LB-100 sensitizes hepatocellular carcinoma cells to the effects of sorafenib during hypoxia by activation of Smad3 phosphorylation
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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. Intriguingly, LB-100 enhanced the effects of sorafenib in HCC cells only during hypoxic environments. 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. In conclusion, LB-100 sensitized HCC cells to sorafenib in hypoxic environments. 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.
Keywordsp-Smad3 Apoptosis Drug resistance PP2A p38 MAPK
We thank Lixte Biotechnology Holdings, Inc. (East Setauket, NY, USA) for the gift of LB-100. This work was financially supported by the National Natural Science Foundation of China (81401954), Science and Technology Program of Traditional Medicine of Zhejiang Province (2014ZZ007), and Medical Science and Technology Program of Zhejiang Province, China (2015KYA114 and 2013KYB264). We appreciate Mr. Wang Yi and Mr. Qin Hao (The Second Affiliated Hospital, Zhejiang University School of Medicine, China) for their help in certain experiments.
Liang TB, Bai XL, and Zhang Q conceived the idea. Fu QH, Zhang Q, Zhang JY, Sun X, Lou Y, Li GG, and Chen ZL performed the experiments. Fu QH and Zhang Q analyzed the data. Fu QH and Zhang Q wrote the manuscript. All authors approved the manuscript.
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Statement on the welfare of animals
All applicable international, national, and institutional guidelines for the care and use of animals have been followed.
All procedures performed in studies involving animals were in accordance with the ethical standards of the second affiliated hospital, Zhejiang University School of Medicine.