Both in vitro and in orthotopic tumor cell xenografts in vivo, and support further development of this agent as a PF-04217903 therapeutic for HCC. Hepatocellular canceris a globally prevalent malignancy for which effective therapies are needed. These studies identify that silvestrol is effective in inhibiting tumor growth in HCC cells both in vitro and in vivo, and thereby provide evidence of a novel therapeutic approach to these cancers. Silvestrol has been shown to inhibit translation, and therapeutic strategies targeting inhibition of protein translation are garnering attention as novel therapeutic agents for diverse human cancers. Thus, our results provide preclinical data that demonstrate the efficacy of targeting translation as a therapeutic strategy for HCC. HCC GDC-0879 frequently arises in the context of chronic hepatic injury resulting in hepatic fibrosis and cirrhosis. The presence of hepatic fibrosis has the potential to impact tumor cell growth and therapeutic impact of anticancer agents. In order to adequately mimic the tumoral microenvironment within which HCC occurs, we developed a disease relevant model of orthotopic HCC tumor cell xenografts in a fibrotic liver to examine the potential in vivo anti-tumor effects of silvestrol. An additional benefit of this model is the ability to examine the effect of anti-cancer therapies under both fibrotic and nonfibrotic conditions, thereby incorporating an assessment of tumor microenvironmental influences on tumor growth as well as anticancer effects. The impact of fibrosis on tumor latency and tumor growth was surprising. While we expected that fibrosis would enhance tumor formation, we were surprised to note that tumor growth was also modulated. Moreover, the differential effects on response to therapy should prompt reevaluation of preclinical data that are derived from in vivo models that do not encompass the fibrotic milieu within which HCC arise. Translation of most mRNAs can be regulated during the ratelimiting stage of initiation. Silvestrol can engage the eukaryotic initiation factor4A and inhibit the initiation of translation by depletion of eIF4A from the eIF4F complex. Importantly, eIF4E is over-expressed in HCC. When eIF4F activity is limiting, mRNAs with a short unstructured 5��-UTR can be translated whereas mRNA with long, G+C rich, highly structured 5��-UTRs are less efficiently translated because efficient ribosome loading is prevented by their complex structure. Thus, the translation of highly structured, malignancy-related mRNAs is sensitive and dependent upon eIF4F for translation. A selective reduction in the translation of mRNAs that contain complex structured 5�� untranslated regions could result from exposure to silvestrol and potentially contribute to its therapeutic efficacy. Over-expression of eIF4E occurs in HCC and in transgenic models has been shown to promote HCC. However, validation of this mechanism as a contributor of the anticancer effects of silvestrol would require selective modulation of eIF4A using other therapeutic strategies, and a systematic analysis of mRNAs that are deregulated by these interventions. Further analysis of selectively translated mRNAs modulated by silvestrol that encode proteins that are engaged in tumor cell survival and growth and tumor cell responses to the tumor microenvironment or to cellular stresses such as chemotherapy may be useful to understand specific pathways involved in HCC progression. Recent studies have suggested 
that modulation of protein translation with depletion of survival factors with short half-life can enhance therapeutic responses. Our findings are consistent with these reports by indicating short term effects of silvestrol on Mcl-1 expression and cell apoptosis.