PROJECT SUMMARY/ABSTRACT Metastasis, the dissemination of cancer from the primary tumor to distant organs, accounts for ~90% of cancer deaths and is a significant source of morbidity. HER2+ breast cancer patients experience elevated rates of brain metastasis despite excellent primary tumor control. The cytokines IL4 and IL13 are overexpressed by a variety of human solid tumors. Both are associated with invasive and metastatic phenotypes; IL13 is additionally consequential in primary brain tumors. These cytokines signal through type I (IL4 only) and type II (IL4/IL13) IL4 receptors (IL4R). Our laboratory has shown in published work that genetic loss of IL4R signaling in tumor cells attenuates lung and liver metastasis in a mouse model. Additionally, we recently identified a role for type II IL4R signaling in modulating glycosylation (the addition of sugar epitopes onto proteins and lipids) in tumor cells. TCGA analysis demonstrates that HER2+ breast cancer has elevated levels of type II IL4R, raising the question of whether type II IL4R signaling may be particularly important for the biology of this disease subtype. We hypothesize that type II IL4R signaling influences HER2+ breast cancer brain metastasis at least in part via modulation of glycosylation. Aim 1 addresses metastatic progression and its possible dependency on type II IL4R using mouse models of HER2+ breast cancer, novel IL4 blockade agents, and a cutting-edge technique called CLARITY which is capable of high-resolution, whole-organ images. Aim 2 probes the influence of IL4R signaling on early metastatic behavior, including transmigration across the blood-brain barrier, tumor growth kinetics, and capacity for vascular co-option and cell-cell adhesion, using a variety of in vitro and ex vivo techniques. Aim 3 addresses the ability of IL4/IL13 stimulation to modulate glycosylation in HER2+ breast cancer cells and the relevance of those changes to early metastatic behavior. Previously identified candidates, including a sialyltransferase implicated in glioblastoma, will be validated. Additionally, we propose to identify and validate novel targets using qRT-PCR arrays and lectin probes. This project will yield novel insights into the mechanism of HER2+ breast cancer brain metastasis. As IL4- and IL13-targeted therapies are already in trials for various indications, the results of this proposal may suggest a feasible clinical approach for control of brain metastasis.