Preparation and targeted delivery of immunoliposomes bearing poly(ethylene glycol)-coupled humanized anti-hepatoma disulfide-stabilized Fv (hdsFv25) in vitro

Peptides in bee venom (PBV) have attracted considerable attention for anti-cancer therapy. In this study, sterically stabilized liposomal PBV (PBV-SL) was prepared using Soybean phosphatidylcholine, cholesterol, and the cholesterol derivatives of PEG with terminal COOH groups. The humanized anti-hepatoma disulfide-stabilized Fv (hdsFv25) was coupled to sterically stabilized liposomes. The hdsFv25-immunoliposome has strong affinity and specificity to SMMC-7721 cells in vitro. PBV-loaded sterically stabilized liposomes modified with the hdsFv25 can kill SMMC-7721 cells in vitro with higher efficiency than non-targeted liposomes. These results demonstrate that this strategy should also be applicable to immunotherapy for other cancers.     

Preparation, characterization, and biodistribution study of technetium-99m-labeled leuprolide acetate-loaded liposomes in ehrlich ascites tumor-bearing mice

The purpose of this study was to prepare conventional and sterically stabilized liposomes containing leuprolide acetate in an attempt to prolong the biological half life of the drug, to reduce the uptake by reticuloendothelial system (RES), and to reduce the injection frequency of intravenously administered peptide drugs. The conventional and sterically stabilized liposomes containing leuprolide acetate were prepared by reverse phase evaporation method and characterized for entrapment efficiency and particle size. Radiolabeling of leuprolide acetate and its liposomes was performed by direct labeling with reduced technetium-99m. Its biodistribution and imaging characteristics were studied in ehrlich ascites tumor (EAT)-bearing mice after labeling with technetium-99m. The systemic pharmacokinetic studies were performed in rabbits. A high uptake by tumor was observed by sterically stabilized liposome containing leuprolide acetate compared with free drug and conventional liposomes. The liver/tumor uptake ratio of free drug, conventional (LL), and sterically stabilized liposomes (SLL5000 and SLL2000) was found to be 20, 7.99, 1.63, and 1.23, respectively, which showed the increased accumulation of sterically stabilized liposomes in tumor compared with the free drug and conventional liposomes at 24 hours postinjection. Liver uptake of sterically stabilized liposomes was still 7-fold less than the conventional liposomes. The marked accumulation of liposomes in the tumor-bearing mice was also documented by gamma scintigraphic studies. The findings demonstrate the distribution of these liposomes within solid tumor and prove that the sterically stabilized liposomes experience increased tumor uptake and prolonged circulation half life. Hence these findings will be relevant for the optimal design of long circulating liposomes for the peptide drugs and for targeting of liposomes toward tumor.     

Liposomes modified with cyclic RGD peptide for tumor targeting

Cyclic RGD peptide anchored sterically stabilized liposomes (RGD-SL) were investigated for selective and preferential presentation of carrier contents at angiogenic endothelial cells overexpressing alphavbeta3 integrins on and around tumor tissue and thus for assessing their targetabilty. Liposomes were prepared using distearoylphosphatidylcholine (DSPC), cholesterol and distearoylphosphatidylethanolamine-polyethyleneglycol-RGD peptide conjugate (DSPE-PEG-RGD) in a molar ratio 56:39:5. The control RAD peptide anchored sterically stabilized liposomes (RAD-SL) and liposome with 5 mol% PEG (SL) without peptide conjugate which had similar lipid composition were used for comparison. The average size of all liposome preparations prepared was approximately 105 nm and maximum drug entrapment was 10.5+/- 1.1%. In vitro endothelial cell binding of liposomes exhibited 7-fold higher binding of RGD-SL to HUVEC in comparison to the SL and RAD-SL. Spontaneous lung metastasis and angiogenesis assays show that RGD peptide anchored liposomes are significantly (p<0.01) effective in the prevention of lung metastasis and angiogenesis compared to free 5-FU, SL and RAD-SL. In therapeutic experiments, 5-FU, SL, RGD-SL and RAD-SL were administered intravenously on day 4 at the dose of 10 mg 5-FU/kg body weight to B16F10 tumor bearing BALB/c mice resulting in effective regression of tumors compared with free 5-FU, SL and RAD-SL. Results indicate that cyclic RGD peptide anchored sterically stabilized liposomes bearing 5-FU are significantly (p<0.01) active against primary tumor and metastasis than the non-targeted sterically stabilized liposomes and free drug. Thus cyclic RGD peptide anchored sterically stabilized liposomes hold potential of targeted cancer chemotherapeutics.     

Target ability and therapy efficacy of immunoliposomes using a humanized antihepatoma disulfide-stabilized Fv fragment on tumor cells

Recently the use of peptides in bee venom (PBV) for cancer therapy has attracted considerable attention. However, PBV's extensive use is prohibited by its intense hemolytic activity. In this study, the sterically stabilized liposomal PBV (PBV-SL) was prepared using soybean phosphatidylcholine, cholesterol, and cholesterol-PEG-COOH. The humanized antihepatoma disulfide-stabilized Fv (hdsFv25) was reengineered, expressed, and coupled to sterically stabilized liposomes using the N-hydroxysuccinimide ester method. The hdsFv25-immunoliposomes (SIL [hdscFv25]) were immunoreactive as determined by ELISA assay. PBV-SIL [hdscFv25] can kill SMMC-7721 cells in vitro with higher efficiency than nontargeted liposomes. PBV-SIL [hdsFv25] displayed high antitumor activity and resulted in a significant reduction in tumor size compared to nontargeted liposomes and PBV. These results indicated that this strategy should be applicable to applicable in the treatment of other cancers.     

蜂毒多肽空间稳定免疫脂质体的制备及体外对肿瘤细胞的选择性

蜂毒多肽在肿瘤治疗中的应用引起研究者的极大兴趣。本研究使用大豆磷脂、胆固醇、羧酸化PEG-胆固醇制备了蜂毒多肽空间稳定脂质体，并将二硫键稳定抗人肝癌单链抗体联结PEG-胆固醇末端。使用酶联免疫法考察了蜂毒多肽空间稳定免疫脂质体的活性。蜂毒多肽空间稳定免疫脂质体有较高的肿瘤细胞选择性。体外实验证明，其对SMMC-7721细胞的杀伤能力远强于蜂毒多肽空间脂质体，而对Hela细胞的杀伤能力与蜂毒多肽空间脂质体无区别。蜂毒多肽空间稳定免疫脂质体对肿瘤细胞的选择性，可使其成为一种有效的靶向制剂。     

Liposomes Modified with Cyclic RGD Peptide for Tumor Targeting

Cyclic RGD peptide anchored sterically stabilized liposomes (RGD-SL) were investigated for selective and preferential presentation of carrier contents at angiogenic endothelial cells overexpressing α_vβ₃ integrins on and around tumor tissue and thus for assessing their targetabilty. Liposomes were prepared using distearoylphosphatidylcholine (DSPC), cholesterol and distearoylphosphatidylethanolamine–polyethyleneglycol–RGD peptide conjugate (DSPE–PEG–RGD) in a molar ratio 56:39:5. The control RAD peptide anchored sterically stabilized liposomes (RAD-SL) and liposome with 5 mol% PEG (SL) without peptide conjugate which had similar lipid composition were used for comparison. The average size of all liposome preparations prepared was approximately 105 nm and maximum drug entrapment was 10.2±1.1%. In vitro endothelial cell binding of liposomes exhibited 7-fold higher binding of RGD-SL to HUVEC in comparison to the SL and RAD-SL. Spontaneous lung metastasis and angiogenesis assays show that RGD peptide anchored liposomes are significantly (p<0.01) effective in the prevention of lung metastasis and angiogenesis compared to free 5-FU, SL and RAD-SL. In therapeutic experiments, 5-FU, SL, RGD-SL and RAD-SL were administered intravenously on day 4 at the dose of 10 mg 5-FU/kg body weight to B16F10 tumor bearing BALB/c mice resulting in effective regression of tumors compared with free 5-FU, SL and RAD-SL. Results indicate that cyclic RGD peptide anchored sterically stabilized liposomes bearing 5-FU are significantly (p<0.01) active against primary tumor and metastasis than the non-targeted sterically stabilized liposomes and free drug. Thus cyclic RGD peptide anchored sterically stabilized liposomes hold potential of targeted cancer chemotherapeutics.     

Assessment of targeting potential of galactosylated and mannosylated sterically stabilized liposomes to different cell types of mouse liver

Galactose and Mannose residues were tagged on the surface of n-glutaryl-phosphatidylethanolamine (NGPE) containing liposomes with and without polyethylene glycol of molecular weight 2000 Da conjugated to distearoyl phosphatidylethanolamine (PEG-2000-DSPE). Biodistribution studies showed that sugar bearing liposomes were cleared more rapidly from circulation than those not bearing the sugar moieties. However, the rate of clearance of glycosylated conventional liposomes was much faster than the sugar bearing sterically stabilized liposomes. Intrahepatic distribution studies showed that a substantial amount of conventional liposomes without sugar residues were taken up by both parenchymal (P) (40%) and non-parenchymal (NP) cells (60%). However, incorporation of PEG-2000-DSPE shifted this uptake slightly in favour of parenchymal cells (47%). While ratio of distribution of galactosylated conventional liposomes to P and NP cells was found to be 74:26, galactosylation of sterically stabilized liposomes further enhanced the affinity of these vesicles towards P cells (P:NP ratio being 93:7). Thus, reduced uptake by Kupffer cells was observed with galactosylated sterically stabilized liposomes as compared to conventional liposomes. Whereas, mannosylation of both the liposomes shifted the distribution towards Kupffer cells in an analogous manner. These findings indicate that sterically stabilized liposomes tagged with galactose residues on their surface are more effective in targeting the entrapped material to hepatocytes as compared to conventional liposomes. This approach can therefore be employed for delivering therapeutic agents like drugs, enzymes, genetic materials, anti-sense oligonucleotides selectively to liver P cells for treatment of hepatic disorders.     

Antagonism of paraoxon intoxication by recombinant phosphotriesterase encapsulated within sterically stabilized liposomes

This investigation effort is focused on increasing organophosphate (OP) degradation by phosphotriesterase to antagonize OP intoxication. For these studies, sterically stabilized liposomes encapsulating recombinant phosphotriesterase were employed. This enzyme was obtained from Flavobacterium sp. and was expressed in Escherichia coli. It has a broad substrate specificity, which includes parathion, paraoxon, soman, sarin, diisopropylfluorophosphate, and other organophosphorous compounds. Paraoxon is rapidly hydrolyzed by phosphotriesterase to the less toxic 4-nitrophenol and diethylphosphate. This enzyme was isolated and purified over 1600-fold and subsequently encapsulated within sterically stabilized liposomes (SL). The properties of this encapsulated phosphotriesterase were investigated. When these liposomes containing phosphotriesterase were incubated with paraoxon, it readily degraded the paraoxon. Hydrolysis of paraoxon did not occur when these sterically stabilized liposomes contained no phosphotriesterase. These sterically stabilized liposomes (SL) containing phosphotriesterases (SL)* were employed as a carrier model to antagonize the toxic effects of paraoxon by hydrolyzing it to the less toxic 4-nitrophenol and diethylphosphate. This enzyme-SL complex (SL)* was administered intravenously to mice either alone or in combination with pralidoxime (2-PAM) and/or atropine intraperitoneally. These results indicate that this carrier model system provides a striking enhanced protective effects against the lethal effects of paraoxon. Moreover when these carrier liposomes were administered with 2-PAM and/or atropine, a dramatic enhanced protection was observed.     

Nasal Delivery. The Use of Animal Models to Predict Performance in Man

Abstract

Galactose and Mannose residues were tagged on the surface of n-glutaryl-phosphatidyl-ethanolamine (NGPE) containing liposomes with and without polyethylene glycol of molecular weight 2000 Da conjugated to distearoyl phosphatidylethanolamine (PEG-2000-DSPE). Biodistribution studies showed that sugar bearing liposomes were cleared more rapidly from circulation than those not bearing the sugar moieties. However, the rate of clearance of glycosylated conventional liposomes was much faster than the sugar bearing sterically stabilized liposomes. Intrahepatic distribution studies showed that a substantial amount of conventional liposomes without sugar residues were taken up by both parenchymal (P) (40%) and non-parenchymal (NP) cells (60%). However, incorporation of PEG-2000-DSPE shifted this uptake slightly in favour of parenchymal cells (47%). While ratio of distribution of galactosylated conventional liposomes to P and NP cells was found to be 74: 26, galactosylation of sterically stabilized liposomes further enhanced the affinity of these vesicles towards P cells (P: NP ratio being 93: 7). Thus, reduced uptake by Kupffer cells was observed with galactosylated sterically stabilized liposomes as compared to conventional liposomes. Whereas, mannosylation of both the liposomes shifted the distribution towards Kupffer cells in an analogous manner. These findings indicate that sterically stabilized liposomes tagged with galactose residues on their surface are more effective in targeting the entrapped material to hepatocytes as compared to conventional liposomes. This approach can therefore be employed for delivering therapeutic agents like drugs, enzymes, genetic materials, anti-sense oligonucleotides selectively to liver P cells for treatment of hepatic disorders.     

全反式维甲酸立体稳定脂质体的制备

目的　制备全反式维甲酸(RA)的立体稳定脂质体,初步研究其物理化学性质。方法　用DSC、¹HNMR、激光粒径测定仪研究其微观结构、粒径大小及其分布,并用TEM拍摄。结果　制备的普通和立体稳定脂质体粒径分别约为0.35和0.42 μm,电镜下可观察到脂质体的立体稳定结构。结论　立体稳定脂质体中磷脂极性头部被吐温-80的聚氧乙烯基所覆盖,吐温-80掺入脂质膜,伸出的亲水性聚氧乙烯基提供了RA立体稳定脂质体的立体位阻。     

Liposomes modified with YIGSR peptide for tumor targeting

YIGSR peptide anchored sterically stabilized liposomes (YIGSR-SL) were investigated for selective and preferential presentation of carrier contents at angiogenic endothelial cells overexpressing laminin receptors on and around tumor tissue and thus for assessing their targetabilty. In vitro endothelial cell binding of liposomes exhibited 7-fold higher binding of YIGSR-SL to HUVEC in comparison to the nontargeted sterically stabilized liposomes (SL). Spontaneous lung metastasis and angiogenesis assays show that YIGSR peptide anchored liposomes are significantly (P ≤ 0.01) effective in the prevention of lung metastasis and angiogenesis compared to free 5-fluorouracil (5-FU) and SL. YIGSR-SL was very effective in regression of tumors in BALB/c mice bearing B16F10 melanoma cells. Results indicate that YIGSR peptide anchored sterically stabilized liposomes bearing 5-FU are significantly (P ≤ 0.01) active against primary tumor and metastasis than the SL and free drug. Thus, YIGSR peptide anchored sterically stabilized liposomes hold potential of targeted cancer chemotherapeutics.     

人鼠嵌合抗肿瘤细胞核单抗-空间稳定脂质体的制备及其体外靶向

目的研究人鼠嵌合抗肿瘤细胞核单抗(chTNT-3)-空间稳定脂质体的制备方法、免疫活性及体外靶向性。方法合成聚乙二醇末端带吡啶二硫丙酰基的磷脂衍生物(PDP-PEG-HSPE)，制备含PDP-PEG-HSPE的空间稳定脂质体，经二巯基苏糖醇还原后共价连接马来酰亚胺衍生化抗体。荧光胺法和钼蓝法测定脂质体与抗体的连接效率及抗体密度，激光散射粒度仪测定其粒径分布，ELISA法检测脂质体表面的抗体免疫活性。体外实验考察该免疫脂质体与固定Raji细胞的结合活性。结果chTNT-3-空间稳定脂质体的粒径分布为(115±33) nm。当初始Ab/PDP-PEG-HSPE=1∶10时，脂质体与抗体的连接效率为71%，抗体密度为106 μg Ab/μmol PL。chTNT-3经化学修饰后连接到脂质体表面，其免疫活性基本保留。chTNT-3-空间稳定脂质体能特异性地结合固定Raji细胞。结论通过PDP-PEG-HSPE法共价连接抗体制备的chTNT-3-空间稳定脂质体能基本保留chTNT-3的免疫活性，具有体外靶向细胞核抗原的能力。     

Effect of surfactants on the stability of modified egg-yolk phosphatidyl choline liposomes

Disintegration by surfactants on egg-yolk phosphatidyl choline (PC) vesicles, stabilized with polycholesteryl methacrylate and carboxy methyl chitosan, was investigated by measuring the amount of marker dye (bromothymol blue) released from the vesicles. In all the studies at pH 7.4 anionic and nonionic surfactants caused vesicle disintegration at low concentrations while cationic surfactants produced breakdown of vesicles at high concentrations. It was found that the modified liposomes disintegrated in the following order: Polymeric liposomes less than carboxymethyl chitosan coated/stearic acid/oleic acid containing PC liposomes less than cholesteryl methacrylate monomer containing PC liposomes/PC liposomes Polymeric liposomes were found to be the most stable compared with all other types. This may be explained due to the filling of the pores in the lipid structure which in turn block the surfactant penetration into phospholipid bilayers. In contrast to unsaturated fatty acid (oleic acid) saturated fatty acid (stearic acid) containing liposomes are more stable.     

Liposomal bleomycin: increased therapeutic activity and decreased pulmonary toxicity in mice

Conventional and sterically stabilized liposomes derived from phosphatidylcholine or the antitumor agents, hexadecylphosphocholine and octadecyl-(1,1-dimethyl-4-piperidino-4-yl)-phosphate, as bilayer forming constituents, containing bleomycin, were developed and tested. Liposomal encapsulation of bleomycin enhanced strongly the antitumor activity against P388 leukemia and the Lewis lung carcinoma. This effect was clearly dependent on the size and lipid composition of the bleomycin-containing liposomes. The therapeutic effects were nearly equal for liposomal and free bleomycin in the B16 melanoma. The partial replacement of phosphatidylcholine by alkylphospholipids and the inclusion of polyethylene glycol modified lipids for sterical stabilization did not further improve the therapeutic efficacy but increased, in some cases, the toxicity of liposomes. Bleomycin-induced lung injury was not observed if liposomal bleomycin was administered.     

Serum-stable, long-circulating paclitaxel-loaded colloidal carriers decorated with a new amphiphilic PEG derivative

The paper describes sterically stabilized lipid nanocapsules (LNC) and multilamellar liposomes (MLV) coated using a new amphiphilic conjugate of PEG(2000) with a 2-alkyl-lipoamino acid (LAA). A complement activation assay (CH50) and uptake experiments by THP-1 macrophage cells were used to assess in vitro the effectiveness of the PEG-LAA derivative of modifying the surface behavior of nanocarriers. Administered to rats or Swiss mice, respectively, the PEG(2000)-LAA-modified LNC and MLV showed plasma half-lives longer than the corresponding naked carriers. To assess the ability of nanocarriers to specifically reach tumor sites, paclitaxel (PTX)-loaded LNC and MLV were administered subcutaneously to rats implanted with a 9L glioma. Animals treated with saline or naked LNC and MLV underwent a quick expansion of tumor mass, up to a volume of 2000 mm(3) 25 days after the injection of tumor cells. On the contrary, treatment with a PEG-LAA modified LNC carrier reduced the growth of the tumor volume, which did not exceed 1000 mm(3) by day 25. Analogous positive results were obtained with the liposomal systems. The experimental findings confirmed that these new PEG-LAA conjugates allow to obtain sterically stable nanocarriers that behave effectively and in a comparable or even better way than the (phospho)lipid PEG derivatives commercially available.     

Subcutaneous administration of sterically stabilized (stealth) liposomes is an effective sustained release system for 1-β-d-arabinofuranosylcytosine

We have previously demonstrated that 1-β-D-arabinofuranosylcytosine (ara-C) entrapped in long-circulating formulations of liposomes (Stealth, or sterically stabilized) was an effective sustained release system following intravenous (iv) or intraperitoneal (ip) administration (Cancer Res. 52, 2431-2439). We have recently shown that, following subcutaneous (sc) administration, Stealth liposomes can achieve substantial levels in the circulation. The therapeutic effect of sc-administered liposomal ara-C against murine L1210 leukemia was examined as a function of route of injection, liposome size, and liposome composition. When the liposomes contained polyethylene glycol-distearoylphosphatidylethanolamine (PEG-DSPE) and cholesterol, sc injection was as effective in increasing lifespan as iv injection against iv or ip tumor. This effect was independent of liposome size or fluidity of the phospholipid. Liposomes lacking PEG-DSPE or lacking cholesterol were significantly less efficacious. Long-term survivors could be obtained following three weekly sc injections of PEG-liposomes.     

A targeted liposome delivery system for combretastatin A4: formulation optimization through drug loading and in vitro release studies

Efficient liposomal therapeutics require high drug loading and low leakage. The objective of this study is to develop a targeted liposome delivery system for combretastatin A4 (CA4), a novel antivascular agent, with high loading and stable drug encapsulation. Liposomes composed of hydrogenated soybean phosphatidylcholine (HSPC), cholesterol, and distearoyl phosphoethanolamine-PEG-2000 conjugate (DSPE-PEG) were prepared by the lipid film hydration and extrusion process. Cyclic arginine-glycine-aspartic acid (RGD) peptides with affinity for alphav beta3-integrins overexpressed on tumor vascular endothelial cells were coupled to the distal end of polyethylene glycol (PEG) on the liposomes sterically stabilized with PEG (non-targeted liposomes; LCLs). Effect of lipid concentration, drug-to-lipid ratio, cholesterol, and DSPE-PEG content in the formulation on CA4 loading and its release from the liposomes was studied. Total liposomal CA4 levels obtained increased with increasing lipid concentration in the formulation. As the drug-to-lipid ratio increased from 10:100 to 20:100, total drug in the liposome formulation increased from 1.05+/-0.11 mg/mL to 1.55+/-0.13 mg/mL, respectively. When the drug-to-lipid ratio was further raised to 40:100, the total drug in liposome formulation did not increase, but the amount of free drug increased significantly, thereby decreasing the percent of entrapped drug. Increasing cholesterol content in the formulation decreased drug loading. In vitro drug leakage from the liposomes increased with increase in drug-to-lipid ratio or DSPE-PEG content in the formulation; whereas increasing cholesterol content of the formulation up to 30 mol-percent, decreased CA4 leakage from the liposomes. Ligand coupling to the liposome surface increased drug leakage as a function of ligand density. Optimized liposome formulation with 100 mM lipid concentration, 20:100 drug-to-lipid ratio, 30 mol-percent cholesterol, 4 mol-percent DSPE-PEG, and 1 mol-percent DSPE-PEG-maleimide content yielded 1.77+/-0.14 mg/mL liposomal CA4 with 85.70+/-1.71% of this being entrapped in the liposomes. These liposomes, with measured size of 123.84+/-41.23 nm, released no significant amount of the encapsulated drug over 48 h at 37 degrees C.     

Long circulating liposomes of 2',3'-dideoxyinosine: Formulation and stability

2',3'-Dideoxyinosine (ddI), an anti-human immunodeficiency virus (HIV) agent, was encapsulated in liposomes. The influence of the phospholipid/cholesterol ratio, concentration of phospholipid (PL), and chain length of PL on the encapsulation of ddI in multilamellar vesicles (MLVs), frozen and thawed multilamellar vesicles (FAT MLVs), and large unilamellar vesicles (LUVs) was studied. An optimum formulation was then selected to prepare long circulating liposomes. Stability studies at 4, 25, and 37°C and under certain stress conditions were performed. Release characteristics in phosphate buffer (pH 7.4) at 37°C were studied. Results show an increase in encapsulation efficiency (EE) with increasing amounts of cholesterol, a decrease in EE and increase in encapsulation yield (EY) with increasing concentrations of PL, and an increase in EE with increases in PL chain length, in both MLVs and LUVs. Freezing and thawing of MLVs had no influence on EE at a PL concentration of 10 mg/mL but increased EE at higher concentrations of PL. Various stability tests showed the formulation to be stable to leakage of entrapped drug when stored at 4, 25, and 37°C for 6 months, when subjected to mechanical stress, and on exposure to human serum. The release studies indicated that 70% of ddI was released over a period of 72 h.     

Long-circulating, pH-sensitive liposomes sterically stabilized by copolymers bearing short blocks of lipid-mimetic units

A major hurdle towards in vivo utilization of pH-sensitive liposomes is their prompt sequestration by reticuloendothelial system and hence short circulation time. Prolonged circulation of liposomes is usually achieved by incorporation of pegylated lipids, which have been frequently reported to deteriorate the acid-triggered release. In this study we evaluate the ability of four novel nonionic copolymers, bearing short blocks of lipid-mimetic units to provide steric stabilization of DOPE:CHEMs liposomes. The vesicles were prepared using the lipid film hydration method and extrusion, yielding liposomes of 120–160 nm in size. Their pH-sensitivity was monitored via the release of encapsulated calcein. The incorporation of the block copolymers at concentration up to 10 mol% did not deteriorate the pH-sensitivity of the liposomes. A selected formulation was tested for stability in presence of 25% human plasma and proved to significantly outclass the plain DOPE:CHEMs liposomes. The ability of calcein-loaded liposomes to deliver their cargo inside EJ cells was investigated using fluorescent microscopy and the results show that the surface-modified vesicles are as effective to ensure intracellular delivery as plain liposomes. The pharmacokinetics and organ distribution of a selected formulation, containing a copolymer bearing four lipid anchors was investigated in comparison to plain liposomes and PEG (2000)–DSPE stabilized liposomes. The juxtaposition of the blood clearance curves and the calculated pharmacokinetic parameters show that the block copolymer confers superior longevity in vivo. The block copolymers utilized in this study can be consider as promising sterically stabilizing agents for pH-sensitive liposomes.     

甲氧基聚乙二醇-磷脂酰乙醇胺的制备及其对脂质体的稳定作用

采用两步反应法制备脂质体空间稳定膜材料甲氧基聚乙二醇-磷脂酰乙醇胺(MPEG—EPE)，并用以制备空间稳定脂质体(SLs)，同时制备不含MPEG—EPE的传统脂质体(CLs)，比较两者放置过程中粒径变化、加乙醇后浊度变化、包封钙黄绿素后在冻干-再水化过程中的荧光泄漏程度及其与人血浆蛋白的吸附指标，评价MPEG2000-EPE对脂质体的稳定作用。结果表明，试验前后SLs的粒径及浊度变化不大，荧光泄漏程度和人血浆蛋白吸附量也远小于CLs，提示其对脂质体有良好的稳定作用。