Amphotericin primarily kills yeast by simply binding ergosterol

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.

Spontaneous Cell Detachment from Temperature Gradients: Getting the Method Ready for Antimicrobial Drug Testing at Cell Culture Level

Spontaneous cell detachment describes an effect in which eukaryotic cells first sediment onto a heated chip and then detach from it spontaneously and collectively after a sharply defined dwell time td. This behavior is triggered by the temperature gradient between the chip and the colder supernatant liquid. Notably, td allows distinguishing between different yeast strains and cancer-cell lines. At the same time, it also varies in the presence of nutrients and cytotoxins, suggesting an added value of this method for pharmacological studies. In the present work, we study the role of fluid convection on the detachment of yeast cells experimentally and by simulations using a sample compartment with a variable aspect ratio. Hereby, we found that the absolute chip temperature, the strength of the temperature gradient and the number of cells inside the sample compartment all affect the dwell time td. To demonstrate the concept, we show that the spontaneous-detachment method can measure the impact of an antibiotic and an antiseptic drug on yeast cultures and corroborate this with reference assays.

Gold nanorods non-functionalised and associated with gallic acid exhibit activity against non-albicans Candida species

Strategies focusing on natural compounds and nanotechnology have been explored to overcome the limitations of conventional therapies in managing Candida infections. In this context, metal nanoparticles, both non-functionalised and combined with gallic acid, may offer a promising alternative. This study investigated the effects of gold nanoparticles non-functionalised (AuNp) and associated with gallic acid (AuNpGA) against planktonic cells and biofilms of Nakaseomyces glabratus, Pichia kudriavzevii, Candida parapsilosis, and Candida tropicalis. Both AuNp and AuNpGA inhibited the growth of all strains at 1.56 µg/mL and exhibited fungicidal effects at concentrations ranging from 1.56 to 3.12 µg/mL. The time-kill curve revealed that AuNpGA and AuNp completely inhibited the viability of all strains in planktonic cultures at 8 and 24 h, respectively, exhibiting greater antifungal activity compared to fluconazole. Treatment with AuNp increased ROS production against N. glabratus and P. kudriavzevii. Oxidative stress was enhanced against all strains after treatment with AuNpGA, and exposure to this compound reduced ergosterol levels of P. kudriavzevii and C. parapsilosis. Furthermore, AuNpGA and AuNp significantly decreased the viability of all Candida biofilms at 7.8 and 15.6 µg/mL, respectively. In summary, both gold nanoparticles exhibited activity against planktonic cells and biofilms, suggesting their potential as agents for treating Candida infections.

Protein-mediated stabilization of amphotericin B increases its efficacy against diverse fungal pathogens

Amphotericin B (AMB), a potent and broad-spectrum antifungal agent, faces solubility and toxicity challenges in clinical use. In this study, we explored the ability of DewY and EASΔ15, class I fungal hydrophobin proteins with unique amphipathic properties and self-assembly capabilities, to stabilize AMB in solution. UV-visible spectroscopy confirmed the ability of hydrophobin proteins to stabilize the monomeric state of AMB in aqueous solution for up to 48 h. Further assays revealed that this effect was not exclusive to hydrophobins, however, as non-hydrophobin proteins provided similar stabilizing effects. AMB-protein combinations exhibited enhanced efficacy against diverse clinically relevant fungal pathogens, with 4- to 32-fold reductions in the effective in vitro dosage compared to AMB alone. Microscopic analyses found fungal cells treated with AMB alone and in combination with proteins had identical morphological changes, suggesting that protein interactions do not alter the mode of action of AMB. Instead, our results indicate that the monomeric state of AMB is stabilized in aqueous solution by non-specific interactions with hydrophobic areas on proteins. We suggest that this protein-mediated enhancement of solubility could reduce the required dose of AMB, providing a basis for optimizing AMB-based antifungal therapies.IMPORTANCEFungal infections are a growing global health concern, yet effective antifungal treatments remain limited by toxicity and poor solubility. AMB, a potent broad-spectrum antifungal, is highly effective but suffers from severe side effects and formulation challenges. Our study demonstrates that proteins, including fungal hydrophobins, can stabilize AMB in its monomeric form, significantly enhancing its solubility and efficacy against a range of fungal pathogens. These findings suggest that protein-mediated stabilization could enhance the effectiveness of AMB by reducing the required dosage and potentially lowering its toxic side effects. This approach offers a promising strategy for optimizing AMB therapies and improving treatment options, especially in resource-limited settings where fungal infections impose a significant health burden.

Highly selective ergosterol binding and impaired redox balance leads to improved antileishmanial efficacy for amphotericin b synthesized silver nanoparticles with reduced toxicity- In vitro and in vivo studies

We aim to develop a low-cost silver nanoparticle (AgNP)-based delivery of AmB (AmB-AgNP) which can replace the costly AmBisome and toxic Fungizone formulation for applications against visceral leishmaniasis (VL) caused by the parasite Leishmania donovani (LD). Using different molar ratios of AmB and silver nitrate, we have identified a specific NP of ∼110 nm (zeta potential of -36.7 mV and PDI of 0.15) as the ideal antileishmanial agent with increased efficacy than AmB against LD promastigotes and amastigotes. These NPs were characterized by UV-visible, DLS, Zeta potential, FT-IR, DSC, and FE-SEM studies.The uptake of metallic silver by ICP-MS studies indicate that AmB-AgNP is internalized >3.4 and > 2.8 fold more than citrate-reduced AgNPs inside the LD and murine macrophage cells, respectively. AmB-AgNPs are less cytotoxic than AmB and show more necrotic mode of death than AmB. Here, production of high amount of recative oxygen speccies, lipid peroxides, protein carbonylations and decreased expression of antioxidant enzymes are also observed. AmB-AgNP causes a dose-dependent ergosterol (ERG) depletion which can be reversed by ERG supplementation. Further, ITC studies established selective and enhanced binding efficacy of AmB-AgNP against ERG and not choesterol. The selective and enhanced inhibition of the ERG and trypanothione biosynthesis pathway by AmB-AgNP, compared to AmB, was proven by proteomics studies. The rate-limiting enzyme of ERG biosynthesis, HMG-CoA-reductase, was downregulated >9-fold in the presence of AmB-AgNP treatment. The acute toxicity studies on mice showed that AmB-AgNP has a selectivity index of > 6-fold compared to AmB. However, AgNP is <30 % less effective than AmB in antileishmanial efficacy with equivalent doses in vivo. The higher selectivity index of AmB-AgNP provides a better therapeutic window than Fungizone, whereas the lost-cost synthesis, compared to AmBisome, makes the AmB-AgNP a viable and cheaper delivery option against VL for future investigations.

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.

Integrated application of selenium and silica reduce arsenic accumulation and enhance the level of metabolites in rice grains

In this study, rice plants were co-exposed to selenium (Se) and silica (Si) under arsenic (As) stress to evaluate As accumulation in rice grains, associated cancer risk, and its impact on the types and numbers of grain metabolites. A total of 58 metabolites were identified, of which, 19 belong to sugars, and drastically altered during different treatments. Arsenic exposure significantly reduced monosaccharides, i.e., D-glucose (83%) >D-galactose (60%) >D-fructose (57%) >D-ribose (29%) but increased that monosaccharide units which have antioxidant properties (i.e. α-D-glucopyranoside and melibiose). However, the levels of D-galactose, fructose, and ribose were significantly increased during co-supplementation of selenite (SeIV) and Si under As stress. Other groups of rice grain metabolites, like sugar alcohols, organic acids, polyphenols, carboxylic acids, fatty acids, and phytosterols, were also significantly altered by As exposure and increased in grains of SeIV and Si supplemented rice compared to alone As exposure. In brief, rice growing in As-affected areas may have a low level of different metabolites. However, supplementation by selenite (SeIV) with Si not only increased metabolites and amylose/amylopectin ratio but also reduced ∼90% of As accumulation in grains. Thus, the use of SeIV with Si might be advantageous for the locals to provide a healthy diet of rice and limit As-induced cancer risk up to 10-fold.

The Hidden Fortress: A Comprehensive Review of Fungal Biofilms with Emphasis on Cryptococcus neoformans

Biofilms are structurally organized communities of microorganisms that adhere to a variety of surfaces. These communities produce protective matrices consisting of polymeric polysaccharides, proteins, nucleic acids, and/or lipids that promote shared resistance to various environmental threats, including chemical, antibiotic, and immune insults. While algal and bacterial biofilms are more apparent in the scientific zeitgeist, many fungal pathogens also form biofilms. These surprisingly common biofilms are morphologically distinct from the multicellular molds and mushrooms normally associated with fungi and are instead an assemblage of single-celled organisms. As a collection of yeast and filamentous cells cloaked in an extracellular matrix, fungal biofilms are an extreme threat to public health, especially in conjunction with surgical implants. The encapsulated yeast, Cryptococcus neoformans, is an opportunistic pathogen that causes both pulmonary and disseminated infections, particularly in immunocompromised individuals. However, there is an emerging trend of cryptococcosis among otherwise healthy individuals. C. neoformans forms biofilms in diverse environments, including within human hosts. Notably, biofilm association correlates with increased expression of multiple virulence factors and increased resistance to both host defenses and antifungal treatments. Thus, it is crucial to develop novel strategies to combat fungal biofilms. In this review, we discuss the development and treatment of fungal biofilms, with a particular focus on C. neoformans.

Is a Fungal Apocalypse Inevitable or Just a Hallucination? An Overview of the Antifungal Armamentarium Used in the Fight against Pathogenic Fungi

The World Health Organization (WHO) fungal priority pathogens list (WHO FPPL) published in 2022 highlighted the inequity and research challenges faced by researchers who study pathogenic fungi that afflict humans. Antifungal drugs are the only weapon available to treat infections; however, these drugs are old, are not effective against multidrug-resistant (MDR) fungal strains, and are associated with substantial toxicity in clinical use. This Microperspective summarizes challenges pertaining to antifungal drug discovery in addition to highlighting recent advances and antifungal agents in clinical trials.

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.

Hoi1 targets the yeast BLTP2 protein to ER-PM contact sites to regulate lipid homeostasis

Membrane contact sites between organelles are important for maintaining cellular lipid homeostasis. Members of the recently identified family of bridge-like lipid transfer proteins (BLTPs) span opposing membranes at these contact sites to enable the rapid transfer of bulk lipids between organelles. While the VPS13 and ATG2 family members use organelle-specific adaptors for membrane targeting, the mechanisms that regulate other bridge-like transporters remain unknown. Here, we identify the conserved protein Ybl086c, which we name Hoi1 (Hob interactor 1), as an adaptor that targets the yeast BLTP2-like proteins Fmp27/Hob1 and Hob2 to ER-PM contact sites. Two separate Hoi1 domains interface with alpha-helical projections that decorate the central hydrophobic channel on Fmp27, and loss of these interactions disrupts cellular sterol homeostasis. The mutant phenotypes of BLTP2 and HOI1 orthologs indicate these proteins act in a shared pathway in worms and flies. Together, this suggests that Hoi1-mediated recruitment of BLTP2-like proteins represents an evolutionarily conserved mechanism for regulating lipid transport at membrane contact sites.

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.

NMR and molecular simulation studies on the structure elucidation of the amphotericin B ion channel using 13C and 19F labelling

Amphotericin B (AmB) has been clinically used for serious fungal infections for over 60 years. The drug is characterized by its specific recognition of ergosterol (Erg) in the fungal cell membrane. AmB and Erg form an ion-channel assembly, which is thought to play a major role in the antibiotic activity of AmB. The precise structure of the ion channel in fungal membranes still remains unelucidated. Recently, the structure of an AmB assembly formed in artificial lipid bilayers was determined using solid-state NMR and molecular dynamics simulations. The structure elucidation was made possible by using 13C- and 19F-labelled AmBs, which were efficiently synthesized using strategies and methods established in previous studies. This review focuses on the structure of the AmB ion channel, which accounts for the antibiotic activity. Additionally, the chemical syntheses of isotope-labelled AmB and Erg used for the structural studies are also reviewed. Solid-state NMR spectra of the labelled AmBs were recorded to measure the distances between labelled sites in the AmB-Erg assembly in lipid bilayers, revealing that the ion channel consisting of seven molecules of AmB spans the bilayer with a single molecule length. Extensive molecular dynamics simulations showed that the conductance of this AmB channel is comparable with those by single-channel recording. The simulations also demonstrated that Erg stabilizes the ion-channel assemblies more efficiently than human cholesterol. The atomic-level structure of the AmB channel in the artificial bilayer will help us to understand the mechanisms of the pharmacological actions and adverse effects of AmB.

Unleashing the role of potential adjuvants in leishmaniasis

Leishmaniasis is amongst one of the most neglected tropical disease, caused by an intracellular protozoan of genus Leishmania. Currently, the most promising strategy to combat leishmaniasis, relies on chemotherapy but the toxicity and increasing resistance of the standard drugs, presses the demand for new alternatives. Immunization is arguably the best strategy for cure because an individual once infected becomes immune to the disease. Yet, there is no efficient vaccine capable of providing enduring immunity against the parasite. Achieving the goal of developing highly efficacious and durable vaccine is limited due to lack of an appropriate adjuvant. Adjuvants are recognized as 'immune potentiators' which redirect or amplify the immune response. A number of adjuvants like alum, MPL-A, CpG ODN, GLA-SE, imiquimod, saponins etc. have been used in combination with various classes of Leishmania antigens. However, only few have reached clinical trials. Thus, the choice of an adjuvant is critically dependent on many factors such as the route of administration, the nature of antigen, formulation, the type of required immune response, their mode of action and the immunization schedule. This review provides an updated status on the types of adjuvants used in leishmaniasis so far and their mechanism of action if known.

Advancing Treatment for Leishmaniasis: From Overcoming Challenges to Embracing Therapeutic Innovations

Protozoan parasite infections, particularly leishmaniasis, present significant public health challenges in tropical and subtropical regions, affecting socio-economic status and growth. Despite advancements in immunology, effective vaccines remain vague, leaving drug treatments as the primary intervention. However, existing medications face limitations, such as toxicity and the rise of drug-resistant parasites. This presents an urgent need to identify new therapeutic targets for leishmaniasis treatment. Understanding the complex life cycle of Leishmania and its survival in host macrophages can provide insights into potential targets for intervention. Current treatments, including antimonials, amphotericin B, and miltefosine, are constrained by side effects, costs, resistance, and reduced efficacy. Exploring novel therapeutic targets within the parasite's physiology, such as key metabolic enzymes or essential surface proteins, may lead to the development of more effective and less toxic drugs. Additionally, innovative strategies like drug repurposing, combination therapies, and nanotechnology-based delivery systems could enhance efficacy and combat resistance, thus improving anti-leishmanial therapies.

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.

Specificity of Membrane-Associated J-Domain Protein, Caj1, in Amphotericin B Tolerance in Budding Yeast

Hsp70:J-domain protein (JDP) machineries play pivotal roles in maintaining cellular proteostasis and governing various aspects of fungal physiology. While Hsp70 is known for its involvement in conferring tolerance to diverse antifungal drugs, the specific contribution of JDPs remains unclear. In this study, we examined the sensitivity of cytosolic JDP deletion strains of budding yeast to amphotericin B (AmB), a polyene antifungal agent widely utilized in fungal disease treatment due to its ability to disrupt the fungal plasma membrane (PM). Deleting Caj1, a PM-associated class II JDP, heightened susceptibility to AmB, and the protection conferred by Caj1 against AmB necessitated both its N-terminal J-domain and C-terminal lipid binding domain. Moreover, Caj1 deficiency compromised PM integrity as evidenced by increased phosphate efflux and exacerbated AmB sensitivity, particularly at elevated temperatures. Notably, phytosphingosine (PHS) addition as well as overexpression of PMP3, a positive PM integrity regulator, significantly rescued AmB sensitivity of caj1Δ cells. Our results align with the notion that Caj1 associates with the PM and cooperates with Hsp70 to regulate PM proteostasis, thereby influencing PM integrity in budding yeast. Loss of Caj1 function at the PM compromises PM protein quality control, thereby rendering yeast cells more susceptible to AmB.

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.

Epoxy-a-lapachone in nanosystem: a prototype drug for leishmaniasis assessed in the binomial BALB/c - Leishmania (Leishmania) amazonensis

This perspective presents and supports arguments for a new formulation of epoxy-α-lapachone loaded microemulsion (ELAP-ME), a nanosystem, as a prototype drug for the treatment of leishmaniasis. The benefits of ELAP as a multitarget compound, with properties that affect key physiological pathways of Leishmania spp. are discussed. ELAP-ME demonstrated efficacy in murine infection models, particularly with the binomial BALB/c-Leishmania (Leishmania) amazonensis. Furthermore, it is proposed that the technological maturity of ELAP-ME be classified as Technology Readiness Level 4 (TLR 4) within the context of innovative drugs for American Cutaneous Leishmaniasis (ACL).

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.

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.

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.

Identification of genes associated with the high-temperature fermentation trait in the Saccharomyces cerevisiae natural isolate BCC39850

The fermentative model yeast Saccharomyces cerevisiae has been extensively used to study the genetic basis of stress response and homeostasis. In this study, we performed quantitative trait loci (QTL) analysis of the high-temperature fermentation trait of the progeny from the mating of the S. cerevisiae natural isolate BCC39850 (haploid#17) and the laboratory strain CEN.PK2-1C. A single QTL on chromosome X was identified, encompassing six candidate genes (GEA1, PTK2, NTA1, NPA3, IRT1, and IML1). The functions of these candidates were tested by reverse genetic experiments. Deletion mutants of PTK2, NTA1, and IML1 showed growth defects at 42 °C. The PTK2 knock-out mutant also showed significantly reduced ethanol production and plasma membrane H+ ATPase activity and increased sensitivity to acetic acid, ethanol, amphotericin B (AMB), and β-1,3-glucanase treatment. The CRISPR-Cas9 system was used to construct knock-in mutants by replacement of PTK2, NTA1, IML1, and NPA3 genes with BCC39850 alleles. The PTK2 and NTA1 knock-in mutants showed increased growth and ethanol production titers at 42 °C. These findings suggest an important role for the PTK2 serine/threonine protein kinase in regulating plasma membrane H+ ATPase activity and the NTA1 N-terminal amidase in protein degradation via the ubiquitin-proteasome system machinery, which affects tolerance to heat stress in S. cerevisiae.

Alternative ergosterol biosynthetic pathways confer antifungal drug resistance in the human pathogens within the Mucor species complex

Mucormycoses are emerging fungal infections caused by a variety of heterogeneous species within the Mucorales order. Among the Mucor species complex, Mucor circinelloides is the most frequently isolated pathogen in mucormycosis patients and despite its clinical significance, there is an absence of established genome manipulation techniques to conduct molecular pathogenesis studies. In this study, we generated a spontaneous uracil auxotrophic strain and developed a genetic transformation procedure to analyze molecular mechanisms conferring antifungal drug resistance. With this new model, phenotypic analyses of gene deletion mutants were conducted to define Erg3 and Erg6a as key biosynthetic enzymes in the M. circinelloides ergosterol pathway. Erg3 is a C-5 sterol desaturase involved in growth, sporulation, virulence, and azole susceptibility. In other fungal pathogens, erg3 mutations confer azole resistance because Erg3 catalyzes the production of a toxic diol upon azole exposure. Surprisingly, M. circinelloides produces only trace amounts of this toxic diol and yet, it is still susceptible to posaconazole and isavuconazole due to alterations in membrane sterol composition. These alterations are severely aggravated by erg3Δ mutations, resulting in ergosterol depletion and, consequently, hypersusceptibility to azoles. We also identified Erg6a as the main C-24 sterol methyltransferase, whose activity may be partially rescued by the paralogs Erg6b and Erg6c. Loss of Erg6a function diverts ergosterol synthesis to the production of cholesta-type sterols, resulting in resistance to amphotericin B. Our findings suggest that mutations or epimutations causing loss of Erg6 function may arise during human infections, resulting in antifungal drug resistance to first-line treatments against mucormycosis.

IMPORTANCE

The Mucor species complex comprises a variety of opportunistic pathogens known to cause mucormycosis, a potentially lethal fungal infection with limited therapeutic options. The only effective first-line treatments against mucormycosis consist of liposomal formulations of amphotericin B and the triazoles posaconazole and isavuconazole, all of which target components within the ergosterol biosynthetic pathway. This study uncovered M. circinelloides Erg3 and Erg6a as key enzymes to produce ergosterol, a vital constituent of fungal membranes. Absence of any of those enzymes leads to decreased ergosterol and consequently, resistance to ergosterol-binding polyenes such as amphotericin B. Particularly, losing Erg6a function poses a higher threat as the ergosterol pathway is channeled into alternative sterols similar to cholesterol, which maintain membrane permeability. As a result, erg6a mutants survive within the host and disseminate the infection, indicating that Erg6a deficiency may arise during human infections and confer resistance to the most effective treatment against mucormycoses.

Souza AB, Levita DP, Mello CC, da Silva AFM, dos Santos TC, Ronconi CM. Innovating Leishmaniasis Treatment: A Critical Chemist's Review of Inorganic Nanomaterials

Leishmaniasis, a critical Neglected Tropical Disease caused by Leishmania protozoa, represents a significant global health risk, particularly in resource-limited regions. Conventional treatments are effective but suffer from serious limitations, such as toxicity, prolonged treatment courses, and rising drug resistance. Herein, we highlight the potential of inorganic nanomaterials as an innovative approach to enhance Leishmaniasis therapy, aligning with the One Health concept by considering these treatments' environmental, veterinary, and public health impacts. By leveraging the adjustable properties of these nanomaterials─including size, shape, and surface charge, tailored treatments for various diseases can be developed that are less harmful to the environment and nontarget species. We review recent advances in metal-, oxide-, and carbon-based nanomaterials for combating Leishmaniasis, examining their mechanisms of action and their dual use as standalone treatments or drug delivery systems. Our analysis highlights a promising yet underexplored frontier in employing these materials for more holistic and effective disease management.

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.

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.

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.

Glycosylated heterocyles emulsified with antifungal fraction of Moringa oleifera for potentiation of mycolytic activity

To enhance the clinical effect of antifungal medications for treating deadly fungal infections there is an increasing demand for novel treatments. Exploration of multiple-drug targeting in antifungal therapeutics is the need of the present era. In this pursuit, we identified potent antifungal compounds that were directed towards the multiple virulent targets in Rhizopus arrhizus. Quinoxaline di-N-oxide and piperazine derivatives were identified to exhibit antifungal activities. 03 bioactive compounds were identified from the docking results and antifungal activity. Furthermore, these compounds which were combined with the alkaline extract of M. olifera to make the aqueous phase, an oil phase containing cinnamon oil or clove oil and a combination of surfactants was made to prepare a bioactive composite emulsion. A significant antimycotic activity was seen for the bioactive composite emulsion when compared with the clinically used antifungal drugs. Our results indicate the synergy and potentiation of antimycotic drugs based on integrative medicine.

Alternative ergosterol biosynthetic pathways confer antifungal drug resistance in the human pathogens within the Mucor species complex

Mucormycoses are emerging fungal infections caused by a variety of heterogeneous species within the Mucorales order. Among the Mucor species complex, Mucor circinelloides is the most frequently isolated pathogen in mucormycosis patients and despite its clinical significance, there is an absence of established genome manipulation techniques to conduct molecular pathogenesis studies. In this study, we generated a spontaneous uracil auxotrophic strain and developed a genetic transformation procedure to analyze molecular mechanisms conferring antifungal drug resistance. With this new model, phenotypic analyses of gene deletion mutants were conducted to define Erg3 and Erg6a as key biosynthetic enzymes in the M. circinelloides ergosterol pathway. Erg3 is a C-5 sterol desaturase involved in growth, sporulation, virulence, and azole susceptibility. In other fungal pathogens, erg3 mutations confer azole resistance because Erg3 catalyzes the production of a toxic diol upon azole exposure. Surprisingly, M. circinelloides produces only trace amounts of this toxic diol and yet, it is still susceptible to posaconazole and isavuconazole due to alterations in membrane sterol composition. These alterations are severely aggravated by erg3Δ mutations, resulting in ergosterol depletion and consequently, hypersusceptibility to azoles. We also identified Erg6a as the main C-24 sterol methyltransferase, whose activity may be partially rescued by the paralogs Erg6b and Erg6c. Loss of Erg6a function diverts ergosterol synthesis to the production of cholesta-type sterols, resulting in resistance to amphotericin B. Our findings suggest that mutations or epimutations causing loss of Erg6 function may arise during human infections, resulting in antifungal drug resistance to first-line treatments against mucormycosis.

The interaction of plant flavones with amphotericin B: Consequences for its pore-forming ability

The growth of antibiotic resistance to antifungal drugs contributes to the search for new ways to enhance their effectiveness and reduce toxicity. The undeniable advantage of polyene macrolide antibiotic amphotericin B (AmB) which ensures low pathogen resistance is its mechanism of action related to the formation of transmembrane pores in target lipid membranes. Here, we investigated the effects of plant flavones, chrysin, wogonin, baicalein, apigenin, scutellarein, luteolin, morin and fisetin on the pore-forming activity of AmB in the sterol-enriched membranes by electrophysiological assays. Сhrysin, wogonin, baicalein, apigenin, scutellarein, and luteolin were shown to decrease the AmB pore-forming activity in the bilayers composed of palmitoyloleylphosphocholine independently of their sterol composition. Morin and fisetin led to the increase and decrease in the AmB pore-forming activity in the ergosterol- and cholesterol-containing bilayers respectively. Differential scanning microcalorimetry of the gel-to-liquid crystalline phase transition of membrane forming lipids, molecular dynamics simulations, and absorbance spectroscopy revealed the possibility of direct interactions between AmB and some flavones in the water and/or in the lipid bilayer. The influence of these interactions on the antibiotic partitioning between aqueous solution and membrane and/or its transition between different states in the bilayer was discussed.

Antibiotic Loaded Phytosomes as a Way to Develop Innovative Lipid Formulations of Polyene Macrolides

BACKGROUND

The threat of antibiotic resistance of fungal pathogens and the high toxicity of the most effective drugs, polyene macrolides, force us to look for new ways to develop innovative antifungal formulations.

OBJECTIVE

The aim of this study was to determine how the sterol, phospholipid, and flavonoid composition of liposomal forms of polyene antibiotics, and in particular, amphotericin B (AmB), affects their ability to increase the permeability of lipid bilayers that mimic the membranes of mammalian and fungal cells.

METHODS

To monitor the membrane permeability induced by various polyene-based lipid formulations, a calcein leakage assay and the electrophysiological technique based on planar lipid bilayers were used.

KEY RESULTS

The replacement of cholesterol with its biosynthetic precursor, 7-dehydrocholesterol, led to a decrease in the ability of AmB-loaded liposomes to permeabilize lipid bilayers mimicking mammalian cell membranes. The inclusion of plant flavonoid phloretin in AmB-loaded liposomes increased the ability of the formulation to disengage a fluorescent marker from lipid vesicles mimicking the membranes of target fungi. I-V characteristics of the fungal-like lipid bilayers treated with the AmB phytosomes were symmetric, demonstrating the functioning of double-length AmB pores and assuming a decrease in the antibiotic threshold concentration.

CONCLUSIONS AND PERSPECTIVES

The therapeutic window of polyene lipid formulations might be expanded by varying their sterol composition. Polyene-loaded phytosomes might be considered as the prototypes for innovative lipid antibiotic formulations.

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

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

Impact of Nitric Oxide-Release Kinetics on Antifungal Activity

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

Antifungal potential of lipopeptides produced by the Bacillus siamensis Sh420 strain against Fusarium graminearum

Biological control is a more sustainable and environmentally friendly alternative to chemical fungicides for controlling Fusarium spp. infestations. In this work, Bacillus siamensis Sh420 isolated from wheat rhizosphere showed a high antifungal activity against Fusarium graminearum as a secure substitute for fungicides. Sh420 was identified as B. siamensis using phenotypic evaluation and 16S rDNA gene sequence analysis. An in vitro antagonistic study showed that Sh420's lipopeptide (LP) extract exhibited strong antifungal properties and effectively combated F. graminearum. Meanwhile, lipopeptides have the ability to decrease ergosterol content, which has an impact on the overall structure and stability of the plasma membrane. The PCR-based screening revealed the presence of antifungal LP biosynthetic genes in this strain's genomic DNA. In the crude LP extract of Sh420, we were able to discover several LPs such as bacillomycin, iturins, fengycin, and surfactins using ultra-high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry. Microscopic investigations (fluorescent/transmission electron microscopy) revealed deformities and alterations in the morphology of the phytopathogen upon interaction with LPs. Sh420 LPs have been shown in grape tests to be effective against F. graminearum infection and to stimulate antioxidant activity in fruits by avoiding rust and gray lesions. The overall findings of this study highlight the potential of Sh420 lipopeptides as an effective biological control agent against F. graminearum infestations.IMPORTANCEThis study addresses the potential of lipopeptide (LP) extracts obtained from the strain identified as Bacillus siamensis Sh420. This Sh420 isolate acts as a crucial player in providing a sustainable and environmentally friendly alternative to chemical fungicides for suppressing Fusarium graminearum phytopathogen. Moreover, these LPs can reduce ergosterol content in the phytopathogen influencing the overall structure and stability of its plasma membrane. PCR screening provided confirmation regarding the existence of genes responsible for biosynthesizing antifungal LPs in the genomic DNA of Sh420. Several antibiotic lipopeptide compounds were identified from this bacterial crude extract using ultra-high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry. Microscopic investigations revealed deformities and alterations in the morphology of F. graminearum upon interaction with LPs. Furthermore, studies on fruit demonstrated the efficacy of Sh420 LPs in mitigating F. graminearum infection and stimulating antioxidant activity in fruits, preventing rust and gray lesions.

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

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

Targeting yeast topoisomerase II by imidazo and triazoloacridinone derivatives resulting in their antifungal activity

Fungal pathogens are considered as serious factors for deadly diseases and are a case of medical concern. Invasive fungal infections also complicate the clinical course of COVID-19, leading to a significant increase in mortality. Furthermore, fungal strains' multidrug resistance has increased the demand for antifungals with a different mechanism of action. The present study aimed to identify antifungal compounds targeting yeast topoisomerase II (yTOPOII) derived from well-known human topoisomerase II (hTOPOII) poisons C-1305 and C-1311. Two sets of derivatives: triazoloacridinones (IKE1-8) and imidazoacridinones (IKE9-14) were synthetized and evaluated with a specific emphasis on the molecular mechanism of action. Our results indicated that their effectiveness as enzyme inhibitors was not solely due to intercalation ability but also as a result of influence on catalytic activity by the formation of covalent complexes between plasmid DNA and yTOPOII. Lysine conjunction increased the strength of the compound's interaction with DNA and improved penetration into the fungal cells. Triazoloacridinone derivatives in contrast to starting compound C-1305 exhibited moderate antifungal activity and at least twice lower cytotoxicity. Importantly, compounds (IKE5-8) were not substrates for multidrug ABC transporters whereas a derivative conjugated with lysine (IKE7), showed the ability to overcome C. glabrata fluconazole-resistance (MIC 32-64 µg mL-1).

Synthetic product-based approach toward potential antileishmanial drug development

Leishmaniasis is a parasitic disease and is categorized as a tropically neglected disease (NTD) with no effective vaccines available. The available chemotherapeutics against leishmaniasis are associated with an increase in the incidence of toxicity and drug resistance. Consequently, targeting metabolic pathways and enzymes of parasites which differs from the mammalian host can be exploited to treat and overcome the resistance. The classical methods of identifying the structural fragments and the moieties responsible for the biological activities from the standard compounds and their modification are options for developing more effective novel compounds. Significant progress has been made in refining the development of potent non-toxic molecules and addressing the limitations of the current treatment available. Several examples of synthetic product-based approach utilizing their core heterocyclic rings including furan, pyrrole, thiazole, imidazole, pyrazole, triazole, quinazoline, quinoline, pyrimidine, coumarin, indole, acridine, oxadiazole, purine, chalcone, carboline, phenanthrene and metal containing derivatives and their structure-activity relationships are discussed in this review. It also analyses the groups/fragments interacting with the host cell receptors and will support the medicinal chemists with novel antileishmanial agents.

Antifungal therapy of Candida biofilms: Past, present and future

Virtually all Candida species linked to clinical candidiasis are capable of forming highly resistant biofilms on different types of surfaces, which poses an additional significant threat and further complicates therapy of these infections. There is a scarcity of antifungal agents, and their effectiveness, particularly against biofilms, is limited. Here we provide a historical perspective on antifungal agents and therapy of Candida biofilms. As we reflect upon the past, consider the present, and look towards the future of antifungal therapy of Candida biofilms, we believe that there are reasons to remain optimistic, and that the major challenges of Candida biofilm therapy can be conquered within a reasonable timeframe.

Tuning sterol extraction kinetics yields a renal-sparing polyene antifungal

Decades of previous efforts to develop renal-sparing polyene antifungals were misguided by the classic membrane permeabilization model1. Recently, the clinically vital but also highly renal-toxic small-molecule natural product amphotericin B was instead found to kill fungi primarily by forming extramembraneous sponge-like aggregates that extract ergosterol from lipid bilayers2-6. Here we show that rapid and selective extraction of fungal ergosterol can yield potent and renal-sparing polyene antifungals. Cholesterol extraction was found to drive the toxicity of amphotericin B to human renal cells. Our examination of high-resolution structures of amphotericin B sponges in sterol-free and sterol-bound states guided us to a promising structural derivative that does not bind cholesterol and is thus renal sparing. This derivative was also less potent because it extracts ergosterol more slowly. Selective acceleration of ergosterol extraction with a second structural modification yielded a new polyene, AM-2-19, that is renal sparing in mice and primary human renal cells, potent against hundreds of pathogenic fungal strains, resistance evasive following serial passage in vitro and highly efficacious in animal models of invasive fungal infections. Thus, rational tuning of the dynamics of interactions between small molecules may lead to better treatments for fungal infections that still kill millions of people annually7,8 and potentially other resistance-evasive antimicrobials, including those that have recently been shown to operate through supramolecular structures that target specific lipids9.

Unraveling the serial glycosylation in the biosynthesis of steroidal saponins in the medicinal plant Paris polyphylla and their antifungal action

Sugar-sugar glycosyltransferases play important roles in constructing complex and bioactive saponins. Here, we characterized a series of UDP-glycosyltransferases responsible for biosynthesizing the branched sugar chain of bioactive steroidal saponins from a widely known medicinal plant Paris polyphylla var. yunnanensis. Among them, a 2'-O-rhamnosyltransferase and three 6'-O-glucosyltrasferases catalyzed a cascade of glycosylation to produce steroidal diglycosides and triglycosides, respectively. These UDP-glycosyltransferases showed astonishing substrate promiscuity, resulting in the generation of a panel of 24 terpenoid glycosides including 15 previously undescribed compounds. A mutant library containing 44 variants was constructed based on the identification of critical residues by molecular docking simulations and protein model alignments, and a mutant UGT91AH1Y187A with increased catalytic efficiency was obtained. The steroidal saponins exhibited remarkable antifungal activity against four widespread strains of human pathogenic fungi attributed to ergosterol-dependent damage of fungal cell membranes, and 2'-O-rhamnosylation appeared to correlate with strong antifungal effects. The findings elucidated the biosynthetic machinery for their production of steroidal saponins and revealed their potential as new antifungal agents.

Drug-Resistant Aspergillus spp.: A Literature Review of Its Resistance Mechanisms and Its Prevalence in Europe

Infections due to the Aspergillus species constitute an important challenge for human health. Invasive aspergillosis represents a life-threatening disease, mostly in patients with immune defects. Drugs used for fungal infections comprise amphotericin B, triazoles, and echinocandins. However, in the last decade, an increased emergence of azole-resistant Aspergillus strains has been reported, principally belonging to Aspergillus fumigatus species. Therefore, both the early diagnosis of aspergillosis and its epidemiological surveillance are very important to establish the correct antifungal therapy and to ensure a successful patient outcome. In this paper, a literature review is performed to analyze the prevalence of Aspergillus antifungal resistance in European countries. Amphotericin B resistance is observed in 2.6% and 10.8% of Aspergillus fumigatus isolates in Denmark and Greece, respectively. A prevalence of 84% of amphotericin B-resistant Aspergillus flavus isolates is reported in France, followed by 49.4%, 35.1%, 21.7%, and 20% in Spain, Portugal, Greece, and amphotericin B resistance of Aspergillus niger isolates is observed in Greece and Belgium with a prevalence of 75% and 12.8%, respectively. The prevalence of triazole resistance of Aspergillus fumigatus isolates, the most studied mold obtained from the included studies, is 0.3% in Austria, 1% in Greece, 1.2% in Switzerland, 2.1% in France, 3.9% in Portugal, 4.9% in Italy, 5.3% in Germany, 6.1% in Denmark, 7.4% in Spain, 8.3% in Belgium, 11% in the Netherlands, and 13.2% in the United Kingdom. The mechanism of resistance is mainly driven by the TR34/L98H mutation. In Europe, no in vivo resistance is reported for echinocandins. Future studies are needed to implement the knowledge on the spread of drug-resistant Aspergillus spp. with the aim of defining optimal treatment strategies.

Evaluation of Antifungal Selective Toxicity Using Candida glabrata ERG25 and Human SC4MOL Knock-In Strains

With only four classes of antifungal drugs available for the treatment of invasive systemic fungal infections, the number of resistant fungi is increasing, highlighting the urgent need for novel antifungal drugs. Ergosterol, an essential component of cell membranes, and its synthetic pathway have been targeted for antifungal drug development. Sterol-C4-methyl monooxygenase (Erg25p), which is a greater essential target than that of existing drugs, represents a promising drug target. However, the development of antifungal drugs must consider potential side effects, emphasizing the importance of evaluating their selective toxicity against fungi. In this study, we knocked in ERG25 of Candida glabrata and its human ortholog, SC4MOL, in ERG25-deleted Saccharomyces cerevisiae. Utilizing these strains, we evaluated 1181-0519, an Erg25p inhibitor, that exhibited selective toxicity against the C. glabrata ERG25 knock-in strain. Furthermore, 1181-0519 demonstrated broad-spectrum antifungal activity against pathogenic Candida species, including Candida auris. The approach of utilizing a gene that is functionally conserved between yeast and humans and subsequently screening for molecular target drugs enables the identification of selective inhibitors for both species.

Recent developments in membrane targeting antifungal agents to mitigate antifungal resistance

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

Artemisinins inhibit oral candidiasis caused by Candida albicans through the repression on its hyphal development

Candida albicans is the most abundant fungal species in oral cavity. As a smart opportunistic pathogen, it increases the virulence by switching its forms from yeasts to hyphae and becomes the major pathogenic agent for oral candidiasis. However, the overuse of current clinical antifungals and lack of new types of drugs highlight the challenges in the antifungal treatments because of the drug resistance and side effects. Anti-virulence strategy is proved as a practical way to develop new types of anti-infective drugs. Here, seven artemisinins, including artemisinin, dihydroartemisinin, artemisinic acid, dihydroartemisinic acid, artesunate, artemether and arteether, were employed to target at the hyphal development, the most important virulence factor of C. albicans. Artemisinins failed to affect the growth, but significantly inhibited the hyphal development of C. albicans, including the clinical azole resistant isolates, and reduced their damage to oral epithelial cells, while arteether showed the strongest activities. The transcriptome suggested that arteether could affect the energy metabolism of C. albicans. Seven artemisinins were then proved to significantly inhibit the productions of ATP and cAMP, while reduced the hyphal inhibition on RAS1 overexpression strain indicating that artemisinins regulated the Ras1-cAMP-Efg1 pathway to inhibit the hyphal development. Importantly, arteether significantly inhibited the fungal burden and infections with no systemic toxicity in the murine oropharyngeal candidiasis models in vivo caused by both fluconazole sensitive and resistant strains. Our results for the first time indicated that artemisinins can be potential antifungal compounds against C. albicans infections by targeting at its hyphal development.

Tannic Acid Interfacial Modification of Prochloraz Ethyl Cellulose Nanoparticles for Enhancing the Antimicrobial Effect and Biosafety of Fungicides

With the poorly soluble and intrinsically unstable feature, prochloraz (Pro) was confronted with lower bioavailability in the crop defense against fungal erosion. Therefore, it was a challenging project to explore the innovative antifungal compound delivery system for improving bioavailability. The superior adhesive fungicide formulation was supposed to be an efficient pathway to enhance transmembrane permeability and biological activity. According to abundant phenolic hydroxyl groups, tannic acid (TA) was an ideal modified adhesive biomaterial to improve interfacial interactions. The fundamental purpose of this research was focused on the synergistic mechanism of TA-interfacial-modified Pro-ethyl cellulose (EC) nanoparticles for improving bioavailability and biosafety. In the stability test, TA-modified Pro-EC nanoparticles had the capacity to reduce Pro initial release burst, extending a persistent validity and improving anti-photodegradation property. The toxicity index of Pro-EC and Pro-EC-TA was approximately 2.93-fold and 4.96-fold that of Pro technical against Fusarium graminearum (F. graminearum), respectively. Compared with nonmodified EC nanoparticles, TA-modified EC nanoparticles obtained eminent transmembrane permeability and superior adherence ability to F. graminearum, for hydroxyl and carboxyl groups of TA to enhance interaction with target cell membranes. The contents of cellular reactive oxygen species induced by Pro-EC and Pro-EC-TA nanoparticles were about 2.31 times and 3.00 times that of the control check (CK), respectively. Compared to the CK group, the membrane potential and ergosterol values of F. graminearum treated with Pro-EC-TA nanoparticles were drastically reduced by 74.91 and 56.20%, respectively. In the biosafety assay, the maximum half-lethal concentration value of the TA-modified Pro-EC nanoparticles indicated that the acute toxicity of the Pro-EC-TA nanoparticles to adult zebrafish was approximately 8.34-fold reduced compared to that of the Pro technical. These findings demonstrated that the successful interfacial modification of Pro-EC nanoparticles with TA was a highly efficient, environmentally safe, and promising alternative for sustainable agricultural application, thus making the fungicide formulation process more simplified, easier fabrication, and lower cost.

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

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