Abstract 1058: Targeting pentose phosphate pathway (PPP) represents a novel therapeutic strategy for hepatocellular carcinoma (HCC) treatment
Authors: Xu Ming Jing , Lai Kit Ho , Lin Shu Hai , Tse Pui Wah , Chiu David Kung Chun , Koh Hui Yu , Law Cheuk Ting , Wong Chun Ming , Cai Zong Wei , Wong Carmen Chak Lui , Ng Irene Oi Lin 
Published: July 2016

Abstract
Background and objectives: Hepatocellular carcinoma (HCC) is the primary liver malignancy with an extremely low survival rate. HCC progression is frequently associated with accelerated glucose consumption that confers growth advantage to tumor cell through two essential metabolic pathways - glycolysis and the pentose phosphate pathway (PPP). Glycolysis utilizes glucose for ATP production, while the PPP converts glycolytic intermediates to generate NADPH, the cellular antioxidant, and ribose-5-phophate, the nucleotide precursor. Although glycolysis has been extensively studied in HCC, how PPP supports HCC growth remains largely unknown. Our study aims at delineating the clinical significance, regulation and functions of PPP in HCC development and explore the therapeutic potential of PPP inhibitors for HCC therapy.
Methods: The expression and abundance of the the PPP genes were examined in 16 pairs of human HCC tumors and adjacent non-tumors by transcriptome sequencing. Level of reactive oxygen species (ROS) and glucose uptake were measured by CM-H2DCFDA and 2-NBDG stainings, respectively. Metabolomics study was performed with CE-TOF-MS analysis. Metabolic flux analysis was conducted using UPLC-MS/MS.
Results: Transcriptome sequencing data showed that enzymes in the PPP were frequently upregulated in HCC. Transketolase (TKT), the gene encodes the reversible enzyme connecting PPP and glycolysis, is the most abundant and most overexpressed PPP gene in HCC. Overexpression of TKT was confirmed in an expanded sample cohort at the mRNA and protein level. Meanwhile, TKT overexpression was significantly correlated with venous invasion, microsatellite formation, tumor size and absence of tumor encapsulation. Notably, TKT expression was controlled by NRF2/KEAP1/BACH1 pathway, which is a major transcription regulator for redox homeostasis. CHIP assay revealed that NRF2 and BACH1 competitively bound to the same antioxidant responsive elements (ARE) in TKT. Functionally, knockdown of TKT in HCC cells retarded cell growth, attenuated glucose uptake and NADPH production, increased intracellular ROS, and induced oxidative stress-associated cell cycle delay. In line with these findings, knockdown of TKT greatly suppressed tumor growth in vivo. Metabolomics and metabolic flux analysis revealed that loss of TKT disrupted the PPP and subsequently reduced NADPH production. Intriguingly, genetic knockdown and pharmacological inhibition of TKT enhanced the efficacy of Sorafenib, the only FDA-approved drug for HCC treatment, both in vitro and in vivo.
Conclusion: Our study suggested the clinical significance of TKT in HCC and illustrated the anti-oxidative role of TKT in HCC progression. We also proposed that disrupting the metabolic machinery by TKT inhibition might be a novel therapeutic strategy for HCC treatment.
Citation Format: Ming Jing Xu, Kit Ho Lai, Shu Hai Lin, Pui Wah Tse, David Kung Chun Chiu, Hui Yu Koh, Cheuk Ting Law, Chun Ming Wong, Zong Wei Cai, Carmen Chak Lui Wong, Irene Oi Lin Ng. Targeting pentose phosphate pathway (PPP) represents a novel therapeutic strategy for hepatocellular carcinoma (HCC) treatment. [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 1058.