BACKGROUND. Epidemiological and laboratory studies support the hypothesis that several plant components influence prostate carcinogenesis and holds promise for disease prevention. Previously we reported that Nexrutine® (bark extract from Phellodendron amurense) inhibits proliferation of prostate cancer cells and prostate tumor development in the transgenic adenocarcinoma of mouse prostate (TRAMP) model through modulation of Akt signaling pathway. In the present investigation we conducted studies to further define the mechanism of action of Nexrutine® and to identify the active component associated with its biological activity. METHODS. Androgen-responsive, androgen-independent human prostate cancer cell lines and tissues from TRAMP mice fed Nexrutine® were used in these studies. Activity guided fractionation identified butanol fraction recapitulating the activities of Nexrutine® assessed by proliferation assays, apoptotic assays (DAPI and TUNEL staining), transient transfections, gel shift assays and Western blotting. In addition ultra-performance liquid chromatography (UPLC) of butanol fraction was used to identify active component of Nexrutine®. RESULTS. Butanol fraction recapitulated the activities of Nexrutine® in (i) inhibiting proliferation; (ii) inducing apoptosis; and (iii) modulating transcriptional activity of NFκB in prostate cancer cells. Our data also indicates that both Nexrutine® and butanol fraction modulates NFκB transcriptional activity by inhibiting IκBα phosphorylation. Expression of p65 and phosphorylated IκBα are high in tumors from TRAMP mice. In contrast dietary administration of Nexrutine® reduced expression of p65 and phosphorylated IκBα in prostate from TRAMP mice. In addition using UPLC, we have identified berberine or closely related compound in the butanol fraction. CONCLUSION. The results suggest that berberine or closely related component of butanol fraction may be responsible for the observed biological activities and induce apoptosis in prostate cancer cells by targeting critical cell survival signaling pathways both in vitro and in vivo.
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