Decay-corrected Yield Research Articles

Synthesis, [18F] radiolabeling, and evaluation of poly (ADP-ribose) polymerase-1 (PARP-1) inhibitors for in vivo imaging of PARP-1 using positron emission tomography

Imaging of poly (ADP-ribose) polymerase-1 (PARP-1) expression in vivo is a potentially powerful tool for developing PARP-1 inhibitors for drug discovery and patient care. We have synthesized several derivatives of benzimidazole carboxamide as PARP-1 inhibitors, which can be 18F-labeled easily for positron emission tomographic (PET) imaging. Of the compounds synthesized, 12 had the highest inhibition potency for PARP-1 (IC50=6.3nM). [18F]12 was synthesized under conventional conditions in high specific activity with 40–50% decay-corrected yield. MicroPET studies using [18F]12 in MDA-MB-436 tumor-bearing mice demonstrated accumulation of [18F]12 in the tumor that was blocked by olaparib, suggesting that the uptake of [18F]12 in the tumor is specific to PARP-1 expression.

Cationic eluate pretreatment for automated synthesis of [68Ga]CPCR4.2

Fostered by the clinical success of sst-ligands, the development and evaluation of (68)Ga-labeled peptides have become a very active field in radiopharmaceutical chemistry. Consequently, various new peptide tracers have been developed, e.g. [(68)Ga]CPCR4.2 for in vivo imaging of solid and haematological tumors or [(68)Ga]TRAP(RGD)₃ for imaging of α(v)β₃ integrin expression. As a consequence of different matrices (TiO₂, SnO₂, polymers) exploited in commercial (68)Ge/(68)Ga-generators, HCl of different concentrations (0.05...1.0 M) is used to obtain (68)Ga as starting material for automated syntheses. We have developed a purification method which reduces the eluate volume and adjusts the HCl concentration. The method may potentially allow standardization of the eluate composition of different commercial generators prior to labeling. Recently, a cationic purification process has been reported which allows the pre-fixation of (68)Ga on a Varian SCX cation exchange cartridge and subsequent elution of (68)Ga with acidified NaCl solutions. As part of the development of ready-to-use cassettes for the automated production of (68)Ga-CPCR4.2 using a SCINTOMICS GRP module and an iThemba Labs generator that is eluted with 0.6...1.0 M HCl, we tested and compared the (68)Ga-trapping efficiency of various commercial available cation exchange cartridges, the efficiency of subsequent (68)Ga-elution from these cartridges by means of various protocols and the influence of these variations on the labeling efficiency of [(68)Ga]CPCR4.2, [(68)Ga]TRAP(RGD)₃ and [(68)Ga]DOTATATE/[(68)Ga]DOTANOC. Finally, we transferred the optimized method to the automated, cassette based synthesis of [(68)Ga]CPCR4.2 and the aforementioned peptides. From seven tested cation exchange cartridges, Chromafix PS-H(+) gave the best extraction results (>95%). Moreover, we observed that acidified solutions of 5 M NaCl or 2.5 M CaCl₂ can be used for efficient cartridge elution. Using a disposable cGMP-compliant cassette system, we obtained [(68)Ga]CPCR4.2 in 80% decay-corrected yield and >99% purity. These data were confirmed by the production of [(68)Ga]DOTATATE, [(68)Ga]DOTANOC and [(68)Ga]TRAP(RGD)3 on the otherwise identical cassette system.

2-[18F]Fluoroethanol and 3-[18F]fluoropropanol: facile preparation, biodistribution in mice, and their application as nucleophiles in the synthesis of [18F]fluoroalkyl aryl ester and ether PET tracers

2-[(18)F]Fluoroethoxy and 3-[(18)F]fluoropropoxy groups are common moieties in the structures of radiotracers used with positron emission tomography. The objectives of this study were (1) to develop an efficient one-step method for the preparation of 2-[(18)F]fluoroethanol (2-[(18)F]FEtOH) and 3-[(18)F]fluoropropanol (3-[(18)F]FPrOH); (2) to demonstrate the feasibility of using 2-[(18)F]FEtOH as a nucleophile for the synthesis of 2-[(18)F]fluoroethyl aryl esters and ethers; and (3) to determine the biodistribution profiles of 2-[(18)F]FEtOH and 3-[(18)F]FPrOH in mice. 2-[(18)F]FEtOH and 3-[(18)F]FPrOH were prepared by reacting n-Bu4N[(18)F]F with ethylene carbonate and 1,3-dioxan-2-one, respectively, in diethylene glycol at 165°C and purified by distillation. 2-[(18)F]fluoroethyl 4-fluorobenzoate and 1-(2-[(18)F]fluoroethoxy)-4-nitrobenzene were prepared by coupling 2-[(18)F]FEtOH with 4-fluorobenzoyl chloride and 1-fluoro-4-nitrobenzene, respectively. Biodistribution and PET/CT imaging studies of 2-[(18)F]FEtOH and 3-[(18)F]FPrOH were performed in normal female Balb/C mice. The preparation of 2-[(18)F]FEtOH and 3-[(18)F]FPrOH took 60 min, and their decay-corrected yields were 88.6 ± 2.0% (n = 9) and 65.6 ± 10.2% (n = 5), respectively. The decay-corrected yields for the preparation of 2-[(18)F]fluoroethyl 4-fluorobenzoate and 1-(2-[(18)F]fluoroethoxy)-4-nitrobenzene were 36.1 ± 5.4% (n = 3) and 27.7 ± 10.7% (n = 3), respectively. Imaging/biodistribution studies in mice using 2-[(18)F]FEtOH showed high initial radioactivity accumulation in all major organs followed by very slow clearance. On the contrary, by using 3-[(18)F]FPrOH, radioactivity accumulated in all major organs was cleared rapidly, but massive in vivo defluorination (31.3 ± 9.57%ID/g in bone at 1h post-injection) was observed. Using 2-[(18)F]FEtOH/3-[(18)F]FPrOH as a nucleophile is a competitive new strategy for the synthesis of 2-[(18)F]fluoroethyl/3-[(18)F]fluoropropyl aryl esters and ethers. Our biodistribution data emphasize the importance of in vivo stability of PET tracers containing a 2-[(18)F]fluoroethyl or 3-[(18)F]fluoropropyl group due to high background and high bone uptake resulting from 2-[(18)F]FEtOH and 3-[(18)F]FPrOH, respectively. This is especially important for their aryl ester derivatives which are prone to in vivo hydrolysis.

First Experience of 18F-Alfatide in Lung Cancer Patients Using a New Lyophilized Kit for Rapid Radiofluorination

(18)F-FPPRGD2, which was approved for clinical study recently, has favorable properties for integrin targeting and showed potential for antiangiogenic therapy and early response monitoring. However, the time-consuming multiple-step synthesis may limit its widespread applications in the clinic. In this study, we developed a simple lyophilized kit for labeling PRGD2 peptide ((18)F-AlF-NOTA-PRGD2, denoted as (18)F-alfatide) using a fluoride-aluminum complex that significantly simplified the labeling procedure. Nine patients with a primary diagnosis of lung cancer were examined by both static and dynamic PET imaging with (18)F-alfatide, and 1 tuberculosis patient was investigated using both (18)F-alfatide and (18)F-FDG imaging. Standardized uptake values were measured in tumors and other main organs at 30 min and 1 h after injection. Kinetic parameters were calculated by Logan graphical analysis. Immunohistochemistry and staining intensity quantification were performed to confirm the expression of integrin α(v)β(3). Under the optimal conditions, the whole radiosynthesis including purification was accomplished within 20 min with a decay-corrected yield of 42.1% ± 2.0% and radiochemical purity of more than 95%. (18)F-alfatide PET imaging identified all tumors, with mean standardized uptake values of 2.90 ± 0.10. Tumor-to-muscle and tumor-to-blood ratios were 5.87 ± 2.02 and 2.71 ± 0.92, respectively. (18)F-alfatide can be produced with excellent radiochemical yield and purity via a simple, 1-step, lyophilized kit. PET scanning with (18)F-alfatide allows specific imaging of αvβ3 expression with good contrast in lung cancer patients. This technique might be used for the assessment of angiogenesis and for planning and response evaluation of cancer therapies that would affect angiogenesis status and integrin expression levels.

Reusable electrochemical cell for rapid separation of [18F]fluoride from [18O]water for flow-through synthesis of 18F-labeled tracers

A brass–platinum electrochemical micro-flow cell was developed to extract [18F]fluoride from an aqueous solution and release it into an organic-based solution, suitable for subsequent radio-synthesis, in a fast and reliable manner. This cell does not suffer electrode erosion and is thus reusable while operating faster by enabling increased voltages. By optimizing temperature, trapping and release potentials, flow rates, and electrode materials, an overall [18F]fluoride trapping and release efficiency of 84±5% (n=7) was achieved. X-ray photoelectron spectroscopy (XPS) was used to analyze electrode surfaces of various metal–metal systems and the findings were correlated with the performance of the electrochemical cell. To demonstrate the reactivity of the released [18F]fluoride, the cell was coupled to a flow-through reactor and automated synthesis of [18F]FDG with a repeatable decay-corrected yield of 56±4% (n=4) was completed in <15min. A multi-human dose of 5.92GBq [18F]FDG was also demonstrated.

Synthesis and Biological Evaluation of O-[3-18F-fluoropropyl]-α-methyl Tyrosine in Mesothelioma-Bearing Rodents

Radiolabeled tyrosine analogs enter cancer cells via upregulated amino acid transporter system and have been shown to be superior to 18F-fluoro-2-deoxy-D-glucose (18F-FDG) in differential diagnosis in cancers. In this study, we synthesized O-[3-19F-fluoropropyl]-α-methyl tyrosine (19F-FPAMT) and used manual and automated methods to synthesize O-[3-18F-fluoropropyl]-α-methyl tyrosine (18F-FPAMT) in three steps: nucleophilic substitution, deprotection of butoxycarbonyl, and deesterification. Manual and automated synthesis methods produced 18F-FPAMT with a radiochemical purity >96%. The decay-corrected yield of 18F-FPAMT by manual synthesis was 34% at end-of-synthesis (88 min). The decay-corrected yield of 18F-FPAMT by automated synthesis was 15% at end-of-synthesis (110 min). 18F-FDG and 18F-FPAMT were used for in vitro and in vivo studies to evaluate the feasibility of 18F-FPAMT for imaging rat mesothelioma (IL-45). In vitro studies comparing 18F-FPAMT with 18F-FDG revealed that 18F-FDG had higher uptake than that of 18F-FPAMT, and the uptake ratio of 18F-FPAMT reached the plateau after being incubated for 60 min. Biodistribution studies revealed that the accumulation of 18F-FPAMT in the heart, lungs, thyroid, spleen, and brain was significantly lower than that of 18F-FDG. There was poor bone uptake in 18F-FPAMT for up to 3 hrs suggesting its in vivo stability. The imaging studies showed good visualization of tumors with 18F-FPAMT. Together, these results suggest that 18F-FPAMT can be successfully synthesized and has great potential in mesothelioma imaging.

Investigations into the synthesis, radiofluorination and conjugation of a new [18F]fluorocyclobutyl prosthetic group and its in vitro stability using a tyrosine model system

The [18F]fluorocyclobutyl group has the potential to be a metabolically stable prosthetic group for PET tracers. The synthesis of the radiolabeling precursor cis-cyclobutane-1,3-diyl bis(toluene-4-sulfonate) 8 was obtained from epibromohydrin in 7 steps (2% overall yield). The radiolabeling of this precursor 8 and its conjugation to l-tyrosine as a model system was successfully achieved to give the new non-natural amino acid 3-[18F]fluorocyclobutyl-l-tyrosine (L-3-[18F]FCBT) [18F]17 in 8% decay-corrected yield from the non-carrier-added [18F]fluoride. L-3-[18F]FCBT was investigated in vitro in different cancer cell lines to determine the uptake and stability. The tracer [18F]17 showed a time dependent uptake into different tumor cell lines (A549, NCI-H460, DU145) with the best uptake of 5.8% injected dose per 5×105 cells after 30min in human lung carcinoma cells A549. The stability of L-3-[18F]FCBT in human and rat plasma and the stability of the non-radioactive L-3-FCBT in rat hepatocytes were both found to be excellent. These results show that the non-natural amino acid L-3-[18F]FCBT is a promising metabolically stable radiotracer for positron emission tomography.

Synthesis and preliminary evaluation of 99mTc-spermine as a tumor imaging agent

Polyamines are essential for the growth and survival of all cells with biosynthesis and transportation of polyamines being very active in tumors. With the aim of developing a new tumor imaging agent, the endogenous polyamine, spermine was labeled with 99mTc, and its characters were also evaluated via in vitro and in vivo studies. 99mTc-labeled spermine probe (99mTc-spermine) was synthesized by the direct pretinning procedure and the labeling procedure was optimized with regard to the pH, reaction time, amounts of spermine and SnCl2. The stability of the 99mTc-spermine and its capacity to accumulate into 4T1 tumor cells were also evaluated. Biodistribution of 99mTc-spermine was studied in 4T1 tumor-bearing mice. In the optimal conditions, the whole radiosynthesis was accomplished within 10 min with a decay-corrected yield of 96.5 ± 1.3 % and radiochemical purity of >95 %.99mTc-spermine was stable at both 37 and 4 °C for at least 6 h. In vitro tests revealed that the ability of 99mTc-spermine to penetrate in 4T1 tumour cells and an excess of spermine blocked the accumulation of the compound in the models. Biodistribution studies showed a high tumor uptake peaked at 30 min post-injection with 1.82 ± 0.19 % ID%/g. The tumor to muscle uptake ratios of the probe were 3.60 ± 0.51, 4.48 ± 0.29, 4.82 ± 0.18, 5.64 ± 0.10, respectively at 30 min, 1, 2 and 4 h postinjection. Block studies indicated that 99mTc-spermine had specific binding of tumor via polyamine transport systems. 99mTc-spermine is a promising radiopharmaceutical in tumor imaging. Further studies are required to determine the usability of 99mTc–spermine for diagnosis purposes.

Synthesis and preclinical evaluation of [11C]D617, a metabolite of (R)-[11C]verapamil

(R)-[(11)C]verapamil is widely used as a positron emission tomography (PET) tracer to evaluate P-glycoprotein (P-gp) functionality at the blood-brain barrier in man. A disadvantage of (R)-[(11)C]verapamil is the fact that its main metabolite, [(11)C]D617, also enters the brain. For quantitative analysis of (R)-[(11)C]verapamil data, it has been assumed that the cerebral kinetics of (R)-[(11)C]verapamil and [(11)C]D617 are the same. The aim of the present study was to investigate whether the cerebral kinetics of (R)-[(11)C]verapamil and [(11)C]D617 are indeed similar and, if so, whether [(11)C]D617 itself could serve as an alternative PET tracer for P-gp. [(11)C]D617 was synthesized and its ex vivo biodistribution was investigated in male rats at four time points following intravenous administration of [(11)C]D617 (50 MBq) without (n=4) or with (n=4) pretreatment with the P-gp inhibitor tariquidar (15 mg·kg(-1), intraperitoneally). Brain distribution was further assessed using consecutive PET scans (n=8) before and after pretreatment with tariquidar (15mg·kg(-1), intravenously), as well as metabolite analysis (n=4). The precursor for the radiosynthesis of [(11)C]D617, 5-amino-2-(3,4-dimethoxy-phenyl)-2-isopropyl-pentanitrile (desmethyl D617), was synthesized in 41% overall yield. [(11)C]D617 was synthesized in 58%-77% decay-corrected yield with a radiochemical purity of ≥99%. The homogeneously distributed cerebral volume of distribution (V(T)) of [(11)C]D617 was 1.1, and this increased 2.4-fold after tariquidar pretreatment. V(T) of [(11)C]D617 was comparable to that of (R)-[(11)C]verapamil, but its increase after tariquidar pretreatment was substantially lower. Hence, (R)-[(11)C]verapamil and [(11)C]D617 do not show similar brain kinetics after inhibition of P-gp with tariquidar.

11C]phenytoin revisited: synthesis by [11C]CO carbonylation and first evaluation as a P-gp tracer in rats.

BackgroundAt present, several positron emission tomography (PET) tracers are in use for imaging P-glycoprotein (P-gp) function in man. At baseline, substrate tracers such as R-[11C]verapamil display low brain concentrations with a distribution volume of around 1. [11C]phenytoin is supposed to be a weaker P-gp substrate, which may lead to higher brain concentrations at baseline. This could facilitate assessment of P-gp function when P-gp is upregulated. The purpose of this study was to synthesize [11C]phenytoin and to characterize its properties as a P-gp tracer.Methods[11C]CO was used to synthesize [11C]phenytoin by rhodium-mediated carbonylation. Metabolism and, using PET, brain pharmacokinetics of [11C]phenytoin were studied in rats. Effects of P-gp function on [11C]phenytoin uptake were assessed using predosing with tariquidar.Results[11C]phenytoin was synthesized via [11C]CO in an overall decay-corrected yield of 22 ± 4%. At 45 min after administration, 19% and 83% of radioactivity represented intact [11C]phenytoin in the plasma and brain, respectively. Compared with baseline, tariquidar predosing resulted in a 45% increase in the cerebral distribution volume of [11C]phenytoin.ConclusionsUsing [11C]CO, the radiosynthesis of [11C]phenytoin could be improved. [11C]phenytoin appeared to be a rather weak P-gp substrate.

Labeling approaches for the GE11 peptide, an epidermal growth factor receptor biomarker

The epidermal growth factor receptor (EGFR) is involved in the proliferation and differentiation of normal and malignant cells and is a major therapeutic target for a variety of human cancers. The peptide GE11 was reported to bind efficiently to the EGFR. Labeling GE11 with radionuclides may aid in the quantification of EGFR expression in tumors via noninvasive imaging. To this end, a GGGK linker was attached to the peptide (GE11′), which was conjugated with prosthetic‐labeled groups such as [18F]N‐succinimidyl 4‐fluorobenzoate ([18F]SFB), [18F](2‐{2‐[2‐(2‐fluoro‐ethoxy)‐ethoxy]‐ethoxy}‐ethoxy)‐propyne ([18F]F‐PEG4‐propyne), [124I]N‐succinimidyl 4‐iodobenzoate, and the NOTA‐Bn‐NCS chelator for 111In labeling. All labeled analogs were successfully prepared with radiochemical purity &gt;95% and were identified by HPLC based on their non‐labeled standards. [18F]SFB and [18F]F‐PEG4‐propyne were obtained with a decay‐corrected yield (DCY) of 26% and 30% and a specific activity (SA) of 844 and 2580 Ci/mmol, respectively. [124I]N‐Succinimidyl 4‐iodobenzoate was obtained with a DCY of 65% and an SA of 3600 Ci/mmol. The DCYs for [18F]4‐fluoro‐benzoate‐GE11′, [18F]F‐PEG4‐1,3‐triazole‐GE11′, and [124I]4‐iodo‐benzoate‐GE11′ were 8%, 10%, and 30%, and the SAs were 108, 500, and 300 Ci/mmol, respectively. [111In]‐NOTA‐GE11′ was prepared with 60% radiochemical yield (RCY) and a SA of 0.35 Ci/mmol. GE11 was also labeled directly with 124I, using chloramine‐T, yielding [124I]GE11 with 47% RCY and a SA of 1030 Ci/mmol. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Fully Automated Preparation and Conjugation of N-Succinimidyl 4-[18F]Fluorobenzoate ([18F]SFB) with RGD Peptide Using a GE FASTlab™ Synthesizer

The aim of this work was to automate the radiosynthesis of [(18)F]SFB, a widely used reagent for the labeling of biomolecules with (18)F on a new generation commercial synthesis module (FASTLab™, GE Healthcare). Two synthesis approaches were implemented on this module: the classical "two-pot radiosynthesis" and the more recently described "one-pot" method. The "two-pot" approach affords [(18)F]SFB with a 42% decay-corrected yield in 57 min (n = 24) with a chemical purity sufficient to avoid an intermediate HPLC purification. The recently established "one-pot" method, afforded a product with a lower chemical purity, in the conditions used in this report. The lower d.c. yield obtained (32% (n = 15)) was related to the low (18)F labeling yields obtained in MeCN compared with DMSO. The subsequent conjugation step with a RGD (PRGD2) peptide was also successfully automated. The formulated [(18)F]FPRGD2 was obtained without any operator manipulation with a d.c. yield of 13% ± 3% (n = 13) in 130 min, a radiochemical purity >98% and a specific activity of 140 ± 40 TBq/mmol.

Click Synthesis and Biologic Evaluation of (R)- and (S)-2-Amino-3-[1-(2-[18F]Fluoroethyl)-1H-[1,2,3]Triazol-4-yl]Propanoic Acid for Brain Tumor Imaging with Positron Emission Tomography

The (R)- and (S)-enantiomers of 2-amino-3-[1-(2-[18F]fluoroethyl)-1H-[1,2,3]triazol-4-yl]propanoic acid (4) were synthesized and evaluated in the rat 9L gliosarcoma brain tumor model using cell uptake assays, biodistribution studies, and micro-positron emission tomography (microPET). The (R)- and (S)-enantiomers of [18F]4 were radiolabeled separately using the click reaction in 57% and 51% decay-corrected yields, respectively. (S)-[18F]4 was a substrate for cationic amino acid transport and, to a lesser extent, system L transport in vitro. In vivo biodistribution studies demonstrated that (S)-[18F]4 provided higher tumor uptake and higher tumor to brain ratios (15:1 at the 30- and 60-minute time points) compared to the (R)-enantiomer (7:1 at the 30- and 60-minute time points). MicroPET studies with (S)-[18F]4 confirmed that this tracer provides good target to background ratios for both subcutaneous and intracranial 9L gliosarcoma tumors. Based on these results, the 1H-[1,2,3]triazole-substituted amino acid (S)-[18F]4 has promising PET properties for brain tumors and represents a novel class of radiolabeled amino acids for tumor imaging.

Development of [F-18]Fluorine-Substituted Tanaproget as a Progesterone Receptor Imaging Agent for Positron Emission Tomography

The level of progesterone receptors (PRs) in breast tumors can be used to guide the selection of endocrine therapies for breast cancer patients. To this end, we have prepared a fluorine-18 labeled analogue of Tanaproget, a nonsteroidal progestin with very high PR binding affinity and low affinity for androgen and glucocorticoid receptors, and have studied its tissue distribution in estrogen-primed rats to evaluate its potential for imaging PR levels by positron emission tomography. 4-[(18)F]Fluoropropyl-Tanaproget ([(18)F]9, FPTP) was prepared in three steps, within 140 min at an overall decay-corrected yield of 5% and effective specific activity of >550 Ci/mmol. In biodistribution studies, [(18)F]9 uptake was high in target tissues at both 1 and 3 h (uterus, 4.55 and 5.26%ID/g; ovary, 2.32 and 2.20%ID/g, respectively) and was cleanly blocked by coinjection of excess unlabeled compound. Uterus to blood and muscle activity ratios were 9.2 and 5.2 at 1 h and 32 and 26 at 3 h, respectively. The biodistribution of [(18)F]9 compares favorably to that of previously prepared F-18 labeled steroidal progestins, FENP and FFNP. Its high target tissue uptake efficiency and selectivity, and prolonged retention, suggest that it has excellent promise as a PET imaging agent for PR-positive breast tumors.

Synthesis and in vitro evaluation of 18F labeled tyrosine derivatives as potential positron emission tomography (PET) imaging agents

Three new 18F labeled fluoroalkyl tyrosine derivatives, O-(2-[18F]fluoroethyl)-α-methyltyrosine (FEMT, [18F]2), O-(2-[18F]fluoroethyl)-2-l-azatyrosine (FEAT, [18F]3), O-(2-[18F]fluoroethyl)-l-tyrosineamide (FETA, [18F]4) have been synthesized and radiofluorinated with 5–34% decay-corrected yield. In vitro studies were carried out in U-138 MG human glioblastoma. Cellular uptake of new tracers was compared to clinically utilized imaging agent O-(2-[18F]fluoroethyl)-l-tyrosine (FET, [18F]1). The uptake of tracers followed the order of FET ([18F]1)>FEAT([18F]3)>FEMT ([18F]2)≈FETA ([18F]4).

Synthesis and Characterization of Rhenium and Technetium-99m Labeled Insulin

A (99m)Tc-labeled insulin analogue was synthesized through a direct labeling method in which the [(99m)Tc(CO)(3)](+) core was combined with a protected insulin derivative (9) bearing a M(I) chelate linked to the first amino acid of the B-chain (B1). Regioselective labeling was achieved by careful control over the pH and the reaction time. Following a TFA-anisole mediated deprotection step (decay-corrected yield of 30 +/- 11%, n = 4), the identity of the final (99m)Tc-labeled product was confirmed by HPLC. Displacement of (125)I-insulin from the insulin receptor (IR) by the Re analogue 6 was similar to that of native insulin (17.8 nM vs 11.7 nM, respectively). The extent of autophosphorylation and Akt activation, as indicated by production of phospho-Akt (pAkt), showed no statistical difference between 6 and native insulin in both assays. These results support the use of the reported (99m)Tc-insulin derivative as a tracer for studying insulin biochemistry in vivo.

Synthesis and biological evaluation of anti-1-amino-2-[ 18F]fluoro-cyclobutyl-1-carboxylic acid ( anti-2-[ 18F]FACBC) in rat 9L gliosarcoma

A new [ 18F] labeled amino acid anti-1-amino-2-[ 18F]fluoro-cyclobutyl-1-carboxylic acid 9 ( anti-2-[ 18F]FACBC) was synthesized in 30% decay-corrected yield with high radiochemical purity over 99%. The cyclic sulfamidate precursor was very stable and highly reactive towards nucleophilic radiofluorination. Cell uptake assays with rat 9L gliosarcoma cells showed that [ 18F] 9 was transported into tumor cells via multiple amino acid transport systems, including L and A systems. Biodistribution study in rats with intracranial 9L gliosarcoma tumors demonstrated that [ 18F] 9 had a rapid and prolonged accumulation in tumors with 26:1 tumor to brain ratio at 120 min post-injection. In this model, [ 18F] 9 is a potential PET tracer for brain tumor imaging.

Synthesis, Radiolabeling, and Biological Evaluation of (R)- and (S)-2-Amino-3-[18F]Fluoro-2-Methylpropanoic Acid (FAMP) and (R)- and (S)-3-[18F]Fluoro-2-Methyl-2-N-(Methylamino)propanoic Acid (NMeFAMP) as Potential PET Radioligands for Imaging Brain Tumors

The non-natural amino acids (R)- and (S)-2-amino-3-fluoro-2-methylpropanoic acid 5 and (R)- and (S)-3-fluoro-2-methyl-2-N-(methylamino)propanoic acid 8 were synthesized in shorter reaction sequences than in the original report starting from enantiomerically pure (S)- and (R)-alpha-methyl-serine, respectively. The reaction sequence provided the cyclic sulfamidate precursors for radiosynthesis of (R)- and (S)-[(18)F]5 and (R)- and (S)-[(18)F]8 in fewer steps than in the original report. (R)- and (S)-[(18)F]5 and(R)- and (S)-[(18)F]8 were synthesized by no-carrier-added nucleophilic [(18)F]fluorination in 52-66% decay-corrected yields with radiochemical purity over 99%. The cell assays showed that all four compounds were substrates for amino acid transport and enter 9L rat gliosarcoma cells in vitro at least in part by system A amino acid transport. The biodistribution studies demonstrated that in vivo tumor to normal brain ratios for all compounds were high with ratios of 20:1 to115:1 in rats with intracranial 9L tumors. The (R)-enantiomers of [(18)F]5 and [(18)F]8 demonstrated higher tumor uptake in vivo compared to the (S)-enantiomers.

Stereoselective synthesis and biological evaluation of syn-1-amino-3-[ 18F]fluorocyclobutyl-1-carboxylic acid as a potential positron emission tomography brain tumor imaging agent

Amino acid syn-1-amino-3-fluoro-cyclobutyl-1-carboxylic acid ( syn-FACBC) 12, the isomer of anti-FACBC, has been selectively synthesized and [ 18F] radiofluorinated in 52% decay-corrected yield using no-carrier-added [ 18F]fluoride. The key step in the synthesis of the desired isomer involved stereoselective reduction using lithium alkylborohydride/zinc chloride, which improved the ratio of anti-alcohol to syn-alcohol from 17:83 to 97:3. syn-FACBC 12 entered rat 9L gliosarcoma cells primarily via L-type amino acid transport in vitro with high uptake of 16% injected dose per 5 × 10 5 cells. Biodistribution studies in rats with 9L gliosarcoma brain tumors demonstrated high tumor to brain ratio of 12:1 at 30 min post injection. In this model, amino acid syn-[ 18F]FACBC 12 is a promising metabolically based radiotracer for positron emission tomography brain tumor imaging.

Syntheses and biological activities of novel 2-methoxyestradiol analogs, 2-fluoroethoxyestradiol and 2-fluoropropanoxyestradiol, and a radiosynthesis of 2-[18F]fluoroethoxyestradiol for positron emission tomography

2-Methoxyestradiol (2ME2) is an endogenous metabolite of the human hormone, estrogen, which has been shown to possess anti-tumor activity. 2-Fluoroethoxyestradiol (2FEE2) and 2-fluoropropanoxyestradiol (2FPE2), novel analogs of 2-methoxyestradiol, were designed and synthesized to be utilized as F-18 radiotracers for positron emission tomography (PET), with which the bio-distribution and intratumoral accumulations of 2ME2 could be measured in vivo for potential translation to human use. 2FEE2 and 2FPE2 were synthesized from 3,17beta-estradiol in five steps respectively. Drug-induced microtubule depolymerization, antiproliferative activity against human cancer cell lines and HIF-1alpha down-regulation by 2FEE2 and 2FPE2 were investigated to examine whether these molecules possess similar anti-tumor activities as 2-methoxyestradiol. 2-[(18)F]Fluoroethoxyestradiol was synthesized for PET. Novel 2ME2 analogs, 2FEE2 and 2FPE2, were synthesized in 29% and 22% overall yield, respectively. 2FEE2 and 2FPE2 showed microtubule depolymerization and cytotoxicities against the human ovarian carcinoma cell line, 1A9, and the human glioma cell line, LN229. HIF-1alpha was down-regulated by 2FEE2 and 2FPE2 under hypoxic conditions. 2FEE2 was chosen as an F-18 radiotracer candidate, since it showed stronger antiproliferative activity than 2ME2 and 2FPE2. 2-[(18)F]Fluoroethoxyestradiol (2[(18)F]FEE2) was prepared in 8.3% decay-corrected yield in 90 min, based on a production of H[(18)F]F with more than 98% radiochemical purity. 2FEE2 and 2FPE2 showed similar activity as 2ME2. 2[(18)F]FEE2 was synthesized to be utilized as a PET radiotracer to measure the biological efficacy of 2ME2 and its analogs in vivo.