A Critical Review of Analytical Methods for Quantification of Amphotericin B in Biological Samples and Pharmaceutical Formulations

Old and new strategies in therapy and diagnosis against fungal infections

Fungal infections represent a serious global health threat. The new emerging pathogens and the spread of different forms of resistance are now hardly challenging the tools available in therapy and diagnostics. With the commonly used diagnoses, fungal identification is often slow and inaccurate, and, on the other hand, some drugs currently used as treatments are significantly affected by the decrease in susceptibility. Herein, the antifungal arsenal is critically summarized. Besides describing the old approaches and their mechanisms, advantages, and limitations, the focus is dedicated to innovative strategies which are designed, identified, and developed to take advantage of the discrepancies between fungal and host cells. Relevant pathways and their role in survival and virulence are discussed as their suitability as sources of antifungal targets. In a similar way, molecules with antifungal activity are reported as potential agents/precursors of the next generation of antimycotics. Particular attention was devoted to biotechnological entities, to their novelty and reliability, to drug repurposing and restoration, and to combinatorial applications yielding significant improvements in efficacy. KEY POINTS: • New antifungal agents and targets are needed to limit fungal morbidity and mortality. • Therapeutics and diagnostics suffer of delays in innovation and lack of targets. • Biologics, drug repurposing and combinations are the future of antifungal treatments.

In vitro antifungal and antibiofilm activities of auranofin against itraconazole-resistant Aspergillus fumigatus

BACKGROUND

Infections caused by azole-resistant Aspergillus are a rising public health threat with high mortality rates, high treatment costs and limited available antifungals, indicating an urgent need for new antifungals or strategies. Our aim was to investigate antifungal and antibiofilm activities of auranofin, an FDA-approved anti-antirheumatic drug.

METHODS

Fungal susceptibility testing for auranofin was carried out by the broth-based microdilution methods. Cell viability treated by auranofin was tested by resazurin dye testing. The synergistic effect of auranofin and antifungal drugs was evaluated using checkboard assay. The inhibitory of biofilms were measured by crystal violet staining. Gene expression level analysis and enzyme activity was investigated with qRT-PCR analysis and DTNB assay. The key amino acid residues in the binding of auranofin with A. fumigatus thioredoxin reductase (AfTrxR) were indicated by structural analyses, site-directed mutagenesis, and microscale thermophoresis (MST) assays.

RESULTS

Auranofin has fungicidal activity and in vitro antifungal spectrum including Aspergillus flavus, Aspergillus fumigatus, Aspergillus terreus, Aspergillus niger, even itraconazole (ITC)-resistant A. fumigatus. Additionally, it has antibiofilm activities against ITC-resistant A. fumigatus by reducing the expression level of SomA and MedA. Moreover, we discovered a synergistic effect of auranofin and ITC or amphotericin B against ITC-resistant A. fumigatus. Auranofin downregulated the gene transcription of AfTrxR, and strongly inhibited the enzyme activity of AfTrxR through interacting with residues C145 and C148.

CONCLUSIONS

Auranofin has fungicidal and antibiofilm activities in Aspergillus spp. and is also a potentiator of ITC or amphotericin B in vitro.

Comparative Colloidal Stability of Commercial Amphotericin B Nanoformulations Using Dynamic and Static Multiple Light Scattering Techniques

Background

Amphotericin B (AmB) nanoformulations have been widely used for the treatment of invasive fungal infections in clinical practice, all of which are lyophilized solid dosage forms that improve storage stability. The colloidal stability of reconstituted lyophilized nanoparticles in an injection medium is a critical quality attribute that directly affects their safety and efficacy during clinical use.

Methods

In the present study, the colloidal stability of commercial AmB nanoformulations, including AmB cholesteryl sulfate complex (AmB-CSC) and AmB liposome (AmB-Lipo), was evaluated using the dynamic (DLS) and static multiple light scattering (SMLS) techniques.

Results

Compared to the DLS technique, the SMLS technique allows for a more objective and accurate evaluation of the colloidal stability of AmB nanoformulations. The results obtained using the SMLS technique demonstrated that AmB-CSC and AmB-Lipo exhibited excellent colloidal stability in both sterile water and 5% dextrose injection. The disk-like structure of the AmB-CSC nanoparticles more readily adsorbed serum proteins to form protein corona compared to the spherical structure of AmB-Lipo after incubation with serum. Additionally, AmB-CSC and AmB-Lipo can significantly reduce the in vitro cytotoxicity and in vivo nephrotoxicity of AmB, which may be attributed to the good colloidal stability and the improved pharmacokinetic profiles of AmB nanoformulations.

Conclusion

To the best of our knowledge, this study is the first to compare the colloidal stability of commercial AmB nanoformulations. These findings will provide useful information not only to inform the clinical use of available AmB nanoformulations but also for improving the design and conduct of translational research on novel AmB nanomedicines.

Advances in Antifungal Development: Discovery of New Drugs and Drug Repurposing

This Special Issue of Pharmaceuticals describes recent advances accomplished in the field of antifungal development, especially the discovery of new drugs and drug repurposing [...]

A review of the antimicrobial activity of thermodynamically stable microemulsions

Microemulsions are thermodynamically stable, transparent, isotropic mixtures of oil, water and surfactant (and sometimes a co-surfactant), which have shown potential for widespread application in disinfection and self-preservation. This is thought to be due to an innate antimicrobial effect. It is suggested that the antimicrobial nature of microemulsions is the result of a combination of their inherent kinetic energy and their containing surfactants, which are known to aid the disruption of bacterial membranes. This review examines the contemporary evidence in support of this theory.

Antifungal Drug Repurposing

Control of fungal pathogens is increasingly problematic due to the limited number of effective drugs available for antifungal therapy. Conventional antifungal drugs could also trigger human cytotoxicity associated with the kidneys and liver, including the generation of reactive oxygen species. Moreover, increased incidences of fungal resistance to the classes of azoles, such as fluconazole, itraconazole, voriconazole, or posaconazole, or echinocandins, including caspofungin, anidulafungin, or micafungin, have been documented. Of note, certain azole fungicides such as propiconazole or tebuconazole that are applied to agricultural fields have the same mechanism of antifungal action as clinical azole drugs. Such long-term application of azole fungicides to crop fields provides environmental selection pressure for the emergence of pan-azole-resistant fungal strains such as Aspergillus fumigatus having TR34/L98H mutations, specifically, a 34 bp insertion into the cytochrome P450 51A (CYP51A) gene promoter region and a leucine-to-histidine substitution at codon 98 of CYP51A. Altogether, the emerging resistance of pathogens to currently available antifungal drugs and insufficiency in the discovery of new therapeutics engender the urgent need for the development of new antifungals and/or alternative therapies for effective control of fungal pathogens. We discuss the current needs for the discovery of new clinical antifungal drugs and the recent drug repurposing endeavors as alternative methods for fungal pathogen control.