EZH1/2 inhibition augments the anti-tumor effects of sorafenib in hepatocellular carcinoma.

Both EZH2 and its homolog EZH1 function as histone H3 Lysine 27 (H3K27) methyltransferases and repress the transcription of target genes. Dysregulation of H3K27 trimethylation (H3K27me3) plays an important role in the development and progression of cancers such as hepatocellular carcinoma (HCC). This study investigated the relationship between the expression of EZH1/2 and the level of H3K27me3 in HCC. Additionally, the role of EZH1/2 in cell growth, tumorigenicity, and resistance to sorafenib were also analyzed. Both the lentiviral knockdown and the pharmacological inhibition of EZH1/2 (UNC1999) diminished the level of H3K27me3 and suppressed cell growth in liver cancer cells, compared with EZH1 or EZH2 single knockdown. Although a significant association was observed between EZH2 expression and H3K27me3 levels in HCC samples, overexpression of EZH1 appeared to contribute to enhanced H3K27me3 levels in some EZH2lowH3K27me3high cases. Akt suppression following sorafenib treatment resulted in an increase of the H3K27me3 levels through a decrease in EZH2 phosphorylation at serine 21. The combined use of sorafenib and UNC1999 exhibited synergistic antitumor effects in vitro and in vivo. Combination treatment canceled the sorafenib-induced enhancement in H3K27me3 levels, indicating that activation of EZH2 function is one of the mechanisms of sorafenib-resistance in HCC. In conclusion, sorafenib plus EZH1/2 inhibitors may comprise a novel therapeutic approach in HCC.

Ex vivo expansion of human hematopoietic stem cells by a small-molecule agonist of c-MPL.

OBJECTIVE: The signaling by thrombopoietin (TPO) via its receptor, c-MPL, plays a crucial role in the maintenance of hematopoietic stem cells (HSCs). Small-molecule c-MPL agonists have recently been shown to be beneficial in the treatment of thrombocytopenia. However, their effects on HSCs have not yet been explored. In this study, we evaluated the effects of NR-101, a novel small-molecule c-MPL agonist, on the ex vivo expansion of human cord blood (hCB) HSCs. MATERIALS AND METHODS: hCB CD34(+) or CD34(+)CD38(-) hematopoietic stem and progenitor cells were cultured for 7 days in the presence of thrombopoietin (TPO) or NR-101, and then subjected to flow cytometric analyses, colony-forming cell assays, and severe combined immunodeficiency-repopulating cell assays. RESULTS: During a 7-day culture of CD34(+) or CD34(+)CD38(-) hematopoietic stem and progenitor cells, NR-101 efficiently increased their numbers, with a greater than twofold increase compared to TPO, although its effect on megakaryocytopoiesis was comparable to that of TPO. Correspondingly, severe combined immunodeficiency-repopulating cells were increased 2.9-fold during a 7-day culture with NR-101 compared to freshly isolated CD34(+) cells, and 2.3-fold compared to that with TPO. Of note, NR-101 persistently activated signal transducer and activator of transcription (STAT) 5 but not signal transducer and activator of transcription 3. Furthermore, NR-101 induced a long-term accumulation of hypoxia-inducible factor-1alpha protein and enhanced activation of its downstream target genes. CONCLUSION: This is the first time that a small-molecule c-MPL agonist has been demonstrated to promote net expansion of HSCs. NR-101 is more efficient in ex vivo expansion of HSCs than TPO. NR-101 could be a useful tool for the therapeutic manipulation of human HSCs.