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[en] Gastroenteropancreatic neuroendocrine tumors (GEP-NET) are slow-growing neoplasms that arise from the neuroendocrine system of the gastrointestinal tract and pancreas. These may be classified based on location into the following: pheochromocytomas and parangangliomas; carcinoids; and pancreatic endocrine tumors. The majority of these tumors are nonfunctional, and thus, molecular imaging methods are critical in detection and staging of disease. Meta-iodobenzyl guanidine (MIBG) is a norepinephrine analog taken up by norepinephrine transporters that are overexpressed in the majority of GEP-NET. Radioactive MIBG can be used to image GEP-NET. The isotopes suitable for imaging include iodine-123 and iodine-131, using single-photon cameras, and iodine-124, using positron emission tomography (PET). Imaging is usually carried out a day or more after administration of the radiotracer, and serial and tomographic imaging may be necessary for optimal delineation. MIBG imaging is more useful for detecting pheochromocytoma, with reported accuracies greater than 80%, than for detecting carcinoid tumors, where the accuracy has been ∼70% and is reportedly higher in mid-gut tumors. MIBG imaging has been invaluable in the accurate staging of children with neuroblastoma, a lethal childhood tumor of the sympathetic nervous system. An important application of MIBG imaging is to demonstrate targeting of therapeutic I-131 MIBG. Imaging is thus useful in the detection of disease as well as in the demonstration of adequate targeting for therapy - either qualitatively or quantitatively with dosimetry. The latter will probably be feasible with PET using isotopes like iodine-124, and perhaps with single photon emission computed tomography/computed tomography. Imaging with MIBG will continue to be the mainstay for detection and staging of GEP-NET. More importantly, perhaps, imaging with MIBG will form part of an imaging continuum, including assessment of glycolytic rate and somatostatin receptor status, that will enable assessment of tumor phenotype and guide management
[en] Introduction: Neuroblastoma is the most common pediatric extracranial solid cancer. This tumor is characterized by metaiodobenzylguanidine (MIBG) avidity in 90% of cases, prompting the use of radiolabeled MIBG for targeted radiotherapy in these tumors. Methods: The available English language literature was reviewed for original research investigating in vitro, in vivo and clinical applications of radiolabeled MIBG for neuroblastoma. Results: MIBG is actively transported into neuroblastoma cells by the norepinephrine transporter. Preclinical studies demonstrate substantial activity of radiolabeled MIBG in neuroblastoma models, with 131I-MIBG showing enhanced activity in larger tumors compared to 125I-MIBG. Clinical studies of 131I-MIBG in patients with relapsed or refractory neuroblastoma have identified myelosuppression as the main dose-limiting toxicity, necessitating stem cell reinfusion at higher doses. Most studies report a response rate of 30-40% with 131I-MIBG in this population. More recent studies have focused on the use of 131I-MIBG in combination with chemotherapy or myeloablative regimens. Conclusions: 131I-MIBG is an active agent for the treatment of patients with neuroblastoma. Future studies will need to define the optimal role of this targeted radiopharmaceutical in the therapy of this disease
[en] Introduction: Nanoscale perfluorocarbon (PFC) droplets have been used to create imaging agents and drug delivery vehicles. However, development and characterization of new formulations of PFC droplets are hindered because of the lack of simple methods for quantitative and sensitive assessment of whole body tissue distribution and pharmacokinetics of the droplets. To address this issue, a general-purpose method for radiolabeling the inner core of nanoscale perfluorocarbon droplets with a hydrophobic and lipophobic fluorine-18 compound was developed, so that positron emission tomography (PET) and quantitative biodistribution studies can be employed to evaluate PFC nanodroplets in vivo. Methods: A robust method to produce [18F]CF3(CF2)7(CH2)3F from a tosylate precursor using [18F]F− was developed. The product's effectiveness as a general label for different PFCs and its ability to distinguish the in vivo behavior of different PFC droplet formulations was evaluated using two types of PFC nanodroplets: fluorosurfactant-stabilized perfluorohexane (PFH) nanodroplets and lipid-stabilized perfluorooctylbromide (PFOB) nanodroplets. In vivo assessment of the 18F-labeled PFH and PFOB nanodroplets were conducted in normal mice following intravenous injection using small animal PET imaging and gamma counting of tissues and fluids. Results: [18F]CF3(CF2)7(CH2)3F was produced in modest yield and was stable with respect to loss of fluoride in vitro. The labeled fluorocarbon was successfully integrated into PFH nanodroplets (~ 175 nm) and PFOB nanodroplets (~ 260 nm) without altering their mean sizes, size distributions, or surface charges compared to their non-radioactive analogues. No leakage of the radiolabel from the nanodroplets was detected after droplet formation in vitro. PET imaging and biodistribution data for the two droplet types tested showed significantly different tissue uptake and clearance patterns. Conclusion: A convenient method for producing 18F-labeled PFC droplets was developed. The results highlight the potential utility of the strategy for pre-clinical evaluation of different PFC droplet formulations through direct PFC core labeling using a fluorinated radiolabel.
[en] Introduction: Good manufacturing practice (GMP)-compliant production of radiopharmaceuticals for parenteral application requires great efforts in maintenance of clean room infrastructure and equipment in order to reliably guarantee the constant hygienic quality of the product (sterility). Terminal sterilization of the product is not always possible due to short half-life or due to thermal instability of the compound. The typical method for sterilization in these cases is sterile filtration prior to dispensing (distribution of product solution from bulk to patient vials). Therefore, aseptic processing techniques have to be in place in order to ensure sterility. Still, there remains some risk of microbial contamination of the product, and hence a risk for the patient to suffer from infection. Due to the short half-life of the labeling radionuclides, this aspect is aggravated by only retrospectively possible testing for sterility. This work investigated the potential of [18F]-radiation to intrinsically inactivate microorganisms (MO) that might have slipped through the aseptic process. Methods: Defined numbers of viable cells of different bacterial strains and molds were incubated with defined amounts of [18F]-activity. After decay of radiation the number of surviving viable cells was determined, D10-values were calculated and evaluated. Results: The MOs tested exhibit a broad range of [18F]-radiation susceptibility, D10-values range from a sensitive 114 MBq/mL (46 Gy) to a durable 2,048 MBq/mL (790 Gy). Conclusion: The intrinsic [18F]-radiation in radiopharmaceuticals is no safe measure to generally ensure sterility of the product solution in terms of “autosterilization”, because of dependence on various parameters. Advances in knowledge and implications for patient care: This work presents for the first time experimental data on the influence of [18F]-radiation on MOs. The results suggest, that aseptic processing techniques are essential and that results of determination of sterility in radiopharmaceuticals should be considered with care (emphasis on importance of media fill campaigns).
[en] Introduction: A positron emission tomography (PET) probe with ultra-high specific radioactivity (SA) enables measuring high receptor specific binding in brain regions by avoiding mass effect of the PET probe itself. It has been reported that PET probe with ultra-high SA can detect small change caused by endogenous or exogenous ligand. Recently, Kealey et al. developed [11C]BU99008, a more potent PET probe for I2-imidazoline receptors (I2Rs) imaging, with a conventional SA (mean 76 GBq/μmol) showed higher specific binding in the brain. Here, to detect small change of specific binding for I2Rs caused by endogenous or exogenous ligand in an extremely small region, such as hypothalamus in the brain, we synthesized and evaluated [11C]BU99008 with ultra-high SA as a useful PET probe for small-animal PET imaging of I2Rs. Methods: [11C]BU99008 was prepared by [11C]methylation of N-desmethyl precursor with [11C]methyl iodide. Biodistribution, metabolite analysis, and brain PET studies were conducted in rats. Results: [11C]BU99008 with ultra-high SA in the range of 5400–16,600 GBq/μmol were successfully synthesized (n = 7), and had appropriate radioactivity for in vivo study. In the biodistribution study, the mean radioactivity levels in all investigated tissues except for the kidney did not show significant difference between [11C]BU99008 with ultra-high SA and that with conventional SA. In the metabolite analysis, the percentage of unchanged [11C]BU99008 at 30 min after the injection of probes with ultra-high and conventional SA was similar in rat brain and plasma. In the PET study of rats' brain, radioactivity level (AUC30–60 min) in the hypothalamus of rats injected with [11C]BU99008 with ultra-high SA (64 [SUV ∙ min]) was significantly higher than that observed for that with conventional SA (50 [SUV ∙ min]). The specific binding of [11C]BU99008 with ultra-high SA (86% of total binding) for I2R was higher than that of conventional SA (76% of total binding). Conclusion: A PET study using [11C]BU99008 with ultra-high SA would thus contribute to the detection of small changes in or small regions with I2R expression and hence may be useful in elucidating new functions of I2R.
[en] Introduction: Alpha particles are radiation of high energy and short range, properties that can lead to radiolysis-mediated complications in labeling chemistry at the high radioactivity levels required for clinical application. In previous papers in this series, we have shown that radiation dose has a profound effect on the astatine species that are present in the labeling reaction and their suitability for the synthesis of N-succinimidyl 3-[211At]astatobenzoate. The purpose of this study was to evaluate the effects of adding N-chlorosuccinimide (NCS) to the methanol solution used for initial isolation of 211At after distillation, a process referred to as 211At stabilization, on 211At chemistry after exposure to high radiation doses. Methods: High performance liquid chromatography was used to evaluate the distribution of 211At species present in methanol in the 500–65,000 Gy radiation dose range and the synthesis of SAB from N-succinimidyl 3-(tri-n-butylstannyl)benzoate in the 500–120,000 Gy radiation dose range using different 211At timeactivity combinations under conditions with/without 211At stabilization. Results: In the absence of NCS stabilization, a reduced form of astatine, At(2), increased with increasing radiation dose, accounting for about half the total activity by about 15,000 Gy, while with stabilization, At(2) accounted for <10% of 211At activity even at doses >60,000 Gy. SAB yields without stabilization rapidly declined with increasing dose, falling to ~20% at about 5000 Gy while with stabilization, yields >80% were obtained with 211At solutions stored for more than 23 h and receiving radiation doses >100,000 Gy. Conclusions: Adding NCS to the methanol solution used for initial isolation of 211At is a promising strategy for countering the deleterious effects of radiolysis on 211At chemistry. Advances in knowledge and implications for patient care: This strategy could facilitate the ability to perform 211At labeling at sites remote from its production and at the high activity levels required for clinical applications.
[en] Introduction: Endarterectomized human atherosclerotic plaques are a valuable basis for gene expression studies to disclose novel imaging biomarkers and therapeutic targets, such as the cannabinoid receptor type 2 (CB2). In this work, CB2 is expressed on activated immune cells, which are abundant in inflamed plaques. We evaluated the CB2-specific radiotracer [11C]RS-016 for imaging vascular inflammation in human and mouse atherosclerotic lesions. Methods: The differential gene expression of microscopically classified human carotid plaques was evaluated using quantitative polymerase chain reaction. In addition, CB2 expression levels in human plaques were investigated by in vitro autoradiography. As an appropriate animal model we used apolipoprotein E knockout mice (ApoE KO) with shear stress-induced atherosclerosis to evaluate CB2 levels in vivo. Positron emission tomography (PET) was performed with both the CB2 radioligand [11C]RS-016 and the metabolic radiotracer [18F]fluorodeoxyglucose ([18F]FDG) at various time points. Retrospectively, carotids were dissected for histopathology and gene expression analysis. Results: We identified 28 human genes differentially expressed in atherosclerotic plaques compared to normal arteries of which 12 were upregulated preferentially in vulnerable plaques. The latter group included members of matrix metalloproteinase family and the T-lymphocyte activation antigens CD80 and CD86. CB2 was upregulated by 2-fold in human atherosclerotic plaques correlating with CD68 expression levels. Specific in vitro binding of [11C]RS-016 was predominantly observed to plaques. In vivo PET imaging of ApoE KO mice revealed accumulation of [11C]RS-016 and [18F]FDG in atherosclerotic plaques. Development of advanced plaques with elevated CB2 and CD68 levels were found in vitro in ApoE KO mice resembling human vulnerable plaques. Conclusion: We identified human genes associated with plaque vulnerability, which potentially could serve as novel imaging or therapeutic targets. The CB2-specific radiotracer [11C]RS-016 detected human plaques by in vitro autoradiography and accumulated in vivo in plaques of ApoE KO mice, however not exclusively in vulnerable plaques.
[en] The possibility of 123I isotope production with the help of the high-intensity bremsstrahlung photons produced by the electron beam of the LUE50 linear electron accelerator at the A.I. Alikhanyan National Science Laboratory (Yerevan Physics Institute [YerPhI]) is considered. The production method has been established and shown to be successful. The 124Xe(γ,n)123Xe → 123I nuclear reaction has been investigated and the cross-section was calculated by nuclear codes TALYS 1.6 and EMPIRE 3.2. The optimum parameter of the thickness of the target was determined by GEANT4 code. For the normalized yield of 123I, the value of 143 Bq/(mg·μA·h) has been achieved.
[en] Introduction: In this study, I2P-RGD2 was used as the example to illustrate a novel approach for dimerization of cyclic RGD peptides. The main objective of this study was to explore the impact of bifunctional linkers (glutamic acid vs. iminodiacetic acid) on tumor-targeting capability and excretion kinetics of the 99mTc-labeled dimeric cyclic RGD peptides. Methods: HYNIC-I2P-RGD2 was prepared by reacting I2P-RGD2 with HYNIC-OSu in the presence of diisopropylethylamine, and was evaluated for its αvβ3 binding affinity against 125I-echistatin bound to U87MG glioma cells. 99mTc-I2P-RGD2 was prepared with high specific activity (~185 GBq/μmol). The athymic nude mice bearing U87MG glioma xenografts were used to evaluate its biodistribution properties and image quality in comparison with those of 99mTc-3P-RGD2. Results: The IC50 value for HYNIC-I2P-RGD2 was determined to be 39 ± 6 nM, which was very close to that (IC50 = 33 ± 5 nM) of HYNIC-3P-RGD2. Replacing glutamic acid with iminodiacetic acid had little impact on αvβ3 binding affinity of cyclic RGD peptides. 99mTc-I2P-RGD2 and 99mTc-3P-RGD2 shared similar tumor uptake values over the 2 h period, and its αvβ3-specificity was demonstrated by a blocking experiment. The uptake of 99mTc-I2P-RGD2 was significantly lower than 99mTc-3P-RGD2 in the liver and kidneys. The U87MG glioma tumors were visualized by SPECT with excellent contrast using both 99mTc-I2P-RGD2 and 99mTc-3P-RGD2. Conclusion: Iminodiacetic acid is an excellent bifunctional linker for dimerization of cyclic RGD peptides. Bifunctional linkers have significant impact on the excretion kinetics of 99mTc radiotracers. Because of its lower liver uptake and better tumor/liver ratios, 99mTc-I2P-RGD2 may have advantages over 99mTc-3P-RGD2 for diagnosis of tumors in chest region. -- Graphical abstract: This report presents novel approach for dimerization of cyclic RGD peptides using iminodiacetic acid as a bifunctional linker. The results from this study clearly show that the bifunctional linker (glutamic acid vs. iminodiacetic acid) have significant impact on pharmacokinetics of their 99mTc radiotracers, and 99mTc-I2P-RGD2 is good as 99mTc-3P-RGD2 for imaging tumors of different origin. Display Omitted
[en] Objective: Scintigraphy using 99mTc-3PRGD2 targeting integrin αvβ3 could assess activation of hepatic stellate cells (HSCs). Liver fibrogenesis is intimately associated with activation of HSCs, and the fibrolytic process is accompanied by the reduction of the activated HSCs. In this study, we aimed to evaluate the feasibility of this method to assess the severity of liver fibrosis and the reversal after the fibrotic stimulus withdrawal. Methods: Liver fibrosis of different stages was induced by thioacetamide (TAA) injection for 2, 4 and 6 weeks (n = 6 for each time point). Another 6 rats with 8-week TAA administration (the 8-week group) and 6 rats which were injected with TAA for 6 weeks, and then withdrawn of TAA for 2 weeks (spontaneous recovery rats, SRR) were designed. The ratios of radioactivity detected in the liver vs. the heart at 30 min post-injection of 99mTc-3PRGD2 (L/H30min), the collagen proportionate area (CPA), the protein and mRNA levels of integrin αv, integrin β3 were analyzed and compared among groups. Results: The Ishak stage scores of the livers in the control and 2, 4, 6-week groups increased when the TAA administration period was extended. L/H30min increased with the upgrading of liver fibrosis and the differences between each pair of groups were statistically significant (p 30 min in the 8-week group was similar to that in the 6-week group (p > 0.05), but was significantly higher than that in the SRR group (p = 0.005). Conclusions: Scintigraphy using 99mTc-3PRGD2 may provide a non-invasive method for grading liver fibrosis and assessing liver fibrosis reversal.