Utilizing metformin to enhance the efficacy of androgen-deprivation therapy in the treatment of prostate cancer.

Abstract

22 Background: Prostate cancer (PCa) incidence varies by geographic location, with developed countries exhibiting higher levels of disease. Some attribute this to the “Westernized lifestyle” of high energy diets and limited physical activity with consequent obesity. Obesity and related diseases like diabetes, cause hyperinsulinemia, which upregulates pro-survival insulin/insulin-like growth factor signalling. Previous work shows diet-induced hyperinsulinemia enhances PCa tumor growth in vivo. Metformin, a diabetic treatment, reduces hyperinsulinemia, and also exhibits anti-neoplastic properties. We assessed the potential benefit of combining a standard PCa treatment (bicalutamide) with metformin in vitro and in vivo. Methods: The effect of bicalutamide and/or metformin on colony formation rates was assessed in LNCaP, PC3, DU145 and PC3AR2 PCa cell lines using clonogenic assay. Western blot and cell cycle analyses were used to elucidate mechanisms of interaction between the drugs. The combination treatment regimen was assessed in vivo using a murine xenograft model. Results: Micromolar bicalutamide or millimolar metformin caused significant dose-dependent reduction in colony formation rates (p<0.001). Combination treatment further significantly reduced colony formation rates (p<0.005). Differing mechanisms of interaction occurred in AR positive and negative cell lines. Following combination treatment LNCaP cells exhibited altered cell proliferation (decreased PCNA) and perturbed cell cycle kinetics (G1/S arrest). PC3 cells showed evidence of enhanced apoptosis (increased BAX, decreased caspase 3, phospho-Akt). Preliminary in vivo results show significantly diminished tumor growth following combination treatment (p<0.0001). Conclusions: Combining bicalutamide and metformin significantly reduces PCa cell colony formation rates further than either monotherapy. In AR positive cells this effect is mediated by reducing cell proliferation rates, whereas in AR negative cells combination treatment promotes apoptosis. This combination drug regimen may potentially improve prostate-cancer specific survival via the direct anti-neoplastic properties outlined. [Table: see text]