Antiangiogenic therapy is initially effective for several solid tumors including hepatocellular carcinoma; however, they finally relapse and progress, resulting in poor prognosis. We here established in vivo drug-tolerant subclones of human hepatocellular carcinoma cells by long-term treatment with VEGF receptor (VEGFR) inhibitor and serial transplantation in immunocompromised mice (total 12 months), and then compared them with the parental cells in molecular and biological features. Gene expression profiles elucidated a G-actin monomer binding protein thymosin β 4 (Tβ4) as one of the genes enriched in the resistant cancer cells relative to the initially sensitive ones. Highlighting epigenetic alterations involved in drug resistance, we revealed that Tβ4 could be aberrantly expressed following demethylation of DNA and active modification of histone H3 at the promoter region. Ectopic overexpression of Tβ4 in hepatocellular carcinoma cells could significantly enhance sphere-forming capacities and infiltrating phenotypes in vitro, and promote growth of tumors refractory to the VEGFR multikinase inhibitor sorafenib in vivo. Clinically, sorafenib failed to improve the progression-free survival in patients with Tβ4-high hepatocellular carcinoma, indicating that Tβ4 expression could be available as a surrogate marker of susceptibility to this drug. This study suggests that Tβ4 expression triggered by epigenetic alterations could contribute to the development of resistance to antiangiogenic therapy by the acquisition of stemness, and that epigenetic control might be one of the key targets to regulate the resistance in hepatocellular carcinoma. Mol Cancer Ther; 16(6); 1155–65. ©2017 AACR.
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