The AR (androgen receptor) is a primary therapeutic target in androgen-dependent prostate cancer. Challenges remain for AR-independent prostate cancer as they exhibit complex cellular signaling in their progression rather than relying on the AR. Currently, prostate cancer metabolic signaling became an achievable target in prostate cancer treatment. In the present study, synthetic steroidal glycoside SBF-1, a potent anti-tumor agent known to have a strong cytotoxic effect on different kinds of cancers. We investigated SBF-1 potentials in AR-independent prostate cancer treatment and its effect on prostate cancer metabolic signaling. SBF-1 inhibited the growth of AR independent prostate cancer cell lines DU145 and PC3. Also, SBF-1 downregulates AKT/mTOR pathway and inhibited the ENO1 (alpha-enolase 1) protein and gene levels. Besides, SBF-1 blocked the interaction between mTOR and SIX1, which, for the first time shown mTOR essential for the regulation of ENO1 through binding to SIX1 (sineoculis homeobox homolog 1), accordingly, nuclear mTOR is an essential coregulator for the transcription of the ENO1 gene. Blocking the interaction between mTOR and SIX resulted in robust cell growth inhibition also the downregulation of ENO1, a consensus target in prostate cancer treatment. Accordingly, the current study suggests that SBF-1 is a leading compound in treating androgen-independent prostate cancer. Also, targeting the interaction between mTOR and SIX1 considered a better strategy in Androgen independent prostate cancer treatment
BACKGROUND AND PURPOSE Targeting AR-DBD is a potential strategy toward the treatment of CRPC, however, rational design of a small molecules targeting AR-DBD is still underdevelopment. EXPERIMENTAL APPROACH MST, ITC and other different assays has been used to confirm the binding of SBF-1 to AR, also CHIP has been used to confirm the blockade of AR binding to its target genes. The associated signaling pathway affected by SBF-1 has been identified by western blotting. Also, mutant AR-LBD and the the AR lacking DBD has led to the identification of the SBF-1 binding location in the AR. KEY RESULTS SBF-1 induced apoptosis and cell cycle arrest in both LNCaP and PC3/AR+ cell lines, also, inhibited the activation of the AR/IGF-1 and IGF1/AKT/FOXO1/PNCA pathways, which evidenced by decreased expression of p-AR, IGF-1, p-AKT, PCNA and Bcl-2. By using multiple methods, we found that SBF-1 could directly bind to AR and block the transcription of its target genes. Moreover, the interaction between SBF-1 and AR-DBD was confirmed, which overcame the re-activation of AR signaling by mutations in the AR-LBD. In the xenograft models of both ARWT and ARmutant prostate cancer, SBF-1 displayed a strong efficacy at very low doses including the inhibition of tumor growth, prolongation of survival time by inhibiting AR signaling. CONCLUSION AND IMPLICATIONS Our study here found a novel identified inhibitor of AR, SBF-1, for the first time, which is different from the current antiandrogens and may serve as a leading compound for the treatment of prostate cancer.