p53 mutations and loss of p53 function confer multidrug resistance in neuroblastoma

Background. Neuroblastomas often acquire sustained drug resistance during t herapy. Sen Sensitivities to carboplatin, etoposide, or melphalan were dete rmined for 18 neuroblastoma cell lines; eight were sensitive and ten were r esistant. As p53 mutations are rare in neuroblastomas studied at diagnosis, we determined if acquired p53 mutations and loss of function conferred mul tidrug resistance. Results. Loss of p53 function (p53-LOF), defined as a fa ilure to induce p21 and/or MDM2 in response to melphalan, was seen in 1/8 d rug-sensitive and 6/10 drug-resistant cell lines. In four cell lines p53-LO F was associated with mutations in the DNA binding region of p53, while thr ee cell lines with LOF and four cell lines with functional p53 had no evide nce of p53 muta-tions. Nonfunctional and mutated p53 was detected in one re sistant cell line, while a sensitive cell line derived from the same patien t prior to treatment had functional and wild type (wt) p53. We transfected HPV 16 E6 (which mediates degradation of p53, causing LOF) into two drug-se nsitive neuroblastoma cell lines with functional p53. LC90 values of HPV 16 E6 transfected cell lines were 3-7-fold (melphalan), 8-109-fold (carboplat in), and 2-158-fold (etoposide) greater than that of LXSN-transfected contr ols. Conclusions. These data suggest that some neuroblastomas acquire p53 m utations during therapy, which is associated with a loss of p53 function, a nd can confer high-level multidrug resistance. (C) 2000 Wiley-Liss, Inc.