利用生物可降解性奈米系統發展癌症新療法

Abstract

傳統化學藥物是針對癌細胞毒殺性來達成治療效果，但近年來發現此種療法仍有許多限制，因此多方研究開始慧眼在腫瘤的微環境。腫瘤微環境中的巨噬細胞可被簡單分為兩種類別: M1和M2型態。M1巨噬細胞是毒殺癌細胞的型態，可促進免疫系統辨識癌細胞；但晚期腫瘤內的巨噬細胞則多以M2型態為主，這種M2型態巨噬細胞會使癌細胞躲過免疫細胞的辨識，並分泌生長因子促進癌細胞的生長，甚至促進癌細胞的轉移。基於以上，本研究目的是以調節腫瘤微環境為治療主軸，開發一種新穎的治療癌症策略，利用PLGA載體，同時承載專一毒殺缺氧環境癌細胞的化學療法藥物-Tirapazamine (TPZ)，以及促進巨噬細胞M1特性的免疫療法藥物-Imiquimod (IMQ)，希望透過奈米載體降低副作用和提高藥物效果，並且利用藥物直接殺死缺氧較惡化癌細胞及抑制腫瘤中巨噬細胞朝向M2型態分化的能力來達成抑制腫瘤生長、預防轉移及使人體產生毒殺性T細胞的改善傳統化療的新抗癌策略研究。此論文以LL/2小鼠肺癌細胞株及RAW264.7小鼠巨噬細胞株被使用為in vitro細胞模式以模擬巨噬細胞M2、M1型態表現的實驗。TPZ藥物的in vitro實驗結果顯示TPZ對LL/2有抑制存活和生長的效果，並且較不影響RAW264.7的存活。而IMQ in vitro實驗結果顯示IMQ能夠抑制RAW264.7轉換成M2型態，並且大量表現M1型態的特徵；並且利用IMQ所誘導出的巨噬細胞去做促進癌細胞爬行(migration)的實驗，結果顯示比起M2型態的巨噬細胞的培養上清液，利用IMQ分化組別的培養上清液能夠有效減少癌細胞的爬行現象。載體效果初步測試發現PLGA@lipid承載之IMQ比起等藥量的free IMQ會更加促進M1型態的基因表現，顯示IMQ搭配奈米載體後將更有效地促進藥物效果。總結來說，本論文所提供的初步結果發現，奈米科技配合化學療法及免疫療法為癌症治療提供一個新的策略方向。

Cancer cells themselves are usually the target in conventional chemotherapy, but many limitations remained with it. To advance the therapeutic success, scientists moved forward to focus on tumor microenvironment (TME) to improve cancer treatment. Both M1-state and M2-state macrophages were found to exist in the TME. M1-state macrophage is viewed as tumor-suppression type. However, macrophages in the TME were often M2-state, which suppressed immune system and promoted cancer cell growth and metastasis. Taking all together, we were motivated to develop a new strategy for cancer treatment, focusing over cancer cells themselves. In this study, we exploited the advantage of phospholipid-capped PLGA nanocarriers to deliver and accumulate drugs at the specific tumor site via EPR effect, and demonstrated a novel combination therapeutic strategy by integrating hypoxia activated drug (Tirapazamine, TPZ), and Imiquimod (IMQ) that enhanced M1 and impaired M2 macrophage polarization. It was anticipated that our new strategy led to reduction of metastasis by directly killing hypoxia-located malignant cancer cells and removal of M2-state macrophages, and subsequently inhibited tumor growth and reduced cancer mortality by activation of cancer specific cytotoxic T cells. Our results indicated that TPZ was able to inhibit LL/2 growth, whereas IMQ was sufficient to impede polarization of M2-state macrophage. In addition, IMQ-induced macrophage was confirmed to reduce LL/2 migration in vitro. In summary, our results showed that nanocarrier-formulated drugs revealed better efficiency in M1 polarization, and combo therapy was proven to be an emerging strategy of cancer treatment.