肿瘤相关巨噬细胞调节微血管的完整性导致胰腺癌化疗反应敏感性的机制研究

Pancreatic cancer (mainly pancreatic ductal adenocarcinoma) ranks the fourth most frequent cause of cancer-related death, with a 5-year overall survival rate less than 7%. Chemotherapy is the major choice of treatment for pancreatic cancer, whereas the efficacy is limited owing to the hypovasculature and with a complex tumor microenvironment. Thus, to strengthen the microvessel integrity may enhance the efficacy of chemotherapy. Our previous study found that pancreatic cancer had a unique immunosuppressive microenvironment, and that tumor-associated macrophages (TAMs) was one of the most important infiltrating subpopulations of immune cells. It has been always showed that the TAMs played only a role in promoting cancer, and drug interventions had the main goal of blocking its activity. However, our clinical analyses revealed that patients with higher TAMs infiltration would have poorer prognosis after resection, whereas, the effect of chemotherapy would be better. Our preliminary experiments showed that the TAMs distributed a gradient around the PDGFR-β positive microvessel-associated cancer-associated fibroblasts (mvaCAFs), suggesting that its efficacy might be achieved by regulation of microvessel; nonetheless, the internal mechanism is still unclear. Based on our previous work, in the present study, we firstly aim to confirm that blocking the function of TAMs will reduce the efficacy of chemotherapy. Furthermore, we need to verify that whether this role of reduction is associated with the decrease of microvessel integrity, through examining the vascular morphology. Moreover, by using of various interventions in vivo and in vitro, we will clarify that the downregulation of PDGFR-β in pericytes after TAMs inhibition is the crucial regulatory mechanism of microvessel integrity. Finally, we also plan to explore whether the CD40 agonist, which has the function of stimulating TAMs activity, could improve the efficacy when combined with chemotherapy. In conclusion, if we got the expected results, we will first report that TAMs can ameliorate the chemosensitivity of pancreatic cancer through up-regulating the expression of PDGFR-β in mvaCAFs and accordingly enhancing microvessel integrity of tumor. Most importantly, we will obtain the desirable medication which may induce this activity of TAMs, and ultimately improving efficacy.

化疗是胰腺癌主要疗法，但效果不佳，肿瘤微环境复杂、微血管完整性较差是主因，增强完整性因而可提高疗效。我们前期发现，胰腺癌具有一个独特的免疫抑制微环境，肿瘤相关巨噬细胞是最重要的浸润亚群。既往认为，巨噬细胞主要起促癌作用，药物干预以阻断其活性为目标。然而临床分析发现，巨噬细胞浸润越高的人群预后越差，但化疗效果反而更好。预实验显示，巨噬细胞在PDGFR-β阳性微血管相关成纤维细胞周围呈梯度分布，提示其效应可能通过调控微血管实现，然机制未明。为此，本课题拟首要确证阻抑巨噬细胞会减弱化疗疗效，进而揭示其主要由微血管完整性下降导致，随后应用体内外干预阐明下调周细胞PDGFR-β为关键调节机制，最后探索诱导巨噬细胞活性的药物CD40激动剂能否增强疗效。本项目如达预期，将首次揭示巨噬细胞可改善胰腺癌化疗敏感性，其机制与上调PDGFR-β增强微血管完整性密切相关，同时证实该活性可被诱导，最终提高化疗疗效。

化疗仍是不可切除胰腺癌的核心疗法，但有效率并不高，胰腺癌微环境复杂、微血管完整度较差是内因，增强微血管完整度因而可能提高化疗疗效。我们前期发现胰腺癌具有独特的免疫抑制微环境表型，其中肿瘤相关巨噬细胞（TAMs）是最重要的免疫浸润亚群。既往认为，TAMs主要起促癌作用，药物干预以阻断其促癌活性为目标。然而我们的临床分析却发现TAMs浸润越高的人群预后越差，但该亚群的化疗效果反而更好。预实验显示，TAMs在PDGFR-β+微血管相关成纤维细胞（mvaCAFs）周围呈高密度分布，提示其效应可能通过调控微血管功能实现，然而其机制未明。基于此，本课题首先采用唑来膦酸不加选择地清除所有TAMs，发现化疗疗效并未显著升高。通过亚群分析我们发现肿瘤内CD86+ TAMs浸润密度越高的区域，间质比例越低，化疗疗效越好；而CD206+ TAMs密度越高的区域，间质比例则越高，化疗效果越差。随后我们发现TAMs和特殊亚型PDGFR-β+ mvaCAFs在空间位置上密切关联，在mvaCAFs较丰富区域聚集的主要为CD40+CD86+ TAMs，而在mvaCAFs低密度区域聚集的主要为CD206+ TAMs。提示前者可能增加微血管的完整度，而后者可能降低微血管的完整度。应用PDGFR受体阻断剂，我们的结果进一步表明下调周细胞PDGFR-β为CD206+ TAMs破坏微血管完整度的关键机制，而CSF-1R受体阻断剂可阻抑该过程提高微血管完整度。最后通过应用CD40激动剂，我们的结果显示CD40+CD86+ TAMs可显著激活并上调mvaCAFs的密度和功能。虽然本课题的核心论文尚未公开发表，但已有结果可支持通过调控TAMs亚群能够显著改善胰腺癌化疗敏感性，其机制与上调PDGFR-β+ mvaCAFs增强微血管完整度密切相关，为临床CD40激动剂和CSF-1R阻断剂与化疗联用提供了有力依据。