Abstract 386: Metastatic models of resistance to next generation tyrosine kinase inhibitors (TKIs) in HER2-positive breast cancer (BC)

Abstract HER2+ BC is an aggressive subtype with increased metastatic tropism towards brain. Small molecule anti-HER TKIs are still a key treatment choice in this setting owing to their competency to cross the blood brain barrier. Despite the efficacy, resistance to HER2-targeted agents often arises either due to compensatory signaling from other HER receptors or due to dysregulation in the downstream signaling pathway. We have previously shown that the mechanism of resistance to each TKI differs based on its HER receptor specificity profile. Here, we sought to evaluate the aggressiveness and metastatic ability of our HER2+ cell models with acquired resistance to different clinically relevant anti-HER TKIs. Dual GFP-Luc tagged HER2+ BT474 naïve parental cells and their acquired lapatinib (LapR), neratinib (NeraR), and tucatinib (TucaR) resistant (Res) derivatives harboring acquired HER2 L755S, HER2 L755S and a pathogenic PIK3CA mutation, or EGFR amplification, respectively were used. We have previously shown that while the LapR and NeraR cells are cross-Res to Tuca, the LapR and TucaR cells remain sensitive to Nera. Changes in cell growth and migration were evaluated by methylene blue or Incucyte wound healing assays, respectively. The metastatic phenotype of parental and the acquired Res models was assessed by intracardiac injection in NSG mice and metastasis was monitored by bioluminescence imaging. Metastatic lesions from different organs/sites were harvested to establish GFP-positive in vitro cell cultures. Our recent data showed that the LapR, NeraR, and TucaR derivatives are significantly more migratory compared to naïve parental cells suggesting their enhanced metastatic potential. Indeed, our in vivo studies revealed that all the Res derivatives and parental cells were highly metastatic to the brain, proving the well-established notion that HER2+ BC cells are brain tropic. Further, the involvement of ovary, lung, and liver, among others, were observed as additional common metastatic sites. We have now successfully established in vitro cultures of harvested metastatic lesions from different sites for each cell model. Growth assays using the cells established from LapR ovary metastatic lesions (LapR/OvMet) revealed that they are indeed Res to Lap, while importantly, consistent with the drug sensitivity profile of the original LapR 2D cells, the LapR/OvMet line was highly sensitive to Nera but cross-Res to Tuca. Additional studies to investigate the organ-specific metastatic tropism of each acquired resistant model are currently ongoing. Molecular and functional characterization of our established metastatic cultures will guide future in vivo studies, including testing the efficacy of new targeted treatment regimens to treat organ-specific metastasis, and expanding such studies to additional relevant cell and patient-derived xenograft/organoid models. Citation Format: Fu-Tien Liao, Lanfang Qin, Martin J. Shea, Igor Bado, Yi-Hsuan Wu, Ling Wu, Yang Gao, Sarmistha Nanda, Tia Gordon, Chia Chia Liu, Xiang H.-F. Zhang, C. Kent Osborne, Mothaffar F. Rimawi, Jamunarani Veeraraghavan, Rachel Schiff. Metastatic models of resistance to next generation tyrosine kinase inhibitors (TKIs) in HER2-positive breast cancer (BC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 386.