Anti-Cancer Effect of Cap-Translation Inhibitor 4EGI-1 in Human Glioma U87 Cells: Involvement of Mitochondrial Dysfunction and ER Stress.

BACKGROUND Cancer cells are frequently addicted to deregulated oncogenic protein translation that usually arises as a consequence of increased signaling flux from eIF4F activation. The small molecule 4EG-I, a potent inhibitor of translation initiation through disrupting eIF4E/eIF4G interaction, has been shown to exert anticancer effects in animal models of human cancers. METHODS Here, we extensively investigated the anticancer activity of 4EGI-1 in human glioma U87 cells. The anti-cancer effects of 4EGI-1 were measured by cell viability, lactate dehydrogenase (LDH) release, TUNEL staining, flow cytometry and western blot analysis in vitro, and also examined in a U87 xenograft model in vivo. The potential underlying molecular mechanisms were investigated by measuring mitochondrial function and ER stress. RESULTS We found that 4EGI-1 impaired the assembly of the eIF4F complex and decreased the expression of the eIF4E regulated proteins. The results of TUNEL staining and flow cytometry showed that 4EGI-1 treatment induced apoptotic cell death in a dose-dependent manner. Furthermore, 4EGI-1-induced apoptosis in U87 cells was associated with mitochondrial dysfunction and activation of the intrinsic mitochondrial pathway, which was dependent on the induction of the pro-apoptotic protein Bax. In addition, 4EGI-1 treatment triggered ER stress, which was evidenced by morphological changes of ER lumen and ER calcium release, as well as the dose-dependent increases in the expression of ER stress related proteins. Moreover, knockdown of the ER chaperone GRP-78 through siRNA was shown to partially reverse the 4EGI-1-induced ER stress in U87 cells. In vivo, 4EGI-1 strongly inhibited growth of U87 glioma xenografts without any apparent organ related toxicities. CONCLUSION These data indicate that the use of inhibitors that directly target the translation initiation complex eIF4F could represent a potential novel approach for human glioma therapy.