Abstract 2571: Metformin inhibits proliferation and acts synergistically with paclitaxel and doxorubicin in triple negative breast cancer cell lines
Authors: Guimaraes Isabella S. , Tessarollo Nayara G. , Oliveira Laura FRL , Zampier Roger C. , Silva Ian V. , Sternberg Cinthya , Rangel Leticia BA 
Published: August 2015

Abstract
Background: Triple-negative breast cancer (TNBC) is a subtype of breast cancer (BC) characterized by its unique molecular profile, aggressive behavior, distinct patterns of metastasis and unavailability of effective target therapy. Indeed, despite good initial response to chemotherapy, even platinum- or anthracyclines-based, TNBC relapse and mortality rates are high even in early-stage disease. Metformin, one of the most commonly used medications for treatment of type 2 diabetes mellitus, has emerged as a potential anticancer agent. This study aimed to evaluate the combination treatment of metformin, at lower concentrations (10uM), with conventional chemotherapeutic agents on TNBC cell lines. We investigated the combination effect of metformin with doxorubicin (DOX), cisplatin (CDDP) and paclitaxel (PTX). Methods: Three TNBC cell lines (MDAMB-231, HCC-70, HCC-1937) and one luminal BC cell line (MCF-7) were used. Cell proliferation was determined by MTT assay. Clonogenic assay was conducted and apoptosis was analyzed by Annexin V-FITC assay. Western immunoblotting was performed to determine the expression of the downstream targets of PI3K, MAPK and AMPK pathways. Findings: Metformin potently inhibited the proliferation of all BC cell lines in a dose-dependent manner. Likewise, metformin caused a significant dose-dependent reduction in clonogenicity of TNBC cell lines (P&lt;0.05), but no difference was noted with regard to MCF-7. The lowest significant inhibitory concentration of metformin for MDAMB-231, HCC-70 and HCC-1937 was 1mM, 100 μM and 1mM, respectively. Of clinical relevance, the combination of metformin, at low concentration (10uM), with PTX or DOX promoted synergistic effects on the inhibition of TNBC cell viability measured by MTT (P&lt;0.05). The combination of CDDP and metformin did not affect the viability in comparison with CDDP alone. Metformin also potentiated PTX and DOX-induced apoptosis (P&lt;0.05). However, there was no significant increase in apoptosis with the combination of metformin and CDDP when compared with CDDP alone. In parallel, treatment of TNBC cells with metformin decreased phosphorylation of the pS6K protein, a key target of the mTOR pathway. Metformin was also found to decrease the phosphorylation of ERK1/2. Furthermore, the combination of metformin and PTX significantly inhibited the phosphorylation of ERK 1/2 and AKT compared with PTX alone in TNBC cells. Conclusions: We herein demonstrate a synergistic effect of metformin, at low and safe concentration, with PTX or DOX in suppressing human TNBC cell lines proliferation and activation of key targets in cancer therapy. Moreover, this combination is appealing because metformin is a low cost drug, with known pharmacokinetics and a favorable safety profile. Our results support the continued investigation of the addition of metformin to anthracyclines- and taxanes-based therapies against TNBC.
Citation Format: Isabella S. Guimaraes, Nayara G. Tessarollo, Laura FRL Oliveira, Roger C. Zampier, Ian V. Silva, Cinthya Sternberg, Leticia BA Rangel. Metformin inhibits proliferation and acts synergistically with paclitaxel and doxorubicin in triple negative breast cancer cell lines. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2571. doi:10.1158/1538-7445.AM2015-2571