title: Radiobiological characteristics of solid tumours depending on the p53 status of the tumour cells, with emphasis on the response of intratumour quiescent cells.
abstract: Human head and neck squamous cell carcinoma cells transfected with mutant TP53 (SAS/mTP53) or with a neo vector as a control (SAS/neo) were inoculated subcutaneously (s.c.) into both hind legs of Balb/cA nude mice. Mice bearing tumours received 5-bromo-2'-deoxyuridine (BrdU) continuously to label all proliferating (P) cells in the tumours. The mice then received gamma-ray irradiation. Another group of mice received a series of test doses of gamma-rays while alive or after tumour clamping to obtain hypoxic fractions (HFs) in the tumours. Right after irradiation, the tumour cells were isolated and incubated with a cytokinesis blocker. The micronucleus (MN) frequency in the cells without BrdU labelling (=quiescent (Q) cells) was determined using immunofluorescence staining for BrdU. Meanwhile, 6 h after irradiation, tumour cell suspensions obtained in the same manner were used for determining the frequency of apoptosis in the Q cells. The MN frequency and apoptosis frequency in total (P+Q) tumour cells were determined from the tumours that were not pretreated with BrdU. In total cell populations, SAS/mTP53 cells were more radioresistant than SAS/neo cells in clonogenic survival. Q tumour cells exhibited a significantly lower apoptosis and MN frequency, probably due to their much larger HF, than total cells. In both total and Q cell fractions, SAS/mTP53 cells were less susceptible to apoptosis and more susceptible to micronucleation than SAS/neo cells. Obviously, TP53 status had the potential to influence the radiosensitivity of not only the total cells, but also the Q cells. However, irrespective of the TP53 status, significant differences in radiosensitivity between total and Q tumour cells were consistently observed. From the viewpoint of tumour control as a whole, including intratumour Q tumour cell control, a treatment modality for enhancing the Q cell response has to be considered.
authors.affiliation: Radiation Oncology Research Laboratory, Research Reactor Institute, Kyoto University, Noda, Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan. smasuna@rri.kyoto-u.ac.jp
authors.forename: S
authors.initials: S
authors.lastname: Masunaga
authors.forename: K
authors.initials: K
authors.lastname: Ono
authors.forename: A
authors.initials: A
authors.lastname: Takahashi
authors.forename: T
authors.initials: T
authors.lastname: Ohnishi
authors.forename: Y
authors.initials: Y
authors.lastname: Kinashi
authors.forename: M
authors.initials: M
authors.lastname: Takagaki
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000528:radiation effects; D002294:Carcinoma, Squamous Cell / Q000235:genetics / Q000473:pathology / Q000532:radiotherapy*; D002455:Cell Division / Q000528:radiation effects; D015687:Cell Hypoxia; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005720:Gamma Rays / Q000627:therapeutic use*; D016158:Genes, p53; D006258:Head and Neck Neoplasms / Q000235:genetics / Q000473:pathology / Q000532:radiotherapy*; D006801:Humans; D020287:In Situ Nick-End Labeling; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D015162:Micronucleus Tests; D009368:Neoplasm Transplantation; D017354:Point Mutation; D011836:Radiation Tolerance / Q000235:genetics*; D011853:Radiobiology; D014162:Transfection; D014407:Tumor Cells, Cultured