Abstract B57: Gnetin C, a novel resveratrol dimer, targets pancreatic cancer metabolism
Authors: Narayanan Narayanan K. , Kunimasa Kazuhiro , Tian Di , Horton Lori , Dolgaev Igor , Heguy Adriana , Miller George , Tiwari Amit , Narayanan Bhagavathi A. 
Published: October 2015

Background: Pancreatic ductal adenocarcinoma (PDAC) is aggressively invasive and treatment-resistant malignancy, and is the fourth leading cause of cancer deaths in the United States. The pancreatic cancer cells alter specific metabolic pathways to meet their tremendous energy and biomass demands which contribute to the progression and dissemination of this disease. More importantly, the oncogenic signaling enables cancer cells to reprogram the cellular metabolism that afford growth and proliferative advantages over normal cells and, thus, may contribute to pancreatic cancer pathophysiology. There is an increasing interest to investigate the oncogenic signaling that controls the metabolic reprogramming of cancer cells.

Objectives: Mammalian Target of Rapamycin (mTOR), a central downstream target of Akt, is a highly conserved protein kinase, and is frequent activated in PDAs. Earlier studies reported that mTOR, a master regulator of cell growth and proliferation downstream of oncogenic signaling pathways, controls specific aspects of cellular metabolism through the induction of metabolic gene expression. In our earlier microarray studies, we observed differential expression of genes associated with glucose and lipid metabolic pathways, with concomitant increase in mTOR expression. However, the mechanism and critical link between mTOR and the pancreatic cancer metabolism has not been fully understood.

Methodology: In the present study, we evaluated the effectiveness of Melinjo (Indonesian name; Gnetum gnemon L.) seed extract (MSE) and gnetin C (GC), a resveratrol dimer found abundantly in MSE in human (Aspc-1 and PANC-1) and mouse (Pan-02) pancreatic cancer cells. MSE has been reported to exert antioxidant, lipase and amylase inhibition, anti-metabolic syndrome effects and anticancer activities. A recent clinical study reported that MSE decreased serum uric acid and increased HDL cholesterol levels in humans, suggesting that MSE may improve lipid metabolism. To test the anti-tumor activities, pancreatic cancer cells were treated with various concentrations of MSE (0 - 400μg/ml) and GC (0 – 100μM) for 48 h. MTS cell proliferation and apoptotic assays were performed to determine the cell growth inhibition and induction of apoptosis. Trans-resveratrol (RES) that is abundant in grapes and wine was used to compare the effects of GC. Real-time PCR was performed to evaluate the effect of a MSE or GC on mTOR and its downstream targets, as well selected glucose and lipid metabolic pathway genes. Western blot was performed to confirm their expression at the protein level.

Results and conclusion: Human (ASPC-1 and PANC-1), and mouse (Pan-02) pancreatic cancer cells treated with MSE, GC and RES showed a dose-dependent decrease in cancer cell proliferation. The IC50 values of MSE, GC and RES related to their anti-proliferative effects revealed that GC, the major metabolite of MSE has superior anti-proliferative properties than resveratrol. Further, flow cytometry analysis showed a pre-G1 peak of apoptosis (&gt;10%) with GC. We observed that GC significantly downregulated mTOR complex, namely (mTORC1 and mTOC2). mTORC1 is a sensor of systemic and local levels of nutrients that regulates cancer cell proliferation and survival. mTORC2 is associated with the ribosome and insulin-stimulated oncogenic PI3K signaling. We also found that GC downregulated p-ribosomal protein S6 (p-RPS6), a downstream target of mTOR that plays important role in both neoplastic and inflammatory processes. In addition, GC also downregulated glycogen synthase kinase 3 alpha and beta (GSK3α and β) that is linked to glycogen metabolism and 3-hydroxy-3-methylglutaryl-CoA synthase 1 (HMGCS1), which is associated with lipids and lipoproteins metabolism (cholesterol biosynthesis). Further analysis on key genes of the lipid metabolism is in progress. Given the preliminary evidence that GC has superior anti-proliferative activities and its ability to inhibit mTOR and metabolic/lipid pathway genes can be expected to yield more potent therapies against this deadly disease. The future goal will be to test the potentials of GC on the antitumor efficacy and the effect on metabolic pathway targets in preclinical animal models of pancreatic cancer.

Citation Format: Narayanan K. Narayanan, Kazuhiro Kunimasa, Di Tian, Lori Horton, Igor Dolgaev, Adriana Heguy, George Miller, Amit Tiwari, Bhagavathi A. Narayanan. Gnetin C, a novel resveratrol dimer, targets pancreatic cancer metabolism. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr B57.