**5. Conclusions**

In this study, a CCK-2R-targeting ligand based on the nastorazepide core was synthetized and functionalized with a DOTA chelator with the aim to provide a suitable platform for a theragnostic approach with radioactive metals. Avoiding the use of peptidebased sequences in the structure, including the linker, allowed us to obtain a molecule with high stability in physiological media and that could be easily labelled with indium-111 as pivotal radionuclide for future studies. The obtained radiotracer was successfully employed in the imaging of CCK-2R-expressing xenograft tumor in mice, but further structural studies are needed for enhancing receptor affinity and biodistribution. Additionally, the presented results are particularly noteworthy since the ability of a targeting probe to image cancers has been demonstrated using human cells expressing physiological levels of CCK-2R instead of transfected cells like the majority of the studies on the topic so far.

**Supplementary Materials:** The following are available online: Figure S1: <sup>1</sup>H NMR spectrum of **3** Figure S2: <sup>1</sup>H NMR spectrum of **4**; Figure S3: <sup>1</sup>H NMR spectrum of **6**; Figure S4: <sup>1</sup>H NMR spectrum of **7**; Figure S5: <sup>1</sup>H NMR spectrum of **8**; Figure S6: <sup>1</sup>H NMR spectrum of IP-001; Figure S7: HRMS analysis of IP-001; Figure S8: Representative RP-HPLC chromatograms of free [111In]In3+ (**A**) and [ <sup>111</sup>In]In-IP-001 (**B**); Figure S9: Representative radio-TLC chromatograms of free-[111In]In3+ (**A**) and [ <sup>111</sup>In]In-IP-001 (**B**); Figure S10. <sup>1</sup>H NMR spectrum of the compound due to the cyclization of the succinyl-group of compound **2**.

**Author Contributions:** Conceptualization, M.A., G.M., and F.M.; methodology, M.V., S.R., S.C., S.S., F.B., M.T., and E.V.; writing—original draft preparation, M.A., S.C.; writing—review and editing, M.V., M.A., S.C, G.M., and F.M.; supervision, M.A., G.M., and F.M.; funding acquisition, M.A. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Italian Ministry of Health as part of the program "5perMille, year 2016" promoted by the AUSL-IRCCS of Reggio Emilia and by the project "ISOL-PHARM\_EIRA", an experiment promoted in the framework of the National Scientific Committee 5 (Technological, inter-disciplinary and accelerators research) of INFN.

**Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the General Directorate of Veterinary Services (Athens, Attica Prefecture, Greece) and by the Bioethical Committee of BIOEMTECH Laboratories (protocol code EL 25 BIOexp 045, 12/3/2019).

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Raw data are available at the following link: https://drive.google. com/drive/u/1/folders/1ohexfcWTNlfLvz5n42\_VpdiXBGlh8DlL.

**Acknowledgments:** Authors thank BIOEMTECH Laboratories (Athens, Greece) for hosting the in vivo and imaging part of this study and Chiara Coruzzi for the bibliographic research.

**Conflicts of Interest:** S.S. is a BIOEMTECH employees. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

**Sample Availability:** Samples of the compound IP-001 are available from the authors.
