Breast cancer (BC) brain/central nervous system (CNS) metastasis is associated with poor survival among U.S. women, with 30-40% of these cases reported as triple receptor-negative (TN) and epidermal growth factor receptor-positive (ErbB2+) BC subtypes. Despite the progress in the diagnostic and therapeutic management of BC, there is still a significant increase in brain metastasis (BM) cases, and the survival rate among these BCBM patients is very bleak. Therefore, there is an urgent need to identify primary molecular drivers of BCBM and novel predictive biomarker(s) for the early detection of BM. In this regard, our global transcriptomic analysis showed that levels of a secretory gel-forming mucin, MUC5AC, is significantly higher in the brain tropic (BT) cells than the parental BC cells. Additionally, an in silico analysis revealed significantly higher levels of MUC5AC in the archived BCBM tissues compared to the primary tumors. Most importantly, the augmented levels of MUC5AC were detected in the serum of BCBM patients compared to non-BM BC patients. These studies strongly suggest that MUC5AC could be a potential predictive biomarker for the early detection of BCBM. Furthermore, MUC5AC knockdown (KD) resulted in reduced motility, cell adhesion, and blood-brain barrier (BBB) transmigration in BT cell lines relative to controls. Importantly, MUC5AC KD cells showed diminished BM potential in an intracardiac mouse model. Our initial mechanistic studies on the MUC5AC-mediated BM showed an important role of the CD44 and cMET pathways in BT cells. MUC5AC interacted with CD44v6, a co-receptor for cMET, and co- localized with the activated form of cMET to establish BCBM. CD44v6 and cMET have been shown to preferentially enhance BM through a feed-forward loop using hyaluronic acid and hepatocyte growth factor pathways. We also observed robust expression of MUC5AC in BT cells in the presence of microglia/astrocyte conditioned media. Targeting MUC5AC with PLB-1001 reduces MUC5AC expression in BT cells. We hypothesize that ?MUC5AC enhances BCBM through CD44v6/cMET-axis? and could thus be a useful marker to predict BCBM.
In Aim 1, we will establish MUC5AC as a novel predictive biomarker for BM in high-risk BC patients, and examine whether high MUC5AC expression in primary tumors predicts BM, and correlates with response to therapy, overall survival, and relapse.
Aim 2 studies will define the regulation of MUC5AC-mediated BM through the cMET/CD44v6/NF-?B-axis using preclinical mouse models.
In Aim 3, we will use a BBB penetrable phase 1 tested cMET inhibitor alone or in combination with cisplatin or neratinib as novel therapeutic strategy for TN and ErbB2+ brain metastatic BC. Altogether, the proposed studies will establish MUC5AC as a novel predictive biomarker for high-risk BM and will help in developing preventive strategies for BCBM, which currently has no cure.

Public Health Relevance

Brain metastases occur in almost half of the triple negative and epidermal growth factor receptor positive breast cancer patients and are strongly associated with a high mortality rate among US women patients. The present application will identify and develop a novel predictive marker to enable early detection of brain metastasis, and the conceptual advances of cMET/MUC5AC-axis in the metastatic brain microenvironment could lead to the development of effective management strategies. The current proposal will block the cMET/MUC5AC-axis as a novel targeting approach for targeting brain metastasis of TN and ErbB2-positive BC patients.

National Institute of Health (NIH)
National Cancer Institute (NCI)
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Developmental Therapeutics Study Section (DT)
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Verma, Sharad Kumar
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University of Nebraska Medical Center
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