Evaluation of Humulus lupulus (hops) compound anti-proliferative properties with mechanisms in human colorectal cancer cells

Colorectal cancer (CRC) is the third most diagnosed cancer in the U.S and is highly associated with daily diet and eating patterns. A plant-based diet rich in phytochemicals is known to be protective against the initiation and progression of CRC. The hop plant, a key ingredient in beer, contains diverse bioactive compounds that possess biological benefits in tumorigenesis. Xanthohumol (XN) is the most abundant prenylated flavonoid; several derivatives including isoxanthohumol (IXN), 8-prenylnaringenin (8-PN), and tetrahydroxanthohumol (TXN) have also been identified. The current study aimed to test the effect of these compounds in suppressing proliferation and to elucidate their anti-cancer mechanisms using human adenocarcinoma CRC cells. The results indicated all four hop compounds to significantly suppress the proliferation of multiple CRC cell lines. We selected TXN and XN for further study. Flow cytometry analysis indicated both to lead to significant induction of S-phase and G2/M-phase arrest. An apoptotic assay showed increases of early and late apoptosis. Western blot data indicated significant decreases of cyclin A and CDK2, increase of poly (ADP-ribose) polymerase (PARP) cleavage, and increase of CCAAT-enhancer-binding protein homologous protein (CHOP), activating transcription factor 4 (ATF4), and inositol requiring enzyme 1 alpha (IRE1 alpha). In addition, dose-dependent increases were observed in intracellular reactive oxygen species (ROS), mitochondrial dysfunction, and LC3II/LC3I ratio. Taken together, our study proposes an anti-cancer mechanism of TXN and XN that involves induction of ROS release, ER stress, mitochondrial dysfunction, apoptosis, and autophagy in human CRC cells.