[99mTc]Tc-DB1 Mimics with Different-Length PEG Spacers: Preclinical Comparison in GRPR-Positive Models.

Theodosia Maina,Berthold A. Nock,Aikaterini Kaloudi,Panagiotis Kanellopoulos,Eric P. Krenning,Emmanouil Lymperis,Marion de Jong

doi:10.3390/molecules25153418

Abstract

Background: The frequent overexpression of gastrin-releasing peptide receptors (GRPRs) in human cancers provides the rationale for delivering clinically useful radionuclides to tumor sites using peptide carriers. Radiolabeled GRPR antagonists, besides being safer for human use, have often shown higher tumor uptake and faster background clearance than agonists. We herein compared the biological profiles of the GRPR-antagonist-based radiotracers [99mTc]Tc-[N4-PEGx-DPhe6,Leu-NHEt13]BBN(6-13) (N4: 6-(carboxy)-1,4,8,11-tetraazaundecane; PEG: polyethyleneglycol): (i) [99mTc]Tc-DB7 (x = 2), (ii) [99mTc]Tc-DB13 (x = 3), and (iii) [99mTc]Tc-DB14 (x = 4), in GRPR-positive cells and animal models. The impact of in situ neprilysin (NEP)-inhibition on in vivo stability and tumor uptake was also assessed by treatment of mice with phosphoramidon (PA). Methods: The GRPR affinity of DB7/DB13/DB14 was determined in PC-3 cell membranes, and cell binding of the respective [99mTc]Tc-radioligands was assessed in PC-3 cells. Each of [99mTc]Tc-DB7, [99mTc]Tc-DB13, and [99mTc]Tc-DB14 was injected into mice without or with PA coinjection and 5 min blood samples were analyzed by HPLC. Biodistribution was conducted at 4 h postinjection (pi) in severe combined immunodeficiency disease (SCID) mice bearing PC-3 xenografts without or with PA coinjection. Results: DB7, -13, and -14 displayed single-digit nanomolar affinities for GRPR. The uptake rates of [99mTc]Tc-DB7, [99mTc]Tc-DB13, and [99mTc]Tc-DB14 in PC-3 cells was comparable and consistent with a radioantagonist profile. The radiotracers were found to be ≈70% intact in mouse blood and >94% intact after coinjection of PA. Treatment of mice with PA enhanced tumor uptake. Conclusions: The present study showed that increase of PEG-spacer length in the [99mTc]Tc-DB7–[99mTc]Tc-DB13–[99mTc]Tc-DB14 series had little effect on GRPR affinity, specific uptake in PC-3 cells, in vivo stability, or tumor uptake. A significant change in in vivo stability and tumor uptake was observed only after treatment of mice with PA, without compromising the favorably low background radioactivity levels.

Highlights

68Ga, 64Cu) for positron-emission tomography (PET) will allow for initial diagnosis, assessment ofThe gastrin-releasing peptide receptor (GRPR) has attracted much attention in nuclear oncology disease spread and progression, and selection of patients eligible for subsequent radionuclide therapy.owing to its high-density expression in frequently occurring human cancers, such as prostate cancer, Molecular imaging is likewise essential for dosimetry, therapy planning, and follow-up, enabling a mammary carcinoma, and others [1,2,3,4,5,6,7]
GRPRfor activation that follows affinity, have been derivatized with the appropriate stable binding of the selected [12,13,14]. Medically Such effects and havedoses been evaluated in animalduring models and in humans [8,11]. It should be notedrestricting the intensifyrelevant at the radiometal higher peptide administered radionuclide therapy, thereby that such analogs internalize into target cells and display agonistic profiles at the Agonism at broader clinical use of GRPR agonists
We previously reported on a series of radiolabeled analogs of theprofiles potent GRPR

Summary

Introduction

Affinity, Molecular have been derivatized with the appropriate chelator binding imaging is likewise essential for dosimetry, therapy planning,for andstable follow-up, enablingofa the selected patient-tailored, Therapy per se is conducted with the respective peptide medically relevant radiometal and have been evaluated in animal models and in humans [8,11] It analog carrying a suitable particle emitter (beta, alpha, or Auger electron emitter). Medically Such effects and havedoses been evaluated in animalduring models and in humans [8,11] It should be notedrestricting the intensifyrelevant at the radiometal higher peptide administered radionuclide therapy, thereby that such analogs internalize into target cells and display agonistic profiles at the GRPR. Notably improved tumor targeting was observed in mice and recently in patients [28,29,30,31,32,33,34,35]

Results

GRPR Affinity of Peptide Conjugates

Radiotracer

In Vivo

Biodistribution expressed asdata

1.33 REVIEW

Chemicals and Radionuclides

Radiolabeling

Quality Control

Cell Lines and Culture

Competitive Binding in PC-3 Cell Membranes

Metabolic Studies in Mice