Abstract 5640: Picropodophyllin downregulates p53 and increases the Warburg effect in pediatric glioblastoma cells.

Abstract

Abstract Picropodophyllin (PPP) is reported to be a potent and selective inhibitor of tyrosine phosphorylation of insulin-like growth factor-1 receptor (IGF-1R) [Girnita et al., Clin Cancer Res 12:1383-91, 2006]. We previously showed increases in glucose uptake and lactate production in paediatric glioblastoma KNS42 cells after 24h of PPP-treatment [Wong Te Fong et al., Proc Mol Tar Ther B61, 2012]. These findings are unexpected for IGF-1R inhibition. Upregulation of c-Myc or downregulation of p53 are known to upregulate glycolysis in cancer [DeBerardinis et al., Cell Metab 7:11-20, 2008a; Kawauchi et al., Nat Cell Bio 30(9): 1792-5, 2007]. In order to identify the molecular mechanism that drives our previously observed upregulation of glycolysis following PPP treatment, we examine the changes in glucose metabolism in PPP-treated cells over a 96h time-course and relate these metabolic changes to c-Myc and p53 expression. KNS42 cells were treated for 6, 24, 48 and 96h with 2.4μM (5xIC50) of PPP. Culture media from the PPP-treated and control cells were analyzed by 1H Magnetic Resonance Spectroscopy (MRS) to examine the effect of PPP on glucose uptake and lactate excretion. pErk, pAkt, c-Myc, p53 and β-actin (loading control) protein expressions were examined by Western blot (WB). No change in cell number was found after 6h of PPP treatment but ∼50% of PPP-treated cells remained by 24h when compared to controls (p<0.001) and similar numbers of treated cells were also observed at 48 and 96h, indicating that a cohort of cells was initially killed by PPP (the doubling time of KNS42 is ∼30h) and that the remaining cell population survived the treatment. WB showed decreases in pErk (from 6h) and pAkt (from 24h) expression in PPP-treated cells, consistent with the mechanism of drug action. 1H MRS analysis of culture media showed significant increases in glucose uptake (p<0.01) and lactate excretion (P<0.0001) in PPP-treated cells at 24, 48 and 96h, and these metabolic changes are associated with decreased expression of p53 at these time-points. No significant metabolic changes were found in PPP-treated cells at 6h and p53 was unchanged compared to controls at this time-point. Reduced expression of c-Myc was found in PPP-treated cells from 24h. Our data indicate that it is p53 downregulation and not changes in c-Myc expression that drives the upregulation of glycolysis in KNS42 cells from 24h of PPP-treatment, and that these cellular and metabolic adaptations help cellular survival during treatment, suggesting a possible mechanism of resistance to PPP. Downregulation of p53 may drive the upregulation of glycolysis, representing a possible mechanism of resistance to PPP treatment in KNS42 cells. We acknowledge the support received from the CRUK and EPSRC Cancer Imaging Centre in association with the MRC and Department of Health (England) grant C1060/A10334, NHS funding to the NIHR Biomedical Research Centre. Citation Format: Anne-Christine LF Wong Te Fong, Chris Jones, John R. Griffiths, Martin O. Leach, Yuen-Li Chung. Picropodophyllin downregulates p53 and increases the Warburg effect in pediatric glioblastoma cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5640. doi:10.1158/1538-7445.AM2013-5640