Stabilization Strategies for Linear Minigastrin Analogues: Further Improvements via the Inclusion of Proline into the Peptide Sequence

Abstract

Minigastrin (MG) analogues, known for their high potential to target cholecystokinin-2 receptor (CCK2R) expressing tumors, have limited clinical applicability due to low enzymatic stability. By introducing site-specific substitutions within the C-terminal receptor-binding sequence, reduced metabolization and improved tumor targeting can be achieved. In this work, the influence of additional modification within the N-terminal sequence has been explored. Three novel 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-conjugated CCK2R ligands with proline substitution at different positions were synthesized. Substitution did not affect CCK2R affinity, and the conjugates labeled with indium-111 and lutetium-177 showed a high enzymatic stability in different incubation media as well as in vivo (57–79% intact radiopeptide in blood of BALB/c mice at 1 h p.i.) combined with enhanced tumor uptake (29–46% IA/g at 4 h in xenografted BALB/c nude mice). The inclusion of Pro contributes significantly to the development of CCK2R ligands with optimal targeting properties for application in targeted radiotherapy.

Die bedeutende nicht-proteinogene Aminosäure Norleucin und ihre komplizierte Namensfindung

“…[15] Humanes Minigastrin (MG) ist ein aus 13 Aminosäuren bestehendes Peptid und natürlicher Ligand des Cholecystokinin-2-Rezeptors (CCK2R), der in bestimmten Tumoren stark überexprimiert ist. [16] Die Verknüpfung von Minigastrin-Analoga bzw. verkürzten Ketten mit geeigneten Chelatoren für radioaktive und daher cytotoxische Metallisotope ist eine seit mehr als 20 Jahren erfolgreich erprobte Strategie.…”

“…verkürzten Ketten mit geeigneten Chelatoren für radioaktive und daher cytotoxische Metallisotope ist eine seit mehr als 20 Jahren erfolgreich erprobte Strategie. [16,17] Ein Beispiel für ein solches Konjugat ist das mit dem Chelator 1,4,7,10-Tetraazacyclododecan-1,4,7,10-tetraessigsäure (DOTA) ausgestattete [Nle 15 ]MG11 16 (Abb. 5, unten).…”

Nonpeptidic Z360-Analogs Tagged with Trivalent Radiometals as Anti-CCK2R Cancer Theranostic Agents: A Preclinical Study

“…As mentioned above, this feature becomes particularly important for therapeutic purposes due to dosimetric restrictions [ 8 ]. Interestingly, the injection of higher peptide amounts was shown to reduce stomach uptake in preclinical models, but it is associated with more biosafety risks in the case of CCK 2 R-agonists [ 54 ].…”

Update on Preclinical Development and Clinical Translation of Cholecystokinin-2 Receptor Targeting Radiopharmaceuticals

“…Recently the synthesis of [ 68 Ga]Ga-DOTA-MGS5 using an automated synthesis module was validated and non-clinical safety studies in support of a first exploratory clinical trial were carried out for this new CCK2R targeting PET imaging agent [ 40 ]. Additional stabilization in the N-terminal part of DOTA-MGS5 by introducing the amino acid proline containing a cyclic pyrrolidine side chain in different positions led to comparable metabolically stable analogs with a biodistribution profile similar to DOTA-MGS5 [ 30 , 41 ]. The introduction of the above C-terminal amino acid substitutions was also investigated for CP04 in combination with additional N-methylation of Gly in position 9.…”

“… Recent developments aiming towards optimizing CCK2R targeting (as described in references: [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ]). …”