Abstract 4064: Overcoming resistance to 2-deoxy-glucose and glucose deprivation in tumor cells under normoxia by modulating the unfolded protein response
Authors: Philips Katherine B. , Kurtoglu Metin , Lampidis Theodore J. 
Published: August 2014

Background: Cancer cells have greater aerobic glycolysis than normal cells and therefore take up more glucose, as demonstrated by the positron emission tomography (PET) scan. This phenomenon can be exploited for cancer therapy using glycolytic inhibitors such as 2-deoxy-glucose (2-DG). Due to its structural similarity to mannose, 2-DG also interferes with N-linked glycosylation, a co-translational modification that directs protein folding. This obstruction triggers an unfolded protein response (UPR), which kills certain tumor types grown under normoxia, for example pancreatic cancer cell line, 1420 (ATCC Mia Paca-2). Since 2-DG is in clinical trials, we are investigating mechanisms by which tumor cells have acquired or are intrinsically resistant to 2-DG. By continuous 2-DG treatment of 1420 cells, we isolated a two-fold resistant variant cell line, 14DG2, and compared it to pancreatic cell line, 1469 (ATCC Panc-1), that intrinsically displays resistance to 2-DG. 2-DG has often been compared to and used as a substitute for glucose deprivation which can also lead to UPR. Glucose deprivation is common in tumor development since cells can outgrow the nutrient supply and may lack functional vasculature. Thus, we investigated the effects of glucose starvation on the same cell lines and compared our results to those where 2-DG induced UPR.

Results: 2-DG resistant cell lines, 1469 and 14DG2, display greater sensitivity to glucose deprivation than 2-DG sensitive cell line 1420 which indicates that 2-DG treatment is not an adequate substitute for glucose deprivation. The resistant cell lines show lower protein levels of glucose transporters and/or hexokinase II, which correlates with their decreased uptake of radioactively-labeled 2-DG. We can deduce that these cells also take up less glucose and this may be the reason for their increased sensitivity to glucose starvation conditions.

2-DG resistant cell lines display higher basal levels of UPR folding chaperone Grp78 when measured by western blot. Using siRNA or versipelostatin to inhibit Grp78, a dramatic increase in 2-DG cytotoxicity in the two resistant cell lines was observed suggesting that the resistant cell lines are prepared to cope with ER stress more so than the sensitive cell line. Interestingly, these cell lines also showed resistance to tunicamycin but not to other ER stressors i.e. thapsigargin, brefeldin and velcade. Thus, it appears that 2-DG resistance in these cell lines is involved with processing of oligosaccharide and/or glycosylation interference.

Conclusions: The manner in which glucose is restricted in tumor cells, i.e. 2-DG treatment or glucose deprivation, dictates resistance to these two different conditions. Resistance to 2-DG, which may arise in the clinical use of this sugar analog, can be overcome by reducing the effectiveness of the unfolded protein response.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4064. doi:10.1158/1538-7445.AM2011-4064