title: Amino acid transport system - A substrate predicts the therapeutic effects of particle radiotherapy.
abstract: L-[methyl-11C]Methionine (11C-Met) is useful for estimating the therapeutic efficacy of particle radiotherapy at early stages of the treatment. Given the short half-life of 11C, the development of longer-lived 18F- and 123I-labeled probes that afford diagnostic information similar to 11C-Met, are being sought. Tumor uptake of 11C-Met is involved in many cellular functions such as amino acid transport System-L, protein synthesis, and transmethylation. Among these processes, since the energy-dependent intracellular functions involved with 11C-Met are more reflective of the radiotherapeutic effects, we evaluated the activity of the amino acid transport System-A as an another energy-dependent cellular function in order to estimate radiotherapeutic effects. In this study, using a carbon-ion beam as the radiation source, the activity of System-A was evaluated by a specific System-A substrate, alpha-[1-14C]-methyl-aminoisobutyric acid (14C-MeAIB). Cellular growth and the accumulation of 14C-MeAIB or 14C-Met were evaluated over time in vitro in cultured human salivary gland (HSG) tumor cells (3-Gy) or in vivo in murine xenografts of HSG tumors (6- or 25-Gy) before and after irradiation with the carbon-ion beam. Post 3-Gy irradiation, in vitro accumulation of 14C-Met and 14C-MeAIB decreased over a 5-day period. In xenografts of HSG tumors in mice, tumor re-growth was observed in vivo on day-10 after a 6-Gy irradiation dose, but no re-growth was detected after the 25-Gy irradiation dose. Consistent with the growth results, the in vivo tumor accumulation of 14C-MeAIB did not decrease after the 6-Gy irradiation dose, whereas a significant decrease was observed after the 25-Gy irradiation dose. These results indicate that the activity of energy dependent System-A transporter may reflect the therapeutic efficacy of carbon-ion radiotherapy and suggests that longer half-life radionuclide-labeled probes for System-A may also provide widely available probes to evaluate the effects of particle radiotherapy on tumors at early stage of the treatment.
authors.affiliation: Department of Molecular Imaging and Radiotherapy, Graduate School of Pharmaceutical Science, Chiba University, Chiba, Japan.
authors.forename: Tomoya
authors.identifier: http://orcid.org/0000-0002-1140-9800
authors.initials: T
authors.lastname: Uehara
authors.affiliation: Department of Molecular Imaging and Radiotherapy, Graduate School of Pharmaceutical Science, Chiba University, Chiba, Japan.
authors.forename: Mariko
authors.initials: M
authors.lastname: Watanabe
authors.affiliation: Department of Molecular Imaging and Radiotherapy, Graduate School of Pharmaceutical Science, Chiba University, Chiba, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Suzuki
authors.affiliation: National Institutes for Quantum and Radiological Science and Technology, National Institute of Radiological Sciences, Chiba, Japan.
authors.forename: Yoshiya
authors.initials: Y
authors.lastname: Furusawa
authors.affiliation: Department of Molecular Imaging and Radiotherapy, Graduate School of Pharmaceutical Science, Chiba University, Chiba, Japan.
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Arano
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D002250:Carbon Radioisotopes / Q000378:metabolism; D045744:Cell Line, Tumor; D064593:Heterografts; D006801:Humans; D008715:Methionine / Q000378:metabolism; D051379:Mice; D011829:Radiation Dosage; D011878:Radiotherapy / Q000379:methods*; D012469:Salivary Glands / Q000378:metabolism
chemical_list: D000596:Amino Acids; D002250:Carbon Radioisotopes; D008715:Methionine