Nebulization of Liposomal rh-Cu/Zn–SOD with a Novel Vibrating Membrane Nebulizer

Liposomes are potential drug carriers for pulmonary drug delivery: They can be prepared from phospholipids, which are endogenous to the respiratory tract as a component of pulmonary surfactant, and at an appropriate dose liposomes do not pose a toxicological risk to this organ. Among the various categories of drug that benefit from liposomal entrapment is the anti-inflammatory enzyme superoxide dismutase, thus prolonging its biological half-life. The delivery of liposomes by nebulization is hampered by stability problems, like physical and chemical changes that may lead to chemical degradation and leakage of the encapsulated drug. Here we present data of liposomes aerosolized with a novel electronic nebulizer based on a vibrating membrane technology (PARI eFlow?), which amends drawbacks like liposomes degradation and product release. The data acquisition included aerosol properties such as aerodynamic particle size, nebulization efficiency, and liposome leakage upon nebulization. In conclusion, this study shows the ability of the PARI eFlow? to nebulize high amounts of liposomal recombinant human superoxide dismutase with reduced vesicle disruption tested in an enclosing experimental protocol.     

Evaluation of tetraether lipid-based liposomal carriers for encapsulation and retention of nucleoside-based drugs

Although liposomal nanoparticles are one of the most versatile class of drug delivery systems, stable liposomal formulation of small neutral drug molecules still constitutes a challenge due to the low drug retention of current lipid membrane technologies. In this study, we evaluate the encapsulation and retention of seven nucleoside analog-based drugs in liposomes made of archaea-inspired tetraether lipids, which are known to enhance packing and membrane robustness compared to conventional bilayer-forming lipids. Liposomes comprised of the pure tetraether lipid generally showed improved retention of drugs (up to 4-fold) compared with liposomes made from a commercially available diacyl lipid. Interestingly, we did not find a significant correlation between the liposomal leakage rates of the molecules with typical parameters used to assess lipophilicity of drugs (such logD or topological polar surface area), suggesting that specific structural elements of the drug molecules can have a dominant effect on leakage from liposomes over general lipophilic character.     

The potential of pectin as a stabilizer for liposomal drug delivery systems

The aim of the present study was to investigate the potential of different types of pectin as stabilizers for liposomal drug delivery systems. Positively charged liposomes were coated with commercially available and purified low-methoxylated (LM), high-methoxylated (HM) and amidated (AM) pectins. The samples were stored for up to 12 weeks at 4°C, at room temperature and at 35°C. The change in liposomal size and size distribution, zeta potential, pH, leakage of encapsulated carboxyfluorescein (CF), and lipid degradation were studied. All the types of pectin were found to protect the liposomes against aggregation during storage. The pectin coat did not affect the permeability of the liposome membrane. HM and LM pectin seemed to be the most promising types of pectin due to minimal changes in the zeta potentials during storage for these samples and no detectable lipid degradation. It is concluded that pectin may be used for stabilizing liposomal drug delivery systems.     

Advanced strategies in liposomal cancer therapy: problems and prospects of active and tumor specific drug release

Tumor specific drug delivery has become increasingly interesting in cancer therapy, as the use of chemotherapeutics is often limited due to severe side effects. Conventional drug delivery systems have shown low efficiency and a continuous search for more advanced drug delivery principles is therefore of great importance. In the first part of this review, we present current strategies in the drug delivery field, focusing on site-specific triggered drug release from liposomes in cancerous tissue. Currently marketed drug delivery systems lack the ability to actively release the carried drug and rely on passive diffusion or slow non-specific degradation of the liposomal carrier. To obtain elevated tumor-to-normal tissue drug ratios, it is important to develop drug delivery strategies where the liposomal carriers are actively degraded specifically in the tumor tissue. Many promising strategies have emerged ranging from externally triggered light- and thermosensitive liposomes to receptor targeted, pH- and enzymatically triggered liposomes relying on an endogenous trigger mechanism in the cancerous tissue. However, even though several of these strategies were introduced three decades ago, none of them have yet led to marketed drugs and are still far from achieving this goal. The most advanced and prospective technologies are probably the prodrug strategies where non-toxic drugs are carried and activated specifically in the malignant tissue by overexpressed enzymes. In the second part of this paper, we review our own work, exploiting secretory phospholipase A2 as a site-specific trigger and prodrug activator in cancer therapy. We present novel prodrug lipids together with biophysical investigations of liposome systems, constituted by these new lipids and demonstrate their degradability by secretory phospholipase A2. We furthermore give examples of the biological performance of the enzymatically degradable liposomes as advanced drug delivery systems.     

Liposomes of terbutaline sulphate: in vitro and in vivo studies

In vitro studies were conducted to understand the comparative drug diffusion pattern, across artificial membrane, of the drug and of the prepared liposomes of different liposomal membrane composition. In vivo studies were carried out to determine the extent and time-course of pulmonary tissue uptake of administered liposomes containing terbutaline sulphate(TER) on rat lungs. In vitro studies revealed that the drug released from the prepared liposomes obeys Higuchi's diffusion controlled model. Different loading doses and release patterns of drug from the liposomes can be obtained by altering the PC:CHOL ratio and incorporation of cholesterol was found to reduce permeability of the membrane. Similarly drug absorption in vivo in rat's lung following intratracheal instillation, prolonged over 12 hr by liposomal entrapment of TER. The findings of present investigation indicated that liposomally encapsulated TER can be used for pulmonary delivery for maximizing the therapeutic efficacy and reducing undesirable side effects.     

Liposomes as carriers for verbascoside: stability and skin permeation studies

In this study the influence of liposomal incorporation on both the stability and the in vitro (trans) dermal delivery of verbascoside was evaluated. The effect of drug entrapment into vesicles on its radical scavenging activity was also studied. Liposomes were obtained from soy phosphatidylcholine and cholesterol according to the film hydration method. Stability of verbascoside-loaded vesicles was studied over 6 months. Results showed that verbascoside can be incorporated in liposomes (E% = 57-66%), preventing its degradation. Stability studies (dynamic lager light scattering [DLLS] measurements and transmission electron microscopy [TEM] visualization) pointed out that vesicles were stable for 90 days and neither verbascoside leakage nor vesicle size alteration occurred during this period. The effects of vesicular incorporation on verbascoside diffusion through skin were investigated in vitro using newborn pig skin. Results showed that liposomes promoted drug accumulation into the stratum corneum but they did not give rise to any significant transdermal verbascoside delivery. Finally, results obtained from a 1, 1-diphenyl-2-pierylhydrazyl (DPPH) radical assay demonstrated that liposomes did not interfere with the radical scavenging activity of verbascoside.     

Liposomes as Carriers for Verbascoside: Stability and Skin Permeation Studies

In this study the influence of liposomal incorporation on both the stability and the in vitro (trans) dermal delivery of verbascoside was evaluated. The effect of drug entrapment into vesicles on its radical scavenging activity was also studied. Liposomes were obtained from soy phosphatidylcholine and cholesterol according to the film hydration method. Stability of verbascoside-loaded vesicles was studied over 6 months. Results showed that verbascoside can be incorporated in liposomes (E%?=?57–66%), preventing its degradation. Stability studies (dynamic lager light scattering [DLLS] measurements and transmission electron microscopy [TEM] visualization) pointed out that vesicles were stable for 90 days and neither verbascoside leakage nor vesicle size alteration occurred during this period. The effects of vesicular incorporation on verbascoside diffusion through skin were investigated in vitro using newborn pig skin. Results showed that liposomes promoted drug accumulation into the stratum corneum but they did not give rise to any significant transdermal verbascoside delivery. Finally, results obtained from a 1, 1-diphenyl-2-pierylhydrazyl (DPPH) radical assay demonstrated that liposomes did not interfere with the radical scavenging activity of verbascoside.     

Aerosol Performance and Long-Term Stability of Surfactant-Associated Liposomal Ciprofloxacin Formulations with Modified Encapsulation and Release Properties

Previously, we showed that the encapsulation and release properties of a liposomal ciprofloxacin formulation could be modified post manufacture, by addition of surfactant in concert with osmotic swelling of the liposomes. This strategy may provide more flexibility and convenience than the alternative of manufacturing multiple batches of liposomes differing in composition to cover a wide range of release profiles. The goal of this study was to develop a surfactant-associated liposomal ciprofloxacin (CFI) formulation possessing good long-term stability which could be delivered as an inhaled aerosol. Preparations of 12.5 mg/ml CFI containing 0.4% polysorbate 20 were formulated between pH 4.7 and 5.5. These formulations, before and after mesh nebulization, and after refrigerated storage for up to 2 years, were characterized in terms of liposome structure by cryogenic transmission electron microscopy (cryo-TEM) imaging, vesicle size by dynamic light scattering, pH, drug encapsulation by centrifugation-filtration, and in vitro release (IVR) performance. Within the narrower pH range of 4.9 to 5.2, these formulations retained their physicochemical stability after 2-year refrigerated storage, were robust to mesh nebulization, and formed respirable aerosols with a volume mean diameter (VMD) of 3.7 μm and a geometric standard deviation (GSD) of 1.7. This study demonstrates that it may be possible to provide a range of release profiles by simple addition of surfactant to a liposomal formulation post manufacture, and that these formulations may retain their physicochemical properties after long-term refrigerated storage and following aerosolization by mesh nebulizer.KEY WORDS: ciprofloxacin, drug delivery, liposome, nebulized aerosol, surfactant     

Liposomal-delivery of phosphodiesterase 5 inhibitors augments UT-15C-stimulated ATP release from human erythrocytes

The use of liposomes to affect targeted delivery of pharmaceutical agents to specific sites may result in the reduction of side effects and an increase in drug efficacy. Since liposomes are delivered intravascularly, erythrocytes, which constitute almost half of the volume of blood, are ideal targets for liposomal drug delivery.In vivo, erythrocytes serve not only in the role of oxygen transport but also as participants in the regulation of vascular diameter through the regulated release of the potent vasodilator, adenosine triphosphate (ATP). Unfortunately, erythrocytes of humans with pulmonary arterial hypertension (PAH) do not release ATP in response to the physiological stimulus of exposure to increases in mechanical deformation as would occur when these cells traverse the pulmonary circulation. This defect in erythrocyte physiology has been suggested to contribute to pulmonary hypertension in these individuals.In contrast to deformation, both healthy human and PAH erythrocytes do release ATP in response to incubation with prostacyclin analogs via a well-characterized signaling pathway. Importantly, inhibitors of phosphodiesterase 5 (PDE5) have been shown to significantly increase prostacyclin analog-induced ATP release from human erythrocytes.Here we investigate the hypothesis that targeted delivery of PDE5 inhibitors to human erythrocytes, using a liposomal delivery system, potentiates prostacyclin analog- induced ATP release. The findings are consistent with the hypothesis that directed delivery of this class of drugs to erythrocytes could be a new and important method to augment prostacyclin analog-induced ATP release from these cells. Such an approach could significantly limit side effects of both classes of drugs without compromising their therapeutic effectiveness in diseases such as PAH.     

Triggered release of ciprofloxacin from nanostructured agglomerated vesicles

Nanostructured agglomerated vesicles encapsulating ciprofloxacin were evaluated for modulated delivery from the lungs in a healthy rabbit model. An aliphatic disulfide crosslinker, cleavable by cysteine was used to form cross-links between nanosized liposomes to form the agglomerates. The blood levels of drug after pulmonary instillation of free ciprofloxacin, liposomal ciprofloxacin, and the agglomerated liposomes encapsulating ciprofloxacin were evaluated. The liposomes and agglomerated vesicles showed extended release of drug into the blood over 24 hours, while the free ciprofloxacin did not. The agglomerates also allowed modulation of the drug release rate upon the introduction of cysteine into the lungs post-drug instillation; the cysteine-cleavable agglomerates accelerated their drug release rate, indicated by an increased level of drug in the blood. This technology holds promise for the post-administration modulation of antibiotic release, for the prevention and treatment of pulmonary and systemic infections.     

多肽、蛋白类药物脂质体的研究进展

脂质体做为多肽、蛋白类药物一种新型给药载体有控制药物释放、降低药物的毒性、提高药物的靶向性等突出优点,具有广阔的应用前景。本文通过查阅近10年来多肽和蛋白类药物脂质体研究的相关资料,总结论述了脂质体作为多肽、蛋白类药物载体在新的制备方法、新型脂质体、给药途径、产业化进展四个方面的最新研究动向,指出了多肽、蛋白类药物脂质体在研究应用中存在的不足,并展望了多肽、蛋白类药物脂质体未来发展的方向。     

Lyophilisation and sterilisation of liposomal vaccines to produce stable and sterile products

The advantages of liposomes as delivery systems for peptide, protein and DNA vaccines is well-recognised, unfortunately their application has been stinted by their instability during storage and their limited shelf-life. Further, sterilisation of these systems has been problematic, with degradation of the liposomes being reported after sterilisation using the various techniques available. Work form our laboratory has investigated techniques that can be applied to particulate liposomal vaccines such that they can be prepared in a freeze-dried and sterile format. In this article, we describe techniques for the lyophilisation, cryoprotection and sterilisation of liposomal vaccines. Applying these methods allows for the retention of both the chemical integrity of the lipids and the key physico-chemical characteristics of the liposomes (e.g., particle size, zeta potential, and dynamic viscosity), thus supporting the enhanced transition of liposomal vaccines from the bench to the clinic.     

A kinetic method for measuring functional delivery of amphotericin B by drug delivery systems.

The human toxicity of amphotericin B can be considerably reduced by associating the drug with liposomes of varying lipid compositions. Some lipid compositions are much more effective than others. We show that a simple kinetic fluorescence assay using pyranine as an indirect probe of amphotericin-induced K+ currents may be used to study different liposomal drug delivery systems in vitro. We find that lipid mixtures composed of DMPC/DMPG/amphotericin at a 7:3:1 mole ratio show very slow functional delivery with a preference for ergosterol over cholesterol-containing membrane vesicles. On the other hand, amphotericin delivered from egg phosphatidylcholine liposomes lead to 100-fold increases in K+ leakage at one-fifth the amphotericin concentration of the 7:3:1 system. The egg phosphatidylcholine system as well as micellar amphotericin also show a slight selectivity towards cholesterol-containing vesicles over ergosterol. These results are consistent with previous clinical and in vitro cellular studies and this technique may prove valuable in screening of other delivery systems.     

In vitro characterization of a novel polymeric-based pH-sensitive liposome system

This study demonstrates rapid and pH-sensitive release of a highly water-soluble fluorescent aqueous content marker, pyranine, from egg phosphatidylcholine liposomes following incorporation of N-isopropylacrylamide (NIPA) copolymers in liposomal membranes. The pH-sensitivity of this system correlates with the precipitation of the copolymers at acidic pH. In vitro release can be significantly improved by increasing the percentage of anchor in the copolymer and thus favoring its binding to the liposomal bilayer. In the case of liposomes containing a poly(ethylene glycol)-phospholipid conjugate, the insertion of the pH-sensitive copolymer in the liposomal membrane appears to be sterically inhibited. Dye release from these formulations at acidic pH can still be achieved by varying the anchor molar ratio and/or molecular mass of the polymers or by including the latter during the liposome preparation procedure. Removal of unbound polymer results in decreased leakage only when the copolymer is inserted by incubation with preformed liposomes, but can be overcome by preparing liposomes in the presence of polymer. Aqueous content and lipid mixing assays suggest contents release can occur without membrane fusion. The results of this study indicate that the addition of pH-sensitive copolymers of NIPA represents promising strategy for improving liposomal drug delivery.     

Release of Active Drug from Intracellular Liposomal Prodrug Depots in Macrophages Controlled by Liposome Composition

Abstract

Several drugs have limited potency due to their rapid elimination or inactivation. The anticancer drug 5-fluoro-deoxyuridine (FUdR), which is frequently used in therapeutic treatment of liver metastases from colon tumors, is an example of such drugs. It is rapidly eliminated from circulation and metabolized, mainly by the hepatocytes in the liver. Over the past few years we have investigated the possibility to keep the drug away from the hepatocytes and to save it from rapid inactivation by encapsulating it in liposomes. In this way the liposomal drug is expected to accumulate in the macrophages of the liver (Kupffer cells), which form a major target site for intravenously administered liposomes. There, as the liposomal structure is gradually degraded by lysosomal enzymes, the drug will be released, initially within the lysosomal compartment, while subsequently it will leak out of the lysosomes and eventually out of the cells so as to become available for uptake by intrahepatically situated tumor cells. In this contribution we describe this system for the prodrug dipalmitoyl-FUdR, incorporated in the liposomal bilayer, requiring an additional step for the drug to become available, i.e. the enzymatic deacylation of the prodrug. It is demonstrated that the rate of intralysosomal degradation of liposomes in Kupffer cells varies substantially with liposomal lipid composition and that the rate of release of active drug from the Kupffer cells parallels the rate of liposome degradation. In addition, it is demonstrated that in this way the antitumor activity of the FUdR can be enhanced by more than two orders of magnitude and that the degree of antitumor activity reflects, to a limited extent, the rate at which the liposomes are degraded.     

Functional characterization of an endosome-disruptive peptide and its application in cytosolic delivery of immunoliposome-entrapped proteins

Antibody-directed liposomes (immunoliposomes) are frequently used for targeted drug delivery. However, delivery of large biotherapeutic molecules (i.e. peptides, proteins, or nucleic acids) with immunoliposomes is often hampered by an inefficient cytosolic release of entrapped macromolecules after target cell binding and subsequent endocytosis of immunoliposomes. To enhance cytosolic drug delivery from immunoliposomes present inside endosomes, a pH-dependent fusogenic peptide (diINF-7) resembling the NH(2)-terminal domain of influenza virus hemagglutinin HA-2 subunit was used. Functional characterization of this dimeric peptide showed its ability to induce fusion between liposome membranes and leakage of liposome-entrapped compounds when exposed to low pH. In a second series of experiments, diINF-7 peptides were encapsulated in immunoliposomes to enhance the endosomal escape of diphtheria toxin A chain (DTA), which inhibits protein synthesis when delivered into the cytosol of target cells. Immunoliposomes targeted to the internalizing epidermal growth factor receptor on the surface of ovarian carcinoma cells (OVCAR-3) and containing encapsulated DTA did not show any cytotoxicity toward OVCAR-3 cells. Cytotoxicity was only observed when diINF-7 peptides and DTA were co-encapsulated in the immunoliposomes. Thus, diINF-7 peptides entrapped inside liposomes can greatly enhance cytosolic delivery of liposomal macromolecules by pH-dependent destabilization of endosomal membranes after cellular uptake of liposomes.     

Glycosylated Sertraline-Loaded Liposomes for Brain Targeting: QbD Study of Formulation Variabilities and Brain Transport

Effectiveness of CNS-acting drugs depends on the localization, targeting, and capacity to be transported through the blood–brain barrier (BBB) which can be achieved by designing brain-targeting delivery vectors. Hence, the objective of this study was to screen the formulation and process variables affecting the performance of sertraline (Ser-HCl)-loaded pegylated and glycosylated liposomes. The prepared vectors were characterized for Ser-HCl entrapment, size, surface charge, release behavior, and in vitro transport through the BBB. Furthermore, the compatibility among liposomal components was assessed using SEM, FTIR, and DSC analysis. Through a thorough screening study, enhancement of Ser-HCl entrapment, nanosized liposomes with low skewness, maximized stability, and controlled drug leakage were attained. The solid-state characterization revealed remarkable interaction between Ser-HCl and the charging agent to determine drug entrapment and leakage. Moreover, results of liposomal transport through mouse brain endothelialpolyoma cells demonstrated greater capacity of the proposed glycosylated liposomes to target the cerebellar due to its higher density of GLUT1 and higher glucose utilization. This transport capacity was confirmed by the inhibiting action of both cytochalasin B and phenobarbital. Using C6 glioma cells model, flow cytometry, time-lapse live cell imaging, and in vivo NIR fluorescence imaging demonstrated that optimized glycosylated liposomes can be transported through the BBB by classical endocytosis, as well as by specific transcytosis. In conclusion, the current study proposed a thorough screening of important formulation and process variabilities affecting brain-targeting liposomes for further scale-up processes.     

Novel camptothecin analogue (gimatecan)-containing liposomes prepared by the ethanol injection method

Small-sized liposomes have several advantages as drug delivery systems, and the ethanol injection method is a suitable technique to obtain the spontaneous formation of liposomes having a small average radius. In this paper, we show that liposomal drug formulations can be prepared in situ, by simply injecting a drug-containing lipid(s) organic solution into an aqueous solution. Several parameters should be optimized in order to obtain a final suitable formulation, and this paper is devoted to such an investigation. Firstly, we study the liposome size distributions determined by dynamic light scattering (DLS), as function of the lipid concentration and composition, as well as the organic and aqueous phases content. This was carried out, firstly, by focusing on POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) then on the novel L-carnitine derivative PUCE (palmitoyl-(R)-carnitine undecyl ester chloride), showing that it is possible to obtain monomodal size distributions of rather small vesicles. In particular, depending on the conditions, it was possible to achieve a population of liposomes with a mean size of 100 nm, when a 50 mM POPC ethanol solution was injected in pure water; in the case of 50 mM PUCE the mean size was around 30 nm, when injected in saline (0.9% NaCl). The novel anticancer drug Gimatecan, a camptothecin derivative, was used as an example of lipophilic drug loading by the injection method. Conditions could be found, under which the resultant liposome size distributions were not affected by the presence of Gimatecan, in the case of POPC as well as in the case of PUCE. To increase the overall camptothecin concentration in the final liposomal dispersion, the novel technique of "multiple injection method" was used, and up to a final 5 times larger amount of liposomal drug could be reached by maintaining approximately the same size distribution. Once prepared, the physical and chemical stability of the liposome formulations was satisfactory within 24, as judged by DLS analysis and HPLC quantitation of lipids and drug. The Gimatecan-containing liposomes formulations were also tested for in vitro and in vivo activity, against the human nonsmall cell lung carcinoma NCI-H460 and a murine Lewis lung carcinoma 3 LL cell lines. In the in vitro tests, we did not observe any improvement or reduction of the Gimatecan pharmacological effect by the liposomal delivery system. More interestingly, in the in vivo Lewis lung carcinoma model, the intravenously administration of liposomal Gimatecan formulation showed a mild but significant increase of Tumor Volume Inhibition with respect to the oral no-liposomal formulation (92% vs. 86 %, respectively; p < 0.05). Finally, our study showed that the liposomal formulation was able to realize a delivery system of a water-insoluble drug, providing a Gimatecan formulation for intravenous administration with a preserved antitumoral activity.     

Novel Camptothecin Analogue (Gimatecan)‐Containing Liposomes Prepared by the Ethanol Injection Method

Small‐sized liposomes have several advantages as drug delivery systems, and the ethanol injection method is a suitable technique to obtain the spontaneous formation of liposomes having a small average radius. In this paper, we show that liposomal drug formulations can be prepared in situ, by simply injecting a drug‐containing lipid(s) organic solution into an aqueous solution. Several parameters should be optimized in order to obtain a final suitable formulation, and this paper is devoted to such an investigation. Firstly, we study the liposome size distributions determined by dynamic light scattering (DLS), as function of the lipid concentration and composition, as well as the organic and aqueous phases content. This was carried out, firstly, by focusing on POPC (1‐palmitoyl‐2‐oleoyl‐sn‐glycero‐3‐phosphocholine) then on the novel L‐carnitine derivative PUCE (palmitoyl‐(R)‐carnitine undecyl ester chloride), showing that it is possible to obtain monomodal size distributions of rather small vesicles. In particular, depending on the conditions, it was possible to achieve a population of liposomes with a mean size of 100 nm, when a 50 mM POPC ethanol solution was injected in pure water; in the case of 50 mM PUCE the mean size was around 30 nm, when injected in saline (0.9% NaCl). The novel anticancer drug Gimatecan, a camptothecin derivative, was used as an example of lipophilic drug loading by the injection method. Conditions could be found, under which the resultant liposome size distributions were not affected by the presence of Gimatecan, in the case of POPC as well as in the case of PUCE. To increase the overall camptothecin concentration in the final liposomal dispersion, the novel technique of “multiple injection method” was used, and up to a final 5 times larger amount of liposomal drug could be reached by maintaining approximately the same size distribution. Once prepared, the physical and chemical stability of the liposome formulations was satisfactory within 24, as judged by DLS analysis and HPLC quantitation of lipids and drug. The Gimatecan‐containing liposomes formulations were also tested for in vitro and in vivo activity, against the human nonsmall cell lung carcinoma NCI‐H460 and a murine Lewis lung carcinoma 3 LL cell lines. In the in vitro tests, we did not observe any improvement or reduction of the Gimatecan pharmacological effect by the liposomal delivery system. More interestingly, in the in vivo Lewis lung carcinoma model, the intravenously administration of liposomal Gimatecan formulation showed a mild but significant increase of Tumor Volume Inhibition with respect to the oral no‐liposomal formulation (92% vs. 86 %, respectively; p < 0.05). Finally, our study showed that the liposomal formulation was able to realize a delivery system of a water‐insoluble drug, providing a Gimatecan formulation for intravenous administration with a preserved antitumoral activity.     

Association of vasoactive intestinal peptide with polymer-grafted liposomes: structural aspects for pulmonary delivery

A polymer-grafted liposomal formulation that has the potential to be developed for aerosolic pulmonary delivery of vasoactive intestinal peptide (VIP), a potent vasodilatory neuropeptide, is described. As VIP is prone to rapid proteolytic degradation in the microenvironment of the lung a proper delivery system is required to increase the half-life and bioavailability of the peptide. Here we investigate structural parameters of unilamellar liposomes composed of palmitoyl-oleoyl-phosphatidylcholine, lyso-stearyl-phosphatidylglycerol and distearyl-phosphatidyl-ethanolamine covalently linked to polyethylene glycol 2000, and report on VIP-lipid interaction mechanisms. We found that the cationic VIP is efficiently entrapped by the negatively charged spherical liposomes and becomes converted to an amphipathic alpha-helix. By fluorescence spectroscopy using single Trp-modified VIP we could show that VIP is closely associated to the membrane. Our data suggest that the N-terminal random-coiled domain is embedded in the interfacial headgroup region of the phospholipid bilayer. By doing so, neither the bilayer thickness of the lipid membrane nor the mobility of the phospholipid acyl chains are affected as shown by small angle X-ray scattering and electron spin resonance spectroscopy. Finally, in an ex vivo lung arterial model system we found that liposomal-associated VIP is recognized by its receptors to induce vasodilatory effects with comparable high relaxation efficiency as free VIP but with a significantly retarded dilatation kinetics. In conclusion, we have designed and characterized a liposomal formulation that is qualified to entrap biologically active VIP and displays structural features to be considered for delivery of VIP to the lung.