Increased Degree of Unsaturation in the Lipid of Antifungal Cationic Amphiphiles Facilitates Selective Fungal Cell Disruption

Programming lipopeptide nanotherapeutics for tandem treatment of postsurgical infection and melanoma recurrence

Tumor recurrence and chronic bacterial infection constitute two major criteria in postsurgical intervention for malignant melanoma. One plausible strategy is the equipment of consolidation therapy after surgery, which relies on adjuvants to eliminate the residual tumor cells and inhibit bacterial growth. Until now, a number of proof-of-concept hybrid nanoadjuvants have been proposed to combat tumor recurrence and postsurgical bacterial infection, which may suffer from the potential bio-unsafety or involve complex design and synthesis. The batch-to-batch inconsistencies in drug composition further delay the clinical trials. To circumvent these issues, herein we develop a programmable strategy to generate lipopeptide nanotherapeutics with identical constitution for tandem intervention of postsurgical bacterial infection and cancer recurrence of melanoma. Increasing the number of hydrophobic linoleic acid within lipopeptides has been found to be a simple and practical strategy to improve the therapeutic outcomes for both tumor cells and bacteria. Self-assembled lipopeptide nanotherapeutics with two linoleic acid molecules possesses excellent antitumor activity and antimicrobial function toward both susceptible strains and drug-resistant bacteria. Arising from the incorporation of unsaturated linoleic acid, the unavoidable hemolysis of cationic peptide drugs was effectively alleviated. In vivo therapeutic abilities of postsurgical infection and tumor recurrence were investigated in BALB/c nude mice bearing a B16-F10 tumor model, with an incomplete surgical resection and in situ infection by methicillin-resistant Staphylococcus aureus (MRSA). Self-assembled lipopeptide nanotherapeutics could effectively inhibit cancer cell growth and bacterial infection, as well as promote wound healing. The easily scalable large-scale production, broad-spectrum antitumor and antibacterial bioactivities as well as fixed component endows lipopeptide nanotherapeutics as promising adjuvants for clinically postsurgical therapy of melanoma.

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.

Biodegradable Cationic and Ionizable Cationic Lipids: A Roadmap for Safer Pharmaceutical Excipients

Cationic and ionizable cationic lipids are broadly applied as auxiliary agents, but their use is associated with adverse effects. If these excipients are rapidly degraded to endogenously occurring metabolites such as amino acids and fatty acids, their toxic potential can be minimized. So far, synthesized and evaluated biodegradable cationic and ionizable cationic lipids already showed promising results in terms of functionality and safety. Within this review, an overview about the different types of such biodegradable lipids, the available building blocks, their synthesis and cleavage by endogenous enzymes is provided. Moreover, the relationship between the structure of the lipids and their toxicity is described. Their application in drug delivery systems is critically discussed and placed in context with the lead compounds used in mRNA vaccines. Moreover, their use as preservatives is reviewed, guidance for their design is provided, and an outlook on future developments is given.

Small Molecule IITR00693 (2-Aminoperimidine) Synergizes Polymyxin B Activity against Staphylococcus aureus and Pseudomonas aeruginosa

The rise of antibiotic resistance among skin-infecting pathogens poses an urgent threat to public health and has fueled the search for new therapies. Enhancing the potency of currently used antibiotics is an alternative for the treatment of infections caused by drug-resistant pathogens. In this study, we aimed to identify a small molecule that can potentiate currently used antibiotics. IITR00693 (2-aminoperimidine), a novel antibacterial small molecule, potentiates the antibacterial activity of polymyxin B against Staphylococcus aureus and Pseudomonas aeruginosa. Herein, we investigated in detail the mode of action of this interaction and the molecule's capability to combat soft-tissue infections caused by S. aureus and P. aeruginosa. A microdilution checkerboard assay was performed to determine the synergistic interaction between polymyxin B and IITR00693 in clinical isolates of S. aureus and P. aeruginosa. Time-kill kinetics, post-antibiotic effect, and resistance generation studies were performed to assess the pharmacodynamics of the combination. Assays based on different fluorescent probes were performed to decipher the mechanism of action of this combination. The in vivo efficacy of the IITR00693-polymyxin B combination was determined in a murine acute wound infection model. IITR00693 exhibited broad-spectrum antibacterial activity. IITR00693 potentiated polymyxin B and colistin against polymyxin-resistant S. aureus. IITR00693 prevented the generation of resistant mutants against multiple antibiotics. The IITR00693-polymyxin B combination decreased the S. aureus count by >3 log₁₀ CFU in a murine acute wound infection model. IITR00693 is a potential and promising candidate for the treatment of soft-tissue infections along with polymyxins.

Amphiphilic aminoglycosides: Modifications that revive old natural product antibiotics

Widely-used Streptomyces-derived antibacterial aminoglycosides have encountered challenges because of antibiotic resistance and toxicity. Today, they are largely relegated to medicinal topical applications. However, chemical modification to amphiphilic aminoglycosides can revive their efficacy against bacterial pathogens and expand their targets to other pathogenic microbes and disorders associated with hyperactive connexin hemichannels. For example, amphiphilic versions of neomycin and neamine are not subject to resistance and have expanded antibacterial spectra, and amphiphilic kanamycins are effective antifungals and have promising therapeutic uses as connexin hemichannel inhibitors. With further research and discoveries aimed at improved formulations and delivery, amphiphilic aminoglycosides may achieve new horizons in pharmacopeia and agriculture for Streptomyces aminoglycosides beyond just serving as topical antibacterials.

Cationic, Steroid-Based Imidazolium Amphiphiles Show Tunable Backbone-Dependent Membrane Selectivity in Fungi

Cationic amphiphiles have been reported to show broad antimicrobial activity. The potential for antimicrobial resistance to these molecules is low owing to their general cell membrane permeabilizing mode of action. However, their applications are often limited by toxicity resulting from their low selectivity for microbial cell membranes. Herein, we report a library of cationic, steroid-based imidazolium amphiphiles that show tunable antifungal activity in a variety of fungal pathogens of the genus Candida. We show that adoption of an ergosterol-derived backbone increases antifungal activity while modestly affecting hemolytic activity, thereby increasing overall selectivity by more than 8-fold in comparison to cholesterol-derived imidazolium salts. We hypothesize that this effect is caused by a privileged integration of the ergosterol-derived salts into fungal membranes leading to increased membrane disorder. We propose that these findings offer a useful platform for the development of improved amphiphilic fungicides.

Guanylated Hyperbranched Polylysines with High In Vitro and In Vivo Antifungal Activity

With the rapid growth of fungal infections and the emergence of multi-drug resistant (MDR) fungal strains, new antifungals with novel mechanisms are a pressing need to tackle this emerging health problem. Herein it is reported for the first time that hyperbranched polylysine (HPL) shows antifungal activities against Candida, especially for drug-sensitive and MDR C. albicans strains, and broad-spectrum antibacterial activities against both Gram-negative and Gram-positive bacteria. The high antimicrobial activities are ascribed to the high charge density and compact size of the globular structure of HPL. The in vitro antifungal activities of HPL3 are further enhanced by the modification of amine groups to form guanylated polylysines (HPL3-Gxs). Similar to antimicrobial peptides (AMPs), HPLs and HPL3-Gxs interact with and lyse the membranes of microbes, which mitigates the emergence of drug resistance. HPLs and HPL3-Gxs demonstrate excellent in vivo antimicrobial efficacies against both lethal C. albicans challenge in the invasive candidiasis model and lethal Methicillin resistant Staphylococcus aureus challenge in the peritonitis model, and have potentials as broad-spectrum antimicrobials.

Mycobacterial Membranes as Actionable Targets for Lipid-Centric Therapy in Tuberculosis

Infectious diseases remain significant health concerns worldwide, and resistance is particularly common in patients with tuberculosis caused by Mycobacterium tuberculosis. The development of anti-infectives with novel modes of action may help overcome resistance. In this regard, membrane-active agents, which modulate membrane components essential for the survival of pathogens, present attractive antimicrobial agents. Key advantages of membrane-active compounds include their ability to target slow-growing or dormant bacteria and their favorable pharmacokinetics. Here, we comprehensively review recent advances in the development of membrane-active chemotypes that target mycobacterial membranes and discuss clinically relevant membrane-active antibacterial agents that have shown promise in counteracting bacterial infections. We discuss the relationship between the membrane properties and the synthetic requirements within the chemical scaffold, as well as the limitations of current membrane-active chemotypes. This review will lay the chemical groundwork for the development of membrane-active antituberculosis agents and will foster the discovery of more effective antitubercular agents.

Interest of Homodialkyl Neamine Derivatives against Resistant P. aeruginosa, E. coli, and β-Lactamases-Producing Bacteria-Effect of Alkyl Chain Length on the Interaction with LPS

Development of novel therapeutics to treat antibiotic-resistant infections, especially those caused by ESKAPE pathogens, is urgent. One of the most critical pathogens is P. aeruginosa, which is able to develop a large number of factors associated with antibiotic resistance, including high level of impermeability. Gram-negative bacteria are protected from the environment by an asymmetric Outer Membrane primarily composed of lipopolysaccharides (LPS) at the outer leaflet and phospholipids in the inner leaflet. Based on a large hemi-synthesis program focusing on amphiphilic aminoglycoside derivatives, we extend the antimicrobial activity of 3′,6-dinonyl neamine and its branched isomer, 3′,6-di(dimethyloctyl) neamine on clinical P. aeruginosa, ESBL, and carbapenemase strains. We also investigated the capacity of 3′,6-homodialkyl neamine derivatives carrying different alkyl chains (C7–C11) to interact with LPS and alter membrane permeability. 3′,6-Dinonyl neamine and its branched isomer, 3′,6-di(dimethyloctyl) neamine showed low MICs on clinical P. aeruginosa, ESBL, and carbapenemase strains with no MIC increase for long-duration incubation. In contrast from what was observed for membrane permeability, length of alkyl chains was critical for the capacity of 3′,6-homodialkyl neamine derivatives to bind to LPS. We demonstrated the high antibacterial potential of the amphiphilic neamine derivatives in the fight against ESKAPE pathogens and pointed out some particular characteristics making the 3′,6-dinonyl- and 3′,6-di(dimethyloctyl)-neamine derivatives the best candidates for further development.

Luminescent Amphiphilic Aminoglycoside Probes to Study Transfection

We report the characterization of amphiphilic aminoglycoside conjugates containing luminophores with aggregation-induced emission properties as transfection reagents. These inherently luminescent transfection vectors are capable of binding plasmid DNA through electrostatic interactions; this binding results in an emission "on" signal due to restriction of intramolecular motion of the luminophore core. The luminescent cationic amphiphiles effectively transferred plasmid DNA into mammalian cells (HeLa, HEK 293T), as proven by expression of a red fluorescent protein marker. The morphologies of the aggregates were investigated by microscopy as well as ζ-potential and dynamic light-scattering measurements. The transfection efficiencies using luminescent cationic amphiphiles were similar to that of the gold-standard transfection reagent Lipofectamine® 2000.

Design Guidelines for Cationic Pillar[n]arenes that Prevent Biofilm Formation by Gram-Positive Pathogens

Bacterial biofilms are a major threat to human health, causing persistent infections that lead to millions of fatalities worldwide every year. Biofilms also cause billions of dollars of damage annually by interfering with industrial processes. Recently, cationic pillararenes were found to be potent inhibitors of biofilm formation in Gram-positive bacteria. To identify the structural features of pillararenes that result in antibiofilm activity, we evaluated the activity of 16 cationic pillar[5]arene derivatives including that of the first cationic water-soluble pillar[5]arene-based rotaxane. Twelve of the derivatives were potent inhibitors of biofilm formation by Gram-positive pathogens. Structure activity analyses of our pillararene derivatives indicated that positively charged head groups are critical for the observed antibiofilm activity. Although certain changes in the lipophilicity of the substituents on the positively charged head groups are tolerated, dramatic elevation in the hydrophobicity of the substituents or an increase in steric bulk on these positive charges abolishes the antibiofilm activity. An increase in the overall positive charge from 10 to 20 did not affect the activity significantly, but pillararenes with 5 positive charges and 5 long alkyl chains had reduced activity. Surprisingly, the cavity of the pillar[n]arene is not essential for the observed activity, although the macrocyclic structure of the pillar[n]arene core, which facilitates the clustering of the positive charges, appears important. Interestingly, the compounds found to be efficient inhibitors of biofilm formation were nonhemolytic at concentrations that are ∼100-fold of their MBIC₅₀ (the minimal concentration of a compound at which at least 50% inhibition of biofilm formation was observed compared to untreated cells). The structure–activity relationship guidelines established here pave the way for a rational design of potent cationic pillar[n]arene-based antibiofilm agents.

Fresh Molecular Concepts to Extend the Lifetimes of Old Antimicrobial Drugs

Antimicrobial drug development generally initiates with target identification and mode of action studies. Often, emergence of resistance and/or undesired side effects that are discovered only after prolonged clinical use, result in discontinuation of clinical use. Since the cost and time required for improvement of existing drugs are considerably lower than those required for the development of novel drugs, academic and pharmaceutical company researchers pursue this direction. In this account we describe selected examples of how chemical probes generated from antimicrobial drugs and chemical and enzymatic modifications of these drugs have been used to modify modes of action, block mechanisms of resistance, or reduce side effects, improving performance. These examples demonstrate how new and comprehensive mechanistic insights can be translated into fresh concepts for development of next-generation antimicrobial agents.

Broad-Spectrum Antifungal Agents: Fluorinated Aryl- and Heteroaryl-Substituted Hydrazones

Fluorinated aryl- and heteroaryl-substituted monohydrazones displayed excellent broad-spectrum activity against various fungal strains, including a panel of clinically relevant Candida auris strains relative to a control antifungal agent, voriconazole (VRC). These monohydrazones displayed less hemolysis of murine red blood cells than that of VRC at the same concentrations, possessed fungicidal activity in a time-kill study, and exhibited no mammalian cell cytotoxicity. In addition, these monohydrazones prevented the formation of biofilms that otherwise block antibiotic effectiveness and did not trigger the development of resistance when exposed to C. auris AR Bank # 0390 over 15 passages.

Synthesis and Investigation of Tetrahydro-β-carboline Derivatives as Inhibitors of Plant Pathogenic Fungi

A series of tetrahydro-ß-carbolines substituted with an alkyl or acyl side chain was synthesized and screened for its antifungal activity against plant pathogenic fungi (Bipolaris oryzae, Curvularia lunata, Fusarium semitectum, and Fusarium fujikuroi). The structure activity relationship revealed that the substituent at the piperidine nitrogen plays an important role for increasing antifungal activities. In this series, 2-octyl-2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole (3g) displayed potent antifungal activities with a minimum inhibitory concentration of 0.1 μg/mL, including good inhibitory activity to the radial growth of fungus at a concentration of 100 μg/mL compared to amphotericin B.

Serum Prevents Interactions between Antimicrobial Amphiphilic Aminoglycosides and Plasma Membranes

Antimicrobial cationic amphiphiles have broad-spectrum activity, and microbes do not readily develop resistance to these agents, highlighting their clinical and industrial potential. Cationic amphiphiles perturb the integrity of membranes leading to cell death, and the lack of discrimination between microbial and mammalian plasma membranes is thought to be one of the main barriers of using these agents for the treatment of systemic infections. Here, we describe the synthesis and study of 20 antimicrobial cationic amphiphiles that are derivatives of the aminoglycoside nebramine with different numbers of alkyl chain ethers that differ in length and degree of unsaturation. We determined antifungal activities and evaluated hemoglobin release from red blood cells as a measure of membrane selectivity and analyzed how serum influences these activities. Microscopic images revealed morphological transformations of red blood cells from the normal double-disc shape to empty ghost cells upon treatment with the cationic amphiphiles. Antifungal activity, hemolysis, and morphological changes in red blood cells decreased as the percentage of serum in the culture medium was increased. In images of red blood cells treated with fluorescently labeled amphiphilic nebramine probes, the accumulation of the cationic amphiphiles in the membranes decreased as serum concentration increased. This suggests that, in addition to its known effect of preventing the deformability of red blood cells, serum prevents interactions between cationic amphiphiles and the plasma membrane. The results of this study indicate that biological activities of cationic amphiphiles are abrogated in serum. Thus, these agents are suitable for external and industrial uses but probably not for effective treatment of systemic infections.

Novel naphthylamide derivatives as dual-target antifungal inhibitors: Design, synthesis and biological evaluation

Fungal infections have become a serious medical problem due to the high infection rate and the frequent emergence of drug resistance. Squalene epoxidase (SE) and 14α-demethylase (CYP51) are considered as the important antifungal targets, they can show the synergistic effect on antifungal therapy. In the study, a series of active fragments were screened through the method of De Novo Link, and these active fragments with the higher Ludi_Scores were selected, which can show the obvious binding ability with the dual targets (SE, CYP51). Subsequently, three series of target compounds with naphthyl amide scaffolds were constructed by connecting these core fragments, and their structures were synthesized. Most of compounds showed the antifungal activity in the treatment of pathogenic fungi. It was worth noting that compounds 10b-5 and 17a-2 with the excellent broad-spectrum antifungal properties also exhibited the obvious antifungal effects against drug-resistant fungi. Preliminary mechanism study has proved these target compounds can block the biosynthesis of ergosterol by inhibiting the activity of dual targets (SE, CYP51). Furthermore, target compounds 10-5 and 17a-2 with low toxicity side effects also demonstrated the excellent pharmacological effects in vivo. The molecular docking and ADMET prediction were performed, which can guide the optimization of subsequent lead compounds.

Amphiphilic Aminoglycosides as Medicinal Agents

The conjugation of hydrophobic group(s) to the polycationic hydrophilic core of the antibiotic drugs aminoglycosides (AGs), targeting ribosomal RNA, has led to the development of amphiphilic aminoglycosides (AAGs). These drugs exhibit numerous biological effects, including good antibacterial effects against susceptible and multidrug-resistant bacteria due to the targeting of bacterial membranes. In the first part of this review, we summarize our work in identifying and developing broad-spectrum antibacterial AAGs that constitute a new class of antibiotic agents acting on bacterial membranes. The target-shift strongly improves antibiotic activity against bacterial strains that are resistant to the parent AG drugs and to antibiotic drugs of other classes, and renders the emergence of resistant Pseudomonas aeruginosa strains highly difficult. Structure–activity and structure–eukaryotic cytotoxicity relationships, specificity and barriers that need to be crossed in their development as antibacterial agents are delineated, with a focus on their targets in membranes, lipopolysaccharides (LPS) and cardiolipin (CL), and the corresponding mode of action against Gram-negative bacteria. At the end of the first part, we summarize the other recent advances in the field of antibacterial AAGs, mainly published since 2016, with an emphasis on the emerging AAGs which are made of an AG core conjugated to an adjuvant or an antibiotic drug of another class (antibiotic hybrids). In the second part, we briefly illustrate other biological and biochemical effects of AAGs, i.e., their antifungal activity, their use as delivery vehicles of nucleic acids, of short peptide (polyamide) nucleic acids (PNAs) and of drugs, as well as their ability to cleave DNA at abasic sites and to inhibit the functioning of connexin hemichannels. Finally, we discuss some aspects of structure–activity relationships in order to explain and improve the target selectivity of AAGs.

Detectives and helpers: Natural products as resources for chemical probes and compound libraries

About 70% of the drugs in use are derived from natural products, either used directly or in chemically modified form. Among all possible small molecules (not greater than 5 kDa), only a few of them are biologically active. Natural product libraries may have a higher rate of finding "hits" than synthetic libraries, even with the use of fewer compounds. This is due to the complementarity between the "chemical space" of small molecules and biological macromolecules such as proteins, DNA and RNA, in addition to the three-dimensional complexity of NPs. Chemical probes are molecules which aid in the elucidation of the biological mechanisms behind the action of drugs or drug-like molecules by binding with macromolecular/cellular interaction partners. Probe development and application have been spurred by advancements in photoaffinity label synthesis, affinity chromatography, activity based protein profiling (ABPP) and instrumental methods such as cellular thermal shift assay (CETSA) and advanced/hyphenated mass spectrometry (MS) techniques, as well as genome sequencing and bioengineering technologies. In this review, we restrict ourselves to a survey of natural products (including peptides/mini-proteins and excluding antibodies), which have been applied largely in the last 5 years for the target identification of drugs/drug-like molecules used in research on infectious diseases, and the description of their mechanisms of action.

Unsaturation and Polar Head Effect on Gelation, Bioactive Release, and Cr/Cu Removal Ability of Glycolipids

Designing of multifunctional soft and smart materials from natural sources is a useful strategy for producing safer chemicals having potential applications in biomedical research and pharmaceutical industries. Herein, eight glycolipids with variation in unsaturation of hydrophobic tail and polar headgroup size were designed. The effect of unsaturation in the tail group and headgroup size on gelation ability, and mechanical and thermal stability of glycolipid hydro/organogels was studied to understand structure and property relationship. Glycolipids are functional amphiphilic molecules having potential applications in the field of drug delivery and metal removal. The encapsulation capacity and kinetic release behavior of hydrophobic/hydrophilic bioactives like curcumin/riboflavin from the hydrophobic/hydrophilic pockets of glycolipids hydro/organogels was examined. A significant observation was that the glucamine moiety of the glycolipid headgroup plays a vital role in removal of Cr and Cu from oil/water biphasic systems. Typical functions of the glycolipid hydrogels are metal chelation and enzyme-triggered release behavior, enabled them as promising material for Cr, Cu removal from edible oils and controlled release of water soluble/insoluble bioactives.

A comprehensive overview of the medicinal chemistry of antifungal drugs: perspectives and promise

The emergence of new fungal pathogens makes the development of new antifungal drugs a medical imperative that in recent years motivates the talents of numerous investigators across the world. Understanding not only the structural families of these drugs but also their biological targets provides a rational means for evaluating the merits and selectivity of new agents for fungal pathogens and normal cells. An equally important aspect of modern antifungal drug development takes a balanced look at the problems of drug potency and drug resistance. The future development of new antifungal agents will rest with those who employ synthetic and semisynthetic methodology as well as natural product isolation to tackle these problems and with those who possess a clear understanding of fungal cell architecture and drug resistance mechanisms. This review endeavors to provide an introduction to a growing and increasingly important literature, including coverage of the new developments in medicinal chemistry since 2015, and also endeavors to spark the curiosity of investigators who might enter this fascinatingly complex fungal landscape.

Promising antifungal agents: A minireview

In the recent past, prevalence of life threatening fungal diseases have increased rapidly in immune-compromised cases such as acquired immunodeficiency syndrome (AIDS), cancer, organ transplant etc. Side by side, the appearance of drug resistance to the presently available antifungal therapeutics is on a rapid rise. It has become a top priority for the academia and pharmaceutical industries to develop new antifungal agents able to combat this resistance, and at the same time, possess potential broad spectrum of activity and minimum toxicity. An understanding of the pharmacological interactions between antifungal agents and their targets offers opportunities for design of new therapeutics. This review discusses the various methodology of drug design, structure activity relationships (SARs), and mode of action of variety of new antifungal agents.

Arginolipid: A membrane-active antifungal agent and its synergistic potential to combat drug resistance in clinical Candida isolates

Antifungal drug resistance exhibits a major clinical challenge for treating nosocomial fungal infections. To find a possible solution, we synthesized and studied the antifungal activities of three different arginolipids (N^α -acyl-arginine ethyl ester) against clinical drug-resistant isolates of Candida. The most active arginolipid, oleoyl arginine ethyl ester (OAEE) consisting of a long unsaturated hydrophobic chain, was tested for its mode of action, which revealed that it altered ergosterol biosynthesis and compromised the fungal cell membrane. Also, OAEE was found to exhibit synergistic interactions with fluconazole (FLU) or amphotericin B (AmB) against planktonic Candida cells, wherein it reduced the inhibitory concentrations of these drugs to their in vitro susceptible range. Studies conducted against the C. tropicalis biofilm revealed that the OAEE+AmB combination synergistically reduced the metabolic activity and hyphal density in biofilms, whereas OAEE+FLU was found to be additive against most cases. Finally, the evaluated selective toxicity of OAEE toward fungal cells over mammalian cells could establish it as an alternative treatment for combating drug-resistant Candida infections.

Scalable and cost-effective tosylation-mediated synthesis of antifungal and fungal diagnostic 6″-Modified amphiphilic kanamycins

Amphiphilic kanamycins bearing hydrophobic modifications at the 6″ position have attracted interest due to remarkable antibacterial-to-antifungal switches in bioactivity. In this report, we investigate a hurdle that hinders practical applications of these amphiphilic kanamycins: a cost-effective synthesis that allows the incorporation of various connecting functionalities to which the hydrophobic moieties are connected to the kanamycin core. A cost-effective tosylation enables various modifications at the 6″ position, which is scalable to a 90-g scale. The connecting functionalities, such as amine and thiol, were not the dominant factor for biological activity. Instead, the linear chain length played the decisive role. Amphiphilic kanamycin attached with tetradecyl (C14) or hexadecyl (C16) showed strong antifungal and modest antibacterial activities than with shorter chains (C6-C10). However, increases in chain length were closely correlated with an increase in HeLa cell toxicity. Thus, a compromise between the antimicrobial activities and cytotoxicities, for optimal efficacy of amphiphilic kanamycins may contain chain lengths between C8 and C12. Finally, the described synthetic protocol also allows the preparation of a fluorescent amphiphilic kanamycin selective toward fungi.

Guiding Drugs to Target-Harboring Organelles: Stretching Drug-Delivery to a Higher Level of Resolution

The ratio between the dose of drug required for optimal efficacy and the dose that causes toxicity is referred to as the therapeutic window. This ratio can be increased by directing the drug to the diseased tissue or pathogenic cell. For drugs targeting fungi and malignant cells, the therapeutic window can be further improved by increasing the resolution of drug delivery to the specific organelle that harbors the drug's target. Organelle targeting is challenging and is, therefore, an under-exploited strategy. Here we provide an overview of recent advances in control of the subcellular distribution of small molecules with the focus on chemical modifications. Highlighted are recent examples of active and passive organelle-specific targeting by incorporation of organelle-directing molecular determinants or by chemical modifications of the pharmacophore. The outstanding potential that lies in the development of organelle-specific drugs is becoming increasingly apparent.

Anti-Candida activity of existing antibiotics and their derivatives when used alone or in combination with antifungals

Fungal infections are a growing challenge in immunocompromised patients, especially candidiasis. The prolonged use of traditional antifungals to treat Candida infection has caused the emergence of drug resistance, especially fluconazole. Therefore, new therapeutic strategies for Candida infection are warranted. Recently, attention has been paid to the anti-Candida activity of antibiotics and their derivatives. Studies revealed that a series of antibiotics/derivatives displayed potential anti-Candida activity and some of them could significantly increase the susceptibility of antifungals. Interestingly, the derivatives of aminoglycosides were even more active than fluconazole/itraconazole/posaconazole. This article reviews the anti-Candida activities and mechanisms of antibiotics/derivatives used alone or in combination with antifungals. This review will helpfully provide novel insights for overcoming Candida resistance and discovering new antifungals.

Antifungal Activities of 4″,6″-Disubstituted Amphiphilic Kanamycins

Amphiphilic kanamycins derived from the classic antibiotic kanamycin have attracted interest due to their novel bioactivities beyond inhibition of bacteria. In this study, the recently described 4″,6″-diaryl amphiphilic kanamycins reported as inhibitors of connexin were examined for their antifungal activities. Nearly all 4″,6″-diaryl amphiphilic kanamycins tested had antifungal activities comparable to those of 4″,6″-dialkyl amphiphilic kanamycins, reported previously against several fungal strains. The minimal growth inhibitory concentrations (MICs) correlated with the degree of amphiphilicity (cLogD) of the di-substituted amphiphilic kanamycins. Using the fluorogenic dyes, SYTOX^TM Green and propidium iodide, the most active compounds at the corresponding MICs or at 2×MICs caused biphasic dye fluorescence increases over time with intact cells. Further lowering the concentrations to half MICs caused first-order dye fluorescence increases. Interestingly, 4×MIC or 8×MIC levels resulted in fluorescence suppression that did not correlate with the MIC and plasma membrane permeabilization. The results show that 4″,6″-diaryl amphiphilic kanamycins are antifungal and that amphiphilicity parameter cLogD is useful for the design of the most membrane-active versions. A cautionary limitation of fluorescence suppression was revealed when using fluorogenic dyes to measure cell-permeation mechanisms with these antifungals at high concentrations. Finally, 4″,6″-diaryl amphiphilic kanamycins elevate the production of cellular reactive oxygen species as other reported amphiphilic kanamycins.

Development of Fungal Selective Amphiphilic Kanamycin: Cost-Effective Synthesis and Use of Fluorescent Analogs for Mode of Action Investigation

Amphiphilic aminoglycosides have attracted interest due to their novel antifungal activities. A crucial but often neglected factor for drug development in academia is cost of production. Herein is reported a one-step, inexpensive synthesis of amphiphilic alkyl kanamycins constituted with only natural components. The synthetic methodology also enabled the preparation of a series fluorescent amphiphilic aryl kanamycins for direct structure-activity mode of action studies. The lead compounds showed prominent antifungal activities against a panel of fungi, including Fusarium graminearum, Cryptococcus neoformans, and several Candida sp., and also significant antibacterial activities. With fluorescence-based whole cell assays, the aryl amphiphilic kanamycins were observed to permeabilize fungal surface membranes at faster rates than bacterial surface membranes. Also, the antifungal action of the amphiphilic kanamycins was observed to occur in a biphasic mode with an initial fast phase correlated with rapid membrane permeabilization at subminimal inhibitory concentrations and a slower phase membrane permeabilization that elevates the reactive oxygen species production leading to cell death. Inactive hydrophobic amphiphilic kanamycins displayed no membrane permeabilization. The results offer cost-effective methods for producing amphiphilic kanamycins and reveal insights into how nonfungal specific amphiphilic kanamycins can be employed for fungal specific diagnostic and therapeutic applications.

Cationic Amphiphiles Induce Macromolecule Denaturation and Organelle Decomposition in Pathogenic Yeast

Cationic amphiphiles are a large and diverse class of antimicrobial agents. Although their mode of action is not fully resolved, it is generally accepted that these antimicrobials perturb the structural integrity of the plasma membrane leading to the microbial cell disruption. Here we report on the development of inherently fluorescent antifungal cationic amphiphiles and on the study of their effects on cells of Candida, one of the most common fungal pathogens in humans. Fluorescent images of Candida yeast cells that express a fluorescent reporter protein revealed that the cationic amphiphiles rapidly accumulated in the cytosol and led to structural changes in proteins and DNA. Using fluorescent organelle-specific dyes, we showed that these antifungal agents also caused organelle disassembly in Candida cells. The results of this study indicate that, in designing antifungal cationic amphiphiles for clinical use, the intracellular activities of these molecules must be addressed to avoid undesired side effects to mammalian cells.

Antifungal amphiphilic kanamycins: new life for an old drug

Classical aminoglycoside antibiotics are obsolete or hampered by the emergence of drug resistant bacteria. Recent discoveries of antifungal amphiphilic kanamycins offer new strategies for reviving and repurposing these old drugs. A simple structural modification turns the clinically obsolete antibacterial kanamycin into an antifungal agent. Structure-activity relationship studies have led to the production of K20, an antifungal kanamycin that can be mass-produced for uses in agriculture as well as in animals. This review delineates the path to the discovery of K20 and other related antifungal amphiphilic kanamycins, determination of its mode of action, and findings in greenhouse and field trials with K20 that could lead to crop disease protection strategies.