Circulation Time Of Liposomes Research Articles

Impact of formulation parameters and circulation time on PEGylated liposomal doxorubicin related hand-foot syndrome

PEGylated liposomal doxorubicin (PLD) has effectively reduced the cardiac toxicity of free doxorubicin (DOX) due to its unique nanoscale properties. However, an unexpected accumulation of PLD in the skin has led to hand-foot syndrome (HFS), negatively impacting quality of life and psychological well-being. In this study, self-limiting HFS rat models were created to mimic human symptoms through varying dosing schedules and intensities of PLD. The effects of PLD formulation parameters on HFS were also investigated. The results demonstrated that replacing ammonium sulfate with citric buffer, increasing liposome size, or reducing DSPE-mPEG2000 modification density alleviated HFS. Additionally, liposomes without DSPE-mPEG2000 modification completely avoided HFS, suggesting that PEGylated phospholipid was the key formulation parameter contributing to PLD-induced HFS. Furthermore, the correlation between liposome pharmacokinetics and HFS indicated that PEGylation, rather than the extended circulation time of liposomes, may mediated PLD-related HFS. Better understanding of the formulation parameters that trigger HFS can guide reformulation strategies to mitigate or prevent this syndrome.

Dexamethasone-Integrated Mesenchymal Stem Cells for Systemic Lupus Erythematosus Treatment via Multiple Immunomodulatory Mechanisms.

The therapeutic application of mesenchymal stem cells (MSCs) has good potential as a treatment strategy for systemic lupus erythematosus (SLE), but traditional MSC therapy still has limitations in effectively modulating immune cells. Herein, we present a promising strategy based on dexamethasone liposome-integrated MSCs (Dexlip-MSCs) for treating SLE via multiple immunomodulatory pathways. This therapeutic strategy prolonged the circulation time of dexamethasone liposomes in vivo, restrained CD4+T-cell proliferation, and inhibited the release of proinflammatory mediators (IFN-γ and TNF-α) by CD4+T cells. In addition, Dexlip-MSCs initiated cellular reprogramming by activating the glucocorticoid receptor (GR) signaling pathway to upregulate the expression of anti-inflammatory factors such as cysteine-rich secretory protein LCCL-containing domain 2 (CRISPLD2) and downregulate the expression of proinflammatory factors. In addition, Dexlip-MSCs synergistically increased the anti-inflammatory inhibitory effect of CD4+T cells through the release of dexamethasone liposomes or Dex-integrated MSC-derived exosomes (Dex-MSC-EXOs). Based on these synergistic biological effects, we demonstrated that Dexlip-MSCs alleviated disease progression in MRL/lpr mice more effectively than Dexlip or MSCs alone. These features indicate that our stem cell delivery strategy is a promising therapeutic approach for clinical SLE treatment.

Ginsenoside Rg3 endows liposomes with prolonged blood circulation and reduced accelerated blood clearance

PEGylated cholesterol-containing liposomes (Chol-PEG-lipo) have been widely used as a drug carrier for their good stealth property in blood circulation where cholesterol maintains the stability of the liposomal lipid bilayer and PEGylation endows liposomes with long circulation capability. However, cholesterol-related disadvantages and the accelerated blood clearance (ABC) phenomenon caused by PEGylation greatly limit the application of conventional stealth liposomes in clinic. Herein, ginsenoside Rg3 was selected to substitute cholesterol and PEG for liposomes preparation (Rg3-lipo). Rg3 was proved with similar liposomal membrane regulation ability to cholesterol and comparable long circulation effect to PEG. In addition, repeated administrations of Chol-PEG-lipo and Rg3-lipo were performed. The circulation time of the second dose of Chol-PEG-lipo was substantially reduced accompanied by a greatly increased accumulation in the liver due to the induction of anti-PEG IgM and the subsequent activated complement system. In contrast, no significantly increased level of relative plasma cells, IgM secretion and the complement activation in blood circulation was observed after the second injection of Rg3-lipo. As a result, Rg3-lipo showed great stealth property without ABC phenomenon. Therefore, developing liposomes utilizing Rg3 instead of PEG and cholesterol presents a promising strategy to prolong the blood circulation time of liposomes without triggering the ABC phenomenon and activated immune responses.

Surface-modified cationic liposomes with a matrix metalloproteinase-degradable polyethylene glycol derivative improved doxorubicin delivery in murine colon cancer

PEGylation is a commonly used approach to prolong the blood circulation time of cationic liposomes. However, PEGylation is associated with the "PEG dilemma", which hinders binding and uptake into tumor cells. The cleavable PEG products are a possible solution to this problem. In the current research, doxorubicin-loaded cationic liposomes (Dox-CLs) surface-conjugated with a matrix metalloproteinase-2 (MMP-2)-sensitive octapeptide linker-PEG derivative were prepared and compared to non-PEGylated and PEGylated CLs in terms of size, surface charge, drug encapsulation and release, uptake, in vivo pharmacokinetics, and anticancer efficacy. It was postulated that PEG deshielding in response to the overexpressed MMP-2 in the tumor microenvironment increases the interaction of protected CLs with cellular membranes and improves their uptake by tumor cells/vasculature. MMP2-responsive Dox-CLs had particle sizes of ∼115-140 nm, surface charges of ∼+25 mV, and encapsulation efficiencies of ∼85-95%. In vitro cytotoxicity assessments showed significantly enhanced uptake and cytotoxicity of PEG-cleavable CLs compared to their non-cleavable PEG-coated counterparts or Caelyx®. Also, the chick chorioallantoic membrane assay showed great antiangiogenesis ability of Dox-CLs leading to target and prevent tumor neovascularization. Besides, in vivo studies showed an effective therapeutic efficacy of PEG-cleavable Dox-CLs in murine colorectal cancer with negligible hematological and histopathological toxicity. Altogether, our results showed that MMP2-responsive Dox-CLs could be served as a promising approach to improve tumor drug delivery and uptake.

Polysarcosine-Coated liposomes attenuating immune response induction and prolonging blood circulation

HypothesisLiposomes coated with long polysarcosine (PSar) chains at a high density might enable long blood circulation and attenuate accelerated blood clearance (ABC) phenomenon. ExperimentsIn this study, we controlled the length (23, 45, 68 mers) and density (5, 10, 15 mol%) of PSar on liposomal coatings and, furthermore, investigated the effects of PSar length and density on the blood circulation time, biodistribution, immune response, and ABC phenomenon induction. Length-controlled PSar-bound lipids (PSar-PEs) were synthesized using a click reaction and inserted into bare liposomes at different combinations of chain lengths and proportions. FindingsAlthough all PSar-coated liposomes (PSar-lipos) had similar morphological, physical, and chemical properties, they had different blood circulation times and biodistribution, and exerted varied effects on the immune system. All PSar-lipos with different PSar length and density showed a similar anti-PSar IgM response. Liposomes modified with the longest PSar chain (68 mers) at a high density (15 mol%) showed the longest blood circulation time and, additionally, attenuated ABC phenomenon compared with PEG-lipo. The ex vivo analysis of the biodistribution of liposomes revealed that a thick PSar layer enhanced the blood circulation time of liposomes due to the reduction of the accumulation of liposomes in the liver and spleen. These findings provide new insights into the relationship between IgM expression and ABC phenomenon inhibition.

Development of stealth liposomal formulation of celecoxib: In vitro and in vivo evaluation.

Celecoxib (CLB) is a highly hydrophobic selective cyclo-oxygenase inhibitor with high plasma protein binding and undergoes extensive hepatic metabolism. CLB is highly effective in the treatment of osteo and rheumatoid arthritis as first line therapy but produces severe gastro-intestinal toxicities and cardiovascular side effects. In this research, stealth liposomes of CLB were developed with the intention to reduce the side effects and increase the accumulation of drug in the sites of inflammation. Stealth liposomes were prepared by thin film hydration technique using distearoylphosphatidylcholine and PE-PEG 2000 with variable amounts of cholesterol and characterized. The effects of various lipids such as hydrogenated soy phosphatidylcholine, dipalmitoyl phosphatidylcholine, distearoylphosphatidylcholine and cholesterol content on % drug encapsulation was investigated. The optimized stealth liposomes were characterized by FT-IR and DSC for possible drug excipients interaction. Pharmacokinetics, pharmacodynamics and biodistribution studies were carried out for the stealth liposomes. The results revealed that the stealth liposomes reduced the inflammation to the larger magnitude and have also sustained the magnitude when compared to free drug along with maximum analgesic response. Higher elimination half-life, AUC, MRT and lowered clearance rate denotes the extended bioavailability of the drug in blood. Biodistribution studies revealed that stealth liposomes extend the circulation time of liposomes in blood by decreasing opsonisation and be less concentrated in kidney, thereby reducing the toxicities to RES and renal organs and facilitate the drug accumulation in the area of inflammation. Our results indicated that CLB, without the requirement of modifications to enhance solubilisation, can be encapsulated and released from liposomal formulations. This new-fangled drug delivery approach may be used to circumvent the low bioavailability and toxic side effects of oral CLB formulations.

Multifunctional Role of Polyvinylpyrrolidone in Pharmaceutical Formulations.

Polyvinylpyrrolidone (PVP), a non-ionic polymer, has been employed in multifarious fields such as paper, fibers and textiles, ceramics, and pharmaceutics due to its superior properties. Especially in pharmacy, the properties of inertness, non-toxicity, and biocompatibility make it a versatile excipient for both conventional formulations and novel controlled or targeted delivery systems, serving as a binder, coating agent, suspending agent, pore-former, solubilizer, stabilizer, etc. PVP with different molecular weights (MWs) and concentrations is used in a variety of formulations for different purposes. In this review, PVP-related researches mainly in recent 10 years were collected, and its main pharmaceutical applications were summarized as follows: (i) improving the bioavailability and stability of drugs, (ii) improving the physicomechanical properties of preparations, (iii) adjusting the release rate of drugs, and (iv) prolonging the in vivo circulation time of liposomes. Most of these applications could be explained by the viscosity, solubility, hydrophilicity, and hydrogen bond-forming ability of PVP, and the specific action mechanisms for each application were also tried to figure out. The effect of PVP on bioavailability improvement establishes it as a promising polymer in the emerging controlled or targeted formulations, attracting growing interest on it. Therefore, given its irreplaceability and tremendous opportunities for future developments, this review aims to provide an informative reference about current roles of PVP in pharmacy for interested readers.

Understanding the Stealth Properties of PEGylated lipids: A Mini-Review

PEGylation is a well-established strategy for improving the target specificity, circulation time and stability of liposomes, thereby improving their stealth properties. This brief review provides an insight on the composition of PEGylated liposomes and the characteristics that dictate the functionality of PEGylated liposomes such as surface density, molecular weight, presence of linkers and acyl groups. Physicochemical techniques used to characterize the PEG liposomes and test their stability are also discussed along with their clinical implications. This review provides the readers with a broad range of understanding of various PEGylated lipids, techniques to access their stability in liposomal formulations and state-of -the-art development of PEGylated liposomal formulations.

Low molecular weight heparin modified bone targeting liposomes for orthotopic osteosarcoma and breast cancer bone metastatic tumors

The standard-of-care chemotherapy is important in the treatment of osteosarcoma and bone metastastic tumors. However, the efficacy is limited by the specific physiological environment of the bone. Thus, developing an efficient antitumor and anti-metastasis chemotherapeutic formulation is desired for treatment of bone tumors. Herein, we utilized the alendronate (ALN) and low molecular weight heparin (LMWH) modified liposomes to deliver the antitumor drug doxorubicin (DOX), where traditionally-believed non-active drug carrier, targeting moiety could also exhibit biological functions and realize anti-tumor and anti-metastasis efficiency synergistically with the antitumor drug. Specifically, ALN could serve as the bone targeting moiety and the therapeutic agents of anti-osteoporosis. LMWH could enhance the blood circulation time of liposomes and exhibit anti-metastasis efficiency. Besides characterization of typical physiochemical properties of the delivery system, both the orthotopic osteosarcoma model and bone metastasis cancer model were adopted to evaluate the in vivo efficacy. The results proved this system could remarkably suppress tumor growth and inhibit tumor metastasis.

Liposome Circulation Time is Prolonged by CD47 Coating.

Bio-degradable nano-particles have many applications as drug delivery vehicles because of their good bio-availability, controlled release, low toxicity and potential for encapsulation. However, the most important obstacle to nanoparticulate drug delivery is elimination by macrophages which reduces the residence time of nanoparticles in the blood. To overcome this problem, the surface of the nanoparticle can be passivated by coating with Polyethylene glycol (PEG). However, the use of PEG has its own disadvantages. CD47 receptor acts as a self marker on the surface of many cells and inhibits phagocytosis. This study used a CD47 mimicry peptide as a substitute for PEG to fabricate "stealth" nanoliposome with reduced macrophage clearance. Doxorubibin was used as a model drug because of its inherent fluorescence. Doxorubicin- containing liposomes were coated with different percentages of CD47 mimicry peptide (0.5% and 1%). PEG-functionalized doxorubicin-containing liposomes, were used as a comparator. The liposomal formulations were intravenously injected into mice. Serum was collected at pre-defined time points and tissue samples were taken at 24 hours. Fluorescence was used to determine the concentration doxorubicin in serum, heart, spleen, kidney, liver and lung tissues. Tissue biodistribution and serum kinetic studies indicated that compared with PEG, the use of CD47 mimicry peptide increased the circulation time of doxorubicin in the circulation. Moreover, unwanted accumulation of doxorubicin in the reticuloendothelial tissues (liver and spleen), kidney and heart was significantly decreased by the CD47 mimicry peptide. The use of a CD47 mimicry peptide on the surface of nanoliposomes improved the residence time of liposomal doxorubicin in the circulation. The accumulation of drug in non-target tissues was reduced, thereby potentially reducing toxicity.

Abstract CT054: Clinical and pharmacokinetic study with a lipidic prodrug of mitomycin-c entrapped in liposomes in metastatic colorectal cancer patients

Abstract Background: A phase 1A/1B study was conducted to investigate the safety of Promitil, a liposomal formulation of a lipidic prodrug of mitomycin-c (MLP) within an open, dose-escalating, phase (1A, n=27) followed by an expanded phase (1B, n=61) restricted to metastatic colorectal cancer (mCRC) patients after failure to two or more lines of therapy. We report here on the correlation between pharmacokinetic (PK) parameters and clinical observations in patients with mCRC. Methods: PK analysis of plasma MLP levels was obtained in 53 mCRC patients (F=26, M=27), who received Promitil every 4 weeks either as single agent (n=28), in combination with capecitabine (Cap) (n=12), or in combination with Cap and bevacizumab (Bev) (n=13). The MLP dose range was 0.5-3.5 mg/kg with most patients (N=29) receiving 2.0-2.5 mg/kg. Out of 53 patients analyzed, 39 patients completed the 3rd cycle (study week 12) and were efficacy-evaluable by CT scan and Recist criteria. PK of plasma MLP levels was analyzed by noncompartmental methods. For statistical analysis and correlations of T½ and Clearance (CL) with age, sex, BMI, baseline neutrophil/lymphocyte ratio (NLR), CEA, and survival, we used t test and Pearson or Spearman coefficients. Results: The PK of MLP was stealth-like with long T½ (~1 day), slow CL, and small Volume of distribution. Stable Disease (SD) was reported in 14 patients (36%), and Progressive Disease (PD) in 25 patients. Median survival of all 39 patients (SD+PD) was 8.3 months. SD patients had significantly longer median survival than PD patients (14.3 vs 6.5 months, p=0.0002). SD patients had significantly longer T½ and slower CL than non-SD patients. A longer T½ and slower CL were significantly correlated with longer survival. A high NLR and high CEA were correlated with shorter T½ and/or faster CL. Dose of MLP, addition of Cap and/or Bev, age and BMI did not have any apparent effect on response or survival. Conclusions: SD was indicative of extended survival. The longer circulation time of the liposomal prodrug in SD patients and its correlation with longer survival are consistent with the well-known correlation between liposome circulation time and localization in tumors. A high NLR may signal inflammatory macrophage activation resulting in shorter liposomal circulation half-life and reducing the chances of disease control. Citation Format: Alberto A. Gabizon, Esther Tahover, Ruth Perets, Talia Golan, Ravit Geva, Yasmine Amitay, Hilary Shmeeda, Patricia Ohana. Clinical and pharmacokinetic study with a lipidic prodrug of mitomycin-c entrapped in liposomes in metastatic colorectal cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr CT054.

Novel ginsenoside-based multifunctional liposomal delivery system for combination therapy of gastric cancer.

The clinical treatment of gastric cancer (GC) is hampered by the development of anticancer drug resistance and the unfavorable pharmacokinetics, off-target toxicity, and inadequate intratumoral accumulation of the current chemotherapy treatments. Ginsenosides combined with paclitaxel (PTX) have been shown to exert synergistic inhibition of human GC cell proliferation. In the present study, we developed a novel multifunctional liposome system, in which ginsenosides functioned as the chemotherapy adjuvant and membrane stabilizer. These had long blood circulation times and active targeting abilities, thus creating multifunctionality of the liposomes and facilitating drug administration to the GC cells.Methods: Three ginsenosides with different structures were used to formulate the unique nanocarrier, which was prepared using the thin-film hydration method. The stability of the ginsenoside liposomes was determined by particle size analysis using dynamic light scattering. The long circulation time of ginsenoside liposomes was compared with that of conventional liposome and polyethylene glycosylated liposomes in vivo. The active targeting effect of ginsenoside liposomes was examined with a GC xenograft model using an in vivo imaging system. To examine the antitumor activity of ginsenoside liposomes against GC, MTT, cell cycle, and apoptosis assays were performed on BGC-823 cells in vitro and PTX-loaded ginsenoside liposomes were prepared to evaluate the therapeutic efficacy on GC in vivo.Results: The ginsenosides stabilized the liposomes in a manner similar to cholesterol. We confirmed the successful delivery of the bioactive combination drugs and internalization into GC cells via analysis of the glucose-related transporter recognition and longer blood circulation time. PTX was encapsulated in different liposomal formulations for use as a combination therapy, in which ginsenosides were found to exert their inherent anticancer activity, as well as act synergistically with PTX. The combination therapy using these targeted liposomes significantly suppressed GC tumor growth and outperformed most reported PTX formulations, including Lipusu® and Abraxane®.Conclusion: We established novel ginsenoside-based liposomes as a tumor-targeting therapy, in which ginsenoside functioned not only as a chemotherapy adjuvant, but also as a functional membrane material. Ginsenoside-based liposomes offer a novel platform for anticancer drug delivery and may lead to a new era of nanocarrier treatments for cancer.

All-Atom Molecular Dynamics Simulation of Stealth Liposomes

Pegylation of liposomes has been widely used in the field of drug delivery to increase the bloodstream circulation time of liposomes; however, simulation studies have focused on simple model of liposomes, including only one or two different kinds of lipids simulated by simplistic coarse-grained models that lack the atomic/chemical details. Implementing all-atom molecular dynamics (MD) simulations, stable structure of solvated stealth liposomes are achieved. The liposomes are composed of different DOPC (dioleoylphosphatidylcholine)/cholesterol/PEG2000-DSPE (polyethylene glycol 2000-distearoylphosphatidylethanolamine) molar ratio. Here we used coarse-graining/backmapping method to speed up mixing of the stealth liposome molecules. The MD simulations revealed that not only are geometric structure of liposomes dominated by the cholesterol molecules, but also PEGylated lipids reduce leakage of contents from liposomes.

FORMULATION AND CHARACTERIZATION OF DOXORUBICIN HYDROCHLORIDE LIPOSOMES BY DOUBLE EMULSION METHOD

Doxorubicin hydrochloride is one of the most commonly used cytotoxic anthracycline antibiotics used in cancer chemotherapy an d has been shown to have activity against a wide variety of neoplasms. Conventional compositi ons of doxorubicin hydrochloride are available as freeze - dried product (or) as a solution of doxorubicin hydrochloride in water. Both these products have been associated with a number of toxicities when administered intravenously. Several approaches have t aken in an effort to increase the circulation time of liposomes by coating the liposomal surface with a hydrophilic polymer s uch as polyethylene glycol , but have new toxic effects appeared like skin toxicity generally known as “Hand - Foot Syndrome” . In the present study Doxorubicin Liposomes we re formulated by “Double emulsion method to form Multivescicular liposomes”. The influence of various formulation and process parameters using different ratios of inner aqueous phase: o il phase : outer aqueous phase, ho mogenization speed, homogenization time on encapsulation efficiency, % f ree drug, particle size, z eta potential, surface morphology and release were investigated. Less than 10 % free drug was achieved with double emulsion method. The Sca nning Electron Micr oscopy image showed the spherical shape having 33 ± 5 µm particle sizes. The in - vitro drug release for optimized formulation was found to be controlled release of drug over a period of 7 days.

Liposomal drug delivery systems for targeted cancer therapy: is active targeting the best choice?

Liposomes are biodegradable and biocompatible self-forming spherical lipid bilayer vesicles. They can encapsulate and deliver one or more hydrophobic and hydrophilic therapeutic agents with poor therapeutic indices to tumor sites. Properties such as lipid bilayer fluidity, charge, size and surface hydration can be modified to extend liposome circulation time in the bloodstream and enhance efficacy. The focus of this review is on ligand-conjugated liposomes and their potential application in tumor-targeted delivery. Ligand-conjugated liposomes are designed to target receptors which are overexpressed on tumor cells to decrease drugs side effects by enhancing their selective delivery to tumor site. Despite the extensive research in this area, no small molecule ligand-conjugated liposome has been approved up to date for cancer therapy.

Repeated Administration of Hyaluronic Acid Coated Liposomes with Improved Pharmacokinetics and Reduced Immune Response.

PEGylated liposomes (PEG-Lip) have been widely used as a drug carrier for their good stealth property in blood circulation. However, the second injection of PEG-Lip was reported to result in the accelerated blood clearance (ABC) phenomenon and trigger hypersensitivity reactions in sensitive individuals for its complement activation effect. To avoid adverse immune responses, HA was selected to modify liposomes to afford HA modified liposomes (HA-Lip). Repeated administrations of PEG-Lip and HA-Lip were performed in rats. Our results showed that PEG-Lip induced the ABC phenomenon accompanied by a greatly increased accumulation of PEG-Lip in the liver. In contrast, HA-Lip showed good stealth property without inducing either the ABC phenomenon or an increase in liver uptake. Moreover, HA-Lip did not trigger complement activation in human serum in vitro and in rat blood in vivo. Consequently, HA modification represents a viable strategy to prolong the blood circulation time of liposomes without inducing the ABC phenomenon and adverse immune responses.

The effect of polymer backbone chemistry on the induction of the accelerated blood clearance in polymer modified liposomes

A variety of water-soluble polymers, when attached to a liposome, substantially increase liposome circulation half-life in animals. However, in certain conditions, liposomes modified with the most widely used polymer, polyethylene glycol (PEG), induce an IgM response resulting in an accelerated blood clearance (ABC) of the liposome upon the second injection. Modification of liposomes with other water-soluble polymers: HPMA (poly[N-(2-hydroxypropyl) methacrylamide]), PVP (poly(vinylpyrrolidone)), PMOX (poly(2-methyl-2-oxazoline)), PDMA (poly(N,N-dimethyl acrylamide)), and PAcM (poly(N-acryloyl morpholine)), increases circulation times of liposomes; but a precise comparison of their ability to promote long circulation or induce the ABC effect has not been reported. To obtain a more nuanced understanding of the role of polymer structure/MW to promote long circulation, we synthesized a library of polymer diacyl chain lipids with low polydispersity (1.04–1.09), similar polymer molecular weights (2.1–2.5kDa) and incorporated them into 100nm liposomes of a narrow polydispersity (0.25–1.3) composed of polymer–lipid/hydrogenated soy phosphatidylcholine/cholesterol/diD: 5.0/54.5/40/0.5. We confirm that HPMA, PVP, PMOX, PDMA and PAcM modified liposome have increased circulation times in rodents and that PVP, PDMA, and PAcM do not induce the ABC effect. We demonstrate for the first time, that HPMA does not cause an ABC effect whereas PMOX induces a pronounced ABC effect in rats. We find that a single dose of liposomes coated with PEG and PMOX generates an IgM response in rats towards the respective polymer. Finally, in this homologous polymer series, we observe a positive correlation (R=0.84 in rats, R=0.92 in mice) between the circulation time of polymer-modified liposomes and polymer viscosity; PEG and PMOX, the polymers that can initiate an ABC response were the two most viscous polymers. Our findings suggest that polymers that do not cause an ABC effect such as, HPMA or PVP, deserve further consideration as polymer coatings to improve the circulation of liposomes and other nanoparticles.

Molecular Dynamics Simulation of PEGylated Membranes with Cholesterol: Building Toward the DOXIL Formulation

PEGylation has been used successfully to increase the circulation time of drug delivery liposomes by providing an external steric sheath. In all FDA approved PEGylated drug delivery liposomes, cholesterol is a key component. In a continuation of our previous work we have simulated a PEGylated membrane with cholesterol added to the membrane formulation to determine the effect on membrane structure of the cholesterol–PEG interaction. We show that, like the case for the liquid crystalline membrane, PEG enters into the lipid bilayer, however, in a specific fashion: the PEG winds along the β face of the cholesterol. Additionally, PEG interferes with the role cholesterol plays in structuring and compacting the membrane; when the membrane is PEGylated, the area per lipid increases, rather than decreases, with increasing cholesterol. Our studies provide mechanistic explanations for existing experimental results concerning the effect of adding cholesterol to the PEGylated liposome, including alteration to the lipo...

Increased tumor targeted delivery using a multistage liposome system functionalized with RGD, TAT and cleavable PEG

Though PEGylation has been widely used to enhance the accumulation of liposomes in tumor tissues through enhanced permeability and retention (EPR) effects, it still inhibits cellular uptake and affects intracellular trafficking of carriers. Active targeting molecules displayed better cell selectivity but were shadowed by the poor tumor penetration effect. Cell penetrating peptides could increase the uptake of the carriers but were limited by their non-specificity. Dual-ligand system may possess a synergistic effect and create a more ideal drug delivery effect. Based on the above factors, we designed a multistage liposome system co-modified with RGD, TAT and cleavable PEG, which combined the advantages of PEG, specific ligand and penetrating peptide. The cleavable PEG could increase the stability and circulation time of liposomes during circulation. After the passive extravasation to tumor tissues, the previously hidden dual ligands on the liposomes were exposed in a controlled manner at the tumor site through exogenous administration of a safe reducing agent L-cysteine. The RGD specifically recognized the integrins overexpressed on various malignant tumors and mediated efficient internalization in the synergistic effect of the RGD and TAT. Invitro cellular uptake and 3D tumor spheroids penetration studies demonstrated that the system could not only be selectively and efficiently taken up by cells overexpress ingintegrins but also penetrate the tumor cells to reach the depths of the avascular tumor spheroids. In vivo imaging and fluorescent images of tumor section further demonstrated that this system achieved profoundly improved distribution within tumor tissues, and the RGD and TAT ligands on C-R/T liposomes produced a strong synergistic effect that promoted the uptake of liposomes into cells after the systemic administration of L-cysteine. The results of this study demonstrated a tremendous potential of this multistage liposomes for efficient delivery to tumor tissue and selective internalization into tumor cells.

Terpene-containing PEGylated liposomes as transdermal carriers of a hydrophilic compound.

We investigated the effect of PEGylated liposomes (PLs) containing a terpene on the penetration of a hydrophilic compound through porcine skin. PLs composed of N-(carbonyl-methoxypolyethyleneglycol-2000)-1,2-distearoyl-sn-glycero-3-phosphoethanolamine (PEG2000-DSPE), the sodium salt of PEG2000-DSPE, phosphatidylcholine (PC), cholesterol (Chol), Tween 20, and d-limonene were prepared as carriers for fluorescein sodium (NaFI). The physicochemical characteristics of PLs and their effects on in vitro skin penetration were evaluated. Tape stripping was used to evaluate NaFI deposition in skin layers, and confocal laser scanning microscopy (CLSM) was used to investigate the depth of skin penetration and the pathways used by NaFI-loaded vesicles. PLs containing d-limonene were smaller and conferred higher entrapment efficiency and skin penetration on NaFI than did PLs and conventional liposomes (CLs). The deposition of NaFI from PLs with d-limonene was greater in epidermis and dermis (6.10±1.74 µg) than stratum corneum (2.06±0.47 µg). CLSM images revealed that NaFI penetrated into the deepest skin layer with maximum fluorescence intensity. NaFI penetrated deeper (180 µm) in follicular than nonfollicular regions (145 µm), suggesting a transfollicular pathway predominates in skin penetration by NaFI-loaded PLs. In conclusion, grafting PEG onto ultra-deformable liposomes may enhance transdermal NaFI delivery and may be used as a carrier to prolong liposome circulation time.