Drug resistance in malignant rhabdoid tumor cell lines

Purpose: We evaluated the in vitro sensitivity of four malignant rhabdoid tumor (MRT) cell lines to six chemotherapeutic agents: 5-fluororuacil, vincristine, carboplatin, doxorubicin, etoposide, and paclitaxel. We also sought to determine whether a defect in the p53 signaling pathway may contribute to the pronounced drug resistance of MRT. Methods: MRT cells were treated with various concentrations of each drug and the effects on DNA synthesis were quantified using a thymidine incorporation assay. In addition, the effect of various concentrations of doxorubicin on cell growth was evaluated in all four cell lines. Functionality of the p53 pathway was evaluated by incubating cells with carboplatin or doxorubicin and monitoring the effects on the levels of the p53, p21WAF1/CIP1, and MDM 2 proteins by Western blot analyses. Results: Vincristine (EC50 0.5–2.9 nM) and doxorubicin (EC50 1.9–5.7 nM) were found to be most effective in inhibiting proliferation and were within clinically relevant concentrations. However, only doxorubicin exhibited cytotoxicity (EC50 2.4–13.1 nM), whereas vincristine and the other drugs tested were cytostatic. Interestingly, all four cell lines had remarkably similar dose response curves to all drugs tested, despite the fact that they were derived from different patients and arose in different tissues. When challenged with DNA-damaging drugs, p53 and the downstream effectors, p21WAF1/CIP1 and MDM 2 were upregulated. Conclusions: These studies indicate that the p53 pathway is functional and responsive to DNA-damaging drugs, and does not likely contribute to the drug resistance of MRT. The in vitro sensitivity of MRT cells to doxorubicin suggests that it may be a clinically important agent for the treatment of MRT.