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Obeid K, Kanellopoulos P, Abouzayed A, Mattsson A, Tolmachev V, Nock BA, Maina T, Orlova A. GRPR-Antagonists Carrying DOTAGA-Chelator via Positively Charged Linkers: Perspectives for Prostate Cancer Theranostics. Pharmaceutics 2024; 16:513. [PMID: 38675174 PMCID: PMC11054746 DOI: 10.3390/pharmaceutics16040513] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2024] [Revised: 04/01/2024] [Accepted: 04/04/2024] [Indexed: 04/28/2024] Open
Abstract
Gastrin-releasing peptide receptor (GRPR)-antagonists have served as motifs in the development of theranostic radioligands for prostate cancer. Our efforts have been focused on the development of radiolabeled RM26 (H-DPhe6-Gln7-Trp8-Ala9-Val10-Gly11-His12-Sta13-Leu14-NH2) analogs, such as [111In]In-DOTAGA-PEG2-RM26. We recently showed that its Gly11/Sar11-substituted version, [111In]In-AU-RM26-M1, resisted degradation by neprilysin (NEP) while in circulation and achieved higher tumor uptake in mice. We herein introduce the following three new AU-RM26-M1 mimics labeled with In-111, with basic residues in the linker: (i) AU-RM26-M2 (PEG2-Pip), (ii) AU-RM26-M3 (PEG2-Arg), and (iii) AU-RM26-M4 (Arg-Arg-Pip). These analogs were compared in PC-3 cells and animal models vs. AU-RM26-M1 (reference). The new analogs showed high affinity and specificity for the GRPR, exhibiting an uptake and distribution pattern in PC-3 cells typical for a radiolabeled GRPR-antagonist. They showed high stability in peripheral mice blood, except for [111In]In-AU-RM26-M3. AU-RM26-M4 achieved the highest tumor uptake and promising background clearance, followed by [111In]In-RM26-M2, showing lower background levels. These findings were confirmed for [111In]In-AU-RM26-M2 and [111In]In-AU-RM26-M4 by micro-SPECT/CT at 4 and 24 h post-injection. Hence, the type of positively charged residues in the linker of AU-RM26-M1 mimics strongly influenced biological behavior. The analogs with Pip next to DPhe6 demonstrated the best overall characteristics and warrant further investigation.
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Affiliation(s)
- Karim Obeid
- Department of Medicinal Chemistry, Uppsala University, 751 83 Uppsala, Sweden; (K.O.); (P.K.); (A.A.); (A.M.)
| | - Panagiotis Kanellopoulos
- Department of Medicinal Chemistry, Uppsala University, 751 83 Uppsala, Sweden; (K.O.); (P.K.); (A.A.); (A.M.)
- Molecular Radiopharmacy, INRaSTES, NCSR “Demokritos”, 15341 Athens, Greece; (B.A.N.); (T.M.)
| | - Ayman Abouzayed
- Department of Medicinal Chemistry, Uppsala University, 751 83 Uppsala, Sweden; (K.O.); (P.K.); (A.A.); (A.M.)
| | - Adam Mattsson
- Department of Medicinal Chemistry, Uppsala University, 751 83 Uppsala, Sweden; (K.O.); (P.K.); (A.A.); (A.M.)
| | - Vladimir Tolmachev
- Department of Immunology, Genetics and Pathology, Uppsala University, 751 83 Uppsala, Sweden;
| | - Berthold A. Nock
- Molecular Radiopharmacy, INRaSTES, NCSR “Demokritos”, 15341 Athens, Greece; (B.A.N.); (T.M.)
| | - Theodosia Maina
- Molecular Radiopharmacy, INRaSTES, NCSR “Demokritos”, 15341 Athens, Greece; (B.A.N.); (T.M.)
| | - Anna Orlova
- Department of Medicinal Chemistry, Uppsala University, 751 83 Uppsala, Sweden; (K.O.); (P.K.); (A.A.); (A.M.)
- Science for Life Laboratory, Uppsala University, 752 37 Uppsala, Sweden
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Kanellopoulos P, Mattsson A, Abouzayed A, Obeid K, Nock BA, Tolmachev V, Maina T, Orlova A. Preclinical evaluation of new GRPR-antagonists with improved metabolic stability for radiotheranostic use in oncology. EJNMMI Radiopharm Chem 2024; 9:13. [PMID: 38366299 PMCID: PMC10873254 DOI: 10.1186/s41181-024-00242-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2023] [Accepted: 02/05/2024] [Indexed: 02/18/2024] Open
Abstract
BACKGROUND The gastrin-releasing peptide receptor (GRPR) has been extensively studied as a biomolecular target for peptide-based radiotheranostics. However, the lack of metabolic stability and the rapid clearance of peptide radioligands, including radiolabeled GRPR-antagonists, often impede clinical application. Aiming at circumventing these drawbacks, we have designed three new GRPR-antagonist radioligands using [99mTc]Tc-DB15 ([99mTc]Tc-N4-AMA-DIG-DPhe-Gln-Trp-Ala-Val-Sar-His-Leu-NHEt; AMA: p-aminomethylaniline; DIG: diglycolate) as a motif, due to its high GRPR-affinity and stability to neprilysin (NEP). The new analogues carry the DOTAGA-chelator (1,4,7,10-tetraazacyclododecane-1-glutaric acid-4,7,10-triacetic acid) through different linkers at the N-terminus to allow for labeling with the theranostic radionuclide pair In-111/Lu-177. After labeling with In-111 the following radioligands were evaluated: (i) [111In]In-AU-SAR-M1 ([111In]In-DOTAGA-AMA-DIG-DPhe-Gln-Trp-Ala-Val-Sar-His-Leu-NHEt), (ii) [111In]In-AU-SAR-M2 ([111In]In-[DOTAGA-Arg]AU-SAR-M1) and (iii) [111In]In-AU-SAR-M3 ([111In]In-[DOTAGA-DArg]AU-SAR-M1). RESULTS These radioligands were compared in a series of in vitro assays using prostate adenocarcinoma PC-3 cells and in murine models. They all displayed high and GRPR-specific uptake in PC-3 cells. Analysis of mice blood collected 5 min post-injection (pi) revealed similar or even higher metabolic stability of the new radioligands compared with [99mTc]Tc-DB15. The stability could be further increased when the mice were treated with Entresto® to in situ induce NEP-inhibition. In PC-3 xenograft-bearing mice, [111In]In-AU-SAR-M1 displayed the most favourable biodistribution profile, combining a good tumor retention with the highest tumor-to-organ ratios, with the kidneys as the dose-limiting organ. CONCLUSIONS These findings strongly point at AU-SAR-M1 as a promising radiotherapeutic candidate when labeled with Lu-177, or other medically appealing therapeutic radiometals, especially when combined with in situ NEP-inhibition. To this goal further investigations are currently pursued.
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Affiliation(s)
- Panagiotis Kanellopoulos
- Department of Medicinal Chemistry, Uppsala University, 75183, Uppsala, Sweden
- Molecular Radiopharmacy, INRaSTES, NCSR "Demokritos", 15341, Athens, Greece
| | - Adam Mattsson
- Department of Medicinal Chemistry, Uppsala University, 75183, Uppsala, Sweden
| | - Ayman Abouzayed
- Department of Medicinal Chemistry, Uppsala University, 75183, Uppsala, Sweden
| | - Karim Obeid
- Department of Medicinal Chemistry, Uppsala University, 75183, Uppsala, Sweden
| | - Berthold A Nock
- Molecular Radiopharmacy, INRaSTES, NCSR "Demokritos", 15341, Athens, Greece
| | - Vladimir Tolmachev
- Department of Immunology, Genetics and Pathology, Uppsala University, 75183, Uppsala, Sweden
| | - Theodosia Maina
- Molecular Radiopharmacy, INRaSTES, NCSR "Demokritos", 15341, Athens, Greece
| | - Anna Orlova
- Department of Medicinal Chemistry, Uppsala University, 75183, Uppsala, Sweden.
- Science for Life Laboratory, Uppsala University, 75237, Uppsala, Sweden.
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Abouzayed A, Kanellopoulos P, Gorislav A, Tolmachev V, Maina T, Nock BA, Orlova A. Preclinical Characterization of a Stabilized Gastrin-Releasing Peptide Receptor Antagonist for Targeted Cancer Theranostics. Biomolecules 2023; 13:1134. [PMID: 37509170 PMCID: PMC10377574 DOI: 10.3390/biom13071134] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2023] [Revised: 07/11/2023] [Accepted: 07/12/2023] [Indexed: 07/30/2023] Open
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.
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Affiliation(s)
- Ayman Abouzayed
- Department of Medicinal Chemistry, Uppsala University, 751 83 Uppsala, Sweden; (A.A.); (P.K.); (A.G.)
| | - Panagiotis Kanellopoulos
- Department of Medicinal Chemistry, Uppsala University, 751 83 Uppsala, Sweden; (A.A.); (P.K.); (A.G.)
- Molecular Radiopharmacy, INRaSTES, NCSR “Demokritos”, 15310 Athens, Greece; (T.M.); (B.A.N.)
| | - Alisa Gorislav
- Department of Medicinal Chemistry, Uppsala University, 751 83 Uppsala, Sweden; (A.A.); (P.K.); (A.G.)
| | - Vladimir Tolmachev
- Department of Immunology, Genetics and Pathology, Uppsala University, 751 83 Uppsala, Sweden;
| | - Theodosia Maina
- Molecular Radiopharmacy, INRaSTES, NCSR “Demokritos”, 15310 Athens, Greece; (T.M.); (B.A.N.)
| | - Berthold A. Nock
- Molecular Radiopharmacy, INRaSTES, NCSR “Demokritos”, 15310 Athens, Greece; (T.M.); (B.A.N.)
| | - Anna Orlova
- Department of Medicinal Chemistry, Uppsala University, 751 83 Uppsala, Sweden; (A.A.); (P.K.); (A.G.)
- Science for Life Laboratory, Uppsala University, 752 37 Uppsala, Sweden
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Nock BA, Kanellopoulos P, Joosten L, Mansi R, Maina T. Peptide Radioligands in Cancer Theranostics: Agonists and Antagonists. Pharmaceuticals (Basel) 2023; 16:ph16050674. [PMID: 37242457 DOI: 10.3390/ph16050674] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2023] [Revised: 04/25/2023] [Accepted: 04/27/2023] [Indexed: 05/28/2023] Open
Abstract
The clinical success of radiolabeled somatostatin analogs in the diagnosis and therapy-"theranostics"-of tumors expressing the somatostatin subtype 2 receptor (SST2R) has paved the way for the development of a broader panel of peptide radioligands targeting different human tumors. This approach relies on the overexpression of other receptor-targets in different cancer types. In recent years, a shift in paradigm from internalizing agonists to antagonists has occurred. Thus, SST2R-antagonist radioligands were first shown to accumulate more efficiently in tumor lesions and clear faster from the background in animal models and patients. The switch to receptor antagonists was soon adopted in the field of radiolabeled bombesin (BBN). Unlike the stable cyclic octapeptides used in the case of somatostatin, BBN-like peptides are linear, fast to biodegradable and elicit adverse effects in the body. Thus, the advent of BBN-like antagonists provided an elegant way to obtain effective and safe radiotheranostics. Likewise, the pursuit of gastrin and exendin antagonist-based radioligands is advancing with exciting new outcomes on the horizon. In the present review, we discuss these developments with a focus on clinical results, commenting on challenges and opportunities for personalized treatment of cancer patients by means of state-of-the-art antagonist-based radiopharmaceuticals.
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Affiliation(s)
- Berthold A Nock
- Molecular Radiopharmacy, INRaSTES, NCSR "Demokritos", 15310 Athens, Greece
| | | | - Lieke Joosten
- Department of Medical Imaging, Nuclear Medicine, Radboud University Medical Center, 6525 GA Nijmegen, The Netherlands
| | - Rosalba Mansi
- Division of Radiopharmaceutical Chemistry, Clinic of Radiology and Nuclear Medicine, University Hospital Basel, 4031 Basel, Switzerland
| | - Theodosia Maina
- Molecular Radiopharmacy, INRaSTES, NCSR "Demokritos", 15310 Athens, Greece
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Günther T, Konrad M, Stopper L, Kunert JP, Fischer S, Beck R, Casini A, Wester HJ. Optimization of the Pharmacokinetic Profile of [ 99mTc]Tc-N 4-Bombesin Derivatives by Modification of the Pharmacophoric Gln-Trp Sequence. Pharmaceuticals (Basel) 2022; 15:ph15091133. [PMID: 36145354 PMCID: PMC9500665 DOI: 10.3390/ph15091133] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2022] [Revised: 09/06/2022] [Accepted: 09/06/2022] [Indexed: 11/16/2022] Open
Abstract
Current radiolabeled gastrin-releasing peptide receptor (GRPR) ligands usually suffer from high accumulation in GRPR-positive organs (pancreas, stomach), limiting tumor-to-background contrast in the abdomen. In novel N4-bombesin derivatives this was addressed by substitutions at the Gln7-Trp8 site within the MJ9 peptide (H-Pip5-phe6-Gln7-Trp8-Ala9-Val10-Gly11-His12-Sta13-Leu14-NH2) either by homoserine (Hse7), β-(3-benzothienyl) alanine (Bta8) or α-methyl tryptophan (α-Me-Trp8), with the aim of optimizing pharmacokinetics. We prepared and characterized the peptide conjugates 6-carboxy-1,4,8,11-tetraazaundecane (N4)-asp-MJ9, N4-asp-[Bta8]MJ9, N4-[Hse7]MJ9 and N4-[α-Me-Trp8]MJ9, and evaluated these compounds in vitro (GRPR affinity via IC50,inverse; internalization; lipophilicity via logD7.4) and in vivo (biodistribution and μSPECT/CT studies at 1 h post injection (p.i.) in PC-3 tumor-bearing CB17-SCID mice). 99mTc-labeling resulted in radiochemical yields (RCYs) > 95%. All 99mTc-labeled MJ9 analogues showed comparable or higher GRPR affinity than the external reference [99mTc]Tc-Demobesin 4. Receptor-bound fractions were noticeably higher than that of the reference. Despite a slightly enhanced lipophilicity, all novel MJ9 derivatives revealed improved in vivo pharmacokinetics compared to the reference. The Bta8-modified ligand revealed the most favorable tumor-to-abdomen contrast at 1 h p.i. Substitutions at the Gln7-Trp8 site within GRPR ligands hold great potential to modify pharmacokinetics for improved imaging.
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Nock BA, Kanellopoulos P, Chepurny OG, Rouchota M, Loudos G, Holz GG, Krenning EP, Maina T. Nonpeptidic Z360-Analogs Tagged with Trivalent Radiometals as Anti-CCK2R Cancer Theranostic Agents: A Preclinical Study. Pharmaceutics 2022; 14:pharmaceutics14030666. [PMID: 35336041 PMCID: PMC8954547 DOI: 10.3390/pharmaceutics14030666] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2022] [Revised: 03/11/2022] [Accepted: 03/15/2022] [Indexed: 02/05/2023] Open
Abstract
(1) Background: Theranostic approaches in the management of cholecystokinin subtype 2 receptor (CCK2R)-positive tumors include radiolabeled gastrin and CCK motifs. Moving toward antagonist-based CCK2R-radioligands instead, we herein present three analogs of the nonpeptidic CCK2R-antagonist Z360, GAS1/2/3. Each was conjugated to a different chelator (DOTA, NODAGA or DOTAGA) for labeling with medically relevant trivalent radiometals (e.g., Ga-68, In-111, Lu-177) for potential use as anti-CCK2R cancer agents; (2) Methods: The in vitro properties of the thee analogs were compared in stably transfected HEK293-CCK2R cells. Biodistribution profiles were compared in SCID mice bearing twin HEK293-CCK2R and wtHEK293 tumors; (3) Results: The GAS1/2/3 analogs displayed high CCK2R-affinity (lower nM-range). The radioligands were fairly stable in vivo and selectively targeted the HEK293-CCK2R, but not the CCK2R-negative wtHEK293 tumors in mice. Their overall pharmacokinetic profile was found strongly dependent on the radiometal-chelate. Results could be visualized by SPECT/CT for the [111In]In-analogs; (4) Conclusions: The present study highlighted the high impact of the radiometal-chelate on the end-pharmacokinetics of a new series of Z360-based radioligands, revealing candidates with promising properties for clinical translation. It also provided the impetus for the development of a new class of nonpeptidic radioligands for CCK2R-targeted theranostics of human cancer.
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Affiliation(s)
- Berthold A. Nock
- Molecular Radiopharmacy, INRASTES, NCSR “Demokritos”, 15341 Athens, Greece; (B.A.N.); (P.K.)
| | | | - Oleg G. Chepurny
- Departments of Medicine and Pharmacology, State University of New York (SUNY), Upstate Medical University, Syracuse, NY 13210, USA and Department of Chemistry, Syracuse University, Syracuse, NY 13244, USA; (O.G.C.); (G.G.H.)
| | - Maritina Rouchota
- BIOEMTECH, Lefkippos Attica Technology Park NCSR “Demokritos”, 15310 Athens, Greece; (M.R.); (G.L.)
| | - George Loudos
- BIOEMTECH, Lefkippos Attica Technology Park NCSR “Demokritos”, 15310 Athens, Greece; (M.R.); (G.L.)
| | - George G. Holz
- Departments of Medicine and Pharmacology, State University of New York (SUNY), Upstate Medical University, Syracuse, NY 13210, USA and Department of Chemistry, Syracuse University, Syracuse, NY 13244, USA; (O.G.C.); (G.G.H.)
| | - Eric P. Krenning
- Cyclotron Rotterdam BV, Erasmus MC, 3015 CE Rotterdam, The Netherlands;
| | - Theodosia Maina
- Molecular Radiopharmacy, INRASTES, NCSR “Demokritos”, 15341 Athens, Greece; (B.A.N.); (P.K.)
- Correspondence: ; Tel.: +30-210-650-3908 or +30-210-650-3891
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Maina T, Nock BA. Gamma camera imaging by radiolabeled gastrin/cholecystokinin analogs. Nucl Med Mol Imaging 2022. [DOI: 10.1016/b978-0-12-822960-6.00183-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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Maina T, Nock BA. Peptide radiopharmaceuticals for targeted diagnosis & therapy of human tumors. Nucl Med Mol Imaging 2022. [DOI: 10.1016/b978-0-12-822960-6.00078-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022] Open
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Mansi R, Nock BA, Dalm SU, Busstra MB, van Weerden WM, Maina T. Radiolabeled Bombesin Analogs. Cancers (Basel) 2021; 13:cancers13225766. [PMID: 34830920 PMCID: PMC8616220 DOI: 10.3390/cancers13225766] [Citation(s) in RCA: 31] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Revised: 11/13/2021] [Accepted: 11/15/2021] [Indexed: 12/16/2022] Open
Abstract
Simple Summary Recent medical advancements have strived for a personalized medicine approach to patients, aimed at optimizing therapy outcomes with minimum toxicity. In this respect, nuclear medicine methodologies have been playing increasingly important roles. For example, the overexpression of peptide receptors, such as the gastrin-releasing peptide receptor (GRPR), on tumor cells as opposed to their lack of expression in healthy surrounding tissues can be elegantly exploited with the aid of “smart” peptide carriers, such as the analogs of the amphibian 14-peptide bombesin (BBN). These molecules can bring clinically attractive radionuclides to malignant lesions in prostate, breast, and other human cancers, sparing healthy tissues. Depending upon the radionuclide in question, diagnostic imaging with single-photon emission computed tomography (SPECT) or positron emission tomography (PET) has been pursued, identifying patients who are eligible for peptide radionuclide receptor therapy (PRRT) in an integrated “theranostic” approach. In the present review, we (i) discuss the major steps taken in the development of anti-GRPR theranostic radioligands, with a focus on those selected for clinical testing; (ii) comment on the present status in this field of research; and (iii) reflect on the current limitations as well as on new opportunities for their broader and more successful clinical applications. Abstract The gastrin-releasing peptide receptor (GRPR) is expressed in high numbers in a variety of human tumors, including the frequently occurring prostate and breast cancers, and therefore provides the rationale for directing diagnostic or therapeutic radionuclides on cancer lesions after administration of anti-GRPR peptide analogs. This concept has been initially explored with analogs of the frog 14-peptide bombesin, suitably modified at the N-terminus with a number of radiometal chelates. Radiotracers that were selected for clinical testing revealed inherent problems associated with these GRPR agonists, related to low metabolic stability, unfavorable abdominal accumulation, and adverse effects. A shift toward GRPR antagonists soon followed, with safer analogs becoming available, whereby, metabolic stability and background clearance issues were gradually improved. Clinical testing of three main major antagonist types led to promising outcomes, but at the same time brought to light several limitations of this concept, partly related to the variation of GRPR expression levels across cancer types, stages, previous treatments, and other factors. Currently, these parameters are being rigorously addressed by cell biologists, chemists, nuclear medicine physicians, and other discipline practitioners in a common effort to make available more effective and safe state-of-the-art molecular tools to combat GRPR-positive tumors. In the present review, we present the background, current status, and future perspectives of this endeavor.
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Affiliation(s)
- Rosalba Mansi
- Division of Radiopharmaceutical Chemistry, Clinic of Radiology and Nuclear Medicine University Hospital Basel, 4031 Basel, Switzerland;
| | - Berthold A. Nock
- Molecular Radiopharmacy, INRaSTES, NCSR “Demokritos”, 15310 Athens, Greece;
| | - Simone U. Dalm
- Erasmus Medical Center Rotterdam, 3000 CA Rotterdam, The Netherlands; (S.U.D.); (M.B.B.); (W.M.v.W.)
| | - Martijn B. Busstra
- Erasmus Medical Center Rotterdam, 3000 CA Rotterdam, The Netherlands; (S.U.D.); (M.B.B.); (W.M.v.W.)
| | - Wytske M. van Weerden
- Erasmus Medical Center Rotterdam, 3000 CA Rotterdam, The Netherlands; (S.U.D.); (M.B.B.); (W.M.v.W.)
| | - Theodosia Maina
- Molecular Radiopharmacy, INRaSTES, NCSR “Demokritos”, 15310 Athens, Greece;
- Correspondence: ; Tel.: +30-650-3908/3891
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