Fig. 4

Clinically relevant dose of metformin inhibits CREB/mTORC1 in a manner that requires AR and STAT3 signaling. A IHC of radical prostatectomy specimens (benign and cancer core) stained with STAT3 and p-4E-BP1. TMA including benign and cancerous tissue with either metformin (n = 41) or patients without antidiabetic medication (n = 39) was employed as described previously [46]. B Gross anatomy assessment of representative 22Rv1 and PC3 xenograft tumors treated with vehicle or metformin (50 mg/kg; i.p.). Scale bars, 10 mm. Mean values are shown; error bars: s.d. (n = 5). C 22Rv1 and PC3 cells were implanted subcutaneously in mice and grown until tumors reached the size of approximately 100mm³. Xenografted mice were randomized and then received (n = 5 per group) vehicle or 50 mg/kg metformin i.p. daily. Mean tumor volume ± s.d. is shown. D Tumor weights assessment of representative 22Rv1 and PC3 xenograft tumors treated with vehicle or metformin (50 mg/kg; i.p.). Scale bars, 10 mm. Mean values are shown; error bars: s.d. (n = 5). E Comparison of IC₅₀ values of metformin for human PCa cell lines (22Rv1, DU-145 and PC3) and untransformed human prostate cell line RWPE-1. F Western blot analysis of STAT3, LKB1, p-CREB, CREB, p-4E-BP1, 4E-BP1, p-S6 and S6 in 22Rv1 and PC3 xenograft tumors. β-actin serves as a loading control. Sal…physiological saline solution; Met…metformin. G Western blot analysis of AR and PSA in 22Rv1 and PC3 xenograft tumors treated with vehicle or metformin (50 mg/kg; i.p.). β-actin serves as a loading control