Analysis of cerebral glucose metabolism following experimental subarachnoid hemorrhage over 7 days.

Little is known about changes in brain metabolism following SAH, possibly leading towards secondary brain damage. Despite sustained progress in the last decade, analysis of in vivo acquired data still remains challenging. The present interdisciplinary study uses a semi-automated data analysis tool analyzing imaging data independently from the administrated radiotracer. The uptake of 2-[18F]Fluoro-2-deoxy-glucose ([18F]FDG) was evaluated in different brain regions in 14 male Sprague-Dawley rats, randomized into two groups: (1) SAH induced by the endovascular filament model and (2) sham operated controls. Serial [18F]FDG-PET measurements were carried out. Quantitative image analysis was performed by uptake ratio using a self-developed MRI-template based data analysis tool. SAH animals showed significantly higher [18F]FDG accumulation in gray matter, neocortex and olfactory system as compared to animals of the sham group, while white matter and basal forebrain region showed significant reduced tracer accumulation in SAH animals. All significant metabolic changes were visualized from 3 h, over 24 h (day 1), day 4 and day 7 following SAH/sham operation. This [18F]FDG-PET study provides important insights into glucose metabolism alterations following SAH-for the first time in different brain regions and up to day 7 during course of disease.

Synthesis and Preliminary Evaluations of [18F]fluorinated Pyridine-2- carboxamide Derivatives for Targeting PD-L1 in Cancer.

BACKGROUND: Treatment with immune checkpoint inhibitors has improved both progressionfree survival and overall survival in a subset of patients with tumors. However, the selection of patients who benefit from immune checkpoint inhibitor treatment remains challenging. Positron Emission Tomography (PET) is a non-invasive molecular imaging tool that offers a promising alternative to the current IHC for detecting the PD-L1 expression in malignant cells in vivo, enabling patient selection and predicting the response to individual patient immunotherapy treatment. OBJECTIVES: Herein, we report the development of novel [18F]labeled pyridine-2-carboxamide derivatives [18F]2 and [18F]3 as small-molecule probes for imaging immune checkpoint (PD-1/PD-L1) in cancer using PET. METHODS AND RESULTS: [18F]2 and [18F]3 were prepared by a one-step radiofluorination in 44 ± 5% and 30 ± 4% radiochemical yield and > 98% radiochemical purity for a potential clinical translation. The total synthesis time, including HPLC purification, was less than 45 min. [18F]2 and [18F]3 showed excellent stability in injection solution and a significant accumulation and retention in PD-1/PD-L1 expressing MDA-MB-231 breast cancer and in HeLa cervix carcinoma cells (2- 5 cpm/1000 cells). In addition, autoradiographic analysis and inhibition experiments on tumor slices confirm the potential of both compounds as specific imaging probes for the PD-1/PD-L1 axis in tumors. CONCLUSION: The in vitro evaluation in PD-L1 expressing cells together with results from autoradiographic analysis in PD-L1 positive tumor sections, suggest that [18F]2 and [18F]3 could be potential imaging probes for assessing PD-L1 expression in tumors and warrant further biological evaluations in vivo.

Gallium-68-Labeled KISS1-54 Peptide for Mapping KISS1 Receptor via PET: Initial Evaluation in Human Tumor Cell Lines and in Tumor-Bearing Mice.

Kisspeptins (KPs, KISS1) and their receptor (KISS1R) play a pivotal role as metastasis suppressor for many cancers. Low or lost KP expression is associated with higher tumor grade, increased metastatic potential, and poor prognosis. Therefore, KP expression has prognostic relevance and correlates with invasiveness in cancers. Furthermore, KISS1R represents a very promising target for molecular imaging and therapy for KISS1R-expressing tumors. The goal of this study was to evaluate the developed KISS1-54 derivative, [68Ga]KISS1-54, as a PET-imaging probe for KISS1R-expressing tumors. The NODAGA-KISS1-54 peptide was labeled by Gallium-68, and the stability of the resulting [68Ga]KISS1-54 evaluated in injection solution and human serum, followed by an examination in different KISS1R-expressing tumor cell lines, including HepG2, HeLa, MDA-MB-231, MCF7, LNCap, SK-BR-3, and HCT116. Finally, [68Ga]KISS1-54 was tested in LNCap- and MDA-MB-231-bearing mice, using µ-PET, assessing its potential as an imaging probe for PET. [68Ga]KISS1-54 was obtained in a 77 ± 7% radiochemical yield and at a >99% purity. The [68Ga]KISS1-54 cell uptake amounted to 0.6-4.4% per 100,000 cells. Moreover, the accumulation of [68Ga]KISS1-54 was effectively inhibited by nonradioactive KISS1-54. In [68Ga]KISS1-54-PET, KISS1R-positive LNCap-tumors were clearly visualized as compared to MDA-MB-231-tumor implant with predominantly intracellular KISS1R expression. Our first results suggest that [68Ga]KISS1-54 is a promising candidate for a radiotracer for targeting KISS1R-expressing tumors via PET.

Changes of cerebral network activity after invasive stimulation of the mesencephalic locomotor region in a rat stroke model.

Motor deficits after stroke reflect both, focal lesion and network alterations in brain regions distant from infarction. This remote network dysfunction may be caused by aberrant signals from cortical motor regions travelling via mesencephalic locomotor region (MLR) to other locomotor circuits. A method for modulating disturbed network activity is deep brain stimulation. Recently, we have shown that high frequency stimulation (HFS) of the MLR in rats has restored gait impairment after photothrombotic stroke (PTS). However, it remains elusive which cerebral regions are involved by MLR-stimulation and contribute to the improvement of locomotion. Seventeen male Wistar rats underwent photothrombotic stroke of the right sensorimotor cortex and implantation of a microelectrode into the right MLR. 2-[18F]Fluoro-2-deoxyglucose ([18F]FDG)-positron emission tomography (PET) was conducted before stroke and thereafter, on day 2 and 3 after stroke, without and with MLR-HFS, respectively. [18F]FDG-PET imaging analyses yielded a reduced glucose metabolism in the right cortico-striatal thalamic loop after PTS compared to the state before intervention. When MLR-HFS was applied after PTS, animals exhibited a significantly higher uptake of [18F]FDG in the right but not in the left cortico-striatal thalamic loop. Furthermore, MLR-HFS resulted in an elevated glucose metabolism of right-sided association cortices related to the ipsilateral sensorimotor cortex. These data support the concept of diaschisis i.e., of dysfunctional brain areas distant to a focal lesion and suggests that MLR-HFS can reverse remote network effects following PTS in rats which otherwise may result in chronic motor symptoms.

A comparison of the monomeric [68Ga]NODAGA-NGR and dimeric [68Ga]NOTA-(NGR)2 as aminopeptidase N ligand for positron emission tomography imaging in tumor-bearing mice.

The aminopeptidase N (APN/CD13) is a key protein specifically expressed on activated endothelial cells and by various tumors, representing a promising target for molecular imaging and therapy of malignant diseases. It is known that the tripeptide NGR is a specific ligand for CD13, therefore radiolabeled NGR peptides are auspicious radiotracers for non-invasive imaging of CD13-positive tumors. From previous studies, it is known that the target affinity could be improved by molecules with multiple ligand sequences. Therefore, the aim of this study was to compare two NGR radioligands [68Ga]NODAGA-NGR (NGR monomer) and [68Ga]NOTA-(NGR)2 (NGR dimer), the latter with two NGR ligand motifs, in vitro and in vivo. CD13 expression was determined by FACS in the human tumor cells A549, SKHep-1, and MDA-MB-231, followed by the investigation of the cell uptake of [68Ga]NODAGA-NGR and [68Ga]NOTA-(NGR)2. For in vivo evaluation of [68Ga]NODAGA-NGR and [68Ga]NOTA-(NGR)2, microPET and biodistribution were carried out in A549- and SKHep-1-bearing mice. After the final examination, tumors were cryo-conserved, cut, and stained against CD13 and CD31. A549 and SKHep-1 cells were identified as CD13 positive, whereas no CD13 expression was detected in MDA-MB-231 cells. The cell uptake study showed relatively low accumulation of both the NGR monomer and dimer in all tumor cell lines examined, with consistently higher cell uptake observed for the dimer than for the monomer. In vivo, [68Ga]NODAGA-NGR and [68Ga]NOTA-(NGR)2 accumulated in the tumors, with slightly higher tumor-to-muscle ratio for the NGR dimer in A549 and SKHep-1. The tumor-to-liver ratio of the NGR dimer was diminished in comparison to the NGR monomer. This finding was confirmed by biodistribution, which revealed higher accumulation in liver and spleen for the NGR dimer. Immunohistochemical staining confirmed the CD13 expression in the tumors and tumor-associated vessels. In conclusion, both the [68Ga]NODAGA-NGR and the [68Ga]NOTA-(NGR)2 were found to be suitable for PET imaging of CD13-positive tumors. Despite slight differences in tumor-to-background ratio and organ accumulation, both radiotracers can be considered comparable.

Development and Validation of a Semi-Automated, Preclinical, MRI-Template Based PET Image Data Analysis Tool for Rodents.

AIM: In PET imaging, the different types of radiotracers and accumulations, as well as the diversity of disease patterns, make the analysis of molecular imaging data acquired in vivo challenging. Here, we evaluate and validate a semi-automated MRI template-based data analysis tool that allows preclinical PET images to be aligned to a self-created PET template. Based on the user-defined volume-of-interest (VOI), image data can then be evaluated using three different semi-quantitative parameters: normalized activity, standardized uptake value, and uptake ratio. MATERIALS AND METHODS: The nuclear medicine Data Processing Analysis tool (NU_DPA) was implemented in Matlab. Testing and validation of the tool was performed using two types of radiotracers in different kinds of stroke-related brain diseases in rat models. The radiotracers used are 2-[18F]fluoro-2-deoxyglucose ([18F]FDG), a metabolic tracer with symmetrical distribution in brain, and [68Ga]Ga-Fucoidan, a target-selective radioligand specifically binding to p-selectin. After manual image import, the NU_DPA tool automatically creates an averaged PET template out of the acquired PET images, to which all PET images are then aligned onto. The added MRI template-based information, resized to the lower PET resolution, defines the VOI and also allows a precise subdivision of the VOI into individual sub-regions. The aligned PET images can then be evaluated semi-quantitatively for all regions defined in the MRI atlas. In addition, a statistical analysis and evaluation of the semi-quantitative parameters can then be performed in the NU_DPA tool. RESULTS: Using ischemic stroke data in Wistar rats as an example, the statistical analysis of the tool should be demonstrated. In this [18F]FDG-PET experiment, three different experimental states were compared: healthy control state, ischemic stroke without electrical stimulation, ischemic stroke with electrical stimulation. Thereby, statistical data evaluation using the NU_DPA tool showed that the glucose metabolism in a photothrombotic lesion can be influenced by electrical stimulation. CONCLUSION: Our NU_DPA tool allows a very flexible data evaluation of small animal PET data in vivo including statistical data evaluation. Using the radiotracers [18F]FDG and [68Ga]Ga-Fucoidan, it was shown that the semi-automatic MRI-template based data analysis of the NU_DPA tool is potentially suitable for both metabolic radiotracers as well as target-selective radiotracers.

Fluorine walk: The impact of fluorine in quinolone amides on their activity against African sleeping sickness.

Human African Trypanosomiasis, also known as African sleeping sickness, is caused by the parasitic protozoa of the genus Trypanosoma. If there is no pharmacological intervention, the parasites can cross the blood-brain barrier (BBB), inevitably leading to death of the patients. Previous investigation identified the quinolone amide GHQ168 as a promising lead compound having a nanomolar activity against T. b. brucei. Here, the role of a fluorine substitution at different positions was investigated in regard to toxicity, pharmacokinetics, and antitrypanosomal activity. This 'fluorine walk' led to new compounds with improved metabolic stability and consistent activity against T. b. brucei. The ability of the new quinolone amides to cross the BBB was confirmed using an 18F-labelled quinolone amide derivative by means of ex vivo autoradiography of a murine brain.

Positron Emission Tomography and Autoradiography Imaging of P-selectin Activation Using 68Ga-Fucoidan in Photothrombotic Stroke.

BACKGROUND: P-selectin is activated early after stroke, followed by a rapid decline. This time course can be used to generate important information on stroke onset. The latter is crucial for therapeutic decision-making of wake-up strokes (i.e. thrombolysis or not). Here, we evaluated the specific p-selectin inhibitor fucoidan labeled with gallium-68 (68Ga-Fucoidan) as an imaging biomarker for assessing p-selectin activation in acute ischemic stroke using Positron Emission Tomography (PET). METHODS: 68Ga-Fucoidan was investigated in rats brain at 2-5 h (n=16), and additionally at 24-26 h (n=9) and 48 h (n=3) after induction of photothrombic stroke or in sham-operated animals (n=6). Correlation of cerebral 68Ga-Fucoidan uptake with p-selectin expression was determined by exposing freshly cut brain cryosections to autoradiography and immunostaining using specific antibodies against p-selectin. RESULTS: PET scans showed an increased accumulation of 68Ga-Fucoidan in the histologically proven ischemic stroke, as compared to the corresponding contralateral hemisphere in all except one animal. The median ratio between the uptake in the ischemic lesion and the contralateral region was 1.95 (1.45-2.41) at 2-5 h, 1.38 (1.05-1.89) at 24-26 h, and 1.09 (0.81-1.38) at 48 h after stroke, compared to 1.22 (0.99-1.49) for sham-operated animals. In the ex vivo autoradiography, 68Ga-Fucoidan accumulation co-localized with p-selectin as assessed by immunostaining. Control animals and those scanned at 24-26 h and 48 h after stroke exhibited no elevated 68Ga-Fucoidan uptake in either hemisphere. CONCLUSION: PET imaging using 68Ga-Fucoidan represents a valuable tool for assessing p-selectin activation in vivo discriminating ischemic stroke early after stroke onset.

Validation of a [Al18F]PSMA-11 preparation for clinical applications.

Imaging prostate-specific membrane antigen (PSMA) using positron emission tomography (PET) has been presented so far as the most sensitive and specific with regard to prostate cancer detection, in particular in high-risk prostate cancer patients. Currently, it mainly features Gallium-68 (68Ga) labeled PSMA ligands, notably [68Ga]Glu-urea-Lys(Ahx)-HBED-CC ([68Ga]-PSMA-11) and [68Ga]DOTAGA-FFK (Sub-KuE termed ([68Ga]PSMA-I&T). However, 68Ga has several shortcomings as radionuclide including a short half-life and non-ideal energies. This has motivated consideration of 18F-labeled analogues for PET imaging of prostate cancer. Here, we describe a simple synthesis and validation of a fluorine-18 labeled Glu-urea-Lys(Ahx)-HBED-CC ([Al18F]PSMA-11) for nuclear medicine applications. An efficient method for preparation of [Al18F]PSMA-11 was developed and validated (according to Pharm Eur) for routinely clinical applications. [Al18F]PSMA-11 was reproducibly obtained in radiochemical yields of 84 ± 6% (n = 15) and > 98% radiochemical purity using an improved one-step radiofluorination in aqueous solution. The total (production/preparation) time, including purification, pharmacological formulation of the isolated product and the quality control of the injectable solution was less than 60min. The [Al18F]PSMA-11 was stable over 4h in 1% EtOH/saline selected as injection solution. The solution was sterile, non-pyrogenic and ready for clinical applications after sterile filtration through a 0.22µm membrane filter under sterile conditions. In addition, [Al18F]PSMA-11 exhibited higher uptake and retention in PMSA-expressing LNCap prostate cells as compared to its clinically established 68Ga-labeled analogues [68Ga]PSMA-11 and [68Ga]PSMA-I&T as well as to [68Ga]NOTA-Bn-PSMA. The simple and fast preparation of [Al18F]PSMA-11 combined with its favorable pharmacological properties warrant its translation to a clinical setting. CONCLUSION: The facile and high-yielding radiosynthesis of [Al18F]PSMA-11as well as its promising in vitro and in-vivo characteristics makes it worthy of clinical development for PET imaging of prostate cancer.

Combined [(18)F]DPA-714 micro-positron emission tomography and autoradiography imaging of microglia activation after closed head injury in mice.

BACKGROUND: Traumatic brain injury (TBI) is a major cause of death and disability. Neuroinflammation contributes to acute damage after TBI and modulates long-term evolution of degenerative and regenerative responses to injury. The aim of the present study was to evaluate the relationship of microglia activation to trauma severity, brain energy metabolism, and cellular reactions to injury in a mouse closed head injury model using combined in vivo PET imaging, ex vivo autoradiography, and immunohistochemistry. METHODS: A weight-drop closed head injury model was used to produce a mixed diffuse and focal TBI or a purely diffuse mild TBI (mTBI) in C57BL6 mice. Lesion severity was determined by evaluating histological damage and functional outcome using a standardized neuroscore (NSS), gliosis, and axonal injury by immunohistochemistry. Repeated intra-individual in vivo µPET imaging with the specific 18-kDa translocator protein (TSPO) radioligand [(18)F]DPA-714 was performed on day 1, 7, and 16 and [(18)F]FDG-µPET imaging for energy metabolism on days 2-5 after trauma using freshly synthesized radiotracers. Immediately after [(18)F]DPA-714-µPET imaging on days 7 and 16, cellular identity of the [(18)F]DPA-714 uptake was confirmed by exposing freshly cut cryosections to film autoradiography and successive immunostaining with antibodies against the microglia/macrophage marker IBA-1. RESULTS: Functional outcome correlated with focal brain lesions, gliosis, and axonal injury. [(18)F]DPA-714-µPET showed increased radiotracer uptake in focal brain lesions on days 7 and 16 after TBI and correlated with reduced cerebral [(18)F]FDG uptake on days 2-5, with functional outcome and number of IBA-1 positive cells on day 7. In autoradiography, [(18)F]DPA-714 uptake co-localized with areas of IBA1-positive staining and correlated strongly with both NSS and the number of IBA1-positive cells, gliosis, and axonal injury. After mTBI, numbers of IBA-1 positive cells with microglial morphology increased in both brain hemispheres; however, uptake of [(18)F]DPA-714 was not increased in autoradiography or in µPET imaging. CONCLUSIONS: [(18)F]DPA-714 uptake in µPET/autoradiography correlates with trauma severity, brain metabolic deficits, and microglia activation after closed head TBI.

Improved synthesis of [¹8F]FS-PTAD as a new tyrosine-specific prosthetic group for radiofluorination of biomolecules.

A novel prosthetic group, 4-(p-([(18)F]fluorosulfonyl)phenyl)-1,2,4-triazoline-3,5-dione ([(18)F]FS-PTAD) for site-specific radiofluorination of tyrosine residue in small molecules is described. Coupling of [(18)F]FS-PTAD with L-tyrosine, N-acetyl-L-tyrosine methyl amide and phenol as model compounds were achieved in buffered aqueous solution at room temperature, resulting in the corresponding fluorinated tyrosine and phenol derivatives. The total synthesis time including radiosynthesis, HPLC purification and formulation was less than 60 min (n=15) with ≥98% radio chemical purity. An initial in vitro evaluation of [(18)F]FS-PTAD-tyrosine in glioma cell lines revealed moderate uptake.

Fullerenols and glucosamine fullerenes reduce infarct volume and cerebral inflammation after ischemic stroke in normotensive and hypertensive rats.

Cerebral inflammation plays a crucial role in the pathophysiology of ischemic stroke and is involved in all stages of the ischemic cascade. Fullerene derivatives, such as fullerenol (OH-F) are radical scavengers acting as neuroprotective agents while glucosamine (GlcN) attenuates cerebral inflammation after stroke. We created novel glucosamine-fullerene conjugates (GlcN-F) to combine their protective effects and compared them to OH-F regarding stroke-induced cerebral inflammation and cellular damage. Fullerene derivatives or vehicle was administered intravenously in normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) immediately after transient middle cerebral artery occlusion (tMCAO). Infarct size was determined at day 5 and neurological outcome at days 1 and 5 after tMCAO. CD68- and NeuN-staining were performed to determine immunoreactivity and neuronal survival respectively. Cytokine and toll like receptor 4 (TLR-4) expression was assessed using quantitative real-time PCR. Magnetic resonance imaging revealed a significant reduction of infarct volume in both, WKY and SHR that were treated with fullerene derivatives. Treated rats showed an amelioration of neurological symptoms as both OH-F and GlcN-F prevented neuronal loss in the perilesional area. Cerebral immunoreactivity was reduced in treated WKY and SHR. Expression of IL-1ß and TLR-4 was attenuated in OH-F-treated WKY rats. In conclusion, OH-F and GlcN-F lead to a reduction of cellular damage and inflammation after stroke, rendering these compounds attractive therapeutics for stroke.

Targeting P-selectin by gallium-68-labeled fucoidan positron emission tomography for noninvasive characterization of vulnerable plaques: correlation with in vivo 17.6T MRI.

OBJECTIVE: Nuclear imaging of active plaques still remains challenging. Advanced atherosclerotic plaques have a strong expression of P-selectin by the endothelium overlying active atherosclerotic plaques, but not on the endothelium overlying inactive fibrous plaques. We proposed a new approach for noninvasive in vivo characterization of P-selectin on active plaques based on (68)Ga-Fucoidan, which is a polysaccharidic ligand of P-selectin with a nanomolar affinity. APPROACH AND RESULTS: (68)Ga-Fucoidan was tested for its potential to discriminate vulnerable plaques on apolipoprotein E-deficient mice receiving a high cholesterol diet by positron emission tomography and in correlation with 17.6T MRI. Furthermore, (68)Ga-Fucoidan was evaluated on endothelial cells in vitro and ex vivo on active plaques using autoradiography. The cellular uptake rate was increased ≈2-fold by lipopolysaccharide induction. Interestingly, on autoradiography, more intensive tracer accumulation at active plaques with thin fibrous caps and high-density foam cells were observed in comparison with a weaker focal uptake in inactive fibrous plaque segments (R=1.7±0.3; P<0.05) and fatty streaks (R=2.4±0.4; P<0.01). Strong uptake of radiotracer colocalized with increased P-selectin expression and high-density macrophage. Focal vascular uptake (mean of target to background ratio=5.1±0.8) of (68)Ga-Fucoidan was detected in all apolipoprotein E-deficient mice. Anatomic structures of plaque were confirmed by 17.6T MRI. The autoradiography showed a good agreement of (68)Ga-Fucoidan uptake with positron emission tomography. CONCLUSIONS: Our data suggest that (68)Ga-Fucoidan represents a versatile imaging biomarker for P-selectin with the potential to specifically detect P-selectin expression using positron emission tomography and to discriminate vulnerable plaques in vivo.

PET imaging with [68Ga]NOTA-RGD for prostate cancer: a comparative study with [¹8F]fluorodeoxyglucose and [¹8F]fluoroethylcholine.

The α(v)ß3 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)ß3 integrin is considered a very promising target for molecular imaging of PCa. This study tested the potential of the novel α(v)ß3 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)ß3 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)ß3 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.

Compressed sensing for reduction of noise and artefacts in direct PET image reconstruction.

AIM: Image reconstruction in positron emission tomography (PET) can be performed using either direct or iterative methods. Direct reconstruction methods need a short reconstruction time. However, for data containing few counts, they often result in poor visual images with high noise and reconstruction artefacts. Iterative reconstruction methods such as ordered subset expectation maximization (OSEM) can lead to overestimation of activity in cold regions distorting quantitative analysis. The present work investigates the possibilities to reduce noise and reconstruction artefacts of direct reconstruction methods using compressed sensing (CS). MATERIALS AND METHODS: Raw data are generated either using Monte Carlo simulations using GATE or are taken from PET measurements with a Siemens Inveon small-animal PET scanner. The fully sampled dataset was reconstructed using filtered backprojection (FBP) and reduced in Fourier space by multiplication with an incoherently undersampled sampling pattern, followed by an additional reconstruction with CS. Different sampling patterns are used and an average of the reconstructions is taken. The images are compared to the results of an OSEM reconstruction and quantified using signal-to-noise ratio (SNR). RESULTS: The application of the proposed CS post-processing technique clearly improves the image contrast. Dependent on the undersampling factor, noise and artefacts are reduced resulting in an SNR that is increased up to 3.4-fold. For short acquisition times with low count statistics the SNR of the CS reconstructed image exceeds the SNR of the OSEM reconstruction. CONCLUSION: Especially for low count data, the proposed CS-based post-processing method applied to FBP reconstructed PET images enhances the image quality significantly.

Specific somatostatin receptor II expression in arterial plaque: (68)Ga-DOTATATE autoradiographic, immunohistochemical and flow cytometric studies in apoE-deficient mice.

BACKGROUND: The rupture of atherosclerotic plaques is triggered by inflammation. Specific detection of inflammation is therefore the focus of many investigations. Noninvasive imaging methods, such as positron emission tomography (PET), also are suited for this purpose. (68)Ga-DOTATATE is a (68)Ga-labeled radiotracer with specific affinity to somatostatin receptor subtype-2 (SSTR-2). SSTR-2 was found specifically expressed on human macrophages/monocytes. OBJECTIVE: We aimed to confirm the distribution of SSTR-2 in inflammatory plaques, and to assess its co-localization with macrophages within the plaques. We also assessed (68)Ga-DOTATATE uptakes in plaques by autoradiography. METHOD: Apolipoprotein E (ApoE)-/- mice on a high-cholesterol diet were injected with (68)Ga-DOTATATE. The animals were sacrificed and aorta sections were examined using autoradiography and immunohistochemistry. Furthermore, expression of SSTR-2 was analyzed by flow cytometry. Western blot was conducted to assess SSTR-2 regulation in basal and lipopolysaccharide (LPS)-activated state. To evaluate the specificity of the (68)Ga-DOTATATE, the sections were pre-incubated with monoclonal SSTR-2 antibody before autoradiography. RESULT: Autoradiographic imaging showed uptake of (68)Ga-DOTATATE co-localized with the macrophage-rich plaques by immunohistochemical examination. A high expression of SSTR-2 on macrophages was found by flow cytometry and western blot. Stimulation with lipopolysaccharide did not alter expression of SSTR-2 in macrophages. CONCLUSION: Due to its specific binding to macrophages, (68)Ga-DOTATATE might be a suitable radiotracer for the evaluation of inflammatory activity in unstable plaques.

68Ga-DOTATATE PET/CT for the detection of inflammation of large arteries: correlation with18F-FDG, calcium burden and risk factors.

BACKGROUND: Ga-[1,4,7,10-tetraazacyclododecane-N,N',N″,N'″-tetraacetic acid]-d-Phe1,Tyr3-octreotate (DOTATATE) positron emission tomography (PET) is commonly used for the visualization of somatostatin receptor (SSTR)-positive neuroendocrine tumors. SSTR is also known to be expressed on macrophages, which play a major role in inflammatory processes in the walls of coronary arteries and large vessels. Therefore, imaging SSTR expression has the potential to visualize vulnerable plaques. We assessed 68Ga-DOTATATE accumulation in large vessels in comparison to 18F-2-fluorodeoxyglucose (FDG) uptake, calcified plaques (CPs), and cardiovascular risk factors. METHODS: Sixteen consecutive patients with neuroendocrine tumors or thyroid cancer underwent both 68Ga-DOTATATE and 18F-FDG PET/CT for staging or restaging purposes. Detailed clinical data, including common cardiovascular risk factors, were recorded. For a separate assessment, they were divided into a high-risk and a low-risk group. In each patient, we calculated the maximum target-to-background ratio (TBR) of eight arterial segments. The correlation of the TBRmean of both tracers with risk factors including plaque burden was assessed. RESULTS: The mean TBR of 68Ga-DOTATATE in all large arteries correlated significantly with the presence of CPs (r = 0.52; p < 0.05), hypertension (r = 0.60; p < 0.05), age (r = 0.56; p < 0.05), and uptake of 18F-FDG (r = 0.64; p < 0.01). There was one significant correlation between 18F-FDG uptake and hypertension (0.58; p < 0.05). Out of the 37 sites with the highest focal 68Ga-DOTATATE uptake, 16 (43.2%) also had focal 18F-FDG uptake. Of 39 sites with the highest 18F-FDG uptake, only 11 (28.2%) had a colocalized 68Ga-DOTATATE accumulation. CONCLUSIONS: In this series of cancer patients, we found a stronger association of increased 68Ga-DOTATATE uptake with known risk factors of cardiovascular disease as compared to 18F-FDG, suggesting a potential role for plaque imaging in large arteries. Strikingly, we found that focal uptake of 68Ga-DOTATATE and 18F-FDG does not colocalize in a significant number of lesions.

The estrogen receptor-α is required and sufficient to maintain physiological glucose uptake in the mouse heart.

Estrogens attenuate cardiac hypertrophy and increase cardiac contractility via their cognate estrogen receptors (ERs) ERα and ERß. Because female sex hormones enhance global glucose use and because myocardial function and mass are tightly linked to cardiac glucose metabolism, we tested the hypothesis that expression and activation of the ERα might be required and sufficient to maintain physiological cardiac glucose uptake in the murine heart. Cardiac glucose uptake quantified in vivo by 18F-fluorodeoxyglucose positron emission tomography was strongly impaired in ovariectomized compared with gonadal intact female C57BL/6JO mice. The selective ERα agonist 16α-LE2 and the nonselective ERα and ERß agonist 17ß-estradiol completely restored cardiac glucose uptake in ovariectomized mice. Cardiac 18F-fluorodeoxyglucose uptake was strongly decreased in female ERα knockout mice compared with wild-type littermates. Analysis of cardiac mRNA accumulation by quantitative RT-PCR revealed an upregulation of genes involved in glycolisis and tricarboxylic acid cycle by ERα treatment. In conclusion, systemic activation of ERα is sufficient, and its expression is required to maintain physiological glucose uptake in the murine heart, which is likely to contribute to known cardioprotective estrogen effects.

Validation of an amino-acid-based radionuclide therapy plus external beam radiotherapy in heterotopic glioblastoma models.

BACKGROUND AND PURPOSE: Malignant gliomas represent a major therapeutic challenge because no efficient treatment is currently available. p-[(131)I]iodo-L-phenylalanine ([(131)I]IPA) is a glioma avid radiopharmaceutical that demonstrated antiproliferative and tumoricidal effects in gliomas. The present study validated the therapeutic efficiency of [(131)I]IPA combined with external beam radiotherapy in experimental gliomas. MATERIALS AND METHODS: Glioma cells derived from the primary human A1207, T5135, Tx3868 and M059K glioblastoma cell lines or rat F98 glioma cell line were treated with various doses of [(131)I]IPA, external photon irradiation (RT) or combined [(131)I]IPA/RT treatment. Responsiveness of glioma cells to the different therapy modalities was investigated at 24, 48 and 72 h after treatments by trypan blue, WST-1 assay, propidium iodide and bisbenzimide staining as well as by clonogenic assay. In addition, the therapy-induced DNA damage and repair were evaluated using phosphorylated histone H2AX (γ-H2AX). In vivo, the effectiveness of the combination treatment was validated in human Tx3868 and A1207 glioblastoma xenografts in CD1 nu/nu mice and RNU rats. RESULTS: In vitro, the combination treatment resulted in a greater than additive increase in cytotoxic effect in glioma cell lines. Cell survival rate following a treatment with 1.0 µCi (37 kBq) of [(131)I]IPA amounted to 70%±15% and 60%±10% after 48 and 72 h, respectively, and decreased under 20% after additional RT with 5 Gy. At higher RT doses, cell survival rate decreased below 5%. As a measure of DNA double-strand break, nuclear γ-H2AX foci were determined as a function of time. Within 24 h, the number of γ-H2AX foci per cell was significantly greater after combined modality compared with the individual treatments. In vivo, when combined with RT, the radionuclide therapy with [(131)I]IPA resulted in an extended tumor growth delay, a reduction of the initial tumor volume and an enhanced radiosensitivity in Tx3868 and A1207 glioblastoma xenografts in CD1 nu/nu mice and RNU rats. On day 90 after monotherapy with [(131)I]IPA (20 MBq) or RT (20 Gy), 35%-50% of the treated rats were still alive. In comparison, up to 70%-80% survival rates were registered after combined [(131)I]IPA/RT treatment on day 100 for all animal models. CONCLUSIONS: These preclinical data convincingly demonstrated that [(131)I]IPA plus external beam photon radiotherapy is a safe and highly effective treatment for experimental gliomas, which may merit a clinical trial to ascertain its potential as a therapeutic approach in patients. As only a low [(131)I]IPA activity and a low RT dose were applied, further optimization strategies should be pursued experimentally, including application of higher radiation doses and conventional fractionated regimens or use of methods aiming to increase target doses and maximize dose effects.

Efficacy of systemic radionuclide therapy with p-131I-iodo-L-phenylalanine combined with external beam photon irradiation in treating malignant gliomas.

UNLABELLED: p-(131)I-iodo-L-phenylalanine ((131)I-IPA) is a tumor-specific amino acid derivative that demonstrated antiproliferative and tumoricidal effects on experimental gliomas. This study tested the efficacy of (131)I-IPA combined with external beam photon radiotherapy as a new therapeutic approach against gliomas. METHODS: Glioma cells derived from the rat F98 glioma or human Tx3868 or A1207 glioblastoma cell lines were stereotactically inoculated into the brains of Fischer 344 rats or RNU rats. Tumor formation was verified radiologically. On day 8, groups of glioma-bearing rats of each tumor model underwent whole-brain radiotherapy with 8 Gy, an intravenous administration of (131)I-IPA (30 MBq), or combined treatment, aiming for a total of 12 rats per group. Another 12 animals were treated with physiologic saline and served as control. RESULTS: Control rats had a combined median survival (+/-SD) of 21 +/- 6 d. All revealed metabolically and histologically large tumor masses. Efficacy of radiotherapy alone or a monotherapy with 30 MBq of (131)I-IPA was statistically insignificant on the syngeneic Fischer-F98 model (P >or= 0.45 and P = 0.10, respectively). In contrast, a subset of long-term survivors (>120 d) was observed in RNU rats bearing Tx3868 and A1207 glioblastoma xenografts (18%-25% and 35%-45% for radiotherapy and (131)I-IPA, respectively). Combined (131)I-IPA and radiotherapy treatment significantly prolonged median survival for the syngeneic Fischer-F98 glioma model (P < 0.01) and human glioblastoma-bearing RNU rats alike (P < 0.05). On day 120 after monotherapy with (131)I-IPA, 45% of the RNU rats were still alive, but after 8 Gy of photon radiotherapy only 18%-25% of the RNU and none of the Fischer rats survived. In comparison, 55%-75% survival rates were registered after combined treatment on day 120 for all animal models. CONCLUSION: These data convincingly demonstrated that systemic radionuclide therapy with (131)I-IPA combined with external photon radiotherapy is a safe and highly effective treatment for experimental gliomas, which may merit a clinical trial to ascertain its potential in patients with gliomas. Because only a low (131)I-IPA activity and low radiotherapy doses were applied, further optimizations including higher radiation doses and conventional fractionated radiotherapy are warranted.