Abstract B114: Variation in glucose availability induces reactive oxygen species and increased P-gp mediated multi-drug resistance to chemotherapeutics.
Authors: Seebacher Nicole , Richardson Des , Jansson Patric 
Published: August 2014

Abstract
Background: Generally, many types of cancer develop resistance to the stress induced by chemotherapy. Moreover, within the tumor, there exists a considerable spatial and temporal gradient of glucose, rendering a significant portion of cancer cells exposed to a stressful micro-environment (Mol Syst Biol, 2012; 8; 589). Notably, hypoxia inducible factor-1 (HIF-1) is a major redox-sensitive transcription factor responsible for regulation of P-glycoprotein (P-gp), the most consistently over-expressed detoxification drug efflux transporter involved in the development of multi-drug resistant (MDR) cancers (Cancer Res 2002; 62; 3387-94). Considering that glucose deficiency is a common stress factor in tumors, this study investigated whether variations to glucose availability could increase drug resistance to the cytotoxic agent and P-gp substrate, doxorubicin (DOX).
Methods: Reactive oxygen species (ROS) were measured under incubation conditions with different concentrations of glucose by flow cytometry using the cellular and mitochondrial stress markers DCFH-DA and MitoSOX, respectively. Stress induced NF-κβ activation was determined by western blotting and immunofluorescent detection of p65. Regulation of HIF-1 and its downstream target genes were assessed by RT-PCR and western blotting. Cellular proliferation was determined via MTT assays.
Results: We demonstrated that changes in glucose availability critically enhanced cellular ROS signaling, thereby conferring P-gp-mediated drug resistance against clinically available chemotherapeutics. Both elevated (50 mM) and restricted (0 and 12.5mM) glucose availability significantly (p&lt;0.001) induced mitochondrial superoxide production which both stabilized HIF-1 activity and also activated the cytosolic transcription factor, NF-κB, by de-phosphorylation of the functional p65 subunit. Following this, the p65 subunit was observed to translocate into the nucleus, resulting in enhanced HIF-1 transcription. The ROS-mediated increase in HIF-1 activity significantly (p&lt;0.05) increased P-gp protein surface expression and function. Notably, the up-regulation of P-gp subsequently led to greater drug resistance to DOX in glucose restricted cells (IC50: 28.3±1.3 µM) compared with cells at basal glucose concentrations (25 mM; IC50: 3.6±0.6 µM). This resistant phenotype was reversible by addition of the specific P-gp inhibitor, Elacridar.
Conclusion: This study demonstrated that as tumor cells become increasingly glucose deprived or alternatively exposed to higher amounts of glucose, this increases stress and consequently leads to a more aggressive MDR phenotype via up-regulation of P-gp. These results reveal important insights into how changes in glucose availability elevate multi-drug resistance in tumors, which is critical for determining chemotherapeutic strategies.
Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B114.
Citation Format: Nicole Seebacher, Des Richardson, Patric Jansson. Variation in glucose availability induces reactive oxygen species and increased P-gp mediated multi-drug resistance to chemotherapeutics. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B114.