40P - YAP1 promotes sorafenib resistance by activation of TGFβ signaling pathway

Background

Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related mortality globally. Sorafenib remains the globally accepted systemic first-line treatment for advanced HCC patients. Due to the heterogeneity of HCC, patients usually develop drug resistance within six months. The underlying mechanisms of sorafenib resistance in HCC remain to be fully elucidated.

Methods

We established sorafenib-resistant HCC cell lines and characterized them using functional and microarray-based approaches. The subcellular localization of target proteins was determined by western blot analysis. Additionally, we generated an inducible system of constitutively active YAP1 mutant (YAP1-8SA) in Huh7. Furthermore, we utilized immunocompetent murine HCC model to evaluate the efficacy of galunisertib, sorafenib or their combination treatment.

Results

Sorafenib-resistant HCC cells exhibited higher IC50 values for sorafenib. Both Huh7 parental (Huh7-P) and sorafenib-resistant cells (Huh7-sorR) were selected for further analysis. Huh7-sorR demonstrated characteristics of EMT and de-differentiation, and both YAP1 and TGFβ1 signaling pathway were activated. Upon TGFβ1 stimulation in Huh7-P, the activation of YAP1 signaling pathway was observed. Similarly, constitutive YAP1 activation in Huh7-YAP8SA increased the protein level of TGFβ1. These results suggesting a positive feedback loop between YAP1 and TGFβ signaling pathways. The treatment of galunisertib suppressed the YAP1 signaling pathway in Huh7-sorR. Furthermore, the combination treatment of galunisertib and sorafenib greatly suppressed the growth of Huh7-sorR cells. In the in vivo study, the combination treatment of galunisertib and sorafenib also demonstrated prolonged overall survival.

Conclusions

We have identified YAP1-TGFβ1 axis as the underlying mechanism driving the sorafenib resistance in HCC. Our results showed that galunisertib could sensitize the resistant cells to sorafenib, by blocking the canonical TGFβ signaling pathway and its positive feedback to YAP pathway. TGFβ1 has been shown to be a potential biomarker for drug resistance and combination of sorafenib and galunisertib treatment would be an effective treatment regime for HCC recurrence patients.

Editorial acknowledgement

Clinical trial identification

Legal entity responsible for the study

National Cancer Centre Singapore.

Funding

National Medical Research Council.

Disclosure

All authors have declared no conflicts of interest.