Non-Insulin-Based Drug Entities Used to Treat Diabetes Type 2 Disease (T2DM), Based on Natural Products from All Sources

Diabetes type 2 (T2DM) is the non-insulin-linked disease that is now becoming a major problem not only in the West but also in Asia (particularly in China and close geographic areas). Unlike the childhood onset diabetic disease (T1DM), which is effectively due to lack of insulin production and is maintained by insulin injection, T2DM is best thought of as an adult disease often being caused by what is now considered "metabolic syndrome" or the culmination of too many insults to the body, in particular obesity and its "coupled diseases" including heart problems. Its symptoms were described in ancient times not only in Europe but also in Asia and with later (1600s) anecdotal reports from South America. In all cases, the diagnostic was "sweet urine" due to the excretion of large amounts of glucose in the urine. This review covers the non-insulin agents approved from 1990 to 2021 from a historical aspect and discussions of the latest agents and can be considered an extension of the author's previous drug source reviews, but this time concentrating on nominally one disease entity, though metabolic syndrome is a collection of ailments.

Caged Xanthones and Biphenyls Isolated from the Tropical Plant Garcinia lateriflora

Four cytotoxic heptacyclic caged-xanthones [gambogefic acids B-E (1-4)], a cytotoxic hexacyclic caged-xanthone [garcilatelic acid (5)], and four biphenyl derivatives [garcilatelibiphenyls A-D (6-9)] were newly isolated in a phytochemical study of a 50% MeOH/CH2Cl2 extract of Garcinia lateriflora (Clusiaceae). The isolated compounds were evaluated for antiproliferative activity against five human tumor cell lines including a vincristine-resistant line. The new caged-xanthones displayed potent activity with IC50 values from 0.5 to 6.7 μM against all tested tumor cell lines.

Unusual Vilasinin-Class Limonoids from Trichilia rubescens

Eight vilasinin-class limonoids, including the unusually chlorinated rubescins K-M (1-3), the 2,3-epoxylated rubescin N (4), and rubescins O-R (5-8), were newly isolated from Trichilia rubescens. The structures of the isolated compounds were determined through spectroscopic and spectrometric analyses, as well as ECD calculations. The natural occurrence of chlorinated limonoids 1-3 was confirmed by chemical methods and HPLC analysis of a roughly fractionated portion of the plant extract. Eight selected limonoids, including previously known and new compounds, were evaluated for antiproliferative activity against five human tumor cell lines. All tested limonoids, except 8, exhibited significant potency, with IC50 values of <10 μM; in particular, limonoid 14 strongly inhibited tumor cell growth, with IC50 values of 0.54-2.06 μM against all tumor cell lines, including multi-drug-resistant cells.

Natural Products and Drug Discovery

This review covers the recent history of a series of very important natural products and their derivatives that are currently in use or under evaluation in the areas of anti-infectives, important cancer treatments that include antibody drug conjugates, followed by a discussion of type 2 diabetes (T2DM) drugs and angiotensin converting enzyme inhibitors. The current structures of the agents are shown, though in the case of some peptides used in T2DM drugs the standard single letter abbreviation for an amino acid is used.

Old and Modern Antibiotic Structures with Potential for Today’s Infections

Due to the lack of new antibiotics with efficacy against the ESKAPE and other resistant microbes, coupled to the demise of major pharmaceutical company antibiotic discovery programs, due to a number of factors but mainly ROI calculations and the lack of efficacy of combinatorial chemistry as a substitute, the search for novel antibiotics may well have moved to the utilization of older structures with significant synthetic chemistry input. This short review demonstrates how modern synthetic chemistry, when applied to either modification of current resistant antibiotics such as glycopeptides, or production of novel peptidic agents based on natural product sourced antimicrobial peptides (AMPs) and other potential initial peptide-based agents from genomic searches and baiting techniques, have produced active agents of significant utility. In addition, synthetic chemistry practitioners have now shown that they can produce bioactive molecules of greater than 800 Daltons in kilogram quantities under cGMP conditions.

Cheminformatic analysis of natural product-based drugs and chemical probes

Covering: 1981 to 2019Natural products continue to play a major role in drug discovery, with half of new chemical entities based structurally on a natural product. Herein, we report a cheminformatic analysis of the structural and physicochemical properties of natural product-based drugs in comparison to top-selling brand-name synthetic drugs, and a selection of chemical probes recently discovered from diversity-oriented synthesis libraries. In this analysis, natural product-based drugs covered a broad range of chemical space based on size, polarity, and three-dimensional structure. Natural product-based structures were also more prevalent in top-selling drugs of 2018 compared to 2006. Further, the drugs clustered well according to biosynthetic origins, but less so based on therapeutic classes. Macrocycles occupied distinctive and relatively underpopulated regions of chemical space, while chemical probes largely overlapped with synthetic drugs. This analysis highlights the continued opportunities to leverage natural products and their pharmacophores in modern drug discovery.

Future Directions for the Discovery of Natural Product-Derived Immunomodulating Drugs

Drug discovery from natural sources is going through a renaissance, having spent many decades in the shadow of synthetic molecule drug discovery, despite the fact that natural product-derived compounds occupy a much greater chemical space than those created through synthetic chemistry methods. With this new era comes new possibilities, not least the novel targets that have emerged in recent times and the development of state-of-the-art technologies that can be applied to drug discovery from natural sources. Although progress has been made with some immunomodulating drugs, there remains a pressing need for new agents that can be used to treat the wide variety of conditions that arise from disruption, or over-activation, of the immune system; natural products may therefore be key in filling this gap. Recognising that, at present, there is no authoritative article that details the current state-of-the-art of the immunomodulatory activity of natural products, this in-depth review has arisen from a joint effort between the International Union of Basic and Clinical Pharmacology (IUPHAR) Natural Products and Immunopharmacology, with contributions from a Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation number of world-leading researchers in the field of natural product drug discovery, to provide a "position statement" on what natural products has to offer in the search for new immunomodulatory argents. To this end, we provide a historical look at previous discoveries of naturally occurring immunomodulators, present a picture of the current status of the field and provide insight into the future opportunities and challenges for the discovery of new drugs to treat immune-related diseases.

Problems that Can Occur when Assaying Extracts to Pure Compounds in Biological Systems

For a significant number of years, scientists of many persuasions have assayed natural product materials ranging from crude extracts to pure compounds, in a multitude of assays causally related to some biological processes. However, in a very significant number of submitted papers and published articles, what may be considered as canned biological assays were used, and if a positive effect was observed, then the authors would claim that the material assayed was a potential drug lead. This also occurred with pure synthetic compounds and compounds derived from natural products by simple chemical modifications.

However, what has now become quite obvious—with all such classes of materials—is that there are many promiscuous players with multiple bioactivities. These can range from relatively crude extracts, pure compounds from natural products, synthetic processes that produce natural product derivatives, and even compounds that are truly synthetic in origin. There is also a potential problem with the data from crude to purified extracts being used to claim some form of beneficial activities for such materials, to sell that particular mixture to the lay public, by very careful descriptions of its possible uses due to legal hurdles.

With the advent of artificial intelligence and very large compound databases, some of which may well contain impure materials, scientists from a variety of backgrounds have begun to utilize such listings to obtain compounds for their low to high throughput biological screens, without realizing that there are very significant numbers of active compounds (eg, pan assay interference compounds and invalid metabolic panaceas), that will hit in many different screens for a variety of reasons, thus leading to significant wasted efforts and published scientific articles that have incorrect results.

This commentary gives some of the history of such materials but is designed to be used as a warning to both researchers and in particular, journal editors, and reviewers, that reports of biological results that are claimed to be the result of the compounds used, need to be very carefully screened for results due to such promiscuous compounds, irrespective of their nominal source(s).

All literature searches were made by the author and the background knowledge has come from more than 55 years of research in industry and governmental laboratories in both the United Kingdom and the United States, for enzyme inhibitors/activators as well as antimicrobial and antitumor lead compounds mainly from natural product sources.

The conclusion that I came up with as a result is this: Caveat emptor. (Curr Ther Res Clin Exp. 2021; 82:XXX–XXX)

© 2021 Elsevier HS Journals, Inc.

Correction: Antiviral drug discovery: preparing for the next pandemic

Correction for 'Antiviral drug discovery: preparing for the next pandemic' by Catherine S. Adamson et al., Chem. Soc. Rev., 2021, 50, 3647-3655, DOI: .

Natural Product Based Antibody Drug Conjugates: Clinical Status as of November 9, 2020

As of early November 2020, there are 10 approved antibody drug conjugates (ADCs) plus two others that are not usually listed. In addition, there are 70 ADCs at stages from phase I to phase III and 23 that are at the preclinical stage. The warheads of all of these drugs and drug candidates have their origins in natural product structures. The sources and modifications are discussed in general and then specifically commented on in each case with either the generic name if known and/or the ADC's ID names. Interestingly, almost all warheads listed are from microbial sources though initially a number were thought to have been from plants. The latest NCT numbers from Clintrials.gov of all phase I to phase III candidates are also given. Three unusual ADCs are also discussed, two of which (an antitumor agent and one directed against autoimmune diseases) are not usually listed as ADCs, with the third being an anti-infective.

Antiviral drug discovery: preparing for the next pandemic

Clinically approved antiviral drugs are currently available for only 10 of the more than 220 viruses known to infect humans. The SARS-CoV-2 outbreak has exposed the critical need for compounds that can be rapidly mobilised for the treatment of re-emerging or emerging viral diseases, while vaccine development is underway. We review the current status of antiviral therapies focusing on RNA viruses, highlighting strategies for antiviral drug discovery and discuss the challenges, solutions and options to accelerate drug discovery efforts.

Prediction of Whole Pork Loin and Individual Chops’ Intramuscular Fat Using Computer Vision System Technology

The objective of this study was to compare different methods of evaluating intramuscular fat (IMF) in pork and test the accuracy of using a computer vision system (CVS) on different locations of the loin. Whole pork loins (n = 1,400) were obtained from 6 pork processing plants. Subjective marbling scores and CVS IMF percentage (CVS IMF%) were assessed on the ventral lean surface of the whole loin and the 3rd (A) and 10th (B) rib chops. Additionally, the A and B chops were evaluated for crude fat percentage (CF%) using ether extract. The CF% of the whole loin was represented by using the average CF% of A and B chops. A combination of the bootstrap method and stepwise regression models was used to increase prediction and robustness for CF% prediction. To better understand whether plants played an effect, models for individual plants and using all plants together were built, tested, and compared. Results were that subjective marbling score had stronger correlations with CF% compared to CVS IMF% for the whole loin (0.70 vs. 0.58), A chop (0.79 vs.0.62), and B chop (0.74 vs. 0.61). When using the stepwise regression models to predict CF%, B chop (71.8%) had the highest prediction accuracy (estimates within 0.5% residual compared to CF% were considered accurate) followed by A chop (58.1%) and whole loin (48.2%). When comparing individual plant models and overall models, the overall accuracy improved; however, this improvement in accuracy was not consistent through every single plant. In conclusion, CVS has shown potential to estimate pork IMF on all locations, especially the posterior pork chop.

Plant Endophytes and Epiphytes: Burgeoning Sources of Known and "Unknown" Cytotoxic and Antibiotic Agents?

In the last 20 or so years, the influence of endophytes and, quite recently, epiphytes of plants upon the compounds found in those plants, which were usually assumed to be phytochemicals produced by the plant for a variety of reasons, often as a defense against predators, is becoming more evident, in particular in the case of antitumor agents originally isolated from plant sources, though antibiotic agents might also be found, particularly from epiphytes. In this review, we started with the first report in 1993 of a taxol-producing endophyte and then expanded the compounds discussed to include camptothecin, the vinca alkaloids, podophyllotoxin, and homoharringtonine from endophytic microbes and then the realization that maytansine is not a plant secondary metabolite at all, and that even such a well-studied plant such as Arabidopsis thaliana has a vast repertoire of potential bioactive agents in its leaf epiphytic bacteria. We have taken data from a variety of sources, including a reasonable history of these discoveries that were not given in recent papers by us, nor in other papers covering this topic. The sources included the Scopus database, but we also performed other searches using bibliographic tools, thus, the majority of the papers referenced are the originals, though we note some very recent papers that have built on previous results. We concluded with a discussion of the more modern techniques that can be utilized to "persuade" endophytes and epiphytes to switch on silent biosynthetic pathways and how current analytical techniques may aid in evaluating such programs. We also comment at times on some findings, particularly in the case of homoharringtonine, where there are repetitious data reports differing by a few years claiming the same endophyte as the producer.

BCG vaccination early in life does not improve COVID-19 outcome of elderly populations, based on nationally reported data

The reported numbers of Covid-19 cases and deaths were compared for 18 countries (14 in Western Europe, plus Australia, Brazil, Israel and the USA) to assess the effect of historic and current national BCG immunizations. In view of the high death rate for Covid-19 patients over 70 years of age, and given the fact that BCG vaccination is typically given early in life, we compared countries that had introduced BCG in the 1950s with those that had not. No effect on Covid-19 case fatality rate (CFR) or number of deaths per population could be demonstrated. Since some countries test for Covid-19 more than others, the effect of tests performed per million population on reported deaths per million was also assessed, but again did not demonstrate an effect of BCG vaccination in the 1950s. Whether countries had never used the vaccine, had historically used it but since ceased to do so, or were presently vaccinating with BCG did not correlate with national total number of deaths or CFR. We conclude that there is currently no evidence for a beneficial effect of BCG vaccination on Covid-19 reported cases or fatalities.

Natural Products as Sources of New Drugs over the Nearly Four Decades from 01/1981 to 09/2019

This review is an updated and expanded version of the five prior reviews that were published in this journal in 1997, 2003, 2007, 2012, and 2016. For all approved therapeutic agents, the time frame has been extended to cover the almost 39 years from the first of January 1981 to the 30th of September 2019 for all diseases worldwide and from ∼1946 (earliest so far identified) to the 30th of September 2019 for all approved antitumor drugs worldwide. As in earlier reviews, only the first approval of any drug is counted, irrespective of how many "biosimilars" or added approvals were subsequently identified. As in the 2012 and 2016 reviews, we have continued to utilize our secondary subdivision of a "natural product mimic", or "NM", to join the original primary divisions, and the designation "natural product botanical", or "NB", to cover those botanical "defined mixtures" now recognized as drug entities by the FDA (and similar organizations). From the data presented in this review, the utilization of natural products and/or synthetic variations using their novel structures, in order to discover and develop the final drug entity, is still alive and well. For example, in the area of cancer, over the time frame from 1946 to 1980, of the 75 small molecules, 40, or 53.3%, are N or ND. In the 1981 to date time frame the equivalent figures for the N* compounds of the 185 small molecules are 62, or 33.5%, though to these can be added the 58 S* and S*/NMs, bringing the figure to 64.9%. In other areas, the influence of natural product structures is quite marked with, as expected from prior information, the anti-infective area being dependent on natural products and their structures, though as can be seen in the review there are still disease areas (shown in Table 2) for which there are no drugs derived from natural products. Although combinatorial chemistry techniques have succeeded as methods of optimizing structures and have been used very successfully in the optimization of many recently approved agents, we are still able to identify only two de novo combinatorial compounds (one of which is a little speculative) approved as drugs in this 39-year time frame, though there is also one drug that was developed using the "fragment-binding methodology" and approved in 2012. We have also added a discussion of candidate drug entities currently in clinical trials as "warheads" and some very interesting preliminary reports on sources of novel antibiotics from Nature due to the absolute requirement for new agents to combat plasmid-borne resistance genes now in the general populace. We continue to draw the attention of readers to the recognition that a significant number of natural product drugs/leads are actually produced by microbes and/or microbial interactions with the "host from whence it was isolated"; thus we consider that this area of natural product research should be expanded significantly.

Prenylated Acetophloroglucinol Dimers from Acronychia trifoliolata: Structure Elucidation and Total Synthesis

The isolation of 12 secondary metabolites, including seven new acetophenone monomers, from the 50% CH₃OH/CH₂Cl₂ extract (N089419-L/6) of Acronychia trifoliolata was reported previously. In the present work, three new prenylated acetophenone dimers (1-3) and five known dimers (4-8) were isolated, and their structures were elucidated by using various NMR spectroscopic techniques and HRMS. Among the new dimers, an unprecedented 4-isobutyl-3-isopropyltetrahydro-2H-pyran ring was observed in the structure of 1. This study is the first to report the formation of a 2H-pyran ring between two prenylated acetophloroglucinols. Only four related dimers have been reported before, and they were formylated phloroglucinol dimers from the family Eucalypteae. Compounds 2 and 3 are acrovestone-like dimers, and the structure of 3 was confirmed by total synthesis. The evaluation of the antiproliferative activity of isolated and synthesized acrovestone-like dimers indicated that a double bond in the prenyl-like moiety as found in the more active compounds might be important for mediating activity, while the pendant isobutyl group seems to be less important.

Spiro[3.5]nonenyl Meroterpenoid Lactones, Cryptolaevilactones G-L, an Ionone Derivative, and Total Synthesis of Cryptolaevilactone M from Cryptocarya laevigata

A CH₃OH-CH₂Cl₂ (1:1) extract (N025439) of the leaves and twigs of Cryptocarya laevigata furnished eight new compounds, 1-8. Based on extensive 1D and 2D NMR spectroscopic data examination, the new δ-lactone derivatives 1-6 are monoterpene-polyketide hybrids containing a unique spiro[3.5]nonenyl moiety. Their trivial names, cryptolaevilactones G-L, follow those of the related known meroterpenoids cryptolaevilactones A-F. Cryptolaevilactone L (6) contains 11,12-cis-oriented substituents, while the other cryptolaevilactones contain trans-oriented groups. The structure of the linear δ-lactone 7, cryptolaevilactone M, was characterized from various spectroscopic data analysis, and the absolute configuration was determined by total synthesis through stereoselective allylation and Grubbs olefin metathesis. Compound 8 was elucidated to be an ionone derivative with a 3,4-syn-diol functionality.

The NCI library of traditional Chinese medicinal plant extracts - Preliminary assessment of the NCI-60 activity and chemical profiling of selected species

Botanical-based natural products are an important resource for medicinal drug discovery and continue to provide diverse pharmacophores with therapeutic potential against cancer and other human diseases. A prototype Traditional Chinese Medicine (TCM) plant extract library has been established at the US National Cancer Institute, which contains both the organic and aqueous extracts of 132 authenticated medicinal plant species that collectively represent the potential therapeutic contents of most commonly used TCM herbal prescriptions. This library is publicly available in 96- and 384- well plates for high throughput screening across a broad array of biological targets, as well as in larger quantities for isolation of active chemical ingredients. Herein, we present the methodology used to generate the library and the preliminary assessment of the anti-proliferative activity of this crude extract library in NCI-60 human cancer cell lines screen. Particularly, we report the chemical profiling and metabolome comparison analysis of four commonly used TCM plants, namely Brucea javanica, Dioscorea nipponica, Cynanchum atratum, and Salvia miltiorrhiza. Bioassay-guided isolation resulted in the identification of the active compounds, and different extraction methods were compared for their abilities to extract cytotoxic compounds and to concentrate biologically active natural products.

The impact of decreasing biodiversity on novel drug discovery: is there a serious cause for concern?

INTRODUCTION

The aim of this perspective is to discuss the current and potential situation concerning the loss of biodiversity and its current and potential effects upon the search for novel bioactive agents from natural sources, be they from marine, microbial or terrestrial environments. Areas covered: Herein, the author covers terrestrial plants, marine organisms (but not vertebrates), and unicellular microbes from both terrestrial and marine sources. The emphasis is on the unknown effects of biodiversity perturbation and/or loss of microbes that are now realized to underlie the production of a significant number of natural products, whether they were first found in plants or marine invertebrates. Expert opinion: From the discussion of the areas above comes the realization that we do not know what we still have. Furthermore, we cannot measure, other than in very gross terms, what we have lost. Thus, deciding how, and where geographically, one should now search for novel bioactive agents is a major and continuing problem.

Erythrofordins D and E, two new cassaine-type diterpenes from Erythrophleum suaveolens

Two new cassaine-type diterpenoids, namely erythrofordins D (1) and E (2), sourced from a Cameroon collection of Erythrophleum suaveolens were isolated and assessed for anti-tumor activity. In the NCI-60 cancer cell assay, erythrofordins D (1) and E (2) were found to be cytotoxic in the low micro molar ranges with a mean GI₅₀ value of 2.45 and 0.71 µM, mean TGI value of 9.77 and 2.29 µM, and a mean LC₅₀ of 26.92 and 11.48 µM for 1 and 2 respectively. Using the COMPARE algorithm, the new compounds were found to have similar NCI-60 response profiles to the known cardiac glycosides hyrcanoside and strophanthin. In addition, in an assay examining the viability and contractile function in human cardiomyocytes derived from induced pluripotent stem-cells, erythrofordins showed cardiotoxicity effects at concentrations as low as 0.03 µg/mL.

NCI Program for Natural Product Discovery: A Publicly-Accessible Library of Natural Product Fractions for High-Throughput Screening

The US National Cancer Institute's (NCI) Natural Product Repository is one of the world's largest, most diverse collections of natural products containing over 230,000 unique extracts derived from plant, marine, and microbial organisms that have been collected from biodiverse regions throughout the world. Importantly, this national resource is available to the research community for the screening of extracts and the isolation of bioactive natural products. However, despite the success of natural products in drug discovery, compatibility issues that make extracts challenging for liquid handling systems, extended timelines that complicate natural product-based drug discovery efforts and the presence of pan-assay interfering compounds have reduced enthusiasm for the high-throughput screening (HTS) of crude natural product extract libraries in targeted assay systems. To address these limitations, the NCI Program for Natural Product Discovery (NPNPD), a newly launched, national program to advance natural product discovery technologies and facilitate the discovery of structurally defined, validated lead molecules ready for translation will create a prefractionated library from over 125,000 natural product extracts with the aim of producing a publicly-accessible, HTS-amenable library of >1,000,000 fractions. This library, representing perhaps the largest accumulation of natural-product based fractions in the world, will be made available free of charge in 384-well plates for screening against all disease states in an effort to reinvigorate natural product-based drug discovery.

Antiproliferative Alkaloids from Alangium longiflorum, an Endangered Tropical Plant Species

Alangium longiflorum is currently in extinction crisis, which will likely severely hamper further phytochemical investigation of this plant species from new collections. A crude extract of leaves of A. longiflorum (N33539), collected for the U.S. National Cancer Institute in 1989, showed potent cancer cell line antiproliferative activity. A phytochemical study resulted in the isolation of 17 secondary metabolites, including two new tetrahydroisoquinoline alkaloids, 8-hydroxytubulosine (1) and 2'- O- trans-sinapoylisoalangiside (2), as well as a new sinapolyloxylupene derivative (3). Using in-house assays and NCI-60 panel screening, compound 1 displayed broad-spectrum inhibitory activity at submicromolar levels against most tested tumor cell lines, except for drug-transporter-overexpressing cells. Compound 1 caused accumulation of sub-G1 cells with no effect on cell cycle progression, suggesting that this substance is an apoptosis inducer.

Secondary Metabolites, Monoterpene-Polyketides Containing a Spiro[3.5]nonane from Cryptocarya laevigata

Six novel lactone derivatives, cryptolaevilactones A-F (1-6), were isolated from Cryptocarya laevigata. Their unique spiro[3.5]nonane moiety by hetero [2 + 2] cyclization with monoterpene and polyketide was found for the first time in nature. Structural elucidation using various nuclear magnetic resonance (NMR) techniques revealed that 1-3 and 4-6 are diastereomers and partially established the absolute configurations.

Novel Modifications of Glycopeptide Antibiotics via Total Synthesis

Although vancomycin has been in clinical use since the late 1950s, resistance due to alteration in the target microbe's peptidoglycan can vary significantly, reducing its activity. Total synthesis of derivatives has now led to a molecule with very significant activity against resistant strains.

Corymbulosins I-W, Cytotoxic Clerodane Diterpenes from the Bark of Laetia corymbulosa

The isolation studies of a crude MeOH/CH₂Cl₂ (1:1) extract (N005829) of the bark of Laetia corymbulosa yielded 15 new clerodane diterpenes, designated corymbulosins I-W (1-15), as well as four known diterpenes, 16-19. The structures of 1-15 were characterized on the basis of extensive 1D and 2D NMR and HRMS analyses. The absolute configurations of newly isolated compounds 1-15, as well as known 16-19, which were reported previously with only relative configurations, were determined through ECD experiments, X-ray analysis, chemical methods, including Mosher esterification, and comparison of their spectroscopic data. The isolated compounds were evaluated for cytotoxicity against human cancer cell lines. Flow cytometric and immunocytochemical observations of cells treated with cytotoxic clerodanes demonstrated that the chromatin was fragmented and dispersed with formation of apoptotic microtubules.

Imaginative Order from Reasonable Chaos: Conformation-Driven Activity and Reactivity in Exploring Protein–Ligand Interactions

Sir Derek Barton’s seminal work on steroid conformational analysis opened up a new era of enquiry into how the preferred conformation of any molecule could have profound effects on its physical–chemical properties and activities. Conformation-based effects on molecular activity and reactivity continue to manifest, with one key area of investigation currently focussed on conformational entropy in driving protein–ligand interactions. Carrying on from Barton’s initial insight on natural product conformational properties, new questions now address how conformational flexibility within a bioactive natural product structural framework (reasonable chaos), can be directed to confer dynamically new protein–ligand interactions beyond the basic lock–key model (imaginative order). Here we summarise our work on exploring conformational diversity from fluorinated natural product fragments, and how this approach of conformation-coupled diversity-oriented synthesis can be used to iteratively derive ligands with enhanced specificity against highly homologous protein domains. Our results demonstrate that the conformation entropic states of highly conserved protein domains differ significantly, and this conformational diversity, beyond primary sequence analysis, can be duly captured and exploited by natural-product derived ligands with complementary conformational dynamics for enhancing recognition specificity in drug lead discovery.

Adult Reference Ranges for Serum Cystatin C, Creatinine and Predicted Creatinine Clearance

Serum cystatin C measurement has been previously shown by ourselves and others to be a better indicator of changes in glomerular filtration rate (GFR) than serum creatinine. However, the available literature on reference values for cystatin C concentration remains surprisingly sparse; we thus set out to determine an adult reference range. Blood was taken from 309 healthy blood donors and creatinine and cystatin C concentrations were measured using commercially available automated methodologies. In addition, predicted creatinine clearances were calculated using the Cockcroft and Gault formula. The 95% reference intervals for creatinine, predicted creatinine clearance and cystatin C for all blood donors, regardless of gender, were 68–118 μmol/L, 58–120 ml/min/1·73 m2 and 0·51–0·98 mg/L, respectively. For women, the intervals were 68–98 μmol/L, 60–119 ml/min/1·73 m2 and 0·49–0·94 mg/L; for men, they were 78–123 μmol/L, 57–122 ml/min/1·73 m2 and 0·56–0·98 mg/L. The mean 95% reference interval for cystatin C in all donors under 50 years of age was 0·53–0·92 mg/L; for those over 50 years of age it was 0·58–1·02 mg/L. The small difference between male and female ranges meant that a single reference range for cystatin C could be established for all adults under 50 years of age without adjustment for body surface area. Serum cystatin C measurement offers a simpler and more sensitive screening test than serum creatinine for early changes in GFR.

Corymbulosins D-H, 2-Hydroxy- and 2-Oxo-clerodane Diterpenes from the Bark of Laetia corymbulosa

A bioactive CH₃OH-CH₂Cl₂ (1:1) extract of the bark of Laetia corymbulosa provided five new clerodane diterpenes with an isozuelanin skeleton, designated as corymbulosins D-H (1-5), as well as the known corymbulosins B (6) and C (7), for which the relative configurations were not previously determined. The structures of 1-5 were characterized on the basis of 1D and 2D NMR spectroscopic and HRMS analysis. The absolute configurations of all isolated compounds 1-7 were verified through chemical methods, including modified Mosher esterifications or oxidation of the hydroxy group at C-2, ECD experiments, and spectroscopic data comparison. The isolated compounds were evaluated for antiproliferative activity against a small panel of human cancer cell lines.

Current Status of Marine-Derived Compounds as Warheads in Anti-Tumor Drug Candidates

In this review, we have attempted to describe all of the antibody–drug conjugates using a marine-derived compound as the “warhead”, that are currently in clinical trials as listed in the current version of the NIH clinical trials database (clinicaltrials.gov). In searching this database, we used the beta-test version currently available, as it permitted more specific search parameters, since the regular version did not always find trials that had been completed in the past with some agents. We also added small discussion sections on candidates that are still at the preclinical stage, including a derivative of diazonamide that has an unusual interaction with tubulin (DZ-23840), which may also be a potential warhead in the future.

(-)-Neocaryachine, an Antiproliferative Pavine Alkaloid from Cryptocarya laevigata, Induces DNA Double-Strand Breaks

Twelve benzylisoquinoline alkaloids, including pavine and phenanthroindolizidine types, were isolated from a MeOH/CH₂Cl₂ extract of Cryptocarya laevigata (stem bark) through bioactivity-guided fractionation for antitumor effects. Selected compounds were evaluated for antiproliferative activity against five human tumor cell lines, including a multidrug-resistant subline. Since more common 2,3,8,9-tetrasubstituted pavine alkaloids, such as crychine (3), exhibit very mild or no cytotoxicity, this compound type has not been well investigated for antitumor activity. Thus, this report is the first discovery of a 7-hydroxylated pavine alkaloid, (-)-neocaryachine (1), to demonstrate strong antiproliferative activity, with IC₅₀ values of 0.06 to 0.41 μM against five tested tumor cell lines, including an MDR subline. Further mechanism of action studies revealed that 1 impacts the cellular S-phase by inducing DNA double-strand breaks.

Acetophenone Monomers from Acronychia trifoliolata

Seven new [acronyculatins I-O (1-7)] and four known acetophenone monomers were isolated from a CH3OH/CH2Cl2 (1:1) extract (N089419) of Acronychia trifoliolata provided by the U.S. National Cancer Institute (NCI, Frederick, MD, USA). Their structures were characterized by using various NMR and HRMS techniques. Among the known compounds, the structure of acronyculatin B (8) was revised. Some of the isolated compounds were evaluated for antiproliferative activity against human cancer cell lines. While most of the tested compounds were not cytotoxic, acronyculatins I (1) and J (2) showed moderate antiproliferative activity.

Predominately Uncultured Microbes as Sources of Bioactive Agents

In this short review, I am discussing the relatively recent awareness of the role of symbionts in plant, marine-invertebrates and fungal areas. It is now quite obvious that in marine-invertebrates, a majority of compounds found are from either as yet unculturable or poorly culturable microbes, and techniques involving “state of the art” genomic analyses and subsequent computerized analyses are required to investigate these interactions. In the plant kingdom evidence is amassing that endophytes (mainly fungal in nature) are heavily involved in secondary metabolite production and that mimicking the microbial interactions of fermentable microbes leads to involvement of previously unrecognized gene clusters (cryptic clusters is one name used), that when activated, produce previously unknown bioactive molecules.

Drugs and Drug Candidates from Marine Sources: An Assessment of the Current "State of Play"

The potential of the marine environment to produce candidate compounds (structures) as leads to, or even direct drugs from, has been actively discussed for the last 50 or so years. Over this time frame, several compounds have led to drugs, usually in the area of cancer (due to funding sources). This review is designed to show where there have been successes, but also to show that in a number of disease areas, there are structures originally isolated from marine invertebrates and free-living microbes that have potential, but will need to be "adopted" by pharmaceutical houses in order to maximize their potential.

Natural Products as Sources of New Drugs from 1981 to 2014

This contribution is a completely updated and expanded version of the four prior analogous reviews that were published in this journal in 1997, 2003, 2007, and 2012. In the case of all approved therapeutic agents, the time frame has been extended to cover the 34 years from January 1, 1981, to December 31, 2014, for all diseases worldwide, and from 1950 (earliest so far identified) to December 2014 for all approved antitumor drugs worldwide. As mentioned in the 2012 review, we have continued to utilize our secondary subdivision of a "natural product mimic", or "NM", to join the original primary divisions and the designation "natural product botanical", or "NB", to cover those botanical "defined mixtures" now recognized as drug entities by the U.S. FDA (and similar organizations). From the data presented in this review, the utilization of natural products and/or their novel structures, in order to discover and develop the final drug entity, is still alive and well. For example, in the area of cancer, over the time frame from around the 1940s to the end of 2014, of the 175 small molecules approved, 131, or 75%, are other than "S" (synthetic), with 85, or 49%, actually being either natural products or directly derived therefrom. In other areas, the influence of natural product structures is quite marked, with, as expected from prior information, the anti-infective area being dependent on natural products and their structures. We wish to draw the attention of readers to the rapidly evolving recognition that a significant number of natural product drugs/leads are actually produced by microbes and/or microbial interactions with the "host from whence it was isolated", and therefore it is considered that this area of natural product research should be expanded significantly.

Prospecting for new bacterial metabolites: a glossary of approaches for inducing, activating and upregulating the biosynthesis of bacterial cryptic or silent natural products

Over the centuries, microbial secondary metabolites have played a central role in the treatment of human diseases and have revolutionised the pharmaceutical industry.

Cheminformatic comparison of approved drugs from natural product versus synthetic origins

Despite the recent decline of natural product discovery programs in the pharmaceutical industry, approximately half of all new drug approvals still trace their structural origins to a natural product. Herein, we use principal component analysis to compare the structural and physicochemical features of drugs from natural product-based versus completely synthetic origins that were approved between 1981 and 2010. Drugs based on natural product structures display greater chemical diversity and occupy larger regions of chemical space than drugs from completely synthetic origins. Notably, synthetic drugs based on natural product pharmacophores also exhibit lower hydrophobicity and greater stereochemical content than drugs from completely synthetic origins. These results illustrate that structural features found in natural products can be successfully incorporated into synthetic drugs, thereby increasing the chemical diversity available for small-molecule drug discovery.

Small-Molecule Reactivation of Mutant p53 to Wild-Type-like p53 through the p53-Hsp40 Regulatory Axis

TP53 is the most frequently mutated gene in human cancer, and small-molecule reactivation of mutant p53 function represents an important anticancer strategy. A cell-based, high-throughput small-molecule screen identified chetomin (CTM) as a mutant p53 R175H reactivator. CTM enabled p53 to transactivate target genes, restored MDM2 negative regulation, and selectively inhibited the growth of cancer cells harboring mutant p53 R175H in vitro and in vivo. We found that CTM binds to Hsp40 and increases the binding capacity of Hsp40 to the p53 R175H mutant protein, causing a potential conformational change to a wild-type-like p53. Thus, CTM acts as a specific reactivator of the p53 R175H mutant form through Hsp40. These results provide new insights into the mechanism of reactivation of this specific p53 mutant.