PD1免疫检查点小分子抑制剂PSdis的抗肿瘤研究

PDL1 expressed on the tumor cells can specifically bind to PD1 receptor of T cells, which can inhibit the activation of T cells and enhance the immune escape of tumor cells. Anti-PD1 or PDL1 monoclonal antibodies have achieved great success in tumor immunotherapy, but the reality of the PD1 inhibitory signaling pathway of T cells is still unclear. We found that PD1 can be phosphorylated by the tyrosine kinase Src, recruiting negative signal regulator protein SHP2 to inhibit the positive TCR signaling pathway adjacent to PD1. Through the large scale of screening, we developed a small molecule compound named PSdis, which can disrupt the interaction between PD1 and SHP2 without affecting the enzyme activity of SHP2. Here we hypothesize that the PSdis can prevent the immunosuppression of PD1 on the TCR signaling pathway by blocking the interaction between PD1 and SHP2. It can activate TCR signaling pathway, prompting T cells to kill tumor cells. We will apply the technology of co-immunoprecipitation, mass spectrometry analysis, animal models, drug-loaded nanosystem, to 1) elucidate the signal transduction mechanism of PD1 tyrosine phosphorylation, reveal the molecular regulatory mechanism of PSdis on the PD1 immune checkpoints; 2) explore the enhancement effect of nano-packaging on targeted delivery PSdis to T cells and its antitumor effects. It provides a theoretical basis for the development of novel clinical therapeutic potential drugs.

肿瘤细胞通过PDL1配体和T细胞的PD1受体特异结合，抑制T细胞激活，从而得以免疫逃逸。抗PD1或PDL1单抗药物用于肿瘤免疫治疗虽已取得巨大成功，但T细胞内PD1抑制性信号通路的真实面目至今不清楚。本项目发现PD1可被酪氨酸激酶Src磷酸化而招募负性信号蛋白SHP2，抑制PD1邻近的TCR正性信号通路。通过大规模筛选，本项目研发出可特异阻断PD1与SHP2互作却不影响SHP2酶活性的小分子化合物PSdis。我们推测：PSdis通过阻断PD1和SHP2互作而防止PD1对TCR信号通路免疫抑制，TCR得以激活促使T细胞杀伤肿瘤细胞。本项目将运用免疫共沉淀、质谱分析、动物模型、纳米载药等技术1）阐明PD1酪氨酸磷酸化信号传导机制，揭示PSdis对PD1免疫检查点分子调控机制；2）探索纳米包装增强PSdis靶向递送T细胞效果及其抗肿瘤作用，为开发具有临床治疗潜力全新药物提供理论基础。

目前PD-L1/PD-1信号通路被认为是肿瘤发生免疫逃逸机制的重要组成部分，也成为了肿瘤免疫研究的热点之一。肿瘤细胞表达PD-L1激活T细胞的PD-1胞内域酪氨酸磷酸化而启动T细胞自我抑制，肿瘤发生免疫逃逸。然而此过程中具体的分子调控机制并不清晰。在本项目主要研究内容（一）中我们发现在PD-L1多肽刺激条件下，T细胞表面PD-1胞内Y223和Y248位点可被激酶Src磷酸化。并且PD-1胞内域酪氨酸磷酸化后，招募磷酸酶SHP2，在PD-1与SHP2相互作用过程中，我们发现PD-1与SHP2的结合模式，与SHP2的两个SH2结构域密切相关。PD-1招募磷酸酶SHP2，从而抑制PD-1邻近的TCR正性信号通路。随后在本项目主要研究内容（二）中我们靶向PD-L1/PD-1信号通路中PD-1酪氨酸磷酸化招募SHP2关键节点，通过计算机模拟以及生物活性筛选，获得了能够不影响SHP2酶活性，但是具有阻断PD-1与SHP2相互作用的特异小分子化合物PSdis。SPR以及NMR等初步实验证实，PSdis与SHP2蛋白的亲和力较高。最后在主要研究内容（三）中我们发现PSdis在体内或是体外实验处理中，均具有激活T细胞抗肿瘤活性，并且在体内抑瘤实验证实，PSdis具有较好的抑制肿瘤生长能力。因此，我们相信PD-1免疫检查点小分子抑制剂PSdis一旦成功，PSdis不仅具有类似于目前单抗药物阻断作用，而且它的口服优势和特异性强等特点将克服单抗药物的静脉注射、价格昂贵等弱点，将开辟靶向免疫节点的小分子抑制剂新篇章。