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.

Accuracy of 18F-FDOPA Positron Emission Tomography and 18F-FET Positron Emission Tomography for Differentiating Radiation Necrosis from Brain Tumor Recurrence.

BACKGROUND: Distinguishing radiation necrosis from brain tumor recurrence remains challenging. We performed a meta-analysis to assess the diagnostic accuracy of 2 different amino acid tracers used in positron emission tomography/computed tomography scans: 18F-FDOPA (6-[18F]-fluoro-L-3,4-dihydroxyphenylalanine) and 18F-FET (O-(2-18F-fluoroethyl)-L-tyrosine). METHODS: We searched for studies in 3 databases: PubMed, Embase, and Chinese Biomedical databases. The data were extracted from eligible studies and then processed with heterogeneity test, threshold effect test, and calculations of sensitivity, specificity, and area under the summary receiver operating characteristic curve. Meta-regression and subgroup analyses were performed to explore the source of heterogeneity. RESULTS: A total of 48 studies (18F-FDOPA, n = 21; 18F-FET, n = 27) were included. Quantitative synthesis determined pooled weight values in the 18F-FDOPA and 18F-FET groups: sensitivity, 0.85 versus 0.82; specificity, 0.77 versus 0.80; diagnostic odds ratio, 21.7 versus 23.03; area under the curve (AUC) values, 0.8771 versus 0.8976 (P = 0.46). Moreover, the type of tumor was identified as the possible source of the significant heterogeneity (I2 = 52%; P = 0.003) found in the 18F-FDOPA group. In meta-regression and subgroup analyses, 18F-FDOPA showed better diagnostic accuracy in patients with glioma compared with patients with brain metastases (AUC values, 0.9691 vs. 0.837; P < 0.01). 18F-FDOPA also showed a significant advantage in the diagnosis of glioma recurrence compared with 18F-FET (AUC values, 0.9691 vs. 0.9124; P = 0.015). CONCLUSIONS: Both 18F-FDOPA and 18F-FET exhibit moderate overall accuracy in diagnosing brain tumor recurrence from radiation necrosis. However, 18F-FDOPA is more adept at diagnosing glioma recurrence compared with brain metastases, and it is more effective than 18F-FET in diagnosing glioma recurrence.

Radiosynthesis and modified quality control of O-(2-[18F]fluoroethyl)-L-tyrosine ([18F]FET) for brain tumor imaging.

O-(2-[18F]fluoroethyl)-L-tyrosine ([18F]FET) is the most promising radio-labeled amino acid tracer for brain tumor imaging due to the limitation of 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) and L-methyl-[11C]methionine (11C-MET). However, it has some limitations in radiosynthesis and related quality control that make it less frequently used in many PET centers, in this study, we report a new modification of [18F]FET production using a commercially available fully automated GRP SCINTOMICS module overcoming some of the existing limitations along with a suggestion of a simplified quality control procedure with special focus placed on enantiomeric and radiochemical purity. ([18F]FET) was produced in high radiochemical and enantiomeric purity more than 99% and non-decay corrected yield 25±5% in about 55min.

Integration of Miniaturized Solid Phase Extraction and LC-MS/MS Detection of 3-Nitrotyrosine in Human Urine for Clinical Applications.

Free 3-nitrotyrosine (3-NT) has been extensively used as a possible biomarker for oxidative stress. Increased levels of 3-NT have been reported in a wide variety of pathological conditions. However, existing methods lack the sufficient sensitivity and/or specificity necessary to measure the low endogenous level of 3-NT reliably and are too cumbersome for clinical applications. Hence, analytical improvement is urgently needed to accurately quantify the levels of 3-NT and verify the role of 3-NT in pathological conditions. This protocol presents the development of a novel liquid chromatography tandem mass spectrometry (LC-MS/MS) detection combined with a miniaturized solid phase extraction (SPE) for the rapid and accurate measurement of 3-NT in human urine as a non-invasive biomarker for oxidative stress. SPE using a 96-well plate markedly simplified the process by combining sample cleanup and analyte enrichment without tedious derivatization and evaporation steps, reducing solvent consumption, waste disposal, risk of contamination and overall processing time. The employment of 25 mM ammonium acetate (NH4OAc) at pH 9 as the SPE elution solution substantially enhanced the selectivity. Mass spectrometry signal response was improved through adjustment of the multiple reaction monitoring (MRM) transitions. Use of 0.01% HCOOH as additive on a pentafluorophenyl (PFP) column (150 mm x 2.1 mm, 3 µm) improved signal response another 2.5-fold and shortened the overall run time to 7 min. A lower limit of quantitation (LLOQ) of 10 pg/mL (0.044 nM) was achieved, representing a significant sensitivity improvement over the reported assays. This simplified, rapid, selective and sensitive method allows two plates of urine samples (n = 192) to be processed in a 24 h time-period. Considering the markedly improved analytical performance, and non-invasive and inexpensive urine sampling, the proposed assay is beneficial for pre-clinical and clinical studies.

Comments in a discussion: differential rates of D- and L-tyrosine crystallization.

We earlier reported that we had observed quantifiable differences in crystallization rates of D and L tyrosine. It has been suggested that these results were due to the presence of impurities. Here we argue that it is premature to conclude that impurities entirely explain the results. More generally, there is an accumulating weight of evidence that D and L enantiomers display unexpected differences in their physical properties and behavior. These should be taken into account as we attempt to understand the origin of biochirality.

Parity violating energetic difference and enantiomorphous crystalsp-caveats; reinvestigation of tyrosine crystallization.

The present article challenges reports claiming to have demonstrated the Parity Violating Energetic Difference (PVED) between enantiomorphous D- and L-crystals. Apart from PVED, the presence of minute quantities and differing profiles of impurities incorporated during their different history of preparation will affect the physical properties of D- and L-crystals. These impurities are anticipated to play a much greater role in affecting crystallization behavior than PVED. The effect of impurities on the growth and dissolution of enantiomorphous crystals is illustrated with some representative examples. Shinitzky et al. (2002) reported recently dramatic differences in the growth and dissolution properties of the D- and L-crystals of tyrosine. We have repeated these experiments using commercial samples from different sources and employing a validated enantioselective gas chromatographic technique. We attribute Shinitzky's findings either to the use of inappropriate analytical techniques for the determination of enantiomeric composition and/or to the presence of unidentified contaminants in the commercial tyrosine samples. Related caveats hold also for the recently published claims by Shinitzky (2006) and Scolnik et al. (2006) to have observed experimentally PVED between enantiomeric helices of poly-glutamic acid composed of 24 repeating units.

The TETAMI trial: the safety and efficacy of subcutaneous enoxaparin versus intravenous unfractionated heparin and of tirofiban versus placebo in the treatment of acute myocardial infarction for patients not thrombolyzed: methods and design.

Patients with acute myocardial infarction (AMI) who do not receive early reperfusion therapy are at high risk of reinfarction or death, and the efficacy and safety of antithrombotic therapy in this group of patients has not been evaluated. Enoxaparin is a low-molecular-weight heparin (LMWH) that has previously been shown to reduce the incidence of ischemic events in patients with unstable angina or non-Q-wave MI. The principal aims of the TETAMI study are to investigate the efficacy and safety of treatment with enoxaparin or tirofiban (a glycoprotein IIb/IIIa receptor antagonist) alone or in combination for 2 to 8 days in patients with AMI who are not eligible for early reperfusion therapy. In this 2 by 2 factorial design study approximately 900 patients will be randomly assigned, in a blinded manner, to one of four treatments: enoxaparin alone, enoxaparin plus tirofiban, unfractionated heparin (UFH), or UFH plus tirofiban, with appropriate matched placebos. The primary end point is the composite of death, recurrent AMI, and recurrent angina, analyzed at 30 days after AMI. The design and methods of the TETAMI study are described in this article.

Gas chromatographic-tandem mass spectrometric quantification of free 3-nitrotyrosine in human plasma at the basal state.

A fully validated gas chromatographic-tandem mass spectrometric (GC-tandem MS) method for the accurate and precise quantification of free 3-nitrotyrosine in human plasma at the basal state is described. In the plasma of 11 healthy humans a mean concentration of 2.8 nM (range 1.4-4.2 nM) for free 3-nitrotyrosine was determined by this method. This is the lowest concentration reported for free 3-nitrotyrosine in plasma of healthy humans. The presence of endogenous free 3-nitrotyrosine in human plasma was unequivocally shown by generating a daughter mass spectrum. Various precautions had to be taken to avoid artifactual formation of 3-nitrotyrosine from nitrate during sample treatment. Endogenous plasma 3-nitrotyrosine and 3-nitro-l-[(2)H(3)]tyrosine added for use as internal standard were isolated by high-performance liquid chromatographic (HPLC) analysis of 200-microl aliquots of plasma ultrafiltrate samples (20 kDa cut-off), extracted from a single HPLC fraction by solid-phase extraction, derivatized to their n-propyl ester-pentafluoropropionyl amide-trimethylsilyl ether derivatives, and quantified by GC-tandem MS. Overall recovery was determined as 50 +/- 5% using 3-nitro-l-[(14)C(9)]tyrosine. The limit of detection of the method was 4 amol of 3-nitrotyrosine, while the limit of quantitation was 125 pM using 3-nitro-l-[(14)C(9)]tyrosine. 3-Nitrotyrosine added to human plasma at 1 nM was quantitated with an accuracy of > or = 80% and a precision of > or = 94%. The method should be useful to investigate the utility of plasma free 3-nitrotyrosine as an indicator of nitric oxide ((.)NO)-associated oxidative stress in vivo in humans.