Neal J C, Stolnik S, Schacht E, Kenawy E R, Garnett M C, Davis S S, Illum L
Department of Pharmaceutical Sciences, University of Nottingham, University Park, Nottingham, NG7 2RD, England.
J Pharm Sci. 1998 Oct;87(10):1242-8. doi: 10.1021/js970462j.
Poloxamer 407 and poloxamine 908 have been used by many research groups to modify the surface of both model latex and biodegradable nanospheres, thereby producing nanospheres that have shown reduced protein adsorption in vitro and extended circulation times in vivo. A potential limitation of such systems is the desorption of the copolymer coating layer. We describe a two-stage process to radiolabel poloxamer 407 and poloxamine 908 that has facilitated an investigation into this potential desorption, in vitro. The first stage of the labeling procedure involved the substitution of the terminal hydroxyl groups in each poly(ethylene oxide) (PEO) chain of poloxamer 407 and poloxamine 908 with an amino group. The aminated copolymers were then radiolabeled with 125Iodine Bolton-Hunter reagent. The efficiency of labeling was calculated to be approximately 20% for the tetramine poloxamine 908 and approximately 33% for the diamine poloxamer 407. Remaining free amino groups were then either acetylated, using acetic anhydride, or left in the free amino form. Covalent linkage of the radiolabel to the copolymer was confirmed by nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy. The stability of the link between radiolabel and copolymer to hydrolysis was also confirmed; <4% loss of radiolabel occurred from poloxamine 908 after incubation in phosphate-buffered saline (PBS) at 37 degrees C for 8 days. The radiolabeled copolymers (with the free amino groups acetylated) were then used in experiments that have given the first direct evidence that adsorbed copolymers can be displaced by serum proteins in significant amounts from the surface of model and biodegradable nanospheres. The displacement was highly dependent on copolymer-nanosphere compatibility, with up to 78% of 125I tetramine poloxamine 908 being displaced from poly(lactide-co-glycolide) (PLGA) nanospheres in 24 h, compared with 20% displacement of 125I tetramine poloxamine 908 in 24 h from polystyrene nanospheres. These results have direct implication for the future design of drug delivery systems based on coated nanospheres.
许多研究小组已使用泊洛沙姆407和泊洛沙明908来修饰模型乳胶和可生物降解纳米球的表面，从而制备出在体外显示出减少蛋白质吸附且在体内具有延长循环时间的纳米球。此类系统的一个潜在局限性是共聚物涂层的解吸。我们描述了一种对泊洛沙姆407和泊洛沙明908进行放射性标记的两阶段方法，该方法有助于在体外对此潜在解吸进行研究。标记程序的第一阶段涉及用氨基取代泊洛沙姆407和泊洛沙明908的每个聚环氧乙烷（PEO）链中的末端羟基。然后用125碘博尔顿-亨特试剂对胺化共聚物进行放射性标记。计算得出四胺泊洛沙明908的标记效率约为20%，二胺泊洛沙姆407的标记效率约为33%。然后，剩余的游离氨基要么用乙酸酐进行乙酰化，要么保持游离氨基形式。通过核磁共振（NMR）和红外（IR）光谱证实了放射性标记与共聚物的共价连接。还证实了放射性标记与共聚物之间的连接对水解的稳定性；在37℃的磷酸盐缓冲盐水（PBS）中孵育8天后，泊洛沙明908的放射性标记损失<4%。然后将放射性标记的共聚物（游离氨基已乙酰化）用于实验，这些实验首次直接证明吸附的共聚物可被血清蛋白从模型和可生物降解纳米球表面大量取代。这种取代高度依赖于共聚物与纳米球的相容性，24小时内多达78%的125I四胺泊洛沙明908从聚（丙交酯-共-乙交酯）（PLGA）纳米球上被取代，而24小时内125I四胺泊洛沙明908从聚苯乙烯纳米球上的取代率为20%。这些结果对基于包被纳米球的药物递送系统的未来设计具有直接影响。
