Loss of p53 function confers high-level multidrug resistance in neuroblastoma cell lines'

Neuroblastomas can acquire a sustained high-level drug resistance during ch emotherapy and especially myeloablative chemoradiotherapy. p53 mutations ar e rare in primary neuroblastomas, but a loss of p53 function could play a r ole in multidrug resistance. We determined p53 function by measuring induct ion of p21 and/or MDM2 proteins in response to melphalan (L-PAM) in seven L -PAM-sensitive and 11 L-PAM-resistant neuroblastoma cell lines. p53 was fun ctional in seven/seven drug-sensitive but in only 4/11 drug-resistant cell lines (P = 0.01). In four of the seven cell lines lacking p53 function, mut ations of p53 were detected by the microarray GeneChip p53 Assay and automa ted sequencing, whereas six cell lines with functional p53 had no evidence of p53 mutations. All of the cell lines with wild-type (wt) p53 showed a st rong transactivation of the p53-HBS/CAT reporter gene, whereas the four cel l lines with mutant p53 failed to transactivate p53 HBS/CAT. Overexpression of MDM2 protein (relative to p53 functional lines) was seen in two p53-non functional cell lines with wt p53; one showed genomic amplification of MDM2 . Nonfunctional and mutated p53 was detected in a resistant cell line, wher eas a sensitive cell line derived from the same patient before treatment ha d functional and wt p53. Loss or p53 function was selectively achieved by t ransduction of human papillomavirus 16 E6 (which degrades p53) into two dru g-sensitive neuroblastoma cell lines with intact p53, causing high-level dr ug resistance to L-PAM, carboplatin, and etoposide. These data obtained wit h neuroblastoma cell lines suggest that the high-level drug resistance obse rved in some recurrent neuroblastomas is attributable to p53 mutations and/ or a loss of p53 function acquired during chemotherapy. If confirmed in pat ient tumor samples, these data support development of p53-independent thera pies for consolidation and/or salvage of recurrent neuroblastomas.