A Novel Actin Binding Drug with In Vivo Efficacy

Determination of the amino linkage of the D-Dab residue of the cyclic lipo-octapeptide occidiofungins A-D and the antifungal activity of their analogues

Recently, the demand for new antifungal drugs has increased due to the presence of antimicrobial resistant bacteria and their side effects. Occidiofungins (Ocfs) are cyclic lipo-octapeptides that possess unusual amino acids and potent antifungal activities. However, the chemical structure of the 2,4-diamino butyric acid (Dab) residue in the backbone of Ocfs has not been clarified thus far. Therefore, we conducted a structural analysis of the tripeptides around the Dab residue in Ocfs using 1H-NMR spectroscopy. We determined that the D-Dab residue in the peptide backbone of Ocfs has an α-amino linkage. Additionally, we found that Ocf A (5) and Bk-1119 have the same chemical structure. Moreover, the analogue possessing D-αDab (13) showed potent antifungal activity against A. oryzae.

AHL-Based Quorum Sensing Regulates the Biosynthesis of a Variety of Bioactive Molecules in Bacteria

Bacteria are social microorganisms that use communication systems known as quorum sensing (QS) to regulate diverse cellular behaviors including the production of various secreted molecules. Bacterial secondary metabolites are widely studied for their bioactivities including antibiotic, antifungal, antiparasitic, and cytotoxic compounds. Besides playing a crucial role in natural bacterial niches and intermicrobial competition by targeting neighboring organisms and conferring survival advantages to the producer, these bioactive molecules may be of prime interest to develop new antimicrobials or anticancer therapies. This review focuses on bioactive compounds produced under acyl homoserine lactone-based QS regulation by Gram-negative bacteria that are pathogenic to humans and animals, including the Burkholderia, Serratia, Pseudomonas, Chromobacterium, and Pseudoalteromonas genera. The synthesis, regulation, chemical nature, biocidal effects, and potential applications of these identified toxic molecules are presented and discussed in light of their role in microbial interactions.

Previously Uncharacterized Variants, OCF-E-OCF-J, of the Antifungal Occidiofungin Produced by Burkholderia contaminans MS14

The rise of multidrug resistant fungal infections highlights the need to identify and develop novel antifungal agents. Occidiofungin is a nonribosomally synthesized glycolipopeptide that has a unique mechanism of action, disrupting actin-mediated functions and inducing cellular apoptosis. Antifungal activity has been observed in vitro against various fungal species, including multidrug resistant Candida auris, and in vivo efficacy has been demonstrated in a murine vulvovaginal candidiasis model. Occidiofungin, a cyclic glycolipopeptide, is composed of eight amino acids and in previous studies, an asparagine residue was assigned at position 7 (ASN7). In this study, new structural variants of occidiofungin have been characterized which have aspartic acid (ASP7), glutamine (GLN7), or glutamic acid (GLU7) at position 7. The side chain of the ASP7 variant contains the only terminal carboxylic acid in the peptide and provides a useful site for selective chemical modifications. Analogues were synthesized at the ASP7 position and tested for antifungal activity. These analogues were shown to be more active as compared to the ASP7 variant against a panel of Candida species. The naturally occurring variants of occidiofungin with a side chain containing a carboxylic acid at the seventh amino acid position can be used to develop semisynthetic analogues with enhanced therapeutic properties.

Genome-guided purification of high amounts of the siderophore ornibactin and detection of potentially novel burkholdine derivatives produced by Burkholderia catarinensis 89T

AIM

The increased availability of genome sequences has enabled the development of valuable tools for the prediction and identification of bacterial natural products. Burkholderia catarinensis 89T produces siderophores and an unknown potent antifungal metabolite. The aim of this work was to identify and purify natural products of B. catarinensis 89T through a genome-guided approach.

MATERIALS AND METHODS

The analysis of B. catarinensis 89T genome revealed 16 clusters putatively related to secondary metabolism and antibiotics production. Of particular note was the identification of a nonribosomal peptide synthetase (NRPS) cluster related to the production of the siderophore ornibactin, a hybrid NRPS-polyketide synthase Type 1 cluster for the production of the antifungal glycolipopeptide burkholdine, and a gene cluster encoding homoserine lactones (HSL), probably involved in the regulation of both metabolites. We were able to purify high amounts of the ornibactin derivatives D/C6 and F/C8, while also detecting the derivative B/C4 in mass spectrometry investigations. A group of metabolites with molecular masses ranging from 1188 to 1272 Da could be detected in MS experiments, which we postulate to be new burkholdine analogs produced by B. catarinensis. The comparison of B. catarinensis BGCs with other Bcc members corroborates the hypothesis that this bacterium could produce new derivatives of these metabolites. Moreover, the quorum sensing metabolites C6-HSL, C8-HSL, and 3OH-C8-HSL were observed in LC-MS/MS analysis.

CONCLUSION

The new species B. catarinensis is a potential source of new bioactive secondary metabolites. Our results highlight the importance of genome-guided purification and identification of metabolites of biotechnological importance.

Occidiofungin inhibition of Candida biofilm formation on silicone elastomer surface

IMPORTANCE

Candida are opportunistic fungal pathogens with medical relevance given their association with superficial to life-threatening infections. An important component of Candida virulence is the ability to form a biofilm. These structures are highly resistant to antifungal therapies and are often the cause of treatment failure. In this work, we evaluated the efficacy of the antifungal compound, occidiofungin, against Candida biofilms developed on a silicone surface. We demonstrate that occidiofungin eliminated cells at all stages of biofilm formation in a dose-dependent manner. Consistent with our understanding of occidiofungin bioactivity, we noted alterations to actin organization and cell morphology following antifungal exposure. Given the challenges associated with the treatment of biofilm-associated infections, occidiofungin exhibits potential as a therapeutic antifungal agent in the future.

Synthesis and characterization of semisynthetic analogs of the antifungal occidiofungin

Occidiofungin is a broad-spectrum antifungal compound produced by Burkholderia contaminans MS14. It is a cyclic glycol-lipopeptide with a novel beta-amino acid (NAA2) containing a hydroxylated C18 fatty acid chain with a xylose sugar. This study reports a strategy to produce semisynthetic analogs of occidiofungin to further explore the structure activity relationships of this class of compounds. Oxidative cleavage of the diol present on carbons five C(5) and six C(6) removes the xylose and twelve carbons of the fatty acid chain. The resulting cyclic peptide product, occidiofungin aldehyde, is devoid of antifungal activity. However, the free aldehyde group on this product can be subjected to reductive amination reactions to provide interesting semisynthetic analogs. This chemistry allows the quick generation of analogs to study the structure activity relationships of this class of compounds. Despite restoring the length of the aliphatic side chain by reductive amination addition with undecylamine or dodecylamine to the free aldehyde group, the obtained analogs did not demonstrate any antifungal activity. The antifungal activity was partially restored by the addition of a DL-dihydrosphingosine. The dodecylamine analog was demonstrated to still bind to the cellular target actin, suggesting that the diol on the side chain of native occidiofungin is important for entry into the cell enabling access to cellular target F-actin. These results show that the alkyl side chain on NAA2 along with the diol present on this side chain is important for occidiofungin's antifungal activity.

Many ways, one microorganism: Several approaches to study Malassezia in interactions with model hosts

Malassezia, a lipophilic and lipid-dependent yeast, is a microorganism of current interest to mycobiologists because of its role as a commensal or pathogen in health conditions such as dermatological diseases, fungemia, and, as discovered recently, cancer and certain neurological disorders. Various novel approaches in the study of Malassezia have led to increased knowledge of the cellular and molecular mechanisms of this yeast. However, additional efforts are needed for more comprehensive understanding of the behavior of Malassezia in interactions with the host. This article reviews advances useful in the experimental field for Malassezia.

Synthesis and Configuration Confirmation of the ATHOD Fatty Amino Acid Residue in the Burkholdines

Eight possible diastereomers of the 3-amino-5,6,7-trihydroxy octadecanoic acid (ATHOD) moiety of the burkholdines (Bks) have been synthesized and their configurations assigned. Though the relative configuration of the triol in the ATHOD residue of the Bks was proposed to be anti-anti-anti in the literature, ¹H NMR spectra of our synthesized anti-anti-anti ATHOD derivative was inconsistent with that of the isolated ATHOD residue, suggesting that the assignment of the relative configuration of that residue in the literature was incorrect. However, by comparison of the NMR data of our ATHOD derivatives with that of configurationally defined samples of 2-amino-4-pentanol using Kishi's NMR database method, we conclude that the absolute configuration of the ATHOD moiety is (3R,5S,6R,7S). In addition, we revealed that the ATHOD residue present in the occidiofungins A-D has the same configuration as that in all the Bks.

Occidiofungin: Actin Binding as a Novel Mechanism of Action in an Antifungal Agent

The identification and development of natural products into novel antimicrobial agents is crucial to combat the rise of multidrug-resistant microorganisms. Clinical fungal isolates have been identified, which have shown resistance to all current clinical antifungals, highlighting a significant need to develop a novel antifungal agent. One of the natural products produced by the bacterium Burkholderia contaminans MS14 is the glycolipopeptide occidiofungin. Occidiofungin has demonstrated in vitro activity against a multitude of fungal species, including multidrug-resistant Candida auris strains, and in vivo effectiveness in treating vulvovaginal candidiasis. Characterization of occidiofungin revealed the mechanism of action as binding to actin to disrupt higher-order actin-mediated functions leading to the induction of apoptosis in fungal cells. Occidiofungin is the first small molecule capable of disrupting higher-order actin functions and is a first-in-class compound that is able to circumvent current antifungal resistant mechanisms by fungal species. Anticancer properties and antiparasitic activities, against Cryptosporidium parvum, have also been demonstrated in vitro. The novel mechanism of action and wide spectrum of activity highlights the potential of occidiofungin to be developed for clinical use.

Occidiofungin Is the Key Metabolite for Antifungal Activity of the Endophytic Bacterium Burkholderia sp. MS455 Against Aspergillus flavus

Aflatoxin is a secondary metabolite produced by Aspergillus fungi and presents a major food safety concern globally. Among the available methods for prevention and control of aflatoxin, the application of antifungal bacteria has gained favor in recent years. An endophytic bacterium MS455, isolated from soybean, exhibited broad-spectrum antifungal activity against economically important pathogens, including Aspergillus flavus. MS455 was identified as a strain of Burkholderia based on genomic analysis. Random and site-specific mutations were used in discovery of the genes that share high homology to the ocf gene cluster of Burkholderia contaminans strain MS14, which is responsible for production of the antifungal compound occidiofungin. RNA sequencing analysis demonstrated that ORF1, a homolog to the ambR1 LuxR-type regulatory gene, regulates occidiofungin biosynthesis in MS455. Additionally, 284 differentially expressed genes, including 138 upregulated and 146 downregulated genes, suggesting that, in addition to its role in occidiofungin production, ORF1 is involved in expression of multiple genes, especially those involved in ornibactin biosynthesis. Plate bioassays showed the growth of A. flavus was significantly inhibited by the wild-type strain MS455 as compared with the ORF1 mutant. Similarly, corn kernel assays showed that growth of A. flavus and aflatoxin production were reduced significantly by MS455 as compared with buffer control and the ORF1 mutant. Collectively, the results demonstrated that production of occidiofungin is essential for antifungal activity of the endophytic bacterium MS455. This research has provided insights about antifungal mechanisms of MS455 and development of biological approaches to prevent aflatoxin contamination in plant production.

The Hydrophobicity and Antifungal Potentiation of Burkholdine Analogues

The burkholdines are a family of cyclic lipopeptides reported to exhibit antifungal activity. We synthesized a series of 18 burkholdine analogues in good yield by conventional Fmoc-SPPS followed by cyclization with DIPCI/HOBt in the solution phase. Although none of the synthesized peptides exhibited antifungal activity, several did potentiate the antibiotic effect of the antibiotic G418, including the Thr-bearing Bk analogue (4b) and the tartaramide-bearing Bk analogue (5b). This work exemplifies the potential of burkholdine analogues as potentiating agents.

Antifungal Peptides from a Burkholderia Strain Suppress Basal Stem Rot Disease of Oil Palm

Basal stem rot (BSR) is the most common disease of oil palm (Elaeis guineensis) in Southeast Asia. BSR is caused by a white-rot fungus Ganoderma boninense. The disease is difficult to manage. Therefore, development of novel and environmentally safe approaches to control the disease is important. Species of Burkholderia are known to have diverse lifestyles, some of which can benefit plants by suppressing diseases or increasing plant growth. In the present study, antifungal peptides produced by a bacterial strain isolated from the rhizosphere of an oil palm tree, Burkholderia sp. strain CP01, exhibited strong growth inhibition on G. boninense. A loss-of-function mutant of CP01 was generated, and it has enabled the identification of a 1.2-kDa peptide and its variants as the active antifungal compounds. High-resolution mass spectrometry revealed six analogous compounds with monoisotopic masses similar to the previously reported cyclic lipopeptides occidiofungin and burkholdine. The antifungal compounds of CP01 were secreted into media, and we sought to use CP01 culture extract without living cells to control BSR disease. Glasshouse experiments showed that CP01 culture extract suppressed BSR disease in oil palm seedlings. The ability of CP01 to produce an antifungal substance and suppress plant disease suggests its potential applications as a biofungicide in agriculture.

Inhibition of morphological transition and hyphae extension in Candida spp. by occidiofungin

AIMS

To assess the efficacy of the antifungal, occidiofungin, against Candida albicans and Candida tropicalis morphological transformation.

METHODS AND RESULTS

Susceptibility assays and morphological data were used to demonstrate that occidiofungin effectively targets C. albicans and C. tropicalis undergoing morphological transformation. Susceptibility assays found that cell sensitivity to occidiofungin varied with the media conditions used for morphological switching. Microscopy data showed that occidiofungin inhibited hyphae formation when added at the time of morphological induction and hyphal extension when added within the first hour following hyphae induction. Immunoblot analysis demonstrated that occidiofungin addition prevented activation of Cek1p MAPK signalling.

CONCLUSIONS

The data indicated that the antimicrobial compound, occidiofungin, effectively targets hyphae elongation in Candida spp. and suggests the biological target of occidiofungin is necessary for the morphological changes associated with yeast-to-hyphae switching.

SIGNIFICANCE AND IMPACT OF THE STUDY

Findings from this study demonstrated that occidiofungin effectively targets the invasive growth of dimorphic Candida which suggests this compound may also inhibit the heterogenous population of cells present in a clinical setting. This presents occidiofungin as a promising candidate for the treatment of Candida associated infections.

Burkholderia in the genomic era: from taxonomy to the discovery of new antimicrobial secondary metabolites

Species of Burkholderia are highly versatile being found not only abundantly in soil, but also as plants and animals' commensals or pathogens. Their complex multireplicon genomes harbour an impressive number of polyketide synthase (PKS) and nonribosomal peptide-synthetase (NRPS) genes coding for the production of antimicrobial secondary metabolites (SMs), which have been successfully deciphered by genome-guided tools. Moreover, genome metrics supported the split of this genus into Burkholderia sensu stricto (s.s.) and five new other genera. Here, we show that the successful antimicrobial SMs producers belong to Burkholderia s.s. Additionally, we reviewed the occurrence, bioactivities, modes of action, structural, and biosynthetic information of thirty-eight Burkholderia antimicrobial SMs shedding light on their diversity, complexity, and uniqueness as well as the importance of genome-guided strategies to facilitate their discovery. Several Burkholderia NRPS and PKS display unusual features, which are reflected in their structural diversity, important bioactivities, and varied modes of action. Up to now, it is possible to observe a general tendency of Burkholderia SMs being more active against fungi. Although the modes of action and biosynthetic gene clusters of many SMs remain unknown, we highlight the potential of Burkholderia SMs as alternatives to fight against new diseases and antibiotic resistance.

Drug discovery through the isolation of natural products from Burkholderia

Introduction: The increasing threat of antibiotic-resistant pathogens makes it imperative that new antibiotics to combat them are discovered. Burkholderia is a genus of Gram-negative, non-sporulating bacteria. While ubiquitous and capable of growing within plants and groundwater, they are primarily soil-dwelling organisms. These include the more virulent forms of Burkholderia such as Burkholderia mallei, Burkholderia pseudomallei, and the Burkholderia cepacia complex (Bcc).Areas covered: This review provides a synopsis of current research on the natural products isolated from the genus Burkholderia. The authors also cover the research on the drug discovery efforts that have been performed on the natural products derived from Burkholderia.Expert opinion: Though Burkholderia has a small number of pathogenic species, the majority of the genus is avirulent and almost all members of the genus are capable of producing useful antimicrobial products that could potentially lead to the development of novel therapeutics against infectious diseases. The need for discovery of new antibiotics is urgent due to the ever-increasing prevalence of antibiotic-resistant pathogens, coupled with the decline in the discovery of new antibiotics.

Systematic Identification of Protein Targets of Sub5 Using Saccharomyces cerevisiae Proteome Microarrays

Antimicrobial peptides (AMPs) are intensively studied in terms of alternative drugs. Sub5 is a synthetic 12-mer AMP with substitutions of five amino acids of bactenecin 2A (Bac2A), a linear-ized bactenecin variant of bovine. Sub5 is highly effective against fungi with an ability to trans-locate cell membrane, but its targets are unknown. Systematic analysis of Sub5 targets will facil-itate our understanding on its mechanism of action. In this study, we used high-throughput Saccharomyces cerevisiae proteome microarrays to explore the potential protein targets of Sub5. The screening results showed 128 potential protein targets of Sub5. Bioinformatics analysis of protein targets of Sub5 revealed significant gene ontology (GO) enrichment in actin related pro-cess of “actin filament-based process”, “actin filament organization”, “actin cortical patch or-ganization”, regulation of “actin filament bundle assembly”. Moreover, the other enriched cat-egories in GO enrichment mostly contained actin associate proteins. In total, 11 actin-associated proteins were identified in the protein targets of Sub5. Protein family (PFAM) enrichment anal-ysis shows protein domain enriched in actin binding, i.e., “Cytoskeletal-regulatory complex EF hand (helix E-loop-helix F motif)”. Being consistent with GO analysis, Search Tool for the Re-trieval of Interacting Genes/Proteins (STRING) analysis of the protein targets of Sub5 showed ac-tin network with involvement of 15 protein targets. Along with actin-network, STRING analysis showed protein–protein interaction network in ribonucleoprotein, transcription and translation, chromosome, histone, and ubiquitin related, DNA repair, and chaperone. Multiple Expression motifs for Motif Elicitation (MEME) suite provided a consensus binding motif of [ED][ED]EEE[ED][ED][ED][ED][ED], in total of 75 protein targets of Sub5. This motif was present in 9 out of 15 actin-related proteins identified among protein targets of Sub5.

Toward understanding the signals of bacteriocin production by Streptococcus spp. and their importance in current applications

Microorganisms have developed quorum sensing (QS) systems to detect small signaling molecules that help to control access to additional nutrients and space in highly competitive polymicrobial niches. Many bacterial processes are QS-regulated; two examples are the highly related traits of the natural genetic competence state and the production of antimicrobial peptides such as bacteriocins. The Streptococcus genus is widely studied for its competence and for its ability to produce bacteriocins, as these antimicrobial peptides have significant potential in the treatment of infections caused by multiple-resistant pathogens, a severe public health issue. The transduction of a two-component system controls competence in streptococci: (1) ComD/E, which controls the competence in the Mitis and Anginosus groups, and (2) ComR/S, which performs the same function in the Bovis, Mutans, Salivarius, and Pyogenic groups. The cell-to-cell communication required for bacteriocin production in the Streptococcus groups is controlled mainly by a paralog of the ComD/E system. The relationships between pheromone signals and induction pathways are related to the bacteriocin production systems. In this review, we discuss the recent advances in the understanding of signaling and the induction of bacteriocin biosynthesis by QS regulation in streptococci. This information could aid in the design of better methods for the development and production of these antimicrobial peptides. It could also contribute to the analysis and emerging applications of bacteriocins in terms of their safety, quality, and human health benefits.

Formulation, Pharmacological Evaluation, and Efficacy Studies of Occidiofungin, a Novel Antifungal

Occidiofungin is a nonribosomally synthesized cyclic lipopeptide that possesses broad-spectrum antifungal properties at submicromolar concentrations. This report explores multiple routes of administration and formulations of occidiofungin, as well as its toxicity in mice. Further, infection studies were performed in mice to assess the application of occidiofungin for treating systemic and intravaginal yeast infections. Formulations for intravenous and intravaginal administration of occidiofungin were prepared. Pharmacokinetic analyses were performed in a murine model, and a liquid chromatography-mass spectrometry (LC-MS) method was developed and used to quantify occidiofungin in mouse plasma samples. Toxicological and histopathological analyses of two repeat-dose studies using occidiofungin were performed. In these animal models, following intravenous administration, a liposomal formulation of occidiofungin improved the half-life and peak plasma drug concentration over that with a liposome-free formulation. Two long-term repeat-dosing toxicity studies of occidiofungin indicated the absence of toxicity in organ tissues. Murine models of a systemic yeast infection and a vulvovaginal yeast infection were performed. The findings of the systemic infection study revealed limitations in the use of occidiofungin that may be alleviated with the development of novel structural analogs or with further formulation studies. The gel formulation of occidiofungin demonstrated improved efficacy over that of the commercial product Monistat 3 in a vulvovaginal candidiasis study. This report outlines the optimal routes of administration of occidiofungin and demonstrates minimal toxicity following chronic exposure. Further, the results of these studies provide a clear indication for the use of occidiofungin for the treatment of recurrent vulvovaginal candidiasis (RVVC), which is a serious and clinically relevant issue.

An actin depolymerizing agent 19,20-epoxycytochalasin Q of Xylaria sp. BCC 1067 enhanced antifungal action of azole drugs through ROS-mediated cell death in yeast

Multidrug resistance is a highly conserved phenomenon among all living organisms and a major veritable public health problem worldwide. Repetitive uses of antibiotics lead to antimicrobial drug resistance. Here, 19,20-epoxycytochalasin Q (ECQ) was isolated from endophytic fungus Xylaria sp. BCC 1067 and, its chemical structure was determined via chromatographic and spectral methods. ECQ displayed an antifungal activity with low MIC₅₀ of 410 and 55 mg/l in the model yeast Saccharomyces cerevisiae wild-type and ScΔpdr5 strains, respectively. ECQ was a new inducer and potential substrate of key multi-drug efflux pumps S. cerevisiae ScPdr5 and Candida albicans CaCdr1. ECQ targeted actin filament, disrupting actin dynamics of yeast cells. ECQ also sensitized the ScΔsrv2 mutant, lacking suppressor of RasVal19. Overexpression of ScPDR5 or CaCDR1 genes prevented aggregation of actin and alleviated antifungal effect of ECQ. Additionally, ECQ induced high accumulation of reactive oxygen species, caused plasma membrane leakage and decreased yeast cell survival. Importantly, a discovery of ECQ implied a cellular connection between multi-drug resistance and actin stability, an important determinant of transporter mediated-drug resistance mechanism. Combination of ECQ and antifungal azoles displayed promising drug synergy against S. cerevisiae strains expressing multi-drug transporters, thereby providing potential solution for antifungal therapy and chemotherapeutic application.

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.

Identification of the Antifungal Metabolite Chaetoglobosin P From Discosia rubi Using a Cryptococcus neoformans Inhibition Assay: Insights Into Mode of Action and Biosynthesis

Cryptococcus neoformans is an important human pathogen with limited options for treatments. We have interrogated extracts from fungal fermentations to find Cryptococcus-inhibiting natural products using assays for growth inhibition, differential thermosensitivity, and synergy with existing antifungal drugs. Extracts from fermentations of strains of Discosia rubi from eastern Texas showed anticryptococcal bioactivity with preferential activity in agar zone of inhibition assays against C. neoformans at 37°C versus 25°C. Assay-guided fractionation led to the purification and identification of chaetoglobosin P as the active component of these extracts. Genome sequencing of these strains revealed a biosynthetic gene cluster consistent with chaetoglobosin biosynthesis and β-methylation of the tryptophan residue. Proximity of genes of the actin-binding protein twinfilin-1 to the chaetoglobosin P and K gene clusters suggested a possible self-resistance mechanism involving twinfilin-1 which is consistent with the predicted mechanism of action involving interference with the polymerization of the capping process of filamentous actin. A C. neoformans mutant lacking twinfilin-1 was hypersensitive to chaetoglobosin P. Chaetoglobosins also potentiated the effects of amphotericin B and caspofungin on C. neoformans.

Novel Antiparasitic Activity of the Antifungal Lead Occidiofungin

Novel antiparasitic activity was observed for the antifungal occidiofungin. It efficaciously and irreversibly inhibited the zoonotic enteric parasite Cryptosporidium parvum in vitro with limited cytotoxicity (50% effective concentration [EC₅₀] = 120 nM versus 50% cytotoxic concentration [TC₅₀] = 988 nM), and its application disrupted the parasite morphology. This study expands the spectrum of activity of a glycolipopeptide named occidiofungin. Occidiofungin has poor gastrointestinal tract absorption properties, supporting future investigations into its potential activities on other enteric parasites.

Targeting and extending the eukaryotic druggable genome with natural products: cytoskeletal targets of natural products

Covering: 2014-2019We review recent progress on natural products that target cytoskeletal components, including microtubules, actin, intermediate filaments, and septins and highlight their demonstrated and potential utility in the treatment of human disease. The anticancer efficacy of microtubule targeted agents identified from plants, microbes, and marine organisms is well documented. We highlight new microtubule targeted agents currently in clinical evaluations for the treatment of drug resistant cancers and the accumulating evidence that the anticancer efficacy of these agents is not solely due to their antimitotic effects. Indeed, the effects of microtubule targeted agents on interphase microtubules are leading to their potential for more mechanistically guided use in cancers as well as neurological disease. The discussion of these agents as more targeted drugs also prompts a reevaluation of our thinking about natural products that target other components of the cytoskeleton. For instance, actin active natural products are largely considered chemical probes and non-selective toxins. However, studies utilizing these probes have uncovered aspects of actin biology that can be more specifically targeted to potentially treat cancer, neurological disorders, and infectious disease. Compounds that target intermediate filaments and septins are understudied, but their continued discovery and mechanistic evaluations have implications for numerous therapeutic indications.

Burkholderia as a Source of Natural Products

Burkholderia bacteria are multifaceted organisms that are ecologically and metabolically diverse. The Burkholderia genus has gained prominence because it includes human pathogens; however, many strains are nonpathogenic and have desirable characteristics such as beneficial plant associations and degradation of pollutants. The diversity of the Burkholderia genus is reflected within the large genomes that feature multiple replicons. Burkholderia genomes encode a plethora of natural products with potential therapeutic relevance and biotechnological applications. This review highlights Burkholderia as an emerging source of natural products. An overview of the taxonomy of the Burkholderia genus, which is currently being revised, is provided. We then present a curated compilation of natural products isolated from Burkholderia sensu lato and analyze their characteristics in terms of biosynthetic class, discovery method, and bioactivity. Finally, we describe and discuss genome characteristics and highlight the biosynthesis of a select number of natural products that are encoded in unusual biosynthetic gene clusters. The availability of >1000 Burkholderia genomes in public databases provides an opportunity to realize the genetic potential of this underexplored taxon for natural product discovery.