## 4 Anti-Cancer Activities of Tanshinones
### Modulation of Androgen Receptor Pathway  
Recently, we have shown the androgen receptor (AR) pathway as a potential target of tanshinones [258]. The rationale was in part due to Danshen being used to treat acne, an androgen-related dermal lesion [259] and tanshinones' structural resemblance to androgen. Anti-androgen action was considered as one mechanism of Danshen against acne [260]. A previous study showed that tanshinones could reduce the wet weights of androgen-dependent organs (prostate and seminal vesicle) of male animals [261]. In our study, tanshinones (TI, TIIA and CT) at sub- and low micromolar concentrations suppressed cell growth and AR-dependent transcription in AR-responsive prostate cancer cells in a concentration-dependent manner [258]. TIIA and CT (\(<\)2.5 \(\upmu\)M) suppressed AR down-stream target prostate specific antigen (PSA) expression without affecting cellular AR level, whereas higher concentrations (\(>\)5 \(\upmu\)M) showed additional actions on the nuclear translocation and 26S proteasomal-dependent degradation of AR. Compared with TIIA and CT, TI showed less activity on AR pathway [258]. Similar observations were made by others, in that CT and PTS33 (a sodium salt derivative of CT with increased water-solubility for structure) at low concentrations (\(<\)2 \(\upmu\)M) inhibited AR-dependent transcription without affecting AR protein level; however, at higher concentrations (5-10 \(\upmu\)M) promoted AR degradation in LNCaP prostate cancer cells [262, 263, 264]. The inhibitory activities of CT and PTS33 at lower concentrations (\(<\)2 \(\upmu\)M) involved the disruption of AR _N-C_ terminal interaction, co-regulator recruitment and DNA binding [262, 263, 264]. Low concentrations of TIIA may share similar mechanism as low concentrations of CT and PTS33, as far as TIIA at \(<\)2.5 \(\upmu\)M suppressed AR-dependent transcription without significantly affecting AR abundance [258]. Furthermore, the 4,4-dimethyl group at ring A of TIIA seemed important for the anti-AR activity of TIIA, for the inhibitory activity was reduced when this group was removed or moved to 2- or 3-position at ring A [265]. _In vivo_, TIIA (oral daily, 25 mg/kg, four weeks) decreased AR and PSA levels in LNCaP prostate cancer xenografts, accompanied by a reduction of tumor burden [258]. CT (5 and 25 mg/kg, every other day by _i.p._ for four weeks) decreased tumor weight and the mRNA levels of AR-dependent transactional genes such as PSA and TMPRSS2 in 22 Rv1 prostate cancer xenografts, all in dose-dependent manners [262]. It is noteworthy that the mechanisms for tanshinones to inhibit AR transcriptional activity are distinct from classical AR antagonists. Classical AR antagonists including flutamide, bicalutamide and the newly-approved drug enzalutamide (MDV3100) suppress ligand-binding activation of AR via competition with androgen ligands (e.g., testosterone and dihydrotestosterone) to bind the hormone binding pocket within the _C_-terminal ligand binding domain (LBD) of AR. TIIA and CT seemed unlikely to competitively bind the hormone binding pocket, in that the substituting capability of these tanshinones was much lower than androgen ligand and bicalutamide as revealed by the AR competitor binding assays [258,262]. However, the inhibitory action of tanshinones (TIIA, CT and PTS33) indeed relied on a full-length AR, in that a truncated AR without LBD could not be regulated by tanshinones [262,263,265]. Several reports also indicated that tanshinones might suppress AR signaling via regulating androgen synthesis or metabolites. [PERSON] _et al._[266] reported that CT (27 mg/kg of CT in Tween 80/saline, oral gavage for 14 days) decreased plasma 17\(\alpha\)-hydroxy progesterone in male offspring with high circulatory androgen stimulated by prenatal androgenization. Similarly, [PERSON] _et al._[267] reported that CT (27 mg/kg, 14 day) attenuated the increased plasma androgen level in female offspring receiving prenatal androgenization, in association with reduction of androgen synthesis enzyme CYP17.