Abstract 3364: Extracellular ATP-induced intracellular ATP concentration elevation mediated by macropinocytosis promotes growth, survival, and drug resistance of cancer cells
Authors: Qian Yanrong , Wang Xuan , Liu Yi , Li Yunsheng , Colvin Robert A. , Tong Lingying , Wu Shiyong , Chen Xiaozhuo 
Published: May 2015

Abstract
Cancer cells switch from highly efficient mitochondrial oxidative phosphorylation (OXPHOS) to low efficiency glycolysis for ATP synthesis even when oxygen is abundant, a phenomenon called the Warburg effect. Because of the higher rates of cell growth and proliferation, cancer cells need more ATP than normal cells of the same tissues. However, the switch is counterintuitive since cancer cells need more ATP but cancer cells prefer to use a low efficiency pathway to produce ATP. How cancer cells secure all their ATP needs is not well understood. On the other hand, extracellular ATP concentration in cancer (intratumoral ATP concentration) are found to be in the range of several hundred μM, ∼10^3-10^4 times higher than those found in normal tissues. Huge differences exist between cancer and normal cells regarding extracellular ATP. Based on these observations, we hypothesized that cancer cells take up ATP from extracellular space to supplement their energy needs. Here we report that in multiple cancer cell lines belonging to multiple cancer types, 0.5-3 mM ATP, within the intratumoral ATP concentration range, elevated intracellular ATP levels by more than 50%. Extracellular ATP also reduced stress and promoted survival of cancer cells that were under OXPHOS and glucose metabolism inhibitions. Furthermore, extracellular ATP increased the viability of cancer cells treated with sunitinib or pazopanib, anticancer drugs working as ATP analogs by competing with ATP for the ATP binding site of targeted tyrosine kinases (TKs). In contrast, extracellular ATP did not affect the activity of paclitaxel, a drug unrelated to ATP. Inhibitor studies revealed that the extracellular ATP-induced intracellular ATP increase shows no dependence on OXPHOS, glycolysis, master ATP regulator AMPK, transcription or translation. These results strongly suggest that not all the increased intracellular ATP is synthesized inside of cancer cells. Fluorescence microscopy study showed that human lung cancer A549 cells, which are KRas oncogene mutation-positive (KRas+), exhibit macropinotcytosis, a type of endocytosis that non-specifically take in extracellular nutritional molecules by “fluid drinking”. Inhibition of macropinocytosis resulted in decrease in dextran take-up and intracellular ATP levels, and alleviated the drug resistance to TKIs in dose-dependent manners. These strongly suggest that macropinocytosis is responsible, at least in part, for transporting extracellular ATP into cancer cells, which led to drug resistance. All these results demonstrate, for the first time, unrecognized roles of extracellular ATP in contributing to the intracellular ATP pool and increase drug resistance in cancer cells and suggest a novel ATP transport mechanism. These findings challenge our traditional view on ATP and shed new lights on ATP homeostasis and ATP-induced drug resistance in cancer cells.
Citation Format: Yanrong Qian, Xuan Wang, Yi Liu, Yunsheng Li, Robert A. Colvin, Lingying Tong, Shiyong Wu, Xiaozhuo Chen. Extracellular ATP-induced intracellular ATP concentration elevation mediated by macropinocytosis promotes growth, survival, and drug resistance of cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3364. doi:10.1158/1538-7445.AM2014-3364