Abstract 4341: Bortezomib primes neuroblastoma cells for TRAIL- triggered apoptosis by linking the death receptor to the mitochondrial pathway

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL In contrast to remarkable improvements in the survival and cure rates that have been encountered for many childhood malignancies, the prognosis of children with advanced stage neuroblastoma remains poor. Searching for novel strategies to modulate apoptosis in neuroblastoma we investigated the potential of the proteasome inhibitor Bortezomib to modulate TRAIL-induced apoptosis in neuroblastoma cell lines, primary neuroblastoma cultures and in an in vivo model of neuroblastoma. Here, we provide first evidence that Bortezomib at subtoxic concentrations synergistically cooperates with TRAIL to induce apoptosis (combination index 0.5). In addition, Bortezomib acts in concert with TRAIL to reduce colony formation of neuroblastoma cells, demonstrating an effect also on longterm survival. Mechanistic studies reveal that Bortezomib profoundly enhances TRAIL-induced cleavage of Bid into tBid, accumulation of tBid in the cytosol and its insertion into mitochondrial membranes, pointing to a concerted effect on Bid cleavage (TRAIL) and stabilization of tBid (Bortezomib), which links the death receptor to the mitochondrial pathway. Additionally, Bortezomib increases expression of p53 and Noxa. All these changes lead to increased activation of Bax and Bak, loss of the mitochondrial membrane potential, cytochrome c release, caspase activation and caspase-dependent apoptosis upon treatment with Bortezomib and TRAIL. Knockdown of either Bid, Noxa or p53 significantly delays the kinetic of Bortezomib- and TRAIL-induced apoptosis, whereas it does not confer longterm protection. By comparison, overexpression of Bcl-2, which simultaneously antagonizes tBid, Noxa and p53, significantly inhibits Bortezomib- and TRAIL-induced apoptosis and even rescues clonogenic survival. Of note, Bortezomib and TRAIL act in concert to trigger apoptosis in several patients’ derived primary neuroblastoma cultures, underscoring the clinical relevance. Importantly, Bortezomib cooperates with TRAIL to suppress tumor growth in an in vivo model of neuroblastoma. In conclusion, these findings demonstrate for the first time that Bortezomib at subtoxic concentrations represents a promising new approach to prime neuroblastoma cells towards TRAIL-induced apoptosis by linking the death receptor to the mitochondrial pathway. Thus, this study provides the rational for future (pre)clinical evaluation of the combination strategy with Bortezomib and TRAIL in neuroblastoma. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4341. doi:10.1158/1538-7445.AM2011-4341