Targeting cancer stem cells and YAP signaling as an effective approach to overcome sorafenib resistance in HCC

Introduction Inhibition of neo-angiogenesis is an effective treatment strategy for advanced HCC. However, development of chemoresistance is observed in the majority of patients. Evidence suggests that cancer stem cells (CSCs) may contribute to the acquisition of resistance in many solid tumors, but their exact role in this process for HCC remains to be defined.

Aim Here, we evaluate the importance of CSCs in the development of resistance and relapse formation after exposure to sorafenib in HCC and define concomitant adaptive molecular changes.

Methods Four HCC cell lines and two primary HCC isolates were exposed to sorafenib for a total of 14 days. The treatment effects on CSCs were estimated by sphere forming capacity in vitro and tumor-initiating potential in vivo, as well as the side-population (SP) approach. Expression of CSC marker EpCAM was assessed by flow cytometry. Whole transcriptome analyses were performed across cell lines and identified potential targets, which were further validated by western blot and administration of specific inhibitors in vitro, as well as in authentic HCC patients.

Results Treatment effectively reduced oncogenic properties in all investigated HCC cells. However, sustained anti-proliferative effect after treatment was observed in three cell lines, while initial treatment effect in other lines was subsequently followed by rapid cellular re-growth. Anti-oncogenic effects in sensitive cell lines were associated with significant reduction in sphere forming and tumor-initiating capacity, number of EpCAM and SP cells, while resistant cells showed transient increased in CSC properties. Adaptive molecular changes developed during acquisition of resistance involved signaling pathways associated to cell survival, proliferation and cell cycle (RAS, AKT, MYC, P53). Furthermore, resistant cell lines showed compensatory upregulation of key oncogenic molecules such as YAP. Combined treatment with sorafenib and specific YAP inhibitor showed beneficial effects in resistant cell lines. Conclusively, IHC and GSEA revealed YAP enrichment in patients resistant to sorafenib treatment and in a group with high content of CSC.

Conclusion Our model recapitulates features of drug resistance observed in human HCC patients. Resistance to sorafenib might be fueled by transient expansion of CSCs. Therefore, specific targeting of CSCs as well as compensatory signaling pathways might be an effective therapeutic strategy to overcome resistance in HCC.

Publication History

Article published online:
04 January 2021