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Background. 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. Results. 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 p53LOF 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 drugsensitive neuroblastoma cell lines with functional p53. LC90 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 LXSNtransfected controls. Conclusions. 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. Med. Pediatr. Oncol. 35:563‐568, 2000. © 2000 Wiley-Liss, Inc.

Background. Recent studies have associated telomerase with prognostic factors and survival in neuroblastoma. Procedure. We examined telomerase activity by telomere repeat amplification protocol (TRAP) and expression of the RNA component of telomerase (hTR) by Northern blotting in 106 primary neuroblastoma tumors and 22 established cell lines. Results. Overall survival at 5 years for all 106 tumors was significantly better for patients with undetectable TRAP (75% vs. 59%; P = 0.03) or low hTR expression (84% vs. 43%; P < 0.0001), and especially for patients whose tumors had both low hTR expression and undetectable TRAP (all patients, 91% vs. 54%, P = 0.0002; for 17 stage IV-S tumors, 100% vs. 72%, P = 0.04). Strong expression of hTR was seen in 22 cell lines from aggressive tumors, and all maintained telomere length, but 3/22 were TRAP negative. Conclusions. These data suggest that both hTR expression and telomerase activity via the TRAP assay should be performed concurrently to predict survival in neuroblastoma patients, particularly in stage 4-S. Med. Pediatr. Oncol. 35:647‐650, 2000. © 2000 Wiley-Liss, Inc.

Maintenance of chromosomal telomeres is necessary for continued cell growth, and this is carried out in germline tissues by telomerase. In contrast to most somatic tissues, many tumours have telomerase activity. The RNA component of human telomerase (hTR) was measured by Northern analyses of 150 primary untreated neuroblastomas and compared with clinical stage at diagnosis. hTR expression > 33 (relative to cell line control = 100) was seen in 41% of all tumours and the frequency of hTR > 33 increased with stage of disease. Expression of hTR may be involved in progression of neuroblastoma.