Pilot study of amphotericin B entrapped in sonicated liposomes in cancer patients with fungal infections

Amphotericin B release rate is the link between drug status in the liposomal bilayer and toxicity

Amphotericin B (AmB) is an amphiphilic drug commonly formulated in liposomes and administered intravenously to treat systemic fungal infections. Recent studies on the liposomal drug product have shed light on the AmB aggregation status in the bilayer, which heat treatment (curing) modifies. Although toxicity was found related to aggregation status - loose aggregates significantly more toxic than tight aggregates - the precise mechanism linking aggregation and toxicity was not well understood. This study directly measured drug release rate from various AmB liposomal preparations made with modified curing protocols to evaluate correlations among drug aggregation state, drug release, and in vitro toxicity. UV–Vis spectroscopy of these products detected unique curing-induced changes in the UV spectral features: a ∼25 nm blue-shift of the main absorption peak (λ_max) in aqueous buffer and a decrease in the OD₃₄₆/OD₃₂₂ ratio upon thermal curing, reflecting tighter aggregation. In vitro release testing (IVRT) data showed, by applying and fitting first-order release kinetic models for one or two pools, that curing impacts two significant changes: a 3–5-fold drop in the overall drug release rate and a ten-fold decrease in the ratio between the loosely aggregated and the tightly aggregated, more thermodynamically stable drug pool. The kinetic data thus corroborated the trend independently deduced from the UV–Vis spectral data. The in vitro toxicity assay indicated a decreased toxicity with curing, as shown by the significantly increased concentration, causing half-maximal potassium release (TC₅₀). The data suggest that the release of AmB requires dissociation of the tight complexes within the bilayer and that the reduced toxicity relates to this slower rate of dissociation. This study demonstrates the relationship between AmB aggregation status within the lipid bilayer and drug release (directly measured rate constants), providing a mechanistic link between aggregation status and in vitro toxicity in the liposomal formulations.

Spectroscopic, molecular dynamics simulation and biological studies of Flavin MonoNucleotide and Flavin Adenine Dinucleotide in biomimetic systems

The present study describes a comprehensive investigation of the spectroscopic characteristics, stability and in vitro antioxidant and cytotoxic properties of the Flavin MonoNucleotide (FMN) and Flavin Adenine Dinucleotide (FAD) in Dextran70 (Dx70) and Dx70/phospatidylcholine (PC) biomimetic systems by means of the UV-Vis absorption, fluorescence spectroscopy, chemiluminescence and Neutral Red assay. The affinity of FMN, FAD and the precursor riboflavin (RF) to an unsaturated phospholipid bilayer model as well as the location of the probes within the lipid bilayer were assessed from united-atom molecular dynamics simulations carried out on an unsaturated phospholipid bilayer model system, and the theoretical and experimental characterization of the two probes within biomembranes was complemented with the light microscopy survey of the cell morphology of L929 fibroblast cells cultivated in the presence of various dosage of FAD/FMN. In lipid bilayers, FMN/FAD resulted in a noticeable improvement of the antioxidant activity (the scavenging of reactive oxygen species up to 40%) and a significant effect on cellular viability in the L929 fibroblast cells. The results are important in the oxidative stress process concerning the redox reactions of flavins in humans as well as in further studies on different systems belonging to the category of flavoenzymes/flavoproteins, required for cellular respiration.

Antioxidant activity of phytoestrogen type isoflavones in biomimetic environments

Oxidation of phytoestrogen type isoflavones in lecithin lipidic bi-layers and in silver nanoparticle complexes by the chemiluminescence method.

Successful management of sequential pulmonary infections in a cardiac transplant recipient

A case of a cardiac allograft recipient who had an initial combined pulmonary infection with cytomegalovirus, Aspergillus fumigatus and Nocardia asteroides, successfully treated with liposomal amphotericin B and sulfisoxazole and followed by an episode of respiratory syncytial virus pneumonitis, is presented. This case illustrates the role of computed tomographic imaging in the recognition, diagnosis and monitoring of complex opportunistic pulmonary infections and the benefits of liposomal amphotericin B in the treatment of aspergillosis.

Ground- and excited-state proton transfer and antioxidant activity of 3-hydroxyflavone in egg yolk phosphatidylcholine liposomes: absorption and fluorescence spectroscopic studies

Excited-state intramolecular proton transfer (ESIPT) and dual luminescence behaviour of 3-hydroxyflavone (3-HF) have been utilized to monitor its binding to liposomal membranes prepared from egg yolk phosphatydilcholine (EYPC). Additionally, absorption spectrophotometric assay has been performed to evaluate the antioxidant activity of 3-HF against lipid peroxidation in this membrane system. When 3-HF molecules are partitioned into EYPC liposomes, a weak long-wavelength absorption band with lambda(abs)(max) approximately 410 nm appears in addition to the principal absorption at approximately lambda(abs)(max) = 345 nm. Selective excitation of the 410 nm band produces the characteristic emission (lambda(em)(max) approximately 460 nm) of the ground-state anionic species, whereas excitation at the higher energy absorption band leads to dual emission with predominatly ESIPT tautomer fluorescence (lambda(em)(max) = 528 nm). Both ESIPT tautomer and the anionic species exhibit fairly high fluorescence anisotropy (r) values (r = 0.122 and 0.180, respectively). Biexponential fluorescence decay kinetics are observed for the ESIPT tautomer as well as the ground-state anionic forms, indicating heterogeneity in the microenvironments of the corresponding emitting species. Furthermore, we demonstrate that lipid peroxidation of EYPC liposomes is significantly inhibited upon 3-HF binding, suggesting that 3-HF can be potentially useful as an inhibitor of peroxidative damage of cell membranes.

Ground and excited state proton transfer and antioxidant activity of 7-hydroxyflavone in model membranes: absorption and fluorescence spectroscopic studies

Steady state and time resolved fluorescence spectroscopy have been used to probe microenvironments of the therapeutically active intrinsically fluorescent flavonoid, 7-hydroxyflavone (7-HF), in model membranes consisting of multilamellar phosphatidylcholine liposomes. Additionally, the antioxidant effects of 7-HF against lipid peroxidation have been evaluated using spectrophotometric assay. Large Stokes shifted emissions with distinct spectroscopic signatures, are observed from the excited state proton transfer (ESPT) tautomer (which is generated by a solvent mediated mechanism) and the ground state anion of 7-HF. The neutral (7-HFN) and anionic (7-HFA) species' appear to be located in the non-polar acyl chain and the polar head group regions of the lipid vesicles respectively. The partition coefficients of 7-HFN and 7-HFA in these vesicles have also been estimated using their intrinsic fluorescence. Anisotropy (r) versus temperature (T) measurements reveal the utility of the tautomer fluorescence anisotropy as a sensitive parameter for exploring structural changes in the membranes. Fluorescence decay kinetics studies indicate heterogeneity in the microenvironments of both 7-HFN and 7-HFA. Furthermore, we demonstrate that lipid peroxidation of the model membranes is partially arrested upon 7-HF binding, suggesting its potential usefulness as an inhibitor of peroxidative damage of cell membranes.

Spontaneous formation of vesicles

his review highlights the relevant issues of spontaneous formation of vesicles. Both the common characteristics and the differences between liposomes and vesicles are given. The basic concept of the molecular packing parameter as a precondition of vesicles formation is discussed in terms of geometrical factors, including the volume and critical length of the amphiphile hydrocarbon chain. According to theoretical considerations, the formation of vesicles occurs in the systems with packing parameters between 1/2 and 1. Using common as well as new methods of vesicle preparation, a variety of structures is described, and their nomenclature is given. With respect to sizes, shapes and inner structures, vesicles structures can be formed as a result of self-organisation of curved bilayers into unilamellar and multilamellar closed soft particles. Small, large and giant uni-, oligo-, or multilamellar vesicles can be distinguished. Techniques for determination of the structure and properties of vesicles are described as visual observations by optical and electron microscopy as well as the scattering techniques, notably dynamic light scattering, small angle X-ray and neutron scattering. Some theoretical aspects are described in short, viz., the scattering and the inverse scattering problem, angular and time dependence of the scattering intensity, the principles of indirect Fourier transformation, and the determination of electron density of the system by deconvolution of p(r) function. Spontaneous formation of vesicles was mainly investigated in catanionic mixtures. A number of references are given in the review.

The choroidal circulation assessed by laser-targeted angiography

The choroid plays an important role in supplying nutrients to and removing waste products from the outer region of the retina. Abnormal choroidal blood flow can disrupt normal retinal function and lead to alterations in visual function. Visualization of the choriocapillaris in vivo is a great challenge to understanding its normal physiology and involvement in the disease process. Laser-targeted angiography (LTA) is a relatively new method used to visualize and analyze the choroidal circulation. Carboxyfluorescein (CF), encapsulated in heat-sensitive liposomes, is released locally in the choroid through the application of a heat beam provided by an infrared laser. Video angiograms are generated with excitation illumination provided by an argon laser. Obtained images are highly selective to the choriocapillaris and are sharply contrasted against underlying and overlying structures. The images can be obtained repetitively, during which period the circulating liposome concentration is sufficient to generate adequate angiograms. These high-quality images have revealed three distinct phases (filling, plateau, and draining) of the choriocapillaris. In the plateau phase, a cluster of lobules fed by a common arteriole has been uniformly illuminated. This defined cluster area does not change in size while an infrared laser is continuously applied to the same spot, which demonstrates that each cluster is functionally independent and no physiological communication exists between them. Only in posterior regions do the angiograms demonstrate during the filling and draining phases that each lobule is filled from a central spot and drained along a peripheral ring, showing honeycomb flow patterns. The regional differences in choriocapillaris flow patterns revealed by LTA suggests that the choriocapillaris provides a more highly efficient system of outflow in posterior regions than in peripheral regions. LTA is useful in analyzing choroidal circulation in vivo and has the potential for clinical application in the future. Additionally, LTA has a unique capability to image choroidal neovascularization in animal models and it promises potential application in age-related macular degeneration (AMD).

A comparative study of plasma concentrations of liposomal amphotericin B (L-AMP-LRC-1) in adults, children and neonates

Amphotericin B (AmpB) incorporated into small unilamellar liposomes prepared from soya phosphatidylcholine and cholesterol (L-AMP-LRC-1) has been shown to be safe and effective in patients with systemic fungal infections. In this report, we compared the plasma levels of AmpB in adults, children and neonates following administration of L-AMP-LRC-1. A 1.0 mg/kg dose of L-AMP-LRC-1 in adult patients resulted in peak concentrations of 1.02+/-0.14 mg/l (mean+/-S.D.) on day 1, which increased to 1.66+/-0.19 mg/l on day 28 after continued therapy. The area under the plasma concentration-time curve also increased from 13.05+/-1.52 on day 1 to 19.85+/-5.41 mg h/l on day 28. In children, the peak plasma concentration following 1.0 mg/kg per day dose of L-AMP-LRC-1 increased from 0.63+/-0.20 on day 1 to 1.10+/-0.53 mg/l on day 28. While in neonates, the levels increased from 0.54+/-0.17 on day 1 to 0.73+/-0.29 mg/l on day 28. These levels of AmpB in children and neonates were found to be significantly lower than in adults. This may be due to higher volume of distribution, since 1.0 mg/kg per day dose of L-AMP-LRC-1 was found to be effective in neonates.

Safety, toxicokinetics and tissue distribution of long-term intravenous liposomal amphotericin B (AmBisome): a 91-day study in rats

PURPOSE

Amphotericin B in small, unilamellar liposomes (AmBisome) is safer and produces higher plasma concentrations than other formulations. Because liposomes may increase and prolong tissue exposures, the potential for drug accumulation or delayed toxicity after chronic AmBisome was investigated.

METHODS

Rats (174/sex) received intravenous AmBisome (1, 4, or 12 mg/kg), dextrose, or empty liposomes for 91 days with a 30-day recovery. Safety (including clinical and microscopic pathology) and toxicokinetics in plasma and tissues were evaluated.

RESULTS

Chemical and histopathologic changes demonstrated that the kidneys and liver were the target organs for chronic AmBisome toxicity. Nephrotoxicity was moderate (urean nitrogen [BUN] < or = 51 mg/dl; creatinine unchanged). Liposome-related changes (vacuolated macrophages and hypercholesterolemia) were also observed. Although plasma and tissue accumulation was nonlinear and progressive (clearance and volume decreased, half-life increased with dose and time), most toxic changes occurred early, stabilized by the end of dosing, and reversed during recovery. There were no delayed toxicities. Concentrations in liver and spleen greatly exceeded those in plasma: kidney and lung concentrations were similar to those in plasma. Elimination half-lives were 1-4 weeks in all tissues.

CONCLUSIONS

Despite nonlinear accumulation, AmBisome revealed predictable hepatic and renal toxicities after 91 days, with no new or delayed effects after prolonged treatment at high doses that resulted in plasma levels >200 microg/ml and tissue levels >3000 microg/g.

Antifungal pharmacodynamics: review of the literature and clinical applications

Invasive fungal infections are seen with growing frequency, likely due to increases in numbers of patients at risk of infection. Optimal selection and dosing of antifungal agents are important, as these infections are often refractory to available therapy. In contrast to antibacterials, studies examining the pharmacodynamic properties of antifungals and their application in treating invasive disease often are lacking. Agents administered for invasive infections are amphotericin B, flucytosine, and azole antifungals. Several drugs are under investigation, such as posiconazole, voriconazole, and the echinocandins, and preliminary pharmacodynamic data likely will help shape dosing regimens. Clinical trials that investigated dosage and administration, as well as the potential benefits of combination and sequential therapy, are addressed. In addition, antifungal susceptibility and animal models of infection are discussed.

Safety and toxicokinetics of intravenous liposomal amphotericin B (AmBisome) in beagle dogs

PURPOSE

Amphotericin B (AmB) in small, unilamellar liposomes (AmBisome) has an improved therapeutic index, and altered pharmacokinetics. The repeat-dose safety and toxicokinetic profiles of AmBisome were studied at clinically relevant doses.

METHODS

Beagle dogs (5/sex/group) received intravenous AmBisome (0.25, 1, 4, 8, and 16 mg/kg/day), empty liposomes or vehicle for 30 days. AmB was determined in plasma on days 1, 14, and 30, and in tissues on day 31. Safety parameters included body weight, clinical chemistry, hematology and microscopic pathology.

RESULTS

Seventeen of twenty animals receiving 8 and 16 mg/kg were sacrificed early due to weight loss caused by reduced food intake. Dose-dependent renal tubular nephrosis, and other effects characteristic of conventional AmB occurred at 1 mg/kg/day or higher. Although empty liposomes and AmBisome increased plasma cholesterol, no toxicities unique to AmBisome were revealed. Plasma ultrafiltrates contained no AmB. AmBisome achieved plasma levels 100-fold higher than other AmB formulations. AmBisome kinetics were non-linear, with clearance and distribution volumes decreasing with increasing dose. This, and nonlinear tissue uptake, suggest AmBisome disposition was saturable.

CONCLUSIONS

AmBisome has the same toxic effects as conventional AmB, but they appear at much higher plasma exposures. AmBisome's non-linear pharmacokinetics are not associated with increased risk, as toxicity increases linearly with dosage. Dogs tolerated AmBisome with minimal to moderate changes in renal function at doses (4 mg/kg/day) producing peak plasma concentrations of 18-94 microg/mL.

Lipid-based amphotericin B formulations: from animals to man

Amphotericin B has been the mainstay of systemic antifungal therapy for over 30 years, despite its serious side-effects, and, although numerous alternative antifungal agents have been developed, none to date has matched the efficacy of amphotericin B. However, modern drug delivery technology has improved the safety of amphotericin B by incorporating it into lipid-based delivery systems, including liposomes. Three such formulations, based on the natural affinity of amphotericin B for lipids, are currently marketed. All increase the therapeutic index of amphotericin B, thereby allowing more aggressive treatment than is possible with the conventional product. However, they differ in structure, side-effect profiles and evidence of proven efficacy as discussed in this review.

Lipid-based amphotericin B for the treatment of fungal infections

The frequency of life-threatening fungal infections has increased dramatically over the past few decades. For more than 30 years amphotericin B has been the standard treatment for systemic and deep-seated fungal infections, primarily because of its broad spectrum of activity. Its usefulness is limited by a relatively high frequency of significant adverse events including infusion-related reactions and nephrotoxicity. In an effort to overcome these side effects, a number of lipid-based formulations were developed, each with its own composition and pharmacokinetic behavior. The clinical significance of these differences is unknown. Available clinical data suggest the formulations have a reduced propensity for causing nephrotoxicity. However, considering limited efficacy data, they should be reserved as second-line therapy for patients who cannot tolerate or fail an adequate trial of conventional amphotericin B or cannot benefit from other antifungal agents.

Development of liposomal amphotericin B formulation

A considerable effort has been spent in the past three decades to investigate various aspects of liposomes as novel drug delivery systems. In 1990, the first amphotericin B (AmB) liposomal preparation (L-AmB) under the brand name AmBisome was introduced into the market by Vestar. The successful marketing of the product moved liposomes out of the stage of experimental obscurity to the realistic stage of clinical utility. The launch of AmBisome sparked off the introduction of other lipid-based AmB products marketed by Liposome Technology (Amphocil) and The Liposome Co. (Abelcet). The drive behind the development of a modified formulation of AmB was to improve the therapeutic index of this drug with respect to its major drawback associated with both acute and chronic toxic effects. In a 30-year-long experience with AmB, several reports were recorded in the literature of acute adverse effects, such as fever, rigors, vomiting, cardiotoxicity and hypotension occurring during infusion; while long-term therapy was reported to be associated with hypokalemia, renal dysfunction and hematological abnormalities. Another serious problem encountered with the drug had been the poor response obtained in immunocompromised patients like those with AIDS, neutropenia and cancer patients on chemotherapy. The encapsulation of amphotericin B in liposomal vesicles was hence targeted not only to obtain an improvement in the therapeutic index but also to see if it was useful in eradicating deep-seated fungal infections in immunocompromised patients. The liposomal AmB was found to have a better therapeutic index and lower toxicity than the commercial AmB preparations. The LD50 of AmBisome in mouse was 175 mg/kg compared with 3.7 mg/kg for Fungizone, the commercial preparation of AmB. Additionally, L-AmB has prolonged circulation time, and extravasates into the site of infection and delivers the drug directly to the site, with no nephrotoxicity and neurotoxicity as experienced with AmB. This review traces the course of development of L-AmB and discusses the rationale behind the development of its liposomal preparation. The results in in vitro, in vivo and clinical studies, mechanism of action, biodistribution, and formulation considerations of L-AmB are described. The clinical experience with the marketed preparation is reviewed.

Pharmacokinetics of liposomal amphotericin B (Ambisome) in critically ill patients

The liposomal formulation of amphotericin B (AmBisome) greatly reduces the acute and chronic side effects of the parent drug. The present study describes the pharmacokinetic characteristics of AmBisome applied to 10 patients at a dose of 2.8 to 3.0 mg/kg of body weight and compares them to the pharmacokinetics observed in 6 patients treated with amphotericin B deoxycholate at the standard dose of 1.0 mg/kg. Interpatient variabilities of amphotericin B peak concentrations (Cmax) and areas under concentration-time curves (AUC) were 8- to 10-fold greater for patients treated with AmBisome than for patients treated with amphotericin B deoxycholate. At the threefold greater dose of AmBisome, median Cmaxs were 8.4-fold higher (14.4 versus 1.7 microg/ml) and median AUCs exceeded those observed with amphotericin B deoxycholate by 9-fold. This was in part explained by a 5.7-fold lower volume of distribution (0.42 liters/kg) in AmBisome-treated patients. The elimination of amphotericin B from serum was biphasic for both formulations. However, the apparent half-life of elimination was twofold shorter for AmBisome (P = 0.03). Neither hemodialysis nor hemofiltration had a significant impact on AmBisome pharmacokinetics as analyzed in one patient. In conclusion, the liposomal formulation of amphotericin B significantly (P = 0.001) reduces the volume of drug distribution, thereby allowing for greater drug concentrations in serum. The low toxicity of AmBisome therefore cannot readily be explained by its serum pharmacokinetics.

Release of amphotericin B from delivery systems and its action against fungal and mammalian cells

Spectroscopic studies of four amphotericin B (AmB) lipid preparations--small negatively charged unilamellar vesicles "AmBisome", positively charged oligolamellar liposomes "Ampholiposomes", AmB Lipid Complex "L-AmpB33"--and AmB association with gamma cyclodextrin demonstrated that the composition of drug delivery system directly influences AmB organization. The aggregation state and release in external medium of AmB was monitored by circular dichroism and UV-visible absorption. AmB short-term activity against Candida albicans (K+ leakage) was found to be correlated with the amount of free AmB released from lipid preparations. These data seem to indicate that lipid composition influences anti-Candida albicans activity, by modulation of AmB binding to lipids.

Preparation, purification and morphology of polymeric nanoparticles as drug carriers

The aim of this work was to prepare biodegradable poly(D,L-lactic acid-co-glycolic acid) copolymer (PLAGA) nanoparticles by the solvent evaporation process and to incorporate an antifungal antibiotic, amphotericin B. Blank nanoparticles obtained were 130 +/- 27 nm in diameter. When amphotericin B was added in the organic phase, the final suspension showed two populations due to unbound drug. Free amphotericin B was removed by contacting the nanoparticle suspension with an adsorbent polymer. Amberlite XAD16, and subsequently ultrafiltering the medium. The drug payload was between 0.7 and 1.3%. To gain more insight in the cause of this low loading, we studied progesterone-loaded nanoparticles using PLAGA and polystyrene as models because progesterone and these polymers exhibit a degree of miscibility. In the case of polystyrene, nanoparticle drug content reached 8%.

Fungal endocarditis--a report on seven cases and a brief review

Candida endocarditis is an unusual but severe complication of systemic infection caused by Candida albicans and occasionally by other fungal species. We describe seven cases that occurred during a period of 20 years in western Sweden. In four cases infections were located on prosthetic valves and in three cases native valves were involved. Three patients died of the disease in the acute phase. A definite diagnosis was established in one of four survivors. This patient had an aortic valve endocarditis and a saddle embolisation and was treated with immediate surgery, followed by intensive treatment with liposomal amphotericin B+ flucytosine. Fungal endocarditis is still a serious disease with a high mortality and whenever the diagnosis is suspected, antifungal therapy must be started and transesophageal sonography should be performed to visualize vegetations. Immediate surgery should be considered.

Modulation of resistance to cisplatin by amphotericin B and aphidicolin in human larynx carcinoma cells

The aim of this study was to examine whether resistance to cisplatin [cis-diamminedichloroplatinum (II)] (CDDP) could be overcome by amphotericin B, cyclosporin A and aphidicolin in two sublines of human larynx carcinoma HEp2 cells. The sensitivity of parental and cisplatin-resistant CA3 and CK2 cells to amphotericin B, cyclosporin A and aphidicolin, and also the effects of these drugs (given in maximal nontoxic concentrations) on cisplatin sensitivity were determined by clonogenic survival assay. CA3 and CK2 cells were sensitive to amphotericin B, and resistant to cyclosporin A and aphidicolin, compared with their parental cells. Amphotericin B increased cisplatin toxicity 2-fold in CA3 cells and 2.7-fold in CK2 cells, while it had no effect in parental HEp2 cells. Cyclosporin A did not influence the sensitivity of examined cells to cisplatin. The sensitizing effect of aphidicolin was more obvious in cisplatin-resistant cells. Cisplatin toxicity was increased by aphidicolin: 1.5-fold in HEp2 cells, 2-fold in CA3 cells, and 1.9-fold in CK2 cells. Therefore, the resistance to cisplatin in human larynx carcinoma CA3 and CK2 cells can be partially reversed by amphotericin B and aphidicolin.

Antifungal drugs on the horizon

In the past 10 years there has been a major expansion in the development of antifungal drugs, but there are still weaknesses in the range and scope of current antifungal chemotherapy. New developments have included the modification of existing drug molecules to eliminate toxicity and improve activity, for instance, the development of the lipid formulations of the polyene antifungal agent amphotericin B. Three different amphotericin B derivatives, a unilamellar liposome (AmBisome), a colloidal dispersion (ABCD--Amphocil), and a lipid complex (ABLC) are undergoing evaluation. New triazoles with broad-spectrum antifungal activity, such as saperconazole, are also being assessed. The development of groups of drugs with novel modes of action such as cell wall biosynthesis inhibitors has been slower, although a number of molecules with activity against key enzymes, including chitin or glucan synthase, have been found. The morpholine antifungal amorolfine, a sterol biosynthesis inhibitor, has been developed for the topical treatment of fungal nail infections. The assessment of these drugs is a major challenge because it will be necessary to show that they have some advantage over existing compounds in efficacy, speed of action, or lack of toxicity.

Alternative modalities of administering amphotericin B: current issues

Numerous studies performed in the field of antifungal therapy during the last decade have resulted in major developments in new modalities of administering amphotericin B including liposomes or other lipid vehicles. Current data available are very encouraging and several preparations are already commercially available in some countries. An improved therapeutic index has been shown in humans but large comparative trials are still needed to establish the definite role and indications of the various preparations as well as the optimal therapeutic regimens. These studies will make a significant contribution to improving the prognosis of patients predisposed to life threatening invasive fungal infections.

Liposomal amphotericin B, AmBisome

The unilamellar liposomal formulation of amphotericin B, AmBisome, is composed of hydrogenated soy phosphatidylcholine, distearoyl phosphatidylglycerol and cholesterol. Early studies of its efficacy in an open design showed that remissions could be induced in candidosis and aspergillosis and that doses of up to 5 mg/kg could be used. Adverse events were infrequent, with the main abnormality seen being hypokalaemia in about 18% of patients. Subsequent developments have extended this work. AmBisome has been used in two open studies of patients with invasive aspergillosis; in one of these remission was achieved in 77% of 17 patients with confirmed infection who had failed to respond to conventional amphotericin B. In AIDS patients with cryptococcosis AmBisome given for 6 weeks at 3 mg/kg daily produced mycological remission of meningitis in 67%. Other infections treated with the drug include zygomycete (mucormycosis) and Fusarium infections. AmBisome has also been used as preventative therapy in bone marrow transplant recipients and was found to reduce fungal colonisation rates. There were fewer systemic fungal infections in the treated versus placebo groups although this did not achieve statistical significance. Lack of renal and liver toxicity or anaemia has been confirmed in subsequent studies. In addition febrile reactions to the AmBisome are rare. The drug has also been used effectively in children, including infants, with systemic fungal infections. In visceral leishmaniasis patients, including HIV positive individuals, remissions have been obtained using drug regimens of 1-2 mg/kg of 2.1 days and 3 mg/kg for 10 days.

In vitro renal toxicity and in vivo therapeutic efficacy in experimental murine cryptococcosis of amphotericin B (Fungizone) associated with Intralipid

We compared the experimental toxicities and activities of deoxycholate amphotericin B (d-AmB) dissolved in glucose (Dd-AmB) or mixed with 20% Intralipid (ILd-AmB). In vitro, ILd-AmB against renal tubular cells in primary culture. In vivo, the toxicities and activities of Dd-AmB and ILd-AmB were studied in DBA2 mice with cryptococcosis. The maximum tolerated dose of intravenously administered d-AmB, i.e., the dose that induced less than 15% mortality because of toxicity, was 1.7 to 2.5 times higher when it was administered as ILd-AmB than when it was administered as Dd-AmB. Both treatments given intravenously at the same dose were equivalent for improving the survival of mice and reducing CFU counts in infected tissue, but at maximum tolerated doses, ILd-AmB (2 mg/kg of body weight) was more effective than Dd-AmB (0.8 to 1.2 mg/kg). AmB concentrations in spleen, liver, lung, and kidney were measured by high-pressure liquid chromatography 4 and 24 h after a single injection of 1.2 mg of Dd-AmB per kg, 1.2 mg of ILd-AmB per kg, or 2 mg of ILd-AmB per kg. In a given organ, AmB levels were similar after administration of 1.2 mg of Dd-AmB or ILd-AmB per kg but were significantly higher after administration of 2 mg of ILd-AmB per kg. The lower level of toxicity of ILd-AmB might be explained by circular dichroism experiments, showing that ILd-AmB contained 10-fold less soluble oligomeric AmB, which is believed to be the toxic form of the drug, than Dd-AmB. We conclude that ILd-AmB is as efficient as Dd-AmB and is better tolerated than Dd-AmB in mice with experimental cryptococcosis. By allowing higher doses of AmB to be infused, Intralipid enhances AmB concentrations in infected sites, and thus the therapeutic activity of the drug.

Selective potentiation of platinum drug cytotoxicity in cisplatin-sensitive and -resistant human ovarian carcinoma cell lines by amphotericin B

Resistance to the clinically used platinum-based drugs cisplatin and carboplatin represents a major limitation to their clinical effectiveness. Using cisplatin-sensitive and -resistant human ovarian carcinoma cell lines previously characterized in terms of their major underlying mechanisms of resistance, we attempted to potentiate the cytotoxic effects of cisplatin and carboplatin using the clinically used antifungal agent amphotericin B (AmB). Using non-toxic concentrations of AmB (up to 15 micrograms/ml) and continuous exposure to cisplatin, a concentration-dependent selective potentiation (maximum of 3.2-fold) of cisplatin cytotoxicity was observed in two cisplatin-resistant cell lines (41McisR6, acquired resistant, and HX/62, intrinsically resistant). In both these cisplatin-resistant cell lines, previous studies have shown resistance to be due primarily to reduced platinum uptake. Notably, no significant potentiation was observed in the parent 41M cell line, in the intrinsically resistant SKOV-3 cell line (where reduced drug accumulation plays only a partial role in determining resistance) or in a pair of cell lines (CH1 and its acquired-resistant variant CH1cisR6) were reduced drug uptake does not play any role in determining resistance. The potentiating effect of AmB was lower with carboplatin and not significant in all cell lines. Platinum uptake following a 2-h exposure of cells to cisplatin was enhanced 3.5-fold in 41McisR6 cells (producing platinum levels similar to those obtained in the parental line) and 1.7-fold in 41M cells by the concomitant exposure to AmB. These data indicate that the potentiation of cisplatin (and carboplatin) cytotoxicity by AmB is not due to a generalized membrane disruption, as effects were observed only in resistant lines where reduced drug transport was apparent. Moreover, AmB did not increase the cytotoxicity of JM216 [bis-acetatoammine(cyclohexylamine)dichloroplatinum (II)], a recently developed, more lipophilic orally active platinum drug, in the 41M/41McisR6 lines. JM216 has previously been shown to circumvent acquired cisplatin resistance due to decreased drug uptake. In vivo, however, using the HX/62 xenograft. AmB (at its maximum tolerated dose of 20 mg/kg; q7d x 4 schedule) did not enhance the antitumour effect of carboplatin (at its maximum tolerated dose of 80 mg/kg; q7d x 4 schedule.

Liposomes in the treatment of infections

The use of liposomes in the treatment of severe infections is under investigation. Classical liposomes which localize in cells of the mononuclear phagocyte system (MPS) can be exploited in two ways. First for targeting of macrophage modulators such as muramyl peptides or IFN-gamma, to stimulate the cells of the MPS to maximal blood clearance capacity. This enhanced nonspecific anti-infectious resistance is important as in immunocompromised patients micro-organisms frequently appear in the blood from a local infection. Secondly, classical liposomes are successfully used as carriers of antibiotics in experimental intracellular parasitic-, viral-, fungal- or bacterial infections in MPS tissues. Based on these data extensive studies in patients with severe fungal infections have demonstrated successful treatment with liposomal or lipid-complexed amphotericin B. More recently, liposomal amphotericin B appeared to be effective in patients with drug-resistant visceral leishmaniasis. For the treatment of Mycobacterium avium complex infection in AIDS patients the efficacy of liposomal gentamicin is under investigation. With respect to infections in non-MPS tissues the applicability of Stealth liposomes characterized by long circulation half-lives is under investigation. Substantial localization of these liposomes in infected lung tissue of rats was demonstrated. Preliminary data in experimental bacterial lung infection showed superior efficacy of antibiotic encapsulated in Stealth liposomes.