Polyketide glycosides phialotides A to H, new potentiators of amphotericin B activity, produced by Pseudophialophora sp. BF-0158

Paranazzamides A and B, new cyclic dipeptides containing a C7-prenylated tryptophan, produced by pathogenic reptile fungi Paranannizziopsis sp. UH-21

Two new cyclic dipeptides, paranazzamides A (1) and B (2) containing a C7-prenylated tryptophan, were isolated from a culture broth of snake fungal disease-isolate Paranannizziopsis sp. UH-21. This is the first report on the new secondary metabolites from Paranannizziopsis sp. The planar structures of 1 and 2 were elucidated using various spectroscopic techniques including MS and 1D/2D NMR. The absolute configuration of 1 was assigned by comparison with the synthesized compound. Compounds 1 and 2 exhibited no antifungal activity, no antibacterial activity, and no cytotoxic activity even at a concentration of 128 µg ml-1, whereas 1 and 2 exhibited amphotericin B potentiating activity against Candida auris in combination treatment.

Synthesis and biological evaluation of nectriatide derivatives, potentiators of amphotericin B activity

Nectriatide 1a, a naturally occurring cyclic tetrapeptide, has been reported to a potentiator of amphotericin B (AmB) activity. In order to elucidate its structure-activity relationships, we synthesized nectriatide derivatives with different amino acids in solution-phase synthesis and evaluated AmB-potentiating activity against Candida albicans. Among them, C-and N-terminal protected linear peptides were found to show the most potent AmB-potentiating activity.

Cytotoxic Polyhydroxy-Isoprenoids from Neodidymelliopsis negundinis

Fungal-derived natural products continue to play a pivotal role in the discovery of drug agents for human, veterinary, and general agricultural use. The fungus Neodidymelliopsis negundinis presents a significant saprobic ascomycete whose metabolites remained hitherto unstudied. Herein we report the isolation of eight unprecedented secondary metabolites named neodidymelliosides A and B (1 and 2), neodidymelliol A (3), and neodidymellioic acids A-E (4-8) produced by the submerged cultures of the fungus. Compound 1 proved to be the most active compound, with IC50 values ranging between 4.8 and 8.8 μM against KB3.1 (cervix), PC-3 (prostate), MCF-7 (breast), SKOV-3 (ovary), A431 (skin), and A549 (lung) cell lines. Compound 1 revealed significant inhibition of Staphylococcus aureus and Candida albicans biofilms.

New potentiators of amphotericin B activity, shodoamides A to C produced by Pseudophialophora sp. BF-0158

During our screening program for new potentiators of amphotericin B activity against Candida albicans, shodoamides A to C (1-3) were isolated from a culture broth of the fungus Pseudophialophora sp. BF-0158 fermented under shaking conditions. A known congener named shodoamide D (4) in this paper was obtained from a culture broth of the BF-0158 strain fermented under static conditions. The structures of 1-4 were assigned based on spectroscopic analyses, including NMR and MS, and were found to have a common N-(2´,3´,4´-trihydroxybutyl)-6-methyl-2,4-tetradecadienamide structure. Compounds 1-3 exhibited no antifungal activity, but they induced up to 32-fold increases in amphotericin B activity against C. albicans by a microdilution method.

New piericidin rhamnosides as potentiators of amphotericin B activity against Candida albicans produced by actinomycete strain TMPU-A0287

Four new piericidin rhamnosides (2, 4-6) together with three known piericidins (1, 3, 7) were isolated from the culture broth of the unidentified actinomycete strain TMPU-A0287 as potentiators of antifungal amphotericin B (AmB) activity. The structures of piericidins were elucidated by spectroscopic analyses, including NMR and MS. Compounds 2 and 4-6 possessed a ketone at C-10 and one or two methoxy groups on the rhamnose in their structures. Compounds 1-7 did not exhibit antifungal activity against Candida albicans and all potentiated AmB activity. The MIC values of AmB against C. albicans combined with 1-7 (4.0 μg ml-1) decreased from 0.50 to 0.063 or 0.031 μg ml-1, yielding an 8- or 16-fold increase in AmB activity.

Recent developments on the anti-Candida effect of amphotericin B combined with a second drug - a mini-review

Invasive Candida infections threaten human health due to the increasing incidence of resistance to the currently available antifungal agents. Amphotericin B (AMB) is the gold standard therapy to treat these infections. Nevertheless, the use of such substance in the clinic is aggravated by its toxicity. Since AMB binds to membrane sterols, it forms pores on human plasma membranes, mainly in kidney cells, leading to nephrotoxicity. The combination of this drug to a second substance could allow for the use of smaller concentrations of AMB, consequently lowering the probability of adverse effects. This mini-review summarizes information regarding an array of substances that enhance AMB antifungal activity. It may be noticed that several of these compounds target plasma membrane. Interestingly, substances approved for human use also presented combinatory anti-Candida activity with AMB. These data reinforce the potential of associating AMB to another drug as a promising therapeutical alternative to treat Candida infections. Further studies, regarding mechanism of action, pharmacokinetics and toxicity parameters must be conducted to confirm the role of these substances as adjuvant agents in candidiasis therapy.

Indispensable role of microbes in anticancer drugs and discovery trends

Recent years have seen an increased focus on the advancement of naturally derived products for the treatment of cancer. Since the beginning of recorded history, nature has provided a variety of medicinal agents, and an overwhelming number of drugs that we have today are derived from natural sources. Such natural agents are prominently used to treat several diseases such as diabetes, malaria, Alzheimer's, pulmonary disorders, etc. with cancer being the highlight of this review. Due to the rapid development of resistance to chemotherapeutic drugs, the hunt for effective novel drugs is still a paramount concern in cancer treatment. Moreover, many chemotherapy drugs typically have high toxicity and adverse side effects, which necessitates the need to develop anti-tumor drugs that can be employed to treat deadly tumors with fewer negative effects on health and better efficacy. Isolation of several chemotherapeutic drugs has been conducted from a wide range of natural sources which include plants, microbes, fungi, and marine microorganisms. Considering the trends of previous decades, microbial diversity has grown to play a significant role in the formulation of pharmaceuticals and drugs, especially antibiotics and anti-cancer medications. Microbe-derived antitumor antibiotics such as anthracycline, epothilones, bleomycin, actinomycin, and staurosporine are amongst the widely used cancer chemotherapeutic agents. This review deals majorly with microbe-derived anticancer drugs taking into account their derivatives, mechanism of action, isolation procedures, limitations, and tumors targeted by them. This article also reports the phase of clinical study these drugs are undergoing. Moreover, it intends to portray the indispensable part that these microbes have been playing since time immemorial in the odyssey of chemotherapeutic agents. KEY POINTS: • Microbial diversity contributes heavily towards the formulation of anticancer drugs. • Polypeptides, carbohydrates, and alkaloids are prevalent microbe-based drug classes. • Microbe-derived anticancer agents target various sarcomas, carcinomas, and lymphomas.

Biochemistry-Guided Prediction of the Absolute Configuration of Fungal Reduced Polyketides

Highly reducing polyketide synthases (HR-PKSs) produce structurally diverse polyketides (PKs). The PK diversity is constructed by a variety of factors, including the β-keto processing, chain length, methylation pattern, and relative and absolute configurations of the substituents. We examined the stereochemical course of the PK processing for the synthesis of polyhydroxy PKs such as phialotides, phomenoic acid, and ACR-toxin. Heterologous expression of a HR-PKS gene, a trans-acting enoylreductase gene, and a truncated non-ribosomal peptide synthetase gene resulted in the formation of a linear PK with multiple stereogenic centers. The absolute configurations of the stereogenic centers were determined by chemical degradation followed by comparison of the degradation products with synthetic standards. A stereochemical rule was proposed to explain the absolute configurations of other reduced PKs and highlights an error in the absolute configurations of a reported structure. The present work demonstrates that focused functional analysis of functionally related HR-PKSs leads to a better understanding of the stereochemical course.

Podogigants A and B, two new potentiators of amphotericin B activity, from Sordariomycete Podostroma giganteum

Two new compounds, podogigants A (1) and B (2), were isolated from the culture broth of Podostroma giganteum. This is the first report on the identification of secondary metabolites in P. giganteum. The structures of 1 and 2 were elucidated through spectroscopic analysis, including 2D NMR spectroscopy assisted by chemical derivatization, which revealed the presence of farnesyl- and geranyl-hydroquinone structures, respectively. Compounds 1 and 2 exhibited no antifungal activity even at a concentration of 64 μg/mL, whereas they potentiated amphotericin B (AmB) activity against several species of fungi. In particular, 1 potentiated AmB activity against C. albicans and R. oryzae by up to 32-fold (MIC value of AmB decreased from 1.0 to 0.032 µg/mL), while 2 potentiated AmB activity against C. albicans by up to 16-fold.