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Several limitations of [ 18 F]FDG have been reported, such as nonspecific uptake of inflammation foci. Moreover, [ 11 C]MET has been found to accumulate in normal and inflammatory tissues as well as tumors. To increase specificity to tumor tissues, PET probes with tumor-specific molecular targets have been actively developed. [ 18 F]FIMP was found to be highly accumulated in LAT1-positive tumors but not in inflamed tissue. The aim of this study was to explore whether [ 18 F]FIMP can be used for the early-phase evaluation of radiotherapy accompanied by inflammation, and compare its effectiveness with those of [ 11 C]MET and [ 18 F]FDG. Tumor uptake of [ 18 F]FIMP decreased at day 1 after irradiation, and remained low until day 14. Comparatively, that of [ 18 F]FDG initially decreased at day 3 but was transiently elevated at day 7 and then decreased again at day 10. Decreased tumor uptake of [ 11 C]MET was observed at day 10. In line with the uptake of [ 18 F]FIMP, the ratio of Ki-67 immuno-positive cells in tumor tissues significantly decreased at day 1, 7, and 10 as compared with that in the control. These findings suggest that [ 18 F]FIMP may be a PET probe involved in the early detection and prediction of radiotherapy efficacy, although further clarification is needed., (© 2023. The Author(s).)

Microcin J25 (MccJ25), a lasso peptide, has a unique 3-D interlocked structure that provides high stability under acidic conditions, at high temperatures, and in the presence of proteases. In this study, we generated a positron emission tomography (PET) probe based on MccJ25 analog with an RGD motif and investigated their pharmacokinetics and utility for integrin α v β 3 imaging in tumors. The MccJ25 variant with an RGD motif in the loop region and a lysine substitution at the C-terminus (MccJ25(RGDF)GtoK) was produced in E. coli transfected with plasmid DNA containing the MccJ25 biosynthetic gene cluster (mcjABCD). [ 64 Cu]Cu-MccJ25(RGDF)GtoK was synthesized using the C-terminal lysine labeled with copper-64 (t 1/2  = 12.7 h) via a bifunctional chelator; it showed stability in 90% mouse plasma for 45 min. Using PET imaging for integrin α v β 3 positive U87MG tumor bearing mice, [ 64 Cu]Cu-MccJ25(RGDF)GtoK could clearly distinguish the tumor, and its accumulation was significantly higher than that of MccJ25(GIGT)GtoK without the binding motif for integrin α v β 3 . Furthermore, MccJ25(RGDF)GtoK enabled visualization of only U87MG tumors but not MCF-7 tumors with low integrin α v β 3 expression in double tumor-bearing mice. In ex vivo biodistribution analysis, the integrin α v β 3 non-specific accumulation of [ 64 Cu]Cu-MccJ25(RGDF)GtoK was significantly lower in various tissues, except for the kidneys, as compared to the control probe ([ 64 Cu]Cu-cyclic RGD peptide). These results of the present study indicate that 64 Cu-labeling methods are appropriate for the synthesis of MccJ25-based PET probes, and [ 64 Cu]Cu-MccJ25 variants are useful tools for cancer molecular imaging., Competing Interests: Disclosure Statement No potential conflict of interest was reported by the authors., (Copyright © 2022 The Author(s). Published by Elsevier B.V. All rights reserved.)

In the first-in-human PET study, we evaluated the biodistribution and tumor accumulation of the novel PET probe, (S)-2-amino-3-[3-(2- 18 F-fluoroethoxy)-4-iodophenyl]-2-methylpropanoic acid ( 18 F-FIMP), which targets the tumor-related L-type amino acid transporter 1 (LAT1), and compared it with L-[methyl- 11 C]methionine ( 11 C-MET) and 2-Deoxy-2- 18 F-fluoro-D-glucose ( 18 F-FDG). 18 F-FIMP biodistribution was revealed by whole-body and brain scans in 13 healthy controls. Tumor accumulation of 18 F-FIMP was evaluated in 7 patients with a brain tumor, and compared with those of 11 C-MET and 18 F-FDG. None of the subjects had significant problems due to probe administration, such as adverse effects or abnormal vital signs. 18 F-FIMP was rapidly excreted from the kidneys to the urinary bladder. There was no characteristic physiological accumulation in healthy controls. 18 F-FIMP PET resulted in extremely clear images in patients with suspected glioblastoma compared with 11 C-MET and 18 F-FDG. 18 F-FIMP could be a useful novel PET probe for LAT1-positive tumor imaging including glioblastoma., Competing Interests: Declaration of competing interest All authors declare no competing interests., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Aromatase is an estrogen synthetic enzyme that plays important roles in brain functions. To quantify aromatase expression in the brain by positron emission tomography (PET), we had previously developed [ 11 C]cetrozole, which showed high specificity and affinity. To develop more efficient PET tracer(s) for aromatase imaging, we synthesized three analogs of cetrozole. We synthesized meta-cetrozole, nitro-cetrozole, and iso-cetrozole, and prepared the corresponding 11 C-labeled tracers. The inhibitory activities of these three analogs toward aromatase were evaluated using marmoset placenta, and PET imaging of brain aromatase was performed using the 11 C-labeled tracers in monkeys. The most promising analog in the monkey study, iso-cetrozole, was evaluated in the human PET study. The highest to lowest inhibitory activity of the analogs toward aromatase in the microsomal fraction from marmoset placenta was in the following order: iso-cetrozole, nitro-cetrozole, cetrozole, and meta-cetrozole. This order showed good agreement with the order of the binding potential (BP) of each 11 C-labeled analog to aromatase in the rhesus monkey brain. A human PET study using [ 11 C]iso-analog showed a similar distribution pattern of binding as that of [ 11 C]cetrozole. The time-activity curves showed that elimination of [ 11 C]iso-cetrozole from brain tissue was faster than that of 11 C-cetrozole, indicating more rapid metabolism of [ 11 C]iso-cetrozole. [ 11 C]Cetrozole has preferable metabolic stability for brain aromatase imaging in humans, although [ 11 C]iso-cetrozole might also be useful to measure aromatase level in living human brain because of its high binding potential., (© 2021. The Author(s).)

Vitamine B 1 thiamine is an essential component for glucose metabolism and energy production. The disulfide derivative, thiamine tetrahydrofurfuryl disulfide (TTFD), is more absorbent compared to readily-available water-soluble thiamine salts since it does not require the rate-limiting transport system required for thiamine absorption. However, the detailed pharmacokinetics of thiamine and TTFD under normal and pathological conditions were not clarified yet. Recently, 11 C-labeled thiamine and TTFD were synthesized by our group, and their pharmacokinetics were investigated by PET imaging in normal rats. In this study, to clarify the whole body pharmacokinetics of [ 11 C]TTFD in human healthy volunteers, we performed first-in-human PET imaging study with [ 11 C]TTFD, along with radiation dosimetry of [ 11 C]TTFD in humans., Methods: Synthesis of [ 11 C]TTFD was improved for clinical study. Dynamic whole-body PET images were acquired on three young male normal subjects after intravenous injection of [ 11 C]TTFD. VOIs were defined for source organs on the PET images to measure time-course of [ 11 C]TTFD uptake as percentage injected dose and the number of disintegrations for each organ. Radiation dosimetry was calculated with OLINDA/EXM., Results: We succeeded in developing the improved synthetic method of [ 11 C]TTFD for the first-in-human PET study. In the whole body imaging, uptake of [ 11 C]TTFD by various tissues was almost plateaued at 10 min after intravenous injection, afterward gradually increased for the brain and urinary bladder (urine). %Injected dose was high in the liver, kidney, urinary bladder, heart, spine, brain, spleen, pancreas, stomach, and salivary glands, in this order. %Injected dose per gram of tissue was high also in the pituitary. By dosimetry, the effective radiation dose of [ 11 C]TTFD calculated was 5.5 μSv/MBq (range 5.2-5.7)., Conclusion: Novel synthetic method enabled clinical PET study with [ 11 C]TTFD, which is a safe PET tracer with a dosimetry profile comparable to other common 11 C-PET tracers. Pharmacokinetics of TTFD in the pharmacological dose and at different nutritional states could be further investigated by future quantitative PET studies. Noninvasive in vivo PET imaging for pathophysiology of thiamine-related function may provide diagnostic evidence of novel information about vitamin B 1 deficiency in human tissues., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: This work was supported in part by an extramural research grant from Takeda Consumer Healthcare Company Limited (Tokyo, Japan)to Yasuyoshi Watanabe and Michio Senda. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results. Other authors declare that there are no conflicts of interest., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Positron emission tomography (PET) imaging can assist in the early-phase diagnostic and therapeutic evaluation of tumors. Here, we report the radiosynthesis, small animal PET imaging, and biological evaluation of a L-type amino acid transporter 1 (LAT1)-specific PET probe, 18 F-FIMP. This probe demonstrates increased tumor specificity, compared to existing tumor-specific PET probes ( 18 F-FET, 11 C-MET, and 18 F-FDG). Evaluation of probes by in vivo PET imaging, 18 F-FIMP showed intense accumulation in LAT1-positive tumor tissues, but not in inflamed lesions, whereas intense accumulation of 18 F-FDG was observed in both tumor tissues and in inflamed lesions. Metabolite analysis showed that 18 F-FIMP was stable in liver microsomes, and mice tissues (plasma, urine, liver, pancreas, and tumor). Investigation of the protein incorporation of 18 F-FIMP showed that it was not incorporated into protein. Furthermore, the expected mean absorbed dose of 18 F-FIMP in humans was comparable or slightly higher than that of 18 F-FDG and indicated that 18 F-FIMP may be a safe PET probe for use in humans. 18 F-FIMP may provide improved specificity for tumor diagnosis, compared to 18 F-FDG, 18 F-FET, and 11 C-MET. This probe may be suitable for PET imaging for glioblastoma and the early-phase monitoring of cancer therapy outcomes.

Background: Multi-modal brain image registration is a prerequisite for accurate mapping of brain structure and function in neuroscience. Image registration is commonly performed using automated software; however, its accuracy decreases when images differ in modality, contrast, uniformity, and resolution. This limitation could be overcome by using an external reference point; however, high-contrast agents in multi-modal imaging have not been previously reported., New Methods: Here, we propose a novel multi-modal fiducial marker that contains Tungsten solution and provides high contrast in magnetic resonance imaging (MRI), computed tomography (CT), and positron emission tomography (PET). The basic characteristics of this multi-modal marker were investigated by assessing major sources of image contrast in the following modalities: density and T1-, T2-relaxivity in comparison with conventional contrast agents., Results: Tungsten solution had lower T1- and T2-relaxivity and high solubility, and showed high contrast in T1- and T2-weighted MR and CT images at a high-density concentration (˜3.0 g/mL), whereas other conventional solutions did not show sufficient contrast in either CT or MRI., Comparison With Existing Methods: The use of this Tungsten-based multi-modal marker allowed more accurate registration than a software-only method in phantom and animal experiments. Application of this method demonstrated accurate cortical surface mapping of neurotransmitter function (dopamine transporter, DAT) using PET and MRI, and provided a neurobiologically relevant cortical distribution consistent with previous literature on histology-based DAT immunoreactivity., Conclusions: The Tungsten-based multi-modal fiducial marker is non-radioactive, easy to handle, and aids precise registration across different modalities of brain imaging., (Copyright © 2019 The Authors. Published by Elsevier B.V. All rights reserved.)

Immuno-positron emission tomography (immuno-PET) is expected to improve the specificity of small chemical tracers such as 18 F-fluorodeoxyglucose. Whole antibodies significantly accumulate in target molecule-expressing tumors but frequently persist too long in the blood circulation for imaging purposes. We investigated the utility of whole antibodies, 64 Cu-labeled via a urokinase-substrate linker, and their exogenous urokinase-responsive cleavage to enhance clearance of immuno-PET probes from the blood and shorten the time required to develop adequate imaging contrast. Specifically, we used 64 Cu-labeled trastuzumab in human epidermal growth factor receptor 2 (HER2)-positive tumor-bearing mice. 64 Cu-labeled trastuzumab with a urokinase-cleavage site ( 64 Cu-CB-TE1A1P-USL-trastuzumab) was synthesized using a bifunctional chelator incorporating an urokinase substrate peptide. Urokinase cleavage was analyzed in vitro by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and radio-gel permeation-high-performance liquid chromatography. Improvements in radioisotope clearance and HER2-imaging by urokinase injection were evaluated by PET imaging and ex vivo biodistribution studies in A431 tumor-bearing mice. 64 Cu-CB-TE1A1P-USL-trastuzumab was cleaved into smaller radioactive fragments by 20 000 IU/mL urokinase treatment in vitro at an efficacy of ∼95%. The probe targeted HER2 in A431 tumors in mice within 24 h post-injection, and approximately two-thirds of the probe in the blood circulation was eliminated via renal clearance of radioactive fragments after three urokinase injections. Therefore, the tumor/blood ratio increased 3.0-fold. Without urokinase injection, the tumor accumulation of 64 Cu-CB-TE1A1P-USL-trastuzumab slowly increased, and the blood radioactivity decreased over 72 h. However, the tumor/blood ratios in mice after three urokinase injections were higher at 24 h than those in mice without injections at 72 h. The results indicate that our approach shortened the time required to develop adequate imaging contrast of immuno-PET by >2 days. Therefore, this approach can benefit high-sensitivity imaging under lower radioactive decay conditions and can decrease patient radiation exposure. In addition, it could reduce other adverse effects of radioimmunotherapy.

Purpose: Thiamine is an essential component of glucose metabolism and energy production. The disulfide derivative, thiamine tetrahydrofurfuryl disulfide (TTFD), is better absorbed than readily-available water-soluble thiamine salts because it does not require the rate-limiting transport system required for thiamine absorption. However, the detailed pharmacokinetics of thiamine and TTFD under normal and pathological conditions have not yet been clarified. C-11-labeled thiamine and TTFD were recently synthesized by our group. In this study, to clarify the differences in pharmacokinetics and metabolism of these probes, a quantitative PET imaging study and radiometabolite analysis of C-11-labeled thiamine and TTFD were performed in the rat heart., Procedures: Positron emission tomography (PET) imaging with [ 11 C]thiamine and [ 11 C]TTFD was performed in normal rats to determine the pharmacokinetics of these probes, and the radiometabolites of both probes from the blood and heart tissue were analyzed by thin-layer chromatography., Results: Accumulation of [ 11 C]TTFD was significantly higher than that of [ 11 C]thiamine in the rat heart. Moreover, as a result of the radiometabolite analysis of heart tissue at 15 min after the injection of [ 11 C]TTFD, thiamine pyrophosphate, which serves as a cofactor for the enzymes involved in glucose metabolism, was found as the major radiometabolite and at a significantly higher level than in the [ 11 C]thiamine-injected group., Conclusions: PET imaging techniques for visualizing the kinetics and metabolism of thiamine using [ 11 C]thiamine and [ 11 C]TTFD were developed in this study. Consequently, noninvasive PET imaging for the pathophysiology of thiamine-related cardiac function may provide novel information about heart failure and related disorders.

Radiolabeled antibodies, polyethylene glycol-conjugated (PEGylated) peptides, liposomes, and other materials were investigated as positron-emission tomography (PET) probes. These substances accumulate in tumors but often remain too long in circulation. We investigated the combination of intravenous urokinase injection and its substrate linker as a triggered radioisotope clearance enhancement system to improve imaging contrast. To this end, we synthesized a four-arm PEGylated 64 Cu-bombesin analog tetramer with a urokinase substrate linker. In mouse blood, it was almost perfectly cleaved and degraded into smaller radioactive fragments in vitro with urokinase (≥20,000 IU/mL). In mouse blood circulation, ∼50-65% of the probe was rapidly degraded after the urokinase injection and the radioactive fragments were eliminated mainly from the kidney. In contrast, tumor radioactivity levels did not change, and therefore, the tumors were clearly visualized. The tumor/blood ratio, an indicator of imaging contrast, increased 2.5 times, while elimination of the radioisotope from the blood was enhanced. This approach has the potential to improve imaging contrast using various PET probes. It could also shorten the time required to obtain sufficient contrast and decrease patient radiation exposure., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Purpose: In vivo detection of pathological insults during the early stages of rheumatoid synovitis is essential to allow early anti-inflammatory treatment for prevention of joint destruction. Whether rheumatoid synovitis pathology and the efficacy of therapies can be visualized by positron emission tomography (PET) tracers specific to the inflammatory process was investigated., Procedures: Using a collagen-induced experimental rat model of rheumatoid arthritis, in vivo imaging using the PET tracers [ 11 C]PK11195, which binds to the translocator protein mainly expressed on myeloid cells, and [ 11 C]ketoprofen, for cyclooxygenase imaging, was performed. To evaluate therapeutic efficacy, model animals were administered the tumour necrosis factor alpha blocker etanercept subcutaneously., Results: [ 11 C]PK11195 and [ 11 C]ketoprofen uptakes were significantly higher in inflamed paws of collagen-induced arthritis rats than in normal rats. The data showed a correlation between tracer uptake values and paw swelling. After treatment with etanercept, [ 11 C]ketoprofen uptake was significantly lower in treated animals than in untreated ones, whereas [ 11 C]PK11195 uptake in the inflamed regions was comparable to that in the untreated group., Conclusions: With [ 11 C]PK11195 and [ 11 C]ketoprofen tracers, non-invasive in vivo PET imaging for rheumatoid synovitis can provide diagnostic evidence of early synovitis and allow monitoring inflammatory cell activity during treatment.

We performed positron emission tomography (PET) using 2-deoxy-2-[(18)F]fluoro-D-glucose ([(18)F]FDG) to evaluate the pharmacokinetics of nasal drug absorption in the rat. The dosing solution of [(18)F]FDG was varied in volume (ranging from 5 to 25 μl) and viscosity (using 0% to 3% concentrations of hydroxypropylcellulose). We modeled the pharmacokinetic parameters regarding the nasal cavity and pharynx using mass balance equations, and evaluated the values that were obtained by fitting concentration-time profiles using WinNonlin® software. The regional nasal permeability was also estimated using the active surface area derived from the PET images. The translocation of [(18)F]FDG from the nasal cavity was visualized using PET. Analysis of the PET imaging data revealed that the pharmacokinetic parameters were independent of the dosing solution volume; however, the viscosity increased the absorption rate constant and decreased the mucociliary clearance rate constant. Nasal permeability was initially higher but subsequently decreased until the end of the study, indicating regional differences in permeability in the nasal cavity. We concluded that the visualization of drug translocation in the nasal cavity in the rat using PET enables quantitative analysis of nasal drug absorption, thereby facilitating the development of nasal formulations for human use., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Unlabelled: Aromatase (an enzyme that converts androgens to estrogens) in the brain is involved in neuroprotection, synaptic plasticity, and regulation of sexual and emotional behaviors. To investigate the physiologic and pathologic importance of aromatase in the brain, including in humans, we here report the development of a novel PET probe for aromatase, (11)C-cetrozole, which allows noninvasive quantification of aromatase expression., Methods: (11)C-cetrozole was synthesized by the C-(11)C-methylation method developed by our group. In vitro autoradiography of frozen sections and a binding study with rat brain homogenates were conducted to demonstrate the specific binding and the dissociation constant. PET studies with anesthetized rhesus monkeys were performed to analyze the dynamics in the brain., Results: In vitro and in vivo studies using (11)C-cetrozole showed its superiority in brain aromatase imaging in terms of specificity and selectivity, compared with previously developed (11)C-vorozole. PET studies showed that (11)C-cetrozole had a higher signal-to-noise ratio, providing a sharper image than (11)C-vorozole, because the radioactive metabolite of (11)C-vorozole was taken up into the brain. High specific binding of (11)C-cetrozole was observed in the amygdala and hypothalamus, and we also noted binding in the nucleus accumbens of rhesus monkeys for the first time., Conclusion: These results suggest that PET imaging with newly developed (11)C-cetrozole is suitable for quantifying the expression of brain aromatase in vivo, possibly providing critical information regarding the functional roles of aromatase in human neurologic and emotional disorders.

Unlabelled: Menkes disease (MD), an X-linked recessive disorder of copper metabolism caused by mutations in the copper-transporting ATP7A gene, results in growth failure and severe neurodegeneration in early childhood. Subcutaneous copper-histidine injection is the standard treatment for MD, but it has limited clinical efficacy. Furthermore, long-term copper injection causes excess copper accumulation in the kidneys, resulting in renal dysfunction. To attempt to resolve this issue, we used PET imaging with (64)Cu to investigate the effects of disulfiram on copper biodistribution in living mice serving as an animal model for MD (MD model mice)., Methods: Macular mice were used as MD model mice, and C3H/He mice were used as wild-type mice. Mice were pretreated with 2 types of chelators (disulfiram, a lipophilic chelator, and d-penicillamine, a hydrophilic chelator) 30 min before (64)CuCl2 injection. After (64)CuCl2 injection, emission scans covering the whole body were performed for 4 h. After the PET scans, the brain and kidneys were analyzed for radioactivity with γ counting and autoradiography., Results: After copper injection alone, marked accumulation of radioactivity ((64)Cu) in the liver was demonstrated in wild-type mice, whereas in MD model mice, copper was preferentially accumulated in the kidneys (25.56 ± 3.01 percentage injected dose per gram [%ID/g]) and was detected to a lesser extent in the liver (13.83 ± 0.26 %ID/g) and brain (0.96 ± 0.08 %ID/g). Copper injection with disulfiram reduced excess copper accumulation in the kidneys (14.54 ± 2.68 %ID/g) and increased copper transport into the liver (29.42 ± 0.98 %ID/g) and brain (5.12 ± 0.95 %ID/g) of MD model mice. Copper injection with d-penicillamine enhanced urinary copper excretion and reduced copper accumulation in most organs in both mouse groups. Autoradiography demonstrated that disulfiram pretreatment induced copper transport into the brain parenchyma and reduced copper accumulation in the renal medulla., Conclusion: PET studies with (64)Cu revealed that disulfiram had significant effects on the copper biodistribution of MD. Disulfiram increased copper transport into the brain and reduced copper uptake in the kidneys of MD model mice. The application of (64)Cu PET for the treatment of MD and other copper-related disorders may be useful in clinical settings.

Recently, we demonstrated the utility of positron emission tomography (PET) imaging-based pharmacokinetic evaluation studies for preclinical experiments and microdose clinical trials, mainly focused on low molecular weight compounds. In order to investigate the pharmacokinetics of nucleic acid drugs and their drug delivery systems (DDSs) in vivo by using PET imaging, we developed a novel and efficient method for radiolabeling oligodeoxynucleotides with the positron-emitting radionuclide (18)F (stoichiometry-focused Huisgen-type (18)F labeling). By using this method, we succeeded in synthesizing a variety of (18)F-labeled oligodeoxynucleotides with not only phosphodiesters (PO) in natural forms, but also phosphorothioate (PS) and bridged nucleic acid (BNA) in artificial forms, and then performed PET studies and radioactive metabolite analyses of these (18)F-labeled oligodeoxynucleotides. The tissue-distribution and dynamic changes in radioactivity showed significantly different profiles between these antisense oligodeoxynucleotides. The radioactivity of (18)F-labeled PO-DNA and PO-BNA rapidly accumulated in the kidneys and liver and then moved to the renal medulla, ureter, bladder, and intestine. However, the radioactivity of (18)F-labeled PS-DNA and PS-BNA, possessing PS backbone structures, was retained in the blood for relatively long periods and then gradually accumulated in the liver and kidneys. The metabolite analysis showed that (18)F-labeled PO-DNA rapidly degraded by 5min and (18)F-labeled PO-BNA gradually degraded over time by 60min. Conversely, (18)F-labeled PS-DNA and PS-BNA were shown to be much more stable. To demonstrate the usefulness of the PET imaging technique for evaluating the improved targeting potential of the DDS, we designed and synthesized a cholesterol-modified oligodeoxynucleotide, that we developed as an antisense nucleic acid drug against proprotein convertase subtilisin/kexin type 9 (PCSK9) for hypercholesterolemia therapy, and evaluated its pharmacokinetics using PET imaging. As expected, the (18)F-labeled cholesterol-modified PS-BNA-type oligodeoxynucleotide showed much higher and more rapid accumulation in the delivery target organ, that is, the liver, which encourages us to develop this drug. These results suggest that dynamic PET studies using (18)F-incorporated oligodeoxynucleotide synthesized by stoichiometry-focused Huisgen-type labeling is useful for quantitative pharmacokinetic evaluation of nucleic acid drugs and their delivery systems., (Copyright © 2014 Elsevier B.V. All rights reserved.)

In order to develop a new positron emission tomography (PET) probe to study hepatobiliary transport mediated by the multi-drug and toxin extrusion transporter 1 (MATE1), (11)C-labelled metformin was synthesized and then evaluated as a PET probe. [(11)C]Metformin ([(11)C]4) was synthesized in three steps, from [(11)C]methyl iodide. Evaluation by small animal PET of [(11)C]4 showed that there was increased concentrations of [(11)C]4 in the livers of mice pre-treated with pyrimethamine, a potential inhibitor of MATEs, inhibiting the hepatobiliary excretion of metformin. Radiometabolite analysis showed that [(11)C]4 was not degraded in vivo during the PET scan. Biodistribution studies were undertaken and the organ distributions were extrapolated into a standard human model. In conclusion, [(11)C]4 may be useful as a PET probe to non-invasively study the in vivo function of hepatobiliary transport and drug-drug interactions, mediated by MATE1 in future clinical investigations., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Diabetes mellitus (DM) is a metabolic disorder characterized by hyperglycemia, and the loss or dysfunction of pancreatic beta cells has been reported before the appearance of clinical symptoms and hyperglycemia. To evaluate beta cell mass (BCM) for improving the detection and treatment of DM at earlier stages, we focused on somatostatin receptors that are highly expressed in the pancreatic beta cells, and developed a positron emission tomography (PET) probe derived from octreotide, a metabolically stable somatostatin analog. Octreotide was conjugated with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), a chelating agent, and labeled with (68)Gallium ((68)Ga). After intravenous injection of (68)Ga-DOTA-octreotide, a 90-min emission scan of the abdomen was performed in normal and DM model rats. The PET studies showed that (68)Ga-DOTA-octreotide radioactivity was highly accumulated in the pancreas of normal rats and that the pancreatic accumulation was significantly reduced in the rats administered with an excess amount of unlabeled octreotide or after treatment with streptozotocin, which was used for the chemical induction of DM in rats. These results were in good agreement with the ex vivo biodistribution data. These results indicated that the pancreatic accumulation of (68)Ga-DOTA-octreotide represented specific binding to the somatostatin receptors and reflected BCM. Therefore, PET imaging with (68)Ga-DOTA-octreotide could be a potential tool for evaluating BCM., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Unlabelled: The purpose of this study was to determine the safety, distribution, internal dosimetry, and initial human epidermal growth factor receptor 2 (HER2)-positive tumor images of (64)Cu-DOTA-trastuzumab in humans., Methods: PET was performed on 6 patients with primary or metastatic HER2-positive breast cancer at 1, 24, and 48 h after injection of approximately 130 MBq of the probe (64)Cu-DOTA-trastuzumab. Radioactivity data were collected from the blood, urine, and normal-tissue samples of these 6 patients, and the multiorgan biodistribution and internal dosimetry of the probe were evaluated. Safety data were collected for all the patients after the administration of (64)Cu-DOTA-trastuzumab and during the 1-wk follow-up period., Results: According to our results, the best timing for the assessment of (64)Cu-DOTA-trastuzumab uptake by the tumor was 48 h after injection. Radiation exposure during (64)Cu-DOTA-trastuzumab PET was equivalent to that during conventional (18)F-FDG PET. The radioactivity in the blood was high, but uptake of (64)Cu-DOTA-trastuzumab in normal tissues was low. In 2 patients, (64)Cu-DOTA-trastuzumab PET showed brain metastases, indicative of blood-brain barrier disruptions. In 3 patients, (64)Cu-DOTA-trastuzumab PET imaging also revealed primary breast tumors at the lesion sites initially identified by CT., Conclusion: The findings of this study indicated that (64)Cu-DOTA-trastuzumab PET is feasible for the identification of HER2-positive lesions in patients with primary and metastatic breast cancer. The dosimetry and pharmacologic safety results were acceptable at the dose required for adequate PET imaging.

We developed a pravastatin derivative, sodium (3R,5R)-3,5-dihydroxy-7-((1S,2S,6S,8S)-6-hydroxy-2-methyl-8-((1-[(11)C]-(E)-2-methyl-but-2-enoyl)oxy)-1,2,6,7,8,8a-hexahydronaphthalen-1-yl)heptanoate ([(11)C]DPV), as a positron emission tomography (PET) probe for noninvasive measurement of hepatobiliary transport, and conducted pharmacokinetic analysis in rats as a feasibility study for future clinical study. Transport activities of DPV in freshly isolated rat hepatocytes and rodent multidrug resistance-associated protein 2 (rMrp2; human, MRP2)-expressing membrane vesicles were similar to those of pravastatin. Rifampicin diminished the uptake of DPV and pravastatin by the hepatocytes, with similar inhibition potency. [(11)C]DPV underwent biotransformation to produce at least two metabolites in rat, but metabolism of [(11)C]DPV occurred negligibly in human hepatocytes during a 90-minute incubation. After intravenous injection, [(11)C]DPV was mainly distributed to the liver and kidneys, where the tissue uptake clearances (CLuptake,liver and CLuptake,kidney) were blood-flow-limited (73.6 ± 4.8 and 24.6 ± 0.6 ml/min per kilogram, respectively). Systemic elimination of [(11)C]DPV was delayed in rifampicin-treated rat and an Mrp2-deficient mutant rat, Eisai hyperbilirubinemic mutant rat (EHBR). Rifampicin treatment decreased both CLuptake,liver and CLuptake,kidney of [(11)C]DPV by 30% (P < 0.05), whereas these parameters were unchanged in EHBR. Meanwhile, the canalicular efflux clearance (CLint,bile) of [(11)C]DPV, which was 12.2 ± 1.5 ml/min per kilogram in the control rat, decreased by 60% and 89% in rifampicin-treated rat and EHBR (P < 0.05), respectively. These results indicate that [(11)C]DPV is taken up into the liver by organic anion-transporting polypeptides (rodent, Oatps; human, OATP) and excreted into bile by Mrp2 in rat, and that rifampicin may inhibit Mrp2 as well as Oatps, and consequently increase systemic exposure of [(11)C]DPV. PET using [(11)C]DPV is feasible for studies prior to the future clinical investigation of OATP and MRP2 functionality, especially for personalized medicine.

Among noninvasive functional brain imaging techniques, (18) F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) has a comparative advantage in detecting active brain regions in freely locomoting animals. We developed an [(18) F]FDG-PET protocol that visualizes active brain regions that respond preferentially to citrate-induced multiple behaviors in freely locomoting rats. In addition, c-Fos immunohistochemistry, an activity-dependent mapping, was performed to examine whether the areas detected by PET correspond to regions with c-Fos-immunopositive neurons. Citrate (0.1 M) was intraorally applied to detect activated brain regions responding to gustation and the rejection behaviors including gaping and tongue protrusion, which would potently activate the limbic system. PET images during citrate stimulation were subtracted from those obtained during free locomotion or during application of distilled water. Citrate increased FDG signals in multiple gustation-related regions: the nucleus accumbens (core and shell), the ventromedial nucleus of the thalamus, the basolateral and central nuclei of the amygdala, the hypothalamus, and the insular cortex. In addition, the ventrolateral striatum and the cingulate and entorhinal cortices, which have received less attention in the field of gustatory studies, also showed an increase in FDG signals. As expected, c-Fos-immunopositive cells were also found in these regions, suggesting that increased FDG signals induced by intraoral citrate injection are likely to reflect neural activity in these regions. Our [(18) F]FDG-PET protocol reveals the contributions of multiple brain regions responding to aversive taste in freely locomoting rats, and this approach may aid in the identification of unknown neural networks especially relating to the limbic information processing., (Copyright © 2013 Wiley Periodicals, Inc.)

Objective: Targeted photodynamic therapy (PDT) is necessary for preventing the side effects associated with PDT, such as photosensitivity caused by the distribution of photosensitizers into normal tissues. In the development of targeted PDT agents, a simple evaluation system of in vivo pharmacokinetics, as well as target cell uptake, is absolutely imperative. We hypothesized that (64)Cu chelation with porphyrin photosensitizer-biomacromolecule conjugates may become a simple and versatile labeling strategy for this purpose., Methods: Protoporphyrin IX (PPIX) and a bombesin (BBN) analog, that interacts with the gastrin-released peptide (GRP) receptor, were used as a photosensitizer and tumor-targeting peptide, respectively. Then, a conjugate of PPIX and BBN analog linked via short polyethylene glycol (PPIX-PEG6-BBN analog) was synthesized and used as a targeted PDT agent. In addition, a (64)Cu-chelated PPIX-PEG6-BBN analog was synthesized under optimized reaction conditions. Lastly, cell uptake study and PET image-based pharmacokinetic analyses of the PPIX-PEG6-BBN analog were carried out in a human prostate cancer cell line, PC-3, which highly expresses the GRP receptor, and PC-3 tumor-bearing mice., Results: It was confirmed that degradation (thought to be based on radiolysis) occurs, and large amounts of (64)Cu-labeling compounds are wasted in the reaction mixture. Interestingly, the addition of ethanol into the reaction mixture provides an effective solution for this problem. As for cell uptake study, the [(64)Cu]PPIX-PEG6-BBN analog demonstrated significantly higher uptake for PC-3 cells than [(64)Cu]PPIX and, in addition, the uptake of [(64)Cu]PPIX-PEG6-BBN analog was significantly inhibited by adding excess cold BBN analog peptide. PET image-based pharmacokinetic evaluation revealed that [(64)Cu]PPIX-PEG6-BBN analog and [(64)Cu]PPIX rapidly accumulate into the liver and kidney, circulate in blood for a long time compared with normal peptides, and distribute at a low level in the tumor. This result suggested that in vivo biodistribution of PPIX-PEG6-BBN analog is mainly dependent on the lipophilicity of PPIX. Ex vivo measurements of radioactivity distribution after PET studies showed that although there was no remarkable difference in the tumor/skin ratio of radioactivity between [(64)Cu]PPIX-PEG6-BBN analog and [(64)Cu]PPIX, the pancreas (an organ that also expresses GRP receptors)/skin ratio was significantly higher in the case of [(64)Cu]PPIX-PEG6-BBN analog., Conclusion: We report on the successful synthesis of (64)Cu-chelated porphyrin photosensitizers and their tumor-targeting peptide conjugates under conditions in which radiolysis is suppressed. This labeling strategy with porphyrin photosensitizers may be of value for the rapid development of ideal targeted PDT agents.

A radiolabeled PET! A (11) C-labeled derivative of N,N'-(methylenedi-4,1-phenylene)bis[2-(1-pyrrolidinyl) acetamide] (GN8), an antiprion agent currently under development, was synthesized by palladium-catalyzed rapid methylation of aryltributylstannane and assessed for brain penetration and organ distribution in rats by positron emission tomography (PET)., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

To develop potent drugs for oral use, information on their pharmacokinetic (PK) properties after oral administration is of great importance. We have recently reported the utility of positron emission tomography (PET) for the analysis of gastrointestinal (GI) absorption of radiolabeled compounds. In this study, PET image analysis was performed in rats using a novel PET probe, [(18)F]deoxyfluoropoly(ethylene glycol)s, with an average molecular weight of 2 kDa ([(18)F]FPEG), as a nonabsorbable marker to elaborate the GI physiology in more detail, such as segmental transition of the administered water, and fluid volume and distribution in the intestine. After oral administration of [(18)F]FPEG solution to rats, a 90 min PET scan with continuous blood sampling was performed, and then the disposition of radioactivity in each part of GI tract was investigated. From blood PK analysis, it was confirmed that the bioavailability of [(18)F]FPEG was quite low in rats. PET image analysis showed that the radioactivity after oral administration of [(18)F]FPEG solution rapidly passed through the stomach, spread into the proximal small intestine, and then transited toward the distal region of the small intestine without decreasing the radioactivity during GI transition. Radiometabolite analysis revealed that the radioactivity in intestinal mucosal tissues, blood, and urine was mainly derived from unchanged [(18)F]FPEG. It was also found that the volume of interest (VOI) after oral administration of the radiotracer enables an understanding of the time-dependent manner of effective fluid volume changes in the stomach and the small intestine. In addition, the rate constant of the intestinal transition of radioactivity in each intestinal segment was calculated by kinetic model analysis, which revealed that PET analysis enables us to determine the GI transit from the same individuals and that it is applicable to determine site-specific intestinal absorption. In conclusion, we demonstrated the high potency of PET imaging technique to elucidate the distribution of orally administered solution in the GI tract in vivo.

Objective: To improve the reliability and convenience of the calibration procedure of positron emission tomography (PET) scanners, we have been developing a novel calibration path based on traceable point-like sources. When using (22)Na sources, special care should be taken to avoid the effects of 1.275-MeV γ rays accompanying β (+) decays. The purpose of this study is to validate this new calibration scheme with traceable point-like (22)Na sources on various types of PET scanners., Method: Traceable point-like (22)Na sources with a spherical absorber design that assures uniform angular distribution of the emitted annihilation photons were used. The tested PET scanners included a clinical whole-body PET scanner, four types of clinical PET/CT scanners from different manufacturers, and a small-animal PET scanner. The region of interest (ROI) diameter dependence of ROI values was represented with a fitting function, which was assumed to consist of a recovery part due to spatial resolution and a quadratic background part originating from the scattered γ rays., Results: The observed ROI radius dependence was well represented with the assumed fitting function (R (2) > 0.994). The calibration factors determined using the point-like sources were consistent with those by the standard cross-calibration method within an uncertainty of ±4 %, which was reasonable considering the uncertainty in the standard cross-calibration method., Conclusion: This novel calibration scheme based on the use of traceable (22)Na point-like sources was successfully validated for six types of commercial PET scanners.

Unlabelled: A quantitative PET imaging method was used to assess the in vivo kinetics of hepatobiliary and renal excretion of the breast cancer resistance protein (Bcrp) substrate (11)C-SC-62807 in mice., Methods: Serial abdominal PET scans were collected in wild-type and Bcrp knockout (Bcrp(-/-)) mice after intravenous injection of (11)C-SC-62807. Venous blood samples and PET images were obtained at frequent intervals up to 30 min after radiotracer administration. Dynamic PET data were analyzed to determine the canalicular and brush-border efflux clearances in the liver and kidney (CL(int,bile,liver) and CL(int,urine,kidney), respectively)., Results: SC-62807 is an in vitro substrate of mouse Bcrp and human BCRP. Radioactivity associated with (11)C-SC-62807 was predominantly found in the blood, liver, bile, and urine 30 min after administration. Both biliary and urinary excretion of radioactivity was markedly lower in Bcrp(-/-) mice than in wild-type mice, suggesting greater systemic exposure in Bcrp(-/-) mice. Both the CL(int,bile,liver) and the CL(int,urine,kidney) were significantly lower in Bcrp(-/-) mice (74% ± 10% and 99% ± 1% lower than controls, respectively). We also found that (11)C-SC-62807 is a substrate of the organic anion-transporting polypeptides OATP1B1 and OATP1B3 in vitro., Conclusion: The present study demonstrated that Bcrp plays a significant role in the efflux of (11)C-SC-62807 in mouse liver and kidney. We also demonstrated the feasibility of PET using (11)C-SC-62807 to study the activity of BCRP in humans.

Background:  High-density lipoprotein (HDL) plays a major role in reverse cholesterol transport. Many researchers have been working to enhance the biochemical function of HDL for use in therapy. Although HDL therapy using injections of apolipoprotein (apo)-A-I mimetics, apo A-I Milano or full-length apo A-I is dramatically effective, it is still unclear whether apo A-I or apo A-I mimetics actually enter atherosclerotic plaque and remove cholesterol from the lipid burden. We synthesized a novel 24-amino acid apo A-I mimetic peptide (known as FAMP) that potently removes cholesterol via specific ATP-binding cassette transporter A1. We then investigated the potential of FAMP to image developing plaque lesions in vivo., Methods and Results:  FAMP was modified with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) and radiolabeled with gallium-68 ((68)Ga) for noninvasive positron emission tomography (PET) in an animal model (familial hypercholesterolemic myocardial infarction-prone rabbits: WHHL-MI) with atherosclerotic lesions. The (68)Ga-DOTA-FAMP was dramatically taken up by atherosclerotic tissues in the blood vessels and aorta of WHHL-MI rabbits, but not the control rabbits., Conclusions:  An apo A-I mimetic peptide with (68)Ga-DOTA is a promising candidate diagnostic tracer for PET imaging of the atherosclerotic lipid burden and may contribute to the development of a tool for the diagnosis of plaque with PET.

Purpose: To dynamically analyze the processes of oral absorption and hepatobiliary distribution of telmisartan using positron emission tomography (PET)., Methods: (11)C-labeled telmisartan ([(11)C]TEL) was orally administered to rats with or without non-radiolabeled telmisartan (0.5, and 10 mg/kg). PET scanning of abdominal region and whole body was performed under conscious condition. In situ intestinal closed loop study in rats and in vitro permeation study in MDR1-MDCK II cell monolayers were also conducted., Results: After oral administration of [(11)C]TEL, systemic bioavailability and hepatic distribution of radioactivity increased non-linearly with dose. In the intestinal lumen, both telmisartan and its glucuronide were detected and the ratio of telmisartan decreased dramatically at high dose of telmisartan. In situ closed loop study showed most of telmisartan-glucuronide detected in the intestinal lumen was derived from the bile excretion. In addition, in vitro permeation study revealed that telmisartan is a substrate of P-glycoprotein., Conclusion: PET imaging analysis successfully demonstrated the processes of intestinal absorption and hepatic distribution of telmisartan. PET study combined with appropriate in situ and in vitro experiments is highly expected to be a potent tool for better understanding of GI absorption and subsequent tissue distribution of various drugs and drug candidates.

Unlabelled: It is well accepted that drug transporters play a pivotal role in hepatobiliary excretion of anionic drugs, in which drug-drug interactions and genetic polymorphisms are known to cause variations. However, PET probes for in vivo functional characterization of these transporters have not been established yet. We used PET to investigate hepatic uptake and subsequent canalicular efflux of (11)C-labeled (15R)-16-m-tolyl-17,18,19,20-tetranorisocarbacyclin methyl ester [(15R)-(11)C-TIC-Me)] in healthy subjects., Methods: Serial PET scans of the abdominal region in healthy male subjects were obtained with or without the organic anion-transporting polypeptide (OATP) inhibitor rifampicin after intravenous injection of (15R)-(11)C-TIC-Me as a radiotracer. Venous blood samples and PET images were obtained at frequent intervals up to 30 min after administration of the PET tracer. Dynamic imaging data were evaluated by integration plots of data collected for 2-10 min and for 10-30 min after tracer administration for the determination of tissue uptake clearance and biliary efflux clearance, respectively., Results: After rapid hydrolysis in blood, the acid form-(11)C-labeled (15R)-16-m-tolyl-17,18,19,20-tetranorisocarbacyclin [(15R)-(11)C-TIC]-accumulated in the liver (37% of the dose by 17 min), and the radioactivity was then excreted into the bile (6.2% by 30 min). Rifampicin (600 mg by mouth), a potent OATP inhibitor, significantly reduced the radioactivity excreted into the bile (by 44%) by inhibiting both uptake (by 45%) and subsequent canalicular efflux (by 62%). (15R)-(11)C-TIC is an in vitro substrate of OATP1B1 and OATP1B3, and clinically relevant concentrations of rifampicin inhibited uptake by OATP1B1 and OATP1B3. These results demonstrated that in humans, (15R)-(11)C-TIC-associated radioactivity is excreted into the bile by organic anion transport systems., Conclusion: We demonstrated that PET image analysis with (15R)-(11)C-TIC-Me is useful for investigating variations in OATP function in the human hepatobiliary transport system.

The purpose of this study was to establish a method for imaging the process of gastrointestinal (GI) absorption and subsequent biodistribution in the human body after oral drug administration, using positron emission tomography (PET) with 2-[(18)F]fluoro-2-deoxy-D-glucose ([(18)F]FDG). First, we developed a method to deliver the radiotracer safely into the stomach using soft gelatin capsules to avoid any significant exposure to the pharyngoesophageal region. Second, we performed pharmacokinetic (PK) analyses on time-radioactivity profiles in GI tissues and blood to calculate the gastric emptying and intestinal elimination rate constants and to estimate the fluid volume in the lumen of the small intestine from PET image analysis. This is the first study involving oral administration of a PET probe in humans, and the results demonstrate the high potential of PET technology to investigate the GI absorption and PK profiles of drugs in humans.

The synthesis and in vivo evaluation of (11)C -labeled uric acid ([(11)C]1), a potential imaging agent for the diagnosis of urate-related life-style diseases, was performed using positron emission tomography (PET) image analysis. First, the synthesis of [(11)C]1 was achieved by reacting 5,6-diaminouracil (2) with (11)C-labeled phosgene ([(11)C]COCl(2)). The radiochemical yield of [(11)C]1 was 37±7% (decay-corrected based on [(11)C]COCl(2)) with specific radioactivities of 96-152GBq/μmol at the end of synthesis (n=6). The average time of radiosynthesis from the end of bombardment, including formulation, was about 30min with >98% radiochemical purity. Second, the synthetic approach to [(11)C]1 was optimized using 5,6-diaminouracil sulfate (3) with [(11)C]COCl(2) in the presence of 1,8-bis(dimethylamino)naphthalene. [(11)C]1 was synthesized in 36±6% radiochemical yield, 89-142GBq/μmol of specific radioactivities, and 98% radiochemical purity by this method (n=5). This allowed the synthesis of [(11)C]1 to be carried out repeatedly and the radiochemical yield, specific radioactivities, average time of synthesis, and radiochemical purity of [(11)C]1 were similar to those obtained using 2. PET studies in rats showed large differences in the accumulation of radioligand in the limbs under normal and hyperuricemic conditions. Thus, an efficient and convenient automated synthesis of [(11)C]1 has been developed, and preliminary PET evaluation of [(11)C]1 confirmed the increased accumulation of radioactivity in the limbs of a rat model of hyperuricemia., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Unlabelled: Aromatase is a rate-limiting enzyme for estrogen biosynthesis and has been implicated in pathophysiological states of various diseases via estrogen production. This enzyme is known to be widely distributed in extragonadal and gonadal tissues including the stomach. In contrast to circulating estrogen, the functional role of gastric aromatase/estrogen has not been elucidated in detail, because there is no efficient methodology to investigate spatiotemporal changes of gastric aromatase/estrogen in vivo. Recently, (S)-(11)C-6-[(4-chlorophenyl)(1H-1,2,4-triazole-1-yl)methyl]-1-methyl-1H-benzotriazole ((11)C-labeled vorozole), based on a potent nonsteroidal aromatase inhibitor, has been developed as a tracer to investigate aromatase distribution in living animals and humans using a noninvasive PET technique. In the present study, we investigated gastric aromatase expression by means of PET with (11)C-vorozole., Methods: After bolus injection of (11)C-vorozole into the tail vein, emission scans were obtained for 90 min on male and female rats under isoflurane anesthesia. Displacement studies with unlabeled vorozole and autoradiographic analysis were conducted for demonstration of specific binding. Immunohistochemistry was performed to confirm aromatase expression., Results: PET scans revealed that (11)C-vorozole highly accumulated in the stomach and adrenal glands. Displacement studies and autoradiography demonstrated that aromatase was expressed in the stomach but that the accumulation of (11)C-vorozole in the adrenal glands might be through nonspecific binding. Immunohistochemical analysis revealed that aromatase is expressed in gastric parietal cells but not in adrenal glands. Moreover, the accumulation of (11)C-vorozole in the stomach was significantly increased in fatigued rats., Conclusion: These results suggest that the (11)C-vorozole PET technique is a useful tool for evaluation of gastric aromatase dynamics in vivo, which may provide important information for understanding the molecular mechanisms of gastric aromatase/estrogen-related pathophysiological processes and for the development of new drugs.

The uncertainty of radioactivity concentrations measured with positron emission tomography (PET) scanners ultimately depends on the uncertainty of the calibration factors. A new practical calibration scheme using point-like (22)Na radioactive sources has been developed. The purpose of this study is to theoretically investigate the effects of the associated 1.275 MeV γ rays on the calibration factors. The physical processes affecting the coincidence data were categorized in order to derive approximate semi-quantitative formulae. Assuming the design parameters of some typical commercial PET scanners, the effects of the γ rays as relative deviations in the calibration factors were evaluated by semi-quantitative formulae and a Monte Carlo simulation. The relative deviations in the calibration factors were less than 4%, depending on the details of the PET scanners. The event losses due to rejecting multiple coincidence events of scattered γ rays had the strongest effect. The results from the semi-quantitative formulae and the Monte Carlo simulation were consistent and were useful in understanding the underlying mechanisms. The deviations are considered small enough to correct on the basis of precise Monte Carlo simulation. This study thus offers an important theoretical basis for the validity of the calibration method using point-like (22)Na radioactive sources.

Amyloid imaging has been used to detect amyloid deposition in the brain. We performed Pittsburgh compound B (PiB)-positron emission tomography on 63 patients with dementia having cognitive decline or memory disturbance. In addition, we measured the patients' apolipoprotein E4 (apo E4) status and cerebrospinal fluid (CSF) levels of amyloid-β (Aβ)1-42, tau, and P-tau. Finally, the patients were diagnosed as having probable Alzheimer disease (AD) on the basis of their neuropsychological findings and because they met the National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer's Disease and Related Disorders Association criteria. Among the patients diagnosed with probable AD, 10 patients were PiB negative. The CSF levels of P-tau and tau in PiB-negative patients were significantly lower than those in the PiB-positive patients. In addition, the CSF levels of Aβ1-42 in the PiB-negative patients were significantly higher than those in the PiB-positive patients. None of the PiB-negative patients were apo E4 carriers. These results suggest that the PiB-negative patient group included not only AD patients but also non-AD-type dementia patients. However, our finding is based on a relatively small number of patients and therefore should be replicated in a larger cohort. In addition, it will be necessary to categorize these participants by longitudinal follow-up and postmortem pathological examinations.

A practical method to prepare precursor of [N-methyl-(11)C]vorozole ([(11)C]vorozole), an efficient positron emission tomography (PET) tracer for imaging aromatase in the living body, was established. Sufficient amount of the racemate including norvorozole, a demethylated vorozole derivative used as a precursor of [(11)C]vorozole, became available by means of high-yield eight-step synthesis. The enantiomers were separated by preparative HPLC using a chiral stationary phase column to give optically pure norvorozole and its enantiomer. From the latter, ent-[(11)C]vorozole, an enantiomer of [(11)C]vorozole, was prepared and used in the PET study for the first time, which was shown to bind very weakly to aromatase in rhesus monkey brain supporting the previous pharmacological results. The stable supply of norvorozole will facilitate further researches on aromatase in the living body including brain by the PET technique., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

A quantitative positron emission tomography (PET) methodology was developed for in vivo kinetic analysis of hepatobiliary transport. Serial abdominal PET scans were performed on normal and multidrug resistance-associated protein 2 (Mrp2)-deficient rats after intravenous injection of (15R)-16-m-[(11)C]tolyl-17,18,19,20-tetranorisocarbacyclin methyl ester (15R-[(11)C] TIC-Me) as a radiotracer. 15R-[(11)C]TIC-Me was rapidly converted to its acid form in blood within 10 s. PET scans revealed that 15R-[(11)C]TIC was localized mainly in the liver within 5 min of injection. By 90 min, total radioactivity in bile of Mrp2-deficient rats was significantly reduced compared with controls. Metabolite analysis by thin-layer chromatography autoradiography showed that 15R-[(11)C]TIC is converted to at least three metabolites (M1, M2, and M3), and M2 and M3 are the major metabolites in plasma and bile, respectively. Hepatic uptake clearance of total radioactivity in normal rats was close to the hepatic blood flow rate and slightly higher than that in Mrp2-deficient rats. The intrinsic canalicular efflux clearance of M3 (CL(int,bile,M3)) in Mrp2-deficient rats was decreased to 12% of controls, whereas clearance of M2 was moderately decreased (54%). An in vitro transport assay detected ATP-dependent uptake of both M2 and M3 by rat Mrp2-expressing membrane vesicles. These results demonstrated that M3 is excreted primarily into the bile by Mrp2 in normal rats. We conclude that PET studies using 15R-[(11)C]TIC-Me could be useful for in vivo analyses of Mrp2-mediated hepatobiliary transport.

Purpose: Thus far, cylindrical phantoms with (18)F or (68)Ge/(68)Ga have been used in the standard techniques for determining the cross-calibration factors (CCFs) of PET scanners. This paper describes a new practical method that uses a point-like (22)Na radioactive source for determining CCFs., Methods: A point-like (22)Na radioactive source (about 700 kBq) was equipped with a spherical aluminium absorber capsule to ensure the symmetry of the emitted photons. During measurements, the source was moved in the axial direction to cover the whole axial field of view (FOV) of a clinical PET scanner, SET-2400 W. The region-of-interest (ROI) values obtained in reconstructed images without scatter and attenuation corrections were used to calculate the CCFs of the PET scanner., Results: The CCFs obtained by the proposed method agreed with those obtained by the standard cross-calibration (CC) method within a precision of 1.5% (σ). The temporal variations in the CCFs by the standard CC method were reproduced by the proposed method with a precision better than 1%., Conclusion: The CC method with a moving (22)Na point-like radioactive source is practically useful for determining the CCFs of PET scanners and monitoring their variations.

Molecular imaging technique by use of positron emission tomography (PET) is a noninvasive tool that allows one to quantitatively analyze the function of endogenous molecules and the pharmacokinetics of therapeutic agents in vivo. This technique is expected to be useful for evaluating the effectiveness of diverse drug delivery systems. We demonstrated previously that intestinal insulin absorption is increased significantly by coadministration of cell-penetrating peptides (CPPs), which are taken up effectively by several cells. However, the distribution behavior of insulin whose absorption is increased by CPPs is not clear. We used PET imaging and quantitatively analyzed the intestinal absorption and subsequent distribution of insulin and the effect of CPPs on its absorption and distribution. An unlabeled insulin solution containing tracer insulin, (68)Ga-DOTA-insulin, was administered with or without CPPs into a rat ileal closed loop. PET imaging showed that the CPPs, particularly D-R8 and L-penetratin, significantly increased the (68)Ga-DOTA-insulin level in the liver, kidney, and circulation. After absorption from the intestine, the (68)Ga-DOTA-insulin passed rapidly through the liver and accumulated in the kidney. The increase in the hepatic and renal distribution of (68)Ga-DOTA-insulin by each CPP coadministration was similar manner as that in intestinal absorption, suggesting that the increased accumulation of insulin in the liver and kidney induced by coadministration of CPPs was associated with the increased intestinal absorption of insulin. This is the first study to show that PET imaging enables one to quantitatively analyze the distribution behavior of intestinally absorbed insulin in several organs. This imaging methodology is likely to be useful for developing effective drug delivery systems targeted to specific organs., (Copyright 2010 Elsevier B.V. All rights reserved.)

Objective: Radioactive sources for evaluating sensitivity and uncertainty in the radioactivity measurements performed using PET scanners must be equipped with absorber materials that ensure the annihilation of positrons. Attenuation and scattering owing to the absorber materials produce uncertainty in the performance evaluation. The aim of this study is to propose a point-like radioactive source with multiple absorber capsules, for which evaluation can be independent of scatter and attenuation owing to the source absorbers., Methods: The point-like source consists of a small spherical radioactive part and a set of successively sized cylindrical aluminum absorber capsules. Data were collected for different total absorber thicknesses. By an extrapolation technique, the effects of the source absorbers were eliminated. Sensitivity and uncertainty in the radioactivity measurements of PET scanners were evaluated with this technique., Results: Sensitivity and uncertainty of radioactivity measurement to the point-like radioactive source were evaluated successfully with this method., Conclusion: The proposed point-like radioactive source is useful for evaluating performance characteristics of PET scanners in a way that is independent of the effects of the source absorbers.

Unlabelled: 18F-FDG PET is used mainly in clinical settings for imaging focal cancer sites, but the usefulness of the modality in imaging gastrointestinal ulcers has not been established. We investigated whether PET can be used for noninvasive monitoring of indomethacin-induced small-intestine ulceration., Methods: Intestinal ulcers were induced in rats by subcutaneous administration of indomethacin. An 18F-FDG PET scan was obtained at 1, 2, and 7 d after indomethacin administration. 18F-FDG uptake in the small intestine was quantified by gamma-counting, and macro- and microautoradiographic studies were performed to determine the site of 18F-FDG uptake in tissue and at the cellular level., Results: Ulcers observed in the intestine (mainly in the ileum) 1-4 d after indomethacin administration were most severe at 1 d after administration and were almost healed at day 7. The PET study showed increased 18F-FDG uptake in the intestine correlating to the severity of ulceration, returning to the basal level on day 7. Ex vivo imaging and gamma-counting showed that these regions of high uptake corresponded to regions of ulceration. A microautoradiographic study combined with immunohistochemistry revealed heavy accumulation of 18F-FDG in inflammatory cells containing peroxidase on day 1 and in cells forming granulation tissue (alpha-smooth muscle actin-positive myofibroblasts and ED2-positive macrophages) on days 2-4 in and around ulcers. Proliferating (Ki67-immunopositive) intestinal crypt cells were also densely labeled with 18F-FDG in intact intestinal tissue taken from the indomethacin-treated and the control animals., Conclusion: Our experimental data suggest that 18F-FDG PET may be useful for evaluating the occurrence of small-intestine ulcers. Ulceration could be visualized early by the prominent uptake of 18F-FDG by inflammatory cells and by the formation of granulation tissue by cells in and around ulcers.

The objective of this study was to evaluate the early changes after radiofrequency ablation (RFA) in VX2 rabbit tumors implanted into the back muscles by diffusion-weighted magnetic resonance (MR) imaging and (18)F-2-fluoro-2-deoxy-D-glucose positron emission tomography ((18)F-FDG PET). Percutaneous CT-guided RFA was conducted in seven rabbits with implanted VX2 tumors. VX2 tumors on the other side were untreated and served as the control. MR imaging was performed with a clinical 1.5-T instrument 2 days after RFA, and FDG-PET, using a high-resolution PET scanner for small animals, was obtained 3 days after the procedure. The mean apparent diffusion coefficient (ADC) values and radioactivity count of untreated and ablated tumors were calculated. Untreated VX2 tumors showed hyperintensity on T1-, T2-, and diffusion-weighted MR images, ring-enhanced on contrast-enhanced T1-weighted imaging, and ring-shaped FDG accumulation on FDG-PET. Ablated VX2 tumors showed slight hyperintensity on T1-, T2-, and diffusion-weighed images, slight enhancement on contrast-enhanced T1-weighted images, and low accumulation on FDG-PET. The ADC value of ablated VX2 tumors (1.52 +/- 0.24 x 10(-3) mm(2)/s) was significantly higher than that of untreated tumors (1.09 +/- 0.12 x 10(-3); p < 0.05). The tumor/muscle ratio of ablated tumors (0.5 +/- 0.3) was significantly lower than that of untreated tumors (11.6 +/- 3.2; p < 0.05). Histopathological examination confirmed the lack of viable tumor cells in the ablated lesions. The results indicate that both ADC value and FDG-PET are potentially useful markers for monitoring the early effects of RFA.

Purpose: Positron emission tomography (PET) is a powerful tool for measuring in vivo functions such as blood flow, metabolism, enzyme activity, receptors, and transporters. However, plural measuring instruments (i.e., the dose-calibrator, the auto well gamma counter, the continuous blood sampling system) are necessary for the quantitative PET measurement as well as the PET scanner. The purpose of this study was to investigate the reliability of plural measuring instruments from the maintenance data for 6 years., Methods: Four kinds of measuring instrument were evaluated: a dose-calibrator (CAPINTEC, CRC-15R), an auto well gamma counter (ALOKA, ARC-400), a continuous blood sampling system (ESPEC Techno, PH type), and a dedicated PET scanner (Siemens, ECAT EXACT HR+). We examined whether the initial performance for system sensitivity is maintained. The reliability of the PET scanner was evaluated from the value of mean time between failures (MTBF) for each part of the system obtained from the maintenance data for 6 years., Results: The sensitivity of a dose-calibrator and an auto well gamma counter were maintained virtually constant during the 6 years, but the sensitivity of a continuous blood sampling system was 0.1+/-3.2%. The sensitivity of a PET scanner was decreased to 92.3% of the initial value. Fifty-one percent of the problems with the PET scanner were for detector block (DB) and analog processor (AP) board. The MTBF of DB and AP board module were 199 and 244 days, respectively. The MTBF of the PET scanner was 56 days., Conclusion: The performance of three measuring instruments, excepting the PET scanner, was relatively stable. The reliability of the PET scanner strongly depends on the MTBF of the DB and AP board. For quantitative PET measurement, it is effective to evaluate the reliability of the system and to make it known to the users.

Purpose: We investigated the optimum time for the differentiation tumor from inflammation using dynamic FDG-microPET scans obtained by a MicroPET P4 scanner in animal models., Materials and Methods: Forty-six rabbits with 92 inflammatory lesions that were induced 2, 5, 7, 14, 30 and 60 days after 0.2 ml (Group 1) or 1.0 ml (Group 2) of turpentine oil injection were used as inflammatory models. Five rabbits with 10 VX2 tumors were used as the tumor model. Helical CT scans were performed before the PET studies. In the PET study, after 4 hours fasting, and following transmission scans and dynamic emission data acquisitions were performed until 2 hours after intravenous FDG injection. Images were reconstructed every 10 minutes using a filtered-back projection method. PET images were analyzed visually referring to CT images. For quantitative analysis, the inflammation-to-muscle (I/M) ratio and tumor-to-muscle (T/M) ratio were calculated after regions of interest were set in tumors and muscles referring to CT images and the time-I/M ratio and time-T/M ratio curves (TRCs) were prepared to show the change over time in these ratios. The histological appearance of both inflammatory lesions and tumor lesions were examined and compared with the CT and FDG-microPET images., Results: In visual and quantitative analysis, All the I/M ratios and the T/M ratios increased over time except that Day 60 of Group 1 showed an almost flat curve. The TRC of the T/M ratio showed a linear increasing curve over time, while that of the I/M ratios showed a parabolic increasing over time at the most. FDG uptake in the inflammatory lesions reflected the histological findings. For differentiating tumors from inflammatory lesions with the early image acquired at 40 min for dual-time imaging, the delayed image must be acquired 30 min after the early image, while imaging at 90 min or later after intravenous FDG injection was necessary in single-time-point imaging., Conclusion: Our results suggest the possibility of shortening the overall testing time in clinical practice by adopting dual-time-point imaging rather than single-time-point imaging.

Unlabelled: The primary goals of this study were to investigate the behavior of normal lung tissues after radiofrequency ablation (RFA) and to determine the suitability of 18F-FDG PET, using a dedicated small-animal scanner, for monitoring the early therapeutic effects of RFA on VX2 lung tumors (VX2s) in rabbits., Methods: Fourteen Japanese white rabbits with normal lungs underwent RFA, followed by 18F-FDG PET at 1 d and at 1, 2, 4, and 8 wk. In addition, 7 rabbits with untreated VX2s underwent 18F-FDG PET, and 13 rabbits with RFA-treated VX2s underwent 18F-FDG PET at 1 d (n = 7) or 1 wk (n = 6) after the treatment., Results: After RFA of normal lungs, ring-shaped accumulations of 18F-FDG, which coincided with inflammation caused by ablation, were observed. The mean early- (40-60 min after injection) and delayed (100-120 min)-phase ablated lesion-to-muscle ratios were, respectively, 2.9 +/- 1.0 and 3.3 +/- 0.8 (1 d), 4.1 +/- 0.6 and 5.2 +/- 0.9 (1 wk), 4.1 +/- 1.0 and 5.3 +/- 1.5 (2 wk), 3.1 +/- 0.5 and 3.6 +/- 1.1 (4 wk), and 1.8 +/- 0.1 and 2.3 +/- 0.1 (8 wk). At 4 and 8 wk, the uptake was less than that at 1 and 2 wk (P < 0.05). VX2s showed mean tumor-to-muscle ratios of 6.6 +/- 2.1 and 8.6 +/- 3.3 at the early and delayed phases, respectively. For ablated tumors, the respective ratios were 0.8 +/- 0.4 and 1.1 +/- 0.7 (1 d) and 1.2 +/- 0.5 and 1.5 +/- 0.7 (1 wk). These values were significantly lower than those for nonablated tumors (P < 0.001). Histopathologic examination confirmed the absence of viable tumors. 18F-FDG accumulation around ablated tumors reflected thermally damaged normal tissues and was significantly lower than that of control VX2s (P < 0.01)., Conclusion: Our data suggest that 18F-FDG PET is promising for evaluating the therapeutic response of lung malignancies to RFA: Accumulation of 18F-FDG in surrounding normal tissues appears to be time dependent, and the data suggest that, clinically, 18F-FDG PET should be performed 4 wk or more after RFA. Delayed-phase images seem to better distinguish tumor from inflammation than do early-phase images.

Purpose: The aim of this study was to determine the potential use of high-resolution FDG-microPET for predicting the primary effects of radiotherapy and/or hyperthermia on tumor-bearing rabbits., Methods: Twenty-eight VX2 xenografts in the thighs of rabbits were divided into the following 5 treatment groups: radiotherapy at a single dose of 10, 20 or 30 Gy, hyperthermia (43 degrees Celsius, 1 hour), and the combination of radiotherapy and hyperthermia (10 Gy + 43 degrees Celsius, 1 hour). FDG-microPET images were obtained by using a microPET P4 system at pretreatment and at 24 hours and 7 days after treatment. For the evaluation by FDG-microPET, tumor/muscle (T/M) ratios, retention index [RI = (T/M ratio at 120 min - T/M ratio at 60 min) / T/M ratio at 60 min], and time activity curve (TAC) were acquired., Results: We divided the xenografts into a responder group (partial response + stable disease, n=14) and a non-responder group (progressive disease, n = 14). The T/M ratio at 24 hours after the treatment in the responder group was decreased remarkably with that at pre-treatment (p < 0.05), while in the non-responder group it showed no significant change between the time points. The RI and TAC patterns were comparable to T/M ratios in each treatment group. T/M ratios, RI, and TAC indicated marked changes at the time point of 24 hours in the responder group, although the tumors did not show any significant hange in volume at that time. Photomicrographs of sections showed that the number of viable tumor cells in the responder group decreased at 24 hours after treatment and that inflammatory cell infiltration was marked and almost all viable tumor cells had disappeared by day 7 after treatment., Conclusion: These results suggest that early evaluation by FDG-microPET, especially 24 hours after treatment, is useful to predict the primary effects of the treatment. Histological analysis showed that inflammatory cell infiltration at 7 days after treatment was considered to be a cause of accumulation of FDG in the tumors that showed a significant decrease in tumor cell number. This false-positive should be noted when predicting tumor response by FDG accumulation.

We present a preliminary study on the design of a high sensitivity small animal DOI-PET scanner: jPET-RD (for Rodents with DOI detectors), which will contribute to molecular imaging. The 4-layer DOI block detector for the jPET-RD that consists of scintillation crystals (1.4 mm x 1.4 mm x 4.5 mm) and a flat panel position-sensitive photomultiplier tube (52 mm x 52 mm) was previously proposed. In this paper, we investigate imaging performance of the jPET-RD through numerical simulations. The scanner has a hexagonal geometry with a small diameter and a large axial aperture. Therefore DOI information is expected to improve resolution uniformity in the whole field of view (FOV). We simulate the scanner for various parameters of the number of DOI channels and the crystal length. Simulated data are reconstructed using the maximum likelihood expectation maximization with accurate system modeling. The trade-off results between background noise and spatial resolution show that only shortening the length of crystal does not improve the trade-off at all, and that 4-layer DOI information improves uniformity of spatial resolution in the whole FOV. Excellent performance of the jPET-RD can be expected based on the numerical simulation results.