Background: One practical and translational approach to control prostate cancer (PCA) and associated death could be its preventive intervention by dietary agents. Several studies in recent years have shown both preventive and interventive efficacy of inositol hexaphosphate (IP6) in different animal tumor models, however, its effects in PCA and associated mechanisms have not been assessed in detail. Since transcription factor NF-kappa B is constitutively active in advanced and androgen-independent human PCA DU145 cells, here we assessed whether IP6 inhibits this constitutively active NF-kappa B and associated upstream effectors and whether such an affect of IP6 has biological relevance in causing inhibition of proliferation and induction of apoptosis in DU145 cells.
Materials and methods: We used DU145 cells and assessed NF-kappa B activation by gel shift assay. Western immunoblot and in-beads kinase assay were used for protein levels and enzyme activity. Proliferation was measured by BrdU labeling and apoptosis by annexin V/PI staining followed by FACS analysis.
Results: Treatment of cells with 1 and 2 mM doses of IP6 resulted in a strong inhibition of NF-kappa B activation, which was consistent with a decrease in nuclear levels of NF-kappa B sub-unit proteins p65 and p50. IP6-treated cells also showed a strong inhibition in phospho-I kappa B alpha protein levels concomitant with a significant increase in total I kappa B alpha levels. This effect of IP6 also corroborated with a significant inhibition in IKK alpha kinase activity. In other studies, IP6-treated cells showed strong inhibition in cell proliferation and induction of apoptosis.
Conclusion: Our results suggest that IP6 could be a potent dietary agent in controlling the growth of advanced PCA cells and inducing their apoptotic death, in part, by its inhibitory effect on constitutively active NF-kappa B signaling pathway.