Synthesis and Evaluation of 68Ga-NOTA-COG1410 Targeting to TREM2 of TAMs as a Specific PET Probe for Digestive Tumor Diagnosis.

Currently, positron emission tomography/computed tomography (PET/CT) is an important method for the discovery and diagnosis of digestive system tumors. However, the shortage of specific imaging tracer limits the effectiveness of PET. Triggering receptor expressed on myeloid cells 2 (TREM2) as an M2-type macrophage biomarker is receiving much attention considering its high abundance and specificity, which could be an ideal target for PET imaging. First, the expression of TREM2 in tumors and corresponding normal tissues was analyzed using a database and was verified by tissue microarrays and murine model slices, and we found that the expression of TREM2 in tumor tissues was significantly higher than that in normal tissues and enteritis tissues. Then, we established a macrophage co-culture system to obtain tumor-associated macrophages (TAMs). Compared with M1-type macrophages and tumor cells, TAMs had a higher expression level of TREM2. The novel radioligand 68Ga-NOTA-COG1410 was successfully synthesized for TREM2 targeting PET imaging. The biodistribution and micro-PET/CT results showed high uptake of 68Ga-NOTA-COG1410 in the tumor but not in areas of inflammation. The data testified that 68Ga-NOTA-COG1410 was a specific radioligand targeting TREM2, which could be used to distinguish tumors from inflammation. Using 68Ga-NOTA-COG1410, the effectiveness of PET on digestive tumors imaging may be enhanced.

P2X7 receptor-specific radioligand 18F-FTTM for atherosclerotic plaque PET imaging.

PURPOSE: P2X7 receptors have been considered as a promising biomarker for vulnerable atherosclerotic plaques, which are highly expressed by that instability-associated factors such as macrophages. Thus, we aim to investigate the feasibility of using specific P2X7-targeted 18F-labeled tracer 18F-FTTM ((2-chloro-3-[18F]fluorophenyl)[1,4,6,7-tetrahydro-1-(2-pyrimidinyl)-5H-1,2,3-triazolo[4,5-c]pyridin-5-yl]methanone) for PET study of vulnerable atherosclerotic plaques identification. METHOD: The radioligand 18F-FTTM was achieved based on the copper-mediated radiofluorination of arylstannane. In vitro and in vivo experiments were performed to verify the biochemical properties. Dynamic 18F-FTTM Micro-PET/CT imaging was performed for 1 h on ApoE-/- mice (10, 20, 30 weeks on high-fat diet) and wild-type C57BL/6 J mice on normal diet. Ex vivo PET imaging was conducted to verify the specificity of the radioligand. Serum inflammatory cytokines, lipids, and lipoproteins profiles were detected by ELISA. The lipid distribution and morphology of plaques were evaluated by Oil Red O, HE, Masson, and immunofluorescence stainings. RESULTS: 18F-FTTM was afforded with decay-corrected radiochemical yields of 5-10%, specific activity of 269-320 MBq/nmol (n = 8, EOS), and radiochemical purity of above 99%. 18F-FTTM showed excellent stability in vitro, rapid blood clearance in mice, good affinity to RAW264.7 cells. We observed an increase in both in vivo and ex vivo imagings as disease progressed, and the imaging signatures correlated with histopathological features. Furthermore, compared with 18F-FDG imaging, the SUVmax values of 18F-FTTM at the aortic arch of ApoE-/- mice of high-fat feeding for 20 and 30 weeks were 43% and 53% higher than those of the control group, respectively. CONCLUSION: We innovatively apply a new type P2X7-targeted PET probe (18F-FTTM) to identify vulnerable atherosclerotic plaques, to detect the inflammatory response of atherosclerosis, and to provide a powerful non-invasive method for the diagnosis of atherosclerotic lesions and new drug screening for accurate treatment.

Targeting Infiltrating Myeloid Cells in Gastric Cancer Using a Pretargeted Imaging Strategy Based on Bio-Orthogonal Diels-Alder Click Chemistry and Comparison with 89Zr-Labeled Anti-CD11b Positron Emission Tomography Imaging.

Gastric cancer (GC) is a common cancer worldwide, with high incidence and mortality rates. Therefore, early and precise diagnosis is critical to improving GC prognosis. Tumor-associated myeloid cells infiltrate the tumor microenvironment (TME) and can produce immunosuppressive effects in the early stage of the tumor. The surface integrin receptor CD11b is widely expressed in the specific subsets of myeloid cells, and it has the characteristics of high abundance, high specificity, and high potential for targeted immunotherapy. In this study, two strategies for labeling anti-CD11b, including 89Zr-DFO-anti-CD11b and pretargeted imaging (68Ga-NOTA-polypeptide-PEG11-Tz/anti-CD11b-TCO), were used to evaluate the value of early diagnosis of GC and confirm the advantages of the pretargeted strategy for the diagnosis of GC. Pretargeted molecular probe 68Ga-NOTA-polypeptide-PEG11-Tz was synthesized. The binding affinity of the Tz-radioligand to CD11b was evaluated in vitro, and its blood pharmacokinetic test was performed in vivo. Moreover, the anti-CD11b antibody was conjugated with a p-isothiocyanatobenzyl-desferrioxamine (SCN-DFO) chelator and radiolabeled with zirconium-89. Biodistribution and positron-emission computed tomography imaging experiments were performed in MGC-803 tumor-bearing model mice to evaluate the value of the early diagnosis of GC. Histological evaluation of MGC-803 tumors was conducted to confirm the infiltration of the GC TME with CD11b+ myeloid cells. 68Ga-NOTA-polypeptide-PEG11-Tz was successfully radiosynthesized, with the radiochemical purity above 95%, as confirmed by reversed-phase high-performance liquid chromatography. The radioligand showed favorable stability in normal saline and phosphate-buffered saline, good affinity to RAW264.7 cells, and rapid blood clearance in mice. The results of biodistribution and imaging experiments using the pretargeted method showed that the tumor/muscle ratios were 5.17 ± 2.98, 5.94 ± 1.46, and 4.46 ± 2.73 at the pretargeting intervals of 24, 48, and 72 h, respectively. The experimental results using the method of the directly labeling antibody (89Zr-DFO-anti-CD11b) showed that, despite radioactive accumulation in the tumor, there was a higher level of radioactive accumulation in normal tissues. The tumor/muscle ratios were 1.09 ± 0.67, 1.66 ± 0.95, 2.94 ± 1.24, 3.64 ± 1.21, and 3.55 ± 1.64 at 1, 24, 48, 72, and 120 h. The current research proved the value of 68Ga-NOTA-polypeptide-PEG11-Tz/anti-CD11b-TCO in the diagnosis of GC using the pretargeted strategy. Compared to 89Zr-DFO-anti-CD11b, the image contrast achieved by the pretargeted strategy was relatively improved, and the background accumulation of the probe was relatively low. These advantages can improve the diagnostic efficiency for GC and provide supporting evidence for radioimmunotherapy targeting CD11b receptors.

124I-Labeled Monoclonal Antibody and Fragment for the Noninvasive Evaluation of Tumor PD-L1 Expression In Vivo.

Lung cancer is a highly heterogeneous cancer and is divided broadly into small and nonsmall cell lung cancer (SCLC or NSCLC). In all NSCLC patients, it is estimated that 50%-60% are programmed cell death ligand 1 (PD-L1) positive, and anti-PD-1/PD-L1 therapies have shown their clinical application prospects in advanced NSCLC. To avoid unnecessary adverse effects and provide anti-PD-1/PD-L1 therapy to the most appropriate patient population, the PD-L1 expression in patients preparing for treatment must be evaluated accurately and in real time. In this study, we noninvasively evaluate the PD-L1 expression in an NSCLC xenograft using 124I-labeled F(ab')2 fragments of durvalumab (Durva) and compared it with the 124I-labeled intact antibody in terms of the biodistribution and dosimetry. The aim is to develop a nuclide labeled molecular probe with better performance for PD-L1 immunoPET imaging. After cleaving using IdeS protease, the F(ab')2 fragments of Durva were labeled with 124I. The radioligand showed a high radiochemical purity (>96%) and outstanding stability. Western blot, quantitative real-time polymerase chain reaction, and flow cytometry were performed on the two selected NSCLC cell lines to measure the in vitro PD-L1 expression. The H460 cells showed a much higher PD-L1 expression than the A549 cells, both at the protein level and the mRNA level. In the following cell binding experiment and binding specificity assay, the labeled radioligand showed good affinity to high PD-L1 expression cells and could be blocked with excess unlabeled intact Durva. The results of the biodistribution and the positron emission tomography (PET) image showed that the peak tumor uptake of 124I-Durva-F(ab')2 was close to 124I-Durva, but much earlier (5.29 ± 0.42% ID/g for 124I-Durva-F(ab')2 at 12 h vs 5.18 ± 0.73% ID/g for 124I-Durva at 48 h). Compared with 124I-Durva, an accelerated blood clearance was observed for 124I-Durva-F(ab')2. The faster blood clearance allowed for a higher tumor-to-background ratio, which was reflected on the image in contrast. The H460 tumors showed excellent contrast as early as 4 h after injection with 124I-Durva-F(ab')2, and for 124I-Durva, the xenograft could not be distinguished clearly until 24 h after injection. Interestingly, 124I-Durva-F(ab')2 showed lower accumulations compared to other metal isotopes labeled PD-L1 antibodies in bone, liver, spleen etc., which will be beneficial for metastasis detection. Another benefit of accelerated blood clearance was a reduction in the radiation dose. According to the results of the OLINDA/EXM, the effective dose for the total body of 124I-Durva was 4.25-times greater than that of 124I-Durva-F(ab')2 (186 µSv/MBq vs 43.8 µSv/MBq). All of these data indicated that 124I-Durva-F(ab')2 is a promising immunoPET tracer for evaluating the in vivo PD-L1 levels in an NSCLC model and is expected to be successful in future clinical application.

Synthesis and biological evaluation of novel PET tracers [18F]AG120 & [18F]AG135 for imaging mutant isocitrate dehydrogenase 1 expression.

Mutations in isocitrate dehydrogenase 1 (IDH1) are commonly found in various human malignancies. Inhibitors of several mutant IDH1 enzymes have entered clinical trials as target therapeutic drugs for the treatment of patients with IDH1 mutations. Herein, we report the synthesis and evaluation of two 18F-labeled tracers, [18F]AG120 and [18F]AG135 for imaging expression of mutated IDH1 in positron emission tomography (PET). [18F]AG120 and [18F]AG135 were synthesized in decay-corrected radiochemical yield of 1 % and 3 %, respectively, high molar activity (52-66 MBq/nmol and 216-339 MBq/nmol, respectively) and high radiochemical purity (>99%). Both tracers showed good in vitro stability, selective uptake into mutated IDH1-expressing cells and good pharmacokinetic profiles with low uptake in most organs/tissues. Furthermore, [18F]AG120 micro-PET/CT imaging displayed significantly greater uptake in IDH1-mutant than in wild-type tumors, Relatively, uptake of [18F]AG135 was observed neither in IDH1-mutant tumor xenografts nor in wild-type tumors. This study suggests that [18F]AG120 is a promising radiotracer for PET imaging of IDH1 mutation, However, further optimization and investigation are necessary for [18F]AG135 due to the limited uptake in mutated IDH1-expressing tumors.

Synthesis and evaluation of 18F labeled crizotinib derivative [18F]FPC as a novel PET probe for imaging c-MET-positive NSCLC tumor.

c-MET-positive NSCLC is an important subtype accounting for about 5%~22% of lung cancer. NSCLC patients with activating c-MET are intensively sensitive to c-MET selective receptor tyrosine kinase (RTK) inhibitors, so we aimed to develop a specific PET probe targeting to c-MET-positive NSCLC for potential patients screened by PET/CT. Herein, PET tracer 18F-radiolabeled crizotinib derivative ([18F]FPC) was successfully achieved through a simple one-step 18F-labeling method. [18F]FPC PET imaging on c-MET-positive (as well as blocking group) and negative NSCLC models were further evaluated, and results showed that [18F]FPC was effective as a PET imaging probe that targeted c-MET-positive tumor. Therefore, [18F]FPC could be a potential PET imaging probe for NSCLC tumor which was sensitive to c-MET-TKIs. By virtue of this property, it will benefit NSCLC patients for c-MET-TKI treatment.

A Neural Network with Convolutional Module and Residual Structure for Radar Target Recognition Based on High-Resolution Range Profile.

In the conventional neural network, deep depth is required to achieve high accuracy of recognition. Additionally, the problem of saturation may be caused, wherein the recognition accuracy is down-regulated with the increase in the number of network layers. To tackle the mentioned problem, a neural network model is proposed incorporating a micro convolutional module and residual structure. Such a model exhibits few hyper-parameters, and can extended flexibly. In the meantime, to further enhance the separability of features, a novel loss function is proposed, integrating boundary constraints and center clustering. According to the experimental results with a simulated dataset of HRRP signals obtained from thirteen 3D CAD object models, the presented model is capable of achieving higher recognition accuracy and robustness than other common network structures.

Longitudinal Positron Emission Tomography Imaging with P2X7 Receptor-Specific Radioligand 18F-FTTM in a Kainic Acid Rat Model of Temporal Lobe Epilepsy.

P2X7 receptors (P2X7R), as a brain inflammation biomarker, play important roles in the epileptogenic progress. Mounting evidence supports their activation in the brain during epilepsy, and inhibition of the P2X7 receptor reduces the seizure frequency and severity. In this study, we investigate P2X7R-targeted (18F-FTTM) position emission tomography (PET) imaging in a rat model of temporal lobe epilepsy to obtain further insights into the role of P2X7R during epileptogenesis. 18F-FTTM (5-10% radiochemical yield, over 99% radiochemical purity, and a specific activity of 270-300 MBq/nmol, n = 6, EOS) was first synthesized. Then, the rat models induced by intrahippocampal injection of saline (1.2 µL, n = 15) or kainic acid (1.2 µL, 0.5 µg/µL, n = 35) were examined using 18F-FTTM Micro-PET/CT longitudinal imaging, respectively. The imaging results showed that increases in the 18F-FTTM uptake was evident after status epilepticus (SE) in the epileptogenesis-associated brain regions, such as the hippocampus, amygdala, or temporal cortex, and this peaked during the latent period. The histopathological analysis revealed that the P2X7R PET uptake reached a peak at 7 days after SE and was mostly related to microglial activation. Thus, P2X7R-targeted PET imaging agent 18F-FTTM may act as a useful tool for identifying brain inflammation during epilepsy. P2X7R PET is a highly potent longitudinal biomarker of epilepsy and could be of interest to determine the therapeutic windows in epilepsy and to monitor treatment response, and it warrants further clinical studies.

Correlation of PD-L1 expression on tumor cell and tumor infiltrating immune cell with 18F-fluorodeoxyglucose uptake on PET/computed tomography in surgically resected pulmonary adenocarcinoma.

OBJECTIVE: The uptake of F-fluorodeoxyglucose (F-FDG) PET/computed tomography (CT) is known to be linked to programmed death ligand 1 (PD-L1) expression on tumor cells (TC). However, the association between PD-L1 expression on immune cells (IC) and F-FDG accumulation is still unclear. Here, we conducted a clinicopathological study to investigate the relationship between PD-L1 expression on TC/IC and F-FDG uptake in patients with surgically resected pulmonary adenocarcinoma (ADC). METHODS: A total of 450 ADC patients who underwent preoperative F-FDG-PET/CT imaging were analyzed retrospectively. Immunohistochemistry analysis was performed for PD-L1 expression on TC and IC in ADC specimens with SP142. PD-L1 expression was performed on whole-tissue sections and given scores (0/1/2/3) according to percent of PD-L1 cells in TC and IC. RESULTS: Compared to TC0 and IC0, PD-L1 positive expression was 90.4% (407/450) in ADC specimens. Both PD-L1 expression score on TC and IC were associated with maximum standardized uptake (SUVmax). SUVmax augmented with increasing PD-L1 expression (TC0 and IC0, 4.3 ± 3.4; TC or IC1/2/3, 7.7 ± 5.6; TC or IC2/3, 8.1 ± 5.6; TC or IC3, 8.4 ± 5.4). The best cut-off value of PD-L1 expression, determined by receiver operating characteristic curve, was 5.1 for TC or IC1/2/3 [area under the curve (AUC) = 0.713, sensitivity 62.2%, specificity 72.1%]. Multivariate analysis demonstrated that TC or IC1/2/3 subset was correlated with histological subtype, PD-1 expression on IC and SUVmax. CONCLUSION: High SUVmax is associated with PD-L1 expression on TC and IC in surgically resected pulmonary ADC. F-FDG-PET/CT imaging can be a potential tool to evaluate PD-L1 expression in pulmonary ADC.

A Pretargeted Imaging Strategy for Immune Checkpoint Ligand PD-L1 Expression in Tumor Based on Bioorthogonal Diels-Alder Click Chemistry.

PURPOSE: The use of antibodies as tracers requires labeling with isotopes with long half-lives due to their slow pharmacokinetics, which creates prohibitively high radiation dose to non-target organs. Pretargeted methodology could avoid the high radiation exposure due to the slow pharmacokinetics of antibodies. In this investigation, we reported the development of a novel pretargeted single photon emission computed tomography (SPECT) imaging strategy (atezolizumab-TCO/[99mTc]HYNIC-PEG11-Tz) for evaluating immune checkpoint ligand PD-L1 expression in tumor based on bioorthogonal Diels-Alder click chemistry. PROCEDURES: The radioligand [99mTc]HYNIC-PEG11-Tz was achieved by the synthesis of a 6-hydrazinonicotinc acid (HYNIC) modified 1,2,4,5-tetrazine (Tz) and subsequently radiolabeled with technetium-99m (Tc-99m). The stability of [99mTc]HYNIC-PEG11-Tz was evaluated in vitro, and its blood pharmacokinetic test was performed in vivo. Atezolizumab was modified with trans-cyclooctene (TCO). The [99mTc]HYNIC-PEG11-Tz and atezolizumab-TCO interaction was tested in vitro. Pretargeted H1975 cell immunoreactivity binding and saturation binding assays were evaluated. Pretargeted biodistribution and SPECT imaging experiments were performed in H1975 and A549 tumor-bearing modal mice to evaluate the PD-L1 expression level. RESULTS: [99mTc]HYNIC-PEG11-Tz was successfully radiosynthesized with a specific activity of 9.25 MBq/µg and a radiochemical purity above 95 % as confirmed by reversed-phase HPLC (RP-HPLC). [99mTc]HYNIC-PEG11-Tz showed favorable stability in NS, PBS, and FBS and rapid blood clearance in mice. The atezolizumab was modified with TCO-NHS ester to produce a conjugate with an average 6.4 TCO moieties as confirmed by liquid chromatograph-mass spectrometer (LC-MS). Size exclusion HPLC revealed almost complete reaction between atezolizumab-TCO and [99mTc]HYNIC-PEG11-Tz in vitro, with the 1:1 Tz-to-mAb reaction providing a conversion yield of 88.65 ± 1.22 %. Pretargeted cell immunoreactivity binding and saturation binding assays showed high affinity to H1975 cells. After allowing 48 h for accumulation of atezolizumab-TCO in H1975 tumor, pretargeted in vivo biodistribution revealed high uptake of the radiotracer in the tumor with a tumor-to-muscle ratio of 27.51 and tumor-to-blood ratio of 1.91. Pretargeted SPECT imaging delineated the H1975 tumor clearly. Pretargeted biodistribution and SPECT imaging in control groups demonstrated a significantly reduced tracer accumulation in the A549 tumor. CONCLUSIONS: We have developed a HYNIC-modified Tz derivative, and the HYNIC-PEG11-Tz was labeled with Tc-99m with a high specific activity and radiochemical purity. [99mTc]HYNIC-PEG11-Tz reacted rapidly and almost completely towards atezolizumab-TCO in vitro with the 1:1 Tz-to-mAb reaction. SPECT imaging using the pretargeted strategy (atezolizumab-TCO/[99mTc]HYNIC-PEG11-Tz) demonstrated high-contrast images for high PD-L1 expression H1975 tumor and a low background accumulation of the probe. The pretargeted imaging strategy is a powerful tool for evaluating PD-L1 expression in xenograft mice tumor models and a potential candidate for translational clinical application.

Gadolinium-Based Nanoparticles for Theranostic MRI-Guided Radiosensitization in Hepatocellular Carcinoma.

Background: Radiation therapy (RT) of hepatocellular carcinoma (HCC) is limited by low tolerance of the liver to radiation, whereas radiosensitizers are effective in reducing the required radiation dose. Multimodality gadolinium-based nanoparticles (AGuIX) are small and have enhanced permeability and retention effects; thus, they are very suitable for radiation sensitizer HCC RT. Here, we evaluated the potential value of AGuIX for theranostic MRI-radiosensitization in HCC. Methods: The radiosensitization effects of AGuIX were evaluated via in vitro and in vivo experiments. Tumor growth, apoptosis imaging, and immunohistochemistry were performed to verify the antitumor effects of RT with AGuIX. Results: In vitro evaluation of the efficacy of radiosensitivity of the AGuIX demonstrated that the presence of AGuIX significantly decreased HepG2 cell survival when combined with an X-ray beam. In vivo MRI imaging showed the ratio of tumor/liver concentration of the AGuIX was the highest 1 h after intravenous injection. For antitumor effects, we found that the tumor size decreased by RT-only and RT with AGuIX. The antitumor effects were more effective with high-dose AGuIX-mediated RT. Apoptosis imaging and immunohistochemistry both demonstrated that the degree of the cell apoptosis was highest with a high dose of AGuIX-mediated RT. Conclusions: This study provides compelling data that AGuIX can facilitate theranostic MRI-radiosensitization in HCC.

Treatment of Hepatocellular Carcinoma by Intratumoral Injection of 125I-AA98 mAb and Its Efficacy Assessments by Molecular Imaging.

Objective: To investigate the therapeutic efficacy of intratumoral injection of 125I-AA98 mAb for hepatocellular carcinoma (HCC) and its therapy efficacy assessment by 99mTc-HYNIC-duramycin and 99mTc-HYNIC-3PRGD2 SPECT/CT imaging. Methods: HCC xenograft tumor mice models were injected intratumorally with a single dose of normal saline, 10 microcurie (µCi) 125I-AA98 mAb, free 125I, AA98 mAb, 80 µCi 125I-AA98 mAb, and 200 µCi 125I-AA98 mAb. 99mTc-HYNIC-duramycin and 99mTc-HYNIC-3PRGD2 micro-SPECT/CT imaging were performed on days 3 and 7, respectively. The T/M ratio for each imaging was compared with the corresponding immunohistochemical staining at each time point. The relative tumor inhibition rates were documented. Results: In terms of apoptosis, the 200 µCi group demonstrated the highest apoptotic index (11.8 ± 3.8%), and its T/M ratio achieved by 99mTc-HYNIC-duramycin imaging on day 3 was higher than that of the normal saline group, 80 µCi group, 10 µCi group and free 125I group on day 3, respectively (all P < 0.05). On day 3, there was a markedly positive correlation between T/M ratio from 99mTc-HYNIC-duramycin imaging and apoptotic index by TUNEL staining (r = 0.6981; P < 0.05). Moreover, the 200 µCi group showed the lowest T/M ratio on 99mTc-HYNIC-3PRGD2 imaging (1.0 ± 0.5) on day 7 (all P < 0.05) comparing to other groups. The T/M ratio on day 7 was not correlated with integrin ανß3 staining (P > 0.05). The relative inhibitory rates of tumor on day 14 in the AA98 mAb, 10 µCi, 80 µCi, free 125I, and 200 µCi groups were 26.3, 55.3, 60.5, 66.3, and 69.5%, respectively. Conclusion: 125I-AA98 mAb showed more effective apoptosis induced ability for CD146 high expression Hep G2 HCC cells and hold the potential for HCC treatment. Moreover, 99mTc-HYNIC-Duramycin (apoptosis-targeted) imaging and 99mTc-HYNIC-3PRGD2 (angiogenesis-targeted) imaging are reliable non-invasive methods to evaluate the efficacy of targeted treatment of HCC.

18F-PBR06 PET/CT imaging for evaluating atherosclerotic plaques linked to macrophage infiltration.

BACKGROUND: The present study explored the 18 kDa translocator protein radioligand [F]N-fluoroacetyl-N-(2,5-dimethoxybenzyl)-2-phenoxyaniline (F-PBR06) targeting macrophages for PET imaging of atherosclerotic plaques and evaluating the vulnerability of atherosclerotic plaques toward rupture. MATERIALS AND METHODS: F-PBR06 was synthesized using a Synthra RNplus module automatically. RAW264.7 cells were used for cell binding study with F-PBR06. In-vivo micro-PET/CT imaging for ApoE mice and C57 mice was performed 1 h after injection of F-PBR06. CD68 and F480 immunofluorescence stainings were performed in the aorta tissues. RESULTS: In-vitro cell studies showed uptake of F-PBR06 to RAW264.7 cells. Micro-PET/CT imaging identified the atherosclerotic lesions in the aortic arch of ApoE mice successfully, whereas no signal was observed in C57 mice. The ratio of plaque-to-muscle in ApoE mice of 32 weeks was significantly higher than that in ApoE mice of 22 weeks, which was confirmed by CD68 immunofluorescence staining and F480 immunofluorescence staining. CONCLUSION: TSPO radioligand F-PBR06 allows noninvasive PET/CT imaging of macrophage-abundant atherosclerotic plaques as well as positive correlation between PET imagings and ex-vivo immunofluorescence staining of plaques in mice with different ages, thereby representing a potential attractive tool for evaluating the vulnerability of atherosclerotic plaques towards rupture.

P2X7 PET Radioligand 18F-PTTP for Differentiation of Lung Tumor from Inflammation.

Site-specific imaging agents play a key role in tumor targeting, but only a few agents are currently available for inflammation targeting. Since the P2X7 receptor (P2X7R) is a promising molecular target for inflammation, we evaluated the potential value of the 18F-labeled tracer 18F-PTTP (5-{[2-Chloro-3-(trifluoromethyl)phenyl]carbonyl}-1-pyrimidin-2-yl-4,5,6,7-tetrahydro-1H-[1,2,3]triazolo[4,5-c]pyridin) for targeting P2X7Rs and thus differentiating inflammation from tumors. Methods: The radioligand 18F-PTTP was achieved by a 1-step 18F-trifluoromethylation reaction. The binding affinity of the ligand for P2X7R and its stability were evaluated in vitro. Blood pharmacokinetics tests and biodistribution studies were performed in vivo. Dynamic 18F-PTTP small-animal PET/CT imaging was performed for 60 min on A549 tumor-bearing mice and inflammation-model mice for targeting differentiation. Results:18F-PTTP was afforded with decay-corrected radiochemical yields of 2.5%-7.0%, specific activity of 296-370 MBq/µmol, and radiochemical purity over 95%. 18F-PTTP showed excellent stability in 0.9% NaCl and 0.1% bovine serum albumin, good affinity to RAW264.7 cells, and rapid blood clearance in mice. In inflammation-model mice, uptake of 18F-PTTP peaked at 5 min after injection and kept at an imageable level till 30 min, whereas no significant radioactivity uptake was found in tumor grafts till 1 h after injection. The specificity of 18F-PTTP was verified by blocking studies and histologic analysis. Conclusion: The current study provides compelling data that 18F-PTTP is a novel radioligand targeting P2X7R and has potential to screen new drugs, quantify peripheral inflammation, and distinguish inflammation from certain solid tumors.