阻断肿瘤相关巨噬细胞表达PD-L1增强直肠癌放疗疗效的作用及机制

Neoadjuvant radiotherapy is one of the most important treatment modalities for local advanced rectal cancers. How to increase the efficacy of radiotherapy, improve the local control and disease-free survival of rectal cancer patients has been a major concern in clinical practice. Our previous work has demonstrated that ionizing radiation activates M1 type anti-tumor macrophages. However, ionizing radiation simultaneously up-regulates PD-L1 expression on macrophages and may induce immune evasion.The mechanisms by which ionizing radiation induce PD-L1 expression on macrophages remain unclear. We plan to use rectal cancer biopsies before neoadjuvant radiotherapy and surgical samples after neoadjuvant radiotherapy to detect the induction of PD-L1 expression on rectal cancer-associated macrophages by ionizing radiation and its association with the efficacy of radiotherapy. We will then demonstrate the molecular mechanisms by which ionizing radiation regulates the expression of PD-L1 and screen small molecular inhibitors to decrease the expression of PD-L1 on tumor-associated macrophages. We will further establish rectal cancer animal models and exam the combined effect of radiotherapy and small molecular inhibitors on inhibiting the expression of PD-L1 on tumor-associated macrophages, activating immune response and improving tumor response. This study will help to demonstrate the molecular mechanism by which ionizing radiation induces PD-L1 expression on tumor-associated macrophages and provide new therapeutic strategies to enhance radiotherapy efficacy in rectal cancer.

新辅助放疗是治疗局部进展期直肠癌的重要方法之一，如何提高放疗疗效、改善直肠癌局部控制率和无病生存，是目前临床工作中的重大难题。我们前期研究显示，放射线既可活化M1型抗肿瘤巨噬细胞，又能诱导巨噬细胞表达免疫抑制性的程序性死亡配体1（PD-L1），进而导致肿瘤免疫逃逸。但放射线诱导巨噬细胞表达PD-L1的分子机制尚不明确。本项目拟在新辅助放疗前、后的直肠癌病理标本中检测放疗前后肿瘤相关巨噬细胞PD-L1表达的变化，分析PD-L1表达水平与放疗疗效的相关性；在细胞水平阐明放射线诱导巨噬细胞PD-L1表达的分子机制，筛选有效降低PD-L1表达的小分子抑制剂；构建小鼠直肠癌移植瘤模型，在动物水平检测小分子抑制剂降低肿瘤相关巨噬细胞PD-L1表达、增强抗肿瘤免疫反应、提高放疗疗效等方面的作用。本项目有助于阐明放射线诱导肿瘤相关巨噬细胞PD-L1表达的分子机制，有望为提高直肠癌放疗疗效提供新的治疗策略。

巨噬细胞是肿瘤微环境中分布最多的免疫细胞之一，也是表达免疫抑制性分子PD-L1的主要细胞。我们发现放射线显著诱导巨噬细胞表达PD-L1，但其分子机制还不明确。本项目中，我们通过离体细胞实验发现放射线照射以及ATM激酶抑制剂可以增加巨噬细胞DNA损伤，活化cGAS/STING/IRF3信号通路，上调I型干扰素表达。后者作用于巨噬细胞IFNaR1受体，活化JAK1/STAT1/STAT3通路，上调PD-L1表达。采用JAK1抑制剂可以显著抑制放射线诱导的巨噬细胞中PD-L1表达，活化抗肿瘤T细胞免疫，并在结直肠癌荷瘤动物模型中显示出较强的放射治疗增敏效果。因此，本研究证实阻断放射线诱导的巨噬细胞PD-L1表达，可以减少PD-L1介导的免疫逃逸，提高直肠癌放射治疗疗效。靶向这一信号通路有望为提高结直肠癌的治疗提供新的思路和实验基础。