放射治療在臨床上是一種很常見的惡性腫瘤的治療方法，放射線不僅可以直接傷害癌細胞也可以調控其腫瘤微環境的變化。腫瘤微環境包含了血管系統，浸潤的免疫細胞，纖維母細胞和其他可以幫助腫瘤生長的族群，這些細胞會影響腫瘤治療之療效。目前在腫瘤治療上的共識是如何去辨明跟利用這些腫瘤微環境的變化進而來促進放射治療的效果。然而在單一大劑量照射(SLDLTI)過後的腫瘤微環境之變化目前仍舊不明，本論文主要是要探討SLDLTI對輻射抗性高的小鼠攝護腺癌腫瘤(TRAMP-C1)照射單一大劑量25Gy後及其腫瘤微環境之特殊變化。我們發現SLDLTI對TRAMP-C1腫瘤照射25Gy後會降低腫瘤內的血管密度，但卻會引起腫瘤微環境之異質性的血管與缺氧區域分布。而且這種異質性的SLDLTI腫瘤微環境會促進缺氧誘導因子的表現，我們利用了缺氧誘導因子之抑制劑chetomin可以成功克服這點並提升放射治療的效果。SLDLTI四小時後，便會快速地誘使能幫助腫瘤生長的源骨髓性免疫抑制細胞浸潤到腫瘤之中，並且隨著時間會讓腫瘤和周邊血液中的源骨髓性免疫抑制細胞數目會大量地上升。我們也發現照射過後的腫瘤內部慢性缺氧區域附近會生一種特殊的免疫細胞分布，其包含了在壞死區域聚集的Ly6G+多葉核型源骨髓性抑制細胞和在慢性缺氧區聚集的CD68+腫瘤巨噬細胞，並且將之定義為能夠幫助放射治療過後的腫瘤再生長的”微利基”。這些聚集的腫瘤巨噬細胞具有特殊的基因表現，包括Arg-1、iNOS、tie2、jag-1和endostatin等等。而這種特殊的聚集現象和一氧化氮分子有關，並且餵食老鼠一氧化氮生成酶之抑制劑能夠阻止腫瘤巨噬細胞的聚集，其可以作為合併放射治療的治療目標。我們也另外使用Gr-1抗體及白喉毒素分別直接地剔除腫瘤內部的源骨髓性免疫抑制細胞和腫瘤巨噬細胞，剔除掉這些特定的細胞後更可以增進放射治療過後腫瘤之控制。這些結果顯示SLDLTI治療過後會產生特殊的異質性腫瘤微環境，針對這些腫瘤微環境之變化可以增進對放射治療抗性高的腫瘤之療效。

Radiotherapy is a conventional modality for malignancy in clinical. Radiation not only damage proliferative tumor cells directly but also exert regulation of tumor microenvironment (TME). TME is consisted of vasculature, infiltrated immune cells, tumor-associated fibroblast and others pro-tumoral stomal cells, which could affect the efficacy of anti-tumor therapy. How to discriminate and utilize the distinct irradiated TME is a consensus for improving radiotherapy efficacy. However, the influence of single large-dose of local tumor irradiation (SLDLTI) on TME is still elusive. In this thesis, relatively radio-resistant murine prostate tumor, TRAMP-C1, was irradiated with a large single dose of 25Gy and its distinct chronological change within TME was verified. SLDLTI could significantly decrease micro-vascular density (MVD) associated with evolving heterogeneous distribution of vasculature and hypoxia. Furthermore, the hypoxia-induced factor (HIF) pathway was induced in TME following SLDLTI, which could be impaired by the administration of HIF inhibitor, chetomin. SLDLTI could rapidly recruit pro-tumoral myeloid-derived suppressor cells (MDSCs) in 4 hours, and subsequently induce systemic MDSCs’ expansion both in tumor and peripheral blood. A specific re-distribution, composed accumulated more immunosuppressive type of Ly6G+ polymorphonuclear MDSCs (PMN-MDSCs) in necrosis and aggregated CD68+ tumor-associated macrophages (TAMs) in chronic hypoxia were found and defined as a “micro-niche” in favoring the regrowth of irradiated tumor. The aggregated CD68+ TAMs in chronic hypoxia possessed distinct gene expression, such as Arg-1, iNOS, tie2, jag-1 and endostatin. Moreover, the aggregation of CD68+ TAMs was nitric oxide (NO) -dependent, which could be attenuated by treating NO inhibitor and serve as a therapeutic target in SLDLTI tumors. The MDSCs and TAMs were further alternatively depleted by administration of Gr-1 antibody and diphtheria toxin (DT) in CD11b-DTR mice, respectively, which benefited SLDLTI on tumors control. Those emerging data suggested that SLDLTI could evolve a distinct heterogeneous TME. Targeting on the chronological response on SLDLTI-treated tumors is potent to improve the efficacy of radiotherapy in radio-resistant tumors.

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