Synthesis and preliminary biological evaluation of a novel P2X7R radioligand [18F]IUR-1601.

The reference standard IUR-1601 ((S)-N-(2-chloro-3-(trifluoromethyl)benzyl)-1-(2-fluoroethyl)-5-oxopyrrolidine-2-carboxamide) was synthesized from tert-butyl (S)-5-oxopyrrolidine-2-carboxylate, fluoroethylbromide, and 2-chloro-3-(trifluoromethyl)benzylamine with overall chemical yield 12% in three steps. The target tracer [18F]IUR-1601 ((S)-N-(2-chloro-3-(trifluoromethyl)benzyl)-1-(2-[18F]fluoroethyl)-5-oxopyrrolidine-2-carboxamide) was synthesized from desmethyl-GSK1482160 with 2-[18F]fluoroethyl tosylate, prepared from 1,2-ethylene glycol-bis-tosylate and K[18F]F/Kryptofix2.2.2, in two steps and isolated by HPLC combined with SPE in 1-3% decay corrected radiochemical yield. The radiochemical purity was >99%, and the molar activity at end of bombardment (EOB) was 74-370 GBq/µmol. The potency of IUR-1601 in comparison with GSK1482160 was determined by a radioligand competitive binding assay using [11C]GSK1482160, and the binding affinity Ki values for IUR-1601 and GSK1482160 are 4.31 and 5.14 nM, respectively.

A new facile synthetic route to [11C]GSK189254, a selective PET radioligand for imaging of CNS histamine H3 receptor.

GSK189254 and its corresponding precursor GSK185071B were synthesized from 3-methoxyphenylacetic acid with 6-chloropyridine-3-carbolic acid or 6-chloronicotinamide in 8 and 7 steps with either 6% or 7% and either 14% or 16% yield, respectively. [(11)C]GSK189254 was prepared from GSK185071B with [(11)C]CH(3)OTf through N-[(11)C]methylation and isolated by HPLC combined with solid-phase extraction (SPE) in 50-60% radiochemical yield based on [(11)C]CO(2) and decay corrected to end of bombardment (EOB), with 370-740 GBq/µmol specific activity at EOB.

Fully automated radiosynthesis and quality control of estrogen receptor targeting radiopharmaceutical 16α-[18F]fluoroestradiol ([18F]FES) for human breast cancer imaging.

16α-[18F]Fluoroestradiol ([18F]FES) is the most successful estrogen receptor (ER) targeting radiopharmaceutical to date. [18F]FES has been extensively used for positron emission tomography (PET) to assess the ER expression in breast cancer and to monitor the response of breast cancer to antiestrogen therapy. To address local investigator needs for [18F]FES-PET, we sought to adapt established literature methods to our in-house multi-purpose 18F-radiosynthesis module for [18F]FES production. Here we describe facile fully automated radiosynthesis and quality control (QC) of [18F]FES using our home-built automated multi-purpose 18F-radiosynthesis module. [18F]FES was produced via two-step-one-pot synthesis using cyclic sulfate precursor, and purified by semi-preparative reversed-phase (RP) high performance liquid chromatography (HPLC) with a C18 column followed by solid-phase extraction (SPE) with a C18 Plus Sep-Pak cartridge trap/release formulation. The overall synthesis time was 75-80 min, and the radiochemical yield was 30-35% decay corrected to end of bombardment (EOB), based on H[18F]F. The radiochemical purity was >99%, and the molar activity (Am) was 182-470 GBq/µmol at EOB. The [18F]FES dose meets all QC criteria for clinical use, and is suitable for clinical PET study of breast cancer.

Facile fully automated radiosynthesis and quality control of O-(2-[18F]fluoroethyl)-l-tyrosine ([18F]FET) for human brain tumor imaging.

O-(2-[18F]Fluoroethyl)-l-tyrosine ([18F]FET) has become one of the most successful amino acid tracers for human brain tumor imaging with positron emission tomography (PET). Facile fully automated radiosynthesis and quality control (QC) of [18F]FET using our home-built automated multi-purpose 18F-radiosynthesis module are described. [18F]FET was produced in 75-80 min overall synthesis time with 20-25% radiochemical yield decay corrected to end of bombardment (EOB), based on H[18F]F. The radiochemical and enantiomeric purities were >99%, and the molar activity (Am) was 189-411 GBq/µmol at EOB. The [18F]FET dose meets all QC criteria for clinical use, and is suitable for clinical PET study of brain tumor.

Synthesis and initial in vitro characterization of a new P2X7R radioligand [18F]IUR-1602.

The overexpression of P2X7R is associated with neuroinflammation and plays an important role in various neurodegenerative diseases. The [18F]fluoropropyl derivative of GSK1482160, [18F]IUR-1602, has been first prepared and examined as a new potential P2X7R radioligand. The reference standard IUR-1602 was synthesized from tert-butyl (S)-5-oxopyrrolidine-2-carboxylate, fluoropropylbromide, and 2-chloro-3-(trifluoromethyl)benzylamine with overall chemical yield 13% in three steps. The target tracer [18F]IUR-1602 was synthesized from desmethyl-GSK1482160 with 3-[18F]fluoropropyl tosylate, prepared from propane-1,3-diyl bis(4-methylbenzenesulfonate) and K[18F]F/Kryptofix2.2.2, in two steps and isolated by HPLC combined with SPE in 2-7% decay corrected radiochemical yield. The radiochemical purity was >99%, and the molar activity at end of bombardment (EOB) was 74-370 GBq/µmol. The potency of IUR-1602 in comparison with GSK1482160 was determined by a radioligand competitive binding assay using [11C]GSK1482160, and the binding affinity Ki values for IUR-1602 and GSK1482160 are 23.6 and 3.07 nM, respectively. The initial in vitro evaluation results, 8-fold less potency of [18F]IUR-1602 compared to [11C]GSK1482160, prevent further in vivo evaluation of [18F]IUR-1602 in animals and human.

[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, 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 [(11)C]methyl ester ([(11)C]FMAME), a novel carbon-11 labeled matrix metalloproteinase (MMP) inhibitor, has been synthesized for evaluation as new potential positron emission tomography (PET) cancer biomarker. [(11)C]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 [(11)C]methyl triflate through O-[(11)C]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 (11)CO(2), decay corrected to end of bombardment, and 15-20 min synthesis time. The biodistribution of [(11)C]FMAME was determined at 30 min post IV injection in breast cancer animal models MCF-7 transfected with IL-1 alpha implanted athymic mice and MDA-MB-435 implanted athymic mice. The results showed the uptakes of [(11)C]FMAME in these tumors were 1.13% dose/g in MCF-7 transfected with IL-1 alpha 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-1 alpha tumor-bearing mice with MMP inhibitor FMA had no effect on [(11)C]FMAME biodistribution. Likewise, pretreatment of MDA-MB-435 tumor-bearing mice with FMA also showed no effect on [(11)C]FMAME biodistribution. The micro-PET images were acquired for 15 min from a MCF-7 transfected with IL-1 alpha tumor-bearing mouse or a MDA-MB-435 tumor-bearing mouse at 30 min post IV injection of 1 mCi of [(11)C]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 [(11)C]FMAME in a MCF-7 transfected with IL-1 alpha 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 [(11)C]FMAME. These results suggest that the localization of [(11)C]FMAME in the tumor is mediated by non-specific processes, and the visualization of [(11)C]FMAME on the tumor using the Indy-PET II scanner is related to non-specific binding.

An automated SPE-based high-yield synthesis of [11C]acetate and [11C]palmitate: no liquid-liquid extraction, solvent evaporation or distillation required.

INTRODUCTION: An automated method is described for the rapid and high-yield synthesis of two of the most commonly used radioactive fatty acids: [(11)C]acetate and [(11)C]palmitate. METHODS: Reaction of [(11)C]CO(2) with the respective Grignard reagents in diethyl ether solution proceeded for 2 min at 40°C. Quenching of the reaction and liberation of nonreacted [(11)C]CO(2) occurred upon addition of a fourfold molar excess of aqueous 0.1 M HCl (acetate) or nonaqueous HCl/Et(2)O (palmitate). Labeled products were then purified by adsorption to an Alumina-N Sep-Pak Plus cartridge and eluted with either aqueous NaH(2)PO(4) solution (acetate) or 100% ethanol (palmitate). RESULTS: High-performance liquid chromatography analysis confirmed that the radiochemical purity of each product was >98%, and decay-corrected radiochemical yields averaged 33% for [(11)C]palmitate and 40% for [(11)C]acetate. CONCLUSION: The method requires no liquid-liquid extraction, solvent evaporation or distillation capabilities and can be readily adapted to existing radiosynthesis modules.

An improved synthesis of dopamine D2/D3 receptor radioligands [11C]fallypride and [18F]fallypride.

Improved syntheses of dopamine D(2)/D(3) receptor radioligands [(11)C]Fallypride and [(18)F]Fallypride are reported. The phenolic precursor (9) for C-11 labeling and the Fallypride (10) reference standard were synthesized from the starting material 2-hydroxy-3-methoxy-5-(2-propenyl)benzoic acid methyl ester (1) in 7 and 8 steps with 16% and 5% overall chemical yields, respectively. The tosylated precursor (15) for F-18 labeling was synthesized from compound 1 in 5 steps with 32% overall chemical yield. An alternate synthetic approach for Fallypride has been developed using the same starting material 1 in 5 steps with 26% overall chemical yield. [(11)C]Fallypride ([(11)C]10) was prepared by O-[(11)C]methylation of the phenolic precursor with [(11)C]methyl triflate and purified with a semi-preparative HPLC method in 50-60% radiochemical yield, decay corrected to end of bombardment (EOB), based on [(11)C]CO(2), and 370+/-185 GBq/micromol specific radioactivity at EOB. [(18)F]Fallypride ([(18)F]10) was prepared by nucleophilic substitution of the tosylated precursor with K[(18)F]F/Kryptofix 2.2.2 and HPLC combined with solid-phase extraction (SPE) purification in variable (up to 50%) decay corrected radiochemical yield from K[(18)F]F and 111-222 GBq/micromol specific activity at EOB.

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.