Improving anti-angiogenic therapy via selective delivery of cationic liposomes to tumour vasculature

Recent advances in lipid-based long-acting injectable depot formulations

Long-acting injectable (LAIs) delivery systems sustain the drug therapeutic action in the body, resulting in reduced dosage regimen, toxicity, and improved patient compliance. Lipid-based depots are biocompatible, provide extended drug release, and improve drug stability, making them suitable for systemic and localized treatment of various chronic ailments, including psychosis, diabetes, hormonal disorders, arthritis, ocular diseases, and cancer. These depots include oil solutions, suspensions, oleogels, liquid crystalline systems, liposomes, solid lipid nanoparticles, nanostructured lipid carriers, phospholipid phase separation gel, vesicular phospholipid gel etc. This review summarizes recent advancements in lipid-based LAIs for delivering small and macromolecules, and their potential in managing chronic diseases. It also provides an overview of the lipid depots available in market or clinical phase, as well as patents for lipid-based LAIs. Furthermore, this review critically discusses the current scenario of using in vitro release methods to establish IVIVC and highlights the challenges involved in developing lipid-based LAIs.

Doxorubicin-loaded liposomes surface engineered with the matrix metalloproteinase-2 cleavable polyethylene glycol conjugate for cancer therapy

Background

Colorectal cancer is one of the prominent leading causes of fatality worldwide. Despite recent advancements within the field of cancer therapy, the cure rates and long-term survivals of patients suffering from colorectal cancer have changed little. The application of conventional chemotherapeutic agents like doxorubicin is limited by some drawbacks such as cardiotoxicity and hematotoxicity. Therefore, nanotechnology has been exploited as a promising solution to address these problems. In this study, we synthesized and compared the anticancer efficacy of doxorubicin-loaded liposomes that were surface engineered with the 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-matrix metalloproteinase-2 (MMP-2) cleavable peptide-polyethylene glycol (PEG) conjugate. The peptide linker was used to cleave in response to the upregulated MMP-2 in the tumor microenvironment, thus exposing a positive charge via PEG-deshielding and enhancing liposomal uptake by tumor cells/vasculature. Liposomal formulations were characterized in terms of size, surface charge and morphology, drug loading, release properties, cell binding and uptake, and cytotoxicity.

Results

The formulations had particle sizes of ~ 100-170 nm, narrow distribution (PDI ˂ 0.2), and various surface charges (- 10.2 mV to + 17.6 mV). MMP-2 overexpression was shown in several cancer cell lines (C26, 4T1, and B16F10) as compared to the normal NIH-3T3 fibroblast cells by gelatin zymography and qRT-PCR. In vitro results demonstrated enhanced antitumor efficacy of the PEG-cleavable cationic liposomes (CLs) as compared to the commercial Caelyx^® (up to fivefold) and the chick chorioallantoic membrane assay showed their great antiangiogenesis potential to target and suppress tumor neovascularization. The pharmacokinetics and efficacy studies also indicated higher tumor accumulation and extended survival rates in C26 tumor-bearing mice treated with the MMP-2 cleavable CLs as compared to the non-cleavable CLs with no remarkable sign of toxicity in healthy tissues.

Conclusion

Altogether, the MMP-2-cleavable CLs have great potency to improve tumor-targeted drug delivery and cellular/tumor-vasculature uptake which merits further investigation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12645-023-00169-8.

Liposomes: structure, composition, types, and clinical applications

Liposomes are now considered the most commonly used nanocarriers for various potentially active hydrophobic and hydrophilic molecules due to their high biocompatibility, biodegradability, and low immunogenicity. Liposomes also proved to enhance drug solubility and controlled distribution, as well as their capacity for surface modifications for targeted, prolonged, and sustained release. Based on the composition, liposomes can be considered to have evolved from conventional, long-circulating, targeted, and immune-liposomes to stimuli-responsive and actively targeted liposomes. Many liposomal-based drug delivery systems are currently clinically approved to treat several diseases, such as cancer, fungal and viral infections; more liposomes have reached advanced phases in clinical trials. This review describes liposomes structure, composition, preparation methods, and clinical applications.

Optimization of the Preparation of Magnetic Liposomes for the Combined Use of Magnetic Hyperthermia and Photothermia in Dual Magneto-Photothermal Cancer Therapy

In this work, we aimed to develop liposomal nanocomposites containing citric-acid-coated iron oxide magnetic nanoparticles (CMNPs) for dual magneto-photothermal cancer therapy induced by alternating magnetic field (AMF) and near-infrared (NIR) lasers. Toward this end, CMNPs were encapsulated in cationic liposomes to form nano-sized magnetic liposomes (MLs) for simultaneous magnetic hyperthermia (MH) in the presence of AMF and photothermia (PT) induced by NIR laser exposure, which amplified the heating efficiency for dual-mode cancer cell killing and tumor therapy. Since the heating capability is directly related to the amount of entrapped CMNPs in MLs, while the liposome size is important to allow internalization by cancer cells, response surface methodology was utilized to optimize the preparation of MLs by simultaneously maximizing the encapsulation efficiency (EE) of CMNPs in MLs and minimizing the size of MLs. The experimental design was performed based on the central composite rotatable design. The accuracy of the model was verified from the validation experiments, providing a simple and effective method for fabricating the best MLs, with an EE of 87% and liposome size of 121 nm. The CMNPs and the optimized MLs were fully characterized from chemical and physical perspectives. In the presence of dual AMF and NIR laser treatment, a suspension of MLs demonstrated amplified heat generation from dual hyperthermia (MH)–photothermia (PT) in comparison with single MH or PT. In vitro cell culture experiments confirmed the efficient cellular uptake of the MLs from confocal laser scanning microscopy due to passive accumulation in human glioblastoma U87 cells originated from the cationic nature of MLs. The inducible thermal effects mediated by MLs after endocytosis also led to enhanced cytotoxicity and cumulative cell death of cancer cells in the presence of AMF–NIR lasers. This functional nanocomposite will be a potential candidate for bimodal MH–PT dual magneto-photothermal cancer therapy.

Development of liposomal drug formulations: quality attributes and methods for quality control

The use of nanostructured components in drug manufacturing and, more specifically, targeted drug delivery has recently become a major trend in the pharmaceutical industry. Nanodrugs encompass a wide range of pharmaceutical agents containing dendrimers, nanocrystals, micelles, liposomes, and polymer nanoparticles. Liposomes are the most well-studied nanoparticles and effective drug carriers. However, the more complex their structure is, the more process controls are needed and the more quality attributes have to be monitored, including the chemical properties of the liposomal fraction such as the shape, size and charge of the nanoparticle, conjugation efficacy, and distribution of the active ingredient. We believe that quality control of key liposome characteristics should rely on dynamic and laser light scattering coupled with electrophoresis, differential scanning calorimetry, cryo-electron microscopy, nuclear magnetic resonance, laser diffraction analysis, and gel filtration chromatography.

Phospholipid-chitosan hybrid nanoliposomes promoting cell entry for drug delivery against cervical cancer

This study emphasizes the development of a novel surface modified liposome as an anticancer drug nanocarrier. Quaternized N,O-oleoyl chitosan (QCS) was synthesized and incorporated into liposome vesicles, generating QCS-liposomes (Lip-QCS). The Lip-QCS liposomes were spherical in shape (average size diameter 171.5±0.8nm), with a narrow size distribution (PDI 0.1±0.0) and zeta potential of 11.7±0.7mV. In vitro mucoadhesive tests indicated that Lip-QCS possesses a mucoadhesive property. Moreover, the presence of QCS was able to induce the cationic charge on the surface of liposome. Cellular internalization of Lip-QCS was monitored over time, with the results revealing that the cell entry level of Lip-QCS was elevated at 24h. Following this, Lip-QCS were then employed to load cisplatin, a common platinum-containing anti-cancer drug, with a loading efficiency of 27.45±0.78% being obtained. The therapeutic potency of the loaded Lip-QCS was investigated using a 3D spheroid cervical cancer model (SiHa) which highlighted their cytotoxicity and apoptosis effect, and suitability as a controllable system for sustained drug release. This approach has the potential to assist in development of an effective drug delivery system against cervical cancer.

Soft Interaction in Liposome Nanocarriers for Therapeutic Drug Delivery

The development of smart nanocarriers for the delivery of therapeutic drugs has experienced considerable expansion in recent decades, with the development of new medicines devoted to cancer treatment. In this respect a wide range of strategies can be developed by employing liposome nanocarriers with desired physico-chemical properties that, by exploiting a combination of a number of suitable soft interactions, can facilitate the transit through the biological barriers from the point of administration up to the site of drug action. As a result, the materials engineer has generated through the bottom up approach a variety of supramolecular nanocarriers for the encapsulation and controlled delivery of therapeutics which have revealed beneficial developments for stabilizing drug compounds, overcoming impediments to cellular and tissue uptake, and improving biodistribution of therapeutic compounds to target sites. Herein we present recent advances in liposome drug delivery by analyzing the main structural features of liposome nanocarriers which strongly influence their interaction in solution. More specifically, we will focus on the analysis of the relevant soft interactions involved in drug delivery processes which are responsible of main behaviour of soft nanocarriers in complex physiological fluids. Investigation of the interaction between liposomes at the molecular level can be considered an important platform for the modeling of the molecular recognition processes occurring between cells. Some relevant strategies to overcome the biological barriers during the drug delivery of the nanocarriers are presented which outline the main structure-properties relationships as well as their advantages (and drawbacks) in therapeutic and biomedical applications.

LHD-Modified Mechanism-Based Liposome Coencapsulation of Mitoxantrone and Prednisolone Using Novel Lipid Bilayer Fusion for Tissue-Specific Colocalization and Synergistic Antitumor Effects

Coencapsulation liposomes are of interest to researchers because they maximize the synergistic effect of loaded drugs. A combination regimen of mitoxantrone (MTO) and prednisolone (PLP) has been ideal for tumor therapy. MTO and PLP offer synergistic antitumor effects confirmed by several experiments in this research. The deduced synergistic mechanism is regulation of Akt signaling pathway including the targets of p-Akt, p-GSK-3β, p-s6 ribosomal protein, and p-AMPK by MTO reactivating PLP-induced apoptosis. The liposome fusion method is adopted to create coencapsulation liposomes (PLP-MTO-YM). Low molecular weight heparin-sodium deoxycholate conjugate (LHD) then is used as a targeting ligand to prove target binding and inhibition of angiogenesis. LHD-modified liposomes (PLP-MTO-HM) have a high entrapment efficiency around 95% for both MTO and PLP. DSC results indicate that both drugs interacted with liposomes to prevent drug leak during liposome fusion. DiD-C6-HM dyes colocalize well to tumor tissue, and coadministration of DiD-HM and C6-CM did not achieve dye colocalization until 24 h after administration. In both CT26 and B16F10 mouse model, PLP-MTO-HM shows a significantly higher tumor inhibition rate relative to the coadministration of MTO-HM and PLP-CM (p < 0.05 or p < 0.01). Thus, the coencapsulation system (PLP-MTO-HM) offers ideal antitumor effects relative to coadministration therapy due to enhanced synergistic effect, and this suggests a promising future for the tumor targeting vectors.

Stearylated cycloarginine nanosystems for intracellular delivery – simulations, formulation and proof of concept

Novel cationic agent liposomes performed better in silico translating in higher cellular uptake with reduced toxicity.

Liposomes as nanomedical devices

Since their discovery in the 1960s, liposomes have been studied in depth, and they continue to constitute a field of intense research. Liposomes are valued for their biological and technological advantages, and are considered to be the most successful drug-carrier system known to date. Notable progress has been made, and several biomedical applications of liposomes are either in clinical trials, are about to be put on the market, or have already been approved for public use. In this review, we briefly analyze how the efficacy of liposomes depends on the nature of their components and their size, surface charge, and lipidic organization. Moreover, we discuss the influence of the physicochemical properties of liposomes on their interaction with cells, half-life, ability to enter tissues, and final fate in vivo. Finally, we describe some strategies developed to overcome limitations of the “first-generation” liposomes, and liposome-based drugs on the market and in clinical trials.

Interactions of DMPC and DMPC/gemini liposomes with the cell membrane investigated by electrorotation

The electrorotation technique was utilized to investigate the interactions between a mouse fibroblast cell line and zwitterionic liposomes formed by a natural phospholipid or cationic liposomes formulated with the same phospholipid and a cationic gemini surfactant. The application of this technique allowed an accurate characterization of the passive dielectric behavior of the plasma membrane by the determination of its specific capacitance and conductance. Changes of these parameters, upon interaction with the liposomes, are related to variations in the structure and or in the transport properties of the membrane. Cells were exposed to both types of liposomes for 1 or 4h. Electrorotation data show a dramatic reduction of the dielectric parameters of the plasma membrane after one hour treatment. After 4h of treatment the effects are still observed only in the case of the cationic liposomes. Surprisingly, these same treatments did not cause a relevant biological damage as assessed by standard viability tests. A detailed discussion to rationalize this phenomenon is presented.

Intracellular delivery of redox cycler-doxorubicin to the mitochondria of cancer cell by folate receptor targeted mitocancerotropic liposomes

Cancer cells reflect higher level of ROS in comparison to the normal cell, so they become more vulnerable to further oxidative stress induced by exogenous ROS-generating agents. Through this a novel therapeutic strategy has evolved, which involves the delivery of redox cycler-doxorubicin (DOX) to the mitochondria of cancer cell where it acts as a source of exogenous ROS production. The purpose of this study is to develop a liposomal preparation which exhibits a propensity to selectively target cancer cell along with the potential of delivering drug to mitochondria of cell. We have rendered liposomes mitocancerotropic (FA-MTLs) by their surface modification with dual ligands, folic acid (FA) for cancer cell targeting and triphenylphosphonium (TPP) cations for mitochondria targeting. The cytotoxicity, ROS production and cell uptake of doxorubicin loaded liposomes were evaluated in FR (+) KB cells and found to be increased considerably with FA-MTLs in comparison to folic acid appended, mitochondria targeted and non-targeted liposomes. As confirmed by confocal microscopy, the STPP appended liposomes delivered DOX to mitochondria of cancer cell and also showed higher ROS production and cytotoxicity in comparison to folic acid appended and non-targeted liposomes. Most importantly, mitocancerotropic liposomes showed superior activity over mitochondria targeted liposomes which confirm the synergistic effect imparted by the presence of dual ligands - folic acid and TPP on the enhancement of cellular and mitochondrial delivery of doxorubicin in KB cells.

Comparative study of the in vitro and in vivo characteristics of cationic and neutral liposomes

Neutral liposomes (NLP) exhibit preferential localization in solid tumors based on the enhanced permeation and retention (EPR) effect. Cationic liposomes (CLP) have a propensity for localizing in newly formed tumor vessels and they have a potentially enhanced antitumor effect. However, an increased amount of cationic lipids in liposomes also induces aggregation through electrostatic interactions between the liposomes and the anionic species in the circulation, which results in a reduced EPR effect. Consequently, it is important to investigate the characteristics of liposomes with different surface potentials in vitro to achieve an optimal intratumoral distribution and antitumor effect in vivo. In this study, the authors evaluated the characteristics of doxorubicin (DOX)-loaded NLPs, CLPs, polyethylene glycol (PEG)-modified NLPs (NLP-PEG), and PEGylated CLPs (CLP-PEG) (ie, encapsulation efficacy, zeta potential, size, membrane fluidity, aggregation in serum, and uptake of liposomes into rat aortic endothelial cells (RAECs)) to further understand their influences on the pharmacokinetics, biodistribution, and antitumor therapy in vivo. The results showed that increased amounts of cationic lipids resulted in severe liposome aggregation in the presence of serum, yet it did not alter the membrane fluidity to a large extent. The uptake of liposomes into RAECs, visualized by confocal fluorescence microscopy, confirmed the rapid uptake of CLP by the endothelial cells compared with NLP. However, the pharmacokinetics, biodistribution and anticancer efficacies of these liposomes in vivo revealed that the CLP with highly positive surface potentials exhibited reduced circulation times and poor distribution in tumors. The NLP-PEG exhibited the highest anticancer efficacy; CLP-PEG, the second highest; and CLP with the most positive surface potential, the lowest. These phenomena were mostly due to the rapid aggregation in serum and subsequent accumulation in the lungs upon the intravenous injection of the CLP. Caution should be exercised when chemotherapeutic drugs are loaded into CLP for tumor therapy.

Recent advances in tumor vasculature targeting using liposomal drug delivery systems

Tumor vessels possess unique physiological features that might be exploited for improved drug delivery. The targeting of liposomal anticancer drugs to tumor vasculature is increasingly recognized as an effective strategy to obtain superior therapeutic efficacy with limited host toxicity compared with conventional treatments. This review introduces recent advances in the field of liposomal targeting of tumor vasculature, along with new approaches that can be used in the design and optimization of liposomal delivery systems. In addition, cationic liposome is focused on as a promising carrier for achieving efficient vascular targeting. The clinical implications are discussed of several approaches using a single liposomal anticancer drug formulation: dual targeting, vascular targeting (targeting tumor endothelial cells) and tumor targeting (targeting tumor cells).

Cationic liposomes target sites of acute neuroinflammation in experimental autoimmune encephalomyelitis

The binding selectivity of charged liposomes to the spinal cord of rats affected by experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis, was investigated. Positively and negatively charged liposomes were injected into the tail vein of rats, and blood/brain barrier (BBB) targeting was determined by confocal microscopy as a function of the temporal evolution of the inflammatory response. Accumulation in spinal cord endoneural vessels was observed for cationic, but not for anionic, liposomes, and only in EAE but not in healthy rats. The overall binding efficacy paralleled the severity of the clinical score, but targeting was observed already before clinical manifestation of inflammation. Preferential binding of positively charged liposomes in the course of acute EAE can be ascribed to subtle changes of BBB morphology and charge distribution in a similar way as for the binding of cationic particles to proliferating vasculature in chronic inflammation and angiogenesis. Our findings suggest that vascular changes related to increased binding affinity for cationic particles are very early events within the inflammatory reaction in acute EAE. Investigation of cationic vascular targeting can help to shed further light on these occurrences, and, potentially, new diagnostic and therapeutic options may become available. In neuroinflammatory diseases, cationic colloidal carrier particles may enable intervention at affected BBB by an approach which is independent from permeability increase.

Polyethylene glycol-complexed cationic liposome for enhanced cellular uptake and anticancer activity

Liposomes as one of the efficient drug carriers have some shortcomings such as their relatively short blood circulation time, fast clearance from human body by reticuloendothelial system (RES) and limited intracellular uptake to target cells. In this study, polyethylene glycol (PEG)-complexed cationic liposomes (PCL) were prepared by ionic complex of cationically charged liposomes with carboxylated polyethylene glycol (mPEG-COOH). The cationic liposomes had approximately 98.6+/-1.0 nm of mean particle diameter and 45.5+/-1.1 mV of zeta potential value. While, the PCL had 110.1+/-1.2 nm of mean particle diameter and 18.4+/-0.8 mV of zeta potential value as a result of the ionic complex of mPEG-COOH with cationic liposomes. Loading efficiency of model drug, doxorubicin, into cationic liposomes or PCL was about 96.0+/-0.7%. Results of intracellular uptake evaluated by flow cytometry and fluorescence microscopy studies showed higher intracellular uptake of PCL than that of Doxil. In addition, in vitro cytotoxicity of PCL was comparable to cationic liposomes. In pharmacokinetic study in rats, PCL showed slightly lower plasma level of DOX than that of Doxil. In vivo antitumor activity of DOX-loaded PCL was comparable to that of Doxil against human SKOV-3 ovarian adenocarcinoma xenograft rat model. Consequently, the PCL, of which surface was complexed with PEG by ionic complex may be applicable as drug delivery carriers for increasing therapeutic efficacy of anticancer drugs.

Development of a bladder instillation of the indoloquinone anticancer agent EO-9 using tert-butyl alcohol as lyophilization vehicle

The purpose of this research was to develop a stable bladder instillation of EO-9 for the treatment of superficial bladder cancer. First, stability and dissolution studies were performed. Subsequently, the freeze-drying process was optimized by determination of the freeze-drying characteristics of the selected cosolvent/water system and differential scanning calorimetry analysis of the formulation solution. Furthermore, the influence of the freeze-drying process on crystallinity and morphology of the freeze-dried product was determined with x-ray diffraction analysis and scanning electron microscopy, respectively. Subsequently, a reconstitution solution was developed. This study revealed that tert-butyl alcohol (TBA) can be used to both dramatically improve the solubility and stability of EO-9 and to shorten the freeze-drying cycle by increasing the sublimation rate. During freeze drying, 3 TBA crystals were found: TBA hydrate-ice crystals, crystals of TBA hydrate, and a third crystal, probably composed of TBA hydrate crystals containing approximately 90% to 95% TBA. Furthermore, it was shown that crystallization of TBA hydrate was inhibited in the presence of both sodium bicarbonate (NaHCO3) and mannitol. Addition of an annealing step resulted in a minor increase in the crystallinity of the freeze-dried product and formation of the delta-polymorph of mannitol. A stable bladder instillation was obtained after reconstitution of the freeze-dried product (containing 8 mg of EO-9, 20 mg of NaHCO3, and 50 mg of mannitol per vial) to 20 mL with a reconstitution solution composed of propylene glycol/water for injection (WfI)/NaHCO3/sodium edetate 60%/40%/2%/0.02% vol/vol/wt/wt, followed by dilution with WfI to a final volume of 40 mL.

The metabolism of fatty alcohols in lipid nanoparticles by alcohol dehydrogenase

Fatty alcohols are commonly used in lipid-based drug delivery systems including parenteral emulsions and solid lipid nanoparticles (NPs). The purpose of these studies was to determine whether horse liver alcohol dehydrogenase (HLADH), a NAD-dependent enzyme, could metabolize the fatty alcohols within the NPs and thus serve as a mechanism to degrade these NPs in the body. Solid nanoparticles (<100 nm) were engineered from oil-in-water microemulsion precursors using emulsifying wax NF as the oil phase and polyoxyethylene 20-stearyl ether (Brij 78) as the surfactant. Emulsifying wax contains both cetyl and stearyl alcohols. NPs were incubated with the enzyme and NAD+ at 37 degrees C for up to 48 h, and the concentrations of fatty alcohols were quantitatively determined over time by gas chromatography (GC). The concentrations of cetyl alcohol and stearyl alcohol within the NPs decreased to only 10-20% remaining after 15-24 h of incubation. In parallel, NP size, turbidity and the fluorescence intensity of NADH all increased over time. It was concluded that horse liver alcohol dehydrogenase/NAD+ was able to metabolize the fatty alcohols within the NPs, suggesting that NPs made of fatty alcohols may be metabolized in the body via endogenous alcohol dehydrogenase enzyme systems.

Targeting of small molecule anticancer drugs to the tumour and its vasculature using cationic liposomes: lessons from gene therapy

Cationic (positively charged) liposomes have been tested in various gene therapy clinical trials for neoplastic and other diseases. They have demonstrated selectivity for tumour vascular endothelial cells raising hopes for both antiangiogenic and antivascular therapies. They are also capable of being selectively delivered to the lungs and liver when administered intravenously. These vesicles are being targeted to the tumour in various parts of the body by using advanced liposomal systems such as ligand-receptor and antibody-antigen combinations. At present, the transferrin receptor is commonly used for cancer-targeted drug delivery systems including cationic liposomes. This review looks at the growing utility of these vesicles for delivery of small molecule anticancer drugs.

Selective gene delivery for cancer therapy using cationic liposomes: in vivo proof of applicability

Targeted gene therapy is essential if cancer treatment is to become a reality with this form of therapy. In the past few years, cationic liposomes, discovered 2 decades ago, and at present, the most commonly used class of transfection reagents, have been tested in various clinical trials for diseases not restricted to cancer. They have been shown to be selective for tumour vascular endothelial cells raising hopes for antiangiogenic and antivascular therapies. They are also capable of being selectively delivered to the lungs and liver when administered intravenously. These vesicles are also being targeted to the tumour in various parts of the body by using advanced liposomal systems such as antibody-antigen and ligand-receptor combinations. This review looks at the state of play in this rapidly growing field.

Increased gene expression by cationic liposomes (TFL-3) in lung metastases following intravenous injection

We recently showed that size, not surface charge, is a major determinant of the in vitro lipofection efficiency of pDNA/TFL-3 complex (lipoplex), even in the presence of serum. In this study, the effect of lipoplex size as a result of interaction with serum proteins on in vitro lipofection and the relationship of this with in vivo lipofection was examined in a murine lung metastasis model. As previously described, the pDNA to lipid ratio (P/L ratio) affected both the size and zeta potential of the lipoplex. In vitro studies also indicated that transgene expression in B16BL6 cells was largely dependent on the size of the lipoplex, both in the absence or presence (50% (v/v)) of serum. An in vivo lipofection experiment showed that predominant gene expression in lungs occurred only in tumor-bearing mice, not in normal mice. Based on the in vitro study, this tumor-related gene expression was not related to lipoplex size in the presence of serum (50% (v/v)), suggesting that the size alteration, as the result of interactions with serum proteins in the blood stream may not play an important role in the case of systemic injections. In addition, the efficient gene expression in tumor-bearing lung was not related to the progression of lung metastases. The area-specific gene expression in tumor-bearing lungs, which was largely dependent on the P/L ratio of the lipoplexes, was observed by fluorescent microscopy. Although the underlying mechanism for the area-specific transgene expression is not clear, it may be related to the interaction of lipoplexes with tumor cells, vascular endothelial cells under angiogenesis and normal cells in the lungs. The possibility that TFL-3 is a useful utility to the targeted delivery of pDNA to lungs and tumor-related lipofection is demonstrated. This result suggests that area-specific gene expression in lung metastases may be achieved by controlling the physicochemical properties of the lipoplex, i.e. the P/L ratio.

Endostatin cDNA/cationic liposome complexes as a promising therapy to prevent lung metastases in osteosarcoma: study in a human-like rat orthotopic tumor

Antiangiogenesis or destruction of tumor neovessels is an effective strategy to prevent tumor growth. Endostatin, one of the many inhibitors of angiogenesis that have been discovered, has shown conflicting results in preclinical assays. We studied the therapeutic potential of lipid/DNA complexes consisting of cationic liposomes and an endostatin-coding plasmid (Endo cDNA/CLP) in an orthotopic osteosarcoma model in rats. Empty plasmid without the endostatin gene complexed with cationic liposomes served as control. Animals were treated intravenously three times a week starting on the day tumors were detectable by (18)FDG tomoscintigraphy. During treatment, tumor progression was followed by PET scan and angioscintigraphy, and the effects of antivascular therapy on primary tumor, metastases, and tumor vascular density were confirmed by histologic analysis. Our results demonstrate that therapy using Endo cDNA/CLP is associated with pronounced delay in tumor growth. Moreover, it effectively prevented the occurrence of lung metastases, the major reason for bad prognosis and death in osteosarcoma patients. This approach could be used as an adjuvant therapy for osteosarcoma.

Protamine enhances uptake of cationic liposomes in angiogenic microvessels of solid tumours

INTRODUCTION

Cationic liposomes have been shown to target angiogenic endothelial cells of solid tumours. Supposing a charge-related mechanism might be responsible for liposome-endothelial interaction, we investigated the effect of intravenous pre-injection of the charged molecules protamine, a polycationic protein, and fucoidan, a polyanionic polysaccharide on the accumulation of cationic liposomes within the blood vessels of a solid tumour.

MATERIALS AND METHODS

Experiments were performed using the amelanotic hamster melanoma A-Mel-3 growing in a dorsal skinfold chamber of hamsters. Accumulation of fluorescently-labelled cationic liposomes was quantified by intravital macroscopy and digital image analysis of tumour (t) and surrounding normal host tissue (n) over an observation period of 6 h. All animals received an i.v. injection of cationic liposomes. Animals of the control group were pre-treated with an i.v. injection of 0.9% saline, while animals of group 2 received positively charged protamine and animals of group 3 negatively charged fucoidan prior to liposome injection.

RESULTS

In control animals i.v. injection of cationic liposomes revealed a preferential targeting of the tumour vessels, indicated by a maximal t/n ratio of 2.2 +/- 0.24 and a maximal fluorescence intensity (fmax) corresponding to the tumour of 66 +/- 12 [% standard]. While there were no significant differences of liposome accumulation within normal host tissue, accumulation of cationic liposomes within the tumour was significantly enhanced after the pre-administration of protamine (fmax: 117 +/- 12 [% standard]). The t/n ratio was significantly increased in protamine pre-treated animals (5.3 +/- 1.7) in comparison to control and fucoidan treated animals. In contrast, pre-injection of fucoidan resulted in reduced maximal fluorescence intensities in tumour (47 +/- 8 [% standard]) and normal surrounding host tissue.

CONCLUSION

Pre-administration of protamine increases the accumulation of cationic liposomes in a solid tumour animal model causing an increased selectivity of cationic liposomes in targeting angiogenic microvessels.