Pharmacokinetics of long-circulating liposomes

PEGylated long-circulating liposomes deliver homoharringtonine to suppress multiple myeloma cancer stem cells

The goal of this investigation was to evaluate the inhibiting effect of high proportion polyethyleneglycol of long-circulating homoharringtonine liposomes on RPMI8226 multiple myeloma cancer stem cells. The CD138^-CD34^- multiple myeloma cancer stem cells isolated from RPMI8226 cell line using magnetic activated cell sorting system were, respectively, incubated with the optimized formulation of polyethyleneglycol of long-circulating homoharringtonine liposomes and the homoharringtonine in vitro, and the multiple myeloma cancer stem cell proliferation, colony formation, and cell cycle were analyzed. The inhibition of the multiple myeloma CD138^-CD34^- cancer stem cell growth was investigated in non-obese-diabetic/severe-combined-immunodeficiency mice that were implanted with multiple myeloma RPMI 8226 cancer stem cells and treated with the LCL-HHT-H-PEG. The results showed that the polyethyleneglycol of long-circulating homoharringtonine liposomes significantly inhibited MM cancer stem cell proliferation, colony formation, and induced cancer stem cell apoptosis in vitro as well as MM cancer stem cell growth in non-obese-diabetic/severe-combined-immunodeficiency mice compared with the homoharringtonine. In addition, the mouse bone mineral density and the red blood cell count were significantly increased in polyethyleneglycol of long-circulating homoharringtonine liposomes group. In conclusion, the data demonstrated that the developed polyethyleneglycol of long-circulating homoharringtonine liposomes formulation may serve as an efficient therapeutic drug for suppressing CD138^-CD34^- multiple myeloma cancer stem cell growth by inducing cancer stem cell apoptosis in non-obese-diabetic/severe-combined-immunodeficiency mouse model. Impact statement Multiple myeloma (MM) remains largely incurable until now. One of the main reasons is that there are cancer stem cells (CSCs) in MM, which are responsible for MM's drug resistance and relapse. In this study, we wanted to extend our previous investigation²² that whether we developed the LCL-HHT-H-PEG formulation have an inhibitory effect on MM CD138^-CD34^-CSCs in MM CSC engrafted NOD/SCID mouse model. Our data from the present study have demonstrated the therapeutic effect of LCL-HHT-H-PEG on MM-bearing mouse model. The study represents the first attempt to demonstrate that the LCL-HHT-H-PEG formulation is available for treatment MM patients in clinic. Therefore, this finding is important and deserves publication in Experimental Biology and Medicine.

Controlling the Stealth Effect of Nanocarriers through Understanding the Protein Corona

The past decade has seen a significant increase in interest in the use of polymeric nanocarriers in medical applications. In particular, when used as drug vectors in targeted delivery, nanocarriers could overcome many obstacles for drug therapy. Nevertheless, their application is still impeded by the complex composition of the blood proteins covering the particle surface, termed the protein corona. The protein corona complicates any prediction of cell interactions, biodistribution, and toxicity. In particular, the unspecific uptake of nanocarriers is a major obstacle in clinical studies. This Minireview provides an overview of what we currently know about the characteristics of the protein corona of nanocarriers, with a focus on surface functionalization that reduces unspecific uptake (the stealth effect). The ongoing improvement of nanocarriers to allow them to meet all the requirements necessary for successful application, including targeted delivery and stealth, are further discussed.

Neuroprotection against cerebral ischemia/reperfusion injury by intravenous administration of liposomal fasudil

Fasudil, a Rho-kinase inhibitor, is a promising neuroprotectant against ischemic stroke; however, its low bioavailability is an obstacle to be overcome. Our previous study revealed that the liposomal drug delivery system is a hopeful strategy to increase the therapeutic efficacy of neuroprotectants. In the present study, the usefulness of intravenously administered liposomal fasudil for cerebral ischemia/reperfusion (I/R) injury treatment was examined in transient middle cerebral artery occlusion (t-MCAO) rats. The results showed that PEGylated liposomes of approximately 100nm in diameter accumulated more extensively in the I/R region compared with those of over 200nm. Confocal images showed that fluorescence-labeled liposomal fasudil was widely distributed in the I/R region, and was not noticeably taken up by microglia, which are well-known resident macrophages in the brain, and neuronal cells. These data indicated that liposomal fasudil mainly exerted its pharmacological activity by releasing fasudil from the liposomes in the I/R region. Moreover, liposomal fasudil effectively suppressed neutrophil invasion and brain cell damage in the t-MCAO rats, resulting in amelioration of their motor function deficits. These findings demonstrated both the importance of particle size for neuroprotectant delivery and the effectiveness of liposomal fasudil for the treatment of cerebral I/R injury.

Multifunctional, stimuli-sensitive nanoparticulate systems for drug delivery

The use of nanoparticulate pharmaceutical drug delivery systems (NDDSs) to enhance the in vivo effectiveness of drugs is now well established. The development of multifunctional and stimulus-sensitive NDDSs is an active area of current research. Such NDDSs can have long circulation times, target the site of the disease and enhance the intracellular delivery of a drug. This type of NDDS can also respond to local stimuli that are characteristic of the pathological site by, for example, releasing an entrapped drug or shedding a protective coating, thus facilitating the interaction between drug-loaded nanocarriers and target cells or tissues. In addition, imaging contrast moieties can be attached to these carriers to track their real-time biodistribution and accumulation in target cells or tissues. Here, I highlight recent developments with multifunctional and stimuli-sensitive NDDSs and their therapeutic potential for diseases including cancer, cardiovascular diseases and infectious diseases.

The use of ultrasound to release chemotherapeutic drugs from micelles and liposomes

Several drug delivery systems have been investigated to reduce the side effects of chemotherapy by encapsulating the therapeutic agent in a nanosized carrier until it reaches the tumor site. Many of these particles are designed to be responsive to the mechanical and thermal perturbations delivered by ultrasound. Once the nanoparticle reaches the desired location, ultrasound is applied to release the chemotherapy drug only in the vicinity of the targeted (cancer) site, thus avoiding any detrimental interaction with healthy cells in the body. Studies using liposomes and micelles have shown promising results in this area, as these nanoparticles with simple, yet effective structures, showed high efficiency as drug delivery vehicles both in vitro and in vivo. This article reviews the design and application of two novel nanosized chemotherapeutic carriers (i.e. micelles and liposomes) intended to be actuated by ultrasound.

Hyaluronan polymer length, grafting density, and surface poly(ethylene glycol) coating influence in vivo circulation and tumor targeting of hyaluronan-grafted liposomes

Hyaluronan-grafted liposomes (HA-liposomes) preferentially target CD44-overexpressing tumor cells in vitro via receptor-mediated endocytosis. We investigated the pharmacokinetics and biodistribution of HA-liposomes with various sizes of HA (MW 5-8, 50-60, and 175-350 kDa) in mice. Incorporation of negatively charged HA on the liposome surface compromised its blood circulation time, which led to decreased tumor accumulation in CD44+ human breast cancer MDA-MB-231 xenografts compared to PEGylated liposomes (PEG-5000). Clearance of HA-liposomes was HA polymer length-dependent; high MW (175-350 kDa, highest ligand binding affinity) HA-liposomes displayed faster clearance compared to low MW (5-8, 50-60 kDa) HA-liposomes or PEGylated liposomes. Surface HA ligand density can also affect clearance of HA-liposomes. Thus, HA is not an effective stealth coating material. When dual coating of PEG and HA was used, the PEG-HA-liposomes displayed similar blood circulation time and tumor accumulation to that of the PEGylated liposomes; however, the PEG-HA-liposomes displayed better cellular internalization capability in vivo. Tumor histology showed that PEG-HA-liposomes had a more direct association with CD44+ cancer cells, while PEGylated liposomes located predominantly in the tumor periphery, with less association with CD44+ cells. Flow cytometry analysis of ex vivo tumor cells showed that PEG-HA-liposomes had significantly higher tumor cell internalization compared to PEGylated liposomes. This study demonstrates that a long blood circulation time is critical for active tumor targeting. Furthermore, the use of the tumor-targeting ligand HA does not increase total tumor accumulation of actively targeted liposomes in solid tumors; however, it can enhance intracellular delivery.

Liposomal corticosteroids for the treatment of inflammatory disorders and cancer

Glucocorticoids (GC) are known for their potent immunosuppressive and anti-inflammatory properties. As a consequence, they have been extensively used for the treatment of many different diseases. Prolonged and/or high-dose GC therapy, however, generally comes with severe side effects, resulting not only from their very diverse mechanism(s) of action, but also from their relatively poor biodistribution. Drug delivery systems, and in particular liposomes, have been extensively used to enhance the biodistribution and the target site accumulation of GC, and to thereby improve the balance between their efficacy and their toxicity. Many different types of liposomes have been employed, and both local and systemic treatments have been evaluated. We here summarize the progress made in the use of liposomal GC formulations for the treatment of asthma, rheumatoid arthritis, multiple sclerosis and cancer, and we show that the targeted delivery of GC to pathological sites holds significant clinical potential.

Pharmacokinetics of liver-targeted docetaxel liposomes modified with 6-O-acyl-D-galactose esters in rabbits

The purpose of the present study was to investigate the pharmacokinetics of docetaxel liposomes modified with 6-O-acyl-D-galactose esters (Gal-DOC-L) in rabbits. A simple, rapid and sensitive high-performance liquid chromatography (HPLC) method was developed for the determination of docetaxel. Gal-DOC-L was intravenously administered to rabbits with norethisterone as the internal standard and the blood samples were collected from ear marginal veins at 0.083, 0.25, 0.5, l, 2, 4, 6, 8, 12, 16 and 24 h after treatment. The plasma concentration of docetaxel was determined by HPLC and the pharmacokinetic parameters were calculated. Docetaxel injection (DOC-I) was studied simultaneously. The results showed that the area under the curve_(0-∞), t_1/2α and t_1/2β of Gal-DOC-L was significantly higher, while the total body clearance was lower than that of DOC-I. The results indicated that Gal-DOC-L was able to maintain a relatively high blood concentration in vivo and prolong the treatment time.

Drug and cell encapsulation: alternative delivery options for the treatment of malignant brain tumors

Malignant brain tumors including glioblastoma are incurable cancers. Over the last years a number of promising novel treatment approaches have been investigated including the application of inhibitors of receptor tyrosine kinases and downstream targets, immune-based therapies and anti-angiogenic agents. Unfortunately so far the major clinical trials in glioblastoma patients did not deliver clear clinical benefits. Systemic brain tumor therapy is seriously hampered by poor drug delivery to the brain. Although in glioblastoma, the blood brain barrier is disrupted in the tumor core, the major part of the tumor is largely protected by an intact blood brain barrier. Active cytotoxic compounds encapsulated into liposomes, micelles, and nanoparticles constitute novel treatment options because they can be designed to facilitate entry into the brain parenchyma. In the case of biological therapeutics, encapsulation of therapeutic cells and their implantation into the surgical cavity represents another promising approach. This technology provides long term release of the active compound at the tumor site and reduces side effects associated with systemic delivery. The proof of principle of encapsulated cell factories has been successfully demonstrated in experimental animal models and should pave the way for clinical application. Here we review the challenges associated with the treatment of brain tumors and the different encapsulation options available for drugs and living cells, with an emphasis on alginate based cell encapsulation technology.

Marqibo® (vincristine sulfate liposome injection) improves the pharmacokinetics and pharmacodynamics of vincristine

Vincristine (VCR) is a mainstay of treatment of hematologic malignancies and solid tumors due to its well-defined mechanism of action, demonstrated anticancer activity and its ability to be combined with other agents. VCR is an M-phase cell cycle-specific anticancer drug with activity that is concentration and exposure duration dependent. The pharmacokinetic profile of standard VCR is described by a bi-exponential elimination pattern with a very fast initial distribution half-life followed by a longer elimination half-life. VCR also has a large volume of distribution, suggesting diffuse distribution and tissue binding. These properties may limit optimal drug exposure and delivery to target tissues as well as clinical utility as a single agent or as an effective component of multi-agent regimens. Vincristine sulfate liposome injection (VSLI), Marqibo^®, is a sphingomyelin and cholesterol-based nanoparticle formulation of VCR that was designed to overcome the dosing and pharmacokinetic limitations of standard VCR. VSLI was developed to increase the circulation time, optimize delivery to target tissues and facilitate dose intensification without increasing toxicity. In xenograft studies in mice, VSLI had a higher maximum tolerated dose, superior antitumor activity and delivered higher amounts of active drug to target tissues compared to standard VCR. VSLI recently received accelerated FDA approval for use in adults with advanced, relapsed and refractory Philadelphia chromosome-negative ALL and is in development for untreated adult ALL, pediatric ALL and untreated aggressive NHL. Here, we summarize the nonclinical data for VSLI that support its continued clinical development and recent approval for use in adult ALL.

In vitro and in vivo studies of galactose-modified liver-targeting liposomes

Oridonin (ORI) is a bioactive diterpenoid compound extracted from the well known Chinese traditional medicine Rabdosia rubescens. The aim of this study was to prepare ORI loaded liposomes surface-modified with galactose (NOH-ORI-LP) and evaluate their characteristics compared with ORI loaded liposomes (ORI-LP) and ORI solution in vitro and in vivo. The NOH-ORI-LP was prepared by ethanol injection method. The NOH-ORI-LP was characterized by their morphology, particle size, zeta potential and encapsulation efficiency. The concentration of ORI in plasma and tissues at different sampling time points were determined. The liver concentration-time curves of NOH-ORI-LP in mice were determined, and the pharmacokinetic parameters were calculated and compared by statistical analysis. Our data revealed that NOH-ORI-LP has a particle size of about (173 ± 12) nm. The particles exhibit a negative electrical charge (-31.5 ± 1.6 mV), and possess high encapsulation efficiency (94.1 ± 1.2%). There were significantly different parameters of k₁₀ and area under the plasma concentration-time curve (AUC_0-t) between liposomes and solution. The mean residence time (MRT_0-t) in plasma of NOH-ORI-LP was 5.56 times longer than that of solution. Compared with solution, NOH-ORI-LP delivered about 4.28 times higher ORI into liver. Thus, an optimum intravenous galactose-modified liposome formulation for ORI could be developed as an alternative to the commercial ORI preparations.

Recent advances in stealth coating of nanoparticle drug delivery systems

Modifying surfaces of nanoparticles (NPs) with polyethylene glycol (PEG), the so-called PEGylation, is the most commonly used method for reducing premature clearance of NPs from the circulation. However, several reports point out that PEGylation may negatively influence the performance of NPs as a drug carrier. Alternative surface modification strategies, including substitute polymers, conditional removal of PEG, and biomimetic surface modification, may provide solutions for the limitations of PEG.

Improved in vivo delivery of m-THPC via pegylated liposomes for use in photodynamic therapy

Pegylated liposomal nanocarriers have been developed with the aim of achieving improved uptake of the clinical PDT photosensitiser, m-THPC, into target tissues through increased circulation time and bioavailability. This study investigates the biodistribution and PDT efficacy of m-THPC in its standard formulation (Foscan®) compared to m-THPC incorporated in liposomes with different degrees of pegylation (FosPEG 2% and FosPEG 8%), following i.v. administration to normal and tumour bearing rats. The plasma pharmacokinetics were described using a three compartmental analysis and gave elimination half lives of 90 h, 99 h and 138 h for Foscan®, FosPEG 2% and 8% respectively. The accumulation of m-THPC in tumour and normal tissues, including skin, showed that maximal tumour to skin ratios were observed at ≤ 24 h with FosPEG 2% and 8%, whilst skin photosensitivity studies showed Foscan® induces more damage compared to the liposomes at drug-light intervals of 96 and 168 h. PDT treatment at 24h post-administration (0.05 mg kg⁻¹) showed higher tumour necrosis using pegylated liposomal formulations in comparison to Foscan®, which is attributed to the higher tumour uptake and blood plasma concentrations. Clinically, this improved selectivity has the potential to reduce not only normal tissue damage, but the drug dose required and cutaneous photosensitivity.

Formulation design considerations for oral vaccines

Whilst oral vaccination is a potentially preferred route in terms of patient adherence and mass vaccination, the ability to formulate effective oral vaccines remains a challenge. The primary barrier to oral vaccination is effective delivery of the vaccine through the GI tract owing to the many obstacles it presents, including low pH, enzyme degradation and bile-salt solubilization, which can result in breakdown/deactivation of a vaccine. For effective immune responses after oral administration, particulates need to be taken up by the M cells however, these are few in number. To enhance M-cell uptake, particle characteristics can be optimized with particle size, surface charge, targeting groups and bioadhesive properties all being considerations. Yet improved uptake may not translate into enhanced immune responses and formulating particulates with inherent adjuvant properties can offer advantages. Within this article, we establish the options available for consideration when building effective oral particulate vaccines.

An in vitro assay based on surface plasmon resonance to predict the in vivo circulation kinetics of liposomes

The adsorption of blood proteins onto liposomes and other colloidal particles is an important process influencing the circulation time. Proteins adsorbed to the surface of liposomes can mediate recognition of the liposomes by macrophages of the reticuloendothelial system (RES) facilitating their clearance from the circulation. Coating liposomes with poly(ethylene glycol) (PEG) decreases the blood clearance considerably, most likely due to reduced protein adsorption and/or liposome aggregation. By using the relation between clearance and protein binding, the present study introduces an in vitro assay measuring interactions of liposomes with proteins to predict their blood clearance in vivo. Such assay is valuable since it limits time and costs, and importantly reduces the number of animals required for pharmacokinetic investigations of new formulations. In the current study, Surface Plasmon Resonance (SPR) and fluorescence Single Particle Tracking (fSPT) were used to study liposome-protein interactions and blood induced liposome aggregation in vitro. By means of SPR the interactions between proteins and liposomes coated with PEG of different molecular weights and at different densities (PEG(2000) in 2.5%, 5% and 7%; PEG(5000) in 0.5%, 1.5% and 2.5%), were measured for several plasma proteins: human serum albumin (HSA), apolipoprotein E (ApoE), α2-macroglobulin (α2-M), β2-glycoprotein (β2-G) and fibronectin (Fn). Liposomes coated with PEG interacted less with all proteins, an effect which increased with the PEG surface density. In parallel, fSPT analysis showed that the exposure of liposomes to full blood did not change the liposome size, indicating that aggregation is not a strong attributive factor in the clearance of these liposomes. In addition, the SPR measurements of the interactions between liposomes and proteins were correlated with the blood clearance of the liposomes. For each protein, the degree of protein-liposome interaction as determined by SPR showed a moderate to strong positive correlation with the clearance of the liposome type.

In vitro and in vivo complement activation and related anaphylactic effects associated with polyethylenimine and polyethylenimine-graft-poly(ethylene glycol) block copolymers

Complement activation by polymeric gene and drug delivery systems has been overlooked in the past. As more reports appear in the literature concerning immunogenicity of polymers and their impact on gene expression patterns, it is important to address possible immune side effects of polymers, namely complement activation. Therefore, in this study the activity of low and high molecular weight poly(ethylene imine) and two PEGylated derivatives to induce complement activation were investigated in human serum. These in vitro results revealed that PEI 25 kDa caused significant and concentration dependent complement activation, whereas none of the other polymers induced such effects at their IC(50) concentrations determined by MTT-assays. To verify these in vitro results, additionally, studies were carried out in a swine model after intravenous administration, showing complement activation-related pseudoallergy (CARPA), reflected in symptoms of transient cardiopulmonary distress. Injections of PEI 25 kDa or PEI(25k)-PEG(2k)(10) at a dose of 0.05 and 0.1 mg/kg caused strong reactivity, while PEI 5 kDa and with PEI(25k)-PEG(20k)(1) were also reactogenic at 0.1 mg/kg. It was found that PEI 25 kDa caused both self- and cross-tolerance, whereas the PEG-PEIs were neither self- nor cross-reactively tachyphylactic. As a result of this study, it was shown that PEGylation of polycations with PEG of 20 kDa or higher molecular weight may be favorable. However, potential safety concerns in the development of PEI-based polymeric carriers for drugs and nucleic acids and their translation from bench to bedside need to be taken into consideration for human application.

Route of administration-dependent anti-inflammatory effect of liposomal alendronate

Innate immunity and inflammation are of major importance in various pathological conditions. Intravenous (IV) and intraperitoneal (IP) liposomal alendronate (LA) treatments have been shown to deplete circulating monocytes and peritoneal macrophages resulting in the inhibition of restenosis and endometriosis (EM), respectively. Nevertheless, the correlation between the extent of circulating monocyte depletion and liposome biodistribution is unknown, and the route of administration-dependent bioactivity in restenosis and EM has not been determined. We found that, LA treatment resulted in a dose-response modified biodistribution following both IV and IP administrations. The biodistribution of high-dose LA (10mg/kg), but not that of the low-dose (1mg/kg), was similar in healthy and diseased animals. It is concluded that LA impedes its own elimination from the circulation by depleting circulating monocytes and/or inhibiting their endocytic activity, in a dose-dependent manner. Both IV and IP administration of LA mediated by the partial and transient depletion of circulating monocytes effected inhibition of restenosis. Inhibition of EM was effected only by IP administration, which depleted both intraperitoneal and circulating monocytes. Thus, EM should be considered as a local inflammatory condition with systemic manifestations as opposed to restenosis, a systemic inflammatory disease.