-labelled exendin in five patients with type 1 diabetes and five healthy individuals. The tracer uptake was determined by quantitative analysis of the SPECT images.

RESULTS

In rats, (111)In-labelled exendin specifically targets the beta cells and pancreatic uptake is highly correlated with BCM. In humans, the pancreas was visible in SPECT images and the pancreatic uptake showed high interindividual variation with a substantially lower uptake in patients with type 1 diabetes.

CONCLUSIONS/INTERPRETATION

These studies indicate that (111)In-labelled exendin may be suitable for non-invasive quantification of BCM.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01825148, EudraCT: 2012-000619-10.

Use of a ray-based reconstruction algorithm to accurately quantify preclinical microSPECT images

This work aimed to measure the in vivo quantification errors obtained when ray-based iterative reconstruction is used in micro-single-photon emission computed tomography (SPECT). This was investigated with an extensive phantom-based evaluation and two typical in vivo studies using 99mTc and 111In, measured on a commercially available cadmium zinc telluride (CZT)-based small-animal scanner. Iterative reconstruction was implemented on the GPU using ray tracing, including (1) scatter correction, (2) computed tomography-based attenuation correction, (3) resolution recovery, and (4) edge-preserving smoothing. It was validated using a National Electrical Manufacturers Association (NEMA) phantom. The in vivo quantification error was determined for two radiotracers: [99mTc]DMSA in naive mice (n  =  10 kidneys) and [111In]octreotide in mice (n  =  6) inoculated with a xenograft neuroendocrine tumor (NCI-H727). The measured energy resolution is 5.3% for 140.51 keV (99mTc), 4.8% for 171.30 keV, and 3.3% for 245.39 keV (111In). For 99mTc, an uncorrected quantification error of 28 ± 3% is reduced to 8 ± 3%. For 111In, the error reduces from 26 ± 14% to 6 ± 22%. The in vivo error obtained with 99mTc-dimercaptosuccinic acid ([99mTc]DMSA) is reduced from 16.2 ± 2.8% to -0.3 ± 2.1% and from 16.7 ± 10.1% to 2.2 ± 10.6% with [111In]octreotide. Absolute quantitative in vivo SPECT is possible without explicit system matrix measurements. An absolute in vivo quantification error smaller than 5% was achieved and exemplified for both [99mTc]DMSA and [111In]octreotide.

Measurement of eosinophil kinetics in healthy volunteers

Radiolabelled leukocyte scans are widely used in nuclear medicine to locate sites of infection and inflammation. Radiolabelling of leukocyte subpopulations can also yield valuable information on cell trafficking and kinetics in vivo, but care must be taken to minimize inadvertent cell activation ex vivo. Here, we describe the use of autologous indium(111)-labelled eosinophils to measure eosinophil intravascular life-span and monitor their distribution and fate using gamma camera imaging in healthy non-atopic individuals.

Skeletal muscle satellite cell migration to injured tissue measured with 111In-oxine and high-resolution SPECT imaging

The delivery of adult skeletal muscle stem cells, called satellite cells, to several injured muscles via the circulation would be useful, however, an improved understanding of cell fate and biodistribution following their delivery is important for this goal to be achieved. The objective of this study was to evaluate the ability of systemically delivered satellite cells to home to injured skeletal muscle using single-photon emission computed tomography (SPECT) imaging of (111)In-labeled satellite cells. Satellite cells labeled with (111)In-oxine and green fluorescent protein (GFP) were injected intravenously after bupivicaine-induced injury to the tibialis anterior muscle. Animals were imaged with a high-resolution SPECT system called FastSPECT II for up to 7 days after transplantation. In vivo FastSPECT II imaging demonstrated a three to five-fold greater number of transplanted satellite cells in bupivicaine-injured muscle as compared to un-injured muscle after transplantation; a finding that was verified through autoradiograph analysis and quantification of GFP expression. Satellite cells also accumulated in other organs including the lung, liver, and spleen, as determined by biodistribution measurements. These data support the ability of satellite cells to home to injured muscle and support the use of SPECT and autoradiograph imaging techniques to track systemically transplanted (111)In labeled satellite cells in vivo, and suggest their homing may be improved by reducing their entrapment in filter organs.

Somatostatin receptor type 2-based reporter expression after plasmid-based in vivo gene delivery to non-small cell lung cancer

Plasmids tend to have much lower expression than viruses. Gene expression after systemic administration of plasmid vectors has not been assessed using somatostatin receptor type 2 (SSTR2)-based reporters. The purpose of this work was to identify gene expression in non-small cell lung cancer (NSCLC) after systemic liposomal nanoparticle delivery of plasmid containing SSTR2-based reporter gene. In vitro, Western blotting was performed after transient transfection with the plasmid cytomegalovirus (CMV)-SSTR2, CMV-TUSC2-IRES-SSTR2, or CMV-TUSC2. SSTR2 is the reporter gene, and TUSC2 is a therapeutic gene. Mice with A549 NSCLC lung tumors were injected intravenously with CMV-SSTR2, CMV-TUSC2-IRES-SSTR2, or CMV-TUSC2 plasmids in DOTAP:cholesterol-liposomal nanoparticles. Two days later, mice were injected intravenously with 111In-octreotide. The next day, biodistribution was performed. The experiment was repeated including single-photon emission computed tomography/computed tomography (SPECT/CT). Immunohistochemistry was performed. In vitro, SSTR2 expression was similar in cells transfected with CMV-SSTR2 or CMV-TUSC2-IRES-SSTR2. TUSC2 expression was similar in cells transfected with CMV-TUSC2 or CMV-TUSC2-SSTR2. Biodistribution demonstrated significantly greater 111In-octreotide uptake in tumors from mice injected with CMV-TUSC2-IRES-SSTR2 or CMV-SSTR2 than the control plasmid, CMV-TUSC2 (p < .05). Gamma-camera and SPECT/CT imaging illustrated SSTR2 expression in tumors in mice injected with CMV-TUSC2-IRES-SSTR2 or CMV-SSTR2 versus background with control plasmid. Immunohistochemistry corresponded with imaging. SSTR2-based reporter imaging can visualize gene expression in lung tumors after systemic liposomal nanoparticle delivery of plasmid containing SSTR2-based reporter gene or SSTR2 linked to a second therapeutic gene, such as TUSC2.

Influence of macrocyclic chelators on the targeting properties of (68)Ga-labeled synthetic affibody molecules: comparison with (111)In-labeled counterparts

Affibody molecules are a class of small (7 kDa) non-immunoglobulin scaffold-based affinity proteins, which have demonstrated substantial potential as probes for radionuclide molecular imaging. The use of positron emission tomography (PET) would further increase the resolution and quantification accuracy of Affibody-based imaging. The rapid in vivo kinetics of Affibody molecules permit the use of the generator-produced radionuclide ⁶⁸Ga (T_1/2 = 67.6 min). Earlier studies have demonstrated that the chemical nature of chelators has a substantial influence on the biodistribution properties of Affibody molecules. To determine an optimal labeling approach, the macrocyclic chelators 1,4,7,10-tetraazacylododecane-1,4,7,10-tetraacetic acid (DOTA), 1,4,7-triazacyclononane-N,N,N-triacetic acid (NOTA) and 1-(1,3-carboxypropyl)-1,4,7- triazacyclononane-4,7-diacetic acid (NODAGA) were conjugated to the N-terminus of the synthetic Affibody molecule Z_HER2:S1 targeting HER2. Affibody molecules were labeled with ⁶⁸Ga, and their binding specificity and cellular processing were evaluated. The biodistribution of ⁶⁸Ga-DOTA-Z_HER2:S1,⁶⁸Ga-NOTA-Z_HER2:S1 and ⁶⁸Ga-NODAGA-Z_HER2:S1, as well as that of their ¹¹¹In-labeled counterparts, was evaluated in BALB/C nu/nu mice bearing HER2-expressing SKOV3 xenografts. The tumor uptake for ⁶⁸Ga-DOTA-Z_HER2:S1 (17.9±0.7%IA/g) was significantly higher than for both ⁶⁸Ga-NODAGA-Z_HER2:S1(16.13±0.67%IA/g) and ⁶⁸Ga-NOTA-Z_HER2:S1 (13±3%IA/g) at 2 h after injection. ⁶⁸Ga-NODAGA-Z_HER2:S1 had the highest tumor-to-blood ratio (60±10) in comparison with both ⁶⁸Ga-DOTA-Z_HER2:S1 (28±4) and ⁶⁸Ga-NOTA-Z_HER2:S1 (42±11). The tumor-to-liver ratio was also higher for ⁶⁸Ga-NODAGA-Z_HER2:S1 (7±2) than the DOTA and NOTA conjugates (5.5±0.6 vs.3.3±0.6). The influence of chelator on the biodistribution and targeting properties was less pronounced for ⁶⁸Ga than for ¹¹¹In. The results of this study demonstrate that macrocyclic chelators conjugated to the N-terminus have a substantial influence on the biodistribution of HER2-targeting Affibody molecules labeled with ⁶⁸Ga.This can be utilized to enhance the imaging contrast of PET imaging using Affibody molecules and improve the sensitivity of molecular imaging. The study demonstrated an appreciable difference of chelator influence for ⁶⁸Ga and ¹¹¹In.

Color Doppler ultrasound and gamma imaging of intratumorally injected 500 nm iron-silica nanoshells

Perfluoropentane gas filled iron-silica nanoshells have been developed as stationary ultrasound contrast agents for marking tumors to guide surgical resection. It is critical to establish their long-term imaging efficacy, as well as biodistribution. This work shows that 500 nm Fe-SiO2 nanoshells can be imaged by color Doppler ultrasound over the course of 10 days in Py8119 tumor bearing mice. The 500 nm nonbiodegradable SiO2 and biodegradable Fe-SiO2 nanoshells were functionalized with diethylenetriamine pentaacetic acid (DTPA) ligand and radiolabeled with (111)In(3+) for biodistribution studies in nu/nu mice. The majority of radioactivity was detected in the liver and kidneys following intravenous (IV) administration of nanoshells to healthy animals. By contrast, after nanoshells were injected intratumorally, most of the radioactivity remained at the injection site; however, some nanoshells escaped into circulation and were distributed similarly as those given intravenously. For intratumoral delivery of nanoshells and IV delivery to healthy animals, little difference was seen between the biodistribution of SiO2 and biodegradable Fe-SiO2 nanoshells. However, when nanoshells were administered IV to tumor bearing mice, a significant increase was observed in liver accumulation of SiO2 nanoshells relative to biodegradable Fe-SiO2 nanoshells. Both SiO2 and Fe-SiO2 nanoshells accumulate passively in proportion to tumor mass, during intravenous delivery of nanoshells. This is the first report of the biodistribution following intratumoral injection of any biodegradable silica particle, as well as the first report demonstrating the utility of DTPA-(111)In labeling for studying silica nanoparticle biodistributions.

Design and evaluation of novel radiolabelled VIP derivatives for tumour targeting

BACKGROUND

Vasoactive intestinal peptide (VIP) receptors are overexpressed in a broad variety of tumours. For the detection of these tumours, novel chemically modified and shortened VIP derivatives were designed.

MATERIALS AND METHODS

1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-derivatised VIP analogues were radiolabelled with (111)In and in vitro and in vivo behaviour was evaluated using stability and internalisation assays, as well as an initial biodistribution study.

RESULTS

Radiolabelling of the VIP analogues resulted in high radiochemical yields, without need for further purification steps. Stability of the VIP derivatives was variable and cell uptake studies in VIP receptor-positive cell lines revealed that only a limited number of derivatives were internalised. In the tumour mouse model, no specific tumour targeting was shown.

CONCLUSION

Since the tested VIP derivatives exhibited impaired in vitro and in vivo characteristics alternative modifications to increase their stability while retaining receptor affinity should be considered to enable the use of synthetic VIP analogues for tumour targeting.

Novel indium-111 labeled gastrin peptide analogues (MG-CL1-4): synthesis and quality control

Radiolabeled neuropeptides are widely investigated to diagnose and therapy of tumors. These peptides get internalization after binding with particular receptors at the surface of cells and finally move to lysosome. Internalization into tumor cells helps in mapping the infected site. Minigastrin peptide analogues (MG-CL1-4) were synthesised and labeled with 111-In radioisotope under different sets of conditions for imaging CCk-2 receptor bearing tumors. Different parameters such as temperature (80-100°C), pH (4-12), incubation time (5-30 minutes) and dilution effect were investigated to get the maximum labeling yield and stability. The results indicated that MG-CL1-4 is successfully labeled with indium-111 at pH 4.5 with heating at 98°C for 15 minute. At these conditions i.e. heating, pH and incubation minimum oxidized and maximum labeling yield, more than 94 %, was obtained. The labeling stability was studied by incubating the radiolabeled complex for predefined time points in PBSA and blood serum. Results show that more than 90% radiolabeled MG-CL1-4 remained intact.

Improving radiopeptide pharmacokinetics by adjusting experimental conditions for bombesin receptor-targeted imaging of prostate cancer

AIM

Prostate cancer (PC) is a major health problem. The Gastrin-Releasing Peptide Receptor (GRPR) offers a promising target for staging and monitoring of PC since it is overexpressed in PC and not in normal prostatic tissue. To improve receptor-mediated imaging we investigated the impact of various experimental conditions on pharmacokinetics using the Indium-111 labelled bombesin (BN) analogue AMBA. Besides frequently used androgen-resistant PC-3 also the clinically more relevant androgen sensitive VCaP celline was used as human PC xenograft in nude mice.

METHODS

Non-purified [111In]AMBA was compared with HPLC-purified [111In]AMBA. Effect of specific activity was studied administering 0.1MBq [111In]AMBA supplemented with different amounts of AMBA (1-3000pmol). GRPR was saturated with Tyr4-BN 1 and 4h prior to injection of [111In]AMBA.

RESULTS

GRPR-positive tissue showed a significant 2 to 3-fold increase in absolute uptake after HPLC-purification while keeping a stable tumor-to-pancreas ratio. Lowering specific activity resulted in decline in uptake to 43% in tumor, 49% in kidney and 92% in pancreas between 10 and 3000 pmol. Tumor-to-pancreas ratio improved six-fold from 0.1±0 after 10 pmol up to 0.6±0.2 after 3000 pmol (P<0.01). When saturating GRPR 4h prior to [111In]AMBA injection tumor-to-pancreas ratio improved from 0.10±0.3 to 0.22±0.2 (P<0.01) and tumor-to-kidney ratio increased from 0.92±0.16 to 3.45±0.5 (P<0.01).

CONCLUSION

Besides specific peptide characteristics also the experimental conditions, such as HPLC-purification, variations in specific activity and saturation of the GRPR prior to [111In]AMBA administration essentially affect radiopeptide pharmacokinetics. Experimental conditions therefore need to be carefully selected in order to compose ideal standardised protocols for optimal targeting.

High payload dual therapeutic-imaging nanocarriers for triggered tumor delivery

The in vitro and in vivo characterization of an optimized formulation of nanoparticles (NPs) loaded with a high content of dexamethasone palmitate (DEX-P), a chemotherapeutic adjuvant that decreases interstitial fluid pressure in tumors, and (111) In, a signaling agent, is described. These NPs are uniform in size and composition. Single photon emission computed tomography imaging demonstrates significant tumor uptake of (111) In-labeled DEX-P NPs in tumor-bearing mice. As with many nanoparticle-based drug delivery systems, significant liver accumulation is observed. Assessment of liver histology and blood tests show no apparent hepatic or renal toxicity of the DEX-P NPs. Conversion of DEX-P to DEX occurs when DEX-P NPs are incubated with mouse plasma, human tumor homogenate and ascites from tumor bearing mice, but not with human plasma. This conversion is slower in plasma from Es1(e) ((-/-)) /SCID mice, a potential alternative animal model that better mimics humans; however, plasma from these mice are not completely devoid of esterase activity. The difference between blood and tumor esterase activity in humans facilitates the delivery of DEX-P NPs to tumors and the release of dexamethasone by an esterase trigger.

Pharmacokinetic analysis of 111 in-labeled liposomal Doxorubicin in murine glioblastoma after blood-brain barrier disruption by focused ultrasound

The goal of this study was to evaluate the pharmacokinetics of targeted and untargeted (111)In-doxorubicin liposomes after these have been intravenously administrated to tumor-bearing mice in the presence of blood-brain barrier disruption (BBB-D) induced by focused ultrasound (FUS). An intracranial brain tumor model in NOD-scid mice using human brain glioblastoma multiforme (GBM) 8401 cells was developed in this study. (111)In-labeled human atherosclerotic plaque-specific peptide-1 (AP-1)-conjugated liposomes containing doxorubicin (Lipo-Dox; AP-1 Lipo-Dox) were used as a microSPECT probe for radioactivity measurements in the GBM-bearing mice. Compared to the control tumors treated with an injection of (111)In-AP-1 Lipo-Dox or (111)In-Lipo-Dox, the animals receiving the drugs followed by FUS exhibited enhanced accumulation of the drug in the brain tumors (p<0.05). Combining sonication with drugs significantly increased the tumor-to-normal brain doxorubicin ratio of the target tumors compared to the control tumors. The tumor-to-normal brain ratio was highest after the injection of (111)In-AP-1 Lipo-Dox with sonication. The (111)In-liposomes micro-SPECT/CT should be able to provide important information about the optimum therapeutic window for the chemotherapy of brain tumors using sonication.

Peptide Receptor Imaging

Radiolabeled cell-surface peptide receptor-binding molecules are emerging as an important class of radiopharmaceuticals. Their binding to specific cell membrane receptors allows for noninvasive assessment of regional receptor proteomics in vivo. Information thus obtained can be used for diagnostic purposes and for predicting and monitoring response to treatment. This paradigm also applies to pulmonary diseases. In this review, available radiopharmaceuticals of great potential or already in clinical use for imaging of lung cancer, lung inflammation and infection and pulmonary embolism are discussed. In lung cancer, somatostatin receptor imaging by means of technetium-99m (99mTc)-octreotide scintigraphy has proven useful for characterizing malignancy in solitary pulmonary nodules. Additionally, several radiopharmaceuticals targeting tyrosine-kinase, e.g. 99mTc labeled epidermal growth factor and indium-111 (111In)-diethylene triamine penta-acetic acid-trastuzumab, or G-protein coupled receptors, e.g. 99mTc-bombesin, iodine-123-vasoactive intestinal peptide and 111In-tetraazacyclododecane tetra-acetic acid (DOTA)-cholecystokinine-B, are being explored for their diagnostic as well as treatment monitoring potential. With the purpose of better evaluating the source of pulmonary embolism, as well as to differentiate acute from chronic deep venous thrombosis, several radiolabeled peptides targeting the glycoprotein IIb/IIIa fibrinogen receptor found on activated platelets have been developed. Out of these, 99mTc-P280 is now approved by the US Food and Drug Administration for scintigraphic imaging of suspected acute venous thrombosis in the lower extremities of patients. In the field of lung inflammation and infection, non-specific 111In and 99mTc-human polyclonal immunoglobulins have been successfully used to identify the presence and extent of Pneumocystis carinii, cytomegalovirus, Mycobaterium avium and fungal infections in patients with HIV infection. The clinical role of other radiopharmaceuticals such as 99mTc-J001X, a nonpyrogenic acylated polygalactoside isolated from Klebsiella pneumoniae and binding with high affinity to CD11b and CD14 lipopolysaccharide receptors expressed on monocytes/macrophages, and 111In-octreotide, binding to up-regulated somatostatin receptors on activated lymphocytes needs to be further defined.

Imaging small human prostate cancer xenografts after pretargeting with bispecific bombesin-antibody complexes and targeting with high specific radioactivity labeled polymer-drug conjugates

PURPOSE

Pretargeting with bispecific monoclonal antibodies (bsMAb) for tumor imaging was developed to enhance target to background activity ratios. Visualization of tumors was achieved by the delivery of mono- and divalent radiolabeled haptens. To improve the ability to image tumors with bsMAb, we have combined the pretargeting approach with targeting of high specific activity radiotracer labeled negatively charged polymers. The tumor antigen-specific antibody was replaced with bombesin (Bom), a ligand that binds specifically to the growth receptors that are overexpressed by many tumors including prostate cancer. Bomanti- diethylenetriaminepentaacetic acid (DTPA) bispecific antibody complexes were used to demonstrate pretargeting and imaging of very small human prostate cancer xenografts targeted with high specific activity ¹¹¹In- or ⁹⁹mTc-labeled negatively charged polymers.

METHODS

Bispecific antibody complexes consisting of intact anti-DTPA antibody or Fab′ linked to Bom via thioether bonds (Bom-bsCx or Bom-bsFCx, respectively) were used to pretarget PC-3 human prostate cancer xenografts in SCID mice. Negative control mice were pretargeted with Bom or anti-DTPA Ab. 111In-Labeled DTPA-succinyl polylysine (DSPL) was injected intravenously at 24 h (7.03 ± 1.74 or 6.88 ± 1.89 MBq ¹¹¹In-DSPL) after Bom-bsCx or 50 ± 5.34 MBq of ⁹⁹mTc-DSPL after Bom-bsFCx pretargeting, respectively. Planar or single photon emission computed tomography (SPECT)/CT gamma images were obtained for up to 3 h and only planar images at 24 h. After imaging, all mice were killed and biodistribution of 111In or 99mTc activities were determined by scintillation counting.

RESULTS

Both planar and SPECT/CT imaging enabled detection of PC-3 prostate cancer lesions less than 1-2 mm in diameter in 1-3 h post 111In-DSPL injection. No lesions were visualized in Bom or anti-DTPA Ab pretargeted controls. 111In-DSPL activity in Bom-bsCx pretargeted tumors (1.21 ± 0.36 %ID/g) was 5.4 times that in tumors pretargeted with Bom or anti-DTPA alone (0.22 ± 0.08, p = 0.001). PC-3 xenografts pretargeted with Bom-bsFCx and targeted with ⁹⁹mTc-DSPL were visualizable by 1-3 h. Exquisite tumor uptake at 24 h (6.54 ± 1.58 %ID/g) was about 15 times greater than that of Bom pretargeted controls (0.44 ± 0.17, p = 0.002).

CONCLUSION

Pretargeting prostate cancer with Bom-bsCx or Bom-bsFCx enabled fast delivery of high specific radioactivity ¹¹¹In- or ⁹⁹mTc-labeled polymer-drug conjugates resulting in visualization of lesions smaller than 1- 2 mm in diameter within 3 h.

In vivo targeting of HER2-positive tumor using 2-helix affibody molecules

Molecular imaging of human epidermal growth factor receptor type 2 (HER2) expression has drawn significant attention because of the unique role of the HER2 gene in diagnosis, therapy and prognosis of human breast cancer. In our previous research, a novel cyclic 2-helix small protein, MUT-DS, was discovered as an anti-HER2 Affibody analog with high affinity through rational protein design and engineering. MUT-DS was then evaluated for positron emission tomography (PET) of HER2-positive tumor by labeling with two radionuclides, 68Ga and 18F, with relatively short half-life (t1/2<2 h). In order to fully study the in vivo behavior of 2-helix small protein and demonstrate that it could be a robust platform for labeling with a variety of radionuclides for different applications, in this study, MUT-DS was further radiolabeled with 64Cu or 111In and evaluated for in vivo targeting of HER2-positive tumor in mice. Design 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) conjugated MUT-DS (DOTA-MUT-DS) was chemically synthesized using solid phase peptide synthesizer and I2 oxidation. DOTA-MUT-DS was then radiolabeled with 64Cu or 111In to prepare the HER2 imaging probe (64Cu/111In-DOTA-MUT-DS). Both biodistribution and microPET imaging of the probe were evaluated in nude mice bearing subcutaneous HER2-positive SKOV3 tumors. DOTA-MUT-DS could be successfully synthesized and radiolabeled with 64Cu or 111In. Biodistribution study showed that tumor uptake value of 64Cu or 111In-labeled DOTA-MUT-DS was 4.66±0.38 or 2.17±0.15%ID/g, respectively, in nude mice bearing SKOV3 xenografts (n=3) at 1 h post-injection (p.i.). Tumor-to-blood and tumor-to-muscle ratios for 64Cu-DOTA-MUT-DS were attained to be 3.05 and 3.48 at 1 h p.i., respectively, while for 111In-DOTA-MUT-DS, they were 2.04 and 3.19, respectively. Co-injection of the cold Affibody molecule ZHER2:342 with 64Cu-DOTA-MUT-DS specifically reduced the SKOV3 tumor uptake of the probe by 48%. 111In-DOTA-MUT-DS displayed lower liver uptake at all the time points investigated and higher tumor to blood ratios at 4 and 20 h p.i., when compared with 64Cu-DOTA-MUT-DS. This study demonstrates that the 2-helix protein based probes, 64Cu/111In DOTA-MUT-DS, are promising molecular probes for imaging HER2-positive tumor. Two-helix small protein scaffold holds great promise as a novel and robust platform for imaging and therapy applications.

The scintigraphic index spleen/liver at 30 minutes predicts the success of splenectomy in persistent and chronic primary immune thrombocytopenia

Splenectomy is considered the second-line of treatment in patients with chronic primary immune thrombocytopenia (ITP) in whom glucocorticoids have failed. Some patients do not respond to splenectomy or they have postoperative complications. Based on our previous experience using kinetic and scintigraphic parameters, we did a retrospective study with the aim of comparing all these parameters as a means of predicting the success of splenectomy in persistent and chronic primary ITP. Forty-one consecutive patients with chronic primary ITP refractory to prednisone, who had been splenectomized, were included in the study. The response to splenectomy was assessed by evaluating bleeding and platelet counts before and at different times after surgery. A complete platelet kinetic study was performed before the splenectomy using autologous (111) In-labeled platelets. The scintigraphic parameters measured included different indices between spleen/heart, liver/hearth, and spleen/liver. Thirty-six patients gave a complete response after splenectomy and five patients did not respond. A statistically significant difference between both groups was found with initial platelet recovery and with some scintigraphic indices which also showed a variable prediction value for the success of splenectomy. Among these indices, the spleen/liver at 30 minutes demonstrated a predictive value with a 100% of sensitivity and a 100% of specificity.

CONCLUSION

some platelet kinetic parameters and scintigraphic indices, in particular the spleen/liver at 30 minutes, were useful to predict the outcome of splenectomy in persistent and chronic primary ITP and, therefore, they should be taken into account when deciding whether or not to perform a splenectomy.

Predicting IGF-1R therapy response in bone sarcomas: immuno-SPECT imaging with radiolabeled R1507

PURPOSE

To investigate whether indium-111-labeled R1507 ((111)In-R1507) immuno-SPECT (single-photon emission computed tomography), a novel noninvasive, in vivo screening method to visualize membranous insulin-like growth factor 1 receptor (IGF-1R) expression and accessibility, can be used to predict IGF-1R treatment (R1507) response in bone sarcomas.

EXPERIMENTAL DESIGN

BALB/c nude mice were subcutaneously implanted with IGF-1R-expressing human bone sarcoma xenografts (OS-1, EW-5, and EW-8) which showed high, modest, or no response, respectively, to R1507, a monoclonal antibody targeting the extracellular domain of IGF-1R. An IGF-1R-negative tumor (OS-33), unresponsive to IGF-1R inhibitors, was examined as well. Mice were injected with (111)In-R1507. Biodistribution and immuno-SPECT/computed tomography imaging studies were carried out 1, 3, and 7 days p.i. in mice with OS-1 and EW-5 xenografts and 3 days p.i. in mice with EW-8 and OS-33 xenografts.

RESULTS

Biodistribution studies showed specific accumulation of (111)In-R1507 in OS-1 and EW-5 xenografts (27.5 ± 6.5%ID/g and 14.0 ± 2.8%ID/g, 3 days p.i., respectively). Most importantly, (111)In-R1507 uptake in IGF-1R positive, but unresponsive, EW-8 xenografts (6.5 ± 1.5%ID/g, 3 days p.i.) was similar to that of the IGF-1R-negative OS-33 tumor (5.5 ± 0.6%ID/g, 3 days p.i.). Uptake in normal tissues was low and nonspecific. Corresponding immuno-SPECT images clearly discriminated between high, modest, and nonresponding tumors by showing a homogeneous (OS-1), heterogeneous (EW-5), or nonspecific (EW-8 and OS-33) tumor uptake of (111)In-R1507.

CONCLUSIONS

(111)In-R1507 immuno-SPECT is an excellent method to visualize membranous IGF-1R expression and target accessibility in vivo in human bone sarcoma xenografts and may serve as an independent marker to predict IGF-1R therapy (R1507) response in bone sarcoma patients.

Influence of affinity and antigen internalization on the uptake and penetration of Anti-HER2 antibodies in solid tumors

Antibody drugs are widely used in cancer therapy, but conditions to maximize tumor penetration and efficacy have yet to be fully elucidated. In this study, we investigated the impact of antibody binding affinity on tumor targeting and penetration with affinity variants that recognize the same epitope. Specifically, we compared four derivatives of the C6.5 monoclonal antibody (mAb), which recognizes the same HER2 epitope (monovalent K(D) values ranging from 270 to 0.56 nmol/L). Moderate affinity was associated with the highest tumor accumulation at 24 and 120 hours after intravenous injection, whereas high affinity was found to produce the lowest tumor accumulation. Highest affinity mAbs were confined to the perivascular space of tumors with an average penetration of 20.4 ± 7.5 μm from tumor blood vessels. Conversely, lowest affinity mAbs exhibited a broader distribution pattern with an average penetration of 84.8 ± 12.8 μm. In vitro internalization assays revealed that antibody internalization and catabolism generally increased with affinity, plateauing once the rate of HER2 internalization exceeded the rate of antibody dissociation. Effects of internalization and catabolism on tumor targeting were further examined using antibodies of moderate (C6.5) or high-affinity (trastuzumab), labeled with residualizing ((111)In-labeled) or nonresidualizing ((125)I-labeled) radioisotopes. Significant amounts of antibody of both affinities were degraded by tumors in vivo. Furthermore, moderate- to high-affinity mAbs targeting the same HER2 epitope with monovalent affinity above 23 nmol/L had equal tumor accumulation of residualizing radiolabel over 120 hours. Results indicated equal tumor exposure, suggesting that mAb penetration and retention in tumors reflected affinity-based differences in tumor catabolism. Together, these results suggest that high-density, rapidly internalizing antigens subject high-affinity antibodies to greater internalization and degradation, thereby limiting their penetration of tumors. In contrast, lower-affinity antibodies penetrate tumors more effectively when rates of antibody-antigen dissociation are higher than those of antigen internalization. Together, our findings offer insights into how to optimize the ability of therapeutic antibodies to penetrate tumors.

The radioguided 111In-pentetreotide surgery in the management of ACTH-secreting bronchial carcinoid

BACKGROUND AND OBJECTIVES

A correct intra-operative detection of the tumour and, therefore, the complete surgical resection is critical to success in ACTH-secreting bronchial carcinoids. To date, all available preoperative and intra-operative procedures remain not entirely satisfactory. The use of intra-operative 111In-pentetreotide detection could offer a potentially reliable and rapid tool of real time assessment to achieve a radical resection.

MATERIALS AND METHODS

In two cases of ACTH-secreting bronchial carcinoids, after a preliminary 111In-pentetreotide scan, radio-guided surgery was performed using a hand-held gamma probe 24 h after i.v. administration of the tracer.

RESULTS

The 111n-pentetreotide radioguided surgery with hand-held gamma probe, if compared with pre-operative 111In-pentetreotide, significantly improved the intra-operative surgical management by detecting a millimetric nodule in one case; detecting mediastinal lymph node metastasis in both cases and ruling out any other disease localization.

DISCUSSION

Intra-operative 111In-pentetreotide detection appears to be safe and easy to perform. This technique allowed to achieve a complete resection of all the tumor locations, that would have been impossible to detect with conventional surgical approach. On the basis of these results we advocate for a wider investigation of the potentialities connected with the radioguided surgery coupled with pre-operative 111In-pentetreotide scan as a promising procedure in the management of ACTH-secreting bronchial carcinoids.

Annexin A5-conjugated polymeric micelles for dual SPECT and optical detection of apoptosis

Imaging of apoptosis can allow noninvasive assessment of disease states and response to therapeutic intervention for a variety of diseases. The purpose of this study was to develop and evaluate a multimodal nanoplatform for the detection of apoptosis.

METHODS

To modulate the pharmacokinetics of annexin A5, a 36-kDa protein that binds specifically with phosphatidylserine, annexin A5 was conjugated to polyethylene glycol-coated, core-cross-linked polymeric micelles (CCPMs) dually labeled with near-infrared fluorescence fluorophores and a radioisotope ((111)In). To evaluate the specificity of the binding of annexin A5-CCPM to apoptotic cells, both fluorescence microscopy and cell-binding studies were performed in vitro. Pharmacokinetics, biodistribution, dual nuclear and optical imaging, and immunohistochemical studies were performed in 2 xenografted tumor models to evaluate the potential applications of annexin A5-CCPM.

RESULTS

In cell-based studies, annexin A5-CCPM exhibited strongly specific binding to apoptotic tumor cells. This binding could be efficiently blocked by annexin A5. In mice, annexin A5-CCPM displayed a mean elimination half-life of 12.5 h. The mean initial concentration in blood was 22.4% of the injected dose/mL, and annexin A5-CCPM was mainly distributed in the central blood compartment. In mice bearing EL4 lymphoma treated with cyclophosphamide and etoposide and in mice bearing MDA-MB-468 breast tumors treated with poly(L-glutamic acid)-paclitaxel and cetuximab (IMC-C225) anti-epidermal growth factor receptor antibody, the tumor apoptosis was clearly visualized by both SPECT and fluorescence molecular tomography. In contrast, there was little accumulation of this nanoradiotracer in the tumors of untreated mice. The biodistribution data were consistent with the imaging data, with tumor-to-muscle and tumor-to-blood ratios of 38.8 and 4.1, respectively, in treated mice, and 14.8 and 2.2, respectively, in untreated mice bearing EL4 lymphoma. Moreover, further studies demonstrated that the conventional (99m)Tc-labeled hydrazinonicotinamide annexin A5 and the plain CCPM control exhibited significantly lower uptake in the tumors of the treated mice than annexin A5-CCPM. Immunohistochemistry staining study showed that radioactivity count correlated with fluorescence signal from the nanoparticles, and both signals colocalized with the region of tumor apoptosis.

CONCLUSION

Annexin A5-CCPM allowed visualization of tumor apoptosis by both nuclear and optical techniques. The complementary information acquired with multiple imaging techniques should be advantageous in assessing and validating early response to therapy.

[Somatostatin receptor-based imaging and therapy of digestive endocrine tumors]

The management of gastroenteropancreatic endocrine tumors is greatly linked to the localization of primary tumor. Morphological imaging methods are thus necessary. However, the expression of somatostatin receptors in endocrine tumors makes their detection possible thanks to radiolabeled somastotatin analogs. [(111)In-DTPA] octreotide is the main radiolabeled analog for somatostatin receptor scintigraphy. Positron emission tomography uses other tracers and currently allows improvement of the diagnosis and the tumoral staging. It also allows to affect the therapeutic management. A further step is about to be taken as far as the therapy of endocrine tumors is concerned with the peptide receptor radionuclide therapy. Those therapies are now being offered in some European and American centers for progressive metastatic tumors. Their place in the therapeutic strategy has to be defined, especially in comparison to targeted therapy. The sudden and delayed adverse events as well as the current legislation on the use of radioactive therapy-aimed products have limited their development in France so far.

Activated platelets in carotid artery thrombosis in mice can be selectively targeted with a radiolabeled single-chain antibody

Background

Activated platelets can be found on the surface of inflamed, rupture-prone and ruptured plaques as well as in intravascular thrombosis. They are key players in thrombosis and atherosclerosis. In this study we describe the construction of a radiolabeled single-chain antibody targeting the LIBS-epitope of activated platelets to selectively depict platelet activation and wall-adherent non-occlusive thrombosis in a mouse model with nuclear imaging using in vitro and ex vivo autoradiography as well as small animal SPECT-CT for in vivo analysis.

Methodology/Principal Findings

LIBS as well as an unspecific control single-chain antibody were labeled with ¹¹¹Indium (¹¹¹In) via bifunctional DTPA ( = ¹¹¹In-LIBS/¹¹¹In-control). Autoradiography after incubation with ¹¹¹In-LIBS on activated platelets in vitro (mean 3866±28 DLU/mm², 4010±630 DLU/mm² and 4520±293 DLU/mm²) produced a significantly higher ligand uptake compared to ¹¹¹In-control (2101±76 DLU/mm², 1181±96 DLU/mm² and 1866±246 DLU/mm²) indicating a specific binding to activated platelets; P<0.05. Applying these findings to an ex vivo mouse model of carotid artery thrombosis revealed a significant increase in ligand uptake after injection of ¹¹¹In-LIBS in the presence of small thrombi compared to the non-injured side, as confirmed by histology (49630±10650 DLU/mm² vs. 17390±7470 DLU/mm²; P<0.05). These findings could also be reproduced in vivo. SPECT-CT analysis of the injured carotid artery with ¹¹¹In-LIBS resulted in a significant increase of the target-to-background ratio compared to ¹¹¹In-control (1.99±0.36 vs. 1.1±0.24; P<0.01).

Conclusions/Significance

Nuclear imaging with ¹¹¹In-LIBS allows the detection of platelet activation in vitro and ex vivo with high sensitivity. Using SPECT-CT, wall-adherent activated platelets in carotid arteries could be depicted in vivo. These results encourage further studies elucidating the role of activated platelets in plaque pathology and atherosclerosis and might be of interest for further developments towards clinical application.

Incremental diagnostic value and impact on patient management of somatostatin receptor scintigraphy with indium-111-pentetreotide in gastroenteropancreatic neuroendocrine tumors

OBJECTIVE

To evaluate the efficacy of somatostatin analog scintigraphy with indium-111-pentetreotide and its overall impact on management in patients with gastroenteropancreatic neuroendocrine tumors (GEP-NET).

SUBJECTS AND METHODS

Twenty-two consecutive patients with a proven or clinically suspected GEP-NET with or without proven metastases were imaged at 24 and 48 h after injection of (111)In-pentetreotide. The scintigraphic findings were compared with results from conventional imaging methods. The final diagnosis was based on histopathological and surgical findings and complementary radiology.

RESULTS

Somatostatin receptor-positive lesions were found in 20 of the patients, whereas conventional methods were positive in 18 patients. Additionally, 13 new tumor sites were discovered by somatostatin receptor scintigraphy in 5 patients (liver: 6; chest: 2; bone: 1; abdomen: 4). The surgical therapeutic strategy was changed in 7 patients (32%).

CONCLUSIONS

Our data reinforced that scintigraphy with (111)In-pentetreotide represents the imaging modality of choice in the initial evaluation of GEP-NET. It is highly accurate and can identify clinically unsuspected lesions and optimize the overall staging. It also guides optimal therapy choice and most importantly identifies patients with inoperable or metastatic disease who might be candidates for high-dose targeted therapy.

Gene expression of somatostatin receptor 4 predicts clinical outcome of patients with metastatic neuroendocrine tumors treated with somatostatin analogs

Somatostatin analogs (SSA) are the standard diagnostic and treatment tools in the clinical management of patients with neuroendocrine tumors (NETs) expressing somatostatin receptors (SSTRs). Although symptomatic and biochemical control is obtained with SSA in the majority of functional NETs, antineoplastic effects of SSA are partial and of limited duration. The aim of this study was to quantify expression levels of five SSTR subtypes (SSTR1-SSTR5) and correlate them with the clinical outcomes of patients with NETs who underwent SSA therapy. The expression levels were analyzed using real-time polymerase chain reaction in a series of 22 metastatic NETs with a median time of 10 months on the SSA therapy (range 2-82 months). The median duration of disease stabilization in patients who developed progression (n = 14) was 9 months (range 3-92 months). The median survival period for all patients was 44 months (range 3-175 months). According to RECIST criteria, one (5%) partial objective tumor response was obtained, disease stabilization was achieved in 10 (45%) patients, and progressive disease was observed in 11 (50%). Analysis of mRNA expression of the SSTR subtypes showed that SSTR2 and SSTR5 were expressed in all of the studied NETs; SSTR1 and SSTR4 in all but 3 tumors (86%); and SSTR3 in only 10 NETs (49%). Interestingly, our preliminary data suggest that only the levels of SSTR4, though it has the lowest affinity for SSA of all SSTR subtypes, were significantly associated with the stabilization of disease during SSA therapy (p = 0.0357). These levels correlated with time to progression (p = 0.0015) and overall survival (p = 0.0017) in NET patients.

Predictors of survival in idiopathic interstitial pneumonia

AIM

To evaluate the ability of newly identified clinical factors to predict prognosis and survival in idiopathic pulmonary fibrosis (IPF) and non-specific interstitial pneumonia (NSIP).

METHODS

Seventy-eight patients referred to the University of Genoa and the Regional Hospital of Aosta between January 1995 and December 2006 were evaluated prospectively. Fifty-nine patients were diagnosed with IPF and 19 with NSIP on the basis of surgical lung biopsy specimens. Gender, age at diagnosis, smoking, New York Heart Association class (NYHA), systolic pulmonary artery pressure (sPAP), Octreoscan uptake index (UI), and therapy were the chosen variables. Primary end-point was survival.

RESULTS

With the exception of gender and smoking history, all baseline patient characteristics correlated significantly with the diagnosis (IPF vs. NSIP). Median survival for the entire study group was 52.7 months. Univariate analysis showed poorer survival for the IPF group versus the NSIP group, and survival was significantly lower for older patients (p < 0.001). Multivariate analysis confirmed the negative prognostic effect of age (p < 0.001) on survival with a risk of death for older patients ( > OR =66 years old) being more than 4 times higher than that for younger patients (<58 yr.). NYHA class and pulmonary artery pressure were also significant predictors of survival, and all patients with a sPAP < OR = 35-mm Hg were alive at the end of the follow-up period. There was a good correlation between Octreoscan uptake index and the diagnosis.

CONCLUSION

Diagnosis (IPF vs. NSIP), NYHA class, sPAP, and especially age appear to represent important prognostic indicators in the two most prevalent forms of idiopathic pulmonary fibrosis (IPF and NSIP). Lower Octreoscan uptake values were found in all patients with IPF, suggesting that this test may have a role as a new predictor of survival for differentiating IPF from NSIP.

Biodistribution of two octreotate analogs radiolabeled with indium and yttrium in rats

BACKGROUND

In this study, two octreotate derivatives N-[4-carboxy-4-[4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane-1-yl]butanoyl]-Tyr(3)-octreotate (DOTAGA-tate) and N-[[4,10-bis(carboxymethyl)-7-(1(1,3-dicarboxypropyl))-1,4,7,10-tetraaza-cyclododec-1-yl]acetyl]-Tyr(3)-octreotate (DOTA-t-GA-tate) were radio-labeled with (111)In or (88)Y and their biodistribution profiles together with their elimination characteristics in rats were compared.

MATERIALS AND METHODS

Radiolabeling of the peptides with high radiochemical purity was carried out in an acetate buffer with gentisic acid as radioprotective compound. Biodistribution profiles of the radiolabeled peptides were determined in intact male Wistar rats after an intravenous dose of 1 microg/kg. For elimination pathways analysis, studies in intact rats in metabolic cages and perfused rat kidney and liver were carried out.

RESULTS

Fast radioactivity clearance from rat tissues (excepting somatostatin receptor-rich organs and the kidney) was determined for all agents under study. Profound radioactivity uptake in organs with a high density of somatostatin receptors (namely the adrenals and pancreas as biomarkers of somatostatin receptor-positive tissue) was slightly higher for radiolabeled DOTAGA-tate when compared with DOTA-t-GA-tate. Significantly higher accumulation in kidney and somewhat lower urinary elimination of (111)In-labeled peptides in comparison with that of (88)Y-agents were determined. Perfused rat kidney experiments confirmed that glomerular filtration was the main elimination mechanism for the compounds under study; their bile clearances in the perfused rat liver were negligible.

CONCLUSION

(111)In((88)Y)-DOTAGA-tates exhibited higher distribution into somatostatin receptor-rich organs when compared with the corresponding radiolabeled DOTA-t-GA-tates. Higher uptake of (111)In-labeled peptides in the kidney is attributed to its different coordination properties.

Molecular imaging of atherosclerotic plaques targeted to oxidized LDL receptor LOX-1 by SPECT/CT and magnetic resonance

BACKGROUND

The oxidized low-density lipoprotein receptor (LDLR) LOX-1 plays a crucial role in atherosclerosis. We sought to detect and assess atherosclerotic plaque in vivo by using single-photon emission computed tomography/computed tomography and magnetic resonance imaging and a molecular probe targeted at LOX-1.

METHODS AND RESULTS

Apolipoprotein E(-/-) mice fed a Western diet and LDLR(-/-) and LDLR(-/-)/LOX-1(-/-) mice fed an atherogenic diet were used. Imaging probes consisted of liposomes decorated with anti-LOX-1 antibodies or nonspecific immunoglobulin G, (111)indium or gadolinium, and 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine fluorescence markers. In vivo imaging was performed 24 hours after intravenous injection (150 microL) of LOX-1 or nonspecific immunoglobulin G probes labeled with either (111)indium (600 muCi) or gadolinium (0.075 mmol/kg), followed by aortic excision for phosphor imaging and Sudan IV staining, or fluorescence imaging and hematoxylin/eosin staining. The LOX-1 probe also colocalized with specific cell types, apoptosis, and matrix metalloproteinase-9 expression in frozen aortic sections. Single-photon emission computed tomography/computed tomography imaging of the LOX-1 probe showed aortic arch "hot spots" in apolipoprotein E(-/-) mice (n=8), confirmed by phosphor imaging. Magnetic resonance imaging showed significant Gd enhancement in atherosclerotic plaques in LDLR(-/-) mice with the LOX-1 (n=7) but not with the nonspecific immunoglobulin G (n=5) probe. No signal enhancement was observed in LDLR(-/-)/LOX-1(-/-) mice injected with the LOX-1 probe (n=5). These results were confirmed by ex vivo fluorescence imaging. The LOX-1 probe bound preferentially to the plaque shoulder, a region with vulnerable plaque features, including extensive LOX-1 expression, macrophage accumulation, apoptosis, and matrix metalloproteinase-9 expression.

CONCLUSIONS

LOX-1 can be used as a target for molecular imaging of atherosclerotic plaque in vivo. Furthermore, the LOX-1 imaging signal is associated with markers of rupture-prone atherosclerotic plaque.

Improving the treatment of non-Hodgkin lymphoma with antibody-targeted radionuclides

Radioimmunotherapy of non-Hodgkin lymphoma comprises a (90)Y- or (131)I-labeled murine anti-CD20 IgG, but both agents also include a substantial dose of unlabeled anti-CD20 IgG given immediately before the radioconjugate to reduce its uptake in the spleen (primary normal B-cell antigen sink); this extends its plasma half-life and improves tumor visualization. Thus, these treatments combine an effective anti-CD20 radioconjugate with an unconjugated anti-CD20 antibody that is also therapeutically active, but the large anti-CD20 IgG predose ( approximately 900 mg) may diminish the tumor localization of the radioimmunoconjugate (eg, 10-35 mg). We have examined alternative approaches that enhance radionuclide targeting and improve antitumor responses. One uses a (90)Y-labeled anti-CD22 IgG (epratuzumab) combined with an antibody therapy regimen of a humanized anti-CD20 IgG (veltuzumab). Pretargeted radionuclide therapy using a trivalent, humanized, recombinant bispecific anti-CD20 antibody with a (90)Y-hapten-peptide is another highly effective method that is also less toxic than directly radiolabeled IgG. Finally, all approaches benefit from the addition of a consolidation-dosing regimen of the anti-CD20 IgG antibody. This article reviews these various options and discusses how some fundamental changes could potentially enhance the response and duration from radionuclide-targeted therapy.

Utility of various functional and anatomic imaging modalities for detection of ectopic adrenocorticotropin-secreting tumors

CONTEXT

Because ectopic ACTH-secreting (EAS) tumors are often occult, improved imaging is needed.

OBJECTIVE

Our objective was to evaluate the utility of [(111)In-DTPA-d-Phe]pentetreotide scintigraphy [octreotide (OCT)] imaging at 6 mCi [low OCT (LOCT)] and 18 mCi [high OCT (HOCT)], [(18)F]fluorodeoxyglucose (FDG)-positron emission tomography (PET) and [(18)F]l-3,4-dihydroxyphenylalanine (F-DOPA)-PET scans, computed tomography (CT), and magnetic resonance imaging (MRI).

DESIGN AND SETTING

The study was a prospective evaluation at a clinical research center.

PATIENTS

Forty-one subjects participated, 30 (17 female) with resected EAS tumors and 11 (three female) with occult EAS, based on inferior petrosal sinus sampling results and imaging studies.

INTERVENTION

INTERVENTION included CT and MRI of neck, chest, abdomen, LOCT (with or without HOCT) and FDG- or F-DOPA-PET without CT every 6-12 months.

MAIN OUTCOME MEASURE

Tumor identification was the main outcome measure.

RESULTS

Most recent results were analyzed. Eighteen patients had tumor resected on the first visit; otherwise, surgery occurred 33 +/- 25 (9-99) months later. Tumor size was 1.9 +/- 1.7 (0.8-8.0) cm; 83% were intrathoracic. CT, MRI, LOCT, HOCT, FDG-PET, and F-DOPA-PET had sensitivities per patient of 93% [95% confidence interval (CI) = 79-98%], 90% (95% CI = 74-96%), 57% (95% CI = 39-73%), 50% (95% CI = 25-75%), 64% (95% CI = 35-85%), and 55% (95% CI = 28-79%) and positive predictive values (PPV) per lesion of 66, 74, 79, 89, 53, and 100%, respectively. LOCT and PET detected only lesions seen by CT/MRI; abnormal LOCT or F-DOPA-PET improved PPV of CT/MRI. By modality, the fraction of patients with one or more false-positive findings was 50% by CT, 31% by MRI, 18% by L/HOCT, and 18% by FDG-PET. Eight occult EAS patients had 64 +/- 58 (9-198) months follow-up; others had none.

CONCLUSIONS

High sensitivity and PPV suggest thoracic CT/MRI plus LOCT scans for initial imaging, with lesion confirmation by two modalities.

Gastrointestinal transit of model mini-tablet controlled release oral dosage forms in fasted human volunteers

The aim of this study was to compare the gastrointestinal transit of multiple unit, small diameter (3.2 mm), non-disintegrating tablets of differing densities with results previously reported in the same volunteers in the fasted state for larger diameter (6.6 and 12.2 mm) tablets. The gastrointestinal transit was observed with gamma-scintigraphy at various intervals over a 9-h period to give an accurate assessment of the transit characteristics. The value for the median emptying time of the first light tablet was significantly shorter than that for the dense tablet, but the total emptying time and the time for the last tablet to empty for both sets of tablets were not statistically different. The value of the median time for initial and final emptying of the small tablets from the stomach was significantly longer than that for the larger diameter tablets. The 9-h time limit of the observations limited the estimation of the time taken to enter the caecum and consequently the small intestine transit times. There was clear evidence that for the dense tablets of all sizes, the value for the small intestine transit time was longer than the 3–4 h reported in the literature. The only tablet system to enter the caecum within the time limit of the study was the normal density 12.2-mm tablets.

Evidence-based mini-review: Is indium-labeled autologous platelet scanning predictive of response to splenectomy in patients with chronic immune thrombocytopenia?

Clinical scenario: An otherwise healthy 25-year-old woman returns to your office for management of chronic primary immune thrombocytopenia. She was diagnosed 6 months earlier and continues to require prednisone 15 mg daily and periodic infusions of intravenous immunoglobulin to maintain a hemostatic platelet count. You discuss second-line treatment options, including splenectomy. The patient asks if there are any means by which to predict likelihood of response to splenectomy. You have heard about the use of indium-labeled autologous platelet scanning for this purpose and wonder what the evidence shows.

Value of 123I-MIBG Scintigraphy in Paraganglioma

AIM

The aim of the study was to evaluate the current role of (123)I-MIBG scintigraphy in the detection and follow-up of patients with paragangliomas.

MATERIALS AND METHODS

117 patients were referred for diagnostic (123)I-MIBG scintigraphy based on a strong clinical suspicion, positive familial history and genetic testing, or for follow-up of paragangliomas.(123)I-MIBG images were analyzed and correlated with (111)In-octreotide scintigraphy, CT or MRI results. Accuracy of the imaging method was calculated per patient and per tumor per site.

RESULTS

A total of 117 patients were referred for (123)I-MIBG diagnostic imaging; 80 patients were diagnosed with paraganglioma; 66 patients had a single neuroendocrine tumor and 14 patients multiple tumors. The total number of all lesions in these patients was 172. (123)I-MIBG scintigraphy demonstrated 65 lesions in 56 patients (overall sensitivity: 56.3%, specificity: 84%). Lesion-per-site analysis revealed that sensitivity and specificity significantly varied per tumor site (lowest sensitivity for the head and neck: 17.5% and lowest specificity for the abdomen: 87.5%). Hormones were elevated in 85 patients: 55 (123)I-MIBG tumors were positive and 35 tumors were negative. In 16 patients (13.7%) with a genetic burden and a single neuroendocrine tumor, (123)I-MIBG whole-body imaging was successful at detecting a second tumor. In 2 patients (1.7%) with paragangliomas, (123)I-MIBG unexpectedly detected metastases, so the restaging was properly done.

CONCLUSION

(123)I-MIBG scintigraphy remains important in pheochromocytoma and functioning neuroendocrine tumors. The value of (123)I-MIBG scintigraphy is high in familial syndromes with multiple neuroendocrine tumors at different sites, multifocal tumors, and relapsing and metastatic disease.

Glucagon-like peptide-1 receptor imaging for localization of insulinomas

CONTEXT

The surgical removal of insulinomas is hampered by difficulties to localize it using conventional radiological procedures. Recently these tumors were shown to exhibit a very high density of glucagon-like peptide-1 receptors (GLP-1R) in vitro that may be used as specific targets for in vivo receptor radiolabeling.

OBJECTIVE

The objective of the study was to test the 111In-labeled GLP-1R agonist 111In-DOTA-exendin-4 in localizing insulinomas using single photon emission computed tomography in combination with computed tomography images.

DESIGN

This was a prospective open-label investigation.

SETTING

The study was conducted at three tertiary referral centers in Switzerland.

PATIENTS

Patients included six consecutive patients with proven clinical and biochemical endogenous hyperinsulinemic hypoglycemia.

INTERVENTION

(111)In-DOTA-exendin-4 was administered iv at a dose of about 90 MBq (30 microg peptide) over 5 min. Whole-body planar images of the abdomen were performed at 20 min, 4 h, 23 h, 96 h, and up to 168 h after injection. After surgical removal of the insulinomas, GLP-1R expression was assessed in the tumor tissue in vitro by GLP-1R autoradiography.

MAIN OUTCOME MEASURE

The detection rate of insulinomas was measured.

RESULTS

In all six cases, the GLP-1R scans successfully detected the insulinomas identified using conventional methods in four cases. By using a gamma-probe intraoperatively, GLP-1R detection permitted a successful surgical removal of the tumors in all patients, diagnosed histopathologically as five pancreatic and one extrapancreatic insulinomas. In vitro GLP-1R autoradiography showed a high density of GLP-1R in all tested insulinomas.

CONCLUSION

In vivo GLP-1R imaging is an innovative, noninvasive diagnostic approach that successfully localizes small insulinomas pre- and intraoperatively and that may in the future affect the strategy of insulinoma localization.

[Protein-losing enteropathy caused by a thoracic cyst]

A case of gastrointestinal protein loss in a 58-year-old man presenting with peripheral oedema and low levels of serum proteins is presented. Measurement of gastrointestinal protein loss with 111Indium-labelled transferrin showed a protein loss of 12.5% over 96 hours. Capsule endoscopy showed villous lymphangiectasia and it was assumed that the protein loss was secondary to a large left-sided thoracic cyst obstructing the thoracic lymph drainage. The patient improved following surgical removal of the cyst.

Gamma scintigraphy imaging of murine invasive pulmonary aspergillosis with a (111)In-labeled cyclic peptide

INTRODUCTION

Invasive pulmonary aspergillosis (IPA) is a leading cause of infection-associated death in immunosuppressed patients. Early detection and early administration of antifungal therapy are critical factors in improving outcome for patients with IPA. Here, we evaluated the imaging properties of a (111)In-labeled cyclic peptide targeted to Aspergillus fumigatus in an immunosuppressed murine model of IPA.

METHODS

A cyclic peptide c(CGGRLGPFC)-NH(2) was labeled with (111)In by means of diethylenetriaminepentaacetic acid (DTPA). Two days after intranasal inoculation of 17.5x10(6) conidia of A. fumigatus, mice were injected (111)In-DTPA-c(CGGRLGPFC)-NH(2) intravenously. Biodistribution data were obtained at 2 h, and gamma-images were acquired at 10 min and 2 h after radiotracer injection. Healthy mice were used as controls. In addition, a group of infected mice were co-injected with the radiotracer and unlabeled c(CGGRLGPFC)-NH(2) to evaluate the inhibition of radiotracer's binding to infected lungs. Autoradiographs of lungs from infected and healthy mice were compared with corresponding photographs of transaxial sections of the lung tissues stained for A. fumigatus hyphae.

RESULTS

The labeling efficiency was >98%, with specific radioactivity of up to 74 MBq/nmol peptide. Significantly higher uptake of (111)In-DTPA-c(CGGRLGPFC)-NH(2) was observed in the lungs of mice infected with A. fumigatus than in those of healthy mice (0.37+/-0.06 %ID/g vs. 0.14+/-0.02 %ID/g, P=.00044). Simultaneous injection with unlabeled peptide reduced radioactivity in the infected lungs by 41% (P=.0037). Increased radioactivity in the lungs of infected mice was visible in gamma images at both 10 min and 2 h after radiotracer injection. Moreover, autoradiography confirmed radiotracer uptake in infected lungs, but not in the lungs of healthy mice or infected mice co-injected with unlabeled peptide.

CONCLUSIONS

Gamma-imaging with (111)In-DTPA-c(CGGRLGPFC)-NH(2) clearly delineated experimental IPA in mice. Peptides directly targeting fungi therefore may be valuable agents for noninvasive detection of opportunistic mycoses.

Dual-isotope lymphoscintigraphy using albumin nanocolloid differentially labeled with 111In and 99mTc

The aim of this study was to develop and evaluate 111In- and 99mTc-labeled derivatives of albumin nanocolloid (NC) for dual-label lymphoscintigraphy to allow simultaneous comparison of lymphatic flow from different tissue planes draining a tumour bed for accurate identification of sentinel lymph nodes (SLN). Using the chelator, p-isothiocyanatobenzyl-1,4,7, 10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), 111In-DOTA-NC and 99mTc-DOTA-NC were compared in vitro with respect to stability of labeling, colloidal status and particle size, then in vivo by measuring their clearance rates from a subcutaneous injection depot. 111In-DOTA-NC and 99mTc-DOTA-NC were indistinguishable on the basis of in vitro criteria. Their in vivo clearance rates, however, were disparate (0.0015 to 0.075 min(-1) for 111In and 0.0072 to 0.067 min(-1) for 99mTc), 111In being faster in three studies and markedly slower in three. This demonstrates that even when dual-labeled radiotracers behave identically in vitro, they will not necessarily do so in vivo. Further work is needed to develop dual-labeled NC.

Improvement of biodistribution and therapeutic index via increase of polyethylene glycol on drug-carrying liposomes in an HT-29/luc xenografted mouse model

Liposomes modified with a high concentration of polyethylene glycol (PEG) could significantly prolong the retention time of the carried drug in the circulation, thus improving the drug accumulation in the tumor. In this study, 6 mol% rather than 0.9 mol% PEGylated liposomes (100 nm in diameter) encapsulated with indium-111 were used in a human colorectal carcinoma HT-29/luc tumor-bearing mouse model for comparing the PEGylation effect. Pharmacokinetics, biodistribution, passive-targeted assay, bioluminescence imaging (BLI) and tumor growth measurements were used for the spatial and temporal distribution, tumor localization and therapeutic evaluation of the drug. Pharmacokinetic studies indicated that the terminal half-life (T((1/2))lambdaz) and C(max) of 6 mol% PEG (111)In liposomes were similar to those of 0.9 mol% PEG (111)In liposomes. In the blood, the total body clearance (Cl) of 6 mol% PEG (111)In liposomes was about 1.7-fold lower and the area under the curve (AUC) was 1.7-fold higher than those of 0.9 mol% PEG (111)In liposomes. These results showed that the long-term circulation and localization of 6 mol% PEGylated liposomes was more appropriate for use in the tumor-bearing animal model. In addition, the biodistribution of 6 mol% PEG (111)In liposomes showed significantly lower uptake in the liver, spleen, kidneys, small intestine and bone marrow than those of 0.9 mol% PEG (111)In liposomes. The clearance rate of both drugs from the blood decreased with time, with the maximum at 24 h post intravenous (i.v.) injection. Prominent tumor uptake and the highest tumor/muscle ratios were found at 48 h post injection. Both AUC and relative ratio of the AUCs (RR-AUC) also showed that 6 mol% PEGylated liposomes significantly reduced the uptake of drugs in the reticuloendothelial system (RES), yet enhanced the uptake in the tumor. Gamma scintigraphy at 48 h post injection also demonstrated more distinct tumor uptake with 6 mol% PEG (111)In liposomes as compared to that of 0.9 mol% PEGylated liposomes (p<0.01). BLI and in vivo tumor growth tracing showed that growth in tumor volume could largely be inhibited by 6 mol% PEG (111)In liposomes. The results suggest that 6 mol% PEGylated liposomes might be a more suitable liposomal carrier for drug delivery than 0.9 mol% PEGylated liposomes, not only by reducing the drug accumulation in the RES or its related organs, but by prolonging drug circulation and eventually enhancing the targeting efficiency in the tumor to reach a better therapeutic index.

Cell tracking and therapy evaluation of bone marrow monocytes and stromal cells using SPECT and CMR in a canine model of myocardial infarction

BACKGROUND

The clinical application of stem cell therapy for myocardial infarction will require the development of methods to monitor treatment and pre-clinical assessment in a large animal model, to determine its effectiveness and the optimum cell population, route of delivery, timing, and flow milieu.

OBJECTIVES

To establish a model for a) in vivo tracking to monitor cell engraftment after autologous transplantation and b) concurrent measurement of infarct evolution and remodeling.

METHODS

We evaluated 22 dogs (8 sham controls, 7 treated with autologous bone marrow monocytes, and 7 with stromal cells) using both imaging of 111Indium-tropolone labeled cells and late gadolinium enhancement CMR for up to12 weeks after a 3 hour coronary occlusion. Hearts were also examined using immunohistochemistry for capillary density and presence of PKH26 labeled cells.

RESULTS

In vivo Indium imaging demonstrated an effective biological clearance half-life from the injection site of ~5 days. CMR demonstrated a pattern of progressive infarct shrinkage over 12 weeks, ranging from 67-88% of baseline values with monocytes producing a significant treatment effect. Relative infarct shrinkage was similar through to 6 weeks in all groups, following which the treatment effect was manifest. There was a trend towards an increase in capillary density with cell treatment.

CONCLUSION

This multi-modality approach will allow determination of the success and persistence of engraftment, and a correlation of this with infarct size shrinkage, regional function, and left ventricular remodeling. There were overall no major treatment effects with this particular model of transplantation immediately post-infarct.

Splenic platelet kinetics and platelet production after major reconstructive vascular surgery

By using 111In-labelled platelets and dynamic gamma camera scintigraphy, platelet production rate and intrasplenic platelet kinetics were determined in 13 patients at 1 and 4 months after aortic reconstructive vascular surgery with implantation of dacron prostheses. A significant decrease in platelet production rate and venous platelet count was recorded over time after surgery. Irrespective of whether the exchangeable splenic platelet pool was estimated from initial recovery of platelet-bound radioactivity or from compartmental analysis, the size of this pool was significantly lower at the first study; a change in intrasplenic platelet transit time accounted for the observed difference. Platelet mean life-span increased over time after surgery but the difference between the duplicate studies was not statistically significant. It can be concluded that there is a reduction of platelet production rate and venous platelet count over time after major reconstructive vascular surgery. The early postoperative elevation in the platelet count is mainly the result of an increased platelet production and to a lesser degree due to redistribution of platelets between the splenic platelet pool and general circulation.