Dexamethasone decreases temozolomide‐induced apoptosis in human gliobastoma T98G cells

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Abstract
Human glioblastoma is a deadly brain tumor that is often treated with a combination of drugs. A new alkylating agent, temozolomide (TMZ), has recently been found efficacious in the clinical trials for glioblastoma. Steroids, such as dexamethasone (DXM), are often used concomitantly as a supportive therapy to treat cerebral edema. However, any possible modulatory effect of the steroids on the efficacy of TMZ has not yet been evaluated experimentally. In this study, we have examined whether DXM provides synergistic or antagonistic effect on TMZ‐induced apoptosis in human glioblastoma T98G cells. T98G cells were pretreated with various doses of DXM followed by TMZ. The cell viability was assessed by the trypan blue dye exclusion test. Wright staining and the TdT‐mediated dUTP nick‐end labeling (TUNEL) assay were used to evaluate apoptotic cell death based on the morphological and biochemical (DNA fragmentation) features, respectively. More biochemical features of apoptotic death, such as upregulation of Bax:Bcl‐2 ratio, calpain activity, and caspase‐3 activity, were assessed by Western blot analysis. A significant number of T98G cells committed apoptosis after treatment with 200 μM TMZ. However, a pretreatment with 100 μM or 200 μM DXM protected T98G cells against TMZ‐induced apoptosis, concomitantly decreasing Bax:Bcl‐2 ratio, calpain activity, and caspase‐3 activity. These experimental results indicate that DXM works as an antagonistic agent in combination with TMZ. Therefore, our investigation strongly implies that the combination of DXM and TMZ may be counteractive in treating human glioblastoma.