I 型黑色素瘤抗原 (MAGE) 家族成员在多种肿瘤类型中均可检测到，其表达与预后不良、肿瘤分级高和转移增加相关。 I 型 MAGE 蛋白通常仅限于生殖组织，但在肿瘤发生过程中可能会重复表达。它们的多种生化功能已被阐明，值得注意的是，MAGE 通过充当 E3 连接酶复合物的底物识别模块来调节蛋白质稳态。可被劫持以进行靶向蛋白质降解的 E3 连接酶复合物的种类不断扩大，并且考虑到其癌症选择性表达，MAGE-E3 复合物是一个特别有吸引力的平台。此外，I 型 MAGE 衍生肽呈递在癌细胞表面，因此靶向 MAGE 降解可能会增加抗原呈递并改善免疫治疗结果。受这些应用的推动，我们开发了 MAGE-A3 的新型小分子配体，MAGE-A3 是一种 I 型 MAGE，在肿瘤中广泛表达，并与 TRIM28（一种 RING E3 连接酶）相关。通过 DNA 编码库 (DEL) 筛选鉴定化学物质，并验证命中化合物与 MAGE-A3 的体外结合。我们获得了具有 DEL 类似物的共晶结构，并假设该小分子在二聚体界面结合。我们利用该配体开发了 PROTAC 分子，该分子通过 VHL 募集诱导 MAGE-A3 降解并抑制 MAGE-A3 阳性细胞系的增殖。这些配体和降解剂可以作为研究 MAGE-A3 生物学的有价值的探针，并作为持续开发肿瘤特异性 PROTAC 的基础。

Type I melanoma antigen (MAGE) family members are detected in numerous tumor types, and expression is correlated with poor prognosis, high tumor grade, and increased metastasis. Type I MAGE proteins are typically restricted to reproductive tissues, but expression can recur during tumorigenesis. Several biochemical functions have been elucidated for them, and notably, MAGEs regulate proteostasis by serving as substrate recognition modules for E3 ligase complexes. The repertoire of E3 ligase complexes that can be hijacked for targeted protein degradation continues to expand, and MAGE-E3 complexes are an especially attractive platform given their cancer-selective expression. Additionally, type I MAGE-derived peptides are presented on cancer cell surfaces, so targeted MAGE degradation may increase antigen presentation and improve immunotherapy outcomes. Motivated by these applications, we developed novel, small-molecule ligands for MAGE-A3, a type I MAGE that is widely expressed in tumors and associates with TRIM28, a RING E3 ligase. Chemical matter was identified through DNA-encoded library (DEL) screening, and hit compounds were validated for in vitro binding to MAGE-A3. We obtained a cocrystal structure with a DEL analog and hypothesize that the small molecule binds at a dimer interface. We utilized this ligand to develop PROTAC molecules that induce MAGE-A3 degradation through VHL recruitment and inhibit the proliferation of MAGE-A3 positive cell lines. These ligands and degraders may serve as valuable probes for investigating MAGE-A3 biology and as foundations for the ongoing development of tumor-specific PROTACs.