Presentation Authors: Qingfeng Yu, Christian Gratzke, Paul Kuppermann, Annika Herlemann, Alexander Tamalunas*, Yiming Wang, Beata Rutz, Anna Ciotkowska, Raphaela Waidelich, Christian G. Stief, Martin Hennenberg, Munich, Germany
Introduction: In benign prostatic hyperplasia, prostate smooth muscle contraction drives urethral obstruction, resulting in lower urinary tract symptoms. Inhibition of prostate contraction is an important strategy for medical therapy, but available options show limited efficacy. Development of future options with higher efficacy requires identification of novel targets and adequate understanding of contractile mechanisms, which are, however, still incompletely understood. Recent findings suggested a possible role of the monomeric GTPase ADP ribosylation factor 6 (ARF6) for smooth muscle contraction in the human prostate. Here, we examined effects of the ARF6 inhibitor NAV2729 on GTPase activities and contraction of human prostate tissues.
Methods: Human prostate tissues were obtained from radical prostatectomy (n=63 patients). Contraction of prostate strips were studied in an organ bath. GTPase activities were examined by pull-down assays. Relationships between ARF6 expression and degree of BPH were studied by RT-PCR and Western blot. Actin organization was studied in cultured stromal cells (WPMY-1).
Results: Electric field stimulation induced frequence-dependent contractions of prostate strips, which were significantly inhibited by NAV2729 (5 ÂµM) (p < 0.04 between NAV2729 and controls). Noradrenaline and the Î±1-agonists phenylephrine and methoxamine induced concentration-dependent contractions of human prostate strips, which were significantly inhibited by NAV2729 (p < 0.001 for noradrenaline, p < 0.002 for phenylephrine, p < 0.001 for methoxamine). RT-PCR and Western blot analyses revealed a positive correlation between prostatic ARF6 expression and content of prostate-specific antigen (PSA), suggesting upregulation of ARF6 with increasing degree of BPH (r=0.657 for mRNA, r=0.762 for protein expression). NAV2729 inhibited ARF6 activity, but not other GTPases (ARF1, RhoA, Rac1) in prostate tissues and in WPMY-1 cells, suggesting a high degree of specificity of NAV2729 for ARF6. This was paralleled by breakdown of actin organization in WPMY-1 cells.
Conclusions: NAV2729 inhibits Î±1-adrenergic smooth muscle contraction and ARF6 activity in the hyperplastic prostate. Urodynamic effects of NAV2729 appear possible in vivo. Our findings point to a role of ARF6 for prostate smooth muscle contraction. A function of ARF6 in promoting smooth muscle contraction has never been described before for any organ. ARF6 may promote Î±1-adrenergic prostate smooth muscle contraction by promoting actin polymerization.
Source of Funding: Deutsche Forschungsgemeinschaft (DFG), Chinese Scholarship Council (CSC)