Key-Protease Inhibition Regimens Promote Tumor Targeting of Neurotensin Radioligands

Abstract

Neurotensin subtype 1 receptors (NTS1R) represent attractive molecular targets for directing radiolabeled neurotensin (NT) analogs to tumor lesions for diagnostic and therapeutic purposes. This approach has been largely undermined by the rapid in vivo degradation of linear NT-based radioligands. Herein, we aim to increase the tumor targeting of three 99mTc-labeled NT analogs by the in-situ inhibition of two key proteases involved in their catabolism. DT1 ([N4-Gly7]NT(7-13)), DT5 ([N4-βAla7,Dab9]NT(7-13)), and DT6 ([N4-βAla7,Dab9,Tle12]]NT(7-13)) were labeled with 99mTc. Their profiles were investigated in NTS1R-positive colon adenocarcinoma WiDr cells and mice treated or not with the neprilysin (NEP)-inhibitor phosphoramidon (PA) and/or the angiotensin converting enzyme (ACE)-inhibitor lisinopril (Lis). Structural modifications led to the partial stabilization of 99mTc-DT6 in peripheral mice blood (55.1 ± 3.9% intact), whereas 99mTc-DT1 and 99mTc-DT5 were totally degraded within 5 min. Coinjection of PA and/or Lis significantly stabilized all three analogs, leading to a remarkable enhancement of tumor uptake for 99mTc-DT1 and 99mTc-DT5, but was less effective in the case of poorly internalizing 99mTc-DT6. In conclusion, NEP and/or ACE inhibition represents a powerful tool to improve tumor targeting and the overall pharmacokinetics of NT-based radioligands, and warrants further validation in the field of NTS1R-targeted tumor imaging and therapy.

Optimizing the Profile of [99mTc]Tc–NT(7–13) Tracers in Pancreatic Cancer Models by Means of Protease Inhibitors

“…The [ 99m Tc]Tc-DT5 was not included in this study, in view of its inferior uptake by AsPC-1 cells compared with [ 99m Tc]Tc-DT1 (Figure 2b). In addition, it displayed high renal values in mice during a previous study, most probably as a result of the pendant δ-amine of Dab 9 in the peptide chain [39]. We observe that the radioactivity in the blood and the body of mice has substantially cleared at 4 h pi.…”

“…Aiming to elucidate these findings, we further studied the cell binding capabilities and in vivo stability of the radiotracer. We observed that the Tle 12 /Ile 12 substitution led to poor binding/internalization of [ 99m Tc]Tc-DT6 in WiDr cells compared with non-Ile 12 -substituted radioligands (e.g., 1.0 ± 0.4% specific cell binding vs. 10.1 ± 2.3% of [ 99m Tc]Tc-DT1 at 1 h incubation; p < 0.0001) [39]. Furthermore, the in vivo stability of [ 99m Tc]Tc-DT6 was found to be surprisingly lower than expected from in vitro assays (only 55.1 ± 3.9% of the radiotracer detected intact in peripheral mice blood at 5 min pi).…”

“…In a recent study, we were able to demonstrate the involvement of ACE and NEP in the in vivo degradation of [ 99m Tc]Tc-DT1 ([ 99m Tc]Tc-[N 4 -Gly 7 ]NT (7)(8)(9)(10)(11)(12)(13)) and [ 99m Tc]Tc-DT5 ([ 99m Tc]Tc-[N 4 -βAla 7 ,Dab 9 ]NT(7-13)) [39]. Furthermore, we showed that co-injection of the NEP inhibitor phosphoramidon (PA) [40] and the ACE inhibitor lisinopril (Lis) [41] resulted in significant stabilization of these radiotracers in peripheral mouse blood.…”

“…Furthermore, we showed that co-injection of the NEP inhibitor phosphoramidon (PA) [40] and the ACE inhibitor lisinopril (Lis) [41] resulted in significant stabilization of these radiotracers in peripheral mouse blood. Consequently, the uptake of both [ 99m Tc]Tc-DT1 and [ 99m Tc]Tc-DT5 in human NTS1R-positive colon adenocarcinoma tumors in mice was significantly enhanced [39]. Following this rationale, we are now interested in translating these positive findings into pancreatic cancer models.…”

Between two storms, vasoactive peptides or bradykinin underlie severity of COVID‐19?

“…Within the context of bradykinin and substance P, and their pro‐inflammatory actions, it is important to recognize that that another bioactive peptide neurotensin is also degraded by ACE and neprilysin (Kanellopoulos et al, 2020; Skidgel & Erdos, 2004). However, the clinical significance of elevated neurotensin levels in response to inhibition of ACE or neprilysin has not been systematically studied.…”