Naturally occurring marine brominated indoles are aryl hydrocarbon receptor ligands/agonists.

The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that mediates the toxic and biological effects of structurally diverse chemicals, including the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). As part of a larger effort to identify the full spectrum of chemicals that can bind to and activate the AhR, we have examined the ability of several naturally occurring marine-derived brominated indoles and brominated (methylthio)indoles (collectively referred to as brominated indoles) to bind to the AhR and stimulate AhR-dependent gene expression. Incubation of mouse, rat, and guinea pig recombinant cell lines containing a stably transfected AhR-responsive luciferase reporter gene with eight brominated indoles revealed that all compounds stimulated luciferase reporter gene activity, although some species-specific differences were observed. All compounds induced significantly more luciferase activity when incubated with cells for 4 h as compared to 24 h, demonstrating that these compounds are transient activators of the AhR signaling pathway. Three of the brominated indoles induced CYP1A1 mRNA in human HepG2 cells in vitro and Cyp1a mRNA in zebrafish embryos in vivo. The identification of the brominated indoles as direct ligands and activators/agonists of the AhR was confirmed by their ability to compete with [(3)H]TCDD for binding to the AhR and to stimulate AhR transformation and DNA binding in vitro. Taken together, these results indicate that marine-derived brominated indoles are members of a new class of naturally occurring AhR agonists.

Four new polyoxygenated gorgosterols from the gorgonian Isis hippuris.

Four new polyoxygenated steroids (1-4) together with four known ones (5-8) have been isolated from the gorgonian Isis hippuris. The structures of the new compounds have been elucidated by spectroscopic analysis and chemical conversion. All of the new steroids showed moderate cytotoxicity against cultured NBT-T2 cells.

Deoxymanoalides from the nudibranch Chromodoris willani.

Two sesterterpenes, deoxymanoalide (1) and deoxysecomanoalide (2), were isolated from the nudibranch Chromodoris willani collected in Okinawa and their structures determined on the basis of spectroscopic data and chemical conversions. The mollusk feeds on a sponge containing manoalide (3) and secomanoalide (4) and is likely to biotransform them into 1 and 2. Both 1 and 2 showed moderate antimicrobial activity against Escherichia coli and Bacillus subtilis and inhibited snake venom phospholipase A2 at 0.2 to 0.5 microM.

Synthesis of carbamate derivatives of iejimalides. Retention of normal antiproliferative activity and localization of binding in cancer cells.

The syntheses of six iejimalide carbamate derivatives are described. Their biological activity and those of the unmodified iejimalides A and B against breast and prostate cancer cell lines were determined. These results show that the serine hydroxyl group of iejimalides A and B is a permissive site that can be functionalized to form carbamate derivatives without significant loss of normal biological activity. This method of derivatization will be valuable for cellular target identification, mechanism of action studies, and drug development efforts. A fluorescent derivative does not exhibit binding to the cytoskeletal features of cancer cells.

Polybrominated diphenyl ethers from the Indonesian sponge Lamellodysidea herbacea.

Four new (1-4) and 10 known polybrominated diphenyl ethers (5-14) have been isolated from the title sponge. The structures of the new entities were elucidated by interpretation of spectroscopic data and chemical transformations. These metabolites showed potent antimicrobial activity against Bacillus subtilis and moderate/weak cytotoxicity against NBT-T2 rat bladder epithelial cells. The major constituent 14 was treated under debromination conditions to give eight derivatives, which were subjected to a structure-activity relationship study. The results indicated that the presence of two phenolic hydroxyl groups and bromines at C-2 and/or C-5, as in 2, is important for the exhibition of antibacterial activity.

Functional characterization of IRESes by an inhibitor of the RNA helicase eIF4A.

RNA helicases are molecular motors that are involved in virtually all aspects of RNA metabolism. Eukaryotic initiation factor (eIF) 4A is the prototypical member of the DEAD-box family of RNA helicases. It is thought to use energy from ATP hydrolysis to unwind mRNA structure and, in conjunction with other translation factors, it prepares mRNA templates for ribosome recruitment during translation initiation. In screening marine extracts for new eukaryotic translation initiation inhibitors, we identified the natural product hippuristanol. We show here that this compound is a selective and potent inhibitor of eIF4A RNA-binding activity that can be used to distinguish between eIF4A-dependent and -independent modes of translation initiation in vitro and in vivo. We also show that poliovirus replication is delayed when infected cells are exposed to hippuristanol. Our study demonstrates the feasibility of selectively targeting members of the DEAD-box helicase family with small-molecule inhibitors.

Terpenoids from Laurencia luzonensis.

Luzodiol (4), a diterpene possessing a new carbon skeleton, and five new sesquiterpenes (5-9) of the snyderane class have been isolated from the red alga Laurencia luzonensis and their structures determined by spectroscopic analysis. The relative stereochemistry of the known luzonensol (3) was assigned by its conversion to palisadin B (10).

Briarane diterpenes from two species of octocorals, Ellisella sp. and Pteroeides sp.

Eight new briarane diterpenes (1-4, 7-10) have been isolated from two species of octocorals and the structures elucidated by spectroscopic analysis. Two diterpenes (2, 3) from the gorgonian Ellisella sp. inhibited cytokinesis, causing multinuclei formation on NBT-II cells, while a known briarane (12) from the sea pen Pteroeides sp. showed reversal of multidrug resistance.

New cytotoxic furanosesterterpenes from an Okinawan marine sponge, Ircinia sp.

Five new sesterterpenes have been isolated from a lipophilic extract of a sponge, Ircinia sp., and their structures elucidated by spectroscopic and chemical methods. The absolute configurations of two metabolites (1, 3) were established by chemical degradation. These compounds showed moderate cytotoxicity against KB cells.

Araguspongines K and L, new bioactive bis-1-oxaquinolizidine N-oxide alkaloids from Red Sea specimens of Xestospongia exigua.

In addition to the previously reported (+)-araguspongine A, (+)-araguspongine C, (+)-araguspongine D, (-)-araguspongine E, and (+)-xestospongin B, two new N-oxide araguspongines, (+)-araguspongine K and (+)-araguspongine L, are described here. Their structures were established on the basis of spectral analyses including (1)H-(15)N HMBC. The promising in vitro antimalarial and antituberculosis activities of araguspongine C are reported.

Bitungolides A-F, new polyketides from the Indonesian sponge Theonella cf. swinhoei.

Six new polyketides, bitungolides A-F (1-6), have been isolated from the Indonesian sponge Theonella cf. swinhoei and their structures elucidated by spectroscopic data and X-ray diffraction analysis. The bitungolides are a new class of Theonella metabolites that inhibit dual-specificity phosphatase VHR.

New scalarane class sesterterpenes from an Indonesian sponge, Phyllospongia sp.

A series of scalarane class sesterterpenes (1-8) have been isolated from an Indonesian sponge, Phyllospongia sp. Their structures were determined by spectroscopic analysis and confirmed by single-crystal X-ray diffraction on compound 1. The absolute stereochemistry of 1 was established by modified Mosher's method.

Pachastrissamine, a cytotoxic anhydrophytosphingosine from a marine sponge, Pachastrissa sp.

An anhydrophytosphingosine named pachastrissamine (3) has been isolated as a cytotoxic principle of a sponge, Pachastrissa sp., and the structure including the absolute configuration determined by spectroscopic and chemical analysis.

Cyclotheonamide E4 and E5, new potent tryptase inhibitors from an Ircinia species of sponge.

Tryptase is a protease released from mast cells and is believed to contribute to the inflammatory process in allergic diseases including asthma. In the course of screening to find tryptase inhibitors, we isolated two new tryptase inhibitors, cyclotheonamide E4 (3) and E5 (4), from a marine sponge of the genus Ircinia. The structures of these molecules were determined by interpretation of 1H and 13C NMR spectra, and they were shown to be closely related to the previously reported cyclotheonamides E (1), E2, and E3 (2). These molecules contain two unusual amino acids, vinylogous tyrosine and alpha-ketohomoarginine, which are involved in strong activities against serine proteases. Cyclotheonamide E4 showed potent inhibitory activity against human tryptase (IC50 5.1 nM). Therefore, cyclotheonamide E4 may be useful as a therapeutic agent in the treatment of allergic diseases including asthma.

The new anti-actin agent dihydrohalichondramide reveals fenestrae-forming centers in hepatic endothelial cells.

BACKGROUND: Liver sinusoidal endothelial cells (LSECs) react to different anti-actin agents by increasing their number of fenestrae. A new structure related to fenestrae formation could be observed when LSECs were treated with misakinolide. In this study, we investigated the effects of two new actin-binding agents on fenestrae dynamics. High-resolution microscopy, including immunocytochemistry and a combination of fluorescence- and scanning electron microscopy was applied. RESULTS: Halichondramide and dihydrohalichondramide disrupt microfilaments within 10 minutes and double the number of fenestrae in 30 minutes. Dihydrohalichondramide induces fenestrae-forming centers, whereas halichondramide only revealed fenestrae-forming centers without attached rows of fenestrae with increasing diameter. Correlative microscopy showed the absence of actin filaments (F-actin) in sieve plates and fenestrae-forming centers. Comparable experiments on umbilical vein endothelial cells and bone marrow sinusoidal endothelial cells revealed cell contraction without the appearance of fenestrae or fenestrae-forming centers. CONCLUSION: (I) A comparison of all anti-actin agents tested so far, revealed that the only activity that misakinolide and dihydrohalichondramide have in common is their barbed end capping activity; (II) this activity seems to slow down the process of fenestrae formation to such extent that it becomes possible to resolve fenestrae-forming centers; (III) fenestrae formation resulting from microfilament disruption is probably unique to LSECs.