(1312-A) High-throughput screening using a novel HER2-positive brain metastatic breast cancer model identifies the pan-ErbB inhibitor poziotinib
Monday, February 5, 2024
12:00 PM – 1:00 PM EST
Location: Exhibit Halls AB
Abstract: Breast-to-brain metastasis occurrence is highest for patients with aggressive cancer subtypes such as HER2-positive breast cancer. Metastatic brain cancer may be treated with surgery and/or stereotactic radiotherapy for solitary metastasis, but the use of these therapies has declined over recent years because of negative effects on cognition. Many chemotherapeutic agents that work on the primary breast tumor are excluded from consideration for brain metastasis as they do not cross the blood brain barrier, highlighting a need for CNS-penetrant therapeutics. Towards identifying such agents, a novel patient-derived luminal-B HER2-positive cancer model was developed, known as BCBM94, which represents one of very few hematogenic luminal-B HER2-positive breast-to-brain metastasis models available for pre-clinical studies. To identify small molecules that can selectively kill BCBM94 cells, we optimized growth in 1536-well plates and screened a collection of over 6,000 compounds (annotated compounds, approved drugs, and investigational oncology agents) using a CellTiter-Glo viability assay. A human mammary epithelial cell line HME1 was used as a counterscreen to remove non-selective cytotoxic agents. Target genes identified from BCBM94 selective compounds were enriched in ErbB receptor tyrosine kinases. We then assembled a set of 50 ErbB inhibitors with varying modes of action (covalent versus reversible), ErbB-selectivity (ErbB1-4), and predicted CNS-penetrance and tested them in the BCBM94 model. Poziotinib, a covalent pan-ErbB inhibitor showed the most selective activity with an AC50 of ~6 nM. Further testing showed that poziotinib was also active in another luminal-B HER2-positive cell line BT474 with similar AC50 to BCBM94, but inactive in the triple-negative breast cancer cell line MDA-MB-231. Additionally, a neuregulin-1 dependent mechanism by which metastatic breast cancer cells can subvert the efficacy of lapatinib, a clinically used ErbB2 inhibitor, was not observed for poziotinib. Pharmacokinetics studies showed that brain concentration of poziotinib in mice was well above the in vitro EC50 for 24 hours after a 5 mg/kg subcutaneous administration, indicating good brain penetration of the compound and feasibility to move it forward to in vivo studies.