Selective potentiation of drug cytotoxicity by NSAID in human glioma cells: the role of COX-1 and MRP

Here, we report that nonsteroidal anti-inflammatory drugs (NSAID) enhance the cytotoxic effects of doxorubicin and vincristine in T98G human malignant glioma cells. The cytotoxicity of BCNU, cisplatin, VM26, camptothecin, and cytarabine is unaffected by NSAID. No free radical formation is induced by doxorubicin or vincristine in the absence or presence of NSAID. Doxorubicin and vincristine cytotoxicity in the absence or presence of NSAID are unaffected by free radical scavengers. Functional inhibitors of phospholipase A2 (PLA2), such as dexamethasone and quinacrine, do not mimick the effects of NSAID. T98G cells, but not LN-18, LN-229, LN-308, or A172 glioma cells, express cyclooxygenase (COX-1) and NSAID do not modulate drug cytotoxicity in the other cell lines, except T98G. Thus, augmentation of doxorubicin and vincristine cytotoxicity by NSAID correlates with COX-1 expression. However, ectopic expression of COX-1 in LN-229 cells does not induce the phenotype of T98G cells, indicating that COX-1 inhibition does not mediate the effects of NSAID on drug cytotoxicity. In contrast, a multidrug resistance (MDR) phenotype due to expression of the multidrug resistance-associated protein (MRP) is most prominent in T98G cells and is amenable to modulation by indomethacin, suggesting that inhibition of MRP is at least in partly responsible for the potentiation of doxorubicin and vincristine cytotoxicity by NSAID.

Topotecan-based combination chemotherapy for human malignant glioma

BACKGROUND

Topotecan has been considered a promising agent for the adjuvant chemotherapy of human malignant glioma because of its novel mode of action, its activity against other solid tumors, and its good penetration across the blood-brain barrier. However, the clinical effects of topotecan monotherapy in malignant glioma have been disappointing.

MATERIALS AND METHODS

We sought to identify suitable partners for topotecan combination chemotherapy of malignant glioma using two well-characterized human malignant glioma cell lines, T98G and LN-229. The effects of co-exposure to topotecan and other chemotherapy drugs were assessed in cytotoxic and clonogenic cell death assays.

RESULTS

We found additive, less-than-additive, or occasional antagonistic effects, but never synergistic activity of topotecan with either CCNU, VM26 or vincristine, in acute cytotoxicity or in clonogenic cell death assays, with simultaneous or sequential drug exposure. VM26 or vincristine followed by topotecan yielded the most favourable results. Further, prolonged exposure of the glioma cells to topotecan and either CCNU, VM26, vincristine, cisplatin, doxorubicin or cytarabine resulted in additive but not synergistic growth inhibition.

CONCLUSIONS

The present study fails to identify a specific partner for topotecan-based combination chemotherapy of malignant glioma among the chemotherapeutic drugs examined here. While this does not exclude a possible synergy of the drug combinations examined here in vivo, a focus on novel partners for topotecan or topotecan-based chemoimmunotherapy may be more promising.

Gemcitabine cytotoxicity of human malignant glioma cells: modulation by antioxidants, BCL-2 and dexamethasone

Gemcitabine is a novel antimetabolite drug that acts by multiple mechanisms, including inhibition of ribonucleoside diphosphate reductase, of dCMP deaminase and of dCTP incorporation into DNA and RNA. Here, we report that gemcitabine induces cytotoxic and clonogenic death of 12 human malignant glioma cell lines at clinically relevant concentrations around 1 microM. Gemcitabine is thus approximately 100-fold more active than the congener drug, cytarabine. Gemcitabine cytotoxicity of glioma cells does not require wild-type p53 activity: (i) there was no difference in the susceptibility to gemcitabine between cell lines with wild-type p53 and cell lines with mutant or deleted p53; (ii) ectopic expression of a temperature-sensitive p53 protein either at wild-type (32.5 degrees C) or at mutant (38.5 degrees C) conformation had no significant influence on gemcitabine-induced cell death. Gemcitabine cytotoxicity was unaffected by the antioxidants, N-acetylcysteine and phenyl-N-tert-butyl-alpha-phenylnitrone. There was no correlation between the susceptibility to gemcitabine and the endogenous expression of the B cell lymphoma-2 (BCL-2)-family proteins BCL-2, BCL-XL, myeloid cell leukemia-1 (MCL-1), BCL-2-associated X protein (BAX), BCL-2 homologous antagonist/killer (BAK) and BCL-XS. Ectopic expression of BCL-2 moderately attenuated gemcitabine-induced cell death. Similarly, preexposure to the synthetic steroid, dexamethasone, which is commonly used to control cerebral edema in brain tumor patients, reduced gemcitabine cytotoxicity. We conclude that the clinical evaluation of gemcitabine for the adjuvant chemotherapy of malignant glioma is warranted.