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Metformin treatment of locally advanced head and neck squamous cell carcinoma (LAHNSCC) patients induces an anti-tumorigenic immune response.

6037 Background: Metformin is a biguanide, widely used oral hypoglycemic agent. Metformin has also shown to inhibit tumor growth and progression in a wide variety of cancers including Head and Neck Squamous Cell Carcinoma (HNSCC). Metformin activates AMP protein kinase (AMPK) related pathways leading to inactivation of mammalian target of rapamycin (mTOR) and suppression of its downstream effectors. In addition, metformin is postulated to alter immune regulation in the tumor microenvironment leading to increased tumor cell killing. Here, we report our findings on the impact of metformin on T cells, NK cells and cytokines from patient peripheral blood mononuclear cells (PBMCs) from a phase I open-label single site dose escalation study combining metformin and chemoradiation (CRT) in HNSCC (NCT02325401). Methods: In this study, we evaluated the immune cell phenotypes and cytokine profiles of peripheral blood in patients before and after metformin treatment on trial by using flow cytometry and cytokine magnetic bead assays (Luminex). Cytokine profiles were further studied in co-culture experiments combining PBMCs, HNSCC cell lines, and metformin. Results: Patients who received metformin developed expanded NK cell populations, increased NKG2D expression, and a shift in their CD8+ T-cell memory phenotypes. Patient serum ELISA examination revealed increased anti-tumorigenic cytokine profiles. Metformin treatment of HNSCC cell lines in vitro as well as HNSCC PBMCs ex vivo resulted in downregulation of STAT3 compared to healthy controls. Downregulation of STAT3 may be a potential mechanism in which metformin stimulates NK cells. Conclusions: Here we show evidence that metformin treatment has a direct effect on the innate immune system in patients with HNSCC, inducing an anti-tumorigenic immune response suggesting that metformin continues to be a good candidate to yield improved clinical outcomes in patients with advanced stage HNSCC. Clinical trial information: NCT02325401.