Preclinical Evaluation of the GRPR-Targeting Antagonist RM26 Conjugated to the Albumin-Binding Domain for GRPR-Targeting Therapy of Cancer.

Ayman Abouzayed,Vladimir Tolmachev,Amelie Eriksson Karlström,Anna Orlova,Sharmishtaa Kumar,Ábel Nagy,Kristina Westerlund,Sara S Rinne,Fadya Wadeea,Hanna Tano

doi:10.3390/pharmaceutics12100977

Abstract

The targeting of gastrin-releasing peptide receptors (GRPR) was recently proposed for targeted therapy, e.g., radiotherapy. Multiple and frequent injections of peptide-based therapeutic agents would be required due to rapid blood clearance. By conjugation of the GRPR antagonist RM26 (D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2) to an ABD (albumin-binding domain), we aimed to extend the blood circulation of peptides. The synthesized conjugate DOTA-ABD-RM26 was labelled with indium-111 and evaluated in vitro and in vivo. The labelled conjugate was stable in PBS and retained specificity and its antagonistic function against GRPR. The half-maximal inhibitory concentration (IC50) of natIn-DOTA-ABD-RM26 in the presence of human serum albumin was 49 ± 5 nM. [111In]In-DOTA-ABD-RM26 had a significantly longer residence time in blood and in tumors (without a significant decrease of up to 144 h pi) than the parental RM26 peptide. We conclude that the ABD-RM26 conjugate can be used for GRPR-targeted therapy and delivery of cytotoxic drugs. However, the undesirable elevated activity uptake in kidneys abolishes its use for radionuclide therapy. This proof-of-principle study justified further optimization of the molecular design of the ABD-RM26 conjugate.

Highlights

Prostate cancer is one of the most commonly diagnosed and deadliest cancers in men worldwide [1]
We aimed to develop and perform preclinical evaluation of the gastrin-releasing peptide receptors (GRPR) antagonist RM26 conjugated to ABD035 and assess the possibility for using the ligand in GRPR-targeting therapy for cancer treatment
The syntheses of DOTA-albumin-binding domain (ABD)-Cl and RM26 were successfully performed in an automated solid phase peptide synthesis (SPPS) systeTmheussyinngthemseicsroofwDaOveT-Aas-sAisBteDd-CcloaunpdliRngM2a6ndweFrme osucccchesesmfuislltyryp. eDrfoourmbleed-cionuapnlinagutostmepastedfoSrPtPhSe ssyesletecmtedusainmginmoicraocwidasvew-aesrseisitnetdrocoduupcelidnginanodrFdmeroctochienmcriestarsye

Summary

Introduction

Prostate cancer is one of the most commonly diagnosed and deadliest cancers in men worldwide [1]. A lot of research has been focused on identifying novel prostate cancer cell targets, raising the sensitivity towards diagnosing prostate cancer, including detection of distant metastases, and expanding the therapeutic options for patients. GRPR is normally expressed in different organs such as the pancreas and the stomach [2], and is overexpressed in various cancers, including prostate and breast cancers. GRPR overexpression in prostate cancer is androgen dependent and is found in 63–100% of primary prostate cancer samples and in more than 50% of lymph node and bone metastases, but not in hyperplastic and benign prostate cells [3,4]. Overexpression of GRPR is high in the early stages of prostate cancer (but decreases with disease progression when tumors dedifferentiate into higher grade) and in androgen-insensitive and spread metastatic lesions [5,6,7]

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