Metformin exerts antitumor activity via induction of multiple death pathways in tumor cells and activation of a protective immune response

Abstract

// Felipe V. Pereira 1, 4 , Amanda Campelo L. Melo 1 , Jun Siong Low 4 , Íris Arantes de Castro 1 , Tárcio T. Braga 1 , Danilo C. Almeida 1 , Ana Gabriela U. Batista de Lima 2 , Meire I. Hiyane 1 , Matheus Correa-Costa 1 , Vinicius Andrade-Oliveira 1 , Clarice S.T. Origassa 1 , Rosana M. Pereira 3 , Susan M. Kaech 4 , Elaine G. Rodrigues 2 and Niels Olsen S. Câmara 1 1 Laboratory of Transplantation Immunobiology, Department of Immunology, University of São Paulo, Institute of Biomedical Sciences, 05508-900 São Paulo, SP, Brazil 2 Laboratory of Cancer Immunobiology, Department of Microbiology, Immunology and Parasitology, Escola Paulista de Medicina, Universidade Federal de São Paulo (EPM-UNIFESP), 04023-062 São Paulo, SP, Brazil 3 Laboratory of Infectious Diseases, Department of Immunology, Institute of Biomedical Sciences, University of São Paulo, 05508-900 São Paulo, SP, Brazil 4 Department of Immunobiology, Yale University School of Medicine, 06520 New Haven, CT, USA Correspondence to: Felipe V. Pereira, email: felipevalencap@yahoo.com.br Keywords: metformin; tumor immunity; T cells; cell death; sitagliptin Received: March 19, 2016      Accepted: April 24, 2018      Published: May 25, 2018 ABSTRACT The antitumor effect of metformin has been demonstrated in several types of cancer; however, the mechanisms involved are incompletely understood. In this study, we showed that metformin acts directly on melanoma cells as well as on the tumor microenvironment, particularly in the context of the immune response. In vitro , metformin induces a complex interplay between apoptosis and autophagy in melanoma cells. The anti-metastatic activity of metformin in vivo was assessed in several mouse models challenged with B16F10 cells. Metformin’s activity was, in part, immune system-dependent, whereas its antitumor properties were abrogated in immunodeficient (NSG) mice. Metformin treatment increased the number of lung CD8-effector-memory T and CD4 + Foxp3 + IL-10 + T cells in B16F10-transplanted mice. It also decreased the levels of Gr-1 + CD11b + and RORγ + IL17 + CD4 + cells in B16F10-injected mice and the anti-metastatic effect was impaired in RAG-1 −/− mice challenged with B16F10 cells, suggesting an important role for T cells in the protection induced by metformin. Finally, metformin in combination with the clinical metabolic agents rapamycin and sitagliptin showed a higher antitumor effect. The metformin/sitagliptin combination was effective in a BRAFV600E/PTEN tamoxifen-inducible murine melanoma model. Taken together, these results suggest that metformin has a pronounced effect on melanoma cells, including the induction of a strong protective immune response in the tumor microenvironment, leading to tumor growth control, and the combination with other metabolic agents may increase this effect.