Summary Constitutive activation mutations of BRAF account for majority of cutaneous melanoma, which activate the mitogen-activated protein kinase (MAPK) pathway, promoting tumorigenesis. While inhibitors for BRAF, alone or in combination with MEK inhibitors, have shown good initial responses, resistant tumors occur eventually, representing a major challenge in melanoma therapy. Recent studies indicate that YAP, the transcription co-activators of the Hippo pathway, plays important roles in the development of resistance to MAPK-blockade (MAPKi) in melanoma. YAP interacts with TEAD transcriptional factors to drive oncogenic transcriptional programs that are important for cancer cell growth, survival, epithelial-mesenchymal transition and regulation of immune response, such as recruitment of immunosuppressive Myeloid- derived suppressor cells (MDSCs). We have recently developed novel small molecule inhibitors of TEADs (MGH-CP1 and its analogues) that target TEAD auto-palmitoylation, disrupt the YAP- TEAD interaction and inhibit their transcriptional activities. Moreover, we have found that the levels of TEADs and MDSC-attracting cytokine CXCL6, a transcriptional target of YAP, are upregulated in MAPKi-resistant melanoma cells, compared to their MAPKi-sensitive counterparts. Based on the strong scientific premise and our preliminary results, we hypothesize that targeting the YAP-TEAD transactivation activity with TEAD inhibitors is an effective therapeutic strategy for MAPKi-resistant melanomas;? and that TEAD upregulation and YAP- dependent recruitment of MDSCs to tumor microenvironment play important role in the development MAPKi resistance in melanomas. The overall goal of the proposal is to understand the role of YAP-TEAD signaling in MAPKi-resistant melanoma and to develop therapeutic strategies to combat MAPKi resistance. In aim 1, we will investigate the contribution of TEAD upregulation to the development of MAPKi-resistance in melanoma. In aim 2, we will evaluate the effects of small molecule inhibitors of TEADs in MAPKi resistant melanomas using both cell culture and animal models. In aim 3, we will elucidate the contribution of YAP- dependent MDSC infiltration to the development of MAPKi resistance in melanoma.