Torchilin V P, Levchenko T S, Whiteman K R, Yaroslavov A A, Tsatsakis A M, Rizos A K, Michailova E V, Shtilman M I
Department of Pharmaceutical Sciences, Bouve College of Health Sciences, Northeastern University, Boston, MA 02115, USA.
Biomaterials. 2001 Nov;22(22):3035-44. doi: 10.1016/s0142-9612(01)00050-3.
Certain amphiphilic water-soluble polymers including amphiphilic derivatives of polyvinyl pyrrolidone (PVP) were found to be efficient steric protectors for liposomes in vivo. In this study, we have tried to develop synthetic pathways for preparing amphiphilic PVP and to investigate the influence of the hydrophilic/hydrophobic blocks on some properties of resulting polymers and polymer-coated liposomes. To prepare amphiphilic PVP with the end stearyl (S) or palmityl (P) residues, amino- and carboxy-terminated PVP derivatives were first synthesized by the free-radical polymerization of vinyl pyrrolidone in the presence of amino- or carboxy-mercaptans as chain transfer agents, and then modified by interaction of amino-PVP with stearoyl chloride or palmitoyl chloride, or by dicyclohexyl carbodiimide coupling of stearylamine with carboxy-PVP. ESR-spectra of the hydrophobic spin-probe, nitroxyl radical N-oxyl-2-hexyl-2-(10-methoxycarbonyl)decyl-4,4'-dimethyl oxazoline, in the presence of amphiphilic PVP demonstrated good accessibility of terminal P- and S-groups for the interaction with other hydrophobic ligands. Spontaneous micellization and low CMC values (in a low micromolar range) were found for amphiphilic PVP derivatives using the pyrene method. In general, S-PVP forms more stable micelles than P-PVP (at similar MW, CMC values for S-PVP are lower than for P-PVP). It was found that amphiphilic PVP incorporated into negatively charged liposomes effectively prevents polycation(poly-ethylpyridinium-4-vinylchloride)-induced liposome aggregation, completely abolishing it at ca. 10 mol% polymer content in liposomes. Additionally, the liposome-incorporated PVP prevents the fluorescence quenching of the membrane-incorporated hydrophobic fluorescent label [N-(4-fluoresceinthiocarbamoyl)dipalmitoyl-PE] by the free polycation. PVP-modified liposomes were loaded with a self-quenching concentration of carboxyfluorescein, and their destabilization in the presence of mouse serum was investigated following the release of free dye. Amphiphilic PVP with MW between 1,500 and 8,000 provides good steric protection for liposomes. The degree of this protection depends on both polymer concentration and molecular size of the PVP block.
某些两亲性水溶性聚合物，包括聚乙烯吡咯烷酮（PVP）的两亲性衍生物，被发现是体内脂质体的有效空间保护剂。在本研究中，我们试图开发制备两亲性PVP的合成途径，并研究亲水/疏水嵌段对所得聚合物和聚合物包被脂质体某些性质的影响。为了制备带有末端硬脂酰基（S）或棕榈酰基（P）残基的两亲性PVP，首先通过在氨基或羧基硫醇作为链转移剂存在下进行乙烯基吡咯烷酮的自由基聚合来合成氨基和羧基末端的PVP衍生物，然后通过氨基-PVP与硬脂酰氯或棕榈酰氯的相互作用，或通过硬脂胺与羧基-PVP的二环己基碳二亚胺偶联进行修饰。在两亲性PVP存在下，疏水自旋探针、硝酰自由基N-氧基-2-己基-2-(10-甲氧基羰基)癸基-4,4'-二甲基恶唑啉的电子自旋共振光谱表明末端P-和S-基团易于与其他疏水配体相互作用。使用芘方法发现两亲性PVP衍生物具有自发胶束化和低临界胶束浓度值（在低微摩尔范围内）。一般来说，S-PVP比P-PVP形成更稳定的胶束（在相似分子量下，S-PVP的临界胶束浓度值低于P-PVP）。发现掺入带负电荷脂质体中的两亲性PVP有效地防止了聚阳离子（聚乙基吡啶-4-乙烯基氯）诱导的脂质体聚集，在脂质体中聚合物含量约为10摩尔%时完全消除了这种聚集。此外，掺入脂质体的PVP可防止游离聚阳离子对膜结合的疏水荧光标记物[N-(4-荧光素硫代氨基甲酰基)二棕榈酰磷脂酰乙醇胺]的荧光猝灭。用自猝灭浓度的羧基荧光素装载PVP修饰的脂质体，并在释放游离染料后研究其在小鼠血清存在下的不稳定情况。分子量在1500至8000之间的两亲性PVP为脂质体提供了良好的空间保护。这种保护程度取决于聚合物浓度和PVP嵌段的分子大小。
