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Biomarkers for the measurement of islets of Langerhans could help elucidate the etiology of diabetes. Synaptic vesicle glycoprotein 2 A (SV2A) is a potential marker reported to be localized in the endocrine pancreas. [11C]UCB-J is a novel positron emission tomography (PET) radiotracer that binds to SV2A and was previously evaluated as a synaptic marker in the central nervous system. Here, we evaluated whether [11C]UCB-J could be utilized as a PET tracer for the islets of Langerhans in the pancreas by targeting SV2A. The mRNA transcription of SV2A was evaluated in human isolated islets of Langerhans and exocrine tissue. In vitro autoradiography was performed on pancreas and brain sections from rats and pigs, and consecutive sections were immunostained for insulin. Sprague–Dawley rats were examined with PET-MRI and ex vivo autoradiography at baseline and with administration of levetiracetam (LEV). Similarly, pigs were examined with dynamic PET-CT over the pancreas and brain after administration of [11C]UCB-J at baseline and after pretreatment with LEV. In vivo radioligand binding was assessed using a one-compartment tissue model. The mRNA expression of SV2A was nearly 7 times higher in endocrine tissue than in exocrine tissue (p < 0.01). In vitro autoradiography displayed focal binding of [11C]UCB-J in the pancreas of rats and pigs, but the binding pattern did not overlap with the insulin-positive areas or with ex vivo autoradiography. In rats, pancreas binding was higher than that in negative control tissues but could not be blocked by LEV. In pigs, the pancreas and brain exhibited accumulation of [11C]UCB-J above the negative control tissue spleen. While brain binding could be blocked by pretreatment with LEV, a similar effect was not observed in the pancreas. Transcription data indicate SV2A to be a valid target for imaging islets of Langerhans, but [11C]UCB-J does not appear to have sufficient sensitivity for this application. [ABSTRACT FROM AUTHOR]

Unimolecular dual agonists for the glucagon-like peptide 1 receptor (GLP1R) and glucagon receptor (GCGR) are emerging as a potential new class of important therapeutics in type 2 diabetes (T2D). Reliable and quantitative assessments of in vivo occupancy on each receptor would improve the understanding of the efficacy of this class of drugs. In this study we investigated the target occupancy of the dual agonist SAR425899 at the GLP1R in pancreas and GCGR in liver by Positron Emission Tomography/Computed Tomography (PET/CT). Patients with T2D were examined by [68Ga]Ga-DO3A-Tuna-2 and [68Ga]Ga-DO3A-Exendin4 by PET, to assess the GCGR in liver and GLP1R in pancreas, respectively. Follow up PET examinations were performed after 17 (GCGR) and 20 (GLP-1R) days of treatment with SAR425899, to assess the occupancy at each receptor. Six out of 13 included patients prematurely discontinued the study due to adverse events. SAR425899 at a dose of 0.2 mg daily demonstrated an average GCGR occupancy of 11.2 ± 14.4% (SD) in N = 5 patients and a GLP1R occupancy of 49.9 ± 13.3%. Fasting Plasma Glucose levels (− 3.30 ± 1.14 mmol/L) and body weight (− 3.87 ± 0.87%) were lowered under treatment with SAR425899. In conclusion, SAR425899 demonstrated strong interactions at the GLP1R, but no clear occupancy at the GCGR. The study demonstrates that quantitative target engagement of dual agonists can be assessed by PET. [ABSTRACT FROM AUTHOR]

The glucagon receptor (GCGR) is an emerging target in anti-diabetic therapy. Reliable biomarkers for in vivo activity on the GCGR, in the setting of dual glucagon-like peptide 1/glucagon (GLP-1/GCG) receptor agonism, are currently unavailable. Here, we investigated [68Ga]Ga-DO3A-S01-GCG as a biomarker for GCGR occupancy in liver, the tissue with highest GCGR expression, in non-human primates (NHP) by PET. [68Ga]Ga-DO3A-S01-GCG was evaluated by dynamic PET in NHPs by a dose escalation study design, where up to 67 µg/kg DO3A-S01-GCG peptide mass was co-injected. The test-retest reproducibility of [68Ga]Ga-DO3A-S01-GCG binding in liver was evaluated. Furthermore, we investigated the effect of pre-treatment with acylated glucagon agonist 1-GCG on [68Ga]Ga-DO3A-S01-GCG binding in liver. [68Ga]Ga-DO3A-S01-GCG bound to liver in vivo in a dose-dependent manner. Negligible peptide mass effect was observed for DO3A-S01-GCG doses <0.2 µg/kg. In vivo Kd for [68Ga]Ga-DO3A-S01-GCG corresponded to 0.7 µg/kg, which indicates high potency. The test-retest reproducibility for [68Ga]Ga-DO3A-S01-GCG binding in liver was 5.7 ± 7.9%. Pre-treatment with 1-GCG, an acylated glucagon agonist, resulted in a GCGR occupancy of 61.5 ± 9.1% in liver. Predicted human radiation dosimetry would allow for repeated annual [68Ga]Ga-DO3A-S01-GCG PET examinations. In summary, PET radioligand [68Ga]Ga-DO3A-S01-GCG is a quantitative biomarker of in vivo GCGR occupancy. [ABSTRACT FROM AUTHOR]