Ethanolic Extract of Polish Propolis: Chemical Composition and TRAIL-R2 Death Receptor Targeting Apoptotic Activity against Prostate Cancer Cells

Propolis possesses chemopreventive properties through direct anticancer and indirect immunomodulatory activities. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) plays a significant role in immunosurveillance and defense against cancer cells. TRAIL triggers apoptosis upon binding to TRAIL-R1 (DR4) and TRAIL-R2 (DR5) death receptors expressed on cancer cell surface. The activation of TRAIL apoptotic signaling is considered an attractive option for cancer prevention. However, as more tumor cells are reported to be resistant to TRAIL-mediated death, it is important to develop new strategies to overcome this resistance. The aim of this study was to investigate the chemical composition and proapoptotic mechanism of ethanolic extract of Polish propolis (EEP-P) against cancer cells. The identification and quantification of phenolic compounds in propolis extract were performed using HPLC-DAD and UPLC-Q-TOF-MS methods. TRAIL-resistant LNCaP prostate cancer cells were treated with EEP-P and TRAIL. Cytotoxicity was measured by MTT and LDH assays. Apoptosis was detected using annexin V-FITC staining by flow cytometry and fluorescence microscopy. Death receptors expression was analyzed using flow cytometry. Pinobanksin, chrysin, methoxyflavanone, p-coumaric acid, ferulic acid and caffeic acid were the main phenolics found in EEP-P. Propolis sensitized LNCaP cells through upregulation of TRAIL-R2. These results suggest that EEP-P supports TRAIL-mediated immunochemoprevention in prostate cancer cells.