Gasdermin B over-expression modulates HER2-targeted therapy resistance through LC3B/Rab7 interaction

Abstract

Tumor resistance to therapy is one of the most important challenges in current oncology. A clear example of this major issue is the HER2-positive tumors characterized by ERBB2 (HER2/neu) overexpression. HER2+ overexpression/ amplification occurs in several tumors, especially in breast and gastric carcinomas that show an aggressive phenotype traditionally associated to poor prognosis. In fact, despite the clinical outcome of these tumors has gradually improved, due to the development of different antiHER2 therapies, many patients will not respond to these treatments or develop acquired resistance. Several potential resistance mechanisms to these targeted therapies have been described. Among them, our laboratory established, for the first time, that the amplification/overexpression of Gasdermin B (GSDMB), which occurs in more than 60% HER2+ breast cancer patients, is a marker of poor prognosis. Moreover, our data in HER2+ tumors revealed that GSDMB overexpression correlated to distant metastasis, poor clinical outcome, and reduced response to anti-HER2 therapies. In this context, we have attempted to elucidate the molecular mechanism whereby GSDMB collaborates in the resistance to anti-HER2 therapies. To decipher the functional relevance of GSDMB in promoting resistance to HER2-targeted therapies we performed several molecular approaches (immunoblot, flow cytometry, immunoprecipitation, etc.) in different breast and gastric carcinoma cell models. Finally, we validated the efficacy of the identified targeted treatment using two complementary in vivo preclinical models (mice and zebrafish). Our results confirmed that similarly to HER2 breast tumors, GSDMB is also over-expressing in more than 50% in HER2 gastric tumors. Furthermore, this over-expression renders HER2 breast and gastric cancer cells more resistant to anti- HER2 agents by promoting protective autophagy. Consistent with this, we proved that the combination of lapatinib with the autophagy inhibitor chloroquine increases the therapeutic response specifically in GSDMB-positive tumors in vitro and in vivo. Mechanistically, we also confirmed that GSDMB forms a complex with LC3B and Rab7. Finally, we validated these results in clinical samples of HER2 breast and gastric cancers, where GSDMB/LC3B/Rab7 co- expression associates significantly with relapse. In conclusion, our data decipher the molecular mechanism that underlies the relation between Gasdermin B and pro-survival autophagy with the final goal of finding a therapy that would be effective in overcoming resistance to anti-HER2 standard therapies in HER2/GSDMB+ tumors.