為了克服藥物不易傳輸至腫瘤缺氧區的限制，本研究企圖利用具缺氧趨化性的巨噬細胞作為藥物傳遞的媒介，開發出結合超音波影像追蹤、超音波控制藥物釋放及癌症治療的多功能型藥物傳遞系統。分別利用脂質含量15與25 mol %的共聚合高分子poly（acrylic acid-co-distearin acrylate） （poly（AAc-co-DSA）製備奈米級高分子液胞與氣胞。高分子液胞不僅具備穩定的結構而且能夠包覆大量的抗癌藥物doxorubicin（DOX）（藥物含量可達22.5 wt %），於無外部（超聲波）刺激時其藥物洩漏量極低。另外，高分子氣胞經證實具有長時間的超音波顯影功能與強烈超聲波對比訊號。巨噬細胞（RAW 264.7）胞飲高分子氣胞與載藥液胞後可維持高存活率達24小時，同時提供強烈的超聲波對比訊號有利於追蹤藥物的傳遞情形。值得一提的是透過施加聚焦式超音波（focused ultrasound）破壞氣胞可產生慣性穴蝕（inertial cavitation），產生震波衝擊載藥液胞後進一步促進藥物釋放。於細胞毒性的測試證實，將聚焦式超聲波處理後之裝載高分子氣/液胞的巨噬細胞分別與TRAMP-C1 cells及HeLa cells共同培養，從巨噬細胞釋放出的藥物能有效地毒殺癌細胞造成細胞死亡。
我們接著利用取自老鼠骨髓細胞分化的單核白血球（bone-marrow derived monocyte）作為裝載高分子氣/液胞的載體。經實驗證實含有高分子氣/液胞的單核白血球展現出與巨噬細胞一致的藥物傳遞功能，亦可藉由聚焦式超聲波的施予將藥物從單核白血球釋放至目標癌細胞。分析單核白血球遷移能力（migration）的結果顯示，單核白血球胞飲高分子氣/液胞後，於模擬腫瘤周遭環境的實驗中仍保有tumor-homing 的能力，故細胞遷移數高於僅利用血清濃度梯度所測得之細胞遷移數。此外，於缺氧（hypoxia）環境中單核白血球仍表現出往腫瘤區域遷移的特性。未來將進一步評估此多功能性細胞型診治系統於動物體內之腫瘤組織的超音波顯影與治療效果。

We proposed an innovative strategy of developing the multifunctional cell-based cancer theranostic systems by employing the tumor-homing macrophages （RAW 267.4） as a vehicle capable of simultaneously carrying doxorubicin （DOX）-loaded polymeric vesicles and polymer bubbles to the target cells and releasing the therapeutic payload via the focused ultrasound treatment. The lipid-containing copolymers, poly（acrylic acid-co-distearin acrylate） （poly（AAc-co-DSA））, with DSA content of 15 and 25 mol% were used respectively as the materials to fabricate the nano-scaled polymer vesicles and polymer bubbles. The results of flow cytometry and confocal laser scanning microscopy clearly demonstrate that the drug-loaded vesicles and polymer bubbles can be effectively engulfed into macrophages via phagocytosis. Taking advantage of the dense lipid-rich membrane structure, the DOX-encapsulated polymeric vesicles after being internalized by macrophages strongly prevent the drug from leakage, thereby allowing the high activity and viability of macrophages at least for 24 h. Moreover, the polymer bubbles within the macrophages still exhibit the long-term profound ultrasound imaging contrast. Interestingly enough, through the focused ultrasound-triggered disruption of polymer bubbles, the generated inertial cavitation most likely impairs the structure of DOX-loaded vesicles, thus facilitating the drug liberation. The in vitro cytotoxicity data further confirm that while being subjected to focused ultrasound treatment and then incubated with either TRAMP-C1 or HeLa cells, the payload-containing macrophages displayed a pronounced anticancer efficacy to inhibit cell proliferation. On the other hand, we found that bone-marrow derived monocytes also served as a carrier for delivery of drug-loaded vesicles and polymer bubbles to tumor sites similar to the above macrophages（RAW 267.4）. It is noteworthy that these monocytes carrying both drug-loaded vesicles and polymer bubbles exhibit better capability of migrating toward tumor cells in the simulated tumoral environment medium than those under the serum concentration gradient conditions. This demonstrates that they still retain tumor-homing nature and can be exploited as a promising candidate for the active delivery of therapeutics and imaging contrast agents.

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