Contextual inhibition of fatty acid synthesis by metformin involves glucose-derived acetyl-CoA and cholesterol in pancreatic tumor cells

Mary Jo Cantoria,László G Boros,Emmanuelle J Meuillet

doi:10.1007/s11306-013-0555-4

Mary Jo Cantoria, László G Boros + Show 1 more

Open Access

https://doi.org/10.1007/s11306-013-0555-4

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Abstract

Metformin, a generic glucose lowering drug, inhibits cancer growth expressly in models that employ high fat/cholesterol intake and/or low glucose availability. Here we use a targeted tracer fate association study (TTFAS) to investigate how cholesterol and metformin administration regulates glucose-derived intermediary metabolism and macromolecule synthesis in pancreatic cancer cells. Wild type K-ras BxPC-3 and HOM: GGT(Gly) → TGT(Cys) K12 transformed MIA PaCa-2 adenocarcinoma cells were cultured in the presence of [1,2-13C2]-d-glucose as the single tracer for 24 h and treated with either 100 μM metformin (MET), 1 mM cholesteryl hemisuccinate (CHS), or the dose matching combination of MET and CHS (CHS–MET). Wild type K-ras cells used 11.43 % (SD = ±0.32) of new acetyl-CoA for palmitate synthesis that was derived from glucose, while K-ras mutated MIA PaCa-2 cells shuttled less than half as much, 5.47 % [SD = ±0.28 (P < 0.01)] of this precursor towards FAS. Cholesterol treatment almost doubled glucose-derived acetyl-CoA enrichment to 9.54 % (SD = ±0.24) and elevated the fraction of new palmitate synthesis by over 2.5-fold in MIA PaCa-2 cells; whereby 100 μM MET treatment resulted in a 28 % inhibitory effect on FAS. Therefore, acetyl-CoA shuttling towards its carboxylase, from thiolase, produces contextual synthetic inhibition by metformin of new palmitate production. Thereby, metformin, mutated K-ras and high cholesterol each contributes to limit new fatty acid and potentially cell membrane synthesis, demonstrating a previously unknown mechanism for inhibiting cancer growth during the metabolic syndrome.Electronic supplementary materialThe online version of this article (doi:10.1007/s11306-013-0555-4) contains supplementary material, which is available to authorized users.

Highlights

Metformin (1,1-dimethylbiguanide) is the first-line oral therapy prescribed for type 2 diabetes (Viollet et al 2012)
The 1 mM cholesteryl hemisuccinate (CHS) dose was used because when compared BxPC3 versus BxPC-3 we observed, via western blot, that the CHS-treated cells were more resistant to the AKT inhibitor PH-427, which indicates in vitro biological activity in K-ras negative cells
The metabolic impacts of CHS and metformin in this study cannot be attributed to cell death inducing properties

Summary

Introduction

Metformin (1,1-dimethylbiguanide) is the first-line oral therapy prescribed for type 2 diabetes (Viollet et al 2012). It is a potent anti-hyperglycemic and insulin-sensitizing drug that works by decreasing hepatic gluconeogenesis, activating insulin receptor tyrosine phosphorylation (Viollet et al 2012), decreasing intestinal glucose absorption, and increasing skeletal muscle and adipose tissue glucose uptake (del Barco et al 2011). Metformin increases the more active mitochondria-bound hexokinase and actin-bound phosphofructokinase in streptozotocininduced diabetic male Swiss mice hearts, enhancing glucose sensitivity of those organs (da Silva et al 2012). Published treatment protocols suggest that lactic acidosis is potentially a very serious (Fitzgerald et al 2009) but a rare side effect of metformin, the link with metformin has been questioned (Preiss and Sattar 2009)

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