Peptidic heterodimer-based radiotracer targeting fibroblast activation protein and integrin αvß3.

PURPOSE: Several studies have demonstrated the advantages of heterodimers over their corresponding monomers due to the multivalency effect. This effect leads to an increased number of effective targeted receptors and, consequently, improved tumor uptake. Fibroblast activation protein (FAP) and integrin αvß3 are found to be overexpressed in different components of the tumor microenvironment. In our pursuit of enhancing tumor uptake and retention, we designed and developed a novel peptidic heterodimer that synergistically targets both FAP and integrin αvß3. METHODS: FAP-RGD was synthesized from FAP-2286 and c(RGDfK) through a multi-step organic synthesis. The dual receptor binding property of 68Ga-FAP-RGD was investigated by cell uptake and competitive binding assays. Preclinical pharmacokinetics were determined in HT1080-FAP and U87MG tumor models using micro-positron emission tomography/computed tomography (micro-PET/CT) and biodistribution studies. The antitumor efficacy of 177Lu-FAP-RGD was assessed in U87MG tumor models. The radiation exposure and clinical diagnostic performance of 68 Ga-FAP-RGD were evaluated in healthy volunteers and cancer patients. RESULTS: Bi-specific radiotracer 68Ga-FAP-RGD exhibited high binding affinity for both FAP and integrin αvß3. In comparison to 68Ga-FAP-2286 and 68Ga-RGDfK, 68Ga-FAP-RGD displayed enhanced tumor uptake and longer tumor retention time in preclinical models. 177Lu-FAP-RGD could efficiently suppress the growth of U87MG tumor in vivo when applied at an activity of 18.5 and 29.6 MBq. The effective dose of 68Ga-FAP-RGD was 1.06 × 10-2 mSv/MBq. 68Ga-FAP-RGD demonstrated low background activity and stable accumulation in most neoplastic lesions up to 3 h. CONCLUSION: Taking the advantages of multivalency effect, the bi-specific radiotracer 68Ga-FAP-RGD showed superior tumor uptake and retention compared to its corresponding monomers. Preclinical studies with 68Ga- or 177Lu-labeled FAP-RGD showed favorable image contrast and effective antitumor responses. Despite the excellent performance of 68Ga-FAP-RGD in clinical diagnosis, experimental efforts are currently underway to optimize the structure of FAP-RGD to increase its potential for clinical application in endoradiotherapy.

Expression of fructose-1,6-bisphosphatase 1 is associated with [18F]FDG uptake and prognosis in patients with mesial temporal lobe epilepsy.

OBJECTIVES: To determine whether fructose-1,6-bisphosphatase 1 (FBP1) expression is associated with [18F]FDG PET uptake and postsurgical outcomes in patients with mesial temporal lobe epilepsy (mTLE) and to investigate whether the molecular mechanism involving gamma-aminobutyric acid type A receptor (GABAAR), glucose transporter-3 (GLUT-3), and hexokinase-II (HK-II). METHODS: Forty-three patients with mTLE underwent [18F]FDG PET/CT. Patients were divided into Ia (Engel class Ia) and non-Ia (Engel class Ib-IV) groups according to more than 1 year of follow-up after surgery. The maximum standard uptake value (SUVmax) and asymmetry index (AI) of hippocampus were measured. The relationship among the SUVmax, AI, prognosis, and FBP1 expression was analyzed. A lithium-pilocarpine acute mTLE rat model was subjected to [18F]FDG micro-PET/CT. Hippocampal SUVmax and FBP1, GABAAR, GLUT-3, and HK-II expression were analyzed. RESULTS: SUVmax was higher in the Ia group than in the non-Ia group (7.31 ± 0.97 vs. 6.56 ± 0.96, p < 0.05) and FBP1 expression was lower in the Ia group (0.24 ± 0.03 vs. 0.27 ± 0.03, p < 0.01). FBP1 expression was negatively associated with SUVmax and AI (p < 0.01). In mTLE rats, the hippocampal FBP1 increased (0.26 ± 0.00 vs. 0.17 ± 0.00, p < 0.0001), and SUVmax, GLUT-3 and GABAAR levels decreased significantly (0.73 ± 0.12 vs. 1.46 ± 0.23, 0.20 ± 0.01 vs. 0.32 ± 0.05, 0.26 ± 0.02 vs. 0.35 ± 0.02, p < 0.05); no significant difference in HK-II levels was observed. In mTLE patients and rats, FBP1 negatively correlated with SUVmax and GLUT-3 and GABAAR levels (p < 0.05). CONCLUSION: FBP1 expression was inversely associated with SUVmax in mTLE, which might inhibit [18F]FDG uptake by regulating GLUT-3 expression. High FBP1 expression was indicative of low GABAAR expression and poor prognosis. KEY POINTS: • It is of paramount importance to explore the deep pathophysiological mechanisms underlying the pathogenesis of mesial temporal lobe epilepsy and find potential therapeutic targets. • [18F]FDG PET has demonstrated low metabolism in epileptic regions during the interictal period, and hypometabolism may be associated with prognosis, but the pathomechanism of this association remains uncertain. • Our results support the possibility that FBP1 might be simultaneously involved in the regulation of glucose metabolism levels and the excitability of neurons and suggest that targeting FBP1 may be a viable strategy in the diagnosis and treatment of mesial temporal lobe epilepsy.

Preclinical and first-in-human evaluation of 18F-labeled D-peptide antagonist for PD-L1 status imaging with PET.

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.