Hanne D. Hansen

No change in [11C]CUMI-101 binding to 5-HT1A receptors after intravenous citalopram in human

The main objective of this study was to determine the sensitivity of [11C]CUMI‐101 to citalopram challenge aiming at increasing extracellular 5‐HT. CUMI‐101 has agonistic properties in human embryonic kidney 293 cells transfected with human recombinant 5‐HT1A receptors (Hendry et al. [2011] Nucl Med Biol 38:273–277; Kumar et al. [2006] J Med Chem 49:125–134) and has previously been demonstrated to be sensitive to bolus citalopram in monkeys (Milak et al. [2011] J Cereb Blood Flow Metab 31:243–249). We studied six healthy individuals. Two PET‐scans were performed on the same day in each individual before and after constant infusion of citalopram (0.15 mg/kg). The imaging data were analyzed using two tissue compartment kinetic modeling with metabolite corrected arterial input and Simplified Reference Tissue Modeling using cerebellum as a reference region. There was no significant difference in regional distribution volume or non‐displaceable binding potential values before and after citalopram infusion. The mean receptor occupancy was 0.03 (range −0.14 to 0.17). Our data imply that [11C]CUMI‐101 binding is not sensitive to citalopram infusion in humans. Synapse, 2012.

The Center for Integrated Molecular Brain Imaging (Cimbi) database

We here describe a multimodality neuroimaging containing data from healthy volunteers and patients, acquired within the Lundbeck Foundation Center for Integrated Molecular Brain Imaging (Cimbi) in Copenhagen, Denmark. The data is of particular relevance for neurobiological research questions related to the serotonergic transmitter system with its normative data on the serotonergic subtype receptors 5-HT1A, 5-HT1B, 5-HT2A, and 5-HT4 and the 5-HT transporter (5-HTT), but can easily serve other purposes. The Cimbi database and Cimbi biobank were formally established in 2008 with the purpose to store the wealth of Cimbi-acquired data in a highly structured and standardized manner in accordance with the regulations issued by the Danish Data Protection Agency as well as to provide a quality-controlled resource for future hypothesis-generating and hypothesis-driven studies. The Cimbi database currently comprises a total of 1100 PET and 1000 structural and functional MRI scans and it holds a multitude of additional data, such as genetic and biochemical data, and scores from 17 self-reported questionnaires and from 11 neuropsychological paper/computer tests. The database associated Cimbi biobank currently contains blood and in some instances saliva samples from about 500 healthy volunteers and 300 patients with e.g., major depression, dementia, substance abuse, obesity, and impulsive aggression. Data continue to be added to the Cimbi database and biobank.

Anti-PSMA labeled liposomes loaded with Actinium-225 for potential antivascular alpha-radiotherapy

The serotonin (5-hydroxytryptamine [5-ΗΤ]) 7 receptor (5-HT7R) is the most recently discovered 5-HT receptor, and its physiologic and possible pathophysiologic roles are not fully elucidated. So far, no suitable 5-HT7R PET radioligand is available, thus limiting the investigation of this receptor in the living brain. Here, we present the radiosynthesis and in vivo evaluation of Cimbi-712 (3-{4-[4-(4-methylphenyl)piperazine-1-yl]butyl}p-1,3-dihydro-2H-indol-2-one) and Cimbi-717 (3-{4-[4-(3-methoxyphenyl)piperazine-1-yl]butyl}-1,3-dihydro-2H-indol-2-one) as selective 5-HT7R PET radioligands in the pig brain. The 5-HT7R distribution in the postmortem pig brain is also assessed. Methods: In vitro autoradiography with the 5-HT7R selective radioligand 3H-labeled (R)-3-(2-(2-(4-methylpiperidin-1-yl)ethyl)pyrrolidine-1-sulfonyl)phenol (SB-269970) was performed on pig brain sections to establish the 5-HT7R binding distribution. Radiolabeling of 5-HT7R selective compounds was performed in an automated synthesis module in which we conducted either palladium-mediated cross coupling (11C-Cimbi-712) or conventional O-methylation (11C-Cimbi-717) using 11C-MeI and 11C-MeOTf, respectively. After intravenous injection of the radioligands in Danish Landrace pigs, the in vivo brain distribution of the ligands was studied. Specific binding of 11C-Cimbi-712 and 11C-Cimbi717 to 5-HT7R was investigated by intravenous administration of SB-269970 before a second PET scan. Results: High 5-HT7R density was found in the thalamus and cortical regions of the pig brain by autoradiography. The radiosynthesis of both radioligands succeeded after optimization efforts (radiochemical yield, ∼20%–30% at the end of synthesis). Time–activity curves of 11C-Cimbi-712 and 11C-Cimbi-717 showed high brain uptake and distribution according to 5-HT7R distribution, but the tracer kinetics of 11C-Cimbi-717 were faster than 11C-Cimbi-712. Both radioligands were specific for 5-HT7R, as binding could be blocked by pretreatment with SB-269970 for 11C-Cimbi-717 in a dose-dependent fashion. For 11C-Cimbi-717, nondisplaceable binding potentials of 6.4 ± 1.2 (n = 6) were calculated in the thalamus. Conclusion: Both 11C-Cimbi-712 and 11C-Cimbi-717 generated a specific binding in accordance with 5-HT7R distribution and are potential PET radioligands for 5-HT7R. 11C-Cimbi-717 is the better candidate because of the more reversible tracer kinetics, and this radioligand showed a dose-dependent decline in cerebral binding after receptor blockade. Thus, 11C-Cimbi-717 is currently the most promising radioligand for investigation of 5-HT7R binding in the living human brain.

11C-labeling and preliminary evaluation of vortioxetine as a PET radioligand

Vortioxetine is a new multi-modal drug against major depressive disorder with high affinity for a range of different serotonergic targets in the CNS. We report the (11)C-labeling of vortioxetine with [(11)C]MeI using a Suzuki-protocol that allows for the presence of an unprotected amine. Preliminary evaluation of [(11)C]vortioxetine in a Danish Landrace pig showed rapid brain uptake and brain distribution in accordance with the pharmacological profile, all though an unexpected high binding in cerebellum was also observed. [(11)C]vortioxetine displayed slow tracer kinetics with peak uptake after 60 min and with limited wash-out from the brain. Further studies are needed but this radioligand may prove to be a valuable tool in unraveling the clinical effects of vortioxetine.

Radiolabelling and PET brain imaging of the α1-adrenoceptor antagonist Lu AE43936

Cerebral α₁-adrenoceptors are a common target for many antipsychotic drugs. Thus, access to positron emission tomography (PET) brain imaging of α₁-adrenoceptors could make important contributions to the understanding of psychotic disorders as well as to the pharmacokinetics and occupancy of drugs targeting the α₁-adrenoceptors. However, so far no suitable PET radioligand has been developed for brain imaging of α₁-adrenoceptors. Here, we report the synthesis of both enantiomers of the desmethyl precursors of the high affinity α₁-adrenoceptor ligand (1). The two enantiomers of 1 were subsequently [¹¹C] radiolabelled and evaluated for brain uptake and binding by PET imaging in Danish Landrace pigs. (S)-[¹¹C]-1 and (R)-[¹¹C]-1 showed very limited brain uptake. Pre-treatment with cyclosporine A (CsA) resulted in a large increase in brain uptake, indicating that (R)-[¹¹C]-1 is a substrate for active efflux-transporters. This was confirmed in Madin Darby canine kidney (MDCK) cells overexpressing permeability glycoprotein (Pgp). In conclusion, the limited brain uptake of both (S)-[¹¹C]-1 and (R)-[¹¹C]-1 in the pig brain necessitates the search for alternative radioligands for in vivo PET brain imaging of α₁-adrenoceptors.

Serotonergic mechanisms in the migraine brain – a systematic review

Background Migraine is one of the most common and disabling of all medical conditions, affecting 16% of the general population, causing huge socioeconomic costs globally. Current available treatment options are inadequate. Serotonin is a key molecule in the neurobiology of migraine, but the exact role of brain serotonergic mechanisms remains a matter of controversy. Methods We systematically searched PubMed for studies investigating the serotonergic system in the migraine brain by either molecular neuroimaging or electrophysiological methods. Results The literature search resulted in 59 papers, of which 13 were eligible for review. The reviewed papers collectively support the notion that migraine patients have alterations in serotonergic neurotransmission. Most likely, migraine patients have a low cerebral serotonin level between attacks, which elevates during a migraine attack. Conclusion This review suggests that novel methods of investigating the serotonergic system in the migraine brain are warranted. Uncovering the serotonergic mechanisms in migraine pathophysiology could prove useful for the development of future migraine drugs.

Direct comparison of [18F]MH.MZ and [18F]altanserin for 5-HT2A receptor imaging with PET

Imaging the cerebral serotonin 2A (5‐HT2A) receptors with positron emission tomography (PET) has been carried out in humans with [11C]MDL 100907 and [18F]altanserin. Recently, the MDL 100907 analogue [18F]MH.MZ was developed combining the selectivity profile of MDL 100907 and the favourable radiophysical properties of fluorine‐18. Here, we present a direct comparison of [18F]altanserin and [18F]MH.MZ. 5‐HT2A receptor binding in pig cortex and cerebellum was investigated by autoradiography with [3H]MDL 100907, [18F]MH.MZ, and [18F]altanserin. [18F]MH.MZ and [18F]altanserin were investigated in Danish Landrace pigs by brain PET scanning at baseline and after i.v. administration of blocking doses of ketanserin. Full arterial input function and high performance liquid chromatography (HPLC) analysis allowed for tissue‐compartment kinetic modeling of PET data. In vitro autoradiography showed high binding in cortical regions with both [18F]MH.MZ and [18F]altanserin. Significant 5‐HT2A receptor binding was also found in the pig cerebellum, thus making this region unsuitable as a reference region for in vivo data analysis in this species. The cortical binding of [18F]MH.MZ and [18F]altanserin was blocked by ketanserin supporting that both radioligands bind to 5‐HT2A receptors in the pig brain. In the HPLC analysis of pig plasma, [18F]MH.MZ displayed a fast and reproducible metabolism resulting in hydrophilic radiometabolites only whereas the metabolic profile of [18F]altanserin as expected showed lipophilic radiometabolites. Due to the slow kinetics of [18F]MH.MZ in high‐binding regions in vivo, we suggest that [18F]MH.MZ will be an appropriate tracer for low binding regions where kinetics will be faster, whereas [18F]altanserin is a suitable tracer for high‐binding regions. Synapse, 2013.

Synthesis and evaluation of 18F-labeled 5-HT2A receptor agonists as PET ligands

INTRODUCTION The serotonin 2A receptor (5-HT2AR) is the most abundant excitatory 5-HT receptor in the human brain and implicated in various brain disorders such as schizophrenia, depression, and Alzheimers disease. Positron emission tomography (PET) can be used to image specific proteins and processes in the human brain and several 5-HT2AR PET antagonist radioligands are available. In contrast to an antagonist radioligand, an agonist radioligand should be able to image the population of functional receptors, i.e., those capable of inducing neuroreceptor signaling. Recently, we successfully developed and validated the first 5-HT2AR agonist PET tracer, [(11)C]Cimbi-36, for neuroimaging in humans and herein disclose some of our efforts to develop an (18)F-labeled 5-HT2AR agonist PET-ligand. METHODS AND RESULTS Three fluorine containing derivatives of Cimbi-36 were synthesized and found to be potent 5-HT2A agonists. (18)F-labeling of the appropriate precursors was performed using [(18)F]FETos, typically yielding 0.2-2.0GBq and specific activities of 40-120GBq/μmol. PET studies in Danish landrace pigs revealed that [(18)F]1 displayed brain uptake in 5-HT2AR rich regions. However, high uptake in bone was also observed. No blocking effect was detected during a competition experiment with a 5-HT2AR selective antagonist. [(18)F]2 and [(18)F]3 showed very low brain uptake. CONCLUSION None of the investigated (18)F-labeled Cimbi-36 derivatives [(18)F]1, [(18)F]2 and [(18)F]3 show suitable tracer characteristics for in vivo PET neuroimaging of the 5-HT2AR. Although for [(18)F]1 there was reasonable brain uptake, we suggest that a large proportion radioactivity in the brain was due to radiometabolites, which would explain why it could not be displaced by a 5-HT2AR antagonist.

Design, synthesis, radiolabeling and in vivo evaluation of potential positron emission tomography (PET) radioligands for brain imaging of the 5-HT7 receptor

Here we describe the design, synthesis, and pharmacological evaluation of a set of compounds structurally related to the high affinity serotonin 5-HT7 receptor agonist N-(4-cyanophenylmethyl)-4-(2-diphenyl)-1-piperazinehexanamide (6, LP-211). Specific structural modifications were performed in order to maintain affinity for the target receptor and to improve the selectivity over 5-HT1A and adrenergic α1 receptors. The synthesized compounds have chemical features that could enable labeling with a positron emitter radioisotope (carbon-11 or fluorine-18) and lipophilicity within the range considered optimal for brain penetration and low non-specific binding. 4-[2-(4-Methoxyphenyl)phenyl]-N-(pyridin-4-ylmethyl)piperazinehexanamide (23a) and N-pyridin-4-ylmethyl-3-[4-[2-(4-methoxyphenyl)phenyl]piperazin-1-yl]ethoxy]propanamide (26a) were radiolabeled on the methoxy group with carbon-11. Positron emission tomography (PET) analysis revealed that [(11)C]-23a and [(11)C]-26a were P-glycoprotein (P-gp) substrates and rapidly metabolized, resulting in poor brain uptake. These features were not predicted by in vitro tests.

11C-labeling and preliminary evaluation of pimavanserin as a 5-HT2A receptor PET-radioligand

Pimavanserin is a selective serotonin 2A receptor (5-HT2AR) inverse agonist that has shown promise for treatment of psychotic symptoms in patients with Parkinsons disease. Here, we detail the (11)C-labeling and subsequently evaluate pimavanserin as a PET-radioligand in pigs. [(11)C]Pimavanserin was obtained by N-methylation of an appropriate precursor using [(11)C]MeOTf in acetone at 60°C giving radiochemical yields in the range of 1-1.7GBq (n=4). In Danish Landrace pigs the radio ligand readily entered the brain and displayed binding in the cortex in accordance with the distribution of 5-HT2ARs. However, this binding could not be blocked by either ketanserin or pimavanserin itself, indicating high nonspecific binding. The lack of displacement by the 5-HT2R antagonist and binding in the thalamus suggests that [(11)C]pimavanserin is not selective for the 5-HT2AR in pigs.