Abstract 1038: Exploiting ROS and metabolic differences to selectively killing cisplatin resistant lung cancer
Authors: Wangpaichitr Medhi , Wu Chunjing , Li Ying Ying , Shah Sumedh , Chen Shu-Mei , Dinh Vy , Kuo Macus T. , Feun Lynn G. , Savaraj Niramol 
Published: July 2016

Abstract
Cisplatin resistance remains a major problem in the treatment of lung cancer. We have discovered that cisplatin resistant (CR) lung cancer cells, regardless of the KRAS mutation status, share one common parameter which is increased reactive oxygen species (ROS) when compared to their parental cells counterpart. Importantly, we found that CR cells were no longer addicted to the glycolytic pathway, but rather relied on oxidative metabolism (OXMET) for energy and biosynthesis. Thus, alteration in mitochondria which resulted in metabolic changes and higher basal levels of ROS may be one of the major factors contributing to cisplatin resistance. We have investigated mitochondrial morphology in parental vs. CR cells using transmission electron microscopy (TEM). Our data clearly showed that CR cells possessed significantly higher number of mitochondria per total cell area (n = 4; p = 0.0006). CR cells also consumed 2-4 fold more oxygen when compared to their parental cells. To further confirm that oxidative phosphorylation was utilized more in CR cells, we assayed mitochondrial membrane potential (MMP) using TMRE staining. MMP was significantly higher in CR cells suggesting that CR cells possess highly active mitochondria. Key glycolytic enzymes hexokinase II (HKII) and lactate dehydrogenase A (LDHA), as well as lactate production were decreased in all CR cell lines which corresponded to the resistance to glycolytic inhibitor, 2DG (n = 8; p&lt;0.03). Moreover, CR cells were highly sensitive to glutamine deprivation. Glutamine withdrawal for 72h resulted in 75-80% cell death in CR cells while only 10-15% cell death occurred in parental cells. CR also take up twice as much L-[G-3H] glutamine when compared to its parental counterpart (n = 4, p&lt;0.05). Here, using Riluzole (the FDA approved drug that interferes with cystine/glutamate pump and results in reduced intracellular glutathione (GSH) levels), can selectively kill CR cells. ROS levels were increased (2-3X) more in resistant cells after Riluzole treatment while no significant change occurred in parental cells. The ID50 dosage of parental cells were 3-4 fold more than theirs CR cell counterparts and no cytotoxicity were found in normal lung fibroblast (n = 8; p&lt;0.05). However, antioxidant, N-acetylcysteine (NAC, 0.1mM), cannot completely abort cell death by Riluzole suggesting other mechanisms are involved. Importantly, Riluzole is also effective in 2 mouse xenograft models (H460CR (KRAS mutant) and SC (wt)). Tumors completely disappeared in wild type mice and were significant reduced in KRAS mutant mice (n = 5 per treatment group; p&lt;0.002). We conclude that addiction to glutamine instead of glucose and higher basal ROS levels seen in CR cells can make them hypersensitive to Riluzole. Repurpose this drug should be considered for future treatment of CR lung cancer patients. Supported by Department of Veterans Affairs, CDA2 award (1K2BX001289) and Woman Cancer Association Fund.
Citation Format: Medhi Wangpaichitr, Chunjing Wu, Ying Ying Li, Sumedh Shah, Shu-Mei Chen, Vy Dinh, Macus T. Kuo, Lynn G. Feun, Niramol Savaraj. Exploiting ROS and metabolic differences to selectively killing cisplatin resistant lung cancer. [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 1038.