title: Evaluation of LMI1195, a novel 18F-labeled cardiac neuronal PET imaging agent, in cells and animal models.
abstract: 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-[18F]fluoro-propoxy)-benzyl]-guanidine (LMI1195) is a newly developed 18F-labeled NET substrate designed to allow cardiac neuronal imaging with the high sensitivity, resolution, and quantification afforded by positron emission tomography (PET).
  
  
  RESULTS
  LMI1195 was evaluated in comparison with norepinephrine (NE) in vitro and 123I-meta-iodobenzylguanidine (MIBG) in vivo. The affinity (Ki) 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 Km and Vmax 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 123I-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 123I-MIBG. In rabbits, desipramine (1 mg/kg), a selective NET inhibitor, blocked LMI1195 heart uptake by 82%, which was more effective than 123I-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.
authors.affiliation: Discovery Research, Lantheus Medical Imaging, North Billerica, MA 01862, USA. ming.yu@lantheus.com
authors.forename: Ming
authors.initials: M
authors.lastname: Yu
authors.forename: Jody
authors.initials: J
authors.lastname: Bozek
authors.forename: Melanie
authors.initials: M
authors.lastname: Lamoy
authors.forename: Mary
authors.initials: M
authors.lastname: Guaraldi
authors.forename: Paula
authors.initials: P
authors.lastname: Silva
authors.forename: Mikhail
authors.initials: M
authors.lastname: Kagan
authors.forename: Padmaja
authors.initials: P
authors.lastname: Yalamanchili
authors.forename: David
authors.initials: D
authors.lastname: Onthank
authors.forename: Mahesh
authors.initials: M
authors.lastname: Mistry
authors.forename: Joel
authors.initials: J
authors.lastname: Lazewatsky
authors.forename: Matthias
authors.initials: M
authors.lastname: Broekema
authors.forename: Heike
authors.initials: H
authors.lastname: Radeke
authors.forename: Ajay
authors.initials: A
authors.lastname: Purohit
authors.forename: Michael
authors.initials: M
authors.lastname: Cdebaca
authors.forename: Michael
authors.initials: M
authors.lastname: Azure
authors.forename: Richard
authors.initials: R
authors.lastname: Cesati
authors.forename: David
authors.initials: D
authors.lastname: Casebier
authors.forename: Simon P
authors.initials: SP
authors.lastname: Robinson
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D003714:Denervation / Q000379:methods; D004195:Disease Models, Animal; D005462:Fluorine Radioisotopes; D005464:Fluorobenzenes / Q000493:pharmacokinetics*; D006146:Guanidines / Q000493:pharmacokinetics*; D006207:Half-Life; D006333:Heart Failure / Q000000981:diagnostic imaging*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008252:Macaca fascicularis; D008297:Male; D009447:Neuroblastoma / Q000378:metabolism; D049268:Positron-Emission Tomography / Q000379:methods*; D011817:Rabbits; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012680:Sensitivity and Specificity; D014018:Tissue Distribution
chemical_list: D005462:Fluorine Radioisotopes; D005464:Fluorobenzenes; D006146:Guanidines; D019275:Radiopharmaceuticals; C561360:flubrobenguane