Checkpoint inhibitors such as PD-1/PD-L1 antibody therapeutics are a promising option for the treatment of multiple cancers. Due to the inherent limitations of antibodies, great efforts have been devoted to developing small-molecule PD-1/PD-L1 signaling pathway inhibitors. In this study we established a high-throughput AlphaLISA assay to discover small molecules with new skeletons that could block PD-1/PD-L1 interaction. We screened a small-molecule library of 4169 compounds including natural products, FDA approved drugs and other synthetic compounds. Among the 8 potential hits, we found that cisplatin, a first-line chemotherapeutic drug, reduced AlphaLISA signal with an EC₅₀ of 8.3 ± 2.2 μM. Furthermore, we showed that cisplatin-DMSO adduct, but not semplice cisplatin, inhibited PD-1/PD-L1 interaction. Thus, we assessed several commercial platinum (II) compounds, and found that bis(benzonitrile) dichloroplatinum (II) disturbed PD-1/PD-L1 interaction (EC₅₀ = 13.2 ± 3.5 μM). Its inhibitory activity on PD-1/PD-L1 interaction was confirmed in co-immunoprecipitation and PD-1/PD-L1 signaling pathway blockade bioassays. Surface plasmon resonance assay revealed that bis(benzonitrile) dichloroplatinum (II) bound to PD-1 (K_D = 2.08 μM) but not PD-L1. In immune-competent wild-type mice but not in immunodeficient nude mice, bis(benzonitrile) dichloroplatinum (II) (7.5 mg/kg, i.p., every 3 days) significantly suppressed the growth of MC38 colorectal cancer xenografts with increasing tumor-infiltrating T cells. These data highlight that platinum compounds are potential immune checkpoint inhibitors for the treatment of cancers.

PD-1/PD-L1 抗体疗法等检查点抑制剂是治疗多种癌症的有前途的选择。由于抗体的固有局限性，人们投入了大量精力来开发小分子 PD-1/PD-L1 信号通路抑制剂。在这项研究中，我们建立了一种高通量 AlphaLISA 检测，以发现具有新骨架的小分子，这些小分子可以阻断 PD-1/PD-L1 相互作用。我们筛选了一个包含 4169 种化合物的小分子库，包括天然产物、FDA 批准的药物和其他合成化合物。在 8 个可能的命中中中，我们发现顺铂是一种一线化疗药物，可降低 AlphaLISA 信号，EC₅₀ 为 8.3 ± 2.2 μM。此外，我们发现顺铂-DMSO 加合物，而不是顺铂，抑制 PD-1/PD-L1 相互作用。因此，我们评估了几种市售铂 （II） 化合物，发现双（苯腈）二氯铂 （II） 干扰了 PD-1/PD-L1 相互作用 （EC₅₀ = 13.2 ± 3.5 μM）。其对 PD-1/PD-L1 相互作用的抑制活性在免疫共沉淀和 PD-1/PD-L1 信号通路阻断生物测定中得到证实。表面等离子体共振测定显示双（苯腈）二氯铂 （II） 与 PD-1 （K_D = 2.08 μM） 结合，但未与 PD-L1 结合。在免疫功能正常的野生型小鼠中，但在免疫缺陷的裸鼠中，双（苯腈）二氯铂 （II） （7.5 mg/kg，腹腔注射，每 3 天一次）显着抑制 MC38 结直肠癌异种移植物的生长，肿瘤浸润 T 细胞增加。这些数据强调铂化合物是治疗癌症的潜在免疫检查点抑制剂。