Abstract LB-100: Exploring the mechanisms of resistance to Salinomycin, a cancer stem cell-specific agent, in budding yeast as a model.

Abstract

Abstract Introduction The antibiotic salinomycin (SM) represents a selective potassium ionophore. It has recently attracted considerable attention due to its stem-cell specific mode of action that has been elucidated in a breast cancer stem cell model [1]. Further studies revealed additional benefits, e.g. the triggering of apoptosis in resistant cancer cell lines and reversal of multidrug resistance [2,3]. In budding yeast, we discovered that this agent prominently causes mitochondrial damage as revealed by the emergence of respiration-defective cells (“petites”), similar to nigericin. We also noted the frequent occurrence of SM-resistant clones - a possible obstacle in therapy. Methods We used the collection of systematic gene deletions in haploid Saccharomyces cerevisiae to characterize genes whose deletion confers SM sensitivity or resistance if a carbon source is provided (glycerol) that requires active respiration for growth. In parallel, the emergence of reactive oxygen species (ROS) was measured by flow cytometry. With this toxicogenomics approach in a model organism, we attempt to elucidate cancer-stem cell specific therapy targets and suggest strategies to avoid the development of salinomycin resistance. Results and Conclusions Among SM-sensitive deletion mutants, mutants that compromise vacuole/Golgi function and autophagy dominate. Novel genes which confer SM sensitivity if deleted were also uncovered, such as CAJ1, a heat shock protein of the dnaJ family. In almost all cases, a strong correlation between SM and nigericin sensitivity was observed. Among the most SM-resistant mutants were deletions of the E2-ubiquitin conjugating enzymes Ubc13 and Mms2 as well as deletions of TOR pathway components Sch9 and Tco89. In the presence of SM, Sch9 (homolog of human Akt) underwent dephosphorylation; a deletion of Sch9 was shown to improve growth in glycerol media and to counteract petite induction in glucose media in SM-treated cells. The observed mitochondria-dependent ROS production by SM, however, was unaltered and we suggest that, while initial damage is not affected, cells acquire resistance to the consequences of such damage. [1] Gupta PB, Onder TT, Jiang G, Tao K, Kuperwasser C, et al. (2009) Cell 138: 645-659. [2] Fuchs D, Heinold A, Opelz G, Daniel V, Naujokat C (2009) Biochem Biophys Res Commun 390: 743-749. [3] Fuchs D, Daniel V, Sadeghi M, Opelz G, Naujokat C (2010) Biochem Biophys Res Commun 394: 1098-1104. Supported by Cancer Prevention and Research Institute of Texas. Citation Format: Donald Rozario, Sammer Zeglam, Wolfram Siede. Exploring the mechanisms of resistance to Salinomycin, a cancer stem cell-specific agent, in budding yeast as a model. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-100. doi:10.1158/1538-7445.AM2013-LB-100