Influence of gallate esterification on the activity of procyanidin B2 in androgen-dependent human prostate carcinoma LNCaP cells

Purpose: Present study assessed the influence of gallate esterification on the anti-cancer activity of procyanidin B2 (B2) in androgen-dependent human prostate carcinoma LNCaP cells employing B2-3,3'-di-O-gallate (B2-G(2)), two mono-gallate esters B2-3-O-gallate (B2-3G) and B2-3'-O-gallate (B2-3'G) and the parent compound B2, all isolated from grape seed extract (GSE).

Materials and methods: Study compounds were isolated from GSE by several chromatographic steps and structures determined by a combination of enzymatic hydrolysis, mass spectrometry and comparisons with standards. Cells, treated with these compounds, were assessed for viability and Apoptosis and examined by western blotting.

Results: Gallate esters B2-G(2), B2-3G and B2-3'G significantly decreased LNCaP cell viability; however, B2 and gallic acid were ineffective. Furthermore, only B2-G(2) also significantly decreased cell growth. Decreases in cell viability were largely due to Apoptosis induction with B2-G(2) and B2-3'G exhibiting comparable effects, whereas B2-3G was less effective. In mechanistic studies, B2-G(2) and B2-3'G treatments caused caspases-9 and -3 and PARP cleavage, and down-regulated Bcl-2, Bcl-xL and Androgen Receptor levels.

Conclusion: Together, our findings demonstrate anti-PCA efficacy of B2-G(2) and suggest that a gallate ester moiety at 3' position of procyanidin B2 contributes more extensively toward the biological activity of the di-gallate ester than esterification of position 3.