Abstract 849: Metformin enhances trastuzumab efficacy for HER2 + gastric cancer cells
Authors: Kim Mi Young , Park Jin Hyun , Hong Sungyoul , Kim Jin-Soo 
Published: August 2019

Abstract
Background: Trastuzumab (Tmab) is an effective monoclonal antibody against advanced gastric cancers (GCs) with HER2 amplification. In TCGA dataset, high mTOR activity was observed in proliferative cluster by RPPA analysis, and almost half of HER2 amplified GC showed increased mTOR expression. Metformin is a widely used antidiabetic drug and an activator of AMP kinase, which could affect mTOR pathway signaling. Here, we describe a therapeutic synergism between Tmab and metformin in HER2+ GC cells.
Material and Methods: The following GC cells were evaluated: HER2 -positive (HER2+) and Tmab -sensitive NCI-N87, YCC-19, YCC-38 and OE19, HER2+ Tmab -resistant OE33 and HER2 negative AGS. We assessed cytotoxic response of these GC cells to Tmab alone or in combination with metformin by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium (MTT) assay and anchorage independent growth in soft agar. MGI (mean growth inhibition) was calculated by dividing the colony number of the treated group by that of the untreated control group. Western blots were performed to assess the cellular activity of Tmab and/or metformin in HER2 signal pathway. GC cells were subjected to the Proteome Profiler Human Phospho-RTK Array Kit (R&D Systems) to evaluate the relative phosphorylation of human receptor tyrosine kinases in GC cells after Tmab and/or metformin exposure. Xenograft studies were performed to evaluate in vivo therapeutic efficacy of trastuzumab and/or metformin with HER2+ human GC cells. The statistical significance of differences were determined by using the Kruskal-Wallis test.
Results: Metformin induced phosphorylation of AMP kinase in all GC cells tested and dephosphorylation of mTOR in Tmab sensitive GC cells. We observed that treatment with Tmab in combination with metformin induced a statistically significant decrease in the number of colonies formed in soft agar by N87, YCC19, YCC-38 and OE19 cells, as compared to the numbers formed by control cells or cells in the single-treatment groups (Kruskal-Wallis test, p &lt; .01). No growth inhibitory effect was detected in OE33 cells with compared to trastuzumab alone. The combination of metformin resulted in decreased phosphorylation of HER2 and downstream targets, such as AKT or ERK, in trastuzumab-sensitive HER2+ cells. Phospho RTK arrays showed that the synergistic decrease of phosphorylation of EGFR, HER2 and HER3 with Tmab and metformin. Furthermore, the combination of Tmab and metformin exhibited enhanced antitumor effects in a xenograft model with N87 cells.
Conclusion: Collectively, these data support that trastuzumab in combination with metformin efficiently suppresses the growth of HER2-positive GC cells. Moreover, metformin synergizes with trastuzumab to induce the therapeutic effect on the HER2+GC cells. Further studies are warranted to test this concept in clinical setting.
Citation Format: Mi Young Kim, Jin Hyun Park, Sungyoul Hong, Jin-Soo Kim. Metformin enhances trastuzumab efficacy for HER2 + gastric cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 849.