Current perspectives on echinocandin class drugs

Biofilm-Associated Candidiasis: Pathogenesis, Prevalence, Challenges and Therapeutic Options

The rising prevalence of fungal infections, especially those caused by Candida species, presents a major risk to global health. With approximately 1.5 million deaths annually, the urgency for effective treatment options has never been greater. Candida spp. are the leading cause of invasive infections, significantly impacting immunocompromised patients and those in healthcare settings. C. albicans, C. parapsilosis and the emerging species C. auris are categorized as highly dangerous species because of their pathogenic potential and increasing drug resistance. This review comparatively describes the formation of microbial biofilms of both bacterial and fungal origin, including major pathogens, thereby creating a novel focus. Biofilms can further complicate treatment, as these structures provide enhanced resistance to antifungal therapies. Traditional antifungal agents, including polyenes, azoles and echinocandins, have shown effectiveness, yet resistance development continues to rise, necessitating the exploration of novel therapeutic approaches. Antimicrobial peptides (AMPs) such as the anti-biofilm peptides Pom-1 and Cm-p5 originally isolated from snails represent promising candidates due to their unique mechanisms of action and neglectable cytotoxicity. This review article discusses the challenges posed by Candida infections, the characteristics of important species, the role of biofilms in virulence and the potential of new therapeutic options like AMPs.

Deletion of core septin gene aspB in Aspergillus fumigatus results in fungicidal activity of caspofungin

Septins are a family of GTP-binding proteins found in many eukaryotic lineages. Although highly conserved throughout many eukaryotes, their functions vary across species. In Aspergillus fumigatus, the etiological agent of invasive aspergillosis, septins participate in a variety of processes such as cell wall organization of conidia, septation, and response to cell wall stress. Previous studies determined that the ΔaspB strain had a greater sensitivity to anti-cell wall drugs, especially the echinocandin caspofungin, yet mechanisms behind this augmented sensitivity are unknown. We performed cell viability staining of the deletion strains post-caspofungin exposure and found that the ΔaspA, ΔaspB, and ΔaspC strains have significantly lower cell viability. Concomitant with the reduced viability, deletion strains are more susceptible to caspofungin on solid media. These results indicate that the septin cytoskeleton is important for A. fumigatus survival in the presence of caspofungin. Due to the potential of improved therapeutic outcome, we followed up using a neutropenic murine model of invasive aspergillosis. Animals infected with the ΔaspB strain and treated with caspofungin showed improved survival compared to the animals infected with akuB KU80 wild-type or complemented strains. Additionally, histological analysis showed reduced fungal burden and inflammation in the ΔaspB infected, caspofungin-treated group. Affinity purification coupled with quantitative proteomics identified proteins involved in the septin-dependent response to caspofungin, includng four candidate interactors involved in cell wall stress response. Deletion of these candidate genes resulted in increased susceptibility to caspofungin and moderately reduced viability post-drug exposure. Taken together, these data suggest that septin AspB contributes to the fungistatic response to caspofungin.

Comparative analysis of polysaccharide and cell wall structure in Aspergillus nidulans and Aspergillus fumigatus by solid-state NMR

Invasive aspergillosis poses a significant threat to immunocompromised patients, leading to high mortality rates associated with these infections. Targeting the biosynthesis of cell wall carbohydrates is a promising strategy for antifungal drug development and will be advanced by a molecular-level understanding of the native structures of polysaccharides within their cellular context. Solid-state NMR spectroscopy has recently provided detailed insights into the cell wall organization of Aspergillus fumigatus, but genetic and biochemical evidence highlights species-specific differences among Aspergillus species. In this study, we employed a combination of 13C, 15N, and 1H-detection solid-state NMR, supplemented by Dynamic Nuclear Polarization (DNP), to compare the structural organization of cell wall polymers and their assembly in the cell walls of A. fumigatus and A. nidulans, both of which are key model organisms and human pathogens. The two species exhibited a similar rigid core architecture, consisting of chitin, α-glucan, and β-glucan, which contributed to comparable cell wall properties, including polymer dynamics, water retention, and supramolecular organization. However, differences were observed in the chitin, galactosaminogalactan, protein, and lipid content, as well as in the dynamics of galactomannan and the structure of the glucan matrix.

The distinctive pharmacokinetic profile of rezafungin, a long-acting echinocandin developed in the era of modern pharmacometrics

Echinocandin drugs are the current first-line therapy for fungal infections caused by Candida spp. Most patients require once-daily intravenous (IV) administration in a hospital or outpatient setting for treatment, which may negatively impact their quality of life and stress healthcare resources. Similar to other echinocandins, the novel FDA-, EMA-, and Medical and Healthcare Products Regulatory Agency-approved echinocandin, rezafungin (CD101), exhibited strong antifungal activity against several fungal pathogens and a low drug-drug interaction liability, which are important for medically complex patients. A pharmacometric-based approach has been adopted throughout the development of rezafungin, which contrasts with older echinocandins where dosing regimens were largely derived empirically, and only recently based on pharmacometric guidance. This state-of-the-art approach used model-based simulations incorporating pre-clinical and clinical data as it became available to optimize the dosing regimen for rezafungin. The enhanced stability of the molecular structure and the safety profile of rezafungin allow for the administration of once-weekly IV doses, compared to the daily dosing requirement for other echinocandin drugs, with this distinctive pharmacokinetic profile of rezafungin resulting in a front-loaded dosing regimen with high exposures early in therapy for enhanced fungal killing. The long shelf-life of rezafungin makes this echinocandin more flexible in terms of storage and manufacturing. Demonstrated across clinical development, rezafungin may provide patients with next-generation first-line antifungal treatment for the treatment of candidaemia and invasive candidiasis.

Antifungal peptides: Therapeutic potential and challenges before their commercial success

Antifungal peptides (AFPs) are small cationic peptides that are found in a diverse range of taxa including bacteria, plants, mammals and insects. AFPs exhibit the strong antifungal activities against several pathogenic fungi, making them potential candidates for developing novel antifungal agents. AFP cause fungal cell death by rupturing the membranes of the fungal cell wall and inhibits the vital enzymes. Since AFPs are isolated from a range of natural sources, efforts are being made to create synthetic versions of these peptides with improved pharmacological properties. One of their key advantages is that they are less likely to develop resistance as compared to conventional antifungal medications. Although AFPs display immense potential as antifungal agents, challenges still exist in their stability, solubility, absorption, and time-consuming extraction process. Still, the possibility for AFPs to evolve into a novel class of antifungal medicine gives hope for improved treatments for fungal infections. This article offers the comprehensive information on AFPs origin, mode of action, prospective use in antifungal treatments. It also discusses about the application of antifungal peptides beyond the therapeutic field, such as in agriculture for crop protection, in food industry and in aquaculture field. It further elaborates on the challenges and potential paths associated with the progression of AFPs as advanced antifungal agents.

Progress in the Stereoselective Synthesis Methods of Pyrrolidine-Containing Drugs and Their Precursors

The presented review systematizes and summarizes the data on the synthesis of pyrrolidine derivatives, which are precursors for obtaining drugs. Based on the analysis of published data, the most promising directions in the synthesis of biologically active compounds containing a pyrrolidine ring are identified. Stereoselective synthesis methods are classified based on the source of the pyrrolidine ring. The first group includes methods that use a pyrrolidine ring as the starting compound. The second group combines stereoselective methods of cyclization of acyclic starting compounds, which lead to optically pure pyrrolidine derivatives.

Disruption to de novo uridine biosynthesis alters β-1,3-glucan masking in Candida albicans

The uridine derivatives UDP-glucose and UDP-N-acetylglucosamine are important for cell wall construction as they are the precursors for the synthesis of β-1,3-glucan and chitin, respectively. Previous studies have demonstrated attenuated virulence of uridine auxotrophs in mice, which has been attributed to insufficient uridine levels for growth in the host. We have discovered that uridine deprivation in the uridine auxotroph ura3ΔΔ disrupts cell wall architecture by increasing surface mannans, exposing β-1,3-glucan and chitin, and decreasing UDP-sugar levels. Cell wall architecture and UDP-sugars can be rescued with uridine supplementation. The cell wall architectural disruptions in the ura3ΔΔ mutant also impact immune activation since the mutant elicited greater TNFα secretion from RAW264.7 macrophages than wild type. To determine if cell wall defects contributed to decreased virulence in the ura3ΔΔ mutant, we used a murine model of systemic infection. Mice infected with the ura3ΔΔ mutant exhibited increased survival and reduced kidney fungal burden compared with mice infected with wild type. However, suppression of the immune response with cyclophosphamide did not rescue virulence in mice infected with the ura3ΔΔ mutant, indicating the attenuation in virulence of uridine auxotrophs can be attributed to decreased growth in the host but not increased exposure of β-1,3-glucan. Moreover, the ura3ΔΔ mutant is unable to grow on ex vivo kidney agar, which demonstrates its inability to colonize the kidneys due to poor growth. Thus, although uridine auxotrophy elicits changes to cell wall architecture that increase the exposure of immunogenic polymers, metabolic fitness costs more strongly drive the observed virulence attenuation.IMPORTANCECandida albicans is a common cause of bloodstream infections (candidemia). Treatment of these bloodstream infections is made difficult because of increasing antifungal resistance and drug toxicity. Thus, new tactics are needed for antifungal drug development, with immunotherapy being of particular interest. The cell wall of C. albicans is composed of highly immunogenic polymers, particularly β-1,3-glucan. However, β-1,3-glucan is naturally masked by an outer layer of mannoproteins, which hampers the detection of the fungus by the host immune system. Alteration in cell wall components has been shown to increase β-1,3-glucan exposure; however, it is unknown how the inability to synthesize precursors to cell wall components affects unmasking. Here, we demonstrate how cell wall architecture is altered in response to a deficit in precursors for cell wall synthesis and how uridine is a crucial component of these precursors.

Bioactive potential of Eugenia luschnathiana essential oil and extract: antifungal activity against Candida species isolated from oncological patients

Immunosuppressed individuals, including those undergoing cancer treatment, are more vulnerable to fungal infections, such as oral candidiasis, impacting their quality of life. Given the limitations of current therapies, the discovery of new antifungal agents, including those of natural origin, is crucial for the proper managing of these infections. We investigated the phytochemical profile and antifungal activity of both the essential oil and crude ethanolic extract (CEE) obtained from Eugenia luschnathiana against reference strains and clinical isolates of Candida from oncology patients. Toxicological characterization was also conducted. Gas chromatography coupled to mass spectrometry (GC-MS) and 1H Nuclear Magnetic Resonance (NMR) were used for phytochemical analysis. Antifungal evaluation was conducted to determine the Minimum Inhibitory Concentration (MIC) and Minimum Fungicidal Concentration (MFC); evaluation of potential mechanisms of action; activity on a fungal biofilm; evaluation of the cytotoxic effect on human keratinocytes of the HaCat lineage by the MTT method; determination of lethality for Artemia salina larvae. GC-MS identified a predominance of sesquiterpenes in the essential oil, notably (E)-Caryophyllene. The 1H NMR spectrum identified aliphatic, osidic, and aromatic compounds in the crude ethanolic extract. The essential oil showed no antifungal activity. However, the CEE exhibited fungicidal activity, with MIC and MFC ranging from 1.95 µg/mL to 3.90 µg/mL. The antifungal effect was affected by sorbitol, indicating a possible mechanism targeting fungal cell wall structures. At low concentration (19.5 µg/mL), the CEE inhibited 62,78% of C. albicans biofilm. The CEE demonstrated a promising toxicity profile, with an LC50 of 142.4 µg/mL against Artemia salina. In conclusion, the CEE from Eugenia luschnathiana exhibited potent antifungal activity, likely through cell wall disruption, biofilm inhibition, and a favorable toxicity profile for further exploration.

Navigating the fungal battlefield: cysteine-rich antifungal proteins and peptides from Eurotiales

Fungi are ubiquitous in the environment and play a key role in the decomposition and recycling of nutrients. On the one hand, their special properties are a great asset for the agricultural and industrial sector, as they are used as source of nutrients, producers of enzymes, pigments, flavorings, and biocontrol agents, and in food processing, bio-remediation and plant growth promotion. On the other hand, they pose a serious challenge to our lives and the environment, as they are responsible for fungal infections in plants, animals and humans. Although host immunity opposes invading pathogens, certain factors favor the manifestation of fungal diseases. The prevalence of fungal infections is on the rise, and there is an alarming increase in the resistance of fungal pathogens to approved drugs. The limited number of antimycotics, the obstacles encountered in the development of new drugs due to the poor tolerability of antifungal agents in patients, the limited number of unique antifungal targets, and the low species specificity contribute to the gradual depletion of the antifungal pipeline and newly discovered antifungal drugs are rare. Promising candidates as next-generation therapeutics are antimicrobial proteins and peptides (AMPs) produced by numerous prokaryotic and eukaryotic organisms belonging to all kingdom classes. Importantly, filamentous fungi from the order Eurotiales have been shown to be a rich source of AMPs with specific antifungal activity. A growing number of published studies reflects the efforts made in the search for new antifungal proteins and peptides (AFPs), their efficacy, species specificity and applicability. In this review, we discuss important aspects related to fungi, their impact on our life and issues involved in treating fungal infections in plants, animals and humans. We specifically highlight the potential of AFPs from Eurotiales as promising alternative antifungal therapeutics. This article provides insight into the structural features, mode of action, and progress made toward their potential application in a clinical and agricultural setting. It also identifies the challenges that must be overcome in order to develop AFPs into therapeutics.

New arsenals for old armour: Biogenic nanoparticles in the battle against drug-resistant Candidaalbicans

Candida albicans is a common commensal fungus and fourth most frequent causative agent of nosocomial infections including life-threatening invasive candidiasis in humans. The effectiveness of present antifungal therapies using azoles, polyenes, flucytosine and echinocandins has plateaued in managing fungal infections. The limitations of these antifungal drugs are related to polymorphic morphology, biofilm formation, emergence of drug-resistant strains and production of several virulence factors. Development of new antifungal agents, which can particularly afflict multiple cellular targets and limiting evolving resistant strains are needed. Recently, metal nanoparticles have emerged as a source of new antifungal agents for antifungal formulations. Furthermore, green nanotechnology deals with the use of biosynthetic routes that offer new avenue for synthesizing antifungal nanoparticles coupled with less toxic chemical inventory and environmental sustainability. This article reviews the recent developments on C. albicans pathogenesis, biofilm formation, drug resistance, mode of action of antifungal drugs and antifungal activities of metal nanoparticles. The antifungal efficacy and mode of action of metal nanoparticles are described in the context of prospective therapeutic applications.

A review of the fernane-type triterpenoids as anti-fungal drugs

Human fungal pathogens could cause a broad plethora of infections in both the immunocompetent and immunocompromised host. Fungal infections have become important causes of morbidity and mortality in recent years, the current arsenal of anti-fungal therapies was restricted. Ibrexafungerp was a novel, highly bioavailable glucan synthase inhibitor formulated for both intravenous and oral administration being developed by Scynexis; it was also the first novel anti-fungal drug class approved in more than 20 years. Ibrexafungerp was one semi-synthetic derivative of enfumafungin, a natural product isolated from fungi. This review reported the discovery of enfumafungin and ibrexafungerp, their anti-fungal mechanism, summed up 63 fernane-type triterpenoids from natural products, including 49 from plants, 9 from fungi and 5 from lichen. In addition, the review summarized the progress of enzymes responsible for the biosynthesis of type II fernane triterpenoid (enfumafungin skeleton) and type I fernane triterpenoid (polytolypin skeleton). The good example kept our confidence up for searching for new leading compounds and discovering drugs from fungi.

Comparative Analysis of Polysaccharide and Cell Wall Structure in Aspergillus nidulans and Aspergillus fumigatus by Solid-State NMR

Invasive aspergillosis poses a significant threat to immunocompromised patients, leading to high mortality rates associated with these infections. Targeting the biosynthesis of cell wall carbohydrates is a promising strategy for antifungal drug development and will be advanced by a molecular-level understanding of the native structures of polysaccharides within their cellular context. Solid-state NMR spectroscopy has recently provided detailed insights into the cell wall organization of Aspergillus fumigatus, but genetic and biochemical evidence highlights species-specific differences among Aspergillus species. In this study, we employed a combination of 13C, 15N, and 1H-detection solid-state NMR, supplemented by Dynamic Nuclear Polarization (DNP), to compare the structural organization of cell wall polymers and their assembly in the cell walls of A. fumigatus and A. nidulans, both of which are key model organisms and human pathogens. The two species exhibited a similar rigid core architecture, consisting of chitin, α-glucan, and β-glucan, which contributed to comparable cell wall properties, including polymer dynamics, water retention, and supramolecular organization. However, differences were observed in the chitin, galactosaminogalactan, protein, and lipid content, as well as in the dynamics of galactomannan and the structure of the glucan matrix.

Adaptative survival of Aspergillus fumigatus to echinocandins arises from cell wall remodeling beyond β-1,3-glucan synthesis inhibition

Antifungal echinocandins inhibit the biosynthesis of β-1,3-glucan, a major and essential polysaccharide component of the fungal cell wall. However, the efficacy of echinocandins against the pathogen Aspergillus fumigatus is limited. Here, we use solid-state nuclear magnetic resonance (ssNMR) and other techniques to show that echinocandins induce dynamic changes in the assembly of mobile and rigid polymers within the A. fumigatus cell wall. The reduction of β-1,3-glucan induced by echinocandins is accompanied by a concurrent increase in levels of chitin, chitosan, and highly polymorphic α-1,3-glucans, whose physical association with chitin maintains cell wall integrity and modulates water permeability. The rearrangement of the macromolecular network is dynamic and controls the permeability and circulation of the drug throughout the cell wall. Thus, our results indicate that echinocandin treatment triggers compensatory rearrangements in the cell wall that may help A. fumigatus to tolerate the drugs' antifungal effects.

Structural and Biophysical Dynamics of Fungal Plasma Membrane Proteins and Implications for Echinocandin Action in Candida glabrata

Fungal plasma membrane proteins represent key therapeutic targets for antifungal agents, yet their structure and spatial distribution in the native context remain poorly characterized. Herein, we employ an integrative multimodal approach to elucidate the structural and functional organization of plasma membrane protein complexes in Candida glabrata , focusing on prominent and essential membrane proteins, the polysaccharide synthase β-(1,3)-glucan synthase (GS) and the proton pump Pma1. Cryo-electron tomography (cryo-ET) and live cell imaging reveal that GS and Pma1 are heterogeneously distributed into distinct plasma membrane microdomains. Treatment with caspofungin, an echinocandin antifungal that targets GS, alters the plasma membrane and disrupts the native distribution of GS and Pma1. Based on these findings, we propose a model for echinocandin action that considers how drug interactions with the plasma membrane environment lead to inhibition of GS. Our work underscores the importance of interrogating the structural and dynamic characteristics of fungal plasma membrane proteins in situ to understand function and facilitate precisely targeted development of novel antifungal therapies.

The Putative Cytochrome b5 Domain-Containing Protein CaDap1 Homologue Is Involved in Antifungal Drug Tolerance, Cell Wall Chitin Maintenance, and Virulence in Candida albicans

Candida albicans (Ca), a prominent opportunistic fungal pathogen in humans, has garnered considerable attention due to its infectious properties. Herein, we have identified and characterized CaCDAP1 (Ca orf19.1034), a homolog of ScDAP1 found in Saccharomyces cerevisiae. CaCDAP1 encodes a 183-amino acid protein with a conserved cytochrome b5-like heme-binding domain. The deletion of CaDAP1 renders Ca cells susceptible to caspofungin and terbinafine. CaDAP1 deletion confers resistance to Congo Red and Calcofluor White, and sensitivity to sodium dodecyl sulfate. The deletion of CaDAP1 results in a 50% reduction in chitin content within the cell wall, the downregulation of phosphorylation levels in CaMkc1, and the upregulation of phosphorylation levels in CaCek1. Notably, CaDAP1 deletion results in the abnormal hyphal development of Ca cells and diminishes virulence in a mouse systemic infection model. Thus, CaDAP1 emerges as a critical regulator governing cellular responses to antifungal drugs, the synthesis of cell wall chitin, and virulence in Ca.

Antifungal effects of echinocandins diminish when exposed to intestinal lumen contents: a finding with potentially significant clinical implications

Echinocandins, a prominent class of antifungals, are known for their broad-spectrum activity and favorable safety profiles. However, their bioavailability and efficacy via oral route are suboptimal. In this study, caspofungin and micafungin, the two most commonly used echinocandins, were evaluated in various in vitro environments simulating intestinal lumen. The results revealed that while both antifungals are effective in standard medium, their efficacy significantly diminishes in the presence of human small bowel aspirates and bovine bile. The study suggests that bowel contents and specifically bile acids may be a suppressive component, hindering the antifungal effects of echinocandins. This novel exploration sheds light on the poor oral bioavailability of echinocandins. The findings imply that echinocandins alone, regardless of administration route, may not be optimal for gastrointestinal (GI) fungal infections or invasive fungal infections originating from intestinal translocation. Further clinical investigations are warranted to validate and expand upon these observations.

Antifungal activity against Candida albicans of methyl 3,5-dinitrobenzoate loaded nanoemulsion

The objective of this study was to evaluate the antifungal activity of free methyl 3,5 dinitrobenzoate (MDNB) and its nanoemulsion (MDNB-NE) against strains of Candida albicans. Additionally, a molecular modeling study was also carried out to propose the mechanism of action and toxicity of MDNB. These results demonstrated the MDNB-NE presented a droplet size of 181.16 ± 3.20 nm and polydispersity index of 0.30 ± 0.03. MDNB and MDNB-NE inhibited the growth of all strains with minimum inhibitory concentrations of 0.27-1.10 mM. The biological results corroborated the molecular model, which pointed to a multi-target antifungal mechanism of action for MDNB in C. albicans. The study could serve as a basis for further research involving compounds with nitro groups with antifungal.

Reshaping Echinocandin Antifungal Drugs To Circumvent Glucan Synthase Point-Mutation-Mediated Resistance

Echinocandins are a class of antifungal drugs that inhibit the activity of the β-(1,3)-glucan synthase complex, which synthesizes fungal cell wall β-(1,3)-glucan. Echinocandin resistance is linked to mutations in the FKS gene, which encodes the catalytic subunit of the glucan synthase complex. We present a molecular-docking-based model that provides insight into how echinocandins interact with the target Fks protein: echinocandins form a ternary complex with both Fks and membrane lipids. We used reductive dehydration of alcohols to generate dehydroxylated echinocandin derivatives and evaluated their potency against a panel of Candida pathogens constructed by introducing resistance-conferring mutations in the FKS gene. We found that removing the hemiaminal alcohol, which drives significant conformational alterations in the modified echinocandins, reduced their efficacy. Conversely, eliminating the benzylic alcohol of echinocandins enhanced potency by up to two orders of magnitude, in a manner dependent upon the resistance-conferring mutation. Strains that have developed resistance to either rezafungin, the most recently clinically approved echinocandin, or its dehydroxylated derivative RZF-1, exhibit high resistance to rezafungin while demonstrating moderate resistance to RZF-1. These findings provide valuable insight for combating echinocandin resistance through chemical modifications.

Promising immunotherapeutic targets for treating candidiasis

In the last twenty years, there has been a significant increase in invasive fungal infections, which has corresponded with the expanding population of individuals with compromised immune systems. As a result, the mortality rate linked to these infections remains unacceptably high. The currently available antifungal drugs, such as azoles, polyenes, and echinocandins, face limitations in terms of their diversity, the escalating resistance of fungi and the occurrence of significant adverse effects. Consequently, there is an urgent need to develop new antifungal medications. Vaccines and antibodies present a promising avenue for addressing fungal infections due to their targeted antifungal properties and ability to modulate the immune response. This review investigates the structure and function of cell wall proteins, secreted proteins, and functional proteins within C. albicans. Furthermore, it seeks to analyze the current advancements and challenges in macromolecular drugs to identify new targets for the effective management of candidiasis.

Rapamycin and caspofungin show synergistic antifungal effects in caspofungin-susceptible and caspofungin-resistant Candida strains in vitro

OBJECTIVES

Caspofungin is an echinocandin antifungal agent that inhibits synthesis of glucan required for the fungal cell wall. Resistance is mediated by mutation of Fks1 glucan synthase, among which S645P is the most common resistance-associated polymorphism. Rapamycin is a macrolide that inhibits the mechanistic target of rapamycin (mTOR) protein kinase activity. This study investigated the interaction between rapamycin and caspofungin in inhibiting the growth of WT Candida albicans and Fks1 S645P mutant clinical isolate, and WT Candida lusitaniae and genetically engineered isogenic strain with Fks1 S645P mutation at equivalent position.

METHODS

Interactions between caspofungin and rapamycin were evaluated using the microdilution chequerboard method in liquid medium. The results were analysed using the Loewe additivity model (FIC index, FICI) and the Bliss independence model (response surface, RS, analysis).

RESULTS

Synergy between rapamycin and caspofungin was shown for C. albicans and C. lusitaniae strains by RS analysis of the chequerboard tests. Synergy was observed in strains susceptible and resistant to caspofungin. Weak subinhibitory concentrations of rapamycin were sufficient to restore caspofungin susceptibility.

CONCLUSIONS

We report here, for the first time, synergy between caspofungin and rapamycin in Candida species. Synergy was shown for strains susceptible and resistant to caspofungin. This study highlights the possible implication of the TOR pathway in sensing antifungal-mediated cell wall stress and in modulating the cellular response to echinocandins in Candida yeasts.

Discovery of Novel 8-Hydroxyquinoline Derivatives with Potent In Vitro and In Vivo Antifungal Activity

Fungal pathogens can cause life-threatening infections, yet current antifungals are inadequate at treating many of these, highlighting the importance of novel drug discovery. Here, we report hit compound L14, a novel 8-hydroxyquinoline derivative with potent and broad-spectrum antifungal activity. In vitro experiments exhibited that L14 had better activity and lower cytotoxicity than that of clioquinol and showed synergy in combination with fluconazole (FLC). In a Candida albicans-infected murine model, L14 at 2 mg/kg showed better in vivo efficacy than clioquinol at reducing fungal burden and extending the survival of C. albicans-infected mice. In addition, L14 alone or in combination with FLC had significant inhibitory activity against hypha and biofilm formation. Overall, our data indicated that 8-hydroxyquinoline derivative L14 has favorable pharmacokinetics and acceptable safety profiles and could be further investigated as a promising antifungal hit compound.

Decreased echinocandin susceptibility in Candida parapsilosis causing candidemia and emergence of a pan-echinocandin resistant case in China

Candida parapsilosis is becoming a predominant non-albicans cause of invasive candidiasis (IC). Echinocandins are the preferred choice for IC treatment and prophylaxis. Resistance to echinocandins in C. parapsilosis has emerged in several countries, but little is known about the susceptibility profile in China or about mechanisms of resistance. Here, we investigated the echinocandin susceptibilities of 2523 C. parapsilosis isolates collected from China and further explored the resistance mechanism among echinocandin-resistant isolates. Anidulafungin exhibited the highest MICs (MIC50/90, 1 and 2 µg/mL; GM, 0.948 µg/mL), while caspofungin showed better activity (0.5 and 1 µg/mL; 0.498 µg/mL). Significantly higher echinocandin MICs were observed among blood-derived isolates compared to others, especially for caspofungin (GM, 1.348 µg/mL vs 0.478 µg/mL). Isolates from ICU and surgical wards also showed higher MICs. Twenty isolates showed intermediate phenotypes for at least one echinocandin. One was resistant to all three echinocandins, fluconazole and voriconazole, which caused breakthrough IC during long-term exposure to micafungin. WGS revealed this isolate carried a mutation S656P in hotspot1 region of Fks1. Bioinformatics analyses suggested that this mutation might lead to an altered protein conformation. CRISPR Cas9-mediated introduction of this mutation into a susceptible reference C. parapsilosis strain increased MICs of all echinocandins 64-fold, with similar results found in the subspecies, C. orthopsilosis and C. metapsilosis. This is the first report of a multi-azole resistant and pan-echinocandin resistant C. parapsilosis isolate, and the identification of a FKS1S656P conferring pan-echinocandin resistance. Our study underscores the necessity of rigorous management of antifungal use and of monitoring for antifungal susceptibility.

Understanding fluconazole tolerance in Candida albicans: implications for effective treatment of candidiasis and combating invasive fungal infections

OBJECTIVES

Fluconazole (FLC) tolerant phenotypes in Candida species contribute to persistent candidemia and the emergence of FLC resistance. Therefore, making FLC fungicidal and eliminating FLC tolerance are important for treating invasive fungal diseases (IFDs) caused by Candida species. However, the mechanisms of FLC tolerance in Candida species remain to be fully explored.

METHODS

This review discusses the high incidence of FLC tolerance in Candida species and the importance of successfully clearing FLC tolerance in treating candidiasis. We further define and characterize FLC tolerance in C. albicans.

RESULTS

This review identifies global factors affecting FLC tolerance and suggest that FLC tolerance is a strategy of C. albicans response to FLC damage whose mechanism differs from FLC resistance.

CONCLUSIONS

This review highlights the significance of the cell membrane and cell wall integrity in FLC tolerance, guiding approaches to combat IFDs caused by Candida species..

Candida auris Genetics and Emergence

Candida auris is a multidrug-resistant fungal pathogen that presents a serious threat to global human health. Since the first reported case in 2009 in Japan, C. auris infections have been reported in more than 40 countries, with mortality rates between 30% and 60%. In addition, C. auris has the potential to cause outbreaks in health care settings, especially in nursing homes for elderly patients, owing to its efficient transmission via skin-to-skin contact. Most importantly, C. auris is the first fungal pathogen to show pronounced and sometimes untreatable clinical drug resistance to all known antifungal classes, including azoles, amphotericin B, and echinocandins. In this review, we explore the causes of the rapid spread of C. auris. We also highlight its genome organization and drug resistance mechanisms and propose future research directions that should be undertaken to curb the spread of this multidrug-resistant pathogen.

Caspofungin-induced β(1,3)-glucan exposure in Candida albicans is driven by increased chitin levels

To successfully induce disease, Candida albicans must effectively evade the host immune system. One mechanism used by C. albicans to achieve this is to mask immunogenic β(1,3)-glucan epitopes within its cell wall under an outer layer of mannosylated glycoproteins. Consequently, induction of β(1,3)-glucan exposure (unmasking) via genetic or chemical manipulation increases fungal recognition by host immune cells in vitro and attenuates disease during systemic infection in mice. Treatment with the echinocandin caspofungin is one of the most potent drivers of β(1,3)-glucan exposure. Several reports using murine infection models suggest a role for the immune system, and specifically host β(1,3)-glucan receptors, in mediating the efficacy of echinocandin treatment in vivo. However, the mechanism by which caspofungin-induced unmasking occurs is not well understood. In this report, we show that foci of unmasking co-localize with areas of increased chitin within the yeast cell wall in response to caspofungin, and that inhibition of chitin synthesis via nikkomycin Z attenuates caspofungin-induced β(1,3)-glucan exposure. Furthermore, we find that both the calcineurin and Mkc1 mitogen-activated protein kinase pathways work synergistically to regulate β(1,3)-glucan exposure and chitin synthesis in response to drug treatment. When either of these pathways are interrupted, it results in a bimodal population of cells containing either high or low chitin content. Importantly, increased unmasking correlates with increased chitin content within these cells. Microscopy further indicates that caspofungin-induced unmasking correlates with actively growing cells. Collectively, our work presents a model in which chitin synthesis induces unmasking within the cell wall in response to caspofungin in growing cells. IMPORTANCE Systemic candidiasis has reported mortality rates ranging from 20% to 40%. The echinocandins, including caspofungin, are first-line antifungals used to treat systemic candidiasis. However, studies in mice have shown that echinocandin efficacy relies on both its cidal impacts on Candida albicans, as well as a functional immune system to successfully clear invading fungi. In addition to direct C. albicans killing, caspofungin increases exposure (unmasking) of immunogenic β(1,3)-glucan moieties. To evade immune detection, β(1,3)-glucan is normally masked within the C. albicans cell wall. Consequently, unmasked β(1,3)-glucan renders these cells more visible to the host immune system and attenuates disease progression. Therefore, discovery of how caspofungin-induced unmasking occurs is needed to elucidate how the drug facilitates host immune system-mediated clearance in vivo. We report a strong and consistent correlation between chitin deposition and unmasking in response to caspofungin and propose a model in which altered chitin synthesis drives increased unmasking during drug exposure.

Candidiasis: From cutaneous to systemic, new perspectives of potential targets and therapeutic strategies

Candidiasis is an infection caused by fungi from a Candida species, most commonly Candida albicans. C. albicans is an opportunistic fungal pathogen typically residing on human skin and mucous membranes of the mouth, intestines or vagina. It can cause a wide variety of mucocutaneous barrier and systemic infections; and becomes a severe health problem in HIV/AIDS patients and in individuals who are immunocompromised following chemotherapy, treatment with immunosuppressive agents or after antibiotic-induced dysbiosis. However, the immune mechanism of host resistance to C. albicans infection is not fully understood, there are a limited number of therapeutic antifungal drugs for candidiasis, and these have disadvantages that limit their clinical application. Therefore, it is urgent to uncover the immune mechanisms of the host protecting against candidiasis and to develop new antifungal strategies. This review synthesizes current knowledge of host immune defense mechanisms from cutaneous candidiasis to invasive C. albicans infection and documents promising insights for treating candidiasis through inhibitors of potential antifungal target proteins.

Fungal Drug Response and Antimicrobial Resistance

Antifungal resistance is a growing concern as it poses a significant threat to public health. Fungal infections are a significant cause of morbidity and mortality, especially in immunocompromised individuals. The limited number of antifungal agents and the emergence of resistance have led to a critical need to understand the mechanisms of antifungal drug resistance. This review provides an overview of the importance of antifungal resistance, the classes of antifungal agents, and their mode of action. It highlights the molecular mechanisms of antifungal drug resistance, including alterations in drug modification, activation, and availability. In addition, the review discusses the response to drugs via the regulation of multidrug efflux systems and antifungal drug-target interactions. We emphasize the importance of understanding the molecular mechanisms of antifungal drug resistance to develop effective strategies to combat the emergence of resistance and highlight the need for continued research to identify new targets for antifungal drug development and explore alternative therapeutic options to overcome resistance. Overall, an understanding of antifungal drug resistance and its mechanisms will be indispensable for the field of antifungal drug development and clinical management of fungal infections.

A host defense peptide mimetic, brilacidin, potentiates caspofungin antifungal activity against human pathogenic fungi

Fungal infections cause more than 1.5 million deaths a year. Due to emerging antifungal drug resistance, novel strategies are urgently needed to combat life-threatening fungal diseases. Here, we identify the host defense peptide mimetic, brilacidin (BRI) as a synergizer with caspofungin (CAS) against CAS-sensitive and CAS-resistant isolates of Aspergillus fumigatus, Candida albicans, C. auris, and CAS-intrinsically resistant Cryptococcus neoformans. BRI also potentiates azoles against A. fumigatus and several Mucorales fungi. BRI acts in A. fumigatus by affecting cell wall integrity pathway and cell membrane potential. BRI combined with CAS significantly clears A. fumigatus lung infection in an immunosuppressed murine model of invasive pulmonary aspergillosis. BRI alone also decreases A. fumigatus fungal burden and ablates disease development in a murine model of fungal keratitis. Our results indicate that combinations of BRI and antifungal drugs in clinical use are likely to improve the treatment outcome of aspergillosis and other fungal infections.

Potential Strategies to Control the Risk of Antifungal Resistance in Humans: A Comprehensive Review

Fungal infections are becoming one of the main causes of morbidity and mortality in people with weakened immune systems. Mycoses are becoming more common, despite greater knowledge and better treatment methods, due to the regular emergence of resistance to the antifungal medications used in clinical settings. Antifungal therapy is the mainstay of patient management for acute and chronic mycoses. However, the limited availability of antifungal drug classes limits the range of available treatments. Additionally, several drawbacks to treating mycoses include unfavourable side effects, a limited activity spectrum, a paucity of targets, and fungal resistance, all of which continue to be significant issues in developing antifungal drugs. The emergence of antifungal drug resistance has eliminated accessible drug classes as treatment choices, which significantly compromises the clinical management of fungal illnesses. In some situations, the emergence of strains resistant to many antifungal medications is a major concern. Although new medications have been developed to address this issue, antifungal drug resistance has grown more pronounced, particularly in patients who need long-term care or are undergoing antifungal prophylaxis. Moreover, the mechanisms that cause resistance must be well understood, including modifications in drug target affinities and abundances, along with biofilms and efflux pumps that diminish intracellular drug levels, to find novel antifungal drugs and drug targets. In this review, different classes of antifungal agents, and their resistance mechanisms, have been discussed. The latter part of the review focuses on the strategies by which we can overcome this serious issue of antifungal resistance in humans.

Antibodies to Combat Fungal Infections: Development Strategies and Progress

The finding that some mAbs are antifungal suggests that antibody immunity may play a key role in the defense of the host against mycotic infections. The discovery of antibodies that guard against fungi is a significant advancement because it gives rise to the possibility of developing vaccinations that trigger protective antibody immunity. These vaccines might work by inducing antibody opsonins that improve the function of non-specific (such as neutrophils, macrophages, and NK cells) and specific (such as lymphocyte) cell-mediated immunity and stop or aid in eradicating fungus infections. The ability of antibodies to defend against fungi has been demonstrated by using monoclonal antibody technology to reconsider the function of antibody immunity. The next step is to develop vaccines that induce protective antibody immunity and to comprehend the mechanisms through which antibodies mediate protective effects against fungus.

Antifungal chemotherapies and immunotherapies for the future

Human fungal pathogens cause a broad plethora of infections, spanning cutaneous dermatophytoses to invasive infections in immunocompromised hosts. As eukaryotic pathogens are capable of morphotype switching, they present unique challenges both for drug development and the immunological response. Whilst current antifungal therapies are limited to the orally available triazoles, intravenous echonocandins and polyenes, and flucytosine and terbinafine, there has been recent significant progress in the antifungal armamentorium with ibrexafungerp, a novel orally available terpanoid that inhibits 1,3-beta-D-glucan-approved by Food and Drug Administration in 2021, and fosmanogepix, an orally available pro-drug of manogepix, which targets glycosylphosphatidylinositol-anchored protein maturation entering Phase 3 studies for candidaemia. A number of further candidates are in development. There has been significant use of existing immunotherapies such as recombinant interferon-γ and G-CSF for fungal disease in immunocompromised patients, and there are emerging opportunities for monoclonal antibodies targeting TH2 inflammation. Omalizumab, an anti-IgE monoclonal antibody in asthma, is now used routinely for the treatment of allergic bronchopulmonary aspergillosis, and further agents targeting IL-4 and IL-5 are being evaluated. In addition, T-cell CAR therapy is showing early promise for fungal disease. Thus, we are likely to see rapid advances to our approach to the management of fungal disease in the near future.

Development of a Heat-Killed fbp1 Mutant Strain as a Therapeutic Agent To Treat Invasive Cryptococcus Infection

In previous studies, we determined that the F-box protein Fbp1, a subunit of the SCF(Fbp1) E3 ligase in Cryptococcus neoformans, is essential for fungal pathogenesis. Heat-killed fbp1Δ cells (HK-fbp1) can confer vaccine-induced immunity against lethal challenge with clinically important invasive fungal pathogens, e.g., C. neoformans, C. gattii, and Aspergillus fumigatus. In this study, we found that either CD4+ T cells or CD8+ T cells were sufficient to confer protection against lethal challenge by C. neoformans in HK-fbp1-induced immunity. Given the potent effect of HK-fbp1 as a preventative vaccine, we further tested the potential efficacy of administering HK-fbp1 cells as a therapeutic agent for treating animals after infection. Remarkably, administration of HK-fbp1 provided robust host protection against preexisting C. neoformans infection. The mice infected with wild-type H99 cells and then treated with HK-fbp1 showed significant reduction of fungal burden in the infected lung and no dissemination of fungal cells to the brain and spleen. We find that early treatment is critical for the effective use of HK-fbp1 as a therapeutic agent. Immune analysis revealed that early treatment with HK-fbp1 cells elicited Th1-biased protective immune responses that help block fungal dissemination and promote better host protection. Our data thus suggest that HK-fbp1 is both an effective prophylactic vaccine candidate against C. neoformans infection in both immunocompetent and immunocompromised populations and a potential novel therapeutic strategy to treat early-stage cryptococcosis. IMPORTANCE Invasive fungal infections, e.g., cryptococcosis, are often life threatening and difficult to treat with very limited therapeutic options. There is no vaccine available in clinical use to prevent or treat fungal infections. Our previous studies demonstrated that heat-killed fbp1Δ cells (HK-fbp1) in Cryptococcus neoformans can be harnessed to confer protection against a challenge by the virulent parental strain, even in immunocompromised animals, such as ones lacking CD4+ T cells. In this study, we further determined that T cells are required for vaccine-induced protection against homologous challenge and that either CD4+ or CD8+ cells are sufficient. This finding is particularly important for the potential utility of this vaccine candidate in the context of HIV/AIDS-induced immune deficiency, the main risk factor for cryptococcosis in humans. Furthermore, in addition to the utility of HK-fbp1 as a prophylactic vaccine, we found that HK-fbp1 administration can inhibit disease dissemination when animals are treated at an early stage during Cryptococcus infection. Our findings could significantly expand the utility of HK-fbp1 not only as a prophylactic vaccine but also as a novel therapy against cryptococcosis. In all, our studies showed that the HK-fbp1 strain can be used both preventively and therapeutically to elicit robust host protection against cryptococcosis.

Candida parapsilosis Virulence and Antifungal Resistance Mechanisms: A Comprehensive Review of Key Determinants

Candida parapsilosis is the second most common Candida species isolated in Asia, Southern Europe, and Latin America and is often involved in invasive infections that seriously impact human health. This pathogen is part of the psilosis complex, which also includes Candida orthopsilosis and Candida metapsilosis. C. parapsilosis infections are particularly prevalent among neonates with low birth weights, individuals who are immunocompromised, and patients who require prolonged use of a central venous catheter or other indwelling devices, whose surfaces C. parapsilosis exhibits an enhanced capacity to adhere to and form biofilms. Despite this well-acknowledged prevalence, the biology of C. parapsilosis has not been as extensively explored as that of Candida albicans. In this paper, we describe the molecular mechanistic pathways of virulence in C. parapsilosis and show how they differ from those of C. albicans. We also describe the mode of action of antifungal drugs used for the treatment of Candida infections, namely, polyenes, echinocandins, and azoles, as well as the resistance mechanisms developed by C. parapsilosis to overcome them. Finally, we stress the importance of the ongoing search for species-specific features that may aid the development of effective control strategies and thus reduce the burden on patients and healthcare costs.

Meyerozyma guilliermondii species complex: review of current epidemiology, antifungal resistance, and mechanisms

Meyerozyma guilliermondii has been accepted as a complex composed of Meyerozyma guilliermondii, Meyerozyma carpophila, and Meyerozyma caribbica. M. guilliermondii is a saprophyte detected on human mucosa and skin. It can lead to serious infections in patients with risk factors like chemotherapy, immunodeficiency, gastrointestinal or cardiovascular surgery, and oncology disorders. Most deaths related to M. guilliermondii infections occur in individuals with malignancy. In recent decades, incidence of M. guilliermondii infections is increased. Sensitivity of this microorganism to conventional antifungals (e.g., amphotericin B, fluconazole, micafungin and anidulafungin) was reduced. Prophylactic and empirical uses of these drugs are linked to elevated minimal inhibitory concentrations (MICs) of M. guilliermondii. Drug resistance has concerned many researchers across the world. They are attempting to discover appropriate solution to combat this challenge. This study reviews the most important mechanisms of resistance to antifungals developed by in M. guilliermondii species complex.

3,5-Dinitrobenzoate and 3,5-Dinitrobenzamide Derivatives: Mechanistic, Antifungal, and In Silico Studies

Fungal infections, including those caused by Candida spp., are recognized in immunocompromised individuals for their high rates of morbidity and mortality. Microorganism resistance to conventional drugs compromises treatment effectiveness and yet also reveals the need to develop new drugs. In many compounds, nitro groups contribute to antimicrobial activity; thus, the inhibitory activity of a collection of twenty esters and amides (derived from 3,5-dinitrobenzoic acid) against Candida spp. was elucidated using microdilution methods to determine the Minimum Inhibitory Concentration (MIC) and Minimum Fungicide Concentration (MFC), as well as probable mechanisms of action. The structures of the synthesized compounds were characterized by FTIR spectroscopy, 1H-NMR, 13C NMR, and HRMS. Of the tested derivatives, ten presented fungicidal activity against at least one of the tested strains. Ethyl 3,5-dinitrobenzoate (2) exhibited the most potent antifungal activity against Candida albicans (MIC = 125 µg/mL; 0.52 mM), Candida krusei (MIC = 100 µg/mL; 4.16 mM), and Candida tropicalis (MIC = 500 µg/ml; 2.08 mM). The structure of the second most potent derivative (propyl 3,5-dinitrobenzoate (3) reveals that esters with short alkyl side chains exhibit better biological activity profiles. Compounds 2 and 3 presented a mechanism of action involving the fungal cell membrane. Though compound 2 modeling against C. albicans revealed a multitarget antifungal mechanism of action, involving various cellular processes, interference in the synthesis of ergosterol was observed. Our results demonstrate that certain ester derivatives containing aromatic ring nitro groups may be useful in the search for new antifungal drugs.

Baicalein Acts against Candida albicans by Targeting Eno1 and Inhibiting Glycolysis

Baicalein (BE) is a promising antifungal small-molecule compound with an extended antifungal spectrum, good synergy with fluconazole, and low toxicity, but its target protein and antifungal mechanism remain elusive. In this study, we found that BE can function against Candida albicans by disrupting glycolysis through targeting Eno1 and inhibiting its function. Eno1 acts as a key therapeutic target of the drug, as BE had no antifungal activity against the eno1 null mutant in a Galleria mellonella model of C. albicans infection. To investigate the mechanism of action, we solved the crystal structure of C. albicans Eno1(CaEno1) and then compared the difference between this structure and that of Eno1 from humans. The predicted primary binding site of BE on CaEno1 is between amino acids D261 and W274, with D263, S269, and K273 playing critical roles in the interaction with BE. Both positions S269 and K273 have different residues in the human Eno1 (hEno1). This finding suggests that BE may bind selectively to CaEno1, which would limit the potential for side effects in humans. Our findings demonstrate that Eno1 is a target protein of BE and thus may serve as a novel target for the development of antifungal therapeutics acting through the inhibition of glycolysis. IMPORTANCE Baicalein (BE) is a promising antifungal agent which has been well characterized, but its target protein is still undiscovered. The protein Eno1 plays a crucial role in the survival of Candida albicans. However, there are few antifungal agents which inhibit the functions of Eno1. Here, we found that BE can function against Candida albicans by disrupting glycolysis through targeting Eno1 and inhibiting its function. We further solved the crystal structure of C. albicans Eno1(CaEno1) and predicted that the primary binding site of BE on CaEno1 is between amino acids D261 and W274, with D263, S269, and K273 playing critical roles in the interaction with BE. Our findings will be helpful to get specific small-molecule inhibitors of CaEno1 and open the way for the development of new antifungal therapeutics targeted at inhibiting glycolysis.

Hassan M. Cytotoxicity and Promising Anti-Biofilm of Curcuma Silver Nanoparticles against Candida albicans

The fungal pathogens considered the major human opportunistic, 50–60% of candidiasis cases patients Candida albicans. Green synthesis of AgNPs from NaNO3 using Curcuma extract was performed. UV–Vis spectrophotometry and TEM characterization were measured. AgNPs absorption peak showed between 420-440 nm and results of TEM observed, the AgNPs has a uniform regular coccus shape and size of AgNPs was ranging from 50 to 12nm with average 37nm. The activity of AgNPs as antifungal agent against Candida albicans was determined using agar well diffusion method. AgNPs showed greater antifungal activity with inhibition zone diameter 28mm at 30μg/ml. The antibiofilm activity of AgNPs was assayed in 96-well polystyrene plates and 3 ml polyethylene tube. Obviously, remarkable progressive inhibition of biofilm formation was noticed with increasing of AgNPs concentrations. Determination of AgNPs cytotoxicity on normal lung fibroblast (WI-38) cells using MTT protocol was performed. The viability observed at concentration 31.25 was 44% with IC50 value 30.5μg ml−1. When Curcuma AgNPs are used to local infected wound, may inhibit Candida cells without bad side effect on host cells surrounding the infected wounds.

Augmenting Azoles with Drug Synergy to Expand the Antifungal Toolbox

Fungal infections impact the lives of at least 12 million people every year, killing over 1.5 million. Wide-spread use of fungicides and prophylactic antifungal therapy have driven resistance in many serious fungal pathogens, and there is an urgent need to expand the current antifungal arsenal. Recent research has focused on improving azoles, our most successful class of antifungals, by looking for synergistic interactions with secondary compounds. Synergists can co-operate with azoles by targeting steps in related pathways, or they may act on mechanisms related to resistance such as active efflux or on totally disparate pathways or processes. A variety of sources of potential synergists have been explored, including pre-existing antimicrobials, pharmaceuticals approved for other uses, bioactive natural compounds and phytochemicals, and novel synthetic compounds. Synergy can successfully widen the antifungal spectrum, decrease inhibitory dosages, reduce toxicity, and prevent the development of resistance. This review highlights the diversity of mechanisms that have been exploited for the purposes of azole synergy and demonstrates that synergy remains a promising approach for meeting the urgent need for novel antifungal strategies.

Benzylic Dehydroxylation of Echinocandin Antifungal Drugs Restores Efficacy against Resistance Conferred by Mutated Glucan Synthase

Each year, infections caused by fungal pathogens claim the lives of about 1.6 million people and affect the health of over a billion people worldwide. Among the most recently developed antifungal drugs are the echinocandins, which noncompetitively inhibit β-glucan synthase, a membrane-bound protein complex that catalyzes the formation of the main polysaccharide component of the fungal cell wall. Resistance to echinocandins is conferred by mutations in FKS genes, which encode the catalytic subunit of the β-glucan synthase complex. Here, we report that selective removal of the benzylic alcohol of the nonproteinogenic amino acid 3S,4S-dihydroxy-l-homotyrosine of the echinocandins anidulafungin and rezafungin, restored their efficacy against a large panel of echinocandin-resistant Candida strains. The dehydroxylated compounds did not significantly affect the viability of human-derived cell culture lines. An analysis of the efficacy of the dehydroxylated echinocandins against resistant Candida strains, which contain mutations in the FKS1 and/or FKS2 genes of the parental strains, identified amino acids of the Fks proteins that are likely to reside in proximity to the l-homotyrosine residue of the bound drug. This study describes the first example of a chemical modification strategy to restore the efficacy of echinocandin drugs, which have a critical place in the arsenal of antifungal drugs, against resistant fungal pathogens.

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.

Fluconazole-COX Inhibitor Hybrids: A Dual-Acting Class of Antifungal Azoles

When used in combination with azole antifungal drugs, cyclooxygenase (COX) inhibitors such as ibuprofen improve antifungal efficacy. We report the conjugation of a chiral antifungal azole pharmacophore to COX inhibitors and the evaluation of activity of 24 hybrids. Hybrids derived from ibuprofen and flurbiprofen were considerably more potent than fluconazole and comparable to voriconazole against a panel of Candida species. The potencies of hybrids composed of an S-configured azole pharmacophore were higher than those with an R-configured pharmacophore. Tolerance, defined as the ability of a subpopulation of cells to grow in the presence of the drug, to the hybrids was lower than to fluconazole and voriconazole. The hybrids were active against a mutant lacking CYP51, the target of azole drugs, indicating that these agents act via a dual mode of action. This study established that azole-COX inhibitor hybrids are a novel class of potent antifungals with clinical potential.

Impact of FKS1 Genotype on Echinocandin In Vitro Susceptibility in Candida auris and In Vivo Response in a Murine Model of Infection

Echinocandins are frontline antifungal agents in the management of invasive infections due to multidrug resistant Candida auris. The study aimed to evaluate echinocandin resistance in C. auris isolates of multicentric origin, identify the resistance mechanism, and analyze the pharmacodynamic response to caspofungin in a neutropenic mouse model of infection. A total of 199 C. auris isolates originating from 30 centers across India were tested for susceptibility to echinocandins. Isolates with reduced susceptibility were evaluated for FKS1 mutations and in vivo response to caspofungin in a murine model of disseminated candidiasis. In addition, the response to echinocandins was assessed in light of in vitro growth kinetics, chitin content; and transcript levels of chitin synthase and FKS1 genes. We report 10 resistant C. auris isolates with four FKS1 mutations: F635Y (n = 2), F635L (n = 4), S639F (n = 3), and R1354S (n = 1). Of these, F635Y and R1354S exhibited the most profound resistance in mouse model of disseminated infection. S639F and F635L mutations conferred a moderate in vivo resistance, whereas wild-type isolates exhibiting borderline MIC were susceptible in vivo. FKS1 genotype was more accurate predictor of in vivo response than the MIC of the isolates. Isolates with high basal or inducible chitin content exhibited higher in vitro MIC in FKS1 mutant compared to wild type. FKS1 mutations play a major role in clinically relevant echinocandin resistance in C. auris with differential in vivo outcomes. This study could have implications for clinical practice and, therefore, warrants further studies.

Micafungin injection for the treatment of invasive candidiasis in pediatric patients under 4 months of age

INTRODUCTION

Neonates and young infants with invasive candidiasis are particularly at increased risk of dissemination including hematogenous Candida meningoencephalitis. The echinocandins including micafungin have emerged as a preferred agent in most cases of candidemia and invasive candidiasis but data in pediatric patients under 4 months of age are limited.

AREAS COVERED

In this report, we review the micafungin use in infants younger than 4 months of age. Animal studies as well as clinical data that support its use in neonatal candidiasis are reviewed. In addition, the status of FDA approval and the rationale of micafungin dosing recommendations in infants <4 months are discussed.

EXPERT OPINION

A dose of 4 mg/kg was approved for treatment of candidemia, Candida peritonitis and abscesses excluding meningoencephalitis or ocular involvement in patients younger than 4 months of age. However, because of the risk of central nervous system dissemination as well as the difficulty in establishing this diagnosis, this dose is inadequate to treat ill infants with candidemia. More studies are needed to establish the safety and efficacy of micafungin daily dose of at least 10 mg/kg in infants younger than 4 months of age when hematogenous Candida meningoencephalitis or ocular involvement cannot be excluded.

Solid-State NMR Investigations of Extracellular Matrixes and Cell Walls of Algae, Bacteria, Fungi, and Plants

Extracellular matrixes (ECMs), such as the cell walls and biofilms, are important for supporting cell integrity and function and regulating intercellular communication. These biomaterials are also of significant interest to the production of biofuels and the development of antimicrobial treatment. Solid-state nuclear magnetic resonance (ssNMR) and magic-angle spinning-dynamic nuclear polarization (MAS-DNP) are uniquely powerful for understanding the conformational structure, dynamical characteristics, and supramolecular assemblies of carbohydrates and other biomolecules in ECMs. This review highlights the recent high-resolution investigations of intact ECMs and native cells in many organisms spanning across plants, bacteria, fungi, and algae. We spotlight the structural principles identified in ECMs, discuss the current technical limitation and underexplored biochemical topics, and point out the promising opportunities enabled by the recent advances of the rapidly evolving ssNMR technology.

Effects of lipopeptide biosurfactants on clinical strains of Malassezia furfur growth and biofilm formation

Lipopeptide biosurfactants (LBs) are biological molecules with low toxicity that have aroused growing interest in the pharmaceutical industry. Their chemical structure confers antimicrobial and antibiofilm properties against different species. Despite their potential, few studies have demonstrated their capability against Malassezia spp., commensal yeasts which can cause dermatitis and serious infections. Thus, the aim of this study was to evaluate the antifungal activity of biosurfactants produced by new strains of Bacillus subtilis TIM10 and B. vallismortis TIM68 against M. furfur and their potential for removal and inhibition of yeast biofilms. Biosurfactants were classified as lipopeptides by FTIR, and their composition was characterized by ESI-Q-TOF/MS, showing ions for iturin, fengycin, and surfactin, with a greater abundance of surfactin. Through the broth microdilution method, both biosurfactants inhibited the growth of clinical M. furfur strains. Biosurfactant TIM10 showed greater capacity for growth inhibition, with no statistical difference compared to those obtained by the commercial antifungal fluconazole for M. furfur 153DR5 and 154DR8 strains. At minimal inhibitory concentrations (MIC-2), TIM10 and TIM68 were able to inhibit biofilm formation, especially TIM10, with an inhibition rate of approximately 90%. In addition, both biosurfactants were able to remove pre-formed biofilm. Both biosurfactants showed no toxicity against murine fibroblasts, even at concentrations above MIC-2. Our results show the effectiveness of LBs in controlling the growth and biofilm formation of M. furfur clinical strains and highlight the potential of these agents to compose new formulations for the treatment of these fungi.

Antifungal activity of thiosemicarbazones, bis(thiosemicarbazones), and their metal complexes

Fungi are ubiquitous in nature, and typically cause little or no environmental or pathogenic damage to their plant, animal, and human hosts. However, a small but growing number of pathogenic fungi are spreading world-wide at an alarming rate threatening global ecosystem health and proliferation. Many of these emerging pathogens have developed multi-drug resistance to front line therapeutics increasing the urgency for the development of new antifungal agents. This review examines the development of thiosemicarbazones, bis(thiosemicarbazones), and their metal complexes as potential antifungal agents against more than 65 different fungal strains. The fungistatic activity of the compounds are quantified based on the zone of inhibition, minimum inhibitory concentration, or growth inhibition percentage. In this review, reported activities were standardized based on molar concentrations to simplify comparisons between different compounds. Of all the fungal strains reported in the review, A. niger in particular was very resistant towards a majority of tested compounds. Our analysis of the data shows that metal complexes are typically more active than non-coordinated ligands with copper(II) and zinc(II) complexes generally displaying the highest activity.

Two Sequential Clinical Isolates of Candida glabrata with Multidrug-Resistance to Posaconazole and Echinocandins

Candida glabrata is one of the most prevalent causative pathogens of invasive candidiasis, and multidrug-resistant strains are emerging. We identified two clinical isolates of C. glabrata, BMU10720 and BMU10722 sequentially isolated from one patient with multidrug-resistance to posaconazole (POS), caspofungin (CAS), micafungin (MCF), and anidulafungin (ANF). Overexpression of ERG11 in BMU10720 and CDR1 in BMU10722 were detected at basal level. When exposed to POS, CDR1 was significantly up-regulated in both isolates compared with susceptible reference strain, while ERG11 was up-regulated considerably only in BMU10720. PDR1 sequencing revealed that both isolates harbored P76S, P143T, and D243N substitutions, while ERG11 was intact. Cdr1 inhibitor FK520 reversed POS-resistance by down-regulating ERG11 expression. FKS sequencing revealed that both isolates harbored S663P substitution in FKS2, and four single nucleotide polymorphisms (SNPs) existed in FKS2 genes between BMU10720 and BMU10722, while FKS1 was intact. Both FKS1 and FKS2 were up-regulated by CAS in BMU10720 and BMU10722. FK520 down-regulated FKS2 expression induced by CAS through inhibiting calcineurin, resulting in synergic effect with echinocandins as well as Congo Red and Calcofluor White, two cell wall-perturbing agents. In conclusion, the multidrug-resistance of C. glabrata isolates in our study was conferred by different mechanisms. CDR1 and ERG11 overexpression in one isolate and only CDR1 overexpression in the other isolate may mediate POS-resistance. S663P mutation in FKS2 and up-regulation of FKS2 may contribute to echinocandin-resistance in both isolates.

Caspofungin-resistance in Candida auris is cell wall-dependent phenotype and potential prevention by zinc oxide nanoparticles

Candida auris is an emergent nosocomial multi-drug-resistant yeast that represents a global health threat. Recently, C. auris clinical isolates with caspofungin resistance were identified. Mutation in FKS1 gene was determined as a mechanism of resistance. However, the ability of C. auris to develop acquired and cross-resistance has never been investigated. Herein, this resistance ability due to caspofungin and associate mechanisms were investigated. C. auris clinical isolate was successively cultured for 10 generations in the presence of caspofungin compared to fluconazole-treatment and untreated controls. This was followed by the analysis of target gene expression and phenotypic changes. The obtained results showed that caspofungin-treated C. auris exhibited elevated MIC50(caspofungin), slower growth, elevated chitin content, overexpression of caspofungin target genes, and cross-resistance to fluconazole. Interestingly, caspofungin exposure induced cell-cell adhesion and biofilm formation. C. auris gradually lost caspofungin resistance after removal of antifungal pressure, while keeping the overexpression of fungal cell wall-related genes including ALS5. We propose that C. auris ageing in the presence of caspofungin caused the development of persistent phenotypic changes in the fungal cell wall, leading to acquired and physical cross-resistance mechanisms. Surprisingly, formulation of caspofungin in zinc oxide nanoparticles prevented the aforementioned behavioral changes regardless of the pathogen generations.

LAY SUMMARY

Candida auris developed resistance against caspofungin. Our data indicated that this resistance mechanism is unique because of changes in the genes related to cell wall adhesions. Formulation of caspofungin in ZnO nanoparticles was able to overcome these phenotypic changes.

In Vitro Selection of Thioether-Closed Macrocyclic Peptide Ligands by Means of the RaPID System

The Random nonstandard Peptides Integrated Discovery (RaPID) system enables efficient screening of macrocyclic peptides with high affinities against target molecules. Random peptide libraries are prepared by in vitro translation using the Flexible In vitro Translation (FIT) system, which allows for incorporation of diverse nonproteinogenic amino acids into peptides by genetic code reprogramming. By introducing an N-chloroacetyl amino acid at the N-terminus and a Cys at the downstream, macrocyclic peptide libraries can be readily generated via posttranslational thioether formation. Here, we describe how to prepare a thioether-closed macrocyclic peptide library, and its application to the RaPID screening.