Abstract 351: Serum ST6GAL1 is a novel biomarker for predicting efficacy of tyrosine kinase inhibitors in hepatocellular carcinoma by detecting FGF19 expressing tumor
Authors: Myojin Yuta , Kodama Takahiro , Hikita Hayato , Sakamori Ryotaro , Takehara Tetsuo 
Published: July 2021

Abstract
Background: Several tyrosine kinase inhibitors (TKIs) have been developed for hepatocellular carcinoma (HCC). However, their efficacy is limited partly due to the diversity of its genetic drivers. In this study, we sought for HCC oncogenes involved in susceptibility of TKIs and aimed to develop their serum biomarkers.
Methods: We created a novel HCC mouse model in which tumor diversity of genetic drivers was recapitulated by transposon-based intrahepatic delivery of a pooled barcode-tagged 10-oncogene cDNA library. Tumor-bearing mice were then treated with lenvatinib (LEN), or sorafenib (SOR), or vehicle until moribund. The relative abundance of each oncogene cDNA in each tumor was quantified by a high-throughput barcode sequence. In vitro LEN susceptibility was assessed in 9 human HCC cell lines and LEN-resistant Hep3B cells (LEN-R) established by its long-term exposure. Tumor-derived secreted proteins were screened via cellular proteomic and secretomic analyses of Huh7 and Hep3B cells. Serum and tumor levels of identified proteins were examined in 62 HCC patients who underwent hepatectomy. Efficacy of biomarker candidates was assessed using pre-treated serum of 96 HCC patients who underwent TKI therapy.
Results: Mice developed multiple genetically heterogeneous liver tumors as early as 2 weeks after delivery of the pooled library. Upon TKI administration, their sequencing analysis showed that LEN selectively eliminated FGF19-expressing tumors, whereas SOR did MET- and NRAS-expressing tumors. Among 9 HCC cell lines, HuH7 and Hep3B cells showed the highest FGF19 levels and LEN susceptibility. FGF19 inhibition eliminated their susceptibility. LEN-R cells showed reduction of FGF19 levels and got resensitized to LEN by FGF19 replenishment. Thus, FGF19-driven HCC is susceptible to LEN. Proteomics identified 6 secreted proteins downregulated by FGF19 inhibition in Hep3B cells. Among them, ST6GAL1 was the most positively correlated with FGF19 in HCC cell lines and in mouse and human HCC tissues. FGF19 knockdown in Hep3B cells decreased phosphorylation of STAT3, whereas FGF19 overexpression increased its phosphorylation with ST6GAL1 upreguation. Silencing of STAT3 signal by inhibitor or siRNA significantly decreased ST6GAL1 expression. In surgically-resected HCC patients, serum ST6GAL1 levels were positively correlated with tumor site FGF19 expression and were markers for disease progression. In TKI-treated HCC patients with high baseline serum ST6GAL1 levels, LEN therapy showed significantly longer survival than SOR.
Conclusion: ST6GAL1 is a tumor-derived secreted protein downstream of FGF19 and may be a useful serum biomarker for identification of patients with FGF19-driven HCC who may benefit from LEN therapy.
Citation Format: Yuta Myojin, Takahiro Kodama, Hayato Hikita, Ryotaro Sakamori, Tetsuo Takehara. Serum ST6GAL1 is a novel biomarker for predicting efficacy of tyrosine kinase inhibitors in hepatocellular carcinoma by detecting FGF19 expressing tumor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 351.