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Lindeman SD, Booth OC, Tudi P, Schleinkofer TC, Moss JN, Kearney NB, Mukkamala R, Thompson LK, Modany MA, Srinivasarao M, Low PS. FAP Radioligand Linker Optimization Improves Tumor Dose and Tumor-to-Healthy Organ Ratios in 4T1 Syngeneic Model. J Med Chem 2024; 67:11827-11840. [PMID: 39013156 DOI: 10.1021/acs.jmedchem.4c00448] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/18/2024]
Abstract
Fibroblast activation protein (FAP) has attracted considerable attention as a possible target for the radiotherapy of solid tumors. Unfortunately, initial efforts to treat solid tumors with FAP-targeted radionuclides have yielded only modest clinical responses, suggesting that further improvements in the molecular design of FAP-targeted radiopharmaceutical therapies (RPT) are warranted. In this study, we report several advances on the previously described FAP6 radioligand that increase tumor retention and accelerate healthy tissue clearance. Seven FAP6 derivatives with different linkers or albumin binders were synthesized, radiolabeled, and investigated for their effects on binding and cellular uptake. The radioligands were then characterized in 4T1 tumor-bearing Balb/c mice using both single-photon emission computed tomography (SPECT) and ex vivo biodistribution analyses to identify the conjugate with the best tumor retention and tumor-to-healthy organ ratios. The results reveal an optimized FAP6 radioligand that exhibits efficacy and safety properties that potentially justify its translation into the clinic.
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Affiliation(s)
- Spencer D Lindeman
- Department of Chemistry and Institute for Drug Discovery, Purdue University, West Lafayette, Indiana 47907, United States
- MorphImmune, Inc., 1281 Win Hentschel Blvd, West Lafayette, Indiana 47906, United States
| | - Owen C Booth
- Department of Chemistry and Institute for Drug Discovery, Purdue University, West Lafayette, Indiana 47907, United States
| | - Pooja Tudi
- Department of Chemistry and Institute for Drug Discovery, Purdue University, West Lafayette, Indiana 47907, United States
| | - Taylor C Schleinkofer
- Department of Chemistry and Institute for Drug Discovery, Purdue University, West Lafayette, Indiana 47907, United States
| | - Jackson N Moss
- Department of Chemistry and Institute for Drug Discovery, Purdue University, West Lafayette, Indiana 47907, United States
| | - Nicholas B Kearney
- Department of Chemistry and Institute for Drug Discovery, Purdue University, West Lafayette, Indiana 47907, United States
| | - Ramesh Mukkamala
- Department of Chemistry and Institute for Drug Discovery, Purdue University, West Lafayette, Indiana 47907, United States
| | - Lauren K Thompson
- Department of Chemistry and Institute for Drug Discovery, Purdue University, West Lafayette, Indiana 47907, United States
| | - Mollie A Modany
- Department of Chemistry and Institute for Drug Discovery, Purdue University, West Lafayette, Indiana 47907, United States
| | - Madduri Srinivasarao
- Department of Chemistry and Institute for Drug Discovery, Purdue University, West Lafayette, Indiana 47907, United States
| | - Philip S Low
- Department of Chemistry and Institute for Drug Discovery, Purdue University, West Lafayette, Indiana 47907, United States
- MorphImmune, Inc., 1281 Win Hentschel Blvd, West Lafayette, Indiana 47906, United States
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de Roode KE, Joosten L, Behe M. Towards the Magic Radioactive Bullet: Improving Targeted Radionuclide Therapy by Reducing the Renal Retention of Radioligands. Pharmaceuticals (Basel) 2024; 17:256. [PMID: 38399470 PMCID: PMC10892921 DOI: 10.3390/ph17020256] [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: 06/23/2023] [Revised: 02/07/2024] [Accepted: 02/09/2024] [Indexed: 02/25/2024] Open
Abstract
Targeted radionuclide therapy (TRT) is an emerging field and has the potential to become a major pillar in effective cancer treatment. Several pharmaceuticals are already in routine use for treating cancer, and there is still a high potential for new compounds for this application. But, a major issue for many radiolabeled low-to-moderate-molecular-weight molecules is their clearance via the kidneys and their subsequent reuptake. High renal accumulation of radioactive compounds may lead to nephrotoxicity, and therefore, the kidneys are often the dose-limiting organs in TRT with these radioligands. Over the years, different strategies have been developed aiming for reduced kidney retention and enhanced therapeutic efficacy of radioligands. In this review, we will give an overview of the efforts and achievements of the used strategies, with focus on the therapeutic potential of low-to-moderate-molecular-weight molecules. Among the strategies discussed here is coadministration of compounds that compete for binding to the endocytic receptors in the proximal tubuli. In addition, the influence of altering the molecular design of radiolabeled ligands on pharmacokinetics is discussed, which includes changes in their physicochemical properties and implementation of cleavable linkers or albumin-binding moieties. Furthermore, we discuss the influence of chelator and radionuclide choice on reabsorption of radioligands by the kidneys.
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Affiliation(s)
- Kim E. de Roode
- Department of Medical Imaging, Nuclear Medicine, Radboud University Medical Center, Geert Grooteplein Zuid 10, 6525 GA Nijmegen, The Netherlands;
- Tagworks Pharmaceuticals, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands
| | - Lieke Joosten
- Department of Medical Imaging, Nuclear Medicine, Radboud University Medical Center, Geert Grooteplein Zuid 10, 6525 GA Nijmegen, The Netherlands;
| | - Martin Behe
- Center for Radiopharmaceutical Sciences ETH-PSI-USZ, Paul Scherrer Institut, 5232 Villigen, Switzerland
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3
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Tao Y, Jakobsson V, Chen X, Zhang J. Exploiting Albumin as a Versatile Carrier for Cancer Theranostics. Acc Chem Res 2023; 56:2403-2415. [PMID: 37625245 DOI: 10.1021/acs.accounts.3c00309] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/27/2023]
Affiliation(s)
- Yucen Tao
- Department of Diagnostic Radiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 119074, Singapore
- Clinical Imaging Research Centre, Centre for Translational Medicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117599, Singapore
- Nanomedicine Translational Research Program, NUS Center for Nanomedicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117597, Singapore
| | - Vivianne Jakobsson
- Department of Diagnostic Radiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 119074, Singapore
- Clinical Imaging Research Centre, Centre for Translational Medicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117599, Singapore
- Nanomedicine Translational Research Program, NUS Center for Nanomedicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117597, Singapore
| | - Xiaoyuan Chen
- Department of Diagnostic Radiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 119074, Singapore
- Clinical Imaging Research Centre, Centre for Translational Medicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117599, Singapore
- Nanomedicine Translational Research Program, NUS Center for Nanomedicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117597, Singapore
- Department of Surgery, Chemical and Biomolecular Engineering, and Biomedical Engineering, Yong Loo Lin School of Medicine and College of Design and Engineering, National University of Singapore, Singapore 119074, Singapore
- Institute of Molecular and Cell Biology, Agency for Science, Technology, and Research (A*STAR), 61 Biopolis Drive, Proteos, Singapore 138673, Singapore
| | - Jingjing Zhang
- Department of Diagnostic Radiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 119074, Singapore
- Clinical Imaging Research Centre, Centre for Translational Medicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117599, Singapore
- Nanomedicine Translational Research Program, NUS Center for Nanomedicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117597, Singapore
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Busslinger SD, Becker AE, Vaccarin C, Deberle LM, Renz ML, Groehn V, Schibli R, Müller C. Investigations Using Albumin Binders to Modify the Tissue Distribution Profile of Radiopharmaceuticals Exemplified with Folate Radioconjugates. Cancers (Basel) 2023; 15:4259. [PMID: 37686538 PMCID: PMC10486429 DOI: 10.3390/cancers15174259] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2023] [Revised: 08/14/2023] [Accepted: 08/19/2023] [Indexed: 09/10/2023] Open
Abstract
Introducing an albumin-binding entity into otherwise short-lived radiopharmaceuticals can be an effective means to improve their pharmacokinetic properties due to enhanced blood residence time. In the current study, DOTA-derivatized albumin binders based on 4-(p-iodophenyl)butanoate (DOTA-ALB-1 and DOTA-ALB-3) and 5-(p-iodophenyl)pentanoate entities (DOTA-ALB-24 and DOTA-ALB-25) without and with a hydrophobic 4-(aminomethyl)benzoic acid (AMBA) linker unit, respectively, were synthesized and labeled with lutetium-177 for in vitro and in vivo comparison. Overall, [177Lu]Lu-DOTA-ALB-1 demonstrated ~3-fold stronger in vitro albumin-binding affinity and a longer blood residence time (T50%IA ~8 h) than [177Lu]Lu-DOTA-ALB-24 (T50%IA ~0.8 h). Introducing an AMBA linker enhanced the albumin-binding affinity, resulting in a T50%IA of ~24 h for [177Lu]Lu-DOTA-ALB-3 and ~2 h for [177Lu]Lu-DOTA-ALB-25. The same albumin binders without or with the AMBA linker were incorporated into 6R- and 6S-5-methyltetrahydrofolate-based DOTA-conjugates (177Lu-RedFols). Biodistribution studies in mice performed with both diastereoisomers of [177Lu]Lu-RedFol-1 and [177Lu]Lu-RedFol-3, which comprised the 4-(p-iodophenyl)butanoate moiety, demonstrated a slower accumulation in KB tumors than those of [177Lu]Lu-RedFol-24 and [177Lu]Lu-RedFol-25 with the 5-(p-iodophenyl)pentanoate entity. In all cases, the tumor uptake was high (30-45% IA/g) 24 h after injection. Both diastereoisomers of [177Lu]Lu-RedFol-1 and [177Lu]Lu-RedFol-3 demonstrated high blood retention (3.8-8.7% IA/g, 24 h p.i.) and a 2- to 4-fold lower kidney uptake than the corresponding diastereoisomers of [177Lu]Lu-RedFol-24 and [177Lu]Lu-RedFol-25, which were more rapidly cleared from the blood (<0.2% IA/g, 24 h after injection). Kidney retention of the 6S-diastereoisomers of all 177Lu-RedFols was consistently higher than that of the respective 6R-diastereoisomers, irrespective of the albumin binder and linker unit used. It was demonstrated that the blood clearance data obtained with 177Lu-DOTA-ALBs had predictive value for the blood retention times of the respective folate radioconjugates. The use of these albumin-binding entities without or with an AMBA linker may serve for fine-tuning the blood retention of folate radioconjugates and also other radiopharmaceuticals and, hence, optimize their tissue distribution profiles. Dosimetry estimations based on patient data obtained with one of the most promising folate radioconjugates will be crucial to identify the dose-limiting organ, which will allow for selecting the most suitable folate radioconjugate for therapeutic purposes.
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Affiliation(s)
- Sarah D. Busslinger
- Center for Radiopharmaceutical Sciences ETH-PSI, Paul Scherrer Institute, Forschungsstrasse 111, 5232 Villigen-PSI, Switzerland; (S.D.B.); (A.E.B.); (C.V.); (L.M.D.); (R.S.)
| | - Anna E. Becker
- Center for Radiopharmaceutical Sciences ETH-PSI, Paul Scherrer Institute, Forschungsstrasse 111, 5232 Villigen-PSI, Switzerland; (S.D.B.); (A.E.B.); (C.V.); (L.M.D.); (R.S.)
| | - Christian Vaccarin
- Center for Radiopharmaceutical Sciences ETH-PSI, Paul Scherrer Institute, Forschungsstrasse 111, 5232 Villigen-PSI, Switzerland; (S.D.B.); (A.E.B.); (C.V.); (L.M.D.); (R.S.)
| | - Luisa M. Deberle
- Center for Radiopharmaceutical Sciences ETH-PSI, Paul Scherrer Institute, Forschungsstrasse 111, 5232 Villigen-PSI, Switzerland; (S.D.B.); (A.E.B.); (C.V.); (L.M.D.); (R.S.)
| | - Marie-Luise Renz
- Merck & Cie KmG, Im Laternenacker 5, 8200 Schaffhausen, Switzerland; (M.-L.R.); (V.G.)
| | - Viola Groehn
- Merck & Cie KmG, Im Laternenacker 5, 8200 Schaffhausen, Switzerland; (M.-L.R.); (V.G.)
| | - Roger Schibli
- Center for Radiopharmaceutical Sciences ETH-PSI, Paul Scherrer Institute, Forschungsstrasse 111, 5232 Villigen-PSI, Switzerland; (S.D.B.); (A.E.B.); (C.V.); (L.M.D.); (R.S.)
- Department of Chemistry and Applied Biosciences, ETH Zurich, Vladimir-Prelog-Weg 1-5/10, 8093 Zurich, Switzerland
| | - Cristina Müller
- Center for Radiopharmaceutical Sciences ETH-PSI, Paul Scherrer Institute, Forschungsstrasse 111, 5232 Villigen-PSI, Switzerland; (S.D.B.); (A.E.B.); (C.V.); (L.M.D.); (R.S.)
- Department of Chemistry and Applied Biosciences, ETH Zurich, Vladimir-Prelog-Weg 1-5/10, 8093 Zurich, Switzerland
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5
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Wen X, Xu P, Zeng X, Liu J, Du C, Zeng X, Cheng X, Wang X, Liang Y, Zhao T, Yang H, Li H, Meng L, Fang J, Liu H, Zhou Z, Zhang J, Zhang X, Guo Z, Chen X. Development of [ 177Lu]Lu-LNC1003 for radioligand therapy of prostate cancer with a moderate level of PSMA expression. Eur J Nucl Med Mol Imaging 2023; 50:2846-2860. [PMID: 37097443 DOI: 10.1007/s00259-023-06229-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2022] [Accepted: 04/07/2023] [Indexed: 04/26/2023]
Abstract
PURPOSE Evans blue as an albumin binder has been widely used to improve pharmacokinetics and enhance tumor uptake of radioligands, including prostate-specific membrane antigen (PSMA) targeting agents. The goal of this study is to develop an optimal Evans blue-modified radiotherapeutic agent that could maximize the absolute tumor uptake and tumor absorbed dose thus the therapeutic efficacy to allow treatment of tumors even with moderate level of PSMA expression. METHODS [177Lu]Lu-LNC1003 was synthesized based on PSMA-targeting agent and Evans blue. Binding affinity and PSMA targeting specificity were verified through cell uptake and competition binding assay in 22Rv1 tumor model that has moderate level of PSMA expression. SPECT/CT imaging and biodistribution studies in 22Rv1 tumor-bearing mice were performed to evaluate the preclinical pharmacokinetics. Radioligand therapy studies were conducted to systematically assess the therapeutic effect of [177Lu]Lu-LNC1003. RESULTS LNC1003 showed high binding affinity (IC50 = 10.77 nM) to PSMA in vitro, which was comparable with that of PSMA-617 (IC50 = 27.49 nM) and EB-PSMA-617 (IC50 = 7.91 nM). SPECT imaging of [177Lu]Lu-LNC1003 demonstrated significantly improved tumor uptake and retention as compared with [177Lu]Lu-EB-PSMA and [177Lu]Lu-PSMA-617, making it suitable for prostate cancer therapy. Biodistribution studies further confirmed the remarkably higher tumor uptake of [177Lu]Lu-LNC1003 (138.87 ± 26.53%ID/g) over [177Lu]Lu-EB-PSMA-617 (29.89 ± 8.86%ID/g) and [177Lu]Lu-PSMA-617 (4.28 ± 0.25%ID/g) at 24 h post-injection. Targeted radioligand therapy results showed noteworthy inhibition of 22Rv1 tumor growth after administration of a single dose of 18.5 MBq [177Lu]Lu-LNC1003. There was no obvious antitumor effect after [177Lu]Lu-PSMA-617 treatment under the same condition. CONCLUSION In this study, [177Lu]Lu-LNC1003 was successfully synthesized with high radiochemical purity and stability. High binding affinity and PSMA targeting specificity were identified in vitro and in vivo. With greatly enhanced tumor uptake and retention, [177Lu]Lu-LNC1003 has the potential to improve therapeutic efficacy using significantly lower dosages and less cycles of 177Lu that promises clinical translation to treat prostate cancer with various levels of PSMA expression.
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Affiliation(s)
- Xuejun Wen
- State Key Laboratory of Molecular Vaccinology and Molecular, Diagnostics & Center for Molecular Imaging and Translational Medicine, School of PublicHealth, Xiamen University, 4221-116 Xiang'An South Rd, Xiamen, 361102, China
| | - Pengfei Xu
- Institute of Clinical Pharmacy & Pharmacology, Jining First People's Hospital, Jining Medical University, Jining, 272000, China
- Department of Diagnostic Radiology, Yong Loo Lin School of Medicine and Faculty of Engineering, National University of Singapore, Singapore, 119074, Singapore
| | - Xinying Zeng
- State Key Laboratory of Molecular Vaccinology and Molecular, Diagnostics & Center for Molecular Imaging and Translational Medicine, School of PublicHealth, Xiamen University, 4221-116 Xiang'An South Rd, Xiamen, 361102, China
| | - Jia Liu
- State Key Laboratory of Molecular Vaccinology and Molecular, Diagnostics & Center for Molecular Imaging and Translational Medicine, School of PublicHealth, Xiamen University, 4221-116 Xiang'An South Rd, Xiamen, 361102, China
| | - Chao Du
- State Key Laboratory of Molecular Vaccinology and Molecular, Diagnostics & Center for Molecular Imaging and Translational Medicine, School of PublicHealth, Xiamen University, 4221-116 Xiang'An South Rd, Xiamen, 361102, China
| | - Xueyuan Zeng
- State Key Laboratory of Molecular Vaccinology and Molecular, Diagnostics & Center for Molecular Imaging and Translational Medicine, School of PublicHealth, Xiamen University, 4221-116 Xiang'An South Rd, Xiamen, 361102, China
| | - Xingxing Cheng
- State Key Laboratory of Molecular Vaccinology and Molecular, Diagnostics & Center for Molecular Imaging and Translational Medicine, School of PublicHealth, Xiamen University, 4221-116 Xiang'An South Rd, Xiamen, 361102, China
| | - Xueqi Wang
- State Key Laboratory of Molecular Vaccinology and Molecular, Diagnostics & Center for Molecular Imaging and Translational Medicine, School of PublicHealth, Xiamen University, 4221-116 Xiang'An South Rd, Xiamen, 361102, China
| | - Yuanyuan Liang
- State Key Laboratory of Molecular Vaccinology and Molecular, Diagnostics & Center for Molecular Imaging and Translational Medicine, School of PublicHealth, Xiamen University, 4221-116 Xiang'An South Rd, Xiamen, 361102, China
| | - Tianzhi Zhao
- Department of Diagnostic Radiology, Yong Loo Lin School of Medicine and Faculty of Engineering, National University of Singapore, Singapore, 119074, Singapore
| | - Hongzhang Yang
- State Key Laboratory of Molecular Vaccinology and Molecular, Diagnostics & Center for Molecular Imaging and Translational Medicine, School of PublicHealth, Xiamen University, 4221-116 Xiang'An South Rd, Xiamen, 361102, China
| | - Huifeng Li
- State Key Laboratory of Molecular Vaccinology and Molecular, Diagnostics & Center for Molecular Imaging and Translational Medicine, School of PublicHealth, Xiamen University, 4221-116 Xiang'An South Rd, Xiamen, 361102, China
| | - Lingxin Meng
- State Key Laboratory of Molecular Vaccinology and Molecular, Diagnostics & Center for Molecular Imaging and Translational Medicine, School of PublicHealth, Xiamen University, 4221-116 Xiang'An South Rd, Xiamen, 361102, China
| | - Jianyang Fang
- State Key Laboratory of Molecular Vaccinology and Molecular, Diagnostics & Center for Molecular Imaging and Translational Medicine, School of PublicHealth, Xiamen University, 4221-116 Xiang'An South Rd, Xiamen, 361102, China
| | - Hongwu Liu
- State Key Laboratory of Molecular Vaccinology and Molecular, Diagnostics & Center for Molecular Imaging and Translational Medicine, School of PublicHealth, Xiamen University, 4221-116 Xiang'An South Rd, Xiamen, 361102, China
| | - Zijian Zhou
- State Key Laboratory of Molecular Vaccinology and Molecular, Diagnostics & Center for Molecular Imaging and Translational Medicine, School of PublicHealth, Xiamen University, 4221-116 Xiang'An South Rd, Xiamen, 361102, China
| | - Jingjing Zhang
- Department of Diagnostic Radiology, Yong Loo Lin School of Medicine and Faculty of Engineering, National University of Singapore, Singapore, 119074, Singapore.
- Nanomedicine Translational Research Program, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, 117597, Singapore.
- Clinical Imaging Research Centre, Centre for Translational Medicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, 117599, Singapore.
| | - Xianzhong Zhang
- State Key Laboratory of Molecular Vaccinology and Molecular, Diagnostics & Center for Molecular Imaging and Translational Medicine, School of PublicHealth, Xiamen University, 4221-116 Xiang'An South Rd, Xiamen, 361102, China.
| | - Zhide Guo
- State Key Laboratory of Molecular Vaccinology and Molecular, Diagnostics & Center for Molecular Imaging and Translational Medicine, School of PublicHealth, Xiamen University, 4221-116 Xiang'An South Rd, Xiamen, 361102, China.
| | - Xiaoyuan Chen
- Department of Diagnostic Radiology, Yong Loo Lin School of Medicine and Faculty of Engineering, National University of Singapore, Singapore, 119074, Singapore.
- Nanomedicine Translational Research Program, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, 117597, Singapore.
- Clinical Imaging Research Centre, Centre for Translational Medicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, 117599, Singapore.
- Departments of Surgery, Chemical and Biomolecular Engineering, and Biomedical Engineering, Yong Loo Lin School of Medicine and Faculty of Engineering, National University of Singapore, Singapore, 119074, Singapore.
- Institute of Molecular and Cell Biology, Agency for Science, Technology, and Research (A*STAR), 61 Biopolis Drive, Proteos, Singapore, 138673, Singapore.
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Tsuchihashi S, Nakashima K, Tarumizu Y, Ichikawa H, Jinda H, Watanabe H, Ono M. Development of Novel 111In/ 225Ac-Labeled Agent Targeting PSMA for Highly Efficient Cancer Radiotheranostics. J Med Chem 2023. [PMID: 37285471 DOI: 10.1021/acs.jmedchem.3c00346] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Prostate-specific membrane antigen (PSMA) is a promising target for metastatic castration-resistant prostate cancer. We previously reported the effectiveness of PSMA-DA1 as a PSMA-targeting radiotheranostic agent containing an albumin binder moiety. To further enhance tumor uptake, we newly designed PSMA-NAT-DA1 (PNT-DA1) by the introduction of a lipophilic linker into PSMA-DA1. The PSMA affinity of [111In]In-PNT-DA1 was increased (Kd = 8.20 nM) compared with that of [111In]In-PSMA-DA1 (Kd = 89.4 nM). [111In]In-PNT-DA1 showed markedly high tumor accumulation (131.6% injected dose/g at 48 h post-injection), and [111In]In-PNT-DA1 enabled the visualization of the tumor clearly at 24 h post-injection with SPECT/CT imaging. The administration of [225Ac]Ac-PNT-DA1 (2.5 kBq) led to shrinkage of the tumor without marked toxicity, and the antitumor effects of [225Ac]Ac-PNT-DA1 were superior to those of [225Ac]Ac-PSMA-DA1 and [225Ac]Ac-PSMA-617, which is the current gold standard for PSMA-targeting 225Ac-endoradiotherapy. These results suggest that the combination of [111In]In-PNT-DA1 and [225Ac]Ac-PNT-DA1 comprises a promising method of PSMA-targeting radiotheranostics.
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Affiliation(s)
- Shohei Tsuchihashi
- Department of Patho-Functional Bioanalysis, Graduate School of Pharmaceutical Sciences, Kyoto University, 46-29 Yoshida Shimoadachi-cho, Sakyo-ku, Kyoto 606-8501, Japan
| | - Kazuma Nakashima
- Department of Patho-Functional Bioanalysis, Graduate School of Pharmaceutical Sciences, Kyoto University, 46-29 Yoshida Shimoadachi-cho, Sakyo-ku, Kyoto 606-8501, Japan
| | - Yuta Tarumizu
- Research Center, Nihon Medi-Physics Co., Ltd., 3-1 Sodegaura-shi, Chiba 299-0266, Japan
| | - Hiroaki Ichikawa
- Research Center, Nihon Medi-Physics Co., Ltd., 3-1 Sodegaura-shi, Chiba 299-0266, Japan
| | - Hiroki Jinda
- Department of Patho-Functional Bioanalysis, Graduate School of Pharmaceutical Sciences, Kyoto University, 46-29 Yoshida Shimoadachi-cho, Sakyo-ku, Kyoto 606-8501, Japan
| | - Hiroyuki Watanabe
- Department of Patho-Functional Bioanalysis, Graduate School of Pharmaceutical Sciences, Kyoto University, 46-29 Yoshida Shimoadachi-cho, Sakyo-ku, Kyoto 606-8501, Japan
| | - Masahiro Ono
- Department of Patho-Functional Bioanalysis, Graduate School of Pharmaceutical Sciences, Kyoto University, 46-29 Yoshida Shimoadachi-cho, Sakyo-ku, Kyoto 606-8501, Japan
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7
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Zhang H, Rao M, Zhao H, Ren J, Hao L, Zhong M, Chen Y, Yang X, Feng Y, Yuan G. Imageological/Structural Study regarding the Improved Pharmacokinetics by 68Ga-Labeled PEGylated PSMA Multimer in Prostate Cancer. Pharmaceuticals (Basel) 2023; 16:ph16040589. [PMID: 37111347 PMCID: PMC10144514 DOI: 10.3390/ph16040589] [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: 03/08/2023] [Revised: 04/07/2023] [Accepted: 04/10/2023] [Indexed: 04/29/2023] Open
Abstract
PMSA (prostate-specific membrane antigen) is currently the most significant target for diagnosing and treating PCa (prostate cancer). Herein, we reported a series 68Ga/177Lu-labeled multimer PSMA tracer conjugating with PEG chain, including [68Ga]Ga-DOTA-(1P-PEG4), [68Ga]Ga-DOTA-(2P-PEG0), [68Ga]Ga-DOTA-(2P-PEG4), and [68Ga]Ga/[177Lu]Lu-DOTA-(2P-PEG4)2, which showed an advantage of a multivalent effect and PEGylation to achieve higher tumor accumulation and faster kidney clearance. To figure out how structural optimizations based on a PSMA multimer and PEGylation influence the probe's tumor-targeting ability, biodistribution, and metabolism, we examined PSMA molecular probes' affinities to PC-3 PIP (PSMA-highly-expressed PC-3 cell line), and conducted pharmacokinetics analysis, biodistribution detection, small animal PET/CT, and SPECT/CT imaging. The results showed that PEG4 and PSMA dimer optimizations enhanced the probes' tumor-targeting ability in PC-3 PIP tumor-bearing mice models. Compared with the PSMA monomer, the PEGylated PSMA dimer reduced the elimination half-life in the blood and increased uptake in the tumor, and the biodistribution results were consistent with PET/CT imaging results. [68Ga]Ga-DOTA-(2P-PEG4)2 exhibited higher tumor-to-organ ratios. When labeled by lutetium-177, relatively high accumulation of DOTA-(2P-PEG4)2 was still detected in PC-3 PIP tumor-bearing mice models after 48 h, indicating its prolonged tumor retention time. Given the superiority in imaging, simple synthetic processes, and structural stability, DOTA-(2P-PEG4)2 is expected to be a promising tumor-targeting diagnostic molecular probe in future clinical practice.
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Affiliation(s)
- Huihui Zhang
- Department of Nuclear Medicine, The Second Affiliated Hospital of Chongqing Medical University, Chongqing 400010, China
| | - Maohua Rao
- Department of Nuclear Medicine, The Second Affiliated Hospital of Chongqing Medical University, Chongqing 400010, China
| | - Huayi Zhao
- Department of Nuclear Medicine, The Second Affiliated Hospital of Chongqing Medical University, Chongqing 400010, China
| | - Jianli Ren
- Chongqing Key Laboratory of Ultrasound Molecular Imaging, Second Affiliated Hospital of Chongqing Medical University, Chongqing 400010, China
| | - Lan Hao
- Chongqing Key Laboratory of Ultrasound Molecular Imaging, Second Affiliated Hospital of Chongqing Medical University, Chongqing 400010, China
| | - Meng Zhong
- Department of Pharmacy, The Affiliated Hospital of Southwest Medical University, Luzhou 646600, China
| | - Yue Chen
- Nuclear Medicine and Molecular Imaging Key Laboratory of Sichuan Province, Luzhou 646600, China
| | - Xia Yang
- Institute of Nuclear Physics and Chemistry, Academy of Engineering Physics, Mianyang 621900, China
| | - Yue Feng
- Nuclear Medicine and Molecular Imaging Key Laboratory of Sichuan Province, Luzhou 646600, China
| | - Gengbiao Yuan
- Department of Nuclear Medicine, The Second Affiliated Hospital of Chongqing Medical University, Chongqing 400010, China
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[ 225Ac]Ac-SibuDAB for Targeted Alpha Therapy of Prostate Cancer: Preclinical Evaluation and Comparison with [ 225Ac]Ac-PSMA-617. Cancers (Basel) 2022; 14:cancers14225651. [PMID: 36428743 PMCID: PMC9688344 DOI: 10.3390/cancers14225651] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2022] [Revised: 11/11/2022] [Accepted: 11/14/2022] [Indexed: 11/19/2022] Open
Abstract
In the present study, SibuDAB, an albumin-binding PSMA ligand, was investigated in combination with actinium-225 and the data were compared with those of [225Ac]Ac-PSMA-617. In vitro, [225Ac]Ac-SibuDAB and [225Ac]Ac-PSMA-617 showed similar tumor cell uptake and PSMA-binding affinities as their 177Lu-labeled counterparts. The in vitro binding to serum albumin in mouse and human blood plasma, respectively, was 2.8-fold and 1.4-fold increased for [225Ac]Ac-SibuDAB as compared to [177Lu]Lu-SibuDAB. In vivo, this characteristic was reflected by the longer retention of [225Ac]Ac-SibuDAB in the blood than previously seen for [177Lu]Lu-SibuDAB. Similar to [225Ac]Ac-PSMA-617, [225Ac]Ac-SibuDAB was well tolerated at 30 kBq per mouse. Differences in blood cell counts were observed between treated mice and untreated controls, but no major variations were observed between values obtained for [225Ac]Ac-SibuDAB and [225Ac]Ac-PSMA-617. [225Ac]Ac-SibuDAB was considerably more effective to treat PSMA-positive tumor xenografts than [225Ac]Ac-PSMA-617. Only 5 kBq per mouse were sufficient to eradicate the tumors, whereas tumor regrowth was observed for mice treated with 5 kBq [225Ac]Ac-PSMA-617 and only one out of six mice survived until the end of the study. The enhanced therapeutic efficacy of [225Ac]Ac-SibuDAB as compared to that of [225Ac]Ac-PSMA-617 and reasonable safety data qualify this novel radioligand as a candidate for targeted α-therapy of prostate cancer.
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9
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Jeitner TM, Babich JW, Kelly JM. Advances in PSMA theranostics. Transl Oncol 2022; 22:101450. [PMID: 35597190 PMCID: PMC9123266 DOI: 10.1016/j.tranon.2022.101450] [Citation(s) in RCA: 26] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2022] [Revised: 05/04/2022] [Accepted: 05/08/2022] [Indexed: 12/15/2022] Open
Abstract
PSMA is an appealing target for theranostic because it is a transmembrane protein with a known substrate that is overexpessed on prostate cancer cells and internalizes upon ligand binding. There are a number of PSMA theranostic ligands in clinical evaluation, clinical trial, or clinically approved. PSMA theranostic ligands increase progression-free survival, overall survival, and pain in patients with metastatic castration resistant prostate cancer. A major obstacle to PSMA-targeted radioligand therapy is off-target toxicity in salivary glands.
The validation of prostate specific membrane antigen (PSMA) as a molecular target in metastatic castration-resistant prostate cancer has stimulated the development of multiple classes of theranostic ligands that specifically target PSMA. Theranostic ligands are used to image disease or selectively deliver cytotoxic radioactivity to cells expressing PSMA according to the radioisotope conjugated to the ligand. PSMA theranostics is a rapidly advancing field that is now integrating into clinical management of prostate cancer patients. In this review we summarize published research describing the biological role(s) and activity of PSMA, highlight the most clinically advanced PSMA targeting molecules and biomacromolecules, and identify next generation PSMA ligands that aim to further improve treatment efficacy. The goal of this review is to provide a comprehensive assessment of the current state-of-play and a roadmap to achieving further advances in PSMA theranostics.
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Affiliation(s)
- Thomas M Jeitner
- Molecular Imaging Innovations Institute, Department of Radiology, Weill Cornell Medicine, Belfer Research Building, 413 East 69th Street, Room BB-1604, New York, NY 10021, USA
| | - John W Babich
- Molecular Imaging Innovations Institute, Department of Radiology, Weill Cornell Medicine, Belfer Research Building, 413 East 69th Street, Room BB-1604, New York, NY 10021, USA; Weill Cornell Medicine, Sandra and Edward Meyer Cancer Center, New York, NY 10021, USA; Weill Cornell Medicine, Citigroup Biomedical Imaging Center, New York, NY 10021, USA
| | - James M Kelly
- Molecular Imaging Innovations Institute, Department of Radiology, Weill Cornell Medicine, Belfer Research Building, 413 East 69th Street, Room BB-1604, New York, NY 10021, USA; Weill Cornell Medicine, Citigroup Biomedical Imaging Center, New York, NY 10021, USA.
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10
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Borgna F, Deberle LM, Busslinger SD, Tschan VJ, Walde LM, Becker AE, Schibli R, Müller C. Preclinical Investigations to Explore the Difference between the Diastereomers [ 177Lu]Lu-SibuDAB and [ 177Lu]Lu-RibuDAB toward Prostate Cancer Therapy. Mol Pharm 2022; 19:2105-2114. [PMID: 35544699 DOI: 10.1021/acs.molpharmaceut.1c00994] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
[177Lu]Lu-Ibu-DAB-PSMA, a radioligand modified with ibuprofen as the albumin binder, showed higher accumulation in PSMA-positive tumors of mice than the clinically used [177Lu]Lu-PSMA-617 but lower retention in non-targeted tissues than previously developed albumin-binding PSMA radioligands. The aim of this study was to investigate whether the stereochemistry of the incorporated ibuprofen affects the radioligand's in vitro and in vivo properties and to select the more favorable radioligand for further development. For this purpose, SibuDAB and RibuDAB containing (S)- and (R)-ibuprofen, respectively, were synthesized and labeled with lutetium-177. In vitro, the two isomers had similar properties; however, [177Lu]Lu-SibuDAB showed increased binding to mouse and human plasma proteins (91 ± 1 and 88 ± 2%, respectively) compared to [177Lu]Lu-RibuDAB (75 ± 2 and 79 ± 2%, respectively). In vivo, [177Lu]Lu-SibuDAB was metabolically more stable than [177Lu]Lu-RibuDAB with ∼90 vs ∼67% intact radioligand detected in the blood at 4 h post injection (p.i.). In line with the lower albumin-binding affinity, the blood clearance of [177Lu]Lu-RibuDAB in mice was considerably faster [27% of injected activity (% IA), 1 h p.i.] than for [177Lu]Lu-SibuDAB (50% IA, 1 h p.i.). Time-dependent biodistribution studies performed in tumor-bearing athymic nude mice showed high PSMA-specific tumor uptake for both isomers. A twofold increased area under the curve (AUC0→8d) of the blood retention was determined for [177Lu]Lu-SibuDAB as compared to [177Lu]Lu-RibuDAB, whereas the kidney AUC0→8d value of [177Lu]Lu-SibuDAB was only half as high as for [177Lu]Lu-RibuDAB. As a result, a more favorable tumor-to-kidney AUC0→8d ratio was obtained for [177Lu]Lu-SibuDAB, which was also visualized on SPECT/CT images. Based on its improved kidney clearance and higher metabolic stability, [177Lu]Lu-SibuDAB was selected as the more favorable radioligand. Therapy studies performed with [177Lu]Lu-SibuDAB (5 MBq/mouse) demonstrated the anticipated therapeutic superiority over the current gold-standard [177Lu]Lu-PSMA-617 (5 MBq/mouse). The significantly increased survival time of mice treated with [177Lu]Lu-SibuDAB as compared to those injected with [177Lu]Lu-PSMA-617 justifies further development of this novel radioligand toward clinical application.
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Affiliation(s)
- Francesca Borgna
- Center for Radiopharmaceutical Sciences ETH-PSI-USZ, Paul Scherrer Institute, Villigen-PSI 5232, Switzerland
| | - Luisa M Deberle
- Center for Radiopharmaceutical Sciences ETH-PSI-USZ, Paul Scherrer Institute, Villigen-PSI 5232, Switzerland
| | - Sarah D Busslinger
- Center for Radiopharmaceutical Sciences ETH-PSI-USZ, Paul Scherrer Institute, Villigen-PSI 5232, Switzerland
| | - Viviane J Tschan
- Center for Radiopharmaceutical Sciences ETH-PSI-USZ, Paul Scherrer Institute, Villigen-PSI 5232, Switzerland
| | - Laura M Walde
- Center for Radiopharmaceutical Sciences ETH-PSI-USZ, Paul Scherrer Institute, Villigen-PSI 5232, Switzerland
| | - Anna E Becker
- Center for Radiopharmaceutical Sciences ETH-PSI-USZ, Paul Scherrer Institute, Villigen-PSI 5232, Switzerland
| | - Roger Schibli
- Center for Radiopharmaceutical Sciences ETH-PSI-USZ, Paul Scherrer Institute, Villigen-PSI 5232, Switzerland.,Department of Chemistry and Applied Biosciences, ETH Zurich, Zurich 8093, Switzerland
| | - Cristina Müller
- Center for Radiopharmaceutical Sciences ETH-PSI-USZ, Paul Scherrer Institute, Villigen-PSI 5232, Switzerland.,Department of Chemistry and Applied Biosciences, ETH Zurich, Zurich 8093, Switzerland
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11
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Neels OC, Kopka K, Liolios C, Afshar-Oromieh A. Radiolabeled PSMA Inhibitors. Cancers (Basel) 2021; 13:6255. [PMID: 34944875 PMCID: PMC8699044 DOI: 10.3390/cancers13246255] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2021] [Revised: 12/10/2021] [Accepted: 12/11/2021] [Indexed: 12/16/2022] Open
Abstract
PSMA has shown to be a promising target for diagnosis and therapy (theranostics) of prostate cancer. We have reviewed developments in the field of radio- and fluorescence-guided surgery and targeted photodynamic therapy as well as multitargeting PSMA inhibitors also addressing albumin, GRPr and integrin αvβ3. An overview of the regulatory status of PSMA-targeting radiopharmaceuticals in the USA and Europe is also provided. Technical and quality aspects of PSMA-targeting radiopharmaceuticals are described and new emerging radiolabeling strategies are discussed. Furthermore, insights are given into the production, application and potential of alternatives beyond the commonly used radionuclides for radiolabeling PSMA inhibitors. An additional refinement of radiopharmaceuticals is required in order to further improve dose-limiting factors, such as nephrotoxicity and salivary gland uptake during endoradiotherapy. The improvement of patient treatment achieved by the advantageous combination of radionuclide therapy with alternative therapies is also a special focus of this review.
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Affiliation(s)
- Oliver C. Neels
- Institute of Radiopharmaceutical Cancer Research, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Bautzner Landstrasse 400, 01328 Dresden, Germany;
| | - Klaus Kopka
- Institute of Radiopharmaceutical Cancer Research, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Bautzner Landstrasse 400, 01328 Dresden, Germany;
- Faculty of Chemistry and Food Chemistry, School of Science, Technical University Dresden, Mommsenstrasse 4, 01062 Dresden, Germany
| | - Christos Liolios
- Department of Pharmaceutical Chemistry, Faculty of Pharmacy, National & Kapodistrian University of Athens, Zografou, 15771 Athens, Greece;
- INRASTES, Radiochemistry Laboratory, NCSR “Demokritos”, Ag. Paraskevi Attikis, 15310 Athens, Greece
| | - Ali Afshar-Oromieh
- Department of Nuclear Medicine, Bern University Hospital (Inselspital), Freiburgstrasse 18, 3010 Bern, Switzerland;
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12
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Alghazo O, Eapen R, Koschel S, Cumberbatch M, Buteau J, Loh R, Lawrentschuk N, Murphy DG. The application of theranostics in different stages of prostate cancer. Future Oncol 2021; 17:3637-3644. [PMID: 34227404 DOI: 10.2217/fon-2020-1209] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Despite the remarkable achievements in treating metastatic prostate cancer over the last two decades, castrate-resistant status is still considered the lethal stage of the disease. Theranostics combines a targeting compound (ligand) with a therapeutic radioisotope (radioactive particle) injected into the blood to target the cancer cells. The most studied radioligand is 177Lu-PSMA-617, which targets PSMA, a protein found in prostate cancer cells. This new approach has shown promising results in treating metastatic castration-resistant prostate cancer. Currently, many trials are using PSMA-targeting radioligands in combination with conventional therapies in advanced prostate cancer or even in the earlier stages of the disease. Other preclinical trials are exploring the possibility of using newer ligands or radioisotopes to treat prostate cancer to increase the specificity and efficacy of this treatment.
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Affiliation(s)
- Omar Alghazo
- Division of Cancer Surgery, Peter MacCallum Cancer Centre, Melbourne 3000, Australia.,Prostate Cancer Theranostics & Imaging Centre of Excellence, Peter MacCallum Cancer Centre, Melbourne 3000, Australia.,The Sir Peter MacCallum Department of Oncology, University of Melbourne, Melbourne 3000, Australia.,Urology Division, Clinical Sciences Department, Yarmouk University, Irbid 21163, Jordan
| | - Renu Eapen
- Division of Cancer Surgery, Peter MacCallum Cancer Centre, Melbourne 3000, Australia.,Prostate Cancer Theranostics & Imaging Centre of Excellence, Peter MacCallum Cancer Centre, Melbourne 3000, Australia.,The Sir Peter MacCallum Department of Oncology, University of Melbourne, Melbourne 3000, Australia
| | - Samantha Koschel
- Division of Cancer Surgery, Peter MacCallum Cancer Centre, Melbourne 3000, Australia
| | - Marcus Cumberbatch
- Division of Cancer Surgery, Peter MacCallum Cancer Centre, Melbourne 3000, Australia.,Department of Academic Urology, University of Sheffield, Sheffield, UK
| | - James Buteau
- Prostate Cancer Theranostics & Imaging Centre of Excellence, Peter MacCallum Cancer Centre, Melbourne 3000, Australia.,Molecular Imaging & Nuclear Medicine Therapeutics, Peter MacCallum Cancer Centre, Melbourne 3000, Australia
| | - Rebecca Loh
- Prostate Cancer Theranostics & Imaging Centre of Excellence, Peter MacCallum Cancer Centre, Melbourne 3000, Australia
| | - Nathan Lawrentschuk
- Division of Cancer Surgery, Peter MacCallum Cancer Centre, Melbourne 3000, Australia.,Prostate Cancer Theranostics & Imaging Centre of Excellence, Peter MacCallum Cancer Centre, Melbourne 3000, Australia.,Department of Urology, Royal Melbourne Hospital, Melbourne 3052, Australia.,E J Whitten Prostate Cancer Research Centre, Epworth Healthcare, Victoria 3121, Australia
| | - Declan G Murphy
- Division of Cancer Surgery, Peter MacCallum Cancer Centre, Melbourne 3000, Australia.,Prostate Cancer Theranostics & Imaging Centre of Excellence, Peter MacCallum Cancer Centre, Melbourne 3000, Australia.,The Sir Peter MacCallum Department of Oncology, University of Melbourne, Melbourne 3000, Australia
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13
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Preparation and Biological Evaluation of [ 99mTc]Tc-CNGU as a PSMA-Targeted Radiotracer for the Imaging of Prostate Cancer. Molecules 2020; 25:molecules25235548. [PMID: 33256058 PMCID: PMC7730407 DOI: 10.3390/molecules25235548] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2020] [Revised: 11/21/2020] [Accepted: 11/23/2020] [Indexed: 12/24/2022] Open
Abstract
Prostate-specific membrane antigen (PSMA) is a well-established biological target that is overexpressed on the surface of prostate cancer lesions. Radionuclide-labeled small-molecule PSMA inhibitors have been shown to be promising PSMA-specific agents for the diagnosis and therapy of prostate cancer. In this study, a glutamate-urea-based PSMA-targeted ligand containing an isonitrile (CNGU) was synthesized and labeled with 99mTc to prepare [99mTc]Tc-CNGU with a high radiochemical purity (RCP). The CNGU ligand showed a high affinity toward PSMA (Ki value is 8.79 nM) in LNCaP cells. The [99mTc]Tc-CNGU exhibited a good stability in vitro and hydrophilicity (log P = −1.97 ± 0.03). In biodistribution studies, BALB/c nude mice bearing LNCaP xenografts showed that the complex had a high tumor uptake with 4.86 ± 1.19% ID/g, which decreased to 1.74 ± 0.90% ID/g after a pre-injection of the selective PSMA inhibitor ZJ-43, suggesting that it was a PSMA-specific agent. Micro-SPECT imaging demonstrated that the [99mTc]Tc-CNGU had a tumor uptake and that the uptake was reduced in the image after blocking with ZJ-43, further confirming its PSMA specificity. All of the results in this work indicated that [99mTc]Tc-CNGU is a promising PSMA-specific tracer for the imaging of prostate cancer.
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