Abstract 1730: Cancer stem cells might sustain stemness by the induction of autophagy in starvation stress

Abstract

Abstract Background: Cancer stem cells (CSCs), which have capacity for self-renewal and cancer cell supply, have been thought to be responsible for tumor initiation, distant metastasis, and chemoresistance. Side population (SP) cells extracted by the fluorescence-activated cell sorting technique using Hoechst 33342 are thought to be enriched for CSCs. Autophagy is an intracellular degradation system that is induced under stress, such as starvation. Although autophagy has been reported to be associated with tumor progression under various stresses, the significance of autophagy in CSCs has still remained to be unknown. The aim of this study is to clarify the role of autophagy of CSCs under starvation stress. Materials and Methods: Two gastric cancer cell lines, OCUM-2MD3 and OCUM-12 were used. Two side population (SP) cell lines, OCUM-2MD3/SP and OCUM-12/SP were sorted by flow cytometry as CSC-rich cells from the parent OCUM-2MD3 and OCUM-12 cells, respectively. The effects of starvation stress, including low glucose, low amino acid, or low serum, on the stemness of CSCs were examined. The expression level of autophagy associated proteins, LC3A and LC3B, was evaluated by RT-PCR and western blotting. The effects of autophagy on the stemness and the proliferation of CSCs were examined by SP fraction and MTT assay. Chloroquine was used as an autophagy inhibitor. Results: The percentages of SP cells were significantly higher in the OCUM-12/SP cells (10.2%) and OCUM-2MD3/SP cells (12.3%) than in their parent OCUM-12 cells (2.1%) and OCUM-2MD3 cells (1.2%). The expression level of LC3A and LC3B was high in both OCUM-2MD3/SP cells and OCUM-12/SP cells, in comparison to that in OCUM-2MD3 cells and OCUM-12 cells. Starvation stress increased the autophagy status of OCUM-2MD3/SP and OCUM-12/SP cells. Chloroquine significantly decreased the SP fraction and proliferation activity of OCUM-2MD3/SP cells and OCUM-12/SP cells. Conclusion: Autophagy acts as a survival pathway in CSCs under starvation stress. CSCs might sustain stemness by the induction of autophagy in sarvation status. The autophagy inhibitor might be a promising therapy for CSCs. Citation Format: Go Masuda, Masakazu Yashiro, Kishu Kitayama, Yuichiro Miki, Hiroaki Kasashima, Tamami Morisaki, Tatsunari Fukuoka, Tsuyoshi Hasegawa, Masaichi Ohira, Kosei Hirakawa. Cancer stem cells might sustain stemness by the induction of autophagy in starvation stress. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1730.