Bortezomib Primes Glioblastoma, Including Glioblastoma Stem Cells, for TRAIL by Increasing tBid Stability and Mitochondrial Apoptosis

Abstract

Purpose: Searching for novel approaches to sensitize glioblastoma for cell death, we investigated the proteasome inhibitor bortezomib.Experimental Design: The effect of bortezomib on tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis signaling pathways was analyzed in glioblastoma cell lines, primary glioblastoma cultures, and in an in vivo model.Results: Bortezomib and TRAIL synergistically trigger cell death and reduce colony formation of glioblastoma cells (combination index < 0.1). Investigations into the underlying molecular mechanisms reveal that bortezomib and TRAIL act in concert to cause accumulation of tBid, the active cleavage product of Bid. Also, the stability of TRAIL-derived tBid markedly increases on proteasome inhibition. Notably, knockdown of Bid significantly decreases bortezomib-and TRAIL-mediated cell death. By comparison, silencing of Noxa, which is also upregulated by bortezomib, does not confer protection. Coinciding with tBid accumulation, the activation of Bax/Bak and loss of mitochondrial membrane potential are strongly increased in cotreated cells. Overexpression of Bcl-2 significantly reduces mitochondrial perturbations and cell death, underscoring the functional relevance of the mitochondrial pathway. In addition, bortezomib cooperates with TRAIL to reduce colony formation of glioblastoma cells, showing an effect on long-term survival. Of note, bortezomib profoundly enhances TRAIL-triggered cell death in primary cultured glioblastoma cells and in patient-derived glioblastoma stem cells, underlining the clinical relevance. Importantly, bortezomib cooperates with TRAIL to suppress tumor growth in an in vivo glioblastoma model.Conclusion: These findings provide compelling evidence that the combination of bortezomib and TRAIL presents a promising novel strategy to trigger cell death in glioblastoma, including glioblastoma stem cells, which warrants further investigation. Clin Cancer Res; 17(12); 4019-30. Ó2011 AACR.

Identification of Mitoxantrone as a TRAIL-sensitizing agent for Glioblastoma Multiforme

“…We included Bortezomib as positive control, since it is a known TRAIL sensitizer in GBM cells. 10 First, we assessed the effect of drugs applied at a concentration of 5 mM as single agents on U87MG cell viability (Fig. 1A).…”

“…7 Apoptosis resistance can be caused by reduced caspase expression, 8 increased expression of antiapoptotic molecules such as the inhibitors of apoptosis proteins (IAPs), overexpression of Bcl-2 family members and other inhibitors of intrinsic apoptosis pathway. 6,9 Accumulating evidence suggest that sensitization of tumor cells to TRAIL is possible 10,11 through secondary agents. A widely studied approach for TRAIL-sensitization involves the use of secondary therapeutics in addition to TRAIL, where the timing and sequence of application of each agent might be different.…”

“…For example, it has been reported that combination of Bortezomib, a proteasome inhibitor, and TRAIL synergize and lead tumor cells to undergo apoptosis, as shown for GBM cell lines and primary tumors. 10 However, most studies have traditionally focused on a small number of compounds rather than large-scale libraries. While there is growing interest in the identification of single therapeutic agents through chemical library screens for all cancer types, there has been relatively much lower attention to identification of novel combination therapies in GBM cells.…”

Regulation of TRAIL-Receptor Expression by the Ubiquitin-Proteasome System

“…The 20S core proteasome inhibitor bortezomib affects many anti- and pro-apoptotic proteins, and induces cytotoxicity through c-Jun NH 2 -terminal kinase/caspase activation in various types of tumors [93,94]. Bortezomib and TRAIL act in concert to cause accumulation of tBID, the active cleavage product of BID and induce mitochondrial dependent apoptosis of tumor cells [95]. …”

Targeting Tumor Necrosis Factor–Related Apoptosis-Inducing Ligand (TRAIL): A Promising Therapeutic Strategy in Gliomas

“…29 Bortezomib, a proteasome inhibitor, and TRAIL synergistically caused accumulation of tBid and suppressed tumor growth in an in vivo glioblastoma model. 30 Smac or Smac peptides have also been found to sensitize tumor cells to TRAIL. 31 Another approach of particular interest in increasing TRAIL sensitivity is by modulation of the phosphatidylinositide 3-kinase (PI3K)/Akt pathway.…”