Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, Illinois 60208, USA.
J Liposome Res. 2011 Dec;21(4):306-14. doi: 10.3109/08982104.2011.565476. Epub 2011 Apr 2.
Analogs of adenosine triphosphate (ATP) with substitutions at the 8-position have been shown to be cytotoxic to multiple myeloma, one of the most prevalent and serious blood cancers. However, these drugs do not readily cross biological membranes and are very sensitive to phosphatases present in body fluids. To circumvent these disadvantages, 8-substituted ATPs were encapsulated into cationic phospholiposomes generated from cationic phosphatidylcholines (EDOPC; 1,2-dioleoyl-sn-glycero-3-ethylphosphocholine, and EDPPC, the corresponding dipalmitoyl homolog), compounds with low toxicity that readily form liposomes. Vortexing was an efficient encapsulation procedure, more so than freeze-thawing. At the lipid:drug ratio of 5:1 (mol/mol), 20% of 8-Br-ATP was encapsulated within EDOPC liposomes. Efficient encapsulation and retention of 8-NH₂-ATP required the inclusion of cholesterol. Liposomes of EDOPC:cholesterol (55:45 mole/mole), at a lipid:drug mole ratio of 10:1, captured ~40% of the drug presented. Cytotoxicity assays of this formulation on multiple myeloma cells in culture showed encapsulated drug to be up to 10-fold more effective than free drug, depending upon dose. Intracellular distribution studies (based on fluorescent derivatives of lipids and of ATP) revealed that both liposomes and drug were taken up by multiple myeloma cells, and that uptake of a fluorescent ATP derivative was significantly greater when encapsulated than when free. Liposomes prepared from EDPPC, having a higher phase-transition temperature than EDOPC, captured 8-NH₂-ATP satisfactorily and released it more slowly than the unsaturated formulations, but were also less cytotoxic. The superior encapsulation efficiencies of the positively charged liposomes can be understood in terms of the electrostatic double layer due to a very high positive charge density on their inner surface. Electrostatic augmentation of encapsulation for small vesicles can be dramatic, easily exceeding an order of magnitude.
三磷酸腺苷（ATP）的 8 位取代类似物已被证明对多发性骨髓瘤具有细胞毒性，多发性骨髓瘤是最常见和最严重的血液癌之一。然而，这些药物不易穿过生物膜，并且对体液中存在的磷酸酶非常敏感。为了规避这些缺点，8 位取代的 ATP 被包裹在阳离子磷脂体中，这些阳离子磷脂体由阳离子磷脂（EDOPC；1,2-二油酰基-sn-甘油-3-乙基磷酸胆碱和 EDPPC，相应的二棕榈酰同系物）生成，这些化合物毒性低，很容易形成脂质体。涡旋是一种有效的包裹程序，比冻融更有效。在脂质：药物比为 5:1（摩尔/摩尔）时，20%的 8-Br-ATP 被包裹在 EDOPC 脂质体中。8-NH₂-ATP 的有效包裹和保留需要胆固醇的存在。EDOPC：胆固醇（55:45 摩尔/摩尔）的脂质体，在脂质：药物摩尔比为 10:1 时，可捕获约 40%的药物。该制剂对培养中的多发性骨髓瘤细胞的细胞毒性试验表明，包裹药物的效力比游离药物高 10 倍，具体取决于剂量。细胞内分布研究（基于脂质和 ATP 的荧光衍生物）表明，脂质体和药物都被多发性骨髓瘤细胞摄取，并且当包裹时，荧光 ATP 衍生物的摄取量明显大于游离时。与 EDOPC 相比，具有较高相转变温度的 EDPPC 制备的脂质体可以令人满意地捕获 8-NH₂-ATP 并释放它更慢，但也毒性更低。正电荷脂质体的优异包裹效率可以根据其内部表面上的非常高的正电荷密度来理解静电双层。对于小泡，静电包裹效率可以显著增强，很容易超过一个数量级。
