Total Synthesis, Structure Reassignment, and Biological Evaluation of the Anti-Inflammatory Macrolactone 13-Hydroxy-14-deoxyoxacyclododecindione

Herein, the first total synthesis of natural 13-hydroxy-14-deoxyoxacyclododecindione along with the revision of the proposed configuration is reported. This natural product, initially discovered in 2018, belongs to the oxacyclododecindione family, renowned for their remarkable anti-inflammatory and antifibrotic activities. The synthetic route involves an esterification/Friedel-Crafts-acylation approach and uses various triol fragments. It allows the preparation of different stereoisomers, including the (revised) natural product, two threo-derivatives, and two Z-isomers of the endocyclic C═C double bond. Furthermore, a late-stage inversion of the C-13 stereocenter could transform the originally proposed structure into the revised natural product. With this comprehensive set of compounds and the previously prepared (13R,14S,15R)-isomer, deeper insights into their structural properties and biological activities were obtained. A detailed analysis of the final macrolactones using spectroscopy (NMR, IR, UV-vis) and X-ray crystallography gave new insights such as the significance of the optical rotation for the elucidation of their configuration and the light-induced E/Z double-bond photoisomerization. The pharmacological potential of the compounds was underlined by remarkably low IC50 values in biological assays addressing the inhibition of cellular inflammatory responses.

A review on Millepachine and its derivatives as potential multitarget anticancer agents

Chalcones have a long history of being used for many medical purposes. These are the most prestigious scaffolds in medicine. The potential of Millepachine and its derivatives to treat various malignancies has been demonstrated in this review. The anticancer effects of Millepachine and its derivatives on ovarian cancer, hepatocellular carcinoma, breast, liver, colon, cervical, prostate, stomach, and gliomas are highlighted in the current review. Several genes that are crucial in reducing the severity of the disease have been altered by these substances. They mainly work by preventing tubulin polymerizing. They also exhibit apoptosis and cell cycle arrest at the G2/M phase. Additionally, these compounds inhibit invasion and migration and have antiproliferative effects. Preclinical studies have shown that Millepachine and its derivatives offer exceptional potential for treating a number of cancers. These results need to be confirmed in clinical research in order to develop viable cancer therapies.

Natural product inspired leads in the discovery of anticancer agents: an update

Natural products have emerged as major leads for the discovery and development of new anti-cancer drugs. The plant-derived anti-cancer drugs account for approximately 60% and the quest for new anti-cancer agents is in progress. Anti-cancer leads have been isolated from plants, animals, marine organisms, and microorganisms from time immemorial. The process of semisynthetic modifications of the parent lead has led to the generation of new anti-cancer agents with improved therapeutic efficacy and minimal side effects. The various chemo-informatics tools, bioinformatics, high-throughput screening, and combinatorial synthesis are able to deliver the new natural product lead molecules. Plant-derived anticancer agents in either late preclinical development or early clinical trials include taxol, vincristine, vinblastine, topotecan, irinotecan, etoposide, paclitaxel, and docetaxel. Similarly, anti-cancer agents from microbial sources include dactinomycin, bleomycin, mitomycin C, and doxorubicin. In this review, we highlighted the importance of natural products leads in the discovery and development of novel anti-cancer agents. The semisynthetic modifications of the parent lead to the new anti-cancer agent are also presented. Further, the leads in the preclinical settings with the potential to become effective anticancer agents are also reviewed.Communicated by Ramaswamy H. Sarma.

Bacterial synthetic biology: tools for novel drug discovery

INTRODUCTION

Bacterial synthetic biology has provided powerful tools to revolutionize the drug discovery process. These tools can be harnessed to generate bacterial novel pharmaceutical compounds with enhanced bioactivity and selectivity or to create genetically modified microorganisms as living drugs.

AREAS COVERED

This review provides a current overview of the state-of-the-art in bacterial synthetic biology tools for novel drug discovery. The authors discuss the application of these tools including bioinformatic tools, CRISPR tools, engineered bacterial transcriptional regulators, and synthetic biosensors for novel drug discovery. Additionally, the authors present the recent progress on reprogramming bacteriophages as living drugs to fight against antibiotic-resistant pathogens.

EXPERT OPINION

The field of using bacterial synthetic biology tools for drug discovery is rapidly advancing. However, challenges remain in developing reliable and robust methods to engineer bacteria. Further advancements in synthetic biology hold promise to speed up drug discovery, facilitating the development of novel therapeutics against various diseases.

Reinstating apoptosis using putative Bcl-xL natural product inhibitors: Molecular docking and ADMETox profiling investigations

Objectives

While a fine balance in the pro-apoptotic and anti-apoptotic family members of the B-cell lymphoma-2 (Bcl-2) protein family represents a normal signaling profile, a tilt in balance towards anti-apoptotic family members has fortified different forms of cancers with survival advantage and resistance against treatment. Induction of apoptosis is a key therapeutic approach in cancer drug discovery, and the inhibition of the anti-apoptotic B cell lymphoma extra-large (Bcl-xL) is a long-standing clinical target for cancer therapy. In this study, we combined computer-aided approaches to report putative binders for this target.

Methods

Before our virtual screening campaign, we conducted a redocking experiment strategy of the x-ray bound inhibitor of the Bcl-xL protein with some of the available docking software at our disposal to determine the software with the best efficiency for this screening. iGEMDOCK emerged to reproduce the x-ray crystallographic information and was used to dock the library of ligand, which was developed from diverse literature reporting compounds with anti-apoptotic profiles through the Bcl-2 family.

Results

Of the compounds in the library, alpha-mangostin and oubain scored as hits with binding energy values of -123.025 kcal/mol and -122.271 kcal/mol, respectively, which is more than -120.8 kcal/mol observed by the standard.

Conclusions

These compounds revealed a more binding affinity potential than ABT-737, which is a standard inhibitor of the protein. In addition, these scaffolds not only interact with relevant and hotspot residues for the inhibition of Bcl-xL but also possess good pharmacokinetic and excellent toxicity, an endpoint that should be considered for further testing and drug development.

Anticancer activity of β-Lapachone derivatives on human leukemic cell lines

β-lapachone is a 1,2-naphthoquinone of great therapeutic interest that induces cell death by autophagy and apoptosis in tumor cells due to oxidative stress increasing. However, its high toxicity in healthy tissues limits its clinical use, which stimulates the planning and synthesis of more selective analogs. The aim of this study was to investigate the cytotoxic activity of three thiosemicarbazones derived from β-lapachone (BV2, BV3 and BV5) in leukemia cells. Cytotoxicity tests were performed on tumor cells (HL-60, K562, K562-Lucena and MOLT-4) and normal peripheral blood mononuclear cells (PBMCs). Subsequently, the mode of action of compounds was accessed by optical microscopy, transmission electron microscopy or fluorescence microscopy. Flow cytometry analysis was performed to investigate apoptosis induction, cell cycle, DNA fragmentation and mitochondrial depolarization. All derivatives inhibited tumor cell growth after 72 h (IC₅₀ < 10 μM to all cell lines, including the resistant K562-Lucena) with less toxic effects in PBMC cells, being BV3 the most selective compound with selective index (SI) of 275 for HL-60; SI of 40 to K562; SI of 10 for MOLT-4 and SI of 50 to K562-Lucena compared to β-lapachone with SI of 18 to HL-60, SI of 3.7 to K562; SI of 2.4 to MOLT-4 and SI of 0.9 to K562-Lucena. In addition, the K562 or MOLT-4 cells treated with BV3 showed characteristics of both apoptosis and autophagy cell death, mainly by autophagy. These results demonstrate the potent cytotoxic effect of thiosemicarbazones derived from β-lapachone as promising anticancer drugs candidates, encouraging the continuity of in vivo tests.

Beating Pain with Psychedelics: Matter over Mind?

Basic pain research has shed light on key cellular and molecular mechanisms underlying nociceptive and phenomenological aspects of pain. Despite these advances, [[we still yearn for] the discovery of novel therapeutic strategies to address the unmet needs of about 70% of chronic neuropathic pain patients whose pain fails to respond to opioids as well as to other conventional analgesic agents. Importantly, a substantial body of clinical observations over the past decade cumulatively suggests that the psychedelic class of drugs may possess heuristic value for understanding and treating chronic pain conditions. The present review presents a theoretical framework for hitherto insufficiently understood neuroscience-based mechanisms of psychedelics' potential analgesic effects. To that end, searches of PubMed-indexed journals were performed using the following Medical Subject Headings' terms: pain, analgesia, inflammatory, brain connectivity, ketamine, psilocybin, functional imaging, and dendrites. Recursive sets of scientific and clinical evidence extracted from this literature review were summarized within the following key areas: (1) studies employing psychedelics for alleviation of physical and emotional pain; (2) potential neuro-restorative effects of psychedelics to remediate the impaired connectivity underlying the dissociation between pain-related conscious states/cognitions and the subcortical activity/function leading to the eventual chronicity through immediate and long-term effects on dentritic plasticity; (3) anti-neuroinflammatory and pro-immunomodulatory actions of psychedelics as the may pertain to the role of these factors in the pathogenesis of neuropathic pain; (4) safety, legal, and ethical consideration inherent in psychedelics' pharmacotherapy. In addition to direct beneficial effects in terms of reduction of pain and suffering, psychedelics' inclusion in the analgesic armamentarium will contribute to deeper and more sophisticated insights not only into pain syndromes but also into frequently comorbid psychiatric condition associated with emotional pain, e.g., depressive and anxiety disorders. Further inquiry is clearly warranted into the above areas that have potential to evolve into further elucidate the mechanisms of chronic pain and affective disorders, and lead to the development of innovative, safe, and more efficacious neurobiologically-based therapeutic approaches.

Synthesis of the Hexahydropyrrolo-[3,2-c]-quinoline Core Structure and Strategies for Further Elaboration to Martinelline, Martinellic Acid, Incargranine B, and Seneciobipyrrolidine

Natural products are rich sources of interesting scaffolds possessing a plethora of biological activity. With the isolation of the martinella alkaloids in 1995, namely martinelline and martinellic acid, the pyrrolo[3,2-c]quinoline scaffold was discovered. Since then, this scaffold has been found in two additional natural products, viz. incargranine B and seneciobipyrrolidine. These natural products have attracted attention from synthetic chemists both due to the interesting scaffold they contain, but also due to the biological activity they possess. This review highlights the synthetic efforts made for the preparation of these alkaloids and formation of analogues with interesting biological activity.

Toward an efficient and eco-friendly route for the synthesis of dimeric 2,4-diacetyl phloroglucinol and its potential as a SARS-CoV-2 main protease antagonist: insight from in silico studies

Dimeric 2,4-diacetyl phloroglucinol derivatives were synthesized under green chemistry protocols and found to be the potential inhibitor of 3CLpro of SARS-CoV-2.

Synthesis and biological evaluation of semi-synthetic albocycline analogs

Albocycline (ALB) is a unique macrolactone natural product with potent, narrow-spectrum activity against methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-intermediate (VISA), and vancomycin-resistant S. aureus (VRSA) strains (MIC = 0.5-1.0 μg/mL). Described herein is the synthesis and evaluation of a novel series analogs derived from albocycline by functionalization at three specific sites: the C2-C3 enone, the tertiary carbinol at C4, and the allylic C16 methyl group. Exploration of the structure-activity relationships (SAR) by means of minimum inhibitory concentration assays (MICs) revealed that C4 ester analog 6 was twice as potent as ALB, which represents a class of lead compound that can be further studied to address multi-drug resistant pathogens.

The role of natural products in revealing NRF2 function

Covering: up to 2020The transcription factor NRF2 is one of the body's major defense mechanisms, driving transcription of >300 antioxidant response element (ARE)-regulated genes that are involved in many critical cellular processes including redox regulation, proteostasis, xenobiotic detoxification, and primary metabolism. The transcription factor NRF2 and natural products have an intimately entwined history, as the discovery of NRF2 and much of its rich biology were revealed using natural products both intentionally and unintentionally. In addition, in the last decade a more sinister aspect of NRF2 biology has been revealed. NRF2 is normally present at very low cellular levels and only activated when needed, however, it has been recently revealed that chronic, high levels of NRF2 can lead to diseases such as diabetes and cancer, and may play a role in other diseases. Again, this "dark side" of NRF2 was revealed and studied largely using a natural product, the quassinoid, brusatol. In the present review, we provide an overview of NRF2 structure and function to orient the general reader, we will discuss the history of NRF2 and NRF2-activating compounds and the biology these have revealed, and we will delve into the dark side of NRF2 and contemporary issues related to the dark side biology and the role of natural products in dissecting this biology.

Small molecule inhibitors and stimulators of inducible nitric oxide synthase in cancer cells from natural origin (phytochemicals, marine compounds, antibiotics)

Nitric oxide synthases (NOS) are a family of isoforms, which generate nitric oxide (NO). NO is one of the smallest molecules in nature and acts mainly as a potent vasodilator. It participates in various biological processes ranging from physiological to pathological conditions. Inducible NOS (iNOS, NOS2) is a calcium-independent and inducible isoform. Despite high iNOS expression in many tumors, the role of iNOS is still unclear and complex with both enhancing and prohibiting actions in tumorigenesis. Nature presents a broad variety of natural stimulators and inhibitors, which may either promote or inhibit iNOS response. In the present review, we give an overview of iNOS-modulating agents with a special focus on both natural and synthetic molecules and their effects in related biological processes. The role of iNOS in physiological and pathological conditions is also discussed.

Retracted Article: The synthesis and biological activity of marine alkaloid derivatives and analogues

The ocean is the origin of life, with a unique ecological environment, which has given birth to a wealth of marine organisms. The ocean is an important source of biological resources and tens of thousands of monomeric compounds have been separated from marine organisms using modern separation technology. Most of these monomeric compounds have some kind of biological activity that has attracted extensive attention from researchers. Marine alkaloids are a kind of compound that can be separated from marine organisms. They have complex and special chemical structures, but at the same time, they can show diversity in biological activities. The biological activities of marine alkaloids mainly manifest in the form of anti-tumor, anti-fungus, anti-viral, anti-malaria, and anti-osteoporosis properties. Many marine alkaloids have good medicinal prospects and can possibly be used as anti-tumor, anti-viral, and anti-fungal clinical drugs or as lead compounds. The limited amounts of marine alkaloids that can be obtained by separation, coupled with the high cytotoxicity and low selectivity of these lead compounds, has restricted the clinical research and industrial development of marine alkaloids. Marine alkaloid derivatives and analogues have been obtained via rational drug design and chemical synthesis, to make up for the shortcomings of marine alkaloids; this has become an urgent subject for research and development. This work systematically reviews the recent developments relating to marine alkaloid derivatives and analogues in the field of medical chemistry over the last 10 years (2010–2019). We divide marine alkaloid derivatives and analogues into five types from the point-of-view of biological activity and elaborated on these activities. We also briefly discuss the optimization process, chemical synthesis, biological activity evaluation, and structure–activity relationship (SAR) of each of these compounds. The abundant SAR data provides reasonable approaches for the design and development of new biologically active marine alkaloid derivatives and analogues.

The ocean is the origin of life, with a unique ecological environment, which has given birth to a wealth of marine organisms.

Algae metabolites: from in vitro growth inhibitory effects to promising anticancer activity

Covering: 1957 to 2017 Algae constitute a heterogeneous group of eukaryotic photosynthetic organisms, mainly found in the marine environment. Algae produce numerous metabolites that help them cope with the harsh conditions of the marine environment. Because of their structural diversity and uniqueness, these molecules have recently gained a lot of interest for the identification of medicinally useful agents, including those with potential anticancer activities. In the current review, which is not a catalogue-based one, we first highlight the major biological events that lead to various types of cancer, including metastatic ones, to chemoresistance, thus to any types of current anticancer treatment relating to the use of chemotherapeutics. We then review algal metabolites for which scientific literature reports anticancer activity. Lastly, we focus on algal metabolites with promising anticancer activity based on their ability to target biological characteristics of cancer cells responsible for poor treatment outcomes. Thus, we highlight compounds that have, among others, one or more of the following characteristics: selectivity in reducing the proliferation of cancer cells over normal ones, potential for killing cancer cells through non-apoptotic signaling pathways, ability to circumvent MDR-related efflux pumps, and activity in vivo in relevant pre-clinical models.

Dendrimers in combination with natural products and analogues as anti-cancer agents

For the first time, an overview of dendrimers in combination with natural products and analogues as anti-cancer agents is presented. This reflects the development of drug delivery systems, such as dendrimers, to tackle cancers. The most significant advantages of using dendrimers in nanomedicine are their high biocompatibility, good water solubility, and their entry - with or without encapsulated, complexed or conjugated drugs - through an endocytosis process. This strategy has accelerated over the years in order to develop nanosystems as nanocarriers, to decrease the intrinsic toxicity of anti-cancer agents, to decrease the drug side effects, to increase the efficacy of the treatment, and consequently to improve patient compliance.

Dendrimers in combination with natural products and analogues as anti-cancer agents

Overview of the use of dendrimers in combination with encapsulated and conjugated natural products and analogues as anti-cancer agents.

Dendrimers in combination with natural products and analogues as anti-cancer agents

Overview of the use of dendrimers in combination with encapsulated and conjugated natural products and analogues as anti-cancer agents.

Natural products used as a chemical library for protein-protein interaction targeted drug discovery

Protein-protein interactions (PPIs), which are essential for cellular processes, have been recognized as attractive therapeutic targets. Therefore, the construction of a PPI-focused chemical library is an inevitable necessity for future drug discovery. Natural products have been used as traditional medicines to treat human diseases for millennia; in addition, their molecular scaffolds have been used in diverse approved drugs and drug candidates. The recent discovery of the ability of natural products to inhibit PPIs led us to use natural products as a chemical library for PPI-targeted drug discovery. In this study, we collected natural products (NPDB) from non-commercial and in-house databases to analyze their similarities to small-molecule PPI inhibitors (iPPIs) and FDA-approved drugs by using eight molecular descriptors. Then, we evaluated the distribution of NPDB and iPPIs in the chemical space, represented by the molecular fingerprint and molecular scaffolds, to identify the promising scaffolds, which could interfere with PPIs. To investigate the ability of natural products to inhibit PPI targets, molecular docking was used. Then, we predicted a set of high-potency natural products by using the iPPI-likeness score based on a docking score-weighted model. These selected natural products showed high binding affinities to the PPI target, namely XIAP, which were validated in an in vitro experiment. In addition, the natural products with novel scaffolds might provide a promising starting point for further medicinal chemistry developments. Overall, our study shows the potency of natural products in targeting PPIs, which might help in the design of a PPI-focused chemical library for future drug discovery.

Twelve-membered macrolactones: privileged scaffolds for the development of new therapeutics

Natural products commonly produced as secondary metabolites of various plants and micro-organisms represent a diverse chemical space of compounds. The diversity of natural products makes them an attractive target for interrogation by both chemists and biologists alike. Indeed, the study of 12-membered macrolactones has already led to the discovery of lead drug compounds and new biological targets, which has motivated the development of diverted total synthetic routes to libraries of analogs. This review explores the discovery, biological characterization, and synthesis of several 12-membered macrolactones, exploiting examples that underscore their importance in the drug discovery field. It is our hope that this review will motivate further interest in this class of natural products, a group of molecules that we think merit the classification of 'privileged scaffolds' within the medicinal chemistry community, to further investigate and develop novel compounds with promising bioactivity.

Total Synthesis of (-)-Albocycline

The macrolactone natural product (-)-albocycline is a promising antibiotic candidate for the treatment of both methicillin resistant Staphylococcus aureus (MRSA) and vancomycin-resistant strains. Herein we report a concise total synthesis of (-)-albocycline in 14 steps from commercially available methyl (R)-3-hydroxybutyrate. Novel key steps include the highly regio- and stereoselective reactions of chiral N-sulfinyl metallodienamines (NSMDs) with aldehydes and the Davis oxaziridine, in addition to the Horner-Wadsworth-Emmons olefination of N-sulfinyl imines.

Discovery of scmR as a global regulator of secondary metabolism and virulence in Burkholderia thailandensis E264

Bacteria produce a diverse array of secondary metabolites that have been invaluable in the clinic and in research. These metabolites are synthesized by dedicated biosynthetic gene clusters (BGCs), which assemble architecturally complex molecules from simple building blocks. The majority of BGCs in a given bacterium are not expressed under normal laboratory growth conditions, and our understanding of how they are silenced is in its infancy. Here, we have addressed this question in the Gram-negative model bacterium Burkholderia thailandensis E264 using genetic, transcriptomic, metabolomic, and chemical approaches. We report that a previously unknown, quorum-sensing-controlled LysR-type transcriptional regulator, which we name ScmR (for secondary metabolite regulator), serves as a global gatekeeper of secondary metabolism and a repressor of numerous BGCs. Transcriptionally, we find that 13 of the 20 BGCs in B. thailandensis are significantly (threefold or more) up- or down-regulated in a scmR deletion mutant (ΔscmR) Metabolically, the ΔscmR strain displays a hyperactive phenotype relative to wild type and overproduces a number of compound families by 18- to 210-fold, including the silent virulence factor malleilactone. Accordingly, the ΔscmR mutant is hypervirulent both in vitro and in a Caenorhabditis elegans model in vivo. Aside from secondary metabolism, ScmR also represses biofilm formation and transcriptionally activates ATP synthesis and stress response. Collectively, our data suggest that ScmR is a pleiotropic regulator of secondary metabolism, virulence, biofilm formation, and other stationary phase processes. A model for how the interplay of ScmR with pathway-specific transcriptional regulators coordinately silences virulence factor production is proposed.

Synthesis and Antitumor Activity of New Thiazole Nortopsentin Analogs

New thiazole nortopsentin analogs in which one of the two indole units was replaced by a naphthyl and/or 7-azaindolyl portion, were conveniently synthesized. Among these, three derivatives showed good antiproliferative activity, in particular against MCF7 cell line, with GI₅₀ values in the micromolar range. Their cytotoxic effect on MCF7 cells was further investigated in order to elucidate their mode of action. Results showed that the three compounds act as pro-apoptotic agents inducing a clear shift of viable cells towards early apoptosis, while not exerting necrotic effects. They also caused cell cycle perturbation with significant decrease in the percentage of cells in the G0/G1 and S phases, accompanied by a concomitant percentage increase of cells in the G2/M phase, and appearance of a subG1-cell population.

Scaffold-Hopping of Aurones: 2-Arylideneimidazo[1,2-a]pyridinones as Topoisomerase IIα-Inhibiting Anticancer Agents

Scaffold-hopping of bioactive natural product aurones has been studied for the first time. 2-Arylideneimidazo[1,2-a]pyridinones as potential topoisomerase IIα (hTopoIIα)-targeting anticancer compounds were considered. A multifunctional activator, polyphosphoric acid, enabled to realize a cascade reaction of 2-aminopyridine with 2,3-epoxyesters toward synthesis of 2-arylideneimidazo[1,2-a]pyridinones. Most of the compounds exhibited hTopoIIα-selective poison activity with efficiency more than etoposide and DNA-binding property, while not interacting with hTopo I. The compounds showed pronounced antiproliferative activities in nanomolar range with relatively poor toxicity to normal cells, inhibition of invasiveness, and apoptotic effect. The activities for inhibition of tubulin assembly, CDK1 and pCDK1, were also observed. Interestingly, the hTopoIIα inhibitory (in vitro and ex vivo studies) and antiproliferative activities of representative potent compounds were found to be manifold higher compared to corresponding parent aurones bearing alike substitutions, indicating the importance of such scaffold-hopping strategy in medicinal chemistry research.

Antibiotic dialogues: induction of silent biosynthetic gene clusters by exogenous small molecules

Natural products have traditionally served as a dominant source of therapeutic agents. They are produced by dedicated biosynthetic gene clusters that assemble complex, bioactive molecules from simple precursors. Recent genome sequencing efforts coupled with advances in bioinformatics indicate that the majority of biosynthetic gene clusters are not expressed under normal laboratory conditions. Termed 'silent' or 'cryptic', these gene clusters represent a treasure trove for discovery of novel small molecules, their regulatory circuits and their biosynthetic pathways. In this review, we assess the capacity of exogenous small molecules in activating silent secondary metabolite gene clusters. Several approaches that have been developed are presented, including coculture techniques, ribosome engineering, chromatin remodeling and high-throughput elicitor screens. The rationale, applications and mechanisms attendant to each are discussed. Some general conclusions can be drawn from our analysis: exogenous small molecules comprise a productive avenue for the discovery of cryptic metabolites. Specifically, growth-inhibitory molecules, in some cases clinically used antibiotics, serve as effective inducers of silent biosynthetic gene clusters, suggesting that old antibiotics may be used to find new ones. The involvement of natural antibiotics in modulating secondary metabolism at subinhibitory concentrations suggests that they represent part of the microbial vocabulary through which inter- and intraspecies interactions are mediated.

Selective activity of deguelin identifies therapeutic targets for androgen receptor-positive breast cancer

Triple-negative breast cancers (TNBC) are aggressive malignancies with no effective targeted therapies. Recent gene expression profiling of these heterogeneous cancers and the classification of cell line models now allows for the identification of compounds with selective activities against molecular subtypes of TNBC. The natural product deguelin was found to have selective activity against MDA-MB-453 and SUM-185PE cell lines, which both model the luminal androgen receptor (LAR) subtype of TNBC. Deguelin potently inhibited proliferation of these cells with GI50 values of 30 and 61 nM, in MDA-MB-453 and SUM-185PE cells, respectively. Deguelin had exceptionally high selectivity, 197 to 566-fold, for these cell lines compared to cell lines representing other TNBC subtypes. Deguelin's mechanisms of action were investigated to determine how it produced these potent and selective effects. Our results show that deguelin has dual activities, inhibiting PI3K/Akt/mTOR signaling, and decreasing androgen receptor levels and nuclear localization. Based on these data, we hypothesized that the combination of the mTOR inhibitor rapamycin and the antiandrogen enzalutamide would have efficacy in LAR models. Rapamycin and enzalutamide showed additive effects in MDA-MB-453 cells, and both drugs had potent antitumor efficacy in a LAR xenograft model. These results suggest that the combination of antiandrogens and mTOR inhibitors might be an effective strategy for the treatment of androgen receptor-expressing TNBC.

A Workflow for Studying Specialized Metabolism in Nonmodel Eukaryotic Organisms

Eukaryotes contain a diverse tapestry of specialized metabolites, many of which are of significant pharmaceutical and industrial importance to humans. Nevertheless, exploration of specialized metabolic pathways underlying specific chemical traits in nonmodel eukaryotic organisms has been technically challenging and historically lagged behind that of the bacterial systems. Recent advances in genomics, metabolomics, phylogenomics, and synthetic biology now enable a new workflow for interrogating unknown specialized metabolic systems in nonmodel eukaryotic hosts with greater efficiency and mechanistic depth. This chapter delineates such workflow by providing a collection of state-of-the-art approaches and tools, ranging from multiomics-guided candidate gene identification to in vitro and in vivo functional and structural characterization of specialized metabolic enzymes. As already demonstrated by several recent studies, this new workflow opens up a gateway into the largely untapped world of natural product biochemistry in eukaryotes.

Silvestrol induces early autophagy and apoptosis in human melanoma cells

BACKGROUND

Silvestrol is a cyclopenta[b]benzofuran that was isolated from the fruits and twigs of Aglaia foveolata, a plant indigenous to Borneo in Southeast Asia. The purpose of the current study was to determine if inhibition of protein synthesis caused by silvestrol triggers autophagy and apoptosis in cultured human cancer cells derived from solid tumors.

METHODS

In vitro cell viability, flow cytometry, fluorescence microscopy, qPCR and immunoblot was used to study the mechanism of action of silvestrol in MDA-MB-435 melanoma cells.

RESULTS

By 24 h, a decrease in cyclin B and cyclin D expression was observed in silvestrol-treated cells relative to control. In addition, silvestrol blocked progression through the cell cycle at the G2-phase. In silvestrol-treated cells, DAPI staining of nuclear chromatin displayed nucleosomal fragments. Annexin V staining demonstrated an increase in apoptotic cells after silvestrol treatment. Silvestrol induced caspase-3 activation and apoptotic cell death in a time- and dose-dependent manner. Furthermore, both silvestrol and SAHA enhanced autophagosome formation in MDA-MB-435 cells. MDA-MB-435 cells responded to silvestrol treatment with accumulation of LC3-II and time-dependent p62 degradation. Bafilomycin A, an autophagy inhibitor, resulted in the accumulation of LC3 in cells treated with silvestrol. Silvestrol-mediated cell death was attenuated in ATG7-null mouse embryonic fibroblasts (MEFs) lacking a functional autophagy protein.

CONCLUSIONS

Silvestrol potently inhibits cell growth and induces cell death in human melanoma cells through induction of early autophagy and caspase-mediated apoptosis. Silvestrol represents a natural product scaffold that exhibits potent cytotoxic activity and could be used for the further study of autophagy and its relationship to apoptosis in cancer cells.

Harnessing natural product assembly lines: structure, promiscuity, and engineering

Many therapeutically relevant natural products are biosynthesized by the action of giant mega-enzyme assembly lines. By leveraging the specificity, promiscuity, and modularity of assembly lines, a variety of strategies has been developed that enables the biosynthesis of modified natural products. This review briefly summarizes recent structural advances related to natural product assembly lines, discusses chemical approaches to probing assembly line structures in the absence of traditional biophysical data, and surveys efforts that harness the inherent or engineered promiscuity of assembly lines for the synthesis of non-natural polyketides and non-ribosomal peptide analogues.

Design and Synthesis of a Screening Library Using the Natural Product Scaffold 3-Chloro-4-hydroxyphenylacetic Acid

The fungal metabolite 3-chloro-4-hydroxyphenylacetic acid (1) was utilized in the generation of a unique drug-like screening library using parallel solution-phase synthesis. A 20-membered amide library (3-22) was generated by first converting 1 to methyl (3-chloro-4-hydroxyphenyl)acetate (2), then reacting this scaffold with a diverse series of primary amines via a solvent-free aminolysis procedure. The structures of the synthetic analogues (3-22) were elucidated by spectroscopic data analysis. The structures of compounds 8, 12, and 22 were confirmed by single X-ray crystallographic analysis. All compounds were evaluated for cytotoxicity against a human prostate cancer cell line (LNCaP) and for antiparasitic activity toward Trypanosoma brucei brucei and Plasmodium falciparum and showed no significant activity at 10 μM. The library was also tested for effects on the lipid content of LNCaP and PC-3 prostate cancer cells, and it was demonstrated that the fluorobenzyl analogues (12-14) significantly reduced cellular phospholipid and neutral lipid levels.

Natural products with antischistosomal activity

In recent years, natural product groups have been gaining prominence as possible sources of new drugs for schistosomiasis. This review attempts to update the antischistosomal natural compounds, or natural product-derived compounds, from the mid-1980s. Some of the main metabolites obtained from plants (e.g., terpenes, alkaloids, phenolic compounds and peptides) with in vitro and/or in vivo antischistosomal properties are discussed. Less thoroughly, due to scarcity of data in the literature, molecules from animals (e.g., peptides) are also described. Special mention of the anthelmintic activity against different parasitic stages of schistosomes is made; the mechanism of action of most of the metabolites is discussed, and a number of bioassay procedures are listed.

Clustered distribution of natural product leads of drugs in the chemical space as influenced by the privileged target-sites

Some natural product leads of drugs (NPLDs) have been found to congregate in the chemical space. The extent, detailed patterns, and mechanisms of this congregation phenomenon have not been fully investigated and their usefulness for NPLD discovery needs to be more extensively tested. In this work, we generated and evaluated the distribution patterns of 442 NPLDs of 749 pre-2013 approved and 263 clinical trial small molecule drugs in the chemical space represented by the molecular scaffold and fingerprint trees of 137,836 non-redundant natural products. In the molecular scaffold trees, 62.7% approved and 37.4% clinical trial NPLDs congregate in 62 drug-productive scaffolds/scaffold-branches. In the molecular fingerprint tree, 82.5% approved and 63.0% clinical trial NPLDs are clustered in 60 drug-productive clusters (DCs) partly due to their preferential binding to 45 privileged target-site classes. The distribution patterns of the NPLDs are distinguished from those of the bioactive natural products. 11.7% of the NPLDs in these DCs have remote-similarity relationship with the nearest NPLD in their own DC. The majority of the new NPLDs emerge from preexisting DCs. The usefulness of the derived knowledge for NPLD discovery was demonstrated by the recognition of the new NPLDs of 2013-2014 approved drugs.

Biology-oriented synthesis of a withanolide-inspired compound collection reveals novel modulators of hedgehog signaling

Biology-oriented synthesis employs the structural information encoded in complex natural products to guide the synthesis of compound collections enriched in bioactivity. The trans-hydrindane dehydro-δ-lactone motif defines the characteristic scaffold of the steroid-like withanolides, a plant-derived natural product class with a diverse pattern of bioactivity. A withanolide-inspired compound collection was synthesized by making use of three key intermediates that contain this characteristic framework derivatized with different reactive functional groups. Biological evaluation of the compound collection in cell-based assays that monitored biological signal-transduction processes revealed a novel class of Hedgehog signaling inhibitors that target the protein Smoothened.

A virtual screening approach for identifying plants with anti H5N1 neuraminidase activity

Recent outbreaks of highly pathogenic and occasional drug-resistant influenza strains have highlighted the need to develop novel anti-influenza therapeutics. Here, we report computational and experimental efforts to identify influenza neuraminidase inhibitors from among the 3000 natural compounds in the Malaysian-Plants Natural-Product (NADI) database. These 3000 compounds were first docked into the neuraminidase active site. The five plants with the largest number of top predicted ligands were selected for experimental evaluation. Twelve specific compounds isolated from these five plants were shown to inhibit neuraminidase, including two compounds with IC50 values less than 92 μM. Furthermore, four of the 12 isolated compounds had also been identified in the top 100 compounds from the virtual screen. Together, these results suggest an effective new approach for identifying bioactive plant species that will further the identification of new pharmacologically active compounds from diverse natural-product resources.

Adaptive cellular stress pathways as therapeutic targets of dietary phytochemicals: focus on the nervous system

During the past 5 decades, it has been widely promulgated that the chemicals in plants that are good for health act as direct scavengers of free radicals. Here we review evidence that favors a different hypothesis for the health benefits of plant consumption, namely, that some phytochemicals exert disease-preventive and therapeutic actions by engaging one or more adaptive cellular response pathways in cells. The evolutionary basis for the latter mechanism is grounded in the fact that plants produce natural antifeedant/noxious chemicals that discourage insects and other organisms from eating them. However, in the amounts typically consumed by humans, the phytochemicals activate one or more conserved adaptive cellular stress response pathways and thereby enhance the ability of cells to resist injury and disease. Examplesof such pathways include those involving the transcription factors nuclear factor erythroid 2-related factor 2, nuclear factor-κB, hypoxia-inducible factor 1α, peroxisome proliferator-activated receptor γ, and forkhead box subgroup O, as well as the production and action of trophic factors and hormones. Translational research to develop interventions that target these pathways may lead to new classes of therapeutic agents that act by stimulating adaptive stress response pathways to bolster endogenous defenses against tissue injury and disease. Because neurons are particularly sensitive to potentially noxious phytochemicals, we focus on the nervous system but also include findings from other cell types in which actions of phytochemicals on specific signal transduction pathways have been more thoroughly studied.

Super Natural II--a database of natural products

Natural products play a significant role in drug discovery and development. Many topological pharmacophore patterns are common between natural products and commercial drugs. A better understanding of the specific physicochemical and structural features of natural products is important for corresponding drug development. Several encyclopedias of natural compounds have been composed, but the information remains scattered or not freely available. The first version of the Supernatural database containing ∼50 000 compounds was published in 2006 to face these challenges. Here we present a new, updated and expanded version of natural product database, Super Natural II (http://bioinformatics.charite.de/supernatural), comprising ∼326 000 molecules. It provides all corresponding 2D structures, the most important structural and physicochemical properties, the predicted toxicity class for ∼170 000 compounds and the vendor information for the vast majority of compounds. The new version allows a template-based search for similar compounds as well as a search for compound names, vendors, specific physical properties or any substructures. Super Natural II also provides information about the pathways associated with synthesis and degradation of the natural products, as well as their mechanism of action with respect to structurally similar drugs and their target proteins.

Studies toward the Development of Antiproliferative Neoclerodanes from Salvinorin A

The success rate for central nervous system (CNS) drug candidates in the clinic is relatively low compared to the industry average across other therapeutic areas. Penetration through the blood-brain barrier (BBB) to reach the therapeutic target is a major obstacle in development. The rapid CNS penetration of salvinorin A has suggested that the neoclerodane nucleus offers an excellent scaffold for developing antiproliferative compounds that enter the CNS. The Liebeskind-Srogl reaction was used as the main carbon-carbon bond-forming step toward the synthesis of quinone-containing salvinorin A analogues. Quinone-containing salvinorin A analogues were shown to have antiproliferative activity against the MCF7 breast cancer cell line, but show no significant activity at the κ-opioid receptors. In an in vitro model of BBB penetration, quinone-containing salvinorin A analogues were shown to passively diffuse across the cell monolayer. The analogues, however, are substrates of P-glycoprotein, and thus further modification of the molecules is needed to reduce the affinity for the efflux transporter.

In situ natural product discovery via an artificial marine sponge

There is continuing international interest in exploring and developing the therapeutic potential of marine–derived small molecules. Balancing the strategies for ocean based sampling of source organisms versus the potential to endanger fragile ecosystems poses a substantial challenge. In order to mitigate such environmental impacts, we have developed a deployable artificial sponge. This report provides details on its design followed by evidence that it faithfully recapitulates traditional natural product collection protocols. Retrieving this artificial sponge from a tropical ecosystem after deployment for 320 hours afforded three actin–targeting jasplakinolide depsipeptides that had been discovered two decades earlier using traditional sponge specimen collection and isolation procedures. The successful outcome achieved here could reinvigorate marine natural products research, by producing new environmentally innocuous sources of natural products and providing a means to probe the true biosynthetic origins of complex marine–derived scaffolds.