髓源性抑制细胞介导肿瘤抗血管生成治疗耐药的机制研究：肿瘤微环境通过Stat3的调控作用

Anti-angiogenic therapy inhibits tumor growth by reducing blood supply to tumor. However, resistance is developed in the majority of patients. Myeloid-derived suppressor cells (MDSCs) are responsible for the resistance to anti-angiogenic therapy. Studies also indicate that transcription factor Stat3, which can be activated by hypoxia and soluble factors released by tumor, is involved in MDSCs-mediated resistance to anti-angiogenic therapy. Tumor microenvironment can “model” the function of MDSCs. Since the expansion and function of MDSCs can be regulated by Stat3, we hypothesize that tumor microenvironment is capable of “modelling” the pro-angiogenic activities of MDSCs, resulting in the differential responsiveness of tumor to anti-angiogenic therapy; furthermore, active Stat3 subsequently enhances the secretion of VEGF and other pro-angiogenic function of MDSCs. In order to test this hypothesis, we will determine the discrepancies in the hypoxic reaction, the ability to recruit and activate MDSCs between anti-VEGF responsive and non-responsive tumors, as well as the discrepancies of corresponding intratumoral MDSCs in their Stat3 activation state and pro-angiogenic activities. The relation between these discrepancies and responsiveness to anti-VEGF therapy will be analyzed. We will also clarify whether or not the generation and transfer of MDSCs-mediated resistance can be reversed by inhibiting Stat3. This research project will further explore the role of tumor microenvironment and Stat3 in MDSCs-mediated resistance to anti-angiogenic therapy, which is essential to improve the therapeutic efficacy.

抗血管生成治疗能减少肿瘤血供抑制肿瘤生长，但大部分患者会产生耐药。髓源性抑制细胞（MDSCs）参与耐药的产生，且研究提示与Stat3有关，后者可被缺氧和肿瘤释放的可溶性因子激活。肿瘤微环境可对MDSCs的功能进行塑造，鉴于Stat3可调控MDSCs的扩增和功能，我们推测肿瘤微环境通过Stat3塑造MDSCs促血管生成功能，导致抗血管生成治疗的不同反应；活化的Stat3促进MDSCs分泌VEGF和增强其它促血管生成功能参与MDSCs介导耐药。为验证此假说我们将检测抗VEGF反应和不反应肿瘤缺氧反应、MDSCs募集和活化能力，相应肿瘤内MDSCs的Stat3活化程度和促血管生成功能差异，分析这些差异与抗VEGF反应性的关系；明确抑制Stat3能否阻止MDSCs介导耐药的产生和转移。本研究将揭示肿瘤微环境和Stat3在MDSCs介导抗血管生成治疗耐药中的作用和机制，对提高治疗疗效有重要意义。

髓源性抑制细胞（myeloid-derived suppressor cells, MDSCs）除了强大的免疫抑制功能，还能通过多种途径促进肿瘤血管生成，参与肿瘤产生抗血管生成治疗耐药。越来越多的研究证实肿瘤微环境可调控MDSCs的分化和免疫抑制功能。但肿瘤微环境对MDSCs的促血管生成功能及其介导的抗血管生成治疗耐药的调控机制尚不明确。本研究前期实验发现减少肿瘤内MDSCs可降低外周血VEGF水平。通过体外培养证实抗VEGF不反应的Lewis细胞较抗VEGF反应的B16F1细胞对缺氧反应更敏感：缺氧条件下Lewis细胞产生更多的ROS，HIF-1α上调更明显，而且产生更多的与MDSCs扩增及募集密切相关的VEGF、GM-CSF和G-CSF。因此我们认为Lewis肿瘤可能在缺氧环境下能募集更多促血管生成的MDSCs。上述结果部分证明了我们提出的假说：缺氧的肿瘤微环境调控MDSCs促血管生成功能，导致肿瘤对抗血管生成治疗的不同反应，提示MDSCs可能是提高抗血管生成治疗的理想靶点。但另一方面，通过小鼠皮下移植瘤模型，我们却发现虽然Lewis肿瘤内ROS水平似乎较高，但其瘤体内和外周血VEGF、GM-CSF和G-CSF却低于B16F1肿瘤，而且两种肿瘤内MDSCs水平及免疫抑制功能无明显差异。该结果似乎与我们的立项依据及体外培养的结果不完全一致。我们认为该部分结果的解读仍有待更多后续实验结果，例如具体的肿瘤内缺氧水平及缺氧相关标志物水平、MDSCs的促血管生成功能等。另外，本研究项目关于Stat3的作用部分仍在进行中。