Pore-forming activity of new conjugate antibiotics based on amphotericin B

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.

Searching for Conjugates as New Structures for Antifungal Therapies

The progressive increase in fungal infections and the decrease in the effectiveness of current therapy explain research on new drugs. The synthesis of compounds with proven antifungal activity, favorable physicochemical and pharmacokinetic properties affecting their pharmaceutical availability and bioavailability, and limiting or eliminating side effects has become the goal of many studies. The publication describes the directions of searching for new compounds with antifungal activity, focusing on conjugates. The described modifications include, among others, azoles or amphotericin B in combination with fatty acids, polysaccharides, proteins, and synthetic polymers. The benefits of these combinations in terms of activity, mechanism of action, and bioavailability were indicated. The possibilities of creating or using nanoparticles, "umbrella" conjugates, siderophores (iron-chelating compounds), and monoclonal antibodies were also presented. Taking into account the role of vaccinations in prevention, the scope of research related to developing a vaccine protecting against fungal infections was also indicated.

Conjugates of amphotericin B to resolve challenges associated with its delivery

INTRODUCTION

Amphotericin B (AmB), a promising antifungal and antileishmanial drug, acts on the membrane of microorganisms. The clinical use of AmB is limited due to issues associated with its delivery including poor solubility and bioavailability, instability in acidic media, poor intestinal permeability, dose and aggregation state dependent toxicity, parenteral administration, and requirement of cold chain for transport and storage, etc.

AREAS COVERED

Scientists have formulated and explored various covalent conjugates of AmB to reduce its toxicity with increase in solubility, oral bioavailability, and payload or loading of AmB by using various polymers, lipids, carbon-based nanocarriers, metallic nanoparticles, and vesicular carriers, etc. In this article, we have reviewed various conjugates of AmB with polymers and nanomaterials explored for its delivery to give a deep insight regarding further exploration in future.

EXPERT OPINION

Covalent conjugates of AmB have been investigated by scientists, and preliminary in vitro and animal investigations have given successful results, which are required to be validated further with systematic investigation on safety and therapeutic efficacy in animals followed by clinical trials.

Semisynthetic Amides of Polyene Antibiotic Natamycin

Natamycin is a macrolide polyene antibiotic, characterized by a potent broad spectrum antifungal activity and low toxicity. However, it is not used for the treatment of systemic mycoses due to its low bioavailability and low solubility in aqueous solutions. In order to create new semisynthetic antifungal agents for treatment of mycoses, a series of water-soluble amides of natamycin were synthesized. Antifungal activities of natamycin derivatives were investigated against Candida spp., including a panel of Candida auris clinical isolates and filamentous fungi. Toxicity for mammalian cells was assayed by monitoring antiproliferative activity against human postnatal fibroblasts (HPF) and human embryonic kidney cells (HEK293). By comparing leakage of contents from ergosterol versus cholesterol containing vesicles, a ratio that characterizes the efficacy and safety of natamycin and its derivatives was determined (EI, efficiency index). Ability of all tested semisynthetic natamycines to prevent proliferation of the yeast Candida spp. cells was comparable or even slightly higher to those of parent antibiotic. Interestingly, amide 8 was more potent than natamycin (1) against all tested C. auris strains (MIC values 2 μg/mL vs 8 μg/mL, respectively). Among 7 derivatives, amide 10 with long lipophilic side chains showed the highest EI and strong antifungal activity in vitro but was more toxic against HPF. In vivo experiments with amide 8 showed in vivo efficacy on a mouse candidemia model with a larger LD₅₀/ED₅₀ ratio in comparison to amphotericin B.

Semisynthetic Amides of Amphotericin B and Nystatin A1: A Comparative Study of In Vitro Activity/Toxicity Ratio in Relation to Selectivity to Ergosterol Membranes

Polyene antifungal amphotericin B (AmB) has been used for over 60 years, and remains a valuable clinical treatment for systemic mycoses, due to its broad antifungal activity and low rate of emerging resistance. There is no consensus on how exactly it kills fungal cells but it is certain that AmB and the closely-related nystatin (Nys) can form pores in membranes and have a higher affinity towards ergosterol than cholesterol. Notably, the high nephro- and hemolytic toxicity of polyenes and their low solubility in water have led to efforts to improve their properties. We present the synthesis of new amphotericin and nystatin amides and a comparative study of the effects of identical modifications of AmB and Nys on the relationship between their structure and properties. Generally, increases in the activity/toxicity ratio were in good agreement with increasing ratios of selective permeabilization of ergosterol- vs. cholesterol-containing membranes. We also show that the introduced modifications had an effect on the sensitivity of mutant yeast strains with alterations in ergosterol biosynthesis to the studied polyenes, suggesting a varying affinity towards intermediate ergosterol precursors. Three new water-soluble nystatin derivatives showed a prominent improvement in safety and were selected as promising candidates for drug development.

Mechanistic insight into the role of mevalonate kinase by a natural fatty acid-mediated killing of Leishmania donovani

We evaluated the anti-leishmanial efficacy of different saturated medium-chain fatty acids (FAs, C8–C18) where FA containing C8 chain, caprylic acid (CA), was found to be most potent against Leishmania donovani, the causative agent for visceral leishmaniasis (VL). Different analogs of CA with C8 linear chain, but not higher, along with a carboxyl/ester group showed a similar anti-leishmanial effect. Ergosterol depletion was the major cause of CA-mediated cell death. Molecular docking and molecular dynamic simulation studies indicated the enzyme mevalonate kinase (MevK) of the ergosterol biosynthesis pathway as a possible target of CA. Enzyme assays with purified recombinant MevK and CA/CA analogs confirmed the target with a competitive inhibition pattern. Using biochemical and biophysical studies; strong binding interaction between MevK and CA/CA analogs was established. Further, using parasites with overexpressed MevK and proteomics studies of CA-treated parasites the direct role of MevK as the target was validated. We established the mechanism of the antileishmanial effect of CA, a natural product, against VL where toxicity and drug resistance with current chemotherapeutics demand an alternative. This is the first report on the identification of an enzymatic target with kinetic parameters and mechanistic insights against any organism for a natural medium-chain FA.

Antifungal Macrocycle Antibiotic Amphotericin B-Its Present and Future. Multidisciplinary Perspective for the Use in the Medical Practice

This review is devoted to a broad analysis of the results of studies of the effect of macrocyclic antifungal polyene antibiotic amphotericin B on cell membranes. A detailed study of polyenes has shown that some of them can have not only antifungal, but also antiviral and antitumor effects. Under conditions of global pandemic fungal pathology develops especially quickly and in this case leads to invasive aspergillosis, which contributes to the complication of coronavirus infection in the lungs and even secondary infection with invasive aspergillosis. The treatment of an invasive form of bronchopulmonary aspergillosis is directly related to the immunomodulatory and immunostimulating properties of the macrocyclic polyene drug amphotericin B. The article presents experimental data on the study of the biological activity and membrane properties of amphotericin B and the effect of its chemically modified derivatives, as well as liposomal forms of amphotericin B on viral, bacterial and fungal infections. The mechanism of action of amphotericin B and its analogues is based on their interaction with cellular and lipid membranes, followed by formation of ion channels of molecular size in the membranes. The importance of these studies is that polyenes are sensitive to membranes that contain sterols of a certain structure. The analysis showed that pathogenic fungal cells containing ergosterol were 10−100 times more sensitive to polyene antibiotics than host cell membranes containing cholesterol. The high sterol selectivity of the action of polyenes opens broad prospects for the use of polyene antifungal drugs in practical medicine and pharmacology in the treatment of invasive mycoses and the prevention of atherosclerosis. In this context, it should be noted that polyene antibiotics are the main tool in the study of the biochemical mechanism of changes in the permeability of cell membranes for energy-dependent substrates. Chemical and genetic engineering transformation of the structure of polyene antibiotic molecules opens prospects for the identification and creation of new biologically active forms of the antibiotic that have a high selectivity of action in the treatment of pathogenic infections.

Influence of amphotericin B on the DPPC/DOPC/sterols mixed monolayer in the presence of calcium ions

Amphotericin B, an acquainted antifungal drug, has reattracted the attention of most scholars due to its one important advantage of making the fungus less resistant. Amphotericin B's antifungal properties are derived from its ability to interact with ergosterols on the fungal cells' membrane to form pores. However, the cholesterol in the human cell membranes is similar in structure to ergosterol, which cause the drug to produce certain toxicity and make the clinical use of amphotericin B limited. The study of the interaction between amphotericin B and lipid monolayer in the presence of cholesterol or ergosterol is crucial to understanding the mechanism of effect of the drug on cell membranes. Langmuir monolayer as a model for half of cell membranes can precisely control the proportion of components and the solution environment, which has been used to do a lot of research about the interaction of amphotericin B with lipids. It is noteworthy that some ions associated with life activities play an important role in it, such as calcium ions. In this work, the surface pressure-mean molecular area isotherms, elastic modulus and the surface pressure-time curves of DPPC/DOPC/sterol mixed monolayer with or without amphotericin B were studied in the different concentration of calcium ions. The morphology of the Langmuir-Blodgett films transferred on the mica were observed by atomic force microscopy. The results shown that AmB changed the elastic modulus and surface morphology of DPPC/DOPC/sterol mxied monolayer, which was significantly different with different types of sterols. Calcium ions can regulate the effect of this drug, which was clearly different due to different types of sterols. This work provides useful information to further understand the influence mechanism of calcium ions on the interaction between AmB and phospholipid/sterol monolayer, which is helpful to find out the effect mechanism of calcium ion on the interaction between AmB and phospholipid monolayer containing ergosterol or cholesterol and to understand the mechanism of AmB influencing on the membrane of fungal or human cells.

[Antifungal macrocycle antibiotic amphotericin B - its present and future. Multidisciplinary perspective for the use in the medical practice]

This review is devoted to a broad analysis of the results of studies of the effect of macrocyclic antifungal polyene antibiotic amphotericin B on cell membranes. A multi-prolonged study of polyenes showed that some of them can have not only antifungal, but also antiviral and antitumor action. Fungal pathology develops especially quickly and in this case leads to invasive aspergillosis, which contributes to the complication of coronavirus infection in the lungs and even secondary infection with invasive aspergillosis in the context of a global pandemic. The treatment of an invasive form of bronchopulmonary aspergillosis is directly related to the immunomodulatory and immunostimulating properties of the macrocyclic polyene drug amphotericin B. The article presents experimental data on the study of the biological activity and membrane properties of amphotericin B and the effect of its chemically modified derivatives, as well as liposomal forms of amphotericin B on viral, bacterial and fungal infections. The mechanism of action of amphotericin B and its analogues is based on their interaction with cellular and lipid membranes, by forming ion channels of molecular size in them. The importance of these studies is that polyenes are sensitive to membranes that contain sterols of a certain structure. The analysis showed that pathogenic fungal cells containing ergosterol were 10-100 times more sensitive to polyene antibiotics than host cell membranes containing cholesterol. The high sterol selectivity of the action of polyenes opens up broad prospects for the use of polyene antifungal drugs in practical medicine and pharmacology in the treatment of invasive mycoses and the prevention of atherosclerosis. In this connection, it should be noted that polyene antibiotics are the main tool in the study of the biochemical mechanism of changes in the permeability of cell membranes for energy-dependent substrates. Chemical and genetic engineering transformation of the structure of polyene antibiotic molecules opens up prospects for the identification and creation of new biologically active forms of the antibiotic that have a high selectivity of action in the treatment of pathogenic infections.

Interaction between polyene antifungal drug and saturated phospholipid monolayer regulated by calcium ions at the air-water interface

Amphotericin B (AmB) is a polyene antifungal drug, which could directly form pores on the sterol-free phospholipid monolayers. The interaction between AmB and phospholipid can be affected by calcium ions, but the mechanism is still unclear. DPPC is a saturated phospholipid with -PC group, which is often used to simulate the outer cell membrane leaflet. And DPPC is also the main constituent of pulmonary surfactants. In this work, the DPPC monolayer was used as a model membrane to study the effect of calcium ions on the interaction between AmB and phospholipid. The influence of different concentration of calcium ions on the elastic modulus, mean molecular area increment, excess Gibbs free energy and stability of the AmB/DPPC mixed monolayer has been researched at the surface pressure of 7.5 mN/m, 12.5 mN/m and 22.5 mN/m. The AmB/DPPC monolayers at the air-water interface have been observed in real-time by Brewster angle microscope and the microstructure of the Langmuir-Blodgett monolayer films transferred onto the mica have been researched by scanning electron microscope and atomic force microscope. The results showed that calcium ions had a significant influence on the elastic modulus, mean molecular area increment, excess Gibbs free energy, stability and microstructure of the AmB/DPPC monolayer. It has been indicated that the influence of calcium ions on the interaction between AmB and DPPC molecules mainly depended on the effect of calcium ions on the orientation of AmB molecules. The calcium ions could regulate the effect of AmB to the stability of the DPPC monolayer. This regulatory role changed with the different concentrations of calcium ions and the different phase states of the monolayer. This work provides useful information to further understand the influence mechanism of calcium ions on the interaction between AmB and saturated phospholipid with -PC group, which is helpful to find out the effect mechanism of calcium ion on the interaction between AmB and the outer layer of cell membrane or pulmonary surfactants in different phase states and to understand the toxicity mechanism of AmB on the cell membrane or lungs.

Sterol Sponge Mechanism Is Conserved for Glycosylated Polyene Macrolides

Amphotericin-like glycosylated polyene macrolides (GPMs) are a clinically and industrially important family of natural products, but the mechanisms by which they exert their extraordinary biological activities have remained unclear for more than half a century. Amphotericin B exerts fungicidal action primarily via self-assembly into an extramembranous sponge that rapidly extracts ergosterol from fungal membranes, but it has remained unclear whether this mechanism is applicable to other GPMs. Using a highly conserved polyene-hemiketal region of GPMs that we hypothesized to represent a conserved ergosterol-binding domain, we bioinformatically mapped the entirety of the GPM sequence-function space and expanded the number of GPM biosynthetic gene clusters (BGCs) by 10-fold. We further leveraged bioinformatic predictions and tetrazine-based reactivity screening targeting the electron-rich polyene region of GPMs to discover a first-in-class methyltetraene- and diepoxide-containing GPM, kineosporicin, and to assign BGCs to many new producers of previously reported members. Leveraging a range of structurally diverse known and newly discovered GPMs, we found that the sterol sponge mechanism of fungicidal action is conserved.

Triphenilphosphonium Analogs of Chloramphenicol as Dual-Acting Antimicrobial and Antiproliferating Agents

In the current work, in continuation of our recent research, we synthesized and studied new chimeric compounds, including the ribosome-targeting antibiotic chloramphenicol (CHL) and the membrane-penetrating cation triphenylphosphonium (TPP), which are linked by alkyl groups of different lengths. Using various biochemical assays, we showed that these CAM-Cn-TPP compounds bind to the bacterial ribosome, inhibit protein synthesis in vitro and in vivo in a way similar to that of the parent CHL, and significantly reduce membrane potential. Similar to CAM-C4-TPP, the mode of action of CAM-C10-TPP and CAM-C14-TPP in bacterial ribosomes differs from that of CHL. By simulating the dynamics of CAM-Cn-TPP complexes with bacterial ribosomes, we proposed a possible explanation for the specificity of the action of these analogs in the translation process. CAM-C10-TPP and CAM-C14-TPP more strongly inhibit the growth of the Gram-positive bacteria, as compared to CHL, and suppress some CHL-resistant bacterial strains. Thus, we have shown that TPP derivatives of CHL are dual-acting compounds targeting both the ribosomes and cellular membranes of bacteria. The TPP fragment of CAM-Cn-TPP compounds has an inhibitory effect on bacteria. Moreover, since the mitochondria of eukaryotic cells possess qualities similar to those of their prokaryotic ancestors, we demonstrate the possibility of targeting chemoresistant cancer cells with these compounds.

pH-Dependent ion permeability control of a modified amphotericin B channel through metal complexation

Amphotericin B incorporating 2,2'-bipyridine (bpy-AmB) forms a membrane channel exhibiting pH-dependent Ca2+ ion permeability with a selective response to Cu2+ ions. The coordination structure at bpy sites depends on the pH and metal ions can control the association state of bpy-AmB in the membrane.

Self-assembly, stability and conductance of amphotericin B channels: bridging the gap between structure and function

Amphotericin B (AmB), one of the most powerful but also toxic drugs used to treat systemic mycoses, is believed to selectively permeabilize fungal cell membranes to ions in a sterol-dependent manner. Unfortunately, the structure of the biologically active AmB channels has long eluded researchers, obstructing the design of safer alternatives. Here, we investigate the structural and thermodynamic aspects of channel formation, stability, and selective ion conduction. We combine fluorescence lifetime imaging and molecular simulations to trace the process of channel assembly until the formation of stable, roughly octameric double-length channels (DLCs). This stoichiometry is confirmed by matching the predicted channel conductances with the past results of patch-clamp measurements. We then use free energy calculations to explain the effect of sterols on DLC stability and discuss the observed cation selectivity in structural terms, addressing several long-standing controversies in the context of their physiological relevance. Simulations of ion permeation indicate that only solvated ions pass through DLCs, revealing surprising solvation patterns in the channel lumen. We conclude our investigation by inspecting the role of the tail hydroxyl in the assembly of functional channels, pointing at possible origins of the cholesterol-ergosterol selectivity.

Discovery of Amphamide, a Drug Candidate for the Second Generation of Polyene Antibiotics

Amphotericin B (AmB, 1) is the drug of choice for treating the most serious systemic fungal or protozoan infections. Nevertheless, its application is limited by low solubility in aqueous media and serious side effects such as infusion-related reactions, hemolytic toxicity, and nephrotoxicity. Owing to these limitations, it is essential to search for the polyene derivatives with better chemotherapeutic properties. With the objective of obtaining AmB derivatives with lower self-aggregation and improved solubility, we synthesized a series of amides of AmB bearing an additional basic group in the introduced residue. The screening of antifungal activity in vitro revealed that N-(2-aminoethyl)amide of AmB (amphamide, 6) had superior antifungal activity compared to that of the paternal AmB. Preclinical studies in mice confirmed that compound 6 had a much lower acute toxicity and higher antifungal efficacy in the model of mice candidosis sepsis compared with that of AmB (1). Thus, the discovered amphamide is a promising drug candidate for the second generation of polyene antibiotics and is also prospective for in-depth preclinical and clinical evaluation.

Main trends in the design of semi-synthetic antibiotics of a new generation

This review summarizes main advances achieved by Russian researchers in the synthesis and characterization of semi-synthetic antibiotics of a new generation in the period from 2004 to 2019. The following classes of compounds are considered as the basis for modification: polycyclic antibacterial glycopeptides of the vancomycin group, classical macrolides, antifungal polyene macrolides, the antitumour antibiotic olivomycin A, antitumour anthracyclines and broad-spectrum antibiotics, in particular, oligomycin A, heliomycin and some other. Main trends in the design of modern anti-infective and antitumour agents over this period are considered in relation to original natural antibiotics, which have been independently discovered by Russian researchers. It is shown that a new type of hybrid structures can, in principle, be synthesized based on glycopeptides, macrolides and other antibiotics, including heterodimers containing a new benzoxaborole pharmacophore. The review addresses the influence of the length of the spacer between two antibiotic molecules on the biological activity of hybrid structures. A combination of genetic engineering techniques and methods of organic synthesis is shown to be useful for the design of new potent antifungal antibiotics based on polyenes of the amphotericin B group. Many new semi-synthetic analogues exhibit important biological properties, such as a broad spectrum of activity and low toxicity. Emphasis is given to certain aspects related to investigation of a broad range of biological activity and mechanisms of action of new derivatives.

The bibliography includes 101 references.

Synthesis, characterization, and mechanistic studies of a gold nanoparticle-amphotericin B covalent conjugate with enhanced antileishmanial efficacy and reduced cytotoxicity

Background

Amphotericin B (AmB) as a liposomal formulation of AmBisome is the first line of treatment for the disease, visceral leishmaniasis, caused by the parasite Leishmania donovani. However, nephrotoxicity is very common due to poor water solubility and aggregation of AmB. This study aimed to develop a water-soluble covalent conjugate of gold nanoparticle (GNP) with AmB for improved antileishmanial efficacy and reduced cytotoxicity.

Methods

Citrate-reduced GNPs (~39 nm) were functionalized with lipoic acid (LA), and the product GNP-LA (GL ~46 nm) was covalently conjugated with AmB using carboxyl-to-amine coupling chemistry to produce GNP-LA-AmB (GL-AmB ~48 nm). The nanoparticles were characterized by dynamic light scattering, transmission electron microscopy (TEM), and spectroscopic (ultraviolet–visible and infrared) methods. Experiments on AmB uptake of macrophages, ergosterol depletion of drug-treated parasites, cytokine ELISA, fluorescence anisotropy, flow cytometry, and gene expression studies established efficacy of GL-AmB over standard AmB.

Results

Infrared spectroscopy confirmed the presence of a covalent amide bond in the conjugate. TEM images showed uniform size with smooth surfaces of GL-AmB nanoparticles. Efficiency of AmB conjugation was ~78%. Incubation in serum for 72 h showed <7% AmB release, indicating high stability of conjugate GL-AmB. GL-AmB with AmB equivalents showed ~5-fold enhanced antileishmanial activity compared with AmB against parasite-infected macrophages ex vivo. Macrophages treated with GL-AmB showed increased immunostimulatory T_h1 (IL-12 and interferon-γ) response compared with standard AmB. In parallel, AmB uptake was ~5.5 and ~3.7-fold higher for GL-AmB-treated (P<0.001) macrophages within 1 and 2 h of treatment, respectively. The ergosterol content in GL-AmB-treated parasites was ~2-fold reduced compared with AmB-treated parasites. Moreover, GL-AmB was significantly less cytotoxic and hemolytic than AmB (P<0.01).

Conclusion

GNP-based delivery of AmB can be a better, cheaper, and safer alternative than available AmB formulations.