Anticancer effects of selected natural products on human colon cancer cells

Abstract

Colon cancer is one of the major causes of morbidity and mortality worldwide. Natural products have been drawing increasing attention for cancer treatment and prevention due to their chemical diversity, inherent biological activity, and ability to modulate various signal transduction pathways and cell processes. The present study aimed to evaluate the anti-colon cancer properties of a few of natural products including 6-C-(E-phenylethenyl)naringenin (6-CEPN), a phenylacetaldehyde-naringenin adduct from naringenin fortified fried beef, 8-C-(E-phenylethenyl)quercetin (8-CEPQ), a phenylacetaldehyde-quercetin adduct from onion/beef soup, brosimone I, an isoprenoid-substituted flavonoid from wood of Artocarpus heterophyllus, and Alisol B 23-acetate (AB23A), a triterpenoid from the rhizome of Alisma orientale. Molecular biological and biochemical experiments were applied to elucidate the mechanism of action of these agents with genome-wide transcriptome expression profiling by RNA-seq for further mechanistic investigation of 6-CEPN. 6-CEPN induced cell cycle G1 phase arrest and necrotic cell death in colon cancer cells. 6-CEPN–mediated gene expression pattern was extremely similar with the transcriptome response induced by a RAS inhibitor Salirasib. Subsequent RAS activity assay showed that 6-CEPN indeed strongly inhibited RAS activation. More importantly, our computational molecular docking data showed that 6-CEPN could bind to the active site of isoprenylcysteine carboxyl methyltransferase (Icmt), a critical enzyme for the activation of RAS. Icmt activity assay further showed that 6-CEPN inhibited its activity significantly. Knockdown of Icmt by siRNA attenuated 6-CEPN–mediated cell death. Thus, 6-CEPN suppressed colon cancer cells growth, at least in part, though inhibition of the Icmt/RAS signaling pathways. 8-CEPQ induced G2 phase cell cycle arrest and autophagic cell death in colon cancer cells. The treatment with 8-CEPQ induced phosphorylation of extracellular signal-regulated kinase (ERK). Inhibition of ERK phosphorylation by the mitogen-activated protein kinase kinase (MEK)/ERK inhibitor U0126 attenuated 8-CEPQ-induced autophagy and reversed 8-CEPQ-mediated cell growth inhibition. Collectively, 8-CEPQ inhibited colon cancer cell growth by inducing autophagic cell death through ERK activation. Brosimone I induced cell cycle G1 phase arrest and apoptosis in human colon cancer cells. Furthermore, the treatment with brosimone I caused reactive oxygen species (ROS) generation and blocking ROS by pretreatment with the ROS scavenger N-acetylcysteine (NAC) attenuated brosimone I-induced cytotoxic effects. Taken together, brosimone I suppressed colon cancer cells growth through ROS-mediated cell cycle G1 phase arrest and apoptosis. AB23A induced cell cycle G1 phase arrest and autophagic-dependent apoptosis in colon cancer cells. The treatment of HCT116 cells with AB23A resulted in the generation of ROS and phosphorylation of c-Jun N-terminal kinase (JNK). NAC and the JNK-specific inhibitor SP600125 attenuated AB23A-induced autophagy and apoptosis. Moreover, NAC eliminated AB23A-induced JNK phosphorylation. Thus, AB23A induced autophagic-dependent apoptotic cell death in colon cancer cells, at least in part, though accumulation of intracellular ROS and subsequent activation of JNK. To conclude, the research contributed to the knowledge of anti-colon cancer effects of natural compounds of three categories: flavonoids derivatives 6-CEPN and 8-CEPQ, flavonoid brosimone I, and triterpenoid AB23A. The findings provided us with insight into the potential of natural compounds, especially flavonoids derivatives produced in food thermal processing, for application in anti-colon cancer.