Translational possibility of [18 F]Mefway to image serotonin 1A receptors in humans: Comparison with [18 F]FCWAY in rodents

P-Glycoprotein, not BCRP, Limits the Brain Uptake of [(18)F]Mefway in Rodent Brain

PURPOSE

The aim of this study was to determine whether the brain uptake of [(18)F]Mefway is influenced by the action of P-glycoprotein (P-gp) and breast cancer resistance protein (Bcrp) in rodents.

PROCEDURES

[(18)F]Mefway was applied to rats pharmacologically inhibited with tariquidar (TQD) and to genetically disrupted mice.

RESULTS

Pretreatment of TQD results in 160% higher hippocampal uptake compared with control rats. In genetically disrupted mice, a maximal brain uptake value of 3.2 SUV in the triple knockout mice (tKO, Mdr1a/b((-/-))Bcrp1((-/-))) was comparable to that of the double knockout mice (dKO, Mdr1a/b((-/-))) and 2-fold those of the wild-type and Bcrp1((-/-)) knockout mice. The differences of binding values were statistically insignificant between control and experimental groups. The brain-to-plasma ratios for tKO mice were also two to five times higher than those for other groups.

CONCLUSIONS

[(18)F]Mefway is modulated by P-gp, and not by Bcrp in rodents.

Optimal timing of [¹⁸F]Mefway PET for imaging the serotonin 1A receptor in healthy male subjects

To determine the optimal acquisition time of [(18)F]Mefway PET, we examined the regional specific-to-nonspecific binding ratios and evaluated the relationship between distribution volume ratios (DVRs) and standardized uptake value ratios (SUVRs) in various time windows. The specific-to-nonspecific binding ratios peaked after 40 min and there was a strong correlation between DVR and SUVR in the 60-80 min. Therefore, we recommend the use of a single time point between 60 and 80 min for [(18)F]Mefway static PET.

18F-Mefway PET imaging of serotonin 1A receptors in humans: a comparison with 18F-FCWAY

Introduction

The purpose of this research is to evaluate the prospects for the use of 4-(trans-¹⁸F-fluoranylmethyl)-N-[2-[4-(2-methoxyphenyl)piperazin-1-yl]ethyl]-N-pyridin-2-ylcyclohexane-1-carboxamide (¹⁸F-Mefway) in comparison to ¹⁸F-trans-4-fluoro-N-2-[4-(2-methoxyphenyl)piperazin-1-yl]ethyl]-N-(2-pyridyl)cyclohexanecarboxamide (¹⁸F-FCWAY) for the quantification of 5-HT_1A receptors in human subjects.

Method

Five healthy male controls were included for two positron emission tomography (PET) studies: ¹⁸F-FCWAY PET after the pretreatment with 500 mg of disulfiram and two months later, ¹⁸F-Mefway PET without disulfiram. Regional time-activity curves (TACs) were extracted from nine cortical and subcortical regions in dynamic PET images. Using cerebellar cortex without vermis as reference tissue, in vivo kinetics for both radioligands were compared based on the distribution volume ratio (DVR) calculated by non-invasive Logan graphical analysis and area under the curve ratio of the TACs (AUC ratio).

Result

Although the pattern of regional uptakes in the ¹⁸F-Mefway PET was similar to that of the ¹⁸F-FCWAY PET (highest in the hippocampus and lowest in the cerebellar cortex), the amount of regional uptake in ¹⁸F-Mefway PET was almost half of that in ¹⁸F-FCWAY PET. The skull uptake in ¹⁸F-Mefway PET was only 25% of that in ¹⁸F-FCWAY PET with disulfiram pretreatment. The regional DVR values and AUC ratio values for ¹⁸F-Mefway were 17—40% lower than those of ¹⁸F-FCWAY. In contrast to a small overestimation of DVR values by AUC ratio values (< 10%) in ¹⁸F-FCWAY PET, the overestimation bias of AUC ratio values was much higher (up to 21%) in ¹⁸F-Mefway PET.

Conclusion

As ¹⁸F-Mefway showed lower DVR values and greater overestimation bias of AUC ratio values, ¹⁸F-Mefway may appear less favorable than ¹⁸F-FCWAY. However, in contrast to ¹⁸F-FCWAY, the resistance to in vivo defluorination of ¹⁸F-Mefway obviates the need for the use of a defluorination inhibitor. Thus, ¹⁸F-Mefway may be a good candidate PET radioligand for 5-HT_1A receptor imaging in human.