LACK OF A CORRELATION BETWEEN P53 PROTEIN EXPRESSION AND RADIATION RESPONSE IN HUMAN TUMOR PRIMARY CULTURES

We investigated the possible relationship between immunohistochemicall y detected p53 expression and in vitro response to gamma-irradiation i n 24 primary cultures of human ovarian cancers and cutaneous melanomas . The frequency of p53-positive tumors was around 60% within each tumo r histotype. The range of the surviving fraction at 2 Gy (SF2) was sim ilar in p53-positive (0.10-0.76) and p53-negative (0.23-0.65) tumors, with median values of 0.36 and 0.33, respectively. No differences were observed in the accumulation of DNA-double strand breaks, assessed by neutral filter elution after exposure to 50 Gy, between p53-positive and p53-negative tumors. As regards DNA lesion repair, after 2 h of re covery the percentage of rejoined DNA-double strand breaks ranged from 19% to 99% in the different cultures, but again the distribution of v alues was similar for p53-positive and p53-negative tumors. Specifical ly, the median percentage of repaired DNA double strand breaks was 70% and 74% in the two groups. On the whole, our data do not support the hypothesis that p53 overexpression is a major determinant of in vitro radiation response.