Radiobiological characteristics of solid tumors depending on the p53 status of the tumor cells -- reference to the response of intratumor quiescent cells

S Masunaga, MD, PhD a, A Takahashi, PhD b, T Ohnishi, PhD b, M Takagaki, MD, Ph.D c, Y Kinashi, MD, PhD a and K Ono, MD, PhD a.

a Research Reactor Institute, Kyoto University, Kumatori, Sennan-gun, Osaka Japan, b Department of Biology, Nara Medical University, Kashihara, Nara, Japan, c Department of Neurosurgery, Aino Junior College Hospital, Ibaraki, Osaka, Japan.

Human head and neck squamous cell carcinoma cells transfected with mutant p53 (SAS/mp53) or with neo vector as a control (SAS/neo) were inoculated subcutaneously into the legs of Balb/cA nude mice. Mice bearing the tumors received 5-bromo-2Õ-deoxyuridine (BrdU) continuously to label all proliferating (P) cells in the tumors. The mice then received gamma-ray irradiation while alive or after tumor clamping to obtain hypoxic fractions (HFs) in the tumors. Right after irradiation, the tumor cells were isolated and incubated with a cytokinesis blocker. The micronucleus (MN) frequency in cells without BrdU labeling ( = quiescent (Q) cells) was determined using immunofluorescence staining for BrdU. Meanwhile, 6 h after irradiation, tumor cell suspensions obtained in the same manner were used for determining the apoptosis frequency in Q cells. The MN and apoptosis frequencies in total (P+Q) tumor cells were determined from the tumors that were not pretreated with BrdU. Q tumor cells exhibited significantly lower MN and apoptosis frequencies probably due to their large HF. In both total and Q cell fractions, SAS/mp53 cells were less susceptible to apoptosis and more susceptible to micronucleation than SAS/neo cells. p53 Status had the potential to influence the radiosensitivity of not only total cells but also Q cells. However, irrespective of p53 status, significant differences in radiosensitivity between total and Q tumor cells were consistently observed. From the viewpoint of tumor control as a whole, a treatment modality for enhancing Q cell response has to be considered.

KEY WORDS: Quiescent cell, p53 status, Apoptosis, Micronucleus, Hypoxic fraction, Radiosensitivity.

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Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Paris, France; February 9 - 12, 2002; in the section on Molecular Pathology.