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Intratumoral heterogeneity and cellular plasticity enable tumors to alter phenotypes and adapt to foreign microenvironments and resist targeted inhibitors. While the ability to switch between phenotypic states has been broadly characterized, the key mechanisms that underlie tumor plasticity remain poorly understood. We studied the neural crest lineage transcription factor, SOX10, in the context of cutaneous melanoma and resistance to targeted therapies. SOX10 is heterogeneously expressed in melanoma samples. Using bio-informatics as well as in vivo and 3D in vitro melanoma models, SOX10 loss was sufficient to induce an invasive but slow proliferating phenotype in vitro and in vivo that was associated with expression of a mesenchymal gene set. Interestingly, while SOX10 knockout initially induced a targeted inhibitor tolerant state, longer exposure of co-mixed populations of SOX10 proficient and SOX10 deficient to targeted therapy drives the clonal selection of SOX10 knockout cells. Furthermore, cell lines generated from xenograft tumors that have acquired resistance to either vemurafenib, paradox-breaking BRAFi or the combination of BRAFi + MEKi showed dramatically reduced SOX10 expression compared to their parental counterparts. Altogether these data suggest that acquired resistant clones may arise from drug tolerant persister cells. As a strategy to selectively target this invasive, drug-tolerant SOX10-deficient sub-population, we screened a drug compound library and identified a class of cIAP1/2 inhibitors to be synthetically lethal for SOX10-deficient cells. Our preliminary data suggest that birinapant can delay or prevent resistance to BRAFi/MEKi in vivo. Together, these data suggest that SOX10 mediates phenotypic switching in cutaneous melanoma and enables tumor adaptation to altered microenvironments and drug treatments which could be targeted using cIAP1/2 inhibitors. Citation Format: Claudia Capparelli, Timothy J. Purwin, Manoela Tiago, Nicole Wilski, Danielle Pomante, McKenna Glasheen, Sheera Rosenbaum, Mai Q. Nguyen, Weijia Cai, Richard Zheng, Gaurav Kumar, Inna Chervoneva, Ayako Shimada, Adam E. Snook, Paolo Fortina, Xiaowei Xu, Kim Hookim, Edna Cukierman, Michael A. Davies, Meenhard Herlyn, Andrew E. Aplin. Targeting SOX10-deficient cells to reduce resistance to targeted therapy in melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 40.