BackgroundThe 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 Eμ-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 FindingsHere, 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 Eμ-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/SignificanceOur 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.

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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.Infection with hepatitis C virus (HCV), the causative agent of hepatitis C, is an important global health burden, with an estimated 120 to 170 million persons chronically infected (7,11). Chronic HCV infection can lead to liver cirrhosis and hepatocellular carcinoma and is the leading cause of liver transplantation (10). The virus is transmitted mainly via bloodblood contact, and spontaneous virus clearance has been estimated to be achieved for 26% of infected subjects (29).HCV is a member of the Flaviviridae family of viruses in the genus Hepacivirus, comprising at least six major genotypes and multiple subtypes. The 9.6-kb positive-sense, single-stranded RNA genome of HCV encodes four structural proteins (the core protein, the envelope glycoproteins E1 and E2, and p7) and six nonstructural proteins responsible for viral replication (NS2, NS3, NS4A, NS4B, NS5A, and NS5B). The nonstructural protein NS5B is an RNA-dependent RNA polymerase (RdRp) responsible for the amplification of the HCV RNA and the assembly of the replicase complex at the endoplasmic reticulum membrane (3, 25).Currently, HCV patients are treated with a combination of weekly pegylated alpha interferon (IFN-␣) injections and twice-daily ribavirin, which has considerable tolerability issues (28) and results in a sustained viral response in only 40 to 50% of patient...