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Imaging the norepinephrine transporter in neuroblastoma: a comparison of [18F]-MFBG and 123I-MIBG.

ABSTRACT: The norepinephrine transporter (NET) is a critical regulator of catecholamine uptake in normal physiology and is expressed in neuroendocrine tumors like neuroblastoma. Although the norepinephrine analog, meta-iodobenzylguanidine (MIBG), is an established substrate for NET, (123)I/(131)I-MIBG has several clinical limitations for diagnostic imaging. In the current studies, we evaluated meta-[(18)F]-fluorobenzylguanidine ([(18)F]-MFBG) and compared it with (123)I-MIBG for imaging NET-expressing neuroblastomas.NET expression levels in neuroblastoma cell lines were determined by Western blot and (123)I-MIBG uptake assays. Five neuroblastoma cell lines and two xenografts (SK-N-BE(2)C and LAN1) expressing different levels of NET were used for comparative in vitro and in vivo uptake studies.The uptake of [(18)F]-MFBG in cells was specific and proportional to the expression level of NET. Although [(18)F]-MFBG had a 3-fold lower affinity for NET and an approximately 2-fold lower cell uptake in vitro compared with that of (123)I-MIBG, the in vivo imaging and tissue radioactivity concentration measurements demonstrated higher [(18)F]-MFBG xenograft uptake and tumor-to-normal organ ratios at 1 and 4 hours after injection. A comparison of 4 hours [(18)F]-MFBG PET (positron emission tomography) imaging with 24 hours (123)I-MIBG SPECT (single-photon emission computed tomography) imaging showed an approximately 3-fold higher tumor uptake of [(18)F]-MFBG, but slightly lower tumor-to-background ratios in mice.[(18)F]-MFBG is a promising radiopharmaceutical for specifically imaging NET-expressing neuroblastomas, with fast pharmacokinetics and whole-body clearance. [(18)F]-MFBG PET imaging shows higher sensitivity, better detection of small lesions with low NET expression, allows same day scintigraphy with a shorter image acquisition time, and has the potential for lower patient radiation exposure compared with (131)I/(123)I-MIBG.

SUBMITTER: Zhang H

PROVIDER: S-EPMC4072734 | biostudies-literature | 2014 Apr

REPOSITORIES: biostudies-literature

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Imaging the norepinephrine transporter in neuroblastoma: a comparison of [18F]-MFBG and 123I-MIBG.

Zhang Hanwen H Huang Ruimin R Cheung Nai-Kong V NK Guo Hongfen H Zanzonico Pat B PB Thaler Howard T HT Lewis Jason S JS Blasberg Ronald G RG

Clinical cancer research : an official journal of the American Association for Cancer Research 20140226 8

<h4>Purpose</h4>The norepinephrine transporter (NET) is a critical regulator of catecholamine uptake in normal physiology and is expressed in neuroendocrine tumors like neuroblastoma. Although the norepinephrine analog, meta-iodobenzylguanidine (MIBG), is an established substrate for NET, (123)I/(131)I-MIBG has several clinical limitations for diagnostic imaging. In the current studies, we evaluated meta-[(18)F]-fluorobenzylguanidine ([(18)F]-MFBG) and compared it with (123)I-MIBG for imaging NE ...[more]

PMID: 24573553

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Project description:Authors' goal is to evaluate the performance of simultaneous (99m)Tc-MDP/(123)I-MIBG tumor imaging with fast Monte-Carlo (MC) based joint iterative reconstruction as compared to sequential (99m)Tc-MDP and (123)I-MIBG tumor imaging.Noise-free (99m)Tc and (123)I SPECT projections were acquired separately using an anthropomorphic torso phantom modified to include a fillable tube around the lungs to mimic ribs. Additionally, (99m)Tc and (123)I projections were acquired separately using a 1-cm spherical "tumor" placed at various distances from one detector. Tumor-present data were generated by adding tumor projections to the torso phantom data, which were scaled to the total counts in typical clinical studies. Twenty-five noise realizations were generated by adding Poisson noise to the projection data for each radionuclide. Dual-radionuclide data were synthesized by summing the (99m)Tc and (123)I projections. Image reconstruction was performed using: (1) SR-OSEM, ordered subset expectation maximization (OSEM) without scatter correction (SC) using single-radionuclide (SR) data; (2) SR-MC-OSEM, OSEM with a fast MC-based SC using SR data; (3) DR-OSEM, OSEM without SC using dual-radionuclide (DR) data; and (4) DR-MC-JOSEM, joint OSEM with a fast MC-based SC using DR data. Ten (99m)Tc-MDP and ten (123)I-MIBG data sets, which had tumors mathematically inserted, were also used to evaluate the performance of authors' approach. For the phantom study, relative bias and relative standard deviation of tumor uptake were computed for each tumor using the tumor uptake in the noise-free single-radionuclide images, which were reconstructed by SR-MC-OSEM, as the gold standard. For both the phantom and constructed patient studies, mean contrast and standard deviation of contrast were computed for each tumor for both the single- and dual-radionuclide images. Additionally, contrast recovery was computed as the ratio between mean contrast and the mean contrast for SR-MC-OSEM.For the phantom study, DR-MC-JOSEM yielded 2.7% on average relative bias of tumor uptake using the images, which were reconstructed from the noise-free SR data with SR-MC-OSEM, as the gold-standard. For both the phantom and constructed patient studies, DR-MC-JOSEM yielded 94.7% and 95.2% tumor contrast recovery on average using SR-MC-OSEM as the reference, in the phantom and constructed patient studies, respectively. DR-MC-JOSEM yielded comparable relative standard deviation of bias and standard deviation of contrast to SR-MC-OSEM.Simultaneous (99m)Tc-MDP/(123)I-MIBG tumor imaging using authors' dual-radionuclide reconstruction approach yielded comparable image quality to sequential (99m)Tc-MDP and (123)I-MIBG imaging. For patients who need to undergo both scans, authors' approach offers perfectly registered dual-tracer images under identical conditions without compromising image quality, and reduces the imaging cost while increasing patient throughput.

Project description:BackgroundThe therapeutic use of [131I]meta-iodobenzylguanidine ([131I]MIBG) is often accompanied by hematological toxicity, primarily consisting of severe and persistent thrombocytopenia. We hypothesize that this is caused by selective uptake of MIBG via the serotonin transporter (SERT) located on platelets and megakaryocytes. In this study, we have investigated whether in vitro cultured human megakaryocytes are capable of selective plasma membrane transport of MIBG and whether pharmacological intervention with selective serotonin reuptake inhibitors (SSRIs) may prevent this radiotoxic MIBG uptake.MethodsPeripheral blood CD34+ cells were differentiated to human megakaryocytic cells using a standardized culture protocol. Prior to [3H]serotonin and [125I]MIBG uptake experiments, the differentiation status of megakaryocyte cultures was assessed by flow cytometry. Real-time quantitative polymerase chain reaction (RT-qPCR) was used to assess SERT and NET (norepinephrine transporter) mRNA expression. On day 10 of differentiation, [3H]serotonin and [125I]MIBG uptake assays were conducted. Part of the samples were co-incubated with the SSRI citalopram to assess SERT-specific uptake. HEK293 cells transfected with SERT, NET, and empty vector served as controls.ResultsIn vitro cultured human megakaryocytes are capable of selective plasma membrane transport of MIBG. After 10 days of differentiation, megakaryocytic cell culture batches from three different hematopoietic stem and progenitor cell donors showed on average 9.2 ± 2.4 nmol of MIBG uptake per milligram protein per hour after incubation with 10-7 M MIBG (range: 6.6 ± 1.0 to 11.2 ± 1.0 nmol/mg/h). Co-incubation with the SSRI citalopram led to a significant reduction (30.1%-41.5%) in MIBG uptake, implying SERT-specific uptake of MIBG. A strong correlation between the number of mature megakaryocytes and SERT-specific MIBG uptake was observed.ConclusionOur study demonstrates that human megakaryocytes cultured in vitro are capable of MIBG uptake. Moreover, the SSRI citalopram selectively inhibits MIBG uptake via the serotonin transporter. The concomitant administration of citalopram to neuroblastoma patients during [131I]MIBG therapy might be a promising strategy to prevent the onset of thrombocytopenia.

Project description:Both (131)I- and (123)I-labeled meta-iodobenzylguanidine (MIBG) have been widely used in the clinic for targeted imaging of the norepinephrine transporter (NET). The human NET (hNET) gene has been imaged successfully with (124)I-MIBG positron emission tomography (PET) at time points of >24 h post-injection (p.i.). (18)F-labeled MIBG analogs may be ideal to image hNET expression at time points of <8 h p.i. We developed improved methods for the synthesis of known MIBG analogs, [(18)F]MFBG and [(18)F]PFBG and evaluated them in hNET reporter gene-transduced C6 rat glioma cells and xenografts.[(18)F]MFBG and [(18)F]PFBG were synthesized manually using a three-step synthetic scheme. Wild-type and hNET reporter gene-transduced C6 rat glioma cells and xenografts were used to comparatively evaluate the (18)F-labeled analogs with [(123)I]/[(124)I]MIBG.The fluorination efficacy on benzonitrile was predominantly determined by the position of the trimethylammonium group. The para-isomer afforded higher yields (75?±?7%) than meta-isomer (21?±?5%). The reaction of [(18)F]fluorobenzylamine with 1H-pyrazole-1-carboximidamide was more efficient than with 2-methyl-2-thiopseudourea. The overall radiochemical yields (decay-corrected) were 11?±?2% (n?=?12) for [(18)F]MFBG and 41?±?12% (n?=?5) for [(18)F]PFBG, respectively. The specific uptakes of [(18)F]MFBG and [(18)F]PFBG were similar in C6-hNET cells, but 4-fold less than that of [(123)I]/[(124)I]MIBG. However, in vivo [(18)F]MFBG accumulation in C6-hNET tumors was 1.6-fold higher than that of [(18)F]PFBG at 1 h p.i., whereas their uptakes were similar at 4 h. Despite [(18)F]MFBG having a 2.8-fold lower affinity to hNET and approximately 4-fold lower cell uptake in vitro compared to [(123)I]/[(124)I]MIBG, PET imaging demonstrated that [(18)F]MFBG was able to visualize C6-hNET xenografts better than [(124)I]MIBG. Biodistribution studies showed [(18)F]MFBG and (123)I-MIBG had a similar tumor accumulation, which was lower than that of no-carrier-added [(124)I]MIBG, but [(18)F]MFBG showed a significantly more rapid body clearance and lower uptake in most non-targeting organs.[(18)F]MFBG and [(18)F]PFBG were synthesized in reasonable radiochemical yields under milder conditions. [(18)F]MFBG is a better PET ligand to image hNET expression in vivo at 1-4 h p.i. than both [(18)F]PFBG and [(123)I]/[(124)I]MIBG.

Project description:PURPOSE:Iodine-131-m-iodobenzylguanidine ([(131)I]mIBG)-targeted radionuclide therapy (TRT) is a standard treatment for recurrent or refractory neuroblastoma with response rates of 30-40 %. The aim of this study is to demonstrate patient-specific dosimetry using quantitative [(124)I]mIBG positron emission tomography/X-ray computed tomography (PET/CT) imaging with a GEometry ANd Tracking 4 (Geant4)-based Monte Carlo method for better treatment planning. PROCEDURES:A Monte Carlo dosimetry method was developed using the Geant4 toolkit with voxelized anatomical geometry and source distribution as input. The presegmented hybrid computational human phantoms developed by the University of Florida and the National Cancer Institute (UF/NCI) were used as a surrogate to characterize the anatomy of a given patient. S values for I-131 were estimated by the phantoms coupled with Geant4 and compared with those estimated by OLINDA|EXM and MCNPX for the newborn model. To obtain patient-specific biodistribution of [(131)I]mIBG, a 10-year-old girl with relapsed neuroblastoma was imaged with [(124)I]mIBG PET/CT at four time points prior to the planned [(131)I]mIBG TRT. The organ- and tumor-absorbed doses of the clinical case were estimated with the Geant4 method using the modified UF/NCI 10-year-old phantom with tumors and the patient-specific residence time. RESULTS:For the newborn model, the Geant4 S values were consistent with the MCNPX S values. The S value ratio of the Geant4 method to OLINDA|EXM ranged from 0.08 to 6.5 of all major organs. The [(131)I]mIBG residence time quantified from the pretherapy [(124)I]mIBG PET/CT imaging of the 10-year-old patient was mostly comparable to those previously reported. Organ-absorbed dose for the salivary glands was 98.0 Gy, heart wall 36.5 Gy, and liver 34.3 Gy, while tumor-absorbed dose ranged from 143.9 to 1,641.3 Gy in different sites. CONCLUSIONS:Patient-specific dosimetry for [(131)I]mIBG TRT was accomplished using pretherapy [(124)I]mIBG PET/CT imaging and a Geant4-based Monte Carlo dosimetry method. The Geant4 method with quantitative pretherapy imaging can provide dose estimates to normal organs and tumors with more realistic simulation geometry, and thus may improve treatment planning for [(131)I]mIBG TRT.

Dataset Information

Imaging the norepinephrine transporter in neuroblastoma: a comparison of [18F]-MFBG and 123I-MIBG.

Publications

Imaging the norepinephrine transporter in neuroblastoma: a comparison of [18F]-MFBG and 123I-MIBG.

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