Investigation of Tumor Cells and Receptor-Ligand Simulation Models for the Development of PET Imaging Probes Targeting PSMA and GRPR and a Possible Crosstalk between the Two Receptors

Abstract

Prostate-specific membrane antigen (PSMA) and gastrin-releasing peptide receptor (GRPR) have both been used in nuclear medicine as targets for molecular imaging and therapy of prostate (PCa) and breast cancer (BCa). Three bioconjugate probes, the PSMA specific: [ 68 Ga]Ga-1, ((HBED-CC)-Ahx-Lys-NH-CO-NH Glu or PSMA-11), the GRPR specific: [ 68 Ga]Ga-2, ((HBED-CC)-4-amino-1-carboxymethyl piperidine-[D-Phe 6 , Sta 13 ]BN(6−14), a bombesin (BN) analogue), and 3 (the BN analogue: 4-amino-1-carboxymethyl piperidine-[(R)-Phe 6 , Sta 13 ]-BN(6−14) connected with the fluorescent dye, BDP-FL), were synthesized and tested in vitro with PCa and BCa cell lines, more specifically, with PCa cells, PC-3 and LNCaP, with BCa cells, T47D, MDA-MB-231, and with the in-house created PSMAoverexpressing PC-3 (PSMA) , T47D (PSMA) , and MDA-MB-231 (PSMA) . In addition, biomolecular simulations were conducted on the association of 1 and 2 with PSMA and GRPR. The PSMA overexpression resulted in an increase of cell-bound radioligand [ 68 Ga]Ga-1 (PSMA) for PCa and BCa cells and also of [ 68 Ga]Ga-2 (GRPR), especially in those cell lines already expressing GRPR. The results were confirmed by fluorescence-activated cell sorting with a PE-labeled PSMA-specific antibody and the fluorescence tracer 3. The docking calculations and molecular dynamics simulations showed how 1 enters the PSMA funnel region and how pharmacophore Glu-urea-Lys interacts with the arginine patch, the S1′, and S1 subpockets by forming hydrogen and van der Waals bonds. The chelating moiety of 1, that is, HBED-CC, forms additional stabilizing hydrogen bonding and van der Waals interactions in the arenebinding site. Ligand 2 is diving into the GRPR transmembrane (TM) helical cavity, thereby forming hydrogen bonds through its amidated end, water-mediated hydrogen bonds, and π−π interactions. Our results provide valuable information regarding the molecular mechanisms involved in the interactions of 1 and 2 with PSMA and GRPR, which might be useful for the diagnostic imaging and therapy of PCa and BCa.

Computer-Assisted Design of Peptide-Based Radiotracers

“…In the study conducted by Liolios et al [ 28 ], the prostate-specific membrane antigen (PSMA) and gastrin-releasing peptide receptor (GRPR) were considered as valuable biological targets for the molecular imaging and therapy of prostate (PCa) and breast (BCa) cancer. They both are widely expressed on the surfaces of PCa cells and BCa cells during the progression of malignancies.…”

Radiolabeled iron oxide nanoparticles functionalized with PSMA/BN ligands for dual-targeting of prostate cancer

“…The surface bound fraction of radioactivity was always higher for the IONs-BN compared to the internalized fraction, at both temperatures studied, indicating that the BN pharmacophore has changed their internalization process and that the IONs-BN have the same behavior as the BN antagonist. The BN antagonists are known for showing minimal internalization and for being mainly surface bound on PC3 cells (36,54,55). Moreover, in most cases, the internalized radioactivity reached a plateau at the highest concentrations studied (4 and 5 μg/ml), indicating a saturation in the process.…”

Bispecific PSMA-617 / RM2 Heterodimer for Theranostics Applications in Prostate Cancer

“…The docking poses of the PSMA-617 part or the RM2 part of the heterodimer (3) into the binding area of PSMA receptor or BBR2 were performed as previously described in ref. Liolios et al 52 and are shown in Figure 6.…”

“…Considering the increased expression of PSMA in the kidneys, the kidney uptake was much lesser than in other heterodimers we previously developed that ranged between 66-122% IA/g. 51,52 The observed off-targeting uptake in the pancreas was due to the normal expression of GRPRs in this tissue and was gradually degraded with time in a faster rate than the activity located in the tumors. In general, [ 68 Ga]Ga-3 showed dual targeting of PSMA-positive tumors and GRPR-positive tumors and fast clearance from the body, while in comparison to the monomers 2,3 a higher cancer cell-uptake and lower kidneys uptake was observed.…”