Background: Hepatocellular carcinoma (HCC), a primary neoplasm derived from hepatocytes, is the second leading cause of cancer mortality worldwide. Previous work has shown that fibroblast growth factor 19 (FGF19), an oncogenic driver, acts as a negative regulator of the therapeutic efficacy of the tyrosine kinase inhibitor sorafenib in HCC cells. The FGF19-mediated mechanism affecting sorafenib treatment, however, still remains to be resolved. Here, we hypothesize that the FGF19-FGFR4 axis may affect the effectiveness of sorafenib in the treatment of HCC.

Methods: FGF19 and FGFR4 cDNAs were cloned into a pcDNA3.1 vector and subsequently used for exogenous over-expression analyses. FGF19 knockdown cells were generated using a lentiviral-mediated short hairpin RNA (shRNA) methodology and FGFR4 knockout cells were generated using a CRISPR-Cas9 methodology. FGFR4 activation in HCC cells was inhibited by BLU9931. The effects of exogenous gene over-expression, expression knockdown and knockout, as well as drug efficacies in HCC cells, were validated using Western blotting. HCC cell proliferation was assessed using a CellTiter 96^® AQueous One Solution Cell Proliferation Assay, whereas NO levels were assessed using DAF-FM DA staining in conjunction with electrochemical biosensors.

Results: We found that FGF19, when exogenously overexpressed, results in a reduced sorafenib-induced NO generation and a decreased proliferation of HCC cells. In contrast, we found that either FGF19 silencing or knockout of its receptor FGFR4 sensitized HCC cells to sorafenib through the induction of NO generation. Concordantly, we found that inactivation of FGFR4 by BLU9931 enhanced the sensitivity of HCC cells to sorafenib.

Conclusion: From our data we conclude that the FGF19-FGFR4 axis may play a critical role in the effects elicited by sorafenib in HCC cells. Blocking the FGF19-FGFR4 axis may provide novel opportunities to improve the efficacy of sorafenib in the treatment of patients with HCC.