Abstract 140: XIAP expression in non-small cell lung cancer cells is a key determinant of threshold to TRAIL-induced apoptotic cell death

Abstract

Abstract Background: Intrinsic resistance to apoptosis-induction by TRAIL is found in the majority of non-small cell lung cancers (NSCLC). Previously, we have shown that intrinsic TRAIL-resistance in NSCLC cells can be markedly attenuated by transient transfection of siRNA directed against XIAP, and accordingly rendering TRAIL-resistant NSCLC cells restored TRAIL-sensitivity, with markedly enhanced apoptosis rates. The objective of the current study is to investigate the effects of XIAP overexpression in intrinsically TRAIL-sensitive lung cancer cells with respect to its threshold to apoptotic cell death. Methods: Lentiviral p-Receiver-lv19-XIAP (GeneCopoeia, Rockville, MD) were transduced in cultured human NSCLC H460 cells to generate stable clones. Subsequently, p-Receiver-lv19-XIAP-H460 cell colonies were screened for optimal vector expression and XIAP overexpression and then propagated in culture for further analysis. Parental H460 and negative control H460-p-empty stable clone cells were used for comparisons. p-Receiver-lv19-XIAP-H460 stable clones, negative control H460-p-empty stable clones, and H460 parental cells were cultured with and without administration of TRAIL. Also, XIAP overexpression stable clones were treated with TRAIL alone, Smac mimetic AEG40730 (Vibrant Pharma, Inc., Ontario, CN), or their combination. Cellular proliferation was measured using MTT assays. Caspase activation was evaluated using Western blot analysis and caspase activity was quantified by fluorescence caspase assays. Results: p-Receiver-lv19-XIAP-H460 stable clone cells exhibited a significant increase in protection against TRAIL-induced cell death compared to TRAIL-sensitive parental H460 and H460-p-empty cells across a spectrum of TRAIL concentrations. Also, marked reductions in caspase activation, as a result of decreased sensitivity to TRAIL, were found in p-Receiver-lv19-XIAP-H460 cells despite TRAIL administration. Rescue treatment of p-Receiver-lv19-XIAP-H460 stable clones with combination Smac mimetic AEG40730 and TRAIL was able to negate the effects of XIAP overexpression and restore intrinsic sensitivity to TRAIL-induced cytotoxicity. Conclusions: TRAIL resistance can be conferred to intrinsically TRAIL-sensitive lung cancer cells via XIAP overexpression alone. The increased threshold to apoptotic cell death is mediated via XIAP's inhibitory effects on the canonical apoptosis pathways. However, TRAIL-sensitivity can be rescued in XIAP overexpressing lung cancer cells by combination treatment with anti-XIAP Smac mimetic and TRAIL administration. These results, along with previous work, demonstrate that XIAP is a key determinant of apoptotic cell death in lung cancer cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 140.