Introduction: Released sympathetic neurotransmitter norepinephrine (NE) in the heart is cleared by neuronal uptake-1 and extraneuronal uptake-2 transporters. Cardiac uptake-1 and -2 expression varies among species, but the uptake-1 is the primary transporter in humans. LMI1195 is an NE analog labeled with F-18 for PET evaluation of cardiac neuronal function. This study investigated the impact of cardiac neuronal uptake-1 associated with different species on LMI1195 heart uptake.Methods: Cardiac uptake-1 was blocked by desipramine, a selective uptake-1 inhibitor, and sympathetic neuronal denervation was induced by 6-hydroxydopamine, a neurotoxin, in rats, rabbits and nonhuman primates (NHP). Tissue biodistribution and cardiac imaging of LMI1195 and I-123-metaiodobenzylguanidine (MIBG) were performed.Results: In rats, uptake-1 blockade did not alter LMI1195 heart uptake compared to the control at 60-min post injection [1.41 +/- 0.07 vs. 1.47 +/- 0.23 % injected dose per gram tissue (%ID/g)]. In contrast, LMI1195 heart uptake was reduced by 80% in uptake-1 blocked rabbits. In sympathetically denervated rats, LMI1195 heart uptake was similar to the control (2.18 +/- 0.40 vs. 2.58 +/- 0.76 %ID/g). However, the uptake decreased by 79% in denervated rabbits. Similar results were found in MIBG heart uptake in rats and rabbits with uptake-1 blockade. Consistently, LMI1195 cardiac imaging showed comparable myocardial activity in uptake-1 blocked or sympathetically denervated rats to the control, but marked activity reduction in uptake-1 blocked or denervated rabbits and NHPs.Conclusions: LMI1195 is retained in the heart of rabbits and NHPs primarily via the neuronal uptake-1 with high selectivity and can be used for evaluation of cardiac sympathetic denervation. Similar to the human, the neuronal uptake-1 is the dominant transporter for cardiac retention,of NE analogs in rabbits and NHPs, but not in rats. (C) 2013 Elsevier Inc. All rights reserved.

Based on a favorable balance between CRF-R1 affinity, lipophilicity and metabolic stability, compound 10 was evaluated for potential development as PET radioligand. Compound [(18)F]10 was prepared with high radiochemical purity and showed promising binding properties in rat brain imaging experiments.

A series of potent and selective β1-adrenoreceptor ligands were identified (IC50 range, 0.04-0.25 nM; β1/β2 selectivity range, 65-450-fold), labeled with the PET radioisotope fluorine-18 and evaluated in normal Sprague-Dawley rats. Tissue distribution studies demonstrated uptake of each radiotracers from the blood pool into the myocardium (0.48-0.62% ID/g), lung (0.63-0.97% ID/g), and liver (1.03-1.14% ID/g). Dynamic μPET imaging confirmed the in vivo dissection studies.

Matrix metalloproteinases (MMPs) play a key role in the development of atherosclerosis and its complications. In vivo detection and quantification of MMP activation can help track the propensity to complications and response to therapy. We sought to establish an in vivo imaging approach for monitoring MMP activation in atherosclerotic mouse aorta and use it to assess the response to dietary modification. Method: Apolipoprotein-deficient mice were fed normal chow or a high-fat diet (HFD) for up to 3 mo or a HFD for 2 mo, followed by 1 mo on normal chow. Then they underwent micro-SPECT/CT, along with autoradiography and oil red O staining of tissues. Results: After 3 mo of HFD, there was considerable atherosclerosis in the aorta. In vivo micro-SPECT/CT using RP782 (an 111In-labeled tracer targeting activated MMPs) showed a heterogeneous pattern of tracer uptake along the aorta. Heterogeneity of RP782 uptake was confirmed by autoradiography, and specificity was demonstrated using excess unlabeled precursor. Tracer uptake quantified by micro-SPECT significantly correlated with uptake quantified by autoradiography. Comparison of oil red O staining with autoradiography demonstrated areas of discordance between plaque presence and tracer uptake. HFD withdrawal led to significant reduction in RP782 uptake beyond the effect on plaque area. MMP expression and macrophage infiltration were similarly heterogeneous along the aorta and significantly reduced after withdrawal from the HFD. Finally, RP782 uptake significantly correlated with aortic macrophage content. Conclusion: Molecular imaging of MMP activation reveals the heterogeneity of atherosclerotic plaques and is a useful tool for tracking plaque biology and response to therapy.

Background—Heart failure has been associated with impaired cardiac sympathetic neuronal function. Cardiac imaging with radiolabeled agents that are substrates for the neuronal norepinephrine transporter (NET) has demonstrated the potential to identify individuals at risk of cardiac events. N-[3-Bromo-4-(3-[F]fluoro-propoxy)-benzyl]-guanidine (LMI1195) is a newly developed F-labeled NET substrate designed to allow cardiac neuronal imaging with the high sensitivity, resolution, and quantification afforded by positron emission tomography (PET). Methods and Results—LMI1195 was evaluated in comparison with norepinephrine (NE) in vitro and I-metaiodobenzylguanidine (MIBG) in vivo. The affinity (Ki) of LMI1195 for NET was 5.16 2.83 mol/L, similar to that of NE (3.36 2.77 mol/L) in a cell membrane–binding assay. Similarly, LMI1195 uptake kinetics examined in a human neuroblastoma cell line had Km and Vmax values of 1.44 0.76 mol/L and 6.05 3.09 pmol/million cells per minute, comparable to NE (2.01 0.85 mol/L and 6.23 1.52 pmol/million cells per minute). In rats, LMI1195 heart uptake at 15 and 60 minutes after intravenous administration was 2.36 0.38% and 2.16 0.38% injected dose per gram of tissue (%ID/g), similar to I-MIBG (2.14 0.30 and 2.19 0.27%ID/g). However, the heart to liver and lung uptake ratios were significantly higher for LMI1195 than for I-MIBG. In rabbits, desipramine (1 mg/kg), a selective NET inhibitor, blocked LMI1195 heart uptake by 82%, which was more effective than I-MIBG (53%), at 1 hour after dosing. Sympathetic denervation with 6-hydroxydopamine, a neurotoxin, resulted in a marked (79%) decrease in LMI1195 heart uptake. Cardiac PET imaging with LMI1195 in rats, rabbits, and nonhuman primates revealed clear myocardium with low radioactivity levels in the blood, lung, and liver. Imaging in rabbits pretreated with desipramine showed reduced heart radioactivity levels in a dose-dependent manner. Additionally, imaging in sympathetically denervated rabbits resulted in low cardiac image intensity with LMI1195 but normal perfusion images with flurpiridaz F 18, a PET myocardial perfusion imaging agent. In nonhuman primates pretreated with desipramine (0.5 mg/kg), imaging with LMI1195 showed a 66% decrease in myocardial uptake. In a rat model of heart failure, the LMI1195 cardiac uptake decreased as heart failure progressed. Conclusions—LMI1195 is a novel F imaging agent retained in the heart through the NET and allowing evaluation of the cardiac sympathetic neuronal function by PET imaging. (Circ Cardiovasc Imaging. 2011;4:435-443.)

Background— Heart failure has been associated with impaired cardiac sympathetic neuronal function. Cardiac imaging with radiolabeled agents that are substrates for the neuronal norepinephrine transporter (NET) has demonstrated the potential to identify individuals at risk of cardiac events. N -[3-Bromo-4-(3-[ 18 F]fluoro-propoxy)-benzyl]-guanidine (LMI1195) is a newly developed 18 F-labeled NET substrate designed to allow cardiac neuronal imaging with the high sensitivity, resolution, and quantification afforded by positron emission tomography (PET). Methods and Results— LMI1195 was evaluated in comparison with norepinephrine (NE) in vitro and 123 I-meta-iodobenzylguanidine (MIBG) in vivo. The affinity (K i ) of LMI1195 for NET was 5.16±2.83 μmol/L, similar to that of NE (3.36±2.77 μmol/L) in a cell membrane–binding assay. Similarly, LMI1195 uptake kinetics examined in a human neuroblastoma cell line had K m and V max values of 1.44±0.76 μmol/L and 6.05±3.09 pmol/million cells per minute, comparable to NE (2.01±0.85 μmol/L and 6.23±1.52 pmol/million cells per minute). In rats, LMI1195 heart uptake at 15 and 60 minutes after intravenous administration was 2.36±0.38% and 2.16±0.38% injected dose per gram of tissue (%ID/g), similar to 123 I-MIBG (2.14±0.30 and 2.19±0.27%ID/g). However, the heart to liver and lung uptake ratios were significantly higher for LMI1195 than for 123 I-MIBG. In rabbits, desipramine (1 mg/kg), a selective NET inhibitor, blocked LMI1195 heart uptake by 82%, which was more effective than 123 I-MIBG (53%), at 1 hour after dosing. Sympathetic denervation with 6-hydroxydopamine, a neurotoxin, resulted in a marked (79%) decrease in LMI1195 heart uptake. Cardiac PET imaging with LMI1195 in rats, rabbits, and nonhuman primates revealed clear myocardium with low radioactivity levels in the blood, lung, and liver. Imaging in rabbits pretreated with desipramine showed reduced heart radioactivity levels in a dose-dependent manner. Additionally, imaging in sympathetically denervated rabbits resulted in low cardiac image intensity with LMI1195 but normal perfusion images with flurpiridaz F 18, a PET myocardial perfusion imaging agent. In nonhuman primates pretreated with desipramine (0.5 mg/kg), imaging with LMI1195 showed a 66% decrease in myocardial uptake. In a rat model of heart failure, the LMI1195 cardiac uptake decreased as heart failure progressed. Conclusions— LMI1195 is a novel 18 F imaging agent retained in the heart through the NET and allowing evaluation of the cardiac sympathetic neuronal function by PET imaging.

1701 Objectives Cardiac sympathetic denervation (CSD) assessed by 123I-metaiodobenzylguanidin (MIBG) imaging has been suggested to predict cardiac events including arrhythmia and death in heart failure patients (ADMIRE-HF trial). LMI1195 is a benzylguanidine derivative, like MIBG, but labeled with 18F to improve image quality and quantification by allowing PET imaging. This study evaluated if imaging with LMI1195 could be used to identify CSD. Methods Rabbit models of regional and systemic CSD were used. To develop regional CSD, a median sternotomy was performed and phenol (89% in liquid) was painted on the anterior and posterior walls of the left ventricle. To develop systemic denervation, the neurotoxin 6-hydroxydopamine (25 mg/kg on days 1, 2, 7 and 8) was administered intravenously. Two weeks following these procedures, rabbits were imaged with LMI1195 (~1.5 mCi, iv) using a microPET camera for 30 minutes. To ensure the denervation procedures did not result in perfusion changes, rabbits were also imaged with the 18F perfusion imaging agent BMS747158. Results In sham-denervated rabbits, cardiac images of LMI1195 showed clear myocardium with uniform radioactivity distribution. The radioactivity was low in the lung and liver and cleared rapidly in blood. In rabbits with systemic denervation, image based quantification indicated ~ 80% global reduction in heart uptake of LMI1195 compared to control animals. Similarly, regional denervation resulted in a marked reduction in LMI1195 uptake in the treated regions. In contrast, cardiac imaging with BMS747158 demonstrated well-perfused myocardium and no differences were observed between control and denervated rabbits. Conclusions Reduced LMI1195 heart uptake in CSD rabbits is due to impaired innervation, not to alterations in perfusion. Cardiac PET imaging with LMI1195 can be used for detection of CSD, like 123I-MIBG, but with improved image quality and quantification

BMS747158 labeled with 18F is being developed for PET myocardial perfusion imaging. Imaging studies showed clear detection of necrotic tissue in acute myocardial infarcted (MI) animals and a good safety profile in normal animals. This study evaluated BMS747158 imaging and cardiovascular safety in a rabbit model of chronic MI with cardiac compromise.

LMI1195 is a new 18F-benzylguanidine analog being developed to assess cardiac neuronal function by targeting the norepinephrine transporter. The objective of this study was to evaluate the prognost...

Matrix metalloproteinases (MMPs) are expressed in atherosclerotic plaques and play an important role in plaque instability. Methods: Using Tc-99m-labeled broad-spectrum MMP inhibitor (MPI), we performed noninvasive imaging of MMP expression with micro-SPECT/micro-CT in mice deficient in apolipoprotein E (ApoE(-/-), n = 14), mice deficient in low-density-lipoprotein receptor (LDLR-/-, n = 14), and C57/BL6 mice as controls (n = 7). Seven ApoE(-/-) and 7 LDLR-/- received a high-cholesterol diet. After in vivo imaging, aortas were explanted, ex vivo images acquired, and the percent injected dose of MPI per gram (%ID/g) determined, followed by histologic characterization of atherosclerotic lesions. Results: MPI uptake was noninvasively visualized in atherosclerotic lesions by micro-SPECT, with confirmation by micro-CT of anatomic location and aortic calcification. %ID/g in each part of the aorta was highest in ApoE(-/-) that were fed a high-cholesterol diet, followed by LDLR-/- that were fed a high-cholesterol diet, ApoE(-/-) that were fed normal chow, and LDLR-/- that were fed normal chow. The control mice had minimal MPI uptake. A significant correlation was noted between %ID/g and % area positive for macrophages (r = 0.81, P = 0.009), MMP-2 (r = 0.65, P = 0.013), and MMP-9 (r = 0.62, P = 0.008). Conclusion: This study demonstrates the usefulness of molecular imaging for noninvasive assessment of the extent of MMP expression in various transgenic mouse models of atherosclerosis receiving a normal or hyperlipidemic diet. It is conceivable that such a strategy may be translationally developed for identification of unstable atherosclerotic plaques.

Myocardial extractions of mitochondria complex I (MC-I) inhibitors were high and well correlated with flow. This study assessed the potential of MC-I inhibitors to be developed as myocardial perfusion imaging (MPI) agents.

BMS747158-02 is an 18F-labeled agent being developed for PET myocardial perfusion imaging. This study examined impacts of feeding state and anesthetic on cardiac imaging and uptake of this agent in rats in comparison with 18F-fluorodeoxyglucose (FDG).