Echinocandins: The Newest Class of Antifungals

How can we optimize antifungal use and stewardship in the treatment of acute leukemia?

INTRODUCTION

The global need for antifungal stewardship is driven by spreading antimicrobial and antifungal resistance. Triazoles are the only oral and relatively well-tolerated class of antifungal medications, and usage is associated with acquired resistance and species replacement with intrinsically resistant organisms. On a per-patient basis, hematology patients are the largest inpatient consumers of antifungal drugs, but are also the most vulnerable to invasive fungal disease.

AREAS COVERED

In this review we discuss available and forthcoming antifungal drugs, antifungal prophylaxis and empiric antifungal therapy, and how a screening based and diagnostic-driven approach may be used to reduce antifungal consumption. Finally, we discuss components of an antifungal stewardship program, interventions that can be employed, and how impact can be measured. The search methodology consisted of searching PubMed for journal articles using the term antifungal stewardship plus program, intervention, performance measure or outcome before 1 January 2024.

EXPERT OPINION

Initial focus should be on implementing effective antifungal stewardship programs by developing and implementing local guidelines and using interventions, such as post-prescription review and feedback, which are known to be effective. Technologies such as microbiome analysis and machine learning may allow the development of truly individualized risk-factor-based approaches to antifungal stewardship in the future.

Re-Engineering Fungal Nonribosomal Peptide Synthetases by Module Dissection and Duplicated Thiolation Domains

Unnatural product (uNP) nonribosomal peptides promise to be a valuable source of pharmacophores for drug discovery. However, the extremely large size and complexity of the nonribosomal peptide synthetase (NRPS) enzymes pose formidable challenges to the production of such uNPs by combinatorial biosynthesis and synthetic biology. Here we report a new NRPS dissection strategy that facilitates the engineering and heterologous production of these NRPSs. This strategy divides NRPSs into "splitting units", each forming an enzyme subunit that contains catalytically independent modules. Functional collaboration between the subunits is then facilitated by artificially duplicating, at the N-terminus of the downstream subunit, the linker - thiolation domain - linker fragment that is resident at the C-terminus of the upstream subunit. Using the suggested split site that follows a conserved motif in the linker connecting the adenylation and the thiolation domains allows cognate or chimeric splitting unit pairs to achieve productivities that match, and in many cases surpass those of hybrid chimeric enzymes, and even those of intact NRPSs, upon production in a heterologous chassis. Our strategy provides facile options for the rational engineering of fungal NRPSs and for the combinatorial reprogramming of nonribosomal peptide production.

Ketoconazole induces reversible antifungal drug tolerance mediated by trisomy of chromosome R in Candida albicans

Background

The emergence of tolerance to antifungal agents in Candida albicans complicates the treatment of fungal infections. Understanding the mechanisms underlying this tolerance is crucial for developing effective therapeutic strategies.

Objective

This study aims to elucidate the genetic and molecular basis of ketoconazole tolerance in C. albicans, focusing on the roles of chromosomal aneuploidy, Hsp90, and calcineurin.

Methods

The wild-type C. albicans strain SC5314 was exposed to increasing concentrations of ketoconazole (0.015-32 μg/mL) to select for tolerant adaptors. Disk diffusion and spot assays were used to assess tolerance. Whole-genome sequencing identified chromosomal changes in the adaptors. The roles of Hsp90 and calcineurin in maintaining and developing ketoconazole tolerance were investigated using specific inhibitors and knockout strains.

Results

Adaptors exhibited tolerance to ketoconazole concentrations up to 16 μg/mL, a significant increase from the parent strain's inhibition at 0.015 μg/mL. All tolerant adaptors showed amplification of chromosome R, with 29 adaptors having trisomy and one having tetrasomy. This aneuploidy was unstable, reverting to euploidy and losing tolerance in drug-free conditions. Both Hsp90 and calcineurin were essential for maintaining and developing ketoconazole tolerance. Inhibition of these proteins resulted in loss of tolerance. The efflux gene CDR1 was not required for the development of tolerance. Chromosome R trisomy and tetrasomy induce cross-tolerance to other azole antifungal agents, including clotrimazole and miconazole, but not to other antifungal classes, such as echinocandins and pyrimidines, exemplified by caspofungin and 5-flucytosine.

Conclusion

Ketoconazole tolerance in C. albicans is mediated by chromosomal aneuploidy, specifically chromosome R amplification, and requires Hsp90 and calcineurin. These findings highlight potential targets for therapeutic intervention to combat antifungal tolerance and improve treatment outcomes.

Opportunities and challenges of RiPP-based therapeutics

Covering: up to 2024Ribosomally synthesised and post-translationally modified peptides (RiPPs) comprise a substantial group of peptide natural products exhibiting noteworthy bioactivities ranging from antiinfective to anticancer and analgesic effects. Furthermore, RiPP biosynthetic pathways represent promising production routes for complex peptide drugs, and the RiPP technology is well-suited for peptide engineering to produce derivatives with specific functions. Thus, RiPP natural products possess features that render them potentially ideal candidates for drug discovery and development. Nonetheless, only a small number of RiPP-derived compounds have successfully reached the market thus far. This review initially outlines the therapeutic opportunities that RiPP-based compounds can offer, whilst subsequently discussing the limitations that require resolution in order to fully exploit the potential of RiPPs towards the development of innovative drugs.

Invasive fungal infections in critically ill children: epidemiology, risk factors and antifungal drugs

Background

Invasive fungal infections (IFIs) are important infectious complications amongst critically ill children. The most common fungal infections are due to Candida species. Aspergillus, Zygomycetes and Fusarium are also emerging because of the empirical use of antifungal drugs. This updated review discusses the epidemiology of IFIs as well as antifungal drugs, dosing and potential adverse effects in critically ill children.

Methods

A PubMed search was conducted with Clinical Queries using the key terms "antifungal", "children", "critical care" AND "paediatric intensive care unit" OR "PICU". The search strategy included clinical trials, randomized controlled trials, meta-analyses, observational studies and reviews and was limited to the English literature in paediatrics.

Results

Candida and Aspergillus spp. are the most prevalent fungi in paediatric IFIs, causing invasive candidiasis infections (ICIs) and invasive aspergillosis infections (IAIs), respectively. These IFIs are associated with high morbidity, mortality and healthcare costs. Candida albicans is the principal Candida spp. associated with paediatric ICIs. The risks and epidemiology for IFIs vary if considering previously healthy children treated in the paediatric intensive care unit or children with leukaemia, malignancy or a severe haematological disease. The mortality rate for IAIs in children is 2.5-3.5-fold higher than for ICIs. Four major classes of antifungals for critically ill children are azoles, polyenes, antifungal antimetabolites and echinocandins.

Conclusions

Antifungal agents are highly efficacious. For successful treatment outcomes, it is crucial to determine the optimal dosage, monitor pharmacokinetics parameters and adverse effects, and individualized therapeutic monitoring. Despite potent antifungal medications, ICIs and IAIs continue to be serious infections with high mortality rates. Pre-emptive therapy has been used for IAIs. Most guidelines recommend voriconazole as initial therapy of invasive aspergillosis in most patients, with consideration of combination therapy with voriconazole plus an echinocandin in selected patients with severe disease. The challenge is to identify critically ill patients at high risks of ICIs for targeted prophylaxis. Intravenous/per os fluconazole is first-line pre-emptive treatment for Candida spp. whereas intravenous micafungin or intravenous liposomal amphotericin B is alternative pre-emptive treatment.This article is part of the Challenges and strategies in the management of invasive fungal infections Special Issue: https://www.drugsincontext.com/special_issues/challenges-and-strategies-in-the-management-of-invasive-fungal-infections.

Formulary Drug Review: Rezafungin

Each month, subscribers to The Formulary Monograph Service receive 5 to 6 well-documented monographs on drugs that are newly released or are in late phase 3 trials. The monographs are targeted to Pharmacy & Therapeutics Committees. Subscribers also receive monthly 1-page summary monographs on agents that are useful for agendas and pharmacy/nursing in-services. A comprehensive target drug utilization evaluation/medication use evaluation (DUE/MUE) is also provided each month. With a subscription, the monographs are available online to subscribers. Monographs can be customized to meet the needs of a facility. Through the cooperation of The Formulary, Hospital Pharmacy publishes selected reviews in this column. For more information about The Formulary Monograph Service, contact Wolters Kluwer customer service at 866-397-3433.

Sequential Induction of Drug Resistance and Characterization of an Initial Candida albicans Drug-Sensitive Isolate

BACKGROUND

The pathogenic fungus Candida albicans is a leading agent of death in immunocompromised individuals with a growing trend of antifungal resistance.

METHODS

The purpose is to induce resistance to drugs in a sensitive C. albicans strain followed by whole-genome sequencing to determine mechanisms of resistance. Strains will be assayed for pathogenicity attributes such as ergosterol and chitin content, growth rate, virulence, and biofilm formation.

RESULTS

We observed sequential increases in ergosterol and chitin content in fluconazole-resistant isolates by 78% and 44%. Surface thickening prevents the entry of the drug, resulting in resistance. Resistance imposed a fitness trade-off that led to reduced growth rates, biofilm formation, and virulence in our isolates. Sequencing revealed mutations in genes involved in resistance and pathogenicity such as ERG11, CHS3, GSC2, CDR2, CRZ2, and MSH2. We observed an increase in the number of mutations in key genes with a sequential increase in drug-selective pressures as the organism increased its odds of adapting to inhospitable environments. In ALS4, we observed two mutations in the susceptible strain and five mutations in the resistant strain.

CONCLUSION

This is the first study to induce resistance followed by genotypic and phenotypic analysis of isolates to determine mechanisms of drug resistance.

Antifungal drug resistance in Candida: a special emphasis on amphotericin B

Invasive fungal infections in humans caused by several Candida species, increased considerably in immunocompromised or critically ill patients, resulting in substantial morbidity and mortality. Candida albicans is the most prevalent species, although the frequency of these organisms varies greatly according to geographic region. Infections with C. albicans and non-albicans Candida species have become more common, especially in the past 20 years, as a result of aging, immunosuppressive medication use, endocrine disorders, malnourishment, extended use of medical equipment, and an increase in immunogenic diseases. Despite C. albicans being the species most frequently associated with human infections, C. glabrata, C. parapsilosis, C. tropicalis, and C. krusei also have been identified. Several antifungal drugs with different modes of action are approved for use in clinical settings to treat fungal infections. However, due to the common eukaryotic structure of humans and fungi, only a limited number of antifungal drugs are available for therapeutic use. Furthermore, drug resistance in Candida species has emerged as a result of the growing use of currently available antifungal drugs against fungal infections. Amphotericin B (AmB), a polyene class of antifungal drugs, is mainly used for the treatment of serious systemic fungal infections. AmB interacts with fungal plasma membrane ergosterol, triggering cellular ion leakage via pore formation, or extracting the ergosterol from the plasma membrane inducing cellular death. AmB resistance is primarily caused by changes in the content or structure of ergosterol. This review summarizes the antifungal drug resistance exhibited by Candida species, with a special focus on AmB.

The biosynthetic logic and enzymatic machinery of approved fungi-derived pharmaceuticals and agricultural biopesticides

Covering: 2000 to 2023The kingdom Fungi has become a remarkably valuable source of structurally complex natural products (NPs) with diverse bioactivities. Since the revolutionary discovery and application of the antibiotic penicillin from Penicillium, a number of fungi-derived NPs have been developed and approved into pharmaceuticals and pesticide agents using traditional "activity-guided" approaches. Although emerging genome mining algorithms and surrogate expression hosts have brought revolutionary approaches to NP discovery, the time and costs involved in developing these into new drugs can still be prohibitively high. Therefore, it is essential to maximize the utility of existing drugs by rational design and systematic production of new chemical structures based on these drugs by synthetic biology. To this purpose, there have been great advances in characterizing the diversified biosynthetic gene clusters associated with the well-known drugs and in understanding the biosynthesis logic mechanisms and enzymatic transformation processes involved in their production. We describe advances made in the heterogeneous reconstruction of complex NP scaffolds using fungal polyketide synthases (PKSs), non-ribosomal peptide synthetases (NRPSs), PKS/NRPS hybrids, terpenoids, and indole alkaloids and also discuss mechanistic insights into metabolic engineering, pathway reprogramming, and cell factory development. Moreover, we suggest pathways for expanding access to the fungal chemical repertoire by biosynthesis of representative family members via common platform intermediates and through the rational manipulation of natural biosynthetic machineries for drug discovery.

Therapeutic drug monitoring of antifungal therapies: do we really need it and what are the best practices?

INTRODUCTION

Despite advancements, invasive fungal infections (IFI) still carry high mortality rates, often exceeding 30%. The challenges in diagnosis, coupled with limited effective antifungal options, make managing IFIs complex. Antifungal drugs are essential for IFI management, but their efficacy can be diminished by drug-drug interactions and pharmacokinetic variability. Therapeutic Drug Monitoring (TDM), especially in the context of triazole use, has emerged as a valuable strategy to optimize antifungal therapy.

AREAS COVERED

This review provides current evidence regarding the potential benefits of TDM in IFI management. It discusses how TDM can enhance treatment response, safety, and address altered pharmacokinetics in specific patient populations.

EXPERT OPINION

TDM plays a crucial role in achieving optimal therapeutic outcomes in IFI management, particularly for certain antifungal agents. Preclinical studies consistently show a link between therapeutic drug levels and antifungal efficacy. However, clinical research in mycology faces challenges due to patient heterogeneity and the diversity of fungal infections. TDM's potential advantages in guiding Echinocandin therapy for critically ill patients warrant further investigation. Additionally, for drugs like Posaconazole, assessing whether serum levels or alternative markers like saliva offer the best measure of efficacy is an intriguing question.

Microbial lipopeptides: their pharmaceutical and biotechnological potential, applications, and way forward

As lead molecules, cyclic lipopeptides with antibacterial, antifungal, and antiviral properties have garnered a lot of attention in recent years. Because of their potential, cyclic lipopeptides have earned recognition as a significant class of antimicrobial compounds with applications in pharmacology and biotechnology. These lipopeptides, often with biosurfactant properties, are amphiphilic, consisting of a hydrophilic moiety, like a carboxyl group, peptide backbone, or carbohydrates, and a hydrophobic moiety, mostly a fatty acid. Besides, several lipopeptides also have cationic groups that play an important role in biological activities. Antimicrobial lipopeptides can be considered as possible substitutes for antibiotics that are conventional to address the current drug-resistant issues as pharmaceutical industries modify the parent antibiotic molecules to render them more effective against antibiotic-resistant bacteria and fungi, leading to the development of more resistant microbial strains. Bacillus species produce lipopeptides, which are secondary metabolites that are amphiphilic and are typically synthesized by non-ribosomal peptide synthetases (NRPSs). They have been identified as potential biocontrol agents as they exhibit a broad spectrum of antimicrobial activity. A further benefit of lipopeptides is that they can be produced and purified biotechnologically or biochemically in a sustainable manner using readily available, affordable, renewable sources without harming the environment. In this review, we discuss the biochemical and functional characterization of antifungal lipopeptides, as well as their various modes of action, method of production and purification (in brief), and potential applications as novel antibiotic agents.

Pneumocystis jirovecii pneumonia in people living with HIV: a review

Pneumocystis jirovecii is a ubiquitous opportunistic fungus that can cause life-threatening pneumonia. People with HIV (PWH) who have low CD4 counts are one of the populations at the greatest risk of Pneumocystis jirovecii pneumonia (PCP). While guidelines have approached the diagnosis, prophylaxis, and management of PCP, the numerous studies of PCP in PWH are dominated by the 1980s and 1990s. As such, most studies have included younger male populations, despite PCP affecting both sexes and a broad age range. Many studies have been small and observational in nature, with an overall lack of randomized controlled trials. In many jurisdictions, and especially in low- and middle-income countries, the diagnosis can be challenging due to lack of access to advanced and/or invasive diagnostics. Worldwide, most patients will be treated with 21 days of high-dose trimethoprim sulfamethoxazole, although both the dose and the duration are primarily based on historical practice. Whether treatment with a lower dose is as effective and less toxic is gaining interest based on observational studies. Similarly, a 21-day tapering regimen of prednisone is used for patients with more severe disease, yet other doses, other steroids, or shorter durations of treatment with corticosteroids have not been evaluated. Now with the widespread availability of antiretroviral therapy, improved and less invasive PCP diagnostic techniques, and interest in novel treatment strategies, this review consolidates the scientific body of literature on the diagnosis and management of PCP in PWH, as well as identifies areas in need of more study and thoughtfully designed clinical trials.

Healthcare-associated fungal infections and emerging pathogens during the COVID-19 pandemic

Historically, fungi were mainly identified as plant and insect pathogens since they grow at 28°C. At the same time, bacteria are known to be the most common human pathogens as they are compatible with the host body temperature of 37°C. Because of immunocompromised hosts, cancer therapy, and malnutrition, fungi are rapidly gaining attention as human pathogens. Over 150 million people have severe fungal infections, which lead to approximately more than one million deaths per year. Moreover, diseases like cancer involving long-term therapy and prophylactic use of antifungal drugs in high-risk patients have increased the emergence of drug-resistant fungi, including highly virulent strains such as Candida auris. This clinical spectrum of fungal diseases ranges from superficial mucocutaneous lesions to more severe and life-threatening infections. This review article summarizes the effect of hospital environments, especially during the COVID-19 pandemic, on fungal infections and emerging pathogens. The review also provides insights into the various antifungal drugs and their existing challenges, thereby driving the need to search for novel antifungal agents.

The impact of extracorporeal membrane oxygenation on antifungal pharmacokinetics: A systematic review

BACKGROUND AND OBJECTIVE

The use of extracorporeal membrane oxygenation (ECMO) as a cardiocirculatory or respiratory support has tremendously increased in critically ill patients. In the setting of ECMO support, invasive fungal infections are a severe cause of morbidity and mortality. This vulnerable population is at risk of suboptimal antifungal exposure due to an increased volume of distribution (Vd), drug sequestration and decreased clearance. Here, we aimed to summarize ex-vivo and clinical studies on the potential impact of ECMO on the pharmacokinetics (PK) of antifungal agents and dosing requirements.

METHODS

A systematic search of the literature within electronic databases PubMed and EMBASE was conducted from database inception to 30 April 2023. Inclusion criteria were as follows: critically ill patients receiving ECMO regardless of age and reporting at least one PK parameter.

RESULTS

Thirty-six studies met inclusion criteria, including seven ex-vivo experiments and 29 clinical studies evaluating three classes of antifungals: polyenes, triazoles and echinocandins. Based on the available ex-vivo PK data, we found a significant sequestration of highly lipophilic and protein-bound antifungals within the ECMO circuit such as voriconazole, posaconazole and micafungin but the PK of several antifungals remains to be addressed such as amphotericin B, isavuconazole and anidulafungin. Most clinical studies have shown increased Vd of some antifungals like fluconazole and micafungin, particularly in the pediatric population. Conflicting data exist about caspofungin exposure.

CONCLUSIONS

The available literature on the antifungal PK changes in ECMO setting is scarce. Whenever possible, therapeutic drug monitoring is highly advised to personalize antifungal therapy.

Antifungal resistance, combinations and pipeline: oh my!

Invasive fungal infections are a strong contributor to healthcare costs, morbidity and mortality, especially amongst hospitalized patients. Historically, Candida was responsible for approximately 15% of all nosocomial bloodstream infections. In the past 10 years, the epidemiology of Candida species has altered, with increasing prevalence of resistant species. With rising fungal resistance, especially in Candida spp., the demand for novel antifungal therapies has exponentially increased over the last decade. Newer antifungal agents have become an attractive option for patients needing long-term therapy for infections or those requiring antifungal prophylaxis. Despite advances in coverage of non-Candida pathogens with newer agents, clinical scenarios involving multidrug-resistant fungal pathogens continue to arise in practice. Combination antifungal therapy can lead to a host of side-effects, some of which can be drug limiting. Additional antifungal therapies with enhanced fungal spectrum of activity and decreased rates of adverse effects are warranted. Fosmanogepix, ibrexafungerp, olorofim and rezafungin may help fill some of these gaps in the antifungal armamentarium. This article is part of the Challenges and strategies in the management of invasive fungal infections Special Issue: https://www.drugsincontext.com/special_issues/challenges-and-strategies-in-the-management-of-invasive-fungal-infections.

Inter-laboratory variability of caspofungin MICs for Nakaseomyces glabrata isolates - an Irish tertiary hospital experience

Background

Nakaseomyces glabrata, formerly Candida glabrata, is an opportunistic yeast and emerging cause of human infections. The use of broth microdilution (BMD) methodologies for caspofungin (CSP) antifungal susceptibility testing (AFST) against N. glabrata is reported to be prone to high inter-laboratory variation. We aimed to compare CSP MICs of N. glabrata isolates from our institution with those obtained by the Reference Laboratory for the same isolates.

Methods

All clinically significant N. glabrata isolates from 2019 to 2021 inclusive were reviewed. AFST was performed locally using the VITEK2 system with the AST-YS08 card, while E-tests were performed at the Mycology Reference Laboratory (MRL), and agreement between these two methods was evaluated - categorical and essential.

Results

Forty-one isolates were reviewed during the study period - 30 from blood cultures, seven from intra-operative theatre specimens and four from sterile site drain fluids. Despite an essential agreement of 100 % within ±2 log2 dilutions, marked discrepancies were noted in interpretative breakpoints between assays with 17 Minor and 16 Major category errors. Categorical agreement was 19.5 %, with the VITEK2 over-estimating resistance. A Mann-Whitney U-test assessed the relationship of MICs across the AFST modalities, and a statistically significant difference was noted, P<0.01, with a higher mean rank for VITKEK2 outputs.

Conclusion

While the VITEK2 system is highly applicable, its performance for CSP AFST is unreliable and potentially results in the mis-classification of susceptible isolates as highlighted in our study. The use of VITEK2 AST-YS08 micafungin as a sentinel echinocandin should be explored and/or the evaluation of CSP-specific E-tests as utilized by the MRL. These methods appear more consistent and less prone to the variation seen with BMD for CSP.

Recent developments in membrane targeting antifungal agents to mitigate antifungal resistance

Fungal infections cause severe and life-threatening complications especially in immunocompromised individuals. Antifungals targeting cellular machinery and cell membranes including azoles are used in clinical practice to manage topical to systemic fungal infections. However, continuous exposure to clinically used antifungal agents in managing the fungal infections results in the development of multi-drug resistance via adapting different kinds of intrinsic and extrinsic mechanisms. The unique chemical composition of fungal membranes presents attractive targets for antifungal drug discovery as it is difficult for fungal cells to modify the membrane targets for emergence of drug resistance. Here, we discussed available antifungal drugs with their detailed mechanism of action and described different antifungal resistance mechanisms. We further emphasized structure-activity relationship studies of membrane-targeting antifungal agents, and classified membrane-targeting antifungal agents on the basis of their core scaffold with detailed pharmacological properties. This review aims to pique the interest of potential researchers who could explore this interesting and intricate fungal realm.

Fungal BGCs for Production of Secondary Metabolites: Main Types, Central Roles in Strain Improvement, and Regulation According to the Piano Principle

Filamentous fungi are one of the most important producers of secondary metabolites. Some of them can have a toxic effect on the human body, leading to diseases. On the other hand, they are widely used as pharmaceutically significant drugs, such as antibiotics, statins, and immunosuppressants. A single fungus species in response to various signals can produce 100 or more secondary metabolites. Such signaling is possible due to the coordinated regulation of several dozen biosynthetic gene clusters (BGCs), which are mosaically localized in different regions of fungal chromosomes. Their regulation includes several levels, from pathway-specific regulators, whose genes are localized inside BGCs, to global regulators of the cell (taking into account changes in pH, carbon consumption, etc.) and global regulators of secondary metabolism (affecting epigenetic changes driven by velvet family proteins, LaeA, etc.). In addition, various low-molecular-weight substances can have a mediating effect on such regulatory processes. This review is devoted to a critical analysis of the available data on the "turning on" and "off" of the biosynthesis of secondary metabolites in response to signals in filamentous fungi. To describe the ongoing processes, the model of "piano regulation" is proposed, whereby pressing a certain key (signal) leads to the extraction of a certain sound from the "musical instrument of the fungus cell", which is expressed in the production of a specific secondary metabolite.

Aspergillosis: an Update on Clinical Spectrum, Diagnostic Schemes, and Management

Purpose of Review

This review gives an overview of the diseases caused by Aspergillus, including a description of the species involved and the infected clinical systems. We provide insight into the various diagnostic methods available for diagnosing aspergillosis, particularly invasive aspergillosis (IA), including the role of radiology, bronchoscopy, culture, and non-culture-based microbiological methods. We also discuss the available diagnostic algorithms for the different disease conditions. This review also summarizes the main aspects of managing infections due to Aspergillus spp., such as antifungal resistance, choice of antifungals, therapeutic drug monitoring, and new antifungal alternatives.

Recent Findings

The risk factors for this infection continue to evolve with the development of many biological agents that target the immune system and the increase of viral illnesses such as coronavirus disease. Due to the limitations of present mycological test methods, establishing a fast diagnosis is frequently difficult, and reports of developing antifungal resistance further complicate the management of aspergillosis. Many commercial assays, like AsperGenius®, MycAssay Aspergillus®, and MycoGENIE®, have the advantage of better species-level identification and concomitant resistance-associated mutations. Fosmanogepix, ibrexafungerp, rezafungin, and olorofim are newer antifungal agents in the pipeline exhibiting remarkable activity against Aspergillus spp.

Summary

The fungus Aspergillus is found ubiquitously around the world and can cause various infections, from harmless saprophytic colonization to severe IA. Understanding the diagnostic criteria to be used in different patient groups and the local epidemiological data and antifungal susceptibility profile is critical for optimal patient management.

[Pharmacological importance of novel spiro derivatives against human pathogenic fungi]

Human mycoses have become a threat to health world-wide. Unfortunately there are only a limited number of antimycotic drugs in use. In the present study, antifungal activity of earlier synthesized spiro-1,4-dihydropyridines (1,4-DHPs) was investigated. The antifungal activity of spiro-1,4-DHPs compounds were screened against Aspergillus flavus, A. fumigatus, and Candida albicans by using Disc Diffusion and Modified Microdilution method. Among six spiro-1,4-DHPs compounds tested all of them showed stronger antifungal activity possibly through inhibiting the synthesis of chitin in cell wall against A. flavus, A. fumigatus, and C. albicans as compared to fluconazole, a standard antifungal drug. The combination of compounds showed that the synthesized compounds had synergistic, additive effects as compared to currently used drugs as an antifungal agent. These results indicated that these designed compounds were potential chitin synthase inhibitors and had excellent antimycotic activity for the treatment of fungal infections.

Mucormycosis: A hidden mystery of fungal infection, possible diagnosis, treatment and development of new therapeutic agents

Mucormycosis is a fungal infection which got worsens with time if not diagnosed and treated. The current COVID-19 pandemic has association with fungal infection specifically with mucormycosis. Already immunocompromised patients are easy target for COVID-19 and mucormycosis as well. COVID-19 infection imparts in weak immune system so chances of infection is comparatively high in COVID-19 patients. Furthermore, diabetes, corticosteroid medicines, and a weakened immune system are the most prevalent risk factors for this infection as we discussed in case studies here. The steroid therapy for COVID-19 patients sometimes have negative impact on the patient health and this state encounters many infections including mucormycosis. There are treatments available but less promising and less effective. So, researchers are focusing on the promising agents against mucormycosis. It is reported that early treatment with liposomal amphotericin B (AmB), manogepix, echinocandins isavuconazole, posacanazole and other promising therapeutic agents have overcome the burden of mucormycosis. Lipid formulations of AmB have become the standard treatment for mucormycosis due to their greater safety and efficacy. In this review article, we have discussed case studies with the infection of mucormycosis in COVID-19 patients. Furthermore, we focused on anti-mucormycosis agents with mechanism of action of various therapeutics, including coverage of new antifungal agents being investigated as part of the urgent global response to control and combat this lethal infection, especially those with established risk factors.

Cdc14 phosphatase contributes to cell wall integrity and pathogenesis in Candida albicans

The Cdc14 phosphatase family is highly conserved in fungi. In Saccharomyces cerevisiae, Cdc14 is essential for down-regulation of cyclin-dependent kinase activity at mitotic exit. However, this essential function is not broadly conserved and requires only a small fraction of normal Cdc14 activity. Here, we identified an invariant motif in the disordered C-terminal tail of fungal Cdc14 enzymes that is required for full enzyme activity. Mutation of this motif reduced Cdc14 catalytic rate and provided a tool for studying the biological significance of high Cdc14 activity. A S. cerevisiae strain expressing the reduced-activity hypomorphic mutant allele (cdc14^hm ) as the sole source of Cdc14 proliferated like the wild-type parent strain but exhibited an unexpected sensitivity to cell wall stresses, including chitin-binding compounds and echinocandin antifungal drugs. Sensitivity to echinocandins was also observed in Schizosaccharomyces pombe and Candida albicans strains lacking CDC14, suggesting this phenotype reflects a novel and conserved function of Cdc14 orthologs in mediating fungal cell wall integrity. In C. albicans, the orthologous cdc14^hm allele was sufficient to elicit echinocandin hypersensitivity and perturb cell wall integrity signaling. It also caused striking abnormalities in septum structure and the same cell separation and hyphal differentiation defects previously observed with cdc14 gene deletions. Since hyphal differentiation is important for C. albicans pathogenesis, we assessed the effect of reduced Cdc14 activity on virulence in Galleria mellonella and mouse models of invasive candidiasis. Partial reduction in Cdc14 activity via cdc14^hm mutation severely impaired C. albicans virulence in both assays. Our results reveal that high Cdc14 activity is important for C. albicans cell wall integrity and pathogenesis and suggest that Cdc14 may be worth future exploration as an antifungal drug target.

A comparative study of in-vitro and in-silico anti-candidal activity and GC-MS profiles of snow mountain garlic vs. common garlic

AIM

The study aimed to profile the volatile phytocomposition of snow mountain garlic (SMG) compared to common garlic and investigate the anti-Candida efficacy against clinically relevant multi-drug resistant isolates of Candida species.

METHODS AND RESULTS

Herein, SMG has shown significantly superior fungicidal power at 2x-MIC dose against C. albicans and C. glabrata in killing kinetic evaluation unlike fungistatic effect of common garlic. GC-MS headspace-based profiling of SMG showed 5 unique volatile compounds and 5-fold higher content of saponins than common garlic. In an in-silico analysis, Cholesta-4,6-dien-3-ol,(3-beta) was uniquely identified in SMG as a potential inhibitor with high binding affinity to the active site of exo-1,3-betaglucan synthase, an established anti-candida drug target crucial for the biofilm matrix formation, thus suggesting a plausible antifungal mechanism.

CONCLUSION

The in-vitro and in-silico study established Candida-cidal and anti-biofilm activities of SMG that differentiate it from Candida-static efficacy of common garlic.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report that identifies several phytochemical signatures of SMG along with a potential anti-fungal compound, i.e. Cholesta-4,6-dien-3-ol,(3-beta)-, which appears worthy of detailed studies in future to explore utility of SMG as a fungal phytotherapy agent, especially against drug resistant Candida sp.

Acute Multiple In-Stent Thromboses in a Patient With Clopidogrel-Fluconazole Interaction

Clopidogrel is an anti-platelet that exerts its function by selectively inhibiting the binding of adenosine di-phosphate (ADP) to the P2Y12 receptor. Fluconazole is a fungistatic agent that alters fungal cell membranes. Both of these drugs act on the cytochrome P450 2C19. We report the case of an 83-year-old male that presented two days following coronary angioplasty with stent thrombosis, following the concomitant use of clopidogrel and fluconazole. We aim to study the interaction between clopidogrel and fluconazole. We hypothesize that fluconazole decreases the therapeutic level of clopidogrel, requiring an increase in dosage to achieve the same anti-thrombotic effect.

Caspofungin resistance in Candida albicans: genetic factors and synergistic compounds for combination therapies

Caspofungin and other echinocandins have been used for the treatment of human infections by the opportunistic yeast pathogen, Candida albicans. There has been an increase in infections by non-albicans Candida species such as Candida glabrata, Candida parapsilosis, Candida tropicalis, Candida krusei, and Candida auris in clinical or hospital settings. This is problematic to public health due to the increasing prevalence of echinocandin resistant species/strains. This review will present a summary on various studies that investigated the inhibitory action of caspofungin on 1,3-β-D-glucan synthesis, on cell wall structure, and biofilm formation of C. albicans. It will highlight some of the issues linked to caspofungin resistance or reduced caspofungin sensitivity in various Candida species and the potential benefits of antimicrobial peptides and other compounds in synergy with caspofungin.

A Review: Antimicrobial Therapy for Human Pythiosis

Human pythiosis is associated with poor prognosis with significant mortality caused by Pythium insidiosum. Antimicrobials’ in vitro and in vivo results against P. insidiosum are inconsistent. Although antimicrobials are clinically useful, they are not likely to achieve therapeutic success alone without surgery and immunotherapy. New therapeutic options are therefore needed. This non-exhaustive review discusses the rationale antimicrobial therapy, minimum inhibitory concentrations, and efficacy of antibacterial and antifungal agents against P. insidiosum. This review further provides insight into the immunomodulating effects of antimicrobials that can enhance the immune response to infections. Current data support using antimicrobial combination therapy for the pharmacotherapeutic management of human pythiosis. Also, the success or failure of antimicrobial treatment in human pythiosis might depend on the immunomodulatory effects of drugs. The repurposing of existing drugs is a safe strategy for anti-P. insidiosum drug discovery. To improve patient outcomes in pythiosis, we suggest further research and a deeper understanding of P. insidiosum virulence factors, host immune response, and host immune system modification by antimicrobials.

Echinocandins - structure, mechanism of action and use in antifungal therapy

With increasing number of immunocompromised patients as well as drug resistance in fungi, the risk of fatal fungal infections in humans increases as well. The action of echinocandins is based on the inhibition of β-(1,3)-d-glucan synthesis that builds the fungal cell wall. Caspofungin, micafungin, anidulafungin and rezafungin are semi-synthetic cyclic lipopeptides. Their specific chemical structure possess a potential to obtain novel derivatives with better pharmacological properties resulting in more effective treatment, especially in infections caused by Candida and Aspergillus species. In this review we summarise information about echinocandins with closer look on their chemical structure, mechanism of action, drug resistance and usage in clinical practice. We also introduce actual trends in modification of this antifungals as well as new methods of their administration, and additional use in viral and bacterial infections.

Small molecule based anti-virulence approaches against Candida albicans infections

Fungi are considered "silent killers" due to the difficulty of, and delays in diagnosis of infections and lack of effective antifungals. This challenge is compounded by the fact that being eukaryotes, fungi share several similarities with human cellular targets, creating obstacles to drug discovery. Candida albicans, a ubiquitous microbe in the human body is well-known for its role as an opportunistic pathogen in immunosuppressed people. Significantly, C. albicans is resistant to all the three classes of antifungals that are currently clinically available. Over the past few years, a paradigm shift has been recommended in the management of C. albicans infections, wherein anti-virulence strategies are considered an alternative to the discovery of new antimycotics. Small molecules, with a molecular weight <900 Daltons, can easily permeate the cell membrane and modulate the signal transduction pathways to elicit desired virulence inhibitory actions against pathogens. This review dissects in-depth, the discoveries that have been made with small-molecule anti-virulence approaches to tackle C. albicans infections.

Therapeutic Drug Monitoring of the Echinocandin Antifungal Agents: Is There a Role in Clinical Practice? A Position Statement of the Anti-Infective Drugs Committee of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology

PURPOSE

Reduced exposure to echinocandins has been reported in specific patient populations, such as critically ill patients; however, fixed dosing strategies are still used. The present review examines the accumulated evidence supporting echinocandin therapeutic drug monitoring (TDM) and summarizes available assays and sampling strategies.

METHODS

A literature search was conducted using PubMed in December 2020, with search terms such as echinocandins, anidulafungin, caspofungin, micafungin, or rezafungin with pharmacology, pharmacokinetics (PKs), pharmacodynamics (PDs), drug-drug interactions, TDM, resistance, drug susceptibility testing, toxicity, adverse drug reactions, bioanalysis, chromatography, and mass spectrometry. Data on PD/PD (PK/PD) outcome markers, drug resistance, PK variability, drug-drug interactions, assays, and TDM sampling strategies were summarized.

RESULTS

Echinocandins demonstrate drug exposure-efficacy relationships, and maximum concentration/minimal inhibitory concentration ratio (Cmax/MIC) and area under the concentration-time curve/MIC ratio (AUC/MIC) are proposed PK/PD markers for clinical response. The relationship between drug exposure and toxicity remains poorly clarified. TDM could be valuable in patients at risk of low drug exposure, such as those with critical illness and/or obesity. TDM of echinocandins may also be useful in patients with moderate liver impairment, drug-drug interactions, hypoalbuminemia, and those undergoing extracorporeal membrane oxygenation, as these conditions are associated with altered exposure to caspofungin and/or micafungin. Assays are available to measure anidulafungin, micafungin, and caspofungin concentrations. A limited-sampling strategy for anidulafungin has been reported.

CONCLUSIONS

Echinocandin TDM should be considered in patients at known risk of suboptimal drug exposure. However, for implementing TDM, clinical validation of PK/PD targets is needed.

Fungal keratitis: A review of clinical presentations, treatment strategies and outcomes

Infectious keratitis is a significant cause of corneal blindness worldwide. Although less prevalent in the developed world, cases of fungal keratitis account for almost half of all keratitis cases, occurring in the developing countries. These cases are one of the most refractory types of infectious keratitis and present various challenges to the treating physician such as delayed presentation, long waiting time for culture positivity, limited availability effective antifungal drugs, prolonged duration for response to therapy, a highly variable spectrum of anti-fungal drug sensitivity and a high recurrence rate following keratoplasty. The advent of rapid diagnostic tools, molecular methods, in vitro anti-fungal drug sensitivity testing, alternatives to natamycin, targeted drug delivery and most importantly the results of large randomized controlled trials have significantly improved our understanding and approach towards the diagnosis and management of cases with fungal keratitis. Overall, Aspergillus and Fusarium species are the most common causes ones of fungal keratitis. History of antecedent trauma is a significant predisposing factor. Corneal scrapings for microscopic evaluation and culture preparation, is the standard of care for establishing the diagnosis of fungal keratitis. Molecular identification of cultures offers accurate identification of fungal pathogens, especially the rare species. Natamycin is an approved first-line drug. Voriconazole is the best alternative, especially for non-fusarium cases. Management involves administration of drugs usually by a combination of various routes, the treatment regimen being individualized depending upon the response to therapy. Photodynamic therapy is a newer treatment modality, being tried for non-responsive cases, before resorting to a therapeutic graft.

Assessing the Bioactive Profile of Antifungal-Loaded Calcium Sulfate against Fungal Biofilms

Calcium sulfate (CS) has been used clinically as a bone- or void-filling biomaterial, and its resorptive properties have provided the prospect for its use as a release mechanism for local antibiotics to control biofilms. Here, we aimed to test CS beads loaded with three antifungal drugs against planktonic and sessile fungal species to assess whether these antifungal beads could be harnessed to provide consistent release of antifungals at biofilm-inhibitory doses. A panel of different fungal species (n = 15) were selected for planktonic broth microdilution testing with fluconazole (FLZ), amphotericin B (AMB), and caspofungin (CSP). After establishing planktonic inhibition, antifungal CS beads were introduced to fungal biofilms (n = 5) to assess biofilm formation and cell viability through a combination of standard quantitative and qualitative biofilm assays. Inoculation of a hydrogel substrate, packed with antifungal CS beads, was also used to assess diffusion through a semidry material, to mimic active infection in vivo In general, antifungals released from loaded CS beads were all effective at inhibiting the pathogenic fungi over 7 days within standard MIC ranges for these fungi. We observed a significant reduction of pregrown fungal biofilms across key fungal pathogens following treatment, with visually observable changes in cell morphology and biofilm coverage provided by scanning electron microscopy. Assessment of biofilm inhibition also revealed reductions in total and viable cells across all organisms tested. These data show that antifungal-loaded CS beads produce a sustained antimicrobial effect that inhibits and kills clinically relevant fungal species in vitro as planktonic and biofilm cells.

Organic Antifungal Drugs and Targets of Their Action

In recent decades, there has been a significant increase in the number of fungal diseases. This is due to a wide spectrum of action, immunosuppressants and other group drugs. In terms of frequency, rapid spread and globality, fungal infections are approaching acute respiratory infections. Antimycotics are medicinal substances endorsed with fungicidal or fungistatic properties. For the treatment of fungal diseases, several groups of compounds are used that differ in their origin (natural or synthetic), molecular targets and mechanism of action, antifungal effect (fungicidal or fungistatic), indications for use (local or systemic infections), and methods of administration (parenteral, oral, outdoor). Several efforts have been made by various medicinal chemists around the world for the development of antifungal drugs with high efficacy with the least toxicity and maximum selectivity in the area of antifungal chemotherapy. The pharmacokinetic properties of the new antimycotics are also important: the ability to penetrate biological barriers, be absorbed and distributed in tissues and organs, get accumulated in tissues affected by micromycetes, undergo drug metabolism in the intestinal microflora and human organs, and in the kinetics of excretion from the body. There are several ways to search for new effective antimycotics: - Obtaining new derivatives of the already used classes of antimycotics with improved activity properties. - Screening of new chemical classes of synthetic antimycotic compounds. - Screening of natural compounds. - Identification of new unique molecular targets in the fungal cell. - Development of new compositions and dosage forms with effective delivery vehicles. The methods of informatics, bioinformatics, genomics and proteomics were extensively investigated for the development of new antimycotics. These techniques were employed in finding and identification of new molecular proteins in a fungal cell; in the determination of the selectivity of drugprotein interactions, evaluation of drug-drug interactions and synergism of drugs; determination of the structure-activity relationship (SAR) studies; determination of the molecular design of the most active, selective and safer drugs for the humans, animals and plants. In medical applications, the methods of information analysis and pharmacogenomics allow taking into account the individual phenotype of the patient, the level of expression of the targets of antifungal drugs when choosing antifungal agents and their dosage. This review article incorporates some of the most significant studies covering the basic structures and approaches for the synthesis of antifungal drugs and the directions for their further development.

Invasive Candidiasis in Patients with Solid Tumors Treated with Anidulafungin: A Post Hoc Analysis of Efficacy and Safety of Six Pooled Studies

Background

Solid tumors are a common predisposing factor for invasive candidiasis (IC) or candidemia due to IC.

Objectives

Post hoc analysis of patient-level efficacy and safety data from six studies of anidulafungin (with similar protocols/endpoints) in adults with IC/candidemia summarized by past or recent diagnosis of solid tumors.

Patients/methods

Patients received a single intravenous (IV) dose of anidulafungin 200 mg, followed by 100 mg once daily. After ≥ 5 to ≥ 10 days of IV treatment, switch to oral voriconazole/fluconazole was permitted in all but one study. Time of solid tumor diagnosis was defined as past, ≥ 6; and recent, < 6 months prior to study entry. Primary endpoint: global response of success (GRS) rate at the end of IV therapy (EOIVT). Secondary endpoints included the GRS rate at the end of all therapy (EOT), all-cause mortality, and safety.

Results

The GRS rate in the overall population was 73.4% at EOIVT and 65.5% at EOT. Past or recent solid tumor diagnosis did not affect GRS at EOIVT or EOT (past: 75.5% and 71.4%; recent: 72.2% and 62.2%, respectively). All-cause mortality was 14.4% on day 14 and 20.1% at day 28. Most treatment-emergent adverse events were mild/moderate in severity (81.6%).

Conclusions

Treatment of IC was effective regardless of the time of solid tumor diagnosis.

Trial Registration

Data were pooled from six studies: NCT00496197 (first posted on ClinicalTrials.gov on July 4, 2007); NCT00548262 (first posted on ClinicalTrials.gov on October 23, 2007); NCT00537329 (first posted on ClinicalTrials.gov on October 1, 2007); NCT00689338 (first posted on ClinicalTrials.gov on June 3, 2008); NCT00806351 (first posted on ClinicalTrials.gov on December 10, 2008); NCT00805740 (first posted on ClinicalTrials.gov on December 10, 2008).

Patients with solid tumor cancers (cancer of internal organs) have increased risk of fungal infections that can spread in the body through the blood. Infection with Candida species, known as invasive candidiasis (IC) (Candida invades the body in places normally free from germs) or candidemia (Candida infection in the blood), can cause severe illness and/or death. Anidulafungin is an antifungal drug recommended to treat IC/candidemia. This post hoc analysis looked at how effective and safe anidulafungin was in adult patients with IC/candidemia with ‘recent’ or ‘past’ history of solid tumors. The analysis included patients diagnosed with cancer less than 6 months before (recent history) or more than 6 months before (past history) they first received anidulafungin. Patients received anidulafungin by injection (intravenously [IV]) into the veins and, for continued treatment, were able to take a different antifungal drug orally. Of 539 patients from six studies, 139 had confirmed IC/candidemia and a history of solid tumors. Approximately 7 out of 10 (72%) patients were cured or no longer had signs of Candida infection at the end of IV anidulafungin treatment. Results were similar in patients with past or recent diagnosis of solid tumors. Treatment side effects reported in approximately 8 out of 10 (82%) patients were mild-to-moderate in severity. This analysis suggests anidulafungin was well tolerated and effective at treating IC/candidemia in patients with solid tumors, whether diagnosed recently or in the past.

Inhibitory mechanism of an antifungal drug, caspofungin against amyloid β peptide aggregation: Repurposing via neuroinformatics and an experimental approach

The multifactorial neurological condition called Alzheimer's disease (AD) primarily affects elderly individuals. Despite the calamitous consequences of AD, curative strategies for a regimen to apply remain inadequate as several factors contribute to AD etiology. Drug repurposing is an advance strategy prior to drug discovery as various effective drugs perform through alteration of multiple targets, and the present "poly-pharmacology" can be a curative approach to complex disorders. AD's multifactorial behavior actively encourages the hypothesis for a drug design approach focused on drug repurposing. In this study, we discovered that an antifungal drug, Caspofungin (CAS) is a potent Aβ aggregation inhibitor that displays significantly reduced toxicity associated with AD. Drug reprofiling and REMD simulations demonstrated that CAS interacts with the β-sheet section, known as Aβ amyloid fibrils hotspot. CAS leads to destabilization of β-sheet and, conclusively, in its devaluation. Later, in vitro experiments were acquired in which the fibrillar volume was reduced for CAS-treated Aβ peptide. For the first time ever, this study has determined an antifungal agent as the Aβ amyloid aggregation's potent inhibitor. Several efficient sequence-reliant potent inhibitors can be developed in future against the amyloid aggregation for different amyloid peptide by the processing and conformational optimization of CAS.

Ibrexafungerp: A novel oral glucan synthase inhibitor

Ibrexafungerp is a novel glucan synthase inhibitor currently undergoing phase II and phase III clinical trials. This compound has demonstrated in vitro activity against clinically important fungal pathogens including Candida spp. and Aspergillus spp. It is able to retain activity against many echinocandin-resistant strains of Candida due to differential avidity for the target site compared to echinocandins. In vivo animal models have demonstrated efficacy in murine models of invasive candidiasis, aspergillosis, and pneumocystis. Due to high bioavailability, it can be administered both orally and intravenously. A favorable drug interaction and tolerability profile is observed with this compound. This review summarizes existing data that have either been published or presented at international symposia.

Using in silico modelling and FRET-based assays in the discovery of novel FDA-approved drugs as inhibitors of MERS-CoV helicase

A Förster resonance energy transfer (FRET)-based assay was used to screen the FDA-approved compound library against the MERS-CoV helicase, an essential enzyme for virus replication within the host cell. Five compounds inhibited the helicase activity with submicromolar potencies (IC₅₀, 0.73-1.65 µM) and ten compounds inhibited the enzyme with micromolar potencies (IC₅₀, 19.6-502 µM). The molecular operating environment (MOE) was used to dock the identified inhibitors on the MERS-CoV helicase nucleotide binding. Strong inhibitors docked well in the nucleotide-binding site and established interactions with some of the essential residues. There was a reasonable correlation between the observed IC₅₀ values and the MOE docking scores of the strong inhibitors (r ² = 0.74), indicating the ability of the in silico docking model to predict the binding of strong inhibitors. In silico docking could be a useful complementary tool used with the FRET-based assay to predict new MERS-CoV helicase inhibitors. The identified inhibitors could potentially be used in the clinical development of new antiviral treatment for MERS-CoV and other coronavirus related diseases, including coronavirus disease 2019 (COVID-19).

Iron Assimilation during Emerging Infections Caused by Opportunistic Fungi with emphasis on Mucorales and the Development of Antifungal Resistance

Iron is a key transition metal required by most microorganisms and is prominently utilised in the transfer of electrons during metabolic reactions. The acquisition of iron is essential and becomes a crucial pathogenic event for opportunistic fungi. Iron is not readily available in the natural environment as it exists in its insoluble ferric form, i.e., in oxides and hydroxides. During infection, the host iron is bound to proteins such as transferrin, ferritin, and haemoglobin. As such, access to iron is one of the major hurdles that fungal pathogens must overcome in an immunocompromised host. Thus, these opportunistic fungi utilise three major iron acquisition systems to overcome this limiting factor for growth and proliferation. To date, numerous iron acquisition pathways have been fully characterised, with key components of these systems having major roles in virulence. Most recently, proteins involved in these pathways have been linked to the development of antifungal resistance. Here, we provide a detailed review of our current knowledge of iron acquisition in opportunistic fungi, and the role iron may have on the development of resistance to antifungals with emphasis on species of the fungal basal lineage order Mucorales, the causative agents of mucormycosis.

Abnormal sterol-induced cell wall glucan deficiency in yeast is due to impaired glucan synthase transport to the plasma membrane

Abnormal sterols disrupt cellular functions through yet unclear mechanisms. In Saccharomyces cerevisiae, accumulation of Δ8-sterols, the same type of sterols observed in patients of Conradi-Hünermann-Happle syndrome or in fungi after amine fungicide treatment, leads to cell wall weakness. We have studied the influence of Δ8-sterols on the activity of glucan synthase I, the protein synthetizing the main polymer in fungal cell walls, its regulation by the Cell Wall Integrity (CWI) pathway, and its transport from the endoplasmic reticulum to the plasma membrane. We ascertained that the catalytic characteristics were mostly unaffected by the presence of abnormal sterols but the enzyme was partially retained in the endoplasmic reticulum, leading to glucan deficit at the cell wall. Furthermore, we observed that glucan synthase I traveled through an unconventional exocytic route to the plasma membrane that is associated with low density intracellular membranes. Also, we found out that the CWI pathway remained inactive despite low glucan levels at the cell wall. Taken together, these data suggest that Δ8-sterols affect cell walls by inhibiting unconventional secretion of proteins leading to retention and degradation of glucan synthase I, while the compensatory CWI pathway is unable to activate. These results could be instrumental to understand defects of bone development in cholesterol biosynthesis disorders and fungicide mechanisms of action.

What do we know about the biology of the emerging fungal pathogen of humans Candida auris?

Candida auris is a worrisome fungal pathogen of humans which emerged merely about a decade ago. Ever since then the scientific community worked hard to understand clinically relevant traits, such as virulence factors, antifungal resistance mechanisms, and its ability to adhere to human skin and medical devices. Whole-genome sequencing of clinical isolates and epidemiological studies outlining the path of nosocomial outbreaks have been the focus of research into this pathogenic and multidrug-resistant yeast since its first description in 2009. More recently, work was started by several laboratories to explore the biology of C. auris. Here, we review the insights of studies characterizing the mechanisms underpinning antifungal drug resistance, biofilm formation, morphogenetic switching, cell aggregation, virulence, and pathogenicity of C. auris. We conclude that, although some progress has been made, there is still a long journey ahead of us, before we fully understand this novel pathogen. Critically important is the development of molecular tools for C. auris to make this fungus genetically tractable and traceable. This will allow an in-depth molecular dissection of the life cycle of C. auris, of its characteristics while interacting with the human host, and the mechanisms it employs to avoid being killed by antifungals and the immune system.

Echinocandins as Biotechnological Tools for Treating Candida auris Infections

Candida auris has been reported in the past few years as an invasive fungal pathogen of high interest. Its recent emergence in healthcare-associated infections triggered the efforts of researchers worldwide, seeking additional alternatives to the use of traditional antifungals such as azoles. Lipopeptides, specially the echinocandins, have been reported as an effective approach to control pathogenic fungi. However, despite its efficiency against C. auris, some isolates presented echinocandin resistance. Thus, therapies focused on echinocandins’ synergism with other antifungal drugs were widely explored, representing a novel possibility for the treatment of C. auris infections.

Determination of antifungal caspofungin in RPMI-1640 cell culture medium by column-switching HPLC-FLD

The actual scenario in the fight against fungal infections forces researchers to carry through with resistance studies to improve the therapies. These studies, which are performed in cell culture media, need accurate and sensitive analytical methodologies. That is why, in this work, an analytical method for caspofungin (CSF) concentration determination in RPMI-1640 cell culture medium with on-line sample treatment was developed and validated. CSF concentration was determined by HPLC-FLD using a column-switching procedure. The chromatographic analysis was carried out in less than 10 min using a C8 column (4 × 4 mm, 5 μm) as extraction stationary phase and a HSS T3 column (4.6 × 100 mm, 5 μm) as the analytical column. The used mobile phases were mixtures of phase A: pH 2 (adjusted with TFA) aqueous phase and phase B: ACN. For the extraction, the composition was (95:5, A:B v/v) and for the analysis (60:40, A:B v/v), both done in isocratic elution mode. These chromatographic conditions allowed reaching a limit of quantification of 10 μg/L, using 100 μL of sample with an injected volume of 40 μL. The proposed method was successfully validated in terms of selectivity, carryover, linear concentration range, accuracy and precision according to the criteria established by the Food and Drug Administration. Available amount of CSF in RPMI-1640 solution was found critical. CSF concentrations remained stable up to 2 h at room temperature. The developed method was applied for the direct analysis of CSF concentrations from in vitro experiments in presence of C. glabrata (CAGL18). The results highlight the decrease of cell proliferation even if the CSF amount decreases too, which asks question about the real value of the efficient concentration for CSF antifungal activity.

Transcriptional regulation of the caspofungin-induced cell wall damage response in Candida albicans

The human fungal pathogen Candida albicans maintains pathogenic and commensal states primarily through cell wall functions. The echinocandin antifungal drug caspofungin inhibits cell wall synthesis and is widely used in treating disseminated candidiasis. Signaling pathways are critical in coordinating the adaptive response to cell wall damage (CWD). C. albicans executes a robust transcriptional program following caspofungin-induced CWD. A comprehensive analysis of signaling pathways at the transcriptional level facilitates the identification of prospective genes for functional characterization and propels the development of novel antifungal interventions. This review article focuses on the molecular functions and signaling crosstalk of the C. albicans transcription factors Sko1, Rlm1, and Cas5 in caspofungin-induced CWD signaling.

Recent Progress in the Discovery of Antifungal Agents Targeting the Cell Wall

Due to the limit of available treatments and the emergence of drug resistance in the clinic, invasive fungal infections are an intractable problem with high morbidity and mortality. The cell wall, as a fungi-specific structure, is an appealing target for the discovery and development of novel and low-toxic antifungal agents. In an attempt to accelerate the discovery of novel cell wall targeted drugs, this Perspective will provide a comprehensive review of the progress made to date on the development of fungal cell wall inhibitors. Specifically, this review will focus on the targets, discovery process, chemical structures, antifungal activities, and structure-activity relationships. Although two types of cell wall antifungal agents are clinically available or in clinical trials, it is still a long way for the other cell wall targeted inhibitors to be translated into clinical applications. Future efforts should be focused on the identification of inhibitors against novel conserved cell wall targets.

Current Antimycotics, New Prospects, and Future Approaches to Antifungal Therapy

Fungal infections represent an increasing threat to a growing number of immune- and medically compromised patients. Fungi are eukaryotic organisms and, as such, there is a limited number of selective targets that can be exploited for antifungal drug development. This has also resulted in a very restricted number of antifungal drugs that are clinically available for the treatment of invasive fungal infections at the present time—polyenes, azoles, echinocandins, and flucytosine. Moreover, the utility of available antifungals is limited by toxicity, drug interactions and the emergence of resistance, which contribute to high morbidity and mortality rates. This review will present a brief summary on the landscape of current antifungals and those at different stages of clinical development. We will also briefly touch upon potential new targets and opportunities for novel antifungal strategies to combat the threat of fungal infections.

1,3-Thiazine, 1,2,3,4-Dithiadiazole, and Thiohydrazide Derivatives Affect Lipid Bilayer Properties and Ion-Permeable Pores Induced by Antifungals

Over the past decade, thiazines, thiadiazoles, and thiohydrazides have attracted increasing attention due to their sedative, antimicrobial, antiviral, antifungal, and antitumor activities. The clinical efficacy of such drugs, as well as the possibility of developing resistance to antimicrobials, will depend on addressing a number of fundamental problems, including the role of membrane lipids during their interaction with plasma membranes. The effects of the eight 1,3- thiazine-, 1,2,3,4- dithiadiazole-, and thiohydrazide-related compounds on the physical properties of model lipid membranes and the effects on reconstituted ion channels induced by the polyene macrolide antimycotic nystatin and antifungal cyclic lipopeptides syringomycin E and fengycin were observed. We found that among the tested agents, the fluorine-containing compound N′-(3,5-difluorophenyl)-benzenecarbothiohydrazide (C6) was the most effective at increasing the electric barrier for anion permeation into the hydrophobic region of the membrane and reducing the conductance of anion-permeable syringomycin pores. A decrease in the membrane boundary potential with C6 adsorption also facilitated the immersion of positively charged syringomycin molecules into the lipid bilayer and increases the pore-forming ability of the lipopeptide. Using differential scanning microcalorimetry, we showed that C6 led to disordering of membrane lipids, possibly by potentiating positive curvature stress. Therefore, we used C6 as an agonist of antifungals forming the pores that are sensitive to membrane curvature stress and lipid packing, i.e., nystatin and fengycin. The dramatic increase in transmembrane current induced by syringomycin E, nystatin, and fengycin upon C6 treatment suggests its potential in combination therapy for treating invasive fungal infections.