In vitro and in vivo antifungal activities of BMY-28864, a water-soluble pradimicin derivative

Marine-Derived Metabolites Act as Promising Antifungal Agents

The incidence of invasive fungal diseases (IFDs) is on the rise globally, particularly among immunocompromised patients, leading to significant morbidity and mortality. Current clinical antifungal agents, such as polyenes, azoles, and echinocandins, face increasing resistance from pathogenic fungi. Therefore, there is a pressing need for the development of novel antifungal drugs. Marine-derived secondary metabolites represent valuable resources that are characterized by varied chemical structures and pharmacological activities. While numerous compounds exhibiting promising antifungal activity have been identified, a comprehensive review elucidating their specific underlying mechanisms remains lacking. In this review, we have compiled a summary of antifungal compounds derived from marine organisms, highlighting their diverse mechanisms of action targeting various fungal cellular components, including the cell wall, cell membrane, mitochondria, chromosomes, drug efflux pumps, and several biological processes, including vesicular trafficking and the growth of hyphae and biofilms. This review is helpful for the subsequent development of antifungal drugs due to its summary of the antifungal mechanisms of secondary metabolites from marine organisms.

d-Mannose binding, aggregation property, and antifungal activity of amide derivatives of pradimicin A

Pradimicin A (PRM-A) and its derivatives comprise a unique family of antibiotics that show antifungal, antiviral, and antiparasitic activities through binding to d-mannose (Man)-containing glycans of pathogenic species. Despite their great potential as drug leads with an exceptional antipathogenic action, therapeutic application of PRMs has been severely limited by their tendency to form water-insoluble aggregates. Recently, we found that attachment of 2-aminoethanol to the carboxy group of PRM-A via amide linkage significantly suppressed the aggregation. Here, we prepared additional amide derivatives (2-8) of PRM-A to examine the possibility that the amide formation of PRM-A could suppress its aggregation propensity. Sedimentation assay and isothermal titration calorimetry experiment confirmed that all amide derivatives can bind Man without significant aggregation. Among them, hydroxamic acid derivative (4) showed the most potent Man-binding activity, which was suggested to be derived from the anion formation of the hydroxamic acid moiety by molecular modeling. Derivative 4 also exhibited significant antifungal activity comparable to that of PRM-A. These results collectively indicate that amide formation of PRM-A is the promising strategy to develop less aggregative derivatives, and 4 could serve as a lead compound for exploring the therapeutic application of PRM-A.

Recent Progress in the Discovery of Antifungal Agents Targeting the Cell Wall

Due to the limit of available treatments and the emergence of drug resistance in the clinic, invasive fungal infections are an intractable problem with high morbidity and mortality. The cell wall, as a fungi-specific structure, is an appealing target for the discovery and development of novel and low-toxic antifungal agents. In an attempt to accelerate the discovery of novel cell wall targeted drugs, this Perspective will provide a comprehensive review of the progress made to date on the development of fungal cell wall inhibitors. Specifically, this review will focus on the targets, discovery process, chemical structures, antifungal activities, and structure-activity relationships. Although two types of cell wall antifungal agents are clinically available or in clinical trials, it is still a long way for the other cell wall targeted inhibitors to be translated into clinical applications. Future efforts should be focused on the identification of inhibitors against novel conserved cell wall targets.

Paving the Way for Practical Use of Sugar-Binding Natural Products as Lectin Mimics in Glycobiological Research

Pradimicins (PRMs) constitute an exceptional class of natural products that show Ca²⁺ -dependent recognition of d-mannose (Man). In addition to therapeutic uses as antifungal drugs, the application of PRMs as lectin mimics for glycobiological research has been attracting considerable interest, since the emerging biological roles of Man-containing glycans have been highlighted. However, only a few attempts have been made to use PRMs for glycobiological purposes. The limited use of PRMs is primarily due to the early assumption that the readily modifiable carboxyl group of PRMs is involved in Ca²⁺ binding, and thus, not available to prepare research tools. Recently, this assumption has been disproved by structural elucidation of the Ca²⁺ complex of PRMs, which paves the way for designing carboxyl group modified derivatives of PRMs for research use. This article outlines studies related to Ca²⁺ -mediated Man binding of PRMs and discusses their application for glycobiology.

Carbohydrate-Binding Non-Peptidic Pradimicins for the Treatment of Acute Sleeping Sickness in Murine Models

Current treatments available for African sleeping sickness or human African trypanosomiasis (HAT) are limited, with poor efficacy and unacceptable safety profiles. Here, we report a new approach to address treatment of this disease based on the use of compounds that bind to parasite surface glycans leading to rapid killing of trypanosomes. Pradimicin and its derivatives are non-peptidic carbohydrate-binding agents that adhere to the carbohydrate moiety of the parasite surface glycoproteins inducing parasite lysis in vitro. Notably, pradimicin S has good pharmaceutical properties and enables cure of an acute form of the disease in mice. By inducing resistance in vitro we have established that the composition of the sugars attached to the variant surface glycoproteins are critical to the mode of action of pradimicins and play an important role in infectivity. The compounds identified represent a novel approach to develop drugs to treat HAT.

HIV-1 gp120 as a therapeutic target: navigating a moving labyrinth

INTRODUCTION

The HIV-1 gp120 envelope (Env) glycoprotein mediates attachment of virus to human target cells that display requisite receptors, CD4 and co-receptor, generally CCR5. Despite high-affinity interactions with host receptors and proof-of-principle by the drug maraviroc that interference with CCR5 provides therapeutic benefit, no licensed drug currently targets gp120.

AREAS COVERED

An overview of the role of gp120 in HIV-1 entry and of sites of potential gp120 vulnerability to therapeutic inhibition is presented. Viral defenses that protect these sites and turn gp120 into a moving labyrinth are discussed together with strategies for circumventing these defenses to allow therapeutic targeting of gp120 sites of vulnerability.

EXPERT OPINION

The gp120 envelope glycoprotein interacts with host proteins through multiple interfaces and has conserved structural features at these interaction sites. In spite of this, targeting gp120 for therapeutic purposes is challenging. Env mechanisms that have evolved to evade the humoral immune response also shield it from potential therapeutics. Nevertheless, substantial progress has been made in understanding HIV-1 gp120 structure and its interactions with host receptors, and in developing therapeutic leads that potently neutralize diverse HIV-1 strains. Synergies between advances in understanding, needs for therapeutics against novel viral targets and characteristics of breadth and potency for a number of gp120-targetting lead molecules bodes well for gp120 as a HIV-1 therapeutic target.

Synergistic actions of tailoring enzymes in pradimicin biosynthesis

Three key tailoring enzymes in pradimicin biosynthesis: PdmJ, PdmW, and PdmN, were investigated. PdmW was characterized as the C-6 hydroxylase by structural characterization of the corresponding product, 6-hydroxy-G-2A. The efficiencies of the C-5 and C-6 hydroxylations, catalyzed respectively by PdmJ and PdmW, were low when they were expressed individually with the early biosynthetic enzymes that form G-2A. When these two cytochrome P450 enzymes were co-expressed, a dihydroxylated product, 5,6-dihydroxy-G-2A, was efficiently produced, indicating that these two enzymes work synergistically in pradimicin biosynthesis. Heterologously expressed PdmN in Streptomyces coelicolor CH999 converted G-2A to JX137a by ligating a unit of D-alanine to the carboxyl group. PdmN has relaxed substrate specificity toward both amino acid donors and acceptors. Through combinatorial biosynthesis, a series of new pradimicin analogues were produced.

Molecular architecture and therapeutic potential of lectin mimics

Lectins are proteins of non-immune origin that bind specific carbohydrates without chemical modification. Coupled with the emerging biological and pathological significance of carbohydrates, lectins have become extensively used as research tools in glycobiology. However, lectin-based drug development has been impeded by high manufacturing costs, low chemical stability, and the potential risk of initiating an unfavorable immune response. As alternatives to lectins, non-protein small molecules having carbohydrate-binding properties (lectin mimics) are currently attracting a great deal of attention because of their ease of preparation and chemical modification. Lectin mimics of synthetic origin are divided roughly into two groups, boronic acid-dependent and boronic acid-independent lectin mimics. This article outlines their representative architectures and carbohydrate-binding properties, and discusses their therapeutic potential by reviewing recent attempts to develop antiviral and antimicrobial agents using their architectures. We also focus on the naturally occurring lectin mimics, pradimicins and benanomicins. They are the only class of non-protein natural products having a C-type lectin-like ability to recognize d-mannopyranosides in the presence of Ca^2 + ions. Their molecular basis of carbohydrate recognition and therapeutic potential are also discussed.

Targeting the glycans of gp120: a novel approach aimed at the Achilles heel of HIV

The development of drug resistance in HIV compromises the long-term efficacy of current therapies. Furthermore, vaccine development faces huge problems, mainly because of the low antigenicity and immunogenicity of the HIV envelope glycoprotein gp120 and the efficient hiding of highly immunogenic epitopes by its glycans. There is evidence that mutant HIV strains containing glycosylation site deletions trigger the production of specific neutralising antibodies to previously hidden gp120 epitopes. I present a hypothesis that development of resistance against drugs that target the glycans on gp120 would result in a marked enhancement of neutralisation of HIV by the immune system--ie, drugs directed against the carbohydrate component of gp120 will select for mutant virus strains that progressively gain deletions in the glycosylation sites of gp120. Previously hidden epitopes would then be uncovered, and the virus will become highly susceptible to markedly increased immunological neutralisation. I believe this novel approach may become an entirely new therapeutic concept that exploits the high mutation rate of HIV and allows drug therapy to act in concert with a triggered immune response to suppress HIV more efficiently. Moreover, this approach could be applied to treat other chronic infections by viruses that contain a glycosylated envelope (eg, hepatitis B and C).

Pradimicin resistance of yeast is caused by a mutation of the putative N-glycosylation sites of osmosensor protein Sln1

Pradimicin, a mannose-binding antifungal antibiotic, induces apoptosis-like cell death in Saccharomyces cerevisiae. Previously we found that the substitution of the 74th amino acid from glycine to cysteine in Ypd1 yields a mutant resistant to pradimicin. In this study, the involvement of a membrane-spanning osomosensor, Sln1, which is located upstream of Ypd1, was investigated. A mutant, sln1 DeltaNG, that lacks the putative N-glycosylation sites in the extracellular domain became resistant to pradimicin. On the other hand, the null mutants of Ssk1, Pbs2, and Hog1, which are located downstream of the Sln1 cascade, were sensitive to pradimicin as well as the wild-type strain. In conclusion, pradimicin exerts its fungicidal action with the involvement of Sln1, but the downstream branch, Ssk1 and the HOG pathway, is not involved.

Compartmental pharmacokinetics and tissue drug distribution of the pradimicin derivative BMS 181184 in rabbits

The pharmacokinetics of the antifungal pradimicin derivative BMS 181184 in plasma of normal, catheterized rabbits were characterized after single and multiple daily intravenous administrations of dosages of 10, 25, 50, or 150 mg/kg of body weight, and drug levels in tissues were assessed after multiple dosing. Concentrations of BMS 181184 were determined by a validated high-performance liquid chromatography method, and plasma data were modeled into a two-compartment open model. Across the investigated dosage range, BMS 181184 demonstrated nonlinear, dose-dependent kinetics with enhanced clearance, reciprocal shortening of elimination half-life, and an apparently expanding volume of distribution with increasing dosage. After single-dose administration, the mean peak plasma BMS 181184 concentration (Cmax) ranged from 120 microg/ml at 10 mg/kg to 648 microg/ml at 150 mg/kg; the area under the concentration-time curve from 0 to 24 h (AUC0-24) ranged from 726 to 2,130 microg . h/ml, the volume of distribution ranged from 0.397 to 0.799 liter/kg, and the terminal half-life ranged from 4.99 to 2.31 h, respectively (P < 0.005 to P < 0.001). No drug accumulation in plasma occurred after multiple daily dosing at 10, 25, or 50 mg/kg over 15 days, although mean elimination half-lives were slightly longer. Multiple daily dosing at 150 mg/kg was associated with enhanced total clearance and a significant decrease in AUC0-24 below the values obtained at 50 mg/kg (P < 0.01) and after single-dose administration of the same dosage (P < 0.05). Assessment of tissue BMS 181184 concentrations after multiple dosing over 16 days revealed substantial uptake in the lungs, liver, and spleen and, most notably, dose-dependent accumulation of the drug within the kidneys. These findings are indicative of dose- and time-dependent elimination of BMS 181184 from plasma and renal accumulation of the compound after multiple dosing.

Antifungal activity of the pradimicin derivative BMS 181184 in the treatment of experimental pulmonary aspergillosis in persistently neutropenic rabbits

The activity of the pradimicin derivative BMS 181184 was evaluated in a model of invasive pulmonary aspergillosis in persistently neutropenic rabbits and compared with that of amphotericin B deoxycholate. BMS 181184 at total daily doses of 50 and 150 mg/kg of body weight was at least as effective as amphotericin B at 1 mg/kg once a day in conferring survival and had comparable activity in reducing organism-mediated tissue injury and excess lung weight. Although treatment at all dosing regimens of BMS 181184 resulted in significant reductions in fungal tissue burden compared to untreated controls, equivalence to amphotericin B occurred only at the higher dosage level. Similar observations were made in bronchoalveolar lavage fluid cultures obtained postmortem. Monitoring of the animals through ultrafast computerized tomography scan revealed a marked resolution of pulmonary lesions during treatment with BMS 181184. The compound was well tolerated at all dosing regimens, and no toxicity was noted. Pharmacokinetic studies revealed nonlinear drug disposition with increased clearance at higher dosages and some evidence for extravascular drug accumulation. BMS 181184 had excellent activity in the treatment of experimental invasive pulmonary aspergillosis in persistently neutropenic rabbits, thus underscoring the potential of pradimicin derivatives in therapy of invasive aspergillosis in the neutropenic host.

Invasive aspergillosis in systemic lupus erythematosus

Invasive aspergillosis is seldomly described in systemic lupus erythematosus. We present two cases of aspergillosis and review 21 cases reported between 1957 and 1994. The typical clinical presentation is fever and cough in a hospitalized SLE patient previously treated with corticosteroids, immunosuppressors, and broad-spectrum antibiotics. Unlike aspergillosis in other conditions, granulocytopenia is uncommon. Chest radiographs show diffuse or patchy infiltration of lung fields. Diagnosis was suspected premortem in 2 patients. Aspergillus fumigatus was identified or isolated in sputum or parenchimal tissues in the majority of cases. Twenty-two patients died (95%). The finding of hyphae in the sputum of a systemic lupus erythematosus patient with a suggestive clinical picture should lead to bronchoscopy, bronchoalveolar lavage, and lung biopsy. Proof of diagnosis will come from the demonstration of hyphae in tissues and isolation of aspergillus from tissue cultures. Long-term therapy with amphotericin B alone or in combination with fluorocytosine or itraconazole may help improve survival.

In vitro antifungal and fungicidal spectra of a new pradimicin derivative, BMS-181184

A new pradimicin derivative, BMS-181184, was compared with amphotericin B and fluconazole against 249 strains from 35 fungal species to determine its antifungal spectrum. Antifungal testing was performed by the broth macrodilution reference method recommended by the National Committee for Clinical Laboratory Standards (document M27-P, 1992). BMS-181184 MICs for 97% of the 167 strains of Candida spp., Cryptococcus neoformans, Torulopsis glabrata, and Rhodotorula spp. tested were < or = 8 micrograms/ml, with a majority of MICs being 2 to 8 micrograms/ml. Similarly, for Aspergillus fumigatus and 89% of the 26 dermatophytes tested BMS-181184 MICs were < or = 8 micrograms/ml. BMS-181184 was fungicidal for the yeasts, dermatophytes, and most strains of A. fumigatus, although the reduction in cell counts was less for A. fumigatus than for the yeasts. BMS-181184 was active against Sporothrix schenckii, dematiaceous fungi, and some members of the non-Aspergillus hyaline hyphomycetes. BMS-181184, however, was not fungicidal against members of the family Dematiaceae. BMS-181184 lacked activity or had poorer activity (MICs, > or = 16 micrograms/ml) against Aspergillus niger, Aspergillus flavus, Malassezia furfur, Fusarium spp., Pseudallescheria boydii, Alternaria spp., Curvularia spp., Exserohilum mcginnisii, and the zygomycetes than against yeasts. The activity of BMS-181184 was minimally (twofold or less) affected by changes in testing conditions (pH, inoculum size, temperature, the presence of serum), testing methods (agar versus broth macrodilution), or test media (RPMI 1640, yeast morphology agar, high resolution test medium). Overall, our results indicate that BMS-181184 has a broad antifungal spectrum and that it is fungicidal to yeasts and, to a lesser extent, to filamentous fungi.