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Vorster M, Sathekge M. Advances in PSMA Alpha Theragnostics. Semin Nucl Med 2024; 54:591-602. [PMID: 38658300 DOI: 10.1053/j.semnuclmed.2024.03.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2024] [Accepted: 03/19/2024] [Indexed: 04/26/2024]
Abstract
Alpha theranostics offer an attractive alternative form of therapy, which has best been investigated and documented with 225Ac-PSMA in patients with prostate cancer. Advantages offered by targeted alpha therapy include overcoming radiation resistance, oxygen independence, effecting double-stranded DNA breakages within the tumors with anticipated improved clinical outcomes and an acceptable side effect profile. The previous Seminars article on this topic, published in 2020, had to rely mostly on published case reports and small observational studies. In the last few years, however, several meta-analyses have emerged that evaluate the safety and efficacy of 225Ac-PSMA in prostate cancer patients, followed most recently by a multi-center retrospective study initiated by WARMTH. The findings of these publications, together with the exploration of TAT offered in clinical conditions other than as a last resort, is the focus of this updated overview. Unresolved clinical issues that remain, include the appropriate selection of patients that would benefit most from treatment with 225Ac-PSMA, treatment timing within the disease landscape, optimal dosing schedule, dosimetry, when and how to best use combination therapies and minimization and treatment of side effects, particularly that of xerostomia.
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Affiliation(s)
- Mariza Vorster
- Department of Nuclear Medicine at Inkosi Albert Luthuli Hospital, University of KwaZulu-Natal, KwaZulu-Natal, South Africa.
| | - Mike Sathekge
- Department of Nuclear Medicine, University of Pretoria & Steve Biko Academic Hospital, Private Bag X169, Pretoria 0001, South Africa; Nuclear Medicine Research Infrastructure (NuMeRI), Steve Biko Academic Hospital, Pretoria 0001, South Africa
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Siebinga H, Hendrikx JJMA, Huitema ADR, de Wit-van der Veen BJ. Predicting the effect of different folate doses on [ 68Ga]Ga-PSMA-11 organ and tumor uptake using physiologically based pharmacokinetic modeling. EJNMMI Res 2023; 13:60. [PMID: 37318681 DOI: 10.1186/s13550-023-01008-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2023] [Accepted: 05/26/2023] [Indexed: 06/16/2023] Open
Abstract
BACKGROUND Folate intake might reduce [68Ga]Ga-PSMA-11 uptake in tissues due to a competitive binding to the PSMA receptor. For diagnostic imaging, this could impact decision making, while during radioligand therapy this could affect treatment efficacy. The relationship between folate dose, timing of dosing and tumor and organ uptake is not well established. The aim of this study was to develop a physiologically based pharmacokinetic (PBPK) model to predict the effect of folates on [68Ga]Ga-PSMA-11 PET/CT uptake in salivary glands, kidneys and tumors. METHODS A PBPK model was developed for [68Ga]Ga-PSMA-11 and folates (folic acid and its metabolite 5-MTHF), with compartments added that represent salivary glands and tumor. Reactions describing receptor binding, internalization and intracellular degradation were included. Model evaluation for [68Ga]Ga-PSMA-11 was performed by using patient scan data from two different studies (static and dynamic), while for folates data from the literature were used for evaluation. Simulations were performed to assess the effect of different folate doses (150 µg, 400 µg, 5 mg and 10 mg) on accumulation in salivary glands, kidney and tumor, also for patients with different tumor volumes (10, 100, 500 and 1000 mL). RESULTS Final model evaluation showed that predictions adequately described data for both [68Ga]Ga-PSMA-11 and folates. Predictions of a 5-MTFH dose of 150 µg and folic acid dose of 400 µg (in case of administration at the same time as [68Ga]Ga-PSMA-11 (t = 0)) showed no clinically relevant effect on salivary glands and kidney uptake. However, the effect of a decrease in salivary glands and kidney uptake was determined to be clinically relevant for doses of 5 mg (34% decrease for salivary glands and 32% decrease for kidney) and 10 mg (36% decrease for salivary glands and 34% decrease for kidney). Predictions showed that tumor uptake was not relevantly affected by the co-administration of folate for all different folate doses (range 150 µg-10 mg). Lastly, different tumor volumes did not impact the folate effect on [68Ga]Ga-PSMA-11 biodistribution. CONCLUSION Using a PBPK model approach, high doses of folate (5 and 10 mg) were predicted to show a decrease of [68Ga]Ga-PSMA-11 salivary glands and kidney uptake, while intake by means of folate containing food or vitamin supplements showed no relevant effects. In addition, tumor uptake was not affected by folate administration in the simulated dose ranges (150 µg-10 mg). Differences in tumor volume are not expected to impact folate effects on [68Ga]Ga-PSMA-11 organ uptake.
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Affiliation(s)
- Hinke Siebinga
- Department of Pharmacy and Pharmacology, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
- Department of Nuclear Medicine, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
| | - Jeroen J M A Hendrikx
- Department of Pharmacy and Pharmacology, The Netherlands Cancer Institute, Amsterdam, The Netherlands
- Department of Nuclear Medicine, The Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Alwin D R Huitema
- Department of Pharmacy and Pharmacology, The Netherlands Cancer Institute, Amsterdam, The Netherlands
- Department of Clinical Pharmacy, University Medical Center Utrecht, Utrecht University, Utrecht, The Netherlands
- Department of Pharmacology, Princess Máxima Center for Pediatric Oncology, Utrecht, The Netherlands
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Heynickx N, Segers C, Coolkens A, Baatout S, Vermeulen K. Characterization of Non-Specific Uptake and Retention Mechanisms of [ 177Lu]Lu-PSMA-617 in the Salivary Glands. Pharmaceuticals (Basel) 2023; 16:ph16050692. [PMID: 37242475 DOI: 10.3390/ph16050692] [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: 03/30/2023] [Revised: 04/24/2023] [Accepted: 04/25/2023] [Indexed: 05/28/2023] Open
Abstract
The radionuclide therapy [177Lu]Lu-PSMA-617 was recently FDA-approved for treatment of metastatic castration-resistant prostate cancer. Salivary gland toxicity is currently considered as the main dose-limiting side effect. However, its uptake and retention mechanisms in the salivary glands remain elusive. Therefore, our aim was to elucidate the uptake patterns of [177Lu]Lu-PSMA-617 in salivary gland tissue and cells by conducting cellular binding and autoradiography experiments. Briefly, A-253 and PC3-PIP cells, and mouse kidney and pig salivary gland tissue, were incubated with 5 nM [177Lu]Lu-PSMA-617 to characterize its binding. Additionally, [177Lu]Lu-PSMA-617 was co-incubated with monosodium glutamate, ionotropic or metabotropic glutamate receptor antagonists. Low, non-specific binding was observed in salivary gland cells and tissues. Monosodium glutamate was able to decrease [177Lu]Lu-PSMA-617 in PC3-PIP cells, mouse kidney and pig salivary gland tissue. Kynurenic acid (ionotropic antagonist) decreased the binding of [177Lu]Lu-PSMA-617 to 29.2 ± 20.6% and 63.4 ± 15.4%, respectively, with similar effects observed on tissues. (RS)-MCPG (metabotropic antagonist) was able to decrease the [177Lu]Lu-PSMA-617 binding on A-253 cells to 68.2 ± 16.8% and pig salivary gland tissue to 53.1 ± 36.8%. To conclude, we showed that the non-specific binding on [177Lu]Lu-PSMA-617 could be reduced by monosodium glutamate, kynurenic acid and (RS)-MCPG.
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Affiliation(s)
- Nathalie Heynickx
- Nuclear Medical Applications Institute, Belgian Nuclear Research Centre (SCK CEN), 2400 Mol, Belgium
- Department of Molecular Biotechnology, Faculty of Bioscience Engineering, Ghent University, 9000 Ghent, Belgium
| | - Charlotte Segers
- Nuclear Medical Applications Institute, Belgian Nuclear Research Centre (SCK CEN), 2400 Mol, Belgium
| | - Amelie Coolkens
- Nuclear Medical Applications Institute, Belgian Nuclear Research Centre (SCK CEN), 2400 Mol, Belgium
| | - Sarah Baatout
- Nuclear Medical Applications Institute, Belgian Nuclear Research Centre (SCK CEN), 2400 Mol, Belgium
- Department of Molecular Biotechnology, Faculty of Bioscience Engineering, Ghent University, 9000 Ghent, Belgium
- Department of Human Structure and Repair, Faculty of Medicine and Health Sciences, Ghent University, 9000 Ghent, Belgium
| | - Koen Vermeulen
- Nuclear Medical Applications Institute, Belgian Nuclear Research Centre (SCK CEN), 2400 Mol, Belgium
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Sheehan B, Guo C, Neeb A, Paschalis A, Sandhu S, de Bono JS. Prostate-specific Membrane Antigen Biology in Lethal Prostate Cancer and its Therapeutic Implications. Eur Urol Focus 2022; 8:1157-1168. [PMID: 34167925 DOI: 10.1016/j.euf.2021.06.006] [Citation(s) in RCA: 31] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2021] [Revised: 05/07/2021] [Accepted: 06/09/2021] [Indexed: 12/16/2022]
Abstract
CONTEXT Prostate-specific membrane antigen (PSMA) is a promising, novel theranostic target in advanced prostate cancer (PCa). Multiple PSMA-targeted therapies are currently in clinical development, with some agents showing impressive antitumour activity, although optimal patient selection and therapeutic resistance remain ongoing challenges. OBJECTIVE To review the biology of PSMA and recent advances in PSMA-targeted therapies in PCa, and to discuss potential strategies for patient selection and further therapeutic development. EVIDENCE ACQUISITION A comprehensive literature search was performed using PubMed and review of American Society of Clinical Oncology and European Society of Medical Oncology annual meeting abstracts up to April 2021. EVIDENCE SYNTHESIS PSMA is a largely extracellular protein that is frequently, but heterogeneously, expressed by PCa cells. PSMA expression is associated with disease progression, worse clinical outcomes and the presence of tumour defects in DNA damage repair (DDR). PSMA is also expressed by other cancer cell types and is implicated in glutamate and folate metabolism. It may confer a tumour survival advantage in conditions of cellular stress. PSMA regulation is complex, and recent studies have shed light on interactions with androgen receptor, PI3K/Akt, and DDR signalling. A phase 2 clinical trial has shown that 177Lu-PSMA-617 causes tumour shrinkage and delays disease progression in a significant subset of patients with metastatic castration-resistant PCa in comparison to second-line chemotherapy. Numerous novel PSMA-targeting immunotherapies, small molecules, and antibody therapies are currently in clinical development, including in earlier stages of PCa, with emerging evidence of antitumour activity. To date, the regulation and function of PSMA in PCa cells remain poorly understood. CONCLUSIONS There has been rapid recent progress in PSMA-targeted therapies for the management of advanced PCa. Dissection of PSMA biology will help to identify biomarkers for and resistance mechanisms to these therapies and facilitate further therapeutic development to improve PCa patient outcomes. PATIENT SUMMARY There have been major advances in the development of therapies targeting a molecule, PSMA, in PCa. Radioactive molecules targeting PSMA can cause tumour shrinkage and delay progression in some patients with lethal disease. Future studies are needed to determine which patients are most likely to respond, and how other treatments can be combined with therapies targeting PSMA so that more patients may benefit.
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Affiliation(s)
| | - Christina Guo
- The Institute of Cancer Research, London, UK; The Royal Marsden NHS Foundation Trust, London, UK
| | - Antje Neeb
- The Institute of Cancer Research, London, UK
| | - Alec Paschalis
- The Institute of Cancer Research, London, UK; The Royal Marsden NHS Foundation Trust, London, UK
| | - Shahneen Sandhu
- Department of Medical Oncology, Peter MacCallum Cancer Centre, Melbourne, Australia; University of Melbourne, Melbourne, Australia
| | - Johann S de Bono
- The Institute of Cancer Research, London, UK; The Royal Marsden NHS Foundation Trust, London, UK.
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Boshomane TM, Lawal IO, Sathekge MM. Nuclear medicine therapy of prostate cancer: State of the art and future perspectives. Nucl Med Mol Imaging 2022. [DOI: 10.1016/b978-0-12-822960-6.00038-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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Jackson P, Hofman M, McIntosh L, Buteau JP, Ravi Kumar A. Radiation Dosimetry in 177Lu-PSMA-617 Therapy. Semin Nucl Med 2021; 52:243-254. [PMID: 34893320 DOI: 10.1053/j.semnuclmed.2021.11.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Radionuclide therapy using the small molecule PSMA bound to the beta-emitting radionuclide, Lutetium-177 (177Lu-PSMA) has demonstrated efficacy and survival benefit castrate resistant metastatic disease and represents a novel new line of therapy. Whilst dosimetry was critical for early development, it was not incorporated into either the TheraP or VISION randomized studies, highlighting the difficulty of adopting dosimetry in routine clinical practice. Accumulated clinical experience has also shown that the common (and generally low grade) toxicities such as nausea, xerostomia, and cytopenias are not readily predicted on the basis of dosimetry estimates. The majority of dosimetry and clinical literature deals with the radiopharmaceutical 177Lu-PSMA-617 which displays relatively consistent patterns of retention among normal tissues and high specificity for metastatic prostate cancer phenotypes. Population dosimetry incorporating estimates to the kidneys, salivary glands, and bone marrow have been widely reported the typical range of doses is becoming well established. There is growing interest on tumor dosimetry in 177Lu-PSMA-617 therapy as an overall modest side-effect profile from primary organ retention has been observed. A focus away from normal organ dosimetry to whole body tumor dosimetry may enable early prediction of treatment failure. Given the safety of 177Lu-PSMA there is also potential to escalate administered radioactivity to further improve outcomes. Importantly, the variability of uptake between individuals, both to tumor and normal organs, has also been highlighted which provides some rationale for the utility of personalized radiation analysis to optimize treatment based on potential toxicity thresholds or tumor control. Methods to perform dosimetry using serial post treatment imaging may incorporate planar, 3D SPECT, or hybrid datasets. Reliable measurements may be obtained through either method, however, continued developments in computational analysis are better suited to fully 3D imaging; particularly in conjunction with volumetric CT to assist with alignment and contouring. Dose analysis over sequential treatment cycles is vital to understand the radiobiology of these treatments which is unique compared to external beam therapy due to dose rate, fractionation scheme, and potential for intratumoral nonuniformity.
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Affiliation(s)
- Price Jackson
- Molecular Imaging and Therapeutic Nuclear Medicine, Dept of Cancer Imaging, The Peter MacCallum Cancer Centre, Melbourne, Australia; Sir Peter MacCallum Dept of Oncology, The University of Melbourne, Melbourne, Australia.
| | - Michael Hofman
- Molecular Imaging and Therapeutic Nuclear Medicine, Dept of Cancer Imaging, The Peter MacCallum Cancer Centre, Melbourne, Australia; Sir Peter MacCallum Dept of Oncology, The University of Melbourne, Melbourne, Australia
| | - Lachlan McIntosh
- Molecular Imaging and Therapeutic Nuclear Medicine, Dept of Cancer Imaging, The Peter MacCallum Cancer Centre, Melbourne, Australia
| | - James Patrick Buteau
- Molecular Imaging and Therapeutic Nuclear Medicine, Dept of Cancer Imaging, The Peter MacCallum Cancer Centre, Melbourne, Australia
| | - Aravind Ravi Kumar
- Molecular Imaging and Therapeutic Nuclear Medicine, Dept of Cancer Imaging, The Peter MacCallum Cancer Centre, Melbourne, Australia; Sir Peter MacCallum Dept of Oncology, The University of Melbourne, Melbourne, Australia
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Sathekge MM, Bruchertseifer F, Vorster M, Morgenstern A, Lawal IO. Global experience with PSMA-based alpha therapy in prostate cancer. Eur J Nucl Med Mol Imaging 2021; 49:30-46. [PMID: 34173838 PMCID: PMC8712297 DOI: 10.1007/s00259-021-05434-9] [Citation(s) in RCA: 28] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2021] [Accepted: 05/25/2021] [Indexed: 12/16/2022]
Abstract
PURPOSE This review discusses the current state of prostate-specific membrane antigen (PSMA)-based alpha therapy of metastatic castration-resistant prostate cancer (mCRPC). With this in-depth discussion on the growing field of PSMA-based alpha therapy (PAT), we aimed to increase the interactions between basic scientists and physician-scientists in order to advance the field. METHODS To achieve this, we discuss the potential, current status, and opportunities for alpha therapy and strategies, attempted to date, and important questions that need to be addressed. The paper reviews important concepts, including whom to treat, how to treat, what to expect regarding treatment outcome, and toxicity, and areas requiring further investigations. RESULTS There is much excitement about the potential of this field. Much of the potential exists because these therapies utilize unique mechanisms of action, difficult to achieve with other conventional therapies. CONCLUSION A better understanding of the strengths and limitations of PAT may help in creating an effective therapy for mCRPC and design a rational combinatorial approach to treatment by targeting different tumor pathways.
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Affiliation(s)
- Mike M Sathekge
- Department of Nuclear Medicine, University of Pretoria & Steve Biko Academic Hospital, Pretoria, South Africa.
- Nuclear Medicine Research Infrastructure, Pretoria, South Africa.
| | - Frank Bruchertseifer
- European Commission, Joint Research Centre, Directorate for Nuclear Safety and Security, Karlsruhe, Germany
| | - Mariza Vorster
- Department of Nuclear Medicine, University of Pretoria & Steve Biko Academic Hospital, Pretoria, South Africa
- Nuclear Medicine Research Infrastructure, Pretoria, South Africa
| | - Alfred Morgenstern
- European Commission, Joint Research Centre, Directorate for Nuclear Safety and Security, Karlsruhe, Germany
| | - Ismaheel O Lawal
- Department of Nuclear Medicine, University of Pretoria & Steve Biko Academic Hospital, Pretoria, South Africa
- Nuclear Medicine Research Infrastructure, Pretoria, South Africa
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Roy J, Warner BM, Basuli F, Zhang X, Zheng C, Goldsmith C, Phelps T, Wong K, Ton AT, Pieschl R, White ME, Swenson R, Chiorini JA, Choyke PL, Lin FI. Competitive blocking of salivary gland [ 18F]DCFPyL uptake via localized, retrograde ductal injection of non-radioactive DCFPyL: a preclinical study. EJNMMI Res 2021; 11:66. [PMID: 34287731 PMCID: PMC8295433 DOI: 10.1186/s13550-021-00803-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2021] [Accepted: 06/09/2021] [Indexed: 12/28/2022] Open
Abstract
Background PSMA-targeted radionuclide therapy (TRT) is a promising treatment for prostate cancer (PCa), but dose-limiting xerostomia can severely limit its clinical adaptation, especially when using alpha-emitting radionuclides. With [18F]DCFPyL as a surrogate for PSMA-TRT, we report a novel method to selectively reduce salivary gland (SG) uptake of systemically administered [18F]DCFPyL by immediate prior infusion of non-radioactive standard of [18F]DCFPyL (DCFPyL) directly into the SG via retrograde cannulation. Methods A dose-finding cohort using athymic nude mice demonstrated proof of principle that SG uptake can be selectively blocked by DCFPyL administered either locally via cannulation (CAN group) or systemically (SYS group). The experiments were repeated in a validation cohort of 22RV1 tumor-bearing mice. Submandibular glands (SMG) of CAN mice were locally blocked with either saline or DCFPyL (dose range: 0.01× to 1000× molar equivalent of the radioactive [18F]DCFPyL dose). The radioactive dose of [18F]DCFPyL was administered systemically 10 min later and the mice euthanized after 1 h for biodistribution studies. Toxicity studies were done at up to 1000× dose. Results In the dose-finding cohort, the SYS group showed a dose-dependent 12–40% decrease in both the SMG T/B and the kidney (tumor surrogate). Mild blocking was observed at 0.01× , with maximal blocking reached at 1× with no additional blocking up to 1000× . In the CAN group, blocking at the 0.1× and 1× dose levels resulted in a similar 42–53% decrease, but without the corresponding decrease in kidney uptake as seen in the SYS group. Some evidence of “leakage” of DCFPyL from the salivary gland into the systemic circulation was observed. However, experiments in 22RV1 tumor-bearing mice at the 0.1× and 1× dose levels confirm that, at the appropriate blocking dose, SG uptake of [18F]DCFPyL can be selectively reduced without affecting tumor uptake and with no toxicity. Conclusion Our results suggest that direct retrograde instillation of DCFPyL into the SG could predictably and selectively decrease salivary uptake of systemically administered [18F]DCFPyL without altering tumor uptake, if given at the appropriate dose. This novel approach is easily translatable to clinical practice and has the potential to mitigate xerostomia, without compromising the therapeutic efficacy of the PSMA-TRT. Supplementary Information The online version contains supplementary material available at 10.1186/s13550-021-00803-9.
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Affiliation(s)
- Jyoti Roy
- Molecular Imaging Program, Center for Cancer Research, National Cancer Institute, NIH, NCI/NIH, Building 10, Room # B3B69F, Bethesda, MD, 20892, USA
| | - Blake M Warner
- National Institute of Dental and Craniofacial Research, NIH, Building 10, 1A08, Bethesda, MD, 20892, USA
| | - Falguni Basuli
- Chemistry and Synthesis Center, National Heart, Lung, and Blood Institute, NIH, Rockville, MD, USA
| | - Xiang Zhang
- Chemistry and Synthesis Center, National Heart, Lung, and Blood Institute, NIH, Rockville, MD, USA
| | - Changyu Zheng
- National Institute of Dental and Craniofacial Research, NIH, Building 10, 1A08, Bethesda, MD, 20892, USA
| | - Corrine Goldsmith
- National Institute of Dental and Craniofacial Research, NIH, Building 10, 1A08, Bethesda, MD, 20892, USA
| | - Tim Phelps
- Molecular Imaging Program, Center for Cancer Research, National Cancer Institute, NIH, NCI/NIH, Building 10, Room # B3B69F, Bethesda, MD, 20892, USA
| | - Karen Wong
- Molecular Imaging Program, Center for Cancer Research, National Cancer Institute, NIH, NCI/NIH, Building 10, Room # B3B69F, Bethesda, MD, 20892, USA
| | - Anita T Ton
- Molecular Imaging Program, Center for Cancer Research, National Cancer Institute, NIH, NCI/NIH, Building 10, Room # B3B69F, Bethesda, MD, 20892, USA
| | - Rick Pieschl
- Chemistry and Synthesis Center, National Heart, Lung, and Blood Institute, NIH, Rockville, MD, USA
| | - Margaret E White
- Laboratory of Genitourinary Cancer Pathogenesis, National Cancer Institute, NIH, Bethesda, MD, USA
| | - Rolf Swenson
- Chemistry and Synthesis Center, National Heart, Lung, and Blood Institute, NIH, Rockville, MD, USA
| | - John A Chiorini
- National Institute of Dental and Craniofacial Research, NIH, Building 10, 1A08, Bethesda, MD, 20892, USA
| | - Peter L Choyke
- Molecular Imaging Program, Center for Cancer Research, National Cancer Institute, NIH, NCI/NIH, Building 10, Room # B3B69F, Bethesda, MD, 20892, USA
| | - Frank I Lin
- Molecular Imaging Program, Center for Cancer Research, National Cancer Institute, NIH, NCI/NIH, Building 10, Room # B3B69F, Bethesda, MD, 20892, USA.
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