Isosilybin B causes androgen receptor degradation in human prostate carcinoma cells via PI3K-Akt-Mdm2-mediated pathway

Abstract

The identification and development of novel nontoxic phytochemicals that target androgen and androgen receptor (AR) signaling remains a priority for prostate cancer (PCA) control. In the present study, we assessed the antiandrogenic efficacy of isosilybin B employing human PCA LNCaP (mutated AR), 22Rv1 (mutated AR) and LAPC4 (wild-type AR) cells. Isosilybin B (10-90 lM) treatment decreased the AR and prostate specific antigen (PSA) levels in LNCaP, 22Rv1 and LAPC4 cells, but not in non-neoplastic human prostate epithelial PWR-1E cells. Isosilybin B treatment also inhibited synthetic androgen R1881-induced nuclear localization of AR, PSA expression and cell growth, and caused G 1 arrest. In mechanistic studies identifying AR degradation, isosilybin B caused increased phosphorylation of Akt (Ser-473 and Thr-308) and Mdm2 (Ser-166), which was linked with AR degradation as pretreatment with PI3K inhibitor (LY294002)-restored AR level. Further, overexpression of kinase-dead Akt largely reversed isosilybin B mediated-AR degradation suggesting a critical role of Akt in AR degradation. Antibody pull-down results also indicated that isosilybin B treatment enhances the formation of complex between Akt, Mdm2 and AR, which promotes phosphorylation-dependent AR ubiquitination and its degradation by proteasome. Together, present findings identify a novel mechanism for isosilybin B-mediated anticancer effects in human PCA cells.

Angiopreventive Efficacy of Pure Flavonolignans from Milk Thistle Extract against Prostate Cancer: Targeting VEGF-VEGFR Signaling

“…Earlier findings [20], [21], [22], [24] and the present study suggested that among the four pure flavonolignans, isosilybin B is the most effective in terms of efficacy against PCA cells but, surprisingly, it has the least efficacy in terms of its effect on HUVEC (inhibition of chemotactic motility or apoptosis induction) (Figs. 6 and 7).…”

“…Therefore, we rationalized the need to identify non-toxic natural agents with broad spectrum anti-angiogenic efficacy; and in this regard, in the present study, we focused on the anti-angiogenic efficacy of four pure diastereoisomers from Milk Thistle ( Silybum marianum ) extract, namely silybin A, silybin B, isosilybin A and isosilybin B. These diastereoisomers are flavonolignans with an identical flavonoid moiety and differ only in their configurations about the lignan moiety, and their chemical and biological properties have been detailed earlier [20], [21], [22], [23], [24]. Here, for the first time we analyzed the angiopreventive efficacy of these flavonolignans in PCA xenograft model and various ex vivo , in vivo and in vitro angiogenesis assays.…”

The role of PI3K/AKT-related PIP5K1α and the discovery of its selective inhibitor for treatment of advanced prostate cancer

“…22Rv1 cells, although less sensitive to ISA-2011B, also displayed reduced proliferation after ISA-2011B treatment. It is known that 22Rv1 cells also have relatively high levels of pAKT and AR (37). Given that amplification of AKT2 or mutations in PIK3CA, in addition to PTEN mutation, are all responsible for activation of PI3K pathway (15,38,39), our data suggest that ISA-2011B exerts its on-target effect on PCa cells by targeting pathways related to AKT/AR, rather than a toxic effect.…”

Estrogen Receptor β in Melanoma: From Molecular Insights to Potential Clinical Utility

“…It must be underlined that silymarin can also bind the androgen receptor, and it activates the same molecular pathways involved in the ERβ signaling, specifically in prostate cancer cells (205, 206). However, the expression and the possible role of this receptor in skin carcinogenesis is still a matter of debate (60, 107, 207, 208).…”