Discovery of bioactive natural products of microbial origin as inhibitors of the PD-1/PD-L1 protein-protein interaction

The PD-1/PD-L1 protein-protein interaction (PPI) controls an adaptive immune resistance mechanism exerted by tumor cells to evade immune responses. The large-molecule nature of current commercial monoclonal antibodies against this PPI hampers their effectiveness by limiting tumor penetration and inducing severe immune-related side effects. Synthetic small-molecule inhibitors may overcome such limitations and have demonstrated promising clinical translation, but their design is challenging. Microbial natural products (NPs) are a source of small molecules with vast chemical diversity that have proved anti-tumoral activities, but which immunotherapeutic properties as PD-1/PD-L1 inhibitors had remained uncharacterized so far. Here, we have developed the first cell-based PD-1/PD-L1 blockade reporter assay to screen NPs libraries. In this study, 6000 microbial extracts of maximum biosynthetic diversity were screened. A secondary metabolite called alpha-cyclopiazonic acid (α-CPA) of a bioactive fungal extract was confirmed as a new PD-1/PD-L1 inhibitor with low micromolar range in the cellular assay and in an additional cell-free competitive assay. Thermal denaturation experiments with PD-1 confirmed that the mechanism of inhibition is based on its stabilization upon binding to α-CPA. The identification of α-CPA as a novel PD-1 stabilizer proves the unprecedented resolution of this methodology at capturing specific PD-1/PD-L1 PPI inhibitors from chemically diverse NP libraries.

Naphthoquinone Derivatives from Angustimassarina populi CF-097565 Display Anti-Tumour Activity in 3D Cultures of Breast Cancer Cells

Cancer is one of the leading causes of death worldwide, with breast cancer being the second cause of cancer-related mortality among women. Natural Products (NPs) are one of the main sources for drug discovery. During a screening campaign focused on the identification of extracts from Fundación MEDINA's library inhibiting the proliferation of cancer cell lines, a significant bioactivity was observed in extracts from cultures of the fungus Angustimassarina populi CF-097565. Bioassay-guided fractionation of this extract led to the identification and isolation of herbarin (1), 1-hydroxydehydroherbarin (4) plus other three naphthoquinone derivatives of which 3 and 5 are new natural products and 2 is herein described from a natural source for the first time. Four of these compounds (1, 3, 4 and 5) confirmed a specific cytotoxic effect against the human breast cancer cell line MCF-7. To evaluate the therapeutic potential of the compounds isolated, their efficacy was validated in 3D cultures, a cancer model of higher functionality. Additionally, an in-depth study was carried out to test the effect of the compounds in terms of cell mortality, sphere disaggregation, shrinkage, and morphology. The cell profile of the compounds was also compared to that of known cytotoxic compounds with the aim to distinguish the drug mode of action (MoA). The profiles of 1, 3 and 4 showed more biosimilarity between them, different to 5, and even more different to other known cytotoxic agents, suggesting an alternative MoA responsible for their cytotoxicity in 3D cultures.

Madurastatins with Imidazolidinone Rings: Natural Products or Side-Reaction Products from Extraction Solvents?

Madurastatins are a group of pentapeptides containing an oxazoline moiety, and, in a few cases, an imidazolidinone ring as an additional structural feature. In our search for new potential antiparasitic metabolites from natural sources, we studied the acetone extracts from a culture of Actinomadura sp. CA-135719. The LC/HRMS analysis of this extract identified the presence of the known madurastatins C1 (1), D1 (4), and D2 (5) together with additional members of the family that were identified as the new madurastatins H2 (2) and 33-epi-D1 (3) after isolation and spectroscopic analysis. The planar structures of the new compounds were established by HRMS, ESI-qTOF-MS/MS, and 1D and 2D NMR data, and their absolute configuration was proposed using Marfey's and bioinformatic analyses of the biosynthetic gene cluster (BGC). A revision of the absolute configuration of madurastatins D1 and D2 is proposed. Additionally, madurastatins containing imidazolidinone rings are proved to be artifacts originating during acetone extraction of the bacterial cultures.

Interactions of Different Streptomyces Species and Myxococcus xanthus Affect Myxococcus Development and Induce the Production of DK-Xanthenes

The co-culturing of microorganisms is a well-known strategy to study microbial interactions in the laboratory. This approach facilitates the identification of new signals and molecules produced by one species that affects other species' behavior. In this work, we have studied the effects of the interaction of nine Streptomyces species (S. albidoflavus, S. ambofaciens, S. argillaceus, S. griseus, S. lividans, S. olivaceus, S. parvulus, S. peucetius, and S. rochei) with the predator bacteria Myxococcus xanthus, five of which (S. albidoflavus, S. griseus, S. lividans, S. olivaceus, and S. argillaceus) induce mound formation of M. xanthus on complex media (Casitone Yeast extract (CYE) and Casitone tris (CTT); media on which M. xanthus does not form these aggregates under normal culture conditions. An in-depth study on S. griseus-M. xanthus interactions (the Streptomyces strain producing the strongest effect) has allowed the identification of two siderophores produced by S. griseus, demethylenenocardamine and nocardamine, responsible for this grouping effect over M. xanthus. Experiments using pure commercial nocardamine and different concentrations of FeSO4 show that iron depletion is responsible for the behavior of M. xanthus. Additionally, it was found that molecules, smaller than 3 kDa, produced by S. peucetius can induce the production of DK-xanthenes by M. xanthus.

Acoustic droplet ejection facilitates cell-based high-throughput screenings using natural products

Natural Products (NPs) are one of the main sources for drug discovery. Many clinical drugs are NPs or NP-inspired compounds, and recently discovered New Chemical Entities (NCEs) of NPs are emerging as promising new drugs. High-Throughput Screening (HTS) of large sample sets or libraries has grown to be vital for the drug discovery field. Industrial-scale HTS of NP libraries can be limited due to the difficulties entailed in working with tiny extract volumes and the variability in viscosity of NP extracts. For these reasons, the implementation of new technologies to miniaturize different reagent volumes grows to be fundamental. Since Acoustic Droplet Ejection (ADE) emerged as a helpful tool in HTS campaigns for the transference of compound libraries. The aim of this work was to test the effectiveness of ADE for the dispensation of NP extract libraries in cell-based HTS assays.

Development and Validation of a HTS Platform for the Discovery of New Antifungal Agents against Four Relevant Fungal Phytopathogens

Fungal phytopathogens are the major agents responsible for causing severe damage to and losses in agricultural crops worldwide. Botrytis cinerea, Colletotrichum acutatum, Fusarium proliferatum, and Magnaporthe grisea are included in the top ten fungal phytopathogens that impose important plant diseases on a broad range of crops. Microbial natural products can be an attractive alternative for the biological control of phytopathogens. The objective of this work was to develop and validate a High-throughput Screening (HTS) platform to evaluate the antifungal potential of chemicals and natural products against these four important plant pathogens. Several experiments were performed to establish the optimal assay conditions that provide the best reproducibility and robustness. For this purpose, we have evaluated two media formulations (SDB and RPMI-1640), several inoculum concentrations (1 × 106, 5 × 105 and 5 × 106 conidia/mL), the germination curves for each strain, each strain's tolerance to dimethyl sulfoxide (DMSO), and the Dose Response Curves (DRC) of the antifungal control (Amphotericin B). The assays were performed in 96-well plate format, where absorbance at 620 nm was measured before and after incubation to evaluate growth inhibition, and fluorescence intensity at 570 nm excitation and 615 nm emission was monitored after resazurin addition for cell viability evaluation. Quality control parameters (RZ' Factors and Signal to Background (S/B) ratios) were determined for each assay batch. The assay conditions were finally validated by titrating 40 known relevant antifungal agents and testing 2400 microbial natural product extracts from the MEDINA Library through both HTS agar-based and HTS microdilution-based set-ups on the four phytopathogens.

Delftia tsuruhatensis TC1 symbiont suppresses malaria transmission by anopheline mosquitoes

Malaria control demands the development of a wide range of complementary strategies. We describe the properties of a naturally occurring, non-genetically modified symbiotic bacterium, Delftia tsuruhatensis TC1, which was isolated from mosquitoes incapable of sustaining the development of Plasmodium falciparum parasites. D. tsuruhatensis TC1 inhibits early stages of Plasmodium development and subsequent transmission by the Anopheles mosquito through secretion of a small-molecule inhibitor. We have identified this inhibitor to be the hydrophobic molecule harmane. We also found that, on mosquito contact, harmane penetrates the cuticle, inhibiting Plasmodium development. D. tsuruhatensis TC1 stably populates the mosquito gut, does not impose a fitness cost on the mosquito, and inhibits Plasmodium development for the mosquito's life. Contained field studies in Burkina Faso and modeling showed that D. tsuruhatensis TC1 has the potential to complement mosquito-targeted malaria transmission control.

Activation and Identification of a Griseusin Cluster in Streptomyces sp. CA-256286 by Employing Transcriptional Regulators and Multi-Omics Methods

Streptomyces are well-known producers of a range of different secondary metabolites, including antibiotics and other bioactive compounds. Recently, it has been demonstrated that "silent" biosynthetic gene clusters (BGCs) can be activated by heterologously expressing transcriptional regulators from other BGCs. Here, we have activated a silent BGC in Streptomyces sp. CA-256286 by overexpression of a set of SARP family transcriptional regulators. The structure of the produced compound was elucidated by NMR and found to be an N-acetyl cysteine adduct of the pyranonaphtoquinone polyketide 3'-O-α-d-forosaminyl-(+)-griseusin A. Employing a combination of multi-omics and metabolic engineering techniques, we identified the responsible BGC. These methods include genome mining, proteomics and transcriptomics analyses, in combination with CRISPR induced gene inactivations and expression of the BGC in a heterologous host strain. This work demonstrates an easy-to-implement workflow of how silent BGCs can be activated, followed by the identification and characterization of the produced compound, the responsible BGC, and hints of its biosynthetic pathway.

Design of High-Throughput Screening of Natural Extracts to Identify Molecules Bypassing Primary Coenzyme Q Deficiency in Saccharomyces cerevisiae

Coenzyme Q₁₀ (CoQ₁₀) deficiency syndrome is a rare disease included in the family of mitochondrial diseases, which is a heterogeneous group of genetic disorders characterized by defective energy production. CoQ₁₀ biosynthesis in humans requires at least 11 gene products acting in a multiprotein complex within mitochondria. The high-throughput screening (HTS) method based on the stabilization of the CoQ biosynthesis complex (Q-synthome) produced by the COQ8 gene overexpression is proven here to be a successful method for identifying new molecules from natural extracts that are able to bypass the CoQ₆ deficiency in yeast mutant cells. The main features of the new approach are the combination of two yeast targets defective in genes with different functions on CoQ₆ biosynthesis to secure the versatility of the molecule identified, the use of glycerol as a nonfermentable carbon source providing a wide growth window, and the stringent conditions required to mark an extract as positive. The application of this pilot approach to a representative subset of 1200 samples of the Library of Natural Products of Fundación MEDINA resulted in the finding of nine positive extracts. The fractionation of three of the nine extracts allowed the identification of five molecules; two of them are present in molecule databases of natural extracts and three are nondescribed molecules. The use of this screening method opens the possibility of discovering molecules with CoQ₁₀-bypassing action useful as therapeutic agents to fight against mitochondrial diseases in human patients.

Fungal endophytes from arid areas of Andalusia: high potential sources for antifungal and antitumoral agents

Native plant communities from arid areas present distinctive characteristics to survive in extreme conditions. The large number of poorly studied endemic plants represents a unique potential source for the discovery of novel fungal symbionts as well as host-specific endophytes not yet described. The addition of adsorptive polymeric resins in fungal fermentations has been seen to promote the production of new secondary metabolites and is a tool used consistently to generate new compounds with potential biological activities. A total of 349 fungal strains isolated from 63 selected plant species from arid ecosystems located in the southeast of the Iberian Peninsula, were characterized morphologically as well as based on their ITS/28S ribosomal gene sequences. The fungal community isolated was distributed among 19 orders including Basidiomycetes and Ascomycetes, being Pleosporales the most abundant order. In total, 107 different genera were identified being Neocamarosporium the genus most frequently isolated from these plants, followed by Preussia and Alternaria. Strains were grown in four different media in presence and absence of selected resins to promote chemical diversity generation of new secondary metabolites. Fermentation extracts were evaluated, looking for new antifungal activities against plant and human fungal pathogens, as well as, cytotoxic activities against the human liver cancer cell line HepG2. From the 349 isolates tested, 126 (36%) exhibited significant bioactivities including 58 strains with exclusive antifungal properties and 33 strains with exclusive activity against the HepG2 hepatocellular carcinoma cell line. After LCMS analysis, 68 known bioactive secondary metabolites could be identified as produced by 96 strains, and 12 likely unknown compounds were found in a subset of 14 fungal endophytes. The chemical profiles of the differential expression of induced activities were compared. As proof of concept, ten active secondary metabolites only produced in the presence of resins were purified and identified. The structures of three of these compounds were new and herein are elucidated.

Hormonemate Derivatives from Dothiora sp., an Endophytic Fungus

A search for cytotoxic agents from cultures of the endophytic fungus Dothiora sp., isolated from the endemic plant Launaea arborescens, led to the isolation of six new compounds structurally related to hormonemate, with moderate cytotoxic activity against different cancer cell lines. By using a bioassay-guided fractionation approach, hormonemates A-D (1-4), hormonemate (5), and hormonemates E (6) and F (7) were obtained from the acetone extract of this fungus. Their structures were determined using a combination of HRMS, ESI-qTOF-MS/MS, 1D and 2D NMR experiments, and chemical degradation. The cytotoxic activities of these compounds were evaluated by microdilution colorimetric assays against human breast adenocarcinoma (MCF-7), human liver cancer cells (HepG2), and pancreatic cancer cells (MiaPaca_2). Most of the compounds displayed cytotoxic activity against this panel.

Co-culturing of Fungal Strains Against Botrytis cinerea as a Model for the Induction of Chemical Diversity and Therapeutic Agents

New fungal SMs (SMs) have been successfully described to be produced by means of in vitro-simulated microbial community interactions. Co-culturing of fungi has proved to be an efficient way to induce cell–cell interactions that can promote the activation of cryptic pathways, frequently silent when the strains are grown in laboratory conditions. Filamentous fungi represent one of the most diverse microbial groups known to produce bioactive natural products. Triggering the production of novel antifungal compounds in fungi could respond to the current needs to fight health compromising pathogens and provide new therapeutic solutions. In this study, we have selected the fungus Botrytis cinerea as a model to establish microbial interactions with a large set of fungal strains related to ecosystems where they can coexist with this phytopathogen, and to generate a collection of extracts, obtained from their antagonic microbial interactions and potentially containing new bioactive compounds. The antifungal specificity of the extracts containing compounds induced after B. cinerea interaction was determined against two human fungal pathogens (Candida albicans and Aspergillus fumigatus) and three phytopathogens (Colletotrichum acutatum, Fusarium proliferatum, and Magnaporthe grisea). In addition, their cytotoxicity was also evaluated against the human hepatocellular carcinoma cell line (HepG2). We have identified by LC-MS the production of a wide variety of known compounds induced from these fungal interactions, as well as novel molecules that support the potential of this approach to generate new chemical diversity and possible new therapeutic agents.

Production of Ramoplanin and Ramoplanin Analogs by Actinomycetes

Ramoplanin is a glycolipodepsipeptide antibiotic obtained from fermentation of Actinoplanes sp. ATCC 33076 that exhibits activity against clinically important multi-drug-resistant, Gram-positive pathogens including vancomycin-resistant Enterococcus (VRE), methicillin-resistant Staphylococcus aureus (MRSA), and vancomycin-intermediate resistant Clostridium difficile. It disrupts bacterial cell wall through a unique mechanism of action by sequestering the peptidoglycan intermediate Lipid II and therefore does not show cross-resistance with other antibiotics. However, while demonstrating excellent antimicrobial activity in systemic use in animal models of infection, ramoplanin presents low local tolerability when injected intravenously. As a consequence of this limitation, new derivatives are desirable to overcome this issue. During a natural product screening program developed to discover compounds that disrupt bacterial cell wall synthesis by inhibiting peptidoglycan transglycosylation through binding to the intermediate Lipid II, 49 actinomycete strains were identified by HR-LCMS as producers of ramoplanin-related compounds. The producing strains were isolated from environmental samples collected worldwide comprising both tropical and temperate areas. To assess the diversity of this microbial population, the 49 isolates were initially identified to the genus level on the basis of their micromorphology, and 16S sequencing confirmed the initial identification of the strains. These analyses resulted in the identification of members of genus Streptomyces, as well as representatives of the families Micromonosporaceae, Nocardiaceae, Thermomonosporaceae, and Pseudonocardiaceae, suggesting that the production of ramoplanins is relatively widespread among Actinomycetes. In addition, all of these isolates were tested against a panel of Gram-positive and Gram-negative bacteria, filamentous fungi, and yeast in order to further characterize their antimicrobial properties. This work describes the diversity of actinomycete strains that produced ramoplanin-related compounds, and the analysis of the antimicrobial activity exhibited by these isolates. Our results strongly suggest the presence of new ramoplanin-analogs among these actinomycete producers.

High-Throughput Screening Platform for the Discovery of New Immunomodulator Molecules from Natural Product Extract Libraries

It is widely accepted that central nervous system inflammation and systemic inflammation play a significant role in the progression of chronic neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease, neurotropic viral infections, stroke, paraneoplastic disorders, traumatic brain injury, and multiple sclerosis. Therefore, it seems reasonable to propose that the use of anti-inflammatory drugs might diminish the cumulative effects of inflammation. Indeed, some epidemiological studies suggest that sustained use of anti-inflammatory drugs may prevent or slow down the progression of neurodegenerative diseases. However, the anti-inflammatory drugs and biologics used clinically have the disadvantage of causing side effects and a high cost of treatment. Alternatively, natural products offer great potential for the identification and development of bioactive lead compounds into drugs for treating inflammatory diseases with an improved safety profile. In this work, we present a validated high-throughput screening approach in 96-well plate format for the discovery of new molecules with anti-inflammatory/immunomodulatory activity. The in vitro models are based on the quantitation of nitrite levels in RAW264.7 murine macrophages and interleukin-8 in Caco-2 cells. We have used this platform in a pilot project to screen a subset of 5976 noncytotoxic crude microbial extracts from the MEDINA microbial natural product collection. To our knowledge, this is the first report on an high-throughput screening of microbial natural product extracts for the discovery of immunomodulators.

Cyclic colisporifungin and linear cavinafungins, antifungal lipopeptides isolated from Colispora cavincola

Colisporifungin (1), a cyclic depsilipopeptide structurally related to the aselacins, and cavinafungins A and B, two linear peptides, were isolated from liquid culture broths of the hitherto unstudied fungus Colispora cavincola using a Candida albicans whole-cell assay as well as a bioassay to detect compounds potentiating the antifungal activity of caspofungin. The structural elucidation, including the absolute configuration of the new molecules, was accomplished using a combination of spectroscopic and chemical techniques, including 1D and 2D NMR, HRMS, and Marfey's analysis. The cyclic peptide colisporifungin displayed a strong potentiation of the growth inhibitory effect of caspofungin against Aspergillus fumigatus and, to a lesser extent, against Candida albicans. The linear peptides displayed broad-spectrum antifungal activities inhibiting growth of Candida species (MIC values 0.5-4 μg/mL) as well as A. fumigatus with a prominent inhibition of 8 μg/mL.

High-throughput screening platform for natural product-based drug discovery against 3 neglected tropical diseases: human African trypanosomiasis, leishmaniasis, and Chagas disease

African trypanosomiasis, leishmaniasis, and Chagas disease are 3 neglected tropical diseases for which current therapeutic interventions are inadequate or toxic. There is an urgent need to find new lead compounds against these diseases. Most drug discovery strategies rely on high-throughput screening (HTS) of synthetic chemical libraries using phenotypic and target-based approaches. Combinatorial chemistry libraries contain hundreds of thousands of compounds; however, they lack the structural diversity required to find entirely novel chemotypes. Natural products, in contrast, are a highly underexplored pool of unique chemical diversity that can serve as excellent templates for the synthesis of novel, biologically active molecules. We report here a validated HTS platform for the screening of microbial extracts against the 3 diseases. We have used this platform in a pilot project to screen a subset (5976) of microbial extracts from the MEDINA Natural Products library. Tandem liquid chromatography-mass spectrometry showed that 48 extracts contain potentially new compounds that are currently undergoing de-replication for future isolation and characterization. Known active components included actinomycin D, bafilomycin B1, chromomycin A3, echinomycin, hygrolidin, and nonactins, among others. The report here is, to our knowledge, the first HTS of microbial natural product extracts against the above-mentioned kinetoplastid parasites.

Development of a Drosophila melanogaster spliceosensor system for in vivo high-throughput screening in myotonic dystrophy type 1

Alternative splicing of pre-mRNAs is an important mechanism that regulates cellular function in higher eukaryotes. A growing number of human genetic diseases involve splicing defects that are directly connected to their pathology. In myotonic dystrophy type 1 (DM1), several clinical manifestations have been proposed to be the consequence of tissue-specific missplicing of numerous genes. These events are triggered by an RNA gain-of-function and resultant deregulation of specific RNA-binding factors, such as the nuclear sequestration of muscleblind-like family factors (MBNL1–MBNL3). Thus, the identification of chemical modulators of splicing events could lead to the development of the first valid therapy for DM1 patients. To this end, we have generated and validated transgenic flies that contain a luciferase-reporter-based system that is coupled to the expression of MBNL1-reliant splicing (spliceosensor flies), to assess events that are deregulated in DM1 patients in a relevant disease tissue. We then developed an innovative 96-well plate screening platform to carry out in vivo high-throughput pharmacological screening (HTS) with the spliceosensor model. After a large-scale evaluation (>16,000 chemical entities), several reliable splicing modulators (hits) were identified. Hit validation steps recognized separate DM1-linked therapeutic traits for some of the hits, which corroborated the feasibility of the approach described herein to reveal promising drug candidates to correct missplicing in DM1. This powerful Drosophila-based screening tool might also be applied in other disease models displaying abnormal alternative splicing, thus offering myriad uses in drug discovery.

Assessing the effects of adsorptive polymeric resin additions on fungal secondary metabolite chemical diversity

Adsorptive polymeric resins have been occasionally described to enhance the production of specific secondary metabolites (SMs) of interest. Methods that induce the expression of new chemical entities in fungal fermentations may lead to the discovery of new bioactive molecules and should be addressed as possible tools for the creation of new microbial chemical libraries for drug lead discovery. Herein, we apply both biological activity and chemical evaluations to assess the use of adsorptive resins as tools for the differential expression of SMs in fungal strain sets. Data automation approaches were applied to ultra high performance liquid chromatography analysis of extracts to evaluate the general influence in generating new chemical entities or in changing the production of specific SMs by fungi grown in the presence of resins and different base media.

High-Content Screening of Natural Products Reveals Novel Nuclear Export Inhibitors

Natural products are considered an extremely valuable source for the discovery of new drugs against diverse pathologies. As yet, we have only explored a fraction of the diversity of bioactive compounds, and opportunities for discovering new natural products leading to new drugs are huge. In the present study, U2nesRELOC, a previously established cell-based imaging assay, was employed to screen a collection of extracts of microbial origin for nuclear export inhibition activity. The fluorescent signal of untreated U2nesRELOC cells localizes predominantly to the cytoplasm. Upon treatment with the nuclear export inhibitor leptomycin B, the fluorescent-tagged reporter proteins appear as speckles in the nucleus. A proprietary collection of extracts from fungi, actinomycetes, and unicellular bacteria that covers an uncommonly broad chemical space was used to interrogate this nuclear export assay system. A two-step image-based analysis allowed us to identify 12 extracts with biological activities that are not associated with previously known active metabolites. The fractionation and structural elucidation of active compounds revealed several chemical structures with nuclear export inhibition activity. Here we show that substrates of the nuclear export receptor CRM1, such as Rev, FOXO3a and NF-κB, accumulate in the nucleus in the presence of the fungal metabolite MDN-0105 with an IC50 value of 3.4 µM. Many important processes in tumor formation and progression, as well as in many viral infections, critically depend on the nucleocytoplasmic trafficking of proteins and RNA molecules. Therefore, the disruption of nuclear export is emerging as a novel therapeutic approach with enormous clinical potential. Our work highlights the potential of applying high-throughput phenotypic imaging on natural product extracts to identify novel nuclear export inhibitors.

A Yeast-Based In Vivo Bioassay to Screen for Class I Phosphatidylinositol 3-Kinase Specific Inhibitors

The phosphatidylinositol 3-kinase (PI3K) pathway couples receptor-mediated signaling to essential cellular functions by generating the lipid second messenger phosphatidylinositol-3,4,5- trisphosphate. This pathway is implicated in multiple aspects of oncogenesis. A low-cost bioassay that readily measures PI3K inhibition in vivo would serve as a valuable tool for research in this field. Using heterologous expression, we have previously reconstituted the PI3K pathway in the model organism Saccharomyces cerevisiae. On the basis of the fact that the overproduction of PI3K is toxic in yeast, we tested the ability of commercial PI3K inhibitors to rescue cell growth. All compounds tested counteracted the PI3K-induced toxicity. Among them, 15e and PI-103 were the most active. Strategies to raise the intracellular drug concentration, specifically the use of 0.003% sodium dodecyl sulfate and the elimination of the Snq2 detoxification pump, optimized the bioassay by enhancing its sensitivity. The humanized yeast-based assay was then tested on a pilot scale for high-throughput screening (HTS) purposes using a collection of natural products of microbial origin. From 9600 extracts tested, 0.6% led to a recovery of yeast growth reproducibly, selectively, and in a dose-dependent manner. Cumulatively, we show that the developed PI3K inhibition bioassay is robust and applicable to large-scale HTS.

A new approach to drug discovery: high-throughput screening of microbial natural extracts against Aspergillus fumigatus using resazurin

Natural products are an inexhaustible source for drug discovery. However, the validation and selection of primary screening assays are vital to guarantee a selection of extracts or molecules with relevant pharmacological action and worthy of following up. The assay must be rapid, simple, easy to implement, and produce quick results and preferably at a low cost. In this work, we developed and validated a colorimetric microtiter assay using the resazurin viability dye. The parameters of the resazurin method for high-throughput screening (HTS) using natural extracts against Aspergillus fumigatus were optimized and set up. The extracts plus RPMI-1640 modified medium containing the spores and 0.002% resazurin were added per well. The fluorescence was read after 24 to 30 h of incubation. The resazurin proved to be as suitable as Alamar Blue for determining the minimal inhibitory concentration of different antifungals against A. fumigatus and effective to analyze fungicidal and fungistatic compounds. An HTS of 12 000 microbial extracts was carried out against two A. fumigatus strains, and 2.7% of the extracts displayed antifungal activity. Our group has been the first to use this methodology for screening a collection of natural extracts to identify compounds with antifungal activity against the medically important human pathogen A. fumigatus.

Manipulating filamentous fungus chemical phenotypes by growth on nutritional arrays

Methods for manipulating and fermenting microorganisms in multi-well plates offer unlimited possibilities for high-throughput parallel experimentation. Furthermore, bar-coded data tracking and downstream processing with modern liquid handling equipment reduce handling errors and are able to format microbial products for autosampler-equipped analytical instruments, e.g., HPLCs, mass spectrometers, and plate readers. An integrated system for high-throughput culturing of filamentous fungi replicating strains across many fermentation parameters, called nutritional arrays, was developed. It takes advantage of this equipment while addressing the age-old dilemma of how to manipulate fungal phenotypes to express a more complete spectrum of their secondary metabolites. Growth of any given strain in a well-designed nutritional array increases the chances of detecting a biologically active metabolite while reducing the manpower and materials needed for preparing individual fermentations and extracts. Fungi fermented in nutritional arrays are directly processed in a semi-automated fashion and the extracts prepared for bioassays and analytical chemistry. The necessary equipment, custom tools, and protocols to grow fungi in nutritional arrays are described along with examples of bioactive secondary metabolites discovered using this system.

Automation of Sample Dispensing Using Pocket Tips for Evaluation of CYP2C9 Isoenzyme Reversible Inhibition in an Evolution Precision Pipetting Platform

Most of the medicinal chemistry compounds received from other Merck Research Laboratories (MRL) for evaluation in our in vitro counterscreenings are in pure DMSO solution. This solvent has shown to be a key interference factor in the radiometric evaluation of cytochrome P-450 (CYP) inhibition. To avoid this problem, we have been using a ternary solvent solution that keeps DMSO concentration to a minimum during the titration of the compounds.

The equipment used at our laboratory to perform the dose—response titration of the compounds in the CYP assays is PerkinElmer Evolution Precision Pipetting Platform (EP3) robots with limited microliter capabilities using disposable tips. The need for a nanoliter dispensing technique that keeps the percentage of DMSO at levels that do not affect the assay, and the need to use pure DMSO solutions at high concentrations to avoid solubility issues of the compounds, moved us to design a new automated sample management process for all compounds that were requested to be tested in these assays.

The PocketTips system (nAscent BioSciences Inc., Wellesley Hills, MA) seemed to be a good option for pipetting very low volumes without acquiring new expensive nanoliter liquid handling equipment. Apparent difficulties with implementation were the unavailability of PocketTips for the 96-tips head of the EP3 (PerkinElmer, Waltham, MA) and the need for testing several CYP isoenzymes (up to four) by using the same rack of tips to save run time and reduce costs.

In this article, we discuss the entire process to introduce and validate a new dispensing process for sampling of compounds with multiple nanoliters dispensing at the assay level, indicating in detail how we implemented the use of recycled PocketTips in our PerkinElmer EP3 workstations.

Enhancement of antibiotic and secondary metabolite detection from filamentous fungi by growth on nutritional arrays

AIMS

We asked to what extent does the application of the OSMAC (one strain, many compounds) approach lead to enhanced detection of antibiotics and secondary metabolites in fungi? Protocols for bacterial microfermentations were adapted to grow fungi in nutritional arrays.

METHODS AND RESULTS

Protocols for microfermentations of non-sporulating fungi were validated using known antifungal-producing fungi. Detection of antifungal activity was often medium dependent. The effects of medium arrays and numbers of strains on detection of antifungal signals were modelled by interpolation of rarefaction curves derived from matrices of positive and negative extracts. Increasing the number of fermentation media for any given strain increased the probability of detection of growth inhibition of Candida albicans. Increasing biodiversity increased detection of antifungal phenotypes, however, nutritional arrays could partly compensate for lost antibiotic phenotypes when biodiversity was limiting.

CONCLUSIONS

Growth and extraction in microtiter plates can enable a discovery strategy emphasizing low-cost medium arrays that can better exploit the metabolic potential of strains.

SIGNIFICANCE AND IMPACT OF THE STUDY

Increasing fermentation parameters raise the probability of detecting bioactive metabolites from strains. The protocols can be used to pre-select strains and their growth conditions for scale up that will most likely yield antibiotics and secondary metabolites.

New antitumoral acetogenin 'Guanacone type' derivatives: isolation and bioactivity. Molecular dynamics simulation of diacetyl-guanacone

We describe herein the isolation and semisynthesis of four acetogenin derivatives (1-4) as well as their ability to inhibit the mitochondrial respiratory chain and several tumor cell lines. In addition, four nanoseconds (ns) of MD simulation of compound 4, in a fully hydrated POPC bilayer, is reported.

Platensimycin is a selective FabF inhibitor with potent antibiotic properties

Bacterial infection remains a serious threat to human lives because of emerging resistance to existing antibiotics. Although the scientific community has avidly pursued the discovery of new antibiotics that interact with new targets, these efforts have met with limited success since the early 1960s. Here we report the discovery of platensimycin, a previously unknown class of antibiotics produced by Streptomyces platensis. Platensimycin demonstrates strong, broad-spectrum Gram-positive antibacterial activity by selectively inhibiting cellular lipid biosynthesis. We show that this anti-bacterial effect is exerted through the selective targeting of beta-ketoacyl-(acyl-carrier-protein (ACP)) synthase I/II (FabF/B) in the synthetic pathway of fatty acids. Direct binding assays show that platensimycin interacts specifically with the acyl-enzyme intermediate of the target protein, and X-ray crystallographic studies reveal that a specific conformational change that occurs on acylation must take place before the inhibitor can bind. Treatment with platensimycin eradicates Staphylococcus aureus infection in mice. Because of its unique mode of action, platensimycin shows no cross-resistance to other key antibiotic-resistant strains tested, including methicillin-resistant S. aureus, vancomycin-intermediate S. aureus and vancomycin-resistant enterococci. Platensimycin is the most potent inhibitor reported for the FabF/B condensing enzymes, and is the only inhibitor of these targets that shows broad-spectrum activity, in vivo efficacy and no observed toxicity.

The discovery of moriniafungin, a novel sordarin derivative produced by Morinia pestalozzioides

A novel sordarin derivative, moriniafungin (1), containing a 2-hydroxysebacic acid residue linked to C-3' of the sordarose residue of sordarin through a 1,3-dioxolan-4-one ring was isolated from the fungus Morinia pestalozzioides. Isolation of moriniafungin employed a highly specific bioassay consisting of a panel of Saccharomyces cerevisiae strains containing chimeric eEF2 for Candida glabrata, Candida krusei, Candida lusitaniae, Crytpococcus neoformans, and Aspergillus fumigatus as well as wild type and human eEF2. Moriniafungin exhibited an MIC of 6 microg/mL versus Candida albicans and IC(50)'s ranging from 0.9 to 70 microg/mL against a panel of clinically relevant Candida strains. Moriniafungin was shown to inhibit in vitro translation in the chimeric S. cerevisae strains at levels consistent with the observed IC(50). Moriniafungin has the broadest antifungal spectrum and most potent activity of any natural sordarin analog identified to date.

Guanaconetins, new antitumoral acetogenins, mitochondrial complex I and tumor cell growth inhibitors

The antitumoral activity of a series of acetylated bis-tetrahydrofuranic acetogenins with a threo/trans/threo/trans/erythro relative configuration was characterized by four new natural and two semisynthetic, 15,24,30-trioxygenated acetogenins that were found to inhibit mitochondrial complex I enzyme as well as growth of several tumor cell lines. Placement of acetyl groups along the alkyl chain modulated the potency of the bis-tetrahydrofuranic acetogenins and could be important for future utilization of these compounds as chemotherapeutic agents.

In Vitro Antitumor Structure–Activity Relationships of threo/trans/threo/trans/erythro bis-Tetrahydrofuranic Acetogenins: Correlations With Their Inhibition of Mitochondrial Complex I

Annonaceous acetogenins are known to be cytotoxic against tumor cell lines by virtue of their inhibition of mitochondrial complex I. We decided to conclude part of our recent revisions of the different structure-activity relationships (SARs) found within these compounds with a detailed description of the cytotoxic activity, and correlations with the inhibition of the target enzyme, of the broadest subclass of this family of natural products, the bis-tetrahydrofuranic acetogenins (bis-THF ACGs) of threo/trans/threo/trans/erythro relative configuration. Five naturally occurring ACGs and more than 10 semisynthetic analogs were tested against the MCF-7 (breast), A-549 (lung), HepG2 (liver), HT-29 (colon), MES-SA (ovary), and a multidrug-resistant (MDR-MES-SA/Dx5) cell lines using the MTr cytotoxicity assay to determine if the mitochondrial complex I inhibition correlated with the in vitro antitumor potency of the most common ACGs. Results indicated that a previously observed trend for other subclasses of ACGs between the ED50 of the cytotoxicity assay and the polarity of compounds was not present in this set and that there were several specific interactions that enhanced the antitumor activity. For example, some of the guanacone derivatives prepared were two orders of magnitude more potent than the parent compound for specific cell lines.

In vitro antitumor structure-activity relationships of threo/trans/threo mono-tetrahydrofuranic acetogenins: correlations with their inhibition of mitochondrial complex I

In this study we evaluated a mono-tetrahydrofuranic subgroup of natural acetogenins that had shown in previous enzyme inhibition studies different potency trends compared with the bis-tetrahydrofuranic acetogenin subgroup. The compounds were tested against colon, breast, lung, liver, and ovarian tumor cell lines. A drug-resistant ovarian cell line was also included in the panel. In general the compounds were more potent than doxorubicin. The goal was to determine how well the mitochondrial complex I inhibition correlates with the in vitro antitumor potency of these natural mono-tetrahydrofuranic acetogenins and of some derivatives. The results indicate that both the reduction of the terminal gamma-lactone after its translactonization and the introduction of an hydroxylimine group in the alkyl chain, near the mono-tetrahydrofuranic moiety, increased the antitumor activity, even against the doxorubicin-resistant cell line.

In vitro antitumor SAR of threo/cis/threo/cis/erythro bis-THF acetogenins: correlations with their inhibition of mitochondrial Complex I

Annonaceous acetogenins (ACG) are a large family of natural products that have been described as the most potent in vitro inhibitors of the mitochondrial respiratory chain Complex I. During the last two decades a large number of related structures have been discovered, increasing the number of members of this family. The large diversity of structural moieties and the general trends observed for inhibiting both growth of tumor cell lines and mitochondrial respiratory chain activity have resulted in the classification of these compounds into several structural groups according to their potency. Among them, the adjacent bis-tetrahydrofuranic acetogenins (bis-THF ACG) with a threo/cis/threo/cis/erythro relative configuration, have been described as the most potent subgroup, the prototypical member of which, rolliniastatin-1, was originally isolated from Rollinia membaranacea seeds. In this report we describe the different structure-activity relationships (SAR) observed for some natural ACG and semisynthetic derivatives as growth inhibitors of human tumor breast, lung, liver, and colon cell lines. All the compounds assayed showed potencies in the micromolar range. Trends observed in the cytotoxicity assay have been compared with previous data reported for these compounds as inhibitors of mitochondrial respiratory chain.

Inhibitory effects on mitochondrial complex I of semisynthetic mono-Tetrahydrofuran acetogenin derivatives

Modifications in the terminal alpha,beta-unsaturated gamma-methyl-gamma-lactone moiety or in the alkyl chain that links this terminal gamma-lactone with the alpha,alpha'-dihydroxylated THF system of the natural mono-tetrahydrofuranic acetogenins, annonacin and annonacinone, led to the preparation of eight semisynthetic derivatives. Their inhibitory effects on mitochondrial complex I is discussed and compared with that of the classical complex I inhibitor, rotenone.

A method for the selection of production media for actinomycete strains based on their metabolite HPLC profiles

The manipulation of growth conditions of microorganisms is a common strategy used by pharmaceutical companies to improve the quantities and spectra of secondary metabolites with potential therapeutic interest. In this work, the effects of fermentation media on secondary metabolite production from a set of Actinomycetes was statistically compared. For this purpose, we created an automated method for comparing the ability of microorganisms to produce different secondary metabolites. HPLC analyses guided the selection of those media in which a wider chemical diversity was obtained from microorganisms inoculated in a wide spectrum of production media. Fermented media yielding a better secondary metabolite profile were included in subsequent drug discovery screening.

HPLC studio: a novel software utility to perform HPLC chromatogram comparison for screening purposes

A new tool, HPLC Studio, was developed for the comparison of high-performance liquid chromatography (HPLC) chromatograms from microbial extracts. The new utility makes it possible to create a virtual chromatogram by mixing up to 20 individual chromatograms. The virtual chromatogram is the first step in establishing a ranking of the microbial fermentation conditions based on either the area or diversity of HPLC peaks. The utility was used to maximize the diversity of secondary metabolites tested from a microorganism and therefore increase the chances of finding new lead compounds in a drug discovery program.

Gamma-lactone-Functionalized antitumoral acetogenins are the most potent inhibitors of mitochondrial complex I

To study the relevance of the terminal alpha,beta-unsaturated gamma-methyl-gamma-lactone moiety of the antitumoral acetogenins of Annonaceae for potent mitochondrial complex I inhibition, we have prepared a series of semisynthetic acetogenins with modifications only in this part of the molecule, from the natural rolliniastatin-1 (1) and cherimolin-1 (2). Some of the hydroxylated derivatives (1b, 1d and 1e) in addition to two infrequent natural beta-hydroxy gamma-methyl gamma-lactone acetogenins, laherradurin (3) and itrabin (4), are more potent complex I inhibitors than any other known compounds.

Semisynthesis of antitumoral acetogenins: SAR of functionalized alkyl-chain bis-tetrahydrofuranic acetogenins, specific inhibitors of mitochondrial complex I

The acetogenins of Annonaceae are known by their potent cytotoxic activity. In fact, they are promising candidates as a new future generation of antitumoral drugs to fight against the current chemiotherapic resistant tumors. The main target enzyme of these compounds is complex I (NADH:ubiquinone oxidoreductase) of the mitochondrial respiratory chain, a key enzymatic complex of energy metabolism. In an attempt to characterize the relevant structural factor of the acetogenins that determines the inhibitory potency against this enzyme, we have prepared a series of bis-tetrahydrofuranic acetogenins with different functional groups along the alkyl chain. They comprise several oxo, hydroxylimino, mesylated, triazido, and acetylated derivatives from the head series compounds rolliniastatin-1, guanacone, and squamocin. Our results suggest a double binding point of acetogenins to the enzyme involving the alpha,alpha'-dihydroxylated tetrahydrofuranic system as well as the alkyl chain that links the terminal alpha, beta-unsaturated-gamma-methyl-gamma-lactone. The former mimics and competes with the ubiquinone substrate. The latter modulates the inhibitory potency following a complex outline in which multiple structural factors probably contribute to an appropriate conformation of the compound to penetrate inside complex I.

Effects of vitamin A deficiency on mitochondrial function in rat liver and heart

The aim of this study was to investigate comparative effects of vitamin A deficiency on respiratory activity and structural integrity in liver and heart mitochondria. Male rats were fed a liquid control diet (control rats) or a liquid vitamin A-deficient diet (vitamin A-deficient rats) for 50 days. One group of vitamin-A deficient rats was refed a control diet for 15 days (vitamin A-recovered rats). To assess the respiratory function of mitochondria the contents of coenzyme Q (ubiquinone, CoQ), cytochrome c and the activities of the whole electron transport chain and of each of its respiratory complexes were evaluated. Chronic vitamin A deficiency promoted a significant increase in the endogenous coenzyme Q content in liver and heart mitochondria when compared with control values. Vitamin A deficiency induced a decrease in the activity of complex I (NADH-CoQ reductase) and complex II (succinate-CoQ reductase) and in the levels of complex I and cytochrome c in heart mitochondria. However, NADH and succinate oxidation rates were maintained at the control levels due to an increase in the CoQ content in accordance with the kinetic behaviour of CoQ as an homogeneous pool. On the contrary, the high CoQ content did not affect the electron-transfer rate in liver mitochondria, whose integrity was preserved from the deleterious effects of the vitamin A deficiency. Ultrastructural assessment of liver and heart showed that vitamin A deficiency did not induce appreciable alterations in the morphology of their mitochondria. After refeeding the control diet, serum retinol, liver and heart CoQ content and the activity of complex I and complex II in heart mitochondria returned to normality. However, the activities of both whole electron transfer chain and complex I in liver were increased over the control values. The interrelationships between physiological antioxidants in biological membranes and the beneficial effects of their administration in mitochondrial diseases are discussed.

New evidence for the multiplicity of ubiquinone- and inhibitor-binding sites in the mitochondrial complex I

Determination of the number of ubiquinone- and inhibitor-binding sites in the mitochondrial complex I (NADH:ubiquinone oxidoreductase) is a controversial question with a direct implication for elaborating a suitable model to explain the bioenergetic mechanism of this complicated enzyme. We have used combinations of both selective inhibitors and common ubiquinone-like substrates to demonstrate the multiplicity of the reaction centers in the complex I in contrast with competition studies that have suggested the existence of a unique binding site for ubiquinone. Our results provide new evidence for the existence of at least two freely exchangeable ubiquinone-binding sites with different specificity for substrates, as well as for a different kinetic interaction of inhibitors with the enzyme.

Synthesis of N-diisopropyl phosphoryl benzyltetrahydroisoquinoline, a new class of mitochondrial complexes I and III inhibitors

The synthesis of N-(O,O-diisopropylphosphoryl)-benzyltetrahydroisoquinoline (3) has been achieved in a 'one pot' procedure from imine (2) and diisopropyl-phosphorochloridate (1) generated in situ (POCl3 + iPrOH). Compound 3 is the first benzyltetrahydroisoquinoline derivative found to be a potent inhibitor of mitochondrial complexes I and III, and therefore it opens a new perspective with this series of compounds as they can be considered as new class of antitumor agents.

Epoxy-acetogenins and other polyketide epoxy derivatives as inhibitors of the mitochondrial respiratory chain complex I

Annonaceous acetogenins (ACG), an extensive group of cytotoxic natural products, are antitumor agents whose main mode of action is inhibition of the mammalian mitochondrial complex I. Herein we describe the importance of the different chemical groups along the alkyl chain for optimal inhibitory potency, discussing the structurally relevant factors present in these compounds. For this purpose, a series of epoxide derivatives from alpha-linolenic acid were prepared and their activity compared with that of epoxy-acetogenins and tetrahydrofuranic (THF) acetogenins isolated from Rollinia membranacea.

Specific interactions of monotetrahydrofuranic annonaceous acetogenins as inhibitors of mitochondrial complex I

Annonaceous acetogenins (ACG) are a wide group of cytotoxic compounds isolated from plants of the Annonaceae family. Some of them are promising candidates to be a future new generation of antitumor drugs due to the ability to inhibit the NADH:ubiquinone oxidoreductase of the respiratory chain (mitochondrial complex I), main gate of the energy production in the cell. ACG are currently being tested on standard antitumor trials although little is known about the structure activity relationship at the molecular level. On recent studies, the relevance of several parts of the molecule for the inhibitory potency has been evaluated. Due to the great diversity of skeletons included in this family of natural products, previous studies on the presence and distribution of oxygenated groups along the alkyl chain only covered the compounds with different bis-tetrahydrofuranic (bis-THF) relative configurations. Therefore, we have investigated the inhibitory action of all the mono-tetrahydrofuranic (mono-THF) acetogenins available, which differ in the oxygenated arrangements along the molecule. Our results show that the hydroxyl and carbonyl groups, placed in the aliphatic chain that links the initial gamma-lactone moiety with the dihydroxylated tetrahydrofuranic ring system, significantly contribute for modulating the inhibitory potency of the ACG through specific effects.

Kinetic characterization of mitochondrial complex I inhibitors using annonaceous acetogenins

The NADH:ubiquinone oxidoreductase (complex I) of the mitochondrial respiratory chain is by far the largest and most complicated of the proton-translocating enzymes involved in the oxidative phosphorylation. Many clues regarding the electron pathways from matrix NADH to membrane ubiquinone and the links of this process with the translocation of protons are highly controversial. Different types of inhibitors become valuable tools to dissect the electron and proton pathways of this complex enzyme. Therefore, further knowledge of the mode of action of complex I inhibitors is needed to understand the underlying mechanism of energy conservation. This study presents for the first time a detailed exploration of the inhibitory action of the Annonaceous acetogenins, the most powerful inhibitors of the mammalian enzyme, taking as the head-series rolliniastatin-1, rolliniastatin-2, and corossolin. Despite their close chemical resemblance, each of them inhibits the complex I with different kinetic features reflecting differential binding to the enzyme.

Enantiospecific semisynthesis of (+)-almuheptolide-A, a novel natural heptolide inhibitor of the mammalian mitochondrial respiratory chain

The development of novel styryl lactone derivatives as bioactive compounds and the semisynthesis of both 4,5-dialkoxylated eight-membered-ring lactones with a heptolide skeleton (almuheptolide-A (1) type) and 7-alkoxylated delta-lactones with a saturated furanopyrone skeleton (etharvensin (8) type) have been successfully achieved from the chiral unsaturated alpha-pyrone altholactone (7). This new method is a direct and one-step enantiospecific alkoxylation of altholactone (7) in concentrated acid medium, followed by formation of the eight-membered-ring zeta-lactone. The reaction mechanism operating in the synthesis of the heptolide skeleton is postulated to be a direct Michael-type addition. Concerted opening of both the alpha-pyrone and tetrahydrofuran rings and subsequent intramolecular rearrangement with the ring closure lead to almuheptolide-A (1). This compound (1) and its diacetated derivative (1a) showed potent and selective inhibitory activity toward mammalian mitochondrial respiratory chain complex I. This mechanism of action, reported here for the first time, provides a possible explanation for the cytotoxic and antitumor activities previously described for related natural compounds.

10-Oximeguanacone, the first nitrogenated acetogenin derivative found to be a potent inhibitor of mitochondrial complex I

A new 10-keto bis-tetrahydrofuran acetogenin, guanacone (1), has been isolated from a cytotoxic extract of Annona aff. spraguei seeds. The 10-oximeguanacone derivative 1f is the first bioactive nitrogenated acetogenin found to be a very potent inhibitor of complex I. In addition, a SAR study of guanacone analogues is reported based on the titration of the NADH oxidase and NADH:ubiquinone oxidoreductase activities.

Cherimolin-1, new selective inhibitor of the first energy-coupling site of the NADH: ubiquinone oxidoreductase (complex I)

The mechanism linking electron transport to proton translocation in the NADH:ubiquinone oxidoreductase (complex I of the mitochondrial respiratory chain) is still unclear. Inhibitors acting at different sites of the enzyme are powerful tools to clarify this mechanism. Up to now, a unique inhibitor, the Annonaceous acetogenin rolliniastatin-2, selectively blocks the most internal proton-translocation site. This study introduces cherimolin-1, a new acetogenin that inhibits the complex I with this special mode of action, which is more easily available from the plant material. Moreover, the mode of action of this scarce type of complex I inhibitor is further characterized.

A deficiency in respiratory complex I in heart mitochondria from vitamin A-deficient rats is counteracted by an increase in coenzyme Q

Defects of NADH:coenzyme Q oxidoreductase (complex I) of mitochondria have been described in many congenital and acquired diseases. Administration of coenzyme Q (CoQ, ubiquinone) has been shown to benefit patients with some of these diseases. However, the mechanisms by which CoQ exerts the therapeutic effects are not clearly understood. A reason could be the lack of saturation of CoQ, in kinetic terms, for complex I activity. However, this hypothesis has not been proved in vivo because of the difficulty to incorporate CoQ into the mitochondrial membranes. We have found a deficiency in respiratory complex I in heart mitochondria from vitamin A-deficient rats which was accompanied by high CoQ content. The defect in complex I activity was compensated by the increase in CoQ to maintain the mitochondrial electron transfer rate. This finding supports, for the first time in an in vivo experimental approach, the kinetic hypothesis to explain the short-term therapeutic effects of CoQ.

Polyalthidin: new prenylated benzopyran inhibitor of the mammalian mitochondrial respiratory chain

Polyalthidin (3), a new benzopyran derivative, was isolated from the stem bark of Polyalthia cerasoides. Its structure was established on the basis of chemical and spectral evidence. Polyalthidin has showed potent biological activity as an inhibitor of the mammalian mitochondrial respiratory chain.