Preclinical Characterization of a Stabilized Gastrin-Releasing Peptide Receptor Antagonist for Targeted Cancer Theranostics

Ayman Abouzayed; Panagiotis Kanellopoulos; Alisa Gorislav; Vladimir Tolmachev; Theodosia Maina; Berthold A Nock; Anna Orlova

doi:10.3390/biom13071134

Preclinical Characterization of a Stabilized Gastrin-Releasing Peptide Receptor Antagonist for Targeted Cancer Theranostics

Biomolecules. 2023 Jul 14;13(7):1134. doi: 10.3390/biom13071134.

Authors

Ayman Abouzayed¹, Panagiotis Kanellopoulos^{1

2}, Alisa Gorislav¹, Vladimir Tolmachev³, Theodosia Maina², Berthold A Nock², Anna Orlova^{1

4}

Affiliations

¹ Department of Medicinal Chemistry, Uppsala University, 751 83 Uppsala, Sweden.
² Molecular Radiopharmacy, INRaSTES, NCSR "Demokritos", 15310 Athens, Greece.
³ Department of Immunology, Genetics and Pathology, Uppsala University, 751 83 Uppsala, Sweden.
⁴ Science for Life Laboratory, Uppsala University, 752 37 Uppsala, Sweden.

Abstract

Radiolabeled gastrin-releasing peptide receptor (GRPR) antagonists have shown great promise for the theranostics of prostate cancer; however, their suboptimal metabolic stability leaves room for improvements. It was recently shown that the replacement of Gly¹¹ with Sar¹¹ in the peptidic [D-Phe⁶,Leu¹³-NHEt,des-Met¹⁴]BBN(6-14) chain stabilized the [^99mTc]Tc-DB15 radiotracer against neprilysin (NEP). We herein present DOTAGA-PEG₂-(Sar¹¹)RM26 (AU-RM26-M1), after Gly¹¹ to Sar¹¹-replacement. The impact of this replacement on the metabolic stability and overall biological performance of [¹¹¹In]In-AU-RM26-M1 was studied using a head-to-head comparison with the unmodified reference [¹¹¹In]In-DOTAGA-PEG₂-RM26. In vitro, the cell uptake of [¹¹¹In]In-AU-RM26-M1 could be significantly reduced in the presence of a high-excess GRPR-blocker that demonstrated its specificity. The cell uptake of both radiolabeled GRPR antagonists increased with time and was superior for [¹¹¹In]In-AU-RM26-M1. The dissociation constant reflected strong affinities for GRPR (500 pM for [¹¹¹In]In-AU-RM26-M1). [¹¹¹In]In-AU-RM26-M1 showed significantly higher stability in peripheral mice blood at 5 min pi (88 ± 8% intact) than unmodified [¹¹¹In]In-DOTAGA-PEG₂-RM26 (69 ± 2% intact; p < 0.0001). The administration of a NEP inhibitor had no significant impact on the Sar¹¹-compound (91 ± 2% intact; p > 0.05). In vivo, [¹¹¹In]In-AU-RM26-M1 showed high and GRPR-mediated uptake in the PC-3 tumors (7.0 ± 0.7%IA/g vs. 0.9 ± 0.6%IA/g in blocked mice) and pancreas (2.2 ± 0.6%IA/g vs. 0.3 ± 0.2%IA/g in blocked mice) at 1 h pi, with rapid clearance from healthy tissues. The tumor uptake of [¹¹¹In]In-AU-RM26-M1 was higher than for [¹¹¹In]In-DOTAGA-PEG₂-RM26 (at 4 h pi, 5.7 ± 1.8%IA/g vs. 3 ± 1%IA/g), concordant with its higher stability. The implanted PC-3 tumors were visualized with high contrast in mice using [¹¹¹In]In-AU-RM26-M1 SPECT/CT. The Gly¹¹ to Sar¹¹-substitution stabilized [¹¹¹In]In-DOTAGA-PEG₂-(Sar¹¹)RM26 against NEP without negatively affecting other important biological features. These results support the further evaluation of AU-RM26-M1 for prostate cancer theranostics after labeling with clinically relevant radionuclides.

Keywords: GRPR antagonist; PC-3 cells; neprilysin; prostate cancer; theranostics.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Animals
Cell Line, Tumor
Humans
Male
Mice
Precision Medicine
Prostatic Neoplasms* / diagnostic imaging
Prostatic Neoplasms* / drug therapy
Prostatic Neoplasms* / metabolism
Receptors, Bombesin* / antagonists & inhibitors
Receptors, Bombesin* / metabolism

Substances

Receptors, Bombesin

Grants and funding

This research was funded by the Swedish Research Council (Vetenskaprådet), grant number 2022-00556, and the Swedish Cancer Society (Cancerfonden), grant number “20 0815 PjF”.