The cationic lipid stearylamine reduces the permeability of the cationic drugs verapamil and prochlorperazine to lipid bilayers: implications for drug delivery

Surface modified niosomal quercetin with cationic lipid: an appropriate drug delivery system against Pseudomonas aeruginosa Infections

The Increase in infections caused by resistant strains of Pseudomonas aeruginosa poses a formidable challenge to global healthcare systems. P. aeruginosa is capable of causing severe human infections across diverse anatomical sites, presenting considerable therapeutic obstacles due to its heightened drug resistance. Niosomal drug delivery systems offer enhanced pharmaceutical potential for loaded contents due to their desirable properties, mainly providing a controlled-release profile. This study aimed to formulate an optimized niosomal drug delivery system incorporating stearylamine (SA) to augment the anti-bacterial and anti-biofilm activities of quercetin (QCT) against both standard and clinical strains of P. aeruginosa. QCT-loaded niosome (QCT-niosome) and QCT-loaded SA- niosome (QCT-SA- niosome) were synthesized by the thin-film hydration technique, and their physicochemical characteristics were evaluated by field emission scanning electron microscopy (FE-SEM), zeta potential measurement, entrapment efficacy (EE%), and in vitro release profile. The anti-P. aeruginosa activity of synthesized niosomes was assessed using minimum inhibitory and bactericidal concentrations (MICs/MBCs) and compared with free QCT. Additionally, the minimum biofilm inhibitory and eradication concentrations (MBICs/MBECs) were carried out to analyze the ability of QCT-niosome and QCT-SA-niosome against P. aeruginosa biofilms. Furthermore, the cytotoxicity assay was conducted on the L929 mouse fibroblasts cell line to evaluate the biocompatibility of the formulated niosomes. FE-SEM analysis revealed that both synthesized niosomal formulations exhibited spherical morphology with different sizes (57.4 nm for QCT-niosome and 178.9 nm for QCT-SA-niosome). The EE% for cationic and standard niosomal formulations was reported at 75.9% and 59.6%, respectively. Both formulations showed an in vitro sustained-release profile, and QCT-SA-niosome exhibited greater stability during a 4-month storage time compared to QCT-niosome. Microbial experiments indicated that both prepared formulations had higher anti-bacterial and anti-biofilm activities than free QCT. Also, the QCT-SA-niosome exhibited greater reductions in MIC, MBC, MBIC, and MBEC values compared to the QCT-niosome at equivalent concentrations. This study supports the potential of QCT-niosome and QCT-SA-niosome as effective agents against P. aeruginosa infections, manifesting significant anti-bacterial and anti-biofilm efficacy alongside biocompatibility with L929 cell lines. Furthermore, our results suggest that optimized QCT-niosome with cationic lipids could efficiently target P. aeruginosa cells with negligible cytotoxic effect.

A PEGylated liposomal formulation of prochlorperazine that limits brain exposure but retains dynamin II activity: A potential adjuvant therapy for cancer patients receiving chemotherapeutic mAbs

Anti-cancer monoclonal antibodies often fail to provide therapeutic benefit in receptor-positive patients due to rapid endocytosis of antibody-bound cell surface receptors. High dose co-administration of prochlorperazine (PCZ) inhibits endocytosis and sensitises tumours to mAbs by inhibiting dynamin II but can also introduce neurological side effects. We examined the potential to use PEGylated liposomal formulations of PCZ (LPCZ) to retain the anti-cancer effects of PCZ, but limit brain uptake. Uncharged liposomes showed complete drug encapsulation and pH-dependent drug release, but cationic liposomes showed limited drug encapsulation and lacked pH-dependent drug release. Uncharged LPCZ showed comparable inhibition of EGFR internalisation to free PCZ in KJD cells. After IV administration to rats, LPCZ reduced the plasma clearance and brain uptake of PCZ compared to IV PCZ. The results suggest that LPCZ may offer some benefit over PCZ as an adjunct therapy in cancer patients receiving mAb treatment.

Halloysite nanotubes-cellulose ether based biocomposite matrix, a potential sustained release system for BCS class I drug verapamil hydrochloride: Compression characterization, in-vitro release kinetics, and in-vivo mechanistic physiologically based pharmacokinetic modeling studies

This study investigated the ability of natural nanotubular clay mineral (Halloysite) and cellulose ether based biocomposite matrix as a controlled release agent for Verapamil HCl (BCS Class-I). Drug-loaded halloysite was prepared and tablet formulations were designed by varying amount of hydroxy propyl methyl cellulose (HPMC K4M). Physical characterization was carried out using SEM, FTIR, and DSC. Tabletability profiles were evaluated using USP1062 guidelines. Drug release kinetics were studied, and physiologically based pharmacokinetic (PBPK) modeling was performed. Compressed tablets possess satisfactory yield pressure of 625 MPa with adequate hardness and disintegration within 30 min. The initial release of the drug was due to surface drug on tablets, while the prolonged release at later time points (around 80 % drug release at 12 h) were due to halloysite loading. The FTIR spectra exhibited electrostatic attraction between the positively charged drug and the negatively charged Si-O-Si functional group of halloysite, while the thermogram showed Verapamil HCl melting point at ~146 °C with enthalpy change of -126.82 J/g. PBPK modeling exhibited PK parameters of optimized matrix formulation (VER-HNT3%) comparable to in vivo data. The study effectively demonstrated the potential of prepared biocomposite matrix as a commercially viable oral release modifying agent for highly soluble drugs.

Designer Liposomic Nanocarriers Are Effective Biofilm Eradicators

Drug delivery via nanovehicles is successfully employed in several clinical settings, yet bacterial infections, forming microbial communities in the form of biofilms, present a strong challenge to therapeutic treatment due to resistance to conventional antimicrobial therapies. Liposomes can provide a versatile drug-vector strategy for biofilm treatment, but are limited by the need to balance colloidal stability with biofilm penetration. We have discovered a liposomic functionalization strategy, using membrane-embedded moieties of poly[2-(methacryloyloxy)ethyl phosphorylcholine], pMPC, that overcomes this limitation. Such pMPCylation results in liposomic stability equivalent to current functionalization strategies (mostly PEGylation, the present gold-standard), but with strikingly improved cellular uptake and cargo conveyance. Fluorimetry, cryo-electron, and fluorescence microscopies reveal a far-enhanced antibiotic delivery to model Pseudomonas aeruginosa biofilms by pMPC-liposomes, followed by faster cytosolic cargo release, resulting in significantly greater biofilm eradication than either PEGylation or free drug. Moreover, this combination of techniques uncovers the molecular mechanism underlying the enhanced interaction with bacteria, indicating it arises from bridging by divalent ions of the zwitterionic groups on the pMPC moieties to the negatively charged lipopolysaccharide chains emanating from the bacterial membranes. Our results point to pMPCylation as a transformative strategy for liposomal functionalization, leading to next-generation delivery systems for biofilm treatment.

Preparation and Evaluation of Stearylamine-Bearing Pemetrexed Disodium-Loaded Cationic Liposomes In Vitro and In Vivo

Pemetrexed disodium (PMX) stands out in the treatment of non-small cell lung cancer (NSCLC), but with short half-life and toxic side effects. This study was to design cationic liposomes for targeting delivery PMX to the lungs. The PMX cationic liposome was prepared by thin-film hydration using stearylamine (SA) as the positive component of charge-regulating charge. Then, the PMX cationic liposome (SA-PMX-Lips) was characterized by particle size, morphology, entrapment efficiency (EE), and drug loading (DL). Finally, the drug release behavior in vitro, the pharmacokinetic study, and tissue distribution of SA-PMX-Lips were evaluated separately, with PMX solution (PMX-Sol) and PMX liposome (PMX-Lips) as the control. According to results, SA-PMX-Lips were spherical and the particle size was 219.7 ± 4.97 nm with a narrow polydispersity index (PDI) (0.231 ± 0.024) and a positive zeta potential 22.2 ± 0.52 mV. Its EE was 92.39 ± 1.94% and DL was 9.15 ± 0.07%. The results of in vitro and in vivo experiments showed that SA-PMX-Lips released slowly, prolonged retention time and increased the value of AUC. More notably, SA-PMX-Lips could improve the accumulation of drugs in the lungs and the relative uptake rate (Re) was 2.35 in the lungs, which indicated its lung targeting. In summary, SA-PMX-Lips showed the potential for the effective delivery of PMX and the treatment of NSCLC.

Theranostics Based on Liposome: Looking Back and Forward

Liposome is one of the oldest yet most successful nanomedicine platforms. Doxil®, PEGylated liposome loaded with doxorubicin (DOX), was approved by the FDA in 1995 for the treatment of AIDS-related Kaposi's sarcoma, and it was the first approval for nanomedicine. Since then, liposome-based therapeutics were approved for the treatment of various diseases and many clinical trials are underway. The success of the liposome-based therapeutics was due to following factors: (1) ease of synthesis, (2) biocompatibility, (3) the ability to load both hydrophilic and hydrophobic agents, and (4) long circulation property after application of polyethylene glycol (PEG). Recently, more functionalities are introduced to liposome platform, which are (1) in vivo imaging probes for optical, magnetic resonance imaging (MRI), positron emission tomography (PET), and single-photon emission computed tomography (SPECT), (2) pH and temperature-sensitive lipid moiety, and (3) novel agents for photodynamic and photothermal therapies (PDT, PTT). These conventional and newly tested advantages make the liposome to be one of the most promising nanoplatforms for theranostics.

The Role of Surface Active Agents in Ophthalmic Drug Delivery: A Comprehensive Review

With the significant advances made in nanotechnology, research efforts focused on developing novel drug delivery platforms that can overcome the multitude of challenges encountered in ophthalmic drug delivery. Surface active agents (SAAs) have been extensively used for the formulation of many of the dosage forms targeting ocular tissues. Novel ophthalmic carriers utilizing SAAs were broadly classified into particulate, vesicular, and controlled release drug delivery systems. Depending on their physicochemical properties, SAAs can perform a variety of roles ranging from wetting agents, emulsifiers, stabilizers, charge inducers, solubilizers, antimicrobial agents, corneal permeation enhancers, and gelling agents. Nevertheless, their use is limited by their potential toxicity and possible interactions with other formulation ingredients. This review provides a comprehensive analysis of the different functional roles of SAAs in novel ophthalmic drug delivery platforms, their mechanism of action, and limitations that need to be considered during formulation to maximize their potential benefit. Understanding the mechanisms by which they perform their different roles and the possible interactions between SAAs and other formulation ingredients can help orientate the choice of formulators toward the SAA most suitable for the intended ocular application at a concentration that is both safe and effective.

Stimulus-responsive liposomes as smart nanoplatforms for drug delivery applications

Liposomes are known to be promising nanoparticles (NPs) for drug delivery applications. Among different types of self-assembled NPs, liposomes stand out for their non-toxic nature, and their possession of dual hydrophilic-hydrophobic domains. Advantages of liposomes include the ability to solubilize hydrophobic drugs, the ability to incorporate different hydrophilic and lipophilic drugs at the same time, lessening the exposure of host organs to potentially toxic drugs and allowing modification of the surface by a variety of different chemical groups. This modification of the surface, or of the individual constituents, may be used to achieve two important goals. Firstly, ligands for active targeting can be attached that are recognized by cognate receptors over-expressed on the target cells of tissues. Secondly, modification can be used to impart a stimulus-responsive or "smart" character to the liposomes, whereby the cargo is released on demand only when certain internal stimuli (pH, reducing agents, specific enzymes) or external stimuli (light, magnetic field or ultrasound) are present. Here, we review the field of smart liposomes for drug delivery applications.

Enhanced efficacy of anti-miR-191 delivery through stearylamine liposome formulation for the treatment of breast cancer cells

MicroRNAs are gaining rapid attention as promising targets for cancer treatment; however, efficient delivery of therapeutic miRNA or anti-miRNA into cancer cells remains a major challenge. Our previous work identified miR-191 as an oncogenic miRNA overexpressed in breast cancer that assists in progression of malignant transformation. Thus, inhibition of miR-191 using antisense miR-191 (anti-miR-191) has immense therapeutic potential. Here, we have developed a stearylamine (SA) based cationic liposome for delivery of miR-191 inhibitor (anti-miR-191), and studied its efficacy in breast cancer cells (MCF-7 and ZR-75-1) in culture. SA liposomes alone inhibited cancer cell growth with lesser IC_50s (50% inhibitory concentration) values as compared to normal mouse fibroblast cells (L929). The efficient delivery of anti-miR-191 in SA liposome complex was found to be highly effective in killing the cancer cells than a comparable dose of SA free anti-miR-191 liposome complex. The formulation also showed negligible cytotoxicity in human erythrocytes. Combined treatment of SA liposome with anti-miR-191 markedly enhanced apoptotic cell death and suppressed the migration of cancer cells in vitro. Notably, anti-miR-191 loaded SA liposome complex increased chemosensitivity of breast cancer cells to currently used anti-cancer drugs (doxorubicin or cisplatin) in free form. Our work demonstrates that anti-miR-191 loaded in SA liposome complex has promising clinical application for breast cancer therapy.

Preparation of nano cationic liposome as carrier membrane for polyhexamethylene biguanide chloride through various methods utilizing higher antibacterial activities with low cell toxicity

This study suggested successful encapsulation of polyhexamethylene biguanide chloride (PHMB) into nano cationic liposome as a biocompatible antibacterial agent with less cytotoxicity and higher activities. Phosphatidylcholine, cholesterol and stearylamine were used to prepare nano cationic liposome using thin film hydration method along with sonication or homogeniser. Sonication was more effective in PHMB loaded nano cationic liposome preparation with smaller size (34 nm). FTIR, ¹H NMR and XRD analyses were used to confirm the encapsulation of PHMB into nano cationic liposome. PHMB inclusion in nano cationic liposome was beneficial for increased antibacterial activity against Staphylococcus aureus and Escherichia coli. PHMB-loaded cationic liposome enables to deliver high concentrations of the antibacterial agent into the infectious cell. The cytotoxicity of PHMB entrapped in positively charged liposome was prominently reduced showing no significant visible detrimental effect on normal primary human skin fibroblast cell lines morphology confirming the effective role of cationic liposome encapsulation. Comparing with PHMB alone, encapsulation of PHMB in nano cationic liposome resulted in significant increase in cell viability from 2.4 to 63%.

Delivery of siRNA via cationic Sterosomes to enhance osteogenic differentiation of mesenchymal stem cells

Noggin is a specific antagonist of bone morphogenetic proteins (BMPs) that can prevent the interaction of BMPs with their receptors. RNA interfering molecules have been used to downregulate noggin expression and thereby stimulate BMP signaling and osteogenesis. Cationic liposomes are considered one of the most efficient non-viral systems for gene delivery. In the past decade, non-phospholipid liposomes (Sterosomes) formulated with single-chain amphiphiles and high content of sterols have been developed. In particular, Sterosomes composed of stearylamine (SA) and cholesterol (Chol) display distinct properties compared with traditional phospholipid liposomes, including increased positive surface charges and enhanced particle stability. Herein, we report SA/Chol Sterosome and small interfering RNA (siRNA) complexes that significantly enhanced cellular uptake and gene knockdown efficiencies in adipose derived mesenchymal stem cells with minimal cytotoxicity compared with commercially available lipofectamine 2000. Furthermore, we confirmed osteogenic efficacy of these Sterosomes loaded with noggin siRNA in in vitro two- and three-dimensional settings as well as in a mouse calvarial defect model. The delivery of siRNA via novel SA/Chol Sterosomes presents a powerful method for efficient gene knockdown. These distinct nanoparticles may present a promising alternative approach for gene delivery.

A review of mechanistic insight and application of pH-sensitive liposomes in drug delivery

The pH-sensitive liposomes have been extensively used as an alternative to conventional liposomes in effective intracellular delivery of therapeutics/antigen/DNA/diagnostics to various compartments of the target cell. Such liposomes are destabilized under acidic conditions of the endocytotic pathway as they usually contain pH-sensitive lipid components. Therefore, the encapsulated content is delivered into the intracellular bio-environment through destabilization or its fusion with the endosomal membrane. The therapeutic efficacy of pH-sensitive liposomes enables them as biomaterial with commercial utility especially in cancer treatment. In addition, targeting ligands including antibodies can be anchored on the surface of pH-sensitive liposomes to target specific cell surface receptors/antigen present on tumor cells. These vesicles have also been widely explored for antigen delivery and serve as immunological adjuvant to enhance the immune response to antigens. The present review deals with recent research updates on application of pH-sensitive liposomes in chemotherapy/diagnostics/antigen/gene delivery etc.

pH-sensitive Liposomes in Drug Delivery

The pH-sensitive liposomes have been extensively studied in recent years as an advantageous alternative to conventional liposomes in effective targeting and accumulation of anticancer drugs in tumors. pH-sensitive liposomes usually contain phosphatidylethanolamine and stabilizing amphiphiles and can destabilize under acidic conditions of the endocytotic pathway. The drug loaded is thought to be delivered into the cytoplasm, probably through destabilization of or fusion with the endosome membrane. This fusogenic property makes the pH-sensitive liposomes more efficient in delivering anticancer drugs than conventional liposomes. The intra-cellular release of drug/gene/diagnostic agents can be achieved without altering their therapeutic efficacy by means of the endosomal escape phenomenon. Cell surface targeting ligands, including antibodies, can be appended on the surface of pH-sensitive liposomes to target specific receptors on tumor cells. This chapter provides an introduction to pH-sensitive liposomes and examples of their therapeutic interest as smart drug-delivery systems.

Treatment of calcium channel blocker-induced cardiovascular toxicity with drug scavenging liposomes

Calcium channel blocker (CCB) overdose is potentially lethal. Verapamil and diltiazem are particularly prone to acute toxicity due to their dual effect on cardiac and vascular tissues. Unfortunately, conventional decontamination measures are ineffective in accelerating blood clearance and, to date, few efforts have been made to develop antidotes. To address the issue, injectable long-circulating liposomes bearing a transmembrane pH-gradient are proposed as efficient detoxifying agents of CCB poisoning. By scavenging the drug in situ, these circulating nanocarriers can restrict its distribution in tissues and hinder its pharmacological effect. In vitro, we showed that liposomes stability in serum and their ability to sequester CCBs could be finely-tuned by modulating their internal pH, surface charge, and lipid bilayer structure. Subsequently, we verified their efficacy in reversing the cardiovascular effects of verapamil in rats implanted with telemetric pressure/biopotential transmitters. In animals orally intoxicated to verapamil, an intravenous injection of the liposomal antidote rapidly attenuated the reduction in blood pressure. Areas under diastolic, systolic, and mean pressures curves were significantly reduced by up to 60% and the time to hemodynamic recovery was shortened from 19 to only 11 h. These findings confirm the protective effect of pH-gradient liposomes against cardiovascular failure after CBB intoxication, and endorse their potential as efficient, versatile antidotes.

Product and process understanding of a novel pediatric anti-HIV tenofovir niosomes with a high-pressure homogenizer

A variety of factors were systemically evaluated in order to establish the characteristics of the niosomes obtained with a high-pressure homogenizer. The vesicular sizing parameters, electrical properties, drug entrapment data and drug release characteristics were investigated using two groups of factors. The first group presented the physical process variables such as pressure of the homogenizer and the times that the samples were processed (cycles). The second group encompassed the compositional variables such as the drug loading, surfactant chain length, cholesterol level and the level of the charge imparting agent. The obtained data showed that the drug distributed within both the aqueous and lipid phases of the formed niosomes. Saturation-like behaviors for both the effect of homogenization cycles on the produced size and the effect of the pressure on the size homogeneity were recorded. In contrast to the drug entrapment and conductivity of the niosomal suspension, the vesicular size parameters as well as the zeta potential were inversely proportional with the homogenization parameters. Drug release was significantly affected by the compositional factors rather than the physical ones. The current study demonstrated the usefulness of the microfluidization for the production and further scale-up of anti-HIV niosomes with very small mean vesicular sizes.

Therapy with sodium stibogluconate in stearylamine-bearing liposomes confers cure against SSG-resistant Leishmania donovani in BALB/c mice

Background

Resistance of Leishmania donovani to pentavalent antimonials, the first-line treatment of visceral leishmaniasis (VL), has become a critical issue worldwide. Second-line and new drugs are also not devoid of limitations. Suitable drug-delivery systems can improve the mode of administration and action of the existing antimonials, thus increasing their clinical life.

Methodology/Principal Findings

We investigated the efficacy of sodium stibogluconate (SSG) in phosphatidylcholine (PC)–stearylamine-bearing liposomes (PC-SA-SSG), PC-cholesterol liposomes (PC-Chol-SSG) and free amphotericin B (AmB) against SSG-resistant L. donovani strains in 8-wk infected BALB/c mice. Animals were sacrificed and parasites in liver, spleen and bone marrow were estimated 4-wk post-treatment by microscopic examination of stamp smears and limiting dilution assay. A set of PC-SA-SSG and AmB treated mice were further studied for protection against reinfection. Serum antibodies and cytokine profiles of ex-vivo cultured splenocytes were determined by ELISA. Uptake of free and liposomal SSG in intracellular amastigotes was determined by atomic absorption spectroscopy. Rhodamine 123 and 5-carboxyfluorescein, known substrates of Pgp and MRP transporter proteins, respectively, were used in free and liposomal forms for efflux studies to estimate intracellular drug retention. Unlike free and PC-Chol-SSG, PC-SA-SSG was effective in curing mice infected with two differentially originated SSG-unresponsive parasite strains at significantly higher levels than AmB. Successful therapy correlated with complete suppression of disease-promoting IL-10 and TGF-β, upregulation of Th1 cytokines and expression of macrophage microbicidal NO. Cure due to elevated accumulation of SSG in intracellular parasites, irrespective of SSG-resistance, occurs as a result of increased drug retention and improved therapy when administered as PC-SA-SSG versus free SSG.

Conclusions/Significance

The design of this single-dose combination therapy with PC-SA-SSG for VL, having reduced toxicity and long-term efficacy, irrespective of SSG-sensitivity may prove promising, not only to overcome SSG-resistance in Leishmania, but also for drugs with similar resistance-related problems in other diseases.

Near-infrared investigations of novel anti-HIV tenofovir liposomes

Near-infrared (NIR) approaches is considered one of the most well-studied process analyzers evolving from the process analytical technology initiatives. The objective of this study was to evaluate NIR spectroscopy and imaging to assess individual components within a novel tenofovir liposomal formulation. By varying stearylamine, as a positive charge imparting agent, five batches were prepared by the thin film method. Each formulation was characterized in terms of drug entrapment efficiency, release characteristics, particle sizing, and zeta potential. Drug excipients compatibility was tested using Fourier transform infrared spectroscopy, differential scanning calorimetry, and X-ray diffraction. The obtained results showed an increase in drug entrapment and a slower drug release by increasing the incorporated percentage of stearylamine. The compatibility testing revealed a significant interaction between the drug and some of the investigated excipients. The developed NIR calibration model was able to assess drug, phospholipid, and stearylamine levels along the batches. The calibration and prediction plots were linear with correlation coefficients of more than 0.9. The root square standard errors of calibration and prediction did not attain 5% of the measured values confirming the accuracy of the model. In contrast, NIR spectral imaging was capable of clearly distinguishing the different batches, both qualitatively and quantitatively. A linear relationship was obtained correlating the actual drug entrapped and the predicted values obtained from the partial least squares images.

Size and Surface Charge Effect of 5-Aminolevulinic Acid-Containing Liposomes on Photodynamic Therapy for Cultivated Cancer Cells

5-Aminolevulinic acid (ALA)-containing liposomes having various average diameters and/or positive surface charges were prepared, and their photodynamic therapy (PDT) efficacy for murine thymic lymphoma cells, EL-4 cells, cultivated in vitro was investigated. The PDT efficacy for EL-4 cells and the accumulation of ALA-induced protoporphyrin IX (PpIX) in the cells increased with a decrease in the average diameter of liposomes. In particular, the ALA-containing liposomes smaller than 63.5 nm in diameter promoted the PDT efficacy in comparison with that of ALA alone. We also found no significant changes in PDT efficacy and PpIX accumulation with increasing positive surface charges of liposomes.

Perturbing effects of carvedilol on a model membrane system: Role of lipophilicity and chemical structure

Carvedilol, a beta-adrenergic blocker used to treat cardiovascular diseases, protects cell membranes from lipid peroxidative damage. Previous studies suggested the drug resides in a non-polar environment and partitions into cell membranes, perturbing their fluidity. Here differential scanning calorimetry (DSC) and fluorescence spectroscopy were applied to further investigate interactions of carvedilol with a liposome model. Results indicate the association is relatively unaffected by pH or temperature, but could be sensitive to liposome composition. The drug's carbazole group plays the dominant role in bilayer perturbation. Compared with other beta-blockers examined, carvedilol produced the strongest liposome DSC perturbation. Locations of carbazole and carvedilol in the liposome were determined using depth-dependent fluorescent probes. Both compounds are situated in the middle of the bilayer, consistent with strong hydrophobic interactions. This combination of high lipophilicity and specific chemical structure appear required for carvedilol's novel antioxidant activity, and may enhance cardioprotection.

Preparation, characterization, and biological analysis of liposomal formulations of vincristine

Vincristine is a dimeric Catharanthus alkaloid derived from the Madagascan periwinkle that acts by binding to tubulin and blocking metaphase in actively dividing cells. While vincristine is widely used in the treatment of a number of human carcinomas, its use is associated with dose-limiting neurotoxicity, manifested mainly as peripheral neuropathy. It is known that the therapeutic activity of vincristine can be significantly enhanced after its encapsulation in appropriately designed liposomal systems. Enhanced efficacy is also associated with a slight decrease in drug toxicity. Thus, the therapeutic index of vincristine can be enhanced significantly through the use of a liposomal delivery system. Vincristine may be encapsulated into liposomes of varying lipid composition by several techniques, including passive loading, pH gradient loading, and ionophore-assisted loading. However, most research has focused on the encapsulation of vincristine in response to a transbilayer pH gradient, which actively concentrates the drug within the aqueous interior of the liposome. This chapter details the preparation and evaluation of liposomal vincristine. Specifically, we elaborate on the components (choice of lipids, molar proportions, etc.), methods (preparation of liposomes, drug loading methods, etc.), critical design features (size, surface charge, etc.), and key biological endpoints (circulation lifetime, bioavailability, efficacy measurements) important to the development of a formulation of vincristine with enhanced therapeutic properties.

Effects of cholesterol on dye leakage induced by multidrug-resistance modulators from anionic liposomes

Multidrug-resistance (MDR) in cancer cells is often associated with marked changes in the membrane cholesterol levels. To assess the cholesterol-dependence of MDR modulator efficiency in terms of the drug-membrane interactions, the ability of 5 MDR-modulators to induce the leakage of Sulphan blue through anionic liposomes was quantified at various mole fractions x(chol) of cholesterol (0-0.42). Depending on the electric charge of the drug, cholesterol modified to a large extent either the permeation dose inducing 50% dye leakage (PD(50)) or the co-operativity (h) of the permeation process. The PD(50) of Triton X-100 (non-ionic) and that of diltiazem and verapamil (mono-basic amines) varied only slightly (0.3 mM) with the cholesterol level, whereas the co-operativity increased by 1.9-2.7. On the reverse, the PD(50) of a thioacridine derivative and mepacrine (di-basic amines) increased by 4.8-7.5 mM in the cholesterol range investigated, whereas the co-operativity (h) increased slightly (0.2-0.7). In the permeation process, the rate-limiting character of the electric charge (z) of the drug is likely to be strengthened by high cholesterol levels. The results provide evidence that in resistant tumours exhibiting high cholesterol levels, the MDR might be reversed by favourable drug-membrane interactions if the modulators are designed in the form of highly lipophilic mono-basic drugs that counteract the effects of cholesterol on the membrane dipolar potential and membrane fluidity.

Development of an in vitro drug release assay that accurately predicts in vivo drug retention for liposome-based delivery systems

The therapeutic activity of numerous drugs can be dramatically improved by liposomal encapsulation. However, this requires that liposomes retain their encapsulated drugs following systemic administration. Often, in vitro drug release assays do not accurately predict the liposomal drug retention properties observed in vivo. We postulate that this discrepancy is due to the large membrane pool present in blood cells and tissues, into which drugs can distribute after in vivo administration. Herein we describe an in vitro drug release assay that more accurately predicts in vivo drug release from liposomes following systemic administration. Drug-encapsulated large unilamellar vesicles (LUVs) approximately 100 nm in diameter were incubated with a 100-fold excess of multilamellar vesicles (MLVs) containing 300 mM sucrose, which served as 'acceptors' for drug release and transfer from 'donor' LUVs. Following incubation at 37 degrees C, the donor and acceptor populations were separated with greater than 90% efficiency by centrifugation at 1600xg for 10 min. The amount of drug in the MLV pellet reflects the degree of drug leakage from the donor liposomes. Drug release profiles using this in vitro assay were compared to those obtained using dialysis-based assays and in vivo results following systemic administration to mice. Our results indicate that this release assay is a better predictor of in vivo drug transfer than dialysis-based systems. We also demonstrate its utility in measuring exchange of lipophilic components.

Identification of two distinct intracellular sites that contribute to the modulation of multidrug resistance in P388/ADR cells expressing P-glycoprotein

Although the ability of chemosensitizers to modulate P-glycoprotein (PGP)-based multidrug resistance (MDR) has been extensively studied, relatively little is known about the cellular pharmacology of the PGP inhibitors themselves in MDR cells. The studies described here have correlated the in vitro accumulation and retention properties of verapamil (VRP) in murine P388 (sensitive) and P388/ADR (MDR) cells with doxorubicin (DOX) uptake and cytotoxicity modulation characteristics in order to better understand VRP-tumor cell interactions that give rise to MDR modulation. VRP is rapidly taken up by DOX-sensitive and -resistant P388 cells where greater than 50% maximal VRP uptake occurs within 10 min of initial exposure at 37 degrees C. Whereas chemosensitization and DOX uptake in P388/ADR cells increase with increasing VRP concentration until a plateau is achieved at approximately 5 microM VRP, cellular modulator levels increase proportionally with increasing VPR concentrations beyond 20 microM. Subsequent to removal of noncell-associated modulator, VRP levels in both sensitive and resistant cells rapidly fall below 10% of those obtained at uptake equilibrium. However, a residual amount of VRP remains associated with the cells for extended time periods after the cells are washed. Pulse exposures of P388/ADR cells to high concentrations of VRP (50-100 microM) are capable of providing extended cell-associated VRP levels comparable to those obtained with continuous exposure at biologically active VRP concentrations (1-3 microM) and this leads to chemosensitization. These results are consistent with the existence of high- and low-affinity intracellular VRP pools in P388 MDR cells, both of which can contribute to the reversal of drug resistance. It is suggested that these properties should be taken into consideration during the design and evaluation of preclinical in vivo MDR models where pulsed exposure to high concentrations of resistance modulators often occurs. Special attention must be given to whether such high concentration pulses are desirable and/or achievable in relevant clinical settings.

Lidocaine-loaded non-ionic surfactant vesicles: characterization and in vitro permeation studies

Our research on topical application of lidocaine-loaded non-ionic surfactant vesicles (NSVs) was prompted by the great interest on new delivery systems for local anaesthetics. This study is focused on a novel formulation of NSVs entrapping lidocaine in the form of a free base (LID) and a hydrochloride (LIDHCl). NSVs were prepared from polyoxyethylene sorbitan monolaurate (Tween20) and cholesterol. The effect of vesicle composition and environmental pH condition (8.6-5.5) on drug encapsulation efficiency (e.e.) was investigated. Experimental strategies involved: freeze-fracture, microscopy technique, dynamic light scattering, permeation through Silastic and mouse abdominal skin, in vitro release kinetics of vesicle-entrapped drugs, fluorescence quenching analyses. Diffusion experiments showed that the flux of charged lidocaine through Silastic membrane was possible only after the vesicle encapsulation. Permeation through mouse abdominal skin of LIDHCl loaded vesicles showed a higher flux and a shorter lag time with respect to classical liposome formulations, while LID permeation rate was quite similar for NSV and liposome formulations. Vesicles were also prepared in the presence of dicetylphosphate (DCP) and N-cetylpyridinium chloride (CP) to obtain negatively and positively charged vesicles respectively, but in this case the e.e. of the drug was negligible. The possible reason of the remarkable lower e.e. observed with charged vesicles was investigated by means of fluorescence quenching experiments.

Membrane permeation by multidrug-resistance-modulators and non-modulators: effects of hydrophobicity and electric charge

This study was designed to test the hypothesis that lipophilic cationic drugs with only roughly similar structures mediate the reversal of multidrug-resistance (MDR) by interacting with membrane phospholipids. The permeation properties of MDR-modulators and non-modulators were studied by quantifying their ability to induce the leakage of Sulphan blue through the membrane of negatively charged unilamellar liposomes. Of the 22 compounds under investigation, only those bearing a net positive electric charge per molecule (z) > or = 0.2 induced dye leakage. All these efficient drugs are well-known MDR-modulators: calcium-channel blockers (propranolol, verapamil, diltiazem and dipyridamole), calmodulin antagonists (clomipramine and thioridazine) and antiparasitic agents (mepacrine, thioacridine derivatives and quinine). The non-modulators tested, including antineoplastic agents and steroids, did not induce any membrane permeation. The permeation process was a co-operative one (1.1 < Hill coefficient < 4.1) and the permeation doses inducing 50% dye leakage (PD50) were 1.9-11.2 mM. The permeation ability of the MDR-modulators (log(1/PD50)) increased significantly with octanol-buffer distributions per unit net electric charge ((logD)/z). The results provide evidence that a complex interplay occurs between the electric charge and the lipophilicity of the MDR-modulators when a dye leakage is induced through model membranes, and probably also when the MDR is reversed in leukaemic cells.

Analysis of the tangled relationships between P-glycoprotein-mediated multidrug resistance and the lipid phase of the cell membrane

P-glycoprotein (Pgp), the so-called multidrug transporter, is a plasma membrane glycoprotein often involved in the resistance of cancer cells towards multiple anticancer agents in the multidrug-resistant (MDR) phenotype. It has long been recognized that the lipid phase of the plasma membrane plays an important role with respect to multidrug resistance and Pgp because: the compounds involved in the MDR phenotype are hydrophobic and diffuse passively through the membrane; Pgp domains involved in drug binding are located within the putative transmembrane segments; Pgp activity is highly sensitive to its lipid environment; and Pgp may be involved in lipid trafficking and metabolism. Unraveling the different roles played by the membrane lipid phase in MDR is relevant, not only to the evaluation of the precise role of Pgp, but also to the understanding of the mechanism of action and function of Pgp. With this aim, I review the data from different fields (cancer research, medicinal chemistry, membrane biophysics, pharmaceutical research) concerning drug-membrane, as well as Pgp-membrane, interactions. It is emphasized that the lipid phase of the membrane cannot be overlooked while investigating the MDR phenotype. Taking into account these aspects should be useful in the search of ways to obviate MDR and could also be relevant to the study of other multidrug transporters.

The electrostatics of lipid surfaces

Charged lipids constitute a substantial fraction of all membrane lipids. Their charges vary in quantity and distribution within their headgroup regions. In long range interactions, their charges' value and electrostatic potential in the vicinity of the membrane surface can be approximated by the Guy-Chapman theory. This theory treats the interface as a charged structureless plain surrounded by uniform environments. However, if one considers intermolecular interactions, such assumptions need to be revised. The interface is in reality a thick region containing the residual charges of lipid headgroups. Their arrangement depends on the type of lipid present in the membrane. The variety of lipids and their biological functions suggests that charge distribution determines the extent and type of interaction with surface associated molecules. Numerous examples show that protein behavior at the lipid bilayer surface is determined by the type of lipid present, indicating protein specificity towards certain surface locations and local properties (determined by lipid composition) of a particular type. Such specificity is achieved by a combination of electrostatic, hydrophobic and enthropic effects. Comparing lipid biological activity, it can be stated that residual charge distribution is one of the factors of intermolecular recognition leading to the specific interaction of lipid molecules and selected proteins in various processes, particularly those involved with signal transduction pathways. Such specificity enables a variety of processes occurring simultaneously on the same membrane surface to function without cross-reaction interference.

Comparison of different hydrophobic anchors conjugated to poly(ethylene glycol): effects on the pharmacokinetics of liposomal vincristine

Poly(ethylene glycol) (PEG) conjugated lipids have been used to increase the circulation longevity of liposomal carriers encapsulating therapeutic compounds. PEG is typically conjugated to distearoylphosphatidylethanolamine (DSPE) via a carbamate linkage that results in a net negative charge on the phosphate moiety at physiological pH. It was anticipated that the presence of this negative charge could have deleterious effects on liposome pharmacokinetic characteristics. We describe here the synthesis of a new class of neutrally charged PEG-lipid conjugates in which the PEG moiety was linked to ceramide (CER). These PEG-CER conjugates were compared with PEG-DSPE conjugates for their effects on the pharmacokinetics of liposomal vincristine. PEG-CER (78% palmitic acid, C16) and PEG-DSPE achieved comparable increases in the circulation lifetimes of sphingomyelin/cholesterol (SM/chol) liposomes. However, PEG-DSPE significantly increased the in vitro and in vivo leakage rates of vincristine from SM/chol-based liposomes compared to vincristine leakage observed when PEG-CER was used. The increase in drug leakage observed in vitro that was due to the presence of PEG-DSPE was likely due to the presence of a negative surface charge. Analysis of the electrophoretic mobilities of these formulations suggested that the negative surface charges were shielded by approx. 80% by the PEG layer extending from the membrane surface. In contrast, formulations containing PEG-CER had no surface charge and no electrophoretic mobility. A comparison of the effects of the ceramide acyl chain length (C8 through C24) on the pharmacokinetics of SM/chol/PEG-CER formulations of vincristine demonstrated that longer acyl chains on the PEG-CER were associated with longer circulation lifetimes of the liposomal carriers and, consequently, higher plasma vincristine concentrations. These data suggest that the short chain PEG-ceramides underwent rapid partitioning from the vesicles after i.v. administration, whereas the longer chain PEG-ceramides had stronger anchoring properties in the liposome bilayers and partitioned slowly from the administered vesicles. These data demonstrate the utility of ceramide-based steric stabilizing lipids as well as the potential for developing controlled release formulations by manipulating the retention of the PEG-ceramide conjugate in liposome bilayers.

Permeability of lipid bilayer to anthracycline derivatives. Role of the bilayer composition and of the temperature

The uptake of three anthracycline derivatives: doxorubicin, daunorubicin and pirarubicin, into large unilamellar vesicles (LUV) in response to a driving force provided by DNA encapsulated inside the LUV has been investigated as a function of the temperature and of the bilayers lipid composition. The kinetics of the decay of the anthracycline fluorescence in the presence of DNA-containing liposome was used to follow the diffusion of the drug through the membrane. For the three drugs, the permeability coefficient of the neutral form of the drug (P0) decreases as the amount of negatively charged phospholipid in the bilayers increases. This can be explained by the fact that the kinetics of passive diffusion of the drugs depends on the amount of neutral form embedded in the polar head group region, which decreases as the quantity of negatively charged phospholipids increases. P0 also decreases as the amount of cholesterol, that makes the bilayer more rigid, increases. The activation energies, Ea, for the passage of the neutral form of these anthracyclines through the bilayers lie within 100 +/- 15 kJ x ml-1, except for pirarubicin and doxorubicin through anionic phospholipid-rich membranes (Ea = 57 kJ x mol-1) and cholesterol-rich membranes (Ea = 167 kJ x mol-1).

Surface charge control of electropermeabilization and glycophorin electroinsertion with 1,2-diacyl-sn-glycero-3-phosphocholine (lecithin) liposomes

Back insertion of a solubilized membrane protein, glycophorin A, has been obtained in lipid multilamellar vesicles by applying calibrated electric field pulses on a lipid/protein mixture. Experimental evidence for insertion is given by means of immunofluorescence. Insertion was obtained only under field conditions that induced the leakage of a soluble hydrophilic molecule, calcein, which was trapped between the lipid layers. Studies were performed on mixed liposomes where charged species were present. The critical permeabilizing field is the same whatever the composition, but with overcritical fields the associated calcein transmembraneous flow is higher with positively charged lipids. Field conditions that where prone to trigger glycophorin insertion were similar to those that induced electropermeabilization. No electroinsertion has been obtained with stearylamine (SteNH2)/1,2-dipalmitoyl-sn-glycero-3-phosphocholine (Pam2GroPCho) liposomes under the same conditions. Calcein efflux as well as glycophorin insertion are controlled by the electric surface charge of the host liposome. These observations confirm our previous conclusions that spontaneous membrane protein insertion is obtained when the host membrane is brought to its electropermeabilized state, but show that a strong control due to the surface charges is nevertheless present.

Action of tertiary phenylalkylamines on cardiac transient outward current from outside the cell membrane

The effects of the phenylalkylamines verapamil (V), gallopamil (G), and devapamil (D) and their corresponding quaternary derivatives on the transient outward current (Ito) were examined in rat ventricular cardiomyocytes using the whole-cell patch-clamp technique. The question was addressed, whether phenylalkylamines act on Ito from the inside or the outside or from both sides of the cell membrane. To this end, the myocytes were either superfused extracellularly or perfused intracellularly with drug-containing solutions. In addition, the effects of verapamil were investigated at different pH-values. V, G, and D (30 microM each), applied extracellularly, reduced the steady state current of Ito, Ito(150 ms), to 34 +/- 3.3, 33 +/- 6, and 30 +/- 5, respectively (% of control; means +/- SEM). The effects of V (30 microM) on Ito were similar at various external pH-values (reduction of Ito(150 ms) by 69 +/- 6 at pH 6.5, by 66 +/- 4 at pH 7.4, by 68 +/- 8 at pH 8.5, and by 58 +/- 10 at pH 9.5; % of control; means +/- SEM). In contrast, the effect of 4-aminopyridine (300 microM) on Ito was enhanced after alkalinisation: the peak current of Ito was reduced to 49 +/- 5 at pH 7.4 and to 5 +/- 2 at pH 9.2 (% of control; means +/- SEM). V, G, and D (300 microM) failed to produce any effect on Ito, when applied intracellularly (values of Ito(150 ms): 97 +/- 6, 105 +/- 4, and 94 +/- 4, respectively; % of control; means +/- SEM). In contrast, 4-aminopyridine (3 mM) depressed the peak current of Ito to 69 +/- 6% of control (mean +/- SEM), when applied intracellularly. The permanently charged quaternary derivatives of the phenylalkylamines q-V, q-G, and q-D (300 microM) did not significantly affect Ito, when applied extracellularly (values of Ito(150 ms): 94 +/- 2, 90 +/- 3, and 94 +/- 3, respectively; % of control; means +/- SEM) but diminished Ito, when applied intracellularly (reduction of Ito(150 ms) to 43 +/- 5, 56 +/- 7, and 63 +/- 4, respectively; % of control; means +/- SEM). Intracellularly applied V (300 microM) did not reduce Ito at pH 6.5 at which V is protonated to 99.4%. It is suggested that tertiary phenylalkylamines act on Ito by binding to a membrane site accessible from the outside, whereas their quaternary derivatives affect Ito by binding to a membrane site located at the inside of the cell membrane. In contrast, 4-aminopyridine is supposed to act on Ito from the inside of the cell membrane.