Molecular Imaging Studies Research Articles

The pig model in brain imaging and neurosurgery

The pig model is increasingly used in the field of neuroscience because of the similarities of its brain with human. This review presents the peculiarities of the anatomy and functions of the pig brain with specific reference to its human counterpart. We propose an approximate mapping of the pig’s cortical areas since a comprehensive description of the equivalent of Brodmann’s areas is lacking. On the contrary, deep brain structures are received more consideration but a true three-dimensional (3D) atlas is still eagerly required. In the second section, we present an overview of former works describing the use of functional imaging and neuronavigation in the pig model. Recently, the pig has been increasingly used for molecular imaging studies using positron emission tomography (PET). Indeed, the large size of its brain is compatible with the limited spatial resolution of the PET scanner built to accommodate a human being. Similarly, neuronavigation is an absolute requirement to target deep brain areas in human and in pig since the surgeon cannot rely on external skull structures for zeroing the 3D reference frame. Therefore, a large body of methodological refinements has been dedicated to image guided surgery in the pig model. These refinements allow now a millimetre precision: an absolute requirement for basal nuclei targeting. In the third section, several examples of ongoing studies in our laboratory were presented to illustrate the intricacies of using the pig model. For both examples, after a brief description of the scientific context of the experiment, we present, in detail, the methodological steps required to achieve the experimental goals, which are specific to the porcine model. Finally, in the fourth section, the anatomical variations depending on the breed and age are discussed in relation with neuronavigation and brain surgery. The need for a digitized multimodality brain atlas is also highlighted.

A high relaxivity Gd(III)DOTA-DSPE-based liposomal contrast agent for magnetic resonance imaging

The field of molecular imaging aims to visualize and quantify (patho)physiological processes at the cellular and molecular level. Sensitive and site-targeted contrast agents are employed to visualize molecular constituents of processes of interest. The principal aim of this study was to develop a magnetic resonance imaging (MRI) detectable liposome with high relaxivity and stability. To this end, Gd(III)DOTA-DSPE was synthesized and incorporated in a liposomal formulation. The resulting liposomes were extensively characterized in vitro in terms of contrast agent efficiency and structural properties. The liposomes were shown to have a high longitudinal relaxivity, which is crucial for the detection of low concentration molecular markers in molecular imaging studies. We also demonstrated that Gd(III)DOTA-DSPE exhibits no detectable transmetallation upon incubation with Zn(II). This is important as it significantly contributes to the biocompatibility of the contrast agent. The present liposome preparation will serve as versatile and well characterized platform for molecular imaging and targeted drug delivery studies.

Preliminary study of molecular imaging of human hepatoceilular carcinoma xenoggaft with Gd-based MR probe containiug arginine-glycine-aspartic acid chelate

Objective To develop a Gd-based MR probe containing arginine-glyeine-aspartic acid (RGD)motif to reveal integrin avβ3 receptor-expressed tumor.Methods Commercially available HYNICRGD conjugate with co-ligand EDDA was labeled with GdCl3,and the mixture was isolated and purified by solid phase extract(SPE)to get the entire probe Gd-EDDA-HYNIC-RGD.Human HCC cell line BEL-7402 was cultured and the cells harvested and suspended then subcutaneously inoculated into athymic nude mice for tumor growth.In vitro cell binding assay to integrin avβ3 receptor and cell viability experiments were conducted.Then in vivo,imaging of the three arms of xenografts were performed by MR scan with a dedicated animal coil at baseline and time points of 0.30,60,90 mninutes and 24 hour post-intravenous injection(P.i.) via the tail vein.Three arms of nude mice then were sacrificed for histological examination to confirm the imaging results.Results Gd-EDDA-HYNIC-RGD was successfully isolated by SPE and validity was verifled on signal enhancement througll in vitro and in vivo experiments.The T1 relaxation rate of the probe is 3.31 mmol/s:It is well tolerated to living cells when the concentration of the probe is below 0.1 μmol/ml;both BEL-7402 Hunlan Hepatocellular Carcinoma cell Iine and the tumor expressed avβ3receptor;The RGD-iigand was observed specificly binding with avβ3 receptor in vitro;The nude mice model bearing HHCC was well estabhshed.The signal intensity(SI)at the tumor site were 2247.6±39.0 at baseline and 2820.9±35.2 at 90 min p.i.respectively,the SI at 90min increased less than 25%of baseline,which is statistically different(t=-38.031,P＜0.05);while the SI at muscle site were 1824.2±32.8 and 1845.8±27.2 respectively,which is not statistically different(t=-1.424,P＞0.05);The signal to time curve for probe-administrated group is straightforward over time in the span of 0 to 90 minute p.i.while the control arms do not show such tendency.Conclusion Gd-EDDA-HYNIC-RGD has the potential to used as an MR probe detecting integrin avβ3 receptor-expressed tumor.This work may offer possibility of early detection and differentiation of specific tumors. Key words: Molecular probes; Integrin alpha Vbeta3; Magnetic resonance imaging; Animal experimentation

Understanding pathophysiology is crucial in linking clinical staging to targeted thera‐peutics

Understanding pathophysiology is crucial in linking clinical staging to targeted thera‐peutics

Accuracy and reproducibility of tumor positioning during prolonged and multi-modality animal imaging studies

Dedicated small-animal imaging devices, e.g. positron emission tomography (PET), computed tomography (CT) and magnetic resonance imaging (MRI) scanners, are being increasingly used for translational molecular imaging studies. The objective of this work was to determine the positional accuracy and precision with which tumors in situ can be reliably and reproducibly imaged on dedicated small-animal imaging equipment. We designed, fabricated and tested a custom rodent cradle with a stereotactic template to facilitate registration among image sets. To quantify tumor motion during our small-animal imaging protocols, ‘gold standard’ multi-modality point markers were inserted into tumor masses on the hind limbs of rats. Three types of imaging examination were then performed with the animals continuously anesthetized and immobilized: (i) consecutive microPET and MR images of tumor xenografts in which the animals remained in the same scanner for 2 h duration, (ii) multi-modality imaging studies in which the animals were transported between distant imaging devices and (iii) serial microPET scans in which the animals were repositioned in the same scanner for subsequent images. Our results showed that the animal tumor moved by less than 0.2–0.3 mm over a continuous 2 h microPET or MR imaging session. The process of transporting the animal between instruments introduced additional errors of ∼0.2 mm. In serial animal imaging studies, the positioning reproducibility within ∼0.8 mm could be obtained.

Dual MET–EGFR combinatorial inhibition against T790M-EGFR-mediated erlotinib-resistant lung cancer

Despite clinical approval of erlotinib, most advanced lung cancer patients are primary non-responders. Initial responders invariably develop secondary resistance, which can be accounted for by T790M-EGFR mutation in half of the relapses. We show that MET is highly expressed in lung cancer, often concomitantly with epidermal growth factor receptor (EGFR), including H1975 cell line. The erlotinib-resistant lung cancer cell line H1975, which expresses L858R/T790M-EGFR in-cis, was used to test for the effect of MET inhibition using the small molecule inhibitor SU11274. H1975 cells express wild-type MET, without genomic amplification (CNV=1.1). At 2 μM, SU11274 had significant in vitro pro-apoptotic effect in H1975 cells, 3.9-fold (P=0.0015) higher than erlotinib, but had no effect on the MET and EGFR-negative H520 cells. In vivo, SU11274 also induced significant tumour cytoreduction in H1975 murine xenografts in our bioluminescence molecular imaging assay. Using small-animal microPET/MRI, SU11274 treatment was found to induce an early tumour metabolic response in H1975 tumour xenografts. MET and EGFR pathways were found to exhibit collaborative signalling with receptor cross-activation, which had different patterns between wild type (A549) and L858R/T790M-EGFR (H1975). SU11274 plus erlotinib/CL-387,785 potentiated MET inhibition of downstream cell proliferative survival signalling. Knockdown studies in H1975 cells using siRNA against MET alone, EGFR alone, or both, confirmed the enhanced downstream inhibition with dual MET–EGFR signal path inhibition. Finally, in our time-lapse video-microscopy and in vivo multimodal molecular imaging studies, dual SU11274-erlotinib concurrent treatment effectively inhibited H1975 cells with enhanced abrogation of cytoskeletal functions and complete regression of the xenograft growth. Together, our results suggest that MET-based targeted inhibition using small-molecule MET inhibitor can be a potential treatment strategy for T790M-EGFR-mediated erlotinib-resistant non-small-cell lung cancer. Furthermore, optimised inhibition may be further achieved with MET inhibition in combination with erlotinib or an irreversible EGFR-TKI.

Hypoxia‐regulated protein expression, patient characteristics, and preoperative imaging as predictors of survival in adults with glioblastoma multiforme

Regions of hypoxia within glioblastoma multiforme (GBM) are common and may influence a tumor's aggressiveness, response to treatment, and the patient's overall survival. In this study, the authors examined 4 markers of hypoxia (hypoxia-inducible factor 1 [HIF-1alpha], glucose transporter 1 [GLUT-1], vascular endothelial growth factor [VEGF], and carbonic anhydrase 9 [CA IX]), cellular proliferation and microvascular density (MVD) indices, extent of surgical resection, and preoperative imaging characteristics and compared them with the overall survival rates of adults with GBM. In this retrospective cohort study, patients who had lower grade astrocytomas were compared with patients who had GBM to verify that the methods used could establish differences between tumor grades. By using preoperative imaging, the amount of necrosis was established versus the overall tumor area. The authors also compared preoperative images with postoperative images to define the amount of tumor resected; and they compared molecular markers, proliferation, MVD, and imaging studies with survival among patients who had GBM. The hypoxia-regulated molecules (HRMs) and indices for MVD and cellular proliferation were associated significantly with tumor grade. Survival was improved when >or=95% of the tumor was resected. Although the total tumor area was associated with overall survival, no differences were observed when the amount of necrosis or a tumor necrosis index (area of necrosis/area of tumor) was compared with survival. The findings indicated that GLUT-1 and VEGF were correlated with survival after controlling for age. Tumor grade was differentiated with HRMs, MVD, and proliferation, but only GLUT-1 predicted survival in this group of patients with GBM. The results suggested that GLUT-1 may be an important independent prognostic indicator.

TLD assessment of mouse dosimetry during microCT imaging

Advances in laboratory animal imaging have provided new resources for noninvasive biomedical research. Among these technologies is microcomputed tomography (microCT) which is widely used to obtain high resolution anatomic images of small animals. Because microCT utilizes ionizing radiation for image formation, radiation exposure during imaging is a concern. The objective of this study was to quantify the radiation dose delivered during a standard microCT scan. Radiation dose was measured using thermoluminescent dosimeters (TLDs), which were irradiated employing an 80 kVp x-ray source, with 0.5 mm A1 filtration and a total of 54 mA s for a full 360 deg rotation of the unit. The TLD data were validated using a 3.2 cm3 CT ion chamber probe. TLD results showed a single microCT scan air kerma of 78.0 +/- 5.0 mGy when using a poly(methylmethacrylate) (PMMA) anesthesia support module and an air kerma of 92.0 +/- 6.0 mGy without the use of the anesthesia module. The validation CT ion chamber study provided a measured radiation air kerma of 81.0 +/- 4.0 mGy and 97.0 +/- 5.0 mGy with and without the PMMA anesthesia module, respectively. Internal TLD analysis demonstrated an average mouse organ radiation absorbed dose of 76.0 +/- 5.0 mGy. The author's results have defined x-ray exposure for a routine microCT study which must be taken into consideration when performing serial molecular imaging studies involving the microCT imaging modality.

TU‐C‐332‐07: Accuracy and Reproducibility of Tumor Position During Prolonged and Multi‐Modality Animal Imaging Studies

Purpose: Dedicated small‐animal imaging devices are being used more frequently for translational molecular imaging studies. However, few studies have investigated the magnitude of animal motion during extended dynamic imaging studies or the precision of animal repositioning in multi‐modality and/or serial imaging protocols. The objective of this work was to determine the positional accuracy and precision with which tumors in situ can be reliably and reproducibly imaged on dedicated small‐animal imaging equipment. Method and Materials: A custom rodent animal cradle with a stereotactic template served to define a coordinate system and to facilitate rigid‐body image registration. Attached to the template were fiduciary markers containing PET tracer and MRI and CT contrast media for visualization on the respective scanners. To quantify animal tumor motion during imaging protocols, “gold standard” point markers were inserted into tumors grown on the hind limb of nude rats. Three types of imaging examination were performed with the animals continuously anesthetized and immobilized: (i) single‐modality imaging (microPET and MRI) in which the animals remained in the same scanner continuously for 2 hours, (ii) multi‐modality imaging studies in which the animals were transported from a microPET to an MR scanner located in another building, and (iii) serial microPET scans in which the animals were removed from the scanner, then re‐positioned and scanned. Results: The animal tumor moved by less than 0.2–0.3 mm over two‐hour microPET or MR imaging sessions. Transporting the animal between instruments introduced additional error of ∼0.2 mm. In serial animal imaging studies, in which the animal was returned to its cage and subsequently re‐positioned, reproducibility within ∼0.8 mm could be obtained. Conclusion: To our knowledge, this is the first study systematically and rigorously evaluating the accuracy and precision with which tumors can be repeatedly imaged in small‐animal imaging devices.

Quantitative ferromagnetic resonance analysis ofCD 133 stem cells labeled with iron oxide nanoparticles

The aim of this work is to provide a quantitative method for analysis of the concentrationof superparamagnetic iron oxide nanoparticles (SPION), determined by means offerromagnetic resonance (FMR), with the nanoparticles coupled to a specific antibody(AC 133), and thus to express the antigenic labeling evidence for the stem cellsCD 133+. The FMR efficiency and sensitivity were proven adequate fordetecting and quantifying the low amounts of iron content in theCD 133+ cells(∼6.16 × 105 pg in thevolume of 2 µl containing 4.5 × 1011 SPION). The quantitative method led to the result of1.70 × 10−13 mol ofFe (9.5 pg), or 7.0 × 106 nanoparticles per cell. For the quantification analysis via the FMR technique it wasnecessary to carry out a preliminary quantitative visualization of iron oxide-labeled cells inorder to ensure that the nanoparticles coupled to the antibodies are indeed tied to theantigen at the stem cell surface and that the cellular morphology was conserved, as proof ofthe validity of this method. The quantitative analysis by means of FMR is necessary fordetermining the signal intensity for the study of molecular imaging by means of magneticresonance imaging (MRI).

Synthesis and Screening of Mono- and Di-Aryl Technetium and Rhenium Metallocarboranes. A New Class of Probes for the Estrogen Receptor

A series of mono and diaryl rhenium(I)-carborane derivatives were prepared using microwave heating and screened for their affinity for two isoforms of the estrogen receptor (ER). The rhenacarborane derivative [(RR'C 2B9H9)Re(CO)3](-) (R = p-PhOH, R' = H), which was generated by taking advantage of a recently discovered cage isomerization process, and the neutral nitrosated analogue [(RR'C2B9H9)Re(CO)2(NO)] (R = p-PhOH, R' = H) showed the highest affinities of the compounds screened. As a result, the (99m)Tc analogue of one of the leads was produced in high yield (84%) and specific activity in a manner that is suitable for routine production in support of future preclinical and molecular imaging studies.

An axis of rotation alignment system for high-resolution pinhole SPECT imaging

We developed a simple geometric calibration method for modified animal pinhole single photon emission computed tomography (SPECT) imaging systems using a laser alignment system that does not require additional calibration scans, and verified the feasibility of this system. An optical system consisting of a laser generator and a reflecting mirror, and an alignment method using this system were developed. After laser alignment had been completed, SPECT scans of a Tc-99m line source were performed. After acquiring data with complete alignment, the rotation stage was moved along the y-axis (parallel to the detector plane) to acquire off-axis data. Using these on- and off-axis settings, a micro-performance phantom with hot-rod inserts was scanned after filling with Tc-99m solution. Reconstructed images of the line source and the hot-rod phantom showed that image degradation was minimized when the rotation center was completely aligned using our system. The spatial resolution of the reconstructed image measured using the line source was finest under complete alignment. Under this condition, the smallest hot rod (1.2mm diameter) was resolved in the SPECT image acquired using a 0.5mm pinhole aperture. The effects of misalignment were clearly observable in off-axis images; only hot rods with more than 3.2mm diameter were resolved in 1mm off-axis image whereas there were no resolvable hot rods with more than 2mm off-axis image. This system of which the feasibility was verified in the present study will be useful for low-cost molecular imaging studies using single photon emitting tracers.

Sleep deprivation predisposes liver to oxidative stress and phospholipid damage: a quantitative molecular imaging study

Sleep disorders are associated with an increased rate of various metabolic disturbances, which may be related to oxidative stress and consequent lipid peroxidation. Since hepatic phosphatidylcholine plays an important role in metabolic regulation, the aim of the present study was to determine phosphatidylcholine expression in the liver following total sleep deprivation. To determine the effects of total sleep deprivation, we used adult rats implanted for polygraphic recording. Phosphatidylcholine expression was examined molecularly by the use of time-of-flight secondary ion mass spectrometry, along with biochemical solid-phase extraction. The parameters of oxidative stress were investigated by evaluating the hepatic malondialdehyde levels as well as heat shock protein 25 immunoblotting and immunohistochemistry. In normal rats, the time-of-flight secondary ion mass spectrometry spectra revealed specific peaks (m/z 184 and 224) that could be identified as molecular ions for phosphatidylcholine. However, following total sleep deprivation, the signals for phosphatidylcholine were significantly reduced to nearly one-third of the normal values. The results of solid-phase extraction also revealed that the phosphatidylcholine concentration was noticeably decreased, from 15.7 micromol g-1 to 9.4 micromol g-1, after total sleep deprivation. By contrast, the biomarkers for oxidative stress were drastically up-regulated in the total sleep deprivation-treated rats as compared with the normal ones (4.03 vs. 1.58 nmol mg-1 for malondialdehyde levels, and 17.1 vs. 6.7 as well as 1.8 vs. 0.7 for heat shock protein 25 immunoblotting and immunoreactivity, respectively). Given that phosphatidylcholine is the most prominent component of all plasma lipoproteins, decreased expression of hepatic phosphatidylcholine following total sleep deprivation may be attributed to the enhanced oxidative stress and the subsequent lipid peroxidation, which would play an important role in the formation or progression of total sleep deprivation-induced metabolic diseases.

Basic pathologies of neurodegenerative dementias and their relevance for state-of-the-art molecular imaging studies

Rising life-expectancy in the modern society has resulted in a rapidly growing prevalence of dementia, particularly of Alzheimer's disease (AD). Dementia turns into one of the most common age-related disorders with deleterious consequences for the concerned patients and their relatives, as well as worrying effects on the socio-economic systems. These facts justify strengthened scientific efforts to identify the pathologic origin of dementing disorders, to improve diagnosis, and to interfere therapeutically with the disease progression. In the recent years, remarkable progress has been made concerning the identification of molecular mechanisms underlying the pathology of neurodegenerative disorders. Growing evidence indicates that a common basis of many neurodegenerative dementias can be found in increased production, misfolding and pathological aggregation of proteins, such as beta-amyloid, tau protein, a-synuclein, or the recently described ubiquitinated TDP-43. This progressive insight in pathological processes is paralleled by the development of new therapeutic approaches. However, the exact contribution or mechanism of different pathologies with regard to the development of disease is not yet sufficiently clear. Considerable overlap of pathologies has been documented in different types of clinically defined dementias post mortem, and it has been difficult to correlate post mortem histopathology data with disease-expression during life. Molecular imaging procedures may play a valuable role to circumvent this limitation. In general, methods of molecular imaging have recently experienced an impressive advance, with numerous new and improved technologies emerging. These exciting tools may play a key role in the future regarding the evaluation of pathomechanisms, preclinical evaluation of new diagnostic procedures in animal models, selection of patients for clinical trials, and therapy monitoring. In this overview, molecular key pathologies, which are currently regarded to be strongly associated with the development of different dementias, will be shortly summarized; it will also be discussed how state-of-the-art imaging technology can assist to visualize these processes now and in the future.

Desorption Electrospray Ionization (DESI) Mass Spectrometry and Tandem Mass Spectrometry (MS/MS) of Phospholipids and Sphingolipids: Ionization, Adduct Formation, and Fragmentation

Desorption electrospray ionization (DESI) mass spectrometry was evaluated for the characterization of glycerophospholipid standards, including glycerophosphocholine (GPCho), glycerophosphoglycerol (GPGro), glycerophosphoethanolamine (GPEtn), glycerophosphoserine (GPSer), glycerophosphoinositol (GPIns), cardiolipin (CL), and sphingolipid standards, including sulfatides (ST) and sphingomyelin (SM). Of specific interest were the effects of surface and solvent composition on signal stability and intensity, along with the ions observed in the full scan mode and the fragmentations seen upon collisional activation for each of the above classes. These experiments were performed without the addition of matrix compounds to the sample and were conducted in the free ambient environment at atmospheric pressure. The compounds GPSer, GPGro, GPIns, ST, and CL were best analyzed in the negative ion mode while PE was ionized efficiently in both positive and negative ion modes. SM and GPCho, which typically generate more abundant ions in the positive ion mode, could be analyzed in the negative ion mode by the addition of anionic reagents such as acetate to the spray solvent. Full scan DESI mass spectra and tandem (MS/MS) spectra for this representative set of physiological phospho/sphingolipids are presented. Similarities with other ionization methods in terms of fragmentation behavior were strong, although ambient ionization of untreated samples is only available with DESI. The effect of surface and solvent properties on signal intensity and stability were determined by depositing standard compounds on several different surfaces and analyzing with various proportions of methanol in the aqueous spray. Analysis was extended to complex mixtures of phospholipids and sphingolipids by examining the total lipid extract of porcine brain and by direct analysis of rat brain cryotome sections. These types of mixture analyses and molecular imaging studies are likely to represent major areas of application of DESI.

Molecular imaging studies of the striatal dopaminergic system in psychosis and predictions for the prodromal phase of psychosis

The dopamine hypothesis has been the major pathophysiological theory of psychosis in recent decades. Molecular imaging studies have provided in vivo evidence of increased dopamine synaptic availability and increased presynaptic dopamine synthesis in the striata of people with psychotic illnesses. These studies support the predictions of the dopamine hypothesis, but it remains to be determined whether dopaminergic abnormalities pre-date or are secondary to the development of psychosis. We selectively review the molecular imaging studies of the striatal dopaminergic system in psychosis and link this to models of psychosis and the functional subdivisions of the striatum to make predictions for the dopaminergic system in the prodromal phase of psychosis.

Correlation between body mass index and striatal dopamine transporter availability in healthy volunteers—A SPECT study

Recent lines of research suggest that, in addition to hypothalamic sites, the striatum dopaminergic system may be a target for regulating homeostasis that may be represented by the body mass index (BMI). Although it has been reported that the striatal dopamine receptor (DRD2) availability of very obese individuals was reduced in proportion to their BMI, the correlation between the striatal dopamine system and the BMI in healthy individuals remains unclear. To investigate this relationship, the striatal dopamine transporter (DAT) availability of 50 healthy volunteers was measured using single position emission computational topography (SPECT) and [99mTc]-TRODAT-1. The serum levels of sugar, C-peptide, insulin, glycosylated hemoglobin and leptin were measured. Our results showed that age and the BMI are significantly negatively associated with the striatal DAT availability. Moreover, BMI was the only significant predictor for striatal DAT availability. These results suggest that the striatal dopamine system may be involved in body mass index regulation. Thus, molecular imaging studies measuring the striatal DAT availability should consider the BMI, rather than age, as a covariant.

Neuroimaging of pain mechanisms

Functional neuroimaging has made a huge impact scientifically, not least within the field of pain research. The noninvasive identification of pain mechanisms that underpin chronicity, such as central sensitization and other amplification processes related to the cognitive or emotional state of the patient, is of considerable interest to the clinical pain community and pharmaceutical industry. Relating data to a person's specific pain report or measure of pain relief provide a clearer understanding of the mechanisms driving and maintaining this complex experience. It is timely, therefore, to review the advances in neuroimaging applications to pain. New data have emerged to further support the descending modulatory system's critical role in chronic pain. The neural correlates that underpin tonic, ongoing and spontaneous pain in patients are being identified. Additionally, the prefrontal cortex is emerging as a critical brain region for pain processing, especially in patients. Finally, data from structural and molecular imaging studies are highlighting the extent of damage the brain sustains when patients live with their chronicity unrelieved. Neuroimaging tools have advanced our understanding of central pain mechanisms in normals and patients, forcing us to reconsider issues related to diagnosis and provision of treatment.

64 Cu-NOTA-8-Aoc-BBN(7-14)NH 2 ] targeting vector for positron-emission tomography imaging of gastrin-releasing peptide receptor-expressing tissues

Radiolabeled peptides hold promise as diagnostic/therapeutic targeting vectors for specific human cancers. We report the design and development of a targeting vector, [(64)Cu-NOTA-8-Aoc-BBN(7-14)NH(2)] (NOTA = 1,4,7-triazacyclononane-1,4,7-triacetic acid, 8-Aoc = 8-aminooctanoic acid, and BBN = bombesin), having very high selectivity and affinity for the gastrin-releasing peptide receptor (GRPr). GRPrs are expressed on a variety of human cancers, including breast, lung, pancreatic, and prostate, making this a viable approach toward site-directed localization or therapy of these human diseases. In this study, [NOTA-X-BBN(7-14)NH(2)] conjugates were synthesized, where X = a specific pharmacokinetic modifier. The IC(50) of [NOTA-8-Aoc-BBN(7-14)NH(2)] was determined by a competitive displacement cell-binding assay in PC-3 human prostate cancer cells using (125)I-[Tyr(4)]-BBN as the displacement ligand. An IC(50) of 3.1 +/- 0.5 nM was obtained, demonstrating high binding affinity of [NOTA-8-Aoc-BBN] for the GRPr. [(64)Cu-NOTA-X-BBN] conjugates were prepared by the reaction of (64)CuCl(2) with peptides in buffered aqueous solution. In vivo studies of [(64)Cu-NOTA-8-Aoc-BBN(7-14)NH(2)] in tumor-bearing PC-3 mouse models indicated very high affinity of conjugate for the GRPr. Uptake of conjugate in tumor was 3.58 +/- 0.70% injected dose (ID) per g at 1 h postintravenous injection (p.i.). Minimal accumulation of radioactivity in liver tissue (1.58 +/- 0.40% ID per g, 1 h p.i.) is indicative of rapid renal-urinary excretion and suggests very high in vivo kinetic stability of [(64)Cu-NOTA-8-Aoc-BBN(7-14)NH(2)] with little or no in vivo dissociation of (64)Cu(2+) from the NOTA chelator. Kidney accumulation at 1 h p.i. was 3.79 +/- 1.09% ID per g. Molecular imaging studies in GRPr-expressing tumor models produced high-contrast, high-quality micro-positron-emission tomography images.

Sleep Deprivation Increases A1Adenosine Receptor Binding in the Human Brain: A Positron Emission Tomography Study

It is currently hypothesized that adenosine is involved in the induction of sleep after prolonged wakefulness. This effect is partially reversed by the application of caffeine, which is a nonselective blocker of adenosine receptors. Here, we report that the most abundant and highly concentrated A1 subtype of cerebral adenosine receptors is upregulated after 24 h of sleep deprivation. We used the highly selective A1 adenosine receptor (A1AR) radioligand [18F]CPFPX ([18F]8-cyclopentyl-3-(3-fluoropropyl)-1-propylxanthine) and quantitative positron emission tomography to assess cerebral A1ARs before and after sleep deprivation in 12 healthy volunteers and a control group (n = 10) with regular sleep. In sleep deprived subjects, we found an increase of the apparent equilibrium total distribution volume in a region-specific pattern in all examined brain regions with a maximum increase in the orbitofrontal cortex (15.3%; p = 0.014). There were no changes in the control group with regular sleep. This is the first molecular imaging study that provides in vivo evidence for an A1AR upregulation in cortical and subcortical brain regions after prolonged wakefulness, indicating that A1AR expression is contributing to the homeostatic sleep regulation.