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

Neuroblastomas often acquire sustained drug resistance during therapy. Sensitivities to carboplatin, etoposide, or melphalan were determined for 18 neuroblastoma cell lines; eight were sensitive and ten were resistant. As p53 mutations are rare in neuroblastomas studied at diagnosis, we determined if acquired p53 mutations and loss of function conferred multidrug resistance.

Loss of p53 function (p53-LOF), defined as a failure to induce p21 and/or MDM2 in response to melphalan, was seen in 1/8 drug-sensitive and 6/10 drug-resistant cell lines. In four cell lines p53-LOF was associated with mutations in the DNA binding region of p53, while three cell lines with LOF and four cell lines with functional p53 had no evidence of p53 muta-tions. Nonfunctional and mutated p53 was detected in one resistant cell line, while a sensitive cell line derived from the same patient 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-sensitive neuroblastoma cell lines with functional p53. LC(90) values of HPV 16 E6 transfected cell lines were 3-7-fold (melphalan), 8-109-fold (carboplatin), and 2-158-fold (etoposide) greater than that of LXSN-transfected controls.

These data suggest that some neuroblastomas acquire p53 mutations during therapy, which is associated with a loss of p53 function, and can confer high-level multidrug resistance.