Evidence for the development of p53 mutations after cytotoxic therapy in aneuroblastoma cell line

p53 mutations are rare in neuroblastomas at diagnosis perhaps accounting fo r their initial response to therapy, but advanced neuroblastoma frequently relapses, and it is possible that p53 mutations develop later. Two neurobla stoma cell lines derived from the same patient before [SKNBE(1n)] and after [SKNBE(2c)] cytotoxic therapy were analyzed for the presence of chromosome 17 and p53 genes by fluorescent in situ hybridization, p53 mutations by DN A sequencing, and p53 function after irradiation by studying the transcript ion of p53-regulated genes, cell cycle arrest, and induction of apoptosis. The SKNBE(1n) cell line was wild-type for p53, had two p53 genes, two copie s of chromosome arm 17p and showed functional p53 after irradiation. The SK NBE(2c) cell line derived from the same patient 5 months later at relapse h ad loss of an entire chromosome 17, resulting in hemizygosity for the p53 l ocus on 17p and a missense p53 mutation in exon 5, and p53 was not function al after irradiation. The appearance of a p53 mutation in a cell line deriv ed from a relapsed neuroblastoma suggests that this may be a mechanism of r esistance to therapy. If p53 mutations develop frequently in relapsed neuro blastoma, cytotoxic agents more sensitive to mutant p53 might be more effec tive at relapse.