Natural products chemistry in the marine environment.

Significant differences and numerous similarities exist in the biosynthetic activities of marine and terrestrial plants and animals. While the more primitive marine biota are recognized to possess the common biosynthetic pathways to produce terpenes, acetogenins, aromatic compounds, and alkaloids, in many cases these pathways have been modified in unusual ways. The halogens in sebwater, for example, appear to be fundamentally involved in terpene biosynthesis and in the production of bromine-containinq acetogenins and phenolic compoupds. Marine metabolites have high physiological activities, and these molecules are conceived to function, in part at least, as defensive adaptations In the marine environment.

Isolation of halimedatrial: chemical defense adaptation in the calcareous reef-building alga halimeda.

Halimedatrial, a structurally unprecedented diterpenoid trialdehyde, has been identified as the major secondary metabolite in six species of the calcareous reef-building alga Halimeda. In laboratory bioassays, halimedatrial is toxic toward reef fishes, significantly reduces feeding in herbivorous fishes, and has cytotoxic and antimicrobial activities. The widespread occurrence of halimedatrial and its potent biological activities suggest that this metabolite represents a chemical defense adaptation in this pantropical marine alga.

Symbiotic marine bacteria chemically defend crustacean embryos from a pathogenic fungus.

Embryos of the shrimp Palaemon macrodactylus are remarkably resistant to infection by the fungus Lagenidium callinectes, a recognized pathogen of many crustaceans. An Alteromonas sp. bacterial strain consistently isolated from the surface of the embryos, produces 2,3-indolinedione (isatin), a compound that inhibits the pathogenic fungus. If exposed to the fungus, bacteria-free embryos quickly die, whereas similar embryos reinoculated with the bacteria or treated only with 2,3-indolinedione live well. The commensal Alteromonas sp. bacteria protect shrimp embryos from fungal infection by producing and liberating the antifungal metabolite 2,3-indolinedione.

Lophotoxin: a novel neuromuscular toxin from Pacific sea whips of the genus Lophogorgia.

A new neuromuscular toxin, lophotoxin, has been isolated from several pacific gorgonians of the genus Lophogorgia. The structure of lophotoxin was deduced by combined spectrochemical methods, and belongs to the well-known cembrene class of diterpenoid molecules. Lophotoxin contains furanoaldehyde and alpha, beta-epoxy-gamma-lactone functional groups, in sharp contrast to the cationic ammonium functional groups of the established neurotoxins.

Eleutherobin, a novel cytotoxic agent that induces tubulin polymerization, is similar to paclitaxel (Taxol).

Eleutherobin is a novel natural product isolated from a marine soft coral that is extremely potent for inducing tubulin polymerization in vitro and is cytotoxic for cancer cells with an IC50 similar to that of paclitaxel. This compound is cross-resistant along with other multidrug-resistant agents against P-glycoprotein-expressing cells and is cross-resistant with paclitaxel against a cell line that has altered tubulin. In mechanistic studies, eleutherobin shares with paclitaxel the ability to induce tubulin polymerization in vitro and is most likely cytotoxic by virtue of this mechanism. Human colon carcinoma cells exposed to eleutherobin contain multiple micronuclei and microtubule bundles, and they arrest in mitosis, depending on concentration, cell line, and length of exposure. These morphological abnormalities appearing in cultured cells are indistinguishable from those induced by paclitaxel. Electron microscopy reveals that eleutherobin induces homogeneous populations of long, rigid microtubules similar to those formed by paclitaxel. Thus, eleutherobin is a new chemotype with a mechanism of action similar to that of paclitaxel and, as such, has promising potential as a new anticancer agent.

New pharmaceuticals from marine organisms.

Definitions of 'marine biotechnology' often refer to the vast potential of the oceans to lead to new cures for human and animal disease; the exploitation of natural drugs has always been the most basic form of biotechnology. Although only initiated in the late 1970s, natural drug discovery from the world's oceans has been accelerated by the chemical uniqueness of marine organisms and by the need to develop drugs for contemporary, difficult to cure, diseases. Current research activities, while primarily within the academic laboratories, have generated convincing evidence that marine drug discovery has an exceedingly bright future.

Structure/activity and molecular modeling studies of the lophotoxin family of irreversible nicotinic receptor antagonists.

Lophotoxin is a small cyclic diterpene that irreversibly inhibits agonist binding to nicotinic acetylcholine receptors by reacting covalently with Tyr190 in the alpha-subunits of the receptor. Structure/activity and molecular modeling studies were undertaken to investigate the structural and conformational features responsible for this unique biological activity. A total of 18 naturally occurring and 7 chemically modified analogues were evaluated for their ability to inhibit the binding of [125I]-alpha-bungarotoxin to nicotinic acetylcholine receptors on membranes prepared from Torpedo electric organ. When the toxins were incubated with the receptor for short durations they did not slow the initial rate of binding of [125I]-alpha-bungarotoxin, suggesting that they have relatively low reversible affinity. However, their ability to inhibit the equilibrium binding of [125I]-alpha-bungarotoxin increased progressively with longer incubation times, consistent with an irreversible mechanism of action. Comparison of active and inactive analogues allowed identification of a conserved pharmacophore that appeared to be required for irreversible inhibition of the receptor. This pharmacophore contains lactone oxygens and an electron-deficient epoxide that may mimic the acetate oxygens and quaternary ammonium group of acetylcholine, respectively. Computer modeling of the toxins using molecular mechanics and dynamics revealed that the toxins have restricted conformational mobility, thus allowing identification of a minimum-energy conformation. The results allow speculation concerning the site of covalent reaction between Tyr190 and the toxins, the normal function of Tyr190 in binding acetylcholine, and the bound conformation of acetylcholine.

Mechanism of action of the marine natural product stypoldione: evidence for reaction with sulfhydryl groups.

Stypoldione, a marine natural product that possesses an o-quinone functional group, has been shown to inhibit a variety of biological processes including cell division. We found that stypoldione binds covalently to sulfhydryl groups of thiol-containing compounds via addition of sulfur to the C-4' position of the quinone ring. We examined the ability of stypoldione to add to sulfhydryl groups of a number of thiol-containing substances, including glutathione, thiophenol, beta-mercaptoethanol, and the protein tubulin. We suggest that the biological actions of stypoldione may be caused by the addition of this compound to thiol groups of biological molecules.

N-Methylsansalvamide, a cytotoxic cyclic depsipeptide from a marine fungus of the genus fusarium.

N-Methylsansalvamide (1), a new cyclic depsipeptide, was isolated from extracts of a cultured marine fungus, strain CNL-619, identified as a member of the genus Fusarium. N-Methylsansalvamide exhibits weak in vitro cytotoxicity in the NCI human tumor cell line screen (GI50 8.3 microM). The structure of 1 was determined by combined spectral and chemical methods.

Two antifeedant lignans from the freshwater macrophyte Saururus cernuus.

Two diarylbutane derivatives of dihydroguaiaretic acid have been isolated from emergent portions of the southeastern United States freshwater angiosperm Saururus cernuus L. (Saururaceae). Bioassay-guided fractionation of organic extracts of S. cernuus led to the compounds, sauriols A and B, in addition to five previously known lignoids. These metabolites deter feeding by the omnivorous crayfish Procambarus clarkii. The two lignans were identified by analysis of nuclear magnetic resonance and mass spectral data, and by comparison with spectral data of dihydroguaiaretic acid.

Pharmacological characterization of the pseudopterosins: novel anti-inflammatory natural products isolated from the Caribbean soft coral, Pseudopterogorgia elisabethae.

Pseudopterosin E (PSE), a C-10 linked fucose glycoside and pseudopterosin A (PSA), a C-9 xylose glycoside isolated from the marine gorgonian Pseudopterogorgia elisabethae were both effective in reducing PMA-induced mouse ear edema when administered topically (ED50 (microg/ear) PSE(38), PSA(8)) or systemically (ED50 (mg/kg, i.p.) PSE (14), PSA (32)). Both compounds exhibited in vivo analgesic activity in phenyl-p-benzoquinone-induced writhing (ED50 (mg/kg, i.p.) PSE(14), PSA(4). PSE inhibited zymosan-induced writhing (ED50 = 6 mg/kg, i.p.), with a concomitant dose-dependent inhibition of peritoneal exudate 6-keto-prostaglandin F1alpha (ED50 = 24 mg/kg) and leukotriene C4 (ED50 = 24 mg/kg). In vitro, the pseudopterosins were inactive as inhibitors of phospholipase A2, cyclooxygenase, cytokine release, or as regulators of adhesion molecule expression. PSA inhibited prostaglandin E2 and leukotriene C4 production in zymosan-stimulated murine peritoneal macrophages (IC50 = 4 microM and 1 microM, respectively); however, PSE was much less effective. These data suggest that the pseudopterosins may mediate their anti-inflammatory effects by inhibiting eicosanoid release from inflammatory cells in a concentration and dose-dependent manner.

Sterols of the cultured dinoflagellate Pyrocystis lunula.

Eighteen components of the sterol fraction of Pyrocystis lunula have been identified. In addition to 4 alpha-methyl sterols (typical dinoflagellate sterols), regular sterols, both with a saturated and delta 5-unsaturated skeleton, were isolated, together with delta 4-3-keto steroids including the hitherto unknown 23,24R-dimethyl-4,22E-cholestadien-3-one.

Sterols of the cultured euglenid Eutreptia viridis: a novel delta 23-unsaturated sterol.

The sterol mixture isolated from the marine alga Eutreptia viridis consists mainly of delta 5,7-dienes which account for 80% of the free sterols. Eighteen different sterols were detected, including a novel sterol with the rare delta 23-unsaturation, viz. 24-ethylcholesta-5,7,23Z-trien-3 beta-o1.

Isolation of two new C30 sterols, (24E)-24-N-propylidenecholesterol and 24 epsilon-N-propylcholesterol, from a cultured marine Chrysophyte.

Two new sterols, (24E)-24-n-propylidenecholesterol and 24 epsilon-n-propylcholesterol, were isolated from a cultured marine Chrysophyte. Since most of the steroids found in marine invertebrates are unchanged or modified sterols of algal or symbiotic origin, the discovery of these two unusual sterols in a unicellular alga grown under well-defined conditions contributes to our knowledge of sterols in marine food chains and offers a potential substrate for biosynthetic labeling experiments.

A cyclized didemnimide alkaloid from the caribbean ascidian didemnumconchyliatum

A novel, cyclized alkaloid of the didemnimide class, 5, has been isolated from extracts of the Caribbean ascidian Didemnum conchyliatum. The structure of 5 was assigned using combined spectral methods that emphasized one- and two-dimensional NMR methods. The new alkaloid is the cyclization product of didemnimide A (1) formed via a C-2 indole condensation with the imidazole nitrogen.

New fish feeding deterrents, including a novel sesquiterpenoid heterogorgiolide, from the brazilian gorgonian heterogorgia uatumani(Octocorallia, gorgonacea)

Studies of the Brazilian gorgonian octocoral Heterogorgia uatumani have resulted in the discovery of two metabolites that inhibit fish feeding under natural conditions. These are the previously reported eunicellane diterpenoid, (6E)-2alpha,9alpha-epoxyeunicella-6, 11(12)-dien-3beta-ol (1) and a new sesquiterpene lactone, heterogorgiolide (2). The structures of 1 and 2 were determined by spectroscopic methods and by comparison of spectral data with literature values. Field bioassays of the two compounds, at their natural concentrations, confirmed that they deter predation by a complex assemblage of reef fishes. This is an unusual observation showing that defenses are derived from both sesqui- and diterpenoid metabolites.

Marizomib, a proteasome inhibitor for all seasons: preclinical profile and a framework for clinical trials.

The proteasome has emerged as an important clinically relevant target for the treatment of hematologic malignancies. Since the Food and Drug Administration approved the first-in-class proteasome inhibitor bortezomib (Velcade) for the treatment of relapsed/refractory multiple myeloma (MM) and mantle cell lymphoma, it has become clear that new inhibitors are needed that have a better therapeutic ratio, can overcome inherent and acquired bortezomib resistance and exhibit broader anti-cancer activities. Marizomib (NPI-0052; salinosporamide A) is a structurally and pharmacologically unique ß-lactone-γ-lactam proteasome inhibitor that may fulfill these unmet needs. The potent and sustained inhibition of all three proteolytic activities of the proteasome by marizomib has inspired extensive preclinical evaluation in a variety of hematologic and solid tumor models, where it is efficacious as a single agent and in combination with biologics, chemotherapeutics and targeted therapeutic agents. Specifically, marizomib has been evaluated in models for multiple myeloma, mantle cell lymphoma, Waldenstrom's macroglobulinemia, chronic and acute lymphocytic leukemia, as well as glioma, colorectal and pancreatic cancer models, and has exhibited synergistic activities in tumor models in combination with bortezomib, the immunomodulatory agent lenalidomide (Revlimid), and various histone deacetylase inhibitors. These and other studies provided the framework for ongoing clinical trials in patients with MM, lymphomas, leukemias and solid tumors, including those who have failed bortezomib treatment, as well as in patients with diagnoses where other proteasome inhibitors have not demonstrated significant efficacy. This review captures the remarkable translational studies and contributions from many collaborators that have advanced marizomib from seabed to bench to bedside.

Marine soft corals of the genus Pseudopterogorgia: a resource for novel anti-inflammatory diterpenoids.

This paper is a brief review of the diterpenoid chemistry of gorgonian corals of the genus Pseudopterogorgia. Previously described compounds and several new diterpenoids are presented in the context of their potential utilization in the development of anti-inflammatory and analgesic drugs.

Lophotoxin irreversibly inactivates the nicotinic acetylcholine receptor by preferential association at one of the two primary agonist sites.

Lophotoxin, a cyclic diterpenoid isolated from coral, irreversibly inactivates the nicotinic acetylcholine receptor on intact BC3H-1 cells. Inactivation can be prevented by simultaneous incubation of lophotoxin with nicotinic agonists and competitive antagonists but not by noncompetitive antagonists such as dibucaine. Analysis of lophotoxin inhibition of carbamylcholine-elicited 22Na+ permeability, KG/KGmax, in relation to the number of sites blocked, y, reveals a function showing greater curvature than the parabolic function kG/kGmax = (1 - y)2 found for cobra alpha-toxin inhibition of 22Na+ permeability. This relationship is consistent with lophotoxin not binding randomly to the two primary agonist-antagonist sites but rather exhibiting a preference for one of the two sites. Binding of lophotoxin to a single site per receptor oligomer is sufficient to render the receptor nonfunctional. A comparison of the concentration dependencies for occupation by competitive antagonists reveals a shift to lower antagonist concentrations and an increase in Hill coefficient to approach unity after partial occupation by lophotoxin. Competitive antagonists are known to bind to two sites of unequal affinity on the receptor, and the preferential site of lophotoxin inactivation is the site of lower affinity for the competitive antagonists. In the case of agonists fractional inactivation of sites by lophotoxin results in a loss of the positive cooperativity and a shift of the concentration dependence for carbamylcholine binding to higher agonist concentrations. Similar behavior is observed for cobra alpha-toxin inactivation, but a comparison of concentration dependencies for agonist binding following partial occupation by lophotoxin and cobra alpha-toxin reveals that lophotoxin blockade yields residual sites with a lower affinity and Hill coefficients for agonists closer to unity. These shifts in agonist and antagonist binding profiles are also in accord with preferential inactivation of one of the two agonist sites by lophotoxin. The findings indicate that the site of lower affinity for antagonists may possess the higher affinity for agonists.