Ebselen sensitizes glioblastoma cells to Tumor Necrosis Factor (TNFα)‐induced apoptosis through two distinct pathways involving NF‐κB downregulation and Fas‐mediated formation of death inducing signaling complex

Resistance to tumor necrosis factor (TNFα)‐induced apoptosis in various cancer cells has been attributed to the activation of the transcription factor NF‐κB. Ebselen (2‐phenyl‐1,2‐benzisoselenazol‐3[2H]one)—a selenoorganic compound is known to prevent TNFα‐mediated NF‐κB activity. As glioblastoma are resistant to the cytotoxic effect of TNFα, we investigated the potential of Ebselen in sensitizing glioma cells to TNFα‐induced apoptosis. Although treatment with Ebselen reduced viability of glioma cells, cotreatment with TNFα enhanced apoptosis further through alteration of TNFα‐mediated signaling pathways. Sensitization of TNFα activated glioma cells to apoptosis by Ebselen involved 2 pathways: (i) abrogation of TNFα induced NF‐κB activation and (ii) induction of Fas‐associated death inducing signaling complex (DISC) formation. Ebselen inhibited the prosurvival pathway mediated by NF‐κB by altering the association of TNF receptor associated factor 2 (TRAF2) with TNFα receptor associated death domain (TRADD) in the TNFR1‐TRADD‐TRAF2 complex —an interaction crucial for mediating NF‐κB activity. Ebselen also induced the formation of DISC involving Fas, Fas‐associated death domain (FADD) and active caspase 8 to transduce apoptotic signals in situations where NF‐κB function was inhibited. Cotreatment with Ebselen and TNFα induced G2/M phase arrest in cell cycle and modulated the expression of molecules involved in cell cycle progression. These results raise the possibility of overcoming resistance to TNFα‐induced apoptosis by cotreatment with organoselenium Ebselen as a strategy to kill glioma cells. © 2008 Wiley‐Liss, Inc.