Ibrexafungerp: An orally active β-1,3-glucan synthesis inhibitor.

We previously reported medicinal chemistry efforts that identified MK-5204, an orally efficacious β-1,3-glucan synthesis inhibitor derived from the natural product enfumafungin. Further extensive optimization of the C2 triazole substituent identified 4-pyridyl as the preferred replacement for the carboxamide of MK-5204, leading to improvements in antifungal activity in the presence of serum, and increased oral exposure. Reoptimizing the aminoether at C3 in the presence of this newly discovered C2 substituent, confirmed that the (R) t-butyl, methyl aminoether of MK-5204 provided the best balance of these two key parameters, culminating in the discovery of ibrexafungerp, which is currently in phase III clinical trials.

MK-5204: An orally active β-1,3-glucan synthesis inhibitor.

Our previously reported efforts to produce an orally active β-1,3-glucan synthesis inhibitor through the semi-synthetic modification of enfumafungin focused on replacing the C2 acetoxy moiety with an aminotetrazole and the C3 glycoside with a N,N-dimethylaminoether moiety. This work details further optimization of the C2 heterocyclic substituent, which identified 3-carboxamide-1,2,4-triazole as a replacement for the aminotetrazole with comparable antifungal activity. Alkylation of either the carboxamidetriazole at C2 or the aminoether at C3 failed to significantly improve oral efficacy.

Preclinical Pharmacokinetics and Pharmacodynamic Target of SCY-078, a First-in-Class Orally Active Antifungal Glucan Synthesis Inhibitor, in Murine Models of Disseminated Candidiasis.

SCY-078 (MK-3118) is a novel, semisynthetic derivative of enfumafungin and represents the first compound of the triterpene class of antifungals. SCY-078 exhibits potent inhibition of β-(1,3)-d-glucan synthesis, an essential cell wall component of many pathogenic fungi, including spp. and spp.

Novel orally active inhibitors of β-1,3-glucan synthesis derived from enfumafungin.

The clinical success of the echinocandins, which can only be administered parentally, has validated β-1,3-glucan synthase (GS) as an antifungal target. Semi-synthetic modification of enfumafungin, a triterpene glycoside natural product, was performed with the aim of producing a new class of orally active GS inhibitors. Replacement of the C2 acetoxy moiety with various heterocycles did not improve GS or antifungal potency.

Synthesis and antifungal evaluation of pentyloxyl-diphenylisoxazoloyl pneumocandins and echinocandins.

Echinocandins and pneumocandins are classes of lipocyclohexapeptides that are broad spectrum antifungal agents. They inhibit fungal specific 1,3-β-glucan synthase activity which is an essential component of the fungal cell wall. Chemical modifications of these two leads have produced three clinical agents namely caspofungin, micafungin and anidulafungin.

Isolation, structure, and biological activity of Phaeofungin, a cyclic lipodepsipeptide from a Phaeosphaeria sp. Using the Genome-Wide Candida albicans Fitness Test.

Phaeofungin (1), a new cyclic depsipeptide isolated from Phaeosphaeria sp., was discovered by application of reverse genetics technology, using the Candida albicans fitness test (CaFT). Phaeofungin is comprised of seven amino acids and a β,γ-dihydroxy-γ-methylhexadecanoic acid arranged in a 25-membered cyclic depsipeptide.

Antifungal spectrum, in vivo efficacy, and structure-activity relationship of ilicicolin h.

Ilicicolin H is a polyketide-nonribosomal peptide synthase (NRPS)-natural product isolated from Gliocadium roseum, which exhibits potent and broad spectrum antifungal activity, with sub-μg/mL MICs against Candida spp., Aspergillus fumigatus, and Cryptococcus spp. It showed a novel mode of action, potent inhibition (IC50 = 2-3 ng/mL) of the mitochondrial cytochrome bc1 reductase, and over 1000-fold selectivity relative to rat liver cytochrome bc1 reductase.

Efficacy of caspofungin in a juvenile mouse model of central nervous system candidiasis.

Neonatal candidiasis is an increasingly common occurrence causing significant morbidity and mortality and a higher risk of dissemination to the central nervous system (CNS) than that seen with older patients. The current understanding of optimal antifungal therapy in this setting is limited. We have developed a model of disseminated candidiasis with CNS involvement in juvenile mice to assess the efficacy of the echinocandin caspofungin relative to amphotericin B (AmB).

Isolation, structure elucidation, and biological activity of virgineone from Lachnum Wirgineum using the genome-wide Candida albicans fitness test.

A glycosylated tetramic acid, virgineone (1), was isolated from saprotrophic Lachnum virgineum. The antifungal activity of the fermentation extract of L. virgineum was characterized in the Candida albicans fitness test as distinguishable from other natural products tested.

Isolation, structure and biological activity of phomafungin, a cyclic lipodepsipeptide from a widespread tropical Phoma sp.

We isolated a cyclic lipodepsipeptide, phomafungin, from a Phoma sp. The distinct antifungal activity of phomafungin in the crude extract was initially discovered by mechanistic profiling in the Candida albicans fitness test. The purified compound contains a 28 member ring consisting of eight amino acids and a beta-hydroxy-gamma-methyl-hexadecanoic acid, and displays a broad spectrum of antifungal activity against Candida spp.

PAP inhibitor with in vivo efficacy identified by Candida albicans genetic profiling of natural products.

Natural products provide an unparalleled source of chemical scaffolds with diverse biological activities and have profoundly impacted antimicrobial drug discovery. To further explore the full potential of their chemical diversity, we survey natural products for antifungal, target-specific inhibitors by using a chemical-genetic approach adapted to the human fungal pathogen Candida albicans and demonstrate that natural-product fermentation extracts can be mechanistically annotated according to heterozygote strain responses. Applying this approach, we report the discovery and characterization of a natural product, parnafungin, which we demonstrate, by both biochemical and genetic means, to inhibit poly(A) polymerase.

In vivo efficacy of a novel oxazolidinone compound in two mouse models of infection.

A novel oxazolidinone, AM 7359, was evaluated in two mouse models of Staphylococcus aureus infection. AM 7359 and linezolid were equally efficacious in a methicillin-susceptible S. aureus organ burden model and a methicillin-resistant S.

Efficacy of caspofungin against Aspergillus flavus, Aspergillus terreus, and Aspergillus nidulans.

The echinocandin caspofungin is a potent inhibitor of the activity of 1,3-beta-D-glucan synthase from Aspergillus flavus, Aspergillus terreus, and Aspergillus nidulans. In murine models of disseminated infection, caspofungin prolonged survival and reduced the kidney fungal burden. Caspofungin was at least as effective as amphotericin B against these filamentous fungi in vivo.

Specific substitutions in the echinocandin target Fks1p account for reduced susceptibility of rare laboratory and clinical Candida sp. isolates.

An association between reduced susceptibility to echinocandins and changes in the 1,3-beta-d-glucan synthase (GS) subunit Fks1p was investigated. Specific mutations in fks1 genes from Saccharomyces cerevisiae and Candida albicans mutants are described that are necessary and sufficient for reduced susceptibility to the echinocandin drug caspofungin. One group of amino acid changes in ScFks1p, ScFks2p, and CaFks1p defines a conserved region (Phe 641 to Asp 648 of CaFks1p) in the Fks1 family of proteins.

A new ene-triyne antibiotic from the fungus Baeospora myosura.

The isolation and structure elucidation of 1 from the Basidomycete fungus Baeospora myosura is described. This new ene-triyne antibiotic was most potent against Gram-positive bacteria, while it was less active against Gram-negative bacteria and a yeast. MICs against several strains of Staphylococcus aureus were as low as 0.

Inactivation of Kex2p diminishes the virulence of Candida albicans.

Deletion of the kexin gene (KEX2) in Candida albicans has a pleiotropic effect on phenotype and virulence due partly to a defect in the expression of two major virulence factors: the secretion of active aspartyl proteinases and the formation of hyphae. kex2/kex2 mutants are highly attenuated in a mouse systemic infection model and persist within cultured macrophages for at least 24 h without causing damage. Pathology is modest, with little disruption of kidney matrix.

Arundifungin, a novel antifungal compound produced by fungi: biological activity and taxonomy of the producing organisms.

Echinocandins, the lipopeptide class of glucan synthase inhibitors, are an alternative to ergosterol-synthesis inhibitors to treat candidiasis and aspergillosis. Their oral absorption, however, is low and they can only be used parenterally. During a natural product screening program for novel types of glucan synthesis inhibitors with improved bioavailability, a fungal extract was found that inhibited the growth of both a wild-type Saccharomyces cerevisiae strain and the null mutant of the FKS1 gene (fks1::HIS).

Antimicrobial activity of ergokonin A from Trichoderma longibrachiatum.

Aims: Natural fungal products were screened for antifungal compounds. The mode of action of one of the hits found and the taxonomy of the producing organism were analysed.

Methods And Results: An extract from a Trichoderma species showed a more potent activity in an agar-based assay against the null mutant fks1::HIS strain than against the wild-type strain, suggesting that it could contain a glucan synthesis inhibitor.

Quantitative PCR assay to measure Aspergillus fumigatus burden in a murine model of disseminated aspergillosis: demonstration of efficacy of caspofungin acetate.

Caspofungin acetate (MK-0991) is an antifungal antibiotic that inhibits the synthesis of 1,3-beta-D-glucan, an essential component of the cell wall of several pathogenic fungi. Caspofungin acetate was recently approved for the treatment of invasive aspergillosis in patients who are refractory to or intolerant of other therapies. The activity of 1,3-beta-D-glucan synthesis inhibitors against Aspergillus fumigatus has been evaluated in animal models of pulmonary or disseminated disease by using prolongation of survival or reduction in tissue CFU as assay endpoints.

The discovery of enfumafungin, a novel antifungal compound produced by an endophytic Hormonema species biological activity and taxonomy of the producing organisms.

In a screening of natural products with antifungal activity derived from endophytic fungi, we detected a potent activity in a culture belonging to the form-genus Hormonema, isolated from leaves of Juniperus communis. The compound is a new triterpene glycoside, showing an antifungal activity highly potent in vitro against Candida and Aspergillus and with moderate efficacy in an in vivo mouse model of disseminated candidiasis. The agent is especially interesting since its antifungal spectrum and its effect on morphology of Aspergillus fumigatus is comparable to that of the glucan synthase inhibitor pneumocandin B,,, the natural precursor of the clinical candidate MK-0991 (caspofungin acetate).

Efficacy of the echinocandin caspofungin against disseminated aspergillosis and candidiasis in cyclophosphamide-induced immunosuppressed mice.

The in vivo efficacy of the echinocandin antifungal caspofungin acetate (caspofungin; MK-0991) was evaluated in models of disseminated aspergillosis and candidiasis in mice with cyclophosphamide (CY)-induced immunosuppression. Caspofungin is a 1, 3-beta-D-glucan synthesis inhibitor efficacious against a number of clinically relevant fungi including Aspergillus and Candida species. Models of CY-induced transient or chronic leukopenia were used with once daily administration of therapy initiated 24 h after microbial challenge.

Discovery of novel antifungal (1,3)-beta-D-glucan synthase inhibitors.

The increasing incidence of life-threatening fungal infections has driven the search for new, broad-spectrum fungicidal agents that can be used for treatment and prophylaxis in immunocompromised patients. Natural-product inhibitors of cell wall (1,3)-beta-D-glucan synthase such as lipopeptide pneumocandins and echinocandins as well as the glycolipid papulacandins have been evaluated as potential therapeutics for the last two decades. As a result, MK-0991 (caspofungin acetate; Cancidas), a semisynthetic analogue of pneumocandin B(o), is being developed as a broad-spectrum parenteral agent for the treatment of aspergillosis and candidiasis.

Identification and purification of the reconstitutively active glutamine carrier from rat kidney mitochondria.

The glutamine carrier from rat kidney mitochondria, solubilized in dodecyl octaoxyethylene ether (C12E8) and partly purified on hydroxyapatite, was identified and completely purified by Celite chromatography. On SDS/PAGE, the purified glutamine carrier consisted of a single protein band with an apparent molecular mass of 41.5 kDa.

Rustmicin, a potent antifungal agent, inhibits sphingolipid synthesis at inositol phosphoceramide synthase.

Rustmicin is a 14-membered macrolide previously identified as an inhibitor of plant pathogenic fungi by a mechanism that was not defined. We discovered that rustmicin inhibits inositol phosphoceramide synthase, resulting in the accumulation of ceramide and the loss of all of the complex sphingolipids. Rustmicin has potent fungicidal activity against clinically important human pathogens that is correlated with its sphingolipid inhibition.

Antibacterial activity of lonchocarpol A.

Lonchocarpol A, a flavanone, demonstrates in vitro inhibitory activity against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium. This activity is antagonized by mouse plasma, which may account for its lack of in vivo activity. This compound demonstrates no differentiation with respect to the inhibition of RNA, DNA, cell wall, and protein synthesis.