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.

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.

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.

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.

Variations of the liver standardized uptake value in relation to background blood metabolism: An 2-[18F]Fluoro-2-deoxy-D-glucose positron emission tomography/computed tomography study in a large population from China.

To investigate the influence of background blood metabolism on liver uptake of 2-[F]fluoro-2-deoxy-D-glucose (F-FDG) and search for an appropriate corrective method.Positron emission tomography/computed tomography (PET/CT) and common serological biochemical tests of 633 healthy people were collected retrospectively. The mean standardized uptake value (SUV) of the liver, liver artery, and portal vein (i.e., SUVL, SUVA, and SUVP) were measured. SUVL/A was calculated as SUVL/SUVA, while SUVL/P was calculated as SUVL/SUVP. SUV of liver parenchyma (SUVLP) was calculated as SUVL - .3 × (.75 × SUVP + .25 × SUVA). The coefficients of variation (CV) of SUVL, SUVL/A, SUVL/P, and SUVLP were compared to assess their interindividual variations. Univariate and multivariate analyses were performed to identify vulnerabilities of these SUV indexes to common factors assessed using serological liver functional tests.SUVLP was significantly larger than SUVL (2.19 ± .497 vs 1.88 ±â€Š.495, P < .001), while SUVL/P was significantly smaller than SUVL (1.72 ±â€Š.454 vs 1.88 ±â€Š.495, P < .001). The difference between SUVL/A and SUVL was not significant (1.83 ±â€Š.500 vs 1.88 ±â€Š.495, P = .130). The CV of SUVLP (22.7%) was significantly smaller than that of SUVL (22.7%:26.3%, P < .001), while the CVs of SUVL/A (27.2%) and SUVL/P (26.4%) were not different from that of SUVL (P = .429 and .929, respectively). Fewer variables independently influenced SUVLP than influenced SUVL, SUVL/A, and SUVL/P; Only aspartate aminotransferase, body mass index, and total cholesterol, all P-values <.05.The activity of background blood influences the variation of liver SUV. SUVLP might be an alternative corrective method to reduce this influence, as its interindividual variation and vulnerability to effects from common factors of serological liver functional tests are relatively lower than the commonly used SUVL.

Does dual-time-point 18F-FDG PET/CT scan add in the diagnosis of hepatocellular carcinoma?

OBJECTIVE: The aim of this study was to evaluate the usefulness of dual-time-point 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) with semiquantitative analyses for patients with hepatocellular carcinoma (HCC). SUBJECTS AND METHODS: The 150 patients with clinically suspected liver malignancies underwent dual-time-point 18F-FDG PET/CT imaging. The maximum standardized uptake value (SUVmax) was calculated at both time points of PET imaging. The change in SUVmax (retention index, RI) was defined as the ratio of increase in SUVmax between the early and delayed scans to the SUVmax in the early scan. The tumor-to-normal liver tissue (T/N) ratio of the early and delayed scan was also calculated. The final diagnoses were confirmed by histopathology. A hundred and twenty four patients had HCC, 4 with grade I, 64 with grade II, 55 with grade III and 1 with grade IV. Twenty six patients had benign liver diseases. RESULTS: There were significant differences in the SUVmax and T/N between the early scan and the delayed scan in the HCC Group (t=4.23, P<0.01; t=6.02, P<0.01). There were no significant differences in the SUVmax or T/N of the early and delayed scans in the benign Group (t=1.20, P=0.24; t=1.63, P=0.12). There was no significant difference in the RI of the HCC Group and that of the benign Group (t=0.52, P=0.60). The SUVmax of the delayed scan was significantly higher than that of the early scan for both Groups (t=3.01, P<0.01 for grade III Group; t=2.93, P<0.01 for grade II Group). Significant differences were detected between the grade III Group and the grade II Group for the SUVmax on the early scan and the delayed scan (t=2.15, P<0.01 for early scan; t=2.11, P<0.01 for the delayed scan). There were no significant differences between the grade III and grade II Groups for the retention index of SUVmax (RI-SUVmax) (t=0.06, P=0.95). The T/N ratio on the delayed scan was significantly higher than that on the early scan for both Groups (t=4.21, P<0.01 for grade III Group; t=4.44, P<0.01 for grade II Group). Significant differences were also detected between the grade III and grade II Groups for the T/N ratio on the early and delayed scans (t=2.69, P<0.01 for the early scan; t=2.06, P<0.01 for the delayed scan). CONCLUSION: Dual-time- point 18F-FDG PET/CT scan with semiquantitative analysis of SUVmax and T/N ratio may support the diagnosis of HCC and that of a higher grade HCC.

Investigation of SP94 Peptide as a Specific Probe for Hepatocellular Carcinoma Imaging and Therapy.

SP94 (SFSIIHTPILPL), a novel peptide, has shown specific binding to hepatocellular carcinoma (HCC) cells. We aimed to investigate the capability of SP94 as a targeting probe for HCC imaging and therapy following labeling with technetium-99m ((99m)Tc) and rhenium-188 ((188)Re). HYNIC-SP94 was prepared by solid phase synthesis and then labeled with (99m)Tc. Cell competitive binding, internalization assay, in vitro and in vivo stability, biodistribution and micro-single photon emission computed tomography /computed tomography (SPECT/CT) imaging studies were performed to investigate the capability of (99m)Tc tricine-EDDA/HYNIC-SP94 as a specific HCC imaging probe. Initial promising targeting results inspired evaluation of its therapeutic effect when labeled by (188)Re. HYNIC-SP94 was then labeled again with (188)Re to perform cell apoptosis, microSPECT/CT imaging evaluation and immunohistochemistry. Huh-7 cells exhibited typical apoptotic changes after (188)Re irradiation. According to (99m)Tc tricine-EDDA/HYNIC-SP94 microSPECT/CT imaging, tumor uptake was significantly decreased compared with that of pre-treatment with (188)Re-HYNIC-SP94. The immunohistochemistry also displayed obvious necrosis and apoptosis as well as inhibition of proliferation in the (188)Re-HYNIC-SP94 treatment group. The results supported that (99m)Tc tricine-EDDA/HYNIC-SP94 is able to target HCC cells and (188)Re-HYNIC- SP94 holds potential as a therapeutic agent for HCC, making (99m)Tc/(188)Re-HYNIC-SP94 a promising targeting probe for HCC imaging and therapy.

Gold nanoparticles-based SPECT/CT imaging probe targeting for vulnerable atherosclerosis plaques.

In order to realize accurate localization and precise evaluation of vulnerability of atherosclerotic plaques via dual-modal imaging, gold nanoparticles (GNPs) were firstly caped with a thin amino-PEGs cover and then conjugated with the targeting molecular Annexin V and radionuclide Tc-99m simultaneously to form SPECT/CT imaging probe targeting apoptotic macrophages. The as-synthesized (99m)Tc-GNPs-Annexin V was with uniform size (30.2 ± 2.9 nm) and high labeling rate (98.9 ± 0.5%) and stability. Targeting ability of Annexin V for apoptotic macrophages was kept and enhanced. For macrophages with 30% apoptosis, cellular uptakes of 3.52 ± 0.35% for (99m)Tc-GNPs-Annexin V, 2.41 ± 0.53% for (99m)Tc-GNPs and 1.68 ± 0.36% for (99m)Tc-Annexin V were achieved after 2 h incubation. ApoE knock out mice with high fat diet-induced atherosclerosis were scanned via (99m)Tc-GNPs-Annexin V SPECT/CT. With the introduction of targeting molecules, imaging probe was more efficient in accumulating in apoptotic macrophages. In practical evaluation, CT helps to restrict the lesions depiction more accurately, meanwhile, SPECT imaging intensity correlated with pathological changes tightly. In conclusion, Annexin V-modified hybrid gold nanoparticles were successfully synthesized, and this imaging system helped to better localize and diagnose those vulnerable AS plaques via specific targeting the apoptotic macrophages.

Bioengineered Magnetoferritin Nanoprobes for Single-Dose Nuclear-Magnetic Resonance Tumor Imaging.

Despite all the advances in multimodal imaging, it remains a significant challenge to acquire both magnetic resonance and nuclear imaging in a single dose because of the enormous difference in sensitivity. Indeed, nuclear imaging is almost 10(6)-fold more sensitive than magnetic resonance imaging (MRI); thus, repeated injections are generally required to obtain sufficient MR signals after nuclear imaging. Here, we show that strategically engineered magnetoferritin nanoprobes can image tumors with high sensitivity and specificity using SPECT and MRI in living mice after a single intravenous injection. The magnetoferritin nanoprobes composed of (125)I radionuclide-conjugated human H-ferritin iron nanocages ((125)I-M-HFn) internalize robustly into cancer cells via a novel tumor-specific HFn-TfR1 pathway. In particular, the endocytic recycling characteristic of TfR1 transporters solves the nuclear signal blocking issue caused by the high dose nanoprobes injected for MRI, thus enabling simultaneous functional and morphological tumor imaging without reliance on multi-injections.

99mTc-labelled anti-CD11b SPECT/CT imaging allows detection of plaque destabilization tightly linked to inflammation.

It remains challenging to predict the risk of rupture for a specific atherosclerotic plaque timely, a thrombotic trigger tightly linked to inflammation. CD11b, is a biomarker abundant on inflammatory cells, not restricted to monocytes/macrophages. In this study, we fabricated a probe named as (99m)Tc-MAG3-anti-CD11b for detecting inflamed atherosclerotic plaques with single photon emission computed tomography/computed tomography (SPECT/CT). The ApoE-knockout (ApoE(-/-)) mice were selected to establish animal models, with C57BL/6J mice used for control. A higher CD11b(+)-cell recruitment with higher CD11b expression and more serious whole-body inflammatory status were identified in ApoE(-/-) mice. The probe showed high in vitro affinity and specificity to the Raw-264.7 macrophages, as well as inflammatory cells infiltrated in atherosclerotic plaques, either in ex vivo fluorescent imaging or in in vivo micro-SPECT/CT imaging, which were confirmed by ex vivo planar gamma imaging, Oil-Red-O staining and CD11b-immunohistochemistry staining. A significant positive relationship was identified between the radioactivity intensity on SPECT/CT images and the CD11b expression in plaques. In summary, this study demonstrates the feasibility of anti-CD11b antibody mediated noninvasive SPECT/CT imaging of inflammatory leukocytes in murine atherosclerotic plaques. This imaging strategy can identify inflammation-rich plaques at risk for rupture and evaluate the effectiveness of inflammation-targeted therapies in atheroma.