Liver Endothelium Microenvironment Promotes HER3-mediated Cell Growth in Pancreatic ductal adenocarcinoma

[~]90% metastatic pancreatic ductal adenocarcinoma (mPDAC) occurs in the liver, and the 5-year survival rate for patients with mPDAC is only at 3%. We previously reported that liver endothelial cells (ECs) secreted soluble factors to promote colorectal cancer cell survival in a paracrine fashion. However, the effects of liver ECs on mPDAC have not been elucidated. In this study, we used primary ECs from non-neoplastic liver tissues. We treated PDAC cells with conditioned medium (CM) from liver ECs, with CM from PDAC as controls, and determined that liver EC-secreted factors increased PDAC cell growth. Using an unbiased receptor tyrosine kinase array, we identified human epidermal growth factor receptor 3 (HER3, also known as ErbB3) as a key mediator in EC-induced growth in PDAC cells that have HER3 expression (HER3 +ve). We found that EC-secreted neuregulins activated the HER3-AKT signaling axis, and that depleting neuregulins from EC CM or blocking HER3 with an antibody, seribantumab, attenuated EC-induced proliferation in HER3 +ve PDAC cells, but not in cells without HER3 expression. Furthermore, we determined that EC CM increased PDAC xenograft growth in vivo, and that seribantumab blocked EC-induced growth in xenografts with HER3 expression. These findings elucidated a paracrine role of liver ECs in promoting PDAC cell growth, and identified the HER3-AKT axis as a key mediator in EC-induced functions in PDAC cells with HER3 expression. Implicationsover 70% mPDAC express HER3. This study suggests the potential of using HER3-targeted therapies for treating patients with HER3 +ve mPDAC.