Drug resistance patterns of human neuroblastoma cell lines derived from patients at different phases of therapy

To determine whether neuroblastomas acquire a sustained drug-resistant phen otype from exposure to chemotherapeutic agents given to patients in vivo, w e studied neuroblastoma cell lines established at different points of thera py: six at diagnosis before therapy (DX), six at progressive disease during induction therapy (PD-Ind), and five at relapse after intensive chemoradio therapy and bone marrow transplantation (PD-BMT). Cells were maintained in the absence of drug selective pressure. Dose-response curves of melphalan, cisplatin, carboplatin, doxorubicin, and etoposide for the cell line panel were determined by measuring cytotoxicity with a 96-well-plate digital imag ing microscopy (DIMSCAN) microassay. Drug resistance of cell lines progress ively increased with the intensity of therapy delivered in vivo. The greate st resistance was seen in PD-BMT cell lines: IC90 values in PD-BMT cell lin es were higher than clinically achievable drug levels by 1-37 times for mel phalan, 1-9 times for carboplatin, 25-78 times for cisplatin, 6-719 times f or doxorubicin, and 3-52 times for etoposide. Genomic amplification of MYCN did not correlate with resistance. Cross-resistance by Pearson correlation (r greater than or equal to 0.6) was observed between: (a) cisplatin + dox orubicin; (b) carboplatin + cisplatin, etoposide, or melphalan; (c) etoposi de + cisplatin, melphalan, or doxorubicin. These data indicate that during therapy, neuroblastomas can acquire resistance to cytotoxic drugs because o f the population expansion of tumor cells possessing stable genetic or epig enetic alterations that confer resistance.