title: Validation of 64Cu-ATSM damaging DNA via high-LET Auger electron emission.
abstract: Radioactive copper (II) (diacetyl-bis N4-methylthiosemicarbazone) (Cu-ATSM) isotopes were originally developed for the imaging of hypoxia in tumors. Because the decay of a (64)Cu atom is emitting not only positrons but also Auger electrons, this radionuclide has great potential as a theranostic agent. However, the success of (64)Cu-ATSM internal radiation therapy would depend on the contribution of Auger electrons to tumor cell killing. Therefore, we designed a cell culture system to define the contributions to cell death from Auger electrons to support or refute our hypothesis that the majority of cell death from (64)Cu-ATSM is a result of high-LET Auger electrons and not positrons or other low-LET radiation. Chinese hamster ovary (CHO) wild type and DNA repair-deficient xrs5 cells were exposed to (64)Cu-ATSM during hypoxic conditions. Surviving fractions were compared with those surviving gamma-radiation, low-LET hadron radiation, and high-LET heavy ion exposure. The ratio of the D(10) values (doses required to achieve 10% cell survival) between CHO wild type and xrs5 cells suggested that (64)Cu-ATSM toxicity is similar to that of high-LET Carbon ion radiation (70 keV/μm). γH2AX foci assays confirmed DNA double-strand breaks and cluster damage by high-LET Auger electrons from (64)Cu decay, and complex types of chromosomal aberrations typical of high-LET radiation were observed after (64)Cu-ATSM exposure. The majority of cell death was caused by high-LET radiation. This work provides strong evidence that (64)Cu-ATSM damages DNA via high-LET Auger electrons, supporting further study and consideration of (64)Cu-ATSM as a cancer treatment modality for hypoxic tumors.
authors.affiliation: Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, Colorado 80523, USA.
authors.forename: Dayton D
authors.initials: DD
authors.lastname: McMillan
authors.affiliation: Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, Colorado 80523, USA.
authors.forename: Junko
authors.initials: J
authors.lastname: Maeda
authors.affiliation: Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, Colorado 80523, USA.
authors.forename: Justin J
authors.initials: JJ
authors.lastname: Bell
authors.affiliation: Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, Colorado 80523, USA.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Genet
authors.affiliation: Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, Colorado 80523, USA.
authors.forename: Garrett
authors.initials: G
authors.lastname: Phoonswadi
authors.affiliation: Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, Colorado 80523, USA.
authors.forename: Kelly A
authors.initials: KA
authors.lastname: Mann
authors.affiliation: Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, Colorado 80523, USA.
authors.forename: Susan L
authors.initials: SL
authors.lastname: Kraft
authors.affiliation: Research, Development and Support Center, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage, Chiba 263-8555, Japan.
authors.forename: Hisashi
authors.initials: H
authors.lastname: Kitamura
authors.affiliation: Research Center for Radiation Protection, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage, Chiba 263-8555, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Fujimori
authors.affiliation: Molecular Imaging Center, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage, Chiba 263-8555, Japan.
authors.forename: Yukie
authors.initials: Y
authors.lastname: Yoshii
authors.affiliation: Molecular Imaging Center, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage, Chiba 263-8555, Japan.
authors.forename: Takako
authors.initials: T
authors.lastname: Furukawa
authors.affiliation: Molecular Imaging Center, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage, Chiba 263-8555, Japan.
authors.forename: Yasuhisa
authors.initials: Y
authors.lastname: Fujibayashi
authors.affiliation: Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, Colorado 80523, USA takamitsu.kato@colostate.edu.
authors.forename: Takamitsu A
authors.initials: TA
authors.lastname: Kato
mesh_terms: D000818:Animals; D016466:CHO Cells; D002244:Carbon; D015687:Cell Hypoxia; D002470:Cell Survival; D002869:Chromosome Aberrations; D056831:Coordination Complexes; D003300:Copper / Q000737:chemistry; D003301:Copper Radioisotopes / Q000737:chemistry*; D006224:Cricetinae; D003412:Cricetulus; D053903:DNA Breaks, Double-Stranded; D004249:DNA Damage; D004260:DNA Repair; D004583:Electrons; D006657:Histones / Q000378:metabolism; D009942:Organometallic Compounds / Q000737:chemistry*; D019275:Radiopharmaceuticals / Q000737:chemistry; D013882:Thiosemicarbazones / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D003301:Copper Radioisotopes; D006657:Histones; D009942:Organometallic Compounds; D019275:Radiopharmaceuticals; D013882:Thiosemicarbazones; C089548:copper (II) diacetyl-di(N(4)-methylthiosemicarbazone); D002244:Carbon; D003300:Copper
keywords: 64Cu-ATSM; CHO; DNA double strand break; auger electron; high LET