Inhibition of eukaryotic initiation factor 4E phosphorylation by cercosporamide selectively suppresses angiogenesis, growth and survival of human hepatocellular carcinoma.

Mnk kinase is required for the phosphorylation and activation of the eukaryotic initiation factor 4E (eIF4E), which regulates translation of proteins involve in important aspects of hepatocellular carcinoma (HCC). Here we investigated whether an antifungal agent, cercosporamide, which had been recently identified as a potent Mnk inhibitor, is active against HCC and angiogenesis. We showed that cercosporamide significantly inhibited growth and induced caspase-dependent apoptosis on numerous HCC cell lines, while sparing normal liver cells. In addition, cercosporamide impaired HCC angiogenesis via inhibiting HCC-endothelial cells (HCC-EC) capillary network formation, migration, proliferation and survival. Importantly, cercosporamide sensitized HCC cells to cisplatin in in vitro cell culture and in vivo HCC xenograft mouse model. Cercosporamide blocked the phosphorylation of eIF4E but not Erk or p38 in a dose- and time-dependent manner in HCC and HCC-EC cells, suggesting that suppression of eIF4E phosphorylation was the result of inhibition of Mnk but not Mnk upstream pathways. Overexpression of constitutively active eIF4E (S209D) but not the nonphosphorylatable eIF4E (S209A) abolished the inhibitory effects of cercosporamide in HepG2 cells. Altogether, our work demonstrates that cercosporamide acts as a Mnk inhibitor through blockage of eIF4E phosphorylation and selectively exhibits anti-HCC activities. Our work suggests that targeting MNK-eIF4E pathway represents a therapeutic strategy to overcome chemo-resistance for HCC treatment.