Combination therapy with PD-1 inhibition plus rapamycin and metformin enhances anti-tumor efficacy in triple negative breast cancer

Abstract

Immunotherapy using PD-1/PD-L1 inhibitors has been proved to be effective in triple negative breast cancer (TNBC), albeit only in a fraction of patients. Emerging evidences indicate mTOR blockade and metformin may re-orchestrate the immune system in tumors. Herein, in this study we aimed to evaluate the anti-tumor efficacy of PD-1 monoclonal antibody with mTOR inhibitor rapamycin or with the anti-diabetic drug metformin. The status of PD-1/PD-L1 and mTOR pathway was determined through analyzing the TCGA and CCLE data in TNBCs as well as by detection at mRNA and protein level. The inhibition of tumor growth and metastasis by anti-PD-1 combined with rapamycin or with metformin was evaluated in allograft mouse model of TNBC. The effects of combination therapy on the AMPK, mTOR and PD-1/PD-L1 pathways were also evaluated. The combination treatment with PD-1 McAb and rapamycin/metformin had additive effects on suppression of tumor growth and distant metastasis in mice. Compared with the control group and the monotherapy, combined PD-1 McAb with either rapamycin or metformin exhibited more obvious effects on induction of necrosis, CD8⁺ T lymphocytes infiltrating and inhibition of PD-L1 expression in TNBC homograft. In vitro study showed either rapamycin or metformin not only decreased PD-L1 expression, but increased p-AMPK expression and therefore led to down-regulation of p-S6. In summary, combination of PD-1 antagonist with either rapamycin or metformin led to more infiltrating TILs and decreased PD-L1 resulting in enhanced antitumor immunity and blockade of PD-1/PD-L1 pathway. Our results suggested such combination therapy may be a potential therapeutic strategy for TNBC patients.

Keywords: Immunotherapy; Metformin; PD-1; Rapamycin; Triple negative breast cancer.