第三代载药免疫脂质体及体内外寻靶研究

目的　研究载阿霉素第三代免疫脂质体的制备及体内外寻靶、抑瘤效果。方法　设计将人膀胱癌单抗与聚乙二醇羧酸(PEG-COOH)端相联,使构成的脂质体既充分发挥PEG的保护功能,延长药物血循环时间,又使单抗伸展在外部充分发挥其寻靶作用,即第三代免疫脂质体(IML)。进而研究载抗癌药的免疫脂质体的制备方案,制备出阿霉素免疫脂质体(IML-ADM)使达到对药物高包封、高稳定,又不降低单抗活性的目的。以人膀胱癌靶细胞EJ和人直肠癌非靶细胞LOVO进行体外杀伤和体内肿瘤的抑瘤实验。结果　IML-ADM对EJ细胞和LOVO细胞杀伤,及对EJ细胞移植瘤体的抑制与对照组比较均有显著性差异。结论　证实脂质体载药以单抗制导达到主动靶向给药是可行的     

单克隆抗体BDI-I导向的阿霉素白蛋白毫微球对人膀胱癌细胞的特异杀伤活性

用化学偶联法将抗人膀胱癌单克隆抗体分子偶联到阿霉素白蛋白毫微球上,构建了一个有靶向杀伤性的免疫毫微球,即:阿霉素白蛋白载单克隆抗体毫微球(ADR-NP-Ab)。改变阿霉素毫微球和单克隆抗体的反应分子比,确定了制备该免疫毫微球的最佳条件。经免疫荧光检测及显微照像分析证明,免疫毫微球可有效地和人膀胱癌细胞结合。体外杀伤试验表明,此免疫毫微球对靶细胞EJ有高度特异杀伤活性,而对无关的人直肠癌Lovo细胞则无明显作用。     

单克隆抗体BDI－I导向的阿霉素白蛋白毫微球对人膀胱癌细胞的特异杀伤活性

用化学偶联法将抗人膀胱癌单克隆抗体分子偶联到阿霉素白蛋白毫微球上，构建了一个有靶向杀伤性的免疫毫微球，即：阿霉素白蛋白载单克隆抗体毫微球（ＡＤＲ－ＮＰ－Ａｂ）。改变阿霉素毫微球和单克隆抗体的反应分子比，确定了制备该免疫毫微球的最佳条件。经免疫荧光检测及显微照像分析证明，免疫毫微球可有效地和人膀胱癌细胞结合。体外杀伤试验表明，此免疫毫微球对靶细胞ＥＪ有高度特异杀伤活性，而对无关的人直肠癌Ｌｏｖｏ细胞则无明显作用。     

免疫脂质体作为靶向给药系统的研究进展

免疫脂质体是用抗体或其片段修饰的脂质体,能与靶细胞表面抗原或受体结合,从而对靶细胞具有分子水平上的识别能力。与游离药物、非特异抗体脂质体、单独单抗等相比,免疫脂质体有更好的选择性和更强的杀伤活性。在动物体内,免疫脂质体可使药物特异性分布在病灶部位,从而增强药物疗效、减轻不良反应,并且表面聚乙二醇化还增强了体内的循环时间。本文综述了用于修饰的不同种类抗体、抗体与免疫脂质体偶联方式,并总结了免疫脂质体在抗肿瘤药、基因治疗、活体成像技术以及在传染病、自身免疫和神经退行性疾病治疗方面的应用。     

大肠癌特异性卡莫氟免疫脂质体的体外抗癌活性研究

目的研制抗人体大肠癌的单克隆抗体的卡莫氟免疫脂质体 ,并对其体外抗癌活性进行了研究。方法由偶联剂将抗大肠癌的单抗与载药脂质体偶联制成免疫脂质体 ,并应用酶联免疫吸附法和MTT法分别测定其免疫活性和体外细胞毒毒性。结果脂质体稳定性良好 ,制成免疫脂质体后 ,单抗免疫活性不丧失 ;体外细胞毒实验结果显示 ,卡莫氟免疫脂质体对人大肠癌细胞的体外抗癌活性优于普通脂质体和游离药物 ,IC50 分别为两者的 1 0 6和 3 5 9倍 ,对非靶细胞的作用与普通脂质体相似。结论卡莫氟免疫脂质体对细胞生长的抑制作用有明显的靶向特异性     

PEG修饰鳖甲肽HGRFG脂质体的药动学研究

目的 制备鳖甲肽HGRFG脂质体以及聚乙二醇（polyethylene glycol,PEG）修饰后的长循环脂质体,考察经修饰的脂质体较未修饰脂质体在动物体内分布及滞留情况。方法 采用BLB/c裸鼠荧光活体成像实验,进行脂质体体内分布及代谢研究;采用药动学实验,初步探究2种载药脂质体在血浆内的滞留时间。结果 2种载药脂质体均能广泛分布于实验动物体内。与未经修饰的脂质体载药组相比,经PEG修饰的长循环脂质体载药组中裸鼠荧光全部消失的时间明显延长,药物在血浆滞留时间也明显延长。结论 经PEG修饰后的长循环脂质体可以延长药物在实验动物体内的滞留时间,延长药物半衰期。     

甘草次酸修饰的阿霉素靶向脂质体的制备及体外抑瘤活性考察

目的：制备甘草次酸（GA）靶向阿霉素脂质体（GA-DOX-Lip）,并初步考察其体外抑瘤活性。方法：采用硫酸铵梯度载药法制备GA-DOX-Lip,单因素考察其处方工艺;采用微柱离心法和粒径仪考察脂质体包封率及其理化性质;通过荧光显微镜和流式细胞仪考察BEL-7402肝癌细胞对脂质体的摄取情况并用MTT法评价其体外杀伤效果。结果：GA-DOX-Lip形态圆整,粒径约为120 nm,包封率达到95%以上,72 h释放约20%;体外细胞摄取量和细胞杀伤效果均显著高于阿霉素普通脂质体。结论：甘草次酸修饰的脂质体有望成为肝肿瘤靶向的新型载体,促进抗肿瘤药物向肿瘤细胞内的递送。     

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。     

冻融抗原冲击致敏的树突状细胞抗肿瘤作用的研究

目的研究MC-38肿瘤冻融抗原致敏的树突状细胞(DC)对荷瘤小鼠是否有抗肿瘤作用。方法用MC-38肿瘤冻融抗原体外冲击致敏小鼠骨髓来源的DC,观察其诱导的CTL对MC-38肿瘤细胞的杀伤活性;体内以1×106DC/只多次接种于已荷瘤小鼠同侧腹股沟皮下,观察抗原冲击的DC对肿瘤生长的抑制作用以及对荷瘤小鼠生存期的影响。结果体外抗原冲击致敏的DC诱导的CTL对MC-38肿瘤细胞具有显著的杀伤作用,在效靶比为50∶1,25∶1,12.5∶1,6.25∶1时其杀伤率分别为68.84%,58.36%,41.56%,24.96%,;抗原冲击致敏的DC体内多次皮下免疫后对肿瘤的生长具有显著的抑制作用,能显著延长荷瘤小鼠的生存期。结论肿瘤冻融抗原致敏DC多次皮下免疫对荷瘤小鼠具有显著的抗肿瘤作用。     

氢化与非氢化卵磷脂对阿霉素脂质体体内外稳定性的影响

目的研究卵磷脂(EPC)和氢化卵磷脂(HEPC)对阿霉素脂质体的体外泄漏及体内循环时间的影响.方法用透析法考察EPC及HEPC普通脂质体在37℃小牛血清及37℃,20℃和4℃PBS中的药物泄漏情况;用高效液相色谱法研究了EPC和HEPC长循环脂质体在大鼠体内的药物动力学.结果在37℃小牛血清中HEPC脂质体较EPC脂质体泄漏慢,而在PBS中则结果相反;大鼠体内药物动力学研究结果表明,HEPC长循环脂质体在血中的平均驻留时间(MRT)较EPC长循环脂质体长得多(23.3h vs 12.0h).结论HEPC长循环脂质体是靶向血管外部位的更好的药物载体.     

表面带活性羧基的新型长循环脂质体的制备和组织分布研究

合成和纯化了一个带末端羧基的新的磷脂酰乙醇胺的聚乙二醇衍生物－DPPE－PEG3000－COOH。将这个化合物掺入脂质体后，脂质体在网状内皮系统（肝，脾）的聚集减少，在血中的循环时间明显延长，并表现为一级对数线性消除。脂质体表面的活性羧基可以和其它活性分子反应，这可能为脂质体带来新的功能。     

Immunotargeting of Liposomes Containing Lipophilic Antitumor Prodrugs

Potential therapeutic applications of recently developed liposomes with a reduced affinity to the reticuloendothelial systems and a prolonged circulation time as targeting systems for lipophilic prodrugs were examined. In these studies, liposomes composed of phosphatidylcholine and cholesterol, additionally containing monosialoganglioside (G_M1) or polyethylene glycol conjugated to phosphatidyl-ethanolamine (PEG-PE), were used. Three antitumor lipophilic prodrugs, N-trifluoroacetyl-adriamycin-14-valerate (AD32), araC-diphosphate-diglyceride (araCdPdG), and 3,5-o-dipalmitoyl-5-fluoro-2-deoxyuridine (dpFUdR), were used to examine the effect of lipophilic prodrug incorporation into long-circulating liposomes and immunoliposomes on their biodistribution in mouse. Biodistribution studies with antibody-free liposomes containing lipophilic prodrugs showed that the activities of G_M1 or PEG2000-PE in prolonging the circulation time of liposomes appeared to be preserved in the presence of each of the three lipophilic prodrugs at a drug/lipid molar ratio of 3:97. The effect of lipophilic prodrug incorporation on target binding of immunoliposomes was then examined using a mouse model. Incorporation of AD32 or dpFUdR into immunoliposomes, directed to the normal endothelium, did not affect the targetability of immunoliposomes, suggesting a potential effectiveness of these lipophilic prodrug-containing immunoliposomes in therapy for lung tumors. On the contrary, incorporation of araCdPdG resulted in significantly reduced target binding of immunoliposomes by yet unknown mechanism(s).     

Possibility of active targeting to tumor tissues with liposomes

In terms of active targeting by immunoliposomes, two anatomical compartments are considerable for targeting sites. One is located a readily accessible site in intravascular, and another is a much less accessible target site located in the extravascular. However, it was made clear that the active targeting with immunoliposomes is determined by two kinetically competing processes, such as binding to the target site and uptake by the RES. To overcome these contradictions, we have designed a new type of long-circulating immunoliposome, which was PEG-immunoliposome attached antibodies at the distal end of PEG chain, so called the pendant type immunoliposome. The pendant type immunoliposome showed much higher targetability than the ordinary immunoliposomes to both targeting sites of lung endothelial cells and solid tumor tissue. This is due to the free PEG chains (not linked to the antibody) effectively avoiding the RES uptake of liposomes, resulting in elevated the blood concentration and enhanced the target binding of immunoliposomes. The presence of free PEG does not interfere with the binding of the terminally linked antibody to the antigen. For targeting to the vascular endothelial surface in the lung, 34A antibody, which is highly specific to mouse pulmonary endothelial cells, was conjugated to make the pendant type immunoliposomes (34A-PEG-ILP). 34A-PFG-ILP showed significantly higher targeting degree than the ordinary type of immunoliposomes. For targeting to the solid tumor tissue, Fab' fragment of 21B2 antibody which is anti-human CFA and transferrin (TF) were used. Both pendant type immunoliposomes (Fab'-PFG-ILP and TF-PEG-ILP) showed the low RES uptake and the long circulation time, and resulted in enhanced accumulation of the liposomes in the solid tumor. TF-PEG-ILP was internalized into tumor cells with receptor mediated endocytosis, after extravasation into tumor tissue. The pendant type immunoliposome can escape from the gaps between adjacent endothelial cells and openings at the vessel termini during tumor angiogenesis by passive convective transport much rather than ligand directed targeting. Active targeting to tumor tissue with the pendant type immunoliposome is particularly important for many highly toxic anticancer drugs for cancer chemotherapy. An ultimate goal of pendant type immunoliposome is the incorporation of a fusogenic molecule that would induce fusion of liposome following their binding to the target cells or their internalization by endocytosis. Such liposomal formulations should be useful for endocytotic internalization of plasmid DNA and other bioactive materials.     

Molecular localization and state of amphotericin B in PEG liposomes

We investigated the molecular localization and state of amphotericin B (AmB) encapsulated in polyethylene glycol (PEG)-coated liposomes. AmB-encapsulating PEG-liposomes composed of dipalmitoylphosphatidylcholine (DPPC), cholesterol (CH) and distearoyl-N-(monomethoxy poly(ethylene glycol)succinyl) phosphatidylethanolamine (DSPE-PEG, average MW of the PEG chain 2000) were prepared by hydration with 9% sucrose solution and extrusion. The amount of AmB encapsulated in the liposomes increased with incorporation of DSPE-PEG and decreased with that of CH. The molecular localization and state of AmB were investigated by PEG/dextran two-phase partition, potassium permeability measurement, fluorescence quenching measurement and circular dichroism (CD) spectroscopy. The results suggest that there are two types of AmB localization in PEG-liposomes, one of which corresponds to the complex of AmB with DSPE-PEG on the membrane surface, while the other corresponds to the pore form of AmB in the hydrophobic core of the liposomal membrane. AmB in PEG liposomes was present in both aggregated and monomeric states.     

Advances in Targeting Drug Delivery to Glomerular Mesangial Cells by Long Circulating Cationic Liposomes for the Treatment of Glomerulonephritis

Purpose Newly designed polyethylene glycol (PEG)-modified cationic liposomes, containing a novel cationic lipid TRX-20 (3,5-dipentadecyloxybenzamidine hydrochloride), bind specifically to cultured human mesangial cells, and not to endothelial cells. In this study, we investigated targeting the delivery of PEG-modified liposomes containing TRX-20 (TRX-liposomes) to mesangial cells and evaluated their pharmacokinetic behavior in a rat experimental glomerulonephritis model, using prednisolone phosphate (PSLP) as a model drug. Material and Methods TRX-liposomes were injected intravenously into experimental glomerulonephritic rats and normal rats to compare its pharmacokinetic behavior with that of non-cationic liposomes (PEG-liposomes). Rhodamine-labeled liposomes were used to evaluate the accumulation in inflamed kidneys. Pharmacological effects of three formulations of PSLP (i.e., a single injection of two liposomal formulations and daily injections of PSLP in saline solution) were estimated in terms of suppressing glomerular cell proliferation in the rat nephritis model. Results TRX-liposomes markedly accumulated in the glomeruli of inflamed kidneys, but did not accumulate in the glomeruli of normal kidneys. Although the PEG-liposomes also accumulated in the glomeruli of the inflamed kidneys, their pharmacological behavior was quite different from that of the TRX-liposomes, which were internalized by the target cells. In a comparison among the three formulations of PSLP, the dose of TRX-liposomes required for significant suppression of glomerular cell proliferation was much less (dose of 0.032 mg/kg and above) than that required for the same effect by the PSLP saline solution (3.2 mg/kg daily; 12.8 mg/kg total) and PEG-liposomes (0.32 mg/kg). Interestingly, significant suppression of mesangial cell activation, as assessed by the expression of α-smooth muscle actin, was observed in nephritic rats treated with TRX-liposomes, but not in the other two treatment groups. Conclusions The pharmaceutical properties of TRX-liposomes due to their preferential binding to mesangial cells and long circulation time make this a likely candidate system for targeted drug delivery to the inflamed glomeruli of glomerulonephritis.     

RETRACTED: Zonula occludens toxin synthetic peptide derivative AT1002 enhances in vitro and in vivo intestinal absorption of low molecular weight heparin

Abstract

Of all the polymers applied to molecule altering structural chemistry, polyethylene glycol (PEG) modification has numerous benefits and relatively few drawbacks. PEG is now increasingly being applied to the problems of tumour targeting, both in the context of the passive targeting of PEG-liposomes and in active targeting strategies using PEGylated anti-tumour antibodies. PEG can also serve as a useful linker molecule between targeting moieties and other agents, including cytotoxic or imaging agents and targeted liposomes. Despite these demonstrated benefits and the level of attention which PEGylation has received, relatively little consideration has been given to two key areas: first, the extent to which the coupling method has an impact on both the functionality of the PEG-adduct and the acquisition of beneficial properties; second, that the impact of PEGylation on biodistribution is complex, thus any attempt to optimise a PEG-peptide or PEG-liposome for a particular task must involve an examination of all the individual facets of the effects of PEGylation. Studies investigating the underlying principles of tumour targeting suggest that current views concerning the optimisation of PEGylated vehicles for tumour localisation need to be re-examined.     

In vitro characterization of binding and stability of single-chain Fv Ni-NTA-liposomes

Recently, we presented a new method for the generation of single-chain Fv (scFv) immunoliposomes, which circumvents the necessity to introduce additional reactive groups in the protein. This method is based on immobilizing scFv fragments via their C-terminal hexahistidyl-tag on liposomes containing nickel-complexed dioleoyl-glycero-succinyl-nitrilotriacetic acid (Ni-NTA-DOGS) as an anchor lipid within the lipid bilayer. Here, we have extended this approach to various other scFv fragments and further demonstrate strong and selective binding of these liposomes to target cells in vitro. In order to evaluate suitability for in vivo applications, we investigated the influence of human plasma on stability and binding behaviour of scFv Ni-NTA-liposomes in vitro using scFv A5 directed against human endoglin (CD105) as a model antibody. We could show that the binding activity to target cells is rapidly lost in the presence of human plasma. Incorporation of polyethylene glycol (PEG) chains into the lipid bilayer did not protect against loss of binding capability. Further studies showed that loss of binding is mainly due to displacement of Ni-NTA-bound scFv fragments caused by plasma proteins. In conclusion, the system allows for a rapid and flexible generation of target cell specific immunoliposomes for in vitro applications but lacks stability for in vivo applications.     

In vivo targeting by liposomes

This review deals with the current status of newly developed pendant-type PEG-immunoliposomes (Type C), carrying monoclonal antibodies or their fragments (Fab') at the distal ends of the PEG chains. In terms of target binding of Type C, two different anatomical compartments are considered. They are mouse lung endothelium as a readily accessible site via the intravascular route and the implanted solid tumor as a much less accessible target site reached via extravasation. Distearoyl phosphatidylethanolamine derivatives of PEG with a carboxyl group (DSPE-PEG-COOH) and dipalmitoyl phosphatidylethanolamine derivatives of PEG with a maleimidyl group (DPPE-PEG-Mal) at the PEG terminus were newly synthesized. Small unilamellar liposomes (90-130 nm in diameter) were prepared from phosphatidylcholine and cholesterol (2 : 1, m/m) containing 6 mol% of DSPE-PEG-COOH or DPPE-PEG-Mal. For targeting to the vascular endothelial surface in the lung, 34A antibody, which is highly specific to mouse pulmonary endothelial cells, was conjugated to PEG-liposomes (34A-Type C). The degree of lung binding of 34A-Type C in BALB/c mouse was significantly higher than that of 34A-Type A, which is an ordinary type of immunoliposome (without PEG derivatives). For targeting to solid tumor tissue, 21B2 antibody (anti-human CEA) and its Fab' fragment were used. The targeting ability of Fab'-Type C was examined by using CEA-positive human gastric cancer strain MKN-45 cells inoculated into BALB/c nu/nu mice. Fab'-Type C showed low RES uptake and a long circulation time, and enhanced accumulation of the liposomes in the solid tumor was seen. The small Fab'-Type C predominantly passed through the leaky tumor endothelium by passive convective transport. These studies offer important insights into the potential of Type C liposomes for target-specific drug delivery.     

Intracellular targeting delivery of liposomal drugs to solid tumors based on EPR effects

The success of an effective drug delivery system using liposomes for solid tumor targeting based on EPR effects is highly dependent on both size ranging from 100-200 nm in diameter and prolonged circulation half-life in the blood. A major development was the synthesis of PEG-liposomes with a prolonged circulation time in the blood. Active targeting of immunoliposomes to the solid tumor tissue can be achieved by the Fab' fragment which is better than whole IgG in terms of designing PEG-immunoliposomes with prolonged circulation. For intracellular targeting delivery to solid tumors based on EPR effects, transferrin-PEG-liposomes can stay in blood circulation for a long time and extravasate into the extravascular of tumor tissue by the EPR effect as PEG-liposomes. The extravasated transferrin-PEG-liposomes can maintain anti cancer drugs in interstitial space for a longer period, and deliver them into the cytoplasm of tumor cells via transferrin receptor-mediated endocytosis. Transferrin-PEG-liposomes improve the safety and efficacy of anti cancer drug by both passive targeting by prolonged circulation and active targeting by transferrin.