Isosilybin B is a flavonolignan extracted from silymarin that exhibits anti-prostate cancer (PCA) activity, inhibits cancer cell proliferation, and contributes to G1-phase blockade and apoptosis.Isosilybin B induces degradation of the androgen receptor.

Isosilybin B also inhibited the microvessel sprouting from mouse dorsal aortas ex vivo, and the VEGF-induced cell proliferation, capillary-like tube formation, and invasiveness of human umbilical vein endothelial cells (HUVEC) in vitro. Further studies in HUVEC showed that these diastereoisomers target cell cycle, apoptosis, and VEGF-induced signaling cascade. Three-dimensional growth assay as well as co-culture invasion and in vitro angiogenesis studies (with HUVEC and DU145 cells) suggested the differential effectiveness of the diastereoisomers toward PCA and endothelial cells.[3]

Isosilybin B (50 and 100 mg/kg body weight; oral) effectively inhibits the growth of advanced human PCA DU145 xenografts. Immunohistochemical analyses revealed that Isosilybin B inhibit tumor angiogenesis biomarkers (CD31 and nestin) and signaling molecules regulating angiogenesis (VEGF, VEGFR1, VEGFR2, phospho-Akt, and HIF-1α±) without adversely affecting the vessel-count in normal tissues (liver, lung, and kidney) of tumor-bearing mice.[3]