Identification of imaging biomarkers for the assessment of tumour response to different treatments in a preclinical glioma model.

PURPOSE: Hypoxia-inducible factor 1α (HIF-1α) activity is one of the major players in hypoxia-mediated glioma progression and resistance to therapies, and therefore the focus of this study was the evaluation of HIF-1α modulation in relation to tumour response with the purpose of identifying imaging biomarkers able to document tumour response to treatment in a murine glioma model. METHODS: U251-HRE-mCherry cells expressing Luciferase under the control of a hypoxia responsive element (HRE) and mCherry under the control of a constitutive promoter were used to assess HIF-1α activity and cell survival after treatment, both in vitro and in vivo, by optical, MRI and positron emission tomography imaging. RESULTS: This cell model can be used to monitor HIF-1α activity after treatment with different drugs modulating transduction pathways involved in its regulation. After temozolomide (TMZ) treatment, HIF-1α activity is early reduced, preceding cell cytotoxicity. Optical imaging allowed monitoring of this process in vivo, and carbonic anhydrase IX (CAIX) expression was identified as a translatable non-invasive biomarker with potential clinical significance. A preliminary in vitro evaluation showed that reduction of HIF-1α activity after TMZ treatment was comparable to the effect of an Hsp90 inhibitor, opening the way for further elucidation of its mechanism of action. CONCLUSION: The results of this study suggest that the U251-HRE-mCherry cell model can be used for the monitoring of HIF-1α activity through luciferase and CAIX expression. These cells can become a useful tool for the assessment and improvement of new targeted tracers for potential theranostic procedures.

Genetic and morphological diversity of Moenkhausia oligolepis (Characiformes: Characidae) populations in the tributaries of the Araguaia River, Brazil: implications for taxonomy and conservation.

Molecular genetic assessments that consider ecological information, in addition to endogamy levels, genetic diversity, and the genetic differentiation among species and populations, are particularly important for the conservation of biological diversity. Prime candidates for conservation genetic review are those subject to human use, including harvests for the ornamental fish trade. Colorful South American tetra, such as Moenkhausia oligolepis and M. forestii, are good examples of fish species that are widely collected and exported worldwide. This study aimed to evaluate the population-specific characteristics of M. oligolepis and M. forestii by comparing morphometric and molecular analyses based on ISSR markers, to provide information that would facilitate the sustainable management of these 2 species. Seventy-two specimens were collected from the Araguaia-Tocantins and Paraguay River Basins in Brazil. All specimens were measured and analyzed using ISSR markers. Population-exclusive bands were found among the 86 detected bands, while morphometric clusters reflected the geographical distribution of individuals. Correlated genetic and morphological variation supported the presence of 3 distinct groups from tributaries of the Araguaia and Mortes Rivers. Using the same techniques, all M. oligolepis populations were isolated from M. forestii. This study on Moenkhausia presents an interesting example that could be used to construct a framework of South American ichthyodiversity, and reinforces the necessity of habitat conservation to prevent the loss of biological diversity.

Development of a new toolbox for mouse PET-CT brain image analysis fully based on CT images and validation in a PD mouse model.

Automatic analysis toolboxes are popular in brain image analysis, both in clinical and in preclinical practices. In this regard, we proposed a new toolbox for mouse PET-CT brain image analysis including a new Statistical Parametric Mapping-based template and a pipeline for image registration of PET-CT images based on CT images. The new templates is compatible with the common coordinate framework (CCFv3) of the Allen Reference Atlas (ARA) while the CT based registration step allows to facilitate the analysis of mouse PET-CT brain images. From the ARA template, we identified 27 volumes of interest that are relevant for in vivo imaging studies and provided binary atlas to describe them. We acquired 20 C57BL/6 mice with [18F]FDG PET-CT, and 12 of them underwent 3D T2-weighted high-resolution MR scans. All images were elastically registered to the ARA atlas and then averaged. High-resolution MR images were used to validate a CT-based registration pipeline. The resulting method was applied to a mouse model of Parkinson's disease subjected to a test-retest study (n = 6) with the TSPO-specific radioligand [18F]VC701. The identification of regions of microglia/macrophage activation was performed in comparison to the Ma and Mirrione template. The new toolbox identified 11 (6 after false discovery rate adjustment, FDR) brain sub-areas of significant [18F]VC701 uptake increase versus the 4 (3 after FDR) macro-regions identified by the Ma and Mirrione template. Moreover, these 11 areas are functionally connected as found by applying the Mouse Connectivity tool of ARA. In conclusion, we developed a mouse brain atlas tool optimized for PET-CT imaging analysis that does not require MR. This tool conforms to the CCFv3 of ARA and could be applied to the analysis of mouse brain disease models.

Myocardial glucose uptake evaluated by positron emission tomography and fluorodeoxyglucose during hyperglycemic clamp in IDDM patients. Role of free fatty acid and insulin levels.

Myocardial and whole-body glucose metabolism was assessed in 19 insulin-dependent diabetes mellitus (IDDM) patients. A hyperglycemic clamp was performed 1) in the absence of insulin at free fatty acid (FFA) levels of 1.0 mmol/l (test 1); 2) in the absence of insulin at low FFA levels (0.1 mmol/l) by means of a lipid-lowering drug, acipimox (test 2); 3) during insulin infusion to achieve systemic levels of 400 pmol/l and FFA levels of 0.1 mmol/l (test 3); and 4) at the insulin levels of test 3 but increasing FFA to 1.0 mmol/l by means of heparin and intralipid infusion (test 4). Myocardial glucose uptake was measured by positron emission tomography (PET) and 2-[18F]fluoro-2-deoxy-D-glucose. Whole-body glucose uptake was measured in the four conditions by the glucose infusion rate during the PET scanning period. Myocardial glucose uptakes were 40.3 +/- 18.0, 395.5 +/- 139.6, 852.2 +/- 99.1, and 1,388.4 +/- 199.1 mumol.kg tissue-1.min-1 (mean +/- SD) and whole-body glucose uptakes were 10.1 +/- 2.3, 10.1 +/- 3.4, 42.8 +/- 5.8, and 30.5 +/- 5.6 mumol.kg body wt-1.min-1 during tests 1, 2, 3, and 4, respectively. Thus, in IDDM patients without coronary artery disease under the condition of hyperglycemia, an increase of myocardial glucose uptake was obtained either by lowering of FFA levels during hypoinsulinemia or by an increase in FFA levels during hyperinsulinemia. In both conditions no significant changes of whole-body glucose uptake were demonstrated.

The use of spectral analysis to determine regional cerebral glucose utilization with positron emission tomography and [18F]fluorodeoxyglucose: theory, implementation, and optimization procedures.

A method for kinetic analysis of dynamic positron emission tomography (PET) data by linear programming that allows identification of the components of a measured PET signal without predefining a compartmental model has recently been proposed by Cunningham and co-workers. The method identifies a small subset of functions from a large input set of feasible functions that best fits the time course of total radioactivity measured by PET. To investigate in detail the properties of this technique, we applied it to PET studies with [18F]fluorodeoxyglucose, a tracer with well-characterized kinetic properties. We examined dynamically acquired data over various time intervals in many brain regions and found that the number of components identified by the method is stable and consistent with the presence of kinetic heterogeneity in every region. We optimized the method for determination of regional rates of glucose utilization; calculated rates were found to be somewhat dependent upon the treatment of noise in the measured tissue data and upon the time interval in which the data were collected. The application of a numerical filter to remove noise in the data resulted in values for regional cerebral glucose utilization that were stable with time and consistent with rates determined by the other established techniques. Based on the results of the current study, we expect that the spectral analysis technique will prove to be a highly flexible tool for kinetic analysis of other tracer compounds; it is capable of producing low-variance, time-stable estimates of physiological parameters when optimized for time interval of application, input spectrum of components, and processing of noise in the data.

Systemic and cerebral kinetics of 16 alpha [18F]fluoro-17 beta-estradiol: a ligand for the in vivo assessment of estrogen receptor binding parameters.

Estrogen receptors are expressed in several brain areas of various animal species, and steroid hormones exert physiologic and biochemical effects on the central nervous system. The aim of the present study was to evaluate in female adult rats, the suitability of 16 alpha [18F]fluoro-17 beta-estradiol ([18F]FES), a selective estrogen receptor ligand, for the in vivo assessment of brain estrogen receptors. This was considered to be a preliminary step in evaluating the potential usefulness of [18F]FES for studies of cerebral estrogen receptors with positron emission tomography (PET) in nonhuman primates and human subjects. We evaluated (a) the time course of the metabolic degradation of [18F]FES in blood; (b) the time course of distribution of the tracer in discrete cerebral areas; (c) the inhibitory effect of increasing doses of cold estradiol on cerebral [18F]FES uptake; and (d) the possibility of in vivo quantification of estrogen receptor binding parameters using both equilibrium and dynamic kinetic analyses. We quantified [18F]FES binding to estrogen receptors using both equilibrium and dynamic kinetic analyses. The results of this study indicate that [18F]FES is a suitable tracer for the measurement of estrogen receptors in the pituitary and hypothalamus, using either the equilibrium or the kinetic analysis. However, [18F]FES is inadequate for the in vivo investigation of estrogen binding sites in brain areas with low receptor density, such as the hippocampus.

Errors introduced by tissue heterogeneity in estimation of local cerebral glucose utilization with current kinetic models of the [18F]fluorodeoxyglucose method.

The effects of tissue heterogeneity on the estimation of regional cerebral glucose utilization (rCMRglc) in normal humans with [18F]2-fluoro-2-deoxy-D-glucose ([18F]FDG) and positron emission tomography (PET) were compared with respect to the various kinetic models of the [18F]FDG method. The kinetic models were conventional homogeneous tissue models of the [18F]FDG method, with (4K Model) and without (3K Model) a rate constant to account for an apparent loss of [18F]2-fluoro-2-deoxy-D-glucose-6-phosphate ([18F]FDG-6-P), and a tissue heterogeneity model (TH Model). When either of the kinetic models designed for homogeneous tissues was applied to heterogeneous tissues, estimates of the rate constant for efflux of [18F]FDG from the tissue (k2*) and of the rate constant for phosphorylation of [18F]FDG (k3*) decreased as the duration of the experimental period was increased. When the 4K Model was used, estimates of the rate constant for the apparent dephosphorylation of [18F]FDG-6-P (k4*) were significantly greater than zero and fell with increasing duration of the experimental period. Although the TH Model included no term to describe an apparent dephosphorylation of [18F]FDG-6-P, the fit of the TH Model to the time course of total tissue radioactivity was at least as good as and often better than the fit of the 4K Model in the 120-min period following the pulse of [18F]FDG. Hence, the high estimates of k4* found in PET studies of less than or equal to 120 min can be explained as the consequence of measuring radioactivity in a heterogeneous tissue and applying a model designed for a homogeneous tissue; there remains no evidence of significant dephosphorylation of [18F]FDG-6-P in this time period. Furthermore, use of the 4K Model led to an overestimation of rCMRglc; whole-brain glucose utilization calculated with the 4K Model was greater than 20% higher than values usually obtained in normal humans by the model-independent Kety-Schmidt technique. rCMRglc was accurately estimated by the TH Model and, in experimental periods sufficiently long to minimize the effects of tissue heterogeneity, also by the original 3K Model of the deoxyglucose method.

Omegaconotoxin binding decreases in aged rat brain.

Omegaconotoxin binding was studied in young (3 months) and old (24 months) male Sprague-Dawley rats. In both groups omegaconotoxin binding displayed high affinity, was specific and saturable. The age-related changes are mainly a decrease in the Bmax in striatum and cortex (-29% and -31%, respectively). Binding parameters were unmodified in hippocampus of the two age groups. These data are consistent with the decrease of calcium uptake and neurotransmitter release observed in the brain of aged rodents.

Labeling and evaluation of N-[11C]methylated quinoline-2-carboxamides as potential radioligands for visualization of peripheral benzodiazepine receptors.

The novel quinoline-2-carboxamide derivatives N-[methyl-11C]-3-methyl-4-phenyl-N-(phenylmethyl)quinoline-2-carboxamide ([11C]4), (+/-)-N-[methyl-11C]-3-methyl-N-(1-methylpropyl)-4-phenylquinoline-2-carboxamide ([11C]5), and (+/-)-N-[methyl-11C]-3-methyl-4-(2-fluorophenyl)-N-(1-methylpropyl)quinoline-2-carboxamide ([11C]6) were labeled with carbon-11 (t1/2 = 20.4 min, beta+ = 99.8%) as potential radioligands for the noninvasive assessment of peripheral benzodiazepine type receptors (PBR) in vivo with positron emission tomography (PET). The radiosynthesis consisted of N-methylation of the desmethyl precursors 3-methyl-4-phenyl-N-(phenylmethyl)quinoline-2-carboxamide (4a), (+/-)-3-methyl-N-(1-methylpropyl)-4-phenylquinoline-2-carboxamide (5a), and (+/-)-4-(2-fluorophenyl)-3-methyl-N-(1-methylpropyl)quinoline-2-carboxamide (6a) with either [11C]methyl iodide or [11C]methyl triflate in the presence of tetrabutylammonium hydroxide or potassium hydroxide in dimethylformamide. The radioligands [11C]4, [11C]5, and [11C]6 were synthesized with over 99% radiochemical purity in 30 min, 30 +/- 5% radiochemical yield, calculated at the end of synthesis (EOS) non-decay-corrected, and 2.5 +/- 1.2 Ci/micromol of specific radioactivity. Inhibition studies in rats following intravenous pre-administration of 1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxamide (PK 11195, 1) showed high specific binding to PBR of [11C]4, [11C]5, and [11C]6 in heart, lung, kidney, adrenal gland, spleen, and brain. The biological data suggest that [11C]5, [11C]6, and particularly [11C]4 are promising radioligands for PBR imaging in vivo with PET.

Measurement of regional cerebral glucose utilization with fluorine-18-FDG and PET in heterogeneous tissues: theoretical considerations and practical procedure.

Functional tissue heterogeneity, i.e., inclusion of tissues with different rates of blood flow and metabolism within a single region of interest, is an unavoidable problem with PET. Errors in determination of regional cerebral glucose utilization (rCMRglc) with [18F]FDG have resulted from the currently used simplifying assumption that all regions examined are homogeneous. We have established an optimal, yet practical procedure to minimize errors due to tissue heterogeneity in determination of rCMRglc. Effects of applying the three-rate constant kinetic model designed for homogeneous tissues with both dynamic and single-scan procedures and the Patlak plot were evaluated in normal subjects in experimental periods up to 120 min following tracer injection. The procedure with a single scan carried out any time within the interval between 60 and 120 min following tracer injection, combined with population average rate constants determined over a 120-min period, was found to be optimal for quantitative rCMRglc studies.

Evaluation of three quinoline-carboxamide derivatives as potential radioligands for the in vivo pet imaging of neurodegeneration.

The peripheral-type benzodiazepine receptors (PBRs) are only minimally expressed in normal brain parenchyma, where they are primarily localized in glial cells. Their basal expression rises in different neurodegenerative disorders, due to the presence of infiltrating inflammatory cells and activated microglia. [11C]PK11195, a selective PBR antagonist, has been used for the in vivo PET monitoring of neurodegeneration in clinical observations. We recently developed and labeled with carbon-11 three new carboxamide derivatives: [11C]VC193M, [11C]VC195 and [11C]VC198M. Aim of this study was to evaluate these ligands for the in vivo measuring of PBRs expression in neurodegenerations and compare their kinetic behavior with that of the reference tracer [11C]PK11195. Radioligands were evaluated in a preclinical model of Huntington's disease consisting in the monolateral striatal injection of quinolinic acid (QA). Activated microglia and astrocytic gliosis was present only within the affected striatum. A concomitant increase in radioactivity accumulation was observed for all the tracers examined (P<0.01). Among the new compounds, [11C]VC195 showed higher levels of lesioned/unlesioned striatum ratios (3.28+/-0.44), in comparison with [11C]VC193M and [11C]VC198M (2.69+/-0.53 and 1.52+/-0.36, respectively), but slightly inferior to that observed for [11C]PK11195 (3.76+/-1.41).In conclusion, the results of the study indicate that [11C]VC195 is a promising candidate for in vivo PET monitoring of neurodegenerative processes but its in vivo behavior overlap that of [11C]PK11195.

Asymmetric synthesis and preliminary evaluation of (R)- and (S)-[11C]bisoprolol, a putative beta1-selective adrenoceptor radioligand.

(+/-)-1-[4-(2-Isopropoxyethoxymethyl)-phenoxy]-3-isopropylamino-2-propanol (bisoprolol) is a potent, clinically used beta(1)-adrenergic agent. (R)-(+) and (S)-(-) enantiomers of bisoprolol were labelled with carbon-11 (t(1/2)=20.4 min) as putative tracers for the non-invasive assessment of the beta(1)-adrenoceptor subtype in the human heart and brain with positron emission tomography (PET). The radiosynthesis consisted of reductive alkylation of des-iso-propyl precursor with [2-11C]acetone in the presence of sodium cyanoborohydride and acetic acid. The stereo-conservative synthesis of (R)-(+) and (S)-(-)-1-[4-(2-isopropoxyethoxymethyl)-phenoxy]-3-amino-2-propanol to be used as the precursors for the radiosynthesis of [11C]bisoprolol enantiomers was readily accomplished by the use of the corresponding chiral epoxide in three steps starting from the commercially available hydroxybenzyl alcohol. The final labelled product (either (+) or (-)-1-[4-(-isopropoxyethoxymethyl)-phenoxy]-3- [11C]isopropylamino-2-propanol) was obtained in 99% radiochemical purity in 30 min with 15+/-5% (EOS, non-decay corrected) radiochemical yield and 3.5+/-1 Ci/micromol specific radioactivity. Preliminary biological evaluation of the tracer in rats showed that about 30% of heart uptake of [11C](S)-bisoprolol is due to specific binding. The high non-specific uptake in lung might mask the heart uptake, thus precluding the use of [11C](S)-bisoprolol for heart and lung studies by PET. The remarkably high uptake of the tracer in rat brain areas rich of beta-adrenergic receptors such as pituitary (1.8+/-0.3% I.D. at 30 min) was blocked by pre-treatment with the beta-adrenergic antagonists propranolol (45%) and bisoprolol (51%, p<0.05). [11C](S)-bisoprolol deserves further evaluation in other animal models as a putative beta(1) selective radioligand for in vivo investigation of central adrenoceptors.

Effect of chronic ethanol treatment on dopamine receptor subtypes in rat striatum.

Chronic exposure to ethanol (6% in the drinking water, 25 days) reduces the responsiveness of both the dopamine-stimulated and of the dopamine-inhibited adenylate cyclase in rat striatum. The changes in the adenylate cyclase activity are paralleled by alterations in dopamine recognition sites, in fact binding studies using selective ligands indicate that the number of both D1- and D2-receptors is reduced in striatal membranes of treated rats.

Effect of chronic calcium antagonist treatment on dopamine recognition sites in rat striatum.

The effects of nimodipine and flunarizine administration (18 days 15 mg/kg/day p.o.) on striatal dopamine recognition sites in rats were investigated in vivo. In vitro flunarizine but not nimodipine displaces [3H]spiroperidol binding. After in vivo treatment both drugs induce a significant increase in the number of sulpiride displaceable spiroperidol binding sites (flunarizine, +114%, nimodipine +61%) concomitant with an increase in the dissociation constant. Binding parameters return toward control values after 1 week of suspension of the treatment. The results suggest that the repeated in vivo treatment with nimodipine and flunarizine may significantly interact with dopaminergic transmission leading to adaptive changes of the dopamine recognition sites.

Preparation of [76Br]FLB 457 and [76Br]FLB 463 for examination of striatal and extrastriatal dopamine D-2 receptors with PET.

Both FLB 457 and FLB 463, two substituted benzamides with high affinity for the dopamine D-2 receptors, were labeled with bromine-76 for PET investigations. [76Br]FLB 457 was prepared by electrophilic substitution of the tributyltin precursor. The radiochemical yield was 80%. [76Br]FLB 463 was prepared by a direct electrophilic substitution enhanced by the hydroxyl group of the debromo analogue, with a total radiochemical yield of 50%. Radiochemical and chemical purity values of the radioligands as analyzed by radio-TLC and HPLC were > 99%, and the specific radioactivity was -40 GBq/mumol. During PET examinations of [76Br]FLB 457 and [76Br]FLB 463 binding in baboons there was a rapid and high uptake in the striatum. The striatal radioactivity concentration reached a plateau 1 h postinjection (p.i.). The striatum-to-cerebellum radioactivity concentration ratio increased from 11 at 1 h p.i., to 28 at 4 h p.i. for [76Br]FLB 457, owing to a continuous wash-out from the cerebellum. For [76Br]FLB 463 the corresponding value increased from 10 to 19.5. [76Br]FLB 457 has in contrast to [76Br]FLB 463 a high uptake in thalamic structures and has therefore an additional potential as a radioligand for PET examination of extrastriatal dopamine D-2 receptors in the living human brain.

Evaluation of [O-methyl-(11)C]fluvoxamine as a tracer for serotonin re-uptake sites.

We evaluated [(11)C]fluvoxamine as a tracer for the serotonin re-uptake site. Studies of the distribution of the tracer in rat and primate brain showed adequate uptake of [(11)C]fluvoxamine, but failed to reveal regions with known high density of serotoninergic re-uptake sites. Pretreatment with unlabeled fluvoxamine did not substantially change the distribution. In rat brain tissue, nearly all radioactivity represented intact [(11)C]fluvoxamine. [(11)C]Fluvoxamine does not function as a tracer for serotonin re-uptake sites, owing to high nonspecific binding in the brain.

Synthesis and in vivo evaluation of [(11)C]CGP62349, a new GABA(B) receptor antagonist.

This paper describes the radiosynthesis of [(11)C]CGP62349, a potential ligand to assess GABA(B) receptors in vivo. (11)C was introduced by O-methylation of the corresponding des-methyl precursor, namely CGP67780. The final product was obtained with a reliable method in good yield. The radioligand was tested in monkey, revealing negligible blood-brain barrier penetration and brain uptake, thus prompting us to search for a new target structure with a better lipophilicity.

Effects of dopamine on the in vivo binding of dopamine D2 receptor radioligands in rat striatum.

The effects of moderate changes in extracellular dopamine concentrations on the in vivo binding of specific dopaminergic D2 radioligands with different affinities and kinetics were investigated in rats. Either [125I]NCQ298 (Kd = 19 pM), or [25I]iodolisuride (Kd = 0.27 nM) or [3H]raclopride (Kd = 1.5 nM) were administered intravenously (IV) to animals 1 h after the intraperitoneal (IP) injection of either alpha-methyl-p-tyrosine (AMPT) (250 mg/kg) or nomifensine (15 mg/kg), or saline. The kinetics of radioactivity concentration in the striatum, cerebellum, and plasma were measured for up to 4 h after [125I]NCQ298 or [125I]iodolisuride injection and up to 1.5 h after [3H]raclopride injection. For each tracer, the striatum-to-cerebellum radioactivity concentration ratios (S/C) and the binding potential (BP), calculated as the association to dissociation binding rate constant ratios (k3/k4), were assessed and related to the changes in extracellular dopamine concentration induced by drug treatments. Results show that S/C and BP of [3H]raclopride were significantly diminished by pretreatment with nomifensine, a drug that increases extracellular dopamine concentration. Nomifensine pretreatment induced no changes in the in vivo binding indexes of the high affinity [125I]NCQ298 and a slight but not significant decrease of the binding indexes of 125I]iodolisuride. Treatment with AMPT, which induced a 40% reduction in dopamine concentration, did not change [125I]NCQ298 binding indexes but slightly increased those of [3H]raclopride and [125I]iodolisuride. In conclusion, the change of dopamine concentration induces modification of radiotracer kinetics. Thus, the combined use of tracers with high and low affinities could allow us to obtain information both on receptor density and neurotransmitter release in vivo. However, as indicated by the [3H]raclopride study with AMPT, small changes in the concentration of intrasynaptic dopamine cannot be easily detected.

Lead neurotoxicity: a role for dopamine receptors.

Chronic lead exposure differentially affects dopamine receptor subtypes (D1 and D2). In particular dopamine D2 recognition sites in striatum are up-regulated while in nucleus accumbens they are down-regulated. These changes may be correlated to the observed alterations of dopamine terminal activity. Consistent with these biochemical changes behavioral studies indicate that lead-treated rats show more pronounced basal activity, attenuation of apomorphine (63 micrograms/kg s.c.) induced hypomotility and tendency to increased stereotyped response to apomorphine (300 micrograms/kg s.c.). On the contrary, both behavioral and biochemical markers of D1 receptors are unmodified by lead treatment. In fact, SKF 38393-induced grooming behavior, [3H]SCH 23390 binding and the dopamine stimulated adenylate cyclase activity are comparable in controls and lead-exposed rats.

Synthesis and in vivo evaluation of [11C]ICI 118551 as a putative subtype selective beta2-adrenergic radioligand.

Erytro-(+/-)-1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[ iso-propylamino]-2-butanol (ICI 118551) a potent clinically used beta2 adrenergic antagonist, was labelled with carbon-11 (t1/2 = 20.4 min) as a potential radioligand for the non-invasive assessment of beta2 adrenergic receptors in the lung with positron emission tomography (PET). The radiolabelled compound was prepared by reductive N-alkylation of its des-isopropyl precursor with [2-11C]acetone. (+/-)-[11C]ICI 118551 was obtained in greater than 98% radiochemical purity in 30 min with a radiochemical yield of 15 + 5% (non-decay corrected) and a specific radioactivity 2.5 +/- 0.5 Ci/micromol. The biological evaluation of racemic erythro (+/-)-[11C]ICI 118551 in rats and Macaca Nemestrina shows a high radioactivity uptake in lung and heart. However, in both animal models no detectable displacement of lung radioactivity concentration was observed after pre-treatment with propranolol or ICI 118551, which indicates that in this organ, radioligand uptake is mostly due to non-specific binding. The biological data suggest that erythro (+/-)-[11C]ICI 118551 is not adequate to be further developed as a tracer for beta2 adrenergic receptor imaging in vivo.