Amphotericin forms an extramembranous and fungicidal sterol sponge

Engineered biosynthesis and characterization of disaccharide-pimaricin

BACKGROUND

Disaccharide polyene macrolides exhibit superior water solubility and significantly reduced hemolytic toxicity compared to their monosaccharide counterparts, making them promising candidates for safer antifungal therapeutics. In this study, we engineered a Streptomyces gilvosporeus (pSET152-nppY) capable of producing disaccharide-pimaricin (DSP) through heterologous expression of the nppY gene, which encodes a glycosyltransferase responsible for the second sugar extension in the biosynthetic pathway.

RESULTS

The novel compound was structurally characterized and designated disaccharide-pimaricin (DSP), featuring an aglycone identical to pimaricin and a unique disaccharide moiety (mycosaminyl-α1-4-N-acetylglucosamine). A purification protocol for DSP was established. Compared to pimaricin, DSP demonstrated a 50% reduction in antifungal activity, a 12.6-fold decrease in hemolytic toxicity, and a remarkable 107.6-fold increase in water solubility. Growth analysis revealed a delayed growth cycle in the mutant strain, suggesting that nppY expression may impose additional metabolic burden. Optimization of the fermentation medium using a statistical design identified an optimal formulation, with a maximum DSP titer of 138.168 mg/L.

CONCLUSIONS

This study underscores the potential of disaccharide polyene macrolides as safer antifungal agents and establishes a robust framework for engineering strains to produce these compounds. The findings provide critical insights into balancing biosynthetic efficiency and strain fitness, advancing the development of next-generation polyene antibiotics.

Identification of a critical gene involved in the biosynthesis of the polyene macrolide lavencidin in Streptomyces lavendulae FRI-5 using the Target-AID (activation-induced cytidine deaminase) base editing technology

Polyene macrolide antibiotics, produced mainly as secondary metabolites of streptomycetes, have distinct chemical structures and include clinically important antifungal drugs. We recently isolated the 28-membered polyene macrolide lavencidin from Streptomyces lavendulae FRI-5. Here, we identify and characterize the lavencidin biosynthetic (lad) gene cluster by combining a gene disruption system based on a base editing technology and in silico analysis. Sequence analysis of the draft genome of S. lavendulae FRI-5 revealed plausible lavencidin biosynthetic genes, which could be assigned roles in the biosynthesis of the polyketide backbone and the peripheral moiety, as well as in the regulation of lavencidin production. The introduction of a stop codon into the ladA5 polyketide synthase (PKS) gene by the base editing system resulted in a complete loss of lavencidin production, indicating that the type I modular PKS system is responsible for the biosynthesis of lavencidin.IMPORTANCEPolyene macrolide antibiotics display a unique mode of action among fungicides and exhibit potent fungicidal activity to which resistance does not readily develop. Deciphering the biosynthetic pathways of these fascinating compounds will provide chemical diversity for the development of industrially and clinically important agents. In this study, the Target-AID (activation-induced cytidine deaminase) system enabled us to identify the lad gene cluster involved in lavencidin biosynthesis, paving the way for the rational design of lavencidin derivatives with new or improved biological activity. Furthermore, this base editing system is capable of precisely and rapidly substituting the target nucleotide in several streptomycetes. Thus, our Target-AID system would be a powerful and versatile tool for the genetic engineering of streptomycetes as well as for analyzing the functions of uncharacterized genes, expanding the chemical diversity of useful bioactive compounds, and discovering novel natural products.

Fungal cell wall biogenesis: structural complexity, regulation and inhibition

The cell wall is the defining organelle of filamentous and yeast-like fungi. It is responsible for morphology, biotic and abiotic interactions and its components confer its unique and variable signature, making it a natural target for antifungal drugs, but a moving target for immune recognition. The wall is however more than the sum of its many parts. The polysaccharides and proteins of the cell wall must be made at the right time and the right place, but also linked together and remodelled throughout the cell cycle and in response to environmental challenges, nutrient availability, damage after predation and to be complaint to the need to establish mutualistic and parasitic associations. This review summarises recent advances in our understanding of the complex and vital process of fungal cell wall biogenesis using the human pathogens Candida albicans and Aspergillus fumigatus as the principal model fungi.

Medical Potential of Insect Symbionts

Insect symbionts and their metabolites are complex and diverse and are gradually becoming an important source of new medical materials. Some culturable symbionts from insects produce a variety of active compounds with medical potential. Among them, fatty acids, antibacterial peptides, polyene macrolides, alkaloids, and roseoflavin can inhibit the growth of human pathogenic bacteria and fungi; lipases, yeast killer toxins, reactive oxygen species, pyridines, polyethers, macrotetrolide nactins, and macrolides can kill human parasites; and peptides and polyketides can inhibit human tumors. However, due to difficulty in the culture of symbionts in vitro, difficulty in targeting bacteria to specific sites in the human body, the limited capability of symbionts to produce active metabolites in vitro, inconsistent clinical research results, adverse reactions on humans, and the development of antibiotic resistance, the application of insect symbionts and their metabolites in the medical field remains in its infancy. This paper summarizes the medical potential of insect symbionts and their metabolites and analyzes the status quo and existing problems with their medical application. Possible solutions to these problems are also proposed, with the aim of hastening the utilization of insect symbionts and their metabolites in the medical field.

Discovery of New Pyrazolone Carbothioamide Derivatives as Potent Antifungal Agents for the Treatment of Candidiasis and Cryptococcosis

The morbidity and mortality of invasive fungal infections are increasing rapidly. Developing effective and safe antifungal drugs with novel chemical scaffolds and mechanisms is urgently needed. On the basis of our previously identified Pdr1-KIX inhibitor 1, a series of new pyrazolone-carbothioamide derivatives were designed and assayed. In particular, compound A7 showed picomolar in vitro antifungal activity against Candida glabrata (MIC = 0.00012 μg/mL) and Cryptococcus neoformans (MIC = 0.00012 μg/mL), with excellent antivirulence effects. In the murine candidiasis and cryptococcosis models, compound A7 exhibited potent in vivo therapeutic efficacy. Interestingly, a mechanism investigation revealed that the antifungal activity of compound A7 is independent of KIX binding. It disrupted the iron homeostasis of fungal cells and then induced oxidative stress damages by accumulating the reactive oxygen species and lipid peroxides. Therefore, compound A7 represents a promising lead with a new mechanism of action to combat candidiasis and cryptococcosis.

Developing the trehalose biosynthesis pathway as an antifungal drug target

Invasive fungal infections are responsible for millions of deaths worldwide each year. Therefore, focusing on innovative approaches to developing therapeutics that target fungal pathogens is critical. Here, we discuss targeting the fungal trehalose biosynthesis pathway with antifungal therapeutics, which may lead to the improvement of human health globally, especially as fungal pathogens continue to emerge due to fluctuations in the climate.

A polyene macrolide targeting phospholipids in the fungal cell membrane

The global spread of multidrug-resistant pathogenic fungi presents a serious threat to human health, necessitating the discovery of antifungals with unique modes of action1. However, conventional activity-based screening for previously undescribed antibiotics has been hampered by the high-frequency rediscovery of known compounds and the lack of new antifungal targets2. Here we report the discovery of a polyene antifungal antibiotic, mandimycin, using a phylogeny-guided natural-product discovery platform. Mandimycin is biosynthesized by the mand gene cluster, has evolved in a distinct manner from known polyene macrolide antibiotics and is modified with three deoxy sugars. It has demonstrated potent and broad-spectrum fungicidal activity against a wide range of multidrug-resistant fungal pathogens in both in vitro and in vivo settings. In contrast to known polyene macrolide antibiotics that target ergosterol, mandimycin has a unique mode of action that involves targeting various phospholipids in fungal cell membranes, resulting in the release of essential ions from fungal cells. This unique ability to bind multiple targets gives it robust fungicidal activity as well as the capability to evade resistance. The identification of mandimycin using the phylogeny-guided natural-product discovery strategy represents an important advancement in uncovering antimicrobial compounds with distinct modes of action, which could be developed to combat multidrug-resistant fungal pathogens.

Beyond Conventional Antifungals: Combating Resistance Through Novel Therapeutic Pathways

The rising burden of fungal infections presents a significant challenge to global healthcare, particularly with increasing antifungal resistance limiting treatment efficacy. Early detection and timely intervention remain critical, yet fungal pathogens employ diverse mechanisms to evade host immunity and develop resistance, undermining existing therapeutic options. Limited antifungal options and rising resistance necessitate novel treatment strategies. This review provides a comprehensive overview of conventional antifungal agents, their mechanisms of action, and emerging resistance pathways. Furthermore, it highlights recently approved and investigational antifungal compounds while evaluating innovative approaches such as nanotechnology, drug repurposing, and immunotherapy. Addressing antifungal resistance requires a multifaceted strategy that integrates novel therapeutics, enhanced diagnostic tools, and future research efforts to develop sustainable and effective treatment solutions.

Coccidioidomycosis

Coccidioidomycosis is the clinical disease caused by the dimorphic pathogenic fungi Coccidioides immitis and C posadasii. The number of clinically recognized coccidioidomycosis cases continues to increase yearly including in regions outside the traditional regions of endemicity. Following inhalation of Coccidioides spores, the course may range from asymptomatic exposure with resultant immunity, to a subacute pulmonary illness, to life-threatening disseminated infection. This review will summarize recent advances in our understanding of the infection and will include the ecology of Coccidioides, epidemiology and risk factors for infection, vaccine and novel antifungals in development, and management of immunosuppressed patients.

Heterogeneity of Candida bloodstream isolates in an academic medical center and affiliated hospitals

Invasive Candida bloodstream infections (candidemia) are a deadly global health threat. Rare Candida species are increasingly important causes of candidemia and phenotypic data, including patterns of antifungal drug resistance, is limited. There is geographic variation in the distribution of Candida species and frequency of antifungal drug resistance, which means that collecting and reporting regional data can have significant clinical value. Here, we report the first survey of species distribution, frequency of antifungal drug resistance, and phenotypic variability of Candida bloodstream isolates from an academic medical center and 5 affiliated hospitals in the Minneapolis-Saint Paul region of Minnesota, collected during an 18-month period from 2019 to 2021. We collected 288 isolates spanning 11 species from 119 patients. C. albicans was the most frequently recovered species, followed by C. glabrata and C. parapsilosis, with 10% of cases representing additional, rare species. We performed antifungal drug susceptibility for the three major drug classes and, concerningly, we identified fluconazole, micafungin and multidrug resistance rates in C. glabrata that were ~ 2 times higher than that reported in other regions of the United States. We report some of the first phenotypic data in rare non-albicans Candida species. Through analysis of serial isolates from individual patients, we identified clinically relevant within-patient differences of MIC values in multiple drug classes. Our results provide valuable clinical data relevant to antifungal stewardship efforts and highlight important areas of future research, including within-patient dynamics of infection and the mechanisms of drug resistance in rare Candida species.

Prodrugging fungicidal amphotericin B significantly decreases its toxic effects

Amphotericin B (AmB) is one of the most effective antifungal drugs, with a strong, dose-dependent activity against most Candida and Aspergillus species responsible for life-threatening infections. However, AmB is severely toxic, which hinders its broad use. In this proof-of-concept study, we demonstrate that prodrugging AmB considerably decreases AmB toxicity without affecting its fungicidal activity. For this purpose, we modified the AmB structure by attaching a designer phosphate promoiety, thereby switching off its mode of action and preventing its toxic effects. The original fungicidal activity of AmB was then restored upon prodrug activation by host plasma enzymes. These AmB prodrugs showed a safer toxicity profile than commercial AmB deoxycholate in Candida and Aspergillus species and significantly prolonged larval survival of infected Galleria mellonella larvae. Based on these findings, prodrugging toxic antifungals may be a viable strategy for broadening the antifungal arsenal, opening up opportunities for targeted prodrug design.

The multidrug-resistant Candida auris, Candida haemulonii complex and phylogenetic related species: Insights into antifungal resistance mechanisms

The rise of multidrug-resistant (MDR) fungal pathogens poses a serious global threat to human health. Of particular concern are Candida auris, the Candida haemulonii complex (which includes C. haemulonii sensu stricto, C. duobushaemulonii and C. haemulonii var. vulnera), and phylogenetically related species, including C. pseudohaemulonii and C. vulturna. These emerging, widespread, and opportunistic pathogens have drawn significant attention due to their reduced susceptibility to commonly used antifungal agents, particularly azoles and polyenes, and, in some cases, therapy-induced resistance to echinocandins. Notably, C. auris is classified in the critical priority group on the World Health Organization's fungal priority pathogens list, which highlights fungal species capable of causing systemic infections with significant mortality and morbidity risks as well as the challenges posed by their MDR profiles, limited treatment and management options. The mechanisms underlying antifungal resistance within these emerging fungal species is still being explored, but some advances have been achieved in the past few years. In this review, we compile current literature on the distribution of susceptible and resistant clinical strains of C. auris, C. haemulonii complex, C. pseudohaemulonii and C. vulturna across various antifungal classes, including azoles (fluconazole, voriconazole, itraconazole), polyenes (amphotericin B), echinocandins (caspofungin, micafungin, anidulafungin), and pyrimidine analogues (flucytosine). We also outline the main antifungal resistance mechanisms identified in planktonic cells of these yeast species. Finally, we explore the impact of biofilm formation, a classical virulence attribute of fungi, on antifungal resistance, highlighting the resistance mechanisms associated with this complex microbial structure that have been uncovered to date.

Amphotericin B Encapsulation in Polymeric Nanoparticles: Toxicity Insights via Cells and Zebrafish Embryo Testing

Background: Amphotericin B (AmB) is a commonly utilized antifungal agent, which is also recommended for the treatment of certain neglected tropical diseases, including leishmaniasis. However, its clinical application is constrained because of its poor oral bioavailability and adverse effects, prompting the investigation of alternative drug delivery systems. Polymeric nanoparticles (PNPs) have gained attention as a potential drug delivery vehicle, providing advantages such as sustained release and enhanced bioavailability, and could have potential as AmB carriers. However, concerns persist regarding nanomaterials' toxicity, requiring more studies. Zebrafish (Danio rerio) embryos were used as a valuable model for toxicity testing, especially because of their genetic similarity to humans and standardized developmental assessments. Methods: In this study, we produced and characterized AmB loaded and non-loaded PNPs by nanoprecipitation, dynamic light scattering, transmission electron microscopy, atomic force microscopy and spectroscopy. Afterwards, we verified their toxicity through in vitro MTT assays in three cell lines (HEK293, HepG2, and J774 A1) and in vivo tests with zebrafish embryos. Results: In both trials, it was noted that nanoencapsulation of the drug led to increased toxicity when compared to non-encapsulated AmB, possibly indicating that they penetrated the embryo's chorion. Nevertheless, it was demonstrated that the polymers used are safe and they are not the cause of toxicity, neither are the nanostructures per se. Conclusions: Therefore, it is believed that the objective of improving the bioavailability of AmB may have been achieved, and the observed toxicity was probably linked to AmB's ability to destabilize cell membranes.

Butyrolactol A is a phospholipid flippase inhibitor that potentiates the bioactivity of caspofungin against resistant fungi

Fungal infections cause millions of deaths annually and are challenging to treat due to limited antifungal options and increasing drug resistance. Cryptococci are intrinsically resistant to the latest generation of antifungals, echinocandins, while Candida auris , a notorious global threat, is also increasingly resistant. We performed a natural product extract screen for rescue of the activity of the echinocandin caspofungin against Cryptococcus neoformans H99, identifying butyrolactol A, which restores echinocandin efficacy against resistant fungal pathogens, including C. auris . Mode of action studies revealed that butyrolactol A inhibits the phospholipid flippase Apt1-Cdc50, blocking phospholipid transport. Cryoelectron-microscopy analysis of the Apt1●butyrolactol A complex revealed that the flippase is locked in a dead-end state. Apt1 inhibition disrupts membrane asymmetry, vesicular trafficking, and cytoskeletal organization, thereby enhancing echinocandin uptake and potency. This study identifies flippases as promising antifungal targets and demonstrates the potential of revisiting natural products to expand the antifungal arsenal and combat resistance.

Progress in antileishmanial drugs: Mechanisms, challenges, and prospects

Leishmaniasis, a neglected tropical disease caused by Leishmania parasites, continues to pose global health challenges. Current treatments face issues like resistance, safety, efficacy, and cost. This review covers the discovery, mechanisms of action, clinical applications, and limitations of key antileishmanial agents: pentavalent antimonials, amphotericin B, miltefosine, paromomycin, and pentamidine. Despite toxicity and resistance (antimonials), hospitalization needs and side effects (amphotericin B), regional efficacy variability (miltefosine), inconsistent outcomes (paromomycin), and severe side effects (pentamidine), these drugs are vital. Novel strategies to overcome the deficiencies of current therapies are highlighted, including combination regimens, advanced drug delivery systems, and immunomodulatory approaches. Comprehensive and cooperative efforts are crucial to fully realize the potential of advancements in antileishmanial pharmacotherapy and to reduce the unacceptable worldwide burden imposed by this neglected disease.

Profiling the LAM Family of Contact Site Tethers Provides Insights into Their Regulation and Function

Membrane contact sites are molecular bridges between organelles that are sustained by tethering proteins and enable organelle communication. The endoplasmic reticulum (ER) membrane harbors many distinct families of tether proteins that enable the formation of contacts with all other organelles. One such example is the LAM (Lipid transfer protein Anchored at Membrane contact sites) family in yeast, which is composed of six members, each containing a putative lipid binding and transfer domain and an ER-embedded transmembrane segment. The family is divided into three homologous pairs each unique in their molecular architecture and localization to different ER subdomains. However, what determines the distinct localization of the different LAMs and which specific roles they carry out in each contact are still open questions. To address these, we utilized a labeling approach to profile the proximal protein landscape of the entire family. Focusing on unique, candidate interactors we could support that Lam5 resides at the ER-mitochondria contact site and demonstrate a role for it in sustaining mitochondrial activity. Capturing shared, putative interactors of multiple LAMs, we show how the Lam1/3 and Lam2/4 paralogous pairs could be associated specifically with the plasma membrane. Overall, our work provides new insights into the regulation and function of the LAM family members. More globally it demonstrates how proximity labeling can help identify the shared or unique functions of paralogous proteins.

Understanding the synergistic interaction between a 1,3,4-thiadiazole derivative and amphotericin B using spectroscopic and theoretical studies

We present a comprehensive spectroscopic study supported by theoretical quantum chemical calculations conducted on a molecular system (4-(5-methyl-1,3,4-thiadiazol-2-yl)benzene-1,3-diol (C1) and the antibiotic Amphotericin B (AmB)) that exhibits highly synergistic properties. We previously reported the strong synergism of this molecular system and now wish to present related stationary measurements of UV-Vis absorption, fluorescence, and fluorescence anisotropy in a polar, aprotic solvent (DMSO and a PBS buffer), followed by time-resolved fluorescence intensity and anisotropy decay studies using different ratios of the selected 1,3,4-thiadiazole derivative to Amphotericin B. Absorption spectra measured for the system revealed discrepancies in terms of the shapes of absorption bands, particularly in PBS. Fluorescence emission spectra revealed that the addition of C1 molecules triggered significant changes in the emission spectra of the system. Measurements of the fluorescence lifetimes and fluorescence anisotropy supported by synchronous spectra clearly showed evidence of disaggregation. The AmB molecular aggregates indicated interaction of C1 with the antibiotic at points responsible for the formation of dimer structures. The spectroscopic results were further corroborated, analyzed, and interpreted using the methods of quantum mechanical modelling. Analyses based on the density functional tight-binding and time-dependent density functional theory confirmed that molecular interactions between "small" molecules and AmB lead to a significant increase in the clinical efficacy of the antibiotic.

Dereplication of Natural Product Antifungals via Liquid Chromatography-Tandem Mass Spectrometry and Chemical Genomics

Recently expanded reports of multidrug-resistant fungal infections underscore the need to develop new and more efficient methods for antifungal drug discovery. A ubiquitous problem in natural product drug discovery campaigns is the rediscovery of known compounds or their relatives; accordingly, we have integrated Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) for structural dereplication and Yeast Chemical Genomics for bioprocess evaluation into a screening platform to identify such compounds early in the screening process. We identified 450 fractions inhibiting Candida albicans and the resistant strains of C. auris and C. glabrata among more than 40,000 natural product fractions. LC-MS/MS and chemical genomics were then used to identify those with known chemistry and mechanisms of action. The parallel deployment of these orthogonal methods improved the detection of unwanted compound classes over the methods applied individually.

Similarities and distinctions in the activation of the Candida glabrata Pdr1 regulatory pathway by azole and non-azole drugs

Incidences of fluconazole (FLC) resistance among Candida glabrata clinical isolates are a growing issue in clinics. The pleiotropic drug response network in C. glabrata confers azole resistance and is defined primarily by the Zn2Cys6 zinc cluster-containing transcription factor Pdr1 and target genes such as CDR1, which encodes an ATP-binding cassette transporter protein thought to act as an FLC efflux pump. Mutations in the PDR1 gene that render the transcription factor hyperactive are the most common cause of fluconazole resistance among clinical isolates. The phenothiazine class drug fluphenazine and a molecular derivative, CWHM-974, which both exhibit antifungal properties, have been shown to induce the expression of Cdr1 in Candida spp. We have used a firefly luciferase reporter gene driven by the CDR1 promoter to demonstrate two distinct patterns of CDR1 promoter activation kinetics: gradual promoter activation kinetics that occur in response to ergosterol limitations imposed by exposure to azole and polyene class antifungals and a robust and rapid CDR1 induction occurring in response to the stress imposed by fluphenazines. We can attribute these different patterns of CDR1 induction as proceeding through the promoter region of this gene since this is the only segment of the gene included in the luciferase reporter construct. Genetic analysis indicates that the signaling pathways responsible for phenothiazine and azole induction of CDR1 overlap but are not identical. The short time course of phenothiazine induction suggests that these compounds may act more directly on the Pdr1 protein to stimulate its activity.

IMPORTANCE

Candida glabrata has emerged as the second-leading cause of candidiasis due, in part, to its ability to acquire high-level resistance to azole drugs, a major class of antifungal that acts to block the biosynthesis of the fungal sterol ergosterol. The presence of azole drugs causes the induction of a variety of genes involved in controlling susceptibility to this drug class, including drug transporters and ergosterol biosynthetic genes such as ERG11. We found that the presence of azole drugs leads to an induction of genes encoding drug transporters and ERG11, while exposure of C. glabrata cells to antifungals of the phenothiazine class of drugs caused a much faster and larger induction of drug transporters but not ERG11. Coupled with further genetic analyses of the effects of azole and phenothiazine drugs, our data indicate that these compounds are sensed and responded to differentially in the yeast cell.

Baicalin promotes β-1,3-glucan exposure in Candida albicans and enhances macrophage response

Among the diverse fungal opportunistic pathogens, Candida albicans garners significant attention due to its wide range of infections and high frequency of occurrence. The emergence of resistance and the limited number of antifungals drives the need to develop novel antifungal drugs. Although the natural product baicalin has been shown to trigger apoptosis in C. albicans in previous experiments, its influence on cell wall (CW) structure along with immune recognition remains elusive. In this work, baicalin showed a significant killing effect against C. albicans SC5314. Moreover, CW destruction, characterized by β-1,3-glucan unmasking and chitin deposition, was observed as a consequence of the treatment with baicalin. The RNA sequencing analysis revealed that treatment with baicalin resulted in eight hundred forty-two differentially expressed genes (DEGs). Sixty-five genes, such as GSC1, ENG1, CHS3, GWT1, and MKC1, were associated with CW organization or biogenesis. Baicalin-pretreated C. albicans SC5314 was phagocytosed more efficiently by RAW264.7 macrophages, accompanied by increased TNF-α and IL-1β production. Accordingly, it is hypothesized that baicalin could stimulate β-1,3-glucan unmasking by governing CW-associated gene expression in C. albicans SC5314, which contributes to macrophage recognition and clearance.

Mono-N-alkylation of Amphotericin B and Nystatin A1 and Its Amides: Effect on the In Vitro Activity, Cytotoxicity and Permeabilization of Model Membranes

Objectives: In 2022, the World Health Organization highlighted the necessity for the development of new antifungal agents. Polyene antibiotics are characterized by a low risk of drug resistance; however, their use is limited by low solubility and severe side effects. Methods: A series of N-alkylated derivatives of amphotericin B and nystatin A1 as well as their N-(2-hydroxyethyl)amides were synthesized. Their antifungal activity was evaluated against various Candida strains and Aspergillus fumigatus using the broth microdilution method. Cytotoxicity was assessed using an MTT assay on human embryonic kidney cells HEK293 and human skin fibroblast cells hFB-hTERT6, as well as a hemolysis assay on erythrocytes. Membrane activity was analyzed by fluorimetric measurement of calcein leakage from model liposomes. Results: Derivatives containing the N-(hydroxyethyl)amino)ethyl fragment (compounds 3 and 4) exhibited relatively high antifungal activity, as did N-(2-hydroxyethyl)amides 5 and 9. Bis-modified compounds 6 and 10 did not outperform their mono-modified analogues in terms of activity or cytotoxicity. The mono-N-alkylated compound 3 showed the highest activity/toxicity ratio, which correlated well with its selectivity for ergosterol-containing model membranes. Discussion: Combining two successful modifications does not necessarily improve the activity/toxicity ratio of polyenes. Further studies can be performed for the optimization of carboxyl group of 3.

Genetic microevolution of clinical Candida auris with reduced Amphotericin B sensitivity in China

The global rate of Amphotericin B (AmB) resistance in Candida auris has surpassed 12%. However, there is limited data on available clinical treatments and microevolutionary analyses concerning reduced AmB sensitivity. In this study, we collected 18 C. auris isolates from five patients between 2019 and 2022. We employed clinical data mining, genomic, and transcriptomic analyses to identify genetic evolutionary features linked to reduced AmB sensitivity in these isolates during clinical treatment. We identified six isolates with a minimum inhibitory concentration (MIC) of AmB below 0.5 µg/mL (AmB0.5) and 12 isolates with an AmB-MIC of 1 µg/mL (AmB1) or ≥ 2 µg/mL (AmB2). All five patients received 24-hour AmB (5 mg/L) bladder irrigation treatment. Evolutionary analyses revealed an ERG3 (c923t) mutation in AmB1 C. auris. Additionally, AmB2 C. auris was found to contain a t2831c mutation in the RAD2 gene. In the AmB1 group, membrane lipid-related gene expression (ERG1, ERG2, ERG13, and ERG24) was upregulated, while in the AmB2 group, expression of DNA-related genes (e.g. DNA2 and PRI1) was up-regulated. In a series of C.auris strains with reduced susceptibility to AmB, five key genes were identified: two upregulated (IFF9 and PGA6) and three downregulated (HGT7, HGT13,and PRI32). In this study, we demonstrate the microevolution of reduced AmB sensitivity in vivo and further elucidate the relationship between reduced AmB sensitivity and low-concentration AmB bladder irrigation. These findings offer new insights into potential antifungal drug targets and clinical markers for the "super fungus", C. auris.

Effects of Different Concentrations of AmB on the Unsaturated Phospholipid-Cholesterol Membrane Using the Langmuir Monolayer and Liposome Models

Amphotericin B (AmB) causes toxicity to the erythrocyte membrane, leading to hemolysis, which limits the clinically effective dose for AmB intravenous therapy in invasive fungal infections. The molecular mechanism by which AmB adheres to the membrane of erythrocytes is the key factor in causing AmB to be toxic to the membrane of erythrocytes, but it is not yet fully understood; the mechanism by which AmB adheres to the liquid microdomains with higher fluidity formed by cholesterol and unsaturated phospholipids remains especially unclear. This study examined the adsorption of AmB at different concentrations, 5, 45, 85, and 125 μg/mL, on unsaturated phospholipid membranes containing 50 mol% cholesterol. The thermodynamic properties and structure of DOPC monolayers and DOPC/cholesterol mixed monolayers at different concentrations of AmB have been investigated using the Langmuir monolayer model and the BAM method. The impact of varying concentrations of AmB on the hydrophilic and hydrophobic domains of the DOPC bilayers and the DOPC/cholesterol mixed bilayers have also been discussed using large unilamellar vesicle liposomes and fluorescence techniques. It is shown that for AmB concentrations greater than 5 μg/mL, with an increase in AmB's concentration, the reorganization time for the DOPC/cholesterol monolayer increases, and the elastic modulus of the DOPC/cholesterol mixed monolayer decreases. In particular, when AmB's concentration is higher than 85 μg/mL, the liquid-condensed phase domains on the DOPC/cholesterol monolayer reduce significantly and the liquid-expanded phase domain enlarges from the BAM images. When the AmB concentration reaches 5 μg/mL, the disorder of the hydrophobic and hydrophilic domains of the DOPC/cholesterol bilayer increases as the AmB concentration increases. The way in which AmB interacts with the DOPC/cholesterol mixed membrane is related to the concentration of AmB. The higher the concentration of AmB, the more likely it is to remove cholesterol from the unsaturated phospholipid membrane. The results are helpful to understand the mechanism of AmB's toxicity to the erythrocyte's membrane, which has a guiding value for seeking ways to reduce the AmB's toxicity.

Gladiolin produced by pathogenic Burkholderia synergizes with amphotericin B through membrane lipid rearrangements

Amphotericin B (AmpB) is an effective but toxic antifungal drug. Thus, improving its activity/toxicity relationship is of interest. AmpB disrupts fungal membranes by two proposed mechanisms: ergosterol sequestration from the membrane and pore formation. Whether these two mechanisms operate in conjunction and how they could be potentiated remains to be fully understood. Here, we report that gladiolin, a polyketide antibiotic produced by Burkholderia gladioli, is a strong potentiator of AmpB and acts synergistically against Cryptococcus and Candida species, including drug-resistant C. auris. Gladiolin also synergizes with AmpB against drug-resistant fungal biofilms, while exerting no mammalian cytotoxicity. To explain the mechanism of synergy, we show that gladiolin interacts with membranes via a previously unreported binding mode for polyketides. Moreover, gladiolin modulates lipid binding by AmpB and, in combination, causes faster and more pronounced lipid rearrangements relative to AmpB alone which include membrane thinning consistent with ergosterol extraction, areas of thickening, pore formation, and increased membrane destruction. These biophysical data provide evidence of a functional interaction between gladiolin and AmpB at the membrane interface. The data further indicate that the two proposed AmpB mechanisms (ergosterol sequestration and pore formation) act in conjunction to disrupt membranes, and that gladiolin synergizes by enhancing both mechanisms. Collectively, our findings shed light on AmpB's mechanism of action and characterize gladiolin as an AmpB potentiator, showing an antifungal mechanism distinct from its proposed antibiotic activity. We shed light on the synergistic mechanism at the membrane, and provide insights into potentiation strategies to improve AmpB's activity/toxicity relationship.

IMPORTANCE

Amphotericin B (AmpB) is one of the oldest antifungal drugs in clinical use. It is an effective therapeutic, but it comes with toxicity issues due to the similarities between its fungal target (the membrane lipid ergosterol) and its mammalian counterpart (cholesterol). One strategy to improve its activity/toxicity relationship is by combinatorial therapy with potentiators, which would enable a lower therapeutic dose of AmpB. Here, we report on the discovery of the antibiotic gladiolin as a potentiator of AmpB against several priority human fungal pathogens and fungal biofilms, with no increased toxicity against mammalian cells. We show that gladiolin potentiates AmpB by increasing and accelerating membrane damage. Our findings also provide insights into the on-going debate about the mechanism of action of AmpB by indicating that both proposed mechanisms, extraction of ergosterol from membranes and pore formation, are potentiated by gladiolin.

Moxidectin elevates Candida albicans ergosterol levels to synergize with polyenes against oral candidiasis

Candida albicans, the most common opportunistic pathogenic fungus, is also the main pathogenic organism for oral candidiasis. This condition is particularly prevalent among the elderly, children, and individuals undergoing radiotherapy or suffering from HIV. The lack of new antifungal drugs, and drug resistance coupled with the side effects of current antifungal agents have increased the challenges of clinical antifungal therapies. Polyenes, including amphotericin B and nystatin, are clinical fungicidal drugs, however, their side effects and low solubility have limited their clinical applications. Here, we identified that moxidectin, a novel approved antiparasitic agent, could synergize with both amphotericin B and nystatin to inhibit the growth and biofilm formation of Candida albicans including 60 clinical isolates. The transcriptome and RT-PCR analysis indicated that moxidectin activated the biosynthesis pathway of ergosterol, the direct target of polyenes, further being verified by the loss of the synergistic activities with polyenes against ergosterol pathway mutants, including Δ/Δerg3, Δ/Δerg11 and Δ/Δerg3 Δ/Δerg11. Moxidectin was then confirmed to elevate the ergosterol biosynthesis levels of C. albicans and enhance the binding between cells and polyenes. In a mouse oral candidiasis model, moxidectin combined with low dosages of polyenes to significantly reduce the infection area, colonization of C. albicans and the inflammatory degree of tongue mucosa. Our study originally demonstrated that moxidectin could activate the ergosterol biosynthesis then elevate the ergosterol contents to enhance the antifungal effects of polyenes against C. albicans and its infections. Moxidectin can serve as the candidate potentiator of polyenes for further clinical practice. KEY POINTS: • Moxidectin synergized with polyenes against Candida albicans. • Moxidectin activated the ergosterol biosynthesis of Candida albicans. • Moxidectin combined with polyenes to effectively combat oral candidiasis in mice.

Improved Broad Spectrum Antifungal Drug Synergies with Cryptomycin, a Cdc50-Inspired Antifungal Peptide

Fungal infections in humans are difficult to treat, with very limited drug options. Due to a confluence of factors, there is an urgent need for innovation in the antifungal drug space, particularly to combat increasing antifungal drug resistance. Our previous studies showed that Cdc50, a subunit of fungal lipid translocase (flippase), is essential for Cryptococcus neoformans virulence and required for antifungal drug resistance, suggesting that fungal lipid flippase could be a novel drug target. Here, we characterized an antifungal peptide, Cryptomycinamide (KKOO-NH2), derived from a 9-amino acid segment of the C. neoformans Cdc50 protein. A fungal killing assay indicated that KKOO-NH2 is fungicidal against C. neoformans. The peptide has antifungal activity against multiple major fungal pathogens with a minimum inhibitory concentration (MIC) of 8 μg/mL against C. neoformans and Candida glabrata, 16 μg/mL against Candida albicans and C. auris, and 32 μg/mL against Aspergillus fumigatus. The peptide has low cytotoxicity against host cells based on our hemolysis assays and vesicle leakage assays. Strikingly, the peptide exhibits strong drug synergy with multiple antifungal drugs, including amphotericin B, itraconazole, and caspofungin, depending on the specific species on which the combinations were assayed. The fluorescently labeled peptide was detected to localize to the plasma membrane, likely inhibiting key interactions of Cdc50 with membrane proteins such as P4 ATPases. Cryptococcus cells exposed to sub-MIC of peptide showed increased reactive oxygen species production and intracellular calcium levels, indicating a peptide-induced stress response. Decreased intracellular proliferation within macrophages was observed after 30 min of peptide exposure and 24 h coincubation with macrophages, providing a potential translational mechanism to explore further in vivo. In aggregate, the synergistic activity of our KKOO-NH2 peptide may offer a potential novel candidate for combination therapy with existing antifungal drugs.

BSC2 modulates AmB resistance via the maintenance of intracellular sodium/potassium ion homeostasis in Saccharomyces cerevisiae

Previous studies on BSC2 have shown that it enhances yeast cell resistance to AmB via antioxidation and induces multidrug resistance by contributing to biofilm formation. Herein, we found that BSC2 overexpression could reverse the sensitivity of pmp3Δ to AmB and help the tested strains restore the intracellular sodium/potassium balance under exposure to AmB. Meanwhile, overexpression of the chitin gene CHS2 could simulate BSC2 to reverse the sensitivity of pmp3Δ and nha1Δ to high salt or AmB. However, BSC2 overexpression in flo11Δ failed to induce AmB resistance, form biofilms, and affect cell wall biogenesis, while CHS2 overexpression compensated the resistance of flo11Δ to AmB. Additionally, BSC2 levels were positively correlated with maintaining cell membrane integrity under exposure to AmB, CAS, or a combination of both. BSC2 overexpression in nha1Δ exhibited a similar function of CHS2, which can compensate for the sensitivity of the mutant to high salt. Altogether, the results demonstrate for the first time that BSC2 may promote ion equilibrium by strengthening cell walls and inhibiting membrane damage in a FLO path-dependent manner, thus enhancing the resistance of yeast cells to AmB. This study also reveals the possible mechanism of antifungal drugs CAS and AmB combined to inhibit fungi.

Drug tolerance and persistence in bacteria, fungi and cancer cells: Role of non-genetic heterogeneity

A common feature of bacterial, fungal and cancer cell populations upon treatment is the presence of tolerant and persistent cells able to survive, and sometimes grow, even in the presence of usually inhibitory or lethal drug concentrations, driven by non-genetic differences among individual cells in a population. Here we review and compare data obtained on drug survival in bacteria, fungi and cancer cells to unravel common characteristics and cellular pathways, and to point their singularities. This comparative work also allows to cross-fertilize ideas across fields. We particularly focus on the role of gene expression variability in the emergence of cell-cell non-genetic heterogeneity because it represents a possible common basic molecular process at the origin of most persistence phenomena and could be monitored and tuned to help improve therapeutic interventions.

Zeolitic Imidazolate Framework-8 Offers an Anti-Inflammatory and Antifungal Method in the Treatment of Aspergillus Fungal Keratitis in vitro and in vivo

Background

Fungal keratitis is a serious blinding eye disease. Traditional drugs used to treat fungal keratitis commonly have the disadvantages of low bioavailability, poor dispersion, and limited permeability.

Purpose

To develop a new method for the treatment of fungal keratitis with improved bioavailability, dispersion, and permeability.

Methods

Zeolitic Imidazolate Framework-8 (ZIF-8) was formed by zinc ions and 2-methylimidazole linked by coordination bonds and characterized by Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Zeta potential. The safety of ZIF-8 on HCECs and RAW 264.7 cells was detected by Cell Counting Kit-8 (CCK-8). Safety evaluation of ZIF-8 on mice corneal epithelium was conducted using the Draize corneal toxicity test. The effects of ZIF-8 on fungal growth, biofilm formation, and hyphae structure were detected by Minimal inhibit concentration (MIC), crystal violet staining, Propidium Iodide (PI) testing, and calcofluor white staining. The anti-inflammatory effects of ZIF-8 on RAW 246.7 cells were evaluated by Quantitative Real-Time PCR Experiments (qPCR) and Enzyme-linked immunosorbent assay (ELISA). Clinical score, Colony-Forming Units (CFU), Hematoxylin-eosin (HE) staining, and immunofluorescence were conducted to verify the therapeutic effect of ZIF-8 on C57BL/6 female mice with fungal keratitis.

Results

In vitro, ZIF-8 showed outstanding antifungal effects, including inhibiting the growth of Aspergillus fumigatus over 90% at 64 μg/mL, restraining the formation of biofilm, and destroying cell membranes. In vivo, treatment with ZIF-8 reduced corneal fungal load and mitigated neutrophil infiltration in fungal keratitis, which effectively reduced the severity of keratitis in mice and alleviated the infiltration of inflammatory factors in the mouse cornea. In addition, ZIF-8 reduces the inflammatory response by downregulating the expression of pro-inflammatory cytokines TNF-α, IL-6, and IL-1β after Aspergillus fumigatus infection in vivo and in vitro.

Conclusion

ZIF-8 has a significant anti-inflammatory and antifungal effect, which provides a new solution for the treatment of fungal keratitis.

The Influence of Aspergillus fumigatus Fatty Acid Oxygenases PpoA and PpoC on Caspofungin Susceptibility

Aspergillus fumigatus can cause invasive pulmonary aspergillosis (IPA). Fungicidal azoles and fungistatic caspofungin (CAS) are the first- and second-line therapies, respectively, used to treat IPA. Treatment of A. fumigatus with CAS or micafungin induces the production of the oxylipin 5,8-diHODE by the fungal oxygenase PpoA. For this article, we investigated the influence of ppo genes, which encode the fatty acid oxygenases responsible for oxylipin biosynthesis, on CAS tolerance. The influence of PpoA and PpoC on CAS tolerance is mediated by MpkA phosphorylation and protein kinase A (PKA) activity. RNAseq transcriptional profiling and the label-free quantitative proteomics of the ppoA and ppoC mutants showed that differentially expressed genes and proteins are related to secondary metabolites and carbohydrate metabolism. We also characterized two clinical isolates, CM7555 and IFM61407, which decrease and increase susceptibility to CAS, respectively. CM7555 does not exhibit increased oxylipin production in the presence of CAS but oxylipin induction upon CAS exposure is increased in IFM61407, suggesting that oxylipins are not the only mechanism involved in CAS tolerance in these isolates. Upon CAS exposure, CM7555 has higher MpkA phosphorylation and PKA activity than IFM61407. Our results reveal the different aspects and genetic determinants involved in A. fumigatus CAS tolerance.

Alligamycin A, an antifungal β-lactone spiroketal macrolide from Streptomyces iranensis

Fungal infections pose a great threat to public health and there are only four main types of antifungal drugs, which are often limited with toxicity, drug-drug interactions and antibiotic resistance. Streptomyces is an important source of antibiotics, represented by the clinical drug amphotericin B. Here we report the discovery of alligamycin A (1) as an antifungal compound from the rapamycin-producer Streptomyces iranensis through genome-mining, genetics and natural product chemistry approaches. Alligamycin A harbors a unique chemical scaffold with 13 chiral centers, featuring a β-lactone moiety, a [6,6]-spiroketal ring, and an unreported 7-oxo-octylmalonyl-CoA extender unit incorporated by a potential crotonyl-CoA carboxylase/reductase. It is biosynthesized by a type I polyketide synthase which is confirmed through CRISPR-based gene editing. Alligamycin A displayed potent antifungal effects against numerous clinically relevant filamentous fungi, including resistant Aspergillus and Talaromyces species. β-Lactone ring is essential for the antifungal activity since alligamycin B (2) with disruption in the ring abolished the antifungal effect. Proteomics analysis revealed alligamycin A potentially disrupts the integrity of fungal cell walls and induces the expression of stress-response proteins in Aspergillus niger. Discovery of the potent antifungal candidate alligamycin A expands the limited antifungal chemical space.

Azole Combinations and Multi-Targeting Drugs That Synergistically Inhibit Candidozyma auris

Limited antifungal treatment options and drug resistance require innovative approaches to effectively combat fungal infections. Combination therapy is a promising strategy that addresses these pressing issues by concurrently targeting multiple cellular sites. The drug targets usually selected for combination therapy are from different cellular pathways with the goals of increasing treatment options and reducing development of resistance. However, some circumstances can prevent the implementation of combination therapy in clinical practice. These could include the increased risk of adverse effects, drug interactions, and even the promotion of drug resistance. Furthermore, robust clinical evidence supporting the superiority of combination therapy over monotherapy is limited and underscores the need for further research. Despite these challenges, synergies detected with different antifungal classes, such as the azoles and echinocandins, suggest that treatment strategies can be optimized by better understanding the underlying mechanisms. This review provides an overview of multi-targeting combination strategies with a primary focus on Candidozyma auris infections.

Ergosterol promotes aggregation of natamycin in the yeast plasma membrane

Polyene macrolides are antifungal substances, which interact with cells in a sterol-dependent manner. While being widely used, their mode of action is poorly understood. Here, we employ ultraviolet-sensitive (UV) microscopy to show that the antifungal polyene natamycin binds to the yeast plasma membrane (PM) and causes permeation of propidium iodide into cells. Right before membrane permeability became compromised, we observed clustering of natamycin in the PM that was independent of PM protein domains. Aggregation of natamycin was paralleled by cell deformation and membrane blebbing as revealed by soft X-ray microscopy. Substituting ergosterol for cholesterol decreased natamycin binding and caused a reduced clustering of natamycin in the PM. Blocking of ergosterol synthesis necessitates sterol import via the ABC transporters Aus1/Pdr11 to ensure natamycin binding. Quantitative imaging of dehydroergosterol (DHE) and cholestatrienol (CTL), two analogues of ergosterol and cholesterol, respectively, revealed a largely homogeneous lateral sterol distribution in the PM, ruling out that natamycin binds to pre-assembled sterol domains. Depletion of sphingolipids using myriocin increased natamycin binding to yeast cells, likely by increasing the ergosterol fraction in the outer PM leaflet. Importantly, binding and membrane aggregation of natamycin was paralleled by a decrease of the dipole potential in the PM, and this effect was enhanced in the presence of myriocin. We conclude that ergosterol promotes binding and aggregation of natamycin in the yeast PM, which can be synergistically enhanced by inhibitors of sphingolipid synthesis.

Minimizing higher-order aggregation maximizes iron mobilization by small molecules

The natural product hinokitiol mobilizes iron across lipid bilayers at low concentrations and restores hemoglobinization in iron transporter protein-deficient systems. But hinokitiol fails to similarly mobilize iron at higher concentrations, limiting its uses in chemical biology and medicine. Here we show that at higher concentrations, hinokitiol3:Fe(III) complexes form large, higher-order aggregates, leading to loss of transmembrane iron mobilization. Guided by this understanding and systematic structure-function studies enabled by modular synthesis, we identified FeM-1269, which minimally aggregates and dose-dependently mobilizes iron across lipid bilayers even at very high concentrations. In contrast to hinokitiol, FeM-1269 is also well-tolerated in animals at high doses for extended periods of time. In a mouse model of anemia of inflammation, FeM-1269 increases serum iron, transferrin saturation, hemoglobin and hematocrit. This rationally developed iron-mobilizing small molecule has enhanced potential as a molecular prosthetic for understanding and potentially treating iron transporter deficiencies.

Understanding the clinical and environmental drivers of antifungal resistance in the One Health context

Antifungal drugs have had a tremendous impact on human health and the yields of crops. However, in recent years, due to usage both in a health setting and in agriculture, there has been a rapid emergence of antifungal drug resistance that has outpaced novel compound discovery. It is now globally recognized that new strategies to tackle fungal infection are urgently needed, with such approaches requiring the cooperation of both sectors and the development of robust antifungal stewardship rationales. In this review, we examine the current antifungal regimes in clinical and agricultural settings, focusing on two pathogens of importance, Candida auris and Aspergillus fumigatus, examining their drivers of antifungal resistance, the impact of dual-use azoles and the impact agricultural practices have on driving the emergence of resistance. Finally, we postulate that a One Health approach could offer a viable alternative to prolonging the efficacy of current antifungal agents.

The progress and future of the treatment of Candida albicans infections based on nanotechnology

Systemic infection with Candida albicans poses a significant risk for people with weakened immune systems and carries a mortality rate of up to 60%. However, current therapeutic options have several limitations, including increasing drug tolerance, notable off-target effects, and severe adverse reactions. Over the past four decades, the progress in developing drugs to treat Candida albicans infections has been sluggish. This comprehensive review addresses the limitations of existing drugs and summarizes the efforts made toward redesigning and innovating existing or novel drugs through nanotechnology. The discussion explores the potential applications of nanomedicine in Candida albicans infections from four perspectives: nano-preparations for anti-biofilm therapy, innovative formulations of "old drugs" targeting the cell membrane and cell wall, reverse drug resistance therapy targeting subcellular organelles, and virulence deprivation therapy leveraging the unique polymorphism of Candida albicans. These therapeutic approaches are promising to address the above challenges and enhance the efficiency of drug development for Candida albicans infections. By harnessing nano-preparation technology to transform existing and preclinical drugs, novel therapeutic targets will be uncovered, providing effective solutions and broader horizons to improve patient survival rates.

Combatting Fungal Infections: Advances in Antifungal Polymeric Nanomaterials

Fungal pathogens cause over 6.5 million life-threatening systemic infections annually, with mortality rates ranging from 20 to 95%, even with medical intervention. The World Health Organization has recently emphasized the urgent need for new antifungal drugs. However, the range of effective antifungal agents remains limited and resistance is increasing. This Review explores the current landscape of fungal infections and antifungal drugs, focusing on synthetic polymeric nanomaterials like nanoparticles that enhance the physicochemical properties of existing drugs. Additionally, we examine intrinsically antifungal polymers that mimic naturally occurring peptides. Advances in polymer characterization and synthesis now allow precise design and screening for antifungal activity, biocompatibility, and drug interactions. These antifungal polymers represent a promising new class of drugs for combating fungal infections.

Otilonium Bromide Exhibits Potent Antifungal Effects by Blocking Ergosterol Plasma Membrane Localization and Triggering Cytotoxic Autophagy in Candida Albicans

Candidiasis, which presents a substantial risk to human well-being, is frequently treated with azoles. However, drug-drug interactions caused by azoles inhibiting the human CYP3A4 enzyme, together with increasing resistance of Candida species to azoles, represent serious issues with this class of drug, making it imperative to develop innovative antifungal drugs to tackle this growing clinical challenge. A drug repurposing approach is used to examine a library of Food and Drug Administration (FDA)-approved drugs, ultimately identifying otilonium bromide (OTB) as an exceptionally encouraging antifungal agent. Mechanistically, OTB impairs vesicle-mediated trafficking by targeting Sec31, thereby impeding the plasma membrane (PM) localization of the ergosterol transporters, such as Sip3. Consequently, OTB obstructs the movement of ergosterol across membranes and triggers cytotoxic autophagy. It is noteworthy that C. albicans encounters challenges in developing resistance to OTB because it is not a substrate for drug transporters. This study opens a new door for antifungal therapy, wherein OTB disrupts ergosterol subcellular distribution and induces cytotoxic autophagy. Additionally, it circumvents the hepatotoxicity associated with azole-mediated liver enzyme inhibition and avoids export-mediated drug resistance in C. albicans.

Insight into Virulence and Mechanisms of Amphotericin B Resistance in the Candida haemulonii Complex

The Candida haemulonii complex includes emerging opportunistic human fungal pathogens with documented multidrug-resistance profiles. It comprises Candida haemulonii sensu stricto, Candida haemulonii var. vulnera, Candida duobushaemulonii, Candida pseudohaemulonii, and Candida vulturna. In recent years, rates of clinical isolation of strains from this complex have increased in multiple countries, including China, Malaysia, and Brazil. Biofilm formation, hydrolytic enzymes, surface interaction properties, phenotype switching and cell aggregation abilities, extracellular vesicles production, stress response, and immune evasion help these fungi to infect the host and exert pathological effects. Multidrug resistance profiles also enhance the threat they pose; they exhibit low susceptibility to echinocandins and azoles and an intrinsic resistance to amphotericin B (AMB), the first fungal-specific antibiotic. AMB is commonly employed in antifungal treatments, and it acts via several known mechanisms. Given the propensity of clinical Candida species to initiate bloodstream infections, clarifying how C. haemulonii resists AMB is of critical clinical importance. This review outlines our present understanding of the C. haemulonii complex's virulence factors, the mechanisms of action of AMB, and the mechanisms underlying AMB resistance.

A synthetic peptide mimic kills Candida albicans and synergistically prevents infection

More than two million people worldwide are affected by life-threatening, invasive fungal infections annually. Candida species are the most common cause of nosocomial, invasive fungal infections and are associated with mortality rates above 40%. Despite the increasing incidence of drug-resistance, the development of novel antifungal formulations has been limited. Here we investigate the antifungal mode of action and therapeutic potential of positively charged, synthetic peptide mimics to combat Candida albicans infections. Our data indicates that these synthetic polymers cause endoplasmic reticulum stress and affect protein glycosylation, a mode of action distinct from currently approved antifungal drugs. The most promising polymer composition damaged the mannan layer of the cell wall, with additional membrane-disrupting activity. The synergistic combination of the polymer with caspofungin prevented infection of human epithelial cells in vitro, improved fungal clearance by human macrophages, and significantly increased host survival in a Galleria mellonella model of systemic candidiasis. Additionally, prolonged exposure of C. albicans to the synergistic combination of polymer and caspofungin did not lead to the evolution of tolerant strains in vitro. Together, this work highlights the enormous potential of these synthetic peptide mimics to be used as novel antifungal formulations as well as adjunctive antifungal therapy.

Nanoformulations for dismantling fungal biofilms: The latest arsenals of antifungal therapy

Globally, fungal infections have evolved as a strenuous challenge for clinicians, particularly in patients with compromised immunity in intensive care units. Fungal co-infection in Covid-19 patients has made the situation more formidable for healthcare practitioners. Surface adhered fungal population known as biofilm often develop at the diseased site to elicit antifungal tolerance and recalcitrant traits. Thus, an innovative strategy is required to impede/eradicate developed biofilm and avoid the formation of new colonies. The development of nanocomposite-based antibiofilm solutions is the most appropriate way to withstand and dismantle biofilm structures. Nanocomposites can be utilized as a drug delivery medium and for fabrication of anti-biofilm surfaces capable to resist fungal colonization. In this context, the present review comprehensively described different forms of nanocomposites and mode of their action against fungal biofilms. Amongst various nanocomposites, efficacy of metal/organic nanoparticles and nanofibers are particularly emphasized to highlight their role in the pursuit of antibiofilm strategies. Further, the inevitable concern of nanotoxicology has also been introduced and discussed with the exigent need of addressing it while developing nano-based therapies. Further, a list of FDA-approved nano-based antifungal formulations for therapeutic usage available to date has been described. Collectively, the review highlights the potential, scope, and future of nanocomposite-based antibiofilm therapeutics to address the fungal biofilm management issue.

Solid-State NMR 13C sensitivity at high magnetic field

Sensitivity is the foundation of every NMR experiment, and the signal-to-noise ratio (SNR) should increase with static (B0) magnetic field, by a proportionality that primarily depends on the design of the NMR probe and receiver. In the low B0 field limit, where the coil geometry is much smaller than the wavelength of the NMR frequency, SNR can increase in proportion to B0 to the power 7/4. For modern magic-angle spinning (MAS) probes, this approximation holds for rotor sizes up to 3.2 mm at 14.1 Tesla (T), corresponding to 600 MHz 1H and 151 MHz 13C Larmor frequencies. To obtain the anticipated benefit of larger coils and/or higher B0 fields requires a quantitative understanding of the contributions to SNR, utilizing standard samples and protocols that reproduce SNR measurements with high accuracy and precision. Here, we present such a systematic and comprehensive study of 13C SNR under MAS over the range of 14.1 to 21.1 T. We evaluate a range of probe designs utilizing 1.6, 2.5 and 3.2 mm rotors, including 24 different sets of measurements on 17 probe configurations using five spectrometers. We utilize N-acetyl valine as the primary standard and compare and contrast with other commonly used standard samples (adamantane, glycine, hexamethylbenzene, and 3-methylglutaric acid). These robust approaches and standard operating procedures provide an improved understanding of the contributions from probe efficiency, receiver noise figure, and B0 dependence in a range of custom-designed and commercially available probes. We find that the optimal raw SNR is obtained with balanced 3.2 mm design at 17.6 T, that the best mass-limited SNR is achieved with a balanced 1.6 mm design at 21.1 T, and that the raw SNR at 21.1 T reaches diminishing returns with rotors larger than 2.5 mm.

Interdisciplinary approaches for the discovery of novel antifungals

Pathogenic fungi are an increasing public health concern. The emergence of antifungal resistance coupled with the scarce antifungal arsenal highlights the need for novel therapeutics. Fortunately, the past few years have witnessed breakthroughs in antifungal development. Here, we discuss pivotal interdisciplinary approaches for the discovery of novel compounds with efficacy against diverse fungal pathogens. We highlight breakthroughs in improving current antifungal scaffolds, as well as the utility of compound combinations to extend the lifespan of antifungals. Finally, we describe efforts to refine candidate chemical scaffolds by leveraging structure-guided approaches, and the use of functional genomics to expand our knowledge of druggable antifungal targets. Overall, we emphasize the importance of interdisciplinary collaborations in the endeavor to develop innovative antifungal strategies.

The intricate link between iron, mitochondria and azoles in Candida species

Invasive fungal infections are rapidly increasing, and the opportunistic pathogenic Candida species are the fourth most common cause of nosocomial systemic infections. The current antifungal classes, of which azoles are the most widely used, all have shortcomings. Azoles are generally considered fungistatic rather than fungicidal, they do not actively kill fungal cells and therefore resistance against azoles can be rapidly acquired. Combination therapies with azoles provide an interesting therapeutic outlook and agents limiting iron are excellent candidates. We summarize how iron is acquired by the host and transported towards both storage and iron-utilizing organelles. We indicate whether these pathways alter azole susceptibility and/or tolerance, to finally link these transport mechanisms to mitochondrial iron availability. In this review, we highlight putative novel intracellular iron shuffling mechanisms and indicate that mitochondrial iron dynamics in relation to azole treatment and iron limitation is a significant knowledge gap.

Biomimetic Antifungal Materials: Countering the Challenge of Multidrug-Resistant Fungi

In light of rising public health threats like antifungal and antimicrobial resistance, alongside the slowdown in new antimicrobial development, biomimetics have shown promise as therapeutic agents. Multidrug-resistant fungi pose significant challenges as they quickly develop resistance, making traditional antifungals less effective. Developing new antifungals is also complicated by the need to target eukaryotic cells without harming the host. This review examines biomimetic antifungal materials that mimic natural biological mechanisms for targeted and efficient action. It covers a range of agents, including antifungal peptides, alginate-based antifungals, chitosan derivatives, nanoparticles, plant-derived polyphenols, and probiotic bacteria. These agents work through mechanisms such as disrupting cell membranes, generating reactive oxygen species, and inhibiting essential fungal processes. Despite their potential, challenges remain in terms of ensuring biocompatibility, optimizing delivery, and overcoming potential resistance. Production scalability and economic viability are also concerns. Future research should enhance the stability and efficacy of these materials, integrate multifunctional approaches, and develop sophisticated delivery systems. Interdisciplinary efforts are needed to understand interactions between these materials, fungal cells, and the host environment. Long-term health and environmental impacts, fungal resistance mechanisms, and standardized testing protocols require further study. In conclusion, while biomimetic antifungal materials represent a revolutionary approach to combating multidrug-resistant fungi, extensive research and development are needed to fully realize their potential.

Sterol 14-alpha demethylase (CYP51) activity in Leishmania donovani is likely dependent upon cytochrome P450 reductase 1

Liposomal amphotericin B is an important frontline drug for the treatment of visceral leishmaniasis, a neglected disease of poverty. The mechanism of action of amphotericin B (AmB) is thought to involve interaction with ergosterol and other ergostane sterols, resulting in disruption of the integrity and key functions of the plasma membrane. Emergence of clinically refractory isolates of Leishmania donovani and L. infantum is an ongoing issue and knowledge of potential resistance mechanisms can help to alleviate this problem. Here we report the characterisation of four independently selected L. donovani clones that are resistant to AmB. Whole genome sequencing revealed that in three of the moderately resistant clones, resistance was due solely to the deletion of a gene encoding C24-sterol methyltransferase (SMT1). The fourth, hyper-resistant resistant clone (>60-fold) was found to have a 24 bp deletion in both alleles of a gene encoding a putative cytochrome P450 reductase (P450R1). Metabolic profiling indicated these parasites were virtually devoid of ergosterol (0.2% versus 18% of total sterols in wild-type) and had a marked accumulation of 14-methylfecosterol (75% versus 0.1% of total sterols in wild-type) and other 14-alpha methylcholestanes. These are substrates for sterol 14-alpha demethylase (CYP51) suggesting that this enzyme may be a bona fide P450R specifically involved in electron transfer from NADPH to CYP51 during catalysis. Deletion of P450R1 in wild-type cells phenocopied the metabolic changes observed in our AmB hyper-resistant clone as well as in CYP51 nulls. Likewise, addition of a wild type P450R1 gene restored sterol profiles to wild type. Our studies indicate that P450R1 is essential for L. donovani amastigote viability, thus loss of this gene is unlikely to be a driver of clinical resistance. Nevertheless, investigating the mechanisms underpinning AmB resistance in these cells provided insights that refine our understanding of the L. donovani sterol biosynthetic pathway.

Overexpression of PDR16 Confers Amphotericin B Resistance in a PMP3-Dependent Manner in Yeast Saccharomyces cerevisiae

Invasive fungal infections in humans with compromised immune systems are the primary cause of morbidity and mortality, which is becoming more widely acknowledged. Amphotericin B (AmB) is one of the antifungal drugs used to treat such infections. AmB binds with plasma membrane ergosterol, inducing cellular ions to leak and causing cell death. Reduction in ergosterol content and modification of cell walls have been described as AmB resistance mechanisms. In addition, when the sphingolipid level is decreased, the cell becomes more susceptible to AmB. Previously, PDR16, a gene that encodes phosphatidylinositol transfer protein in Saccharomyces cerevisiae, was shown to enhance AmB resistance upon overexpression. However, the mechanism of PDR16-mediated AmB resistance is not clear. Here, in this study, it was discovered that a plasma membrane proteolipid 3 protein encoded by PMP3 is essential for PDR16-mediated AmB resistance. PDR16-mediated AmB resistance does not depend on ergosterol, but a functional sphingolipid biosynthetic pathway is required. Additionally, PMP3-mediated alteration in membrane integrity abolishes PDR16 mediated AmB resistance, confirming the importance of PMP3 in the PDR16 mediated AmB resistance.

A Study on the Effect of Quaternization of Polyene Antibiotics' Structures on Their Activity, Toxicity, and Impact on Membrane Models

Polyene antibiotics have been used in antifungal therapy since the mid-twentieth century. They are highly valued for their broad spectrum of activity and the rarity of pathogen resistance to their action. However, their use in the treatment of systemic mycoses often results in serious side-effects. Recently, there has been a renewed interest in the development of new antifungal drugs based on polyenes, particularly due to the emergence of highly dangerous pathogenic strains of fungi, such as Candida auris, and the increased incidence of mucormycosis. Considerable understanding has been established regarding the structure-biological activity relationships of polyene antifungals. Yet, no previous studies have examined the effect of introducing quaternized fragments into their molecular structure. In this study, we present a series of amides of amphotericin B, nystatin, and natamycin bearing a quaternized group in the side chain, and discuss their biological properties: antifungal activity, cytotoxicity, and effects on lipid bilayers that mimic fungal and mammalian cell membranes. Our research findings suggest that the nature of the introduced quaternized residue plays a more significant role than merely the introduction of a constant positive charge. Among the tested polyenes, derivatives 4b, 5b, and 6b, which contain a fragment of N-methyl-4-(aminomethyl)pyridinium in their structure, are particularly noteworthy due to their biological activity.