title: Temporo-spatial cell-cycle kinetics in HeLa cells irradiated by Ir-192 high dose-rate remote afterloading system (HDR-RALS).
abstract: BACKGROUND
  Intracavitary irradiation plays a pivotal role in definitive radiotherapy for cervical cancer, and the Ir-192 high dose-rate remote afterloading system (HDR-RALS) is often used for this purpose. Under this condition, tumor tissues receive remarkably different absorption doses, with a steep gradient, depending on distance from the radiation source. To obtain temporo-spatial information regarding cell-cycle kinetics in cervical cancer following irradiation by Ir-192 HDR-RALS, we examined HeLa cells expressing the fluorescence ubiquitination-based cell cycle indicator (Fucci), which allowed us to visualize cell-cycle progression.
  
  
  METHODS
  HeLa-Fucci cells, which emit red and green fluorescence in G1 and S/G2/M phases, respectively, were grown on 35-mm dishes and irradiated by Ir-192 HDR-RALS under normoxic and hypoxic conditions. A 6 French (Fr) catheter was used as an applicator. A radiation dose of 6 Gy was prescribed at hypothetical treatment point A, located 20 mm from the radiation source. Changes in Fucci fluorescence after irradiation were visualized for cells from 5 to 20 mm from the Ir-192 source. Several indices, including first green phase duration after irradiation (FGPD), were measured by analysis of time-lapse images.
  
  
  RESULTS
  Cells located 5 to 20 mm from the Ir-192 source became green, reflecting arrest in G2, in a similar manner up to 12 h after irradiation; at more distant positions, however, cells were gradually released from the G2 arrest and became red. This could be explained by the observation that the FGPD was longer for cells closer to the radiation source. Detailed observation revealed that FGPD was significantly longer in cells irradiated in the green phase than in the red phase at positions closer to the Ir-192 source. Unexpectedly, the FGPD was significantly longer after irradiation under hypoxia than normoxia, due in large part to the elongation of FGPD in cells irradiated in the red phase.
  
  
  CONCLUSIONS
  Using HeLa-Fucci cells, we obtained the first temporo-spatial information about cell-cycle kinetics following irradiation by Ir-192 HDR-RALS. Our findings suggest that the potentially surviving hypoxic cells, especially those arising from positions around point A, exhibit different cell-cycle kinetics from normoxic cells destined to be eradicated.
authors.affiliation: Department of Radiation Oncology, Juntendo University, 3-1-3 Hongo, Bunkyo-ku, Tokyo, 113-8431, Japan.
authors.forename: Taito
authors.initials: T
authors.lastname: Asahina
authors.affiliation: Department of Oral Radiation Oncology, Department of Oral Health Science, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo, 113-8549, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kaida
authors.affiliation: Department of Oral Radiation Oncology, Department of Oral Health Science, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo, 113-8549, Japan.
authors.forename: Tatsuaki
authors.initials: T
authors.lastname: Goto
authors.affiliation: Department of Radiation Therapeutics and Oncology, Division of Maxillofacial and Neck Reconstruction, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo, 113-8549, Japan.
authors.forename: Ryo-Ichi
authors.initials: R
authors.lastname: Yoshimura
authors.affiliation: Department of Radiation Oncology, Juntendo University, 3-1-3 Hongo, Bunkyo-ku, Tokyo, 113-8431, Japan.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Sasai
authors.affiliation: Department of Oral Radiation Oncology, Department of Oral Health Science, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo, 113-8549, Japan. masa.mdth@tmd.ac.jp.
authors.forename: Masahiko
authors.initials: M
authors.lastname: Miura
mesh_terms: D002453:Cell Cycle / Q000502:physiology* / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D005434:Flow Cytometry; D005453:Fluorescence; D005456:Fluorescent Dyes / Q000737:chemistry*; D006367:HeLa Cells; D006801:Humans; D007496:Iridium Radioisotopes; D007700:Kinetics; D008856:Microscopy, Fluorescence; D011506:Proteins / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D005456:Fluorescent Dyes; D007496:Iridium Radioisotopes; D011506:Proteins
keywords: Cervical cancer; Fucci; G2 arrest; HDR-RALS; Intracavitary irradiation; Ir-192