P53 MUTATIONS ASSOCIATED WITH INCREASED SENSITIVITY TO IONIZING-RADIATION IN HUMAN HEAD AND NECK-CANCER CELL-LINES

The p53 tumour suppressor gene is activated following cellular exposur e to DNA-damaging agents. The functions of wild-type p53 protein inclu de transient blocking of cell cycle progression, direct or indirect st imulation of DNA repair machinery and triggering of apoptosis if DNA r epair fails. Therefore, the status of p53 protein may be critically as sociated with tumour cell radiosensitivity. In the present study we ex amine the intrinsic radiosensitivity of 20 human carcinoma cell lines derived from 15 patients with different types of head and neck tumour. Radiosensitivities were measured in a 96-well plate clonogenic assay in terms of the mean inactivation dose, surviving fraction at 2 Gy, an d constants alpha and beta in the linear quadratic survival curve. The p53 allele status was determined by amplifying exons 4-10 by the poly merase chain reaction (PCR), screening for mutations using single-stra nd conformation polymorphism (SSCP) analysis and determining the exact type and location of a mutation by direct sequencing. The results sho wed that prevalence of p53 mutations in squamous cell carcinoma (SCC) cell lines is high (80%), and that deletion of one or both wild-type a lleles is common (75%). Intrinsic radiosensitivity of the cell lines v aried greatly in terms of mean inactivation dose, from 1.4+/-0.1 to 2. 6+/-0.2 Gy. Radiosensitivity correlated well with the p53 allele statu s so that cell lines carrying a wild-type p53 allele were significantl y (P<0.01) more radioresistant (mean inactivation dose 2.23+/-0.15 Gy) than cell lines which lacked a wild-type gene (1.82+/-0.24 Gy). Evalu ation of our own results and those published in the literature lead us to conclude that absence of the wild-type p53 allele in human head an d neck cancer cell lines is associated with increased radiosensitivity . However, the sensitivity is also strongly dependent on the exact typ e and location of the p53 mutation.