Molecular Analysis of the Superior Efficacy of a Dual Epidermal Growth Factor Receptor (EGFR)-DNA-Targeting Combi-Molecule in Comparison with Its Putative Prodrugs 6-Mono-Alkylamino- and 6,6-Dialkylaminoquinazoline in a Human Osteosarcoma Xenograft Model.

Background: ZR2002 is a dual EGFR-DNA-targeting combi-molecule that carries a chloroethyl group at the six-position of the quinazoline ring designed to alkylate DNA. Despite its good pharmacokinetics, ZR2002 is metabolized in vivo into dechlorinated metabolites, losing the DNA-alkylating function required to damage DNA. To increase the DNA damage activity in tumor cells in vivo, we compared ZR2002 with two of its 6-N,N-disubstituted analogs: "JS61", with a nitrogen mustard function at the six-position of the quinazoline ring, and "JS84", with an N-methyl group. Methods: Tumor xenografts were performed with the human Saos-2 osteosarcoma cell line expressing EGFR. Mice were treated with ZR2002, JS84 or JS61, and the tumor burden was measured with a caliper and CT/PET imaging. Drug metabolism was analyzed with LC-MS. EGFR and ɣ-H2AX phosphorylation were quantified via Western blot analysis and immunohistochemistry. Results: In vivo analysis showed that significant tumor growth inhibition was only achieved when ZR2002 was administered in its naked form. The metabolic dealkylation of JS61 and JS84 did not release sufficient concentrations of ZR2002 for the intratumoral inhibition of P-EGFR or enhanced levels of P-H2AX. Conclusions: The results in toto suggest that intratumoral concentrations of intact ZR2002 are correlated with the highest inhibition of P-EGFR and induction of DNA damage in vivo. ZR2002 may well represent a good drug candidate for the treatment of EGFR-expressing osteosarcoma.

Discordance and Concordance Between Cerebrospinal and [18F]FDG-PET Biomarkers in Assessing Atypical and Early-Onset AD Dementia Cases.

BACKGROUND AND OBJECTIVES: To assess the concordance and discordance between the core Alzheimer disease (AD) CSF biomarkers and [18F]fluorodeoxyglucose (FDG)-PET patterns evaluated clinically in memory clinic patients who meet appropriate use criteria for AD biomarker investigations. METHODS: We retrospectively assessed participants with atypical and/or early-onset dementia evaluated at a tertiary care memory clinic. All individuals underwent CSF evaluations for Aß42, phosphorylated tau (P-tau181) and total tau, and brain [18F]FDG-PET. [18F]FDG-PET data were visually interpreted by 2 nuclear medicine experts as being consistent with AD or non-AD. CSF biomarker results were similarly grouped into AD biomarker positive/negative. Contingency tables and Kappa coefficients were used to establish the level of agreement and disagreement between CSF and [18F]FDG-PET results in all individuals. RESULTS: One hundred thirty-six individuals had both [18F]FDG-PET and lumbar puncture performed as part of the early-onset and/or atypical dementia assessments. [18F]FDG-PET showed a pattern suggestive of AD in 43% of patients, while CSF biomarkers showed results consistent with AD in 57% of participants. In patients who met criteria for AD biomarker investigations, we found that [18F]FDG-PET was discordant with CSF AD biomarkers in nearly 20% of cases; 12% of individuals with [18F]FDG-PET scans consistent with AD had AD-negative CSF results; and 7% of individuals with [18F]FDG-PET scans not consistent with AD had AD-positive CSF results, potentially suggesting atypical AD variants or less advanced neurodegeneration. [18F]FDG-PET discriminated patients with an AD-positive CSF profile from patients with an AD-negative profile with a sensitivity and specificity higher than 80% (sensitivity: 81%, 95% CI = 71-88%, SP: 81%, 95% CI = 68-89%). Furthermore, [18F]FDG-PET had a positive predictive value of 87% (95% CI = 78-93%) and a negative predictive value of 72% (95% CI = 60-82%). DISCUSSION: CSF and [18F]FDG-PET disagreed in nearly 20% of the cases studied in this clinical series. While CSF Aß42 and P-tau181 biomarkers are specific for AD, the topographical information from [18F]FDG-PET may provide complementary information.

Multimodal Imaging in Rat Model Recapitulates Alzheimer's Disease Biomarkers Abnormalities.

Imaging biomarkers are frequently proposed as endpoints for clinical trials targeting brain amyloidosis in Alzheimer's disease (AD); however, the specific impact of amyloid-ß (Aß) aggregation on biomarker abnormalities remains elusive in AD. Using the McGill-R-Thy1-APP transgenic rat as a model of selective Aß pathology, we characterized the longitudinal progression of abnormalities in biomarkers commonly used in AD research. Middle-aged (9-11 months) transgenic animals (both male and female) displayed mild spatial memory impairments and disrupted cingulate network connectivity measured by resting-state fMRI, even in the absence of hypometabolism (measured with PET [18F]FDG) or detectable fibrillary amyloidosis (measured with PET [18F]NAV4694). At more advanced ages (16-19 months), cognitive deficits progressed in conjunction with resting connectivity abnormalities; furthermore, hypometabolism, Aß plaque accumulation, reduction of CSF Aß1-42 concentrations, and hippocampal atrophy (structural MRI) were detectable at this stage. The present results emphasize the early impact of Aß on brain connectivity and support a framework in which persistent Aß aggregation itself is sufficient to impose memory circuits dysfunction, which propagates to adjacent brain networks at later stages.SIGNIFICANCE STATEMENT The present study proposes a "back translation" of the Alzheimer pathological cascade concept from human to animals. We used the same set of Alzheimer imaging biomarkers typically used in large human cohorts and assessed their progression over time in a transgenic rat model, which allows for a finer spatial resolution not attainable with mice. Using this translational platform, we demonstrated that amyloid-ß pathology recapitulates an Alzheimer-like profile of biomarker abnormalities even in the absence of other hallmarks of the disease such as neurofibrillary tangles and widespread neuronal losses.

Imaging in vivo glutamate fluctuations with [(11)C]ABP688: a GLT-1 challenge with ceftriaxone.

Molecular imaging offers unprecedented opportunities for investigating dynamic changes underlying neuropsychiatric conditions. Here, we evaluated whether [(11)C]ABP688, a positron emission tomography (PET) ligand that binds to the allosteric site of the metabotropic glutamate receptor type 5 (mGluR5), is sensitive to glutamate fluctuations after a pharmacological challenge. For this, we used ceftriaxone (CEF) administration in rats, an activator of the GLT-1 transporter (EAAT2), which is known to decrease extracellular levels of glutamate. MicroPET [(11)C]ABP688 dynamic acquisitions were conducted in rats after a venous injection of either saline (baseline) or CEF 200 mg/kg (challenge). Binding potentials (BP(ND)) were obtained using the simplified reference tissue method. Between-condition statistical parametric maps indicating brain regions showing the highest CEF effects guided placement of microdialysis probes for subsequent assessment of extracellular levels of glutamate. The CEF administration increased [(11)C]ABP688 BP(ND) in the thalamic ventral anterior (VA) nucleus bilaterally. Subsequent microdialysis assessment revealed declines in extracellular glutamate concentrations in the VA. The present results support the concept that availability of mGluR5 allosteric binding sites is sensitive to extracellular concentrations of glutamate. This interesting property of mGluR5 allosteric binding sites has potential applications for assessing the role of glutamate in the pathogenesis of neuropsychiatric conditions.

Syntheses and evaluation of carbon-11- and fluorine-18-radiolabeled pan-tropomyosin receptor kinase (Trk) inhibitors: exploration of the 4-aza-2-oxindole scaffold as Trk PET imaging agents.

Tropomyosin receptor kinases (TrkA/B/C) are critically involved in the development of the nervous system, in neurological disorders as well as in multiple neoplasms of both neural and non-neural origins. The development of Trk radiopharmaceuticals would offer unique opportunities toward a more complete understanding of this emerging therapeutic target. To that end, we first developed [(11)C]GW441756 ([(11)C]9), a high affinity photoisomerizable pan-Trk inhibitor, as a lead radiotracer for our positron emission tomography (PET) program. Efficient carbon-11 radiolabeling afforded [(11)C]9 in high radiochemical yields (isolated RCY, 25.9% ± 5.7%). In vitro autoradiographic studies in rat brain and TrkB-expressing human neuroblastoma cryosections confirmed that [(11)C]9 specifically binds to Trk receptors in vitro. MicroPET studies revealed that binding of [(11)C]9 in the rodent brain was mostly nonspecific despite initial high brain uptake (SUVmax = 2.0). Modeling studies of the 4-aza-2-oxindole scaffold led to the successful identification of a small series of high affinity fluorinated and methoxy derivatized pan-Trk inhibitors based on our lead compound 9. Out of this series, the fluorinated compound 10 was selected for initial evaluation and radiolabeled with fluorine-18 (isolated RCY, 2.5% ± 0.6%). Compound [(18)F]10 demonstrated excellent Trk selectivity in a panel of cancer relevant kinase targets and a promising in vitro profile in tumors and brain sections but high oxidative metabolic susceptibility leading to nonspecific brain distribution in vivo. The information gained in this study will guide further exploration of the 4-aza-2-oxindole scaffold as a lead for Trk PET ligand development.

Metabolic brain activity suggestive of persistent pain in a rat model of neuropathic pain.

Persistent pain is a central characteristic of neuropathic pain conditions in humans. Knowing whether rodent models of neuropathic pain produce persistent pain is therefore crucial to their translational applicability. We investigated the spared nerve injury (SNI) model of neuropathic pain and the formalin pain model in rats using positron emission tomography (PET) with the metabolic tracer [18F]fluorodeoxyglucose (FDG) to determine if there is ongoing brain activity suggestive of persistent pain. For the formalin model, under brief anesthesia we injected one hindpaw with 5% formalin and the FDG tracer into a tail vein. We then allowed the animals to awaken and observed pain behavior for 30min during the FDG uptake period. The rat was then anesthetized and placed in the scanner for static image acquisition, which took place between minutes 45 and 75 post-tracer injection. A single reference rat brain magnetic resonance image (MRI) was used to align the PET images with the Paxinos and Watson rat brain atlas. Increased glucose metabolism was observed in the somatosensory region associated with the injection site (S1 hindlimb contralateral), S1 jaw/upper lip and cingulate cortex. Decreases were observed in the prelimbic cortex and hippocampus. Second, SNI rats were scanned 3weeks post-surgery using the same scanning paradigm, and region-of-interest analyses revealed increased metabolic activity in the contralateral S1 hindlimb. Finally, a second cohort of SNI rats was scanned while anesthetized during the tracer uptake period, and the S1 hindlimb increase was not observed. Increased brain activity in the somatosensory cortex of SNI rats resembled the activity produced with the injection of formalin, suggesting that the SNI model may produce persistent pain. The lack of increased activity in S1 hindlimb with general anesthetic demonstrates that this effect can be blocked, as well as highlights the importance of investigating brain activity in awake and behaving rodents.

PET imaging with [¹8F]fluoroethoxybenzovesamicol ([¹8F]FEOBV) following selective lesion of cholinergic pedunculopontine tegmental neurons in rat.

INTRODUCTION: [(18)F]fluoroethoxybenzovesamicol ([(18)F]FEOBV) is a PET radiotracer with high selectivity and specificity to the vesicular acetylcholine transporter (VAChT). It has been shown to be a sensitive in vivo measurement of changes of cholinergic innervation densities following lesion of the nucleus basalis of Meynert (NBM) in rat. The current study used [(18)F]FEOBV with PET imaging to detect the effect of a highly selective lesion of the pedunculopontine (PPTg) nucleus in rat. METHODS: After bilateral and selective lesions of the PPTg cholinergic neurons, rats were scanned using [(18)F]FEOBV, then sacrificed, and their brain tissues collected for immunostaining and quantification of the VAChT. RESULTS: Comparisons with control rats revealed that cholinergic losses can be detected in the brainstem, lateral thalamus, and pallidum by using both in vivo imaging methods with [(18)F]FEOBV, and ex vivo measurements. In the brainstem PPTg area, significant correlations were observed between in vivo and ex vivo measurements, while this was not the case in the thalamic and pallidal projection sites. CONCLUSIONS: These findings support PET imaging with [(18)F]FEOBV as a reliable in vivo method for the detection of neuronal terminal losses resulting from lesion of the PPTg. Useful applications can be found in the study of neurodegenerative diseases in human, such as Parkinson's disease, multiple system atrophy, progressive supranuclear palsy, or dementia with Lewy bodies.

Concordance between in vivo and postmortem measurements of cholinergic denervation in rats using PET with [18F]FEOBV and choline acetyltransferase immunochemistry.

BACKGROUND: Fluorine-18 fluoroethoxybenzovesamicol ([18F]FEOBV) is a radioligand for the selective imaging of the vesicular acetylcholine transporter with positron emission tomography (PET). The current study demonstrates that pathological cortical cholinergic deafferentation can be quantified in vivo with [18F]FEOBV PET, yielding analogous results to postmortem histological techniques. METHODS: Fifteen male rats (3 months old) underwent a cerebral infusion of 192 IgG-saporin at the level of the nucleus basalis magnocellularis. They were scanned using [18F]FEOBV PET, then sacrificed, and their brain tissues collected for immunostaining and quantification of cholinergic denervation using optical density (OD). RESULTS: For both PET binding and postmortem OD, the highest losses were found in the cortical areas, with the highest reductions in the orbitofrontal, sensorimotor, and cingulate cortices. In addition, OD quantification in the affected areas accurately predicts [18F]FEOBV uptake in the same regions when regressed linearly. CONCLUSIONS: These findings support [18F]FEOBV as a reliable imaging agent for eventual use in human neurodegenerative conditions in which cholinergic losses are an important aspect.

A new rechargeable device for deep brain stimulation: a prospective patient satisfaction survey.

BACKGROUND: Deep brain stimulation (DBS) is highly successful in treating Parkinson's disease (PD), dystonia, and essential tremor (ET). Until recently implantable neurostimulators were nonrechargeable, battery-driven devices, with a lifetime of about 3-5 years. This relatively short duration causes problems for patients (e.g. programming and device-use limitations, unpredictable expiration, surgeries to replace depleted batteries). Additionally, these batteries (relatively large with considerable weight) may cause discomfort. To overcome these issues, the first rechargeable DBS device was introduced: smaller, lighter and intended to function for 9 years. METHODS: Of 35 patients implanted with the rechargeable device, 21 (including 8 PD, 10 dystonia, 2 ET) were followed before and 3 months after surgery and completed a systematic survey of satisfaction with the rechargeable device. RESULTS: Overall patient satisfaction was high (83.3 ± 18.3). Dystonia patients tended to have lower satisfaction values for fit and comfort of the system than PD patients. Age was significantly negatively correlated with satisfaction regarding process of battery recharging. CONCLUSIONS: Dystonia patients (generally high-energy consumption, severe problems at the DBS device end-of-life) are good, reliable candidates for a rechargeable DBS system. In PD, younger patients, without signs of dementia and good technical understanding, might have highest benefit.

PET imaging of cholinergic deficits in rats using [18F]fluoroethoxybenzovesamicol ([18F]FEOBV).

[(18)F]fluoroethoxybenzovesamicol ([(18)F]FEOBV) is one of the most promising radioligands for imaging the vesicular ACh transporter (VAChT) with positron emission tomography (PET). We report here that this method can detect subtle cholinergic terminals losses such as those associated with aging, or those following a partial lesion of the nucleus basalis magnocellularis (NBM). Twenty-one adult rats were evenly distributed in three groups including 1) aged rats (18 months); 2) young rats (3 months); and 3) rats with unilateral lesion of the NBM, following a local stereotaxic infusion of 192 IgG-saporin. In both normal and lesioned rats, our results revealed the highest [(18)F]FEOBV binding to be in the striatum, followed by similar values in both frontal cortex and thalamus, while lower values were observed in both hippocampus and temporo-parietal cortex. This binding distribution is consistent with the known anatomy of brain cholinergic systems. In the lesioned rats, [(18)F]FEOBV binding was found to be reduced mostly in the ventral frontal cortex on the side of the lesion, but some reductions were also observed in the homologous region of the contralateral hemisphere. Aging was found to be associated with a [(18)F]FEOBV binding reduction limited to the hippocampus of both hemispheres. [(18)F]FEOBV appears to be a very promising marker for the in vivo quantification of the brain VAChT; PET imaging of this agent allows in vivo detection of both physiological and pathological reductions of cholinergic terminals density.

Test-retest stability of cerebral mGluR5 quantification using [¹¹C]ABP688 and positron emission tomography in rats.

This study evaluates the reproducibility of the quantification of metabotropic glutamate receptor type 5 (mGluR5) densities in rats using the PET radiotracer [¹¹C]ABP688 and pharmacokinetic models that are based on an input function, which is derived from a reference tissue. Seven rats underwent dynamic PET scans (60 min) after bolus injection of [¹¹C]ABP688. Kinetic analyses included: binding potential (BP(ND) ) determined by calculating (a) the simplified reference tissue model (SRTM) and (b) its two-steps simplified version (SRTM2); (c) multilinear reference tissue model (MRTM) and (d) its 2-parameter version (MRTM2); (e) noninvasive graphical analysis (NIGA). Parametric images were generated representing BP(ND) by the MRTM2 model. BP(ND) determinations were reproducible with low to acceptable variability ranging from 5 to 10% and reproducibility scores (intraclass correlation coefficient) between 0.51 and 0.88. The pharmacokinetic model that showed lowest overall variability was the SRTM. In contrast, the use of the NIGA was associated with significantly lower reproducibility scores. Comparison of parametric images revealed no significant bias between test and retest measurements and is therefore suitable to compare groups at voxel levels. In conclusion, our results suggest that noninvasive quantification of [¹¹C]ABP688 imaging is reproducible and reliable for PET studies of the cerebral mGluR5 in rats.

Oxalic acid supported Si-18F-radiofluorination: one-step radiosynthesis of N-succinimidyl 3-(di-tert-butyl[18F]fluorosilyl)benzoate ([18F]SiFB) for protein labeling.

N-Succinimidyl 3-(di-tert-butyl[(18)F]fluorosilyl)benzoate ([(18)F]SiFB), a novel synthon for one-step labeling of proteins, was synthesized via a simple (18)F-(19)F isotopic exchange. A new labeling technique that circumvents the cleavage of the highly reactive active ester moiety under regular basic (18)F-labeling conditions was established. In order to synthesize high radioactivity amounts of [(18)F]SiFB, it was crucial to partially neutralize the potassium oxalate/hydroxide that was used to elute (18)F(-) from the QMA cartridge with oxalic acid to prevent decomposition of the active ester moiety. Purification of [(18)F]SiFB was performed by simple solid-phase extraction, which avoided time-consuming HPLC and yielded high specific activities of at least 525 Ci/mmol and radiochemical yields of 40-56%. In addition to conventional azeotropic drying of (18)F(-) in the presence of [K(+)⊂2.2.2.]C(2)O(4), a strong anion-exchange (SAX) cartridge was used to prepare anhydrous (18)F(-) for nucleophilic radio-fluorination omitting the vacuum assisted drying of (18)F(-). Using a lyophilized mixture of [K(+)⊂2.2.2.]OH resolubilized in acetonitrile, the (18)F(-) was eluted from the SAX cartridge and used directly for the [(18)F]SiFB synthesis. [(18)F]SiFB was applied to the labeling of various proteins in likeness to the most commonly used labeling synthon in protein labeling, N-succinimidyl-4-[(18)F]fluorobenzoate ([(18)F]SFB). Rat serum albumin (RSA), apo-transferrin, a ß-cell-specific single chain antibody, and erythropoietin were successfully labeled with [(18)F]SiFB in good radiochemical yields between 19% and 36%. [(18)F]SiFB- and [(18)F]SFB-derivatized RSA were directly compared as blood pool imaging agents in healthy rats using small animal positron emission tomography. Both compounds demonstrated identical biodistributions in healthy rats, accurately visualizing the blood pool with PET.

Metformin abolishes increased tumor (18)F-2-fluoro-2-deoxy-D-glucose uptake associated with a high energy diet.

Insulin regulates glucose uptake by normal tissues. Although there is evidence that certain cancers are growth-stimulated by insulin, the possibility that insulin influences tumor glucose uptake as assessed by ( 18) F-2-Fluoro-2-Deoxy-d-Glucose Positron Emission Tomography (FDG-PET) has not been studied in detail. We present a model of diet-induced hyperinsulinemia associated with increased insulin receptor activation in neoplastic tissue and with increased tumor FDG-PET image intensity. Metformin abolished the diet-induced increases in serum insulin level, tumor insulin receptor activation and tumor FDG uptake associated with the high energy diet but had no effect on these measurements in mice on a control diet. These findings provide the first functional imaging correlate of the well-known adverse effect of caloric excess on cancer outcome. They demonstrate that, for a subset of neoplasms, diet and insulin are variables that affect tumor FDG uptake and have implications for design of clinical trials of metformin as an antineoplastic agent.

Intact memory in TGF-ß1 transgenic mice featuring chronic cerebrovascular deficit: recovery with pioglitazone.

The roles of chronic brain hypoperfusion and transforming growth factor-beta 1 (TGF-ß1) in Alzheimer's disease (AD) are unresolved. We investigated the interplay between TGF-ß1, cerebrovascular function, and cognition using transgenic TGF mice featuring astrocytic TGF-ß1 overexpression. We further assessed the impact of short, late therapy in elderly animals with the antioxidant N-acetyl-L-cysteine (NAC) or the peroxisome proliferator-activated receptor-γ agonist pioglitazone. The latter was also administered to pups as a prophylactic 1-year treatment. Elderly TGF mice featured cerebrovascular dysfunction that was not remedied with NAC. In contrast, pioglitazone prevented or reversed this deficit, and rescued the impaired neurovascular coupling response to whisker stimulation, although it failed to normalize the vascular structure. In aged TGF mice, neuronal and cognitive indices--the stimulus-evoked neurometabolic response, cortical cholinergic innervation, and spatial memory in the Morris water maze--were intact. Our findings show that impaired brain hemodynamics and cerebrovascular function are not accompanied by memory impairment in this model. Conceivably in AD, they constitute aggravating factors against a background of aging and underlying pathology. Our data further highlight the ability of pioglitazone to protect the cerebrovasculature marked by TGF-ß1 increase, aging, fibrosis, and antioxidant resistance, thus of high relevance for AD patients.

In vivo and in vitro validation of reference tissue models for the mGluR(5) ligand [(11)C]ABP688.

The primary objective of this study was to verify the suitability of reference tissue-based quantification methods of the metabotropic glutamate receptor type 5 (mGluR(5)) with [(11)C]ABP688. This study presents in vivo (Positron Emission Tomography (PET)) and in vitro (autoradiography) measurements of mGluR(5) densities in the same rats and evaluates both noninvasive and blood-dependent pharmacokinetic models for the quantification of [(11)C]ABP688 binding. Eleven rats underwent [(11)C]ABP688 PET scans. In five animals, baseline scans were compared with blockade experiments with the antagonist 1,2-methyl-6-(phenylethynyl)-pyridine (MPEP), and arterial blood samples were drawn and corrected for metabolites. Afterward, saturation-binding autoradiography was performed. Blocking with MPEP resulted in an average decrease of the total distribution volume (V(T)) between 43% and 58% (thalamus and caudate-putamen, respectively) but had no significant effect on cerebellar V(T) (mean reduction: -0.01%). Comparing binding potential (BP(ND)) based on the V(T) with noninvasively determined BP(ND) revealed an average negative bias of 0.7% in the caudate-putamen and an average positive bias of 3.1% in the low-binding regions. Scan duration of 50 minutes is required. The cerebellum is a suitable reference region for the quantification of mGluR(5) availability as measured with [(11)C]ABP688 PET in rats. Blood-based and reference region-based PET quantification shows a significant linear relationship to autoradiographic determinations.

MicroPET imaging of 5-HT 1A receptors in rat brain: a test-retest [18F]MPPF study.

PURPOSE: Earlier studies have shown that positron emission tomography (PET) imaging with the radioligand [(18)F]MPPF allows for measuring the binding potential of serotonin 5-hydroxytryptamine(1A) (5-HT(1A)) receptors in different regions of animal and human brain, including that of 5-HT(1A) autoreceptors in the raphe nuclei. In the present study, we sought to determine if such data could be obtained in rat, with a microPET (R4, Concorde Microsystems). METHODS: Scans from isoflurane-anaesthetised rats (n = 18, including six test-retest) were co-registered with magnetic resonance imaging data, and binding potential, blood to plasma ratio and radiotracer efflux were estimated according to a simplified reference tissue model. RESULTS: Values of binding potential for hippocampus (1.2), entorhinal cortex (1.1), septum (1.1), medial prefrontal cortex (1.0), amygdala (0.8), raphe nuclei (0.6), paraventricular hypothalamic nucleus (0.5) and raphe obscurus (0.5) were comparable to those previously measured with PET in cats, non-human primates or humans. Test-retest variability was in the order of 10% in the larger brain regions (hippocampus, medial prefrontal and entorhinal cortex) and less than 20% in small nuclei such as the septum and the paraventricular hypothalamic, basolateral amygdaloid and raphe nuclei. CONCLUSIONS: MicroPET brain imaging of 5-HT(1A) receptors with [(18)F]MPPF thus represents a promising avenue for investigating 5-HT(1A) receptor function in rat.

FDG-PET imaging for the evaluation of antiglioma agents in a rat model.

The increasing development of novel anticancer agents demands parallel advances in the methods used to rapidly assess their therapeutic efficacy (TE) in the preclinical phase. We evaluated the ability of small-animal PET, using the (18)F-fluoro-deoxy-D-glucose (FDG) radiotracer, to predict the TE of a number of anticancer agents in the rat C6 glioma model following 3 days of treatment. Semi-quantitative measurements of changes in FDG uptake during the course of treatment (standardized uptake value response [SUV(r)]) were found to be significantly lower in tumors treated with the hypoxia-inducible factor-1alpha inhibitor YC-1 (15 mg/kg) than in tumors in the control group. No significant SUV(r) change was observed following a similar 3-day regimen with the proapoptotic agent NS1619 (20 microg/kg), the combination of YC-1 and NS1619, or the alkylating agent temozolomide (7.5 mg/kg). Quantitative immunohistochemical studies demonstrated significantly lower levels of glucose transporter-1 (GLUT-1) expression in the YC-1-treated tumors, thereby correlating with the low SUV(r) observed in this group. The ability of SUV(r) to predict gold-standard outcomes of TE was further validated as YC-1-treated tumors had decreased volumes compared to control tumors. As such, we successfully demonstrated the ability of FDG-PET to rapidly determine the TE of novel agents for the treatment of glioma in the preclinical phase of evaluation.

[18F]Fluorinated estradiol derivatives for oestrogen receptor imaging: impact of substituents, formulation and specific activity on the biodistribution in breast tumour-bearing mice.

PURPOSE: The biodistribution and tumour uptake of a series of 16alpha-[(18)F]fluoroestradiol ([18F]FES) derivatives was determined in oestrogen receptors-positive (ER+) tumour-bearing mice to assess the impact of substituents, formulation and specific activity on target tissue uptake. METHODS: MC4-L2 and MC7-L1 murine ER+ cells were inoculated in Balb/c mice. The animals were injected with various [(18)F]FES derivatives substituted with 2- or 4-fluorine and/or an 11beta-methoxy group. The radiopharmaceuticals were formulated in 10% ethanol/saline or 10% ethanol/lipid emulsion. The organs were counted, and radioactivity concentrations were expressed as the percentage of the injected dose per gram tissue (%ID/g). To estimate the effect of specific activity on tumour uptake, the 4-fluoro-11beta-methoxy-16alpha-[(18)F]-fluoroestradiol (4F-M[(18)F]FES) was co-injected with different concentrations of non-radioactive estradiol to give an in vivo competitive inhibition curve. RESULTS: 4F-M[(18)F]FES exhibited the highest average uterine uptake (%ID/g = 15.7 +/- 2.1). The highest uptake by the two mammary tumours was observed with [(18)F]FES (%ID/g = 3.1 and 3.4 +/- 0.3) and 11beta-methoxy-16alpha[(18)F]-fluoroestradiol (M-[(18)F]FES) (%ID/g = 3.2 and 3.3 +/- 0.6), followed by 4F-M[(18)F]FES (%ID/g = 2.5 and 2.3 +/- 0.3). The formulation had little influence on the biodistribution pattern. Co-injection with a total mass of estradiol >10(-10) mol blocked 4F-M[(18)F]FES tumour uptake. CONCLUSION: All of the radiolabelled estradiol derivatives achieved significant target tissue uptake in vivo, both in ER+ tumours and the uterus. The formulation had little impact on the biodistribution of these compounds but some compounds (4F-M[(18)F]FES, M-[(18)F]FES and [(18)F]FES) had more favourable target tissue uptake and target-to-background ratios.

A small animal positron emission tomography study of the effect of chemotherapy and hormonal therapy on the uptake of 2-deoxy-2-[F-18]fluoro-D-glucose in murine models of breast cancer.

PURPOSE: We used small animal positron emission tomography (PET) imaging to monitor the time-course of tumor metabolic response to hormone and chemotherapy in a murine model of hormone-sensitive breast cancer. PROCEDURES: Estrogen receptor positive murine mammary carcinomas were inoculated in Balb/c mice. Small animal PET imaging using 2-deoxy-2-[F-18]fluoro-D: -glucose (FDG) was used to assess tumor metabolic activity. Imaging was done before and at days 1, 7, and 14 after the administration of doxorubicin, methotrexate, letrozole, or placebo. The tumor uptake of FDG was calculated from a region-of-interest drawn around the tumor. RESULTS: All treatments resulted in a decrease in tumor growth rate and end volume compared to untreated control. FDG uptake was also markedly decreased after treatment although a flare reaction was observed on PET at day 7, the intensity of which varied according to the treatment modality. CONCLUSION: PET imaging is sensitive to detect early changes associated with therapy in murine breast cancer models. A flare reaction was observed 7 days after the initiation of therapy.

Impact on estrogen receptor binding and target tissue uptake of [18F]fluorine substitution at the 16alpha-position of fulvestrant (faslodex; ICI 182,780).

Fulvestrant (Faslodex; ICI 182,780) is a pure estrogen receptor (ER) antagonist recently approved for the treatment of hormone-sensitive breast cancer in post-menopausal women with disease progression following antiestrogen therapy. Fulvestrant strongly binds to the ER and its mode of action consists of inhibition of ER dimerization leading to a down regulation of ER protein cellular levels. With the aim to develop a probe for positron emission tomography (PET) imaging capable of predicting the potential therapeutic efficacy of selective ER modulators (SERM), we prepared three new 16alpha-[18F]fluoro-fulvestrant derivatives. These new radiopharmaceuticals were evaluated for their binding affinity to the human ERalpha and for their target tissue uptake in immature female rats. Substitution of one of the side-chain F-atoms of fulvestrant for 18F would have led to a product of low specific activity; instead we selected the 16alpha-position for 18F-labeling, which at least in the case of estradiol (ES) is well tolerated by the ER. Radiochemical synthesis proceeds by stereoselective introduction of the [18F]fluoride at the 16-18F-position of fulvestrant via opening of an intermediate O-cyclic sulfate followed by hydrolysis of the protecting methoxymethyl (MOM) ether and sulfate groups. Three analogs with different oxidation states of the side chain sulfur, i.e. sulfide, sulfone or sulfoxide (fulvestrant) were prepared. Introduction of the 16(18)F-fluorine led to a dramatic decrease of the apparent binding affinity for ER, as reported by Wakeling et al. (Cancer Res. 1991;51:3867-73). Likewise, in vivo ER-mediated uterus uptake values in immature female rats were disappointing. Overall, our findings suggest that these new PET radiopharmaceuticals are not suitable as tracers to predict ER(+) breast cancer response to hormonal therapy with selective ER modulators.