Pao Pereira Extract Suppresses Castration-Resistant Prostate Cancer Cell Growth, Survival, and Invasion Through Inhibition of NFκB Signaling

Pao extract, derived from bark of Amazonian tree Pao Pereira, is commonly used in South American medicine. A recent study showed that Pao extract repressed androgen-dependent LNCaP prostate cancer cell growth. We hypothesize that Pao extract asserts its anticancer effects on metastatic castration-resistant prostate cancer (CRPC) cells. Pao extract suppressed CRPC PC3 cell growth in a dose- and time-dependent manner, through induction of apoptosis and cell cycle arrest. Pao extract treatment induced cell cycle inhibitors, p21 and p27, and repressed PCNA, Cyclin A and Cyclin D1. Furthermore, Pao extract also induced the upregulation of pro-apoptotic Bax, reduction of anti-apoptotic Bcl-2, Bcl-x(L), and XIAP expression, which were associated with the cleavage of PARP protein. Moreover, Pao extract treatment blocked PC3 cell migration and invasion. Mechanistically, Pao extract suppressed phosphorylation levels of AKT and NFB/p65, NFB DNA binding activity, and luciferase reporter activity. Pao inhibited TNF-induced relocation of NFB/p65 to the nucleus, NFB/p65 transcription activity, and MMP9 activity as shown by zymography. Consistently, NFB/p65 downstream targets involved in proliferation (Cyclin D1), survival (Bcl-2, Bcl-x(L), and XIAP), and metastasis (VEGFa, MMP9, and GRO/CXCL1) were also downregulated by Pao extract. Finally, forced expression of NFB/p65 reversed the growth inhibitory effect of Pao extract. Overall, Pao extract induced cell growth arrest, apoptosis, partially through inhibiting NFB activation in prostate cancer cells. These data suggest that Pao extract may be beneficial for protection against CRPC.