Potential Positron Emission Tomography Research Articles

Synthesis of [ 18F]Xeloda as a novel potential PET radiotracer for imaging enzymes in cancers

Xeloda (Capecitabine), a prodrug of antitumor agent 5-fluorouracil, is the first and only oral fluoropyrimidine to be approved for use as second-line therapy in metastatic breast cancer, colorectal cancer, and other solid malignancies. Fluorine-18 labeled Xeloda may serve as a novel radiotracer for positron emission tomography (PET) to image enzymes such as thymidine phosphorylase and uridine phosphorylase in cancers. The precursor 2′,3′-di-O-acetyl-5′-deoxy-5-nitro-N 4-(pentyloxycarbonyl)cytidine ( 11) was synthesized from D-ribose and cytosine in 8 steps with approximately 18% overall chemical yield. The reference standard 5′-deoxy-5-fluoro-N 4-(pentyloxycarbonyl)cytidine (Xeloda; 1) was synthesized from D-ribose and 5-fluorocytosine in eight steps with approximately 28% overall chemical yield. The target radiotracer 5′-deoxy-5-[ 18F]fluoro-N 4-(pentyloxycarbonyl)cytidine ([ 18F]Xeloda; [ 18F] 1) was prepared by nucleophilic substitution of the nitro-precursor with K 18F/Kryptofix 2.2.2 followed by a quick deprotection reaction and purification with the HPLC method in 20–30% radiochemical yields.

Facile synthesis and initial PET imaging of novel potential heart acetylcholinesterase imaging agents [ 11C]pyridostigmine and its analogs

A series of 11C-labeled analogs of the acetylcholinesterase (AChE) inhibitor pyridostigmine have been synthesized for evaluation as new potential positron emission tomography (PET) imaging agents for heart AChE. The appropriate precursors for radiolabeling were slightly modified from commercial reagents. The new tracers [ 11C]pyridostigmine ( 1), [ 11C] para-pyridostigmine ( 2) and [ 11C] ortho-pyridostigmine ( 3) were prepared by N-[ 11C]methylation of the precursors using [ 11C]methyl triflate. Pure target compounds were isolated by a solid-phase extraction (SPE) purification procedure with 60–85% radiochemical yields (decay corrected to end of bombardment), and a synthesis time of 10–15 min. The initial PET dynamic studies of compounds ( 1– 3) in rat heart showed rapid heart uptake and blood pool clearance to give high quality heart images. These results suggest the new tracers delineate the heart very clearly and could be potential heart AChE imaging agents.

Synthesis and amine transporter affinities of novel phenyltropane derivatives as potential positron emission tomography (PET) imaging agents

A series of novel fluoroalkyl-containing tropane derivatives ( 6– 8, 10– 14, 17, and 18) were synthesized from cocaine. Novel compounds were evaluated for affinity and selectivity in competitive radioligand binding assays selective for cerebral serotonin (5-HT), dopamine (DA), and norepinephrine (NE) transporters (SERT, DAT, and NET). The nortropane-fluoroalkyl esters ( 7, 10, 11) were most potent for SERT ( K i: 0.18, 0.24, and 0.30 nM, respectively). Tosylate esters 17 and 18, synthesized as precursors for [ 18F]-labeled, Positron Emission Tomography (PET) imaging agents, also showed high affinity for DAT.

Quantitation of cell number by a positron emission tomography reporter gene strategy

Purpose An important potential of positron emission tomography (PET) is the capacity for quantitation of cell signals in an anatomic regions of interest. However, little is known about the constraints and parameters for using PET signal detection to establish cell numbers in regions of interest. In this study, we determined the correlation of PET signal to cell number, and characterized the cellular limit of detection for PET imaging. Procedures Cells expressing the herpes simplex virus type I thymidine kinase PET reporter gene (HSV1-sr39TK) were detected following accumulation of [ 18F]FHBG (9-[4-[ 18F]-fluoro-3-(hydroxymethyl) butyl]guanine) by microPET scanning and quantitation. Results When cells were cultured with [ 18F]FHBG in vitro, and then transferred to a model vascularized site, 73% retention was observed one hour post-transfer. Using this information, and the measured attenuation of PET signal in whole mouse scans, we assessed the per-cell uptake of [ 18F]FHBG in the vascularized site following standard parenteral administration of the substrate. We observed a cell number-dependent signal, with a limit of detection calculated as 10 6 cells in a region of interest of 0.1 mL volume. Quantitatively similar parameters were observed with stably tranfected N2a glioma cells and retrovirally transduced primary T lymphocytes. Conclusion These methods and findings provide a strategy for quantitation of cellularity using PET imaging that has implications for both experimental models and clinical diagnosis.

Novel carbon-11 labeled 4-dimethylamino-but-2-enoic acid [4-(phenylamino)-quinazoline-6-yl]-amides: potential PET bioprobes for molecular imaging of EGFR-positive tumors

We have previously reported of labeled reversible and irreversible EGFR inhibitors, such as 4-(3,4-dichloro-6-fluoroanilino)-6,7-dimethoxyquinazoline (ML01) and 6-acrylamido-4-(3,4-dichloro-6-fluoroanilino)quinazoline (ML03), to be suboptimal as imaging agents. On the basis of these studies, a new generation of novel, more chemically stable irreversible inhibitors was labeled with carbon-11 as potential positron emission tomography (PET) biomarkers for molecular imaging of epidermal growth factor receptor (EGFR)–positive tumors. In these new labeled, irreversible inhibitors the acryl-amide group at the 6-position of the quinazoline ring was replaced with a 4-dimethylamino-but-2-enoic amide. The nonlabeled compounds were evaluated in vitro to determine their EGFR autophosphorylation IC 50 values. The IC 50 values indicated that these new irreversible compounds possess similar potencies towards the EGFR, as the parent compound, ML03. These compounds were labeled with carbon-11 at the dimethylamine moiety, using the well known labeling reagent C-11 MeI. The labeling procedure was automated using a commercial module. The final products were obtained with 10% decay corrected radiochemical yield, 99% radiochemical purity, 96% chemical purity, and a high specific activity of 2.7 Ci/μmol EOB. The high potency of these new labeled bioprobes towards the EGFR establishes their potential to serve as PET agents for molecular imaging of EGFR-positive tumors.

5-substituted derivatives of 6-halogeno-3-((2-(S)-azetidinyl)methoxy)pyridine and 6-halogeno-3-((2-(S)-pyrrolidinyl)methoxy)pyridine with low picomolar affinity for alpha4beta2 nicotinic acetylcholine receptor and wide range of lipophilicity: potential probes for imaging with positron emission tomography.

Potential positron emission tomography (PET) ligands with low picomolar affinity at the nicotinic acetylcholine receptor (nAChR) and with lipophilicity (log D) ranging from -1.6 to +1.5 have been synthesized. Most members of the series, which are derivatives of 5-substituted-6-halogeno-A-85380, exhibited a higher binding affinity at alpha4beta2-nAChRs than epibatidine. An analysis, by molecular modeling, revealed an important role of the orientation of the additional heterocyclic ring on the binding affinity of the ligands with nAChRs. The existing nicotinic pharmacophore models do not accommodate this finding. Two compounds of the series, 6-[(18)F]fluoro-5-(pyridin-3-yl)-A-85380 ([(18)F]31) and 6-chloro-3-((2-(S)-azetidinyl)methoxy)-5-(2-[(18)F]fluoropyridin-5-yl)pyridine) ([(18)F]35), were radiolabeled with (18)F. Comparison of PET data for [(18)F]31 and 2-[(18)F]FA shows the influence of lipophilicity on the binding potential. Our recent PET studies with [(18)F]35 demonstrated that its binding potential values in Rhesus monkey brain were ca. 2.5 times those of 2-[(18)F]FA. Therefore, [(18)F]35 and several other members of the series, when radiolabeled, will be suitable for quantitative imaging of extrathalamic nAChRs.

Synthesis, biodistribution and micro-PET imaging of radiolabeled antimitotic agent T138067 analogues

Radiolabeled antimitotic agents [11C]T138067 and [18F]T138067 have been synthesized for evaluation as new potential positron emission tomography (PET) biomarkers for cancer imaging. In vivo biodistribution and micro-PET imaging of [11C]T138067 were performed in breast cancer animal models MCF-7 transfected with IL-1α implanted athymic mice and MDA-MB-435 implanted athymic mice. The results suggest that the uptakes of [11C]T138067 in both MCF-7 transfected with IL-1α tumor and MDA-MB-435 tumor are non-specific binding.

Comparative studies of potential cancer biomarkers carbon-11 labeled MMP inhibitors (S)-2-(4′-[ 11C]methoxybiphenyl-4-sulfonylamino)-3-methylbutyric acid and N-hydroxy-(R)-2-[[(4′-[ 11C]methoxyphenyl)sulfonyl]benzylamino]-3-methylbutanamide

(S)-2-(4′-[ 11C]methoxybiphenyl-4-sulfonylamino)-3-methylbutyric acid ([ 11C]MSMA) and N-hydroxy-(R)-2-[[(4′-[ 11C]methoxyphenyl)sulfonyl]benzylamino]-3-methylbutanamide ([ 11C]CGS 25966), carbon-11 labeled matrix metalloproteinase (MMP) inhibitors, have been synthesized for evaluation as new potential positron emission tomography (PET) cancer biomarkers. [ 11C]MSMA was prepared by appropriate precursor (S)-2-(4′-hydroxybiphenyl-4-sulfonylamino)-3-methylbutyric acid tert-butyl ester, which was synthesized in eight steps from amino acid (L)-valine in 39.4% chemical yield. This precursor was labeled by [ 11C]methyl triflate through O-[ 11C]methylation method at the hydroxyl position of biphenol under basic conditions, followed by a quick acid hydrolysis and isolated by solid-phase extraction (SPE) purification to produce pure target compound [ 11C]MSMA in 35-55% radiochemical yield, based on 11CO 2, decay corrected to end of bombardment (EOB), and 20-25 min synthesis time. [ 11C]CGS 25966 was prepared in our previous work starting from amino acid (D)-valine. The biodistribution of [ 11C]MSMA and [ 11C]CGS 25966 were determined at 45 min post iv injection in breast cancer animal models MCF-7's transfected with IL-1α implanted athymic mice and MDA-MB-435 implanted athymic mice. The results showed the uptakes of [ 11C]MSMA and [ 11C]CGS 25966 in these tumors were 0.95 and 0.42%dose/g in MCF-7's transfected with IL-1α implanted mice, 0.98 and 1.53%dose/g in MDA-MB-435 implanted mice, respectively; the ratios of tumor/muscle (T/M) and tumor/blood (T/B) were 1.21 and 1.09 (T/M, MCF-7's), 0.99 and 0.84 (T/B, MCF-7's), 1.38 and 1.27 (T/M, MDA-MB-435), 1.27 and 1.95 (T/B, MDA-MB-435), respectively. The micro-PET images of [ 11C]MSMA and [ 11C]CGS 25966 in both breast cancer athymic mice were acquired for 15 min from a MCF-7's transfected with IL-1α and/or MDA-MB-435 implanted mouse at 45 min post iv injection of 1 mCi of the tracer using a dedicated high resolution (<3 mm full-width at half-maximum) small FOV (field-of-view) PET imaging system, Indy-PET II scanner, developed in our laboratory, which showed both tumors were invisible with both tracers. The results were compared. From our results, we concluded that both [ 11C]MSMA and [ 11C]CGS 25966 might be unsuitable as PET tracers for cancer imaging.

Synthesis, biodistribution and micro-PET imaging of a potential cancer biomarker carbon-11 labeled MMP inhibitor (2R)-2-[[4-(6-fluorohex-1-ynyl)phenyl]sulfonylamino]-3-methylbutyric acid [ 11C]methyl ester

(2R)-2-[[4-(6-fluorohex-1-ynyl)phenyl]sulfonylamino]-3-methylbutyric acid [ 11C]methyl ester ([ 11C]FMAME), a novel carbon-11 labeled matrix metalloproteinase (MMP) inhibitor, has been synthesized for evaluation as new potential positron emission tomography (PET) cancer biomarker. [ 11C]FMAME was prepared by appropriate precursor (2R)-2-[[4-(6-fluorohex-1-ynyl)phenyl]sulfonylamino]-3-methylbutyric acid (FMA), which was synthesized in six steps from (D)-valine in 71% chemical yield. This acid precursor was labeled by [ 11C]methyl triflate through O-[ 11C]methylation method under basic conditions and isolated by solid-phase extraction (SPE) purification to produce pure target compound in 40-55% radiochemical yield, based on 11CO 2, decay corrected to end of bombardment, and 15-20 min synthesis time. The biodistribution of [ 11C]FMAME was determined at 30 min post IV injection in breast cancer animal models MCF-7 transfected with IL-1α implanted athymic mice and MDA-MB-435 implanted athymic mice. The results showed the uptakes of [ 11C]FMAME in these tumors were 1.13% dose/g in MCF-7 transfected with IL-1α implanted mice and 1.37% dose/g in MDA-MB-435 implanted mice, respectively; the ratios of tumor/muscle (T/M) and tumor/blood (T/B) were 1.05 ± 0.29 (T/M, MCF-7’s), 0.77 ± 0.20 (T/B, MCF-7’s) and 0.99 ± 0.35 (T/M, MDA-MB-435), 1.44 ± 0.69 (T/B, MDA-MB-435), respectively. Pretreatment of MCF-7 transfected with IL-1α tumor-bearing mice with MMP inhibitor FMA had no effect on [ 11C]FMAME biodistribution. Likewise, pretreatment of MDA-MB-435 tumor-bearing mice with FMA also showed no effect on [ 11C]FMAME biodistribution. The micro-PET images were acquired for 15 min from a MCF-7 transfected with IL-1α tumor-bearing mouse or a MDA-MB-435 tumor-bearing mouse at 30 min post IV injection of 1 mCi of [ 11C]FMAME using a dedicated high resolution (<3 mm full-width at half-maximum) PET imaging system (Indy-PET II scanner). The initial dynamic micro-PET images of [ 11C]FMAME in a MCF-7 transfected with IL-1α tumor-bearing mouse during different time periods of 0-15, 15-30, 30-45 and 45-60 min were performed by Indy-PET II. The PET images clearly showed both tumors were visible with [ 11C]FMAME. These results suggest that the localization of [ 11C]FMAME in the tumor is mediated by non-specific processes, and the visualization of [ 11C]FMAME on the tumor using the Indy-PET II scanner is related to non-specific binding.

Synthesis and Preliminary Biological Evaluation of 6‐O‐[11C]‐[(methoxymethyl)benzyl]guanines, New Potential PET Breast Cancer Imaging Agents for the DNA Repair Protein AGT.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of radiolabeled biphenylsulfonamide matrix metalloproteinase inhibitors as new potential PET cancer imaging agents.

Novel matrix metalloproteinase (MMP) inhibitor radiotracers, (S)-3-methyl-2-(2',3',4'-methoxybiphenyl-4-sulfonylamino)-butyric acid [(11)C]methyl ester (1a-c), (S)-3-methyl-2-(2',3',4'-fluorobiphenyl-4-sulfonylamino)-butyric acid [(11)C]methyl ester (1d-f), and (S)-3-methyl-2-(4'-nitrobiphenyl-4-sulfonylamino)-butyric acid [(11)C]methyl ester (1g), a series of substituted biphenylsulfonamide derivatives, have been synthesized for evaluation as new potential positron emission tomography (PET) cancer imaging agents.

Synthesis and preliminary biological evaluation of radiolabeled O 6-benzylguanine derivatives, new potential PET imaging agents for the DNA repair protein O 6-alkylguanine-DNA alkyltransferase in breast cancer

Novel radiolabeled O 6-benzylguanine (O 6-BG) derivatives, 2-amino-6-O-[ 11C]-[(methoxymethyl)benzyloxy]-9-methyl purines ([ 11C] p-O 6-AMMP, 1a; [ 11C] m-O 6-AMMP, 1b; [ 11C] o-O 6-AMMP, 1c), 2-amino-6-O-benzyloxy-9-[ 11C]-[(methoxycarbonyl)methyl]purine ([ 11C]ABMMP, 2), and 2-amino-6-O-benzyloxy-9-[ 11C]-[(4′-methoxycarbonyl)benzyl]purine ([ 11C]ABMBP, 3), have been synthesized for evaluation as new potential positron emission tomography (PET) imaging agents for the DNA repair protein O 6-alkylguanine-DNA alkyltransferase (AGT) in breast cancer. The appropriate precursors for radiolabeling were obtained in two to three steps from starting material 2-amino-6-chloropurine with moderate to excellent chemical yields. Tracers were prepared by O-[ 11C]methylation of hydroxymethyl or acid precursors using [ 11C]methyl triflate. Pure target compounds were isolated by solid-phase extraction (SPE) purification procedure in 45–65% radiochemical yields (decay corrected to end of bombardment), and a synthesis time of 20–25 min. The activity of unlabeled standard samples of 1–3 was evaluated via an in vitro AGT oligonucleotide assay. Preliminary findings from biological assay indicate the synthesized analogs have similar strong inhibitory effectiveness on AGT in comparison with the parent compound O 6-BG. The results warrant further evaluation of these radiotracers as new potential PET imaging agents for the DNA repair protein AGT in breast cancer in vivo.

Facile synthesis of [ 11C]edrophonium and its analogues as new potential PET imaging agents for heart acetylcholinesterase

[ 11C]Edrophonium and its analogues have been synthesized for evaluation as new potential positron emission tomography (PET) imaging agents for heart acetylcholinesterase. The tracers were prepared by N-[ 11C]methylation of precursors using [ 11C]methyl triflate and isolated by solid-phase extraction (SPE) purification procedure in 50–65% radiochemical yields.

Synthesis of MMP inhibitor radiotracer [11C]CGS 25966, a new potential pet tumor imaging agent

Abstract[11C]CGS 25966, a novel radiolabeled matrix metalloproteinase (MMP) inhibitor, has been synthesized for evaluation as new potential positron emission tomography (PET) tumor imaging agent. The precursor was labeled by [11C]methyl triflate through O‐[11C]methylation method at the hydroxyl position of phenol under basic conditions and isolated by HPLC purification to produce pure target compound in 15–25% radiochemical yield, based on 11CO2, decay corrected to end of bombardment. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Synthesis and preliminary biological evaluation of 6- O-[ 11C]-[(methoxymethyl)benzyl]guanines, new potential PET breast cancer imaging agents for the DNA repair protein AGT

Novel radiolabeled O 6-benzylguanine derivatives, 6- O-[ 11C]-[(methoxymethyl)benzyl]guanines ([ 11C] p- O 6-MMBG, 1a; [ 11C] m- O 6-MMBG, 1b; ([ 11C] o- O 6-MMBG, 1c), have been synthesized for evaluation as new potential positron emission tomography (PET) breast cancer imaging agents for DNA repair protein, O 6-alkylguanine-DNA alkyltransferase (AGT).

Synthesis of radiolabeled O6‐benzylguanine derivatives as new potential PET tumor imaging agents for the DNA repair protein O6‐alkylguanine‐DNA alkyltransferase

AbstractNovel radiolabeled O6‐benzylguanine derivatives, 2‐amino‐6‐O‐[11C]‐[(methoxymethyl)benzyloxy]‐9‐benzyl purines ([11C]p‐O6‐AMBP, 1a; [11C]m‐O6‐AMBP, 1b; [11C]o‐O6‐AMBP, 1c), have been synthesized for evaluation as new potential positron emission tomography (PET) tumor imaging agents for the DNA repair protein, O6‐alkylguanine‐DNA alkyltransferase (AGT). The appropriate precursors for radiolabeling were obtained in three steps from starting material 2‐amino‐6‐chloropurine with moderate to excellent chemical yields. Tracers were prepared by O‐[11C]methylation of hydroxymethyl precursors using [11C]methyl triflate. Pure target compounds were isolated by solid‐phase extraction (SPE) purification procedure in 45–60% radiochemical yields (decay corrected to the end of bombardment), and a synthesis time of 20–25min. Copyright © 2002 John Wiley &amp; Sons, Ltd.

11C]choline as a potential PET marker for imaging of breast cancer athymic mice

[ 11C]Choline has been evaluated as a potential positron emission tomography (PET) marker for imaging of breast cancer. The biodistribution of [ 11C]choline was determined at 45 min post iv injection in MCF-7’s transfected with IL-1alpha implanted athymic mice and MDA-MB-435 implanted athymic mice. The results showed the uptake of [ 11C]choline in these tumors was high, 2.0% dose/g in MCF-7’s transfected with IL-1alpha implanted mice and 1.8% dose/g in MDA-MB-435 implanted mice; the ratios of tumor/muscle (T/M) and tumor/blood (T/B) were 1.7 (T/M, MCF-7’s), 2.1 (T/M, MDA-MB-435) and 6.9 (T/B, MCF-7’s), 12.5 (T/B, MDA-MB-435), respectively; the tumor/muscle ratios are moderate, and the tumor/blood ratios are high. The micro-PET imaging of [ 11C]choline in both breast cancer athymic mice was acquired for 15 min from a MCF-7’s transfected with IL-1alpha and/or MDA-MB-435 implanted mouse at 45 min post iv injection of 1 mCi of the tracer using a dedicated high resolution (<3 mm full-width at half-maximum) small FOV (field-of-view) PET imaging system, Indy-PET II scanner, developed in our laboratory, which showed the uptake of [ 11C]choline in MCF-7’s transfected with IL-1alpha tumor or MDA-MB-435 tumor implanted in a nude athymic mouse. These results suggest that [ 11C]choline may be a potential PET breast cancer imaging agent.

Synthesis and preliminary biological evaluation of MMP inhibitor radiotracers [ 11C]methyl-halo-CGS 27023A analogs, new potential PET breast cancer imaging agents

A series of [ 11C]methyl-halo-CGS 27023A analogs (2-F, 1a; 4-F, 1b; 2-Cl, 1c; 3-Cl, 1d; 4-Cl, 1e; 2-Br, 1f; 3-Br, 1g; 4-Br, 1h; 4-I, 1i), novel radiolabeled matrix metalloproteinase (MMP) inhibitors, have been synthesized for evaluation as new potential positron emission tomography (PET) breast cancer imaging agents. The precursors halo-CGS 27023A analogs (2-F, 6a; 4-F, 6b; 2-Cl, 6c; 3-Cl, 6d; 4-Cl, 6e; 2-Br, 6f; 3-Br, 6g; 4-Br, 6h; 4-I, 6i) for radiolabeling were obtained in four steps from starting material amino acid D-valine with moderate to excellent chemical yields. Precursors were labeled by [ 11C]methyl triflate through 11C-O-methylation method at the aminohydroxyl position under basic conditions and isolated by solid-phase extraction (SPE) purification to produce pure target compounds in 40–60% radiochemical yields (decay corrected to end of bombardment), in 20–25 min synthesis time.

Adenovirus biodistribution and noninvasive imaging of gene expression in vivo by positron emission tomography using human sodium/iodide symporter as reporter gene.

Amongst the various methods that can be developed for noninvasive monitoring of gene expression in vivo, the use of positron emission tomography (PET) appears to be the most promising both for preclinical and clinical studies. Various genes have been described as potential PET reporters, but there is a need to develop new approaches that exploit transgenes with both therapeutic and imaging potential. The Na/I symporter (NIS) gene is expressed mainly in the thyroid and is responsible for iodide accumulation in this organ. The NIS gene has been used in gene therapy experimentation. Ectopic expression of this gene in various type of malignant cells has led to radiosensitization and in some cases tumor regression in xenograft models in nude mice, highlighting the therapeutic potential of this approach. In the present study, we demonstrate the potential of the human NIS gene (hNIS) as a reporter gene. Expression of hNIS, after plasmid transfection or adenoviral gene delivery, can be monitored in vitro on incubation with (125)I. Iodide uptake in the transduced cells can be directly correlated with the levels of gene expression in vitro. Ectopic expression of the NIS gene in vivo can be monitored in biodistribution studies on intravenous injection of (125)I. Adenovirus delivery induces gene expression essentially in the liver, adrenal glands, lungs, pancreas, and spleen. Expression of hNIS in tumor xenograft models can also be detected when the virus is injected intratumorally. Finally, hNIS expression was monitored by PET after intravenous injection of (124)I, demonstrating the potential of this approach for noninvasive imaging.

New PET imaging agent for the serotonin transporter: [(18)F]ACF (2-[(2-amino-4-chloro-5-fluorophenyl)thio]-N,N-dimethyl-benzenmethanamine).

A new F-18-labeled phenylthiophenyl derivative specific for imaging of serotonin transporters (SERT) in the brain by positron emission tomography (PET) is described. Fluorinated phenylthiophenyl derivative, ACF, 2-[(2-amino-4-chloro-5-fluorophenyl)thio]-N,N-dimethyl-benzenmethanamine, was prepared by first coupling 2,5-dichloro-4-nitroaniline with 2-mercapto-N,N-dimethylbenzamide. The amino group of the coupled adduct was converted to a fluoro group through a Schiemann reaction. Subsequently, a one pot reduction of both nitro and amide groups by BH(3)-tetrahydrofuran yielded the nonradioactive ACF (yield 25%). In vitro binding assays using cell membrane homogenates of LLC cells expressing SERT, dopamine transporters (DAT), or norepinephrine transporters (NET) showed excellent binding affinity and selectivity for SERT (K(i) = 0.05, 3020, and 650 nM for SERT, DAT, and NET, respectively). For preparation of the [(18)F]ACF, the NH(2) group of the initially coupled adduct was converted to the trimethylammonium salt, which was replaced by [(18)F]fluoride in the presence of Kryptofix 222 and potassium carbonate. The final product, [(18)F]ACF, was obtained after a borane and stannous chloride reduction reaction. The combined two step reaction gave a radiochemical yield of 10-15% (EOB) and a radiochemical purity of >99%. Synthesis of the novel PET tracer, [(18)F]ACF, as a probe for binding to SERT in the brain was successfully achieved. The new tracer [(18)F]ACF showed excellent brain penetration and selective localization after an iv injection in rats (brain uptake at 2, 30, 60, 120, and 240 min was 3.27, 1.28, 0.69, 0.21, and 0.06% dose/organ, respectively). The hypothalamus/cerebellum ratio at 60 min post iv injection was 3.55. This specific localization in the hypothalamus was blocked by pretreatment of (+)McN5652. This novel ligand is a potential PET tracer for in vivo evaluation of SERT in the brain.