Repeated injections of PEGylated liposomal topotecan induces accelerated blood clearance phenomenon in rats

The "accelerated blood clearance (ABC) phenomenon" of PEGylated liposomes following multiple injections has been reported recently. This immunogenicity poses a problem for research into liposomes and hinders their clinical application. However, since doxorubicin liposomes and mitoxantrone liposomes have been reported to fail to induce the ABC phenomenon, some people believe that cytotoxic drugs loaded liposomes will not produce this ABC phenomenon under multiple-dosing regimens. Nevertheless, in the present study, we report that a first injection of the PEGylated liposomal topotecan (a cell cycle-specific drug for the S phase) still produced a strong ABC phenomenon. Likewise, when the first dose of "empty" PEGylated liposomes or topotecan liposomes was increased, the ABC phenomenon of the subsequent dose was accordingly attenuated. Unlike doxorubicin and mitoxantrone, the blood clearance rate of topotecan was dramatically rapid, and the hepatic and splenic accumulations of topotecan liposomes were anomalous because of the ABC phenomenon. These findings may present new challenges to the clinical application of formulations of cytotoxic drugs loaded liposomes that require repeated administrations.     

Liposomal topotecan formulation with a low polyethylene glycol grafting density: pharmacokinetics and antitumour activity

Objectives PEGylated liposomes could evade recognition by the reticulo‐endothelial system and prolong the circulation time of vesicles, resulting in enhanced targeting efficiency and antitumour effect. Typically, vesicles are modified with distearoylphosphatidylethanolamine (DSPE)‐polyethylene glycol (PEG) at a high PEG grafting density. However, long circulation time and slow drug release rate might induce severe hand‐foot syndrome in clinical practice. In this study, a liposomal topotecan formulation with a low PEG grafting density was prepared and its pharmacokinetics, acute toxicity and antitumour effect were investigated. Methods Topotecan was loaded into liposomes using an ammonium sulfate gradient. The resulting formulation was injected to healthy Wistar rats at different dose levels to investigate whether its clearance followed linear kinetics. Biodistribution was performed in Lewis lung cancer‐bearing mice. The acute toxicity was evaluated in healthy mice and beagle dogs. To compare the antitumour effects of different formulations and dose schedule, RM‐1 prostate, Lewis lung, H446 and L1210 cancer models were used. Key findings Topotecan could be encapsulated into low DSPE‐PEG liposomes with ～100% loading efficiency. The clearance of the liposomal formulation followed linear kinetics at a dose level ranging from 0.5 to 4 mg/kg despite the fact that the vesicles were coated at a low PEG density. Compared with free topotecan the liposomal formulation preferentially accumulated into tumour zones instead of normal tissues. Both formulations could rapidly accumulate into liver and tumour, but the liposomal formulation was cleared from tissues at a slow rate relative to the conventional formulation. In rats and beagle dogs, liposomal formulations could not induce skin toxicity. In all the tumour models, smaller split doses were more therapeutically active than larger doses when the overall dose intensity was equivalent. Conclusions This has been the first report that plasma kinetics of a liposomal formulation with a low PEG density followed linear kinetics. Moreover, due to its short circulation half‐life, the formulation did not induce skin toxicity. Our data revealed that the dose schedule of liposomal drugs should be adjusted in accordance with the biophysical and biological properties of the formulations to achieve the optimal therapeutic efficacy.     

Time Interval of Two Injections and First-Dose Dependent of Accelerated Blood Clearance Phenomenon Induced by PEGylated Liposomal Gambogenic Acid: The Contribution of PEG-Specific IgM

Repeated injection of PEGylated liposomes can cause the disappearance of long circulating property because of the induction of anti-PEG IgM antibody referred to as “accelerated blood clearance (ABC) phenomenon.” Although ABC phenomenon typically occurs when entrapped drugs are chemotherapeutic agent with low cytotoxic, there is little evidence of accelerated blood clearance of PEGylated herbal-derived compound on repeated injection. Herein, we investigated the blood concentration of PEGylated liposomal gambogenic acid (PEG-GEA-L), a model PEGylated liposomal herbal extract, on its repeated injection to rats. We found time interval between injections had considerable impact on the magnitude of ABC phenomenon induced by PEG-GEA-L. When time interval was prolonged from 3 days to 7 days, ABC phenomenon could be attenuated. Furthermore, its magnitude was enhanced accompanied by a marked rise in the accumulation of PEG-GEA-L in the liver and spleen in a first-dose–dependent manner. Consistently, the level of anti-PEG IgM significantly increased with the first dose of PEG-GEA-L and decreased with the extended time interval between injections, which implies anti-PEG IgM is a major contributor to the ABC phenomenon. Notably, the increased expression of liver anti-PEG IgM was accompanied by an increased expression of efflux transporters in the induction process of the ABC phenomenon.     

Accelerated blood clearance (ABC) phenomenon upon repeated injection of PEGylated liposomes

We and a Dutch group reported that "empty" PEGylated liposomes (approximately 100 nm) lose their long-circulating characteristic when they are administrated twice in the same animal with certain intervals (referred to as the accelerated blood clearance (ABC) phenomenon). Very recently, we showed that anti-PEG IgM, induced by the first dose of "empty" PEGylated liposomes, is responsible for inducing the phenomenon, based on the observation that IgM thus produced selectively binds to the surface of subsequently injected PEGylated liposomes, leading to substantial complement activation. It is generally believed that nanocarriers coated with a polymer, such as PEG, have no or lower immunogenicity. However, the results indicated evidence that unexpected immune responses occur even to such polymer-coated liposomes. Such immunogenicity of "empty" liposomes presents a serious concern in the development of liposomal formulations and their use in the clinic. In addition, through series of our studies, it was demonstrated that the magnitude of the ABC phenomenon depends on the physicochemical property of injected liposomes as a first dose, time interval between injection, lipid dose and drug-encapsulation.     

Accelerated blood clearance (ABC) phenomenon induced by administration of PEGylated liposome

PEGylated liposomes (approximately 100 nm in diameter) lose their long-circulating characteristic upon repeated injection at certain intervals in the same animal (referred to as the "accelerated blood clearance (ABC) phenomenon"), as described by our group and by researchers in the Netherlands. Recently, it was demonstrated by our group that anti-PEG IgM, induced by the first dose of PEGylated liposomes, is responsible for the ABC phenomenon. The IgM produced in this manner then selectively bound to the surface of subsequently injected PEGylated liposomes, leading to substantial complement activation. It is generally believed that nanocarriers coated with a polymer, such as PEG, have no immunogenicity. However, unexpected immune responses occurred even in response to polymer-coated liposomes. This immunogenicity to PEGylated liposomes presents a serious concern in the development and clinical use of liposomal formulations. In this review, we demonstrate our recent observations regarding with the ABC phenomenon against liposomes.     

Dose Dependency of Pharmacokinetics and Therapeutic Efficacy of Pegylated Liposomal Doxorubicin (DOXIL) in Murine Models

Stealth (pegylated) liposomal doxorubicin (Doxil) has been extensively studied at the pre-clinical and clinical level in recent years. However, one issue not yet addressed is the effect of dose on tumor localization and therapeutic efficacy of Doxil. Although it has been reported that the pharmacokinetics of drug-free Stealth liposomes is independent of dose within a certain range, clinical pharmacokinetic analysis of Doxil suggests a dose-dependent clearance saturation phenomenon when a broad dose range is examined. In addition, liposome-encapsulated doxorubicin can exert toxic effects on the liver macrophage population in the form of impairment of the phagocytic function and reduced ability of colloid particle clearance. In studies with tumor-bearing mice in which the dose of Doxil was escalated from 2.5 to 20 mg/kg, we demonstrate that dose escalation results in a saturation of Doxil clearance and a disproportional increase of the amount of liposomal drug accumulating in tumor. Experiments with radiolabeled highly negatively-charged liposomes injected into mice previously treated with Doxil are consistent with a partial blockade of the reticulo-endothelial system with relative reduction of liver uptake and greater prolongation of liposome circulation time. The clearance saturation effect is seen after Doxil in a dose-dependent fashion, and not after a similar free doxorubicin dose or similar phospholipid dose in drug-free liposomes. A trend to superior therapeutic efficacy for treatments based on larger doses as compared to smaller split doses, while maintaining an equivalent dose intensity, was also observed. These observations may be relevant to the choice of dose-schedule of Doxil to ensure optimal anti-tumor activity. Therefore, dose-dependent liposomal doxorubicin blockade of the reticulo-endothelial system may prolong liposome circulation time and enhance significantly drug delivery to tumors.     

Dose dependency of pharmacokinetics and therapeutic efficacy of pegylated liposomal doxorubicin (DOXIL) in murine models

Stealth (pegylated) liposomal doxorubicin (Doxil) has been extensively studied at the pre-clinical and clinical level in recent years. However, one issue not yet addressed is the effect of dose on tumor localization and therapeutic efficacy of Doxil. Although it has been reported that the pharmacokinetics of drug-free Stealth liposomes is independent of dose within a certain range, clinical pharmacokinetic analysis of Doxil suggests a dose-dependent clearance saturation phenomenon when a broad dose range is examined. In addition, liposome-encapsulated doxorubicin can exert toxic effects on the liver macrophage population in the form of impairment of the phagocytic function and reduced ability of colloid particle clearance. In studies with tumor-bearing mice in which the dose of Doxil was escalated from 2.5 to 20 mg/kg, we demonstrate that dose escalation results in a saturation of Doxil clearance and a disproportional increase of the amount of liposomal drug accumulating in tumor. Experiments with radiolabeled highly negatively-charged liposomes injected into mice previously treated with Doxil are consistent with a partial blockade of the reticulo-endothelial system with relative reduction of liver uptake and greater prolongation of liposome circulation time. The clearance saturation effect is seen after Doxil in a dose-dependent fashion, and not after a similar free doxorubicin dose or similar phospholipid dose in drug-free liposomes. A trend to superior therapeutic efficacy for treatments based on larger doses as compared to smaller split doses, while maintaining an equivalent dose intensity, was also observed. These observations may be relevant to the choice of dose-schedule of Doxil to ensure optimal anti-tumor activity. Therefore, dose-dependent liposomal doxorubicin blockade of the reticulo-endothelial system may prolong liposome circulation time and enhance significantly drug delivery to tumors.     

Hepatocellular carcinoma targeting effect of PEGylated liposomes modified with lactoferrin

A hepatocellular carcinoma targeting lactoferrin (Lf) modified PEGylated liposome system was developed for improving drug efficacies to hepatic cancer cells. In this present work, PEGylated liposomes (PLS) were successfully prepared by the thin film hydration method combined with peglipid post insertion. Lf was covalently conjugated to the distal end of DSPE-PEG2000-COOH lipid by amide bound and loaded onto PEGylated liposomes surface as the targeting ligand. To confirm the targeting efficacies to hepatic cancer, coumarin-6 and DiR were encapsulated as fluorescent probes. The confocal microscopy and flow cytometry demonstrated that Lf conjugated PEGylated liposomes (Lf-PLS) were efficiently associated by HepG2 cells, while limited interaction was found for liposomes modified with a negative control protein. A similar pharmacokinetic behavior was observed in pharmacokinetics study of the liposomal formulations. Meanwhile, the in vivo imaging of liposomes in HepG2 tumor bearing mice indicated that Lf-PLS achieved more accumulation in tumor compared with PLS without Lf conjugated. The significant in vitro and in vivo results suggested that Lf-PLS might be a promising drug delivery system for hepatocellular carcinoma therapy with low toxicity.     

The effect of lipid composition of small unilamellar liposomes containing melphalan and vincristine on drug clearance after injection into mice

Melphalan and vincristine together with their radiolabelled derivatives were entrapped in small unilamellar liposomes of varying choleresterol content and phospholipid composition. After intravenous injection of drug-containing egg phosphatidylcholine liposomes into mice, drug clearance rates from the blood were reduced with increasing cholesterol content. Circulating drugs were partially associated with the carrier and partly free, mostly bound to plasma proteins. The ratio of drug associated with liposomes to that circulating as free was dependent on the type of liposomes used and highest when these were cholesterol-rich. Drug clearance rates were reduced and entrapped:free drug ratios increased further when egg phosphatidylcholine in cholesterol-rich liposomes was replaced by sphingomyelin. Drug-containing cholesterol-rich liposomes injected intraperitoneally were found capable of entering the periphery intact and quantitatively to assume clearance rates similar to those observed after intravenous treatment. Such manipulations in liposomal lipid composition can alter pharmacokinetics in ways that could provide optimal conditions for drug distribution into tumours and a therapeutic effect.     

聚乙二醇修饰脂质体的ABC现象研究进展

通常聚乙二醇(polyethylene glycol,PEG)修饰脂质体被认为几乎没有或仅有很低的免疫原性。最新的文献报道,重复注射PEG修饰脂质体发生了免疫反应。当向同一动物体内重复注射(间隔几天)PEG化脂质体时,二次注射的PEG化脂质体导致体内循环时间降低,于肝和脾的聚集量增加,这种现象称为加速血液清除(accelerated blood clearance,ABC)现象。该免疫反应使PEG化制剂的发展和临床应用面临严峻的挑战,可能造成药物或基因治疗效率的下降,甚至引起临床的毒副作用。本文综述了ABC现象的定义、验证ABC现象的方法和手段、ABC现象成因的研究进展及影响因素,并对其他PEG修饰载体是否也会发生ABC现象进行了探讨。     

Accelerated blood clearance of PEGylated liposomes containing doxorubicin upon repeated administration to dogs

The accelerated blood clearance phenomenon involving anti-PEG IgM production has been recognized as an important issue for the design and development of PEGylated liposomes. Here, we show that empty PEGylated liposomes and Doxil, PEGylated liposomes containing doxorubicin, both caused anti-PEG IgM production and thereby a rapid clearance of the second and/or third dose of Doxil in Beagle dogs in a lipid-dose, inverse-dependent manner. It appears that the pharmacokinetic profile of the second and third administration of Doxil reflected the presence of anti-PEG IgM circulating in the blood. Doxil plus an excess amount of empty PEGylated liposomes rather enhanced the production of anti-PEG IgM compared to Doxil of the same doxorubicin dose. During sequential administration, increasing the lipid dose of Doxil in each dose by the addition of empty PEGylated liposomes strongly attenuated the magnitude of the ABC phenomenon during the effectuation phase of a second and third dose of Doxil. Our results suggest that the pre-clinical study of anti-cancer drug-containing PEGylated liposomes with dogs must be carefully designed and performed with monitoring of the anti-PEG IgM and liposomal drugs circulating in the blood.     

Particle size-dependent triggering of accelerated blood clearance phenomenon

A repeat-injection of polyethylene glycol-modified liposomes (PEGylated liposomes) causes a rapid clearance of them from the blood circulation in certain cases that is referred to as the accelerated blood clearance (ABC) phenomenon. In the present study, we examined whether polymeric micelles trigger ABC phenomenon or not. As a preconditioning treatment, polymeric micelles (9.7, 31.5, or 50.2nm in diameter) or PEGylated liposomes (119, 261 or 795nm) were preadministered into BALB/c mice. Three days after the preadministration [(3)H]-labeled PEGylated liposomes (127nm) as a test dose were administered into the mice to determine the biodistribution of PEGylated liposomes. At 24h after the test dose was given, accelerated clearance of PEGylated liposomes from the bloodstream and significant accumulation in the liver was observed in the mice preadministered with 50.2-795nm nanoassemblies (PEGylated liposomes or polymeric micelles). In contrast, such phenomenon was not observed with 9.7-31.5nm polymeric micelles. The enhanced blood clearance and hepatic uptake of the test dose (ABC phenomenon) were related to the size of triggering nanoassemblies. Our study provides important information for developing both drug and gene delivery systems by means of nanocarriers.     

Safety, efficacy and pharmacokinetics of tuftsin-loaded nystatin liposomes in murine model

Present study was performed to evaluate the efficacy, toxicity and pharmacokinetics of antifungal drug nystatin incorporated in immunomodulator tuftsin-bearing liposomes. In vitro toxicity of free nystatin and nystatin incorporated in tuftsin-free or tuftsin-loaded liposomes was assessed by incubation of nystatin formulations with human erythrocytes. The toxicity profile of free nystatin and liposomal formulations of nystatin with or without tuftsin was also analyzed by monitoring the level of blood urea nitrogen (BUN) and serum creatinine in the treated BALB/c mice. The results of the present work showed that tuftsin-loaded nystatin liposomes like conventional nystatin liposomes exerted less toxicity to human erythrocytes as compared with free nystatin. Moreover, mice treated with tuftsin-loaded nystatin liposomes showed insignificant elevation in the biochemical values of serum creatinine and blood urea. The stability of nystatin liposomes upon incorporation of tuftsin was evaluated by monitoring the leakage of the entrapped drug in human serum. Tuftsin-loaded liposomes held nystatin for longer duration in the presence of serum than identical nystatin liposomes without tuftsin. Pharmacokinetics of the both tuftsin-free or tuftsin-loaded liposomal formulations nystatin was analyzed by determining the level of nystatin in the systemic circulation of mice at different time points. Mice injected with tuftsin-loaded nystatin liposomes showed higher level of the drug in the systemic circulation compared with those treated with conventional nystatin liposomes. The efficacy of tuftsin-loaded nystatin liposomes against A. fumigatus was evaluated by assessing the fungal burden in the lungs of treated mice. Treatment with tuftsin-loaded nystatin liposomes was most effective in eliminating fungal burden from lung tissues of infected mice compared to those treated with free nystatin or nystatin liposomes without tuftsin. The immunopotentiating activity, increased stability and less toxicity of tuftsin-incorporated nystatin liposomes, supports the idea for its prophylactic and therapeutic use in the clinical setting.     

The effect of PEG coating on in vitro cytotoxicity and in vivo disposition of topotecan loaded liposomes in rats

Amphoteric drugs encapsulated in PEGylated liposomes may not show superior therapeutic antitumor activity due to increased leakage rate of these drugs in presence of PEG-lipids. In order to investigate the effect of PEG coating on in vitro and in vivo characteristics of topotecan loaded liposomes, an amphoteric anticancer drug, PEGylated and conventional liposomes were prepared by lipid film hydration method. Various properties of the prepared nanoliposomes such as encapsulation efficiency, size, zeta potential, physical stability as well as the chemical stability of lactone form of topotecan, cytotoxicity and topotecan pharmacokinetics were evaluated. In vitro cytotoxic activity was evaluated on murine Lewis lung carcinoma (LLC) and human mammary adenocarcinoma (BT20) cells. Pharmacokinetic was evaluated in Wistar rats after i.v. injection of topotecan, formulated in PBS pH 7.4 or in conventional or in PEGylated liposomes. The conventional liposome (CL) formulation was composed of DSPC/cholesterol/DSPG (molar ratio; 7:7:3), while for PEGylated liposome the composition was DSPC/cholesterol/DSPG/DSPE-PEG(2000) (molar ratio; 7:7:3:1.28). The size of both liposomes was around 100 nm with polydispersity index of about 0.1. In comparison with free drug, liposomal topotecan showed more stability for topotecan lactone form in vitro. Compared to free topotecan, PEGylated and conventional liposomes improved cytotoxic effect of topotecan against the two cancer cell line studied. The results of pharmacokinetic studies in rats showed that both CL and PEGylated liposomal formulations increased the concentration of total topotecan in plasma, however, initial concentration and the values of AUC, MRT and t(1/2 beta) were much higher (P<0.001) for PEGylated liposomal drug than for conventional one or free drug. PEGylated liposome resulted in a 52-fold and 2-fold increases in AUC(0-infinity) compared with that of free topotecan and CL, respectively. These results indicated that PEG modified liposome might be an effective carrier for topotecan.     

Safety,efficacy and pharmacokinetics of tuftsin-loaded nystatin liposomes in murine model

Present study was performed to evaluate the efficacy, toxicity and pharmacokinetics of antifungal drug nystatin incorporated in immunomodulator tuftsin-bearing liposomes. In vitro toxicity of free nystatin and nystatin incorporated in tuftsin-free or tuftsin-loaded liposomes was assessed by incubation of nystatin formulations with human erythrocytes. The toxicity profile of free nystatin and liposomal formulations of nystatin with or without tuftsin was also analyzed by monitoring the level of blood urea nitrogen (BUN) and serum creatinine in the treated BALB/c mice. The results of the present work showed that tuftsin-loaded nystatin liposomes like conventional nystatin liposomes exerted less toxicity to human erythrocytes as compared with free nystatin. Moreover, mice treated with tuftsin-loaded nystatin liposomes showed insignificant elevation in the biochemical values of serum creatinine and blood urea. The stability of nystatin liposomes upon incorporation of tuftsin was evaluated by monitoring the leakage of the entrapped drug in human serum. Tuftsin-loaded liposomes held nystatin for longer duration in the presence of serum than identical nystatin liposomes without tuftsin. Pharmacokinetics of the both tuftsin-free or tuftsin-loaded liposomal formulations nystatin was analyzed by determining the level of nystatin in the systemic circulation of mice at different time points. Mice injected with tuftsin-loaded nystatin liposomes showed higher level of the drug in the systemic circulation compared with those treated with conventional nystatin liposomes. The efficacy of tuftsin-loaded nystatin liposomes against A. fumigatus was evaluated by assessing the fungal burden in the lungs of treated mice. Treatment with tuftsin-loaded nystatin liposomes was most effective in eliminating fungal burden from lung tissues of infected mice compared to those treated with free nystatin or nystatin liposomes without tuftsin. The immunopotentiating activity, increased stability and less toxicity of tuftsin-incorporated nystatin liposomes, supports the idea for its prophylactic and therapeutic use in the clinical setting.     

Photothrombic activity of m-THPC-loaded liposomal formulations: pre-clinical assessment on chick chorioallantoic membrane model.

The objective of this study was to evaluate the ability of meso-tetra(hydroxyphenyl)chlorin (m-THPC) encapsulated into liposomal formulations to occlude neovascularization. Two m-THPC formulations including conventional or plain liposomes (Foslip) based on dipalmitoylphosphatidylcholine (DPPC) and the corresponding long-circulating poly(ethylene glycol) (PEG)-modified liposomes (PEGylated liposomes: Fospeg) were evaluated as delivery systems. Using the chick chorioallantoic membrane (CAM) as in vivo model, the fluorescence pharmacokinetic behaviour of encapsulated m-THPC reflecting the rate of the extravasation of the dye from the CAM vasculature and its photothrombic effectiveness were determined. This study was focused on the influence of the drug and/or light doses on the mean retention time of m-THPC within the CAM blood vessels after intravenous injection, and its photothrombic efficacy. Irrespective of the formulations tested and the drug doses injected, similar fluorescence pharmacokinetic profiles were obtained. The fluorescence contrast reached a steady state 30 s after injection. Constant positive values of the fluorescence contrast suggest that m-THPC is confined into the intravascular compartment during the experimental time (500 s). However, the photodynamic therapy assays showed that Foslip appears to be less potent than Fospeg in terms of photothrombic activities on the CAM model. For instance, the light dose necessary to induce the desired vascular damage with Foslip was twice (100 J/cm2) higher than with Fospeg (50 J/cm2). It can be inferred that this pre-clinical study showed that the formulation based on PEGylated liposomes technology offers a suitable delivery system for the treatment of choroidal neovascularization associated with age-related macular degeneration.     

Artemisinin and artemisinin plus curcumin liposomal formulations: enhanced antimalarial efficacy against Plasmodium berghei-infected mice

The therapeutic efficacies of novel liposomal delivery systems based on artemisinin or artemisinin-based combination therapy with curcumin have been investigated and reported in this study. The developed liposomal formulations had proper characteristics as drug carriers for parental administration in terms of particle size, polydispersity, encapsulation efficacy and ζ-potential. Their physical and chemical stabilities were also evaluated. Furthermore, the in vivo antimalarial activity of artemisinin-based liposomal formulations was tested in Plasmodium berghei NK-65 infected mice, a suitable model for studying malaria because the infection presents structural, physiological and life cycle analogies with the human disease. Artemisinin, alone or in combination with curcumin, was encapsulated in conventional and PEGylated liposomes and its in vivo performance was assessed by comparison with the free drug. Mice were treated with artemisinin at the dosage of 50 mg/kg/days alone or plus curcumin as partner drug, administered at the dosage of 100 mg/kg/days. Artemisinin alone began to decrease parasitaemia levels only 7 days after the start of the treatment and it appeared to have a fluctuant trend in blood concentration which is reflected in the antimalarial effectiveness. By contrast, treatments with artemisinin-loaded conventional liposomes (A-CL), artemisinin-curcumin-loaded conventional liposomes (AC-CL), artemisinin-loaded PEGylated liposomes (A-PL), artemisinin-curcumin-loaded PEGylated liposomes (AC-PL) appeared to have an immediate antimalarial effect. Both nanoencapsulated artemisinin and artemisinin plus curcumin formulations cured all malaria-infected mice within the same post-inoculation period of time. Additionally, all formulations showed less variability in artemisinin plasma concentrations which suggested that A-CL, AC-CL, A-PL and AC-PL give a modified release of drug(s) and, as a consequence, a constant antimalarial effect during time. In particular, A-PL seems to give the most pronounced and statistically significant therapeutic effect in this murine model of malaria. The enhanced permanency in blood of A-PL suggests the use of these nanosystems as suitable passive targeted carriers for parasitic infections; this strong effect of formulation is added up to the mechanism of action of artemisinin which acts in the erythrocyte cycle stage of human host as a blood schizonticide.     

PEGylated liposomes loading palmitoyl prednisolone for prolonged blood concentration of prednisolone

We investigated the pharmacokinetic behavior of palmitoyl prednisolone (Pal-PLS) and its liposomes with L-alpha-distearoylphosphatidylcholine (DSPC) and cholesterol (Chol) with or without L-alpha-distearoylphosphatidylethanolamine-polyethylene glycol 2000 (DSPE-PEG 2000) after their intravenous administration in rats. Pal-PLS rapidly disappeared from the systemic circulation and prednisolone (PLS) was regenerated after the administration of DSPC/Chol liposomes. PEGylated liposomes including DSPE-PEG 2000, however, successfully maintained high blood concentrations of Pal-PLS and PLS. The blood profiles of drugs after the administration of liposomal Pal-PLS were analyzed according to a two-compartment model. The larger content of DSPE-PEG 2000 in DSPC/Chol liposomes showed a lower first order elimination rate constant from the central compartment (K(el)) and clearance (CL). The area under the concentration-time curve (AUC) of Pal-PLS and PLS in PEGylated liposomes was larger than DSPC/Chol liposomes. The mean resident time (MRT) of Pal-PLS and PLS was also prolonged by PEGylated liposomes. Although DSPC/Chol liposomes showed a high distribution of Pal-PLS in the liver and spleen, PEGylated liposomes significantly decreased the liver distribution of Pal-PLS. The biliary and urinary excretions of drugs for 240 min after drug administration were less than 1% of the administrated dose in any formulations. In conclusion, PEGylated liposomes, including Pal-PLS, are useful for maintain the PLS concentration in the blood after intravenous administration.     

RGD环肽介导的靶向脂质体体内药动学及荷瘤动物活体成像研究

本文测定了大鼠单剂量(5 mg.kg1)尾静脉注射RGD环肽介导的羟基喜树碱(hydroxycamptothecin,HCPT)靶向脂质体(HCPT-RGD-LP)和HCPT长循环脂质体(HCPT-LP)的血药浓度,比较两组的药动学行为;研究了HCPT-LP及HCPT注射剂在正常小鼠血浆和心、肝、脾、肺、肾中的分布情况;采用人肝癌HepG2细胞移植裸鼠,以DiR为荧光探针,通过活体成像比较RGD环肽修饰的DiR靶向脂质体(DiR-RGD-LP)和DiR长循环脂质体(DiR-LP)在荷瘤裸鼠体内的分布。结果显示,HCPT-RGD-LP组和HCPT-LP组的主要药动学参数t1/2β、CL、Vc、AUC048 h、AUC0∞、MRT048 h和MRT0∞均无显著性差异(P>0.05);HCPT-LP在小鼠体内的循环时间明显长于HCPT注射剂,且药物在肝脏中的分布浓度较高;荷瘤裸鼠中,DiR-RGD-LP组肿瘤部位的荧光强度显著高于DiR-LP组,提示RGD环肽用于脂质体修饰能明显提高给药系统的肿瘤靶向性。     

“加速血流清除”现象中的免疫机制分析

目的对"加速血流清除"(accelerated blood clearance,ABC)现象的产生机制和影响因素进行综述,并探讨可能的解决途径。方法参阅近年来国内外文献共42篇,从免疫学角度对聚乙二醇(polyethyleneglycol,PEG)化脂质体ABC现象的产生机制与影响因素进行归纳、总结和分析。结果首次注射的PEG化脂质体作为抗原诱发机体分泌特异性抗体,此抗体与二次注射的PEG化脂质体相结合并介导其从血液中加速清除。PEG包衣、PEG植入密度、载体粒径/大小、载体电荷、磷脂剂量、给药间隔及包封药物等因素均对脂质体的ABC现象产生影响。结论为解决PEG化脂质体ABC现象及PEG化制剂的开发提供了参考。