Fully automated synthesis of O-(3-[F]fluoropropyl)-L-tyrosine by direct nucleophilic exchange on a quaternary 4-aminopyridinium resin

A fully automated synthesis of O-(3-[¹⁸F]fluoropropyl)-L-tyrosine (FPT), an amino acid tracer for tumor imaging with positron emission tomography, is described. FPT was prepared by a two-step reaction sequence. Direct nucleophilic fluorination substitution of [¹⁸F]fluoride with 1,3-di(4-methylphenylsulfonyloxy)propane on a quaternary 4-(4-methylpiperidinyl)pyridinium functionalized polystyrene anion exchange resin, followed by [¹⁸F]fluoro-1-(4-methylphenylsulfonyloxy)propane yielded FPT. The overall radiochemical yield with no decay correction was about 12%; the whole synthesis time was about 52 min, and the radiochemical purity was above 95%.     

Fully automated synthesis of [18F]fluoromisonidazole using a conventional [18F]FDG module

We developed a new fully automated method for the synthesis of [¹⁸F]fluoromisonidazole ([¹⁸F]FMISO) by modifying a commercial FDG synthesizer and its disposable fluid pathway. A three-step procedure was used to prepare the tosylate precursor, 1-(2′-nitro-1′-imidazolyl)-2-O-tetrahydrofuranyl-3-O-toluenesulfonylpropanediol. Using glycerol as the starting material, the precursor was synthesized with a yield of 21%. The optimal labeling conditions for the automated synthesis of [¹⁸F]FMISO was 10 mg of precursor in acetonitrile (2 ml heated at 105°C for 360 s, followed by heating at 75°C for 280 s and hydrolysis with 1 N HCl at 105°C for 300 s. Using 3.7 GBq of [¹⁸F]F⁻ as a starting activity, [¹⁸F]FMISO was obtained with high end-of-synthesis (EOS) radiochemical yields of 58.5±3.5% for 60.0±5.2 min with high-performance liquid chromatography (HPLC) purification. When solid-phase purification steps were added, the EOS radiochemical yields were 54.5±2.8% (337±25 GBq/μmol) for 70.0±3.8 min (n=10 for each group, decay-corrected). With a high starting radioactivity of 37.0 GBq, we obtained radiochemical yields of 54.4±2.9% and 52.8±4.2%, respectively (n=3). The solid-phase purification removed unreacted [¹⁸F]fluoride and polar impurities before the HPLC procedure. Long-term tests showed a good stability of 98.2±1.5%. This new automated synthesis procedure combines high and reproducible yields with the advantage of using a disposable cassette system.     

In vitro characterization of the thyroidal uptake of O-(2-[(18)F]fluoroethyl)-L-tyrosine

OBJECTIVES: Positron emission tomography (PET) using O-(2-[(18)F]fluoroethyl)-l-tyrosine (FET) has been successfully employed in the diagnostic workup of brain tumors. Knowledge on the mechanisms of the uptake of radiolabeled amino acids into thyroidal tissues and well-differentiated thyroid carcinomas is limited. We therefore studied several factors potentially governing the uptake of FET in the rat thyroid cell line FRTL-5 in comparison with thyroid tumor cell lines of human origin. METHODS: FET uptake was determined in thyroid-stimulating hormone (TSH)-stimulated and TSH-deprived FRTL-5 cells, as well as in the cell lines U-138 MG (human glioblastoma), Onco DG-1 (human papillary thyroid carcinoma) and ML-1 (human follicular thyroid carcinoma). The TSH responsiveness of cells was measured by the incubation of TSH-treated and untreated control cells with 2-[(18)F]fluoro-2-deoxyglucose (FDG). All cellular tracer uptake values were related to total protein mass and expressed as percentage per milligram. For countertransport studies, FRTL-5 cells were exposed to 10-300 microM tyrosine methyl ester. TSH-stimulated and TSH-deprived FRTL-5 cells were incubated with 100 kBq/ml FET for 20 min. 2-Aminobicyclo-[2,2,1]heptane-2-carboxylic acid (BCH), alpha-(methylamino)-isobutyric acid, L-serine and tryptophan were used as competitive inhibitors of FET uptake. All inhibition experiments were repeated with the human thyroid carcinoma cell lines to obtain comparative FET uptake values. RESULTS: The FET uptake was 155+/-30%/mg in FRTL-5 cells (n=6), 108+/-14%/mg in U-138 MG cells (n=6), 194+/-60%/mg in ML-1 cells (n=9) and 64+/-23%/mg in Onco DG-1 cells (n=6) under identical incubation conditions. Preloading with tyrosine methyl ester increased cellular FET uptake dose dependently in FRTL-5 cells (165+/-25%, n=6). While TSH increased the uptake of FDG in FRTL-5 cells by sixfold, there was no TSH effect on FET accumulation. FET uptake by TSH-treated FRTL-5 cells was sodium independent and significantly inhibited by BCH (91.4+/-3.0%, n=9), tryptophan (94.8+/-1.6%, n=8) and serine (83.2+/-10.8%, n=12). TSH-starved FRTL-5 cells had a sodium-dependent component with a similar inhibition pattern. Onco DG-1 mainly confirmed the inhibition pattern of FET uptake in FRTL-5 cells, reflecting System-L-mediated FET uptake that was blocked by BCH and serine (72-85%, n=9). ML-1 cells revealed a pronounced sodium-dependent FET uptake that was inhibited by tryptophan (70+/-10%, n=9, P<.05) in the presence and in the absence of sodium, suggesting a contribution of alternative amino acid carriers. CONCLUSION: FET uptake by FRTL-5 cells is not TSH dependent. FET uptake by FRTL-5 cells seems to be mainly mediated by a carrier exhibiting the characteristics of the System L amino acid transporter. FET uptake in thyroid cells and thyroid carcinoma cells was in the same range as that in a glioblastoma cell line. This encourages further research efforts towards the clinical evaluation of FET for the diagnostic workup of well-differentiated thyroid carcinomas.     

Fully automated synthesis of 4-[18F]fluorobenzylamine based on borohydride/NiCl2 reduction

Introduction4-[¹⁸F]Fluorobenzylamine ([¹⁸F]FBA) is an important building block for the synthesis of ¹⁸F-labeled compounds. Synthesis of [¹⁸F]FBA usually involves application of strong reducing agents like LiAlH₄ which is challenging to handle in automated synthesis units (ASUs). Therefore, alternative methods for the preparation of [¹⁸F]FBA compatible with remotely-controlled syntheses in ASUs are needed.Methods¹⁸F]FBA was prepared in a remotely-controlled synthesis unit (GE TRACERlab? FX) based on Ni(II)-mediated borohydride exchange resin (BER) reduction of 4-[¹⁸F]fluorobenzonitrile ([¹⁸F]FBN). [¹⁸F]FBA was used for the synthesis of novel thiol-reactive prosthetic group 4-[¹⁸F]fluorobenzyl)maleimide [¹⁸F]FBM and Hsp90 inhibitor 17-(4-[¹⁸F]fluorobenzylamino)-17-demethoxy-geldanamycin [¹⁸F] GA.Results[¹⁸F]FBA could be prepared in high radiochemical yield greater than 80% (decay-corrected) within 60 min. In a typical experiment, 7.4 GBq of [¹⁸F]FBA could be obtained in high radiochemical purity of greater than 95% starting from 10 GBq of cyclotron-produced n.c.a. [¹⁸F]fluoride. [¹⁸F]FBA was used for the preparation of 4-[¹⁸F]fluorobenzyl)maleimide as a novel prosthetic group for labeling of thiol groups as demonstrated with tripeptide glutathione. [¹⁸F]FBA was also used as building block for the syntheses of small molecules as exemplified by the preparation of Hsp90 inhibitor 17-(4-[¹⁸F]fluorobenzylamino)-17-demethoxy-geldanamycin.ConclusionThe described remotely-controlled synthesis of [¹⁸F]FBA will significantly improve the availability of [¹⁸F]FBA as an important and versatile building block for the development of novel ¹⁸F-labeled compounds containing a fluorobenzylamine moiety.     

N(3)-Substituted thymidine analogues V: synthesis and preliminary PET imaging of N(3)-[(18)F]fluoroethyl thymidine and N(3)-[(18)F]fluoropropyl thymidine

INTRODUCTION: [(18)F]-Labeled analogues of thymidine have demonstrated efficacy for PET imaging of cellular proliferation. We have synthesized two [(18)F]-labeled N(3)-substituted thymidine analogues, N(3)-[(18)F]fluoroethyl thymidine (N(3)-[(18)F]-FET) and N(3)-[(18)F]fluoropropyl thymidine (N(3)-[(18)F]-FPrT), and performed preliminary PET imaging studies in tumor-bearing mice. METHODS: Thymidine was converted to its 3',5'-O-bis-tetrahydropyranyl ether, which was then converted to the N(3)-ethyl and propyl-substituted mesylate precursors. Reactions of these mesylate precursors with n-Bu(4)N[(18)F] or K[(18)F]/kryptofix followed by acid hydrolysis and HPLC purification yielded N(3)-[(18)F]-FET and N(3)-[(18)F]-FPrT, respectively. Subcutaneous (sc) xenografts of H441 human non-small cell lung cancer were established in two groups of mice (each n=6). Micro-PET images of the tumor-bearing animals were acquired after intravenous injection of N(3)-[(18)F]-FET or N(3)-[(18)F]-FPrT (3700 KBq/animal). RESULTS: The radiochemical yields were 2-12% (d.c.) for N(3)-[(18)F]-FET and 30-38% (d.c.) for N(3)-[(18)F]-FPrT. Radiochemical purity was >99% and calculated specific activity was >74 GBq/mumol at the end of synthesis. The accumulation of N(3)-[(18)F]-FET and N(3)-[(18)F]-FPrT in the tumor tissue at 2 h postinjection was 1.81+/-0.78 and 2.95+/-1.14 percent injected dose per gram (%ID/g), respectively; tumor/muscle ratios were 5.57+/-0.82 and 7.69+/-2.18, respectively; the unidirectional influx rates (K(i)) were 0.013 and 0.018 ml/g per minute, respectively. CONCLUSION: Two novel [(18)F]- N(3)-substituted thymidine analogues have been synthesized in good yields, high purity and high specific activity. Preliminary in vivo studies demonstrated the efficacy of these [(18)F]- N(3)-substituted thymidine analogues for PET imaging of tumors.     

Comparison of 3'-deoxy-3'-[(18)F]fluorothymidine PET and O-(2-[(18)F]fluoroethyl)-L-tyrosine PET in patients with newly diagnosed glioma

PurposeThe purpose of this prospective study was to clarify the value of FLT PET and FET PET for the noninvasive grading and prognosis of newly diagnosed gliomas.Materials and methodsTwenty patients with newly diagnosed gliomas were investigated with FLT and FET PET before surgery. FLT and FET uptakes were assessed by the maximum standardized uptake (SUVmax) of tumor, and the ratio to uptake in the normal brain parenchyma (TNR). All tumors were graded by WHO system.ResultsFLT PET detected all 17 high-grade gliomas (HGG) and did not detect all 3 low-grade gliomas (LGG). FET PET detected all 20 HGG and LGG regardless of grading. The average FLT SUVmax in HGG and LGG was 1.51 ± 0.72 and 0.30 ± 0.07, and the average FLT TNR in HGG and LGG was 5.52 ± 3.09 and 1.12 ± 0.14, respectively. The differences of FLT SUVmax and TNR between HGG and LGG were statistically significant (p = 0.0069, p = 0.0070). The average FET SUVmax in HGG and LGG was 2.68 ± 0.86 and 1.36 ± 0.15, and the average FET TNR in HGG and LGG was 2.31 ± 0.73 and 1.27 ± 0.12, respectively. The differences of FET SUVmax and TNR between HGG and LGG were statistically significant (p = 0.0129, p = 0.0095).ConclusionsFET PET has higher sensitivity in detection of gliomas rather than FLT PET, but it seems that FLT PET is better than FET PET for noninvasive grading and predicting prognosis of newly diagnosed gliomas, considering high contrast of FLT and overlap of FET uptakes between HGG and LGG.     

Electrochemical nucleophilic synthesis of di-tert-butyl-(4-[18F]fluoro-1,2-phenylene)-dicarbonate

An electrochemical method with the ability to conduct ¹⁸F-fluorination of aromatic molecules through direct nucleophilic fluorination of cationic intermediates is presented in this paper. The reaction was performed on a remote-controlled automatic platform. Nucleophilic electrochemical fluorination of tert-butyloxycarbonyl (Boc) protected catechol, an intermediate model molecule for the positron emission tomography (PET) probe (3,4-dihydroxy-6-[¹⁸F]fluoro-l-phenylalanine), was performed. Fluorination was achieved under potentiostatic anodic oxidation in acetonitrile containing Et₃N·3HF and other supporting electrolytes. Radiofluorination efficiency was influenced by a number of variables, including the concentration of the precursor, concentration of Et₃N·3HF, type of supporting electrolyte, temperature and time, as well as applied potentials. Radio-fluorination efficiency of 10.4±0.6% (n=4) and specific activity of up to 43 GBq/mmol was obtained after 1 h electrolysis of 0.1 M of 4-tert-butyl-diboc-catechol in the acetonitrile solution of Et₃N·3HF (0.033 M) and NBu₄PF₆ (0.05 M). Density functional theory (DFT) was employed to explain the tert-butyl functional group facilitation of electrochemical oxidation and subsequent fluorination.     

An automated synthesis of N,N-dimethyl-2-(2-amino-4-[18F]fluorophenylthio)benzylamine (4-[18F]-ADAM) for imaging serotonin transporters.

N,N-dimethyl-2-(2-amino-4-[(18)F]fluorophenylthio)benzylamine (4-[(18)F]-ADAM, 3) is a potent serotonin transporter (SERT) imaging agent. In order to fulfill the demand of pre-clinical studies, we have developed an automated synthesis unit to synthesize this radioligand. The 4-[(18)F]-ADAM was synthesized using TracerLab FN and FE modules and a modified module control program (TracerLab-Fx). The synthesis sequences were similar to that of the manual synthesis, i.e. nucleophilic fluorination of N,N-dimethyl-2-(2,4-dinitrophenylthio)benzylamine (1) with K[(18)F]/K(2.2.2) followed by reduction with NaBH(4)/Cu(OAc)(2) and purifications with high-performance liquid chromatography (HPLC) and solid phase extraction. The radiochemical yield of 3 was 1.5+/-0.3% (n=13, EOS). The synthesis time was 120 min and the specific activity was 1.75+/-0.77 Ci/micromol (n=13, EOS). The 4-[(18)F]-ADAM synthesized by this module was stable over 4h at room temperature and is suitable for imaging SERT in humans.     

Module-assisted synthesis of the bifunctional labelling agent N-succinimidyl 4-[(18)F]fluorobenzoate ([(18)F]SFB).

The three-step radiosynthesis of N-succinimidyl 4-[(18)F]fluorobenzoate ([(18)F]SFB) was adapted to a remotely controlled synthesis module. After optimization of the reaction conditions, the final [(18)F]SFB was obtained in decay-corrected radiochemical yields of 34-38% (related to [(18)F]fluoride; n=12) within a synthesis time of 68 min. The radiochemical purity was in the range of 93-96%.     

Whole-body distribution and dosimetry of O-(2-[18F]fluoroethyl)-L-tyrosine

The whole-body distribution of O-(2-[(18)F]fluoroethyl)- l-tyrosine (FET) was studied in seven patients with brain tumours by positron emission tomography (PET). Based on the IMEDOSE and MIRDOSE procedures, radiation absorbed doses were estimated from whole-body PET scans acquired approximately 70 and 200 min after i.v. injection of 400 MBq FET. After injection of FET, the peak of radioactivity in the blood was observed after 1.5 min, and a plateau of nearly constant radioactivity was reached at 20 min. The whole-body distribution of FET showed the highest activities in the urinary tract. All other organs exhibited only moderate FET uptake (SUV 相似文献   

Fully automated synthesis procedure of 4-[18F]fluorobenzaldehyde by commercial synthesizer: Amino-oxi peptide labelling prosthetic group

Automatic synthesis of 4-[18F]fluorobenzaldehyde has been developed by a commercially available TRACERlab™ FX_F−N synthesis module to be used as prosthetic group for amino-oxy functionalized peptide labelling in clinical routine application. In addition a handmade purification device (HPD) has been setup to perform automatic cartridge purification as well as to back-up the reactor where one-pot synthesis is not applicable. Cartridges for solid phase extraction such as C18, C8, phenyl has been tested to best perform purification as well as activity recovery. Radiochemical yield (RCY) at end of synthesis (EOS) was in average 67% after about 45 min (90% decay corrected at EOB). The RCY of the entire procedure was 54% with a radiochemical purity above 99%.     

Computer-aided synthesis (CAS) of no-carrier-added 2-[18F]Fluoro-2-deoxy-d-glucose: an efficient automated system for the aminopolyether-supported nucleophilic fluorination

A microcomputer-controlled automated synthesis of 2-[¹⁸F]fluoro-2-deoxy-d-glucose (2-[¹⁸F]FDG) is described. The modular setup of the apparatus permits reliable and facile routine synthesis of ¹⁸F-labelled radiopharmaceuticals based on aminopolyether (APE)-mediated nucleophilic fluorination. The uncorrected radiochemical yield is in the range of 40–55%. Batches up to 600 mCi of 2-[¹⁸F]FDG are prepared from 1.1 Ci [¹⁸F]fluoride in <1 h. The apparatus can also be used for other APE-supported nucleophilic fluorination procedures.     

O-(2-[18F]fluoroethyl)-L-tyrosine: uptake mechanisms and clinical applications

O-(2-[18F]fluoroethyl)-L-tyrosine (FET) is a promising tracer for PET that has demonstrated convincing results especially in the diagnostics of brain tumors. In contrast to other radiolabeled amino acids, it can be produced with high efficiency and distributed in a satellite concept like the widely used 2-[18F]fluoro-2-deoxy-D-glucose. Although FET is not incorporated into proteins, it shows high uptake in cerebral gliomas and in extracranial squamous cell carcinomas owing to increased transport. The tracer exhibits high in vivo stability, low uptake in inflammatory tissue and suitable uptake kinetics for clinical imaging, which indicates that it may become a new standard tracer for PET. In this article, the present knowledge on the uptake mechanisms and the clinical applications of FET are reviewed and the clinical perspectives are discussed.     

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.     

Fully automated preparation of n.c.a. 4-[18F]fluorobenzoic acid and N-succinimidyl 4-[18F]fluorobenzoate using a Siemens/CTI chemistry process control unit (CPCU).

The widely used bifunctional labeling reagent 4-[18F]fluorobenzoic acid ([18F]FBA) and its activated form N-succinimidyl 4-[18F]fluorobenzoate ([18F]SFB) were prepared using a modified Siemens/CTI chemistry process control unit (CPCU) double vessel [18F]FDG module. The products were obtained with a radiochemical yield greater than 99% with decay corrected yields of 77+/-5% (n=4) for [18F]FBA and 46+/-5% (n=4) for [18F]SFB. The presented synthetic procedure is highly reproducible and fully automated.     

Automatic synthesis of 16 alpha-[(18)F]fluoro-17beta-estradiol using a cassette-type [(18)F]fluorodeoxyglucose synthesizer

16 alpha-[(18)F]fluoro-17beta-estradiol ([(18)F]FES) is a radiotracer for imaging estrogen receptors by positron emission tomography. We developed a clinically applicable automatic preparation system for [(18)F]FES by modifying a cassette-type [(18)F]fluorodeoxyglucose synthesizer. Two milligrams of 3-O-methoxymethyl-16,17-O-sulfuryl-16-epiestriol in acetonitrile was heated at 105 degrees C for 10 min with dried [(18)F]fluoride. The resultant solution was evaporated and hydrolyzed with 0.2 N HCl in 90% acetonitrile/water at 95 degrees C for 10 min under pressurized condition. The neutralization was carried out with 2.8% NaHCO(3), and then the high-performance liquid chromatography (HPLC) purification was performed. The desired radioactive fraction was collected and the solvent was replaced by 10 ml of saline, and then passed through a 0.22-microm filter into a pyrogen-free vial as the final product. The HPLC purification data demonstrated that [(18)F]FES was synthesized with a yield of 76.4+/-1.9% (n=5). The yield as the final product for clinical use was 42.4+/-3.2% (n=5, decay corrected). The total preparation time was 88.2+/-6.4 min, including the HPLC purification and the solvent replacement process. The radiochemical purity of the final product was >99%, and the specific activity was more than 111 GBq/micromol. The final product was stable for more than 6 h in saline containing sodium ascorbate. This new preparation system enables us to produce [(18)F]FES safe for clinical use with high and reproducible yield.     

Synthesis and biological evaluation of N-(2-[18F]Fluoropropionyl)-L-methionine for tumor imaging

IntroductionN-position radiolabeled amino acids, such as N-(2-[¹⁸F]fluoropropionyl)-L-methionine ([¹⁸F]FPMET) as a derivative of L-methionine (MET), can potentially serve as a PET tracer for tumor imaging. In the current study, radiosynthesis and biological evaluation of [¹⁸F]FPMET as a new PET tumor agent are performed.Methods[¹⁸F]FPMET was synthesized by reacting 4-nitrophenyl 2-[¹⁸F]fluoropropionate ([¹⁸F]NFP) with MET. In vitro competitive inhibition and protein incorporation experiments were performed with Hepa1-6 hepatoma cell lines. The biodistribution of [¹⁸F]FPMET was determined in S180 fibrosarcoma-bearing mice. PET/CT studies of [¹⁸F]FPMET were conducted in S180 fibrosarcoma-bearing mice, A549 lung adenocarcinoma-bearing nude mice, and PC-3 prostate cancer-bearing nude mice.Results[¹⁸F]FPMET was synthesized in 72% ± 4% uncorrected radiochemical yield (n = 10) from [¹⁸F]NFP. In vitro experiments showed that [¹⁸F]FPMET was primarily transported through Na⁺-dependent system A, system ASC, and system B^0,+, and was not incorporated into protein. Biodistribution and PET/CT imaging studies indicated that [¹⁸F]FPMET could delineate S180 fibrosarcoma, A549 lung adenocarcinoma, and PC-3 prostate cancer.ConclusionAn efficient synthesis of N-position [¹⁸F]labeled amino acids with a classic [¹⁸F]NFP prosthetic group is developed. The results support that [¹⁸F]FPMET seems to be a potential tracer for tumor imaging with PET.