Altering Chemosensitivity by Modulating Translation Elongation

BACKGROUND: The process of translation occurs at a nexus point downstream of a number of signal pathways and developmental processes. Modeling activation of the PTEN/AKT/mTOR pathway in the Emu-Myc mouse is a valuable tool to study tumor genotype/chemosensitivity relationships in vivo. In this model, blocking translation initiation with silvestrol, an inhibitor of the ribosome recruitment step has been showed to modulate the sensitivity of the tumors to the effect of standard chemotherapy. However, inhibitors of translation elongation have been tested as potential anti-cancer therapeutic agents in vitro, but have not been extensively tested in genetically well-defined mouse tumor models or for potential synergy with standard of care agents. METHODOLOGY/PRINCIPAL FINDINGS: Here, we chose four structurally different chemical inhibitors of translation elongation: homoharringtonine, bruceantin, didemnin B and cycloheximide, and tested their ability to alter the chemoresistance of Emu-myc lymphomas harbouring lesions in Pten, Tsc2, Bcl-2, or eIF4E. We show that in some genetic settings, translation elongation inhibitors are able to synergize with doxorubicin by reinstating an apoptotic program in tumor cells. We attribute this effect to a reduction in levels of pro-oncogenic or pro-survival proteins having short half-lives, like Mcl-1, cyclin D1 or c-Myc. Using lymphomas cells grown ex vivo we reproduced the synergy observed in mice between chemotherapy and elongation inhibition and show that this is reversed by blocking protein degradation with a proteasome inhibitor. CONCLUSION/SIGNIFICANCE: Our results indicate that depleting short-lived pro-survival factors by inhibiting their synthesis could achieve a therapeutic response in tumors harboring PTEN/AKT/mTOR pathway mutations

Antiviral Activity and Mode of Action of TMC647078, a Novel Nucleoside Inhibitor of the Hepatitis C Virus NS5B Polymerase▿‡

Chronic infection with hepatitis C virus (HCV) is a major global health burden and is associated with an increased risk of liver cirrhosis and hepatocellular carcinoma. Current therapy for HCV infection has limited efficacy, particularly against genotype 1 virus, and is hampered by a range of adverse effects. Therefore, there is a clear unmet medical need for efficacious and safe direct antiviral drugs for use in combination with current treatments to increase cure rates and shorten treatment times. The broad genotypic coverage achievable with nucleosides or nucleotides and the high genetic barrier to resistance of these compounds observed in vitro and in vivo suggest that this class of inhibitors could be a valuable component of future therapeutic regimens. Here, we report the in vitro inhibitory activity and mode of action of 2′-deoxy-2′-spirocyclopropylcytidine (TMC647078), a novel and potent nucleoside inhibitor of the HCV NS5B RNA-dependent RNA polymerase that causes chain termination of the nascent HCV RNA chain. In vitro combination studies with a protease inhibitor resulted in additive efficacy in the suppression of HCV RNA replication, highlighting the potential for the combination of these two classes in the treatment of chronic HCV infection. No cytotoxic effects were observed in various cell lines. Biochemical studies indicated that TMC647078 is phosphorylated mainly by deoxycytidine kinase (dCK) without inhibiting the phosphorylation of the natural substrate, and high levels of triphosphate were observed in Huh7 cells and in primary hepatocytes in vitro. TMC647078 is a potent novel nucleoside inhibitor of HCV replication with a promising in vitro virology and biology profile