Jong, M. de

Gastrin-releasing peptide receptor-based targeting using bombesin analogues is superior to metabolism-based targeting using choline for in vivo imaging of human prostate cancer xenografts (Article)

2011-07-01T00:00:00Z

Purpose: Prostate cancer (PC) is a major health problem. Overexpression of the gastrin-releasing peptide receptor (GRPR) in PC, but not in the hyperplastic prostate, provides a promising target for staging and monitoring of PC. Based on the assumption that cancer cells have increased metabolic activity, metabolism-based tracers are also being used for PC imaging. We compared GRPR-based targeting using the68Ga-labelled bombesin analogue AMBA with metabolism-based targeting using18F-methylcholine (18F-FCH) in nude mice bearing human prostate VCaP xenografts. Methods: PET and biodistribution studies were performed with both68Ga-AMBA and18F-FCH in all VCaP tumour-bearing mice, with PC-3 tumour-bearing mice as reference. Scanning started immediately after injection. Dynamic PET scans were reconstructed and analysed quantitatively. Biodistribution of tracers and tissue uptake was expressed as percent of injected dose per gram tissue (%ID/g). Results: All tumours were clearly visualized using68Ga-AMBA.18F-FCH showed significantly less contrast due to poor tumour-to-background ratios. Quantitative PET analyses showed fast tumour uptake and high retention for both tracers. VCaP tumour uptake values determined from PET at steady-state were 6.7±1.4%ID/g (20-30 min after injection, N=8) for68Ga-AMBA and 1.6±0.5%ID/g (10-20 min after injection, N=8) for18F-FCH, which were significantly different (p<0.001). The results in PC-3 tumour-bearing mice were comparable. Biodistribution data were in accordance with the PET results showing VCaP tumour uptake values of 9.5±4.8%ID/g (N=8) for68Ga-AMBA and 2.1±0.4%ID/g (N=8) for18F-FCH. Apart from the GRPR-expressing organs, uptake in all organs was lower for68Ga-AMBA than for18F-FCH. Conclusion: Tumour uptake of68Ga-AMBA was higher while overall background activity was lower than observed for18F-FCH in the same PC-bearing mice. These results suggest that peptide receptor-based targeting using the bombesin analogue AMBA is superior to metabolism-based targeting using choline for scintigraphy of PC.

Dynamic and static small-animal SPECT in rats for monitoring renal function after177Lu-labeled Tyr3-octreotate radionuclide therapy (Article)

2010-12-01T00:00:00Z

High kidney radiation doses during clinical peptide receptor radionuclide therapy (PRRT) with β-particle-emitting radio-labeled somatostatin analogs will lead to renal failure several months after treatment, urging the coinfusion of the cationic amino acids lysine and arginine to reduce the renal radiation dose. In rat PRRT studies, renal protection by the coadministration of lysine was confirmed by histologic examination of kidney specimens indicating nephrotoxicity. In the current study, we investigated dedicated small-animal SPECT/CT renal imaging in rats to monitor renal function in vivo during follow-up of PRRT, with and without lysine. Methods: The following 3 groups of rats were imaged using a multipinhole SPECT/CT camera: controls (group 1) and rats at more than 90 d after therapy with 460 MBq (15 μg) of 177Lu-DOTA-Tyr3-octreotate without (group 2) or with (group 3) a 400-mg/kg lysine coinjection as kidney protection (n ≥ 6 per group). At 90 and 140 d after therapy, static kidney scintigraphy was performed at 2 h after injection of 25 MBq of 99mTc-dimercaptosuccinic acid (99mTc-DMSA). In addition, dynamic dual-isotope renography was performed using 50 MBq of 111In-diethylenetriaminepentaacetic acid (111In-DTPA) and 50 MBq of 99mTc-mercaptoacetyltriglycine (99mTc-MAG3) at 100-120 d after therapy. Results: 111In-DTPA and 99mTc-MAG3 studies revealed a time-activity pattern comparable to those in patients, with a peak at 2-6 min followed by a decline of renal radioactivity. Reduced 111In-DTPA, 99mTc-MAG3, and 99mTc-DMSA uptake indicated renal damage in group 2, whereas group 3 showed only a decrease of 99mTc-MAG3 peak activity. These results indicating nephrotoxicity in group 2 and renal protection in group 3 correlated with levels of urinary protein and serum creatinine and urea and were confirmed by renal histology. Conclusion: Quantitative dynamic dual-isotope imaging using both 111In-DTPA and 99mTc-MAG3 and static 99mTc-DMSA imaging in rats is feasible using small-animal SPECT, enabling longitudinal monitoring of renal function. 99mTc-MAG3 renography, especially, appears to be a more sensitive marker of tubular function after PRRT than serum chemistry or 99mTc-DMSA scintigraphy.

A standardised study to compare prostate cancer targeting efficacy of five radiolabelled bombesin analogues (Article)

2010-07-01T00:00:00Z

Purpose: Prostate-specific antigen (PSA)-based screening for prostate cancer (PC) has dramatically increased early diagnosis. Current imaging techniques are not optimal to stage early PC adequately. A promising alternative to PC imaging is peptide-based scintigraphy using radiolabelled bombesin (BN) analogues that bind to gastrin-releasing peptide receptors (GRPR) being overexpressed in PC. When labelled to appropriate radionuclides BN targeting of GRPRs may also provide applications for peptide radionuclide receptor therapy (PRRT). Assessment studies under identical experimental conditions allowing a reliable comparison of the potential of such analogues are lacking. This study was performed to evaluate and directly compare five promising radiolabelled BN analogues for their targeting efficacy for PC under standardised conditions. Methods: The BN agonists [111In]DOTA-PESIN, [111In]AMBA, [111In]MP2346 and [111In]MP2653 and one antagonist [99mTc]Demobesin-1 were evaluated in GRPR-overexpressing human PC-3 tumour-bearing mice to determine peptide stability in vivo, biodistribution and GRPR targeting potential by animal SPECT/CT imaging and ex vivo autoradiography. Results: HPLC analysis of blood showed intact Demobesin-1 at 5 and 15 min after injection (64.1 ± 1.6% and 41.0 ± 01%, respectively) being much less for the other compounds. AMBA, the second most stable analogue, showed 36.1 ± 2.7% and 9.8 ± 1.1% intact peptide after 5 and 15 min. PC-3 tumour uptake at 1 h was comparable for Demobesin-1, AMBA, PESIN and MP2346 (3.0 ± 0.4, 2.7 ± 0.5, 2.3 ± 0.5 and 2.1 ± 0.9%ID/g, respectively), but very low for MP2653 (0.9 ± 0.2%ID/g). In addition, MP2346 showed undesirably high uptake in the kidneys (7.9 ± 1.9%ID/g) being significantly less for the other analogues. AMBA, MP2346 and PESIN revealed favourable increases in tumour to blood ratios over time while changes in tumour to kidney and pancreas ratios for Demobesin-1 from 1 to 24 h after injection were significantly better than for the other analogues. All analogues visualised PC-3 tumours by SPECT/CT and autoradiography. Conclusion: In the present study the BN antagonist Demobesin-1 was the best performing analogue showing superior in vivo stability, highest tumour uptake and retention while pancreatic and renal clearance were rapid. PESIN and AMBA were the best GRP agonists with sufficient in vivo stabilities as well as high tumour uptake and retention. Based on these results all three analogues deserve further evaluation for clinical use in PC patients.

Somatostatin receptor-based imaging and therapy of gastroenteropancreatic neuroendocrine tumors (Article)

2010-03-01T00:00:00Z

Somatostatin receptor imaging (SRI) with [111In-DTPA 0]octreotide has proven its role in the diagnosis and staging of gastroenteropancreatic neuroendocrine tumors (GEPNETs). Newer radiolabeled somatostatin analogs which can be used in positron emission tomography (PET) imaging, and which have a higher affinity for the somatostatin receptor, especially receptor subtype-2, have been developed. It would be desirable, however, if one radiolabeled analog became the new standard for PET imaging, because the current application of a multitude of analogs implies a fragmented knowledge on the interpretation of the images that are obtained in clinical practice. In our view, the most likely candidates for such a universal PET tracer for SRI are [68Ga-DOTA0,Tyr3]octreotate or [68Ga-DOTA0,Tyr3]octreotide. Treatment with radiolabeled somatostatin analogs is a promising new tool in the management of patients with inoperable or metastasized neuroendocrine tumors. Symptomatic improvement may occur with all 111In-, 90Y-, or 177Lu-labeled somatostatin analogs that have been used for peptide receptor radionuclide therapy (PRRT). The results that were obtained with [ 90Y-DOTA0,Tyr3]octreotide and [ 177Lu-DOTA0,Tyr3]octreotate are very encouraging in terms of tumor regression. Also, if kidney protective agents are used, the side effects of this therapy are few and mild, and the median duration of the therapy response for these radiopharmaceuticals is 30 and 40 months respectively. The patients' self-assessed quality of life increases significantly after treatment with [177Lu-DOTA0,Tyr 3]octreotate. Lastly, compared to historical controls, there is a benefit in overall survival of several years from the time of diagnosis in patients treated with [177Lu-DOTA0,Tyr3]- octreotate. These data compare favorably with the limited number of alternative treatment approaches. If more widespread use of PRRT can be guaranteed, such therapy may well become the therapy of first choice in patients with metastasized or inoperable GEPNETs.

Tumor uptake of 68Ga-DOTA-Tyr3-octreotate: animal PET studies of tumor flow and acute somatostatin receptor modulation in the CA20948 rat model (Article)

2010-02-01T00:00:00Z

Introduction: Factors determining the in vivo uptake of radiolabeled somatostatin analogs by neuroendocrine tumors are poorly known. The aim is to evaluate in vivo tumor perfusion and regulation of somatostatin receptors (sstr) following acute exposure to octreotide, in an animal model of neuroendocrine tumor. Methods: H215O flow studies were performed in 8 CA20948 tumor-bearing rats and another 36 rats underwent three [68Ga]-DOTA-Tyr3-octreotate imaging sessions at 24-h intervals. After baseline (Day 0) imaging, scanning was repeated on Day 1 after octreotide injection (175 μg/kg), with a variable delay: no injection (controls, n=7), coinjection (n=6), and octreotide injection 20 min (n=7), 2 h (n=8) and 4 h (n=8) before imaging. Repeat images without octreotide was performed at Day 2 followed by sacrifice and tumor counting. Results: H215O studies failed to measure quantitative tumor perfusion in this model. On Day 1, ratio of tumor uptake to Day 0 was 1.2±0.3 in controls; 0.6±0.2 in the coinjection group; 0.9±0.2, 1.1±0.1 and 1.2±0.2 in the other groups, respectively. Uptake in the coinjection group showed a statistically significant reduction of tumor uptake (P<.0001). All groups showed increased uptake on Day 2, without statistical differences between groups. In vivo tumor counts showed good correlation with ex vivo countings (R2=0.946). Conclusion: Acute exposure to unlabeled octreotide in this neuroendocrine tumor model results in a rapid recycling or resynthesis of sstr. Positron emission tomography (PET) allowed to reliably assess quantitative uptake of [68Ga]-DOTA-Tyr3-octreotate over time in the same animal, but failed in this model to measure tumor perfusion.

Reducing renal uptake of radiolabeled peptides using albumin fragments (Article)

2008-09-01T00:00:00Z

In most types of peptide receptor radionuclide therapy, the maximum activity dose that can be administered is limited by high and persistent renal retention of the radiolabeled peptides, which is, at least partly, mediated by the megalin receptor. Several agents that interfere with renal reabsorption of radiolabeled peptides have been identified (e.g., lysine, arginine, succinylated gelatin solution), but none of these inhibit renal reabsorption completely. Albumin, a naturally abundant megalin ligand, might be a safe and potent alternative. In this study, we analyzed the effects of albumin and fragments of albumin (FRALB) on the renal reabsorption of 111In- diethylenetriaminepentaacetic acid (DTPA)-D-Phe1-octreotide ( 111In-octreotide), [Lys40(aminohexoic acid-DTPA- 111In)NH2]-exendin-4 (111In-exendin), and 111In-1,4,7,10-tetraazacyclododecane-N,N′,N″, N‴-tetraacetic acid (DOTA)-Glu1-minigastrin ( 111In-minigastrin). Methods: The effects of albumin and FRALB on megalin-associated binding of 111In-octreotide, 111In- exendin, and 111In-minigastrin were assessed in vitro using rat yolk sac epithelial (BN16) cells. In vivo, uptake and localization of 111In-albumin and 111In-FRALB in the kidneys of Wistar rats were determined, as well as the effect of lysine, succinylated gelatin solution, albumin, and FRALB on the kidney uptake of 111In- octreotide, 111In-exendin, and 111In-minigastrin. Results: FRALB significantly reduced binding and uptake of 111In-octreotide, 111In-exendin, and 111In-minigastrin by BN16 cells. In rats, renal uptake of 111In-labeled FRALB was significantly higher than that of 111In-labeled intact albumin (P < 0.001). FRALB administration effectively reduced renal uptake of 111In-octreotide, 111In-exendin, and 111In-minigastrin. Administration of 1-2 mg of FRALB reduced renal uptake of 111In-octreotide as efficiently as 80 mg of lysine. Conclusion: Renal uptake of 111In- octreotide and other radiolabeled peptides in rats can be effectively reduced by administration of albumin fragments. Additional studies to identify the albumin fragments responsible for inhibition of renal peptide uptake are warranted.

Increased extracellular matrix synthesis by smooth-muscle cells obtained from in vivo restenotic lesions by directional coronary atherectomy. (Article)

1996-01-01T00:00:00Z

Proliferation and extracellular matrix synthesis of smooth muscle cells cultured from human coronary atherosclerotic and restenotic lesions (Article)

1994-01-01T00:00:00Z

OBJECTIVES. The purpose of this study was to examine the proliferative capacity and extracellular matrix synthesis of human coronary plaque cells in vitro. BACKGROUND. Common to both primary atherosclerosis and restenosis are vascular smooth muscle cell proliferation and production of extracellular matrix proteins. The applicability to humans of experimental animal models of these processes has been questioned. METHODS. Primary atherosclerotic and restenotic lesions were excised by percutaneous directional coronary atherectomy in 93 patients. Smooth muscle cells were cultivated by an explant technique and identified by their morphology in culture, ultrastructural features under electron microscopy and immunostaining using monoclonal antibodies to smooth muscle cell alpha-actin. Proliferation in secondary culture was assessed with growth curves and the synthesis of collagen and sulfated glycosaminoglycans by the incorporation of 3H-proline and 35S-sulfate, respectively. These studies were also performed in cells derived from human umbilical artery media. RESULTS. Success rates for primary (45%) and secondary (12%) culture of coronary cells were not influenced by clinical variables or lesion category. Primary culture success was improved by the presence of organized thrombus in the plaque and in relation to increased maximal cell density of the atherectomy specimen. Restenotic cells displayed more rapid growth than did cells of primary atherosclerotic origin, which grew in a manner similar to that of umbilical artery cells. Mean calculated population-doubling times for the three cell groups were 52 h (95% confidence interval [CI] 48 to 58 h), 71 h (95% CI 62 to 83 h) and 74 h (95% CI 65 to 84 h), respectively. Restenotic and primary atherosclerotic cells did not differ in the synthesis of collagen ([mean +/- SEM] 0.034 +/- 0.004 vs. 0.033 +/- 0.004 nmol isotope.microgram protein-1, p = NS) or sulfated glycosaminoglycans (11.47 +/- 1.07 vs. 15.37 +/- 3.10 nmol isotope.microgram protein-1, p = NS), but the coronary cells synthesized significantly more collagen and sulfated glycosaminoglycans than did umbilical artery cells (0.019 +/- 0.004 and 5.43 +/- 1.00 nmol isotope.microgram protein-1, respectively, both p < 0.05). CONCLUSIONS. These data indicate that increased smooth muscle cell proliferation contributes to coronary restenosis in humans and support the concept that the extracellular matrix synthesis of adult smooth muscle cells is important to lesion formation.

Uptake of thyroxine in cultured anterior pituitary cells of euthyroid rats (Article)

1994-01-01T00:00:00Z

The uptake of [125I]T4 was investigated in cultured anterior pituitary cells isolated from adult fed Wistar rats and cultured for 3 days in medium containing 10% fetal calf serum. Experiments were performed with [125I]T4 (10(5) to 2 x 10(6) cpm; 0.35-7 nM) in medium containing 0.5% or 0.1% BSA. The uptake of [125I]T4 increased with time and showed equilibrium after around 1 h of incubation. The presence of 10 microM unlabeled T4 during incubation decreased the uptake of [125I]T4 by 65-70% at all time intervals. After 24 h of incubation, 1.5% iodide and 3.2% conjugates were detected in the medium, whereas around 20% of cellular radioactivity represented [125I]T3. The 15-min uptake of [125I]T4 was significantly reduced by simultaneous incubation with 100 nM T4 (by 24%; P < 0.05), 100 nM T3 (by 38%; P < 0.001), or 10 microM rT3 (by 32%; P < 0.001), whereas 10 microM tetraiodothyroacetic acid (Tetrac) had no effect. Furthermore, preincubation (30 min) and incubation (15 min) with 10 microM monodansylcadaverine, oligomycin, or monensin reduced the uptake of [125I]T4 by 30%, 50%, and 40%, respectively (all P < 0.001). Substitution of Na+ in the buffer by K+ diminished the uptake of [125I]T4 by 39% (P < 0.005); 2 mM phenylalanine, tyrosine, or tryptophan reduced [125I]T4 uptake by 18% (P < 0.05), 18% (P = NS), and 33% (P < 0.005), respectively. Our data suggest that the pituitary contains a specific carrier-mediated energy-requiring mechanism for [125I]T4 uptake that is partly dependent on the Na+ gradient. In addition, part of [125I]T4 uptake in the pituitary might occur through an amino acid transport system. When expressed per pM of free hormone, the 15-min uptake of [125I]T4 was approximately as high as that of [125I]T3. Because the reduction of [125I]T4 uptake by T4, T3, monodansylcadaverine, oligomycin, and monensin was roughly the same as the previously reported reduction of [125I]T3 uptake by the same compounds, it is further suggested that T4 and T3 share a common carrier in cultured anterior pituitary cells.

Histologic characteristics of tissue excised during directional coronary atherectomy in stable and unstable angina pectoris (Article)

1993-01-01T00:00:00Z

Directional atherectomy: combining basic research and intervention (Article)

1993-01-01T00:00:00Z

Clinical and histological determinants of smooth-muscle cell outgrowth in cultured atherectomy specimens: importance of thrombus organization (Article)

1993-01-01T00:00:00Z

BACKGROUND: Coronary atherectomy provides a unique opportunity to obtain plaque tissue from a wide variety of clinical syndromes. We investigated the relation between the clinical status and histopathological substrate of tissue retrieved during directional coronary atherectomy and the proliferative and migratory potential of smooth-muscle cells judged from successful outgrowth during cell culture. METHODS: After directional coronary atherectomy, tissue samples were examined macroscopically, divided into two equal pieces, and separately subjected to cell culture and histopathological study. Cell culture was performed using an explant technique. In-vitro smooth-muscle cell outgrowth was related to clinical and histological variables. RESULTS: Atherosclerotic tissue was obtained from 98 consecutive atherectomy procedures. Histological examination revealed a broad spectrum of appearances, ranging from complex atheroma containing dense fibrous tissue, calcium deposits, macrophages, and necrotic debris to neointimal proliferation and organized thrombi. Smooth-muscle cell outgrowth was observed in 43 of the 98 samples (44%). Although not affected by any of the clinical variables, cell outgrowth was influenced by histological variables, in particular the presence of organizing thrombi. Outgrowth was successful in eight out of 10 samples with thrombus (80%) and in only 35 out of 88 (40%) without (P = 0.03). CONCLUSION: The presence of organizing thrombi in the retrieved tissue facilitates smooth-muscle cell outgrowth and suggests an enhanced proliferative and migratory potential. These findings may be relevant to the understanding of neointimal proliferation in coronary syndromes where mural thrombosis is likely to occur.