Microautoradiography of [123I]ADAM in mice treated with fluoxetine and serotonin reuptake inhibitors.

A radiopharmaceutical, (123)I-labeled 2-((2-((dimethylamino)methyl)phenyl)thio)-5-iodophenylamine ([(123)I]ADAM), has been developed recently for evaluation of how serotonin transporters (SERT) function in the brain. However, the detailed biodistribution and specific binding in certain brain areas are not well investigated. In this study, both phosphor plate imaging and microautoradiography were applied to explore the binding characteristics of [(123)I]ADAM in SERT neurons. The effect of two psychotropics and one narcotic on the binding of [(123)I]ADAM to SERT was also studied. Fluoxetine and desipramine, both are psychotropics and specific SERT ligands and decreased the affinity of [(123)I]ADAM, while p-chloroamphetamine (PCA), a narcotic, destroyed most of serotonergic neurons, as well as reducing the concentration of serotonin and the number of SERT in the brain as shown by the biodistribution of [(123)I]ADAM. Significant and selective accumulation of [(123)I]ADAM in the areas from midbrain to brain stem in normal mice with maximum target-to-background ratio was found at 90 minutes postinjection. A rapid clearance of [(131)I]ADAM at 120 minutes postinjection was found in the CA1, CA3 and ThN brain areas. In addition, the inhibition effect on binding ability of [(123)I]ADAM to SERT by the psychotropics and the narcotic was found to have the order of: PCA > fluoxetine > desipramine.

Evaluation of 4-borono-2-18F-fluoro-L-phenylalanine-fructose as a probe for boron neutron capture therapy in a glioma-bearing rat model.

UNLABELLED: L-p-Boronophenylalanine (BPA) has been applied as a potential boron carrier for the treatment of malignant glioma in clinical boron neutron capture therapy (BNCT) since 1994. To provide the pharmacokinetics of BPA for clinical use of BNCT in Taiwan, 4-borono-2-(18)F-fluoro-L-phenylalanine-fructose ((18)F-FBPA-Fr) was synthesized and the biologic characteristics of this radiotracer in glioma-bearing rats were investigated. METHODS: Radiolabeled (18)F-F(2) was produced via the (20)Ne(d,alpha)(18)F reaction, and (18)F-acetyl hypofluorite ((18)F-AcOF) was generated by passing (18)F-F(2) through a column filled with tightly packed KOAc/HOAc powder. The effluent containing (18)F-AcOF was bubbled into BPA in trifluoroacetic acid, then purified by high-performance liquid chromatography, and further composited with fructose to afford (18)F-FBPA-Fr. Male Fischer 344 rats bearing F98 glioma in the left brain were used for biologic studies. The biodistribution of BPA-Fr and (18)F-FBPA-Fr was determined, and the microautoradiography and PET imaging of (18)F-FBPA-Fr were performed, on the 13th day after tumor inoculation. RESULTS: The radiochemical purity of (18)F-FBPA-Fr was >97% and the radiochemical yield of (18)F-FBPA-Fr was 20%-25%. In glioma-bearing rats, the accumulation ratios of B-10 for glioma-to-normal brain were 2.05, 1.86, 1.24, and 1.10 at 0.5, 1, 2, and 4 h, respectively, after administration of 43 mg BPA-Fr via the tail vein. The accumulation ratios of (18)F-FBPA-Fr for glioma-to-normal brain were 3.45, 3.13, 2.61, and 2.02, whereas the tumor-to-heart blood ratios were 1.72, 2.61, 2.00, and 1.93, respectively, for the same time points. The uptake characteristics of BPA-Fr and (18)F-FBPA-Fr in F98 glioma were similar with a maximum at 1 h after the drugs' administration. The results obtained from the biodistribution studies indicated that 0.5-1 h after BPA-Fr injection would be the optimal time for BNCT. Biodistribution, PET images, and brain microautoradiography of (18)F-FBPA-Fr all confirmed this finding. CONCLUSION: (18)F-FBPA-Fr showed specific tumor uptake in F98 glioma-bearing rats and could be used as a probe for BPA-Fr in BNCT. This study provides useful information for the future clinical application of BNCT in brain tumor therapy.