Abstract 1545: Combinatorial efficacy of TRAIL and MN58b against colon cancer to overcome TRAIL resistance

Abstract

Abstract BACKGROUND: Tumor resistance is one of the major problems for cancer treatment and new approaches to overcome resistance are required. TNF-Related Apoptosis Inducing Ligand (TRAIL) has recently emerged as a promising therapy due to its selectivity towards tumor cells and is currently being evaluated in phase I and phase II clinical trials. Choline kinase alpha (ChoKα) inhibition has also recently proven to be an efficient strategy to specifically induce tumor cell death without affecting normal cells. The aim of this study is to investigate the potential use of combinatorial treatment of TRAIL and MN58b, a specific ChoKα inhibitor, to potentiate tumor cell death. EXPERIMENTAL PROCEDURES: Two different colon cancer-derived cell lines were used: DLD-1 and SW620. The antiproliferative effect of MN58b, TRAIL, or both was determined using MTT method. Western blots were carried out to measure PARP degradation and caspase-3 activation, and Annexin V- PI staining was used to verify cell death induction in response to drugs by flow cytometry. The results obtained in vitro were verified in vivo using xenograft models for both cell lines. RESULTS: Using different concentrations of both drugs, it has been established that the best strategy of combination is a simultaneous treatment. Our data shows that when MN58b and TRAIL are simultaneously combined, a strong synergistic effect is observed in DLD-1 cells, with a combination index (CI) of 0.196. Moreover, MN58b treatment is able to overcome TRAIL resistance in SW620 cell line (CI=0.155). The synergistic effect was verified by both PARP and Caspase-3 analysis as apoptosis markers. Cell death was also analyzed by flow cytometry. This in vitro synergistic effect was confirmed in vivo using xenograft models of both cell lines. DLD-1 induced tumor growth was inhibited by 42% and 51% when treated with MN58b or TRAIL respectively. When both drugs were combined the effect was much stronger, reaching 78% inhibition. These findings suggest that MN58b cooperates with TRAIL in suppressing tumor growth in DLD-1 xenograft model. SW620 xenograft response to MN58b was weaker, with 26% inhibition. TRAIL alone produced no significant decrease of tumor growth in keeping with the observation of this cell line being resistant to TRAIL. When MN58b and TRAIL were combined, there was a marked 71% tumor growth inhibition, suggesting that MN58b is able to sensitize SW620 to TRAIL-induced apoptosis in vivo, and confirming all the in vitro observed effects. CONCLUSION: ChoKα inhibition can enhance TRAIL-induced apoptosis in DLD-1 cells and is able to abrogate TRAIL resistance in SW620 cells. Considering that MN58b when used alone exhibits anticancer activities in vitro and in vivo against a wide variety of tumor-derived cell lines, this study establishes its additional potential use in combination with TRAIL on tumors that develop TRAIL resistance. 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 1545.