Pharmacokinetics of targeting with liposomes

The optimization of drug disposition in the body leads to an increase in its therapeutic effect and to a decrease in adverse effects. Liposomes can serve as a potential drug carrier for achieving this. However, the behavior of a drug carrier system under in vivo conditions is complex. Therefore, a more complete understanding of the pharmacokinetics of liposomes themselves, as well as that of the encapsulated drug, is required. The optimization of the pharmacokinetics of liposomes can be performed by linking a pharmacodynamic model of the free drugs that are encapsulated into liposomes. Sensitivity analysis was applied to optimize the delivery system to maximize the antitumor effect of liposomal doxorubicin (DOX). Advanced technology for ligand-mediated selective targeting and intracellular targeting is also introduced for antitumor agents and for gene delivery systems.     

Mannosylated liposomes for bio-film targeting

Vesicular systems in general are investigated to achieve bacterial bio-film targeting as their architecture mimics bio-membranes in terms of structure and bio-behavior. This paper elaborates upon the role of the inherent characteristics of the carrier system and further envisages the role of anchored ligands in navigating the contents in the vicinity of bio-films. Vesicles in the present study were coated with hydrophobic derivatives of mannan (cholesteryl mannan and sialo-mannan). The prepared vesicles were characterized for size, shape, percentage entrapment and ligand binding specificity and results were compared with the uncoated versions. Using a set of in vitro and in vivo models, the bio-film targeting potential of plain and mannosylated liposomal formulations were compared. Results suggested that mannosylated vesicles could be effectively targeted to the model bacterial bio-films, compared with plain vesicles. Moreover, the sialo-mannan coated liposomes recorded superior targetability as reflected in the significantly higher percentage growth inhibition when compared with cholesteryl mannan coated liposomes. The engineered systems thus have the potential use for the delivery of anti-microbial agents to the bio-films.     

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.     

Immunospecific targeting of liposomes to erythrocytes

Immunoliposomes were made by covalently linking Fab' fragments (from rabbit antimouse erythrocyte IgG) to reverse-phase evaporation vesicles (REV) via maleimido-4-(p-phenylbutyrate) phosphatidylethanolamine (MPB-PE) as anchor molecule. These immunoliposomes were characterized in terms of size, charge, stability and antigen binding capacity. The effect of the liposomal Fab' density on the interaction with the target cell was studied. Two isolation methods were tested to separate free Fab' from liposomally bound Fab'. The necessity of deactivation of remaining reactive sites with dithiothreitol preincubation to increase the specificity of immunoliposome target cell interactions was demonstrated.     

葡萄糖受体靶向的钆喷酸葡胺长循环脂质体的肿瘤细胞靶向研究

目的：制备葡萄糖受体靶向的钆喷酸葡胺（GdDTPA）长循环脂质体，并研究其对高表达葡萄糖受体肿瘤细胞的靶向性。方法：合成新型含葡萄糖表面活性剂（N-棕榈酰葡萄糖胺），利用逆向蒸发法制备Gd—DTPA脂质体、PEG修饰Gd—DTPA脂质体、葡萄糖修饰Gd-DTPA脂质体以及葡萄糖PEG修饰GdDTPA脂质体。将4种脂质体分别与前列腺癌细胞一起培养，用MRI检测前列腺癌细胞摄取的Gd-DTPA浓度。结果：成功合成新型含葡萄糖表面活性荆（N棕榈酰葡萄糖胺），以及制备4种Gd-DTPA脂质体。前列腺癌细胞对4种脂质体都有摄取，每种脂质体MRI检测的SBTIW信号值分别为Gd-DTPA脂质体362、PEG修饰Gd-DTPA脂质体299、葡萄糖修饰GdDTPA脂质体397、葡萄糖PEG修饰GdDTPA脂质体377。结论：葡萄糖的修饰有利于脂质体对肿瘤细胞的靶向。     

Vascular targeting of doxorubicin using cationic liposomes

Tumor vessel has been recognized as an important target for anticancer therapy. Cationic liposomes have been shown to selectively target tumor endothelial cells, thus can potentially be used as a carrier for chemotherapy agents. In this study, cationic liposomes containing 20 mol% cationic lipid dimethyl dioctadecyl ammonium bromide (DDAB) and loaded with doxorubicin (DOX) were prepared and characterized. The cationic liposomal DOX showed 10.8 and 9.1 times greater cytotoxicity than control PEGylated liposomal DOX in KB oral carcinoma and L1210 murine lymphocytic leukemia cells, and 7.7- and 6.8-fold greater cytotoxicity compared to control neutral non-PEGylated liposomal DOX, repectively, in these two cell lines. Although cationic liposomal DOX had higher tumor accumulation at 30 min after intravenous administration compared to control liposomes (p<0.05), DOX uptake of these liposomes at 24h post-injection was similar to that of PEGylated liposomal DOX (p>0.05) and approximately twice the levels of the free drug and non-PEGylated liposomes. In a murine tumor model generated using L1210 cells, increased survival rate was obtained with cationic liposomal DOX treatment compared to free DOX (p<0.01), neutral liposome control (p<0.01), as well as PEGylated liposomes (p<0.05). In conclusion, the cationic liposomal DOX formulation produced superior in vitro cytotoxicity and in vivo antitumor activity, and warrants further investigation.     

Transferrin As A targeting ligand for liposomes and anticancer drugs.

In cancer treatment, one of the approaches is targeting of the drug to tumor cells via receptor specific ligands. Transferrin (molecular weight 80,000) has been used as a ligand for delivering anticancer drugs or drug containing liposomes mostly due to the increased number of transferrin (trf) receptors found on tumor cells as compared to normal cells. Transferrin was linked to methotrexate (MTX) containing small unilamellar liposomes and its activity was compared to antitransferrin receptor antibody (7D-3) linked to MTX liposomes. In each of these conjugates, the method of coupling was the same and a disulphide linkage was formed between the ligand and MTX liposomes. No significant differences in the potency of 7D-3 conjugate or trf conjugate with MTX liposomes were observed in studies performed in vitro against various human tumor cell lines (Hela, KB and Colon). Trf was also linked to adriamycin via a schiff base which was formed by using glutaraldehyde. This conjugate was found to be effective in vitro against various human tumors (Lovo, HL-60, SW 403 and Hep2) and also in vivo against H-mesothelioma tumors. Transferrin receptor has also been used for gene delivery. Gene delivery to K562 haematopoietic leukaemic cells was achieved by using a transferrin-polycation (poly-L-lysine or protamine) conjugate. This review will cover the various important applications of transferrin based drug delivery formulations in the chemotherapy of cancer and the related work performed in our and other laboratories.     

Nuclear gene targeting using negatively charged liposomes

Oligonucleotides are a very useful tool to control gene activity. Oligos work by complementary base-pairing with target sequences either in the nucleus or in the cytosol (Zelphati, O., Szoka, F.C., Jr., 1996. Liposomes as a carrier for intracellular delivery of antisense oligonucleotides: a real or magic bullet? J. Contr. Rel. 41, 99-119). In a new approach using chimeric oligonucleotides (Yoon, K., Cole Strauss, A., Kmiec, E.B., 1996. Targeted gene correction of episomal DNA in mammalian cells mediated by a chimeric RNA-DNA oligonucleotide. Proc. Natl. Acad. Sci. USA 93, 2071-2076) conversion of single base mutations with help of intranuclear repair mechanisms maybe an advantageous method to cure genetic diseases which are based on single point mutations. These chimeric oligonucleotides are constructed in a way that they form an intramolecular double strand of DNA and modified RNA-bases. We used a fluorescent labelled pure 68-mer DNA-analogue of a chimeric oligonucleotides to follow the intracellular fate of these kind of genetic material. The oligos were complexed with protamine sulfate and coated with three different liposomal formulations. The AVE-3 formulation shows enhanced properties compared to a classical neutral and negatively charged formulation. Nuclear localisation of oligos could only be observed with the AVE-3 formulation. Furthermore only the negatively charged liposome formulations interact with the protamine-complexed oligonucleotides.     

抗肿瘤热敏靶向脂质体的研究进展

脂质体具有靶向传递药物进入肿瘤部位的优势,被广泛用于肿瘤的临床治疗,但是靶向传递并不能保证药物在肿瘤部位被生物利用。为了解决此问题,热敏靶向脂质体(TTL)已经成为目前的研究热点。TTL既能提高药物在肿瘤部位的浓度,又能在加热条件下触发释放所载药物,从而显著改善所载药物的抗肿瘤效果。本文主要综述了近年来该领域的研究进展。     

High-affinity targeting of biotin-labeled liposomes to streptavidin-conjugated ligands

Abstract

Cell-specific delivery of drug-loaded liposomal carrier systems can be achieved through the use of liposomes with covalently attached proteins. For such targeting strategies to be successful a number of potential difficulties, related to the preparation of the liposomes as well as optimization of properties that maximize in vivo access and binding to a defined target cell population, must be overcome. The studies summarized here have attempted to identify specific factors that will promote binding of targeted liposomes to defined target surfaces. Liposomes containing biotinylated phospha-tidylethanolamine were used to demonstrate that the avidity of a targeted liposome for streptavidin-coated ELISA plates and cells is influenced by liposome lipid composition, the amount of targeting molecule present per liposome, the nature of the targeting ligand, and the target surface. Specifically, it is demonstrated that the three most important factors (in order of importance) controlling the apparent affinity of targeted liposomes are (1) target ligand concentration in the liposomal membrane; (2) the presence of a spacer grout between the biotin and the phospholipid headgroup; and (3) the addition of cholesterol. Other less important factors that influence target liposome binding include whether the target ligand is attached to a saturated phospholipid compared to an unsaturated lipid and whether the bulk phospholipid species in the liposome is unsaturated versus saturated. These studies suggest that targeted liposomes exhibiting a broad range of binding avidities, as estimated by the concentration of liposomes required to achieve saturation of a target surface, can be prepared by selective design of the liposomal carrier. Advantages of the biotinylated liposome for targeting include the relative ease of preparation the possibility of preparation of large-scale batches suitable for clinical development), the ease of incorporation of the targeting ligand, and, importantly, the ability to alter the apparent affinity of the liposome for the target cell through choice of the biotin-labeled lipid and targeting molecule concentration. The potential for developing a two-step targeting strategy based on the use of biotinylated liposomes is discussed.     

Fibrin targeting of tissue plasminogen activator-loaded echogenic liposomes

We recently reported entrapment of tissue-plasminogen activator (tPA) into echogenic liposomes (ELIP) with retention of echogenicity and thrombolytic effect. Integral to the potential of this agent for ultrasound-detectable local drug delivery is the specific binding of tPA-ELIP to clots. tPA contains fibrin-binding sites; we hypothesized that tPA when associated with ELIP, will maintain fibrin binding properties, rendering further manipulation for targeting of the tPA-ELIP unnecessary. We demonstrated strong fibrin binding of the ELIP-associated tPA. Fibrin binding for ELIP-associated tPA was twice that of free tPA. This strong affinity for fibrin was confirmed using echogenicity analysis of porcine clots in vitro. Both objective (mean gray scale analysis) and subjective (visual estimation by two experienced echocardiographers) evaluation of the clots showed enhanced highlighting of clots treated with tPA-ELIP when compared to control. The findings in this study represent new approaches for fibrin-targeted, ultrasound-directed and enhanced local delivery of a thrombolytic agent.     

High-affinity targeting of biotin-labeled liposomes to streptavidin-conjugated ligands

Cell-specific delivery of drug-loaded liposomal carrier systems can be achieved through the use of liposomes with covalently attached proteins. For such targeting strategies to be successful a number of potential difficulties, related to the preparation of the liposomes as well as optimization of properties that maximize in vivo access and binding to a defined target cell population, must be overcome. The studies summarized here have attempted to identify specific factors that will promote binding of targeted liposomes to defined target surfaces. Liposomes containing biotinylated phospha-tidylethanolamine were used to demonstrate that the avidity of a targeted liposome for streptavidin-coated ELISA plates and cells is influenced by liposome lipid composition, the amount of targeting molecule present per liposome, the nature of the targeting ligand, and the target surface. Specifically, it is demonstrated that the three most important factors (in order of importance) controlling the apparent affinity of targeted liposomes are (1) target ligand concentration in the liposomal membrane; (2) the presence of a spacer grout between the biotin and the phospholipid headgroup; and (3) the addition of cholesterol. Other less important factors that influence target liposome binding include whether the target ligand is attached to a saturated phospholipid compared to an unsaturated lipid and whether the bulk phospholipid species in the liposome is unsaturated versus saturated. These studies suggest that targeted liposomes exhibiting a broad range of binding avidities, as estimated by the concentration of liposomes required to achieve saturation of a target surface, can be prepared by selective design of the liposomal carrier. Advantages of the biotinylated liposome for targeting include the relative ease of preparation the possibility of preparation of large-scale batches suitable for clinical development), the ease of incorporation of the targeting ligand, and, importantly, the ability to alter the apparent affinity of the liposome for the target cell through choice of the biotin-labeled lipid and targeting molecule concentration. The potential for developing a two-step targeting strategy based on the use of biotinylated liposomes is discussed.     

反义核酸药物脂质体肝靶向性的研究

目的研究反义核酸药物脂质体给药系统的肝主动靶向性。方法采用薄膜分散法制备脂质体,以花青染料荧光标记脂质体,以荧光分光光度法定量分析;利用肝组织的体内冷冻切片和小鼠体内组织分布研究肝靶向性;检测大鼠肝非实质细胞与肝实质细胞的荧光强度(INPC和IPC)。结果主动靶向脂质体在肝脏中的荧光强度明显强于非主动靶向脂质体,相对摄取率(re)为5.64;非主动靶向脂质体的荧光值比(IPC/INPC)为1.16±0.89,主动靶向脂质体的IPC/INPC为8.24±1.37。结论主动靶向脂质体具有良好的肝实质细胞靶向性和肝靶向性。     

Galactosylated liposomes as oligodeoxynucleotides carrier for hepatocyte-selective targeting

18mer oligodeoxynucleotides (ODNs) which can inhibit survivin gene expression were selected as a model gene drug. The glycolipid (5-cholestan-3beta-yl)-1-[2-(lactobionyl amido) ethylamido] formate (CHE-LA) which specific target to the cells expressing galactose receptors was synthesized through the reaction of lactone of lactobiono-1,5-lactone (LA) and the amino-group of 2-(cholesteryloxycarbonylamino) ethylamine (CHE). The galactosylated liposome incorporated with CHE-LA containing oligodeoxynucleotides was prepared with SPC, cholesterol, CHE-LA and oligodeoxynucleotides by the thin-film hydration method. 1,1'-Dioctadecyl-3,3,3',3'tetramethylindocarbocyanine perchlorate (Dil) was used as a marker for all the liposome preparations. Compared with conventional liposomes (CL), the galactosylated liposomes (GL) exhibited a drastically increased distribution to the liver in vivo and the galactosylated liposomes containing oligodeoxynucleotides (GLO) can also more efficiently induced an apoptosis of HepG2 cells in vitro than the conventional liposome containing oligodeoxynucleotides (CLO). In addition, the GLO represented an improving of the ODNs entrapment efficiency.     

Passive targeting of doxorubicin with polymer coated liposomes in tumor bearing rats.

The purpose of this study was to reveal the effectiveness of the polymer coated liposomes as a carrier of the anticancer drug doxorubicin in intravenous administration. The size controlled doxorubicin-loaded liposomes (egg phosphatidylcholine : cholesterol = 1:1 in molar ratio) were coated with hydrophilic polymers (polyvinyl alcohol; PVA and hydroxypropylmethylcellulose; HPMC) having a hydrophobic moiety in the molecules (PVA-R, HPMC-R). The existence of a thick polymer layer on the surface of the polymer coated liposomes was confirmed by measuring the change in particle size and the amount of polymer on the liposomal surface. The polymer coating effects on the tumor accumulation of the drug encapsulated in the liposomes were evaluated in Walker rat carcinoma 256 cell bearing rats. The doxorubicin-loaded liposomes coated with PVA-R and HPMC-R showed higher drug accumulation into the tumor site by prolonging the systemic circulation in tumor-bearing rats. The targeting efficiency of the polymer coated liposomes calculated with the total and tumorous clearance of the drug was ca. 5 times larger than that of non-coated liposomes. We ascertained that polymers having a hydrophobic moiety in the molecule such as PVA-R and HPMC-R are suitable materials for modifying the surfaces of the doxorubicin-loaded liposome to improve its targeting properties.     

双重修饰的主动靶向脂质体研究进展

主动靶向脂质体是靶向递药体系的一个重要角色。由于传统的单一基团修饰的主动靶向脂质体存在靶向效率不高、细胞摄取率不高等缺点,人们不断探索采用两种或多种不同识别分子或其他协同分子共同修饰脂质体。本文拟针对双重修饰脂质体技术的研究进展进行综述。通过对两种特异性配体或抗体共同修饰、特异性配体与细胞穿透肽共同修饰、两种细胞穿透肽共同修饰等不同类型的双重修饰脂质体的综述分析,我们发现双重修饰技术具有提高靶向准确性和靶向效率,提高药物摄取,提高对靶点的黏附能力和血流稳定性等优势,尤其在跨膜穿越屏障系统的应用中凸显作用。     

Surface modification of liposomes for cardiomyocytes targeting in vitro

The effect of novel 3-{4-[2-hydroxyl-(1-methyl ethylamine) propyl oxygen]phenyl}propionic acid cetylester (PAC) as a surface modification ligand on the delivery of liposomes into cultured cardiomyocytes was investigated. Small unilamellar liposomes with and without PAC (PAC-liposome and Plain-liposome) were labeled with a fluorescence marker. The cultured neonatal cardiomyocytes were incubated with liposomes under normoxia or hypoxia conditions, and then the cell-associated fluorescence was measured. A high affinity of the PAC-liposomes to cardiomyocytes was observed. The amount of cell uptake of PAC-liposomes under normoxia conditions was 4-fold higher than that of plain-liposome, and the increase was 8.5-fold when hypoxia occured. The results suggested that PAC is a potential surface modification ligand for liposome targeting the ischemic myocardium.     

Novel galactosylated liposomes for hepatocyte-selective targeting of lipophilic drugs

Novel galactosylated neutral liposomes containing cholesten-5-yloxy-N-(4-((1-imino-2-beta-D-thiogalactosylethyl)amino)butyl)formamide (Gal-C4-Chol) as a "homing" device were developed for hepatocyte-selective drug targeting. Distearoylphosphatidylcholine (DSPC)/cholesterol (Chol) (60:40) and DSPC/Chol/Gal-C4-Chol (60:35:5) liposomes were prepared and labeled with [3H]cholesteryl hexadecyl ether (CHE). [3H]Prostaglandin E1 (PGE1) and [14C]probucol were incorporated in liposomes as model lipophilic drugs. After intravenous injection of the liposomes, mice were sacrificed at suitable time periods, and the lung, liver, kidney, spleen, and heart were excised. DSPC/Chol/Gal-C4-Chol liposomes rapidly disappeared from the blood, and 85% of the dose had accumulated in the liver within 10 min compared with hepatic accumulation of DSPC/Chol liposomes of 12%. The liver was perfused with collagenase, and liver parenchymal cells (PC) and liver nonparenchymal cells (NPC) were separated by centrifugal differentiation to determine the cellular distribution. The PC/NPC ratios for DSPC/Chol/Gal-C4-Chol and DSPC/Chol liposomes were 15.1 and 1.1, respectively. The hepatic uptake of DSPC/Chol/Gal-C4-Chol liposomes, but not that of DSPC/Chol liposomes, was significantly inhibited by the predosing of galactosylated bovine serum albumin. [14C]Probucol and [3H]PGE1 incorporated in DSPC/Chol/Gal-C4-Chol liposomes was also efficiently delivered to the liver. In conclusion, newly developed galactosylated liposomes have been proven to be a useful carrier for hepatocyte-selective targeting that will have many practical applications.