Efficacy and toxicity of a tropically stable lipid-based formulation of amphotericin B (iCo-010) in a rat model of invasive candidiasis

Development of an Oral Amphotericin B Formulation as an Alternative Approach to Parenteral Amphotericin B Administration in the Treatment of Blood-Borne Fungal Infections

In the Fall of 1999, we presented at medical "Grand Rounds" to a number of Infectious Diseases physicians at Vancouver General Hospital about the co-administration of several antifungal compounds in the treatment of blood-borne fungal infections to patients who were immunocompromised (i.e. cancer patients, patients waiting organ transplantation, HIV/AIDs patients, etc.). During the presentation, a physician from the back of the room called out "can you develop an oral formulation of amphotericin B which could be effective and not have the side-effects associated with the parenteral formulations of the drug". The physician stated that an oral formulation would be a big step forward, improving patient compliance, helping in pre-treatment without admitting patients to the hospital prior to organ transplantation and it would be cost-effective. Initially, I responded to the physician, that it would not be possible to develop an oral amphotericin B formulation that could be absorbed from the gastrointestinal (GI) tract in a high enough concentration to be effective in treating blood-borne fungal infections and yet remains non-toxic due to the physical chemical properties of the drug. However, as I travelled back to my lab from the meeting, it struck me that our understanding of how lipids had been processed and orally absorbed from the GI had advanced to the point the maybe incorporating amphotericin B into such lipids might work. Within several years, our laboratory was able to develop a novel oral amphotericin B formulation that was indeed effective in treating systemic fungal infections without the side-effects associated with the drug in a variety of fungal animal models.

Design of amphotericin B oral formulation for antifungal therapy

Amphotericin B (AmB) remains the "gold standard" for systemic antifungal therapy, even though new drugs are emerging as the attractive antifungal agents. Since AmB has negligible oral absorption as a consequence of its unfavorable physicochemical characterizations, its use is restricted to parenteral administration which is accompanied by severe side effects. As greater understanding of the gastrointestinal tract has developed, the advanced drug delivery systems are emerging with the potential to overcome the barriers of AmB oral delivery. Much research has demonstrated that oral AmB formulations such as lipid formulations may have beneficial therapeutic efficacy with reduced adverse effects and suitable for clinical application. Here we reviewed the different formulation strategies to enhance oral drug efficacy, and discussed the current trends and future perspectives for AmB oral administration in the treatment of antifungal infections.

Evaluating the potential of cubosomal nanoparticles for oral delivery of amphotericin B in treating fungal infection

The oral administration of amphotericin B (AmB) has a major drawback of poor bioavailability. The aim of this study was to investigate the potential of glyceryl monoolein (GMO) cubosomes as lipid nanocarriers to improve the oral efficacy of AmB. Antifungal efficacy was determined in vivo in rats after oral administration, to investigate its therapeutic use. The human colon adenocarcinoma cell line (Caco-2) was used in vitro to evaluate transport across a model of the intestinal barrier. In vivo antifungal results showed that AmB, loaded in GMO cubosomes, could significantly enhance oral efficacy, compared against Fungizone®, and that during a 2 day course of dosage 10 mg/kg the drug reached effective therapeutic concentrations in renal tissue for treating fungal infections. In the Caco-2 transport studies, GMO cubosomes resulted in a significantly larger amount of AmB being transported into Caco-2 cells, via both clathrin- and caveolae-mediated endocytosis, but not macropinocytosis. These results suggest that GMO cubosomes, as lipid nanovectors, could facilitate the oral delivery of AmB.

Efficacy of an oral and tropically stable lipid-based formulation of Amphotericin B (iCo-010) in an experimental mouse model of systemic candidiasis

OBJECTIVE

An oral lipid based formulation that exhibits tropical stability (iCo-010) was developed to enhance the absorption of orally administered amphotericin B (AmB). iCo-010 has previously shown high efficacy in an acute model of systemic candidiasis in rats, directing the focus of this study to be its efficacy in a chronic model of systemic candidiasis in mice.

METHODS

Mice were infected with 0.6 to 1×108 CFUs of Candida albicans ATCC 18804 strain by tail vein injection and were left for three days to develop the infection after which time treatment was initiated. The infected animals were assigned to the following treatment groups: no treatment (control) or iCo-010 at 5, 10 and 20 mg/kg administered by oral gavage once daily (QD) for 5 consecutive days. The animals were sacrificed 7 days after the last dose and the concentration of AmB and the fungal burden were assessed within the liver, kidneys, heart, lungs, spleen and brain.

RESULTS

Although the infection was relatively low (~ 60-100 CFUs/ 1 ml tissue homogenate) in the liver, lungs and heart, the infection level was very high (70 000 CFUs / 1 ml tissue homogenate) in the kidney tissues for the control group. The highest concentrations of AmB were recovered in the kidneys and the spleen. The fungal burden in the tissues was lowered by 69-96% in the treatment groups when compared to the control group.

CONCLUSION

Oral iCo-010 is an effective treatment of systemic candidiasis in the mouse model.

Development of oil-in-water microemulsions for the oral delivery of amphotericin B

Amphotericin B (AmB) is a very efficient drug against serious diseases such as leishmaniasis and systemic fungal infections. However, its oral bioavailability is limited due to its poor solubility in water. Nevertheless, it is marketed as high-cost lipid parenteral formulations that may induce serious infusion-related side effects. In this study, oil-in-water (O/W) microemulsions (MEs) were developed and characterized with a view to their use as solubility enhancers and oral delivery systems for AmB. Therefore, different nonionic surfactants from the Tween(®) and Span(®) series were tested for their solubilization capacity in combination with several oils. Based on pseudoternary phase diagrams, AmB-loaded MEs with mean droplet sizes about 120 nm were successfully produced. They were able to improve the drug solubility up to 1000-fold. Rheological studies showed the MEs to be low-viscosity formulations with Newtonian behavior. Circular dichroism and absorption spectra revealed that part of the AmB in the MEs was aggregated as an AmB reservoir carrier. Cytotoxicity studies revealed limited toxicity to macrophage-like cells that may allow the formulations to be considered as suitable carriers for AmB.

Strategies for the design of orally bioavailable antileishmanial treatments

Leishmaniasis is one of the six major tropical diseases targeted by the World Health Organization. The most serious, life-threatening form is visceral leishmaniasis (VL). No vaccine is yet available for human use and chemotherapy is the main mean of dealing with this disease. This review focuses on the development of drug delivery systems (DDS) for treatment of leishmaniasis. After an overview of the significance of leishmaniasis in 2013, current chemotherapy and its limitations are considered, leading to possible strategies to improve the treatment of VL: new drugs, combinations of existing drugs and DDS, particularly for oral administration. Nanostructured biomaterials such as lipid-based or polymeric nanoparticles have unique physicochemical properties, ultra-small and controllable size, large surface area to mass ratio and the possibility of surface modification which can be used to advantage for the oral administration of antileishmanial drugs. They can improve the rate of dissolution of poorly water-soluble drugs, increase intestinal residence time by bioadhesion and, especially when lipid additives are used, influence the route and efficiency of absorption. These recent advances in this very active field should lead to better management of this serious disease.