YAP as a therapeutic target to reverse trastuzumab resistance.

Background: Trastuzumab resistance in HER2-positive cancers remains a significant clinical challenge with limited therapeutic options. Although the tumor-promoting role of the Yes-associated protein (YAP) pathway is well established, its role in trastuzumab resistance remains unclear.

Methods: We established four trastuzumab-resistant (HR) cell lines (NCI-N87HR, SNU216HR, SNU2670HR, and SNU2773HR) from HER2-positive gastric cancer and biliary tract cancer cell lines. YAP pathway activation was assessed using Phospho-RTK arrays, bulk RNA-Seq, and immunofluorescence. Antitumor effects of YAP targeting were evaluated with MTT assays, cell-cycle analysis, migration assays, RT-qPCR, ELISA, and xenograft models of SNU-2773 and SNU-2773HR cells. Immune modulation by YAP was studied through co-culture experiments with human PBMCs and cancer cells, followed by flow cytometry analysis of immune markers.

Results: Upregulation and activation of the YAP/TAZ pathway were observed in HR cells, indicated by elevated ROR2 levels and nuclear translocation of YAP. This activation, driven by YAP/TEAD-dependent Wnt5a expression, suggests a positive-feedback mechanism that amplifies YAP activity. Elevated YAP and TEAD levels were observed in patient tumor tissues during disease progression following HER2-targeted therapies. Targeting YAP disrupted its oncogenic effects and restored sensitivity to trastuzumab, increased activation of CD4⁺ and CD8⁺ T cells in PBMCs, likely via PD-L1 downregulation and enhanced immunogenic cell death. Verteporfin, a YAP-TEAD inhibitor, effectively reduced tumor growth and increased apoptosis in mouse models bearing HR tumors.

Conclusions: Targeting the ROR2-YAP/TEAD axis presents a promising therapeutic approach to overcome trastuzumab resistance in HER2-positive cancers, offering a potential strategy for enhancing treatment efficacy and improving clinical outcomes.