Synergistic antitumor effect of histone deacetylase class IIa inhibitor with lenvatinib in hepatocellular carcinoma.

Background: Histone deacetylase (HDAC) class I and IIa are highly expressed in hepatocellular carcinoma (HCC) and associated with decreased survival. However, clinically used pan and class I inhibitors have serious adverse events. In this study, we assessed the antitumor effects and tolerability of class IIa HDAC inhibitor (HDACI) with lenvatinib, which is a standard therapy for HCC.

Methods And Result: Combination therapy with class IIa HDACI and lenvatinib exerted synergistic antitumor effect in human HCC cell lines. In mouse models, this therapy showed significant antitumor effects, and few adverse events occurred. In immunoblotting, the expression of fibroblast growth factor receptor 4 (FGFR4) and fibroblast growth factor 19 (FGF19) was high in cell lines that showed a high antitumor effect. In addition, class IIa HDACI administration decreased the expression of FGFR4. In the small interfering RNA (siRNA) analysis, knockdown of HDAC9, which is an isoform of HDAC class IIa, reduced the expression of FGFR4 and induced apoptosis. Immunohistochemistry of human clinical specimens showed a positivity rate of 32% for FGFR4 and 84% for HDAC9 in HCC, and all FGFR4-positive patients were HDAC9 positive.

Conclusion: Class IIa HDACI and lenvatinib combination therapy induces apoptosis by downregulating FGFR4 and blocking the FGFR signaling in FGFR4-positive HCC cell lines and has demonstrated synergistic antitumor effects and safety. This combination therapy overcomes the problems of conventional therapies and will be beneficial for FGFR4-positive HCC patients.