Targeting of cholecystokinin-2 receptor (CCK2R) expressing tumors using radiolabeled minigastrin (MG) analogs is hampered by rapid digestion of the linear peptide in vivo. In this study, a new MG analog stabilized against enzymatic degradation was investigated in preclinical studies to characterize the metabolites formed in vivo. The new MG analog DOTA-DGlu-Pro-Tyr-Gly-Trp-(N-Me)Nle-Asp-1Nal-NH2 comprising site-specific amino acid substitutions in position 2, 6 and 8 and different possible metabolites thereof were synthesized. The receptor interaction of the peptide and selected metabolites was evaluated in a CCK2R-expressing cell line. The enzymatic stability of the 177Lu-labeled peptide analog was evaluated in vitro in different media as well as in BALB/c mice up to 1 h after injection and the metabolites were identified based on radio-HPLC analysis. The new radiopeptide showed a highly increased stability in vivo with >56% intact radiopeptide in the blood of BALB/c mice 1 h after injection. High CCK2R affinity and cell uptake was confirmed only for the intact peptide, whereas enzymatic cleavage within the receptor specific C-terminal amino acid sequence resulted in complete loss of affinity and cell uptake. A favorable biodistribution profile was observed in BALB/c mice with low background activity, preferential renal excretion and prolonged uptake in CCK2R-expressing tissues. The novel stabilized MG analog shows high potential for diagnostic and therapeutic use. The radiometabolites characterized give new insights into the enzymatic degradation in vivo.

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The outbreak of the second severe acute respiratory syndrome coronavirus (SARS-CoV-2) known as COVID-19 has caused global concern. No effective vaccine or treatment to control the virus has been approved yet. Social distancing and precautionary protocols are still the only way to prevent person-to-person transmission. We hope to identify anti-COVID-19 activity of the existing drugs to overcome this pandemic as soon as possible. The present study used HEX and AutoDock Vina softwares to predict the affinity of about 100 medicinal structures toward the active site of 3-chymotrypsin-like protease (3Clpro) and RNA-dependent RNA polymerase (RdRp), separately. Afterwards, MOE software and the pharmacophore-derived query methodology were employed to determine the pharmacophore model of their inhibitors. Tegobuvir ( 19 ) and compound 45 showed the best binding affinity toward RdRp and 3Clpro of SARS-CoV-2 in silico, respectively. Tegobuvir -previously applied for hepatitis C virus- formed highly stable complex with uncommon binding pocket of RdRp (E total: −707.91 Kcal/mol) in silico. In addition to compound 45 , tipranavir ( 28 ) and atazanavir ( 26 ) as FDA-approved HIV protease inhibitors were tightly interacted with the active site of SARS-CoV-2 main protease as well. Based on pharmacophore modelling, a good structural pattern for potent candidates against SARS-CoV-2 main enzymes is suggested. Re-tasking or taking inspiration from the structures of tegobuvir and tipranavir can be a proper approach toward coping with the COVID-19 in the shortest possible time and at the lowest cost.