Acquired resistance with epigenetic alterations under long-term anti-angiogenic therapy for hepatocellular carcinoma. Homo sapiens

Anti-angiogenic therapy is initially effective for several solid tumors including hepatocellular carcinoma (HCC); however, they finally relapse and progress, resulting in poor prognosis. We here established in vivo drug-tolerant subclones of human HCC cells by long-term treatment with vascular endothelial growth factor 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 HCC cells could significantly enhance sphere-forming capacities and infiltrating phenotypes in vitro, and promote growth of tumors refractory to the VEGFR mutltikinase inhibitor sorafenib in vivo. Clinically, sorafenib failed to improve the progression-free survival in patients with Tβ4-high HCC, 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 anti-angiogenic therapy by the acquisition of stemness, and that epigenetic control might be one of the key targets to regulate the resistance in HCC. Overall design: The human HCC cell line HuH7 was obtained from the Human Science Research Resources Bank (Osaka, Japan). Microarray analysis was performed to compare gene expression patterns between the parental (HuH7-F0) and drug-resistant cells (HuH7-F6 and -F12). The expression levels of 119 genes were more than four-fold upregulated in HuH7-F6 cells while those of 2199 genes in HuH7-F12.