Abstract 801: Dual inhibition of distinct metabolic features targets osteosarcoma stem cells
Authors: Kishi Shingo , Honoki Kanya , Tsukamoto Shinji , Fujii Hiromasa , Kondo Yumiko , Tanaka Yasuhito , Kuniyasu Hiroki 
Published: August 2019

Abstract
[Objective] Mitochondria are the places for the energy production of the cells, while reactive oxygen species (ROS) are also produced alongside. In recent years, it has been reported that cancer stem cells metabolize predominantly through oxidative phosphorylation (OXPHOS) rather than glycolysis in certain cancer cells. Targeting OXPHOS achieved by suppression of ATP synthesis through mitochondrial ATP synthase could be a potential therapeutic option against cancer stem cells. In the current study, we have identified the mitochondria metabolism as the potential therapeutic target in osteosarcoma (OS) stem cells, presenting the synergistic effects of combination of OXPHOS inhibition by pterostilebene (PTE) with c-Myc inhibitor, which target both OXPHOS-dominant cancer stem cells and glycolysis-dominant non-cancer stem cells as a ‘two hit’ or ‘dual inhibition’ of metabolic pathways, OXPHOS and glycolysis.
[Materials & Methods] Using human OS cell lines of SaOS2, U2OS and MG63 cells, cell survival and the ability of sphere formation was assessed with or without PTE, and the expression of stem cell markers mRNA such as Oct3, NS, CD44 was examined by RT-PCR. Next, the activity of mitochondrial ATP synthase, mitochondrial respiration capacity of oxygen consumption rate, and the amount of ATP as well as ROS production were measured under the treatment of PTE. Furthermore, we examined the synergistic effect of PTE with cMyc transcription inhibitors of JQ1 or Honokiol (HNK).
[Results] PTE treatment on human OS cell lines reduced the viabilities of all cell lines in dose-dependent manner and expression of stem cell marker and the ability of sphere formation were also decrease in terms of sphere number and size. PTE reduced the activity of F0F1-ATP synthase; Complex V predominantly, and the mitochondrial oxygen consumption rates and synthetic amount of ATP were also decreased in spheroid condition. These results suggest that PTE possibly targets stem cell population which preferably relies on OXPHOS, suppressing ATP synthesis via F0F1-ATP synthase inhibition as well as increased ROS production in OS cells and changes metabolic flax to glycolysis dependent feature. The dual inhibition of OXPHOS by PTE and c-Myc inhibition by HNK or JQ1 showed the synergistically inhibition of OS cell growth in a dose-dependent manner.
[Discussion] Prognosis of the patients with osteosarcoma has reached to plateau without any breakthroughs over the last quarter century, and nearly 30% of patients still have to face very severe poor prognosis, especially with metastatic disease. Current study suggests that modulation of metabolic flux by c-Myc and OXPHOS inhibitors showed a greater synergistic effect with ‘two metabolic hit’ or ‘dual metabolic inhibition’ of distinct metabolic features and it could be a novel therapeutic strategy against osteosarcoma, possibly targeting both stem-like cell population and general tumor cell population.
Citation Format: Shingo Kishi, Kanya Honoki, Shinji Tsukamoto, Hiromasa Fujii, Yumiko Kondo, Yasuhito Tanaka, Hiroki Kuniyasu. Dual inhibition of distinct metabolic features targets osteosarcoma stem cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 801.