The compound 2-benzylthio-5,8-dimethoxynaphthalene-1,4-dione leads to apoptotic cell death by increasing the cellular reactive oxygen species levels in Ras-mutated liver cancer cells

The aim of the present study was to verify the pro-apoptotic anticancer potential of several 5,8-dimethoxy-1,4-phthoquinone (DMNQ) derivatives in Ras-mediated tumorigenesis. MTT assays were used to detect cellular viability and flow cytometry was performed to assess intracellular reactive oxygen species (ROS) levels and apoptosis. The expression levels of proteins were detected via western blotting. Among the 12 newly synthesized DMNQ derivatives, 2-benzylthio-5,8-dimethoxynaphthalene-1,4-dione (BZNQ; component #1) significantly reduced cell viability both in mouse NIH3T3 embryonic fibroblasts cells (NC) and H-Ras(G12V) transfected mouse NIH3T3 embryonic fibroblasts cells (NR). Moreover, BZNQ resulted in increased cytotoxic sensitivity in Ras-mutant transfected cells. Furthermore, the reactive oxygen species (ROS) levels in H-Ras(G12V) transfected HepG2 liver cancer cells (HR) were significantly higher compared with the levels in HepG2 liver cancer cells (HC) following BZNQ treatment, which further resulted in increased cellular apoptosis. Eliminating cellular ROS using an ROS scavenger N-acetyl-L-cysteine markedly reversed BZNQ-induced cellular ROS accumulation and cell apoptosis in HC and HR cells. Western blotting results revealed that BZNQ significantly downregulated H-Ras protein expression and inhibited the Ras-mediated downstream signaling pathways such as protein kinase B, extracellular signal-related kinase and glycogen synthase kinase phosphorylation and beta -catenin protein expression. These results indicated that the novel DMNQ derivative BZNQ may be a therapeutic drug for Ras-mediated liver tumorigenesis. The results of the current study suggest that BZNQ exerts its effect by downregulating H-Ras protein expression and Ras-mediated signaling pathways.