br Prostate cancer is the most
Prostate cancer is the most common cancer species in the world as well as a significant cause of cancer-induced death in men. Although
various chemotherapy drugs have shown transient eﬃcacy for prostate cancer, significant side eﬀects are induced by continuous utilization of cancer therapeutics (Karavelioglu et al., 2016; Frederiks et al., 2015). To avoid the side eﬀects of conventional chemotherapies for cancer treatment, development of ideal therapeutics that induce cancer-se-lective apoptosis has been carried out by numerous researchers. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a member of the TNF ligand superfamily of cytokines broadly expressed by neu-trophils, natural killer cells, and lymphocytes (Guimarães et al., 2018). TRAIL can bind to death domain-containing receptors, such as death receptor 4 (DR4) and death receptor 5 (DR5), and non-death domain-containing receptors, such as designated decoy receptor 1 (DcR1), DcR2, and DcR3 (Johnstone et al., 2008). Upon binding of TRAIL to extracellular DR4 and DR5, a cascade of downstream proteins is acti-vated after development of death-inducing signal complex (DISC) and FAS-associated protein death domain (FADD) (Bertsch et al., 2014).
∗ Corresponding author. Department of Biotechnology, Dong-A University, 37, Nakdong-daero 550 street, Saha-gu, Busan, 49315, Republic of Korea. E-mail address: [email protected] (K.-I. Seo).
Consequently, TRAIL triggers caspase-dependent and/or -independent apoptosis directly activating caspase-8 as well as truncates BH3-inter-acting domain death agonist (BID) (Woo et al., 2017).
However, certain types of cancer cck8 have demonstrated TRAIL resistance caused by mutational inactivation of pro-apoptotic genes (Bax, and Bak), overexpression of anti-apoptotic genes (Bcl-2, and Bcl-XL), and dysfunction of death receptors (DR4, and DR5) (Burris HA 3rd, 2013). This diverse range of resistance mechanisms presents new challenges for long-term tumor control. Furthermore, Kim et al. (2011) reported that primary prostate cancer cells are less sensitive to TRAIL-induced apoptosis than metastatic prostate cancer cells, and Lemke et al. (2014) reported that TRAIL can trigger non-apoptotic signaling pathways, which can induce malignancy in some TRAIL-resistant pri-mary cancer cells. To overcome TRAIL resistance in various cancer cells, numerous strategies that exert promising cancer suppressing ac-tivity have been developed and are at the pre-clinical stage. Especially, a number of researchers have shown that cancer cells with TRAIL re-sistance can be sensitized by bioactive compounds from natural pro-ducts, including curcumin (Jung et al., 2006), methylseleninic acid (Yamagucci et al., 2005), and ursolic acid (Shin and Park, 2013). Therefore, anti-cancer reports using combined treatments with non-toxic concentrations of natural compounds and TRAIL in TRAIL-re-sistant primary prostate cancer cells have drawn increasing interest.
Auriculasin (AC) is a prenylated isoflavone in various food in-gredients, such as roots of Flemingia philippinensis (Wang et al., 2013), stem bark of Erythrina senegalensis (Oh et al., 1998), and osage orange fruits (Peter and Krammer, 1998). It is known to activate the caspase-independent signaling pathway and inhibit proliferation of prostate cancer cells, confirming its strong anti-tumor activity (Wang et al., 2013; Cho et al., 2018). In our previous study, AC treatment (5 μM) significantly induced caspase-independent apoptosis in LNCaP meta-static prostate cancer cells without significant RWPE-1 prostate epi-thelial cell toxicity (Cho et al., 2018). Although AC is an interesting candidate to suppress metastatic prostate cancer due to its lack of normal cell cytotoxicity, the molecular mechanisms underlying the anti-cancer activity of AC in TRAIL-resistant primary prostate cancer cells have not been fully elucidated.
The present study investigated the anti-cancer activity of single or combined treatment with AC and TRAIL against TRAIL-resistant pri-mary prostate cancer cells as well as identified potential mechanisms. Interestingly, non-cytotoxic concentrations of AC eﬃciently induced DR5-mediated apoptosis by TRAIL in RC-58T/h/SA#4 primary prostate cancer cells. Collectively, our results elucidate the mechanisms behind the synergistic anti-cancer activities of AC and TRAIL at non-toxic concentrations in primary prostate cancer cells and could help facilitate the development of promising cancer strategies without significant side eﬀects.
2. Material and method
a C18 column using MeOHeH2O (70:30) to aﬀord (102 mg) AC that was identified on the basis of the following spectroscopic data.
Cell signaling 9901S
2.3. Cell culture and cell proliferation
The RWPE-1 (human prostate epithelial cells) was purchased from American Type Culture Collection (ATCC, Rockville, ND, USA). RC-58T/h/SA#4 cells were obtained from the Center for Prostate Disease Research (Washington, DC, USA). The cells were cultured in Keratinocyte-SFM (RWPE-1), and DMEM (RC-58T/h/SA#4) medium supplemented with 10% fetal bovine serum (FBS), penicillin (100 IU/ mL), and streptomycin (100 μg/mL) (Gibco BRL, Life Technologies, Grand Island, NY) in an incubator containing a humidified atmosphere of 5% CO2 at 37 °C.