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Anti-Cancer Agents in Medicinal Chemistry

Editor-in-Chief

ISSN (Print): 1871-5206
ISSN (Online): 1875-5992

Review Article

Recent Achievements about Targeted Alpha Therapy-Based Targeting Vectors and Chelating Agents

Author(s): Soghra Farzipour, Zahra Shaghaghi, Sahar Abbasi, Hajar Albooyeh and Maryam Alvandi*

Volume 22, Issue 8, 2022

Published on: 27 July, 2021

Page: [1496 - 1510] Pages: 15

DOI: 10.2174/1871520621666210727120308

Price: $65

Abstract

One of the most rapidly growing options in the management of cancer therapy is Targeted Alpha Therapy (TAT) through which lethal α-emitting radionuclides conjugated to tumor-targeting vectors selectively deliver high amount of radiation to cancer cells.225Ac, 212Bi, 211At, 213Bi, and 223Ra have been investigated by plenty of clinical trials and preclinical researches for the treatment of smaller tumor burdens, micro-metastatic disease, and post-surgery residual disease. In order to send maximum radiation to tumor cells while minimizing toxicity in normal cells, a high affinity of targeting vectors to cancer tissue is essential. Besides that, the stable and specific complex between chelating agent and α-emitters was found as a crucial parameter. The present review was planned to highlight recent achievements about TAT-based targeting vectors and chelating agents and provide further insight for future researches.

Keywords: Targeted alpha therapy, bifunctional chelators, carrier molecule, radionuclide, radioimmunotherapy, actinium.

Graphical Abstract

[1]
Middendorp, M.; Grünwald, F. Update on recent developments in the therapy of differentiated thyroid cancer. Semin. Nucl. Med., 2010, 40(2), 145-152.
[http://dx.doi.org/10.1053/j.semnuclmed.2009.10.006] [PMID: 20113682]
[2]
Kim, Y.S.; Brechbiel, M.W. An overview of targeted alpha therapy. Tumour Biol., 2012, 33(3), 573-590.
[http://dx.doi.org/10.1007/s13277-011-0286-y] [PMID: 22143940]
[3]
Kassis, A.I.; Adelstein, S.J. Radiobiologic principles in radionuclide therapy. J. Nucl. Med., 2005, 46(Suppl. 1), 4S-12S.
[PMID: 15653646]
[4]
Mulford, D.A.; Scheinberg, D.A.; Jurcic, J.G. The promise of targeted alpha-particle therapy. J. Nucl. Med., 2005, 46(Suppl. 1), 199S-204S.
[PMID: 15653670]
[5]
Makvandi, M.; Dupis, E.; Engle, J.W.; Nortier, F.M.; Fassbender, M.E.; Simon, S.; Birnbaum, E.R.; Atcher, R.W.; John, K.D.; Rixe, O.; Norenberg, J.P. Alpha-emitters and targeted alpha therapy in oncology: From basic science to clinical investigations. Target. Oncol., 2018, 13(2), 189-203.
[http://dx.doi.org/10.1007/s11523-018-0550-9] [PMID: 29423595]
[6]
Ferrier, M.G.; Radchenko, V.; Wilbur, D.S. Radiochemical aspects of alpha emitting radionuclides for medical application. Radiochim. Acta, 2019, 107(9-11), 1065.
[http://dx.doi.org/10.1515/ract-2019-0005]
[7]
Blöcher, D. DNA double-strand break repair determines the RBE of alpha-particles. Int. J. Radiat. Biol., 1988, 54(5), 761-771.
[http://dx.doi.org/10.1080/09553008814552201] [PMID: 2902170]
[8]
Hatcher-Lamarre, J.L.; Sanders, V.A.; Rahman, M.; Cutler, C.S.; Francesconi, L.C. Alpha emitting nuclides for targeted therapy. Nucl. Med. Biol., 2021, 92, 228-240.
[http://dx.doi.org/10.1016/j.nucmedbio.2020.08.004] [PMID: 33558017]
[9]
Parker, C.; Lewington, V.; Shore, N.; Kratochwil, C.; Levy, M.; Lindén, O.; Noordzij, W.; Park, J.; Saad, F. Targeted alpha therapy, an emerging class of cancer agents: A review. JAMA Oncol., 2018, 4(12), 1765-1772.
[http://dx.doi.org/10.1001/jamaoncol.2018.4044] [PMID: 30326033]
[10]
Zhuikov, B.L. Production of medical radionuclides in Russia: status and future--a review. Appl. Radiat. Isot., 2014, 84, 48-56.
[http://dx.doi.org/10.1016/j.apradiso.2013.11.025] [PMID: 24315977]
[11]
Volkert, W.A.; Goeckeler, W.F.; Ehrhardt, G.J.; Ketring, A.R. Therapeutic radionuclides: production and decay property considerations. J. Nucl. Med., 1991, 32(1), 174-185.
[PMID: 1988628]
[12]
Guérard, F.; Gestin, J.F.; Brechbiel, M.W. Production of [(211)At]-astatinated radiopharmaceuticals and applications in targeted α-particle therapy. Cancer Biother. Radiopharm., 2013, 28(1), 1-20.
[http://dx.doi.org/10.1089/cbr.2012.1292] [PMID: 23075373]
[13]
Kozak, R.W.; Atcher, R.W.; Gansow, O.A.; Friedman, A.M.; Hines, J.J.; Waldmann, T.A. Bismuth-212-labeled anti-Tac monoclonal anti-body: alpha-particle-emitting radionuclides as modalities for radioimmunotherapy. Proc. Natl. Acad. Sci. USA, 1986, 83(2), 474-478.
[http://dx.doi.org/10.1073/pnas.83.2.474] [PMID: 3079913]
[14]
Elgqvist, J.; Frost, S.; Pouget, J.P.; Albertsson, P. The potential and hurdles of targeted alpha therapy - clinical trials and beyond. Front. Oncol., 2014, 3, 324.
[http://dx.doi.org/10.3389/fonc.2013.00324] [PMID: 24459634]
[15]
Abou, D.S.; Pickett, J.; Mattson, J.E.; Thorek, D.L.J.A. Radium-223 microgenerator from cyclotron-produced trace Actinium-227. Appl. Radiat. Isot., 2017, 119, 36-42.
[http://dx.doi.org/10.1016/j.apradiso.2016.10.015] [PMID: 27835737]
[16]
Dekempeneer, Y.; Keyaerts, M.; Krasniqi, A.; Puttemans, J.; Muyldermans, S.; Lahoutte, T.; D’huyvetter, M.; Devoogdt, N. Targeted alpha therapy using short-lived alpha-particles and the promise of nanobodies as targeting vehicle. Expert Opin. Biol. Ther., 2016, 16(8), 1035-1047.
[http://dx.doi.org/10.1080/14712598.2016.1185412] [PMID: 27145158]
[17]
Meares, C.F.; Moi, M.K.; Diril, H.; Kukis, D.L.; McCall, M.J.; Deshpande, S.V.; DeNardo, S.J.; Snook, D.; Epenetos, A.A. Macrocyclic chelates of radiometals for diagnosis and therapy. Br. J. Cancer Suppl., 1990, 10, 21-26.
[PMID: 2383477]
[18]
Cole, W.C.; DeNardo, S.J.; Meares, C.F.; McCall, M.J.; DeNardo, G.L.; Epstein, A.L.; O’Brien, H.A.; Moi, M.K. Comparative serum stabil-ity of radiochelates for antibody radiopharmaceuticals. J. Nucl. Med., 1987, 28(1), 83-90.
[PMID: 3794813]
[19]
Avery, S.V.; Tobin, J.M. Mechanism of adsorption of hard and soft metal ions to Saccharomyces cerevisiae and influence of hard and soft anions. Appl. Environ. Microbiol., 1993, 59(9), 2851-2856.
[http://dx.doi.org/10.1128/aem.59.9.2851-2856.1993] [PMID: 8215359]
[20]
Hancock, R.D. The pyridyl group in ligand design for selective metal ion complexation and sensing. Chem. Soc. Rev., 2013, 42(4), 1500-1524.
[http://dx.doi.org/10.1039/C2CS35224A] [PMID: 23092949]
[21]
Hancock, R.D.; Martell, A.E. Ligand design for selective complexation of metal ions in aqueous solution. Chem. Rev., 1989, 89(8), 1875-1914.
[http://dx.doi.org/10.1021/cr00098a011]
[22]
Tei, L.; Baranyai, Z.; Gaino, L.; Forgács, A.; Vágner, A.; Botta, M. Thermodynamic stability, kinetic inertness and relaxometric properties of monoamide derivatives of lanthanide(III) DOTA complexes. Dalton Trans., 2015, 44(12), 5467-5478.
[http://dx.doi.org/10.1039/C4DT03939D] [PMID: 25695351]
[23]
Sarko, D.; Eisenhut, M.; Haberkorn, U.; Mier, W. Bifunctional chelators in the design and application of radiopharmaceuticals for onco-logical diseases. Curr. Med. Chem., 2012, 19(17), 2667-2688.
[http://dx.doi.org/10.2174/092986712800609751] [PMID: 22455579]
[24]
Moi, M.K.; DeNardo, S.J.; Meares, C.F. Stable bifunctional chelates of metals used in radiotherapy. Cancer Res., 1990, 50(3)(Suppl.), 789s-793s.
[PMID: 2297725]
[25]
Thiele, N.A.; Brown, V.; Kelly, J.M.; Amor-Coarasa, A.; Jermilova, U.; MacMillan, S.N.; Nikolopoulou, A.; Ponnala, S.; Ramogida, C.F.; Robertson, A.K.H.; Rodríguez-Rodríguez, C.; Schaffer, P.; Williams, C., Jr; Babich, J.W.; Radchenko, V.; Wilson, J.J. An eighteen-membered macrocyclic ligand for actinium-225 targeted alpha therapy. Angew. Chem. Int. Ed. Engl., 2017, 56(46), 14712-14717.
[http://dx.doi.org/10.1002/anie.201709532] [PMID: 28963750]
[26]
Vaidyanathan, G.; Zalutsky, M.R. Applications of 211At and 223Ra in targeted alpha-particle radiotherapy. Curr. Radiopharm., 2011, 4(4), 283-294.
[http://dx.doi.org/10.2174/1874471011104040283] [PMID: 22202151]
[27]
Aneheim, E.; Albertsson, P.; Bäck, T.; Jensen, H.; Palm, S.; Lindegren, S. Automated astatination of biomolecules-a stepping stone to-wards multicenter clinical trials. Sci. Rep., 2015, 5, 12025.
[http://dx.doi.org/10.1038/srep12025] [PMID: 26169786]
[28]
Liu, B.L.; Jin, Y.T.; Liu, Z.H.; Luo, C.; Kojima, M.; Maeda, M. Halogen exchanges using crown ethers: synthesis and preliminary biodis-tribution of 6-[211At]astatomethyl-19-norcholest-5(10)-en-3 beta-ol. Int. J. Appl. Radiat. Isot., 1985, 36(7), 561-563.
[http://dx.doi.org/10.1016/0020-708X(85)90110-3] [PMID: 2933343]
[29]
Brown, I.; Carpenter, R.; Link, E.; Mitchell, J. Potential diagnostic and therapeutic agents for malignant melanoma: Synthesis of heavy radiohalogenated derivatives of methylene blue by electrophilic and nucleophilic methods 2005, 107(6), 337.
[30]
Meyer, G.J.; Walte, A.; Sriyapureddy, S.R.; Grote, M.; Krull, D.; Korkmaz, Z.; Knapp, W.H. Synthesis and analysis of 2-[211At]-L-phenylalanine and 4-[211At]-L-phenylalanine and their uptake in human glioma cell cultures in-vitro. Appl. Radiat. Isot., 2010, 68(6), 1060-1065.
[http://dx.doi.org/10.1016/j.apradiso.2009.12.043] [PMID: 20137958]
[31]
Vaidyanathan, G.; Affleck, D.J.; Alston, K.L.; Zhao, X.G.; Hens, M.; Hunter, D.H.; Babich, J.; Zalutsky, M.R. A kit method for the high level synthesis of [211At]MABG. Bioorg. Med. Chem., 2007, 15(10), 3430-3436.
[http://dx.doi.org/10.1016/j.bmc.2007.03.016] [PMID: 17387017]
[32]
Garg, P.K.; John, C.S.; Zalutsky, M.R. Preparation and preliminary evaluation of 4-[211At]astato-N-piperidinoethyl benzamide. Nucl. Med. Biol., 1995, 22(4), 467-473.
[http://dx.doi.org/10.1016/0969-8051(94)00134-6] [PMID: 7550023]
[33]
Vaidyanathan, G.; Larsen, R.H.; Zalutsky, M.R. 5-[211 At]astato-2¢-deoxyuridine, an alpha particle-emitting endoradiotherapeutic agent undergoing DNA incorporation. Cancer Res., 1996, 56(6), 1204-1209.
[PMID: 8640798]
[34]
Vaidyanathan, G.; Zalutsky, M.R. 1-(m-[211At]astatobenzyl)guanidine: synthesis via astato demetalation and preliminary in vitro and in vivo evaluation. Bioconjug. Chem., 1992, 3(6), 499-503.
[http://dx.doi.org/10.1021/bc00018a006] [PMID: 1463779]
[35]
Larsen, R.H.; Murud, K.M.; Akabani, G.; Hoff, P.; Bruland, O.S.; Zalutsky, M.R. 211At- and 131I-labeled bisphosphonates with high in vivo stability and bone accumulation. J. Nucl. Med., 1999, 40(7), 1197-1203.
[PMID: 10405142]
[36]
Vaidyanathan, G.; Affleck, D.J.; Schottelius, M.; Wester, H.; Friedman, H.S.; Zalutsky, M.R. Synthesis and evaluation of glycosylated octreotate analogues labeled with radioiodine and 211At via a tin precursor. Bioconjug. Chem., 2006, 17(1), 195-203.
[http://dx.doi.org/10.1021/bc0502560] [PMID: 16417269]
[37]
Lesch, H.P.; Kaikkonen, M.U.; Pikkarainen, J.T.; Ylä-Herttuala, S. Avidin-biotin technology in targeted therapy. Expert Opin. Drug Deliv., 2010, 7(5), 551-564.
[http://dx.doi.org/10.1517/17425241003677749] [PMID: 20233034]
[38]
Li, Y.; Chyan, M.K.; Hamlin, D.K.; Nguyen, H.; Vessella, R.; Wilbur, D.S. Evaluation of radioiodinated protein conjugates and their poten-tial metabolites containing lysine-urea-glutamate (LuG), PEG and closo-decaborate(2-) as models for targeting astatine-211 to metastatic prostate cancer. Nucl. Med. Biol., 2020.
[http://dx.doi.org/10.1016/j.nucmedbio.2020.04.005] [PMID: 32409263]
[39]
Morgenstern, A.; Bruchertseifer, F.; Apostolidis, C. Targeted alpha therapy with 213Bi. Curr. Radiopharm., 2011, 4(4), 295-305.
[http://dx.doi.org/10.2174/1874471011104040295] [PMID: 22202152]
[40]
Jaggi, J.S.; Kappel, B.J.; McDevitt, M.R.; Sgouros, G.; Flombaum, C.D.; Cabassa, C.; Scheinberg, D.A. Efforts to control the errant prod-ucts of a targeted in vivo generator. Cancer Res., 2005, 65(11), 4888-4895.
[http://dx.doi.org/10.1158/0008-5472.CAN-04-3096] [PMID: 15930310]
[41]
Dadwal, M.; Kang, C.S.; Song, H.A.; Sun, X.; Dai, A.; Baidoo, K.E.; Brechbiel, M.W.; Chong, H.S. Synthesis and evaluation of a bifunc-tional chelate for development of Bi(III)-labeled radioimmunoconjugates. Bioorg. Med. Chem. Lett., 2011, 21(24), 7513-7515.
[http://dx.doi.org/10.1016/j.bmcl.2011.06.107] [PMID: 22047687]
[42]
Song, H.A.; Kang, C.S.; Baidoo, K.E.; Milenic, D.E.; Chen, Y.; Dai, A.; Brechbiel, M.W.; Chong, H.S. Efficient bifunctional decadentate ligand 3p-C-DEPA for targeted α-radioimmunotherapy applications. Bioconjug. Chem., 2011, 22(6), 1128-1135.
[http://dx.doi.org/10.1021/bc100586y] [PMID: 21604692]
[43]
Chong, H.S.; Song, H.A.; Birch, N.; Le, T.; Lim, S.; Ma, X. Efficient synthesis and evaluation of bimodal ligand NETA. Bioorg. Med. Chem. Lett., 2008, 18(11), 3436-3439.
[http://dx.doi.org/10.1016/j.bmcl.2008.03.084] [PMID: 18445528]
[44]
Kang, C.S.; Song, H.A.; Milenic, D.E.; Baidoo, K.E.; Brechbiel, M.W.; Chong, H.S. Preclinical evaluation of NETA-based bifunctional ligand for radioimmunotherapy applications using 212Bi and 213Bi: radiolabeling, serum stability, and biodistribution and tumor uptake studies. Nucl. Med. Biol., 2013, 40(5), 600-605.
[http://dx.doi.org/10.1016/j.nucmedbio.2013.01.012] [PMID: 23541026]
[45]
Garmestani, K.; Yao, Z.; Zhang, M.; Wong, K.; Park, C.W.; Pastan, I.; Carrasquillo, J.A.; Brechbiel, M.W. Synthesis and evaluation of a macrocyclic bifunctional chelating agent for use with bismuth radionuclides. Nucl. Med. Biol., 2001, 28(4), 409-418.
[http://dx.doi.org/10.1016/S0969-8051(00)00203-1] [PMID: 11395314]
[46]
Wilson, J.J.; Ferrier, M.; Radchenko, V.; Maassen, J.R.; Engle, J.W.; Batista, E.R.; Martin, R.L.; Nortier, F.M.; Fassbender, M.E.; John, K.D.; Birnbaum, E.R. Evaluation of nitrogen-rich macrocyclic ligands for the chelation of therapeutic bismuth radioisotopes. Nucl. Med. Biol., 2015, 42(5), 428-438.
[http://dx.doi.org/10.1016/j.nucmedbio.2014.12.007] [PMID: 25684650]
[47]
Šimeček, J.; Hermann, P.; Seidl, C.; Bruchertseifer, F.; Morgenstern, A.; Wester, H.J.; Notni, J. Efficient formation of inert Bi-213 chelates by tetraphosphorus acid analogues of DOTA: towards improved alpha-therapeutics. EJNMMI Res., 2018, 8(1), 78.
[http://dx.doi.org/10.1186/s13550-018-0431-3] [PMID: 30091088]
[48]
Matazova, E.V.; Egorova, B.V.; Konopkina, E.A.; Aleshin, G.Y.; Zubenko, A.D.; Mitrofanov, A.A.; Karpov, K.V.; Fedorova, O.A.; Fedo-rov, Y.V.; Kalmykov, S.N. Benzoazacrown compound: a highly effective chelator for therapeutic bismuth radioisotopes. MedChemComm, 2019, 10(9), 1641-1645.
[http://dx.doi.org/10.1039/C9MD00251K] [PMID: 31814957]
[49]
Thiele, N.A.; Wilson, J.J. Actinium-225 for targeted α therapy: Coordination chemistry and current chelation approaches. Cancer Biother. Radiopharm., 2018, 33(8), 336-348.
[http://dx.doi.org/10.1089/cbr.2018.2494] [PMID: 29889562]
[50]
Morgenstern, A.; Apostolidis, C.; Kratochwil, C.; Sathekge, M.; Krolicki, L.; Bruchertseifer, F. An overview of targeted alpha therapy with 225Actinium and 213Bismuth. Curr. Radiopharm., 2018, 11(3), 200-208.
[http://dx.doi.org/10.2174/1874471011666180502104524] [PMID: 29732998]
[51]
Price, E.W.; Orvig, C. Matching chelators to radiometals for radiopharmaceuticals. Chem. Soc. Rev., 2014, 43(1), 260-290.
[http://dx.doi.org/10.1039/C3CS60304K] [PMID: 24173525]
[52]
Deal, K.A.; Davis, I.A.; Mirzadeh, S.; Kennel, S.J.; Brechbiel, M.W. Improved in vivo stability of actinium-225 macrocyclic complexes. J. Med. Chem., 1999, 42(15), 2988-2992.
[http://dx.doi.org/10.1021/jm990141f] [PMID: 10425108]
[53]
McDevitt, M.R.; Ma, D.; Simon, J.; Frank, R.K.; Scheinberg, D.A. Design and synthesis of 225Ac radioimmunopharmaceuticals. Appl. Radiat. Isot., 2002, 57(6), 841-847.
[http://dx.doi.org/10.1016/S0969-8043(02)00167-7] [PMID: 12406626]
[54]
Chen, X.; Ji, M.M.; Wai, C.; Chen, X.R.; Fisher, D. Carboxylate-derived calixarenes with high selectivity for actinium-225. Chem. Commun., 1998, 3, 377-378.
[55]
Ramogida, C.F.; Robertson, A.K.H.; Jermilova, U.; Zhang, C.; Yang, H.; Kunz, P.; Lassen, J.; Bratanovic, I.; Brown, V.; Southcott, L.; Rodríguez-Rodríguez, C.; Radchenko, V.; Bénard, F.; Orvig, C.; Schaffer, P. Evaluation of polydentate picolinic acid chelating ligands and an α-melanocyte-stimulating hormone derivative for targeted alpha therapy using ISOL-produced 225Ac. EJNMMI Radiopharm Chem, 2019, 4(1), 21.
[http://dx.doi.org/10.1186/s41181-019-0072-5] [PMID: 31659557]
[56]
Henriksen, G.; Hoff, P.; Larsen, R.H. Evaluation of potential chelating agents for radium. Appl. Radiat. Isot., 2002, 56(5), 667-671.
[http://dx.doi.org/10.1016/S0969-8043(01)00282-2] [PMID: 11993940]
[57]
Abou, D.; Thiele, N.; Villmer, A.; Gustche, N.; Escorcia, F.; Wilson, J.; Thorek, D. MACROPA highly stable chelator of Radium-223 and functionalization attempts for targeted treatment of cancer. J. Nucl. Med., 2020, 61(Suppl. 1), 587.
[58]
Jadvar, H.; Colletti, P.M. Targeted α-therapy in non-prostate malignancies. Eur. J. Nucl. Med. Mol. Imaging, 2021.
[http://dx.doi.org/10.1007/s00259-021-05405-0] [PMID: 33993386]
[59]
Vaidyanathan, G. Meta-iodobenzylguanidine and analogues: chemistry and biology. Q. J. Nucl. Med. Mol. Imaging, 2008, 52(4), 351-368.
[PMID: 19088690]
[60]
Batra, V.; Ranieri, P.; Makvandi, M.; Tsang, M.; Hou, C.; Li, Y.; Vaidyanathan, G.; Pryma, D.A.; Maris, J.M. Abstract 1610: Development of meta-[211At]astatobenzylguanidine ([211At]MABG) as an alpha particle emitting systemic targeted radiotherapeutic for neuroblastoma. Cancer Res., 2015, 75(15)(Suppl.), 1610-1610.
[61]
Ohshima, Y.; Sudo, H.; Watanabe, S.; Nagatsu, K.; Tsuji, A.B.; Sakashita, T.; Ito, Y.M.; Yoshinaga, K.; Higashi, T.; Ishioka, N.S. Anti-tumor effects of radionuclide treatment using α-emitting meta-211At-astato-benzylguanidine in a PC12 pheochromocytoma model. Eur. J. Nucl. Med. Mol. Imaging, 2018, 45(6), 999-1010.
[http://dx.doi.org/10.1007/s00259-017-3919-6] [PMID: 29350258]
[62]
Makvandi, M.; Lieberman, B.P.; LeGeyt, B.; Hou, C.; Mankoff, D.A.; Mach, R.H.; Pryma, D.A. The pre-clinical characterization of an alpha-emitting sigma-2 receptor targeted radiotherapeutic. Nucl. Med. Biol., 2016, 43(1), 35-41.
[http://dx.doi.org/10.1016/j.nucmedbio.2015.10.001] [PMID: 26702785]
[63]
Kiess, A.P.; Minn, I.; Vaidyanathan, G.; Hobbs, R.F.; Josefsson, A.; Shen, C.; Brummet, M.; Chen, Y.; Choi, J.; Koumarianou, E.; Baidoo, K.; Brechbiel, M.W.; Mease, R.C.; Sgouros, G.; Zalutsky, M.R.; Pomper, M.G. (2S)-2-(3-(1-Carboxy-5-(4-211At-Astatobenzamido)Pentyl)Ureido)-Pentanedioic Acid for PSMA-Targeted α-Particle Radiopharmaceutical Therapy. J. Nucl. Med., 2016, 57(10), 1569-1575.
[http://dx.doi.org/10.2967/jnumed.116.174300] [PMID: 27230930]
[64]
Nonnekens, J.; Chatalic, K.L.; Molkenboer-Kuenen, J.D.; Beerens, C.E.; Bruchertseifer, F.; Morgenstern, A.; Veldhoven-Zweistra, J.; Schottelius, M.; Wester, H.J.; van Gent, D.C.; van Weerden, W.M.; Boerman, O.C.; de Jong, M.; Heskamp, S. 213Bi-labeled prostate-specific membrane antigen-targeting agents induce DNA double-strand breaks in prostate cancer xenografts. Cancer Biother. Radiopharm., 2017, 32(2), 67-73.
[http://dx.doi.org/10.1089/cbr.2016.2155] [PMID: 28301262]
[65]
Sathekge, M.; Knoesen, O.; Meckel, M.; Modiselle, M.; Vorster, M.; Marx, S. 213Bi-PSMA-617 targeted alpha-radionuclide therapy in metastatic castration-resistant prostate cancer. Eur. J. Nucl. Med. Mol. Imaging, 2017, 44(6), 1099-1100.
[http://dx.doi.org/10.1007/s00259-017-3657-9] [PMID: 28255795]
[66]
Kratochwil, C.; Bruchertseifer, F.; Rathke, H.; Hohenfellner, M.; Giesel, F.L.; Haberkorn, U.; Morgenstern, A. Targeted α-therapy of meta-static castration-resistant prostate cancer with 225Ac-PSMA-617: Swimmer-plot analysis suggests efficacy regarding duration of tumor con-trol. J. Nucl. Med., 2018, 59(5), 795-802.
[http://dx.doi.org/10.2967/jnumed.117.203539] [PMID: 29326358]
[67]
Kelly, J.M.; Amor-Coarasa, A.; Ponnala, S.; Nikolopoulou, A.; Williams, C., Jr; Thiele, N.A.; Schlyer, D.; Wilson, J.J.; DiMagno, S.G.; Babich, J.W. A single dose of 225Ac-RPS-074 induces a complete tumor response in an LNCaP xenograft model. J. Nucl. Med., 2019, 60(5), 649-655.
[http://dx.doi.org/10.2967/jnumed.118.219592] [PMID: 30413660]
[68]
Zacherl, M.J.; Gildehaus, F.J.; Mittlmeier, L.; Böning, G.; Gosewisch, A.; Wenter, V.; Unterrainer, M.; Schmidt-Hegemann, N.; Belka, C.; Kretschmer, A.; Casuscelli, J.; Stief, C.G.; Unterrainer, M.; Bartenstein, P.; Todica, A.; Ilhan, H. First clinical results for PSMA-targeted α-therapy using 225Ac-PSMA-I&T in advanced-mCRPC patients. J. Nucl. Med., 2021, 62(5), 669-674.
[http://dx.doi.org/10.2967/jnumed.120.251017] [PMID: 33008928]
[69]
Sofou, S. Radionuclide carriers for targeting of cancer. Int. J. Nanomedicine, 2008, 3(2), 181-199.
[http://dx.doi.org/10.2147/IJN.S2736] [PMID: 18686778]
[70]
Dadachova, E. Cancer therapy with alpha-emitters labeled peptides. Semin. Nucl. Med., 2010, 40(3), 204-208.
[http://dx.doi.org/10.1053/j.semnuclmed.2010.01.002] [PMID: 20350629]
[71]
Miao, Y.; Hylarides, M.; Fisher, D.R.; Shelton, T.; Moore, H.; Wester, D.W.; Fritzberg, A.R.; Winkelmann, C.T.; Hoffman, T.; Quinn, T.P. Melanoma therapy via peptide-targeted alpha-radiation. Clin. Cancer Res., 2005, 11(15), 5616-5621.
[http://dx.doi.org/10.1158/1078-0432.CCR-05-0619] [PMID: 16061880]
[72]
Qu, C.F.; Song, E.Y.; Li, Y.; Rizvi, S.M.; Raja, C.; Smith, R.; Morgenstern, A.; Apostolidis, C.; Allen, B.J. Pre-clinical study of 213Bi la-beled PAI2 for the control of micrometastatic pancreatic cancer. Clin. Exp. Metastasis, 2005, 22(7), 575-586.
[http://dx.doi.org/10.1007/s10585-005-5788-9] [PMID: 16475028]
[73]
Li, Y.; Rizvi, S.M.; Ranson, M.; Allen, B.J. 213Bi-PAI2 conjugate selectively induces apoptosis in PC3 metastatic prostate cancer cell line and shows anti-cancer activity in a xenograft animal model. Br. J. Cancer, 2002, 86(7), 1197-1203.
[http://dx.doi.org/10.1038/sj.bjc.6600179] [PMID: 11953871]
[74]
Knör, S.; Sato, S.; Huber, T.; Morgenstern, A.; Bruchertseifer, F.; Schmitt, M.; Kessler, H.; Senekowitsch-Schmidtke, R.; Magdolen, V.; Seidl, C. Development and evaluation of peptidic ligands targeting tumour-associated urokinase plasminogen activator receptor (uPAR) for use in alpha-emitter therapy for disseminated ovarian cancer. Eur. J. Nucl. Med. Mol. Imaging, 2008, 35(1), 53-64.
[http://dx.doi.org/10.1007/s00259-007-0582-3] [PMID: 17891393]
[75]
Delpassand, E.S.; Samarghandi, A.; Zamanian, S.; Wolin, E.M.; Hamiditabar, M.; Espenan, G.D.; Erion, J.L.; O’Dorisio, T.M.; Kvols, L.K.; Simon, J.; Wolfangel, R.; Camp, A.; Krenning, E.P.; Mojtahedi, A. Peptide receptor radionuclide therapy with 177Lu-DOTATATE for patients with somatostatin receptor-expressing neuroendocrine tumors: the first US phase 2 experience. Pancreas, 2014, 43(4), 518-525.
[http://dx.doi.org/10.1097/MPA.0000000000000113] [PMID: 24632546]
[76]
Nayak, T.; Norenberg, J.; Anderson, T.; Atcher, R. A comparison of high- versus low-linear energy transfer somatostatin receptor targeted radionuclide therapy in vitro. Cancer Biother. Radiopharm., 2005, 20(1), 52-57.
[http://dx.doi.org/10.1089/cbr.2005.20.52] [PMID: 15778581]
[77]
Norenberg, J.P.; Krenning, B.J.; Konings, I.R.; Kusewitt, D.F.; Nayak, T.K.; Anderson, T.L.; de Jong, M.; Garmestani, K.; Brechbiel, M.W.; Kvols, L.K. 213Bi-[DOTA0, Tyr3]octreotide peptide receptor radionuclide therapy of pancreatic tumors in a preclinical animal model. Clin. Cancer Res., 2006, 12(3 Pt 1), 897-903.
[http://dx.doi.org/10.1158/1078-0432.CCR-05-1264] [PMID: 16467104]
[78]
Werner, R.A.; Weich, A.; Kircher, M.; Solnes, L.B.; Javadi, M.S.; Higuchi, T.; Buck, A.K.; Pomper, M.G.; Rowe, S.P.; Lapa, C. The theranostic promise for Neuroendocrine Tumors in the late 2010s - Where do we stand, where do we go? Theranostics, 2018, 8(22), 6088-6100.
[http://dx.doi.org/10.7150/thno.30357] [PMID: 30613284]
[79]
Vaidyanathan, G.; Boskovitz, A.; Shankar, S.; Zalutsky, M.R. Radioiodine and 211At-labeled guanidinomethyl halobenzoyl octreotate conjugates: potential peptide radiotherapeutics for somatostatin receptor-positive cancers. Peptides, 2004, 25(12), 2087-2097.
[http://dx.doi.org/10.1016/j.peptides.2004.08.018] [PMID: 15572196]
[80]
Wild, D.; Frischknecht, M.; Zhang, H.; Morgenstern, A.; Bruchertseifer, F.; Boisclair, J.; Provencher-Bolliger, A.; Reubi, J.C.; Maecke, H.R. Alpha- versus beta-particle radiopeptide therapy in a human prostate cancer model (213Bi-DOTA-PESIN and 213Bi-AMBA versus 177Lu-DOTA-PESIN). Cancer Res., 2011, 71(3), 1009-1018.
[http://dx.doi.org/10.1158/0008-5472.CAN-10-1186] [PMID: 21245097]
[81]
Aoki, M.; Zhao, S.; Takahashi, K.; Washiyama, K.; Ukon, N.; Tan, C.; Shimoyama, S.; Nishijima, K.I.; Ogawa, K. Preliminary evaluation of astatine-211-labeled bombesin derivatives for targeted alpha therapy. Chem. Pharm. Bull. (Tokyo), 2020, 68(6), 538-545.
[http://dx.doi.org/10.1248/cpb.c20-00077] [PMID: 32475858]
[82]
Królicki, L.; Bruchertseifer, F.; Kunikowska, J.; Koziara, H.; Królicki, B.; Jakuciński, M.; Pawlak, D.; Apostolidis, C.; Mirzadeh, S.; Rola, R.; Merlo, A.; Morgenstern, A. Safety and efficacy of targeted alpha therapy with 213Bi-DOTA-substance P in recurrent glioblastoma. Eur. J. Nucl. Med. Mol. Imaging, 2019, 46(3), 614-622.
[http://dx.doi.org/10.1007/s00259-018-4225-7] [PMID: 30498897]
[83]
Majkowska-Pilip, A.; Rius, M.; Bruchertseifer, F.; Apostolidis, C.; Weis, M.; Bonelli, M.; Laurenza, M.; Królicki, L.; Morgenstern, A. In vitro evaluation of 225 Ac-DOTA-substance P for targeted alpha therapy of glioblastoma multiforme. Chem. Biol. Drug Des., 2018, 92(1), 1344-1356.
[http://dx.doi.org/10.1111/cbdd.13199] [PMID: 29611298]
[84]
Lyczko, M.; Pruszynski, M.; Majkowska-Pilip, A.; Lyczko, K.; Was, B.; Meczynska-Wielgosz, S.; Kruszewski, M.; Szkliniarz, K.; Ja-strzebski, J.; Stolarz, A.; Bilewicz, A. 211At labeled substance P (5-11) as potential radiopharmaceutical for glioma treatment. Nucl. Med. Biol., 2017, 53, 1-8.
[http://dx.doi.org/10.1016/j.nucmedbio.2017.05.008] [PMID: 28683361]
[85]
Essler, M.; Gärtner, F.C.; Neff, F.; Blechert, B.; Senekowitsch-Schmidtke, R.; Bruchertseifer, F.; Morgenstern, A.; Seidl, C. Therapeutic efficacy and toxicity of 225Ac-labelled vs. 213Bi-labelled tumour-homing peptides in a preclinical mouse model of peritoneal carcinoma-tosis. Eur. J. Nucl. Med. Mol. Imaging, 2012, 39(4), 602-612.
[http://dx.doi.org/10.1007/s00259-011-2023-6] [PMID: 22237842]
[86]
Tafreshi, N.; Pandya, D.; Doligalski, M.; Budzevich, M.; McLaughlin, M.; Morse, D.; Wadas, T. 225Ac-DOTA-MC1RL, a potential radio-therapy for the treatment of uveal melanoma. J. Nucl. Med., 2018, 59(Suppl. 1), 316.
[87]
Zalutsky, M.R.; Stabin, M.G.; Larsen, R.H.; Bigner, D.D. Tissue distribution and radiation dosimetry of astatine-211-labeled chimeric 81C6, an alpha-particle-emitting immunoconjugate. Nucl. Med. Biol., 1997, 24(3), 255-261.
[http://dx.doi.org/10.1016/S0969-8051(97)00060-7] [PMID: 9228660]
[88]
Elgqvist, J.; Andersson, H.; Bäck, T.; Claesson, I.; Hultborn, R.; Jensen, H.; Lindegren, S.; Olsson, M.; Palm, S.; Warnhammar, E.; Jacob-sson, L. Fractionated radioimmunotherapy of intraperitoneally growing ovarian cancer in nude mice with 211At-MX35 F(ab’)2: therapeu-tic efficacy and myelotoxicity. Nucl. Med. Biol., 2006, 33(8), 1065-1072.
[http://dx.doi.org/10.1016/j.nucmedbio.2006.07.009] [PMID: 17127181]
[89]
Raja, C.; Graham, P.; Abbas Rizvi, S.M.; Song, E.; Goldsmith, H.; Thompson, J.; Bosserhoff, A.; Morgenstern, A.; Apostolidis, C.; Kears-ley, J.; Reisfeld, R.; Allen, B.J. Interim analysis of toxicity and response in phase 1 trial of systemic targeted alpha therapy for metastatic melanoma. Cancer Biol. Ther., 2007, 6(6), 846-852.
[http://dx.doi.org/10.4161/cbt.6.6.4089] [PMID: 17495524]
[90]
Roscher, M.; Hormann, I.; Leib, O.; Marx, S.; Moreno, J.; Miltner, E.; Friesen, C. Targeted alpha-therapy using [Bi-213]anti-CD20 as novel treatment option for radio- and chemoresistant non-Hodgkin lymphoma cells. Oncotarget, 2013, 4(2), 218-230.
[http://dx.doi.org/10.18632/oncotarget.817] [PMID: 23474846]
[91]
Abedin, S.; Guru Murthy, G. S.; Runaas, L.; Michaelis, L. C.; Atallah, E. L.; Hamadani, M.; Harrington, A. M.; Carlson, K. Lintuzumab Ac-225 in combination with CLAG-M chemotherapy in relapsed/refractory AML: Interim results of a phase I study. Blood, 2019, 134(Supplement_1), 2605-2605.
[92]
Ballangrud, A.M.; Yang, W.H.; Palm, S.; Enmon, R.; Borchardt, P.E.; Pellegrini, V.A.; McDevitt, M.R.; Scheinberg, D.A.; Sgouros, G. Al-pha-particle emitting atomic generator (Actinium-225)-labeled trastuzumab (herceptin) targeting of breast cancer spheroids: efficacy ver-sus HER2/neu expression. Clin. Cancer Res., 2004, 10(13), 4489-4497.
[http://dx.doi.org/10.1158/1078-0432.CCR-03-0800] [PMID: 15240541]
[93]
Dekempeneer, Y.; Bäck, T.; Aneheim, E.; Jensen, H.; Puttemans, J.; Xavier, C.; Keyaerts, M.; Palm, S.; Albertsson, P.; Lahoutte, T.; Caveliers, V.; Lindegren, S.; D’Huyvetter, M. Labeling of anti-HER2 nanobodies with astatine-211: Optimization and the effect of differ-ent coupling reagents on their in Vivo behavior. Mol. Pharm., 2019, 16(8), 3524-3533.
[http://dx.doi.org/10.1021/acs.molpharmaceut.9b00354] [PMID: 31268724]
[94]
Palm, S.; Bäck, T.; Aneheim, E.; Hallqvist, A.; Hultborn, R.; Jacobsson, L.; Jensen, H.; Lindegren, S.; Albertsson, P. Evaluation of thera-peutic efficacy of 211At-labeled farletuzumab in an intraperitoneal mouse model of disseminated ovarian cancer. Transl. Oncol., 2021, 14(1)100873
[http://dx.doi.org/10.1016/j.tranon.2020.100873] [PMID: 32987283]
[95]
Vaidyanathan, G.; Affleck, D.J.; Bigner, D.D.; Zalutsky, M.R. N-succinimidyl 3-[211At]astato-4-guanidinomethylbenzoate: an acylation agent for labeling internalizing antibodies with alpha-particle emitting 211At. Nucl. Med. Biol., 2003, 30(4), 351-359.
[http://dx.doi.org/10.1016/S0969-8051(03)00005-2] [PMID: 12767391]
[96]
Choi, J.; Vaidyanathan, G.; Koumarianou, E.; Kang, C.M.; Zalutsky, M.R. Astatine-211 labeled anti-HER2 5F7 single domain antibody fragment conjugates: radiolabeling and preliminary evaluation. Nucl. Med. Biol., 2018, 56, 10-20.
[http://dx.doi.org/10.1016/j.nucmedbio.2017.09.003] [PMID: 29031230]
[97]
Green, D.J.; Shadman, M.; Jones, J.C.; Frayo, S.L.; Kenoyer, A.L.; Hylarides, M.D.; Hamlin, D.K.; Wilbur, D.S.; Balkan, E.R.; Lin, Y.; Miller, B.W.; Frost, S.H.; Gopal, A.K.; Orozco, J.J.; Gooley, T.A.; Laird, K.L.; Till, B.G.; Bäck, T.; Sandmaier, B.M.; Pagel, J.M.; Press, O.W. Astatine-211 conjugated to an anti-CD20 monoclonal antibody eradicates disseminated B-cell lymphoma in a mouse model. Blood, 2015, 125(13), 2111-2119.
[http://dx.doi.org/10.1182/blood-2014-11-612770] [PMID: 25628467]
[98]
Rosenblat, T.L.; McDevitt, M.R.; Mulford, D.A.; Pandit-Taskar, N.; Divgi, C.R.; Panageas, K.S.; Heaney, M.L.; Chanel, S.; Morgenstern, A.; Sgouros, G.; Larson, S.M.; Scheinberg, D.A.; Jurcic, J.G. Sequential cytarabine and alpha-particle immunotherapy with bismuth-213-lintuzumab (HuM195) for acute myeloid leukemia. Clin. Cancer Res., 2010, 16(21), 5303-5311.
[http://dx.doi.org/10.1158/1078-0432.CCR-10-0382] [PMID: 20858843]
[99]
Qu, C.F.; Li, Y.; Song, Y.J.; Rizvi, S.M.; Raja, C.; Zhang, D.; Samra, J.; Smith, R.; Perkins, A.C.; Apostolidis, C.; Allen, B.J. MUC1 expres-sion in primary and metastatic pancreatic cancer cells for in vitro treatment by (213)Bi-C595 radioimmunoconjugate. Br. J. Cancer, 2004, 91(12), 2086-2093.
[http://dx.doi.org/10.1038/sj.bjc.6602232] [PMID: 15599383]
[100]
Chérel, M.; Gouard, S.; Gaschet, J.; Saï-Maurel, C.; Bruchertseifer, F.; Morgenstern, A.; Bourgeois, M.; Gestin, J.F.; Bodéré, F.K.; Barbet, J.; Moreau, P.; Davodeau, F. 213Bi radioimmunotherapy with an anti-mCD138 monoclonal antibody in a murine model of multiple mye-loma. J. Nucl. Med., 2013, 54(9), 1597-1604.
[http://dx.doi.org/10.2967/jnumed.112.111997] [PMID: 24003167]
[101]
Li, Y.; Tian, Z.; Rizvi, S.M.; Bander, N.H.; Allen, B.J. In vitro and preclinical targeted alpha therapy of human prostate cancer with Bi-213 labeled J591 antibody against the prostate specific membrane antigen. Prostate Cancer Prostatic Dis., 2002, 5(1), 36-46.
[http://dx.doi.org/10.1038/sj.pcan.4500543] [PMID: 15195129]
[102]
Milenic, D.E.; Brady, E.D.; Garmestani, K.; Albert, P.S.; Abdulla, A.; Brechbiel, M.W. Improved efficacy of alpha-particle-targeted radia-tion therapy: dual targeting of human epidermal growth factor receptor-2 and tumor-associated glycoprotein 72. Cancer, 2010, 116(4)(Suppl.), 1059-1066.
[http://dx.doi.org/10.1002/cncr.24793] [PMID: 20127951]
[103]
Adams, G.P.; Shaller, C.C.; Chappell, L.L.; Wu, C.; Horak, E.M.; Simmons, H.H.; Litwin, S.; Marks, J.D.; Weiner, L.M.; Brechbiel, M.W. Delivery of the alpha-emitting radioisotope bismuth-213 to solid tumors via single-chain Fv and diabody molecules. Nucl. Med. Biol., 2000, 27(4), 339-346.
[http://dx.doi.org/10.1016/S0969-8051(00)00103-7] [PMID: 10938467]
[104]
Milenic, D.E.; Garmestani, K.; Brady, E.D.; Albert, P.S.; Ma, D.; Abdulla, A.; Brechbiel, M.W. Alpha-particle radioimmunotherapy of disseminated peritoneal disease using a (212)Pb-labeled radioimmunoconjugate targeting HER2. Cancer Biother. Radiopharm., 2005, 20(5), 557-568.
[http://dx.doi.org/10.1089/cbr.2005.20.557] [PMID: 16248771]
[105]
Miederer, M.; McDevitt, M.R.; Sgouros, G.; Kramer, K.; Cheung, N.K.; Scheinberg, D.A. Pharmacokinetics, dosimetry, and toxicity of the targetable atomic generator, 225Ac-HuM195, in nonhuman primates. J. Nucl. Med., 2004, 45(1), 129-137.
[PMID: 14734685]
[106]
Kennel, S.J.; Chappell, L.L.; Dadachova, K.; Brechbiel, M.W.; Lankford, T.K.; Davis, I.A.; Stabin, M.; Mirzadeh, S. Evaluation of 225Ac for vascular targeted radioimmunotherapy of lung tumors. Cancer Biother. Radiopharm., 2000, 15(3), 235-244.
[http://dx.doi.org/10.1089/108497800414329] [PMID: 10941530]
[107]
Song, H.; Hobbs, R.F.; Vajravelu, R.; Huso, D.L.; Esaias, C.; Apostolidis, C.; Morgenstern, A.; Sgouros, G. Radioimmunotherapy of breast cancer metastases with alpha-particle emitter 225Ac: comparing efficacy with 213Bi and 90Y. Cancer Res., 2009, 69(23), 8941-8948.
[http://dx.doi.org/10.1158/0008-5472.CAN-09-1828] [PMID: 19920193]
[108]
Rojas, J.V.; Woodward, J.D.; Chen, N.; Rondinone, A.J.; Castano, C.H.; Mirzadeh, S. Synthesis and characterization of lanthanum phos-phate nanoparticles as carriers for (223)Ra and (225)Ra for targeted alpha therapy. Nucl. Med. Biol., 2015, 42(7), 614-620.
[http://dx.doi.org/10.1016/j.nucmedbio.2015.03.007] [PMID: 25900730]
[109]
Kucka, J.; Hrubý, M.; Konák, C.; Kozempel, J.; Lebeda, O. Astatination of nanoparticles containing silver as possible carriers of 211At. Appl. Radiat. Isot., 2006, 64(2), 201-206.
[http://dx.doi.org/10.1016/j.apradiso.2005.07.021] [PMID: 16154358]
[110]
Mokhodoeva, O.; Vlk, M.; Málková, E.; Kukleva, E.; Mičolová, P.; Štamberg, K.; Šlouf, M.; Dzhenloda, R.; Kozempel, J. Study of 223Ra uptake mechanism by Fe3O4 nanoparticles: towards new prospective theranostic SPIONs. J. Nanopart. Res., 2016, 18(10), 301.
[http://dx.doi.org/10.1007/s11051-016-3615-7]
[111]
Silindir-Gunay, M.; Karpuz, M.; Ozer, A.Y. Targeted Alpha Therapy and Nanocarrier Approach. Cancer Biother. Radiopharm., 2020, 35(6), 446-458.
[http://dx.doi.org/10.1089/cbr.2019.3213] [PMID: 32302510]
[112]
Westrøm, S.; Bønsdorff, T.B.; Bruland, Ø.S.; Larsen, R.H. Therapeutic effect of α-emitting 224Ra-labeled calcium carbonate microparticles in mice with intraperitoneal ovarian cancer. Transl. Oncol., 2018, 11(2), 259-267.
[http://dx.doi.org/10.1016/j.tranon.2017.12.011] [PMID: 29413758]
[113]
Dziawer, L.; Koźmiński, P.; Męczyńska-Wielgosz, S.; Pruszyński, M.; Łyczko, M.; Wąs, B.; Celichowski, G.; Grobelny, J.; Jastrzębski, J.; Bilewicz, A. Gold nanoparticle bioconjugates labelled with 211At for targeted alpha therapy. RSC Advances, 2017, 7(65), 41024-41032.
[http://dx.doi.org/10.1039/C7RA06376H]
[114]
Piotrowska, A.; Męczyńska-Wielgosz, S.; Majkowska-Pilip, A.; Koźmiński, P.; Wójciuk, G.; Cędrowska, E.; Bruchertseifer, F.; Morgen-stern, A.; Kruszewski, M.; Bilewicz, A. Nanozeolite bioconjugates labeled with 223Ra for targeted alpha therapy. Nucl. Med. Biol., 2017, 47, 10-18.
[http://dx.doi.org/10.1016/j.nucmedbio.2016.11.005] [PMID: 28043005]
[115]
Kozempel, J.; Mokhodoeva, O.; Vlk, M. Progress in targeted alpha-particle therapy. what We learned about recoils release from in vivo generators. Molecules, 2018, 23(3)E581
[http://dx.doi.org/10.3390/molecules23030581] [PMID: 29510568]

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