Failure of taxol-based combination chemotherapy for malignant glioma cannot be overcome by G2/M checkpoint abrogators or altering the p53 status

In an effort to develop more effective forms of adjuvant chemotherapy for malignant brain tumors, we sought to develop a taxol-based combination chemotherapy regimen for glioma cell lines in vitro. Here, we report that coexposure of LN-229 or T98G glioma cells to taxol and either doxorubicin, camptothecin, cytarabine, or VM26 resulted in antagonistic effects rather than additive or synergistic cytotoxicity. There were no interactions of taxol with the effects of carmustine (BCNU) or vincristine. Antagonism was more prominent in cytotoxic cell death assays than in clonogenic cell death assays and was not overcome by G(2)/M checkpoint abrogators such as caffeine or pentoxyfilline. Ectopic expression of mutant and wild-type p53val(135) attenuated taxol cytotoxicity in both T98G cells, which are mutant for p53, and LN-229 cells, which exhibit functional wildtype p53 activity. Interestingly, wild-type p53val(135) abrogated the taxol-imposed G2/M arrest in both cell lines. However, wild-type p53val(135) did not promote glioma cell killing by combinations of taxol and any of the other drugs. Further, an analysis of a panel of 12 human glioma cell lines revealed no relationship between genetic or functional p53 status and taxol sensitivity. In summary, combination either with other chemotherapy drugs, with abrogators of the G(2)/M checkpoint, with wild-type p53 gene transfer was not a promising approach for a taxol-based combination chemotherapy regimen in malignant glioma.