Targeting tumor-initiating cells and compensatory YAP pathway to overcome sorafenib resistance in hepatocellular carcinoma

Induction of chemoresistance upon systemic therapy is frequently observed in most of HCC patients. New evidence suggests that tumor-initiating cells (TICs) may contribute to the acquisition of resistance in solid tumors, but their exact role in HCC remains to be defined. Here, we evaluate the importance of TICs in development of resistance and relapse formation after exposure to sorafenib in HCC and define adaptive molecular targets.

Primary and established HCC cell lines were exposed to sorafenib for a total of 14 days. Treatment effects on TICs were estimated by sphere forming capacity in vitro and tumor-initiating potential in vivo, as well as the side-population (SP) approach. Expression of key CSC marker EpCAM was assessed by flow cytometry. Whole transcriptome analyses were performed across the cell lines and identified potential targets, which were validated by immunohistochemistry, western blot and administration of specific inhibitors.

Treatment with sorafenib reduced oncogenic properties in all investigated HCC cells. Sustained anti-proliferative effect after treatment was observed in half of the cell lines, while initial treatment effect in other lines was followed by rapid re-growth thereby resembling the responses observed in patients. Anti-oncogenic effects in sensitive cell lines were associated with significant reduction in sphere-forming and tumor-initiating capacity, CSC marker EpCAM as well as SP cells, while resistant cell lines showed transient induction in TIC properties. Activation of adaptive molecular changes involved signaling pathways associated to cell survival, proliferation and cell cycle (RAS, IL6, MYC, E2F3). Furthermore, resistant cell lines showed compensatory upregulation of key oncogenic molecules such as EGFR and YAP. Conclusively, combined treatment including sorafenib and specific YAP inhibitor showed beneficial effects in resistant cell lines which resulted in complete response to the therapy.Our model recapitulates features of drug resistance observed in HCC patients. Resistance to sorafenib therapy might be fueled by transient expansion of TICs. Therefore, specific targeting of TICs and pro-oncogenic compensatory signaling pathways might be an effective therapeutic strategy to overcome resistance in HCC.

Publication History

Article published online:
07 September 2021