Search

Positron emission tomography (PET) is a sophisticated method for the quantitative and noninvasive imaging of biological functions by monitoring the delivery of tracers labeled with positron emitters (1C, 'aN, '"O, and 8F). The distribution and kinetic patterns of a labeled compound in relation to the specific biomolecule in the target tissue are assumed to reflect specific biological functions in the living body. A wide variety of labeled compounds as molecular probes have been developed to measure biochemical and physiological parameters, such as blood flow, glucose and oxygen metabolism, protein synthesis, and neurotransmitter receptor functions. Recently, PET has gradually been introduced into the research field of drug development both in pre-clinical and clinical stages. In the present chapter, the applications of animal PET with small animals (rats and mice) and non-human primates in drug development in the pre-clinical stage will be discussed based on our own experiences. In the course of drug development, the pre-clinical studies with experimental animals are indispensable, and these studies are expected to provide useful information to facilitate the development of drug candidates with more efficacy and fewer adverse effects in the clinical stage with

The present study demonstrates the effects of 6R- l -erythro-5,6,7,8-tetrahydrobiopterin (6R-BH 4 ) on turnover of dopamine and serotonin (5-HT) in rat striatum during continuous infusion of the amino acids tyrosine and tryptophan. By monitoring with microdialysis, it was found that the increase in dopamine and homovanillic acid (HVA) concentrations in rat striatal extracellular fluid (ECF) induced by 6R-BH 4 was further enhanced by the continuous infusion of tyrosine at a relatively low dose (1 μmol/min/kg) as compared with the concentration which saturates tyrosine hydroxylation. This dose of tyrosine alone did not induce the elevation of dopamine and HVA concentrations in ECF. In contrast, though the concentration of 5-HT and 5-HIAA in striatal ECF was gradually increased by tryptophan infusion, 6R-BH 4 had no further effect. Although the higher output of dopamine into ECF was induced by the dialytic perfusion of 6R-BH 4 via the microdialysis probe into striatum, tyrosine infusion had no further effect on dopamine concentration in the dialysates. The in vivo measurement of DOPA accumulation during NSD 1015 perfusion suggests that the enhancement of dopamine concentration in ECF induced by tyrosine infusion and 6R-BH 4 might be attributable to an increase in tyrosine hydroxylase activity in striatum. Tryptophan hydroxylase was also activated by tyrptophan infusion and/or 6R-BH 4 , however, it did not induce an increase in 5-HT concentration in striatal ECF.

dissolved in phosphate-buffered saline strongly evokes the antibody response to phage particles. 2) This response was dependent on MyD88 signaling. 3) A few copies of Abeta42 fibril mimotope-displaying phage clone induce anti-Abeta42 conformer antibody response in C57BL/6 and J20 mice Conclusions: B6-phage may provide a promising vaccination strategy for immunotherapy of Alzheimer’s diseasewithout the involvement of Abeta42-specific T cell immunity since the safety of bacteriophage for human has been investigated in a number of studies of phage therapy.

Although antimuscarinic agents are widely used to treat overactive bladder (OAB), they have been shown to induce side effects including dry mouth and cognitive impairment. The present study was aimed to investigate the effects of antimuscarinic agents, oxybutynin and imidafenacin, on temporal changes in cognitive function and central mAChR occupancy in conscious monkeys (Macaca mulatta). Three conscious monkeys underwent positron emission tomography (PET) scans with a mAChR radioligand N-[(11)C]methyl-3-piperidyl benzilate ([(11)C](+)3-MPB). The scan sequence was pre, and 1, 4, and 24h post oral administration of oxybutynin (0.1-1.0mg/kg) or imidafenacin (0.01-0.1mg/kg). Maximum cognitive impairment was observed 1h post-oxybutynin at oral doses of 0.3 and 1.0mg/kg, in a dose-dependent manner, and oxybutynin produced significant positive correlations between mAChR occupancy and cognitive impairment in the cortices, thalamus, brainstem, and striatum. The most significant correlation was observed in the brainstem, and then cortices. In contrast, imidafenacin did not induce discernible cognitive impairment, despite having obtained some lesser occupancy in cortices and brainstem. We propose that the thresholds of mAChR occupancy to produce cognitive impairment by antimuscarinic agents are ca. 30-40% in cortices and ca. 20-30% in brainstem, and a desirable drug for OAB treatment should not occupy central mAChR above these thresholds.

In vivo and ex vivo binding of α(1)-adrenoceptor and muscarinic receptors involved in voiding function is reviewed with therapeutic agents (α(1)-adrenoceptor antagonists: prazosin, tamsulosin and silodosin; and muscarinic receptor antagonists: oxybutynin, tolterodine, solifenacin, propiverine, imiafenacin and darifenacin) in lower urinary tract symptoms. This approach allows estimation of the inhibition of a well-characterized selective (standard) radioligand by unlabelled potential drugs or direct measurement of the distribution and receptor binding of a standard radioligand or radiolabelled form of a novel drug. In fact, these studies could be conducted in various tissues from animals pretreated with radioligands and/or unlabelled novel drugs, by conventional radioligand binding assay, radioactivity measurement, autoradiography and positron emission tomography. In vivo and ex vivo receptor binding with α(1)-adrenoceptor antagonists and muscarinic receptor antagonists have been proved to be useful in predicting the potency, organ selectivity and duration of action of drugs in relation to their pharmacokinetics. Such evaluations of drug-receptor binding reveal that adverse effects could be avoided by the use of new α(1)-adrenoceptor antagonists and muscarinic receptor antagonists for the treatment of lower urinary tract symptoms. Thus, the comparative analysis of α(1)-adrenoceptor and muscarinic receptor binding characteristics in the lower urinary tract and other tissues after systemic administration of therapeutic agents allows the rationale for their pharmacological characteristics from the integrated viewpoint of pharmacokinetics and pharmacodynamics. The current review emphasizes the usefulness of in vivo and ex vivo receptor binding in the discovery and development of novel drugs for the treatment of not only urinary dysfunction but also other disorders.

[¹⁸F]DeoxyfluoroPEG methyl ethers with an average molecular weight of 2 kDa ([¹⁸F]1a) and 10 kDa ([¹⁸F]1b) were synthesized by the fluorination of the tosylates 3a,b with [¹⁸F]nBu₄NF at 80°C for 20 min followed by flash filtration through a Sep-Pak Plus Alumina-N cartridge. After the intravenous administration of [¹⁸F]1a and [¹⁸F]1b to rats, their pharmacokinetics was analyzed by noninvasive, real-time, whole-living-body monitoring using positron imaging technology. The effect of PEG's molecular weight on their blood circulation and organ clearance were quantitatively visualized for the first time.

Introduction Glycine transporter 1 (GlyT-1) is an attractive target in positron emission tomography (PET) studies. Here, we report the in vivo evaluation of three carbon-11-labelled non-sarcosine-type GlyT-1 inhibitors — [ 11 C]SA1, [ 11 C]SA2 and [ 11 C]SA3 — as novel PET tracers for GlyT-1. Methods The regional brain distributions of the three compounds in mice were studied at baseline and under receptor-blockade conditions with co-injection of carrier loading or pretreatment with an excess of selective GlyT-1 inhibitors (ALX-5407 and SSR504734). Metabolic stability was investigated by radio high-performance liquid chromatography. Dynamic PET scans in conscious monkeys were performed with/without selective GlyT-1 inhibitors. Results The IC 50 values of SA1, SA2 and SA3 were 9.0, 6400 and 39.7 nM, respectively. The regional brain uptakes of [ 11 C]SA1 and [ 11 C]SA3 in mice were heterogeneous and consistent with the known distribution of GlyT-1. [ 11 C]SA2 showed low and homogeneous uptake in the brain. Most radioactivity in the brain was detected in unchanged form, although peripherally these compounds were degraded. Carrier loading decreased the uptake of [ 11 C]SA1 in GlyT-1-rich regions. However, similar reductions were not observed with [ 11 C]SA3. Pretreatment with ALX-5407 decreased the uptake of [ 11 C]SA1 in GlyT-1-rich regions. In the monkey at baseline, regional brain uptake of [ 11 C]SA1 was heterogeneous and consistent with the known GlyT-1 distribution. Pretreatment with selective GlyT-1 inhibitors significantly decreased the distribution volume ratio of [ 11 C] SA1 in GlyT-1-rich regions. Conclusions [ 11 C]SA1 has the most suitable profile among the three carbon-11-labelled GlyT-1 inhibitors. Lead optimization of [ 11 C]SA1 structure will be required to achieve in vivo selective GlyT-1 imaging.

1632 Objectives With the small bones of the foot and ankle, bone scan (Bo) is often requested to evaluate any swelling or chronic ulcers. Labeled leukocyte (WBC) imaging is often reserved for abnormal Bo. This study evaluated the utility of 3-phase Bo (3Pbo), and WBC/Bo imaging for diagnosing complicating osteomyelitis in the foot and ankle. Methods Images of 27 pts presenting with 24 ulcers involving the ankle (n= 15), heel (n=4), toe (n= 4) and midfoot (n=1) and 3 swelling in Charcot joints were evaluated. Criteria for osteomyelitis: 3Pbo, abnormal on all phases, WBC/Bo, ROI abnormal activity on both images. In 11 pts with ankle ulcers, WBC and marrow images (WBC/Ma) were also evaluated for discordant distribution of activity and compared with 3Pbo and WBC/Bo. Imaging results were compared with histopathologic/microbiologic confirmation for all cases. Results In the group of 27 pts, 4 had osteomyelitis, 3 acute and 1 chronic, the rest only had soft tissue infection. In the 11 pts with ankle ulcers, there was 1 case of chronic osteomyelitis and 10 with soft tissue infection. 3Pbo and WBC/Bo were false negative in a patient with chronic osteomyelitis in a Charcot joint. WBC/Ma was false negative in a patient with chronic osteomyelitis and marrow hyperplasia. Imaging results are presented in the table: Conclusions Bone imaging alone or in combination with WBC imaging is not very specific for diagnosing complicating osteomyelitis in the ankle and foot. For the ankle, WBC/Ma may offer better accuracy due to high specificity; however, this needs to be confirmed with larger patient population

N-[¹¹C]methyl-3-piperidyl benzilate ([¹¹C]+3-MPB) was developed as a positron emission tomography (PET) ligand for muscarinic cholinergic receptor (mAChR). The aim of the present study was to validate a Logan reference tissue method as an analytical method for in vivo binding of [¹¹C]+3-MPB to mAChR. Seven monkeys (Macaca mulatta) underwent [¹¹C]+3-MPB PET scans with an arterial blood sampling. Logan plot with arterial input function (Logan arterial input method) was performed to determine the binding potential (BP(ND)). The BP(ND) was also determined by Logan plot with the cerebellum as the reference region (Logan reference tissue method). BP(ND) values determined by Logan arterial input method and Logan reference tissue method showed a significant linear relationship. The present study suggests that the cerebellum is a suitable reference region for quantification of mAChR in the living brain with [¹¹C]+3-MPB and PET.

Aims The current study was conducted to evaluate, by the noninvasive positron emission tomography (PET), the binding of antimuscarinic agents used to treat overactive bladder (OAB) to muscarinic receptors in rat brain. Main methods Muscarinic receptor occupancy in the rat brain after the intravenous (i.v.) injection of oxybutynin, darifenacin and imidafenacin was evaluated by using a small animal PET system, and compared with the results by ex vivo autoradiographic and ex vivo radioligand binding experiments. Key findings In PET study, the i.v. injection of oxybutynin but not darifenacin or imidafenacin at pharmacological doses decreased significantly binding potential (BP) of (+)N-[11C]methyl-3-piperidyl benzilate ([11C](+)3-MPB) in the rat cerebral cortex and corpus striatum in a dose-dependent manner. Similarly, in the in vivo autoradiographic experiment, oxybutynin dose-dependently reduced binding of [11C](+)3-MPB in the brain, whereas darifenacin and imidafenacin did not. Following the i.v. injection of oxybutynin, darifenacin and imidafenacin, there was a similar degree of binding to muscarinic receptors in the bladder as demonstrated by a significant increase in apparent dissociation constant (Kd) values for specific [N-methyl-3H]scopolamine methyl chloride ([3H]NMS) binding. Significant binding of muscarinic receptors in the brain was observed after the injection of oxybutynin but not darifenacin or imidafenacin. Significance Oxybutynin but not darifenacin or imidafenacin has potential side effects on the central nervous system (CNS) in patients with OAB. The results reveal the noninvasive characterization of brain receptor occupancy by PET to be a powerful tool for precise evaluation of adverse CNS effects of antimuscarinic agents in pre-clinical and clinical evaluations.

PET（Positron Emission Tomography: 陽電子断層画像装置）は，生体内分子ターゲットを特異的に認識するポジトロン標識化合物の生体内動態・分布を非侵襲的に体外から計測する事で，生体内機能を画像化・定量化できる分子イメージング法として，実験動物を対象にした基礎研究からヒト患者を対象にした臨床研究まで，幅広く応用されてきた．例えば，がん細胞に高い集積を示すグルコースの類縁物質である［18F］FDGを用いた「がん検診」に活用されている．創薬研究の分野では，膨大な開発期間と費用を要する医薬品開発の効率化のため，これらのPETの優れた特性を利用しようという試みが，既に欧米では1990年代初頭から始まっており，この数年ようやく国内にも広がってきた．本稿では，中枢作動薬開発における疾患モデル動物を対象にした，前臨床段階におけるPET研究の有効性と課題について概説する．

Repeated injection of polyethyleneglycol-modified (PEGylated) liposomes causes a rapid clearance of them from the bloodstream, this phenomenon is called accelerated blood clearance (ABC). In the present study, we focused on the immune system responsible for the ABC phenomenon. PEGylated liposomes were preadministered to BALB/c mice and [(3)H]-labeled ones were then administered to them 3 days after the preadministration. Consistent with our previous results, the preadministration with PEGylated liposomes triggered the rapid clearance of [(3)H]-labeled PEGylated liposomes from the bloodstream, but that with PEGylated liposomes encapsulating doxorubicin (Dox) did not. In addition, we found that the ABC phenomenon was observed when a mixture of free Dox and PEGylated liposomes was preadministered. These data indicate that immune cells responsible for the ABC phenomenon might be selectively damaged by the Dox encapsulated in PEGylated liposomes. The ABC phenomenon was also observed in BALB/c nu/nu mice, but not in BALB/c SCID mice. The amount of anti-PEG IgM antibody induced by the stimulation with the PEGylated liposomes was significantly increased in the BALB/c nu/nu mice, but not in the BALB/c SCID ones. These data indicate that a T cell-independent B cell response would play a significant role in the ABC phenomenon. Furthermore, the present study suggests that PEGylated liposomes might be recognized by B cells as a thymus-independent type 2 (TI-2) antigen. The present study provides important information for the future development of liposomal medicines.

Human neuroimaging studies have demonstrated the presence of a “default system” in the brain, which shows a “default mode of brain activity,” i.e., greater activity during the resting state than during an attention-demanding cognitive task. The default system mainly involves the medial prefrontal and medial parietal areas, including the anterior and posterior cingulate cortex. It has been proposed that this default activity is concerned with internal thought processes. Recently, it has been indicated that chimpanzees show high metabolic levels in these medial brain areas during rest. Correlated low-frequency spontaneous activity as measured by functional magnetic resonance imaging was observed between the medial parietal and medial prefrontal areas in the anesthetized monkey. However, there have been few attempts to demonstrate a default system that shows task-induced deactivation in nonhuman primates. We conducted a positron emission tomography study with [15O]H2O to demonstrate a default mode of brain activity in the awake monkey sitting on a primate chair. Macaque monkeys showed higher level of regional blood flow in these medial brain areas as well as lateral and orbital prefrontal areas during rest compared with that under a working memory task, suggesting the existence of internal thought processes in the monkey. However, during rest in the monkey, the highest level of blood flow relative to that in other brain regions was observed not in the default system but in the dorsal striatum, suggesting that regions with the highest cerebral blood flow during rest may differ depending on the resting condition and/or species.

Recent advances in functional imaging of human brain activity in stroke patients, e.g., functional magnetic resonance imaging, have revealed that cortical hemisphere contralateral to the infarction plays an important role in the recovery process. However, underlying mechanisms occurring in contralateral hemisphere during functional recovery have not been elucidated. We experimentally induced a complete infarction of somatosensory cortex in right hemisphere of mice and examined the neuronal changes in contralateral (left) somatosensory cortex during recovery. Both basal and ipsilateral somatosensory stimuli-evoked neuronal activity in left (intact) hemisphere transiently increased 2 d after stroke, followed by an increase in the turnover rate of usually stable mushroom-type synaptic spines at 1 week, observed by using two-photon imagingin vivo. At 4 weeks after stroke, when functional recovery had occurred, a new pattern of electrical circuit activity in response to somatosensory stimuli was established in intact ipsilateral hemisphere. Thus, the left somatosensory cortex can compensate for the loss of the right somatosensory cortex by remodeling neuronal circuits and establishing new sensory processing. This finding could contribute to establish the effective clinical treatments targeted on the intact hemisphere for the recovery of impaired functions and to achieve better quality of life of patients.

A new synthetic methodology for the rapid methylation and fluoromethylation on aryl and alkenyl frameworks by using methyl and fluoromethyl iodide with an organoboronic acid ester has been developed under the simple and mild conditions of [Pd(2)(dba)(3)]/P(o-CH(3)C(6)H(4))(3)/K(2)CO(3) (dba= dibenzylideneacetone) in DMF at 60 degrees C for 5 min (see scheme). This boron protocol provides a firm chemical basis for the synthesis of (11)C- and (18)F-incorporated PET tracers.The rapid methylation and fluoromethylation on aryl and alkenyl carbon frameworks by reacting methyl and fluoromethyl iodide with aryl and alkenyl boronates have been studied with the focus on the realization of the synthesis of [(11)C]CH(3)- and [(18)F]FCH(2)-labeled positron emission tomography (PET) tracers. The coupling of methyl iodide and pinacol phenylboronate (40 equiv) is accomplished in91 % yield within 5 min at 60 degrees C under the conditions of [Pd(2)(dba)(3)]/P(o-CH(3)C(6)H(4))(3)/K(2)CO(3) (0.5:2:2; dba=dibenzylideneacetone) in DMF. The reaction shows a high generality and is applicable to various types of aryl and alkenyl boronates, giving the corresponding methylated derivatives in high yields (80-99 %). This reaction is also useful for the rapid incorporation of the fluoromethyl group. Thus, this boron protocol provides a firm chemical basis for the synthesis of (11)C- and (18)F-incorporated PET tracers and can be used as a complementary method for [(11)C]methylation together with our previous and ongoing processes using organotributylstannanes.

Positron emission tomography (PET) is a noninvasive imaging technology that enables the determination of biodistribution of positron emitter-labeled compounds. Lipidic nanoparticles are useful for drug delivery system (DDS), including the artificial oxygen carriers. However, there has been no appropriate method to label preformulated DDS drugs by positron emitters. We have developed a rapid and efficient labeling method for lipid nanoparticles and applied it to determine the movement of liposome-encapsulated hemoglobin (LEH). Distribution of LEH in the rat brain under ischemia was examined by a small animal PET with an enhanced resolution. While the blood flow was almost absent in the ischemic region observed by [(15)O]H(2)O imaging, distribution of (18)F-labeled LEH in the region was gradually increased during 60-min dynamic PET scanning. The results suggest that LEH deliver oxygen even into the ischemic brain from the periphery toward the core of ischemia. The real-time observation of flow pattern, deposition, and excretion of LEH in the ischemic rodent brain was possible by the new methods of positron emitter labeling and PET system with a high resolution.

Cell-free hemoglobin-based oxygen carriers have well-documented safety and efficacy problems such as nitric oxide (NO) scavenging and extravasation that preclude clinical use. To counteract these effects, we developed S-nitrosylated pegylated hemoglobin (SNO-PEG-Hb, P(50) = 12 mm Hg) and tested it in a brain ischemia and reperfusion model. Neurological function and extent of cerebral infarction was determined 24 h after photochemically induced thrombosis of the middle cerebral artery in the rat. Infarction extent was determined from the integrated area in the cortex and basal ganglia detected by triphenyltetrazolium chloride staining in rats receiving various doses of SNO-PEG-Hb (2, 0.4, and 0.08 mL/kg) and compared with rats receiving pegylated hemoglobin without S-nitrosylation (PEG-Hb) or saline of the same dosage. Results indicated that successive dilution revealed SNO-PEG-Hb but not PEG-Hb to be effective in reducing the size of cortical infarction but not neurological function at a dose of 0.4 mL/kg. In conclusion, SNO-PEG-Hb in a dose of 0.4 mL/kg (Hb 24 mg/kg) showed to be most effective in reducing the size of cortical infarction, however, without functional improvement.

O-18F-fluoromethyl-d-tyrosine (d-18F-FMT) is a promising novel agent for tumor imaging by PET. The aim of this study was to evaluate the potential of d-18F-FMT and the other conventional ligands used for tumor imaging, namely, 18F-FDG, l-11C-methionine (l-11C-MET), and 3′-deoxy-3′-18F-fluorothymidine (18F-FLT), as a PET ligand for monitoring early responses to radiotherapy in tumor-bearing mice. Methods: C3H/HeN mice inoculated with murine squamous cell carcinomas were treated with a single dose of x-ray irradiation at 2, 6, 20, or 60 Gy. Tumor uptake of each ligand was examined 1, 3, and 7 d after the irradiation. Results: Tumor uptake of d-18F-FMT was decreased on day 1 after irradiation at 6, 20, or 60 Gy, and the decrease persisted until day 7. Tumor uptake of 18F-FDG was elevated on days 1 and 3 after irradiation at 2, 6, or 20 Gy, followed by a decrease in uptake on day 7 in mice irradiated at 20 or 60 Gy. Decreased tumor uptake of l-11C-MET was observed only on day 3 after the irradiation. Decreased tumor uptake of 18F-FLT was detected on day 1 after irradiation at 2, 6, 20, or 60 Gy; thereafter, the dose-dependent decrease in uptake was no longer seen. Only for d-18F-FMT were significant positive correlations found between ligand uptake at all the time points examined and tumor volume on day 14 after various doses of irradiation. Conclusion: The findings suggest that d-18F-FMT is a promising PET ligand for early-phase detection and prediction of the effects of radiation therapy.

(-)-o-Methylvesamicol ((-)-OMV) exhibited in vitro a high affinity for a vesicular acetylcholine transporter (VAChT) (Ki, 6.7 nM), and (-)-o-[(11)C]methylvesamicol [(-)-[(11)C]OMV] exhibited appropriate kinetics and bound mainly to VAChTs in the rat brain. In this study, the in vivo distribution and kinetics of (-)-[(11)C]OMV were evaluated in comparison with [(11)C]SA4503 in disability model monkeys produced by selectively destroying the p75NTR-positive cells in the right hemisphere of the brain using positron emission tomography. Time-activity curves of (-)-[(11)C]OMV showed peaks within 20 min in regions rich in acetylcholine transporters (AchT). (-)-[(11)C]OMV binding in the ipsilateral cortex to the lesion was significantly reduced by 22.0% +/- 6.7% when compared with that in the contralateral region. The decrease (19.3% +/- 2.2%) in (-)-[(11)C]OMV binding in the ipsilateral temporal cortex to the lesion was greater than that (7.4% +/- 4.6%) of [(11)C]SA4503. These results suggested that (-)-[(11)C]OMV may be useful in the study of dementia characterized by degeneration of the cholinergic neurotransmitter system.

Nicotine/tobacco are prototypic substances used throughout the world. Nicotine abstinence produces some depressive-like effects which are treated by the dopamine (DA) and norepinephrine reuptake inhibitor bupropion. A quantitative measure of the regional brain utilization of these catecholamines (CA) during nicotine dependence and withdrawal is important.The aim of this study was to prove that regional brain DA utilization by nicotine can be quantified by positron emission tomography (PET) using L-[beta-(11)C]DOPA.Eight young Macaca mulatta monkeys were given 0.9% NaCl or nicotine in doses of 32 or 100 microg/kg i.m. bid for 9 days to produce minimal dependence. On the tenth day, PET measurements were repeated before and after i.v. nicotine administration. PET studies were done in habituated, trained, and fully conscious animals.Compared to a 0.9% NaCl control, acute i.v. nicotine as a bolus plus infusion for 30 min in similar doses to maintain a steady-state level for 30 min did not affect the utilization rate constant (k (3)) in dorsal or ventral striatum as measured by L-[beta-(11)C]DOPA. When monkeys were given nicotine bid repeatedly after overnight nicotine abstinence, CA utilization was reduced. A subsequent nicotine dose normalized utilization to slightly above control levels. Changes in ventral striatum were similar to those in dorsal striatum. The reduced rate of utilization demonstrated with L-[beta-(11)C]DOPA after overnight nicotine abstinence and its reversal by nicotine the next day provides an important PET measure of brain nicotine dependence and withdrawal. This method can be applied to other substances of abuse that release DA.

This study with monkeys was designed to answer two questions. 1) Does acute nicotine preferentially release more dopamine in the striatum than in the prefrontal cortex? 2) Do repeated doses of nicotine produce sensitization of striatal dopamine release? Microdialysis techniques were used to measure extracellular dopamine in both brain regions in two separate groups of conscious animals. The acute nicotine i.v. dose schedule was a bolus of 32 microg/kg plus an infusion of +/-0.8 microg/kg/min and a 100 microg/kg bolus plus an infusion of +/-2.53 microg/kg/min for 30 min to mimic human tobacco smoking arterial plasma nicotine concentrations. Acute nicotine given i.v. released more dopamine in the striatum than in the prefrontal cortex. In the second experiment, for convenience, daily nicotine was given i.m. and not i.v. bid in doses of 32 or 100 microg/kg for nine days. Dopamine release was measured after overnight nicotine abstinence using the i.v. dose schedule from the first experiment. Baseline dopamine release was significantly reduced (77.6% of control, P

BackgroundThe alpha7 nicotinic acetylcholine receptors (nAChRs) play an important role in the pathophysiology of neuropsychiatric diseases such as schizophrenia and Alzheimer's disease. However, there are currently no suitable positron emission tomography (PET) radioligands for imaging alpha7 nAChRs in the intact human brain. Here we report the novel PET radioligand [11C]CHIBA-1001 for in vivo imaging of alpha7 nAChRs in the non-human primate brain.Methodology/principal findingsA receptor binding assay showed that CHIBA-1001 was a highly selective ligand at alpha7 nAChRs. Using conscious monkeys, we found that the distribution of radioactivity in the monkey brain after intravenous administration of [11C]CHIBA-1001 was consistent with the regional distribution of alpha7 nAChRs in the monkey brain. The distribution of radioactivity in the brain regions after intravenous administration of [11C]CHIBA-1001 was blocked by pretreatment with the selective alpha7 nAChR agonist SSR180711 (5.0 mg/kg). However, the distribution of [11C]CHIBA-1001 was not altered by pretreatment with the selective alpha4beta2 nAChR agonist A85380 (1.0 mg/kg). Interestingly, the binding of [11C]CHIBA-1001 in the frontal cortex of the monkey brain was significantly decreased by subchronic administration of the N-methyl-D-aspartate (NMDA) receptor antagonist phencyclidine (0.3 mg/kg, twice a day for 13 days); which is a non-human primate model of schizophrenia.Conclusions/significanceThe present findings suggest that [11C]CHIBA-1001 could be a novel useful PET ligand for in vivo study of the receptor occupancy and pathophysiology of alpha7 nAChRs in the intact brain of patients with neuropsychiatric diseases such as schizophrenia and Alzheimer's disease.

[11C]PIB and [18F]FDDNP were examined on five aged and five young adult male rhesus macaques using positron emission tomography. Both tracers showed increased accumulation in the striatum, thalamus, cingulate and pons in the aged group. Compared to [11C]PIB, [18F]FDDNP showed higher accumulation in the cortical regions of aged animals as well as young animals. Although [18F]FDDNP may have possible usefulness for imaging, including other proteins, [11C]PIB may be better for amyloid imaging owing to lower non-specific binding. Synapse 62:472–475, 2008. © 2008 Wiley-Liss, Inc.

We evaluated the effects of five clinically used antimuscarinic agents for overactive bladder (OAB) treatment on in vivo muscarinic receptor binding in rat brain by quantitative autoradiography. There was a dose-related decrease in in vivo specific +N-[11C]methyl-3-piperidyl benzilate ([11C](+)3-MPB) binding in each brain region of rats 10 min after i.v. injection of oxybutynin, propiverine, solifenacin, and tolterodine. Rank order of the i.v. dose for 50% receptor occupancy (RO(50)) of antimuscarinic agents in rat brain regions was propiverine > solifenacin > tolterodine, oxybutynin. There was a good linear relationship between in vivo (pRO(50) values in the rat hippocampus) and in vitro (pK(i) values in human M(1) receptors) receptor binding activities of propiverine, solifenacin, and tolterodine. The observed RO(50) value of oxybutynin was approximately five times smaller than the predicted in vitro K(i) value. The dose ratios of antimuscarinic agents for the brain receptor occupancy (RO(50)) to the inhibition of carbachol- and volume-induced increases in intravesical pressure (ID(50)), which reflects in vivo selectivity for the urinary bladder over the brain, were greater for solifenacin, tolterodine, and propiverine than oxybutynin. Darifenacin displayed only a slight decrease in specific [11C](+)3-MPB binding in the rat brain regions, and it was not dose-related. In conclusion, in vivo quantitative autoradiographic analysis of brain muscarinic receptor occupancy may provide fundamental basis for managing central nervous system (CNS) side effects in antimuscarinic therapy for OAB. It is suggested that in the treatment of OAB, CNS side effects can be avoided by antimuscarinic agents with high selectivity for the urinary bladder over the brain.

Positron-emission tomography (PET) is a noninvasive real-time functional imaging system and is expected to be useful for the development of new drug candidates in clinical trials. For its application with preformulated liposomes, we devised an optimized [18F]-compound and developed a direct liposome modification method that we termed the “solid-phase transition method”. We were successful in using 1-[18F]fluoro-3,6-dioxatetracosane ([18F]7a) for in vivo trafficking of liposomes. This method might be a useful tool in preclinical and clinical studies of lipidic particle-related drugs.

Transection of the direct cortico-motoneuronal pathway at the mid-cervical segment of the spinal cord in the macaque monkey results in a transient impairment of finger movements. Finger dexterity recovers within a few months. Combined brain imaging and reversible pharmacological inactivation of motor cortical regions suggest that the recovery involves the bilateral primary motor cortex during the early recovery stage and more extensive regions of the contralesional primary motor cortex and bilateral premotor cortex during the late recovery stage. These changes in the activation pattern of frontal motor-related areas represent an adaptive strategy for functional compensation after spinal cord injury.

Adiponectin (Adipo), an adipocyte hormone involved in the regulation of glucose and lipid metabolism, has already been identified as a potential therapeutic target for the treatment of diabetes. However, successful delivery of Adipo to the receptors is difficult due to their peptide characteristics. Receptors for Adipo are abundantly expressed in the liver and skeletal muscle.Uptake of 2-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-2-deoxyglucose (2-NBDG) in hepatoblastoma HepG2 cells expressing Adipo was examined. Adipo-expressing plasmid DNA (10-50 microg) in saline solution (0.1 ml/g body weight) was rapidly injected into the tail vein of 4-week-old diabetic mice after 4-6 weeks of treatment with streptozotocin (STZ). Uptake of glucose in diabetic mice also was measured using a planar positron imaging system featuring 18-fluorodeoxyglucose.HepG2 cells expressing Adipo exhibited significantly increased 2-NBDG uptake compared with cells transfected with control plasmid even in the absence of insulin. STZ-induced diabetic mice showed decreased serum Adipo levels compared with non-diabetic mice. A single hydrodynamic injection of 10-50 microg Adipo-expressing plasmid DNA into diabetic mice led to approximately 10-15-fold elevation in serum Adipo levels, and resulted in decreased serum levels of glucose and triglyceride. As well as exhibiting higher levels of Adipo expression, diabetic mice also had higher hepatic glucose uptake than similar mice injected with control plasmid.We report that STZ-induced diabetic mice exhibited decreased Adipo levels and hyperglycemia which may be alleviated by hydrodynamic injection of the Adipo gene. This type of gene delivery system to the liver offers a different approach in developing novel treatments for type 1 and 2 diabetes.

The objective of this study was to evaluate whether the radioactivity of tumor tissues inoculated into mice can be monitored quantitatively with a planar positron imaging system (PPIS).(18)F-fluoro-D-glucose, (18)F-fluorothymidine, or D-(18)F-fluoromethyl tyrosine were intravenously administered into HeLa-bearing mice. In vivo uptake of each labeled compound in tumors was monitored with the PPIS, followed by the measurement of radioactivity in tumor tissue using tissue dissection analysis. The standardized uptake values (SUVs) in PPIS measurement and ex vivo tissue dissection analysis were derived using the tumor volume and tumor weight, respectively.Radioactivities of tumors in mice obtained via PPIS imaging correlated significantly with those by tissue dissection analysis. The SUV derived by the PPIS data and the estimated tumor volume correlated roughly with those by ex vivo tissue dissection analysis.The results of our experiment indicate the feasibility of noninvasive, quantitative tumor monitoring in mouse/rat studies with the PPIS.

The [ 18 F]fluoromethyl analog of the sigma 1 selective ligand 1-(3,4-dimethoxyphenethyl)-4-(3-phenylpropyl)piperazine dihydrochloride (SA4503) ([ 18 F]FM-SA4503) was prepared and its potential evaluated for the in vivo measurement of sigma 1 receptors with positron emission tomography (PET). FM-SA4503 had selective affinity for the sigma 1 receptor ( K i for sigma 1 receptor, 6.4 nM; K i for sigma 2 receptor, 250 nM) that was compatible with the affinity of SA4503 ( K i for sigma 1 receptor, 4.4 nM; K i for sigma 2 receptor, 242 nM). [ 18 F]FM-SA4503 was synthesized by 18 F-fluoromethylation of O -demethyl SA4503 in the radiochemical yield of 2.9–16.6% at the end of bombardment with a specific activity of 37.8–283 TBq/mmol at the end of synthesis. In mice, the uptake of [ 18 F]FM-SA4503 in the brain was gradually increased for 30 min after injection, and then decreased. In the blocking study, brain uptake was significantly decreased by co-injection of haloperidol to 32% of control, and FM-SA4503 to 52% of control. In PET study of the monkey brain, high uptake was found in the cerebral cortex, thalamus and striatum. The radioactivity level of [ 18 F]FM-SA4503 in the brain regions gradually increased over a period of 120 min after injection, followed by a stable plateau phase until 180 min after injection. In pretreatment with haloperidol measurement of the monkey brain, the radioactivity level was 22–32% and 11–25% of the baseline at 60 and 180 min, respectively, after injection, suggesting high receptor-specific binding. [ 18 F]FM-SA4503 showed specific binding to sigma 1 receptors in mice and monkeys; therefore, [ 18 F]FM-SA4503 has the potential for mapping sigma 1 receptors in the brain.

Serial arterial blood sampling is required to measure a blood input function in quantitative estimation of physiological parameters in dynamic positron emission tomography (PET) studies. However, blood sampling is problematic for animal PET study due to limited amount of blood allowed. Therefore, it is of interest to obviate arterial blood sampling. We have previously proposed a method for estimating a blood input curve based on independent component analysis in human study. In this paper, we applied the method to monkey [18F]fluorodeoxyglucose studies, and validated its applicability by comparing the estimated regional cerebral metabolic rates of glucose using the estimated and the measured blood input function. Experimental results suggest that the proposed method enables quantitative analysis in PET without serial arterial blood sampling not only in human data but also in monkey data.

Background Accumulating evidence suggests that α7 nicotinic receptor (α7 nAChR) agonists could be potential therapeutic drugs for cognitive deficits in schizophrenia. The present study was undertaken to examine the effects of the novel selective α7 nAChR agonist SSR180711 on cognitive deficits in mice after repeated administration of the N-methyl-D-aspartate receptor antagonist phencyclidine (PCP). Methods Saline or PCP (10 mg/kg/day for 10 days) was administered to mice. Subsequently, vehicle, SSR180711 (.3 or 3.0 mg/kg/day), SSR180711 (3.0 mg/kg/day) + the selective α7 nAChR antagonist methyllycaconitine (MLA; 3.0 mg/kg/day), or MLA (3.0 mg/kg/day) was administered IP for 2 consecutive weeks. Twenty-four hours after the final administration, a novel object recognition test was performed. Results The PCP-induced cognitive deficits were significantly improved by subsequent subchronic (2-week) administration of SSR180711 (3.0 mg/kg). The effects of SSR180711 (3.0 mg/kg) were significantly antagonized by co-administration of MLA (3.0 mg/kg). Furthermore, Western blot analysis and immunohistochemistry revealed that levels of α7 nAChRs in the frontal cortex and hippocampus of the PCP (10 mg/kg/day for 10 days)-treated mice were significantly lower than those of saline-treated mice. Conclusions These findings suggest that repeated PCP administration significantly decreased the density of α7 nAChRs in the brain and that the α7 nAChR agonist SSR180711 could ameliorate cognitive deficits in mice after repeated administration of PCP. Therefore, α7 nAChR agonists including SSR180711 are potential therapeutic drugs for treating cognitive deficits in schizophrenic patients.

Background and Purpose— Recently, we found that a novel subtype of prostacyclin (PGI 2 ) receptor clearly distinct from the peripheral subtype in terms of ligand specificity is expressed in the central nervous system (CNS). (15R)-16- m -tolyl-17,18,19,20-tetranorisocarbacyclin (15R-TIC) was synthesized and demonstrated to be a specific ligand for this CNS-type PGI 2 receptor. Previously, we demonstrated 15R-TIC to be neuroprotective in vivo during transient forebrain ischemia in gerbils and permanent middle cerebral artery occlusion (MCAO) in rats. Furthermore, this compound was shown to exert an anti-apoptotic effect on primary cultured hippocampal neurons, indicating its neuroprotective effect against ischemic insults occurs via direct action on CNS-type PGI 2 receptor. Methods— Local cerebral hemodynamics and oxygen metabolism were measured simultaneously by using positron emission tomography with the 15 O steady-state method, before and up to 18 hours after 3-hour transient MCAO reperfusion in cynomolgus monkeys. Methyl ester of 15R-TIC (50 μg/kg, n=4) or its vehicle (10% Intralipos, n=4) was injected intravenously within 5 minutes after onset of MCAO and continuously infused for 5 hours (50 μg/kg per hour). Results— Neuropathology showed that 15R-TIC significantly reduced cortical damage after 3-hour MCAO. Positron emission tomography results showed 15R-TIC significantly reduced the volume of “infarct” region of interest and attenuated the decrease in cerebral metabolic rate of oxygen and oxygen extraction fraction, and these protective effects were not attributable to improvement of cerebral circulation. Conclusions— These results suggest that 15R-TIC has a potent neuroprotective effect against focal cerebral ischemia in a monkey MCAO via its direct action on CNS-type PGI 2 receptors.

Parkin is the causal gene of autosomal recessive juvenile parkinsonism (AR-JP). Dopamine (DA) metabolism has been linked to Parkinson's disease (PD). To understand the pathogenesis of AR-JP, we generated parkin-deficient mice to assess the status of DA signaling pathway and examine DA release and DA receptor by ex vivo autoradiography. Ex vivo autoradiography using [11C]raclopride showed a clear decrease in endogenous DA release after methamphetamine challenge in parkin-deficient mice. Furthermore, parkin deficiency was associated with considerable upregulation of DA (D1 and D2) receptor binding in vivo in the striatum and increased DA levels in the midbrain. Our results suggest that dopaminergic neurons could behave abnormally before neuronal death. © 2006 Wiley-Liss, Inc.

(-)-O-Methylvesamicol ((-)-OMV) exhibited in vitro a high affinity for vesicular acetylcholine transporter (VAChT) (Ki, 6.7 nM) and a relatively low affinity for sigmal receptor (Ki, 33.7 nM). We prepared (-)-[11C]OMV by a palladium-promoted cross-coupling reaction using [11C]methyl iodide, in a radiochemical yield of 38 +/- 6.9% (n=3), a radiochemical purity of 98 +/- 2.3% (n = 5), and a specific activity of 11 +/- 7.0 TBq/mmol at 30 minutes after EOB (n=5). Then, we evaluated in vivo whether (-)-[11C]OMV has properties as a PET radioligand for mapping VAChT. In rats, the brain uptake of (-)-[11C]OMV was 1.1%ID/g at 5 minutes postinjection, and was retained of a high level for 60 minutes. The brain uptake was significantly inhibited by the co-injection (500 nmol/kg) of cold (-)-OMV (58-66%), (-)-vesamicol (57-65%), and two sigma receptor ligands with modulate affinities for VAChTs: SA4503 (56-71%) and haloperidol (39-64%) in all of the brain regions, including the cerebellum with a low density of VAChTs, but not of sigmal-selective ligand (+)-pentazocine. However, the pretreatment with a large excess amount of (+/-)-pentazocine (50 micromol/kg) reduced the uptake in a different manner in the brain regions: 25% reduction in the striatum with a high density of VAChTs, and a 50-55% reduction in the other regions with a lower density of VAChTs. Ex vivo autoradiography using (-)-[11C]OMV showed a similar regional brain distribution of [3H](-)-vesamicol. In the PET study of the monkey brain, the regional brain distribution pattern of (-)-[11C]OMV was different from that of [11C]SA4503. The uptake of (-)-[11C]OMV was relatively higher in the striatum, was reversible, and an apparent equilibrium state was found at 20-40 minutes. In conclusion, (-)-[11C]OMV exhibited appropriate brain kinetics during the time frame of 11C-labeled tracers and bound mainly to VAChTs; however, the binding to sigmal receptors was not disregarded. Therefore, (-)-[11C]OMV-PET together with help of [11C]SA4503-PET may evaluate VAChTs.

The aim of this study was to investigate whether D-amino acid isomers of O-(11)C-methyl tyrosine ((11)C-CMT) and O-(18)F-fluoromethyl tyrosine ((18)F-FMT) were better than the corresponding L-isomers as tumor- detecting agents with PET in comparison with the difference between L- and D-methyl-(11)C-methionine ((11)C-MET).L- and D-(11)C-MET, (11)C-CMT, and (18)F-FMT were injected intravenously into BALB/cA Jcl-nu mice bearing HeLa tumor cells. At 5, 15, 30, and 60 min after injection, normal abdominal organs and xenotransplanted HeLa cells were sampled, and the uptake of each ligand was determined. Metabolic analyses of these compounds in the plasma were also performed. Accumulation of the d-isomers of (11)C-MET, (11)C-CMT, and (18)F-FMT in turpentine-induced inflammatory tissue was assayed in comparison with (18)F-FDG. The whole-body distribution of each tracer was imaged with a planar positron imaging system (PPIS).Although the tumor uptake (standardized uptake value [SUV]) levels of the D-isomers of (11)C-MET, (11)C-CMT, and (18)F-FMT were 261%, 72%, and 95% of each L-isomer 60 min after administration, the tumor-to-blood ratios of these D-isomers were 130%, 140%, and 182% of the corresponding L-isomers. In the blood, the D-isomers of these labeled compounds revealed a relatively faster elimination rate compared with their L-isomers, with a high peak uptake in the blood and kidney 5 min after administration. Compared with the natural amino acid ligand l-(11)C-MET, the uptake of L-isomers of (11)C-CMT and (18)F-FMT was relatively low and stable in the abdominal organs, whereas D-isomers revealed much lower levels and faster clearance rates compared with corresponding L-isomers. Among the abdominal organs, the pancreas showed a relatively high uptake of (11)C-CMT and (18)F-FMT; the uptake of these D-isomers was much lower than that of L-isomers. Pretreatment with cycloheximide, a protein synthesis inhibitor, resulted in a marked reduction of L-(11)C-MET uptake and a slight reduction of D-(11)C-MET uptake into protein fractions, whereas no significant changes were detected with L- and D-(11)C-CMT and (18)F-FMT. D-Isomers of (11)C-MET, (11)C-CMT, and (18)F-FMT did not accumulate in turpentine-induced inflammatory tissue, where (18)F-FDG revealed a high uptake. Whole-body imaging with a PPIS provided consistent distribution data obtained from the tissue dissection analysis.These results suggest that D-isomers of (11)C-CMT and (18)F-FMT could be potentially better tracers than L- and D-(11)C-MET for tumor imaging with PET.

Context In animals, methamphetamine is known to have a neurotoxic effect on serotonin neurons, which have been implicated in the regulation of mood, anxiety, and aggression. It remains unknown whether methamphetamine damages serotonin neurons in humans. Objective To investigate the status of brain serotonin neurons and their possible relationship with clinical characteristics in currently abstinent methamphetamine abusers. Design Case-control analysis. Setting A hospital research center. Participants Twelve currently abstinent former methamphetamine abusers (5 women and 7 men) and 12 age-, sex-, and education-matched control subjects recruited from the community. Interventions The brain regional density of the serotonin transporter, a structural component of serotonin neurons, was estimated using positron emission tomography and trans -1,2,3,5,6,10-beta-hexahydro-6-[4-(methylthio)phenyl]pyrrolo-[2,1-a]isoquinoline ([ 11 C](+)McN-5652). Estimates were derived from region-of-interest and statistical parametric mapping methods, followed by within-case analysis using the measures of clinical variables. Main Outcome Measures The duration of methamphetamine use, the magnitude of aggression and depressive symptoms, and changes in serotonin transporter density represented by the [ 11 C](+)McN-5652 distribution volume. Results Methamphetamine abusers showed increased levels of aggression compared with controls. Region-of-interest and statistical parametric mapping analyses revealed that the serotonin transporter density in global brain regions (eg, the midbrain, thalamus, caudate, putamen, cerebral cortex, and cerebellum) was significantly lower in methamphetamine abusers than in control subjects, and this reduction was significantly inversely correlated with the duration of methamphetamine use. Furthermore, statistical parametric mapping analyses indicated that the density in the orbitofrontal, temporal, and anterior cingulate areas was closely associated with the magnitude of aggression in methamphetamine abusers. Conclusions Protracted abuse of methamphetamine may reduce the density of the serotonin transporter in the brain, leading to elevated aggression, even in currently abstinent abusers.

The aim of this study was to evaluate the neuroprotective effect of TRA-418, an antiplatelet agent, using PET in a monkey model of stroke. TRA-418 is a nonprostanoid compound with dual action: antagonistic effects on thromboxane A(2) receptors and agonistic effects on prostaglandin I(2) receptors.Via a transorbital approach, cynomolgus monkeys underwent a 3-h occlusion of the right middle cerebral artery (MCA), followed by reperfusion and observation for 4 d. Starting 2 h after the MCA occlusion, TRA-418 was administered at low and high doses (6 animals at each dose). Six control animals received a bolus and infusion of drug vehicle after MCA occlusion. Steady-state (15)O continuous inhalation was used for assessment of local cerebral blood flow, cerebral metabolic rate of oxygen, and oxygen extraction fraction using high-resolution PET. Five consecutive PET scans (before occlusion; 2 h after occlusion; and 2 h, 24 h, and 4 d after reperfusion) were obtained for each monkey. The extent of the cerebral damage due to ischemia was measured histologically at 4 d after reperfusion.Histologic observation 4 d after MCA occlusion showed that cerebral damage was less (P = 0.05) in animals treated with high-dose TRA-418 than in control animals. Although not affecting cerebral blood flow during the experiments, treatment with TRA-418 significantly (P0.05) suppressed reduction of the cerebral metabolic rate of oxygen after reperfusion.Our observations suggest that TRA-418 has neuroprotective action, as displayed in a primate model of stroke using PET monitoring.

[(18)F]MPPF is a selective and reversible antagonist to the serotonin-1A (5-HT(1A)) receptor. The aim of the present study was to investigate whether the binding of [(18)F]MPPF is sensitive to increases in 5-HT levels. We used the 5-HT releasing agent and reuptake inhibitor fenfluramine (FEN) to increase the concentration of 5-HT. [(18)F]MPPF binding was assessed using positron emission tomography (PET) in conscious monkeys. Possible effects of blood flow on ligand binding were excluded by using a bolus-infusion paradigm. Control scans were obtained to assess the state of ligand equilibrium. FEN (5 or 10 mg/kg, i.v.) was administered between 90 and 130 min after the start of the [(18)F]MPPF infusion. The binding potential (BP) was calculated for an early interval (30 min preceding FEN administration) and late interval (20-50 min after administration of FEN). Microdialyses results showed a 20- and 35-fold increase in extracellular 5-HT levels in the prefrontal cortex after injection of FEN at a dose of 5 mg/kg and 10 mg/kg respectively. However, despite these large increases in 5-HT levels, no differences in BP were found between the control and FEN scans. These results may imply that the majority of 5-HT(1A) receptors is in the low affinity state in the living brain.

The aim of this study was to evaluate the properties of the D-amino acid isomers O-(18)F-fluoromethyl tyrosine ((18)F-FMT), O-(18)F-fluoroethyl tyrosine ((18)F-FET) and O-(18)F-fluoropropyl tyrosine ((18)F-FPT) as tumour-detecting agents with PET in comparison with the corresponding L-isomers. L- or D-(18)F-FMT, (18)F-FET or (18)F-FPT, prepared by (18)F-fluoromethylation, (18)F-fluoroethylation or (18)F-fluoropropylation of L- and D-tyrosine, was intravenously injected into BALB/cA Jcl-nu mice bearing HeLa tumour cells. At 5, 15, 30 and 60 min post intravenous administration, the uptake of each compound in normal abdominal organs and xenotransplanted HeLa cells was determined using the tissue dissection method. Metabolic stability analyses of these compounds in the plasma were performed with the thin-layer chromatography method. In the plasma fraction, although L- and D-isomers of (18)F-FMT, (18)F-FET and (18)F-FPT provided comparable metabolic stability, D-isomers of these labelled compounds revealed a faster elimination rate than their L-isomers, with a higher peak uptake in the blood and kidney 5 min post administration. Compared with natural amino acid ligands, such as L-(11)C-methionine, the uptake of L-isomers of these labelled compounds was relatively low and stable in the abdominal organs, while D-isomers revealed much lower and faster clearance rates compared with the corresponding L-isomers. Among the abdominal organs, the pancreas showed relatively high uptake of all the labelled compounds used here, and the uptake of D-isomers was much lower than that of the L-isomers. Although tumour uptake levels of D-isomers of (18)F-FMT, (18)F-FET and (18)F-FPT were almost 95%, 43% and 39% of the uptake levels of each of the L-isomers 60 min post administration, the tumour-to-blood ratios of these D-isomers were 181%, 137% and 101% of the ratios of the corresponding L-isomers. D-isomers of (18)F-FMT and (18)F-FET indicated improved tumour-to-liver ratios compared with the corresponding L-isomers, and D-(18)F-FPT showed the highest tumour-to-pancreas ratio among all the other compounds assayed here. These results suggest that D-isomers of (18)F-fluoroalkyl tyrosine analogues are potential tracers for tumour imaging with PET.

This study demonstrates that dizocilpine (MK-801), a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, impairs working memory of conscious behaving monkeys. In addition, acute and chronic MK-801 produces different effects on D(1) and D(2) receptor binding in prefrontal cortex (PFC). Extrastriatal neocortical receptor D(1) (D(1)R) and D(2) (D(2)R) binding were assayed by [(11)C]NNC112 and [(11)C]FLB457, respectively, using high-specific radioactivity and a specially designed monkey positron emission tomograph (PET). Acute single dose (0.03, 0.1, and 0.3 mg/kg) i.v. administration of MK-801 resulted in dose-related impairment of working memory performance of an oculomotor delayed response (ODR) task. There was no impairment of performance of a visually guided saccade (VGS) task with low doses of 0.03 and 0.1, but it was depressed with 0.3 mg/kg. Chronic daily MK-801 (0.03 mg/kg, i.m., b.i.d. for 13 days) induced impaired ODR task performance with no effect on the VGS task. Although acute single doses of MK-801 caused no significant changes in [(11)C]NNC112 binding to PFC D(1)R, chronic daily treatment increased binding about 14% (P

3'-Deoxy-3'-18F-fluorothymidine (18F-FLT) has been suggested as a new PET tracer for imaging tumor proliferation. We investigated the use of 18F-FLT to monitor the response of tumors to radiotherapy and photodynamic therapy (PDT) in mice.C3H/He mice bearing an SCCVII tumor were treated with single-dose x-ray irradiation of 20 Gy. Tumor uptake was examined for 18F-FLT, 3H-thymidine (3H-Thd), 18F-FDG, and 14C-deoxyglucose (14C-DG) at 6 h, 12 h, 24 h, 3 d, and 7 d after radiotherapy. BALB/c nu/nu mice bearing a HeLa tumor were treated with PDT. Tumor uptake was examined for the 4 tracers at 24 h after PDT. Expression of proliferating cell nuclear antigen (PCNA) was determined in untreated and treated tumors.In the biodistribution study, considerable uptake of 18F-FLT was observed in both tumor types. Tumor volumes decreased to 39.3% +/- 22.4% at 7 d after radiotherapy. The PCNA labeling index was reduced in x-ray-irradiated tumors (control, 53.2% +/- 8.7%; 6 h, 38.5% +/- 5.3%; 24 h after radiotherapy, 36.8% +/- 5.3%). 18F-FLT uptake in tumor expressed as the percentage of the injected dose per gram of tumor (%ID/g) decreased significantly at 6 h and remained low until 3 d after radiotherapy (control, 9.7 +/- 1.2 %ID/g; 6 h, 5.9 +/- 0.4 %ID/g; 24 h, 6.1 +/- 1.3 %ID/g; 3 d after radiotherapy, 6.4 +/- 1.1 %ID/g). 18F-FDG uptake tended to gradually decrease but a significant decrease was found only at 3 d (control, 12.1 +/- 2.7 %ID/g; 6 h, 13.3 +/- 2.3 %ID/g; 24 h, 8.6 +/- 1.8 %ID/g; 3 d after radiotherapy, 6.9 +/- 1.2 %ID/g). PDT resulted in a reduction of the PCNA labeling index (control, 82.0% +/- 8.6%; 24 h after PDT, 13.5% +/- 12.7%). Tumor uptake of 18F-FLT decreased (control, 11.1 +/- 1.3 %ID/g; 24 h after PDT, 4.0 +/- 2.2 %ID/g), whereas 18F-FDG uptake did not decrease significantly after PDT (control, 3.5 +/- 0.6 %ID/g; 24 h after PDT, 2.3 +/- 1.1 %ID/g). Changes in the uptake of 18F-FLT and 18F-FDG were similar to those of 3H-Thd and 14C-DG, respectively.In our model system, changes in 18F-FLT uptake after radiotherapy and PDT were correlated with those of 3H-Thd and the PCNA labeling index. The decrease in 18F-FLT uptake after treatments was more rapid or pronounced than that of 18F-FDG. Therefore, 18F-FLT may be a feasible PET tracer for monitoring response to therapy in oncology.

Recent animal PET research has led to the development of PET scanners for small animals. A planar positron imaging system (PPIS) was newly developed to study physiological function in small animals and plants in recent years. To examine the usefulness of PPIS for functional study in small animals, we examined dopaminergic images of mouse striata in MPTP-induced parkinsonism.Male C57BL/6NCrj mice were treated with MPTP 7 days before the PPIS study. Scans were performed to measure dopamine D1 receptor binding and dopamine transporter availability with [11C]SCH23390 (about 2 MBq) and [11C]beta-CFT (about 2 MBq), respectively. After the PPIS study, dopamine content in the striatum was measured by HPLC.The MPTP treatment significantly reduced dopamine content in the striatum 7 days after treatment. In the MPTP-treated group, [11C]beta-CFT binding in the striatum was significantly decreased compared with the control group, while striatal [11C]SCH23390 binding was not affected. Dopamine content in the striatum was significantly correlated with the striatal binding of [11C]beta-CFT.The present results suggest that PPIS is able to determine brain function in a small animal. Using PPIS, high throughput imaging of small animal brain functions could be achieved.

Mecamylamine is a well-described non specific antagonist of nicotinic acetylcholine receptors (nAChRs), used in therapy and in psychopharmacological studies. [ 11 C]-Mecamylamine was prepared and evaluated as a putative radioligand for positron emission tomography to study nicotinic acetylcholine receptors. The radiosynthesis consisted in the [ 11 C]-methylation of the desmethyl precursor within 40 min with 30–40% radiochemical yield decay corrected. Biodistribution studies in rats showed that radioligand crossed the blood-brain barrier (0.39% ID at 30 min) and only unmetabolized tracer was recovered from brain at 45 min. Ex vivo autoradiography studies in rats did not indicate preferential uptake, and pre-treatment mecamylamine or with chlorisondamine, an nicotinic receptor inhibitor, did not demonstrate a significant specific binding. To investigate possible specie differences and effects of anesthesia, in vivo positron emission tomography (PET) studies were carried out on anaesthetized baboons and conscious macaques. The regional brain distribution of [ 11 C]-mecamylamine in the two species of primates exhibited similar kinetics as did the rat with steady state reached about 45–50 min after radiotracer administration. Uptake values were two-fold higher in brain of conscious macaque than in anaesthetized baboon (thalamus: 0.258% ID/(kg mL) in conscious macaques and 0.129% ID/(kg mL) in baboons). PET images showed a radioactivity distribution which was quite homogeneous throughout the brain but with somewhat higher uptake in grey matter than in white. Brain distribution was unaltered by saturation or displacement studies. Possible explanation for the failure to establish specific binding in vivo could be long-lived structural modifications of the ionotropic channel by the unlabeled ligand administered before the tracer. In conclusion, [ 11 C]-mecamylamine did not satisfy the requirements for a PET tracer of nicotinic acetylcholine receptors.

We performed preclinical and clinical studies of O -[ 11 C]methyl-l-tyrosine, a potential tracer for imaging amino acid transport of tumors by positron emission tomography (PET). Examinations of the radiation-absorbed dose by O -[ 11 C]methyl-l-tyrosine and the acute toxicity and mutagenicity of O -methyl-l-tyrosine showed suitability of the tracer for clinical use. The whole-body imaging of monkeys and healthy humans by PET showed low uptake of O -[ 11 C]methyl-l-tyrosine in all normal organs except for the urinary track and bladder, suggesting that the O -[ 11 C]methyl-l-tyrosine PET has the potential for tumor imaging in the whole-body. Finally, the brain tumor imaging was preliminarily demonstrated.