Radiolabelled CCK₂R Antagonists Containing PEG Linkers: Design, Synthesis and Evaluation

Abstract

The cholecystokinin‐2/gastrin receptor (CCK2R) is considered a suitable target for the development of radiolabelled antagonists, due to its overexpression in various tumours, but no such compounds are available in clinical use. Therefore, we designed novel 1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid‐conjugated ligands based on CCK2R antagonist Z360/nastorazepide. As a proof of concept that CCK2R antagonistic activity can be retained by extending the Z360/nastorazepide structure using suitable linker, we present herein three compounds containing various PEG linkers synthesised on solid phase and in solution. The antagonistic properties were measured in a functional assay in the A431‐CCK2R cell line (in the presence of agonist G17), with IC50 values of 3.31, 4.11 and 10.4 nM for compounds containing PEG4, PEG6 and PEG12, respectively. All compounds were successfully radiolabelled with indium‐111, lutetium‐177 and gallium‐68 (incorporation of radiometal >95 %). The gallium‐68‐labelled compounds were stable for up to 2 h (PBS, 37 °C). log D7.4 values were determined for indium‐111‐ and gallium‐68‐labelled compounds, showing improved hydrophilicity compared to the reference compound.

Peptide Radioligands in Cancer Theranostics: Agonists and Antagonists

“…Most efforts have used nastorazepide or else Z-360 (3-[[1-cyclohexyl-5-(3,3-dimethyl-2-oxobutyl)-4-oxo-2,3-dihydro-1,5-benzo-diazepin-3-yl]-carbamoylamino-benzoic acid) as a motif, with a free carboxy group amenable for coupling of suitable chelators either directly or via different linkers [ 154 , 155 ]. Coupling of N 3 S [ 156 ] or N 4 [ 14 ] chelators has allowed for labeling with Tc-99m for SPECT imaging, whereas coupling of DOTA, DOTAGA and NODAGA allows the stable coordination of theranostic trivalent radiometals for SPECT or PET imaging and for radionuclide therapy, as presented in Figure 11 [ 157 , 158 , 159 ]. Preclinical results thus far acquired are quite promising and further studies are warranted to provide evidence on the validity of this option.…”

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

“…Although a hitherto restricted number of other Z360 analogs carrying the DOTA-chelator through different linkers was developed [ 55 ], animal data was only reported for [ 111 In]In-IP-001, but in a mice model different to ours [ 56 ]. Thus, an A549 non-small cell lung cancer xenograft was implanted in the shoulder of homozygous female BALB/c nude mice.…”

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

“…However, this was accompanied by a higher kidney retention, impairing the tumor-to-kidney ratios for both radioligands. Furthermore, DOTA-conjugated CCK2R antagonists for possible theranostic use have recently been developed [ 31 , 51 ]. Z-360 conjugated to DOTA through a combination of a tripeptide linker and PEG spacers of different length yielded derivatives with retained CCK2R affinity and antagonistic properties.…”

“…Z-360 conjugated to DOTA through a combination of a tripeptide linker and PEG spacers of different length yielded derivatives with retained CCK2R affinity and antagonistic properties. The DOTA-conjugates radiolabeled with indium-111, lutetium-177 and gallium-68 further showed improved hydrophilicity [ 31 , 51 , 52 ]. [ 111 In]In-IP-001, containing Z-360 conjugated to DOTA through a short alkyl chain followed by a PEGylated portion, has been evaluated in a human cell line with physiological CCK2R expression.…”

“… 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 ]). …”