Embelin对髓系来源抑制性细胞的调控机制及其在炎症相关性结直肠癌中的作用

Chronic colonic inflammation promotes the accumulation of myeloid-derived suppressor cells (MDSCs) that down-regulate immune surveillance and antitumor immunity, thereby facilitating tumor growth. Infiltration of the tumor tissue by MDSCs is associated with inherent anti-VEGF refractoriness. Our previous studies have showen that embelin effectively suppressed AOM/DSS induced colitis-associated tumorigenesis in mice, and its antitumor effect was partly mediated by modulating immune response. Meanwhile, embelin reduced MDSCs recruitment in CT26WT tumor-bearing mice. We therefore speculate that embelin inhibits colitis-associated tumorigenesis by limiting MDSCs function. In this study, we aim to elucidate the effects of embelin on the recruitment, expansion, and activation of MDSCs. In addition, we will investigate the in vivo effects of embelin on immune function in colitis associated cancer-bearing mice to examine if a favorable immunomodulatory effect accompanies tumor suppression, with a particular focus on their ability to modulate T-cell responses and the phenotype of macrophages. Furthermore, we will test therapeutic regimen combining embelin and anti-VEGF treatment to examine a synergistic effect on tumor growth. The results will deepen our understanding into the role of embelin in regulating the MDSCs in colitis-associated tumorigenesis. The insight gained from this study will facilitate the development of novel therapeutic approaches for colorectal cancer.

髓系来源抑制性细胞(MDSCs)抑制抗肿瘤免疫应答，促进结直肠癌发生和进展，并与抗VEGF靶向治疗耐药相关。我们前期发现信筒子素(Embelin)可抑制小鼠炎症相关性结直肠癌，机制与对肿瘤免疫微环境的调节有关。Embelin还可减少荷瘤小鼠肿瘤中MDSCs，并影响其它免疫细胞数量和功能。基于MDSCs在肿瘤微环境中的重要作用，推测炎症相关性结直肠癌中Embelin可能通过调控MDSCs发挥抗肿瘤作用。本研究拟体外探讨Embelin对MDSCs聚集、增殖和活化的直接调控作用；及通过MDSCs对T细胞增殖及功能、对Th17细胞分化及对巨噬细胞表型转化的影响及机制。研究Embelin对炎症相关性结直肠癌小鼠体内MDSCs数量和功能的影响，及与肿瘤发生进展的关系。探讨Embelin是否通过对MDSCs的抑制而增强抗VEGF靶向治疗效果，阐明二者联合应用的协同作用。为探寻结直肠癌防治新策略提供依据。

肿瘤微环境（TME）在肿瘤发生、进展过程中起重要作用。TME中的髓系来源抑制细胞（MDSCs）是连接炎症与肿瘤的重要中介，与炎症相关性结直肠癌（CAC）关系密切。MDSCs抑制机体免疫监视和抗肿瘤免疫应答，促进肿瘤生长。我们前期研究发现：Embelin抑制CAC发生和进展，其抗肿瘤作用可能与对TME的调节有关。本项目旨在深入研究CAC中Embelin通过调控TME特别是MDSCs而发挥抗肿瘤作用的分子机制。结果显示：在AOM/DSS诱导的CAC小鼠模型中，Embelin明显抑制脾脏及结肠肿瘤组织中MDSCs聚集，显著减少多型核细胞样MDSCs及单核细胞样MDSCs数量，并增加组织中具有抗肿瘤作用的CD8+T细胞、NK细胞及成熟树突状细胞数量，降低调节性T细胞数量；同时Embelin下调肿瘤组织中促炎、促肿瘤因子IL-1β，IL-6，TNFα，COX-2及iNOS水平，从而显著改善TME。Embelin还可降低MDSCs对T细胞的免疫抑制功能，恢复机体的抗肿瘤免疫应答。Embelin影响MDSCs功能的机制主要通过抑制STAT3通路，并降低关键免疫抑制分子活性氧簇和精氨酸酶1的生成和活性介导。此外，Embelin还可通过抑制转录因子C/EBPβ，直接减少细胞因子诱导的体外MDSCs生成并降低对T细胞的免疫抑制活性。MDSCs与肿瘤相关巨噬细胞关系密切，MDSCs可促进巨噬细胞向促肿瘤的M2表型转化，有利于肿瘤血管形成和侵袭、转移。我们发现：Embelin通过下调TME中巨噬细胞趋化因子CCL2，CSF-1及GM-CSF水平，而降低CAC小鼠结肠组织中巨噬细胞数量；通过增加Th1型细胞因子INFγ，IL-12水平，同时降低Th2型细胞因子IL-4水平抑制巨噬细胞M2型转化，从而减少结肠组织中M2型巨噬细胞数量。进一步体外实验证实：Embelin可通过抑制NF-κB 通路激活而直接抑制LPS诱导的巨噬细胞活化；Embelin还可直接阻断Th2型细胞因子诱导的巨噬细胞M2型转化。此外，Embelin明显减少CAC小鼠结肠肿瘤组织中血管形成，并抑制MMP2表达，而影响肿瘤的侵袭性。综上所述：Embelin显著抑制小鼠CAC发生和进展，Embelin通过调控MDSCs及巨噬细胞的数量和功能，改善TME，发挥抗肿瘤作用。该研究为Embelin临床应用于结直肠癌防治提供了理论依据。