Synthesis and Evaluation of Mefway Analogs as Ligands for Serotonin 5HT1A Receptors.

18F-Mefway (N-{2-[4-(2'-methoxyphenyl)piperazinyl]ethyl}-N-(2-pyridyl)-N-(4'-18F-fluoro-methylcyclohexane)carboxamide) was developed and evaluated for use as a PET ligand for imaging 5-HT1A receptors. Ongoing studies of 18F-Mefway have shown it to be an effective PET radiotracer. We have synthesized isomers of Mefway by changing the position of the methyl-group in attempts to evaluate stability for imaging purposes. 2-Methyl-, 3-methyl-, and 4-methyl-cyclohexane-1-carboxylic acids and 3-carbomethoxy-, 4-carbomethoxycyclohexane-1-carboxylic acids were coupled with WAY-100634 to provide the methylcyclohexyl derivatives (2-, 3- and 4-methyl). Mefway and 3-Mefway analogs were prepared by reduction of carbomethoxy-derivatives followed by fluorination. In vitro binding affinities for the methylated derivatives in rat brain homogenates was found to be 10.4 nM (2-methyl), 77 nM (3-methyl) and 21.5 nM (4-methyl). Binding affinity of 3-Mefway and 4-Mefway was found to be 17.4 nM and 6.26 nM, respectively. Our results suggest that 3-methyl/3-fluoromethyl substituent has approx. 3-fold lower affinities compared to the 4-methyl/4-fluoromethyl substituent.

Evaluation of serotonin 5-HT(1A) receptors in rodent models using [¹8F]mefway PET.

INTRODUCTION: Serotonin 5-HT(1A) receptors have been investigated in various CNS disorders, including epilepsy, mood disorders, and neurodegeneration. [¹8F]Mefway (N-{2-[4-(2'-methoxyphenyl)piperazinyl]ethyl}-N-(2-pyridyl)-N-(cis/trans-4'-[¹8F]fluoromethylcyclohexane)-carboxamide) has been developed as a suitable positron emission tomography (PET) imaging agent for these receptors. We have now evaluated the suitability of [¹8F]trans-mefway in rat and mouse models using PET and computerized tomography (CT) imaging and corroborated with ex vivo and in vitro autoradiographic studies. METHODS: Normal Sprague-Dawley rats and Balb/C mice were used for PET/CT imaging using intravenously injected [¹8F]trans-mefway. Brain PET data were coregistered with rat and mouse magnetic resonance imaging template and regional distribution of radioactivity was quantitated. Selected animals were used for ex vivo autoradiographic studies to confirm regional brain distribution and quantitative measures of binding, using brain region to cerebellum ratios. Binding affinity of trans-mefway and WAY-100635 was measured in rat brain homogenates. Distribution of [¹8F]trans-4-fluoromethylcyclohexane carboxylate ([¹8F]FMCHA), a major metabolite of [¹8F] trans-mefway, was assessed in the rat by PET/CT. RESULTS: The inhibition constant, K(i) for trans-mefway was 0.84 nM and that for WAY-100635 was 1.07 nM. Rapid brain uptake of [¹8F]trans-mefway was observed in all rat brain regions and clearance from cerebellum was fast and was used as a reference region in all studies. Distribution of [¹8F]trans-mefway in various brain regions was consistent in PET and in vitro studies. The dorsal raphe was visualized and quantified in the rat PET but identification in the mouse was difficult. The rank order of binding to the various brain regions was hippocampus > frontal cortex > anterior cingulate cortex > lateral septal nuclei > dorsal raphe nuclei. CONCLUSION: [¹8F]trans-Mefway appears to be an effective 5-HT(1A) receptor imaging agent in rodents for studies of various disease models.

Update on Coccidioidomycosis in the United States and Beyond.

Coccidioidomycosis is a fungal infection that is prevalent in western United States, Central America, and South America. The infection is acquired by inhalation. It can affect persons of all ages including infants and children. The majority of cases are asymptomatic and the incidence of infection is greater during a dry summer season after heavy rainfall in prior winter. For those with symptoms, they may experience a self-limiting influenza-like illness. However, some may progress toward pneumonia or disseminated diseases involving skeletal system and central nervous system. The diagnosis is based mainly on various serology testing. Antifungal treatment is generally not required for those with mild symptoms. For those with moderate to severe infections, the mainstay of treatment is azole, with fluconazole being often considered as the first line therapy. Currently there is no effective solution to prevent coccidioidomycosis. Those who work in high-risk conditions should be given appropriate protective equipment as well as education on proper precaution.

Comparative assessment of (18) F-Mefway as a serotonin 5-HT1A receptor PET imaging agent across species: Rodents, nonhuman primates, and humans.

We have developed (18) F-trans-Mefway ((18) F-Mefway) for positron emission tomography (PET) imaging studies of serotonin 5-HT1A receptors which are implicated in various brain functions. Translation of imaging the 5-HT1A receptor in animal models to humans will facilitate an understanding of the role of the receptor in human brain disorders. We report comparative brain distribution of (18) F-Mefway in normal mice, rats, monkeys, and healthy human volunteers. Mefway was found to be very selective, with subnanomolar affinity for the 5-HT1A receptor. Affinities of >55 nM were found for all other human-cloned receptor subtypes tested. Mefway was found to be a poor substrate (>30 µM) for the multidrug resistance 1 protein, suggesting low likelihood of brain uptake being affected by P-glycoprotein. Cerebellum was used as a reference region in all imaging studies across all species due to the low levels of (18) F-Mefway binding. Consistent binding of (18) F-Mefway in cortical regions, hippocampus, and raphe was observed across all species. (18) F-Mefway in the human brain regions correlated with the known postmortem distribution of 5-HT1A receptors. Quantitation of raphe was affected by the resolution of the PET scanners in rodents, whereas monkeys and humans showed a raphe to cerebellum ratio of approximately 3. (18) F-Mefway appears to be an effective 5-HT1A receptor imaging agent in all models, including humans. (18) F-Mefway therefore may be used to quantify 5-HT1A receptor distribution in brain regions for the study of various CNS disorders. J. Comp. Neurol. 524:1457-1471, 2016. © 2015 Wiley Periodicals, Inc.

Initial in vivo PET imaging of 5-HT1A receptors with 3-[(18)F]mefway.

4-trans-[(18)F]Mefway is a PET radiotracer with high affinity for 5-HT1A receptors. Our preliminary work indicated the positional isomer, 3-[(18)F]mefway, would be suitable for PET imaging of 5-HT1A receptors. We now compare the in vivo behaviour of 3-mefway with 4-mefway to evaluate 3-[(18)F]mefway as a potential 5-HT1A PET radiotracer. Two male rhesus macaques were given bolus injections of both 3- and 4-trans-[(18)F]mefway in separate experiments. 90 minute dynamic PET scans were acquired. TACs were extracted in the mesial temporal lobe (MTL) and caudal anterior cingulate gyrus (cACg). The cerebellum (CB) was used as a reference region. In vivo behavior of the radiotracers in the CB was compared based upon the ratio of normalized PET uptake for 3- and 4-trans-[(18)F]mefway. Specific binding was compared by examining MTL/CB and cACg/CB ratios. The subject-averaged ratio of 3-[(18)F]mefway to 4-trans-[(18)F]mefway in the cerebellum was 0.96 for 60-90 minutes. MTL/CB reached plateaus of ~2.7 and ~6 by 40 minutes and 90 minutes for 3- and 4-trans-[(18)F]mefway, respectively. cACg/CB reached plateaus of ~2.5 and ~6 by 40 minutes and 70 minutes for 3- and 4-trans-[(18)F]mefway, respectively. The short pseudoequilibration times and sufficient uptake of 3-[(18)F]mefway may be useful in studies requiring short scan times. Furthermore, the similar nondisplaceable clearance in the CB to 4-trans-[(18)F]mefway suggests the lower BPND of 3-[(18)F]mefway is due to a lower affinity. The lower affinity of 3-[(18)F]mefway may make it useful for measuring changes in endogenous 5-HT levels, however, this remains to be ascertained.

First-in-human evaluation of 18F-mefway, a PET radioligand specific to serotonin-1A receptors.

UNLABELLED: The serotonin-1A (5-HT1A; 5-HT is 5-hydroxytryptamine) receptor is implicated in an array of neurologic and psychiatric disorders. Current PET radioligands targeting 5-HT1A receptors have limitations hindering widespread PET studies of this receptor system. The 5-HT1A-specific antagonist radioligand N-{2-[4-(2-methoxyphenyl)piperazinyl]ethyl}-N-(2-pyridyl)-N-(trans-4-(18)F-fluoromethylcyclohexane)carboxamide ((18)F-mefway) exhibited promising in vivo properties in rhesus monkeys. The goal of this work was to examine the in vivo cerebral binding profile and metabolism of (18)F-mefway in humans. METHODS: Dynamic (18)F-mefway PET data were acquired for 6 healthy volunteers (4 women, 2 men; age, 22-38 y). Scans were initiated with the injection of 192-204 MBq of radiotracer, and data were acquired for 2 h. Venous blood samples were collected and assayed to examine the in vivo metabolism profile of (18)F-mefway. To examine the test-retest variability of (18)F-mefway, a second PET scan was acquired at least 2 wk later for 4 subjects. Regional binding potentials (BPNDs) were calculated with the multilinear reference tissue model, and voxelwise BPND maps were calculated with Logan graphical analysis. Regions surrounding the brain were carefully inspected for uptake of radiolabeled species in bone. RESULTS: (18)F-mefway uptake in the brain occurred quickly, with a peak standardized uptake value (SUV) of 1.7. Rapid washout in the cerebellum resulted in SUVs of 0.2 at 120 min, whereas regions with specific 5-HT1A binding exhibited retention of radioligand, yielding SUVs of 0.4-0.9 at 120 min. Rapid metabolism of (18)F-mefway was observed, with no detected (18)F-fluoride ions in plasma. BPND values of 2.4 were measured in the mesial temporal lobe, with values of 1.6 in the insular cortex and 0.7-1.0 in other cortical regions. Stable BPND estimates were obtained using 90 min of dynamic data. Average test-retest variability was 8%. No evidence of radioactivity uptake in bone was observed. CONCLUSION: (18)F-mefway exhibits favorable in vivo properties for serotonin 5-HT1A receptor measurements in humans. The simple radiosynthesis, high specific binding profile, and absence of PET signal in bone make (18)F-mefway an attractive radiotracer for PET experiments examining the 5-HT1A receptor in neuropsychiatric disorders and drug intervention.