Project Summary Brain metastasis is prevalent among patients with metastatic breast cancer. Brain metastasis can emerge as multi-focal, inoperable, and radiation-resistant lesions and remains a leading cause of death for breast cancer patients. No effective therapies nor cures are currently available for breast cancer brain metastasis (BCBM). Emerging evidence indicates that one of the rate-limiting steps in brain metastatic evolution is the overt outgrowth of disseminated cancer cells through concurrent engagement of proliferative and survival pathways. One key protein involved in these pathways is the Yes Associated Protein (YAP) transcriptional co-activator. YAP is a target of the Hippo signaling cascade; its nuclear localization and association with the TEAD family transcription factors activates downstream genes required for proliferation and resistance to apoptosis. Work from Dr. Er (co-PI) and others have shown that YAP-TEAD association is necessary and sufficient for breast cancer cells’ metastatic outgrowth in the brain downstream of cell adhesion signaling and mechanotransduction, suggesting that targeting the YAP-TEAD interaction can potentially provide clinical benefit for inhibiting metastatic outgrowth of disseminated cancer cells in the brain. Several TEAD auto- palmitoylation inhibitors such as VT104 have been identified as a new class of potent YAP inhibitors that can effectively inhibit cancer cell proliferation and tumor growth. However, one challenge in using these drugs for brain metastasis treatment is their limited accumulation to the multi-focal metastatic lesions because of the presence of multiple biological barriers such as the blood-brain and blood-tumor barriers. Currently existing drug delivery approaches are not sufficiently effective in overcoming these barriers. Driven by this pressing need, we propose to develop a macrophage-based technology (Macrophage Enabled brain Metastasis Targeting, MEMT) for targeted delivery of YAP/TEAD-targeting drugs to multi-focal brain metastases. MEMT is composed of macrophages carrying YAP inhibitor loaded nanoparticles (NPs) on their surface. Leveraging the active migration of macrophages toward tumor, MEMT shuttles surface-anchored NPs to brain metastatic lesions. We hypothesize that targeted disruption of the YAP-TEAD interaction in metastatic cells enabled by MEMT could inhibit metastasis growth, offering a new approach for treating BCBM. Two independent aims have been planned. In Aim 1, we will develop and optimize MEMT capable of delivering NPs to multi-focal brain metastatic lesions. We will study the tissue- and cell-level distribution of MEMT to assess its capability in delivering NPs to brain metastatic lesions in murine and humanized BCBM models. In Aim 2, by incorporating a preclinically-tested YAP inhibitor into MEMT, we will evaluate MEMT’s efficacy in disrupting the YAP-TEAD interaction and inhibiting brain metastasis progression in vivo. If successful, MEMT will revo...