VEGFR2-TKI重塑肿瘤微环境在增强非小细胞肺癌抗PD-1/PD-L1疗效中的机制研究

The era of immunotherapy has entered the clinical practice for patients with advanced non-small cell lung cancer. However, the response rate is only approximately 20% by anti-PD-1/PD-L1 monotherapy. It is urgent to improve its efficacy. Our group previously found that vascular endothelial growth factor receptor 2 (VEGFR2) tyrosine kinase inhibitor (TKI) could dramatically enhance the effect of anti-PD-L1 monoclonal antibody in lung cancer mice model and significantly reduce the number of immune suppressive cells e.g. tumor associated macrophage (TAM) and myeloid-derived suppressive cells (MDSC) in the tumor microenvironment (TME). Based on these findings and previous reports, we infer that VEGFR2 TKI could remodel TME via inhibiting the activation of PI3K/AKT signaling pathway to prevent the recruitment of TAM and M2 polarization together with MDSC production, recruitment and activation. As a result, the immunosuppressive effects of T cells would be unleashed and the anti-cancer effects of PD-L1 antibody could be improved. Based on these previous results, the current project will further establish Lewis lung cancer and LA-4 lung adenocarcinoma mice model to investigate the role of VEGFR2-TKI to enhance the efficacy of PD-1/PD-L1 antibody. We aimed to clarify the specific cellular and molecular mechanisms by using flow cytometry, MDSC or macrophage removal experiments, western blot and so on. These findings will be confirmed in clinical tissue samples. This project will not only provide important clues to guide the clinical trials design for anti-PD-1/PD-L1 immunotherapy in NSCLC, but also has social and economic merits.

晚期非小细胞肺癌的免疫治疗时代已经来临，但抗PD-1/PD-L1单药治疗总体有效率仅20%左右，其治疗策略亟待优化。课题组前期发现VEGFR2-TKI可增强PD-L1抗体免疫治疗的疗效，且使肿瘤微环境内免疫抑制细胞（TAM和MDSC）数目显著下降。结合既往报道我们推测：VEGFR2-TKI通过阻断PI3K/AKT信号通路，抑制TAM募集及向M2型极化，抑制MDSC产生、募集与活化，进而解除T细胞免疫抑制效应，增强PD-L1抗体免疫治疗疗效。在前期工作基础上，本项目通过建立Lewis和LA-4小鼠肺癌模型，进一步明确VEGFR2-TKI增强PD-1/PD-L1抗体免疫治疗的作用；采用流式细胞术、MDSC或巨噬细胞清除实验、免疫印迹等分子生物学实验阐明具体细胞和分子机制；并在临床标本中进行验证。本项目的开展，不但对NSCLC免疫治疗临床试验设计具有重要的指导意义，而且具有一定的社会和经济效益。

本项目通过构建小鼠Lewis肺癌皮下及肺部转移瘤模型，验证抗血管生成药物血管内皮生长因子受体2-酪氨酸激酶抑制剂（vascular endothelial growth factor receptor 2 – tyrosine kinase inhibitor, VEGFR2-TKI）增强PD-L1抗体免疫治疗的疗效，并且发现VEGFR2-TKI仅在低剂量范围内具有显著增强PD-L1抗体治疗疗效的作用。基于此发现，我们进一步探明VEGFR2-TKI增强免疫治疗疗效的独特作用机制。首先，我们探讨了VEGFR2-TKI对肿瘤细胞的直接作用。VEGFR2-TKI治疗不影响Lewis肺癌细胞的增殖和凋亡水平，PD-L1表达水平也无明显差异，提示VEGFR2-TKI增强免疫治疗的疗效不是基于对肿瘤细胞的直接作用。因此，我们进一步阐释了VEGFR2-TKI治疗对肿瘤微环境的（Tumor microenvironment，TME）的影响。发现低剂量VEGFR2-TKI作用的Lewis肿瘤内血管趋于正常化，组织内缺氧也较未治疗组改善；而中、高剂量促进异常肿瘤血管新生，组织内缺氧明显。通过进一步探讨TME特征，发现低剂量治疗后肿瘤TME内免疫抑制性细胞TAM及MDSC数量下降，从而肿瘤内浸润CD8+T细胞数量及增殖也相应改善，从而解除T细胞免疫抑制效应。并将这一方案向临床应用转化，在临床上开展了一项临床研究，证实低剂量VEGFR2-TKI（阿帕替尼）联合PD-1单抗显著提升晚期NSCLC患者的ORR及PFS。因此，该项目的开展为抗血管生成联合免疫治疗在晚期NSCLC的应用提供了新证据。