Auriculasin sensitizes primary prostate cancer cells to TRAIL-mediated apoptosis through up-regulation of the DR5-dependent pathway

Primary prostate cancer cells frequently develop resistance toward chemotherapy as well as most chemotherapeutics have been reported to induce undesirable cytotoxicity in normal cells. In this study, we performed sensitizing activity analysis of auriculasin (AC) to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in RC-58T/h/SA#4 primary prostate cancer cells without significant cytotoxicity in RWPE-1 prostate epithelial cells. Combined treatment with AC and TRAIL at optimal concentrations resulted in tumor-specific apoptotic cell death in RC-58T/h/SA#4 cells, characterized by DNA fragmentation, accumulation of apoptotic cell population, and nuclear condensation. Compared to single treatment with AC or TRAIL, co-treatment with AC and TRAIL significantly increased expression of Bax, cleaved PARP, AIF, endo G, and cytochrome c but decreased expression of phosphorylation of AKT and mammalian target of rapamycin (mTOR), phosphoinositide 3-kinase (PI3K), Bcl-2 and caspases-9, -8, -3, and -10. The sensitizing effect of AC to TRAIL was well correlated with inhibition of death receptor 5 (DR5) CHOP, and p53 expression. Moreover, pre-treatment with a chimeric blocking antibody for DR5 effectively reduced AC-TRAIL-induced cell death and apoptosis-related protein expression. These results suggest that non-toxic concentrations of AC sensitize TRAIL-resistant primary prostate cancer cells to TRAIL-mediated apoptosis via up-regulation of DR5 and downstream signaling pathways.

Effects of auriculasin on vascular endothelial growth factor (VEGF)-induced angiogenesis via regulation of VEGF receptor 2 signaling pathways in vitro and in vivo

Angiogenesis plays an important role in various pathological conditions such as cancer via excessive delivery of oxygen and nutrients. Recent studies have demonstrated that understanding the molecular basis of natural agents in angiogenesis is critical for the development of promising cancer therapeutics. In this study, auriculasin, an active component from Flemingia philippinensis, was found to exert strong anti-angiogenesis activity. Treatment with auriculasin suppressed proliferation of human umbilical vein endothelial cells (HUVECs) by modulating expression of Bcl-2, Bcl-_XL, and vascular endothelial growth factor (VEGF). Further, auriculasin inhibited VEGF-induced chemotactic migration, invasion, and capillary-like structure formation of endothelial cells. In addition, auriculasin abrogated VEGF-induced vascular network formation around rat aortic rings as well as blocked accumulation of hemoglobin, endothelial cells and VEGF in the Matrigel plug of C57BL/6 mice. The inhibitory effect of auriculasin on angiogenesis was well correlated with inhibition of VEGF receptor 2 (VEGFR2) activation as well as phosphorylation of intracellular downstream protein kinases of VEGFR2 containing Akt, mammalian target of rapamycin (mTOR), phosphoinositide 3-kinase (PI3K), p-38, extracellular signal-related kinase (ERK), and Src. Taken together, this study reports that auriculasin potently inhibits angiogenesis by modulating VEGFR2-related signaling pathways, which further validates its great potential in clinical applications.

Auriculasin-induced ROS causes prostate cancer cell death via induction of apoptosis

Recent studies have demonstrated that natural agents targeting the accumulation of reactive oxygen species (ROS) that selectively kill, leaving normal cells undamaged, can suppress prostate cancer. Here, we show that auriculasin, derived from Flemingia philippinensis, induces significant cell death and apoptosis via ROS generation in prostate cancer cells. Auriculasin treatment resulted in selective apoptotic cell death in LNCaP prostate cancer cells, characterized by DNA fragmentation, accumulation of sub-G1 cell population, cleavage of poly (ADP-ribose) polymerase (PARP), regulation of Bax/Bcl-2 ratio, increase of cytosolic apoptosis-inducing factor (AIF) and endonuclease G (EndoG), in addition to inhibiting tumor growth in a xenograft mouse model. Interestingly, auriculasin-induced apoptosis did not result in caspase-3, -8, and -9 activations. We found that auriculasin treatment decreased phosphorylation of AKT/mTOR/p70s6k in a dose- and time-dependent manner. Further, cellular ROS levels increased in LNCaP cells treated with auriculasin and blocking ROS accumulation with ROS scavengers resulted in inhibition of auriculasin-induced PARP cleavage, AIF increase, upregulation of Bax/Bcl-2 ratio, and decrease in AKT/mTOR phosphorylation. Taken together, these data suggest that auriculasin targets ROS-mediated caspase-independent pathways and suppresses PI3K/AKT/mTOR signaling, which leads to apoptosis and decreased tumor growth.