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

Abstract

Resistance to tumor necrosis factor (TNFalpha)-induced apoptosis in various cancer cells has been attributed to the activation of the transcription factor NF-kappaB. Ebselen (2-phenyl-1,2-benzisoselenazol-3[2H]one)-a selenoorganic compound is known to prevent TNFalpha-mediated NF-kappaB activity. As glioblastoma are resistant to the cytotoxic effect of TNFalpha, we investigated the potential of Ebselen in sensitizing glioma cells to TNFalpha-induced apoptosis. Although treatment with Ebselen reduced viability of glioma cells, cotreatment with TNFalpha enhanced apoptosis further through alteration of TNFalpha-mediated signaling pathways. Sensitization of TNFalpha activated glioma cells to apoptosis by Ebselen involved 2 pathways: (i) abrogation of TNFalpha induced NF-kappaB activation and (ii) induction of Fas-associated death inducing signaling complex (DISC) formation. Ebselen inhibited the prosurvival pathway mediated by NF-kappaB by altering the association of TNF receptor associated factor 2 (TRAF2) with TNFalpha receptor associated death domain (TRADD) in the TNFR1-TRADD-TRAF2 complex -an interaction crucial for mediating NF-kappaB 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-kappaB function was inhibited. Cotreatment with Ebselen and TNFalpha 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 TNFalpha-induced apoptosis by cotreatment with organoselenium Ebselen as a strategy to kill glioma cells.