Probing sponge-derived terpenoids for human 15-lipoxygenase inhibitors

Structurally Diverse Diterpenoids from the Sanya Bay Nudibranch Hexabranchus sanguineus and Its Sponge-Prey Chelonaplysilla sp

Investigation of the South China Sea nudibranch Hexabranchus sanguineus from Sanya Bay afforded, in addition to three known compounds, nine new diterpenoids of the 5,19-cycloclerodane- (sanyanolides A-D), clerodane- (sanyanolide E) and subersin- (sanyanolides F-I) type. Remarkably, six diterpenoids aforementioned from H. sanguineus were also isolated from the sponge Chelonaplysilla sp. from the same water region, suggesting a trophic relationship between H. sanguineus and Chelonaplysilla sp. The structure and absolute configuration of new compounds were established by a combination of spectroscopic data, X-ray diffraction analysis and/or time-dependent density functional theory/electronic circular dichroism calculations. A plausible biogenetic relationship between these diterpenoids, along with the chemo-ecological implications of their co-occurrence in the two organisms investigated, was proposed and discussed. In in vitro bioassays, echinoclerodane A exhibited a potent inhibitory effect (IC₅₀ =2.81 μM) on LPS-induced inflammatory response in RAW 264.7 macrophage cells. In addition, echinoclerodane A and oculatolide showed considerable antibacterial activities with MIC values ranging from 1.0 to 8.0 μg/mL.

Reevaluation of a Bicyclic Pyrazoline as a Selective 15-Lipoxygenase V-Type Activator Possessing Fatty Acid Specificity

Regulation of lipoxygenase (LOX) activity is of great interest due to the involvement of the various LOX isoforms in the inflammatory process and hence many diseases. The bulk of investigations have centered around the discovery and design of inhibitors. However, the emerging understanding of the role of h15-LOX-1 in the resolution of inflammation provides a rationale for the development of activators as well. Bicyclic pyrazolines are known bioactive molecules that have been shown to display antibiotic and anti-inflammatory activities. In the current work, we reevaluated a previously discovered bicyclic pyrazoline h15-LOX-1 activator, PKUMDL_MH_1001 (written as 1 for this publication), and determined that it is inactive against other human LOX isozymes, h5-LOX, h12-LOX, and h15-LOX-2. Analytical characterization of 1 obtained in the final synthesis step identified it as a mixture of cis- and trans-diastereomers: cis-1 (12%) and trans-1 (88%); and kinetic analysis indicated similar potency between the two. Using compound 1 as the cis-trans mixture, h15-LOX-1 catalysis with arachidonic acid (AA) (AC50 = 7.8 +/- 1 μM, A max = 240%) and linoleic acid (AC50 = 5.3 +/- 0.7 μM, A max = 98%) was activated, but not with docosahexaenoic acid (DHA) or mono-oxylipins. Steady-state kinetics demonstrate V-type activation for 1, with a β value of 2.2 +/- 0.4 and an K x of 16 +/- 1 μM. Finally, it is demonstrated that the mechanism of activation for 1 is likely not due to decreasing substrate inhibition, as was postulated previously. 1 also did not affect the activity of the h15-LOX-1 selective inhibitor, ML351, nor did 1 affect the activity of allosteric effectors, such as 12S-hydroxy-5Z,8Z,10E,14Z-eicosatetraenoic acid (12S-HETE) and 14S-hydroperoxy-4Z,7Z,10Z,12E,16Z,19Z-docosahexaenoic acid (14S-HpDHA). These data confirm that 1 binds to a distinct activation binding site, as previously postulated. Future work should be aimed at the development of selective activators that are capable of activating h15-LOX-1 catalysis with DHA, thus enhancing the production of DHA-derived pro-resolution biomolecules.

Total Synthesis and Structure Revision of Halioxepine

The first total synthesis of halioxepine is accomplished using a 1,4-addition for constructing the quaternary center at C10 and a halo etherification for the generation of the tertiary ether at C7. The correct structure of halioxepine was determined by assembling different enantiomeric building blocks and by changing the relative configuration between C10 and C15.

Chemical Diversity and Biological Activities of Marine Sponges of the Genus Suberea: A Systematic Review

Marine natural products (MNPs) continue to be in the spotlight in the global drug discovery endeavor. Currently, more than 30,000 structurally diverse secondary metabolites from marine sources have been isolated, making MNPs a profound, renewable source to investigate novel drug compounds. Marine sponges of the genus Suberea (family: Aplysinellidae) are recognized as producers of bromotyrosine derivatives, which are considered distinct chemotaxonomic markers for the marine sponges belonging to the order Verongida. This class of compounds exhibits structural diversity, ranging from simple monomeric molecules to more complex molecular scaffolds, displaying a myriad of biological and pharmacological potentialities. In this review, a comprehensive literature survey covering the period of 1998⁻2018, focusing on the chemistry and biological/pharmacological activities of marine natural products from marine sponges of the genus Suberea, with special attention to the biogenesis of the different skeletons of halogenated compounds, is presented.

New antibacterial and 5-lipoxygenase activities of synthetic benzyl phenyl ketones: Biological and docking studies

We investigated twelve benzyl phenyl ketone derivatives which are synthetic precursors of isoflavonoids that are shown be good 5-hLOX inhibitors, especially those that have the catechol group, but these precursors never have been assayed as 5-hLOX inhibitors being a novelty as inhibitors of the enzyme, due to sharing important structural characteristics. Screening assays, half maximal inhibitory concentration (IC₅₀) and kinetic assays of all the studied molecules (5 µg/ml in media assay) showed that 1-(2,4-dihydroxy-3-methylphenyl)-2-(3-chlorophenyl)-ethanone (K205; IC₅₀ = 3.5 µM; K_i = 4.8 µM) and 1-(2,4-dihydroxy-3-methylphenyl)-2-(2-nitrophenyl)-ethanone (K206; IC₅₀ = 2.3 µM; K_i = 0.7 µM) were potent, selective, competitive and nonredox inhibitors of 5-hLOX. Antioxidant behavior was also assayed by DPPH, FRAP, and assessing ROS production, and those with antibacterial and antiproliferative properties relating to 1-(2,4-dihydroxy-3-methylphenyl)-2-(2-chlorophenyl)-ethanone (K208) established it as the most interesting and relevant compound studied, as it showed nearly 100% inhibition of bacterial growth of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Finally, docking studies were done that helped to characterize how the inhibitor structures correlated to decreased 5-hLOX activity.

Isolation and identification of chitin from heavy mineralized skeleton of Suberea clavata (Verongida: Demospongiae: Porifera) marine demosponge

Since the discovery of chitin in skeletal structures of sponges (Porifera) in 2007, studies on search of novel species which possess this structural aminopolysaccharide continue up today. The most potential source of chitin is suggested to be localized in the four families of sponges related to the order Verongida (Demospongiae) which nevertheless require further clarification. Here, we report for the first time the isolation and identification of α-chitin from the Suberea clavata demosponge (Aplysinidae: Verongida). Raman spectroscopy, Calcofluor White staining, chitinase test and ESI-MS techniques were used to identify chitin. We suggest that the presence of chitin within fibrous skeletons of diverse species of Verongida order, and, especially in all species of the Aplysinidae family, may be useful for the identification of novel, previously unidentified marine demosponges.

Marine Sponges as a Drug Treasure

Marine sponges have been considered as a drug treasure house with respect to great potential regarding their secondary metabolites. Most of the studies have been conducted on sponge's derived compounds to examine its pharmacological properties. Such compounds proved to have antibacterial, antiviral, antifungal, antimalarial, antitumor, immunosuppressive, and cardiovascular activity. Although, the mode of action of many compounds by which they interfere with human pathogenesis have not been clear till now, in this review not only the capability of the medicinal substances have been examined in vitro and in vivo against serious pathogenic microbes but, the mode of actions of medicinal compounds were explained with diagrammatic illustrations. This knowledge is one of the basic components to be known especially for transforming medicinal molecules to medicines. Sponges produce a different kind of chemical substances with numerous carbon skeletons, which have been found to be the main component interfering with human pathogenesis at different sites. The fact that different diseases have the capability to fight at different sites inside the body can increase the chances to produce targeted medicines.

Bioactive secondary metabolites from the Red Sea marine Verongid sponge Suberea species

In a continuation of our efforts to identify bioactive compounds from Red Sea Verongid sponges, the organic extract of the sponge Suberea species afforded seven compounds including two new dibrominated alkaloids, subereamollines C and D (1 and 2), together with the known compounds aerothionin (3), homoaerothionin (4), aeroplysinin-1 (5), aeroplysinin-2 (6) and a revised subereaphenol C (7) as ethyl 2-(2,4-dibromo-3,6-dihydroxyphenyl)acetate. The structures of the isolated compounds were assigned by different spectral data including optical rotations, 1D (1H and 13C) and 2D (COSY, multiplicity-edited HSQC, and HMBC) NMR and high-resolution mass spectroscopy. Aerothionin (3) and subereaphenol C (7) displayed potent cytotoxic activity against HeLa cell line with IC50 values of 29 and 13.3 µM, respectively. In addition, aeroplysinin-2 (6) showed potent antimigratory activity against the human breast cancer cell line MDA-MB-231 with IC50 of 18 µM. Subereamollines C and D are new congeners of the previously reported compounds subereamollines A and B with methyl ester functionalities on the side chain. These findings provide further insight into the biosynthetic capabilities of members of the genus Suberea and the chemical diversity as well as the biological activity of these compounds.

Unusual cyclic terpenoids with terminal pendant prenyl moieties: from occurrence to synthesis

The paper reviews the known examples of cyclic terpenoids produced from open chain polyenic precursors by an "unusual" biosynthetic pathway, involving selective electrophilic attack on an internal double bond followed by cyclization. The resulting compounds possess cyclic backbones with pendant terminal prenyl groups. Synthetic approaches applied for the synthesis of such specifically functionalized compounds are also discussed, as well as biological activity of reported representatives.

Synthesis of the putative structure of 15-oxopuupehenoic acid

Synthesis of the putative structure of the marine natural 15-oxopuupehenoic acid has been achieved starting from commercial (-)-sclareol. Key steps of the synthetic sequence are the Robinson annulation of a β-ketoester and methyl vinyl ketone and an unprecedented cyclization of the resulting α,β-enone, which is mediated by tin(IV) chloride in the presence of N-phenylselenophthalimide. The physical properties of the synthetic compound are somewhat different from those reported for the natural product.

Potent and selective inhibitors of human reticulocyte 12/15-lipoxygenase as anti-stroke therapies

A key challenge facing drug discovery today is variability of the drug target between species, such as with 12/15-lipoxygenase (12/15-LOX), which contributes to ischemic brain injury, but its human and rodent isozymes have different inhibitor specificities. In the current work, we have utilized a quantitative high-throughput (qHTS) screen to identify compound 1 (ML351), a novel chemotype for 12/15-LOX inhibition that has nanomolar potency (IC₅₀ = 200 nM) against human 12/15-LOX and is protective against oxidative glutamate toxicity in mouse neuronal HT22 cells. In addition, it exhibited greater than 250-fold selectivity versus related LOX isozymes, was a mixed inhibitor, and did not reduce the active-site ferric ion. Lastly, 1 significantly reduced infarct size following permanent focal ischemia in a mouse model of ischemic stroke. As such, this represents the first report of a selective inhibitor of human 12/15-LOX with demonstrated in vivo activity in proof-of-concept mouse models of stroke.

Meroterpenes from marine invertebrates: structures, occurrence, and ecological implications

Meroterpenes are widely distributed among marine organisms; they are particularly abundant within brown algae, but other important sources include microorganisms and invertebrates. In the present review the structures and bioactivities of meroterpenes from marine invertebrates, mainly sponges and tunicates, are summarized. More than 300 molecules, often complex and with unique skeletons originating from intra- and inter-molecular cyclizations, and/or rearrangements, are illustrated. The reported syntheses are mentioned. The issue of a potential microbial link to their biosynthesis is also shortly outlined.

Subereamolline A as a potent breast cancer migration, invasion and proliferation inhibitor and bioactive dibrominated alkaloids from the Red Sea sponge Pseudoceratina arabica

A new collection of several Red Sea sponges was investigated for the discovery of potential breast cancer migration inhibitors. Extracts of the Verongid sponges Pseudoceratina arabica and Suberea mollis were selected. Bioassay-directed fractionation of both sponges, using the wound-healing assay, resulted into the isolation of several new and known brominated alkaloids. Active fractions of the sponge Pseudoceratina arabica afforded five new alkaloids, ceratinines A-E (2-6), together with the known alkaloids moloka'iamine (1), hydroxymoloka'iamine (7) and moloka'iakitamide (8). The active fraction of the sponge Suberea mollis afforded the three known alkaloids subereamolline A (9), aerothionin (10) and homoaerothionin (11). Ceratinine B (3) possesses an unprecedented 5,7-dibrominated dihydroindole moiety with an epoxy ring on the side chain of a fully substituted aromatic moiety. Ceratinines D (5) and E (6) possess a terminal formamide moiety at the ethylamine side chain. Subereamolline A (9) potently inhibited the migration and invasion of the highly metastatic human breast cancer cells MDA-MB-231 at the nanomolar doses. Subereamolline A and related brominated alkaloids are novel scaffolds appropriate for further future use for the control of metastatic breast cancer.

Halicloic acids A and B isolated from the marine sponge Haliclona sp. collected in the Philippines inhibit indoleamine 2,3-dioxygenase

Two new merohexaprenoids, halicloic acids A (1) and B (2), have been isolated from the marine sponge Haliclona (Halichoclona) sp. collected in the Philippines. The glycolic acids 1 and 2 slowly decomposed during acquisition of NMR data to aldehydes 3 and 4, respectively, via an oxidative decarboxylation. Halicloic acid B (2) has the new rearranged "haliclane" meroterpenoid carbon skeleton. The halicloic acids 1 and 2 are indoleamine 2,3-dioxygenase inhibitors that are significantly more active than the decomposition products 3 and 4.

A fluorimetric assay for human reticulocyte 15-lipoxygenase-1 activity

A rapid and sensitive fluorescence-based assay for the determination of human 15-lipoxygenase-1 (15-LOX-1) activity is described in this article. The assay utilizes the ability of 15-LOX-1-generated lipid hydroperoxides to oxidize nonfluorescent dihydrorhodamine 123, producing the highly fluorescent dye rhodamine 123. Formation of rhodamine 123 can be monitored through fluorescence spectroscopy using Ex/Em of 500 nm/536 nm. The IC(50) values of three well-known 15-LOX-1 inhibitors, nordihydroguaiaretic acid, quercetin, and fisetin, were evaluated in 96- and 384-well formats, and they conform to previously reported data. We believe this assay can be broadly used for the discovery of novel lipoxygenase inhibitors.

Bioactive compounds from marine sponges and their symbiotic microbes: a potential source of nutraceuticals

Sponges are considered as the chemical factory in marine environment because of its immense production of chemically diverse compounds. Other than the chemical diversity, these compounds possess remarkable bioactivities. This great potential has aroused applications of sponge-derived compounds as therapeutics and at present, a number of promising compounds are in clinical and preclinical trials. Recently, nutraceuticals have received considerable interest among the health conscious community because of its multiple therapeutic effects. Natural health-promoting substances gain continuous popularity as nutraceuticals due to its reduced risk of side effects. This overview discusses the potentials of marine sponge-derived bioactivities as natural health-promoting compounds.

Discovery of potent and selective inhibitors of human platelet-type 12- lipoxygenase

We report the discovery of novel small molecule inhibitors of platelet-type 12-human lipoxygenase, which display nanomolar activity against the purified enzyme, using a quantitative high-throughput screen (qHTS) on a library of 153607 compounds. These compounds also exhibit excellent specificity, >50-fold selectivity vs the paralogues, 5-human lipoxygenase, reticulocyte 15-human lipoxygenase type-1, and epithelial 15-human lipoxygenase type-2, and >100-fold selectivity vs ovine cyclooxygenase-1 and human cyclooxygenase-2. Kinetic experiments indicate this chemotype is a noncompetitive inhibitor that does not reduce the active site iron. Moreover, chiral HPLC separation of two of the racemic lead molecules revealed a strong preference for the (-)-enantiomers (IC(50) of 0.43 ± 0.04 and 0.38 ± 0.05 μM) compared to the (+)-enantiomers (IC(50) of >25 μM for both), indicating a fine degree of selectivity in the active site due to chiral geometry. In addition, these compounds demonstrate efficacy in cellular models, which underscores their relevance to disease modification.

Brominated arginine-derived alkaloids from the red sea sponge Suberea mollis

Investigation of a new collection of the Red Sea sponge Suberea mollis afforded two new brominated arginine-derived alkaloids, subereamines A (1) and B (2), a new brominated phenolic compound, subereaphenol D (3), and the known compounds dichloroverongiaquinol (4), aerothionin (5), and purealdin L (6). The structures of the isolated compounds were assigned using one- and two-dimensional NMR spectra and HRFABMS data. The absolute configurations of subereamines A (1) and B (2) were determined by acid hydrolysis followed by chiral-phase LC-MS. The antimicrobial and antioxidant activities of the isolated compounds have been evaluated. Dichloroverongiaquinol and subereaphenol D displayed significant antimicrobial activity. Using the DPPH TLC autographic rapid screen for free radical scavenging effects, subereaphenol D displayed a significant antioxidant effect. In addition, the cytotoxic activities of the isolated compounds were investigated.

Rhabdastrellic acid-A induced autophagy-associated cell death through blocking Akt pathway in human cancer cells

Background

Autophagy is an evolutionarily conserved protein degradation pathway. A defect in autophagy may contribute to tumorigenesis. Autophagy inducers could have a potential function in tumor prevention and treatment.

Methodology/Principal Findings

Our results showed that Rhabdastrellic acid-A, an isomalabaricane triterpenoid isolated from the sponge Rhabdastrella globostellata, inhibited proliferation of human cancer cell lines Hep3B and A549 and induced caspase-independent cell death in both the cell lines. Further investigation showed that Rhabdastrellic acid-A induced autophagy of cancer cells determined by YFP-LC3 punctation and increased LC3-II. The pretreatment with autophagy inhibitor 3-MA inhibited Rhabdastrellic acid-A-induced cell death. Knockdown of autophagy-related gene Atg5 inhibited Rhabdastrellic acid-A-induced cell death in A549 cells. Also, phospho-Akt and its downstream targets significantly decreased after treatment with Rhabdastrellic acid-A in both cancer cell lines. Transfection of constitutive active Akt plasmid abrogated autophagy and cell death induced by Rhabdastrellic acid-A.

Conclusions/Significance

These results suggest that Rhabdastrellic acid-A could induce autophagy-associated cell death through blocking Akt pathway in cancer cells. It also provides the evidence that Rhabdastrellic acid-A deserves further investigation as a potential anticancer or cancer preventive agent.

Development of a fluorescent intensity assay amenable for high-throughput screening for determining 15-lipoxygenase activity

15-Lipoxygenase-1 catalyzes the introduction of molecular oxygen into polyunsaturated fatty acids to form a lipid hydroperoxide. The authors have developed an assay for the detection of lipid hydroperoxides formed by human 15-lipoxygenase (15-LO) in enzyme or cellular assays using either a 96-well or a 384-well format. The assays described take advantage of the ability of lipid hydroperoxides to oxidize nonfluorescent diphenyl-1-pyrenylphosphine (DPPP) to a fluorescent phosphine oxide. Oxidation of DPPP yields a fluorescent compound, which is not sensitive to temperature and is stable for more than 2 h. The assay is sensitive toward inhibition and robust with a Z' value of 0.79 and 0.4 in a 96- and 384-well format, respectively, and thus amenable for high-throughput screening. The utility of DPPP as a marker for 15-lipoxygenase activity was demonstrated with both enzyme- and cell-based assays for the identification of hits and to determine potency by IC(50) determinations.

A cell-based assay for screening lipoxygenase inhibitors

Lipoxygenases (LOX) form a family of lipid peroxidizing enzymes within the plant and animal kingdoms. In humans, six functional lipoxygenase isoforms have been identified. 5-LOX, "platelet-type" 12-LOX (p12-LOX) and 15-LOX type 1 (15-LOX1), originally identified in leukocytes, platelets, and reticulocytes, respectively, generate lipid mediators involved in host cellular functions and in the pathophysiology of asthma, cardiovascular diseases, and cancer. The pharmaceutical industry has reinvigorated their programs to develop novel LOX inhibitors in view of recent findings. However, high throughput LOX screening assays to test novel agents against these intracellular enzymes are limited. We describe a cell-based 96-well microplate fluorescence assay tested against several existing LOX inhibitors, and validate the assay by comparing known IC(50) values and HPLC analysis, which may provide a useful screen for novel LOX inhibitors.

Marine natural products

This review covers the literature published in 2007 for marine natural products, with 948 citations(627 for the period January to December 2007) referring to compounds isolated from marine microorganisms and phytoplankton, green algae, brown algae, red algae, sponges, cnidarians,bryozoans, molluscs, tunicates, echinoderms and true mangrove plants. The emphasis is on new compounds (961 for 2007), together with the relevant biological activities, source organisms and country of origin. Biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.1 Introduction, 2 Reviews, 3 Marine microorganisms and phytoplankton, 4 Green algae, 5 Brown algae, 6 Red algae, 7 Sponges, 8 Cnidarians, 9 Bryozoans, 10 Molluscs, 11 Tunicates (ascidians),12 Echinoderms, 13 Miscellaneous, 14 Conclusion, 15 References.

Bioactive brominated metabolites from the red sea sponge Suberea mollis

Reinvestigation of the Red Sea sponge Suberea mollis afforded two new bromotyrosine-derived alkaloids, subereamollines A (1) and B (2), two new brominated phenolic compounds, subereaphenols B (7) and C (9), and the known compounds aerothionin (3), homoaerothionin (4), 11,19-dideoxyfistularin-3 (5), aeroplysinin-1 (6), and aeroplysinin-2 (8). The structure determination of the isolated compounds was assigned using one- and two-dimensional NMR spectra and HRFABMS data. The antimicrobial and antioxidant activities of the isolated compounds have been evaluated. Aeroplysinin-1 displayed significant antimicrobial activity against S. aureus, P. aerugenosa, and K. pneumoniae. The isolated compounds were examined for their antioxidant activity using a 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) solution-based chemical assay. Among the tested compounds, only subereaphenols B and C displayed a significant effect.

Subereaphenol A, a new Cytotoxic and Antimicrobial Dibrominated Phenol from the Red Sea Sponge Suberea Mollis

An investigation of the sponge Suberea mollis collected at the Egyptian Red Sea coast afforded a new cytotoxic and antimicrobial dibrominated phenol, subereaphenol A (1), together with the previously reported compounds 2-(3′,5′-dibromo-2′-hydroxy-4′-methoxyphenyl)acetamide (2), dibromoverongiaquinol (3), bromochloroverongiaquinol (4), and 2-(3′,5′-dibromo-4′-ethoxy-1′-hydroxy-4′-methoxy-2′,5′-cyclohexadien-1-yl)acetamide (5). The structure of the compounds was determined by a combination of 1D and 2D NMR techniques and High-resolution mass spectral determinations. Complete and new NMR data for the known compounds has been reported. The cytotoxic and the antimicrobial activities of the compounds are reported.

Rhabdastrellic acid-A inhibited PI3K/Akt pathway and induced apoptosis in human leukemia HL-60 cells

Increasing evidence suggests that aberrant activation of PI3K/Akt is involved in many human cancers, and that inhibition of the PI3K/Akt pathway might be a promising strategy for cancer treatment. Our investigation indicates that Rhabdastrellic acid-A, an isomalabaricane triterpenoid isolated from the sponge, Rhabdastrella globostellata, inhibits proliferation of HL-60 cells with an IC(50) value of 0.68mug/ml, and induces apoptosis. Rhabdastrellic acid-A also induces cleavage of the death substrate poly (ADP-ribose) polymerase (PARP) and caspase-3. Pretreatment of HL-60 cells with the caspase-3 specific inhibitor, DEVD-CHO, prevents Rhabdastrellic acid-A-induced DNA fragmentation and PARP cleavage. Activated PI3K and Akt significantly decreases after treatment with Rhabdastrellic acid-A in HL-60 cells. Expression levels of protein bcl-2, bax remain unchanged in response to Rhabdastrellic acid-A treatment in HL-60 cells. These results suggest that Rhabdastrellic acid-A inhibits PI3K/Akt pathway and induces caspase-3 dependent-apoptosis in HL-60 human leukemia cells.

Structure-activity relationship studies of flavonoids as potent inhibitors of human platelet 12-hLO, reticulocyte 15-hLO-1, and prostate epithelial 15-hLO-2

Human lipoxygenase (hLO) isozymes have been implicated in a number of disease states and have attracted much attention with respect to their inhibition. One class of inhibitors, the flavonoids, have been shown to be potent lipoxygenase inhibitors but their study has been restricted to those compounds found in nature, which have limited structural variability. We have therefore carried out a comprehensive study to determine the structural requirements for flavonoid potency and selectivity against platelet 12-hLO, reticulocyte 15-hLO-1, and prostate epithelial 15-hLO-2. We conclude from this study that catechols are essential for high potency, that isoflavones and isoflavonones tend to select against 12-hLO, that isoflavons tend to select against 15-hLO-1, but few flavonoids target 15-hLO-2.

Discovery of platelet-type 12-human lipoxygenase selective inhibitors by high-throughput screening of structurally diverse libraries

Human lipoxygenases (hLO) have been implicated in a variety of diseases and cancers and each hLO isozyme appears to have distinct roles in cellular biology. This fact emphasizes the need for discovering selective hLO inhibitors for both understanding the role of specific lipoxygenases in the cell and developing pharmaceutical therapeutics. To this end, we have modified a known lipoxygenase assay for high-throughput (HTP) screening of both the National Cancer Institute (NCI) and the UC Santa Cruz marine extract library (UCSC-MEL) in search of platelet-type 12-hLO (12-hLO) selective inhibitors. The HTP screen led to the characterization of five novel 12-hLO inhibitors from the NCI repository. One is the potent but non-selective michellamine B, a natural product, anti-viral agent. The other four compounds were selective inhibitors against 12-hLO, with three being synthetic compounds and one being alpha-mangostin, a natural product, caspase-3 pathway inhibitor. In addition, a selective inhibitor was isolated from the UCSC-MEL (neodysidenin), which has a unique chemical scaffold for a hLO inhibitor. Due to the unique structure of neodysidenin, steady-state inhibition kinetics were performed and its mode of inhibition against 12-hLO was determined to be competitive (K(i)=17microM) and selective over reticulocyte 15-hLO-1 (K(i) 15-hLO-1/12-hLO>30).

Extending the record of meroditerpenes from Cacospongia marine sponges

A new meroditerpene, (+)-isojaspic acid (1), along with two known meroditerpenes, cacospongin D (2) and jaspaquinol (3), have been isolated from a marine sponge Cacospongia. Comprehensive taxonomic identification distinguished this Cacospongia apart from morphologically similar Psammocinia. The absolute stereochemistry of 1 was elucidated on the basis of extensive 1D and 2D NMR techniques and analysis of the optical rotation versus (+)-zonarol (8), (+)-isozonarol (9), (-)-dactylosponol (10), and (+)-hyatellaquinone (11). Furthermore, bioactivity evaluation showed that the meroditerpenes isolated significantly inhibited Staphylococcus epidermidis.

Oculatol, oculatolide, and A-nor sterols from the sponge Haliclona oculata

Chemical investigation of the marine sponge Haliclona oculata resulted in the isolation of eight new compounds including oculatol (1) and oculatolide (2) and six unusual A-nor steroids, 2-ethoxycarbonyl-2beta-hydroxy-A-nor-ergosta-5,24(28)-dien-4-one (3), 2-ethoxycarbonyl-24-ethyl-2beta-hydroxy-A-nor-cholesta-5-en-4-one (4), 2-ethoxycarbonyl-2beta,7beta-dihydroxy-A-nor-ergosta-5,24(28)-dien-4-one (5), 2-ethoxycarbonyl-2beta,7beta-dihydroxy-A-nor-cholesta-5-en-4-one (6), 2-ethoxycarbonyl-2beta,7beta-dihydroxy-24-methyl-A-nor-cholesta-5,22(E)-dien-4-one (7), and 2-ethoxycarbonyl-2beta,7beta-dihydroxy-A-nor-cholesta-5,22(E)-dien-4-one (8), along with 16 known steroids and indole derivatives. Their structures were unambiguously determined on the basis of extensive spectroscopic analyses.

Hemisynthesis of new labdane derivatives from (−)-sclareol

A straightforward and very simple access to different analogues of (+)-subersic acid 7, the unnatural enantiomer (compounds 12) from naturally occurring (-)-sclareol 1 is described. We also report new conditions for the preparation of keto-intermediate 8 using maleic acid and describe hemiketal 11 as the new intermediate of degradative oxidation of 1.

Novel human lipoxygenase inhibitors discovered using virtual screening with homology models

We report the discovery of new, low micromolar, small molecule inhibitors of human platelet-type 12- and reticulocyte 15-lipoxygenase-1 (12-hLO and 15-hLO) using structure-based methods. Specifically, we created homology models of 12-hLO and 15-hLO, based on the structure of rabbit 15-lipoxygenase, for in silico screening of a large compound library followed by in vitro screening of 20 top scoring molecules. Eight of these compounds inhibited either 12- or 15-human lipoxygenase with lower than 100 microM affinity. Of these, we obtained IC50 values for the three best inhibitors, all of which displayed low micromolar inhibition. One compound showed specificity for 15-hLO versus 12-hLO; however, a selective inhibitor for 12-hLO was not identified. As a control we screened 20 randomly selected compounds, of which none showed low micromolar inhibition. The new low-micromolar inhibitors appear to be suitable as leads for further inhibitor development efforts against 12-hLO and 15-hLO, based on the fact their size and chemical properties are appropriate to classify them as drug-like compounds. The models of these protein-inhibitor complexes suggest strategies for future development of selective lipoxygenase inhibitors.

Baicalein is a potent in vitro inhibitor against both reticulocyte 15-human and platelet 12-human lipoxygenases

Lipoxygenases (LO) have been implicated in asthma, immune disorders, and various cancers and as a consequence, there is great interest in isolating selective LO isozyme inhibitors. Currently, there is much use of baicalein as a selective human platelet 12-LO (12-hLO) inhibitor, however, our current steady-state inhibition data indicate that baicalein is not selective against 12-hLO versus human reticulocyte 15-LO-1 (15-hLO-1) (15/12=1.3), in vitro. However, in the presence of detergents baicalein is slightly more selective (15/12=7) as seen by the steady-state inhibition kinetics, which may imply greater selectivity in a cell-based assay but has yet to be proven. The mechanism of baicalein inhibition of 15-hLO-1 is reductive, which molecular modeling suggests is through direct binding of the catecholic moiety of baicalein to the iron. A structurally related flavonoid, apigenin, is not reductive, however, molecular modeling suggests a hydrogen bond with Thr591 may account for its inhibitor potency.