One Step Closer to Clinical Translation: Enhanced Tumor Targeting of [(99m)Tc]Tc-DB4 and [(111)In]In-SG4 in Mice Treated with Entresto

Background: Peptide radioligands may serve as radionuclide carriers to tumor sites overexpressing their cognate receptor for diagnostic or therapeutic purposes. Treatment of mice with the neprilysin (NEP)-inhibitor phosphoramidon was previously shown to improve the metabolic stability and tumor uptake of biodegradable radiopeptides. Aiming to clinical translation of this methodology, we herein investigated the impact of the approved pill Entresto, releasing the potent NEP-inhibitor LBQ657 in vivo, on the stability and tumor uptake of two radiopeptides. Methods: The metabolic stability of [(99m)Tc]Tc-DB4 (DB4, N(4)-Pro-Gln-Arg-Tyr-Gly-Asn-Gln-Trp-Ala-Val-Gly-His-Leu-Nle-NH(2)) and [(111)In]In-SG4 (SG4, DOTA-DGlu-Ala-Tyr-Gly-Trp-Nle-Asp-Phe-NH(2)) was tested in LBQ657/Entresto-treated mice vs. untreated controls. The uptake in gastrin-releasing peptide receptor (GRPR)-, or cholecystokinin subtype 2 receptor (CCK(2)R)-positive tumors respectively, was compared between LBQ657/Entresto-treated mice and untreated controls. Results: LBQ657/Entresto treatment induced marked stabilization of [(99m)Tc] Tc-DB4 and [(111)In]In-SG4 in peripheral mice blood, resulting in equally enhanced tumor uptake at 4 h post-injection. Accordingly, the [(99m)Tc]Tc-DB4 uptake of 7.13 ± 1.76%IA/g in PC-3 tumors increased to 16.17 ± 0.71/17.50 ± 3.70%IA/g (LBQ657/Entresto) and the [(111)In]In-SG4 uptake of 3.07 ± 0.87%IA/g in A431-CCK(2)R(+) tumors to 8.11 ± 1.45/9.61 ± 1.70%IA/g. Findings were visualized by SPECT/CT. Conclusions: This study has shown the efficacy of Entresto to notably improve the profile of [(99m)Tc]Tc-DB4 and [(111)In]In-SG4 in mice, paving the way for clinical translation of this approach.