Rapidly determining the biological effect of perturbing a site within a potential drug target could guide drug discovery efforts, but it remains challenging. Here, we describe a facile target validation approach that exploits monobodies, small synthetic binding proteins that can be fully functionally expressed in cells. We developed a potent and selective monobody to WDR5, a core component of the mixed lineage leukemia (MLL) methyltransferase complex. The monobody bound to the MLL interaction site of WDR5, the same binding site for small-molecule inhibitors whose efficacy has been demonstrated in cells but not in animals. As a genetically encoded reagent, the monobody inhibited proliferation of an MLL-AF9 cell line in vitro, suppressed its leukemogenesis and conferred a survival benefit in an in vivo mouse leukemia model. The capacity of this approach to readily bridge biochemical, structural, cellular characterization and tests in animal models may accelerate discovery and validation of druggable sites.

快速确定扰动潜在药物靶标内某个部位的生物学效应可以指导药物发现工作，但仍具有挑战性。在这里，我们描述了一种简便的靶标验证方法，该方法利用了单克隆抗体，即可以在细胞中完全功能表达的小型合成结合蛋白。我们为WDR5（混合谱系白血病（MLL）甲基转移酶复合物的核心成分）开发了一种有效且选择性的单体。单体与WDR5的MLL相互作用位点结合，小分子抑制剂的结合位点与WDR5的作用相同，小分子抑制剂的作用已在细胞中证实，但在动物中未证实。作为遗传编码试剂，该单体在体外可抑制MLL-AF9细胞系的增殖，抑制其白血病发生并在体内小鼠白血病模型中具有生存优势。