BRD8 is a therapeutic vulnerability for overcoming resistance to dual ER/HER2 blockade therapy in HR+/HER2+ breast cancer [bulkRNA-seq]

However, how anti-HER2 agents activate ER as a mechanism of resistance remains unknown. Using single-cell RNA sequencing, we identified Bromodomain Containing Protein 8 (BRD8) as a major mediator of ER activation in response to neratinib, a HER2 tyrosine kinase inhibitor.

BRD8 expression was rapidly induced by various anti-HER2 agents (neratinib, lapatinib and trastuzumab) and its expression positively correlates with ER. BRD8 regulates both ER-dependent and -independent growth promoting pathways. Moreover, BRD8 ablation re-sensitizes fulvestrant- or neratinib-resistant HR+/HER2+ cells to neratinib, suggesting that combinatorial targeting of BRD8 and HER2 attenuates signal crosstalk and possibly overcomes treatment resistance to dual anti-ER/HER2 blockade therapy.