Prostate cancer (PCa) is a major cause of morbidity and mortality in men in both developed and developing countries. Androgens and the androgen receptor (AR) play predominant roles in the progression of PCa. Neoisoliquiritin (NEO) belongs to the class of licorice (Glycyrrhiza) flavonoids, which have a variety of biological activities including anti-depressant, anti-tumor-promoting, and anti-inflammation properties. Licorice root has cancer chemopreventive effects and has been given to PCa patients as an ingredient of PC-SPES, a commercially available combination of eight herbs. Therefore, we determined if NEO can suppress the proliferation of PCa cells.
We investigated whether and how NEO exerts its anti-neoplastic activity against PCa.
The Cell Counting Kit 8 and flow cytometry were used to evaluate the effects of NEO on the proliferation and cell cycle progression of AR-dependent (LNCaP) and AR-independent (PC3) PCa cells. RNA sequencing was employed to examine the genome-wide changes in responsiveness to NEO in LNCaP cells. Quantitative PCR, Western blotting, docking, chromatin immunoprecipitation, and dual-luciferase reporter assays were conducted to determine the mechanism of action of NEO and its potential cross-talk with AR. A LNCaP xenograft nude mouse model was used to determine the inhibitory effects of NEO on AR-dependent PCa tumors in vivo.
NEO inhibited LNCaP cell proliferation in vitro by inducing G0/G1 phase cell cycle arrest. Conversely, NEO treatment had no effect on PC3 cells. Transcriptomic analysis indicated that AR signaling might be the key target of NEO in preventing PCa. NEO regulated AR-mediated cell growth suppression and AR-sensitized cell cycle arrest in LNCaP cells. NEO also blocked several key steps in the AR signaling pathway, including proposed targeting to the ligand binding pocket of AR by computer modeling, modulating AR-androgen response element DNA-binding activity, inhibiting the expression and transcriptional activity of AR, and suppressing downstream AR signaling.
NEO negatively regulates AR expression and activity, thus supporting the tumor suppressive role for NEO in AR-dependent PCa.

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