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GCP‐mediated growth inhibition and apoptosis of prostate cancer cells via androgen receptor‐dependent and ‐independent mechanisms
Author(s) -
Tepper Clifford G.,
Vinall Ruth L.,
Wee Christopher B.,
Xue Lingru,
Shi XuBao,
Burich Rebekah,
Mack Philip C.,
de Vere White Ralph W.
Publication year - 2007
Publication title -
the prostate
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.295
H-Index - 123
eISSN - 1097-0045
pISSN - 0270-4137
DOI - 10.1002/pros.20548
Subject(s) - lncap , androgen receptor , genistein , cancer research , androgen , protein kinase b , prostate cancer , cell growth , biology , pi3k/akt/mtor pathway , endocrinology , signal transduction , medicine , microbiology and biotechnology , cancer , biochemistry , hormone
BACKGROUND Genistein combined polysaccharide (GCP) is a nutritional supplement that can inhibit prostate cancer growth experimentally and clinically. It is composed predominantly of the isoflavones genistein, daidzein, and glycitein, which have anti‐cancer properties. Although genistein is well studied, the properties of GCP are not well defined. The goal of this work was to better characterize the signaling pathways impacted by GCP in an effort to optimize its efficacy. METHODS Cell growth and apoptosis were evaluated by MTS proliferation, caspase‐based assays, and flow cytometry. Modulation of androgen receptor (AR) levels and activation status of signaling molecules were monitored by immunoblot analysis. AR function was measured by evaluating prostate‐specific antigen (PSA) message and protein levels and by reporter assays. RESULTS GCP inhibited proliferation of androgen‐dependent LNCaP and androgen‐independent LNCaP‐ p53 GOF and 22R v1 cell lines in a dose‐dependent manner and cells were more responsive in the presence of androgen. GCP markedly suppressed mTOR‐p70S6K signaling while Akt and p53 were only modestly modulated. GCP significantly attenuated androgen signaling as evidenced by diminished AR protein levels and a consequent reduction in transcriptional activity and PSA expression. AR expression was enhanced by de‐repression of translation with inhibitors of PI3K‐Akt‐mTOR signaling and by inhibition of proteasome‐dependent degradation. Neither inhibitor could counteract GCP‐mediated AR downregulation, suggesting the involvement of a mechanism(s) independent of these pathways. CONCLUSIONS Our results suggest that GCP mediates growth inhibition and apoptosis through multiple mechanisms including (1) molecular mimicry of androgen ablation (via AR downregulation) and (2) by providing an AR‐independent, pro‐apoptotic signal (mTOR inhibition). Prostate 67: 521–535, 2007. © 2007 Wiley‐Liss, Inc.