Objectives: Metformin is a well-tolerated drug that is widely used to treat type 2 diabetes mellitus and insulin resistance. Retrospective studies have shown that the use of metformin is associated with decreased incidence of prostate cancer (PCa) and PCa specific mortality. However, the mechanism of metformin’s anti-cancer effect is still not clearly defined. The current models we use for testing therapeutics in vitro have very high levels of some nutrients, while completely lacking others, which creates an artificial dependency on certain metabolic pathways that cells relay on for growth. Physiological culture medium such as Plasmax containing a more balanced nutrients level that resembles the metabolic profile of human plasma would reveal more reliable therapeutic responses. By applying a more physiologically relevant model will unravel the metabolic and signalling pathways involved in metformin’s anti-tumour effect in PCa cells.
Methods: Cell viability assay used compare growth rates of PCa cell in traditional and physiological media with metformin alone or in combination with anti-androgen enzalutamide. Colony formation assay performed to assess colony formation capability. Western blot used to examine cell signalling pathways regulated by metformin.
Results: Plasmax sustains PCa cell growth in vitro and increases colony forming capacity. Combination of metformin and enzalutamide resulted in the most significant inhibition in cell growth in both medium. Metformin stimulated AMPK, and downregulated insulin-like growth factor 2 (IGF2), resulting in decreased androgen receptor (AR) signalling and Akt activation. Combination of metformin and enzalutamide produced the most significant activation of AMPK and reduction in IGF2 expression, AR signalling and Akt activation.
Conclusions: Physiological nutrient culture better represents clinically relevant models to test therapeutic response to combat treatment resistance in patients. This research provides the first comprehensive evidence of a novel mechanism for metformin’s anti-tumour effect via the reduction of IGF2 expression and consequently the reduction in PI3K/Akt signalling and AR signalling.