ABL tyrosine kinases promote colonization and outgrowth of metastatic breast cancer cells by activating not only transcriptional, but also translational programs. Human epidermal growth factor receptor 2-positive (HER2/ERBB2) breast cancer patients often present with brain metastasis. HER2-targeted therapies have not been successful to treat brain metastases in part due to poor blood-brain barrier (BBB) penetrance and emergence of resistance. We found that treatment of preclinical mouse models with ABL kinase allosteric inhibitors improves overall animal survival and impairs HER2+ brain metastatic outgrowth in vivo (Figure 1). Human HER2+ brain metastatic HCC1954-LCC1 cells labeled with luciferase-GFP were injected intra-cranially into athymic nude mice, and mice bearing intracranial tumors were treated with vehicle or the ABL kinase allosteric inhibitor GNF5 (Figure 1A). Treatment with the ABL inhibitor decreased colonization of the brain parenchyma and increased overall survival in mice compared to vehicle (Figures 1B-C). To evaluate whether ABL kinases promote brain metastatic outgrowth in an immunocompetent mouse model, we employed the mouse HER2+ breast cancer brain metastatic cell line ErbB2-BrM2, derived from the MMTV-NeuNT mouse model. ErbB2-BrM2 cells were injected intracranially into FVB mice, and mice were treated with vehicle or the ABL allosteric inhibitor ABL001 (Figure 1D). Brain metastatic outgrowth was significantly impaired in mice treated with ABL001 compared to vehicle (Figures 1E-F). These data showed that ABL kinase allosteric inhibition impairs metastatic outgrowth and enhances survival of mice bearing brain metastatic HER2+ breast cancer cells. Mechanistically, we found that ABL kinases phosphorylate the RNA binding protein Y-box-binding protein 1 (YB-1), and that ABL kinase inhibition disrupts binding of YB-1 to the ERBB2 mRNA and impairs translation, leading to a profound decrease in HER2 protein levels (Figure 1 model diagram, right). Notably, loss of YB-1 inhibits brain metastatic outgrowth and impairs expression of HER2 and a subset of ABL-dependent brain metastatic targets. These data support a role for ABL kinases in the translational regulation of brain metastatic targets through YB-1 and uncovers a potential therapeutic target for treatment of HER2+ brain metastasis patients. Published in 2022 Cell Reports (Cell Press), 40: 111268. PMID: 36044842. PMCID: PMC9472557.