Figure 10. Diastereoisomers exhibit anti-angiogenic effects through targeting signaling molecules in both prostate cancer cells and endothelial cells. Silybin A, silybin B, isosilybin A and isosilybin B target angiogenesis in prostate tumors through targeting signaling molecules in PCA cells as well as in endothelial cells, the important component of PCA microenvironment. doi:10.1371/journal.pone.0034630.g010 long retention time in most reverse-phase HPLC systems. The pre- clinical or future clinical use of these pure compounds needed advancement in their isolation; therefore, we developed a hybrid chromatographic/precipitative technique for gram scale purifica- tion of flavonolignan diastereoisomers from Milk Thistle extract [26]. We believe that this is a major advancement towards the future translational significance of these pure flavonolignans. References 1. Jemal A, Siegel R, Xu J, Ward E (2010) Cancer statistics, 2010. CA Cancer J Clin 60: 277–300. 2. 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Prostate Cancer Angioprevention by Flavonolignans The results from the present study adequately proved that the pure diastereoisomers from Milk Thistle have strong angiopre- ventive efficacy through targeting the pro-angiogenic signaling in PCA cells as well as in endothelial cells; the important component of PCA microenvironment (Fig. 10). Furthermore, based upon the overall in vitro and in vivo analyses, it is also clear that the comparative efficacy of isosilybin B occupies two opposite ends in terms of its effect on PCA cells and endothelial cells. Specifically, it is the lead agent in terms of its efficacy against PCA cells but it is the least effective agent against endothelial cells. On the contrary, silybin A appears to be the most promising agent in terms of its effects on endothelial cells. Therefore, it is prudent to suggest that a defined mixture of silybin A and isosilybin B should be tested, particularly in vivo, with an expectation of these two compounds acting in concert to exert maximum benefits via targeting both the tumor and the tumor microenvironment components. In summary, the present study, for the first time, report the anti- cancer efficacy of four flavonolignans from Milk Thistle extract in an in vivo system of advanced stage human PCA. These results further suggest the stereochemistry based differential efficacy of these flavonolignans towards cancer and endothelial cells. Furthermore, these results confirm the non-toxicity as well as PCA specific anti-angiogenic effects of the pure diastereoisomers, which suggest their usefulness in PCA angioprevention. Acknowledgments We thank Tyler N. Graf, M.S. for purification and preparation of the flavonolignans used in these studies. Author Contributions Conceived and designed the experiments: GD RA SCG. 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