Metronomic cyclophosphamide and metformin inhibited tumor growth and repopulated tumor-infiltrating lymphocytes in an experimental carcinoma model.

Metformin is a widely used antidiabetic biguanide. Retrospective data demonstrated the association of metformin use with survival benefit in multiple tumor types. Interest in repurposing metformin to treat cancer has not been translated into encouraging clinical benefit. In animal models, metformin activated cytotoxic T cells and exerted an immune-mediated anticancer effect. The current research was conducted to investigate the possible therapeutic benefit of metformin in combination with metronomic cyclophosphamide in an experimental cancer model. Ehrlich ascites carcinoma was injected into the subcutaneous tissue to induce solid tumors in syngeneic mice. Exponential solid tumor growth ensued and was effectively arrested with the administration of a cytotoxic dose of parenteral cyclophosphamide. Alternatively, oral metformin and continuous, low-dose cyclophosphamide significantly inhibited tumor growth relative to untreated mice. The drug combination was well tolerated. Histopathological examination of the tumor showed an increased number of tumor-infiltrating lymphocytes and enhanced expression of granzyme B by this drug combination. The current data suggests a potential role of metformin and metronomic chemotherapy that warrants further investigation.