In vitro and in vivo evaluation of novel glibenclamide derivatives as imaging agents for the non-invasive assessment of the pancreatic islet cell mass in animals and humans.

Pancreatic islet cell mass (PICM) is a major determinant of the insulin secretory capacity in humans. Currently, the only method for accurate assessment of the PICM is an autopsy study. Thus, development of a technique allowing the non-invasive quantification of PICM is of great interest. The aim of this study was to develop such a non-invasive technique featuring novel fluorine- and (99m)Tc-labelled glibenclamide derivatives. Despite the structural modifications necessary to introduce fluorine into the glibenclamide molecule, all derivatives retained insulin stimulating capacity as well as high affinity binding to human SUR1 when compared to the original glibenclamide. Contrastingly, the lipophilicity of the fluorine-labelled derivatives was altered depending on the particular modification. In the human PET-study a constant but weak radioactive signal could be detected in the pancreas using a fluorine-labelled glibenclamide derivative. However, a reliable assessment and visualisation of the PICM could not be obtained. It can be assumed that the high uptake of the fluorine-labelled tracer e.g. into the the liver and the high plasma protein binding leads to a relatively low signal-to-noise ratio. In case of the presented fluorine-labelled glibenclamide based compounds this could be the result of their invariably high lipophilicity. The development of a (99 m)Tc-labelled glibenclamide derivative with a lower lipophilicity and differing in vivo behaviour, glibenclamide based compounds for non-invasive imaging of the pancreatic islet cell mass may be possible.

Synthesis and evaluation of (S)-2-(2-[18F]fluoroethoxy)-4-([3-methyl-1-(2-piperidin-1-yl-phenyl)-butyl-carbamoyl]-methyl)-benzoic acid ([18F]repaglinide): a promising radioligand for quantification of pancreatic beta-cell mass with positron emission tomography (PET).

18F-labeled non-sulfonylurea hypoglycemic agent (S)-2-(2-[(18)F]fluoroethoxy)-4-((3-methyl-1-(2-piperidin-1-yl-phenyl)-butylcarbamoyl)-methyl)-benzoic acid ([(18)F]repaglinide), a derivative of the sulfonylurea-receptor (SUR) ligand repaglinide, was synthesized as a potential tracer for the non-invasive investigation of the sulfonylurea 1 receptor status of pancreatic beta-cells by positron emission tomography (PET) in the context of type 1 and type 2 diabetes. [(18)F]Repaglinide could be obtained in an overall radiochemical yield (RCY) of 20% after 135 min with a radiochemical purity higher than 98% applying the secondary labeling precursor 2-[(18)F]fluoroethyltosylate. Specific activity was in the range of 50-60 GBq/micromol. Labeling was conducted by exchanging the ethoxy-moiety into a 2-[(18)F]fluoroethoxy group. To characterize the properties of fluorinated repaglinide, the affinity of the analogous non-radioactive (19)F-compound for binding to the human SUR1 isoform was assessed. [(19)F]Repaglinide induced a complete monophasic inhibition curve with a Hill coefficient close to 1 (1.03) yielding a dissociation constant (K(D)) of 134 nM. Biological activity was proven via insulin secretion experiments on isolated rat islets and was comparable to that of repaglinide. Finally, biodistribution of [(18)F]repaglinide was investigated in rats by measuring the concentration of the compound in different organs after i.v. injection. Pancreatic tissue displayed a stable accumulation of approximately 0.12% of the injected dose from 10 min to 30 min p.i. 50% of the radioactive tracer could be displaced by additional injection of unlabeled repaglinide, indicating that [(18)F]repaglinide might be suitable for in vivo investigation with PET.

Synthesis and evaluation of fluorine-18 labeled glyburide analogs as beta-cell imaging agents.

Glyburide is a prescribed hypoglycemic drug for the treatment of type 2 diabetic patients. We have synthesized two of its analogs, namely N-[4-[beta-(2-(2'-fluoroethoxy)-5-chlorobenzenecarboxamido)ethyl]benzenesulfonyl]-N'-cyclohexylurea (2-fluoroethoxyglyburide, 8b) and N-[4-[beta-(2-(2'-fluoroethoxy)-5-iodobenzenecarboxamido)ethyl]benzenesulfonyl]-N'-cyclohexylurea (2-fluoroethoxy-5-deschloro-5-iodoglyburide, 8a), and their fluorine-18 labeled analogs as beta-cell imaging agents. Both F-18 labeled compound 8a and compound 8b were synthesized by alkylation of the corresponding multistep synthesized hydroxy precursor 4a and 4b with 2-[(18)F]fluoroethyl tosylate in DMSO at 120 degrees C for 20 minutes followed by HPLC purification in an overall radiochemical yield of 5-10% with a synthesis time of 100 minutes from EOB. The octanol/water partition coefficients of compounds 8a and 8b were 141.21 +/- 27.77 (n = 8) and 124.33 +/- 21.61 (n = 8), respectively. Insulin secretion experiments of compounds 8a and 8b on rat islets showed that both compounds have a similar stimulating effect on insulin secretion as that of glyburide. In vitro binding studies showed that approximately 2% of compounds 8a and 8b bound to beta TC3 and Min6 cells and that the binding was saturable. Preliminary biodistribution studies in mice showed that the uptake of both compounds 8a and 8b in liver and small intestine were high, whereas the uptake in other organs studied including pancreas were low. Additionally, the uptake of compound 8b in vivo was nonsaturable. These results tend to suggest that compounds 8a and 8b may not be the ideal beta-cell imaging agents.

A simplified one-pot synthesis of 9-[(3-[18F]fluoro-1-hydroxy-2-propoxy)methyl]guanine([18F]FHPG) and 9-(4-[18F]fluoro-3-hydroxymethylbutyl)guanine ([18F]FHBG) for gene therapy.

9-[(3-[18F]Fluoro-1-hydroxy-2-propoxy)methyl]guanine ([18F]FHPG, 2) has been synthesized by nucleophilic substitution of N(2)-(p-anisyldiphenylmethyl)-9-[[1-(p-anisyldiphenylmethoxy)-3-toluenesulfonyloxy-2-propoxy]methyl]guanine (1) with potassium [18F]fluoride/Kryptofix 2.2.2 followed by deprotection with 1 N HCl and purification with different methods in variable yields. When both the nucleophilic substitution and deprotection were carried out at 90 degrees C and the product was purified by HPLC (method A), the yield of compound 2 was 5-10% and the synthesis time was 90 min from EOB. However, if both the nucleophilic substitution and deprotection were carried out at 120 degrees C and the product was purified by HPLC, the yield of compound 2 decreased to 2%. When compound 2 was synthesized at 90 degrees C and purified by Silica Sep-Pak (method B), the yield increased to 10-15% and the synthesis time was 60 min from EOB. Similarly, 9-(4-[18F]fluoro-3-hydroxymethylbutyl)guanine ([18F]FHBG, 4) was synthesized with method A and method B in 9% and 10-15% yield, respectively, in a synthesis time of 90 and 60 min, respectively, from EOB. Compound 2 was relatively unstable in acidic medium at 120 degrees C while compound 4 was stable under the same condition. Both compound 2 and compound 4 had low lipid/water partition coefficient (0.126 +/- 0.022, n=5 and 0.165 +/- 0.023, n=5, respectively). Although it contains non-radioactive ganciclovir ( approximately 5-30 microg) as a chemical by-product, compound 2 synthesized by method B has a similar uptake in 9L glioma cells as that synthesized by method A, and is a potential tracer for imaging herpes simplex virus thymidine kinase gene expression in tumors using PET. Similarly, compound 4 synthesized by method B contains approximately 10-25 microg of penciclovir as a chemical by-product. Thus, the simplified one pot synthesis (method B) is a useful method for synthesizing both compound 2 and compound 4 in good yield for routine clinical use, and the method is readily amenable for automation.

Imaging in vivo herpes simplex virus thymidine kinase gene transfer to tumour-bearing rodents using positron emission tomography and.

Radiolabelled ganciclovir analogues have shown promise as imaging agents to detect herpes simplex virus thymidine kinase (HSVtk) expression. This study evaluated the use of positron emission tomography (PET) imaging with 9-[(3-[18F]fluoro-1-hydroxy-2-propoxy)methyl]guanine ([18F]FHPG) to assess gene transfer into tumours. HSVtk-positive and HSVtk-negative cell lines were first treated in vitro with [18F]FHPG. To assess the efficacy of PET in detecting HSVtk expression following in vivo gene transfer, mice were injected intravenously with an adenovirus encoding HSVtk (Ad.HSVtk), a control vector (Ad.Bgl2) or saline. Subcutaneous human glioma xenografts were grown in mice and treated by direct injection of Ad.HSVtk or Ad.Bgl2. Imaging was performed 48 h after transduction. Similar experiments were performed using Fischer rats implanted with syngeneic tumours. The presence of the HSVtk protein was confirmed by immunohistochemistry. Biodistribution studies were also obtained in 14 naive mice. In vitro studies showed high and specific uptake of [18F]FHPG in HSVtk-positive cell lines, with an uptake ratio of up to 27:1. PET imaging and direct counting of major organs demonstrated HSVtk-specific tracer retention. In mice, HSVtk-positive tumours retained 3.4% dose/gram as compared to 0.6% for control tumours (P=0.03). They were clearly seen on the PET images as early as 100 min post injection. Similar results were obtained with syngeneic rat tumours. Biodistribution studies demonstrated the rapid distribution and clearance of the tracer in all major organs. Our results demonstrate that PET imaging of HSVtk gene transfer to tumours is feasible and is highly specific for HSVtk expression.

[18F]-EF5, a marker for PET detection of hypoxia: synthesis of precursor and a new fluorination procedure.

There is a great deal of clinical and experimental interest in determining tissue hypoxia using non-invasive imaging methods. We have developed EF5, 2-(2-nitro-1[H]-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl)-acetamide, with both invasive and non-invasive hypoxia detection in mind. EF5 and other 2-nitroimidazoles are used to detect hypoxia, because the rate of their bioreductive metabolism is inversely dependent on oxygen partial pressure. Such metabolism leads to the formation of covalent adducts within the metabolizing cells. Previously, we have described the invasive detection of these adducts by highly specific monoclonal antibodies after tissue biopsy. In this report, we demonstrate the synthesis of 18F-labeled EF5, [18F]-2-(2-nitro-1[H]-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl)-acetamide, in greater than 10% yield by direct fluorination of the newly synthesized precursor 2-(2-nitro-1[H]-imidazol-1-yl)-N-(2,3,3-trifluoroallyl)-acetamide by [18F]-F2 in trifluoroacetic acid. Our objective was to optimize the electrophilic fluorination of the fluorinated alkene bond with fluorine gas, a new method of 18F-labeling of polyfluorinated molecules. Previous biodistribution studies in mice have demonstrated uniform access of EF5 to all tissues with bioelimination dominated by renal excretion. When [18F]-EF5 was injected into a rat followed by urine collection and analysis, we found no detectable metabolism to other radioactive compounds. Thus, [18F]-EF5 should be well suited for use as a non-invasive hypoxia marker with detection using positron emission tomography (PET).

Noninvasive detection of tumor hypoxia using the 2-nitroimidazole [18F]EF1.

UNLABELLED: The noninvasive assessment of tumor hypoxia in vivo is under active investigation because hypoxia has been shown to be an important prognostic factor for therapy resistance. Various nuclear medicine imaging modalities are being used, including PET imaging of 18F-containing compounds. In this study, we report the development of 18F-labeled EF1 for noninvasive imaging of hypoxia. EF1 is a 3-monofluoro analog of the well-characterized hypoxia marker EF5, 2(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl)acetami de, which has been used to detect hypoxia in tumor and nontumor systems using immunohistochemical methods. METHODS: We have studied 2 rat tumor types: the hypoxic Morris 7777 (Q7) hepatoma and the oxic 9LF glioma tumor, each grown in subcutaneous sites. PET studies were performed using a pharmacological dose of nonradioactive carrier in addition to [18F]EF1 to optimize and assess drug biodistribution. After PET imaging of the tumor-bearing rats, tissues were obtained for gamma-counting of the 18F in various tissues and immunohistochemical detection of intracellular drug adducts in tumors. In one pair of tumors, Eppendorf needle electrode studies were performed. RESULTS: [18F]EF1 was excreted dominantly through the urinary tract. The tumor-to-muscle (T/M) ratio of [18F]EF1 in the Q7 tumors was 2.7 and 2.4 based on PET studies and 2.1, 2.5, and 3.0 based on gamma-counting of the tissues (n = 3). In contrast, the T/M ratio of [18F]EF1 in the 9LF glioma tumor was 0.8 and 0.5 based on PET studies and 1.0, 1.2, and 1.4 based on gamma-counting of the tissues (n = 3). Immunohistochemical analysis of drug adducts for the two tumor types agreed with the radioactivity analysis. In the Q7 tumor, substantial heterogeneous binding was observed throughout the tumor, whereas in the 9LF tumor minimal binding was found. CONCLUSION: [18F]EF1 is an excellent radiotracer for noninvasive imaging of tumor hypoxia.

Synthesis of new hypoxia markers EF1 and [18F]-EF1.

We report on the preparation of a hypoxia marker 2-(2-nitroimidazol-1[H]-yl)-N-(3-fluoropropyl)acetamide (EF1) and its 18F analog, 2-(2-nitroimidazol-1[H]-yl)-N- (3-[18F]fluoropropyl)acetamide ([18F]-EF1). Two methods for the preparation of 3-fluoropropylamine, the EF1 side chain, are described. [18F]-EF1 was prepared with a radiochemical yield of 2% by nucleophilic substitution of bromine in 2-(2-nitroimidazol-1[H]-yl)-N-(3-bromopropyl)acetamide (EBr1) by carrier-added 18F in DMSO at 120 degrees C. Our results demonstrate the preparation of clinically relevant amounts of [18F]-EF1 for use as a non-invasive hypoxia marker with detection using positron emission tomography (PET).

In vivo imaging of serotonin transporters with [99mTc]TRODAT-1 in nonhuman primates.

[99mTc]TRODAT-1 was the first 99mTc-labeled imaging agent to show specific binding to dopamine transporters (DAT) in the striatum (STR) of human brain. Additionally, in vitro binding and autoradiographic experiments demonstrated that this tracer also binds to serotonin transporters (SERT) in the midbrain/hypothalamus (MB) area. In this study, [99mTc]TRODAT-1 was investigated as a potentially useful ligand to image SERT in the MB of living brain. A total of eight single-photon emission tomography (SPET) scans were performed in two baboons (Papio anubis) after intravenous (i.v.) injection of 740 MBq (20 mCi) of [99mTc]TRODAT-1 using a triple-head gamma camera equipped with ultra-high-resolution fan-beam collimators (scan time: 0-210 min). In four blocking studies, baboons were pretreated with (+)McN5652 (1 mg/kg, i.v.) or methylphenidate (1 mg/kg, i.v.) to specifically block SERT or DAT, respectively. After co-registration with magnetic resonance images of the same baboon, a region of interest analysis was performed using predefined templates to calculate specific uptake in the midbrain area and the striatum, with the cerebellum as the background region [(MB-CB)/CB, (STR-CB)/CB]. Additionally, two PET scans of the same baboons were performed after i.v. injections of 74-111 MBq (2-3 mCi) of [11C](+)McN5652 to identify the SERT sites. In [99mTc]TRODAT-1/SPET scans, the SERT sites in the MB region were clearly visualized. Semiquantitative analysis revealed a specific uptake in MB ([MB-CB]/CB) of 0.30+/-0.02, which was decreased to 0. 040+/-0.005 after pretreatment with nonradioactive (+)McN5652, a selective SERT ligand. Pretreatment with methylphenidate reduced the specific binding of [99mTc]TRODAT-1 to DAT sites [(STR-CB)/CB] from 2.45+/-0.13 to 0.32+/-0.04 without any effect on its binding to SERT sites [(MB-CB)/CB], which was confirmed by the co-registration of the [11C](+)McN5652/PET scans. This preliminary study suggests that specific binding of [99mTc]TRODAT-1 to SERT sites can be detected by in vivo SPET imaging despite the low target to background ratio. These findings provide impetus for further development of similar compounds with improved binding affinity and selectivity to SERT sites.

N-(N-benzylpiperidin-4-yl)-2-[18F]fluorobenzamide: a potential ligand for PET imaging of sigma receptors.

Four nitro- and fluorobenzamides (1-4) have been synthesized in good yields from nitro- and fluoro-substituted benzoyl chloride with 4-amino-1-benzylpiperidine. In vitro studies showed that these compounds have high affinities to sigma receptors. N-(N-Benzylpiperidin-4-yl)-2-fluorobenzamide (3), in particular, bound to sigma receptors with high affinity (Ki = 3.4 nM, guinea pig brain membranes) and high selectivity (sigma-2/sigma-1 = 120). It was, therefore, labeled with 18F and evaluated as a sigma receptor radioligand. N-(N-Benzylpiperidin-4-yl)-2-[18F]fluorobenzamide (3a) was synthesized in one step by nucleophile substitution of the 2-nitro precursor (1) with [18F]fluoride in DMSO at 140 degrees C for 20 min followed by purification with HPLC in 4-10% yield (decay corrected). The synthesis time was 90 min and the specific activity was 0.4-1.0 Ci/mumol. Tissue distribution in mice revealed that the uptakes of 3a in the brain, heart, liver, lungs, spleen, kidneys and small intestine were high, and the radioactivity in these organs remained constant from 60 to 120 min post-injection. The radioactivity in the bone did not significantly increase, suggesting in vivo defluorination may not be the major route of metabolism of 3a in mice. Blocking studies with haloperidol in rats indicated that the uptake of compound 3a in the rat brain was selective to haloperidol-sensitive sigma sites. These results suggest that compound 3a is a potent sigma receptor radioligand and may be a potential ligand for PET imaging of sigma receptors in humans.

Carbon-11 labelled ketamine-synthesis, distribution in mice and PET studies in baboons.

No-carrier-added (NCA)[11C](+/-)-ketamine (2a) and its enantiomers (+)-2b and (-)-2c were synthesized by methylation of the corresponding norketamine (1a-c) with [11C]H3I in an overall radiochemical yield of 20% (EOB) with specific activities of 0.35-0.45 Ci/mumol at EOB in a synthesis time of 40 min from EOB. Compound 2a was metabolized rapidly in mouse brain and labeled metabolites appeared in baboon plasma. PET studies of compounds 2a-c in a baboon showed that influx of compounds 2a-c into the brain was high for the first few min but radioactivity then declined rapidly. Although the retention of radioactivity in the baboon striatum was not significantly different for 2a-c 20 min post-injection, graphical analysis of time-activity data for each enantiomer and for the racemate in baboon striatum suggested that (+)-ketamine may interact with receptors slightly more effectively than its (-)-enantiomer or racemate. However, due to its rapid metabolism in the brain and a similar uptake in the striatum and cerebellum, [11C]ketamine may not be an ideal tracer for studying NMDA receptor with PET.

P-[18F]-MPPF: a potential radioligand for PET studies of 5-HT1A receptors in humans.

The purpose of this study was to develop a radiopharmaceutical that could be used to selectively image 5-HT1A receptors with positron emission tomography (PET). No-carrier-added 4-(2'-methoxyphenyl)-1-[2'-(N-2"-pyridinyl)-p-[18F] fluorobenzamido]ethylpiperazine (p-[18F]-MPPF, 2) was synthesized by the nucleophilic substitution of the corresponding nitro precursor 1 with K[18F]/Kryptofix 2.2.2. in dimethyl sulfoxide (DMSO) at 140 degrees C for 20 min followed by purification with high-performance liquid chromatography (HPLC) in 10% yield in a synthesis time of 90 min from end of bombardment (EOB). Specific activity was 1-4 Ci/microM. Biodistribution studies in rats showed that the initial uptake of 2 in the brain was high (0.7% dose/g tissue at 2 min). It was then rapidly eliminated. Rates of elimination were significantly slower in brain regions with high concentrations of 5-HT1A receptors (hippocampus, cortex, and hypothalamus) than in control regions. The maximum hippocampal/cerebellar ratio was 5.6:1 at 30 min postinjection. Uptake values in serotonergic, but not in control, regions were significantly reduced by prior treatment with either (+/-)-8-OH-DPAT (2 mg/kg, i.v., 5 min prior) or WAY 100635 (1 mg/kg, i.v., 5 min prior). Radioactivity in the femur did not increase with time, suggesting that in vivo defluorination may not be the major route of metabol sm. PET studies of 2 in a monkey demonstrated selective uptake and retention of 2 in the hippocampus. The hippocampal/cerebellar ratio was 3:1 at 30 min postinjection. The ratio was reduced to 1:1 by administering (+/-)-8-OH-DPAT (2 mg/kg, i.v.) 23 min postinjection of 2. Analyses of arterial plasma by HPLC revealed that 20% of radioactivity in the plasma remained as the parent compound 2 at 30 min postinjection. The results suggest that p-[18F]-MPPF may be a useful radioligand for studying cerebral 5-HT1A receptors in humans with PET techniques.

Radiosynthesis and biodistribution of the S-[18F]fluoroethyl analog of McN5652.

[11C]McN5652 has been reported to exhibit favorable properties as a PET radiotracer for studying serotonin uptake sites. However, the use of this radiotracer may be limited by the short half-life of11C. To obtain a tracer with longer physical half-life, we have synthesized the S-[18F]fluoroethyl analog of McN5652 (trans-1,2,3,5,6,10b-hexahydro-6-[4-([18F]fluoroethylthio)-phenyl] pyrrolo-[2,1-a]-isoquinoline) ([18F]FEMcN) and evaluated as a PET radiotracer for imaging serotonin uptake sites. The radiosynthesis was performed via a one-pot, two-step procedure. In the first step, 1-bromo-2-[18F]fluoroethane was prepared from 2-bromoethyl triflate and K18F/Kryptofix 2.2.2. in THF at room temperature. The second step, the S-fluoroalkylation of the normethyl McN5652, a thiol, was carried out, without isolating the 1-bromo-2-[18F]fluoroethane, by adding the normethyl McN5652 to the reaction vial, which was warmed at 45 degrees C for 1 min. The fluoroalkylation reaction proceeded quickly, giving [18F]FEMcN in an average overall radio-chemical yield of 13 +/- 7%. The specific activity was 1593 +/- 625 mCi/mumol. Ex vivo autoradiographic studies revealed that [18F]FEMcN accumulated into regions with high densities of 5-HT uptake sites such as hypothalamus, substantia nigra, and raphe nuclei. With blockade by nitroquipazine, a selective and highly potent 5-HT uptake blocker, the activity level in these regions was close to that in regions low in 5-HT uptake sites such as cerebellum, suggesting that this radiotracer binds specifically to 5-HT uptake sites. The regional distribution of [18F]FEMcN at 60 min postinjection correlated with the distribution of [11C]McN5652 reported in the literature. The specific binding of this radiotracer determined as the difference in radioactivity accumulation with and without blocking by the 5-HT uptake blocker agreed with the distribution of the number of 5-HT uptake sites measured in vitro. Thus, 5-HT uptake sites were visualized in vivo with [18F]FEMcN. However, comparison with the in vivo behavior of [11C]McN5652 indicated less favorable properties of [18F]FEMcN as a PET radiotracer for imaging 5-HT uptake sites, including lower blood-brain barrier penetration and lower target-to-nontarget ratios.

PET study of the distribution of [11C]fluoxetine in a monkey brain.

No-carrier-added [11C]fluoxetine (2) was synthesized by methylation of norfluoxetine (1) with [11C]H3I in 20% radiochemical yield in a synthesis time of 40 min from EOB with a specific activity of 0.48 Ci/microM (EOB). In vivo study in mouse indicated that the uptake of 2 in mouse tissues was high and the radioactivity remained constant throughout the study. The uptake of 2 in mouse brain was 4%/g. PET study in a Rhesus monkey also showed that the uptakes of 2 in different brain regions were similar and the retention of radioactivity in these regions remained constant throughout the study (80 min). Analysis of arterial plasma by HPLC showed that only 20% of radioactivity in the plasma remained as 2 at 30 min post-injection. These results suggest that the uptake of fluoxetine in monkey brain is probably not receptor mediated. Rather, blood flow, lipophilicity or other transport mechanisms may play a role in its uptake.

Comparative PET studies of the distribution of (-)-3,4-methylenedioxy-N-[11C]methamphetamine and (-)-[11C]methamphetamine in a monkey brain.

Carbon-11 labeled (-)-methamphetamine and (-)-3,4-methylenedioxy-N-methamphetamine were synthesized by methylation of the corresponding desmethyl precursors with [11C]H3I in 40-60% yield in a synthesis time of 30 min from EOB with a specific activity of 0.5-1.2 Ci/microM. PET studies in a Rhesus monkey revealed that the uptakes of both compounds in different brain regions were similar, and the retention of radioactivity in these brain regions remained constant throughout the study for the former while it was washed out slowly for the latter. The half-life of (-)-3,4-methylenedioxy-N-methamphetamine in monkey brain was approximately 70 min. Analyses of arterial plasma by HPLC revealed that 50% of radioactivity in the plasma remained as (-)-methamphetamine while only 3% remained as (-)-3,4-methylenedioxy-N-methamphetamine at 60 min post-injection. These results suggest that the uptakes of both compounds in monkey brain are probably not receptor mediated. Rather, blood flow, lipophilicity of the compounds or other transport mechanisms may play a role in their uptakes.

Fluorine-18 and carbon-11 labeled amphetamine analogs--synthesis, distribution, binding characteristics in mice and rats and a PET study in monkey.

No-carrier-added (NCA) (+-)-p-[18F]fluoroamphetamine (2a) and (+-)-6-[18F]fluoro-3,4-methylene-dioxy-amphetamine (2b) were synthesized through a multistep synthesis by nucleophilic substitution of the appropriate precursors (p-nitrobenzaldehyde, 1a and 6-nitropiperonal 1b, respectively) with [18F]fluoride followed by condensation with nitroethane and reduction with LAH in 20-30% yield (EOB) in a synthesis time of 90-109 min from EOB. NCA (-)-[11C]methamphetamine (4a) and (+-)-3,4-methylene-dioxy-N-[11C]methamphetamine (4b) were synthesized by methylation of the appropriate desmethyl precursors 3a and 3b with [11C]H3I in 40-60% yield (EOB) in a synthesis time of 30 min from EOB. Animal studies in mouse and rat revealed that the relative tissue uptake of these radiotracers was kidneys > lungs > liver > spleen > brain > heart > blood. The uptakes of these radiotracers in mouse brain were high and similar at 5 min post-injection (approx. 5%/g) but radioactivity then declined rapidly (approx. 1%/g at 60 min post-injection). For compounds 2a and 2b, the activity in the femur did not increase with time indicating in vivo defluorination may not be the major route of metabolism. Monoamine uptake inhibitors (nomifensine, fluoxetine and nisoxetine) did not inhibit but enhance the uptake of (-)-[11C]methamphetamine (4a) in the rat brain by greater than 50%. A PET study in a Rhesus monkey revealed that the uptakes of (-)-[11C]methamphetamine in different brain regions were similar and the retention of the radioactivity in these regions remained constant throughout the study. Analysis of arterial plasma by HPLC showed that 50% of radioactivity remained as 4a at 60 min post-injection.

Synthesis of (+/-)-[18F]BMY 14802, its enantiomers and their anatomical distributions in rodents.

A potential antipsychotic drug, BMY 14802 was labeled with 18F and its distribution in rodents was studied. No-carrier-added (NCA) (+/-)-[18F]BMY 14802 (5) was synthesized by two methods in 5-10% radiochemical yield in a synthesis time of 130-140 min from EOB with a specific activity of 0.5-1.5 Ci/microM. (+)- and (-)-[18F]BMY 14802 was synthesized by the chiral reduction of alpha-(4-[18F]fluorophenyl)-4-(5-fluoro-2-pyrimidinyl)-1-piperazine-b utanone (4) with chiral reducing agent, (+)- and (-)-beta-chlorodiisopinocampheylborane [(+)- and (-)-DIP chloride] in 6-10% radiochemical yield in a synthesis time of 150 min from EOB. Animal studies in mouse and in rat revealed that the distribution of 5 in each tissue was high at 5 min, the radioactivity then declined rapidly in all tissues studied except in the liver and in the small intestine. The radioactivity in the femur did not increase with time indicating in vivo defluorination may not occur. The uptakes of (+/-)-[18F]BMY 14802 and its enantiomers, (+)- and (-)-[18F]BMY 14802 in rat cerebellum, brain stem, hippocampus and spinal cord were similar and were significantly reduced by prior treatment of rat with haldol. This suggests that (+/-)-[18F]BMY 14802 and its enantiomers bind to sigma-receptors in a similar fashion.

Ion chromatographic analysis of high specific activity 18FDG preparations and detection of the chemical impurity 2-deoxy-2-chloro-D-glucose.

Because of the widespread use of 2-deoxy-2-[18F]fluoro-D-glucose (FDG) prepared by the "Julich" method or its variants it was decided necessary to determine the major chemical impurities present in the final product. An analytical system for quantifying FDG was developed using pulsed amperometry after separation by high-performance anion exchange chromatography. With this system a heretofore unidentified impurity, 2-deoxy-2-chloro-D-glucose (C1DG, ca 20-2000 micrograms; typically < 100 micrograms), was found in our preparation and in those from other laboratories using the "Julich" method. C1DG arises from Cl- ion displacement during the labeling procedure where Cl- ion comes from several sources, and Cl- ion displacement from the HCl used in the hydrolysis step. FDG mass was present in the same preparations at a level of ca 1-40 micrograms. Other major chemical constituents were glucose (ca 1-6 mg) and mannose (ca 10-18 micrograms). Glycerol, arising from sterilizing filters, was also detected in most preparations. Although C1DG is a chemical impurity which has not been detected previously in nca FDG preparations, its biochemical and pharmacological properties are similar to FDG and 2-deoxy-D-glucose. Thus it is unlikely that the presence of small quantities of C1DG found in typical FDG preparations (ca 100 micrograms) would have adverse pharmacological or toxicological consequences that would limit continued application of this radiopharmaceutical in basic and clinical studies.

Considerations in setting up a positron emission tomography center.

Clinically oriented imaging with position emission tomography (PET) has come of age. Given an adequate referral base and physician interest, a compelling argument can be made at all levels of the review process for setting up a PET program in a clinical setting. PET is expensive. It is obvious that the cost of running a PET service depends heavily on an institution's ability to obtain reasonable financing. Educational institutions have the opportunity to acquire special funding through a variety of sources. On the other hand, money can be expensive for private entrepreneurs. It appears that in the near future PET centers will probably remain at educational institutions or large well-financed community hospitals able to raise money at reasonable rates until reimbursement issues are better resolved. Finally, the future of clinical PET may hinge significantly on the ability of commercial radiopharmaceutical suppliers to provide regional fluorodeoxyglucose distribution. As an institutional program development, PET offers opportunities by providing unique clinical data aiding the referral pattern. PET may serve as a magnet for recruitment in many areas and may promote interdisciplinary cooperation. A clinical PET center serves both as a model for future and more widespread use of PET and as a training ground for medical personnel. Finally, the unique capabilities of PET may facilitate grant opportunities.

Regional distribution and kinetics of haloperidol binding in human brain: a PET study with [18F]haloperidol.

The regional distribution and the kinetics of haloperidol uptake in human brain were examined using [18F]haloperidol and PET in 9 controls and 5 schizophrenics while on haloperidol medication and after haloperidol washout. The regional distribution of [18F]N-methylspiroperidol, a tracer for D2 receptors, was measured in 1 normal subject for comparison. The uptake of [18F]haloperidol in the whole brain in normals was high (6.6% of the injected dose at 2 hr), and regional distribution was much more extensive than could be accounted for by the distribution of dopamine D2 receptors. In normals, the cerebellum, basal ganglia, and thalamus showed a greater concentration than the cortex, and there was minimal clearance of 18F from the brain during the 10-hr period of the study. Medicated schizophrenics showed a total brain uptake of 4.0% and had a significant clearance of [18F]haloperidol from brain and a higher concentration of [18F]haloperidol in plasma. After withdrawal from medication, [18F]haloperidol clearance from brain became slower than while on medication. These results are discussed in terms of the pharmacokinetics of haloperidol in the human brain and its binding to dopamine D2 receptors and to sigma receptors.