Positron tomographic assessment of 16 alpha-[18F] fluoro-17 beta-estradiol uptake in metastatic breast carcinoma

The positron-emitting estrogenic steroid 16 alpha-[18F]fluoro-17 beta-estradiol (FES) has been shown to exhibit selective uptake in primary breast carcinomas; the uptake of tracer by positron emission tomography (PET) is strongly correlated with the tumor estrogen-receptor concentration. We have now extended the use of this radiopharmaceutical for imaging of metastases of breast carcinoma by PET in 16 patients with clinical or radiographic evidence of metastatic disease. Increased uptake of FES was identified on PET images in 53 of 57 metastatic lesions (93%); only two apparent false-positive foci of FES uptake were seen. In seven of the patients, evaluable PET studies were obtained both before and after initiation of antiestrogen therapy. In all cases, there was a decrease in FES uptake in the tumor deposits after initiation of antiestrogen therapy, and the mean (+/- standard deviation) uptake decreased from 2.22 (+/- 1.23) to 0.80 (+/- 0.42) x 10(3)+ dose/ml. These results indicate that PET with FES has high sensitivity and specificity for detecting metastatic breast carcinoma and provide additional confirmatory evidence that the tumor uptake of this ligand is a receptor-mediated process.     

A remote controlled system for the preparation of 7 alpha-[18F]fluoro-17 alpha-methyl 5 alpha-dihydrotestosterone ([18F]FMDHT) using microwave.

For non-invasive imaging of the prostate cancer, we synthesized 7 alpha-fluoro-17 alpha-methyl 5 alpha-dihydrotestosterone ([(18)F]FMDHT) for androgen receptor mediated PET imaging. Preliminary in vitro and in vivo evaluations of this compound show promise. We designed and implemented a remote controlled system for reliable, efficient, and safe handling of radioactivity during the radiochemical synthesis of [(18)F]FMDHT. The key features of this report are the microwave assisted radiochemical synthesis, increased radiochemical yields, improved radiochemical purity, reduced overall synthesis time, and remote controlled automation of the entire synthesis. The overall synthesis using microwave reaction took 60-70 min and provided the desired product in 20-30% radiochemical yields with >99% radiochemical purity.     

Automated synthesis of 11beta-methoxy-4,16alpha-[16alpha-(18)F]difluoroestradiol (4F-M[(18)F]FES) for estrogen receptor imaging by positron emission tomography

Addition of both a 4-fluoro and 11beta-methoxy group onto 16alpha-[(18)F]fluoroestradiol ([(18)F]FES) yields 11beta-methoxy-4,16alpha-[16alpha-(18)F]difluoroestradiol (4F-M[(18)F]FES) with potential improved properties for positron emission tomography (PET) imaging of estrogen receptor densities in breast cancer patients. In order to provide 4F-M[(18)F]FES as a radiopharmaceutical for clinical trials, we developed an automated synthesis procedure using 3-O-methoxymethyl-11beta-methoxy-4-fluoro-16,17-O-sulfuryl-16-epiestriol as precursor. The radio synthesis involves stereoselective opening of the protected cyclic sulfone precursor via nucleophilic fluorination with [(18)F]fluoride in acetonitrile. After removal of the protecting ether and 17beta-sulphate groups by rapid hydrolysis in acidic ethanol and subsequent reversed-phase HPLC purification, the pure 4F-M[(18)F]FES was obtained as a sterile physiological saline solution in 45-50% radiochemical yield (decay corrected). The radiochemical purity of the final product was >98% and the effective specific activity (ESA) of 4F-M[(18)F]FES prepared under optimized conditions was >15,000 Ci/mmol. The total preparation time was 110+/-5 min and the product was shown to be stable for at least 6 h.     

7alpha-18F]fluoro-17alpha-methyl-5alpha-dihydrotestosterone: a ligand for androgen receptor-mediated imaging of prostate cancer

We have synthesized a 18F-labeled androgen, [7alpha-18F]fluoro-17alpha-methyl-5alpha-dihydrotestosterone, in a no-carrier-added radiosynthesis by exchange of 18F- (tetrabutylammonium fluoride) with the 7beta-tosyloxy of 17alpha-methyl-5alpha-dihydrotestosterone. The nonradioactive steroid binds with high affinity and specificity to the androgen receptor and binds poorly, if at all, to other steroid receptors and plasma sex hormone binding globulin. The 7alpha-18F-androgen concentrates markedly in the prostate of rats by an androgen receptor-dependent mechanism. It is likely that [7alpha-18F]fluoro-17alpha-methyl-5alpha-dihydrotestosterone will be an excellent positron emission tomography imaging agent for prostate cancer.     

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.     

Automated synthesis of 16alpha-[18F]fluoroestradiol-3,17beta-disulphamate.

After 16alpha-[15F]fluoroestradiol ([18F]FES) has been successfully prepared in an automated module, the synthesis of 16alpha-[18F]fluoroestradiol-3,17beta-disulphamate ([18F]FESDS) is described as a module-assisted one-pot procedure which can provide 10GBq [18F]FESDS with a radiochemical purity better than 99%. The procedure is reliable and reproducible and requires a time of about 90 min. Because of its high sulphatase-inhibitory effect [15F]FESDS is thought to be a new PET tracer to image sites of high sulphatase activity.     

Synthesis of 17-[18F]fluoro-5-methylheptadecanoic acid

5-Methyl-branched fatty acid, which was designed for less hindrance by the methyl group in heart uptake as compared with the 3-methyl-branched fatty acid, was labeled with fluorine-18 at the ω-position. The total time of synthesis, including HPLC purification and emulsification was 85–100 min from the start of reactive ¹⁸F^- production. The decay-corrected isolated yields of 17-[¹⁸F]fluoro-5-methyl-heptadecanoic acid after emulsification were 10–17% and the radiochemical purities were >97%.     

N-[(18)F]Fluoroethylpiperidinyl,N-[(18)F]fluoroethylpiperidinemethyl and N-[(18)F]fluoroethylpyrrolidinyl esters as radiotracers for acetylcholinesterase

A series of N-fluoroethylpiperidinyl (1), N-fluoroethylpiperidinemethyl (2) and N-fluoroethylpyrrolidinyl (3) esters were synthesized and examined as new (18)F-labeled radiotracers for measuring brain cholinesterase activity. The fluoroethyl group, instead of methyl group, results in slower in vitro enzymatic cleavage rates and higher selectivity for AChE. Based on metabolism in mouse blood and PET time-activity curves in rats, two radiotracers were identified as potential candidates for further in vivo evaluation in higher species.     

Biodistribution and dosimetry of [(18)F]fluorodeoxyglucose labelled leukocytes in normal human subjects

SUMMARY: This study was performed in order to assess [(18)F]fluorodeoxyglucose white blood cell ((18)F-FDG WBC) dosimetry in normal human subjects. Using previously reported methods, mixed cell suspensions of autologous leukocytes were prepared from four normal volunteers. Leukocytes were labelled in heparin-saline by incubation with (18)F-FDG at 37 degrees C for 20 min. After washing and resuspension, (18)F-FDG WBCs (225-315 MBq) were administered by intravenous injection. Whole-body imaging was performed at 0.5, 1, 2, 4 and 6 h using a GE Varicam with 511 keV collimation. Blood samples were obtained at corresponding times as well as fractionated urinary collection. Whole-body anterior and posterior images were used for calculation of organ dosimetry. Uptake of (18)F-FDG WBCs occurred predominantly within the reticulo-endothelial system. Plasma activity, urinary excretion (9.9+/-2.3% at 6 h), and brain uptake (1.7+/-0.4%) were consistent with partial elution of (18)F-FDG. Positron emission tomography imaging performed at 5-6 h after injection yielded good quality images of reticulo-endothelial uptake. Whole-body and organ dosimetry for (18)F-FDG WBCs in doses of 225-250 MBq are comparable with reported results for conventional doses of (111)In oxine labelled leukocytes. Further studies of (18)F-FDG WBC as an agent for positron emission tomography imaging of inflammatory disease appear warranted.     

The automatic production of 16alpha-[18F]fluoroestradiol using a conventional [18F]FDG module with a disposable cassette system.

We have developed a fully automatic method for the synthesis of 16alpha-[18F]fluoroestradiol ([18F]FES) using a disposable cassette system and conventional [18F]FDG module. [18F]FES was synthesized using a GE TracerLab MX module and a modified module control program. Following [18F]fluorination, we hydrolyzed the product three times with a mixture of 2N HCl and CH(3)CN. After HPLC purification, the decay corrected radiochemical yield of [18F]FES was 45.3+/-2.8%, which was stable to 98.2+/-0.2% at 6h after synthesis. This new automated synthesis method provides high and reproducible yields with the advantage of a disposable cassette system.     

Positron emission tomography using 2-[(18)F] fluoro-2-deoxy-D-glucose in the diagnosis of uterine leiomyosarcoma: a case report.

The preoperative diagnosis of uterine leiomyosarcoma (LMS) is very difficult. Magnetic resonance (MR) imaging is usually used for it; however, precise diagnosis by MR imaging is limited to typical LMS with coagulative tumor cell necrosis. We presented a case of LMS that was diagnosed preoperatively by positron emission tomography (PET) using 2-[(18)F] fluoro-2-deoxy-D-glucose (FDG).     

Comparative breast tumor imaging and comparative in vitro metabolism of 16alpha-[18F]fluoroestradiol-17beta and 16beta-[18F]fluoromoxestrol in isolated hepatocytes

16beta-[18F]Fluoromoxestrol ([18]betaFMOX) is an analog of 16alpha-[18F]fluoroestradiol-17beta ([18F]FES), a radiopharmaceutical known to be an effective positron emission tomography (PET) imaging agent for estrogen receptor-positive (ER+) human breast tumors. Based on comparisons of target tissue uptake efficiency and selectivity in a rat model, [18F]betaFMOX was predicted to be as effective an imaging agent as [18F]FES. However, in a preliminary PET imaging study with [18F]FMOX of 12 patients, 3 of whom had ER+ breast cancer, no tumor localization of [18F]betaFMOX was observed. In search for an explanation for the unsuccessful [18F]betaFMOX clinical trial, we have examined the rate of metabolism of [18F]FMOX and [18F]FES in isolated rat, baboon, and human hepatocytes. We have also studied the effect of the serum protein sex hormone-binding globulin (SHBG), which binds [18F]FES better than [18F]betaFMOX, on these rates of metabolism. Immature rat hepatocytes were found to metabolize [18F]FES 31 times faster than [18F]betaFMOX, whereas mature rat cells metabolized [18F]FES only 3 times faster, and baboon and human hepatocytes only 2 times faster than [18F]betaFMOX. In the presence of SHBG, the metabolic consumption rate for [18F]FES in mature rat hepatocytes decreased by 26%. Thus, the very favorable target tissue uptake characteristics of [18F]betaFMOX determined in the rat probably result from its comparative resistance to metabolism (vis-a-vis [18F]FES) in this species, an advantage that is strongly reflected in comparative metabolism rates in rat hepatocytes. In the baboon and human, [18F]FES is extensively protein bound and protected from metabolism, an effect that may be reflected to a degree as a decrease in the rate of metabolism of this compound in baboon and human hepatocytes relative to [18F]betaFMOX. Thus in primates, SHBG may potentiate the ER-mediated uptake of [18F]FES in ER+ tumors by selectively protecting this ligand from metabolism and ensuring its delivery to receptor-containing cells. In addition to current screening methods for 18F-estrogens that involve evaluating in vivo ER-mediated uptake in the immature female rat, studies comparing the metabolism of the new receptor ligands in isolated hepatocytes, especially those from primates or humans, may assist in predicting the potential of these ligands for human PET imaging.     

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%.     

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.     

Evaluation of pyrimidine metabolising enzymes and in vitro uptake of 3'-[(18)F]fluoro-3'-deoxythymidine ([(18)F]FLT) in pancreatic cancer cell lines

Here we report the expression of major pyrimidine metabolising enzymes in pancreatic cancer cell lines, chronic pancreatitis tissue and human pancreatic cancer and the in vitro uptake of 3'-[(18)F]fluoro-3'-deoxythymidine ([(18)F]FLT). The expression of pyrimidine metabolising enzymes was evaluated with real-time PCR, Western blot and immunostaining. Thymidine kinase 1 (TK-1) activity was measured with a fluorocytometric assay. The cellular uptake and intracellular metabolism of [(18)F]FLT were evaluated in pancreatic lobules and in transformed cancer cell lines. TK-1 and thymidine synthetase mRNA were increased in six pancreatic cancer cell lines, while mRNA levels of thymidine kinase 2 and deoxycytidine kinase were down-regulated. High TK-1 activity was confirmed in all cell lines. Furthermore, TK-1 was overexpressed in human pancreatic cancer as compared with normal pancreatic tissue and samples from patients with chronic pancreatitis. The cellular uptake of [(18)F]FLT was 18.4%+/-3.6% and 5.2%+/-1.4% of the applied radioactivity after 240 min in SW-979 and BxPc-3 cells, respectively, while uptake of [(18)F]fluorodeoxyglucose ([(18)F]FDG) was only 0.6%+/-0.04% (SW-979) and 0.3%+/-0.13% (BxPc-3) after 240 min of incubation. In contrast, cellular uptake of [(18)F]FLT in isolated pancreatic lobules and growth-arrested HT1080 cells was lower as compared with the uptake of [(18)F]FDG and with the malignant pancreatic cancer cell lines. HPLC analysis of the perchloric acid-soluble cell fraction demonstrated the phosphorylation of [(18)F]FLT to the respective monophosphate in both cell lines. Furthermore, 0.8%+/-0.12% (BxPc-3) and 1.3%+/-0.38% (SW-979) of the applied radioactivity was detected in the perchloric acid-insoluble cell fraction, indicating the incorporation of [(18)F]FLT into the DNA. Our results demonstrate the cellular uptake, intracellular trapping and incorporation into the DNA of [(18)F]FLT in pancreatic cancer cells in vitro. TK-1, as the rate-limiting enzyme of [(18)F]FLT metabolism, is overexpressed in pancreatic cancer cell lines and in human pancreatic cancer. Thus, we propose [(18)F]FLT as a promising tracer for positron emission tomography that might overcome current limitations in the diagnosis of pancreatic cancer.     

Dynamic evaluation of absorbed dose to the bladder wall with a balloon-bladder phantom during a study using [(18)F]fluorodeoxyglucose positron emission imaging

An accurate evaluation of the absorbed dose to the bladder wall from 2-[(18)F]fluoro-2-deoxy-d-glucose (FDG) is clinically important because the bladder is considered as a critical organ in most positron emission tomography (PET) studies that cumulate about 20% of the total activity injection during image procedures. In the MIRD calculation, no allowance is made for the inclusion of all the dynamic parameters that affect the actual dose to the bladder wall to be taken in the dose assessment. The goal of the study is to propose a dose evaluation model by using a dynamic bladder phantom and time-activity curves from the bladder PET imaging. The proposed model takes all dynamic parameters into account and provides a much more accurate dose estimation to the bladder. In this study, the lowest dose to the bladder wall was obtained at the conditions of having a larger initial volume for the bladder contents and a higher production rate for urine. It is then advised patients to drink a bulk amount of water before the FDG injection or after urine voiding to facilitate urine production and to enlarge the bladder surface area, which are the most crucial steps in reducing the dose to the bladder wall. In our study, the voiding schedule in dose calculation plays certain roles although it is much more critical in the conventional MIRD calculation. The model estimated that the lowest dose to the bladder would occur at an initial void about 40 min after the FDG injection and the urine voiding was as complete as possible.     

(18)F]fluorodeoxyglucose PET in large vessel vasculitis

[(18)F]fluorodeoxyglucose (FDG) PET is a noninvasive metabolic imaging modality based on the regional distribution of [18F]FDG that is highly effective in assessing the activity and extent of giant cell arteritis and Takayasu's arteritis, respectively. Metabolic imaging using [18F]FDG-PET has been shown to identify more affected vascular regions than morphologic imaging with MRI in both diseases. The visual grading of vascular [18F]FDG uptake helps to discriminate arteritis from atherosclerosis and therefore provides high specificity. High sensitivity is attained by scanning during the active inflammatory phase. Thus, [18F]FDG-PET has the potential to develop into a valuable tool in the diagnostic workup of giant cell arteritis and Takayasu's arteritis.