Abstract A12: Metformin treatment in LAHNSCC induces an antitumorigenic immune response

Epidemiologic studies and meta-analyses have indicated that metformin is associated with a lower incidence of tumorigenesis among type 2 diabetic patients, including those with head and neck squamous cell carcinoma (HNSCC). HNSCC patients are often treated with concurrent cisplatin-based chemotherapy and radiation (CRT). However, the cure rate remains low at 50% in HPV-negative smokers. Metformin has been shown to inhibit tumor growth and progression, both in vitro and in mouse models, in a wide variety of cancers including HNSCC. The mechanism through which this occurs is thought to be via the inhibition of the mammalian target of rapamycin (mTOR) pathway directly and indirectly through activation of AMPK. Recent studies indicate that increasing the activity of AMPK reduces the expression of PD-L1 found on the surface of cancer cells, thus allowing a greater influx of CD8+ T cells and further activity of NKT cells correlated with increased tumor cell killing. Given the potential antitumorigenic activity of metformin in HNSCC and that biguanide is generally well tolerated compared to other mTOR inhibitors, we hypothesized that the addition of metformin to CRT would be safe and would result in enhanced antitumor responses through activation of AMPK and the immune system. Therefore, in accordance with the phase I open-label, single-site, dose-escalation study combining metformin and CRT in LAHNSCC (NCT02325401), we investigated the effects of metformin on T cells, NK cells, and cytokines from patient PBMCs. Using flow cytometry and cytokine magnetic bead assays (Luminex), we evaluated the immune cell phenotypes and cytokine profiles of peripheral blood in patients before and after metformin treatment on trial. Cytokine profiles were further studied in coculture experiments combining PBMCs, HNSCC cell lines, and metformin. Following metformin treatment, patients developed an increase in activated NK cell populations, determined via NKG2D expression, as well as a shift in their CD8+ T-cell memory phenotypes. Patient serum ELISA examination revealed alterations in cytokine profiles, which were recapitulated in ex vivo experiments. 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 activates NK cells. Here we show evidence that metformin treatment has a direct effect on the innate immune system in patients with LAHNSCC, inducing an antitumorigenic immune response. Our study thus demonstrates that metformin continues to be a good candidate in combination with other therapeutic agents to yield improved clinical outcomes in patients with advanced-stage HNSCC. Citation Format: Sarah M. Palackdharry, Benyamin Yaniv, Melissa Orr-Asman, Nooshin Hashemi, Vinita Takiar, Trisha Wise-Draper. Metformin treatment in LAHNSCC induces an antitumorigenic immune response [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Optimizing Survival and Quality of Life through Basic, Clinical, and Translational Research; 2019 Apr 29-30; Austin, TX. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(12_Suppl_2):Abstract nr A12.