Abstract 5388: Altered regulation of metabolic pathways by the hormone glucagon-like peptide 1 in breast cancer induces growth inhibition.
Authors: Rubinek Tami , Ligumsky Hagai , Karasik Avraham , Wolf Ido 
Published: August 2014

Ample data indicate an association between Type 2 diabetes mellitus (T2DM) and increased risk of breast cancer. The incretin hormone glucagon-like peptide-1 (GLP-1) is a 31-amino acids long peptide-hormone, secreted from intestinal L cells in response to food intake and, through activation of G-protein coupled receptor (GPCR) located on pancreatic β cells, serves as the major regulator of postprandial insulin secretion. In hepatocytes and adipocytes GLP-1 regulates metabolic pathways like glucose uptake and lipid biosynthesis. GLP-1 levels are reduced in T2DM, and long acting GLP-based medications are currently approved for treatment of T2DM.

We have recently discovered GLP-1 as a novel player in the complex interaction between T2DM and breast cancer. GLP-1 inhibited proliferation of breast cancer cells in vitro and in vivo, induced cAMP accumulation and inhibited AKT activation. Tumor cells acquire a metabolic switch essential for their survival, allowing cells to function under stress and produce precursors needed for the synthesis of macromolecules. This phenomenon is associated with activation of the AKT pathway and inhibition of AMP activated protein kinase (AMPK). Based on our observations and on known metabolic activities of GLP-1in other cell types, we hypothesized that it may reverse the metabolic switch in breast cancer cells, thus, leading to cell death.

AMPK inhibition, using compound C and siRNA, abolished GLP1-mediated MCF-7 and MDA-MB-231 cell death, implying this metabolic pathway as central to GLP-1 activity in breast cancer. Indeed, GLP1 induced AMPK phosphorylation in breast cancer cell lines. Accordingly, acetyl CoA carboxylase (ACC), an essential enzyme for fatty acid synthesis and a downstream target of AMPK, was phosphorylated by AMPK. Adenylate cyclase inhibitor 2′5′dideoxy adenosine prevented GLP-1-induced AMPK and ACC phosphorylation, suggesting cAMP as a regulator of this pathway. AMPK can be activated generally by LKB1 or CAMKK1β. As MDA-MB231 cells do not express LKB1 we suspected that GLP-1 utilizes CAMKK1β for AMPK activation in breast cancer cells. Indeed, we discovered that CAMKK1β inhibition abrogated AMPK activation by GLP-1. The mammalian target of rapamycin (mTOR) pathway is regulated by AMPK. We monitored pathway activity by measuring phosphorylation of S6-kinase and its substrate S6 in MCF-7 cells. Phosphorylation of the two p-S6Kinase isoforms (P85 and P70), and of pS6, was decreased following GLP-1 treatment. We conducted metabolomics screen using NMR and preliminary data indicated reduced lactic acid levels and increased glutamic acid levels following GLP-1 treatment.

Thus, we show that regulation of AKT-mTOR and AMPK metabolic pathways by GLP-1 in breast cancer, mediate GLP-1 growth inhibitory effect. As GLP-1 levels are lower in T2DM, we suggest this activity of GLP-1 as a novel link associating T2DM and breast cancer.

Citation Format: Tami Rubinek, Hagai Ligumsky, Avraham Karasik, Ido Wolf. Altered regulation of metabolic pathways by the hormone glucagon-like peptide 1 in breast cancer induces growth inhibition. [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 5388. doi:10.1158/1538-7445.AM2013-5388