Metformin Induces Pro-Tumorigenic Cytokines And Natural Killer Cells In Patients With Locally Advanced Head and Neck Squamous Cell Carcinoma

Abstract

Concurrent chemotherapy and radiation (CRT) continues to be standard of care for unresectable locally advanced head and neck squamous cell carcinoma (LAHNSCC). In the HPV (human papillomavirus) positive non-smoker population the cure rate approaches greater than 90%. However, the cure rate can be as low as 50% in HPV negative smokers necessitating newer and more effective treatments. Interestingly, diabetic HNSCC patients taking the biguanide, metformin, have been shown to have superior survival outcomes. However, the mechanism by which metformin results in superior outcomes for these patients is unclear. In vivo, metformin was shown to prevent HNSCC tumor formation in mouse models via activation of AMPK and inhibition of the mTOR pathway. Metformin has also been shown to activate CD8+ T cells and activation of AMPK has been shown to activate NKT cells. Therefore, we hypothesized that the addition of metformin to CRT would be safe and would result in enhanced tumor responses through activation of AMPK and activation of the innate immune system. Here we report our findings on the effect of metformin on the immune system utilizing our phase 1 open label clinical trial (NCT02325401) entitled “Dose-finding Study of Metformin With Chemoradiation in Locally Advanced Head and Neck Squamous Cell Carcinoma”. Trial eligibility criteria included newly diagnosed, non-diabetic, LAHNSCC patients eligible for definitive CRT. Patients received a 14-day lead-in of metformin in escalating dose cohorts (1000, 2550, or 3000 mg daily in divided doses) followed by a combination of metformin and standard of care CRT (cisplatin 100mg/m2 days 1, 22, and 43, 70 Gy radiation in 35 fractions) using a modified toxicity probability interval design. Blood was collected before and after metformin treatment and was processed for serum and separation of peripheral blood mononuclear cells (PBMCs). PBMCs were analyzed by flow cytometry to determine immune cell subsets and serum was analyzed by Luminex (Human 10-plex) for cytokine release. Eighteen patients have been enrolled out of 18 planned patients for dose escalation. Median time to follow-up is 21 months (range 3-29 months). Patient serum ELISA examination revealed overall increases in the pro-tumor immune cytokines TNF-a, IL-2, and decrease in the anti-tumor immune cytokine IL-4 in response to metformin. Metformin treatment also resulted in increased populations of cytotoxic T cells, NK and NKT cells and overall activation of innate immunity. Clinically, median overall survival has not been reached, and in fact, no patients on study have relapsed. Metformin administration in LAHNSCC results in activation of pro-tumorigenic immunity which may result in enhanced tumor responses and decreased tumor relapse.