Introduction
[18F]Mefway is a serotonin 5-HT1A PET radiotracer with high specificity and favorable in vivo imaging properties. The chemical structure of 18F]mefway permits 18F labeling in either the cis- or trans- positions at the 4-cyclohexyl site. We have previously reported on the in vivo kinetics of trans-[18F]mefway in the nonhuman primate. In this work we compare in vivo binding of cis-[18F]mefway and trans-[18F]mefway to evaluate the properties of cis-[18F]mefway for 5-HT1A PET imaging.
Methods
The cis- and trans- [18F]mefway tracers were synthesized via nucleophilic substitution with their respective tosylate precursors. Two monkeys (1m, 1f) were given bolus injections of both cis- and trans- labeled [18F]mefway in separate experiments. Dynamic scans were acquired for 90 minutes with a microPET P4 scanner. Time activity curves were extracted in the areas of the mesial temporal cortex (MTC), anterior cingulate gyrus (aCG), insular cortex (IC), raphe nuclei (RN), and cerebellum (CB). The in vivo behavior of the radiotracers were compared based upon the nondisplaceable binding potential (BPND) using the CB as a reference region.
Results
Averaged over the 2 subjects, BPND values were MTC: 7.7, 0.58; aCG: 4.95, 0.32; IC: 3.27, 0.2; and RN: 3.05, 0.13 for trans-[18F]mefway and cis-[18F]mefway, respectively.
Conclusion
The cis- labeled [18F]mefway tracer has low specific binding throughout the 5-HT1A regions of brain compared to trans-[18F]mefway suggesting that the target to background binding of cis-[18F]mefway may limit its use for in vivo assessment of 5-HT1A binding.