Serotonin 5HT1A receptors have been investigated in a number of CNS disorders, including depression, anxiety, sleep disorders, epilepsy, Parkinson's disease (PD) and Alzheimer's disease (AD). Our particular interest is to apply 5HT1A receptor imaging for the study of mood disorders and AD. Efforts are underway to improve in vivo properties of 5-HT1A agents, 11 C-WAY-100635, 18 F-MPPF and 18 F-FCWAY currently in human use. We have identified and synthesized F-Mefway, which contains a fluorine-18 on a primary carbon 18 to make the compound more stable to defluorination. Mefway has high affinity for 5HT1A receptors and in vitro rodent brain slices exhibited selective binding of F-mefway in hippocampus, cortex and other brain regions, 18 with limited binding in the cerebellum. Preliminary in vitro studies showed serotonin displaced 18 F-mefway from various brain regions with IC50 in the range of 169-243 nM. PET studies in a rhesus monkey showed F- 18 mefway binding to temporal cortex, hippocampus, raphe and other brain regions with ratios of hippocampus to cerebellum = 10. Plasma analysis indicated the presence of approx. 30% of 18 F-mefway and no observed defluorination. The high ratios in specific brain regions such as the hippocampus suggest that F-mefway has 18 potential as a PET imaging agent for 5HT1A receptors in humans. Therefore, our overall goals in this application are to synthesize and characterize pure cis- and trans-isomers of Mefway, study pharmacological characteristics of the isomers and investigate PET imaging characteristics of the 18 F-fluorine radiolabeled analogs in order to identify which of the isomers will be more suitable for human PET studies. In order to extend our findings to human studies, dosimetry of 18F-mefway will be measured in rats and monkeys. Drug- induced serotonin competition studies will be carried out using PET imaging studies in rodents to study serotonin effects. In order to assess the value of F-mefway in AD, two important areas of expertise at UCI 18 have come together in this application to address specific hypotheses using multidisciplinary approaches that include expertise in brain imaging techniques and a research group focusing on animal models of brain aging at the PET Brain Imaging Center and the Institute for Brain Aging and Dementia, respectively. In vitro studies will be carried out on two mice transgenic models of AD, the Tg2576 and 3xTg mice in order to correlate senile plaque and neurofibrillary tangle formation with the loss of serotonin 5HT1A receptors using F-mefway. Due 18 to the high hippocampus to cerebellum ratio (approx 10) and advantages of the fluorine-18 radiolabel, 18 F- mefway may have potential use in the study of AD. Development of imaging methods for understanding serotonin effects in the brain will help understand mood disorders and methods to study alterations of the serotonin receptor abnormailites in transgenic mice models will have implications in diagnosis, treatment planning and therapeutics development of Alzheimer's disease and other disorders of the central nervous system.
