以超音波刺激可注射溫感生物相容水膠之藥物釋放

Abstract

生物體內的正常生理功能，在特定狀況下需間歇性而非持續性的生物活性物質釋放才能完成，例如目前在臨床上用來治療嚴重的骨質疏鬆，是採用一天一次的副甲狀腺素施予（持續的副甲狀腺素反而破壞骨骼結構），由於合成副甲狀腺素是一種胜肽類藥物，使用口服方式會被消化酵素分解。因此這類治療除價格昂貴，最大的問題是病人需每日接受注射，很不方便且需忍受每天接受注射之疼痛感。如何減少注射次數，並達成週期性升高的藥物濃度，是臨床上重要的需求。 在本研究中嘗試建立一個釋藥系統，該系統以溫感兩相水膠為基礎，將目標藥物包住，此水膠在常溫下呈液態，不需切開皮膚，可以注射方式注入體內，溫度升至體溫時轉為膠態，停留在注射部位而不會流至他處，而內含藥在無外特殊刺激下進行局部緩釋，僅在超音波刺激之狀況下，才將其內含藥物釋放發揮作用，希望減少病人每日注射之不適。 首先應用較熟悉的雙相水膠（NIPAM-based），並以適當的超音波參數以刺激大分子釋放，發現只要調整NIPAM和MBAm之間量的不同，便可調控牛血清白蛋白和葡聚糖（分子量：3000-5000）在有超音波和無超音波刺激下釋放量差距的大小，初步證實此構想之可行性。 由於 NIPAM 降解後仍有細胞毒性，我們找到一種生物相容的mPEG-PLGA-BOX 水膠，且其液態及膠態之間的相變明顯，有利以注射方式將釋藥系統植入生體內。此水膠控制釋放系統，可包覆小分子（阿黴素，分子量：580）或大分子（異硫氰酸螢光素-葡聚糖，分子量：20000）藥物並緩釋至少七天，而在適當的超音波參數刺激下，在生體外可達基礎釋放量之70倍。 而此水膠可以臨床常用的針頭注射，在小鼠皮下可觀察到過了一週後仍將藥物包覆在原注射處，有助於局部的藥物釋放，而在適當的超音波參數刺激下，在生體內亦可達基礎釋放量之10倍。 本研究首度將可注射性生物相容溫感水膠和超音波刺激釋放兩個概念合而為一，並在生體外及生體內證實其可行性。此系統在未來可應用在「平時血中低濃度，需要時高濃度」才有最佳作用之藥物，例如胰島素、各種荷爾蒙及某些抗生素等。

Episodic release of bioactive compounds plays an important role in biological systems. “On-demand” release systems which based on polymeric materials and activated by external stimuli may provide the necessary functionality. For proof of this concept, firstly an ultrasound-responsive hydrogel based on N-isopropylacrylamide (NIPAM) and N,N’-methylenebisacrylamide (MBAm) was proposed, which is suitable for triggered release of two large molecules: bovine serum albumin (BSA, 66 kDa) and dextran (3-5 kDa). It is shown that the release amount of these two large molecules increased with increasing hydrogel temperature, and the application of ultrasound further increased the release. By simply adjusting the contents of NIPAM and MBAm, the difference of BSA release between the presence and absence of ultrasound could be adjusted from 1.5 to 84 folds. There was also a positive correlation between the ultrasound intensity and release amount. These properties made the NIPAM-based hydrogel a tunable platform for focal drug delivery. Further, an injectable, biocompatible, and thermosensitive hydrogel system for ultrasound (US)-triggered drug release was investigated. An mPEG-PLGA-BOX block copolymer hydrogel was synthesized. The viscosity of 15 wt% hydrogel is 0.03 Pa*s at 25 °C (liquid form) and 34.37 Pa*s at 37 °C (gel form). Baseline and US-responsive in vitro release profile of a small molecule (doxorubicin, M.W. 580) and that of a large molecule (FITC-dextran, M.W. 20000), from the hydrogel, was tested. A constant baseline release was observed in vitro for 7 d. When triggered by US (1 MHz, continuous, 0.4 W/cm2), the release rate increased by approximately 70 times. Without US, the release rate returned to baseline.

Baseline and US-responsive in vivo release profile of doxorubicin was tested by subcutaneous injection in the back of mice and rats. Following injection into the subcutaneous layer, in vivo results also suggested that the hydrogels remained in situ and provided a steady release for at least 7 d; in the presence of the US-trigger, in vivo release from the hydrogel increased by approximately 10 times. Therefore, the mPEG-PLGA-BOX block copolymer hydrogel may serve as an injectable, biocompatible, and thermosensitive hydrogel system that is applicable for US-triggered drug release. This system may be suitable for drugs which “on-demand” release is necessary, such as insulin, certain hormones or antibiotics.