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Purpose: Stimulator of interferon genes (STING) protein plays a vital role in the immune surveillance of tumor microenvironment. Monitoring STING expression in tumors benefits the relevant STING therapy. This study aimed to develop a novel 18F-labeled agonist, dimeric amidobenzimidazole (diABZI), and firstly evaluate the feasibility of noninvasive positron emission tomography (PET) imaging of STING expression in the tumor microenvironment. Methods: An analog of the STING agonist NOTA-DABI was synthesized and labeled with 18F via Al18F-NOTA complexation (denoted as [18F]F-DABI). Physicochemical properties, STING protein-binding affinity, and specificity of [18F]F-DABI were evaluated using cell uptake and docking assays. In vivo small-animal PET imaging and biodistribution studies of [18F]F-DABI in tumor-bearing mice were performed to verify the pharmacokinetics and tumor targeting ability. The correlation between tumor uptake and STING expression was also analyzed. Results: [18F]F-DABI was produced conveniently with high radiochemical yield (44 ± 15%), radiochemical purity (> 97%) and molar activity (15–30 GBq/μmol). In vitro binding assays demonstrated that [18F]F-DABI has a favorable affinity and specificity for STING with a KD of 12.98 ± 2.07 nM. In vivo studies demonstrated the specificity of [18F]F-DABI for PET imaging of STING expression with B16F10 tumor uptake of 10.93 ± 0.93%ID/g, which was significantly different from that of blocking groups (3.13 ± 0.88%ID/g, ***p < 0.0001). Furthermore, tumor uptake of [18F]F-DABI was well positively correlated with STING expression in different tumor types. Biodistribution results demonstrated that [18F]F-DABI was predominately uptaken in the liver and intestines, indicating its hepatobiliary elimination. Conclusion: This proof-of-concept study demonstrated a STING-binding radioligand for PET imaging, which could be used as a potential companion diagnostic tool for related STING-agonist therapies. [ABSTRACT FROM AUTHOR]

Purpose: PD-L1 PET imaging allows for the whole body measuring its expression across primary and metastatic tumors and visualizing its spatiotemporal dynamics before, during, and after treatment. In this study, we reported a novel 18F-labeled D-peptide antagonist, 18F-NOTA-NF12, for PET imaging of PD-L1 status in preclinical and first-in-human studies. Methods: Manual and automatic radiosynthesis of 18F-NOTA-NF12 was performed. Cell uptake and binding assays were completed in MC38, H1975, and A549 cell lines. The capacity for imaging of PD-L1 status, biodistribution, and pharmacokinetics were investigated in preclinical models. The PD-L1 status was verified by western blotting, immunohistochemistry/fluorescence, and flow cytometry. The safety, radiation dosimetry, biodistribution, and PD-L1 imaging potential were evaluated in healthy volunteers and patients. Results: The radiosynthesis of 18F-NOTA-NF12 was achieved via manual and automatic methods with radiochemical yields of 41.7 ± 10.2 % and 70.6 ± 4.2 %, respectively. In vitro binding assays demonstrated high specificity and affinity with an IC50 of 78.35 nM and KD of 85.08 nM. The MC38 and H1975 tumors were clearly visualized with the optimized tumor-to-muscle ratios of 5.36 ± 1.17 and 7.13 ± 1.78 at 60 min after injection. Gemcitabine- and selumetinib-induced modulation of PD-L1 dynamics was monitored by 18F-NOTA-NF12. The tumor uptake correlated well with their PD-L1 expression. 18F-NOTA-NF12 exhibited renal excretion and rapid clearance from blood and other non-specific organs, contributing to high contrast imaging in the clinical time frame. In NSCLC and esophageal cancer patients, the specificity of 18F-NOTA-NF12 for PD-L1 imaging was confirmed. The 18F-NOTA-NF12 PET/CT and 18F-FDG PET/CT had equivalent findings in patients with high PD-L1 expression. Conclusion: 18F-NOTA-NF12 was developed successfully as a PD-L1-specific tracer with promising results in preclinical and first-in-human trials, which support the further validation of 18F-NOTA-NF12 for PET imaging of PD-L1 status in clinical settings. [ABSTRACT FROM AUTHOR]

Purpose: While TIGIT has been propelled as a next-generation target in cancer immunotherapy, anti-TIGIT therapy seems to be promising for a fraction of patients in clinical trials. Therefore, patient stratification is critical for this therapy, which could benefit from a whole-body, non-invasive, and quantitative evaluation of TIGIT expression in cancers. In this study, a 68Ga-labeled D-peptide antagonist, 68Ga-GP12, was developed and validated for PET imaging of TIGIT expression in vitro, in vivo, and in an exploratory human study. Methods: The D-enantiomer peptide antagonists were modified and radiolabeled with 68Ga. In vitro binding assays were performed in human peripheral blood mononuclear cells (PBMCs) to assess their affinity and specificity. The imaging capacity, biodistribution, pharmacokinetics, and radiation dosimetry were investigated. Flow cytometry, autoradiography, and immunohistochemical staining were used to confirm the expression of TIGIT. The safety and potential of 68Ga-GP12 for PET/CT imaging of TIGIT expression were evaluated in NSCLC patients. Results: 68Ga-labeled D-peptides were conveniently produced with high radiochemical yields, radiochemical purities and molar activities. In vitro binding assays demonstrated 68Ga-GP12 has high affinity and specificity for TIGIT with a KD of 37.28 nM. In vivo and ex vivo studies demonstrated the capacity of 68Ga-GP12 for PET imaging of TIGIT expression with high tumor uptake of 4.22 ± 0.68 %ID/g and the tumor-to-muscle ratio of 12.94 ± 2.64 at 60 min post-injection. In NSCLC patients, primary and metastatic lesions found in 68Ga-GP12 PET images were comparable to that in 18F-FDG PET images. Moreover, tracer uptake in primary and metastatic lesions and intra-tumoral distribution in the large tumor were inhomogenous, indicating the heterogeneity of TIGIT expression. Conclusion: 68Ga-GP12 is a promising radiotracer for PET imaging of TIGIT expression in cancers, indicating its potential as a potential companion diagnostic for anti-TIGIT therapies. [ABSTRACT FROM AUTHOR]