Efficacy of NS-718, a novel lipid nanosphere-encapsulated amphotericin B, against Cryptococcus neoformans

Activity, reduced toxicity, and scale-up synthesis of amphotericin B-conjugated polysaccharide

Amphotericin B (AMB) arabinogalactan (AG) conjugate was synthesized by the conjugation of AMB to oxidized AG by reductive amination. The conjugate was evaluated for in vitro antifungal activity and in vivo toxicity. Optimization of the conjugation process was investigated using large batches of 100 g, which are 20 times larger than previously reported for AMB-AG conjugation. The efficacy of AMB-AG conjugates was studied as a function of reaction conditions and time, aldehyde/reducing agent mole ratio, and purification procedure. The most potent AMB-AG conjugate having low minimal inhibitory concentration (MIC) and high maximal tolerated dose (MTD) was obtained following reduction with NaBH4 at 1:2 mol ratio (AG units/NaBH4) at 25 °C for 24 h. AMB-AG conjugate prepared under these conditions demonstrated MIC of 0.5 mg/L (equiv of AMB) in Candida albicans, and an MTD of 60 mg/kg (equiv of AMB) in mice, while AMB clinical formulation (Fungizone) demonstrated high toxicity (MTD = 3 mg/kg). These findings confirm the simplicity and reproducibility of the conjugation allowing this method to be applied on larger scale production.

Amphotericin B lipid preparations: what are the differences?

To reduce the in-vivo toxicity of the broad-spectrum antifungal drug amphotericin B, various lipid formulations of amphotericin B, ranging from lipid complexes to small unilamellar liposomes, have been developed and subsequently commercialized. These structurally diverse formulations differ in their serum pharmacokinetics as well as their tissue localisation, tissue retention and toxicity. These differences can affect the choice of formulation for a given infection, the time of initiation of treatment, and the dosing regimen. Although preclinical studies have shown similarities in the in-vitro and in-vivo antifungal activity of the formulations with comparable dosing, their acute and chronic toxicity profiles are not the same, and this has a significant impact on their therapeutic indices, especially in high-risk, immunosuppressed patients. With the recent introduction of new antifungal drugs to treat the increasing numbers of infected patients, the amphotericin B lipid formulations are now being studied to evaluate their potential in combination drug regimens. With proven efficacy demonstrated during the past decade, it is expected that amphotericin B lipid formulations will remain an important part of antifungal drug therapy.

Optimizing efficacy of amphotericin B through nanomodification

Fungal infections and leishmaniasis are an important cause of morbidity and mortality in immunocompromised patients. The macrolide polyene antibiotic amphotericin B (AmB) has long been recognized as a powerful fungicidal and leishmanicidal drug. A conventional intravenous dosage form of AmB, AmB- deoxycholate (Fungizone or D-AmB), is the most effective clinically available for treating fungal and parasitic (leishmaniasis) infections. However, the clinical efficacy of AmB is limited by its adverse effects mainly nephrotoxicity. Efforts to lower the toxicity are based on synthesis of AmB analogues such as AmB esters or preparation of AmB-lipid associations in the forms of liposomal AmB (L-AmB or AmBisome), AmB lipid complex (Abelcet or ABLC), AmB colloidal dispersion (Amphocil or ABCD), and intralipid AmB. These newer formulations are substantially more expensive, but allow patients to receive higher doses for longer periods of time with decreased renal toxicity than conventional AmB. Modifications of liposomal surface in order to avoid RES uptake, thus increased targetability has been attempted. Emulsomes and other nanoparticles are special carrier systems for intracellular localization in macrophage rich organs like liver and spleen. Injectable nano-carriers have important potential applications as in site-specific drug delivery.

Drug-incorporating calcium carbonate nanoparticles for a new delivery system

We devised a simple method for incorporating drugs into solid calcium carbonate nanoparticles (nano-CaCO3). The size of nano-CaCO3 was controlled by mixing speed. Washing the nanoparticles released little incorporated drug but much drug that was adsorbed on the surface. In an in vitro releasing test, granulocyte colony-stimulating factor incorporated in nano-CaCO3 was chemically stable and released very slowly. Subcutaneous injection of nano-CaCO3 incorporating betamethasone phosphate (BP) resulted in a smaller initial increase in plasma concentration and a subsequent sustained release in compared with betamethasone phosphate solution. Nano-CaCO3 may be useful to deliver hydrophilic drugs and bioactive proteins.

The role of murine models in the development of antifungal therapy for systemic mycoses

Animal testing is crucial to the development of new antifungal compounds. This review describes the role that murine and other animal models have played in the development of three classes of antifungal agents: the polyenes, the triazoles and the echinocandins and the ways in which these models have been either the positive link in the path from in vitro studies to the patient, or have foreclosed later clinical evaluation. Efficacy studies in particular mycoses are discussed, as well as studies designed to determine whether combinations of antifungal drugs may have value over single agents. Copyright 2000 Harcourt Publishers Ltd.

New investigational antifungal agents for treating invasive fungal infections

Systemic fungal infections have been recognised as a major cause of morbidity and mortality during the last two decades. There are only a few therapeutic options for these infections. Severe toxicity, such as impairment of renal function, limits the use of amphotericin B. Flucytosine is associated with side effects and drug resistance. Fluconazole and itraconazole are safer, though emergence of resistance and innate resistance in some fungal pathogens is a concern in their use. Therefore, there is a need for developing novel drugs and/or treatment strategies to combat these infections. In recent years, increased efforts by the pharmaceutical industry and academia have led to the discovery of new re-engineered or reconsidered antifungal agents that are more efficacious, safer and have a broad spectrum of activity. Lipid formulations of polyene antifungal agents, amphotericin B and nystatin, have the advantage of improved therapeutic index. Activity against resistant fungi, high bioavailability, safety and longer half-life are the properties that encourage development of the newer triazoles (e.g., voriconazole, ravuconazole and posaconazole). Echinocandin-like lipopeptide antibiotics are among the antifungal agents with a novel mode of action. In addition to these lead investigational compounds, development of newer antifungal agents is underway.

In-vitro and in-vivo activities of SCH56592 against Cryptococcus neoformans

The in-vitro and in-vivo activities of SCH56592, a triazole antifungal agent, against Cryptococcus neoformans were studied. MIC(90)s for 16 strains of C. neoformans measured by microdilution method (NCCLS M27-A) were 1 mg/L of SCH56592, 16 mg/L of fluconazole, 32 mg/L of flucytosine, and 0.5 mg/L of amphotericin B. In a murine model of pulmonary cryptococcosis, 10 mg/kg of SCH56592 was more effective than fluconazole. The fungal burden of the lung of animals treated with SCH56592 was significantly reduced (7.40 +/- 0.21 log(10) cfu/g), as compared with fluconazole (7.77 +/- 0.07 log(10) cfu/g) and control (7.79 +/- 0.1 log(10) cfu/g) (P < 0.01). For C. neoformans-infected mice following 7 days treatment with 10 mg/kg of SCH56592 there was a higher concentration in lung (3.36 +/- 0.62 ng/ml) than in plasma (2.16 +/- 0.86 ng/mL), and this was maintained for 12 h after administration.

In vitro and in vivo activities of NS-718, a new lipid nanosphere incorporating amphotericin B, against Aspergillus fumigatus

We evaluated the in vitro and in vivo potencies of a new lipid nanosphere that incorporates amphotericin B (AmB), NS-718, against Aspergillus fumigatus. The in vitro activity of NS-718 (the MIC at which 90% of strains are inhibited [MIC90], 0.25 microgram/ml) against 18 isolates of A. fumigatus was similar to that of deoxycholate AmB (D-AmB; Fungizone; MIC90, 0.25 microgram/ml), but NS-718 was more potent than liposomal AmB (L-AmB; AmBi-some; MIC90, 1.0 microgram/ml). The in vivo efficacy of NS-718 in a rat model of invasive pulmonary aspergillosis was compared with those of D-AmB and L-AmB. A low dose (1 mg/kg of body weight) of L-AmB was ineffective (survival rate, 0%), although equivalent doses of D-AmB and NS-718 were more effective (survival rate, 17%). However, a higher dose of NS-718 (3 mg/kg) was more effective (survival rate, 100%) than equivalent doses of D-AmB and L-AmB (survival rate, 0%). To explain these differences, pharmacokinetic studies showed higher concentrations of AmB in the plasma of rats treated with NS-718 than in the plasma of those treated with D-AmB. Our results suggest that NS-718, a new preparation of AmB, is a promising antifungal agent with activity against pulmonary aspergillosis.