μPET Imaging Research Articles

Quantitative μPET Imaging of Cerebral Glucose Metabolism and Amyloidosis in the TASTPM Double Transgenic Mouse Model of Alzheimer's Disease.

Positron emission tomography studies of cerebral glucose utilization and amyloid-β deposition with fluoro-deoxy-D-glucose ([(18)F]-FDG) and amyloid tracers have shown characteristic pathological changes in Alzheimer's Disease that can be used for disease diagnosis and monitoring. Application of this technology to preclinical research with transgenic animal models would greatly facilitate drug discovery and further understanding of disease processes. The results from preclinical studies with these imaging biomarkers have however been highly inconsistent, causing doubts over whether animal models can truly replicate an AD-like phenotype. In this study we performed in vivo imaging with [(18)F]-FDG and [(18)F]-AV45 in double transgenic TASTPM mice, a transgenic model that been previously demonstrated high levels of fibrillar amyloid-β and decreases in cerebral glucose utilization with ex vivo techniques. Our results show widespread and significant retention of [(18)F]-AV45 (p < 0.0001) in aged TASTPM mice in addition to significant regional decreases in [(18)F]-FDG uptake (p < 0.05). In vivo quantification of amyloid-β showed a strong (Pearson's r = 0.7078), but not significant (p = 0.1156), positive correlation with ex vivo measures suggesting some limitations on tracer sensitivity. In the case of [(18)F]-FDG, voxelwise analysis greatly enhanced detection of hypometabolic regions. We further evidenced modest neuronal loss (thalamus p = 0.0318) that could underlie the observed hypometabolism. This research was performed in conjunction with the European Community's Seventh Framework Program (FP7/2007-2013) for the Innovative Medicine Initiative under the PharmaCog Grant Agreement no.115009.

Sequential [(18)F]FDG µPET whole-brain imaging of central vestibular compensation: a model of deafferentation-induced brain plasticity.

Unilateral inner ear damage is followed by a rapid behavioural recovery due to central vestibular compensation. In this study, we utilized serial [(18)F]Fluoro-deoxyglucose ([(18)F]FDG)-µPET imaging in the rat to visualize changes in brain glucose metabolism during behavioural recovery after surgical and chemical unilateral labyrinthectomy, to determine the extent and time-course of the involvement of different brain regions in vestibular compensation and test previously described hypotheses of underlying mechanisms. Systematic patterns of relative changes of glucose metabolism (rCGM) were observed during vestibular compensation. A significant asymmetry of rCGM appeared in the vestibular nuclei, vestibulocerebellum, thalamus, multisensory vestibular cortex, hippocampus and amygdala in the acute phase of vestibular imbalance (4h). This was followed by early vestibular compensation over 1-2days where rCGM re-balanced between the vestibular nuclei, thalami and temporoparietal cortices and bilateral rCGM increase appeared in the hippocampus and amygdala. Subsequently over 2-7days, rCGM increased in the ipsilesional spinal trigeminal nucleus and later (7-9days) rCGM increased in the vestibulocerebellum bilaterally and the hypothalamus and persisted in the hippocampus. These systematic dynamic rCGM patterns during vestibular compensation, were confirmed in a second rat model of chemical unilateral labyrinthectomy by serial [(18)F]FDG-µPET. These findings show that deafferentation-induced plasticity after unilateral labyrinthectomy involves early mechanisms of re-balancing predominantly in the brainstem vestibular nuclei but also in thalamo-cortical and limbic areas, and indicate the contribution of spinocerebellar sensory inputs and vestibulocerebellar adaptation at the later stages of behavioural recovery.

Small-animal repetitive transcranial magnetic stimulation combined with [18F]-FDG microPET to quantify the neuromodulation effect in the rat brain

Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive neurostimulation technique for the treatment of various neurological and psychiatric disorders. To investigate the working mechanism of this treatment approach, we designed a small-animal coil for dedicated use in rats and we combined this neurostimulation method with small-animal positron emission tomography (microPET or μPET) to quantify regional 2-deoxy-2-(18F)fluoro-d-glucose ([18F]-FDG) uptake in the rat brain, elicited by a low- (1Hz) and a high- (50Hz) frequency paradigm. Rats (n=6) were injected with 1mCi of [18F]-FDG 10min after the start of 30min of stimulation (1Hz, 50Hz or sham), followed by a 20-min μPET image acquisition. Voxel-based statistical parametric mapping (SPM) image analysis of 1-Hz and 50-Hz versus sham stimulation was performed. For both the 1-Hz and 50-Hz paradigms we found a large [18F]-FDG hypermetabolic cluster (2.208mm3 and 2.616mm3, resp.) (analysis of variance (ANOVA), p<0.05) located in the dentate gyrus complemented with an additional [18F]-FDG hypermetabolic cluster (ANOVA, p<0.05) located in the entorhinal cortex (2.216mm3) for the 50-Hz stimulation. The effect on [18F]-FDG metabolism was 2.9±0.8% at 1Hz and 2.5±0.8% at 50Hz for the dentate gyrus clusters and 3.3±0.5% for the additional cluster in the entorhinal cortex at 50Hz. The maximal (4.19 vs. 2.58) and averaged (2.87 vs. 2.21) T-values are higher for 50Hz versus 1Hz.This experimental study demonstrates the feasibility to combine μPET imaging in rats stimulated with rTMS using a custom-made small-animal magnetic stimulation setup to quantify changes in the cerebral [18F]-FDG uptake as a measure for neuronal activity.

PET Imaging with [&lt;sup&gt;68&lt;/sup&gt;Ga]NOTA-RGD for Prostate Cancer: A Comparative Study with [&lt;sup&gt;18&lt;/sup&gt;F]Fluorodeoxyglucose and [&lt;sup&gt;18&lt;/sup&gt;F]Fluoroethylcholine

The α(v)β₃ integrin is highly expressed in prostate cancer (PCa), in which it is a key player in tumour invasion, angiogenesis and metastasis formation. Therefore, α(v)β₃ integrin is considered a very promising target for molecular imaging of PCa. This study tested the potential of the novel α(v)β₃ integrin affine agent [⁶⁸Ga]NOTA-RGD in comparison with the established [¹⁸F]fluoroethylcholine (FEC) and [¹⁸F]fluorodeoxyglucose (FDG) for assessing PCa using positron emission tomography (PET). [⁶⁸Ga]NOTA-RGD showed a lower uptake in PC-3 and DU-145 cells compared with FEC and FDG. µPET imaging studies showed a good delineation of the PCa xenografts in mice. The means tumor-to-muscle and tumor-to-bone-ratio amounted 5.1 ± 1.4 and 5.2 ± 1.2 for [⁶⁸Ga]NOTA-RGD compared with 2.6 ± 0.9 and 2.9 ± 1.6 for FDG, and 2.4 ± 0.7 and 0.8 ± 0.2 for FEC, respectively. The uptake of [⁶⁸Ga]NOTA-RGD into tumor was fully inhibited by c(RGDfV), known to bind specifically to α(v)β₃ integrin, confirming the specificity of the tumor uptake in vivo. These results suggest that [⁶⁸Ga]NOTA-RGD is a promising candidate for PET imaging of α(v)β₃ integrin expression in PCa and warrant further in vivo validations to ascertain its potential as an imaging agent for clinical use. The simple and fast preparation of [⁶⁸Ga]NOTA-RGD may greatly facilitate its translation to a clinical setting.

In vivo evaluation of (18)F-labeled TCO for pre-targeted PET imaging in the brain.

The tetrazine-trans-cylooctene cycloaddition using radiolabeled tetrazine or radiolabeled trans-cyclooctene (TCO) has been reported to be a very fast, selective and bioorthogonal reaction that could be useful for in vivo radiolabeling of molecules. We wanted to evaluate the in vivo biodistribution profile and brain uptake of (18)F-labeled TCO ([(18)F]TCO) to assess its potential for pre-targeted imaging in the brain. We evaluated the in vivo behavior of [(18)F]TCO via an ex vivo biodistribution study complemented by in vivo μPET imaging at 5, 30, 60, 90, 120 and 240 min post tracer injection. An in vivo metabolite study was performed at 5 min, 30 min and 120 min post [(18)F]TCO injection by RP-HPLC analysis of plasma and brain extracts. Incubation with human liver microsomes was performed to further evaluate the metabolite profile of the tracer. μPET imaging and ex-vivo biodistribution revealed an high initial brain uptake of [(18)F]TCO (3.8%ID/g at 5 min pi) followed by a washout to 3.0%ID/g at 30 min pi. Subsequently the brain uptake increased again to 3.7%ID/g at 120 min pi followed by a slow washout until 240 min pi (2.9%ID/g). Autoradiography confirmed homogenous brain uptake. On the μPET images bone uptake became gradually visible after 120 min pi and was clearly visible at 240 min pi. The metabolite study revealed a fast metabolization of [(18)F]TCO in plasma and brain into three main polar radiometabolites. Although [(18)F]TCO has previously been described to be a useful tracer for radiolabeling of tetrazine modified targeting molecules, our study indicates that its utility for in vivo chemistry and pre-targeted imaging will be limited. Although [(18)F]TCO clearly enters the brain, it is quickly metabolized with a non-specific accumulation of radioactivity in the brain and bone.

HPMA-LMA Copolymer Drug Carriers in Oncology: An in Vivo PET Study to Assess the Tumor Line-Specific Polymer Uptake and Body Distribution

Polymeric drug carriers aim to selectively target tumors in combination with protecting normal tissue. In this regard polymer structure and molecular weight are key factors considering organ distribution and tumor accumulation of the polymeric drug delivery system. Four different HPMA based copolymer structures (random as well as block copolymers with lauryl methacrylate as hydrophobic block) varying in molecular weight, size and resulting architecture were analyzed in two different tumor models (AT1 prostate carcinoma and Walker-256 mammary carcinoma) in vivo. Polymers were labeled with (18)F and organ/tumor uptake was followed by μPET imaging and ex vivo biodistribution. Vascular permeability was measured by dextran extravasation and vascular density by immunohistochemistry. Cellular polymer uptake was determined in vitro using fluorescence-labeled polymers. Most strikingly, the high molecular weight HPMA-LMA random copolymer demonstrated highest tumor uptake and blood pool concentration. The molecular structure (e.g., amphiphilicity) is holding a higher impact on desired in vivo properties than polymer size. The results also revealed pronounced differences between the tumor models although vascular permeability was almost comparable. Accumulation in Walker-256 carcinomas was much higher, presumably due to a better cellular uptake in this cell line and a denser vascular network in the tumors. These investigations clearly indicate that the properties of the individual tumor determine the suitability of polymeric drug carriers. The findings also illustrate the general necessity of a preclinical screening to analyze polymer uptake for each individual patient (e.g., by noninvasive PET imaging) in order to individualize polymer-based chemotherapy.

Detection of glioblastoma response to temozolomide combined with bevacizumab based on µMRI and µPET imaging reveals [18F]-fluoro-l-thymidine as an early and robust predictive marker for treatment efficacy

The individualized care of glioma patients ought to benefit from imaging biomarkers as precocious predictors of therapeutic efficacy. Contrast enhanced MRI and [(18)F]-fluorodeoxyglucose (FDG)-PET are routinely used in clinical settings; their ability to forecast the therapeutic response is controversial. The objectives of our preclinical study were to analyze sensitive µMRI and/or µPET imaging biomarkers to predict the efficacy of anti-angiogenic and/or chemotherapeutic regimens. Human U87 and U251 orthotopic glioma models were implanted in nude rats. Temozolomide and/or bevacizumab were administered. µMRI (anatomical, diffusion, and microrheological parameters) and µPET ([(18)F]-FDG and [(18)F]-fluoro-l-thymidine [FLT]-PET) studies were undertaken soon (t(1)) after treatment initiation compared with late anatomical µMRI evaluation of tumor volume (t(2)) and overall survival. In both models, FDG and FLT uptakes were attenuated at t(1) in response to temozolomide alone or with bevacizumab. The distribution of FLT, reflecting intratumoral heterogeneity, was also modified. FDG was less predictive for treatment efficacy than was FLT (also highly correlated with outcome, P < .001 for both models). Cerebral blood volume was significantly decreased by temozolomide + bevacizumab and was correlated with survival for rats with U87 implants. While FLT was highly predictive of treatment efficacy, a combination of imaging biomarkers was superior to any one alone (P < .0001 in both tumors with outcome). Our results indicate that FLT is a sensitive predictor of treatment efficacy and that predictability is enhanced by a combination of imaging biomarkers. These findings may translate clinically in that individualized glioma treatments could be decided in given patients after PET/MRI examinations.

Lapatinib and 17AAG Reduce 89Zr-Trastuzumab-F(ab′)2 Uptake in SKBR3 Tumor Xenografts

Human epidermal growth factor receptor-2 (HER2) directed therapy potentially can be improved by insight in drug effects on HER2 expression. This study evaluates the effects of the EGFR/HER2 tyrosine kinase inhibitor lapatinib, the heat shock protein-90 inhibitor 17AAG, and their combination, on HER2 expression with in vivo HER2-PET imaging. Lapatinib and 17AAG effects on EGFR and HER2 membrane expression were determined in vitro using flow cytometry of human SKBR3 tumor cells. Effect of lapatinib on HER2 internalization was studied in vitro by (89)Zr-trastuzumab-F(ab')(2) internalization. For in vivo evaluation, (89)Zr-trastuzumab-F(ab')(2) μPET imaging was performed two times with a 7 day interval. Lapatinib was administered for 6 days, starting 1 day after the baseline scan. 17AAG was given 1 day before the second (89)Zr-trastuzumab-F(ab')(2) injection. Imaging data were compared with ex vivo biodistribution analysis and HER2 immunohistochemical staining. 17AAG treatment lowered EGFR expression by 41% (P = 0.016) and HER2 by 76% (P = 0.022). EGFR/HER2 downregulation by 17AAG was inhibited by lapatinib pretreatment. Lapatinib reduced internalization of (89)Zr-trastuzumab-F(ab')(2) with 25% (P = 0.0022). (89)Zr-trastuzumab-F(ab')(2) tumor to blood ratio was lowered 32% by lapatinib (P = 0.00004), 34% by 17AAG (P = 0.0022) and even 53% by the combination (P = 0.011). Lapatinib inhibits HER2 internalization and 17AAG lowers HER2 membrane expression. Both drugs reduce (89)Zr-trastuzumab-F(ab')(2) tumor uptake. Based on our findings, supported by previous preclinical data indicating the antitumor potency of lapatinib in combination with HSP90 inhibition, combination of these drugs deserves further investigation.

Imaging of Protein Synthesis: In Vitro and In Vivo Evaluation of 44Sc-DOTA-Puromycin

The purpose of this study was to investigate whether (44)Sc-labeled puromycin can be utilized for imaging of protein synthesis in vivo. For micro-positron emission tomographic (μPET) studies, 20-25MBq of [(44)Sc]-DOTA-puromycin was administered to tumor-bearing rats, and animals were scanned for 1h dynamically. Results were further validated by dissecting organs and tissues of the animals after the measurement and in vitro blocking experiments using puromycin or cycloheximide to block protein synthesis. μPET images of tumor-bearing rats showed significant tumor uptake of [(44)Sc]-DOTA-puromycin and a clear-cut tumor visualization. In both blocking experiments, cellular uptake of [(44)Sc]-DOTA-puromycin ([(44)Sc]-DOTA-Pur) could be suppressed by blocking protein synthesis. We report for the first time successful μPET imaging with (44)Sc obtained from a (44)Ti/(44)Sc generator, as well as noninvasive μPET imaging of ribosomal activity, respectively protein synthesis, with a puromycin-based radiopharmaceutical and the direct correlation between cellular uptake of [(44)Sc]-DOTA-Pur and protein synthesis.

Preclinical evaluation of two 68Ga-siderophores as potential radiopharmaceuticals for Aspergillus fumigatus infection imaging

PurposeInvasive pulmonary aspergillosis is mainly caused by Aspergillus fumigatus, and is one of the major causes of morbidity and mortality in immunocompromised patients. The mortality associated with invasive pulmonary aspergillosis remains high, mainly due to the difficulties and limitations in diagnosis. We have shown that siderophores can be labelled with 68Ga and can be used for PET imaging of A. fumigatus infection in rats. Here we report on the further evaluation of the most promising 68Ga-siderophore candidates, triacetylfusarinine (TAFC) and ferrioxamine E (FOXE).MethodsSiderophores were labelled with 68Ga using acetate buffer. Log P, protein binding and stability values were determined. Uptake by A. fumigatus was studied in vitro in cultures with high and low iron loads. In vivo biodistribution was determined in normal mice and an infection model was established using neutropenic rats inoculated with A. fumigatus. Static and dynamic μPET imaging was performed and correlated with CT images, and lung infection was evaluated ex vivo.Results 68Ga-siderophores were labelled with high radiochemical purity and specific activity. 68Ga-TAFC and 68Ga-FOXE showed high uptake by A. fumigatus in iron-deficient cultures. In normal mice, 68Ga-TAFC and 68Ga-FOXE showed rapid renal excretion with high metabolic stability. In the rat infection model focal lung uptake was detected by μPET with both compounds and increased with severity of the infection, correlating with abnormal CT images.Conclusion 68Ga-TAFC and 68Ga-FOXE displayed excellent in vitro stability and high uptake by A. fumigatus. Both compounds showed excellent pharmacokinetics, highly selective accumulation in infected lung tissue and good correlation with severity of disease in a rat infection model, which makes them promising agents for A. fumigatus infection imaging.Electronic supplementary materialThe online version of this article (doi:10.1007/s00259-012-2110-3) contains supplementary material, which is available to authorized users.

Conflict Processing in the Rat Brain: Behavioral Analysis and Functional μPET Imaging Using [18F]Fluorodeoxyglucose

Conflicts in spatial stimulus–response tasks occur when the task-relevant feature of a stimulus implies a response toward a certain location which does not match the location of stimulus presentation. This conflict leads to increased error rates and longer reaction times, which has been termed Simon effect. A model of dual route processing (automatic and intentional) of stimulus features has been proposed, predicting response conflicts if the two routes are incongruent. Although there is evidence that the prefrontal cortex, notably the anterior cingulate cortex (ACC), plays a crucial role in conflict processing, the neuronal basis of dual route architecture is still unknown. In this study, we pursue a novel approach using positron emission tomography (PET) to identify relevant brain areas in a rat model of an auditory Simon task, a neuropsychological interference task, which is commonly used to study conflict processing in humans. For combination with PET we used the metabolic tracer [18F]fluorodeoxyglucose, which accumulates in metabolically active brain cells during the behavioral task. Brain areas involved in conflict processing are supposed to be activated when automatic and intentional route processing lead to different responses (dual route model). Analysis of PET data revealed specific activation patterns for different task settings applicable to the dual route model as established for response conflict processing. The rat motor cortex (M1) may be part of the automatic route or involved in its facilitation, while premotor (M2), prelimbic, and ACC seemed to be essential for inhibiting the incorrect, automatic response, indicating conflict monitoring functions. Our findings and the remarkable similarities to the pattern of activated regions reported during conflict processing in humans demonstrate that our rodent model opens novel opportunities to investigate the anatomical basis of conflict processing and dual route architecture.

Synthesis and Cardiac Imaging of (18)F-Ligands Selective for β1-Adrenoreceptors.

A series of potent and selective β1-adrenoreceptor ligands were identified (IC50 range, 0.04-0.25 nM; β1/β2 selectivity range, 65-450-fold), labeled with the PET radioisotope fluorine-18 and evaluated in normal Sprague-Dawley rats. Tissue distribution studies demonstrated uptake of each radiotracers from the blood pool into the myocardium (0.48-0.62% ID/g), lung (0.63-0.97% ID/g), and liver (1.03-1.14% ID/g). Dynamic μPET imaging confirmed the in vivo dissection studies.

Modifying the Body Distribution of HPMA-Based Copolymers by Molecular Weight and Aggregate Formation

There is a recognized need to create well-defined polymer probes for in vivo and clinical positron emission tomography (PET) imaging to guide the development of new generation polymer therapeutics. Using the RAFT polymerization technique in combination with the reactive ester approach, here we have synthesized well-defined and narrowly distributed N-(2-hydroxypropyl)methacrylamide homopolymers (pHPMA) (P1* and P2*) and random HPMA copolymers consisting of hydrophilic HPMA and hydrophobic lauryl methacrylate comonomers (P3* and P4*). The polymers had molecular weights below (P1* and P3*) and above the renal threshold (P2* and P4*). Whereas the homopolymers dissolve in isotonic solution as individual coils, the random copolymers form larger aggregates above their critical micelle concentration (∼ 40 nm), as determined by fluorescence correlation spectroscopy. Structure-property relationships of the pharmacokinetics and biodistribution of the different polymer architectures were monitored in the living organism following radiolabeling with the positron emitter (18)F via fluoroethylation within a few hours. Ex vivo organ biodistribution and in vivo μPET imaging studies in male Copenhagen rats revealed that both size and the nature of the aggregate formation (hydrophobically modified copolymers) played a major role in blood clearance and biodistribution, especially concerning liver and kidney accumulation. The high-molecular-weight random copolymer P4* (hydrophobically modified), in particular, combines low liver uptake with enhanced blood circulation properties, showing the potential of hydrophobic interactions, as seen for the represented model system, that are valuable for future drug carrier design.

Effects of burn injury, cold stress and cutaneous wound injury on the morphology and energy metabolism of murine brown adipose tissue (BAT) in vivo

AimsCold stress has been shown to produce dramatic increases in 2-fluoro-2-deoxy-D-Glucose (18FDG) accumulation by brown adipose tissue (BAT) in rodents. However, neither the effects of other types of stress on 18FDG accumulation nor the effects of stressors on the accumulation of tracers of other aspects of energy metabolism have been evaluated. In this report we studied the effects of cold stress, burn injury and cutaneous wounds on murine BAT at the macroscopic, microscopic and metabolic level. Main methodsGlucose metabolism was studied with 18FDG, fatty acid accumulation was evaluated with trans-9(RS)-18F-fluoro-3,4(RS,RS)-methyleneheptadecanoic acid (FCPHA) and tricarboxcylic acid cycle (TCA) activity was evaluated with 3H acetate. Key findingsAll three stressors produced dramatic changes in BAT at the macroscopic and microscopic level. Macroscopically, BAT from the stressed animals appeared to be a much darker brown in color. Microscopically BAT of stressed animals demonstrated significantly fewer lipid droplets and an overall decrease in lipid content. Accumulation of 18FDG by BAT was significantly (p<0.01) increased by all 3 treatments (Cold: ~16 fold, burn ~7 Fold and cutaneous wound ~14 fold) whereas uptake of FDG by white fat was unchanged. This effect was also demonstrated non invasively by μPET imaging. Although less prominent than with 18FDG, BAT uptake of FCPHA and acetate were also significantly increased by all three treatments. These findings suggest that in addition to cold stress, burn injury and cutaneous wounds produce BAT activation in mice. SignificanceThis study demonstrates brown fat activated by several stressors leads to increased uptake of various substrates.

Abstract 5303: Serial HER2-PET imaging with 89Zr-trastuzumab-F(ab’)2 of lapatinib and 17AAG treated mice bearing SKBR3 xenografts

Abstract Background: Understanding molecular responses involved in human epidermal growth factor receptor-2 (HER2) targeted drugs may improve treatment of HER2 positive breast cancer. In vivo assessment of effects on HER2 expression is of value in this setting. The EGFR/HER2 tyrosine kinase inhibitor lapatinib inhibits HER2 signaling and stabilizes HER2 at the cell membrane, while the heat shock protein-90 (HSP90) inhibitor 17AAG degrades HER2/EGFR. We therefore evaluated the effect on HER2 dynamics in vivo with 89Zr-trastuzumab-F(ab’)2 HER2-PET imaging in human tumor bearing mice treated with lapatinib and 17AAG. Materials and methods: Effects of lapatinib and 17AAG on EGFR and HER2 membrane expression were evaluated in vitro in the human breast cancer cell line SKBR3 using flow cytometry. In vivo effects on HER2 expression were evaluated with 89Zr-trastuzumab-F(ab’)2 μPET imaging in SKBR3 xenograft bearing mice. 89Zr-trastuzumab-F(ab’)2 (5 MBq; 20 μg) was injected two times with a 7 day interval and μPET imaging was performed 24 hours after tracer injection. Lapatinib was dosed 100 mg/kg/day orally for 6 days, starting 1 day after the first μPET scan. 17AAG was dosed 3×50 mg intraperitoneal in the 24 hours prior to the second tracer injection. A non-treated group of mice served as control and for validation of 89Zr-trastuzumab-F(ab’)2 μPET imaging. Imaging data were compared with ex vivo biodistribution analysis, immunohistochemistry, and with an in vitro HER2 internalization experiment. Results: On flow cytometry, lapatinib induced upregulation of EGFR (+70%; P = 0.0011), but not HER2 (+19%; P = 0.1275). 17AAG treatment lowered both EGFR (−41%; P = 0.016) and HER2 (−76%; P = 0.022) expression. This EGFR/HER2 reduction by 17AAG was inhibited by lapatinib. In vivo, 89Zr-trastuzumab-F(ab’)2 tumor uptake on the second μPET scan was lowered by lapatinib (−32%; P = 0.00004), 17AAG (−34%; P = 0.0022) and the lapatinib plus 17AAG combination (−53%; P = 0.011). 89Zr-trastuzumab-F(ab’)2 tumor uptake in mice treated with lapatinib plus 17AAG was lower than with either lapatinib or 17AAG alone (P = 0.0043 and P = 0.0022, respectively). In vitro, 89Zr-trastuzumab-F(ab’)2 internalization was reduced by lapatinib (−25%; P = 0.0022), explaining the lower 89Zr-trastuzumab-F(ab’)2 tumor uptake after lapatinib. Conclusion: 89Zr-trastuzumab-F(ab’)2 μPET visualized treatment induced impact on HER2 expression and -dynamics. Lapatinib inhibited HER2 internalization, and thereby decreased 89Zr-trastuzumab-F(ab’)2 tumor uptake. HSP90 inhibition lowered HER2 membrane expression and thereby 89Zr-trastuzumab-F(ab’)2 tumor uptake. This knowledge on HER2 dynamics ameliorates understanding of efficacy of several combinations of HER2 targeted agents. Supported by grant 2007-3739 of the Dutch Cancer Society. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5303. doi:10.1158/1538-7445.AM2011-5303

Site-specific 68Ga-labeled Annexin A5 as a PET imaging agent for apoptosis

Two variants of Annexin A5 (Cys2-AnxA5 and Cys165-AnxA5) were labelled with Gallium-68 in order to evaluate their biological properties. Biodistribution and pharmacokinetics of the radiotracers were studied with μPET in healthy mice and in a mouse model of hepatic apoptosis. μPET imaging after IV injection of the tracers in combination with μMRI was performed in Daudi tumor bearing mice before and after treatment with a combination of chemotherapy and radiotherapy. The biodistribution data indicated a fast urinary clearance with only minor hepatobilliary clearance, although a high retention in the kidneys was observed. Animals treated with anti-Fas showed a 3 to 8 times higher liver uptake as compared to healthy animals. Tumor uptake of (68)Ga-Cys2-AnxA5 and (68)Ga-Cys165-AnxA5 was low but significantly increased after therapy. Both (68)Ga-Cys2-AnxA5 and (68)Ga-Cys165-AnxA5 show a clear binding to apoptotic cells and are promising tracers for rapid evaluation of cancer therapy.

The DAT Ligand [18F]PR17.MZ Mirrors the in vivo Pharmacokinetic Profile of [11C]Cocaine with Significantly Improved Monoamine Transporter Selectivity

Better than cocaine for your PET? The radiotracer [18F]PR17.MZ shows high in vitro and in vivo selectivity to the dopamine transporter. Its extraordinarily rapid pharmacokinetic profile is demonstrated in a μPET imaging study. The relatively long half-life of the fluorine-18 label is an added advantage over short-lived (−)-N-[11C]cocaine PET ligands. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Food restriction markedly increases dopamine D2 receptor (D2R) in a rat model of obesity as assessed with in‐vivo μPET imaging ([11C] raclopride) and in‐vitro ([3H] spiperone) autoradiography

Dopamine (DA) regulates food intake by modulating food reward and motivation but its involvement in obesity is much less understood. Recent evidence points to the involvement of leptin in the DA-related modulation of food intake. Here we assess DA D2 receptors (D2R) in a genetic rodent obesity model characterized by leptin-receptor deficiency and assess the influence of food restriction on these receptors. We compared D2R levels between Zucker Obese (fa/fa) and Lean (Fa/Fa) rats at 1 and 4 months of age and in two different feeding conditions (restricted and unrestricted food access) using in-vivo muPET imaging ([11C] raclopride, which is a method sensitive to competition with endogenous DA) and in-vitro ([3H] spiperone washed to ensure no competition with endogenous DA) autoradiography (ARG). Both ARG and muPET showed that D2R were higher at 1 month than at 4 months of age and that food restricted animals had higher D2R than unrestricted animals. However there were significant differences in the results obtained at 4 months between ARG and muPET. ARG showed that at 1 month and at 4 months unrestricted lean rats (Le U) had significantly higher D2R binding than obese unrestricted rats (Ob U) but showed no differences between restricted obese (Ob R) and restricted lean rats (Le R). It also showed that D2R decline between 1 and 4 months of age was significantly attenuated in food restricted rats [both obese and lean]. In contrast, muPET showed that at 4 months of age, Ob U showed greater D2R availability than Le U rats but like ARG showed no differences between Ob R and Le R rats. The lower D2R binding in Ob U than Le U rats observed with ARG most likely reflects decreases in striatal D2 receptors levels whereas the increased availability observed with muPET is likely to reflect reduced DA release (resulting in decreased competition with endogenous DA). Lack of a significant difference between Ob R and Le R suggests that the differences in dopamine activity and D2R levels between Ob and Le Zucker rats are modulated by access to food. The ARG finding of an attenuation of the age-related loss of D2R binding corroborates previous studies of the salutary effects of food restriction in the aging process. Because [11C] raclopride is sensitive to competition with endogenous DA, the higher D2R binding in obese rats with raclopride despite the lower D2R levels shown with spiperone could reflect lower extracellular DA in the Ob rats and merits further investigation.

New trends in γ-ray imaging with CdZnTe/CdTe at CEA-Leti

Increasing interest in CdTe/CZT for γ-ray imaging has marked the last 10 years with progress in crystal growth, device technology, integrated electronics and signal processing. The purpose of this paper is to present recent advances in these four fields at CEA-LETI. A new method to grow very large dimension CZT up to 300 mm in diameter is presented. MS-contact process control allows design of very small electrodes (100 μm pitch) and results on long-term stability are presented. The development of low-noise front-end integrated electronics and new interconnects technologies have made “pixel detectors” feasible. Significant effort has been focused on reaching high-energy resolution as well as high detection efficiency. The combination of signal processing such as bi-parametric (BP) approaches and electrode design presents an interest in charge loss compensation for a large range of μτ products, tailing reduction due to geometric effect and depth of interaction information. New digital approaches may give drastic advantages to push the limit of spectrometric performance. In the field of γ-ray application, single-channel device for per-operative probes and small 2-D imager for molecular imaging are the most promising ones. By using a tailored “mixed” electrode (small anode and capacitive grid Frich effect) and a BP correction, an energy resolution of 1% at 662 keV has been demonstrated with CZT based 8×8×15 mm 3 detector. New results of 3-D CZT detectors for μPET imaging are presented with a measured coincidence time of 2.6 ns FWHM and an expected spatial resolution of 1 mm FWHM.

A syndrome produced by diverse nocuous agents. 1936.

A syndrome produced by diverse nocuous agents. 1936.