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Houvast RD, Badr N, March T, de Muynck LDAN, Sier VQ, Schomann T, Bhairosingh S, Baart VM, Peeters JAHM, van Westen GJP, Plückthun A, Burggraaf J, Kuppen PJK, Vahrmeijer AL, Sier CFM. Preclinical evaluation of EpCAM-binding designed ankyrin repeat proteins (DARPins) as targeting moieties for bimodal near-infrared fluorescence and photoacoustic imaging of cancer. Eur J Nucl Med Mol Imaging 2024; 51:2179-2192. [PMID: 37642704 PMCID: PMC11178671 DOI: 10.1007/s00259-023-06407-w] [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: 05/27/2023] [Accepted: 08/17/2023] [Indexed: 08/31/2023]
Abstract
PURPOSE Fluorescence-guided surgery (FGS) can play a key role in improving radical resection rates by assisting surgeons to gain adequate visualization of malignant tissue intraoperatively. Designed ankyrin repeat proteins (DARPins) possess optimal pharmacokinetic and other properties for in vivo imaging. This study aims to evaluate the preclinical potential of epithelial cell adhesion molecule (EpCAM)-binding DARPins as targeting moieties for near-infrared fluorescence (NIRF) and photoacoustic (PA) imaging of cancer. METHODS EpCAM-binding DARPins Ac2, Ec4.1, and non-binding control DARPin Off7 were conjugated to IRDye 800CW and their binding efficacy was evaluated on EpCAM-positive HT-29 and EpCAM-negative COLO-320 human colon cancer cell lines. Thereafter, NIRF and PA imaging of all three conjugates were performed in HT-29_luc2 tumor-bearing mice. At 24 h post-injection, tumors and organs were resected and tracer biodistributions were analyzed. RESULTS Ac2-800CW and Ec4.1-800CW specifically bound to HT-29 cells, but not to COLO-320 cells. Next, 6 nmol and 24 h were established as the optimal in vivo dose and imaging time point for both DARPin tracers. At 24 h post-injection, mean tumor-to-background ratios of 2.60 ± 0.3 and 3.1 ± 0.3 were observed for Ac2-800CW and Ec4.1-800CW, respectively, allowing clear tumor delineation using the clinical Artemis NIRF imager. Biodistribution analyses in non-neoplastic tissue solely showed high fluorescence signal in the liver and kidney, which reflects the clearance of the DARPin tracers. CONCLUSION Our encouraging results show that EpCAM-binding DARPins are a promising class of targeting moieties for pan-carcinoma targeting, providing clear tumor delineation at 24 h post-injection. The work described provides the preclinical foundation for DARPin-based bimodal NIRF/PA imaging of cancer.
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Affiliation(s)
- Ruben D Houvast
- Department of Surgery, Leiden University Medical Center, Leiden, the Netherlands.
| | - Nada Badr
- Department of Surgery, Leiden University Medical Center, Leiden, the Netherlands
| | - Taryn March
- Department of Clinical Pharmacy and Toxicology, Leiden University Medical Center, Leiden, the Netherlands
| | | | - Vincent Q Sier
- Department of Surgery, Leiden University Medical Center, Leiden, the Netherlands
| | - Timo Schomann
- Department of Surgery, Leiden University Medical Center, Leiden, the Netherlands
- Department of Radiology, Leiden University Medical Center, Leiden, the Netherlands
| | - Shadhvi Bhairosingh
- Department of Surgery, Leiden University Medical Center, Leiden, the Netherlands
| | - Victor M Baart
- Department of Surgery, Leiden University Medical Center, Leiden, the Netherlands
| | - Judith A H M Peeters
- Department of Surgery, Leiden University Medical Center, Leiden, the Netherlands
| | - Gerard J P van Westen
- Division of Drug Discovery and Safety, Leiden Academic Centre for Drug Research, Leiden, the Netherlands
| | - Andreas Plückthun
- Department of Biochemistry, University of Zürich, Zurich, Switzerland
| | - Jacobus Burggraaf
- Department of Surgery, Leiden University Medical Center, Leiden, the Netherlands
- Centre for Human Drug Research, Leiden, the Netherlands
| | - Peter J K Kuppen
- Department of Surgery, Leiden University Medical Center, Leiden, the Netherlands
| | | | - Cornelis F M Sier
- Department of Surgery, Leiden University Medical Center, Leiden, the Netherlands
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Sun S, Yang Q, Jiang D, Zhang Y. Nanobiotechnology augmented cancer stem cell guided management of cancer: liquid-biopsy, imaging, and treatment. J Nanobiotechnology 2024; 22:176. [PMID: 38609981 PMCID: PMC11015566 DOI: 10.1186/s12951-024-02432-5] [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: 12/31/2023] [Accepted: 03/20/2024] [Indexed: 04/14/2024] Open
Abstract
Cancer stem cells (CSCs) represent both a key driving force and therapeutic target of tumoral carcinogenesis, tumor evolution, progression, and recurrence. CSC-guided tumor diagnosis, treatment, and surveillance are strategically significant in improving cancer patients' overall survival. Due to the heterogeneity and plasticity of CSCs, high sensitivity, specificity, and outstanding targeting are demanded for CSC detection and targeting. Nanobiotechnologies, including biosensors, nano-probes, contrast enhancers, and drug delivery systems, share identical features required. Implementing these techniques may facilitate the overall performance of CSC detection and targeting. In this review, we focus on some of the most recent advances in how nanobiotechnologies leverage the characteristics of CSC to optimize cancer diagnosis and treatment in liquid biopsy, clinical imaging, and CSC-guided nano-treatment. Specifically, how nanobiotechnologies leverage the attributes of CSC to maximize the detection of circulating tumor DNA, circulating tumor cells, and exosomes, to improve positron emission computed tomography and magnetic resonance imaging, and to enhance the therapeutic effects of cytotoxic therapy, photodynamic therapy, immunotherapy therapy, and radioimmunotherapy are reviewed.
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Affiliation(s)
- Si Sun
- Department of Obstetrics and Gynecology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China
| | - Qiang Yang
- Department of Obstetrics and Gynecology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China
| | - Dawei Jiang
- Department of Nuclear Medicine, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China.
- Hubei Key Laboratory of Molecular Imaging, Wuhan, 430022, China.
- Key Laboratory of Biological Targeted Therapy, the Ministry of Education, Wuhan, 430022, China.
| | - Yuan Zhang
- Department of Obstetrics and Gynecology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China.
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Lopez BP, Kappadath SC. Monte Carlo-derived 99m Tc uptake quantification with commercial planar MBI: Tumor and breast activity concentrations. Med Phys 2023; 50:4388-4398. [PMID: 36625713 PMCID: PMC10331527 DOI: 10.1002/mp.16213] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2022] [Revised: 12/23/2022] [Accepted: 01/01/2023] [Indexed: 01/11/2023] Open
Abstract
BACKGROUND Current molecular breast imaging (MBI) images are limited to qualitative evaluation, not absolute measurement, of 99m Tc uptake in benign and malignant breast tissues. PURPOSE This work assesses the accuracy of previously-published and newly-proposed tumor and normal breast tissue 99m Tc uptake MBI measurements using simulations of a commercial dual-headed planar MBI system under typical clinical and acquisition protocols. METHODS Quantification techniques were tested in over 4000 simulated acquisitions of spherical and ellipsoid tumors with clinically relevant uptake conditions using a validated Monte Carlo application of the GE Discovery NM750b system. The evaluated techniques consisted of four tumor total activity methodologies (two single-detector-based and two geometric-mean-based), two tumor MBI volume methodologies (diameter-based and ROI-based), and two normal tissue activity concentration methodologies (single-detector-based and geometric-mean-based). The most accurate of these techniques were then used to estimate tumor activity concentrations and tumor to normal tissue relative activity concentrations (RC). RESULTS Single-detector techniques for tumor total activity quantification achieved mean (standard deviation) relative errors of 0.2% (4.3%) and 1.6% (4.4%) when using the near and far detector images, respectively and were more accurate and precise than the measured 8.1% (5.8%) errors of a previously published geometric-mean technique. Using these activity estimates and the true tumor volumes resulted in tumor activity concentration and RC errors within 10% of simulated values. The precision of tumor activity concentration and RC when using only MBI measurements were largely driven by the errors in estimating tumor MBI volume using planar images (± 30% inter-quartile range). CONCLUSIONS Planar MBI images were shown to accurately and reliably be used to estimate tumor total activities and normal tissue activity concentrations in this simulation study. However, volumetric tumor uptake measurements (i.e., absolute and relative concentrations) are limited by inaccuracies in MBI volume estimation using two-dimensional images, highlighting the need for either tomographic MBI acquisitions or anatomical volume estimates for accurate three-dimensional tumor uptake estimates.
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Affiliation(s)
- Benjamin P Lopez
- Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA
- MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences, Houston, Texas, USA
| | - S Cheenu Kappadath
- Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA
- MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences, Houston, Texas, USA
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Xu T, Liu Y, Schulga A, Konovalova E, Deyev S, Tolmachev V, Vorobyeva A. Epithelial cell adhesion molecule‑targeting designed ankyrin repeat protein‑toxin fusion Ec1‑LoPE exhibits potent cytotoxic action in prostate cancer cells. Oncol Rep 2022; 47:94. [PMID: 35315504 PMCID: PMC8968790 DOI: 10.3892/or.2022.8305] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2022] [Accepted: 03/08/2022] [Indexed: 11/13/2022] Open
Abstract
Targeted anticancer therapeutics offer the advantage of reducing cytotoxic side effects to normal cells by directing the cytotoxic payload selectively to cancer cells. Designed ankyrin repeat proteins (DARPins) are promising non-immunoglobulin-based scaffold proteins for payload delivery to cancer-associated molecular targets. Epithelial cell adhesion molecule (EpCAM) is overexpressed in 40–60% of prostate cancers (PCs) and is associated with metastasis, increased risk of PC recurrence and resistance to treatment. Here, we investigated the use of DARPin Ec1 for targeted delivery of Pseudomonas exotoxin A variant (LoPE) with low immunogenicity and low non-specific toxicity to EpCAM-expressing prostate cancer cells. Ec1-LoPE fusion protein was radiolabeled with tricarbonyl technetium-99m and its binding specificity, binding kinetics, cellular processing, internalization and cytotoxicity were evaluated in PC-3 and DU145 cell lines. Ec1-LoPE showed EpCAM-specific binding to EpCAM-expressing prostate cancer cells. Rapid internalization mediated potent cytotoxic effect with picomolar IC50 values in both studied cell lines. Taken together, these data support further evaluation of Ec1-LoPE in a therapeutic setting in a prostate cancer model in vivo.
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Affiliation(s)
- Tianqi Xu
- Department of Immunology, Genetics and Pathology, Uppsala University, SE-75185 Uppsala, Sweden
| | - Yongsheng Liu
- Department of Immunology, Genetics and Pathology, Uppsala University, SE-75185 Uppsala, Sweden
| | - Alexey Schulga
- Research Centrum for Oncotheranostics, Research School of Chemistry and Applied Biomedical Sciences, National Research Tomsk Polytechnic University, 634050 Tomsk, Russia
| | - Elena Konovalova
- Molecular Immunology Laboratory, Shemyakin‑Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, 117997 Moscow, Russia
| | - Sergey Deyev
- Research Centrum for Oncotheranostics, Research School of Chemistry and Applied Biomedical Sciences, National Research Tomsk Polytechnic University, 634050 Tomsk, Russia
| | - Vladimir Tolmachev
- Department of Immunology, Genetics and Pathology, Uppsala University, SE-75185 Uppsala, Sweden
| | - Anzhelika Vorobyeva
- Department of Immunology, Genetics and Pathology, Uppsala University, SE-75185 Uppsala, Sweden
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Tolmachev VM, Chernov VI, Deyev SM. Targeted nuclear medicine. Seek and destroy. RUSSIAN CHEMICAL REVIEWS 2022. [DOI: 10.1070/rcr5034] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Imaging-Guided Therapy Simultaneously Targeting HER2 and EpCAM with Trastuzumab and EpCAM-Directed Toxin Provides Additive Effect in Ovarian Cancer Model. Cancers (Basel) 2021; 13:cancers13163939. [PMID: 34439094 PMCID: PMC8393281 DOI: 10.3390/cancers13163939] [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: 06/05/2021] [Revised: 07/23/2021] [Accepted: 08/02/2021] [Indexed: 12/29/2022] Open
Abstract
Efficient treatment of disseminated ovarian cancer (OC) is challenging due to its heterogeneity and chemoresistance. Overexpression of human epidermal growth factor receptor 2 (HER2) and epithelial cell adhesion molecule (EpCAM) in approx. 30% and 70% of ovarian cancers, respectively, allows for co-targeted treatment. The clinical efficacy of the monoclonal antibody trastuzumab in patients with HER2-positive breast, gastric and gastroesophageal cancers makes it readily available as the HER2-targeting component. As the EpCAM-targeting component, we investigated the designed ankyrin repeat protein (DARPin) Ec1 fused to a truncated variant of Pseudomonas exotoxin A with reduced immunogenicity and low general toxicity (LoPE). Ec1-LoPE was radiolabeled, evaluated in ovarian cancer cells in vitro and its biodistribution and tumor-targeting properties were studied in vivo. The therapeutic efficacy of Ec1-LoPE alone and in combination with trastuzumab was studied in mice bearing EpCAM- and HER2-expressing SKOV3 xenografts. SPECT/CT imaging enabled visualization of EpCAM and HER2 expression in the tumors. Co-treatment using Ec1-LoPE and trastuzumab was more effective at reducing tumor growth and prolonged the median survival of mice compared with mice in the control and monotherapy groups. Repeated administration of Ec1-LoPE was well tolerated without signs of hepatic or kidney toxicity. Co-treatment with trastuzumab and Ec1-LoPE might be a potential therapeutic strategy for HER2- and EpCAM-positive OC.
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Deyev SM, Xu T, Liu Y, Schulga A, Konovalova E, Garousi J, Rinne SS, Larkina M, Ding H, Gräslund T, Orlova A, Tolmachev V, Vorobyeva A. Influence of the Position and Composition of Radiometals and Radioiodine Labels on Imaging of Epcam Expression in Prostate Cancer Model Using the DARPin Ec1. Cancers (Basel) 2021; 13:cancers13143589. [PMID: 34298801 PMCID: PMC8304184 DOI: 10.3390/cancers13143589] [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: 06/23/2021] [Revised: 07/13/2021] [Accepted: 07/15/2021] [Indexed: 12/16/2022] Open
Abstract
Simple Summary Metastasis-targeting therapy might improve outcomes in oligometastatic prostate cancer. Epithelial cell adhesion molecule (EpCAM) is overexpressed in 40–60% of prostate cancer cases and might be used as a target for specific delivery of toxins and drugs. Radionuclide molecular imaging could enable non-invasive detection of EpCAM and stratification of patients for targeted therapy. Designed ankyrin repeat proteins (DARPins) are scaffold proteins, which can be selected for specific binding to different targets. The DARPin Ec1 binds strongly to EpCAM. To determine an optimal design of Ec1-based probes, we labeled Ec1 at two different positions with four different nuclides (68Ga, 111In, 57Co and 125I) and investigated the impact on Ec1 biodistribution. We found that the C-terminus is the best position for labeling and that 111In and 125I provide the best imaging contrast. This study might be helpful for scientists developing imaging probes based on scaffold proteins. Abstract The epithelial cell adhesion molecule (EpCAM) is intensively overexpressed in 40–60% of prostate cancer (PCa) cases and can be used as a target for the delivery of drugs and toxins. The designed ankyrin repeat protein (DARPin) Ec1 has a high affinity to EpCAM (68 pM) and a small size (18 kDa). Radiolabeled Ec1 might be used as a companion diagnostic for the selection of PCa patients for therapy. The study aimed to investigate the influence of radiolabel position (N- or C-terminal) and composition on the targeting and imaging properties of Ec1. Two variants, having an N- or C-terminal cysteine, were produced, site-specifically conjugated to a DOTA chelator and labeled with cobalt-57, gallium-68 or indium-111. Site-specific radioiodination was performed using ((4-hydroxyphenyl)-ethyl)maleimide (HPEM). Biodistribution of eight radiolabeled Ec1-probes was measured in nude mice bearing PCa DU145 xenografts. In all cases, positioning of a label at the C-terminus provided the best tumor-to-organ ratios. The non-residualizing [125I]I-HPEM label provided the highest tumor-to-muscle and tumor-to-bone ratios and is more suitable for EpCAM imaging in early-stage PCa. Among the radiometals, indium-111 provided the highest tumor-to-blood, tumor-to-lung and tumor-to-liver ratios and could be used at late-stage PCa. In conclusion, label position and composition are important for the DARPin Ec1.
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Affiliation(s)
- Sergey M. Deyev
- Research Centrum for Oncotheranostics, Research School of Chemistry and Applied Biomedical Sciences, Tomsk Polytechnic University, 634050 Tomsk, Russia; (S.M.D.); (A.S.); (M.L.); (A.O.); (A.V.)
- Molecular Immunology Laboratory, Shemyakin & Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, 117997 Moscow, Russia;
- Bio-Nanophotonic Lab., Institute of Engineering Physics for Biomedicine (PhysBio), National Research Nuclear University “MEPhI”, 115409 Moscow, Russia
| | - Tianqi Xu
- Department of Immunology, Genetics and Pathology, Uppsala University, 751 85 Uppsala, Sweden; (T.X.); (Y.L.); (J.G.)
| | - Yongsheng Liu
- Department of Immunology, Genetics and Pathology, Uppsala University, 751 85 Uppsala, Sweden; (T.X.); (Y.L.); (J.G.)
| | - Alexey Schulga
- Research Centrum for Oncotheranostics, Research School of Chemistry and Applied Biomedical Sciences, Tomsk Polytechnic University, 634050 Tomsk, Russia; (S.M.D.); (A.S.); (M.L.); (A.O.); (A.V.)
- Molecular Immunology Laboratory, Shemyakin & Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, 117997 Moscow, Russia;
| | - Elena Konovalova
- Molecular Immunology Laboratory, Shemyakin & Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, 117997 Moscow, Russia;
| | - Javad Garousi
- Department of Immunology, Genetics and Pathology, Uppsala University, 751 85 Uppsala, Sweden; (T.X.); (Y.L.); (J.G.)
- Department of Protein Science, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, 114 17 Stockholm, Sweden; (H.D.); (T.G.)
| | - Sara S. Rinne
- Department of Medicinal Chemistry, Uppsala University, 751 23 Uppsala, Sweden;
| | - Maria Larkina
- Research Centrum for Oncotheranostics, Research School of Chemistry and Applied Biomedical Sciences, Tomsk Polytechnic University, 634050 Tomsk, Russia; (S.M.D.); (A.S.); (M.L.); (A.O.); (A.V.)
- Department of Pharmaceutical Analysis, Siberian State Medical University (SSMU), 2, Moscow Trakt, 634050 Tomsk, Russia
| | - Haozhong Ding
- Department of Protein Science, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, 114 17 Stockholm, Sweden; (H.D.); (T.G.)
| | - Torbjörn Gräslund
- Department of Protein Science, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, 114 17 Stockholm, Sweden; (H.D.); (T.G.)
| | - Anna Orlova
- Research Centrum for Oncotheranostics, Research School of Chemistry and Applied Biomedical Sciences, Tomsk Polytechnic University, 634050 Tomsk, Russia; (S.M.D.); (A.S.); (M.L.); (A.O.); (A.V.)
- Department of Medicinal Chemistry, Uppsala University, 751 23 Uppsala, Sweden;
- Science for Life Laboratory, Uppsala University, 751 23 Uppsala, Sweden
| | - Vladimir Tolmachev
- Research Centrum for Oncotheranostics, Research School of Chemistry and Applied Biomedical Sciences, Tomsk Polytechnic University, 634050 Tomsk, Russia; (S.M.D.); (A.S.); (M.L.); (A.O.); (A.V.)
- Department of Immunology, Genetics and Pathology, Uppsala University, 751 85 Uppsala, Sweden; (T.X.); (Y.L.); (J.G.)
- Correspondence:
| | - Anzhelika Vorobyeva
- Research Centrum for Oncotheranostics, Research School of Chemistry and Applied Biomedical Sciences, Tomsk Polytechnic University, 634050 Tomsk, Russia; (S.M.D.); (A.S.); (M.L.); (A.O.); (A.V.)
- Department of Immunology, Genetics and Pathology, Uppsala University, 751 85 Uppsala, Sweden; (T.X.); (Y.L.); (J.G.)
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Li F, Zeng Z, Hamilton D, Zu Y, Li Z. EpCAM-Targeting Aptamer Radiotracer for Tumor-Specific PET Imaging. Bioconjug Chem 2021; 32:1139-1145. [PMID: 34014641 DOI: 10.1021/acs.bioconjchem.1c00188] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Noninvasive in vivo imaging to measure the expression of EpCAM, a biomarker overexpressed in the majority of carcinoma tumors and metastatic lesions, is highly desirable for accurate tumor staging and therapy evaluation. Here, we report the use of an aptamer radiotracer to enable tumor-specific EpCAM-targeting PET imaging. Oligonucleotide aptamers are small molecular ligands that specifically bind with high affinity to their target molecules. For specific tumor imaging, an aptamer radiotracer was formulated by chelating a 64Cu isotope and DOTA-PEGylated aptamer sequence to target EpCAM. In vitro cell uptake assays demonstrated that the aptamer radiotracer specifically bound EpCAM-expressing breast cancer cells but did not react with off-target tumor cells. For in vivo tumor imaging, aptamer radiotracer was systemically administered into xenograft mice. MicroPET/CT scans revealed that the aptamer radiotracer rapidly highlighted xenograft tumors derived from MDA-MB-231 breast cancer cells (EpCAM positive) as early as 2 h postadministration with a gradually increasing tumor uptake signal that peaked at 24 h but not in lymphoma 937 tumors (EpCAM negative). In contrast, nonspecific background signals in the liver and kidneys were rapidly decreased postadministration. This proof-of-concept study demonstrates the utility of aptamer radiotracers for tumor-specific PET imaging.
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