Inhibition of the programmed cell death-1 (PD-1)/programmed cell death-ligand 1 (PD-L1) interaction by small-molecule inhibitors is emerging cancer immunotherapy. A series of novel 1,3,4-oxadiazole derivatives were designed, synthesized, and evaluated for their activities in vitro and vivo to find potent inhibitors of the PD-1/PD-L1 interaction. Among them, compound Ⅱ-14 exhibited outstanding biochemical activity, with an IC₅₀ of 0.0380 μM. Importantly, compound II-14, with a TGI value of 35.74 %, had more potent efficacy in a mouse tumor model compared to that in the control group. Surprisingly, when compound II-14 combined with 5-FU in a mouse tumor model having a TGI value of 64.59 %, which showed potential anti-tumor synergistic effects. Furthermore, immunohistochemistry analysis demonstrated that compound II-14 activated the immune microenvironment by promoting the infiltration of CD4⁺ T cells into tumor tissues. These results indicate that compound II-14 is a promising lead compound for further development of small-molecule PD-1/PD-L1 inhibitors for cancer therapy.

小分子抑制剂对程序性细胞死亡-1 (PD-1)/程序性细胞死亡-配体 1 (PD-L1) 相互作用的抑制是新兴的癌症免疫疗法。一系列新型 1,3,4-恶二唑衍生物被设计、合成并评估其体外和体内活性，以寻找 PD-1/PD-L1 相互作用的有效抑制剂。其中，化合物Ⅱ-14表现出优异的生化活性，IC ₅₀为0.0380 μM。重要的是，化合物II-14的 TGI 值为 35.74%，与对照组相比，在小鼠肿瘤模型中具有更有效的功效。令人惊讶的是，当化合物II-14与5-FU结合时   在小鼠肿瘤模型中，TGI值为64.59%，显示出潜在的抗肿瘤协同作用。此外，免疫组织化学分析表明， 化合物II-14通过促进 CD4 ⁺ T 细胞浸润到肿瘤组织中来激活免疫微环境。这些结果表明，化合物II-14是一种有前景的先导化合物，可用于进一步开发用于癌症治疗的小分子 PD-1/PD-L1 抑制剂。