Liposomes as carriers of cancer chemotherapy. Current status and future prospects

Encapsulation for Cancer Therapy

The current rapid advancement of numerous nanotechnology tools is being employed in treatment of many terminal diseases such as cancer. Nanocapsules (NCs) containing an anti-cancer drug offer a very promising alternative to conventional treatments, mostly due to their targeted delivery and precise action, and thereby they can be used in distinct applications: as biosensors or in medical imaging, allowing for cancer detection as well as agents/carriers in targeted drug delivery. The possibility of using different systems-inorganic nanoparticles, dendrimers, proteins, polymeric micelles, liposomes, carbon nanotubes (CNTs), quantum dots (QDs), biopolymeric nanoparticles and their combinations-offers multiple benefits to early cancer detection as well as controlled drug delivery to specific locations. This review focused on the key and recent progress in the encapsulation of anticancer drugs that include methods of preparation, drug loading and drug release mechanism on the presented nanosystems. Furthermore, the future directions in applications of various nanoparticles are highlighted.

Technology overview and drug delivery application of proniosome

Rapid advancement in the field of colloidal science has shown a great progress in the development of proniosome technology (PT) as an impending drug delivery system. PT is a valuable carrier system for delivery of hydrophobic as well as hydrophilic drugs. It is a liquid crystalline compact niosomal hybrid, which upon hydration gives niosomes. They can augment the bioavailability of encapsulated drug and provide better therapeutic activity in a controlled manner. Non-toxicity, penetration enhancing the effect of surfactant and modified drug release from the proniosomal transdermal gel has attracted a greater attention of formulation scientist toward PT. Free flowing dry proniosomal powder are suitable for unit dosage forms such as tablet and capsules. Proniosomes are auspicious drug delivery system for the future. Proniosomes-derived niosomes are a better alternative to the other vesicular system due to their superior physicochemical stability and effective drug delivery capability. The focus of this review is to bring out all the aspects of proniosomes including their different compositions, various methods of preparation, characterization and recent development in their therapeutic applications.

Topical delivery of aceclofenac: challenges and promises of novel drug delivery systems

Osteoarthritis (OA), a common musculoskeletal disorder, is projected to affect about 60 million people of total world population by 2020. The associated pain and disability impair the quality of life and also pose economic burden to the patient. Nonsteroidal anti-inflammatory drugs (NSAIDs) are widely prescribed in OA, while diclofenac is the most prescribed one. Oral NSAIDs are not very patient friendly, as they cause various gastrointestinal adverse effects like bleeding, ulceration, and perforation. To enhance the tolerability of diclofenac and decrease the common side effects, aceclofenac (ACE) was developed by its chemical modification. As expected, ACE is more well-tolerated than diclofenac and possesses superior efficacy but is not completely devoid of the NSAID-tagged side effects. A series of chemical modifications of already planned drug is unjustified as it consumes quanta of time, efforts, and money, and this approach will also pose stringent regulatory challenges. Therefore, it is justified to deliver ACE employing tools of drug delivery and nanotechnology to refine its safety profile. The present review highlights the constraints related to the topical delivery of ACE and the various attempts made so far for the safe and effective topical delivery employing the novel materials and methods.

Inflammatory angiogenesis and the tumor microenvironment as targets for cancer therapy and prevention

In addition to aberrant transformed cells, tumors are tissues that contain host components, including stromal cells, vascular cells (ECs) and their precursors, and immune cells. All these constituents interact with each other at the cellular and molecular levels, resulting in the production of an intricate and heterogeneous complex of cells and matrix defined as the tumor microenvironment. Several pathways involved in these interactions have been investigated both in pathological and physiological scenarios, and diverse molecules are currently targets of chemotherapeutic and preventive drugs. Many phytochemicals and their derivatives show the ability to inhibit tumor progression, angiogenesis, and metastasis, exerting effects on the tumor microenvironment. In this review, we will outline the principal players and mechanisms involved in the tumor microenvironment network and we will discuss some interesting compounds aimed at interrupting these interactions and blocking tumor insurgence and progression. The considerations provided will be crucial for the design of new preventive approaches to the reduction in cancer risk that need to be applied to large populations composed of apparently healthy individuals.

Flash nanoprecipitation: particle structure and stability

Flash nanoprecipitation (FNP) is a process that, through rapid mixing, stabilizes an insoluble low molecular weight compound in a nanosized, polymer-stabilized delivery vehicle. The polymeric components are typically amphiphilic diblock copolymers (BCPs). In order to fully exploit the potential of FNP, factors affecting particle structure, size, and stability must be understood. Here we show that polymer type, hydrophobicity and crystallinity of the small molecule, and small molecule loading levels all affect particle size and stability. Of the four block copolymers (BCP) that we have studied here, poly(ethylene glycol)-b-poly(lactic-co-glycolic acid) (PEG-b-PLGA) was most suitable for potential drug delivery applications due to its ability to give rise to stable nanoparticles, its biocompatibility, and its degradability. We found little difference in particle size when using PLGA block sizes over the range of 5 to 15 kDa. The choice of hydrophobic small molecule was important, as molecules with a calculated water-octanol partition coefficient (clogP) below 6 gave rise to particles that were unstable and underwent rapid Ostwald ripening. Studies probing the internal structure of nanoparticles were also performed. Analysis of differential scanning calorimetry (DSC), cryogenic transmission electron microscopy (cryo-TEM), and (1)H NMR experiments support a three-layer core-shell-corona nanoparticle structure.

Preparation, characterization, and assessment of the antiglioma effects of liposomal celastrol

The role of celastrol in the treatment of cancer has been an area of growing interest. To circumvent the issues of low solubility, poor bioavailability, and systemic toxicity of celastrol, we prepared liposomal celastrol using the thin-film dispersion method. We characterized particle size, encapsulation efficiency, and pharmacological parameters of liposomal celastrol. The drug concentration in plasma and tissues was measured using LC-MS/MS. In addition, the sulforhodamine B assay was used to determine the 50% inhibiting concentration. We assessed the effects of the compound in SHG-44 glioma subcutaneous xenografts in BALB/c nude mice. To compare the toxic effects of liposomal and free celastrol, the weight as well as hematologic, heart, liver, and kidney parameters were measured weekly and the morphology of organ tissues was observed pathologically. We found that liposomal celastrol had high encapsulation efficiency (71.67%) and liposomal celastrol had a higher C(max) and area under the curve, longer t(1/2), and better biodistribution than free celastrol. A cytotoxicity assay indicated that free celastrol had lower 50% inhibiting concentration values than the liposomal celastrol; however, treatment of subcutaneous xenografts with 1 mg/kg of liposomal celastrol induced greater antitumor activity than free celastrol at an equimolar concentration. In addition, a 4 mg/kg dose of liposomal celastrol had fewer severe side effects than free celastrol at the same dose. In this study, we found that the use of liposomes as a carrier of celastrol increased the bioavailability and reduced the side effects of the compound. Our findings suggest that liposomal celastrol should be further investigated in the clinical setting.

Phosphatidylinositol induces fluid phase formation and packing defects in phosphatidylcholine model membranes

Liposomes consisted of phosphatidylinositol (PI) and phosphatidylcholine (PC) have been utilized as delivery vehicle for drugs and proteins. In the present work, we studied the effect of soy PI on physical properties of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes such as phase state of lipid bilayer, lipid packing and phase properties using multiple orthogonal biophysical techniques. The 6-dodecanoyl-2-dimethylamino naphthalene (Laurdan) fluorescence studies showed that presence of PI induces the formation of fluid phases in DMPC. Differential scanning calorimetry (DSC), temperature dependent fluorescence anisotropy measurements, and generalized polarization values for Laurdan showed that the presence of as low as 10mol% of PI induces substantial broadening and shift to lower temperature of phase transition of DMPC. The fluorescence emission intensity of DPH labeled, PI containing DMPC lipid bilayer decreased possibly due to deeper penetration of water molecules in lipid bilayer. In order to further delineate the effect of PI on the physico chemical properties of DMPC is due to either significant hydrophobic mismatch between the acyl chains of the DMPC and that of soy PI or due to the inositol head group, we systematically replaced soy PI with PC species of similar acyl chain composition (DPPC and 18:2 (Cis) PC) or with diacylglycerol (DAG), respectively. The anisotropy of PC membrane containing soy PI showed largest fluidity change compared to other compositions. The data suggests that addition of PI alters structure and dynamics of DMPC bilayer in that it promotes deeper water penetration in the bilayer, induces fluid phase characteristics and causes lipid packing defects that involve its inositol head group.

Novel sugar esters proniosomes for transdermal delivery of vinpocetine: preclinical and clinical studies

Vinpocetine (Vin) existing oral formulations suffer poor bioavailability (∼7%) since Vin undergoes a marked first-pass effect (∼75%) and its absorption is dissolution rate-limited. In this study, a novel sustained release proniosomal system was designed using sugar esters (SEs) as non-ionic surfactants in which proniosomes were converted to niosomes upon skin water hydration following topical application under occlusive conditions. Different in vitro aspects (encapsulation efficiency, vesicle size and shape, effect of occlusion, in vitro release, skin permeation and stability) were studied leading to an optimized formula that was assessed clinically for transdermal pharmacokinetics and skin irritation. All formulae exhibited high entrapment efficiencies, regardless of the surfactant HLB. Vesicle size analysis showed that all vesicles were in the range from 0.63 μm to 2.52 μm which favored efficient transdermal delivery. The extent of drug permeation through the skin from the optimized formula--containing laurate SE with shorter fatty acid chain length and high HLB--was quite high (91%) after 48 h under occlusive conditions. The extent of absorption of Vin from proniosomes was larger when compared to the oral tablet with a relative bioavailability (F(rel)) of 206%. Histopathological evaluation revealed only moderate skin irritation when using SEs compared to skin inflammation when using Tween 80. Sugar esters proniosomes may be a promising carrier for vinpocetine, especially due to their simple scaling up and their ability to control drug release.

Lipid microspheres loaded with antigenic membrane proteins of the Leishmania amazonensis as a potential biotechnology application

Lipid microspheres (LM) are excellent drug delivery or vaccines adjuvant systems and are relatively stable. The aim of this work is to develop and characterize a system that is able to encapsulate and present antigenic membrane proteins from Leishmania amazonensis. Membrane proteins are important for vaccine's formulation because these proteins come in contact with the host cell first, triggering the cell mediated immune response. This is a useful tool to avoid or inactivate the parasite invasion. The LM are constituted by soybean oil (SO), dipalmitoylphosphatidilcholine (DPPC), cholesterol and solubilized protein extract (SPE). The particles formed presented an average diameter of 200 nm, low polydispersion and good stability for a period of 30 days, according to dynamic light scattering assays. Isopycnic density gradient centrifugation of LM-protein showed that proteins and lipids floated in the sucrose gradient (5-50%w/v) suggesting that the LM-protein preparation was homogeneous and that the proteins are interacting with the system. The results show that 85% of SPE proteins were encapsulated in the LM. Studies of cellular viability of murine peritoneal macrophages show that our system does not present cytotoxic effect for the macrophages and still stimulates their NO production (which makes its application as a vaccine adjuvant possible). LM-protein loaded with antigenic membrane proteins from L. amazonensis seems to be a promising vaccine system for immunization against leishmaniasis.

Magnetic nanoparticle temperature estimation

The authors present a method of measuring the temperature of magnetic nanoparticles that can be adapted to provide in vivo temperature maps. Many of the minimally invasive therapies that promise to reduce health care costs and improve patient outcomes heat tissue to very specific temperatures to be effective. Measurements are required because physiological cooling, primarily blood flow, makes the temperature difficult to predict a priori. The ratio of the fifth and third harmonics of the magnetization generated by magnetic nanoparticles in a sinusoidal field is used to generate a calibration curve and to subsequently estimate the temperature. The calibration curve is obtained by varying the amplitude of the sinusoidal field. The temperature can then be estimated from any subsequent measurement of the ratio. The accuracy was 0.3 degree K between 20 and 50 degrees C using the current apparatus and half-second measurements. The method is independent of nanoparticle concentration and nanoparticle size distribution.

The use of immunoliposome for nutrient target regulation (a review)

Although research on the role of genetically engineered antibodies and liposomes in the immunology or the nutrition field is extensive, there is no case for immunoliposome to nutrient target regulation. It is known that liposomes are spherical particles that encapsulate a fraction of the solvent, in which they freely diffuse (float) into their interior. Therefore, identification of immunoliposomes in hypothalamic site or intestinal epithelial cells that are differentially regulated by liposomes encapsulating nutrients or drugs will be an important step toward understanding the role of immunoliposomes in nutrition regulation progression and ingredient stability. Consequently, a useful model (immunoliposomal nutrient delivery system, ILNDS) of nutrient target regulation via immunoliposomes is designed to regulate the endocrine system effectively. This review focuses on antibody libraries' construction, display and selection, a brief introduction of immunoliposome, and how to use ILNDS for nutrient target regulation.

A strategy for efficient cross-presentation of CTL-epitope peptides leading to enhanced induction of in vivo tumor immunity

The activation of antitumor cytotoxic T-lymphocytes (CTLs) depends on how efficiently the relevant tumor antigen peptides are delivered into the major histocompatibility complex (MHC) class I presentation pathway in antigen presenting cells (APCs). An elegant approach to promote the peptide-MHC class I association has been described for enhanced peptide transportation into the endoplasmic reticulum (ER) by adding an ER insertion signal sequence (Eriss). Nevertheless, this approach does not appear potent enough to induce in vivo tumor protective immunity. Herein, we present a novel peptide-vaccine strategy based on the combined utilization of Eriss and fusogenic liposomes (FLs) capable of directly introducing encapsulated CTL-epitope peptides into the MHC class I pathway of APCs. APCs pulsed with free peptides, FL-encapsulated peptides, or FL-encapsulated Eriss-conjugated peptides exhibited comparable levels of antigen-presenting activity at early phases after pulsing. Interestingly, whereas in the first two methods the APC ability began to decline 40 to 60 h after pulsing, FL-encapsulated Eriss(+) peptides allowed APCs to retain peptide-presentation activity for at least 140 h. This advantage of FL-encapsulated Eriss(+) peptides correlated with the induction of more potent antitumor immunity compared with soluble Eriss(+) or Eriss(-) peptides or FL-encapsulated Eriss(-) peptides when they were administered in vivo. Thus, Eriss-conjugated CTL-epitope peptides encapsulated in FLs provide a highly efficient tumor-vaccine to enhance the induction of in vivo tumor immunity.

MRI thermometry based on PARACEST agents

A novel magnetic resonance imaging (MRI) thermometry technique is demonstrated in vitro based upon the use of a PARACEST (PARAmagnetic Chemical Exchange Saturation Transfer) agent. This new method takes advantage of the high concentration of bulk water (the readout signal for imaging) and the hyperfine frequency shift properties of PARACEST agents. For two prototypes, Dy(1)3+ and Eu(2)-, the chemical shifts (delta, in ppm) of the Ln3+-bound water molecules are linearly dependent on temperature (T, in degrees C) over the range of 20-50 degrees C (delta = 6.9 x T - 944.7 and delta = -0.4 x T + 64.6, respectively). This offers the exciting possibility of improving the temperature dependencies approximately 690- and approximately 40-fold over the most widely used water PRF thermometry (Proton Resonance Frequency: -0.01 ppm/ degrees C).

Assessment of a liposomal formulation of ivermectin in rabbit after a single subcutaneous administration

Ivermectin is a member of the macrocyclic lactone family widely used in livestock, pets, and humans as a potent parasiticide. Slight differences in formulation may change the plasma kinetics and efficacy of these compounds. The aim of the study is to evaluate the ability of a liposomal formulation of ivermectin to generate an efficient exposure of the animal to the drug. Ten rabbits were subcutaneously administered with 0.3 mg kg(-1) of ivermectin using Ivomec (n=5) or a liposomal formulation (n=5). The areas under serum concentration-time curve were similar after both treatments, indicating the same bioavailability for the two formulations. However, the liposomal formulation gave a higher C(max) value (33.33 ng ml(-1)) compared with Ivomec (20.82 ng ml(-1)) and a significantly faster absorption as indicated by the T(max) of 0.23 days compared with 1.13 days for the Ivomec formulation. The use of liposomal formulation shows promise as this system improves the efficacy of ivermectin and related drugs.

Polyethylene Glycol (PEG) Modified 99mTc-HMPAOLiposome for Improving Blood Circulation and Biodistribution: The Effect of the Extent of PEGylation

Modification of liposomes using polyethylene glycol (PEG) results in steric hindrance to the phagocyte system and prolongation of blood circulation time. However, PEGylation can reduce radiolabeling efficiency (RE) when using the glutathione method for radiolabeling the liposomes. Therefore, we investigated the effect of the extent of PEGylation (PEG extent (PEGExt): 0, 5, 9.6, and 13.7 mol%) on the in vivo biodistribution of liposomes in Wistar rats, and RE with technetium-(99m) ((99m)Tc). PEGylated liposomes were prepared with egg phosphatidylcholine (egg PC, 1.85 mol%), cholesterol (1.0 mol%), and distearoylphosphatidylethanolamine-N-[polyethylene glycol] (DSPE-PEG; 0, 5, 9.6, and 13.7 mol%, respectively). The size distribution of the PEGylated liposomes was analyzed by a dynamic light scattering. The (99m)Tc-hexamethylpropylene-amine oxime ((99m)Tc-HMPAO) complexes were used for radiolabeling of preformed liposomes. The labeling efficiency and stability was analyzed with Sephadex G-15 column, and the biodistribution studies of (99m)Tc-liposomes after intravenous (i.v.) injection were also investigated with Wistar rats. The sizes of PEGylated liposomes decreased by increasing the PEGExt to 9.6 mol%, whereas sizes increased at 13.7 mol%. RE of (99m)Tc were greater than 90% for all PEGExt tested, and radiolabeling stability in human plasma was enhanced as a function of PEGExt. Liposomes without PEG were cleared rapidly from the blood and accumulated preferentially in the liver and the spleen. When PEGExt was increased, the accumulation in the organs decreased. This accumulation of PEG was maximized at 9.6 mol%. Accumulation of the liposomes in the spleen was increased again when PEGExt increased to 13.7 mol%. The splenic uptake of liposomes seemed to be dependent not only on PEGExt but also on the size of the liposomes. In conclusion, the PEG chains on the surface of liposome have no influence on the labeling efficiency, and the prolongation of circulation time was maximized at the 9.6 mol% of PEGylation.

Anti-hepatocarcinoma effects of 5-fluorouracil encapsulated by galactosylceramide liposomes in vivo and in vitro

AIM: To study the anti-hepatocarcinoma effects of 5-fluorouracil (5-Fu) encapsulated by galactosylceramide liposomes (5-Fu-GCL) in vivo and in vitro.

METHODS: Tumor-bearing animal model and HepA cell line were respectively adopted to evaluate the anti-tumor effects of 5-Fu-GCL in vivo and in vitro. Tumor cell growth inhibition effects of 5-Fu-GCL in vitro were assessed by cell viability assay and MTT assay. In vivo experiment, the inhibitory effects on tumor growth were evaluated by tumor inhibition rate and animal survival days. High performance liquid chromatography was used to detect the concentration-time course of 5-Fu-GCL in intracellular fluid in vitro and the distribution of 5-Fu-GCL in liver tumor tissues in vivo. Apoptosis and cell cycle of tumor cells were demonstrated by flow cytometry.

RESULTS: In vitro experiment, 5-Fu-GCL (6.25-100 μmol/L) and free 5-Fu significantly inhibited HepA cell growth. Furthermore, IC₅₀ of 5-Fu-GCL (34.5 μmol/L) was lower than that of free 5-Fu (51.2 μmol/L). In vivo experiment, 5-Fu-GCL (20, 40, 80 mg/kg) significantly suppressed the tumor growth in HepA bearing mice model. Compared with free 5-Fu, the area under curve of 5-Fu-GCL in intracellular fluid increased 2.6 times. Similarly, the distribution of 5-Fu-GCL in liver tumor tissues was significantly higher than that of free 5-Fu. After being treated with 5-Fu-GCL, the apoptotic rate and the proportion of HepA cells in the S phase increased, while the proportion in the G0/G1 and G2/M phases decreased.

CONCLUSION: 5-Fu-GCL appears to have anti-hepato-carcinoma effects and its drug action is better than free 5-Fu. Its mechanism is partly related to increased drug concentrations in intracellular fluid and liver tumor tissues, enhanced tumor cell apoptotic rate and arrest of cell cycle in S phase.

Proniosomes as a drug carrier for transdermal delivery of ketorolac

Niosomes are nonionic surfactant vesicles that have potential applications in the delivery of hydrophobic and hydrophilic drugs. Permeation of a potent nonsteroidal anti-inflammatory, ketorolac, across excised rabbit skin from various proniosome gel formulations was investigated using Franz diffusion cells. Each of the prepared proniosomes significantly improved drug permeation and reduced the lag time (P<0.05). Proniosomes prepared with Span 60 provided a higher ketorolac flux across the skin than did those prepared with Tween 20 (7- and 4-fold the control, respectively). A change in the cholesterol content did not affect the efficiency of the proniosomes, and the reduction in the lecithin content did not significantly decrease the flux (P>0.05). The encapsulation efficiency and size of niosomal vesicles formed by proniosome hydration were also characterized by specific high performance liquid chromatography method and scanning electron microscopy. Each of the prepared niosomes achieved about 99% drug encapsulation. Vesicle size was markedly dependent on the composition of the proniosomal formulations. Proniosomes may be a promising carrier for ketorolac and other drugs, especially due to their simple production and facile up.

Distal cationic poly(ethylene glycol) lipid conjugates in large unilamellar vesicles prepared by extrusion enhance liposomal cellular uptake

Cationic poly(ethylene glycol)-lipid conjugates (CPLs), a class of lipid designed to enhance the interaction of liposomes with cells, possess the following architectural features: 1) a hydrophobic lipid anchor of distearoylphosphatidylethanolamine (DSPE); 2) a hydrophilic spacer of poly(ethylene glycol); and 3) a cationic head group prepared with 0, 1, 3, or 7 lysine residues located at the distal end of the PEG chain, giving rise to CPL possessing 1, 2, 4, or 8 positive charges, respectively (CPL1 to CPL8). Previously we have described the synthesis of CPL, have characterized the postinsertion of CPL into PEG-containing LUVs and SPLP (stabilized plasmid-lipid particles), have shown significant increases in the binding of CPL-LUV to cells, and have observed dramatically enhanced transfection (up to a million-fold) of cells with CPL-SPLP in the presence of calcium [Chen et al. (2000) Bioconjugate Chem. 11, 433-437; Fenske et al. (2001) Biochim. Biophys. Acta 1512, 259-272; Palmer et al. (2003) Biochim. Biophys. Acta 1611, 204-216]. In the present study, we examine a variety of CPL properties (such as polarity and CMC) and characterize CPL-vesicular systems formed by extrusion and examine their interaction with cells. While CPL polarity was observed to increase dramatically with increasing charge number, CMC values were all found to be low, in the range of other PEGylated lipids, and exhibited only a small increase, going from CPL1 (1.3 microM) to CPL8 (2 microM). The CPLs were almost quantitatively incorporated into large unilamellar vesicles (LUVs) prepared by the extrusion method and were evenly distributed across the lipid bilayer. Lower levels of incorporation were obtained when CPLs were incubated with preformed liposomes (DSPC/Chol, 55:45) at 60 degrees C. The binding of CPL-LUVs to BHK cells in vitro was found to be dependent on the distal charge density of the CPL rather than total surface charge. Liposomes possessing CPL4 or CPL8 were observed to bind efficiently to cell surfaces and enhance cellular uptake in BHK cells (as observed with both lipid and aqueous content markers), whereas those possessing CPL1 or CPL2 exhibited little or no binding. These results suggest new directions for the design of liposomal systems capable of in vivo delivery of both conventional and genetic (plasmid and antisense) drugs.

Temperature mapping of laser-induced hyperthermia in an ocular phantom using magnetic resonance thermography

Laser-induced heating in an ocular phantom is measured with magnetic resonance thermography (MRT) using temperature-dependent phase changes in proton resonance frequency. The ocular phantom contains a layer of melanosomes isolated from bovine retinal pigment epithelium. The phantom is heated by the 806-nm output of a continuous wave diode laser with an irradiance of 2.4 to 21.6 W/cm2 in a beam radius of 0.8 or 2.4 mm, depending on the experiment. MRT is performed with a 2 T magnet, and a two-turn, 6-cm-diam, circular radio frequency coil. Two-dimensional temperature gradients are measured within the plane of the melanin layer, as well as normal to it, with a temperature resolution of 1 degrees C or better. The temperature gradients extending within the melanin layer are broader than those orthogonal to the layer, consistent with the higher optical absorption and consequent heating in the melanin. The temperature gradients in the phantom measured by MRT closely approximate the predictions of a classical heat diffusion model. Three-dimensional temperature maps with a spatial resolution of 0.25 mm in all directions are also made. Although the temporal resolution is limited in the prototype system (22.9 s for a single image "slice"), improvements in future implementations are likely. These results indicate that MRT has sufficient spatial and temperature resolution to monitor target tissue temperature during transpupillary thermotherapy in the human eye.

A randomized trial of liposomal daunorubicin and cytarabine versus liposomal daunorubicin and topotecan with or without thalidomide as initial therapy for patients with poor prognosis acute myelogenous leukemia or myelodysplastic syndrome

BACKGROUND

Because angiogenesis may play a role in the pathogenesis of acute myeloid leukemia (AML) and high-risk myelodysplastic syndrome (MDS), and thalidomide (Th) has shown significant anti-angiogenic activity, this study was designed to investigate the potential role of Th in the treatment of patients with AML and MDS and the possible role of a non-ara-C-containing regimen.

METHODS

Adults with AML or high-risk MDS and cytogenetic abnormalities other than inv (16), t(8;21), -Y or -X were randomized to receive liposomal daunorubicin (DNX) and ara-C (DA) or DNX and topotecan (DT). Within each arm, patients were randomized to receive chemotherapy alone (DA or DT) or with thalidomide (DATh or DTTh). Vascular endothelial growth factor (VEGF) plasma levels and microvascular density was measured before and after therapy. Eighty-four patients (median age, 65 years; range, 27-84 years) were treated.

RESULTS

None of 11 patients treated with DT or DTTh responded and these arms were closed. Seventeen of 37 patients treated with DA and 15 of 36 treated with DATh achieved an early complete remission. Median complete response duration was 38 and 34 weeks (P = 0.57) and median survival 35 and 28 weeks (P = 0.15), respectively. Patients with high pretreatment VEGF levels had an inferior survival. There was no significant difference in the changes in VEGF levels or microvascular density after treatment in patients who did versus those who did not receive thalidomide.

CONCLUSIONS

The authors concluded that thalidomide in combination with chemotherapy does not result in clinical benefit in patients with AML or high-risk MDS.

Attaching histidine-tagged peptides and proteins to lipid-based carriers through use of metal-ion-chelating lipids

The therapeutic potential of selected peptides and proteins is enormous, with applications ranging from use as therapeutic vaccines, as modulators of intracellular signaling pathways and as highly selective agents capable of recognizing unique extracellular targets. We have been pursuing development of hybrid lipid-based carrier formulations designed to take advantage of the therapeutic benefits of peptides selected for their ability to act in a complementary fashion with the carrier system. In this regard, it is critical to have simple and versatile methods to promote and control the binding of diverse peptides to a broad range of carrier formulations. As demonstrated here, recombinant proteins and synthetic peptides containing poly-histidine residues (4 to 10) can be specifically bound to liposomes containing a metal-ion-chelating lipid, DOGS-NTA-Ni. The potential of this approach is demonstrated using two functional peptides, AntpHD-Cw3 (applications for vaccine production) and AHNP (specificity for Her-2 expressing cells).

Clinical pharmacokinetics of cytarabine formulations

Cytarabine (cytosine arabinoside, Ara-C) is an effective chemotherapeutic agent for the treatment of acute myelogenous leukaemia and lymphocytic leukaemias. As cytarabine is an S-phase-specific drug, prolonged exposure of cells to cytotoxic concentrations is critical to achieve maximum cytotoxic activity. However, the activity of cytarabine is decreased by its rapid deamination to the biologically inactive metabolite uracil arabinoside. This rapid deamination is the reason for the ongoing search for effective formulations and derivatives of cytarabine that cannot be deaminated and exhibit better pharmacokinetic parameters. Protection of cytarabine from fast degradation and elimination has been investigated by encapsulating the drug into pharmaceutically acceptable carriers. Cytarabine derivatives have shown promise in vitro and in animal models. For example, ancitabine (cyclocytidine), enocitabine and cytarabine ocfosfate have been used clinically in Japan. Cytarabine encapsulated into multivesicular liposomes has been approved in several countries for the intrathecal treatment of lymphomatous meningitis. Although many compounds have been investigated, few cytarabine derivatives are currently available for clinical use. Further research is needed to improve the efficacy of cytarabine against haematological and solid tumours.

Automatic control of hyperthermic therapy based on real-time Fourier analysis of MR temperature maps

Local hyperthermia is increasingly being used for therapeutic purposes, such as tumor ablation. Heat conduction and energy absorption in vivo during the hyperthermic procedure are largely unknown, thus making feedback temperature control highly desirable. Here, a general method for temperature control based on Fourier transformation (FT) of the bio-heat equation is presented, taking into account heat diffusion (D) and energy absorption (alpha) together with temperature distribution derived from rapid, continuous MR temperature mapping. The main advantages of the new method are: 1) the spatial distribution of heat deposition and conduction over the full region of interest (ROI) is taken into account, and 2) the high speed resulting from the use of fast FT (FFT) of temperature maps allows rapid feedback coupling. Initial tests based on MRI-guided focused ultrasound (FUS) demonstrated that high-quality temperature regulation can be obtained even for erroneous values of D and alpha, so long as their relative error remained in the same range. Performance of the automated control procedure was validated ex vivo and in vivo on rabbit thigh using moderate FUS heating. During the procedure, the standard deviation (SD) of the temperature remained in the range of temperature noise obtained by MRI, indicative of the performance of the regulation algorithm.

Host-vs.-altered-host eruptions in patients on liposomal doxorubicin

BACKGROUND

Anthracycline antitumor antibiotics are the most commonly used chemotherapeutic agents. One of these is doxorubicin. Liposomal doxorubicin was developed as a drug delivery system in order to deliver the active drug intracellularly while decreasing the systemic toxicity, particularly hematological and cardiac toxicity.

METHODS

The clinical and histologic findings of the cutaneous eruptions of associated with liposomal doxorubicin are reviewed.

RESULTS

The eruptions occurred in three women with metastatic ovarian carcinoma who were treated with liposomal doxorubicin. These three patients developed erythematous macular/papular to plaque cutaneous lesions, and in one patient a vesicular component. The eruptions involved the trunk and extremities approximately 3-4 weeks after completions of therapy. None of the patients had any documented infections, and none of the patients had symptoms other than pruritus. The eruptions cleared over a period of weeks to months. Histologic features included an interface dermatitis with numerous apoptotic/dyskeratotic cells within the epidermis, with involvement the intra-epidermal sweat ducts and the infundibulum of hair follicles.

CONCLUSION

We believe that these eruptions represented a chemotherapy induced host-vs.-altered host reaction.

Characterization of a novel pH-sensitive peptide that enhances drug release from folate-targeted liposomes at endosomal pHs

Although liposomes have proven useful for the delivery of drugs and gene therapy vectors, their potencies are often compromised by poor unloading following uptake into their target cells. We have consequently explored the properties of a novel 29-residue amphipathic peptide that was designed by arrangement of hydrophobic and hydrophilic residues to disrupt liposomes at lower peptide concentrations than previously tested peptides. The peptide was indeed found to promote pH-dependent liposome unloading with improved efficiency. A peptide of the same sequence, but half the length, however, promoted pH-dependent permeabilization only at much higher concentrations. Further characterization of the longer peptide revealed that release of liposome contents (i) occurred at a pH of approximately 6, (ii) became less efficient as the size of the encapsulated cargo increased, and (iii) was moderately suppressed in cholesterol-containing liposomes. Use of this peptide to enhance the cytotoxicity of cytosine arabinoside encapsulated in folate-targeted liposomes demonstrated an increase in drug potency of approximately 30-fold. Gene expression by a serum-stable folate-targeted liposomal vector was also measurably enhanced by inclusion of the peptide. We conclude that intracellular unloading of liposomal contents can be significantly improved by co-encapsulation of an optimally designed, pH-sensitive peptide.

Efficient delivery of Antennapedia homeodomain fused to CTL epitope with liposomes into dendritic cells results in the activation of CD8+ T cells

The in vivo induction of a CTL response using Antennapedia homeodomain (AntpHD) fused to a poorly immunogenic CTL epitope requires that the Ag is given in presence of SDS, an unacceptable adjuvant for human use. In the present report, we developed a hybrid CTL epitope delivery system consisting of AntpHD peptide vector formulated in liposomes as an alternative approach to bypass the need for SDS. It is proposed that liposomes will prevent degradation of the Ag in vivo and will deliver AntpHD recombinant peptide to the cytosol of APCs. We show in this work that dendritic cells incubated with AntpHD-fused peptide in liposomes can present MHC class I-restricted peptide and induce CTL response with a minimal amount of Ag. Intracellular processing studies have shown that encapsulated AntpHD recombinant peptide is endocytized before entering the cytosol, where it is processed by the proteasome complex. The processed liposomal peptides are then transported to the endoplasmic reticulum. The increase of the CTL response induced by AntpHD-fused peptide in liposomes correlates with this active transport to the class I-processing pathway. In vivo studies demonstrated that positively charged liposomes increase the immunogenicity of AntpHD-Cw3 when injected s.c. in mice in comparison to SDS. Moreover, addition of CpG oligodeoxynucleotide immunostimulatory sequences further increase the CD8+ T cell response. This strategy combining lipid-based carriers with AntpHD peptide to target poorly immunogenic Ags into the MHC class I processing pathway represents a novel approach for CTL vaccines that may have important applications for development of cancer vaccines.

Liposome-encapsulated tumor necrosis factor-alpha enhances the effects of radiation against human colon tumor xenografts

Recent reports have shown that tumor necrosis factor-alpha (TNF-alpha) can augment the effects of radiation against certain tumor types. However, the high concentrations of intravenous infusion of TNF-alpha needed to cause tumor regression can induce many systemic side effects. The aims of this study were to determine if TNF-alpha encapsulated in sterically stabilized (Stealth, ALZA Corporation, Mountain View, CA), PEGylated liposomes (SL) augments the antitumor effects of radiation and to compare its efficacy and possible toxicity with free TNF-alpha in the LS174T human colon tumor xenograft model. Nude mice were injected subcutaneously (s.c.) with LS174T cells and treated intravenously (i.v.) with Stealth-liposomal TNF-alpha (SL-TNF-alpha) with and without radiation or TNF-alpha with or without radiation when tumor size was approximately 200 mm(3). In phase 1, a significant decrease (p = 0.047) in tumor growth was observed with radiation at day 21 but not with SL-TNF-alpha or free TNF-alpha alone. By the end of phase 1 (day 27) with continued treatments, the SL-TNF-alpha plus radiation group had significantly smaller tumors (p = 0.044) than those in the free TNF-alpha plus radiation group. In phase 2, where a similar tumor growth reduction pattern was observed, the addition of TNF-alpha to radiation, either as free protein or within SL, increased lymphocyte activation and natural killer (NK) cell numbers in both blood and spleen. The effect was generally more pronounced with SL-TNF-alpha. Systemic toxicity, based on hematologic analyses and body weight, was absent or minimal. Collectively, the data show that pretreatment with SL-TNF-alpha can enhance more effectively, and possibly more safely, the effects of radiation against human colon tumor xenografts than can free TNF-alpha and that the increased antitumor action may involve upregulation of lymphocytes.

Characterization of hybrid CTL epitope delivery systems consisting of the Antennapedia homeodomain peptide vector formulated in liposomes

Peptide carriers, such the homeodomain of Antennapedia molecule (AntpHD), which spontaneously cross cellular membranes, have been exploited to deliver antigenic peptide Cw3 to the major histocompatibility complex (MHC) class-I presentation pathway and to prime cytotoxic T cells (CTL). However, the in vivo use of AntpHD recombinant peptide has been limited because CTLs can only be primed in the presence of sodium dodecyl sulfate (SDS) as adjuvant. In this report, we have exploited liposomes to protect the AntpHD-Cw3 from serum degradation and to facilitate the delivery of the recombinant peptide into the MHC class-I pathway of antigen-presenting cells. We have demonstrated that AntpHD recombinant peptide spontaneously associates with liposomes and this association is stable in vitro. However, exchange studies assessing the transfer of the peptide to model membranes or cells in vitro indicates that approximately 50% of the liposome-associated peptide is readily exchangeable. This is consistent with trypsin-protection assays, which have shown that approximately 40% of the liposome-associated peptide is protected from hydrolysis. Importantly, macrophages and dendritic cells are able to internalize AntpHD recombinant peptide associated with liposomes resulting in efficient delivery of the CTL peptide into the cytosol. These studies have demonstrated that dendritic cells treated with AntpHD-Cw3 in liposomes sensitize CTL clones to lyse syngeneic target cells expressing Cw3 epitope. This strategy, which combines liposomes and a peptide vector, provides a new approach for introducing molecules into the MHC class-I antigen presentation pathway of dendritic cells.

High-dose liposomal daunorubicin and high-dose cytarabine combination in patients with refractory or relapsed acute myelogenous leukemia

BACKGROUND

Liposomal encapsulation of daunorubicin (DaunoXome, DNX; Nexstar Pharmaceutical, Boulder, CO) changes the pharmacology profile to increase delivery to tumor sites and decrease toxicity. The authors investigated the effect of daunorubicin in combination with ara-C in patients with refractory or recurring acute myelogenous leukemia (AML). PATIENTS AND METHODS Sixty-two patients with refractory or recurring AML received escalating doses of daunorubicin of 75, 100, 125, or 135 mg/m(2) daily for 3 days together with ara-C 1 g/m(2) intravenous continuous infusion daily for 4 days.

RESULTS

Eighteen patients (29%) achieved a complete remission (CR) and 7 (11%) a hematologic improvement (i.e., met all criteria for CR except for platelet count < 100 x 10(9)/L) for an overall response rate of 40%. The dose-limiting toxicity was mucositis in 4 in 9 (44%) patients treated at the 150 mg/m(2) dose level, but minimal at 125 mg/m(2) (2 of 32, 6%) or 135 mg/m(2) (1 of 13, 8%). Cardiotoxicity Grade 2 was observed in 4 patients (6%) and Grade 3 or higher in 4 patients (6%). The median CR duration was 63 weeks, and overall survival rate was 25 weeks, with 28% patients alive after 1 year.

CONCLUSIONS

The combination of DNX (or liposomal daunorubicin) and ara-C has significant antileukemia activity with acceptable toxicity. Further studies are warranted to investigate the role of high-dose anthracyclines in frontline AML therapy.

A cell-based drug delivery system for lung targeting: II. Therapeutic activities on B16-F10 melanoma in mouse lungs

The in vitro and in vivo anticancer activities of doxorubicin-loaded B16-F10 murine melanoma cells (DLTC) were evaluated. DLTC showed similar growth-inhibitory effects against live B16-F10 cells with doxorubicin solution in cell culture system, with the IC50 of 0.11 microM and 0.17 microM, respectively. However, DLTC demonstrated higher effectiveness than the free solution in treating mouse lung cancer caused by live B16-F10 cells. Syngeneic C57BL mice were inoculated intravenously with live B16-F10 cells first, and then received daily treatment of intravenous injections of doxorubicin in either DLTC or free solution form. Compared with the control group treated with phosphate-buffered saline, DLTC eradicated almost all the lung cancer colonies (>99%), while the free solution form reduced the colonies by 61%, when the treatment was given at an early stage. If the treatment started after the establishment of micrometastatic colonies in the mouse lungs, DLTC and free solution treatment resulted in 85% and 30% cancer reduction, respectively. Additional experiments demonstrated that the reduction of lung cancer colonies by DLTC was related to the initial treatment time: the earlier the treatment, the greater the effect. In conclusion, DLTC showed better therapeutic outcomes than free solution form in treating lung cancer of our animal model.

Efficacy of intrathecal liposomal fasudil for experimental cerebral vasospasm after subarachnoid hemorrhage

OBJECTIVE

To investigate the safety and efficacy of liposomal fasudil in a sustained-release form for the prevention of cerebral vasospasm after subarachnoid hemorrhage (SAH).

METHODS

Eighteen rats were divided into three groups, each of which received 2.5 mg/kg of liposomal fasudil, 5 mg/kg of liposomal fasudil, or drug-free liposomes after SAH. Next, experimental SAH was induced in 15 dogs by injection of autologous arterial blood into the cisterna magna twice after baseline vertebral angiography. In six dogs, 0.94 mg/kg of liposomal fasudil was injected into the cisterna magna (treatment group). In four dogs, drug-free liposomes were similarly injected (placebo group), and the remaining five dogs were not treated with liposomal injection after SAH (control group). Angiography was repeated on Day 7, and cerebrospinal fluid was collected before the dogs were killed.

RESULTS

A high dose of liposomal fasudil caused no significant changes in mean arterial blood pressure and did not induce seizures during the observation period. Gross and microscopic examination of the brains revealed no abnormalities, but severe vasospasm was noted in the rat basilar artery, mainly in the group treated with drug-free liposomes. Likewise, in the canine placebo and control groups, significant vasospasm occurred in the basilar artery on Day 7. In the treatment group, vasospasm in the basilar artery was significantly ameliorated (P < 0.01). In vivo, 90% of fasudil was released from liposomes in the cerebrospinal fluid.

CONCLUSION

A single injection of intrathecal liposomal fasudil is safe and effective for the prevention of vasospasm in experimental SAH.

Bispecific MAb aided liposomal drug delivery

We have developed a new method for specifically delivering liposomal model drugs to tumor cells. Bispecific monoclonal antibodies (bsMAb) (174H.64 x anti-biotin) which can bind tumor-specific antigen and biotin were developed and characterized. Biotinylated stealth liposome loaded with model drug 99mTc-DTPA can bind to the biotin-binding arm of bsMAb. This targeted liposomal delivery strategy was tested in mouse KLN-205 squamous carcinoma model. bsMAbs were administered 24h in advance into tumor allograft bearing mice, which allow them to bind to tumor cells through the anti-tumor binding arm. After clearance of circulating bsMAb, biotinylated stealth liposomes were introduced to specifically bind to the tumor sites where bsMAb localized earlier. The results show that pretargeted bsMAb can enhance liposomal drug targeting by four times, 3.61% dose/g vs. 0.89% dose/g. This bsMAb/liposome strategy show the broad possibilities of selective delivery of cytotoxic drugs or genes to the specific targets.

Disposition characteristics of emulsions and incorporated drugs after systemic or local injection

Lipid emulsions are useful tools for controlling the in vivo disposition of drugs and plasmid DNA. The dispositions of lipid emulsions are determined by their tissue interaction depending on the anatomical and physiological characteristics of each tissue and the physicochemical and biological properties of lipid emulsions. In addition, the retention of drugs is another issue, as too rapid a release of the drug would lead to failure of exerting its therapeutic potency. This review presents an overview about the disposition profiles and various physicochemical properties of lipid emulsions and incorporated drugs after systemic or local injection. Controlled biodistribution of lipid emulsions and incorporated drugs are also discussed.

Magnetic resonance temperature imaging for guidance of thermotherapy

Continuous thermometry during a hyperthermic procedure may help to correct for local differences in heat conduction and energy absorption, and thus allow optimization of the thermal therapy. Noninvasive, three-dimensional mapping of temperature changes is feasible with magnetic resonance (MR) and may be based on the relaxation time T(1), the diffusion coefficient (D), or proton resonance frequency (PRF) of tissue water. The use of temperature-sensitive contrast agents and proton spectroscopic imaging can provide absolute temperature measurements. The principles and performance of these methods are reviewed in this paper. The excellent linearity and near-independence with respect to tissue type, together with good temperature sensitivity, make PRF-based temperature MRI the preferred choice for many applications at mid to high field strength (>/= 1 T). The PRF methods employ radiofrequency spoiled gradient-echo imaging methods. A standard deviation of less than 1 degrees C, for a temporal resolution below 1 second and a spatial resolution of about 2 mm, is feasible for a single slice for immobile tissues. Corrections should be made for temperature-induced susceptibility effects in the PRF method. If spin-echo methods are preferred, for example when field homogeneity is poor due to small ferromagnetic parts in the needle, the D- and T(1)-based methods may give better results. The sensitivity of the D method is higher that that of the T(1) methods provided that motion artifacts are avoided and the trace of D is evaluated. Fat suppression is necessary for most tissues when T(1), D, or PRF methods are employed. The latter three methods require excellent registration to correct for displacements between scans.

Targeted drug delivery to C6 glioma by transferrin-coupled liposomes

Recent advances in liposome technology have shown promise relative to the introduction of chemotherapeutic agents with reduced toxicity, extended longevity, and potential for cell-specific targeting. In this study we report the engineering of a liposomal delivery system for the chemotherapeutic drug doxorubicin. The system was targeted specifically to C6 glioma in vitro by coupling transferrin to the distal ends of liposomal polyethylene glycol (PEG) chains. The transferrin receptor is overexpressed on glioma, with the extent of overexpression correlated to the severity of the tumor. Significantly increased gliomal doxorubicin uptake was achieved by drug encapsulation within transferrin-coupled liposomes compared to other liposome populations. Doxorubicin encapsulated within transferrin-coupled liposomes exhibited 70% of free doxorubicin uptake as compared to 54, 14, and 34% for non-PEG, PEG, and albumin-coupled PEG liposomes, respectively. Competitive binding assays support the receptor-mediated mechanism of targeting. The addition of one microM free transferrin reduced the uptake of doxorubicin encapsulated within transferrin-coupled liposomes by 30%.

Liposomal formulations of anticancer drugs: selectivity and effectiveness

After a delay of roughly 30 years, liposomes are becoming important as drug-targeting systems especially in anticancer therapy. Two liposomal anthracycline formulations are now available for cancer treatment and more are in preclinical tests or in clinical trials. This review summarizes the possibilities to improve the anticancer activity of certain drugs by entrapment in liposomes. We will briefly examine the problems and limitations of liposomal systems, from a pharmacokinetic as well as from a manufacturing viewpoint. Moreover, the anticancer properties of the two new liposomal anthracycline formulations will be discussed with regard to anticancer activity and side effects and compared with the properties of the respective free drugs. Copyright 2000 Harcourt Publishers Ltd.

Modulation of daunorubicin toxicity by liposomal encapsulation and use of specific inhibitors in vitro

Anthracyclines serve as a valuable tool in chemotherapy, but their usefulness is often limited by the occurrence of resistance mechanisms in tumor cells. Resistance of tumor cells is a multifactorial event, where several mechanisms act concurrently, including drug efflux and enzymatic drug inactivation. Liposomal encapsulation of anthracyclines has been discussed as a successful regimen to overcome drug resistance. Our investigations were carried out on a daunorubicin (DRC) sensitive breast cancer cell line and two DRC resistant sublines generated thereof. In all three cell lines, the extent of DRC detoxification via carbonyl reduction to daunorubicinol (DRCOL) was determined. In addition, rutin, the most effective inhibitor of carbonyl reducing enzymes, was tested to affect DRCOL formation. DRC IC(50) values were determined in relation to several combinations of DRC administration, (a) liposomal encapsulated DRC, (b) addition of verapamil (inhibitor of drug efflux), (c) addition of rutin (inhibitor of DRC carbonyl reduction). We could show that DRC sensitive and resistant breast cancer cell lines are able to catalyze DRC detoxification via carbonyl reduction to DRCOL. Rutin was shown to inhibit this reaction, but could not serve as an enhancer of DRC toxicity in MTT tests. Verapamil was effective only in resistant cells due to the overexpression of P-glycoprotein 170. Liposomal encapsulation of DRC did not show the expected increase in DRC toxicity in the present tumor cell model.

Long-circulating liposomes of indomethacin in arthritic rats--a biodisposition study

To improve the targeting efficiency of liposomes of indomethacin to the arthritic joints, circulation half-life of the liposomes was increased by grafting amphipathic polyethylene glycol-2000 to the bilayer surface. A comparative biodistribution study was performed between the conventional liposomes (PC:CH:PE--1:0.5:0.16) and long-circulating liposomes (PC:CH:PE-PEG--1:0.5:0.16) in arthritic rats. Pharmacokinetics of the drug changed significantly when administered in liposomal form. Pharmacokinetic parameters of the drug such as AUC0-t (trapezoidal), clearance and t1/2 (elimination half-life) changed significantly (p < 0.05) when encapsulated in liposomes. Significant difference in pharmacokinetics was observed in AUC0-t and clearance between the conventional liposomes and long-circulating liposomes. The increased AUC0-t and reduced clearance of the drug with long-circulating liposomes, increased the availability of the drug by reducing RES uptake, in turn localization in arthritic paw tissue was also increased. A concentration of 0.33 microgram of indomethacin/g of the tissue was achieved with S-liposomes after 24 h whereas it was only 0.26 microgram of drug/g of the tissue with conventional liposomes. From the study, in may be concluded that the targeting efficiency of the long-circulating liposomes was about four times more than the conventional liposomes.