Preclinical evaluation of Affibody molecule for PET imaging of human pancreatic islets derived from stem cells

Pierre Cheung; Julia Thorngren; Bo Zhang; Svitlana Vasylovska; Francesco Lechi; Jonas Persson; Stefan Ståhl; John Löfblom; Olle Korsgren; Jonas Eriksson; Joey Lau; Olof Eriksson

doi:10.1186/s13550-023-01057-3

Preclinical evaluation of Affibody molecule for PET imaging of human pancreatic islets derived from stem cells

EJNMMI Res. 2023 Dec 15;13(1):107. doi: 10.1186/s13550-023-01057-3.

Authors

Affiliations

¹ Science for Life Laboratory, Department of Medicinal Chemistry, Uppsala University, Uppsala, Sweden.
² Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden.
³ Department of Protein Science, Division of Protein Engineering, KTH Royal Institute of Technology, Stockholm, Sweden.
⁴ Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden.
⁵ Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden. joey.lau@mcb.uu.se.
⁶ Science for Life Laboratory, Department of Medicinal Chemistry, Uppsala University, Uppsala, Sweden. olof.eriksson@ilk.uu.se.

^# Contributed equally.

Abstract

Background: Beta-cell replacement methods such as transplantation of isolated donor islets have been proposed as a curative treatment of type 1 diabetes, but widespread application is challenging due to shortages of donor tissue and the need for continuous immunosuppressive treatments. Stem-cell-derived islets have been suggested as an alternative source of beta cells, but face transplantation protocols optimization difficulties, mainly due to a lack of available methods and markers to directly monitor grafts survival, as well as their localization and function. Molecular imaging techniques and particularly positron emission tomography has been suggested as a tool for monitoring the fate of islets after clinical transplantation. The integral membrane protein DGCR2 has been demonstrated to be a potential pancreatic islet biomarker, with specific expression on insulin-positive human embryonic stem-cell-derived pancreatic progenitor cells. The candidate Affibody molecule Z_DGCR2:AM106 was radiolabeled with fluorine-18 using a novel click chemistry-based approach. The resulting positron emission tomography tracer [¹⁸F]Z_DGCR2:AM106 was evaluated for binding to recombinant human DGCR2 and cryosections of stem-cell-derived islets, as well as in vivo using an immune-deficient mouse model transplanted with stem-cell-derived islets. Biodistribution of the [¹⁸F]Z_DGCR2:AM106 was also assessed in healthy rats and pigs.

Results: [¹⁸F]Z_DGCR2:AM106 was successfully synthesized with high radiochemical purity and yield via a pretargeting approach. [¹⁸F]Z_DGCR2:AM106 retained binding to recombinant human DCGR2 as well as to cryosectioned stem-cell-derived islets, but in vivo binding to native pancreatic tissue in both rat and pig was low. However, in vivo uptake of [¹⁸F]Z_DGCR2:AM106 in stem-cell-derived islets transplanted in the immunodeficient mice was observed, albeit only within the early imaging frames after injection of the radiotracer.

Conclusion: Targeting of DGCR2 is a promising approach for in vivo detection of stem-cell-derived islets grafts by molecular imaging. The synthesis of [¹⁸F]Z_DGCR2:AM106 was successfully performed via a pretargeting method to label a site-specific covalently bonded fluorine-18 to the Affibody molecule. However, the rapid washout of [¹⁸F]Z_DGCR2:AM106 from the stem-cell-derived islets graft indicates that dissociation kinetics can be improved. Further studies using alternative binders of similar classes with improved binding potential are warranted.

Keywords: Affibody molecule; DGCR2; Diabetes; Fluorine-18 chemistry; PET; Stem cells.