Costimulatory interactions are required for T cell activation and development of an effective immune response; hence, they are valuable therapeutic targets for immunomodulation. However, they, as all other protein–protein interactions, are difficult to target by small molecules. Here, we report the identification of novel small-molecule inhibitors of the CD40–CD40L interaction designed starting from the chemical space of organic dyes. For the most promising compounds such as DRI-C21045, activity (IC₅₀) in the low micromolar range has been confirmed in cell assays including inhibition of CD40L-induced activation in NF-κB sensor cells, THP-1 myeloid cells, and primary human B cells as well as in murine allogeneic skin transplant and alloantigen-induced T cell expansion in draining lymph node experiments. Specificity versus other TNF-superfamily interactions (TNF-R1–TNF-α) and lack of cytotoxicity have also been confirmed at these concentrations. These novel compounds provide proof-of-principle evidence for the possibility of small-molecule inhibition of costimulatory protein–protein interactions, establish the structural requirements needed for efficient CD40–CD40L inhibition, and serve to guide the search for such immune therapeutics.

中文翻译：

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CD40–CD40L共刺激蛋白–蛋白质相互作用的小分子抑制剂

共刺激相互作用是T细胞活化和发展有效免疫反应所必需的；因此，它们是免疫调节的有价值的治疗靶标。但是，它们与所有其他蛋白质-蛋白质相互作用一样，很难被小分子靶向。在这里，我们报告了从有机染料的化学空间出发设计的新型CD40–CD40L相互作用小分子抑制剂的鉴定。对于最有前途的化合物（例如DRI-C21045），活性（IC ₅₀）已在细胞试验中证实了在低微摩尔范围内的抑制作用，包括在NF-κB传感器细胞，THP-1髓样细胞和原代人B细胞以及小鼠同种异体皮肤移植和同种异体抗原诱导的T中抑制CD40L诱导的活化引流淋巴结实验中的细胞扩增。在这些浓度下，也证实了特异性相对于其他TNF超家族相互作用（TNF-R1-TNF-α）的缺乏细胞毒性。这些新颖的化合物提供了小分子抑制共刺激蛋白-蛋白相互作用的可能性的原理证据，确立了有效抑制CD40-CD40L所需的结构要求，并指导寻找此类免疫疗法。