Growth inhibition of androgen-responsive prostate cancer cells with brefeldin A targeting cell cycle and androgen receptor

摘要

BackgroundAndrogen ablation is one of the viable therapeutic options for patients with primary hormone (androgen)-dependent prostate cancer. However, an antibiotic brefeldin A (BFA) has been shown to exhibit the growth inhibitory effect on human cancer cells. We thus investigated if BFA might inhibit proliferation of androgen-responsive prostate cancer LNCaP cells and also explored how it would be carried out, focusing on cell cycle and androgen receptor (AR).MethodsAndrogen-mediated cellular events in LNCaP cells were induced using 5α-dihydrotestosterone (DHT) as an androgenic mediator. Effects of BFA on non-DHT-stimulated or DHT-stimulated cell growth were assessed. Its growth inhibitory mechanism(s) was further explored; performing cell cycle analysis on a flow cytometer, assessing AR activity by AR binding assay, and analyzing AR protein expression using Western blot analysis.ResultsDHT (1 nM) was capable of stimulating LNCaP cell growth by ~40% greater than non-stimulated controls, whereas BFA (30 ng/ml) completely inhibited such DHT-stimulated proliferation. Cell cycle analysis showed that this BFA-induced growth inhibition was associated with a ~75% reduction in the cell number in the S phase and a concomitant increase in the G_(1) cell number, indicating a G_(1) cell cycle arrest. This was further confirmed by the modulations of specific cell cycle regulators (CDK2, CDK4, cyclin D_(1), and p21~(WAF1)), revealed by Western blots. In addition, the growth inhibition induced by BFA was accompanied by a profound (~90%) loss in AR activity, which would be presumably attributed to the significantly reduced cellular AR protein level.ConclusionsThis study demonstrates that BFA has a potent growth inhibitory activity, capable of completely inhibiting DHT (androgen)-stimulated LNCaP proliferation. Such inhibitory action of BFA appears to target cell cycle and AR: BFA led to a G_(1) cell cycle arrest and the down-regulation of AR activity/expression, possibly accounting for its primary growth inhibitory mechanism. Thus, it is conceivable that BFA may provide a more effective therapeutic modality for patients with hormone-dependent prostate cancer.