Ontogeny and Vulnerabilities of Lapatinib Drug-Tolerant Persisters in HER2+ Breast Cancer

Despite advances in targeted therapeutics, resistance remains a significant clinical problem in HER2-positive (HER2+) breast cancer and can lead to recurrence, metastasis, and death. “Drug-tolerant persisters” (DTPs), a sub-population of cancer cells that survive via reversible, non-genetic mechanisms, are implicated in resistance to tyrosine kinase inhibitors (TKIs) in several cancer models, but DTPs following HER2 TKIs exposure have not been characterized extensively. We found that treatment of HER2+ breast cancer lines with lapatinib evoked DTPs with either a luminal-like or a mesenchymal-like transcriptional program and differential sensitivity to lapatinib/anti-estradiol combinations. Lentiviral barcoding and single cell RNA-sequencing showed that luminal-like HER2+ cells cycle stochastically through a “pre-DTP” state, characterized by a G-like signature, which uniquely gives rise to DTPs upon lapatinib exposure. Lapatinib-DTPs from luminal-like HER2+ cells survive via estrogen receptor-dependent induction of , thereby rewiring their PI3K/AKT/mTORC1 pathway to enable AKT-independent mTORC1 activation. These results provide new insights into DTP ontogeny and therapeutic vulnerabilities.