Background: Nanobodies are single-domain antibodies that have gained popularity for various imaging techniques, including positron emission tomography (PET) due to their small size, high affinity and specificity to the target, and rapid blood clearance. A novel nanobody, NOTA-4hD29 with nanomolar affinity for human dipeptidyl peptidase 6 (DPP6) was developed as an alpha and beta cell-specific biomarker for the detection of pancreatic islets by PET. It enables non-invasive, longitudinal detection and quantification of islets of Langerhans, in the human pancreas or graft site post islet transplantation.

Method: The synthesis of [68Ga]NCS-NOTA-4hD29 was performed manually using a 68Ge/68Ga generator. Binding specificity was assessed via autoradiography with frozen sections of human islets (24%, 43%, and 90% purity) and islet-devoid exocrine pancreatic tissue. Specificity was validated by pre-blocking with excess unlabeled NOTA-4hD29. Stability of [68Ga]NCS-NOTA-4hD29 was tested in human plasma and in vivo in rats. In vivo biodistribution and plasma stability were evaluated in healthy rats and pig using PET/CT. Fluorescence labeling of 4hD29 evaluated its stability and internalization in EndoC-βH1 cells.

Results: [68Ga]NCS-NOTA-4hD29 radiosynthesis yielded 96.9% ± 1.47, with 99.6% ± 0.2 radiochemical purity. It demonstrated high affinity to human islets (r=0.98, p<0.05), minimal binding to the exocrine pancreas, and complete signal abolition with blocking. In vitro stability in human plasma exceeded 90% after 60 min; in vivo rat plasma stability was ∼55% after 60 min. In vivo biodistribution in rats and pig showed renal excretion (kidney SUV > 10) with low background. The 4hD29 nanobody underwent EndoC-βH1 cell endocytosis, remaining detectable in the cytosol for 6 h.

Conclusions: [68Ga]NCS-NOTA-4hD29 demonstrated excellent specificity and could differentiate between small differences in islet numbers.

Disclosure

A. Khalil: None. A. Roca Rivada: None. I. Velikyan: None. A. Bitzios: None. P. Serafini: None. D.L. Eizirik: None. O. Eriksson: Employee; Antaros Medical. Stock/Shareholder; Antaros Tracer AB.

© 2024 by the American Diabetes Association
2024
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