LB-100 Sensitizes Hepatocellular Carcinoma Cells To The Effects Of Sorafenib During Hypoxia

Background and aims:Hepatocellular Carcinoma (HCC) is a common cancer with poor prognosis. The multikinase inhibitor sorafenib is the only clinically proved systematic treatment for HCC. However, few patients respond to sorafenib. Hypoxic microenvironments contribute to sorafenib resistance. LB-100, a serine/threonine protein phosphatase 2A (PP2A) inhibitor was previously found to be a chemosensitizer in HCC. Here, we tested whether LB-100 could sensitize HCC to the effects of sorafenib.Methods:Cell viability was evaluated by using Cell Counting Kit-8. Cell apoptosis assay were performed with Annexin V-FITC Detection Kit. Relative protein expression changes were assessed by immunoblotting. PP2A activity assays were tested using a Ser/Thr phosphatase assay kit I. Xenograft models of HCC were treated with sorafenib in present or absence of LB-100.Results:Intriguingly, LB-100 enhanced the effects of sorafenib in HCC cells only during hypoxic environment. LB-100 dramatically increased intracellular p-Smad3 level, which was responsible for the effect of LB-100 as a sensitizer. LB-100 downregulated Bcl-2 expression and enhanced sorafenib-induced apoptosis in HCC cells. We further proved that PP2A mediated LB-100-induced p-Smad3 overexpression. In addition, p38 mitogen-activated protein kinase pathway was activated in hypoxic conditions, and enhanced p-Smad3-dependent Bcl-2 inhibition and consequent apoptosis.Conclusion:LB-100 sensitized HCC cells to sorafenib in hypoxic enviroments. This effect was mediated by inactivation of PP2A, resulting in enhanced level of p-Smad3. Increased p-Smad3 downregulated Bcl-2 causing increased apoptosis of HCC cells.