Natural products as leads to potential drugs: an old process or the new hope for drug discovery?

Marine Mollusk-Derived Agents with Antiproliferative Activity as Promising Anticancer Agents to Overcome Chemotherapy Resistance

The chemical investigation of marine mollusks has led to the isolation of a wide variety of bioactive metabolites, which evolved in marine organisms as favorable adaptations to survive in different environments. Most of them are derived from food sources, but they can be also biosynthesized de novo by the mollusks themselves, or produced by symbionts. Consequently, the isolated compounds cannot be strictly considered as "chemotaxonomic markers" for the different molluscan species. However, the chemical investigation of this phylum has provided many compounds of interest as potential anticancer drugs that assume particular importance in the light of the growing literature on cancer biology and chemotherapy. The current review highlights the diversity of chemical structures, mechanisms of action, and, most importantly, the potential of mollusk-derived metabolites as anticancer agents, including those biosynthesized by mollusks and those of dietary origin. After the discussion of dolastatins and kahalalides, compounds previously studied in clinical trials, the review covers potentially promising anticancer agents, which are grouped based on their structural type and include terpenes, steroids, peptides, polyketides and nitrogen-containing compounds. The "promise" of a mollusk-derived natural product as an anticancer agent is evaluated on the basis of its ability to target biological characteristics of cancer cells responsible for poor treatment outcomes. These characteristics include high antiproliferative potency against cancer cells in vitro, preferential inhibition of the proliferation of cancer cells over normal ones, mechanism of action via nonapoptotic signaling pathways, circumvention of multidrug resistance phenotype, and high activity in vivo, among others. The review also includes sections on the targeted delivery of mollusk-derived anticancer agents and solutions to their procurement in quantity.

Marine microorganisms as a promising and sustainable source of bioactive molecules

There is an urgent need to discover new drug entities due to the increased incidence of severe diseases as cancer and neurodegenerative pathologies, and reducing efficacy of existing antibiotics. Recently, there is a renewed interest in exploring the marine habitat for new pharmaceuticals also thanks to the advancement in cultivation technologies and in molecular biology techniques. Microorganisms represent a still poorly explored resource for drug discovery. The possibility of obtaining a continuous source of bioactives from marine microorganisms, more amenable to culturing compared to macro-organisms, may be able to meet the challenging demands of pharmaceutical industries. This would enable a more environmentally-friendly approach to drug discovery and overcome the over-utilization of marine resources and the use of destructive collection practices. The importance of the topic is underlined by the number of EU projects funded aimed at improving the exploitation of marine organisms for drug discovery.

Hepatotoxicity and nephrotoxicity of saponin-enriched extract of Asparagus cochinchinensis in ICR mice

The inhibitory effects of Asparagus cochinchinensis against inflammatory response induced by lipopolysaccharide (LPS), substance P and phthalic anhydride (PA) treatment were recently reported for some cell lines and animal models. To evaluate the hepatotoxicity and nephrotoxicity of A. cochinchinensis toward the livers and kidneys of ICR mice, alterations in related markers including body weight, organ weight, urine composition, liver pathology and kidney pathology were analyzed in male and female ICR mice after oral administration of 150, 300 and 600 mg/kg body weight/day saponin-enriched extract of A. cochinchinensis (SEAC) for 14 days. The saponin, total flavonoid and total phenol levels were found to be 57.2, 88.5 and 102.1 mg/g in SEAC, respectively, and the scavenging activity of SEAC gradually increased in a dose-dependent manner. Moreover, body and organ weight, clinical phenotypes, urine parameters and mice mortality did not differ between the vehicle and SEAC treated group. Furthermore, no significant alterations were measured in alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), blood urea nitrogen (BUN) and the serum creatinine (Cr) in the SEAC treated group relative to the vehicle treated group. Moreover, the specific pathological features induced by most toxic compounds were not observed upon liver and kidney histological analysis. Overall, the results of the present study suggest that SEAC does not induce any specific toxicity in the livers and kidneys of male and female ICR mice at doses of 600 mg/kg body weight/day.

Biosynthesis of Fluorinated Peptaibols Using a Site-Directed Building Block Incorporation Approach

Synthetic biological approaches, such as site-directed biosynthesis, have contributed to the expansion of the chemical space of natural products, making possible the biosynthesis of unnatural metabolites that otherwise would be difficult to access. Such methods may allow the incorporation of fluorine, an atom rarely found in nature, into complex secondary metabolites. Organofluorine compounds and secondary metabolites have both played pivotal roles in the development of drugs; however, their discovery and development are often via nonintersecting tracks. In this context, we used the biosynthetic machinery of Trichoderma arundinaceum (strain MSX70741) to incorporate a fluorine atom into peptaibol-type molecules in a site-selective manner. Thus, fermentation of strain MSX70741 in media containing ortho- and meta-F-phenylalanine resulted in the biosynthesis of two new fluorine-containing alamethicin F50 derivatives. The fluorinated products were characterized using spectroscopic (1D and 2D NMR, including ¹⁹F) and spectrometric (HRESIMS/MSⁿ) methods, and their absolute configurations were established by Marfey's analysis. Fluorine-containing alamethicin F50 derivatives exhibited potency analogous to the nonfluorinated parent when evaluated against a panel of human cancer cell lines. Importantly, the biosynthesis of fluorinated alamethicin F50 derivatives by strain MSX70741 was monitored in situ using a droplet-liquid microjunction-surface sampling probe coupled to a hyphenated system.

Antiparasitic Sesquiterpenes from the Cameroonian Spice Scleria striatinux and Preliminary In Vitro and In Silico DMPK Assessment

The antiparasitic activity and preliminary in vitro and in silico drug metabolism and pharmacokinetic (DMPK) assessment of six isomeric sesquiterpenes (1-6), isolated from the Cameroonian spice Scleria striatinux De Wild (Cyperaceae) is reported. The study was prompted by the observation that two of the compounds (1 and 2) exhibited varying levels of antiparasitic activity on Plasmodium falciparum, Trypanosoma brucei rhodesiense, Trypanosoma cruzi and Leishmania donovani. The in silico method employed a total of 46 descriptors, calculated using Schrödinger QikProp software. 18 of these molecular descriptors that are often used to predict DMPK profiles of drug-like molecules have been selected for discussion. In vitro experimental assessment of metabolic stability made use of human liver microsomes, which was used to correlate theoretical predictions with experimental findings. Overall, the test compounds have been found to have acceptable physicochemical properties and fall within the ranges associated with "drug-like" molecules. Moreover, the compounds exhibited minimal degradation in incubations with human liver microsomes. Although some of these compounds have been reported previously (1, 2, 4 and 5), this is the first report on their antiparasitic activities, as well as assessment of their DMPK profiles. These results have therefore provided a window for further development of this novel class of sesquiterpene molecules as potential antiparasitic drugs.

Highly Stereoselective Synthesis of a Compound Collection Based on the Bicyclic Scaffolds of Natural Products

Despite the great contribution of natural products in the history of successful drug discovery, there are significant limitations that persuade the pharmaceutical industry to evade natural products in drug discovery research. The extreme scarcity as well as structural complexity of natural products renders their practical synthetic access and further modifications extremely challenging. Although other alternative technologies, particularly combinatorial chemistry, were embraced by the pharmaceutical industry to get quick access to a large number of small molecules with simple frameworks that often lack three-dimensional complexity, hardly any success was achieved in the discovery of lead molecules. To acquire chemotypes beholding structural features of natural products, for instance high sp³ character, the synthesis of compound collections based on core-scaffolds of natural products presents a promising strategy. Here, we report a natural product inspired synthesis of six different chemotypes and their derivatives for drug discovery research. These bicyclic hetero- and carbocyclic scaffolds are highly novel, rich in sp³ features and with ideal physicochemical properties to display drug likeness. The functional groups on the scaffolds were exploited further to generate corresponding compound collections. Synthesis of two of these collections exemplified with ca. 350 compounds are each also presented. The whole compound library is being exposed to various biological screenings within the European Lead Factory consortium.

Eupafolin Exhibits Potent Anti-Angiogenic and Antitumor Activity in Hepatocellular Carcinoma

Eupafolin is a flavonoid extracted from the common sage herb which has been used in China as traditional medicine. Previous studies had reported that eupafolin had antioxidative, anti-inflammatory and antitumor effects. However, the function and the mechanism of eupafolin to exert its antitumor activity, especially its effect on tumor angiogenesis, have not been elucidated. Herein, we showed that eupafolin significantly inhibited vascular endothelial growth factor (VEGF)-induced cell proliferation, migration and tube formation of human umbilical vascular endothelial cells (HUVECs) in a dose-dependent manner. Meanwhile, the new blood microvessels induced by VEGF in the matrigel plug were also substantially suppressed by eupafolin. The results of HCC xenograft experiments demonstrated eupafolin remarkably inhibited tumor growth and tumor angiogenesis in vivo, suggesting the antitumor activity exerted by eupafolin was closely correlated with its potency on tumor angiogenesis. Mechanism investigations revealed that eupafolin significantly blocked VEGF-induced activation of VEGFR2 in HUVEC cells as well as its downstream signaling pathway. In addition to the effect on endothelial cells, through inhibiting Akt activity in tumor cells, VEGF secretion in HepG2 was dramatically decreased after eupafolin treatment. Our study was the first to report the activity of eupafolin against tumor angiogenesis as well as the underlying mechanism by which eupafolin to exert its anti-angiogenic activity.

The antibiotic resistance crisis, with a focus on the United States

Beginning with the discovery of penicillin by Alexander Fleming in the late 1920s, antibiotics have revolutionized the field of medicine. They have saved millions of lives each year, alleviated pain and suffering, and have even been used prophylactically for the prevention of infectious diseases. However, we have now reached a crisis where many antibiotics are no longer effective against even the simplest infections. Such infections often result in an increased number of hospitalizations, more treatment failures and the persistence of drug-resistant pathogens. Of particular concern are organisms such as methicillin-resistant Staphylococcus aureus, Clostridium difficile, multidrug and extensively drug-resistant Mycobacterium tuberculosis, Neisseria gonorrhoeae, carbapenem-resistant Enterobacteriaceae and bacteria that produce extended spectrum β-lactamases, such as Escherichia coli. To make matters worse, there has been a steady decline in the discovery of new and effective antibiotics for a number of reasons. These include increased costs, lack of adequate support from the government, poor returns on investment, regulatory hurdles and pharmaceutical companies that have simply abandoned the antibacterial arena. Instead, many have chosen to focus on developing drugs that will be used on a chronic basis, which will offer a greater profit and more return on investment. Therefore, there is now an urgent need to develop new and useful antibiotics to avoid returning to the 'pre-antibiotic era'. Some potential opportunities for antibiotic discovery include better economic incentives, genome mining, rational metabolic engineering, combinatorial biosynthesis and further exploration of the earth's biodiversity.

Phragmalin-type limonoids from the roots of Trichilia sinensis

Twelve new limonoids were isolated from Trichilia sinensis. Some compounds exhibited cytotoxicity and acetylcholinesterase-inhibiting activity.

Mimics of pramanicin derived from pyroglutamic acid and their antibacterial activity

Mono and dihydroxypyrrolidinones are readily available by direct oxygenation of a pyroglutamate-derived bicyclic lactam with high diastereoselectivity, and these may be manipulated further in protected or unprotected form by Grignard addition to a pendant Weinreb amide to give acylhydroxypyrrolidinones.

"Click" reaction mediated synthesis of costunolide and dehydrocostuslactone derivatives and evaluation of their cytotoxic activity

As part of pharmacological-phytochemical integrated studies on medicinal plants from Indian flora, costunolide (1) and dehydrocostus lactone (2), were isolated as major phytochemicals from Saussurea lappa, a plant traditionally used in different Asian systems of medicine. A series of 1,4-disubstituted-1,2,3-triazoles conjugates were synthesized through diastereo selective Michael addition followed by regioselective Huisgen 1,3-dipolar cycloaddition reactions. All these triazolyl derivatives (5a-5j) & (7a-7j) were well characterized using modern spectroscopic techniques and evaluated for their anticancer activity against a panel of five human cancerous celllines. The results indicated that all the analogs displayed moderate cytotoxic activity.

Stereoselective Synthesis of Alkylidene Phthalides

The N,O-diacylhydroxylamine derivative 4 has been prepared and its reactivity with nucleophiles investigated. On reaction with lithium enolates of cyclic or acyclic ketones, 4 is converted stereoselectively to the corresponding alkylidene phthalide. The stereochemical outcome of the transformation can be modified by changing the polarity of the reaction medium and the products isomerized under acidic conditions.

Verbesina encelioides: cytotoxicity, cell cycle arrest, and oxidative DNA damage in human liver cancer (HepG2) cell line

BACKGROUND

Cancer is a major health problem and exploiting natural products have been one of the most successful methods to combat this disease. Verbesina encelioides is a notorious weed with various pharmacological properties. The aim of the present investigation was to screen the anticancer potential of V. encelioides extract against human lung cancer (A-549), breast cancer (MCF-7), and liver cancer (HepG2) cell lines.

METHODS

A-549, MCF-7, and HepG2 cells were exposed to various concentrations of (10-1000 μg/ml) of V. encelioides for 24 h. Further, cytotoxic concentrations (250, 500, and 1000 μg/ml) of V. encelioides induced oxidative stress (GSH and LPO), reactive oxygen species (ROS) generation, mitochondrial membrane potential (MMP), cell cycle arrest, and DNA damage in HepG2 cells were studied.

RESULTS

The exposure of cells to 10-1000 μg/ml of extract for 24 h, revealed the concentrations 250-1000 μg/ml was cytotoxic against MCF-7 and HepG2 cells, but not against A-549 cells. Moreover, the extract showed higher decrease in the cell viability against HepG2 cells than MCF-7 cells. Therefore, HepG2 cells were selected for further studies viz. oxidative stress (GSH and LPO), reactive oxygen species (ROS) generation, mitochondrial membrane potential (MMP), cell cycle arrest, and DNA damage. The results revealed differential anticancer activity of V. encelioides against A-549, MCF-7 and HepG2 cells. A significant induction of oxidative stress, ROS generation, and MMP levels was observed in HepG2 cells. The cell cycle analysis and comet assay showed that V. encelioides significantly induced G2/M arrests and DNA damage.

CONCLUSION

These results indicate that V. encelioides possess substantial cytotoxic potential and may warrant further investigation to develop potential anticancer agent.

Characterization of Yuhushiella sp. TD-032 from the Thar Desert and its antimicrobial activity

During a screening program for antimicrobial compounds from underexplored habitats, a Gram-positive bacterium TD-032, was isolated from arid soil, Thar Desert (India), and analyzed for its morphological, physicochemical, and antimicrobial properties. The 16S ribosomal DNA (rDNA) sequence of the isolate was further studied for the novelty of γ-hyper variable region. TD-032 was grown in large-scale culture, and aqueous and organic solvent extracts analyzed for antimicrobial activity. Culture characteristics showed a lack of diffusible and melanoid pigments. The morphological features were pale yellow aerial mycelium colony color with brownish yellow substrate mycelium and leathery texture. The isolate could grow at 1% concentration of sodium chloride, temperature of 40°C, and a wide range of pH (7.0–12.0). An evaluation for extracellular enzymatic activities showed secretion of gelatinase(s), cellulase(s), and lipase(s). The γ-hyper variable region of 16S rDNA sequence of TD-032 showed 98.33% relatedness to Yuhushiella deserti, indicating a potential new species. Aqueous and ethyl acetate extracts showed antimicrobial activity against Gram-positive and Gram-negative bacteria inclusive clinical isolates. Inhibition of both test bacteria suggests that TD-032 produces a broad spectrum of antimicrobial substances.

In silico identification of anti-cancer compounds and plants from traditional Chinese medicine database

There is a constant demand to develop new, effective, and affordable anti-cancer drugs. The traditional Chinese medicine (TCM) is a valuable and alternative resource for identifying novel anti-cancer agents. In this study, we aim to identify the anti-cancer compounds and plants from the TCM database by using cheminformatics. We first predicted 5278 anti-cancer compounds from TCM database. The top 346 compounds were highly potent active in the 60 cell lines test. Similarity analysis revealed that 75% of the 5278 compounds are highly similar to the approved anti-cancer drugs. Based on the predicted anti-cancer compounds, we identified 57 anti-cancer plants by activity enrichment. The identified plants are widely distributed in 46 genera and 28 families, which broadens the scope of the anti-cancer drug screening. Finally, we constructed a network of predicted anti-cancer plants and approved drugs based on the above results. The network highlighted the supportive role of the predicted plant in the development of anti-cancer drug and suggested different molecular anti-cancer mechanisms of the plants. Our study suggests that the predicted compounds and plants from TCM database offer an attractive starting point and a broader scope to mine for potential anti-cancer agents.

Antimalarial activity of fractions of aqueous extract of Acacia nilotica root

BACKGROUND

The problem of resistance of malarial parasites to available antimalarial drugs makes the development of new drugs imperative, with natural plant products providing an alternative source for discovering new drugs.

AIM

To evaluate the antimalarial activity of eluted fractions of Acacia nilotica root extract and determine the phytochemicals responsible for its antimalarial activity.

MATERIALS AND METHODS

The extract was eluted successively in gradients of solvent mixture (hexane, ethyl acetate, and methanol) in multiples of 100 ml, and each fraction was collected separately. Eluates that showed similar thin layer chromatographic profiles and Rf values were combined to produce 4 main fractions (F-1, F-2, F-3, and F-4), which were tested separately for antimalarial activity using the curative test. Changes in body weight, temperature, and packed cell volume (PCV) were also recorded.

RESULTS

Fraction F-1 of A. nilotica at 50 and 100 mg/kg b/w produced significant and dose-dependent reduction in parasite count in Plasmodium berghei infected mice compared to the control, and also significantly increased the survival time of the mice compared to the control group. This fraction also ameliorated the malaria-induced anemia by improving PCV in treated mice.

CONCLUSION

Antimalarial activity of extract of A. nilotica root is probably localized in the F-1 fraction of the extract, which was found to be rich in alkaloids and phenolics. Further study will provide information on the chemical properties of the active metabolites in this fraction.

Synthesis and anticancer activity of novel fluorinated asiatic acid derivatives

A series of novel fluorinated Asiatic Acid (AA) derivatives were successfully synthesized, tested for their antiproliferative activity against HeLa and HT-29 cell lines, and their structure activity relationships were evaluated. The great majority of fluorinated derivatives showed stronger antiproliferative activity than AA in a concentration dependent manner. The most active compounds have a pentameric A-ring containing an α,β-unsaturated carbonyl group. The compounds with better cytotoxic activity were then evaluated against MCF-7, Jurkat, PC-3, A375, MIA PaCa-2 and BJ cell lines. Derivative 14 proved to be the most active compound among all tested derivatives and its mechanism of action was further investigated in HeLa cell line. The results showed that compound 14 induced cell cycle arrest in G0/G1 stage as a consequence of up-regulation of p21(cip1/waf1) and p27(kip1) and down-regulation of cyclin D3 and Cyclin E. Furthermore, compound 14 was found to induce caspase driven-apoptosis with activation of caspases-8 and caspase-3 and the cleavage of PARP. The cleavage of Bid into t-Bid, the up-regulation of Bax and the down-regulation of Bcl-2 were also observed after treatment of HeLa cells with compound 14. Taken together, these mechanistic studies revealed the involvement of extrinsic and intrinsic pathways in the apoptotic process induced by compound 14. Importantly, the antiproliferative activity of this compound on the non-tumor BJ human fibroblast cell line is weaker than in the tested cancer cell lines. The enhanced potency (between 45 and 90-fold more active than AA in a panel of cancer cell lines) and selectivity of this new AA derivative warrant further preclinical evaluation.

Resveratrol attenuates constitutive STAT3 and STAT5 activation through induction of PTPε and SHP-2 tyrosine phosphatases and potentiates sorafenib-induced apoptosis in renal cell carcinoma

BACKGROUND

Signal transducers and activators of transcription (STAT) proteins are critical transcription factor that are aberrantly activated in various types of malignancies, including renal cell carcinoma (RCC).

METHODS

We investigated the effect of resveratrol (RES), an edible polyphenol phytoalexin on STAT3 and STAT5 activation cascade in both Caki-1 and 786-O RCC cell lines.

RESULTS

We found that RES suppressed both constitutive STAT3 (tyrosine residue 705 and serine residue 727) and STAT5 (tyrosine residue 694 and 699) activation, which correlated with the suppression of the upstream kinases (JAK1, JAK2, and c-Src) in RCC. Also, RES abrogated DNA binding capacity and nuclear translocation of these two transcription factors. RES-induced an increased expression of PTPε and SHP-2 and the deletion of these two genes by small interfering RNA abolished the ability of RES to inhibit STAT3 activation, suggesting the critical role of both PTPε and SHP-2 in its possible mechanism of action. Moreover, RES induced S phase cell cycle arrest, caused induction of apoptosis, loss of mitochondrial membrane potential, and suppressed colony formation in RCC. We also found that RES downregulated the expression of STAT3/5-regulated antiapoptotic, proliferative, and metastatic gene products; and this correlated with induction of caspase-3 activation and anti-invasive activity. Beside, RES potentiated sorafenib induced inhibitory effect on constitutive STAT3 and STAT5 phosphorylation, apoptotic effects in 786-O cells, and this correlated with down-regulation of various oncogenic gene products.

CONCLUSION

Overall, our results suggest that RES is a blocker of both STAT3 and STAT5 activation and thus may exert potential growth inhibitory effects against RCC cells.

Genetic regulation and manipulation for natural product discovery

Natural products are an important source of modern medical development, e.g., antibiotics, anticancers, immune modulators, etc. and will continue to be a powerful driving force for the discovery of novel potential drugs. In the heterologous hosts, natural products are biosynthesized using dedicated metabolic networks. By gene engineering, pathway reconstructing, and enzyme engineering, metabolic networks can be modified to synthesize novel compounds containing enhanced structural feature or produce a large quantity of known valuable bioactive compounds. The review introduces some important technical platforms and relevant examples of genetic regulation and manipulation to improve natural product titers or drive novel secondary metabolite discoveries.

Naturally occurring proteinaceous nanoparticles in Coptidis Rhizoma extract act as concentration-dependent carriers that facilitate berberine absorption

Pharmacological activities of some natural products diminish and even disappear after purification. In this study, we explored the mechanisms underlying the decrease of acute oral toxicity of Coptidis Rhizoma extract after purification. The water solubility, in vitro absorption, and plasma exposure of berberine (the major active compound) in the Coptidis Rhizoma extract were much better than those of pure berberine. Scanning electron microscopy, laser scanning confocal microscopy (LSCM), and dynamic light scattering experiments confirmed that nanoparticles attached to very fine precipitates existed in the aqueous extract solution. The LSCM experiment showed that the precipitates were absorbed with the particles by the mouse intestine. High-speed centrifugation of the extract could not remove the nanoparticles and did not influence plasma exposure or acute oral toxicity. However, after extract dilution, the attached precipitates vanished, although the nanoparticles were preserved, and there were no differences in the acute oral toxicity and plasma exposure between the extract and pure berberine. The nanoparticles were then purified and identified as proteinaceous. Furthermore, they could absorb co-dissolved berberine. Our results indicate that naturally occurring proteinaceous nanoparticles in Coptidis Rhizoma extract act as concentration-dependent carriers that facilitate berberine absorption. These findings should inspire related studies in other natural products.

Investigations to the Antibacterial Mechanism of Action of Kendomycin

Purpose

The emergence of bacteria that are resistant to many currently used drugs emphasizes the need to discover and develop new antibiotics that are effective against such multi-resistant strains. Kendomycin is a novel polyketide that has a unique quinone methide ansa structure and various biological properties. This compound exhibits strong antibacterial activity against Gram-negative and Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). Despite the promise of kendomycinin in several therapeutic areas, its mode of action has yet to be identified.

Methods

In this study, we used a multidisciplinary approach to gain insight into the antibacterial mechanism of this compound.

Results

The antibacterial activity of kendomycin appears to be bacteriostatic rather than bactericidal. Kendomycin inhibited the growth of the MRSA strain COL at a low concentration (MIC of 5 μg/mL). Proteomic analysis and gene transcription profiling of kendomycin-treated cells indicated that this compound affected the regulation of numerous proteins and genes involved in central metabolic pathways, such as the tricarboxylic acid (TCA) cycle (SdhA) and gluconeogenesis (PckA and GapB), cell wall biosynthesis and cell division (FtsA, FtsZ, and MurAA), capsule production (Cap5A and Cap5C), bacterial programmed cell death (LrgA and CidA), the cellular stress response (ClpB, ClpC, ClpP, GroEL, DnaK, and GrpE), and oxidative stress (AhpC and KatA). Electron microscopy revealed that kendomycin strongly affected septum formation during cell division. Most kendomycin-treated cells displayed incomplete septa with abnormal morphology.

Conclusions

Kendomycin might directly or indirectly affect the cell division machinery, protein stability, and programmed cell death in S. aureus. Additional studies are still needed to obtain deeper insight into the mode of action of kendomycin.

Strategies for the Optimization of Natural Leads to Anticancer Drugs or Drug Candidates

Natural products have made significant contribution to cancer chemotherapy over the past decades and remain an indispensable source of molecular and mechanistic diversity for anticancer drug discovery. More often than not, natural products may serve as leads for further drug development rather than as effective anticancer drugs by themselves. Generally, optimization of natural leads into anticancer drugs or drug candidates should not only address drug efficacy, but also improve absorption, distribution, metabolism, excretion, and toxicity (ADMET) profiles and chemical accessibility associated with the natural leads. Optimization strategies involve direct chemical manipulation of functional groups, structure-activity relationship directed optimization and pharmacophore-oriented molecular design based on the natural templates. Both fundamental medicinal chemistry principles (e.g., bioisosterism) and state-of-the-art computer-aided drug design techniques (e.g., structure-based design) can be applied to facilitate optimization efforts. In this review, the strategies to optimize natural leads to anticancer drugs or drug candidates are illustrated with examples and described according to their purposes. Furthermore, successful case studies on lead optimization of bioactive compounds performed in the Natural Products Research Laboratories at UNC are highlighted.

Flavans with cytotoxic activity from the stem and root bark of Daphne giraldii

Thirteen new flavan compounds named daphnegiravans A–M (1–13) and eight known analogues (14–21) were isolated from the stem and root bark of Daphne giraldii. Further cytotoxicity investigation was conducted on 3 and 9–12.

Anti-inflammatory labdane-type diterpenoids from Physalis angulata

Twelve new labdane-type diterpenoid glycosides were isolated from the stems and leaves of P. angulata.

Strategies for the Discovery and Development of New Antibiotics from Natural Products: Three Case Studies

Natural products continue to be a predominant source for new anti-infective agents. Research at the Helmholtz Institute for Pharmaceutical Research Saarland (HIPS) and the Helmholtz Centre for Infection Research (HZI) is dedicated to the development of new lead structures against infectious diseases and, in particular, new antibiotics against hard-to-treat and multidrug-resistant bacterial pathogens. In this chapter, we introduce some of the concepts currently being employed in the field of antibiotic discovery. In particular, we will exemplarily illustrate three approaches: (1) Current sources for novel compounds are mainly soil-dwelling bacteria. In the course of our antimicrobial discovery program, a biodiverse collection of myxobacterial strains has been established and screened for antibiotic activities. Based on this effort, one successful example is presented in this chapter: Antibacterial cystobactamids were discovered and their molecular target, the DNA gyrase, was identified soon after the analysis of myxobacterial self-resistance making use of the information found in the respective biosynthesis gene cluster. (2) Besides our focus on novel natural products, we also apply strategies to further develop either neglected drugs or widely used antibiotics for which development of resistance in the clinical setting is an issue: Antimycobacterial griselimycins were first described in the 1960s but their development and use in tuberculosis therapy was not further pursued. We show how a griselimycin derivative with improved pharmacokinetic properties and enhanced potency against Mycobacterium tuberculosis revealed and validated a novel target for antibacterial therapy, the DNA sliding clamp. (3) In a third approach, biosynthetic engineering was used to modify and optimize natural products regarding their pharmaceutical properties and their production scale: The atypical tetracycline chelocardin is a natural product scaffold that was modified to yield a more potent derivative exhibiting activity against multidrug-resistant pathogens. This was achieved by genetic engineering of the producer strain and the resulting compound is now subject to further optimization by medicinal chemistry approaches.

Inhibition of perillyl alcohol on cell invasion and migration depends on the Notch signaling pathway in hepatoma cells

Cell metastasis, especially the process of invasion and migration, is considered as the main cause for the high mortality rate of hepatocellular carcinoma (HCC), which has become the sixth most common cancer worldwide and the third leading cause of cancer death. In this present study, we aimed to exploit the effects of perillyl alcohol on cell invasion and migration and the underlying molecular mechanisms in HCC. According to the transwell assays, cell invasiveness and migratory capacity were markedly higher in hepatoma cells (HepG2, SMMC-7721 and MHCC97H) than those in normal liver cells (HL-7702), and then significantly suppressed by perillyl alcohol treatment (P < 0.05). Meanwhile, the mRNA levels of Notch signaling pathway downstream target genes, HES1, HES5, and HEY1, were notably higher in hepatoma cells detected with real-time reverse transcription polymerase chain reaction (RT-PCR) (P < 0.05). After treated with perillyl alcohol, these mRNA levels were significantly decreased in hepatoma cells (P < 0.05). In addition, compared with the normal liver cells, the protein expression levels of Notch1 intracellular domain (N1ICD) and Snail were significantly increased, while E-cadherin protein expression was significantly decreased in hepatoma cells (P < 0.05). However, perillyl alcohol treatment significantly decreased N1ICD and Snail protein expressions and increased E-cadherin protein expression in hepatoma cells (P < 0.05). In conclusion, perillyl alcohol might play an important role in the process of hepatoma cell invasion and migration via decreasing the activity of Notch signaling pathway and increasing E-cadherin expression regulated by Snail.

An Efficient Synthesis of Bis-Purine Derivatives by a PPh3-catalysed Double Addition of Dialkylated Xanthine Derivatives to Alkyl Propiolates

Reaction between 5,7-dialkylated xanthine derivatives (2 equiv.) and an alkyl propiolate in the presence of catalytic amounts of triphenyl phosphine yields alkyl 2,3-bis(1,3-dialkyl-2,6-dioxo/oxothio-2,3-dihydro-1H-purin-7(6H)-yl)propanoates in excellent yield.

Hepatotoxicity and nephrotoxicity of gallotannin-enriched extract isolated from Galla Rhois in ICR mice

To evaluate the hepatotoxicity and nephrotoxicity of Galla Rhois (GR) toward the liver and kidney of ICR mice, alterations in related markers including body weight, organ weight, urine composition, liver pathology and kidney pathology were analyzed after oral administration of 250, 500 and 1,000 mg/kg body weight/day of gallotannin-enriched extract of GR (GEGR) for 14 days. GEGR contained 68.7±2.5% of gallotannin, 25.3±0.9% of gallic acid and 4.4±0.1% of methyl gallate. Also, the level of malondialdehyde (MDA), a marker of lipid peroxidation, was decreased with 19% in the serum of high dose GEGR (HGEGR)-treated mice. The body and organ weight, clinical phenotypes, urine parameters and mice mortality did not differ among GEGR-treated groups and the vehicle-treated group. Furthermore, no significant increase was observed in alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), blood urea nitrogen (BUN) and the serum creatinine (Cr) in the GEGR-treated group relative to the vehicle-treated group. Moreover, the specific pathological features induced by most toxic compounds such as CCl4 were not observed upon liver and kidney histological analysis. Overall, the results of the present study suggest that GEGR does not induce any specific toxicity in liver and kidney organs of ICR at doses of 1,000 mg/kg body weight/day, indicating that this is no observed adverse effect level (NOAEL).

Spirulina platensis Lacks Antitumor Effect against Solid Ehrlich Carcinoma in Female Mice

Spirulina is a blue-green alga used as a dietary supplement. It has been shown to possess anti-inflammatory, antioxidant, and hepatoprotective properties. This study was designed to evaluate the antitumor effect of spirulina (200 and 800 mg/kg) against a murine model of solid Ehrlich carcinoma compared to a standard chemotherapeutic drug, 5-fluorouracil (20 mg/kg). Untreated mice developed a palpable solid tumor after 13 days. Unlike fluorouracil, spirulina at the investigated two dose levels failed to exert any protective effect. In addition, spirulina did not potentiate the antitumor effect of fluorouracil when they were administered concurrently. Interestingly, their combined administration resulted in a dose-dependent increase in mortality. The present study demonstrates that spirulina lacks antitumor effect against this model of solid Ehrlich carcinoma and increased mortality when combined with fluorouracil. However, the implicated mechanism is still elusive.

Induction of Apoptosis and Reduction of Endogenous Glutathione Level by the Ethyl-Acetate Soluble Fraction of the Methanol Extract of the Roots of Potentilla fulgens in Cancer Cells

Potentilla fulgens root traditionally used as a folk remedy in Meghalaya, India. However, systematic evaluation of its anticancer efficacy was limited. We investigated the anticancer potentials of the various extracts prepared by partitioning of the methanol extract of the root with the aim to discover major contributing factors from the most effective fractions. Methanol extract of P. fulgens roots (PRE) was prepared by maceration which was subsequently fractionated into hexane, ethyl-acetate (EA) and n-butanol soluble fractions. Various assays (clonogenic assay, Flow cytometry analysis, western blot, semiquantitative RT-PCR and the level of endogenous glutathione) were used to evaluate different parameters, such as Cell survivability, PARP-1 proteolysis, expression pattern of anti-apoptotic and γ-glutamyl-cysteine synthetase heavy subunit (GCSC) genes in both MCF-7 and U87 cancer cell lines. Since the EA-fraction showed most efficient growth inhibitory effect, it was further purified and a total of nine compounds and some monomeric and dimeric flavan-3-ols were identified and characterized. Three compounds viz., epicatechin (EC), gallic acid (GA) and ursolic acid (UA) were taken on the basis of their higher yield and 10 μg/ml of each was mixed together. The concentration used in this study for PRE, EA- and Hex-fraction was 100 μg/ml, which was higher than the IC₅₀ value. Apoptotic cell death in the PRE, EA-fraction and EC+GA+UA treated cancer cell cultures was significantly greater than in normal cells due to suppression of anti-apoptotic protein Bcl2 following treatment. Depletion of glutathione by downregulating GCSC was also observed. Induction of apoptosis and lowering the level of glutathione are considered to be positive activity for an anticancer agent. Therefore, modulation of GSH concentration in tumor cells by PRE and its EA-fraction opened up the possibility of a new therapeutic approach because these plant products are not harmful to normal cells and may regulate the tumor cellular response to different anticancer treatments. Thus, it would be interesting to examine efficacy of these plant products or EA-fraction in human cancer treatment.

CDK4 inhibitors an emerging strategy for the treatment of melanoma

Research into the cyclin-dependent kinases and their inhibitors is finally coming into the forefront of clinical research in cancer. Targeted therapies such as BRAF inhibitors have led the way in improving treatment outcomes in advanced melanoma. Based on detailed genomic knowledge of melanoma it is now time to extend targeted therapies beyond BRAF to fulfill the vision of precision medicine. The p16^INK4A-cyclin D-CDK4/6-retinoblastoma protein pathway (RB pathway) is dysregulated in more than 90% of melanomas and interacts biochemically and genetically with the RAS/RAF/MEK/ERK pathway. Recognizing and understanding these processes that drive melanomagenesis is essential to rationally develop new therapies. This paper reviews the mechanisms, background and progress of small molecule CDK4 inhibitors in the management of melanoma.

Naphthopyranones--isolation, bioactivity, biosynthesis and synthesis

The 1H-naphtho[2,3-c]pyran-1-one (naphthopyranone) moiety forms the structural framework of a group of secondary metabolites that have been isolated from a range of organisms including fungi, bacteria, lichen and plants. This review documents the known naturally occurring naphthopyranones - their isolation, biosynthesis and biological activity. A survey of methods reported for the synthesis of naphthopyranone natural products is presented.

A Metabolomic Approach to Target Compounds from the Asteraceae Family for Dual COX and LOX Inhibition

The application of metabolomics in phytochemical analysis is an innovative strategy for targeting active compounds from a complex plant extract. Species of the Asteraceae family are well-known to exhibit potent anti-inflammatory (AI) activity. Dual inhibition of the enzymes COX-1 and 5-LOX is essential for the treatment of several inflammatory diseases, but there is not much investigation reported in the literature for natural products. In this study, 57 leaf extracts (EtOH-H₂O 7:3, v/v) from different genera and species of the Asteraceae family were tested against COX-1 and 5-LOX while HPLC-ESI-HRMS analysis of the extracts indicated high diversity in their chemical compositions. Using O2PLS-DA (R² > 0.92; VIP > 1 and positive Y-correlation values), dual inhibition potential of low-abundance metabolites was determined. The O2PLS-DA results exhibited good validation values (cross-validation = Q² > 0.7 and external validation = P² > 0.6) with 0% of false positive predictions. The metabolomic approach determined biomarkers for the required biological activity and detected active compounds in the extracts displaying unique mechanisms of action. In addition, the PCA data also gave insights on the chemotaxonomy of the family Asteraceae across its diverse range of genera and tribes.