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.

Pestalone, a new antibiotic produced by a marine fungus in response to bacterial challenge.

The isolation and structure determination of a new chlorinated benzophenone antibiotic, pestalone (1), is described. The new compound was produced by a cultured marine fungus only when a unicellular marine bacterium, strain CNJ-328, was co-cultured in the fungal fermentation. The fungus, isolated from the surface of the brown alga Rosenvingea sp. collected in the Bahamas Islands, was identified as an undescribed member of the genus Pestalotia. The structure of 1, initially assigned with only modest confidence by combined spectral and chemical data, was confirmed by single-crystal X-ray analysis. Pestalone (1) exhibits moderate in vitro cytotoxicity in the National Cancer Institute's 60 human tumor cell line screen (mean GI(50) = 6.0 microM). More importantly, pestalone shows potent antibiotic activity against methicillin-resistant Staphylococcus aureus (MIC = 37 ng/mL) and vancomycin-resistant Enterococcus faecium (MIC = 78 ng/mL), indicating that pestalone should be evaluated in advanced models of infectious disease.

New antifeedant triterpene glycosides from the Caribbean sponge Erylus formosus.

Two groups of antifeedant triterpene glycosides were identified from the Caribbean sponge Erylus formosus. The structure of formoside B, a novel N-acetyl amino derivative of the known penasterol tetrasaccharide formoside, was elucidated using NMR and mass spectral data. Four triterpene hexasaccharides and two triterpene trisaccharides, characterized by a 31-carbon aglycone, proved difficult to isolate and therefore only the structure of their aglycone was determined. Gas chromatographic analysis of derivatized saccharides from these mixtures established the carbohydrate content of these compounds. All of the triterpene glycosides isolated contributed to the chemical defenses of this sponge, although with differing activities.

New cytotoxic sterol glycosides from the octocoral Carijoa (Telesto) riisei.

Two new steroidal glycosides, 3beta-O-(3'-O-acetyl-beta-D-arabinopyranosyl)-25xi-choles tan e-3beta, 5alpha,6beta,26-tetrol-26-acetate (riisein A, 2) and 3beta-O-(4'-O-acetyl-beta-D-arabinopyranosyl)-25xi-choles tan e-3beta, 5alpha,6beta,26-tetrol-26-acetate (riisein B, 3), were isolated from extracts of the Brazilian telestacean octocoral Carijoa (Telesto) riisei collected near Rio de Janeiro. The new glycosides co-occur with the polyhydroxy sterol, 25xi-cholestane-3beta,5alpha,6beta, 26-tetrol-26-acetate (1), an inseparable diastereomeric mixture previously reported from Telesto riisei collected in Micronesia. The structures of the new glycosides were assigned by spectroscopic methods and by comparison with spectral data for sterol 1. Riiseins A and B showed in vitro cytotoxicity toward HCT-116 human colon adenocarcinoma with IC(50) values of 2.0 microg/mL.

Mangicols: structures and biosynthesis of A new class of sesterterpene polyols from a marine fungus of the genus Fusarium.

A marine fungal isolate, tentatively identified as Fusarium heterosporum, has been found to produce a series of structurally novel sesterterpene polyols, the mangicols A-G (4-10). The structures of the new compounds, including the stereochemistry of mangicol A, were assigned by interpretation of spectral data derived from both natural products and synthetic derivatives. The mangicols, which possess unprecedented spirotricyclic skeletal components, show only weak to modest cytotoxicities toward a variety of cancer cell lines in in vitro testing. Mangicols A and B, however, showed significant antiinflammatory activity in the PMA (phorbol myristate acetate)-induced mouse ear edema model. A biosynthetic pathway for the neomangicol and mangicol carbon skeletons is proposed on the basis of the incorporation of appropriate radiolabeled precursors.

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.

Oxepinamides A-C and fumiquinazolines H--I: bioactive metabolites from a marine isolate of a fungus of the genus Acremonium.

Three new oxepin-containing natural products (1-3) and two new fumiquinazoline metabolites (4-5) have been isolated from organic extracts of the culture broth and mycelia of an Acremonium sp., a fungus obtained from the surface of the Caribbean tunicate Ecteinascidia turbinata. The structures of the five compounds were determined through extensive analysis of 1D- and 2D-NMR data, and mass spectrometry. Compound 1 exhibited good anti-inflammatory activity in a topical RTX-induced mouse ear edema assay. Compounds 4 and 5 exhibited weak antifungal activity toward Candida albicans in a broth microdilution assay.

Tamandarins A and B: new cytotoxic depsipeptides from a Brazilian ascidian of the family Didemnidae.

The structures of two new, naturally occurring cytotoxic depsipeptides, tamandarins A and B (1 and 2), are presented. The tamandarins were isolated from an unidentified Brazilian marine ascidian of the family Didemnidae. The structures of the new cytotoxins were assigned by interpretation of FABMS data and by extensive 2D NMR analyses. The absolute configurations of the tamandarins were assigned by acid and alkaline hydrolysis to yield their corresponding amino acids, which were then analyzed as their Marfey derivatives. The cytotoxicity of tamandarin A (1) was evaluated against various human cancer cell lines and shown to be slightly more potent than didemnin B. A qualitative discussion of the conformation of tamandarin A (1) in solution, obtained from NMR J-value data, variable temperature experiments, and NOESY/ROESY data, is included.

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.

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.

Lobophorins A and B, new antiinflammatory macrolides produced by a tropical marine bacterium.

Two new antiinflammatory macrolides, lobophorins A and B (1 and 2), have been isolated from fermentation broths of a marine bacterium isolated from the surface the Caribbean brown alga Lobophora variegata (Dictyotales). The new compounds, distantly related to antibiotics of the kijanimicin class, are potent inhibitors of topical PMA-induced edema in the mouse ear assay when administered either topically or IP.

Mechanism of inhibition of a poxvirus topoisomerase by the marine natural product sansalvamide A.

At present no antiviral agents are available for treatment of infection by the pathogenic poxvirus molluscum contagiosum virus (MCV). Here we report the identification and characterization of an inhibitor active against the virus-encoded type-1 topoisomerase, an enzyme likely to be required for MCV replication. We screened a library of marine extracts and natural products from microorganisms using MCV topoisomerase assays in vitro. The cyclic depsipeptide sansalvamide A was found to inhibit topoisomerase-catalyzed DNA relaxation. Sansalvamide A was inactive against two other DNA-modifying enzymes tested as a counterscreen. Assays of discrete steps in the topoisomerase reaction cycle revealed that sansalvamide A inhibited DNA binding and thereby covalent complex formation, but not resealing of a DNA nick in a preformed covalent complex. Sansalvamide A also inhibits DNA binding by the isolated catalytic domain, thereby specifying the part of the protein sensitive to sansalvamide A. These data specify the mechanism by which sansalvamide A inhibits MCV topoisomerase. Cyclic depsipeptides related to sansalvamide A represent a potentially promising chemical family for development of anti-MCV agents.

Arenaric acid, a new pentacyclic polyether produced by a marine bacterium (Actinomycetales).

Arenaric acid (1a), a new pentacyclic polyether related to the antibiotics K-41A and oxolonomycin, was isolated as its sodium salt (1b) from the culture broth of an estuarine bacterial isolate of the genus Streptomyces. The structure of arenaric acid was established by spectroscopic methods involving comprehensive 2D NMR measurements.

Luisols A and B, new aromatic tetraols produced by an estuarine marine bacterium of the genus Streptomyces (Actinomycetales).

Luisols A (1) and B (2), two new aromatic tetraols, have been isolated from the cultivation broth of an estuarine marine actinomycete of the genus Streptomyces (strain #CNH-370). The structures of luisols A and B were assigned by combined spectroscopic methods, including extensive 2D NMR experiments. Luisol A appears related to the anthraquinone antibiotics of the granaticin class, while the structure of luisol B contains the rare epoxynaphtho[2,3c]furan, a structural feature found in only one natural product, the fungal metabolite anthrinone.

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.

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.

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.

Evidence that a New Antibiotic Flavone Glycoside Chemically Defends the Sea Grass Thalassia testudinum against Zoosporic Fungi.

Significantly fewer thraustochytrid protists (zoosporic fungi) were observed in association with healthy leaf tissue of the marine angiosperm Thalassia testudinum than in association with sterilized samples that were returned to the collection site for 48 h. In support of the hypothesis that sea grass secondary metabolites were responsible for these differences, extracts of healthy T. testudinum leaf tissues inhibited the growth of the co-occurring thraustochytrid Schizochytrium aggregatum and deterred the attachment of S. aggregatum motile zoospores to an extract-impregnated substrate. By using S. aggregatum for bioassay-guided chemical fractionation, a new flavone glycoside was isolated and structurally characterized as luteolin 7-O-beta-d-glucopyranosyl-2"-sulfate. Whole-leaf tissue concentrations of this metabolite (4 mg/ml of wet leaf tissue) inhibited S. aggregatum attachment, and a significantly lower concentration (270 mug/ml) reduced thraustochytrid growth by 50%, suggesting that natural concentrations are at least 15 times greater than that needed for significant microbiological effects. These results offer the first complete chemical characterization of a sea grass sulfated flavone glycoside and provide evidence that a secondary metabolite chemically defends T. testudinum against fouling microorganisms.

Evidence that a New Antibiotic Flavone Glycoside Chemically Defends the Sea Grass Thalassia testudinum against Zoosporic Fungi.

[This corrects the article on p. 1491 in vol. 64.].