以小鼠模型探討腫瘤微粒參與胰臟癌相關靜脈血栓之機制

Abstract

癌症相關靜脈血栓是癌症病患常見的併發症，且為癌症病患的第二大死因。 現行治療藥物多以凝血路徑或血小板為標的，不僅增加癌症病患出血的風險，患者經治療後仍有靜脈栓塞復發的機率，且癌症類型不同其誘發靜脈栓塞的機制也相異，因此深入探討癌症相關靜脈血栓機制，並針對癌症類型找出其適合作用的藥物標的，來預防病患血栓的形成，是當前重要的問題。 腫瘤微粒已被許多文獻指出是導致癌症相關靜脈血栓形成的重要因子，但臨床研究對於腫瘤微粒與癌症相關靜脈血栓是否存在相關性，仍存在爭議。本論文以靜脈栓塞併發率最高的胰臟癌為討論材料，以期釐清胰臟癌腫瘤微粒誘發癌症相關靜脈血栓之機制。本論文在以胰臟癌腫瘤微粒誘導凝血相關因子缺陷的基因改造小鼠發現，在A型血友病小鼠和B型血友病小鼠難以觀察到血栓，而TXAS-/-小鼠產生的血栓也明顯小於野生型小鼠，顯示腫瘤微粒tissue factor(TF) 的表現是影響小鼠血栓形成的主因，且內在途徑及血小板亦參與TF陽性腫瘤微粒介導之靜脈血栓的生成。癌症移植小鼠模型亦呈現相似結果，移植腫瘤後的野生型NSG小鼠可以誘發靜脈血栓的生成，但在A型血友病胰臟癌腫瘤小鼠則無法觀察到血栓的產生。綜上而論，TF在腫瘤微粒誘導血栓形成上扮演重要的起始角色，而若少了後續凝血內在途徑增幅凝血反應，會大幅抑制血栓的形成。血小板的缺陷亦會影響到TF陽性腫瘤微粒所誘導形成的血栓大小，但就靜脈血栓生成的重要性而言不比內在途徑凝血因子的影響大。而注射胰臟癌TF剔除株釋放之腫瘤微粒，發現少數小鼠有血栓的形成，未來將針對血栓成分作分析，希望能更了解腫瘤微粒在TF啟動的凝血外在路徑外，其他誘發靜脈血栓形成的機轉。

Cancer-associated thrombosis(CAT) is a common complication in patients with malignant disease, and VTE is the second cause of death in cancer. The anticoagulant drugs and antiplatelet agents used for treating cancer-associated thrombosis remain challenging because these patients have increase risks of both bleeding and recurrent VTE. VTE incidence varies widely among different cancer types , implicating there are cancer type specific mechanisms in cancer-associated VTE. Investigating the underlying mechanisms in CAT and finding possible targets to prevent the thrombosis in cancer population is the urgent need to action. Many studies suggest that tumor-derived microvesicles are risk markers for CAT . However, the correlation of tumor-derived microvesicles and CAT remains controversial. In this study we discuss pancreatic cancer-associated venous thrombosis, the most common malignancies associated with VTE. In the study we injected exogenous ASPC-1 microvesicles into various coagulation gene defected C57BL/6 mice , discovering tissue factor expressing on microvesicles plays a leading role in cancer-associated thrombosis. And we proved that both intrinsic pathway and platelets involved in tissue factor positive tumor-derived microvesicles mediated VTE. This study also performed tumor xenograft mouse model and shows a similar results. We observed clot formation in tumor bearing WT NSG mice but not in tumor bearing hemophilia A ones. Of all, tissue factor plays a important role to initiate microvesicles mediated thrombosis, which need essential intrinsic pathway to further amplify the coagulation cascade. The defect of platelet activation also reduced tissue factor positive microvesicles induced thrombosis, but the importance for thrombus formation is less than intrinsic coagulation factors. Which can’t be ignored is that we find clot forms in few mice injected with tissue factor knockout tumor-derived microvesicles. We’ll analyzed the composition of these thrombus in the future, to study the mechanisms of microvesicles-mediated thrombosis excluded extrinsic pathway.