本研究旨在製備一新的腦部給藥載體，使用乳鐵蛋白(lactoferrin，簡稱Lf)修飾在多乙烯醇微脂體(PEG-liposome，簡稱PL)表面，以期藉由血腦屏蔽上特殊的乳鐵蛋白受器(lactoferrin receptor)，使此藥物載體可藉由乳鐵蛋白以配位子－受器結合（ligand-receptor binding）方式穿吞 (transcytosis) 進入腦中。在本研究中將微脂體包埋入放射性核種99mTc作為放射示踪劑。另一方面，藉此包埋之放射性核種可將此載體應用於腦癌放射性診斷藥物，或替換另一同族放射性核種188Re，則可作為一腦癌放射性治療藥物。
方法：首先將乳鐵蛋白 (Lf) 耦合至多乙烯醇微脂體 (PL)表面，接著將放射性核種塔-99m（99mTc）以塔-99m-螯合劑（99mTc-BMEDA）型態包埋至微脂體中，得到產物，簡稱為Lf-PL[99mTc]。藉由Lf　ELISA實驗、體外穩定性實驗、以及小鼠體內藥物動力學實驗，評估此試劑的活性及穩定性，接著使用穿越血腦屏蔽效果體外評估常用之bEND.3細胞做攝取實驗以及體內小鼠生物分佈做為穿腦效能評估。
結果：在Lf ELISA實驗中證實，將乳鐵蛋白修飾微脂體（Lf-PL）仍保持Lf之活性。99mTc-BMEDA包埋至Lf-PL的包埋效率為26.4±4.45%，較包埋至單純PL中的包埋效率(75.31±5.52%)為低，推測可能因為乳鐵蛋白修飾在微脂體表面造成之立體障礙影響所致。在體外穩定度實驗中證實無論在食鹽水或大鼠血清中，於48小時後Lf-PL[99mTc]仍具87%以上之穩定度。藥物動力學實驗中，Lf-PL[99mTc]的循環半衰期(elimination half-life, T1/2)及平均滯留時間(mean residence time, MRT)分別為13.88±2.52小時及19.81±4.12小時。 Lf-PL[99mTc]的細胞攝取實驗及活體腦部攝取實驗和PL[99mTc]相比較，分別有約3倍及1.5倍的增加。
結論：本實驗在細胞實驗及活體腦部攝取實驗皆證實藉由在藥物載體微脂體表面修飾乳鐵蛋白可成功增加微脂體進入腦部的量。未來可進一步針對此載體作為一腦腫瘤放射線診斷或治療的評估做探討。

Objective: Lactoferrin (Lf) conjugated polyethylene glycolated liposome (PL) was constructed and was entrapped with 99mTc as a radiotracer for study as a novel brain drug delivery system across the blood-brain barrier.
Methods: Lf was thiolated and conjugated via maleimide functional group on the surface of polyethylene glycolated liposome to form the modified liposome, referred to Lf-PL. The biorecognitive activity of Lf-PL was investigated by Lf ELISA assay following DLS analysis. The 99mTc radionuclide by its complex with N,N-bis (2-mercaptoethyl)-N’,N’-diethyl-ethylenediamine (BMEDA) was entrapped in the core of the liposomes, PL and Lf-PL with ammonium sulfate gradient. The resulted 99mTc loaded liposomes, referred to PL[99mTc] and Lf-PL[99mTc] were taken for in vitro stability study and in vivo pharmacokinetic study. The effect of Lf-PL[99mTc] on improving brain drug delivery was assessed by in vitro bEND.3 cell uptake study and in vivo brain uptake study using BALB/c mice via intravenous injection in comparison with PL[99mTc].
Results and Discussion: According to DLS analysis, the size of PL was 91.23±17.88 nm in diameter and increased to 96±17.84 nm after Lf conjugation. The average number of Lf conjugated on each liposome was ca. 60. The Lf ELISA assay results confirmed the biorecognitive activity of Lf-PL. The 99mTc-BMEDA loaded efficiency for Lf-PL[99mTc] (26.4±4.45%) was lower than that for PL[99mTc] (75.31±5.52%), indicating that the coupled Lf ligands might somewhat obstacle the 99mTc-BMEDA trapping in the liposome. The radiochemical purities of PL[99mTc] and Lf-PL[99mTc] all maintained high above 87% during 48 h incubation in normal saline or in rat plasma at 37 °C. The particle sizes of the 99mTc-BMEDA loaded liposomes were similar to the unloaded liposomes. From pharmacokinetic study, the area under the concentration-time curve (AUC0→24h) was calculated with 653.57±40.84 h □ %ID/g for Lf-PL[99mTc] in comparison with 746.37±119.26 h □ %ID/g for PL[99mTc], being without significant difference (P-value = 0.33). From the results, Lf-PL[99mTc] likely maintained a long circulation property as PL[99mTc]. The in vitro uptake of Lf-PL[99mTc] by bEND.3 cells (26.53±0.4%) presented at ca. 15-fold and 3-fold higher than that of 99mTc-BMEDA (1.89±0.8%) and that of PL[99mTc] (8.99±1.19%), respectively at 1 h postinjection. The in vivo brain uptake of Lf-PL[99mTc] (1.02±0.06% %ID/g) presented at ca. 1.47-fold higher than that of PL[99mTc] (0.69±0.06% %ID/g) at 1 h postinjection, respectively (P-value < 0.01).
Conclusion: The aforementioned in vitro and in vivo studies suggest that Lf-PL may be a potential brain drug delivery system.

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