Suppression of VEGF-mediated autocrine and paracrine interactions between prostate cancer cells and vascular endothelial cells by soy isoflavones

Angiogenesis is an essential process involved in the development and progression of prostate cancer. Vascular endothelial growth factor (VEGF) is hypothesized to be a critical regulator of angiogenesis during prostate carcinogenesis. We have reported that dietary soy products inhibit prostate tumor progression in animal models, in association with a reduction in tumor microvessel density. The goal of the present study is to investigate potential antiangiogenic mechanisms of genistein, the major soy isoflavone, using in vitro systems. Genistein (5–50 μM) significantly inhibited the growth of human umbilical vein endothelial cells (HUVECs) in control media when stimulated by supplemental VEGF or when cultured in hypoxia-exposed PC-3 prostate adenocarcinoma cell conditioned media. These in vitro studies suggest detectable inhibitory effects by 5–10 μM genistein (P<.05) with an IC50 of approximately 20 μM or less. Genistein (10–50 μM) caused significant inhibition of basal VEGF expression and hypoxia-stimulated VEGF expression in both human prostate cancer PC-3 cells and HUVECs based on semiquantitative reverse transcription–polymerase chain reaction (P<.05). In parallel, VEGF secretion by PC-3 cells quantitated by enzyme-linked immunosorbent assay was significantly (P<.05) reduced by genistein (10–50 μM). Furthermore, genistein (10–50 μM) significantly (P<.05) reduced PC-3 nuclear accumulation of hypoxia-inducible factor-1α, the principle transcription factor that regulates VEGF expression in response to hypoxia. Expression of the VEGF receptor fms-like tyrosine kinase-1, but not kinase insert domain-containing kinase, in HUVECs was also reduced (P<.05) by genistein (10–50 μM). These observations support the hypothesis that genistein may inhibit prostate tumor angiogenesis through the suppression of VEGF-mediated autocrine and paracrine signaling pathways between tumor cells and vascular endothelial cells.