Abstract #LB-250: Inhibition of hedgehog signaling in prostate cancer cell lines by phytoestrogens:Indications for crosstalk between estrogen- and hedgehog-signaling pathways

Many botanical compounds have been proposed to prevent cancer and some may potentially work via inhibition of the hedgehog signaling pathway. We investigated the cancer treatment and prevention abilities of apigenin, baicalein, curcumin, EGCG, genistein, quercetin, and resveratrol, both in vivo in TRAMP (TRansgenic Adenocarcinoma of the Mouse Prostate) mice, as well as in vitro in human (PC3, LNCaP) and mouse (TRAMP-C2) prostate cancer cell lines. Hypothesis: The selected botanical compounds will decrease or delay cancer incidence in vivo and inhibit prostate cancer growth in vitro . Mechanistically, those compounds will have an impact on the hedgehog (Hh) signaling pathway, acting through Estrogen Receptors. Results: All 7 compounds when fed as pure compounds or as crude plant extracts to TRAMP mice inhibit well differentiated carcinoma of the prostate, by up to 82%. They are working primarily through the estrogen receptor as demonstrated by lack of significant effects in ERKO studies. In vitro all 7 compounds also inhibit cell growth in human, as well as in mouse prostate cancer cell lines. In our experiments, all 7 botanical compounds act similarly to the hedgehog antagonist, cyclopamine, a teratogenic plant alkaloid, which has been shown to \#8220;cure\#8221; prostate cancer in a mouse xenograft model. With IC 50 values ranging from Gli1 mRNA concentration by up to 95% and down regulate Gli-reporter activity by 80%, with curcumin being the strongest inhibitor. We show that four compounds, genistein, curcumin, EGCG, and resveratrol, inhibit hedgehog signaling as monitored by real-time RT-PCR analysis of Gli1 mRNA concentration or by Gli-reporter activity. Three compounds, apigenin, baicalein, and quercetin, decreased Gli1 mRNA concentration but not Gli-reporter activity. We were also interested to investigate possible crosstalk between hedgehog and estrogen signaling since all of these botanical compounds show estrogenic activity. We show that E2, and both the ER\#945; selective compound PPT, and the ER\#946; selective DPN are able to inhibit Gli1 mRNA in TRAMP-C2. Surprisingly, the pure antiestrogen ICI is also able to inhibit Gli1 expression. CONCLUSIONS : Combined, these results indicate a potential regulatory role of estrogen-signaling on the hedgehog signaling pathway. Finally, the phytoestrogens investigated are potentially a cheap, safe and effective alternative to cyclopamine in cancer treatment trials. Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr LB-250.