The Liposomal Formulation of Doxorubicin

Controlled release mechanisms of spontaneously forming unilamellar vesicles

Spontaneously forming small unilamellar vesicles (SULVs) are easy to prepare and show great promise for use in delivering therapeutic payloads. We report of SULVs made up of the ternary phospholipid mixture, dimyristoyl-phosphatidylcholine (DMPC), dihexanoyl-phosphatidylcholine (DHPC) and dimyristoyl-phosphatidylglycerol (DMPG), which have been characterized by small angle neutron scattering (SANS). These low-polydispersity (0.14-0.19) SULVs range in size (i.e., radius) from 110 to 215 A and are capable of entrapping, and subsequently releasing, hydrophilic molecules (e.g., fluorescent dyes and quenchers) in a controlled fashion over two different temperature ranges. The low-temperature release mechanism involves the SULVs transforming into discoidal micelles, with an onset temperature (T(o)) of ~32 degrees C, while the high-temperature release mechanism is more gradual, presumably the result of defects formed through the continuous dissolution of DHPC into solution. Both of these mechanisms differ from other, previously reported thermosensitive liposomes.

Preparation of uniform rich cholesterol unilamellar nanovesicles using CO2-expanded solvents

Nanoscopic and uniform unilamellar vesicles, rich in cholesterol, have been prepared by a new procedure, named "DELOS-SUSP", which is based on the depressurization of a cholesterol solution in CO2-expanded acetone into an aqueous solution containing a surfactant. The CO2 is used here as a cosolvent medium, allowing the straightforward preparation of vesicular systems with controlled size distribution, uniform shape, and stability unachievable by conventional mixing technologies. The resulting nanoscopic vesicular systems dispersed in water were characterized using dynamic light scattering, zeta potential, turbidity, and cryogenic transmission electron microscopy. The influence of operational parameters of this new methodology on the physicochemical characteristics of the vesicular systems is also reported.

Liposomal Nanomedicines: An Emerging Field

Liposomal nanoparticles (LNs) encapsulating therapeutic agents, or liposomal nanomedicines (LNMs), represent one of the most advanced classes of drug delivery systems, with several currently on the market and many more in clinical trials. During the past 20 years, a variety of techniques have been developed for encapsulating both conventional drugs and the new genetic drugs (plasmid DNA–containing therapeutic genes, anti-sense oligonucleotides, and small, interfering RNA [siRNA]) within LNs encompassing a very specific set of properties: a diameter centered on 100 nm, a high drug-to-lipid ratio, excellent retention of the encapsulated drug, and a long (> 6 hours) circulation lifetime. Particles with these properties tend to accumulate at sites of disease, such as tumors, where the endothelial layer is “leaky” and allows extravasation of particles with small diameters. Thus, LNs protect the drug during circulation, prevent it from reaching healthy tissues, and permit its accumulation at sites of disease. We will discuss recent advances in this field involving conventional anticancer drugs as well as gene-delivery, immunostimulatory, and gene-silencing applications involving the new genetic drugs. LNMs have the potential to offer new treatments in such areas as cancer therapy, vaccine development, and cholesterol management.

Multiple lipid compartments slow vesicle contents release in lipases and serum

Unilamellar vesicles or "liposomes" are commonly used as simple cell models and as drug delivery vehicles. A major limitation of unilamellar liposomes in these applications has been premature contents release in physiological environments. This premature release is likely due to enzyme degradation or protein insertion into the liposome membrane, which significantly increases the bilayer permeability. Encapsulating unilamellar liposomes within a second bilayer to form multicompartment "vesosomes" extends contents retention by 2 orders of magnitude by preventing enzymes and/or proteins from reaching the interior bilayers. The multicompartment structure of the vesosome can also allow for independent optimization of the interior compartments and exterior bilayer; however, just the bilayer-within-a-bilayer structure of the vesosome is sufficient to increase drug retention from minutes to hours. The vesosome is a better mimic of eukaryotic cell structure and demonstrates the benefits of multiple internal bilayer-enclosed compartments.

Surfactant vesicles for high-efficiency capture and separation of charged organic solutes

We demonstrate the unique ability of catanionic vesicles, formed by mixing single-tailed cationic and anionic surfactants, to capture ionic solutes with remarkable efficiency. In an initial study (Wang, X.; Danoff, E. J.; Sinkov, N. A.; Lee, J.-H.; Raghavan, S. R.; English, D. S. Langmuir 2006, 22, 6461) with vesicles formed from cetyl trimethylammonium tosylate (CTAT) and sodium dodecylbenzenesulfonate (SDBS), we showed that CTAT-rich (cationic) vesicles could capture the anionic solute carboxyfluorescein with high efficiency (22%) and that the solute was retained by the vesicles for very long times (t1/2 = 84 days). Here we expand on these findings by investigating the interactions of both anionic and cationic solutes, including the chemotherapeutic agent doxorubicin, with both CTAT-rich and SDBS-rich vesicles. The ability of these vesicles to capture and hold dyes is extremely efficient (>20%) when the excess charge of the vesicle bilayer is opposite that of the solute (i.e., for anionic solutes in CTAT-rich vesicles and for cationic solutes in SDBS-rich vesicles). This charge-dependent effect is strong enough to enable the use of vesicles to selectively capture and separate an oppositely charged solute from a mixture of solutes. Our results suggest that catanionic surfactant vesicles could be useful for a variety of separation and drug delivery applications because of their unique properties and long-term stability.

Use of nanoparticles for drug delivery in glioblastoma multiforme

Treatment of glioblastoma multiforme (GBM), a primary malignant tumor of the brain, is one of the most challenging problems as no currently available treatment is curative. Surgery remains the basic treatment in which the bulk of the tumor is removed and the peripheral infiltrating part is the target of supplementary treatments. The currently available anticancer therapeutics have less than optimal usefulness for GBM, mainly owing to delivery problems to the tumor, including those due to blood-brain barrier. Several new therapies in development for GBM will require innovative methods of delivery besides the current practice of direct introduction of drugs and devices into the tumor. Nanobiotechnology, particularly nanoparticles, is making a significant contribution to the improvement of drug delivery in cancer and many of these technologies can be applied to GBM. Nanobiotechnology can provide a platform for combination of diagnostics, therapeutics, and its delivery to the tumor with subsequent monitoring of response. These technologies are reviewed and the prospects of improvement of therapeutic delivery to the brain are excellent during the next 5 years. Curing of GBM, however, depends on discovery of an anticancer agent that will destroy GBM completely.

Interleukin-13 receptor-targeted nanovesicles are a potential therapy for glioblastoma multiforme

The difficulties associated with treatment of malignant brain tumors are well documented. For example, local infiltration of high-grade astrocytomas prevents the complete resection of all malignant cells. It is, therefore, critical to develop delivery systems for chemotherapeutic agents that ablate individual cancer cells without causing diffuse damage to surrounding brain tissue. Here, we describe sterically stable human interleukin-13 (IL-13)-conjugated liposomes, which efficiently bind to the brain cancer cells that overexpress the IL-13 receptor alpha2 protein. The conjugated liposomes bind to glioblastoma multiforme tissue specimens but not to normal cortex. Conjugating the liposomes with human IL-13 allows for specific binding to glioma cells and uptake of the liposomes via endocytosis. Delivering doxorubicin to glioma cells by IL-13-conjugated liposomes results in enhanced cytotoxicity and increased accumulation and retention of drug in the glioma cells compared with delivery of free drug. The therapeutic potential and targeting efficacy of the IL-13-conjugated liposomes carrying doxorubicin was tested in vivo using a s.c. glioma tumor mouse model. Animals receiving i.p. injections of IL-13-conjugated liposomes carrying doxorubicin for 7 weeks had a mean tumor volume of 37 mm3 compared with a mean volume of 192 mm3 in animals injected with nontargeted liposomes. These results strongly suggest that IL-13-conjugated liposomes carrying cytotoxic agents are a feasible approach for creating a nanovesicle drug delivery system for brain tumor therapy.

Injectable in situ forming drug delivery system for cancer chemotherapy using a novel tissue adhesive: Characterization and in vitro evaluation

Injectable polymers that are biocompatible and biodegradable are important biomaterials for drug delivery system (DDS) and tissue engineering. We have already developed novel tissue adhesives consisting of biomacromolecules and organic acid derivatives with active ester groups. The resulting tissue adhesive forms in situ as a gel and has high bonding strength for living tissue as well as it has good biocompatibility and biodegradability. Here, we report on the physicochemical properties and in vitro evaluation of this novel tissue adhesive consisting of human serum albumin (HSA) and tartaric acid derivative (TAD) containing doxorubicin hydrochloride (DOX). The results of the measurement of physicochemical characteristics indicate that the gelation time and gel strength of HSA-TAD gels can be controlled according to the material composition. The bonding strength of HSA-TAD adhesives was found to be sufficient to adhere at focus and to correspond with the cross-linking density of HSA-TAD gels. Furthermore, the release of DOX from HSA-TAD gels was sustained for approximately 100 h in an in vitro evaluation. The novel tissue adhesive, therefore, is expected to be applicable for use as an injectable in situ forming DDS.

Liposomal drug delivery

Liposomes are composed of phospholipids, the basic components of human cell walls. Liposome encapsulation improves a medication's bioavailability, which can extend treatment effects and reduce drug dosing. The therapeutic advantages of liposomal drug delivery, such as the ability of long-circulating liposomes to accumulate preferentially at disease sites, including tumors and sites of inflammation, are well recognized. In cases in which a single active has more than one liposome product available, formulation changes leading to differences in pharmacokinetics, toxicity, and clinical efficacy are described.

Adriamycin-induced myocardial toxicity: New solutions for an old problem?

Adriamycin is a potent and broad-spectrum antineoplastic agent that plays a major role in cancer chemotherapy. Unfortunately, its use has been hampered by conventional toxicities and cardiotoxicity manifested by congestive cardiomyopathy. Adriamycin is particularly toxic to heart tissue and constitutes a major cause of morbidity and mortality due to its complex pathogenesis. In this review, the different forms of cardiotoxicity produced by adriamycin as well as the biochemical changes induced by this drug are summarized. Secondly, the current hypotheses proposed to explain adriamycin-induced myocardial damage (the iron and free-radical hypothesis, the metabolic hypothesis, the "unifying hypothesis" and apoptosis) and the attempts to reduce adriamycin-induced myocardial toxicity are discussed (e.g. dose limitation, close cardiac monitoring, alteration of dosage schedules, development of new anthracycline analogs, and the administration of protective agents and liposomal encapsulation). Finally, we summarized our own experimental and clinical experience in ameliorating and or preventing adriamycin-induced cardiotoxicity and the latest attempts to prevent and/or monitor cardiac function. According to this, a combination of usual doses of calcium antagonist drugs plus vitamins A and E seems advisable.

Antitumor effect of an injectable in-situ forming drug delivery system composed of a novel tissue adhesive containing doxorubicin hydrochloride

Our group has developed a novel tissue adhesive composed of biomacromolecules and organic acid derivatives which have good biocompatibility and exhibit high bonding strength to living tissues. We propose to use this tissue adhesive for in-situ forming drug delivery system (DDS) for cancer chemotherapy. In a previous work, we had prepared a novel in-situ forming DDS composed of human serum albumin (HSA) and tartaric acid derivative (TAD) containing doxorubicin hydrochloride (DOX), and we had demonstrated an in vitro release profile of DOX from HSA-TAD gel for approximately up to 100h. Here, we report on antitumor effect of this injectable in-situ forming DDS. Local injection of DOX by the HSA-TAD was administered to human colon carcinoma (WiDr) implanted subcutaneously onto the immunodeficient mouse. The results of the in vivo experiments showed that the presence of DOX in blood of mice was detectable for up to 3days, and that the tumor volume was effectively minimized with injection of HSA-TAD containing DOX. The in-situ forming DDS with the novel tissue adhesive containing DOX, therefore, is a useful technique for cancer chemotherapy.

Novel therapeutic approaches in pediatric and young adult sarcomas

Novel therapy as part of sarcoma treatment schemas can enhance quality of life and is important in improving outcomes of high-risk sarcomas. Additional chemotherapy and biotherapy options to reduce tumor burden and prevent metastases include intra-arterial chemotherapy in osteosarcoma; intrapleural chemotherapy, aerosol 9-nitrocamptothecin, or protracted irinotecan and temozolomide in Ewing's sarcoma; continuous hyperthermic peritoneal perfusion for malignancy involving the peritoneum, such as desmoplastic small round cell tumor; and ifosfamide with muramyl tripeptide phosphatidyl ethanolamine liposomes in osteosarcoma. These treatments bring improved control of symptoms, including reduction in nausea, mucositis, cardiotoxicity, and central nervous system toxicity. Portable infusion devices have facilitated introduction of outpatient doxorubicin, ifosfamide, and methotrexate regimens and home-infusion irinotecan. Physical approaches to eliminate sarcoma tumors and metastases are critical for durable responses. Novel local control measures include embolization before surgery, radiosensitization, anti-vascular endothelial growth factor therapy during chemo-radiotherapy, proton therapy, samarium, thermal ablation (radiofrequency ablation), and cryoablation.

Cholesterol-rich membrane coatings for interaction studies in capillary electrophoresis: Application to red blood cell lipid extracts

The purpose was to develop a stable biological membrane coating for CE useful for membrane interaction studies. The effect of cholesterol (chol) on the stability of dipalmitoylphosphatidylcholine (DPPC) and sphingomyelin (SM) coatings was studied. In addition, a fused-silica capillary for CE was coated with human red blood cell (RBC) ghost lipids. Liposomes prepared of DPPC/SM with and without chol or RBC ghost lipids were flushed through the capillary and the stability of the coating was measured electrophoretically. Similar mixtures of DPPC/SM with and without chol were further studied by differential scanning calorimetry. The presence of phosphatidylcholine as a basic component in the coating solution of DPPC/SM/chol was found to be essential to achieve a good and stable coating. The results also confirmed the stability of coatings obtained with solutions of DPPC with 0-30 mol% of chol and SM in different ratios, which more closely resemble natural membranes. Finally, the electrophoretic measurements revealed that a stable coating is formed when capillaries are coated with liposomes of RBC ghost lipids.

Controlled release of bioactive doxorubicin from microspheres embedded within gelatin scaffolds

We have encapsulated the chemotherapeutic agent doxorubicin into biodegradable polymer microspheres, and incorporated these microspheres into gelatin scaffolds, resulting in a controlled delivery system. Doxorubicin was encapsulated in poly(D,L-lactide-co-glycolide) (PLGA) using a double emulsion/solvent extraction method. Characterization of the microspheres including diameter, surface morphology, and in vitro drug release was determined. The release of doxorubicin up to 30 days in phosphate buffered solution was assessed by measuring the absorbance of the releasate solution. Gelatin scaffolds were crosslinked using glutaraldehyde and microspheres were added to gelatin during gelation. The murine mammary mouse tumor cell line, 4T1, was treated with various doses of doxorubicin. A propidium iodide assay was utilized to visualize dead cells. Using a Transwell basket assay, PLGA microspheres and gelatin constructs were suspended above 4T1 cells for 48 h. Viable cells were determined using the CyQUANT cell proliferation assay. Results indicate that the release was controlled by the incorporation of PLGA microspheres into gelatin constructs. A significant difference was seen in the cumulative release over days 5-16 (p < 0.05). The bioactivity of doxorubicin released from the microspheres and scaffolds was maintained as proven by significant reduction in viable cells after treatment with PLGA microspheres as well as with the gelatin constructs (p < 0.001). The drug-polymer conjugate can be used as a controlled drug delivery system in a biocompatible scaffold that could potentially promote preservation of soft tissue contour.

Copper–topotecan complexation mediates drug accumulation into liposomes

These studies describe the role of transition metal ions in the liposomal encapsulation of topotecan. Liposomes (1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and cholesterol (CH) (55:45, mole ratio)) were prepared with manganese (Mn), copper (Cu), zinc (Zn) or cobalt (Co) ion gradients (metal inside). Subsequently, topotecan was added to the liposome exterior (final drug-to-lipid ratio (mol/mol) of 0.2) and drug encapsulation was measured as a function of time and temperature. No drug loading was achieved with liposomes containing Co or Zn. Topotecan could be encapsulated into Mn-containing liposomes only in the presence of the ionophore, A23187 suggesting that a transmembrane pH gradient was necessary. However, Cu-containing liposomes, in the presence or absence of an imposed pH gradient, efficiently encapsulated topotecan. It has been reported that Cu(II) can form transition metal complexes with camptothecin; therefore, the Cu-topotecan interaction was characterized in solution as a function of pH. These investigations demonstrated that topotecan inhibited formation of an insoluble Cu hydroxide precipitate. Cryo-TEM analysis of the topotecan-loaded Cu liposomes showed electron-dense intravesicular precipitates. Further studies demonstrated that only the active lactone form of the drug was encapsulated and this form predominated in Cu-containing liposomes. Copper complexation reactions define a viable methodology to prepare liposomal camptothecin formulations.

In vitro and in vivo characterization of nanoparticles made of MeO-PEG amine/PLA block copolymer and PLA

The preparative method of a block copolymer of poly(dl-lactic acid) (PLA) and methoxypolyethylene glycol amine (MeO-PEG(N)), named PLA-(MeO-PEG), was refined. The degree of introduction of MeO-PEG(N) into PLA increased up to 55% (mol/mol) using a dichloromethane/methanol mixture (1:1, v/v) as a solvent at the reductive amination and taking all the fractions of the first peak in gel-chromatography. Plain and 1,1'-Dioctadecyl-3,3,3',3'-tetramethylindodicarbocyanine (DiD)-loaded nanoparticles prepared using the PLA/PLA-(MeO-PEG) mixture of 45:55 (mol/mol) showed a mean size of 113 and 154 nm, respectively, and a positive zeta potential in water. DiD solution, i.v. administered, showed a lower plasma level and high distribution in liver, though DiD was distributed into the blood cells to a fair extent. Nanoparticles exhibited a higher plasma concentration of DiD than the DiD solution at 1 and 8h, though DiD was distributed into the liver and spleen to a fair extent. Nanoparticles made of the PLA/PLA-(MeO-PEG) mixture of 44:55 (mol/mol) showed better plasma retention than those made of the PLA/PLA-(MeO-PEG) mixture of 64:36 (mol/mol). It is suggested that the PLA/PLA-(MeO-PEG) mixture nanoparticles with a higher PEG/PLA ratio should be useful as a carrier for the elevation of the plasma concentration of lipophilic drugs.

Current strategies for the development of peptide-based anti-cancer therapeutics

The completion of the human genome sequence and the development of new techniques, which allow the visualisation of comprehensive gene expression patterns, has led to the identification of a large number of gene products differentially expressed in tumours and corresponding normal tissues. The task at hand is the sorting of these genes into correlative and causative ones. Correlative genes are merely changed as a consequence of transformation and have no decisive effects upon transformation. In contrast, causative genes play a direct role in the process of cellular transformation and the maintenance of the transformed state, which can be exploited for therapeutic purposes. Oncogenes and tumour suppressor genes are prime targets for the development of new inhibitors and gene therapeutic strategies. However, many target oncogene products do not exhibit enzymatic activity that can be inhibited by conventional small molecular weight compounds. They exert their functions through regulated protein-protein or protein-DNA interactions and might require other compounds for efficient interference with such functions. Peptides are emerging as a novel class of drugs for cancer therapy, which could fulfil these tasks. Peptide therapy aims at the specific inhibition of inappropriately activated oncogenes. This review will focus on the selection procedures, which can be employed to identify useful peptides for the treatment of cancer. Before peptide-based therapeutics can become useful, it will be necessary to increase their stability by modifications or the use of scaffolds. Additionally, various delivery methods including liposomes and particularly the use of protein transduction domains (PTDs) have to be explored. These strategies will yield highly specific and more effective peptides and improve the potential of peptide-based anti-cancer therapeutics.

Preparation and characterization of dehydration–rehydration vesicles loaded with aminoglycoside and macrolide antibiotics

Enhanced activity of liposomes-encapsulated antibiotics against clinical isolates of Pseudomonas aeruginosa has been documented with liposomes of low encapsulation efficiency. We sought to construct liposomes with high yield entrapment of aminoglycoside and macrolide antibiotics as well as favorable stability in storage and physiological conditions. Liposome-entrapped aminoglycosides (amikacin, gentamicin, tobramycin) and a macrolide (erythromycin) were prepared by a modified dehydration-rehydration vesicles (DRVs) method, and their particle size and entrapment efficiency were determined. We studied in vitro stability of these vesicles over a 48 h period at 4 and 37 degrees C in phosphate-buffered saline (PBS) and in plasma at 37 degrees C. The mean particle size of DRVs loaded with antibiotics varied from 163.37+/-38.44 to 259.83+/-11.80 nm with no significant difference in regard with the type of the antibiotics encapsulated. Encapsulation efficiency of DRVs loaded with amikacin, gentamicin, tobramycin, and erythromycin were 29.27+/-1.17, 33+/-0.76, 22.33+/-1.48 and 32.06+/-0.82% of initial amount of the drug, respectively. These vesicles were stable regardless of the experimental temperature. Indeed, the liposomes retained more than 75% of the initially encapsulated drugs for the study period of 48 h. DRVs incubated in plasma however, released more antibiotics than those incubated in PBS. In conclusion, using this modified DRV method, we obtained small sized vesicles with high yield entrapment for aminoglycoside and macrolide antibiotics. The technique may be utilized to overcome the low encapsulation efficiency associated with aminoglycoside and macrolide antibiotics.

Preferential extravasation and accumulation of liposomal vincristine in tumor comparing to normal tissue enhances antitumor activity

To quantitatively evaluate the extravasation, accumulation and selectivity to tumor tissues of liposomal vincristine (LV), dorsal skin-fold window chambers on athymic mice with or without LX-1, a human small cell lung cancer, xenograft implants and fluorescent intravital microscopy imaging were used. In vitro studies show that minimal loss of fluorescence marker DiI from liposomes occurs after 4 days of inoculation in murine plasma, and the release profiles of DiI-LV and LV were essentially the same with approximately 40% of the encapsulated vincristine sulfate (VCR) released after 26 h. Significantly faster extravasation of DiI-LV from tumor vessels was shown compared to non-tumor tissue after single dose i.v. administration. The relative interstitial amounts at 60 min (RIA(60)) for tumor and non-tumor tissues were 0.837+/-0.314 and 0.012+/-0.091, respectively (P=0.01). DiI-LV accumulation was significantly higher in tumor than in normal tissue, which continued beyond 48 h. Both DiI-LV and LV showed significant antitumor effects in window chambers and in flank tumors, compared with controls and VLS alone. The preferential extravasation of DiI-LV from tumor vasculature as well as its differential retention in tumor tissue provides the basis for the enhancement in antitumor activity of LV over VCR.

Liposomalization of SN-38 as active metabolite of CPT-11

Although many drugs have been developed for the treatment of disease, some drugs have complications such as adverse effects, and antitumor agents should target tumors or cells more selectively. It is therefore necessary to develop drug delivery systems, and liposomes are reportedly useful as an effective drug carrier. An antitumor agent, CPT-11, inhibits DNA synthesis by the inhibition of topoisomerase1 and has a strong antitumor activity. SN-38 is converted from CPT-11 as an active metabolite by carboxylesterase in the liver. As SN-38 is insoluble, it has not been applied at the clinical stage as an injection. It is expected that SN-38 liposomalization may increase its usefulness in cancer chemotherapy. Our purpose is to have a clinical application of SN-38 by a novel method of liposomalization to expand the application for the other insolubility drugs. As SN-38 is hydrophobic, SN-38-trapped liposome preparation was attempted using the Bangham method, which is effective for general preparation. However, a high ratio of SN-38 trapped in liposome was not achieved, and this was not improved by the freezing-thawing method or the freeze-drying method. On the other hand, the ratio of SN-38 trapped in liposome by the modified remote loading method was about 4 times that by the Bangham method, and the ratio by the film loading method, novel method of liposomal preparation, reached 2 times and 8 times that by the modified remote loading method and Bangham method, respectively, showing a remarkable increase. In conclusion, it was suggested that the preparation of SN-38 liposome using the film loading method effectively entraps SN-38. Thus, it is expected that SN-38 liposome can be applied as an injection. This preparation method is useful if application is possible in the other insolubility drugs.