The Future of Antifungal Drug Therapy: Novel Compounds and Targets

Nanomaterial-based therapeutics for enhanced antifungal therapy

The application of nanotechnology in antifungal therapy is gaining increasing attention. Current antifungal drugs have significant limitations, such as severe side effects, low bioavailability, and the rapid development of resistance. Nanotechnology offers an innovative solution to address these issues. This review discusses three key strategies of nanotechnology to enhance antifungal efficacy. Firstly, nanomaterials can enhance their interaction with fungal cells via ingenious surface tailoring of nanomaterials. Effective adhesion of nanoparticles to fungal cells can be achieved by electrostatic interaction or specific targeting to the fungal cell wall and cell membrane. Secondly, stimuli-responsive nanomaterials are developed to realize smart release of drugs in the specific microenvironment of pathological tissues, such as the fungal biofilm microenvironment and inflammatory microenvironment. Thirdly, nanomaterials can be designed to cross different physiological barriers, effectively addressing challenges posed by skin, corneal, and blood-brain barriers. Additionally, some new nanomaterial-based strategies in treating fungal infections are discussed, including the development of fungal vaccines, modulation of macrophage activity, phage therapy, the application of high-throughput screening in drug discovery, and so on. Despite the challenges faced in applying nanotechnology to antifungal therapy, its significant potential and innovation open new possibilities for future clinical antifungal applications.

Assessing the efficacy of carbon nanodots derived from curcumin on infectious diseases

INTRODUCTION

The threat of new, emerging, and multidrug-resistant microbes is increasing which has created the necessity for new antimicrobials. In this regard, nanotechnology can be an alternative for the treatment of infectious microbes. Curcumin has been used since ancient times as antimicrobials; however, it has limitations due to its less aqueous solubility, bioavailability, and biocompatibility. This problem can be solved by curcumin-derived carbon nanodots which are emerging antimicrobials of <10 nm size, water-soluble, biocompatible, less toxic, and fluorescent.

AREA COVERED

The review discusses the application of curcumin-derived carbon nanodots against various pathogenic microbes including bacteria and dreaded viruses like SARS-CoV-2. In addition, the role of curcumin carbon nanodots in biolabelling of pathogenic microbes, mechanism of action, bioimaging, and therapy has been critically examined.

EXPERT OPINION

Carbon nanodots play an important role in combating pathogenic microbes by early diagnosis, bioimaging, nanocarrier for antimicrobial drugs, and therapy of infectious diseases. Curcumin carbon nanodots have already demonstrated their benefits of being water soluble, bioavailable, and biocompatible. However, more thorough research is needed to understand the efficacy and safety of curcumin carbon nanodots. In the future, curcumin-derived carbon nanodots can be used as alternative antimicrobial agents to fight microbial infections including multidrug-resistant microbes.

Nanoscale fluconazole-constructed metal-organic frameworks with smart drug release for eradication of Candida biofilms in vulvovaginitis infection

Fungal infections associated with oral, gynecological, and skin ailments pose significant clinical challenges. The presence of biofilms often hampers the efficacy of conventional antifungal drugs owing to the complex microenvironment they create. In this study, the widely used antifungal medication fluconazole is utilized as a foundational component to be incorporated into zinc 2-methylimidazolate frameworks, resulting in the synthesis of nanoscale fluconazole-constructed metal-organic frameworks (F-ZIF). The F-ZIF is constructed through coordination interactions between zinc and fluconazole, retaining the structure and pH-responsiveness of the zinc 2-methylimidazolate framework. The pH-responsiveness F-ZIF makes sure the fluconazole can be released in acidic biofilm, which prevents the undesired release in healthy tissue, resulting in good biocompatibility both in vitro and in vivo. The in vitro studies demonstrated that F-ZIF exhibits enhanced efficacy in eradicating fungal pathogens in their biofilm growth state compared with the free fluconazole. Furthermore, in vivo experiments reveal the better effectiveness of F-ZIF in treating Candida albicans-induced vulvovaginal candidiasis, and less infection-related inflammation was observed. Hence, the one-port synthetic F-ZIF presents a promising solution for addressing fungal biofilm-related infections.

MIG1, TUP1 and NRG1 mediated yeast to hyphal morphogenesis inhibition in Candida albicans by ganciclovir

Candida albicans is a polymorphic human fungal pathogen and the prime etiological agent responsible for candidiasis. The main two aspects of C. albicans virulence that have been suggested are yeast-to-hyphal (Y-H) morphological transitions and biofilm development. Anti-fungal agents targeting these virulence attributes enhances the antifungal drug development process. Repositioning with other non-fungal drugs offered a one of the new strategies and a potential alternative option to counter the urgent need for antifungal drug development. In the current study, an antiviral drug ganciclovir was screened as an antifungal agent against ATCC 90028, 10231 and clinical isolate (C1). Ganciclovir at 0.5 mg/ml concentration reduced 50% hyphal development on a silicon-based urinary catheter and was visualized using scanning electron microscopy. Ganciclovir reduced ergosterol biosynthesis in both strains and C1 isolate of C. albicans in a concentration-dependent manner. Additionally, a gene expression profile study showed that ganciclovir treatment resulted in upregulation of hyphal-specific repressors MIG1, TUP1, and NRG1 in C. albicans. Additionally, an in vivo study on the Bombyx mori silkworm model further evidenced the virulence inhibitory ability of ganciclovir (0.5 mg/ml) against C. albicans. This is the first report that explore the novel anti-morphogenic activities of ganciclovir against the pathogenic C. albicans strains, along with clinical isolates. Further, ganciclovir may be considered for therapeutic purpose after combinations with standard antifungal agents.

Novel targets and improved immunotherapeutic techniques with an emphasis on antimycosal drug resistance for the treatment and management of mycosis

Infections due to pathogenic fungi are endemic in particular area with increased morbidity and mortality. More than a thousand people are infected per year and the way of treatment is of high demand having a significant impact on the population health. Medical practitioners confront various troublesome analytic and therapeutical challenges in the administration of immunosuppressed sufferer at high danger of expanding fungal infections. An upgraded antimycosal treatment is fundamental for a fruitful result while treating intrusive mycoses. A collection of antimycosal drugs keeps on developing with their specific antifungal targets including cell membrane, mitochondria, cell wall, and deoxyribonucleic acid (DNA)/ribonucleic acid (RNA) or protein biosynthesis. Some fundamental classes of ordinarily directed medications are the polyenes, amphotericin B, syringomycin, allylamines, honokiol, azoles, flucytosine, echinocandins etc. However, few immunotherapy processes and vaccinations are being developed to mark this need, although one presently can't seem to arrive at the conclusion. In this review article, there has been a trial to give details upgradation about the current immune therapeutic techniques and vaccination strategies against prevention or treatment of mycosis as well as the difficulties related with their turn of events. There has been also a visualization in the mentioned review paper about the various assorted drugs and their specific target analysis along with therapeutic interventions.

Toll-like receptor 4 (TLR4) is the major pattern recognition receptor triggering the protective effect of a Candida albicans extracellular vesicle-based vaccine prototype in murine systemic candidiasis

Systemic candidiasis remains a significant public health concern worldwide, with high mortality rates despite available antifungal drugs. Drug-resistant strains add to the urgency for alternative therapies. In this context, vaccination has reemerged as a prominent immune-based strategy. Extracellular vesicles (EVs), nanosized lipid bilayer particles, carry a diverse array of native fungal antigens, including proteins, nucleic acids, lipids, and glycans. Previous studies from our laboratory demonstrated that Candida albicans EVs triggered the innate immune response, activating bone marrow-derived dendritic cells (BMDCs) and potentially acting as a bridge between innate and adaptive immunity. Vaccination with C. albicans EVs induced the production of specific antibodies, modulated cytokine production, and provided protection in immunosuppressed mice infected with lethal C. albicans inoculum. To elucidate the mechanisms underlying EV-induced immune activation, our study investigated pathogen-associated molecular patterns (PAMPs) and pattern recognition receptors (PRRs) involved in EVs-phagocyte engagement. EVs from wild-type and mutant C. albicans strains with truncated mannoproteins were compared for their ability to stimulate BMDCs. Our findings revealed that EV decoration with O- and N-linked mannans and the presence of β-1,3-glucans and chitin oligomers may modulate the activation of specific PRRs, in particular Toll-like receptor 4 (TLR4) and dectin-1. The protective effect of vaccination with wild-type EVs was found to be dependent on TLR4. These results suggest that fungal EVs can be harnessed in vaccine formulations to selectively activate PRRs in phagocytes, offering potential avenues for combating or preventing candidiasis.IMPORTANCESystemic candidiasis is a serious global health concern with high mortality rates and growing drug resistance. Vaccination offers a promising solution. A unique approach involves using tiny lipid-coated particles called extracellular vesicles (EVs), which carry various fungal components. Previous studies found that Candida albicans EVs activate the immune response and may bridge the gap between innate and adaptive immunity. To understand this better, we investigated how these EVs activate immune cells. We demonstrated that specific components on EV surfaces, such as mannans and glucans, interact with receptors on immune cells, including Toll-like receptor 4 (TLR4) and dectin-1. Moreover, vaccinating with these EVs led to strong immune responses and full protection in mice infected with Candida. This work shows how harnessing fungal EVs might lead to effective vaccines against candidiasis.

Verapamil enhances the activity of Caspofungin against Cryptococcus neoformans， coinciding with inhibited Ca2+/CN pathway and damage to cell wall integrity

OBJECTIVES

Given the challenges posed by toxicity and drug resistance in the treatment of cryptococcal infections, we sought to explore the antifungal potential of verapamil (VER), a calcium channel blocker, against Cryptococcus neoformans (C. neoformans), and its potential synergy with antifungals, specifically caspofungin (CAS).

MATERIALS AND METHODS

In vitro and in vivo (Galleria mellonella) models were employed to assess VER's antifungal activity and its interaction with CAS. Mechanisms underlying the synergism were explored through analysis of cell wall integrity, membrane permeability, and gene expression related to the calcineurin pathway. Additionally, the influence of Ca2+ on chitin deacetylase activity was investigated.

RESULTS

VER exhibited a pronounced antifungal effect on C. neoformans and synergized with CAS, enhancing antifungal efficacy in Galleria mellonella. VER reduced chitosan content and disrupted cell wall integrity, evidenced by melanin leakage and fluorescence staining. VER+CAS modified membrane permeability, triggering intracellular ROS accumulation and mitochondrial membrane potential alterations. VER mitigated CAS-induced calcium fluctuations and downregulated calcineurin pathway genes. Furthermore, it was found that the enzyme activity of chitin deacetylase of C. neoformans is significantly influenced by the presence of Ca2+, suggesting that the use of VER may affect this activity.

CONCLUSIONS

The synergistic antifungal effect of VER and CAS represents a promising therapeutic strategy for cryptococcal infections. The multifaceted mechanisms, including disruption of cell wall integrity and modulation of membrane permeability, and regulation of intracellular calcium signaling pathways, offer new insights into antifungal drug development.

Antifungal Activity of 3-Hydrazinoquinoxaline-2-Thiol, a Novel Quinoxaline Derivative against Candida Species

Candida ranks as among the most frequently encountered fungal infections that associated with high morbidity and mortality. Quinoxaline derivatives are a group of small molecules that showed a promising antimicrobial activity. This study aimed to investigate the fungicidal effects of 3-hydrazinoquinoxaline-2-thiol against Candida in comparison with Amphotericin B in vitro as a reference. Also, we aim to assess the efficacy of 3-hydrazinoquinoxaline-2-thiol in vivo using mice oral candidiasis model. Fifty-six Candida isolates were subjected to susceptibility testing by broth microdilution method for 3-hydrazinoquinoxaline-2-thiol and Amphotericin B. Therefore, Minimal inhibitory concentrations (MIC) were assessed and compared. The oral candidiasis mice model was used to evaluate the activity of 3-hydrazinoquinoxaline-2-thiol in vivo. Microbiological evaluation of progression and ELISA were used in this study. 3-hydrazinoquinoxaline-2-thiol was more effective than Amphotericin B against most clinical isolates of Candida albicans. Higher effectiveness was seen against Candida glabrata and Candida parapsilosis isolates. However, the efficiency against Candida tropicalis isolates varies. 3-hydrazinoquinoxaline-2-thiol was also effective against Pichia kudriavzevii and Clavispora lusitaniae. 3-hydrazinoquinoxaline-2-thiol showed a good efficacy in mice model against C. albicans cells ATCC 10231. 3-hydrazinoquinoxaline-2-thiol has shown promising antifungal and anti-inflammatory activity against different Candida species. More tests and experiments are needed.

The Combination of 3-Hydrazinoquinoxaline-2-Thiol with Thymoquinone Demonstrates Synergistic Activity Against Different Candida Strains

Introduction

Candida is the primary cause of invasive fungal disease, candidiasis, especially in developed nations. The increasing resistance observed in multiple antibiotics, coupled with the prolonged process of creating new antibiotics from the ground up, emphasizes the urgent requirement for innovative methods and new compounds to combat Candida infections. Employing a treatment strategy that combines antibiotics can improve efficacy, broaden the spectrum of targeted fungal, and reduce the chances of resistance emergence. This approach shows potential in tackling the escalating problem of antibiotic resistance. The objective of this research is to explore the potential synergistic effects of combining 3-hydrazinoquinoxaline-2-thiol and thymoquinone against a variety of Candida isolates. This investigation aims to offer an understanding of the collective antimicrobial action of these compounds.

Methods

Broth microdilution was utilized to assess the Minimum Inhibitory Concentrations (MICs) of 3-hydrazinoquinoxaline-2-thiol and thymoquinone for 22 clinical Candida isolates. Following this, a checkerboard assay was employed to analyze the interaction between 3-hydrazinoquinoxaline-2-thiol and thymoquinone, with a specific focus on the Fractional Inhibitory Concentration Index (FICI).

Results

The MICs of thymoquinone and 3-hydrazinoquinoxaline-2-thiol were determined for 22 clinical Candida strains, with thymoquinone exhibiting MICs ranging from 64 to 8 µg/mL, and 3-hydrazinoquinoxaline-2-thiol displaying MICs varying from 64 to 8 µg/mL. Notably, the combination of 3-hydrazinoquinoxaline-2-thiol and thymoquinone resulted in a synergistic effect, leading to a significant reduction in MICs, with reductions of up to 64-fold with FICI below 0.5 against tested strains.

Conclusion

The prospect of using 3-hydrazinoquinoxaline-2-thiol in combination with thymoquinone as an effective solution against Candida looks encouraging. Nevertheless, to validate its practical applicability, additional comprehensive testing and experiments are imperative.

New insides into chimeric and hybrid azines derivatives with antifungal activity

During the last decades, five or six member rings azaheterocycles compounds appear to be an extremely valuable source of antifungal agents. Their use seems to be a very attractive solution in antifungal therapy and to overcome antifungal resistance in agriculture. The present review highlights the main results obtained in the field of hybrid and chimeric azine (especially pyridine, quinoline, phenanthroline, bypyridine, naphthyridine and their fused derivatives) derivatives presented in scientific literature from the last 10 years, with emphasis on antifungal activity of the mentioned compounds. A special attention was played to hybrid and chimeric azole-azine class, having in view the high antifungal potential of azoles.

Bioinformatics Approaches in the Development of Antifungal Therapeutics and Vaccines

Fungal infections are considered a great threat to human life and are associated with high mortality and morbidity, especially in immunocompromised individuals. Fungal pathogens employ various defense mechanisms to evade the host immune system, which causes severe infections. The available repertoire of drugs for the treatment of fungal infections includes azoles, allylamines, polyenes, echinocandins, and antimetabolites. However, the development of multidrug and pandrug resistance to available antimycotic drugs increases the need to develop better treatment approaches. In this new era of -omics, bioinformatics has expanded options for treating fungal infections. This review emphasizes how bioinformatics complements the emerging strategies, including advancements in drug delivery systems, combination therapies, drug repurposing, epitope-based vaccine design, RNA-based therapeutics, and the role of gut-microbiome interactions to combat anti-fungal resistance. In particular, we focused on computational methods that can be useful to obtain potent hits, and that too in a short period.

Exploring the antifungal, antibiofilm and antienzymatic potential of Rottlerin in an in vitro and in vivo approach

Candida species have been responsible for a high number of invasive infections worldwide. In this sense, Rottlerin has demonstrated a wide range of pharmacological activities. Therefore, this study aimed to evaluate the antifungal, antibiofilm and antivirulence activity of Rottlerin in vitro against Candida spp. and its toxicity and antifungal activity in vivo. Rottlerin showed antifungal activity against all yeasts evaluated, presenting Minimum Inhibitory and Fungicidal Concentration (MIC and MFC) values of 7.81 to > 1000 µg/mL. Futhermore, it was able to significantly inhibit biofilm production, presenting Biofilm Inhibitory Concentration (MICB50) values that ranged from 15.62 to 250 µg/mL and inhibition of the cell viability of the biofilm by 50% (IC50) from 2.24 to 12.76 µg/mL. There was a considerable reduction in all hydrolytic enzymes evaluated, with emphasis on hemolysin where Rottlerin showed a reduction of up to 20%. In the scanning electron microscopy (SEM) analysis, Rottlerin was able to completely inhibit filamentation by C. albicans. Regarding in vivo tests, Rottlerin did not demonstrate toxicity at the therapeutic concentrations demonstrated here and was able to increase the survival of C. elegans larvae infected. The results herein presented are innovative and pioneering in terms of Rottlerin's multipotentiality against these fungal infections.

Impact of Nitric Oxide-Release Kinetics on Antifungal Activity

Pathogenic fungi are an increasing health threat due to the rise in drug resistance. The limited number of antifungals currently available and growing incidence of multi-drug-resistant fungi has caused rising healthcare costs and a decreased quality of life for patients with fungal infections. Nitric oxide (NO) has previously been shown to act as an antimicrobial agent, albeit with a limited understanding of the effects of the NO-release kinetics against pathogenic fungi. Herein, the antifungal effects of four nitric oxide-releasing small molecules were studied against the pathogenic fungi Candida albicans, Candida auris, Cryptococcus neoformans, and Aspergillus fumigatus, to demonstrate the broad-spectrum antifungal activity of NO. A bolus dose of NO was found to eradicate fungi after 24 h, where nitric oxide donors with shorter half-lives achieved antifungal activity at lower concentrations and thus had wider selectivity indexes. Each NO donor was found to cause a severe surface destruction of fungi, and all NO donors exhibited compatibility with currently prescribed antifungals against several different fungi species.

Divergent mitochondrial responses and metabolic signal pathways secure the azole resistance in Crabtree-positive and negative Candida species

Azole drugs are the main therapeutic drugs for invasive fungal infections. However, azole-resistant strains appear repeatedly in the environment, posing a major threat to human health. Several reports have shown that mitochondria are associated with the virulence of pathogenic fungi. However, there are few studies on the mechanisms of mitochondria-mediated azoles resistance. Here, we first performed mitochondrial proteomic analysis on multiple Candida species (Candida albicans, Nakaseomyces glabrata, Pichia kudriavzevii, and Candida auris) and analyzed the differentially expressed mitochondrial proteins (DEMPs) between azole-sensitive and azole-resistant Candida species. Subsequently, we performed Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, gene ontology analysis, and protein-protein interaction network analysis of DEMPs. Our results showed that a total of 417, 165, and 25 DEMPs were identified in resistant C. albicans, N. glabrata, and C. auris, respectively. These DEMPs were enriched in ribosomal biogenesis at cytosol and mitochondria, tricarboxylic acid cycle, glycolysis, transporters, ergosterol, and cell wall mannan biosynthesis. The high activations of these cellular activities, found in C. albicans and C. auris (at low scale), were mostly opposite to those observed in two fermenter species-N. glabrata and P. kudriavzevii. Several transcription factors including Rtg3 were highly produced in resistant C. albicans that experienced a complex I activation of mitochondrial electron transport chain (ETC). The reduction of mitochondrial-related activities and complex IV/V of ETC in N. glabrata and P. kudriavzevii was companying with the reduced proteins of Tor1, Hog1, and Snf1/Snf4.IMPORTANCECandida spp. are common organisms that cause a variety of invasive diseases. However, Candida spp. are resistant to azoles, which hinders antifungal therapy. Exploring the drug-resistance mechanism of pathogenic Candida spp. will help improve the prevention and control strategy and discover new targets. Mitochondria, as an important organelle in eukaryotic cells, are closely related to a variety of cellular activities. However, the role of mitochondrial proteins in mediating azole resistance in Candida spp. has not been elucidated. Here, we analyzed the mitochondrial proteins and signaling pathways that mediate azole resistance in Candida spp. to provide ideas and references for solving the problem of azole resistance. Our work may offer new insights into the connection between mitochondria and azoles resistance in pathogenic fungi and highlight the potential clinical value of mitochondrial proteins in the treatment of invasive fungal infections.

Discovery of New Antimicrobial Metabolites in the Coculture of Medicinal Mushrooms

Bioactivity screening revealed that the antifungal activities of EtOAc extracts from coculture broths of Trametes versicolor SY630 with either Vanderbylia robiniophila SY341 or Ganoderma gibbosum SY1001 were significantly improved compared to that of monocultures. Activity-guided isolation led to the discovery of five aromatic compounds (1-5) from the coculture broth of T. versicolor SY630 and V. robiniophila SY341 and two sphingolipids (6 and 7) from the coculture broth of T. versicolor SY630 and G. gibbosum SY1001. Tramevandins A-C (1-3) and 17-ene-1-deoxyPS (6) are new compounds, while 1-deoxyPS (7) is a new natural product. Notably, compound 2 represents a novel scaffold, wherein the highly modified p-terphenyl bears a benzyl substituent. The absolute configurations of those new compounds were elucidated by X-ray diffraction, ECD calculations, and analysis of physicochemical constants. Compounds 1, 2, and 5-7 exhibited different degrees of antimicrobial activity, and the antifungal activities of compounds 6 and 7 against Candida albicans and Cryptococcus neoformans are comparable to those of fluconazole, nystatin, and sphingosine, respectively. Transcriptome analysis, propidium iodide staining, ergosterol quantification, and feeding assays showed that the isolated sphingolipids can extensively downregulate the late biosynthetic pathway of ergosterol in C. albicans, representing a promising mechanism to combat antibiotic-resistant fungi.

Rational Design of Antifungal Peptides Based on the γ-Core Motif of a Neosartorya (Aspergillus) fischeri Antifungal Protein to Improve Structural Integrity, Efficacy, and Spectrum

Antifungal peptides offer promising alternative compounds for the treatment of fungal infections, for which new antifungal compounds are urgently needed. Constant and broad antifungal spectra of these peptides play essential roles in their reliable therapeutic application. It has been observed that rationally designed peptides using the evolutionarily conserved γ-core region (GXC-X3-9-C) of an antifungal protein from Neosartorya (Aspergillus) fischeri highly inhibit the growth of fungi. The cysteines in these peptides have free sulfhydryl groups, which allow cyclization and dimerization under oxidative conditions, thereby impairing antifungal efficacy. To overcome this problem, one or two cysteine residues were substituted by serines or S-tert-butyl was applied as a cysteine-protecting group. Furthermore, structural integrity and antifungal efficacy investigations before and after oxidative exposure revealed that substituting both cysteines with serines and S-tert-butylation helped maintain the structural integrity. However, it slightly decreased the antifungal efficacy against a yeast, Candida albicans. Interestingly, S-tert-butylation maintained the efficacy and could extend the antifungal activity to a mold, Aspergillus fumigatus. Usually, cyclization and dimerization did not influence the antifungal efficacy of most peptides. Additionally, hemolysis tests and Galleria mellonella toxicity model experiments indicated that none of the applied modifications made the peptides harmful to animals.

Trans-kingdom fungal pathogens infecting both plants and humans, and the problem of azole fungicide resistance

Azole antifungals are abundantly used in the environment and play an important role in managing fungal diseases in clinics. Due to the widespread use, azole resistance is an emerging global problem for all applications in several fungal species, including trans-kingdom pathogens, capable of infecting plants and humans. Azoles used in agriculture and clinics share the mode of action and facilitating cross-resistance development. The extensive use of azoles in the environment, e.g., for plant protection and wood preservation, contributes to the spread of resistant populations and challenges using these antifungals in medical treatments. The target of azoles is the cytochrome p450 lanosterol 14-α demethylase encoded by the CYP51 (called also as ERG11 in the case of yeasts) gene. Resistance mechanisms involve mainly the mutations in the coding region in the CYP51 gene, resulting in the inadequate binding of azoles to the encoded Cyp51 protein, or mutations in the promoter region causing overexpression of the protein. The World Health Organization (WHO) has issued the first fungal priority pathogens list (FPPL) to raise awareness of the risk of fungal infections and the increasingly rapid spread of antifungal resistance. Here, we review the main issues about the azole antifungal resistance of trans-kingdom pathogenic fungi with the ability to cause serious human infections and included in the WHO FPPL. Methods for the identification of these species and detection of resistance are summarized, highlighting the importance of these issues to apply the proper treatment.

A novel zinc-chelating compound has antifungal activity against a wide range of Candida species, including multidrug-resistant Candida auris

Objectives

In recent years, the incidence of invasive fungal infections has increased, resulting in considerable morbidity and mortality, particularly among immunocompromised individuals. Potential challenges in treating these infections with the few existing antifungal agents highlight the urgency of developing new ones. Here, we evaluated six alkyl polyamine compounds (APCs), not previously reported as antifungal drugs to our knowledge, that could deprive fungi of essential transition metals.

Methods

The APC with confirmed antifungal activity against Candida spp. was analysed by using transcriptomics, followed by metal-addition experiments, mass spectrometric analyses and intracellular zinc quantification with a fluorescent probe.

Results

A cyclic APC with three pyridylmethyl groups, APC6, had high antifungal activity against a wide range of Candida species, including MDR Candida auris. We conclusively demonstrated that APC6 was able to capture zinc within fungal cells. APC6 not only exhibited activity against C. auris as a single agent but also enhanced the efficacy of an azole antifungal agent, voriconazole, in vitro and in vivo. APC6 disrupted the biofilms formed by Candida species.

Conclusions

This zinc-chelating compound has potential as an antifungal agent, and the control of zinc levels in Candida species could be a powerful approach to treating drug-resistant candidiasis.

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.

Biochanin A Inhibits the Growth and Biofilm of Candida Species

The aim of this study was to investigate the antifungal activity of biochanin A (BCA) against planktonic growth and biofilms of six Candida species, including C. albicans, C. parapsilosis, C. glabrata, C. tropicalis, C. auris, and C. krusei. We applied various assays that determined (a) the antimicrobial effect on growth of Candida species, (b) the effect on formation of hyphae and biofilm, (c) the effect on the expression of genes related to hyphal growth and biofilm formation, (d) the influence on cell wall structure, and (e) the effect on cell membrane integrity and permeability. Moreover, disk diffusion tests were used to investigate the effect of a combination of BCA with fluconazole to assess their possible synergistic effect on drug-resistant C. albicans, C. glabrata, and C. auris. Our results showed that the BCA MIC50 values against Candida species ranged between 125 µg/mL and 500 µg/mL, and the MIC90 values were in a concentration range from 250 µg/mL to 1000 µg/mL. The treatment with BCA inhibited adhesion of cells, cell surface hydrophobicity (CSH), and biofilm formation and reduced hyphal growth in all the analyzed Candida species. Real-time qRT-PCR revealed that BCA down-regulated the expression of biofilm-specific genes in C. albicans. Furthermore, physical destruction of C. albicans cell membranes and cell walls as a result of the treatment with BCA was observed. The combination of BCA and fluconazole did not exert synergistic effects against fluconazole-resistant Candida.

Nanotherapeutics for the delivery of antifungal drugs

The treatment of fungal infections is challenging with high death rates reported among immunocompromised patients. The currently available antifungals suffer from poor bioavailability and solubility, pharmacokinetics, and drug resistance, with limited cellular uptake. The clinical pipeline of new antifungals is dry. The incorporation of antifungal drugs into polymer-based nanocarriers to form nanotherapeutics is a promising approach to enhance the therapeutic outcomes of the available antifungal drugs. This review summarizes different polymer-based nanotherapeutics strategies that have been explored for the delivery of antifungals, resulting in enhanced therapeutic outcomes, such as improved pharmacokinetics, targeted/sustained delivery, prolonged drug circulation, retention of the drugs at the localized site of action, and overcoming drug resistance when compared with the free antifungal drugs.

Therapeutic advances in neuroinfectious diseases

There have been several major advances in therapeutic options for the treatment of neurological infections over the past two decades. These advances encompass both the development of new antimicrobial therapies and the repurposing of existing agents for new indications. In addition, advances in our understanding of the host immune response have allowed for the development of new immunomodulatory strategies in the treatment of neurological infections. This review focuses on the key advances in the treatment of neurological infections, including viral, bacterial, fungal, and prion diseases, with a particular focus on immunomodulatory treatment options. This review also highlights the process by which clinicians can request access to therapeutic agents on a compassionate or emergency basis when they may not be commercially available. While many therapeutic advances have been achieved in the past several years, there remains a pressing need for the continued development of additional therapeutic agents in the treatment of neurological infections.

An Insight into the Repurposing of Phytoconstituents obtained from Delhi's Aravalli Biodiversity Park as Antifungal Agents

The global prevalence of fungal infections is alarming in both the pre- and post- COVID period. Due to a limited number of antifungal drugs, there are hurdles in treatment strategies for fungal infections due to toxic potential, drug interactions, and the development of fungal resistance. All the antifungal targets (existing and newer) and pipeline molecules showing promise against these targets are reviewed. The objective was to predict or repurpose phyto-based antifungal compounds based on a dual target inhibition approach (Sterol-14-α- demethylase and HSP-90) using a case study. In pursuit of repurposing the phytochemicals as antifungal agents, a team of researchers visited Aravalli Biodiversity Park (ABP), Delhi, India, to collect information on available medicinal plants. From 45 plants, a total of 1149 ligands were collected, and virtual screening was performed using Schrodinger Suite 2016 software to get 83 hits against both the target proteins: Sterol-14-α-demethylase and HSP-90. After analysis of docking results, ligands were selected based on their interaction against both the target proteins and comparison with respective standard ligands (fluconazole and ganetespib). We have selected Isocarthamidin, Quercetin and Boeravinone B based on their docking score and binding interaction against the HSP-90 (Docking Score -9.65, -9.22 and -9.21, respectively) and 14-α-demethylase (Docking Score -9.19, -10.76 and -9.74 respectively). The docking protocol was validated and MM/GBSA studies depicted better stability of selected three ligands (Isocarthamidin, Quercetin, Boeravinone B) complex as compared to standard complex. Further, MD simulation studies were performed using the Desmond (67) software package version 2018-4. All the findings are presented as a case study for the prediction of dual targets for the repurposing of certain phytochemicals as antifungal agents.

A Membrane-Targeted Photosensitizer Prevents Drug Resistance and Induces Immune Response in Treating Candidiasis

Candida albicans (C. albicans), a ubiquitous polymorphic fungus in humans, causes different types of candidiasis, including oral candidiasis (OC) and vulvovaginal candidiasis (VVC), which are physically and mentally concerning and financially costly. Thus, developing alternative antifungals that prevent drug resistance and induce immunity to eliminate Candida biofilms is crucial. Herein, a novel membrane-targeted aggregation-induced emission (AIE) photosensitizer (PS), TBTCP-QY, is developed for highly efficient photodynamic therapy (PDT) of candidiasis. TBTCP-QY has a high molar absorption coefficient and an excellent ability to generate 1 O2 and •OH, entering the interior of biofilms due to its high permeability. Furthermore, TBTCP-QY can efficiently inhibit biofilm formation by suppressing the expression of genes related to the adhesion (ALS3, EAP1, and HWP1), invasion (SAP1 and SAP2), and drug resistance (MDR1) of C. albicans, which is also advantageous for eliminating potential fungal resistance to treat clinical infectious diseases. TBTCP-QY-mediated PDT efficiently targets OC and VVC in vivo in a mouse model, induces immune response, relieves inflammation, and accelerates the healing of mucosal defects to combat infections caused by clinically isolated fluconazole-resistant strains. Moreover, TBTCP-QY demonstrates excellent biocompatibility, suggesting its potential applications in the clinical treatment of OC and VVC.

Immunization with a heat-killed prm1 deletion strain protects the host from Cryptococcus neoformans infection

Systemic infection with Cryptococcus neoformans, a dangerous and contagious pathogen found throughout the world, frequently results in lethal cryptococcal pneumonia and meningoencephalitis, and no effective treatments and vaccination of cryptococcosis are available. Here, we describe Prm1, a novel regulator of C. neoformans virulence. C. neoformans prm1Δ cells exhibit extreme sensitivity to various environmental stress conditions. Furthermore, prm1Δ cells show deficiencies in the biosynthesis of chitosan and mannoprotein, which in turn result in impairment of cell wall integrity. Treatment of mice with heat-killed prm1Δ cells was found to facilitate the host immunological defence against infection with wild-type C. neoformans. Further investigation demonstrated that prm1Δ cells strongly promote pulmonary production of interferon-γ, leading to activation of macrophage M1 differentiation and inhibition of M2 polarization. Therefore, our findings suggest that C. neoformans Prm1 may be a viable target for the development of anti-cryptococcosis medications and, cells lacking Prm1 represent a promising candidate for a vaccine.

Microemulsions, nanoemulsions and emulgels as carriers for antifungal antibiotics

According to estimates, up to 25% of the world's population has fungal skin diseases, making them the most prevalent infectious disease. Several chemical classes of antifungal drugs are available to treat fungal infections. However, the major challenges of conventional formulations of antifungal drugs include poor pharmacokinetic profiles like solubility, low permeability, side effects and decreased efficacy. Novel drug delivery is a promising approach for overcoming pharmacokinetic limitations and increasing the effectiveness of antibiotics. In this review, we have shed light on microemulsions, nanoemulsions, and emulgels as novel drug delivery approaches for the topical delivery of antifungal antibiotics. We believe these formulations have potential translational value and could be developed for treating fungal infections in humans.

Molecular association of Candida albicans and vulvovaginal candidiasis: focusing on a solution

Candida albicans-mediated vulvovaginal candidiasis (VVC) is a significant challenge in clinical settings, owing to the inefficacy of current antifungals in modulating virulence, development of resistance, and poor penetration into the biofilm matrix. Various predisposition factors are molecular drivers that lead to the dysbiosis of normal microflora of the vagina, upregulation of central metabolic pathways, morphogenesis, hyphal extension, adhesion, invasion, and biofilm formation leading to chronic infection and recurrence. Hence, it is crucial to understand the molecular mechanism behind the virulence pathways driven by those drivers to decode the drug targets. Finding innovative solutions targeting fungal virulence/biofilm may potentiate the antifungals at low concentrations without affecting the recurrence of resistance. With this background, the present review details the critical molecular drivers and associated network of virulence pathways, possible drug targets, target-specific inhibitors, and probable mode of drug delivery to cross the preclinical phase by appropriate in vivo models.

Design, Synthesis, and Activity Evaluation of Novel Dual-Target Inhibitors with Antifungal and Immunoregulatory Properties

Dual-target (CYP51/PD-L1) plays an important role in the process of fungal proliferation and immune suppression. A series of novel quinazoline compounds with dual-target inhibition function was constructed using the skeleton growth method, and their structures were synthesized, characterized, and evaluated. Among them, the perfected compounds (L11, L20, L21) were selected for further study, which exhibited remarkable biological activity against different fungal strains (MIC50, 0.25-2.0 μg/mL) in vitro. On the one hand, these compounds inhibited CYP51 activity, induced ROS aggregation, and mitochondrial damage; this ultimately caused fungal lysis and death. On the other hand, they also effectively activated the body's immune ability by blocking the interaction between PD-L1 and PD-1, slowed down the inflammatory reaction, and accelerated the recovery process of fungal infections.

Confronting antifungal resistance, tolerance, and persistence: Advances in drug target discovery and delivery systems

Human pathogenic fungi pose a serious threat to human health and safety. Unfortunately, the limited number of antifungal options is exacerbated by the continuous emergence of drug-resistant variants, leading to frequent drug treatment failures. Recent studies have also highlighted the clinical importance of other modes of fungal survival of antifungal treatment, including drug tolerance and persistence, pointing to the complexity of the fungal response to antifungal drugs. A lack of understanding of the fungal drug response has hampered the identification of new targets, the development of alternative antifungal strategies and the design of appropriate delivery systems. In this review we summarize recent advances in the study of antifungal resistance, tolerance and persistence, with an emphasis on promising drug targets and drug delivery systems that may yield important insights into the development of new or improved antifungal therapies against fungal infections.

Isomerization of bioactive acylhydrazones triggered by light or thiols

The acylhydrazone unit is well represented in screening databases used to find ligands for biological targets, and numerous bioactive acylhydrazones have been reported. However, potential E/Z isomerization of the C=N bond in these compounds is rarely examined when bioactivity is assayed. Here we analysed two ortho-hydroxylated acylhydrazones discovered in a virtual drug screen for modulators of N-methyl-D-aspartate receptors and other bioactive hydroxylated acylhydrazones with structurally defined targets reported in the Protein Data Bank. We found that ionized forms of these compounds, which are populated under laboratory conditions, photoisomerize readily and the isomeric forms have markedly different bioactivity. Furthermore, we show that glutathione, a tripeptide involved with cellular redox balance, catalyses dynamic E⇄Z isomerization of acylhydrazones. The ratio of E to Z isomers in cells is determined by the relative stabilities of the isomers regardless of which isomer was applied. We conclude that E/Z isomerization may be a common feature of the bioactivity observed with acylhydrazones and should be routinely analysed.

Recent Progress in Research on Mitochondrion-Targeted Antifungal Drugs: a Review

Fungal infections, which commonly occur in immunocompromised patients, can cause high morbidity and mortality. Antifungal agents act by disrupting the cell membrane, inhibiting nucleic acid synthesis and function, or inhibiting β-1,3-glucan synthase. Because the incidences of life-threatening fungal infections and antifungal drug resistance are continuously increasing, there is an urgent need for the development of new antifungal agents with novel mechanisms of action. Recent studies have focused on mitochondrial components as potential therapeutic drug targets, owing to their important roles in fungal viability and pathogenesis. In this review, we discuss novel antifungal drugs targeting mitochondrial components and highlight the unique fungal proteins involved in the electron transport chain, which is useful for investigating selective antifungal targets. Finally, we comprehensively summarize the efficacy and safety of lead compounds in clinical and preclinical development. Although fungus-specific proteins in the mitochondrion are involved in various processes, the majority of the antifungal agents target dysfunction of mitochondria, including mitochondrial respiration disturbance, increased intracellular ATP, reactive oxygen species generation, and others. Moreover, only a few drugs are under clinical trials, necessitating further exploration of possible targets and development of effective antifungal agents. The unique chemical structures and targets of these compounds will provide valuable hints for further exploiting new antifungals.

Non-self glycan structures as possible modulators of cancer progression: would polysaccharides from Cryptococcus spp. impact this phenomenon?

Invasive fungal infections (IFI) are responsible for a large number of annual deaths. Most cases are closely related to patients in a state of immunosuppression, as is the case of patients undergoing chemotherapy. Cancer patients are severely affected by the worrisome proportions that an IFI can take during cancer progression, especially in an already immunologically and metabolically impaired patient. There is scarce knowledge about strategies to mitigate cancer progression in these cases, beyond conventional treatment with antifungal drugs with a narrow therapeutic range. However, in recent years, ample evidence has surfaced describing the possible interferences that IFI may have both on the progression of pre-existing cancers and in the induction of newly transformed cells. The leading gambit for modulation of tumor progression comes from the ability of fungal virulence factors to modulate the host's immune system, since they are found in considerable concentrations in the tumor microenvironment during infection. In this context, cryptococcosis is of particular concern, since the main virulence factor of the pathogenic yeast is its polysaccharide capsule, which carries constituents with high immunomodulatory properties and cytotoxic potential. Therefore, we open a discussion on what has already been described regarding the progression of cryptococcosis in the context of cancer progression, and the possible implications that fungal glycan structures may take in both cancer development and progression.

Design, synthesis and biological evaluation of novel spiro-quinazolinone derivatives as chitin synthase inhibitors and antifungal agents

A series of spiro-quinazolinone scaffolds were constructed based on the bioactivity of quinazolinone and the inherent feature of spirocycle to design novel chitin synthase inhibitors that possess mode of action different from that of the currently used antifungal agents. Among them, the spiro[thiophen-quinazolin]-one derivatives containing α, β-unsaturated carbonyl fragments had shown inhibitory activities against chitin synthase and antifungal activities. The enzymatic experiments showed that among the sixteen compounds, compounds 12d, 12g, 12j, 12l and 12m exhibited inhibitions against chitin synthase with IC₅₀ values of 116.7 ± 19.6 μM, 106.7 ± 14.2 μM, 102.3 ± 9.6 μM, 122.7 ± 22.2 μM and 136.8 ± 12.4 μM, respectively, which were comparable to that of polyoxin B (IC₅₀ = 93.5 ± 11.1 μM). The assays of enzymatic Kinetic parameters showed that compound 12g was a non-competitive inhibitor of chitin synthase. The antifungal assays showed that compounds 12d, 12g, 12j, 12l and 12m exhibited a broad-spectrum of antifungal activity against the four strains tested in vitro. In which, compounds 12g and 12j had stronger antifungal activity against four tested strains than that of polyoxin B and similar to that of fluconazole, while compounds 12d, 12l and 12m showed antifungal activity comparable to that of polyoxin B against four tested strains. Meanwhile, compounds 12d, 12g, 12j, 12l and 12m exhibited good antifungal activity against fluconazole-resistant and micafungin-resistant fungi variants with MIC values ranging from 4 to 32 μg/mL while the MIC values of reference drugs were above 256 μg/mL. Furthermore, the results of drug-combination experiments showed that compounds 12d, 12g, 12j, 12l and 12m had synergistic or additive effects with fluconazole or polyoxin B. The results of sorbitol protection experiment and the experiment of antifungal activity against micafungin-resistant fungi further demonstrated that these compounds target chitin synthase. The result of cytotoxicity assay showed that compound 12g had low toxicity toward human lung cancer A549 cells and the ADME analysis in silico displayed that compound 12g possessed promising pharmacokinetic properties. The molecular docking indicated that compound 12g formed multiple hydrogen bond interactions binding to chitin synthase, which might be conductive to increasing the binding affinity and inhibiting the activity of chitin synthase. The above results indicated that the designed compounds were chitin synthase inhibitors with selectivity and broad-spectrum antifungal activity and could be act as the lead compounds against drug-resistant fungi.

Combined Transcriptome and Metabolome Analysis Reveals That the Potent Antifungal Pyrylium Salt Inhibits Mitochondrial Complex I in Candida albicans

Based on the structural modification of SM21, xy12, a new pyrylium salt derivative with enhanced antifungal activities, was synthesized. The MICs (MIC90) of xy12 against Candida albicans ranged from 0.125 to 0.25 μg/mL, about 2-fold lower than those of SM21. In addition, xy12 inhibited hypha and biofilm formation in C. albicans in a dose-dependent manner. A total of 3,454 differentially expressed genes and 260 differential metabolites were identified in the xy12-treated C. albicans by RNA-seq and non-targeted metabolomics. By integrating KEGG pathway enrichment analysis, we found that inhibition of oxidative phosphorylation was the important antifungal mechanism of action of xy12. Electron transport through mitochondrial respiratory complexes I to IV is the common process of oxidative phosphorylation. Compared with the sensitivity of the wild-type SC5314 to xy12, decreased sensitivities in mitochondrial complex I (CI)-deficient mutants and increased sensitivities in mitochondrial complex III- and IV-deficient mutants suggested that the antifungal effects of xy12 were dependent on CI. Consistently, xy12 exhibited antagonism with rotenone, an inhibitor of CI, and significantly inhibited the expression and activity of CI. Meanwhile, the phenotypes in the xy12-treated C. albicans were similar to those in the CI-deficient mutants, such as decreased ATP production, reduced mitochondrial membrane potential, loss of mitochondrial DNA, inability to utilize nonfermentative carbon sources, and decreased cell wall N-linked mannoproteins. Collectively, our results revealed that the pyrylium salt xy12 could constrain oxidative phosphorylation by inhibiting mitochondrial complex I in C. albicans, providing a novel lead compound for the development of mitochondria-targeted antifungal drugs. IMPORTANCE The development of new antifungal drugs is critical for solving the problem of antifungal resistance and expanding the limited variety of clinical antifungal drugs. Based on the modification of the pyrylium salt SM21, a new lead compound, xy12, was synthesized which was effective against Candida species both in vitro and in vivo. In this study, conjoined analysis of the transcriptome and metabolome elucidated the antifungal mechanism of action of xy12, which inhibited the activity of mitochondrial complex I in C. albicans. Targeting fungi-specific mitochondrial complex proteins has been reported as a promising antifungal strategy. Our study provided a new lead compound for targeting C. albicans mitochondrial complex I, which could be beneficial for discovering novel antifungal drugs.

Controlling antifungal activity with light: Optical regulation of fungal ergosterol biosynthetic pathway with photo-responsive CYP51 inhibitors

Invasive fungal infections (IFIs) have been associated with high mortality, highlighting the urgent need for developing novel antifungal strategies. Herein the first light-responsive antifungal agents were designed by optical control of fungal ergosterol biosynthesis pathway with photocaged triazole lanosterol 14α-demethylase (CYP51) inhibitors. The photocaged triazoles completely shielded the CYP51 inhibition. The content of ergosterol in fungi before photoactivation and after photoactivation was 4.4% and 83.7%, respectively. Importantly, the shielded antifungal activity (MIC₈₀ ≥ 64 μg/mL) could be efficiently recovered (MIC₈₀ = 0.5-8 μg/mL) by light irradiation. The new chemical tools enable optical control of fungal growth arrest, morphological conversion and biofilm formation. The ability for high-precision antifungal treatment was validated by in vivo models. The light-activated compound A1 was comparable to fluconazole in prolonging survival in Galleria mellonella larvae with a median survival of 14 days and reducing fungal burden in the mouse skin infection model. Overall, this study paves the way for precise regulation of antifungal therapy with improved efficacy and safety.

Surface-enhanced Raman spectral characterization of antifungal activity of selenium and zinc based organometallic compounds

Surface-enhanced Raman spectroscopy (SERS) is used to identify the biochemical changes associated with the antifungal activities of selenium and zinc organometallic complexes against Aspergillus niger fungus. These biochemical changes identified in the form of SERS peaks can help to understand the mechanism of action of these antifungal agents which is important for development of new antifungal drugs. The SERS spectral changes indicate the denaturation and conformational changes of proteins and fungal cell wall decomposition in complex exposed fungal samples. The SERS spectra of these organometallic complexes exposed fungi are analyzed by using statistical tools like principal component analysis (PCA) and partial least square discriminant analysis (PLS-DA). PCA is employed to differentiate the SERS spectra of fungal samples exposed to ligands and complexes. The PLS-DA discriminated different groups of spectra with 99.8% sensitivity, 100% specificity, 98% accuracy and 86 % area under receiver operating characteristic (AUROC) curve.

Fungal Sterol Analyses by Gas Chromatography-Mass Spectrometry Using Different Derivatives

Sterols are the main components of the fungal membrane. Their study can be used to describe the chemical biodiversity among the strains and species or to work on antifungal treatment. Those molecules can be analyzed by gas chromatography coupled with mass spectrometry (GC-MS) as free molecules or after derivation as acetate or trimethylsilyl ether (TMSi). Here we describe how to extract sterols from fungal biomass according to its physiological form and the culture conditions (liquid and solid media). The different methodologies that can be used to obtain free sterols, acetate, and/or TMSi derivatives are presented. Identification keys using the fragmentation at 70 eV are also described.

Existing and emerging therapies for the treatment of invasive candidiasis and candidemia

INTRODUCTION

Invasive candidiasis or candidemia is a severe infection affecting more than 250,000 people worldwide every year. It is present in up to 16% of ICU patients. The prognosis of these infections is unfavorable, with global death estimated around 50,000 per year, which corresponds to up to 40% depending on patient severity and comorbidities. Therapeutic failure is not rare due to the emergence of multiresistant strains and of new species poorly responsive to current therapies like Candida auris.

AREAS COVERED

We first review the positioning of antifungal drugs used to treat candidiasis, namely polyenes, azoles, echinocandins and pyrimidine analogues. We then discuss the progresses brought by new formulations, new derivatives within these classes, compounds acting on new targets or repurposed drugs in terms of pharmacokinetic profile, spectrum of activity, potency, safety or risk of drug-drug interactions.

EXPERT OPINION

While new formulations (amphotericin B cochleate) improve oral bioavailability of the corresponding drugs, new azoles or echinocandins offer higher potency including against strains resistant to former generations of drugs. Repurposed drugs show synergism with current therapies in vitro. Results from ongoing and future clinical trials will be decisive to establish the interest for these drugs in our arsenal.

Structural Characterization and Optimization of a Miconazole Oral Gel

The development of semisolid formulations, gels in particular, has raised the attention of scientists more and more over the last decades. Because of their biocompatibility, hydrophilic nature, and capacity of absorbing large quantities of water, hydrogels are still one of the most promising pharmaceutical formulations in the pharmaceutical industry. The purpose of this study is to develop an optimal formulation capable of incorporating a water-poorly soluble active ingredient such as miconazole used in the treatment of fungal infections with Candida albicans and Candida parapsilosis. A D-optimal design was applied to study the relationship between the formulation parameter and the gel characteristics. The independent parameters used in this study were the Carbopol 940 concentration (the polymer used to obtain the gel matrix), the sodium hydroxide amount, and the presence/absence of miconazole. Ten different dependent parameters (Y1-Y10) were evaluated (penetrometry, spreadability, viscosity, and tangential tension at 1 and 11 levels of speed whilst destructuring and during the reorganization of the gel matrix). The consistency of the gels ranged from 23.2 mm (GO2) to 29.6 mm (GM5). The least spreadable gel was GO7 (1384 mm²), whilst the gel that presented the best spreadability was GO1 (3525 mm²). The viscosity and the tangential stress at the selected levels (1 and 11) varied due to the different compositions of the proposed gels. The gels were also tested for drug content and antifungal activity. All determinations had satisfying results; the drug content was within limits accepted by Ph. Eur. 10 and all formulations containing miconazole exhibited antifungal activity. An optimal formulation with miconazole was attained, consisting of 0.84% Carbopol 940 and 0.32% sodium hydroxide.

Application of the Mutant Libraries for Candida albicans Functional Genomics

Candida albicans is a typical opportunistic pathogen in humans that causes serious health risks in clinical fungal infections. The construction of mutant libraries has made remarkable developments in the study of C. albicans molecular and cellular biology with the ongoing advancements of gene editing, which include the application of CRISPR-Cas9 and novel high-efficient transposon. Large-scale genetic screens and genome-wide functional analysis accelerated the investigation of new genetic regulatory mechanisms associated with the pathogenicity and resistance to environmental stress in C. albicans. More importantly, sensitivity screening based on C. albicans mutant libraries is critical for the target identification of novel antifungal compounds, which leads to the discovery of Sec7p, Tfp1p, Gwt1p, Gln4p, and Erg11p. This review summarizes the main types of C. albicans mutant libraries and interprets their applications in morphogenesis, biofilm formation, fungus-host interactions, antifungal drug resistance, and target identification.

Antifungal Combinations against Candida Species: From Bench to Bedside

Candida spp. is the major causative agent of fungal infections in hospitalized patients and the fourth most common cause of nosocomial bloodstream infection (BSI). The availability of standardized methods for testing the in vitro activity of antifungals along with the expanding of antifungal armamentarium, the rising of drug-resistance and the persistence of a high mortality rate in systemic candidiasis have led to an increased interest in combination therapy. Therefore, we aimed to review the scientific literature concerning the antifungal combinations against Candida. A literature search performed in PubMed yielded 92 studies published from 2000 to 2021: 29 articles referring to in vitro studies, six articles referring to either in vitro and in vivo (i.e., animal models) studies and 57 clinical articles. Pre-clinical studies involved 735 isolates of Candida species and 12 unique types of antifungal combination approaches including azoles plus echinocandins (19%), polyenes plus echinocandins (16%), polyenes plus azoles (13%), polyenes plus 5-flucytosine ([5-FC], 13%), azoles plus 5-FC (11%) and other types of combinations (28%). Results varied greatly, often being species-, drug- and methodology-dependent. Some combinatorial regimens exerted a synergistic effect against difficult-to-treat Candida species (i.e., azoles plus echinocandins; polyenes plus 5-FC) or they were more effective than monotherapy in prevent or reducing biofilm formation and in speeding the clearance of infected tissues (i.e., polyenes plus echinocandins). In 283 patients with documented Candida infections (>90% systemic candidiasis/BSI), an antifungal combination approach could be evaluated. Combinations included: azoles plus echinocandins (36%), 5-FC-combination therapies (24%), polyenes plus azoles (18%), polyenes plus echinocandins (16%) and other types of combination therapy (6%). Case reports describing combination therapies yielded favorable response in most cases, including difficult-to-treat fungal infections (i.e., endocarditis, osteoarticular infections, CNS infections) or difficult-to-treat fungal pathogens. The only randomized trial comparing amphotericin-B deoxycholate (AMB) plus FLU vs. AMB alone for treatment of BSI in nonneutropenic patients showed that the combination trended toward improved success and more-rapid clearance from the bloodstream. In summary, antifungal combinations against Candida have produced great interest in the past two decades. To establish whether this approach can become a reliable treatment option, additional in vitro and clinical data are warranted.

Emerging Fungal Infections: from the Fields to the Clinic, Resistant Aspergillus fumigatus and Dermatophyte Species: a One Health Perspective on an Urgent Public Health Problem

Purpose of Review

For this review, we use a One Health approach to examine two globally emerging public health threats related to antifungal drug resistance: triazole-resistant Aspergillus fumigatus infections, which can cause a life-threatening illness in immunocompromised hosts, and antifungal-resistant dermatophytosis, which is an aggressive skin infection caused by dermatophyte molds. We describe the state of current scientific knowledge and outline necessary public health actions to address each issue.

Recent Findings

Recent evidence has identified the agricultural use of triazole fungicides as an important driver of triazole-resistant A. fumigatus infections. Antifungal-resistant dermatophyte infections are likely driven by the inappropriate use of antifungal drugs and antibacterial and corticosteroid creams.

Summary

This review highlights the need for a One Health approach to address emerging antifungal resistant infections, emphasizing judicious antifungal use to preserve available treatments; strengthened laboratory capacity to identify antifungal resistance; and improved human, animal, and environmental surveillance to detect emerging resistance, monitor trends, and evaluate the effectiveness of efforts to decrease spread.

iTRAQ-based proteomics revealed baicalein enhanced oxidative stress of Candida albicans by up-regulating CPD2 expression

Baicalein could inhibit the growth and biofilm formation of Candida albicans, the most common clinical fungal pathogen. However, the antifungal mechanism of baicalein has not been elucidated. In this study, isobaric tags for relative and absolute quantification (iTRAQ) was used to verify the mechanism of antifungal fluconazole and baicalein. A total of 58 common proteins were detected in cells treated with fluconazole. These proteins encompassed fluconazole-targeted sterol synthesis pathway, including Erg11p, Erg6p, Erg3p, Erg25p, Erg5p, Erg10p and Ncp1p. Next, iTRAQ was applied to the comparison of baicalein-treated C. albicans proteins, which detected 16 common proteins. The putative NADH dehydrogenase Cpd2p and the ATP-binding cassette transporter Snq2p were the most up-regulated proteins with the treatment of baicalein. Our results showed that CPD2 disruption elevated C. albicans resistance to baicalein significantly both in vitro and in vivo. Further in-depth studies revealed that CPD2 disruption reduced the activation of C. albicans metacaspase and partially restored the mitochondrial membrane potential reduction caused by the treatment of baicalein, which indicated that CPD2 was involved in the apoptosis induced by baicalein. Consistently, under the treatment of baicalein, CPD2Δ/Δ mutant produced lower reactive oxygen species (ROS) that was critical in causing oxidative damage and apoptosis in C. albicans. These results indicated that baicalein could increase intracellular oxidative damage by up-regulating the expression of Cpd2p so as to inhibit the growth of C. albicans, which provides new insights for investigating the antifungal target of baicalein.

The Anti-Fungal Activity of Nitropropenyl Benzodioxole (NPBD), a Redox-Thiol Oxidant and Tyrosine Phosphatase Inhibitor

Phylogenetically diverse fungal species are an increasing cause of severe disease and mortality. Identification of new targets and development of new fungicidal drugs are required to augment the effectiveness of current chemotherapy and counter increasing resistance in pathogens. Nitroalkenyl benzene derivatives are thiol oxidants and inhibitors of cysteine-based molecules, which show broad biological activity against microorganisms. Nitropropenyl benzodioxole (NPBD), one of the most active antimicrobial derivatives, shows high activity in MIC assays for phylogenetically diverse saprophytic, commensal and parasitic fungi. NPBD was fungicidal to all species except the dermatophytic fungi, with an activity profile comparable to that of Amphotericin B and Miconazole. NPBD showed differing patterns of dynamic kill rates under different growth conditions for Candida albicans and Aspergillus fumigatus and was rapidly fungicidal for non-replicating vegetative forms and microconidia. It did not induce resistant or drug tolerant strains in major pathogens on long term exposure. A literature review highlights the complexity and interactivity of fungal tyrosine phosphate and redox signaling pathways, their differing metabolic effects in fungal species and identifies some targets for inhibition. A comparison of the metabolic activities of Amphotericin B, Miconazole and NPBD highlights the multiple cellular functions of these agents and the complementarity of many mechanisms. The activity profile of NPBD illustrates the functional diversity of fungal tyrosine phosphatases and thiol-based redox active molecules and contributes to the validation of tyrosine phosphatases and redox thiol molecules as related and complementary selective targets for antimicrobial drug development. NPBD is a selective antifungal agent with low oral toxicity which would be suitable for local treatment of skin and mucosal infections.

Bioactive Antimicrobial Peptides: A New Weapon to Counteract Zoonosis

Zoonoses have recently become the center of attention of the general population and scientific community. Notably, more than 30 new human pathogens have been identified in the last 30 years, 75% of which can be classified as zoonosis. The complete eradication of such types of infections is far out of reach, considering the limited understanding of animal determinants in zoonoses and their causes of emergence. Therefore, efforts must be doubled in examining the spread, persistence, and pathogenicity of zoonosis and studying possible clinical interventions and antimicrobial drug development. The search for antimicrobial bioactive compounds has assumed great emphasis, considering the emergence of multi-drug-resistant microorganisms. Among the biomolecules of emerging scientific interest are antimicrobial peptides (AMPs), potent biomolecules that can potentially act as important weapons against infectious diseases. Moreover, synthetic AMPs are easily tailored (bioinformatically) to target specific features of the pathogens to hijack, inducing no or very low resistance. Although very promising, previous studies on SAMPs' efficacy are still at their early stages. Indeed, further studies and better characterization on their mechanism of action with in vitro and in vivo assays are needed so as to proceed to their clinical application on human beings.

Present scenarios and future prospects of herbal nanomedicine for antifungal therapy

The current COVID-19 epidemic is a sobering reminder that human susceptibility to infectious diseases remains even in our modern civilization. After all, infectious diseases are still the major reason of death globally. Healthcare authorities have often underestimated and ignored the threat posed by "microbial dangers," although they put millions of lives at risk every year. Overlooked developing diseases including fungal infections (FIs) contribute to roughly 1.7 million fatalities per year. As many as 150 million cases of severe and potentially life-threatening FIs are reported each year. In the last few years, the number of instances has steadily increased. Most of them are invasive fungal infections that require specialized treatment and hospital care. In recent years herbal antifungal compounds have been explored to acquire effective and safe therapy against fungal infections. However, potential therapeutic effects are hampered by the poor solubility, stability, and bioavailability of these important chemicals as well as the gastric degradation that occurs in the gastrointestinal tract. To get around this issue, researchers have turned to novel drug delivery systems such as nanoemulsions, ethosomes, metallic nanoparticles, liposomes, lipid nanoparticles, transferosomes, etc by improving their limits, nanocarriers can enhance the medicinal effects of herbal oils and extracts. The present review article focuses on the available antifungal agents and their characteristics, mechanism of antifungal drugs resistance, herbal oils and extract as antifungal agents, challenges in the delivery of herbal drugs, and application of nano-drug delivery systems for effective delivery of antifungal herbal compounds.