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Targeting Tumor Cells Overexpressing the Human Epidermal Growth Factor Receptor 3 with Potent Drug Conjugates Based on Affibody Molecules. Biomedicines 2022; 10:biomedicines10061293. [PMID: 35740315 PMCID: PMC9219639 DOI: 10.3390/biomedicines10061293] [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: 04/19/2022] [Revised: 05/27/2022] [Accepted: 05/28/2022] [Indexed: 12/22/2022] Open
Abstract
Increasing evidence suggests that therapy targeting the human epidermal growth factor receptor 3 (HER3) could be a viable route for targeted cancer therapy. Here, we studied a novel drug conjugate, ZHER3-ABD-mcDM1, consisting of a HER3-targeting affibody molecule, coupled to the cytotoxic tubulin polymerization inhibitor DM1, and an albumin-binding domain for in vivo half-life extension. ZHER3-ABD-mcDM1 showed a strong affinity to the extracellular domain of HER3 (KD 6 nM), and an even stronger affinity (KD 0.2 nM) to the HER3-overexpressing pancreatic carcinoma cell line, BxPC-3. The drug conjugate showed a potent cytotoxic effect on BxPC-3 cells with an IC50 value of 7 nM. Evaluation of a radiolabeled version, [99mTc]Tc-ZHER3-ABD-mcDM1, showed a relatively high rate of internalization, with a 27% internalized fraction after 8 h. Further in vivo evaluation showed that it could target BxPC-3 (pancreatic carcinoma) and DU145 (prostate carcinoma) xenografts in mice, with an uptake peaking at 6.3 ± 0.4% IA/g at 6 h post-injection for the BxPC-3 xenografts. The general biodistribution showed uptake in the liver, lung, salivary gland, stomach, and small intestine, organs known to express murine ErbB3 naturally. The results from the study show that ZHER3-ABD-mcDM1 is a highly potent and selective drug conjugate with the ability to specifically target HER3 overexpressing cells. Further pre-clinical and clinical development is discussed.
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Luo R, Liu H, Cheng Z. Protein scaffolds: Antibody alternative for cancer diagnosis and therapy. RSC Chem Biol 2022; 3:830-847. [PMID: 35866165 PMCID: PMC9257619 DOI: 10.1039/d2cb00094f] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2022] [Accepted: 05/23/2022] [Indexed: 12/01/2022] Open
Abstract
Although antibodies are well developed and widely used in cancer therapy and diagnostic fields, some defects remain, such as poor tissue penetration, long in vivo metabolic retention, potential cytotoxicity, patent limitation, and high production cost. These issues have led scientists to explore and develop novel antibody alternatives. Protein scaffolds are small monomeric proteins with stable tertiary structures and mutable residues, which emerged in the 1990s. By combining robust gene engineering and phage display techniques, libraries with sufficient diversity could be established for target binding scaffold selection. Given the properties of small size, high affinity, and excellent specificity and stability, protein scaffolds have been applied in basic research, and preclinical and clinical fields over the past two decades. To date, more than 20 types of protein scaffolds have been developed, with the most frequently used being affibody, adnectin, ANTICALIN®, DARPins, and knottin. In this review, we focus on the protein scaffold applications in cancer therapy and diagnosis in the last 5 years, and discuss the pros and cons, and strategies of optimization and design. Although antibodies are well developed and widely used in cancer therapy and diagnostic fields, some defects remain, such as poor tissue penetration, long in vivo metabolic retention, potential cytotoxicity, patent limitation, and high production cost.![]()
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Affiliation(s)
- Renli Luo
- Department of Molecular Medicine, College of Life and Health Sciences, Northeastern University Shenyang China
| | - Hongguang Liu
- Department of Molecular Medicine, College of Life and Health Sciences, Northeastern University Shenyang China
| | - Zhen Cheng
- State Key Laboratory of Drug Research, Molecular Imaging Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences Shanghai 201203 China
- Drug Discovery Shandong Laboratory, Bohai Rim Advanced Research Institute for Drug Discovery Yantai Shandong 264117 China
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HER3 PET Imaging: 68Ga-Labeled Affibody Molecules Provide Superior HER3 Contrast to 89Zr-Labeled Antibody and Antibody-Fragment-Based Tracers. Cancers (Basel) 2021; 13:cancers13194791. [PMID: 34638277 PMCID: PMC8508546 DOI: 10.3390/cancers13194791] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2021] [Revised: 09/10/2021] [Accepted: 09/22/2021] [Indexed: 12/20/2022] Open
Abstract
Simple Summary HER3 is a known driver for oncogenesis and therapy resistance in solid cancers. PET imaging could be a useful tool to non-invasively detect and monitor HER3 expression and aid in the selection of patients for HER3-targeted therapy. PET tracers based on therapeutic antibodies have thus far shown limited success in reliably imaging HER3-expressing tumors in clinical trials. Smaller-sized tracers specifically designed for imaging might be needed for higher contrast imaging and sufficient sensitivity. Our group has previously studied the use of radiolabeled affibody molecules for imaging of HER3 expression. In the present study, we compared four different types of potential PET tracers for imaging of HER3 expression in a preclinical model. We demonstrated that the affibody-based tracer, [68Ga]Ga-ZHER3, could provide overall superior imaging contrast to antibody- and antibody-fragment-based tracers shortly after injection. Our results indicate that HER3-targeting affibody molecules are promising agents for PET imaging of HER3 expression. Abstract HER3 (human epidermal growth factor receptor type 3) is a challenging target for diagnostic radionuclide molecular imaging due to the relatively modest overexpression in tumors and substantial expression in healthy organs. In this study, we compared four HER3-targeting PET tracers based on different types of targeting molecules in a preclinical model: the 89Zr-labeled therapeutic antibody seribantumab, a seribantumab-derived F(ab)2-fragment labeled with 89Zr and 68Ga, and the 68Ga-labeled affibody molecule [68Ga]Ga-ZHER3. The novel conjugates were radiolabeled and characterized in vitro using HER3-expressing BxPC-3 and DU145 human cancer cells. Biodistribution was studied using Balb/c nu/nu mice bearing BxPC-3 xenografts. HER3-negative RAMOS xenografts were used to demonstrate binding specificity in vivo. Autoradiography was conducted on the excised tumors. nanoPET/CT imaging was performed. New conjugates specifically bound to HER3 in vitro and in vivo. [68Ga]Ga-DFO-seribantumab-F(ab’)2 was considered unsuitable for imaging due to the low stability and high uptake in normal organs. The highest tumor-to-non-tumor contrast with [89Zr]Zr-DFO-seribantumab and [89Zr]Zr-DFO-seribantumab-F(ab’)2 was achieved at 96 h and 48 h pi, respectively. Despite lower tumor uptake, [68Ga]Ga-ZHER3 provided the best imaging contrast due to the fastest clearance from blood and normal organs. The results of our study suggest that affibody-based tracers are more suitable for PET imaging of HER3 expression than antibody- and antibody-fragment-based tracers.
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Molavipordanjani S, Hosseinimehr SJ. The Radiolabeled HER3 Targeting Molecules for Tumor Imaging. IRANIAN JOURNAL OF PHARMACEUTICAL RESEARCH : IJPR 2021; 20:141-152. [PMID: 34400948 PMCID: PMC8170765 DOI: 10.22037/ijpr.2021.114677.14991] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The human epidermal growth factor receptor (HER) family plays pivotal roles in physiologic and pathologic conditions (such as tumor growth, proliferation, and progression in multiple epithelial malignancies). All the family members are considered tyrosine kinase, while HER3 as a member of this family shows no intrinsic tyrosine kinase. HER3 is called ‘pseudokinase’ because it undergoes heterodimerization and forms dimers such as HER2-HER3 and HER1 (EGFR)-HER3. The exact role of HER3 in cancer is still unclear; however, the overexpression of this receptor is involved in the poor prognosis of malignancies. To that end, different studies investigated the development of radiotracers for imaging of HER3. The main focus of this review is to gather all the studies on developing new radiotracers for imaging of HER3.
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Affiliation(s)
- Sajjad Molavipordanjani
- Department of Radiology and Nuclear Medicine, Faculty of Medicine, Cardiovascular Research Center, Mazandaran University of Medical Sciences, Sari, Iran
| | - Seyed Jalal Hosseinimehr
- Department of Radiopharmacy, Faculty of Pharmacy, Mazandaran University of Medical Sciences, Sari, Iran
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Barrett KE, Houson HA, Lin W, Lapi SE, Engle JW. Production, Purification, and Applications of a Potential Theranostic Pair: Cobalt-55 and Cobalt-58m. Diagnostics (Basel) 2021; 11:diagnostics11071235. [PMID: 34359318 PMCID: PMC8306844 DOI: 10.3390/diagnostics11071235] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2021] [Revised: 06/29/2021] [Accepted: 07/01/2021] [Indexed: 11/16/2022] Open
Abstract
The emerging success of [68Ga/177Lu]Ga/Lu-DOTATATE as a theranostic pair has spurred interest in other isotopes as potential theranostic combinations. Here, we review cobalt-55 and cobalt-58m as a potential theranostic pair. Radionuclidically pure cobalt-55 and cobalt-58m have been produced on small cyclotrons with high molar activity. In vitro, DOTATOC labeled with cobalt has shown greater affinity for SSTR2 than DOTATOC labeled with gallium and yttrium. Similarly, [58mCo]Co-DOTATATE has shown improved cell-killing capabilities as compared to DOTATATE labeled with either indium-111 or lutetium-177. Finally, PET imaging with an isotope such as cobalt-55 allows for image acquisition at much later timepoints than gallium, allowing for an increased degree of biological clearance of non-bound radiotracer. We discuss the accelerator targetry and radiochemistry used to produce cobalt-55,58m, emphasizing the implications of these techniques to downstream radiotracers being developed for imaging and therapy.
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Affiliation(s)
- Kendall E. Barrett
- Department of Medical Physics, University of Wisconsin, 1111 Highland Avenue, Madison, WI 53711, USA; (K.E.B.); (W.L.)
| | - Hailey A. Houson
- Department of Radiology, University of Alabama at Birmingham, 619 19th Street, Birmingham, AL 35294, USA; (H.A.H.); (S.E.L.)
| | - Wilson Lin
- Department of Medical Physics, University of Wisconsin, 1111 Highland Avenue, Madison, WI 53711, USA; (K.E.B.); (W.L.)
| | - Suzanne E. Lapi
- Department of Radiology, University of Alabama at Birmingham, 619 19th Street, Birmingham, AL 35294, USA; (H.A.H.); (S.E.L.)
| | - Jonathan W. Engle
- Department of Medical Physics, University of Wisconsin, 1111 Highland Avenue, Madison, WI 53711, USA; (K.E.B.); (W.L.)
- Department of Radiology, University of Wisconsin, 600 Highland Avenue, Madison, WI 53792, USA
- Correspondence:
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Rinne SS, Orlova A, Tolmachev V. PET and SPECT Imaging of the EGFR Family (RTK Class I) in Oncology. Int J Mol Sci 2021; 22:ijms22073663. [PMID: 33915894 PMCID: PMC8036874 DOI: 10.3390/ijms22073663] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2021] [Revised: 03/24/2021] [Accepted: 03/29/2021] [Indexed: 12/12/2022] Open
Abstract
The human epidermal growth factor receptor family (EGFR-family, other designations: HER family, RTK Class I) is strongly linked to oncogenic transformation. Its members are frequently overexpressed in cancer and have become attractive targets for cancer therapy. To ensure effective patient care, potential responders to HER-targeted therapy need to be identified. Radionuclide molecular imaging can be a key asset for the detection of overexpression of EGFR-family members. It meets the need for repeatable whole-body assessment of the molecular disease profile, solving problems of heterogeneity and expression alterations over time. Tracer development is a multifactorial process. The optimal tracer design depends on the application and the particular challenges of the molecular target (target expression in tumors, endogenous expression in healthy tissue, accessibility). We have herein summarized the recent preclinical and clinical data on agents for Positron Emission Tomography (PET) and Single Photon Emission Tomography (SPECT) imaging of EGFR-family receptors in oncology. Antibody-based tracers are still extensively investigated. However, their dominance starts to be challenged by a number of tracers based on different classes of targeting proteins. Among these, engineered scaffold proteins (ESP) and single domain antibodies (sdAb) show highly encouraging results in clinical studies marking a noticeable trend towards the use of smaller sized agents for HER imaging.
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Affiliation(s)
- Sara S. Rinne
- Department of Medicinal Chemistry, Uppsala University, 751 23 Uppsala, Sweden; (S.S.R.); (A.O.)
| | - Anna Orlova
- Department of Medicinal Chemistry, Uppsala University, 751 23 Uppsala, Sweden; (S.S.R.); (A.O.)
- Science for Life Laboratory, Uppsala University, 752 37 Uppsala, Sweden
- Research Centrum for Oncotheranostics, Research School of Chemistry and Applied Biomedical Sciences, Tomsk Polytechnic University, 634050 Tomsk, Russia
| | - Vladimir Tolmachev
- Research Centrum for Oncotheranostics, Research School of Chemistry and Applied Biomedical Sciences, Tomsk Polytechnic University, 634050 Tomsk, Russia
- Department of Immunology, Genetics and Pathology, Uppsala University, 752 37 Uppsala, Sweden
- Correspondence: ; Tel.: +46-704-250-782
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Rinne SS, Abouzayed A, Gagnon K, Tolmachev V, Orlova A. 66Ga-PET-imaging of GRPR-expression in prostate cancer: production and characterization of [ 66Ga]Ga-NOTA-PEG 2-RM26. Sci Rep 2021; 11:3631. [PMID: 33574368 PMCID: PMC7878787 DOI: 10.1038/s41598-021-82995-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2020] [Accepted: 01/26/2021] [Indexed: 12/16/2022] Open
Abstract
Molecular imaging of the gastrin-releasing peptide receptor (GRPR) could improve patient management in prostate cancer. This study aimed to produce gallium-66 (T½ = 9.5 h) suitable for radiolabeling, and investigate the imaging properties of gallium-66 labeled GRPR-antagonist NOTA-PEG2-RM26 for later-time point PET-imaging of GRPR expression. Gallium-66 was cyclotron-produced using a liquid target, and enriched [66Zn]Zn(NO3)2. In vitro, [66Ga]Ga-NOTA-PEG2-RM26 was characterized in GRPR-expressing PC-3 prostate cancer cells. In vivo, specificity test and biodistribution studies were performed 3 h and 22 h pi in PC-3 xenografted mice. microPET/MR was performed 3 h and 22 h pi. Biodistribution of [66Ga]Ga-NOTA-PEG2-RM26 was compared with [68Ga]Ga-NOTA-PEG2-RM26 3 h pi. [66Ga]Ga-NOTA-PEG2-RM26 was successfully prepared with preserved binding specificity and high affinity towards GRPR. [66Ga]Ga-NOTA-PEG2-RM26 cleared rapidly from blood via kidneys. Tumor uptake was GRPR-specific and exceeded normal organ uptake. Normal tissue clearance was limited, resulting in no improvement of tumor-to-organ ratios with time. Tumors could be clearly visualized using microPET/MR. Gallium-66 was successfully produced and [66Ga]Ga-NOTA-PEG2-RM26 was able to clearly visualize GRPR-expression both shortly after injection and on the next day using PET. However, delayed imaging did not improve contrast for Ga-labeled NOTA-PEG2-RM26.
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Affiliation(s)
- Sara S Rinne
- Department of Medicinal Chemistry, Uppsala University, Uppsala, Sweden
| | - Ayman Abouzayed
- Department of Medicinal Chemistry, Uppsala University, Uppsala, Sweden
| | | | - Vladimir Tolmachev
- Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden
- Centrum for Oncotheranostics, National Research Tomsk Polytechnic University, Tomsk, Russia
| | - Anna Orlova
- Department of Medicinal Chemistry, Uppsala University, Uppsala, Sweden.
- Centrum for Oncotheranostics, National Research Tomsk Polytechnic University, Tomsk, Russia.
- Science for Life Laboratory, Uppsala University, Uppsala, Sweden.
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Tsurubuchi T, Shirakawa M, Kurosawa W, Matsumoto K, Ubagai R, Umishio H, Suga Y, Yamazaki J, Arakawa A, Maruyama Y, Seki T, Shibui Y, Yoshida F, Zaboronok A, Suzuki M, Sakurai Y, Tanaka H, Nakai K, Ishikawa E, Matsumura A. Evaluation of a Novel Boron-Containing α-D-Mannopyranoside for BNCT. Cells 2020; 9:E1277. [PMID: 32455737 PMCID: PMC7290312 DOI: 10.3390/cells9051277] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2020] [Revised: 05/18/2020] [Accepted: 05/18/2020] [Indexed: 12/18/2022] Open
Abstract
Boron neutron capture therapy (BNCT) is a unique anticancer technology that has demonstrated its efficacy in numerous phase I/II clinical trials with boronophenylalanine (BPA) and sodium borocaptate (BSH) used as 10B delivery agents. However, continuous drug administration at high concentrations is needed to maintain sufficient 10B concentration within tumors. To address the issue of 10B accumulation and retention in tumor tissue, we developed MMT1242, a novel boron-containing α-d-mannopyranoside. We evaluated the uptake, intracellular distribution, and retention of MMT1242 in cultured cells and analyzed biodistribution, tumor-to-normal tissue ratio and toxicity in vivo. Fluorescence imaging using nitrobenzoxadiazole (NBD)-labeled MMT1242 and inductively coupled mass spectrometry (ICP-MS) were performed. The effectiveness of BNCT using MMT1242 was assessed in animal irradiation studies at the Kyoto University Research Reactor. MMT1242 showed a high uptake and broad intracellular distribution in vitro, longer tumor retention compared to BSH and BPA, and adequate tumor-to-normal tissue accumulation ratio and low toxicity in vivo. A neutron irradiation study with MMT1242 in a subcutaneous murine tumor model revealed a significant tumor inhibiting effect if injected 24 h before irradiation. We therefore report that 10B-MMT1242 is a candidate for further clinical BNCT studies.
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Affiliation(s)
- Takao Tsurubuchi
- Department of Neurosurgery, Faculty of Medicine, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8575, Japan; (M.S.); (F.Y.); (K.N.); (E.I.); (A.M.)
| | - Makoto Shirakawa
- Department of Neurosurgery, Faculty of Medicine, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8575, Japan; (M.S.); (F.Y.); (K.N.); (E.I.); (A.M.)
- Department of Pharmaceutical Sciences, University of Fukuyama, 1 Sanzo, Gakuen-cho, Fukuyama 729-0292, Japan
| | - Wataru Kurosawa
- Institute for Innovation, Ajinomoto Co., Inc., 1-1 Suzukichō, Kawasaki-ku, Kawasaki 210-8681, Japan; (W.K.); (K.M.); (R.U.); (H.U.); (Y.S.); (J.Y.); (A.A.); (Y.M.); (T.S.); (Y.S.)
| | - Kayo Matsumoto
- Institute for Innovation, Ajinomoto Co., Inc., 1-1 Suzukichō, Kawasaki-ku, Kawasaki 210-8681, Japan; (W.K.); (K.M.); (R.U.); (H.U.); (Y.S.); (J.Y.); (A.A.); (Y.M.); (T.S.); (Y.S.)
| | - Risa Ubagai
- Institute for Innovation, Ajinomoto Co., Inc., 1-1 Suzukichō, Kawasaki-ku, Kawasaki 210-8681, Japan; (W.K.); (K.M.); (R.U.); (H.U.); (Y.S.); (J.Y.); (A.A.); (Y.M.); (T.S.); (Y.S.)
| | - Hiroshi Umishio
- Institute for Innovation, Ajinomoto Co., Inc., 1-1 Suzukichō, Kawasaki-ku, Kawasaki 210-8681, Japan; (W.K.); (K.M.); (R.U.); (H.U.); (Y.S.); (J.Y.); (A.A.); (Y.M.); (T.S.); (Y.S.)
| | - Yasuyo Suga
- Institute for Innovation, Ajinomoto Co., Inc., 1-1 Suzukichō, Kawasaki-ku, Kawasaki 210-8681, Japan; (W.K.); (K.M.); (R.U.); (H.U.); (Y.S.); (J.Y.); (A.A.); (Y.M.); (T.S.); (Y.S.)
| | - Junko Yamazaki
- Institute for Innovation, Ajinomoto Co., Inc., 1-1 Suzukichō, Kawasaki-ku, Kawasaki 210-8681, Japan; (W.K.); (K.M.); (R.U.); (H.U.); (Y.S.); (J.Y.); (A.A.); (Y.M.); (T.S.); (Y.S.)
| | - Akihiro Arakawa
- Institute for Innovation, Ajinomoto Co., Inc., 1-1 Suzukichō, Kawasaki-ku, Kawasaki 210-8681, Japan; (W.K.); (K.M.); (R.U.); (H.U.); (Y.S.); (J.Y.); (A.A.); (Y.M.); (T.S.); (Y.S.)
| | - Yutaka Maruyama
- Institute for Innovation, Ajinomoto Co., Inc., 1-1 Suzukichō, Kawasaki-ku, Kawasaki 210-8681, Japan; (W.K.); (K.M.); (R.U.); (H.U.); (Y.S.); (J.Y.); (A.A.); (Y.M.); (T.S.); (Y.S.)
| | - Takuya Seki
- Institute for Innovation, Ajinomoto Co., Inc., 1-1 Suzukichō, Kawasaki-ku, Kawasaki 210-8681, Japan; (W.K.); (K.M.); (R.U.); (H.U.); (Y.S.); (J.Y.); (A.A.); (Y.M.); (T.S.); (Y.S.)
| | - Yusuke Shibui
- Institute for Innovation, Ajinomoto Co., Inc., 1-1 Suzukichō, Kawasaki-ku, Kawasaki 210-8681, Japan; (W.K.); (K.M.); (R.U.); (H.U.); (Y.S.); (J.Y.); (A.A.); (Y.M.); (T.S.); (Y.S.)
| | - Fumiyo Yoshida
- Department of Neurosurgery, Faculty of Medicine, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8575, Japan; (M.S.); (F.Y.); (K.N.); (E.I.); (A.M.)
| | - Alexander Zaboronok
- Department of Neurosurgery, Faculty of Medicine, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8575, Japan; (M.S.); (F.Y.); (K.N.); (E.I.); (A.M.)
| | - Minoru Suzuki
- Institute for Integrated Radiation and Nuclear Science, Kyoto University, 2 Asashiro-Nishi, Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan; (M.S.); (Y.S.); (H.T.)
| | - Yoshinori Sakurai
- Institute for Integrated Radiation and Nuclear Science, Kyoto University, 2 Asashiro-Nishi, Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan; (M.S.); (Y.S.); (H.T.)
| | - Hiroki Tanaka
- Institute for Integrated Radiation and Nuclear Science, Kyoto University, 2 Asashiro-Nishi, Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan; (M.S.); (Y.S.); (H.T.)
| | - Kei Nakai
- Department of Neurosurgery, Faculty of Medicine, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8575, Japan; (M.S.); (F.Y.); (K.N.); (E.I.); (A.M.)
- Department of Radiation Oncology, Faculty of Medicine, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8575, Japan
| | - Eiichi Ishikawa
- Department of Neurosurgery, Faculty of Medicine, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8575, Japan; (M.S.); (F.Y.); (K.N.); (E.I.); (A.M.)
| | - Akira Matsumura
- Department of Neurosurgery, Faculty of Medicine, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8575, Japan; (M.S.); (F.Y.); (K.N.); (E.I.); (A.M.)
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