We recently reported that
gallic acid is a major active agent responsible for
grape seed extract activity in DU145 human prostate
carcinoma cells. The present study was conducted to examine its efficacy and associated mechanism.
Gallic acid treatment of DU145 cells resulted in a strong cell growth inhibition, cell cycle arrest, and apoptotic death in a dose- and time-dependent manner, together with a decrease in
cyclin-dependent kinases and
cyclins but strong induction in Cip1/p21. Additional mechanistic studies showed that
gallic acid induces an early Tyr(15) phosphorylation of cell division cycle 2 (cdc2). Further upstream,
gallic acid also induced phosphorylation of both cdc25A and cdc25C via
ataxia telangiectasia mutated (ATM)-
checkpoint kinase 2 (Chk2) activation as
a DNA damage response evidenced by increased phospho-
histone 2AX (H2A.X) that is phosphorylated by ATM in response to DNA damage. Time kinetics of ATM phosphorylation, together with those of H2A.X and Chk2, was in accordance with an inactivating phosphorylation of cdc25A and cdc25C
phosphatases and cdc2
kinase, suggesting that
gallic acid increases cdc25A/C-cdc2 phosphorylation and thereby inactivation via ATM-Chk2 pathway following DNA damage that induces cell cycle arrest.
Caffeine, an ATM/
ataxia telangiectasia-rad3-related inhibitor, reversed
gallic acid-caused ATM and H2A.X phosphorylation and cell cycle arrest, supporting the role of ATM pathway in
gallic acid-induced cell cycle arrest. Additionally,
gallic acid caused
caspase-9,
caspase-3, and
poly(ADP)ribose polymerase cleavage, but pan-
caspase inhibitor did not reverse apoptosis, suggesting an additional
caspase-independent apoptotic mechanism. Together, this is the first report identifying
gallic acid efficacy and associated mechanisms in an advanced and
androgen-independent human prostate
carcinoma DU145 cells, suggesting future in vivo efficacy studies with this agent in preclinical
prostate cancer models.