Synthesis of carbon-11-labeled aminoalkylindole derivatives as new candidates of cannabinoid receptor radioligands for PET imaging of alcohol abuse

Carbon-11-labeled aminoalkylindole derivatives (1-butyl-7-[¹¹C]methoxy-1H-indol-3-yl)(naphthalene-1-yl)methanone ([¹¹C]3), 1-butyl-7-[¹¹C]methoxy-3-(naphthalene-1-ylmethyl)-1H-indole ([¹¹C]5), and 1-butyl-7-[¹¹C]methoxy-3-(naphthalene-2-yl)-1H-indole ([¹¹C]8) were prepared by O-[¹¹C]methylation of their corresponding precursors with [¹¹C]CH₃OTf under basic condition (2 N NaOH) and isolated by a simplified solid-phase extraction (SPE) method in 50–60% radiochemical yields based on [¹¹C]CO₂ and decay corrected to end of bombardment (EOB). The overall synthesis time from EOB was 23 min, the radiochemical purity was >99%, and the specific activity at end of synthesis (EOS) was 185–555 GBq/μmol.     

Metabolic conversion of 24-methyl-Delta25-cholesterol to 24-methylcholesterol in higher plants

Feeding of chemically synthesized [27-13C]codisterol ([27-13C]2), [27-13C]24-epicodisterol ([27-13C]3), [23,24-2H2]codisterol ([23,24-2H2]2), and [26,27-2H6]24-methyldesmosterol ([26,27-2H6]8) to Oryza sativa cell cultures, followed by MS and NMR analysis of the biosynthesized dihydrobrassicasterol (9)/campesterol (10), revealed that both (24R)- and (24S)-epimers of 24-methyl-Delta25-cholesterol (2/3) were converted to 9 and 10 via the common intermediate 24-methyldesmosterol (8).     

Synthesis of carbon-11-labeled casimiroin analogues as new potential PET agents for imaging of quinone reductase 2 and aromatase expression in breast cancer

Carbon-11-labeled casimiroin analogues were first designed and synthesized as new potential PET agents for imaging of quinone reductase (QR) 2 and aromatase expression in breast cancer. [¹¹C]casimiroin (6-[¹¹C]methoxy-9-methyl-[1,3]dioxolo[4,5-h]quinolin-8(9H)-one, [¹¹C]11) and its carbon-11-labeled analogues 5,6,8-trimethoxy-1-[¹¹C]methyl-4-methylquinolin-2(1H)-one ([¹¹C]17), 8-methoxy-1-[¹¹C]methyl-4-methylquinolin-2(1H)-one ([¹¹C]21a), 6,8-dimethoxy-1-[¹¹C]methyl-4-methylquinolin-2(1H)-one ([¹¹C]21b), and 5,8-dimethoxy-1-[¹¹C]methyl-4-methylquinolin-2(1H)-one ([¹¹C]21c), were prepared from their corresponding precursors with [¹¹C]methyl triflate ([¹¹C]CH₃OTf) under basic conditions (NaH) through either O- or N-[¹¹C]methylation and isolated by semi-preparative HPLC method in 40-50% radiochemical yields decay corrected to end of bombardment (EOB), based on [¹¹C]CO₂, and 111-185 GBq/μmol specific activity at the end of synthesis (EOS).     

Radiosynthesis of [11C]BBAC and [11C]BBPC as potential PET tracers for orexin2 receptors

Radiosynthesis of [N-methyl-(11)C](S)-N-([1,1'-biphenyl]-2-yl)-1-(2-((1-methyl-1H-benzo[d]imidazol-2-yl)thio)acetyl)pyrrolidine-2-carboxamide ([(11)C]BBAC or [(11)C]3) and [N-methyl-(11)C] (S)-N-([1,1'-biphenyl]-2-yl)-1-(3-(1-methyl-1H-benzo[d]imidazol-2-yl)propanoyl)pyrrolidine-2-carboxamide ([(11)C]BBPC or [(11)C]-4), two potential PET tracers for orexin2 receptors are described. Syntheses of non-radioactive standards 3, 4 and corresponding desmethyl precursors 1, 2 were achieved from common intermediate (S)-2-([1,1'-biphenyl]-2-yl)-1-(pyrrolidin-2-yl)ethanone. Methylation using [(11)C]CH(3)OTf in the presence of base in acetone afforded [(11)C]3 and [(11)C]4 in 30±5% yield (EOS) with >99 % radiochemical purities with a specific activity ranged from 2.5±0.5 Ci/μmol (EOB). The logP of [(11)C]3 and [(11)C]4 were determined as 3.4 and 2.8, respectively. The total synthesis time was 30 min from EOB. However, PET scans performed in a rhesus monkey did not show tracer retention or appropriate brain uptake. Hence [(11)C]3 and [(11)C]4 cannot be used as PET tracers for imaging orexin2 receptors.     

Synthesis of 2-amino-6-(4-[11C]methoxyphenylthio)-9-[2-(phosphonomethoxy)ethyl]purine bis(2,2,2-trifluoroethyl) ester as a novel potential PET gene reporter probe for HBV and HSV-tk in cancers

Acyclic nucleoside 2-amino-6-(4-methoxyphenylthio)-9-[2-(phosphonomethoxy)ethyl]purine bis(2,2,2-trifluoroethyl) ester (ABE, 1) is a new hepatitis B virus (HBV) specific antiviral reagent and shows high anti-HBV activity. Carbon-11 labeled ABE may serve as a novel reporter probe for positron emission tomography (PET) to image HBV and herpes simplex virus thymidine kinase (HSV-tk) in cancers. The radiolabeling precursors 2-amino-6-(4-hydroxyphenylthio)-9-[2-(phosphonomethoxy)ethyl]purine bis(2,2,2-trifluoroethyl) ester (10) and 2-N-Boc protected analogue 2-N-bis(Boc)amino-6-(4-hydroxyphenylthio)-9-[2-(phosphonomethoxy)ethyl]purine bis(2,2,2-trifluoroethyl) ester (12), and the reference standard ABE were synthesized from bis(trifluoroethyl) (2-iodoethoxy)methylphosphonate (5), guanine (6), and 2-amino-6-chloropurine (8). The target radiotracer 2-amino-6-(4-[11C]methoxyphenylthio)-9-[2-(phosphonomethoxy)ethyl]purine bis(2,2,2-trifluoroethyl) ester ([11C]ABE, [11C]1) was prepared by O-[11C]methylation of the unprotected HO-precursor 10, or 2-N-Boc protected HO-precursor 12 with [11C]methyl triflate followed by a quick deprotection reaction, and isolated by solid-phase extraction (SPE) purification in 40-55% radiochemical yields.     

Facile synthesis of carbon-11-labeled sEH/PDE4 dual inhibitors as new potential PET agents for imaging of sEH/PDE4 enzymes in neuroinflammation

To develop PET tracers for imaging of neuroinflammation, new carbon-11-labeled sEH/PDE4 dual inhibitors have been synthesized. The reference standard N-(4-methoxy-2-(trifluoromethyl)benzyl)benzamide (1) and its corresponding desmethylated precursor N-(4-hydroxy-2-(trifluoromethyl)benzyl)benzamide (2) were synthesized from (4-methoxy-2-(trifluoromethyl)phenyl)methanamine and benzoic acid in one and two steps with 84% and 49% overall chemical yield, respectively. The standard N-(4-methoxy-2-(trifluoromethyl)benzyl)-1-propionylpiperidine-4-carboxamide (MPPA, 4) and its precursor N-(4-hydroxy-2-(trifluoromethyl)benzyl)-1-propionylpiperidine-4-carboxamide (5) were synthesized from methyl 4-piperidinecarboxylate, propionyl chloride and (4-methoxy-2-(trifluoromethyl)phenyl)methanamine in two and three steps with 62% and 34% overall chemical yield, respectively. The target tracers N-(4-[¹¹C]methoxy-2-(trifluoromethyl)benzyl)benzamide ([¹¹C]1) and N-(4-[¹¹C]methoxy-2-(trifluoromethyl)benzyl)-1-propionylpiperidine-4-carboxamide ([¹¹C]MPPA, [¹¹C]4) were prepared from their corresponding precursors 2 and 5 with [¹¹C]CH₃OTf through O-[¹¹C]methylation and isolated by HPLC combined with SPE in 25–35% radiochemical yield, based on [¹¹C]CO₂ and decay corrected to end of bombardment (EOB). The radiochemical purity was >99%, and the molar activity (A_M) at EOB was 370–740 GBq/μmol with a total synthesis time of 35–40-minutes from EOB.     

Four steroidal alkaloids from the leaves of Buxus sempervirens

Four new steroidal alkaloids, N20-formylbuxaminol E [(20S)-16alpha-hydroxy-20-(formylamino)-3beta-(dimethylamino)-9,10 -seco-buxa-9(11),10(19)-diene] (1), O16-syringylbuxaminol E [(20S)-16alpha-syringoyl-3beta-(dimethylamino)-20-(amino)-9, 10-seco-buxa-9(11),10(19)-diene] (2), N20-acetylbuxamine G [(20S)-20-(acetylamino)-3beta-(methylamino)-9,10-seco-buxa-9(11),1 0(19)-diene] (3) and N20-acetylbuxamine E [(20S)-20-(acetylamino)-3beta-(dimethylamino)-9,10-seco-buxa-9(11) ,10(19)-diene] (4) were isolated from the leaves of Buxus sempervirens. Their structures were determined mainly on the basis of 2D NMR studies.     

Radiolabeling and biodistribution of methyl 2-(methoxycarbonyl)-2-(methylamino) bicyclo[2.1.1] -hexane -5-carboxylate,a potential neuroprotective drug

Methyl 2-(methoxycarbonyl) -2-(methylamino) bicyclo[2.1.1] -hexane -5-carboxylate (MMMHC) is developed as a potential neuroprotective drug. It was labeled with C-11 from the desmethyl precursor methyl 2-(methoxycarbonyl)-2-amino bicyclo[2.1.1]-hexane-5-carboxylate with [11C]methyl triflate in acetone solution at 60 degrees C with labeling yield of 69% and with radiochemical purity of >99%. Positron Emission Tomography (PET) studies in a normal rat showed that Methyl 2-(methoxycarbonyl)-2-([11C]methylamino)bicyclo[2.1.1]-hexane-5-carboxylate ([11C] MMMHC) accumulated mainly in the cortical brain areas after iv administration. Frontal cortex/cerebellum ratios in a rat brain were 8.0/6.0, 6.8/4.2, 6.3/4.3, 5.5/4.2 and 5.2/4.5 percent of the injected dose in 100 ml at 2 min, 5 min, 10 min, 20 min and 40 min respectively after i.v. injection. During 20-40 min, 2.9+/-0.4% of the total activity stayed in the brain. These results showed that MMMHC could be labeled with C-11 with high yield, and it passed the brain-blood barrier and accumulated in several brain regions.     

Development of new brain imaging agents based upon nocaine-modafinil hybrid monoamine transporter inhibitors

11C-labeled (+)-trans-2-[[(3R,4S)-4-(4-chlorophenyl)-1-methylpiperidin-3-yl]methylsulfanyl]ethanol ([11C]5) and (+)-trans-2-[[(3R,4S)-4-(4-chlorophenyl)-1-methylpiperidin-3-yl]methylsulfanyl]-1-(piperidin-1-yl)ethanone ([11C]6) were synthesized and evaluated as new imaging agents for the norepinephrine transporter (NET). [11C]5 and [11C]6 display high affinity for the NET in vitro (Ki = 0.94 and 0.68 nM, respectively) and significant selectivity over the dopamine (DAT) and serotonin transporters (SERT). Because of their high affinity and favorable transporter selectivities we speculated that these ligands might serve as useful PET agents for imaging NET in vivo. Contrary to our expectations, both of these ligands provided brain images that were more typical of those shown by agents binding to the DAT.     

Synthesis of carbon-11-labeled 5-HT6R antagonists as new candidate PET radioligands for imaging of Alzheimer’s disease

Carbon-11-labeled serotonin (5-hydroxytryptamine) 6 receptor (5-HT₆R) antagonists, 1-[(2-bromophenyl)sulfonyl]-5-[¹¹C]methoxy-3-[(4-methyl-1-piperazinyl)methyl]-1H-indole (O-[¹¹C]2a) and 1-[(2-bromophenyl)sulfonyl]-5-methoxy-3-[(4-[¹¹C]methyl-1-piperazinyl)methyl]-1H-indole (N-[¹¹C]2a), 5-[¹¹C]methoxy-3-((4-methylpiperazin-1-yl)methyl)-1-(phenylsulfonyl)-1H-indole (O-[¹¹C]2b) and 5-methoxy-3-((4-[¹¹C]methylpiperazin-1-yl)methyl)-1-(phenylsulfonyl)-1H-indole (N-[¹¹C]2b), 1-((4-isopropylphenyl)sulfonyl)-5-[¹¹C]methoxy-3-((4-methylpiperazin-1-yl)methyl)-1H-indole (O-[¹¹C]2c) and 1-((4-isopropylphenyl)sulfonyl)-5-methoxy-3-((4-[¹¹C]methylpiperazin-1-yl)methyl)-1H-indole (N-[¹¹C]2c), 1-((4-fluorophenyl)sulfonyl)-5-[¹¹C]methoxy-3-((4-methylpiperazin-1-yl)methyl)-1H-indole (O-[¹¹C]2d) and 1-((4-fluorophenyl)sulfonyl)-5-methoxy-3-((4-[¹¹C]methylpiperazin-1-yl)methyl)-1H-indole (N-[¹¹C]2d), were prepared from their O- or N-desmethylated precursors with [¹¹C]CH₃OTf through O- or N-[¹¹C]methylation and isolated by HPLC combined with SPE in 40–50% radiochemical yield, based on [¹¹C]CO₂ and decay corrected to end of bombardment (EOB). The radiochemical purity was >99%, and the molar activity (MA) at EOB was 370–740?GBq/μmol with a total synthesis time of ～40-min from EOB.     

L-[methyl-(11C)]-methionine of high enantiomeric purity production via on-line 11C-methylation of L-homocysteine thiolactone hydrochloride

L-[methyl-(11C)]-methionine ([11C]MET), labelled with carbon-11 (T1/2 = 20 min), is the most commonly used amino acid radiotracer for PET diagnostics of brain tumors. The production of [11C]MET via on-line 11C-methylation of L-homocysteine thiolactone hydrochloride (lactone) on C18 solid-phase extraction cartridge creates a problem of insufficient enantiomeric purity (content of L-isomer) of the product. The results of a systematic study of the influence of reaction parameters (lactone/base and the EtOH/H20 ratios, time of 11C-methylation) on the content of L-isomer in the preparation are presented. The developed method of on-line [11C]MET synthesis allows to obtain a product with a sufficiently high radiochemical yield (75 +/- 3%, n = 100, based on [11C]CH3I) and reliably high content of L-isomer (93.7 +/- 0.5%) satisfying the requirements of clinical applications. [11C] MET synthesis was performed on a fully automated module designed by the Institute of Human Brain (IHB RAS).     

Synthesis and in vivo evaluation of [11C]SN003 as a PET ligand for CRF1 receptors

Synthesis and evaluation of [O-methyl-11C](4-methoxy-2-methylphenyl)[1-(1-methoxymethylpropyl)-6-methyl-1H-[1,2,3]triazolo[4,5-c]pyridin-4-yl]amine or [11C]SN003 ([11C]6), as a PET imaging agent for CRF1 receptors, in baboons is described. 4-[1-(1-Methoxymethylpropyl)-6-methyl-1H-[1,2,3]triazolo[4,5-c]pyridin-4-ylamino]-3-methylphenol (5), the precursor molecule for the radiolabeling, was synthesized from 2,4-dichloro-6-methyl-3-nitropyridine in seven steps with 20% overall yield. The total time required for the synthesis of [11C]SN003 is 30 min from EOB using [11C]methyl triflate in the presence of NaOH in acetone. The yield of the synthesis is 22% (EOS) with >99% chemical and radiochemical purities and a specific activity of >2000 Ci/mmol. PET studies in baboon show that [11C]6 penetrates the BBB and accumulates in brain. No detectable specific binding was observed, likely due to the rapid metabolism or low density of CRF1 receptors in primate brain.     

In vitro cytotoxicity of 5-aminosubstituted 20(S)-camptothecins. Part 1.

A number of 5-aminosubstituted 20(S)-camptothecin analogues were prepared via semi-synthesis starting from 20(S)-camptothecin and 9-methoxy 20(S)-camptothecin. In vitro anti-cancer activity of these analogues was determined using 60 human tumor cell line assay. Although water solubility of most of these compounds was improved compared to 20(S)-camptothecin, their anti-cancer activity was considerably diminished. However, only smaller substituents such as methylamine or hydroxylamine as present in 8s and 8t, respectively, showed good activity with improved water solubility.     

A flat squared conformation of an ascidiacyclamide derivative caused by chiral modification of an oxazoline residue

We designed a deoxazoline-ascidiacyclamide (dASC), cyclo(-L-Ile-L-allo-Thr-D-Val-thiazole-)(2), diastereomer having 10S, 11R, 37R, and 38S configurations ([SR,RS]dASC) and a corresponding product having 10S, 11S, 37R, and 38R configurations ([SS,RR]ASC) with the aim of understanding better the relationship between conformational behaviour and chirality. X-ray diffraction analysis revealed that [SR,RS]dASC is folded in a manner similar to other dASC analogues. By contrast, [SS,RR]ASC is a novel, flat conformer that is larger than the major square and folded ASC conformers and contains a cavity created by the flat peptide ring. In addition, [SS,RR]ASC retains approximately 60% of the cytotoxicity of the parent molecule.     

Activation of phospholipase C associated with isolated rabbit platelet membranes by guanosine 5''-[gamma-thio]triphosphate and by thrombin in the presence of GTP.

Rabbit platelets were labelled with [3H]inositol and a membrane fraction was isolated in the presence of ATP, MgCl2 and EGTA. Incubation of samples for 10 min with 0.1 microM-Ca2+free released [3H]inositol phosphates equivalent to about 2.0% of the membrane [3H]phosphoinositides. Addition of 10 microM-guanosine 5'-[gamma-thio]triphosphate (GTP[S]) caused an additional formation of [3H]inositol phosphates equivalent to 6.6% of the [3H]phosphoinositides. A half-maximal effect was observed with 0.4 microM-GTP[S]. The [3H]inositol phosphates that accumulated consisted of 10% [3H]inositol monophosphate, 88% [3H]inositol bisphosphate ([3H]IP2) and 2% [3H]inositol trisphosphate ([3H]IP3). Omission of ATP and MgCl2 led to depletion of membrane [3H]polyphosphoinositides and marked decreases in the formation of [3H]inositol phosphates. Thrombin (2 units/ml) or GTP (4-100 microM) alone weakly stimulated [3H]IP2 formation, but together they acted synergistically to exert an effect comparable with that of 10 microM-GTP[S]. The action of thrombin was also potentiated by 0.1 microM-GTP[S]. Guanosine 5'-[beta-thio]diphosphate not only inhibited the effects of GTP[S], GTP and GTP with thrombin, but also blocked the action of thrombin alone, suggesting that this depended on residual GTP. Incubation with either GTP[S] or thrombin and GTP decreased membrane [3H]phosphatidylinositol 4-phosphate ([H]PIP) and prevented an increase in [3H]phosphatidylinositol 4,5-bisphosphate ([3H]PIP2) observed in controls. Addition of unlabelled IP3 to trap [3H]IP3 before it was degraded to [3H]IP2 showed that only about 20% of the additional [3H]inositol phosphates that accumulated with GTP[S] or thrombin and GTP were derived from the action of phospholipase C on [3H]PIP2. The results provide further evidence that guanine-nucleotide-binding protein mediates signal transduction between the thrombin receptor and phospholipase C, and suggest that PIP may be a major substrate of this enzyme in the platelet.     

Synthesis of carbon-11-labeled 4-(phenylamino)-pyrrolo[2,1-f][1,2,4]triazine derivatives as new potential PET tracers for imaging of p38α mitogen-activated protein kinase

The reference standards methyl 4-(2-methyl-5-(methoxycarbamoyl)phenylamino)-5-methylpyrrolo[2,1-f][1,2,4]triazine-6-carboxylate (10a), methyl 4-(2-methyl-5-(ethoxycarbamoyl)phenylamino)-5-methylpyrrolo[2,1-f][1,2,4]triazine-6-carboxylate (10b) and corresponding precursors 4-(2-methyl-5-(methoxycarbamoyl)phenylamino)-5-methylpyrrolo[2,1-f][1,2,4]triazine-6-carboxylic acid (11a), methyl 4-(2-methyl-5-(ethoxycarbamoyl)phenylamino)-5-methylpyrrolo[2,1-f][1,2,4]triazine-6-carboxylic acid (11b) were synthesized from methyl crotonate and 3-amino-4-methylbenzoic acid in multiple steps with moderate to excellent yields. The target tracer [¹¹C]methyl 4-(2-methyl-5-(methoxycarbamoyl)phenylamino)-5-methylpyrrolo[2,1-f][1,2,4]triazine-6-carboxylate ([¹¹C]10a) and [¹¹C]methyl 4-(2-methyl-5-(ethoxycarbamoyl)phenylamino)-5-methylpyrrolo[2,1-f][1,2,4]triazine-6-carboxylate ([¹¹C]10b) were prepared from their corresponding precursors with [¹¹C]CH₃OTf under basic condition through O-[¹¹C]methylation and isolated by a simplified solid-phase extraction (SPE) method in 50–60% radiochemical yields at end of bombardment (EOB) with 185–555 GBq/μmol specific activity at end of synthesis (EOS).     

Facile synthesis of carbon-11-labeled cholesterol-based cationic lipids as new potential PET probes for imaging of gene delivery in cancer

Gene therapy based on gene delivery is a promising strategy for the treatment of various human diseases such as cancer. Cationic lipids represent one of the important synthetic gene delivery systems. There is a great interest in imaging of gene therapy using the biomedical imaging technique positron emission tomography (PET). Carbon-11-labeled cholesterol-based cationic lipids were first designed and synthesized as new potential PET probes for imaging of gene delivery in cancer. The [¹¹C-methyl]quaternary amine target tracers, N-[¹¹C]methyl-N-[4-(cholest-5-en-3β-yloxycarbonyl)butyl]pyrrolidinium iodide ([¹¹C]4a), N-[¹¹C]methyl-N′-[4-(cholest-5-en-3β-yloxycarbonyl)butyl]imidazolium iodide ([¹¹C]4b), N-[¹¹C]methyl-N-[4-(cholest-5-en-3β-yloxycarbonyl)butyl]piperidinium iodide ([¹¹C]4c), N-[¹¹C]methyl-N-[4-(cholest-5-en-3β-yloxycarbonyl)butyl]-4-methylpiperidinium iodide ([¹¹C]4d), and N-[¹¹C]methyl-N-[4-(cholest-5-en-3β-yloxycarbonyl)butyl]morpholinium iodide ([¹¹C]4e), were prepared from their corresponding tertiary amine precursors with [¹¹C]methyl iodide ([¹¹C]CH₃I) through N-[¹¹C]methylation and isolated by a simplified solid-phase extraction (SPE) method using a Silica Sep-Pak cartridge in 50-60% radiochemical yields decay corrected to end-of-bombardment (EOB), based on [¹¹C]CO₂, and 111-185 GBq/μmol specific activity at the end of synthesis (EOS).     

Dose-responsive effect of radiotherapy on the tumor uptake of l-[methyl-11C]methionine; feasibility for monitoring recurrence of tumor

The l-[methyl-¹¹C]methionine ([¹¹C]Met) uptake by rat AH109A tumor was decreased irradiation-dose dependently from the control to 5, 10 and 20 Gy. After 10 Gy irradiation, the [¹¹C]Met uptake decreased earlier than the tumor volume reduction, and later, it significantly increased earlier than the recurrent growth. Double tracer autoradiography with [¹⁴C]Met and 4-[¹⁸F]fluoroantipyrine showed a decrease in the [¹⁴C]Met tumor uptake without change of blood flow after irradiation. The [¹¹C]Met uptake representing amino acid metabolism is a sensitive indicator for monitoring radiotherapeutic effect on tumor.     

Synthesis and in vivo evaluation of ¹⁸F-fluoroethyl GF120918 and XR9576 as positron emission tomography probes for assessing the function of drug efflux transporters

The purpose of this study was to synthesize two new positron emission tomography (PET) probes, N-(4-(2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl)phenyl)-9,10-dihydro-5-[1?F]fluoroethoxy-9-oxo-4-acridine carboxamide ([1?F]3) and quinoline-3-carboxylic acid [2-(4-{2-[7-(2-[1?F]fluoroethoxy)-6-methoxy-3,4-dihydro-1H-isoquinolin-2-yl]ethyl}phenylcarbamoyl)-4,5-dimethoxyphenyl]amide ([1?F]4), and to evaluate the potential of these PET probes for assessing the function of two major drug efflux transporters, P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP). [1?F]3 and [1?F]4 were synthesized by 1?F-alkylation of each O-desmethyl precursor with [1?F]2-fluoroethyl bromide for injection as PET probes. In vitro accumulation assay showed that treatment with P-gp/BCRP inhibitors (1 and 2) enhanced the intracellular accumulation capacity of P-gp- and BCRP-overexpressing MES-SA/Dx5 cells. In PET studies, the uptake (AUC(brain[0-)?? (min])) of [1?F]3 and [1?F]4 in wild-type mice co-injected with 1 were approximately sevenfold higher than that in wild-type mice, and the uptake of [1?F]3 and [1?F]4 in P-gp/Bcrp knockout mice were eight- to ninefold higher than that in wild-type mice. The increased uptake of [1?F]3 and [1?F]4 was similar to that of parent compounds ([11C]1 and [11C]2) previously described, indicating that radioactivity levels in the brain after injection of [1?F]3 and [1?F]4 are related to the function of drug efflux transporters. Also, these results suggest that the structural difference between parent compounds ([11C]1 and [11C]2) and fluoroethyl analogs ([1?F]3 and [1?F]4) do not obviously affect the potency against drug efflux transporters. In metabolite analysis of mice, the unchanged form in the brain and plasma at 60 min after co-injection of [1?F]4 plus 1 were higher (95% for brain; 81% for plasma) than that after co-injection of [1?F]3 plus 1. [1?F]4 is a promising PET probe to assess the function of drug efflux transporters.     

Selective effect of microembolization on pulmonary removal of biogenic amines

Pulmonary amine extraction (E) was measured by triple-indicator dilution techniques from bolus injections of trace amounts of 5-hydroxy[14C]tryptamine ([14C]HT)m [3H]norepinephrine ([3H]NE), indocyanine green dye before and after glass-bead embolization in 23 anesthetized dogs. Control E(5-[14C]-HT) was 89.7 +/- 1.7%; 10 min after embolization (which approximately doubled pulmonary artery pressure and pulmonary vascular resistance), E(5-[14C]HT) was significantly reduced to 65.9 +/- 3.0% (kappa +/- SE; n = 10) (P less than 0.01). Control E([3H]NE) (40.1 +/- 4.5%) was unaffected by embolization. Imipramine (8 mg/kg) depressed control E(5-[14C]HT) to 38.7 +/- 1.5% and control E([3H]NE)d to 35.0 +/- 3.9% (P less than 0.05; n = 4). In these animals, pulmonary hemodynamic changes secondary to embolization were comparable to those in non-drug-treated dogs, but E(5-[14C]HT) and E([3H]NE) were not further depressed. Progressive pulmonary lobar artery ligation (n = 5) did not affect amine extraction until perfusion was limited to one lobe. The selectivity of the effect of embolization on E(5-[14C]HT), the lack of an effect on imipramine-insensitive E(5-[14C]HT) extraction, and the much smaller changes after progressive lobar ligation indicate that, although derecruitment of vascular surface area secondary to mechanical obstruction may contribute to postembolization depression of E(5-[14C]HT), additional mechanisms such as local saturation of 5-HT uptake or selective damage to endothelial cell transport of 5-HT may underlie these observations.