Purpose: The emergence of multidrug resistance (MDR) in neuroblastoma is a critical issue for chemotherapy. In order to study low-level MDR, we developed variants derived from two neuroblastoma cell lines, TGW and GOTO, by exposure to low doses of cisplatin (CDDP). The cross-resistance to other cytotoxic agents and expression of MDR-related proteins in the variants and their clones were examined.
Materials and methods: Cells were exposed to 3 or 10 micro M CDDP and three variants were obtained from each cell line, TGW and GOTO. Clones TR1 and TR2, derived from the TGW variants, were also established. Cytotoxicity was determined using a dye-staining method. Expression of MDR-related proteins was detected by immunoblotting.
Results: Resistant variants exhibited 1.1- to 2.5-fold increased resistance to CDDP, N-methyl- N'-nitro- N-nitrosoguanidine (MNNG), doxorubicin and vincristine. The cytotoxicity of these agents varied between clones of resistant variants. The microsatellite profiles of the TR1 clones differed, indicating that the TR1 variant comprised a heterogeneous cell population. The cytotoxicities of cytosine beta- D-arabinofuranoside (Ara-C) and chlorambucil in these variants and clones were similar to those in the parent cells. No significant changes in the cellular levels of MDR1, MRP, hMLH1 and hMSH2 were detected in the TGW variants. Cyclosporin A increased the sensitivity of both parental cell lines and the variants to doxorubicin and vincristine, but not to CDDP or MNNG.
Conclusions: Ara-C and chlorambucil may be useful for the treatment of neuroblastoma exhibiting an MDR phenotype. These CDDP-resistant variants and clones may be useful for studying the mechanisms of low-level drug resistance in neuroblastoma.