Phillip Crews

The marine sponge metabolite mycothiazole: A novel prototype mitochondrial complex I inhibitor

A natural product chemistry-based approach was applied to discover small-molecule inhibitors of hypoxia-inducible factor-1 (HIF-1). A Petrosaspongia mycofijiensis marine sponge extract yielded mycothiazole (1), a solid tumor selective compound with no known mechanism for its cell line-dependent cytotoxic activity. Compound 1 inhibited hypoxic HIF-1 signaling in tumor cells (IC(50) 1nM) that correlated with the suppression of hypoxia-stimulated tumor angiogenesis in vitro. However, 1 exhibited pronounced neurotoxicity in vitro. Mechanistic studies revealed that 1 selectively suppresses mitochondrial respiration at complex I (NADH-ubiquinone oxidoreductase). Unlike rotenone, MPP(+), annonaceous acetogenins, piericidin A, and other complex I inhibitors, mycothiazole is a mixed polyketide/peptide-derived compound with a central thiazole moiety. The exquisite potency and structural novelty of 1 suggest that it may serve as a valuable molecular probe for mitochondrial biology and HIF-mediated hypoxic signaling.

Small-molecule antagonists of the oncogenic Tcf/β-catenin protein complex

Key molecular lesions in colorectal and other cancers cause beta-catenin-dependent transactivation of T cell factor (Tcf)-dependent genes. Disruption of this signal represents an opportunity for rational cancer therapy. To identify compounds that inhibit association between Tcf4 and beta-catenin, we screened libraries of natural compounds in a high-throughput assay for immunoenzymatic detection of the protein-protein interaction. Selected compounds disrupt Tcf/beta-catenin complexes in several independent in vitro assays and potently antagonize cellular effects of beta-catenin-dependent activities, including reporter gene activation, c-myc or cyclin D1 expression, cell proliferation, and duplication of the Xenopus embryonic dorsal axis. These compounds thus meet predicted criteria for disrupting Tcf/beta-catenin complexes and define a general standard to establish mechanism-based activity of small molecule inhibitors of this pathogenic protein-protein interaction.

Jasplakinolide, a cyclodepsipeptide from the marine sponge, Jaspis sp.

Abstract A new cyclodepsipeptide comprised of three amino acids, and an oxy-trimethyl-nonanoyl group, has been characterized which has antifungal and anthelminthic bioactivity.

Polyketide assembly lines of uncultivated sponge symbionts from structure-based gene targeting

There is increasing evidence that uncultivated bacterial symbionts are the true producers of numerous bioactive compounds isolated from marine sponges. The localization and heterologous expression of biosynthetic genes could clarify this issue and provide sustainable supplies for a wide range of pharmaceuticals. However, identification of genes in the usually highly complex symbiont communities remains a challenging task. For polyketides, one of the most important groups of sponge-derived drug candidates, we have developed a general strategy that allows one to rapidly access biosynthetic gene clusters based on chemical moieties. Using this method, we targeted polyketide synthase genes from two different sponge metagenomes. We have obtained from a sponge-bacterial association a complete pathway for the rare and potent antitumor agent psymberin from Psammocinia aff. bulbosa. The data support the symbiont hypothesis and provide insights into natural product evolution in previously inaccessible bacteria.

Phenolic constituents of Psammaplysilla

The cytotoxic extract of Psammaplysilla sp. collected from Tonga contains monobromo tyrosine derivatives, 3-bromo-4-hydroxyphenylacetonitrile (1) which is known and psammaplin A (2) which is the first disulfide to be isolated from a sponge.

The antifouling activity of natural and synthetic phenolic acid sulphate esters

p-(sulphooxy) Cinnamic acid was isolated as a natural product for the first time from the seagrass Zostera marina (eelgrass) and was found to prevent attachment of marine bacteria and barnacles to artificial surfaces at nontoxic concentrations. Analogous synthetic sulphate esters had similar antifouling properties, while the non-sulphated phenolic acid precursors were ineffective. The antifouling properties of phenolic acid sulphates are consistent with an emerging pattern of biological activity exhibited by other sulphate esters isolated from a variety of marine organisms, and their low toxicity offers promise for the development of environmentally benign antifouling agents to protect structures in aquatic environments.

Jasplakinolide Induces Apoptosis in Various Transformed Cell Lines by a Caspase-3-Like Protease-Dependent Pathway

ABSTRACT To clarify the mechanisms underlying the antiproliferative effects of jasplakinolide, a cyclic depsipeptide from marine sponges, we examined whether jasplakinolide induces apoptosis in a variety of transformed and nontransformed cells. Jasplakinolide inhibited proliferation of human Jurkat T cells, resulting in cell death. This was accompanied by chromatin condensation and DNA cleavage at the linker regions between the nucleosomes. When caspase-3-like activity in the cytosolic extracts of Jurkat T cells was examined with a fluorescent substrate, DEVD-MAC (N-acetyl-Asp-Glu-Val-Asp-4-methyl-coumaryl-7-amide), the activity in the cells treated with jasplakinolide was remarkably increased in a time-dependent manner. Pretreatment of Jurkat T cells with the caspase inhibitor zVAD [benzyloxycarbonyl(Cbz)-Val-Ala-β-Asp(OMe)-fluoromethylketone] or DEVD-CHO (N-acetyl-Asp-Glu-Val-Asp-1-aldehyde) prevented the induction of apoptosis by jasplakinolide. Moreover, exposure of various murine transformed cell lines to jasplakinolide resulted in cell death, which was inhibited by zVAD. Although it has been well established that murine immature thymocytes are sensitive to apoptosis when exposed to various apoptotic stimuli, these cells as well as mature T lymphocytes were resistant to jasplakinolide-induced apoptosis. The results suggest that jasplakinolide induces apoptotic cell death through a caspase-3-like protease-dependent pathway. Another important outcome is that transformed cell lines were more susceptible to jasplakinolide-induced apoptosis than normal nontransformed cells.

The structures and stereochemistry of cytotoxic sesquiterpene quinones from dactylospongia elegans

Abstract The cytotoxicity of a crude extract from Dactylospongia elegans stimulated a search for the active constituents. The structures and absolute stereochemistry are elucidated for four new 9, 11,18, 19, and thirteen previously described compounds, 3, 4, 6a, 7, 8, 10, 12 - 17, 21. These compounds were isolated from collections of D. elegans obtained from three different Indo-Pacific regions, Fiji, Papua New Guinea, and Thailand. This species appears to elaborate a broader range of the mixed biogenesis sesquiterpene-hydroquinone (-quinone) metabolites in comparison to those of other sponges or seaweeds. Three compounds, 4, 9, and 13, were potent (IC50s were less than 1 μg/mL). The quinone ring appears to be essential for this in vitro activity.

Novel marine sponge derived amino acids 13. Additional psammaplin derivatives from Psammaplysilla purpurea

Abstract An investigation of a sponge rich in psammaplin derivatives provides some insight into the biogenesis of this group of amino acid derivatives. Accompanying psammaplin A (1) were a new cysteine dimer, prepsammaplin A (2), and three new bromotyrosine-cysteine derivatives, psammaplins B (3), C (4), and D (5). Two other compounds were isolated including (3-bromo-4-hydroxy) benzaldehyde (6) and (3-bromo-4-hydroxyphenyl)-acetonitrile (7) which appear to be bromotyrosine derivatives. Psammaplin D (5) showed antimicrobial and mild tyrosine kinase inhibition activity.

Highlights of marine invertebrate-derived biosynthetic products: Their biomedical potential and possible production by microbial associants

Coral reefs are among the most productive marine ecosystems and are the source of a large group of structurally unique biosynthetic products. Annual reviews of marine natural products continue to illustrate that the most prolific source of bioactive compounds consist of coral reef invertebrates-sponges, ascidians, mollusks, and bryozoans. This account examines recent milestone developments pertaining to compounds from invertebrates designated as therapeutic leads for biomedical discovery. The focus is on the secondary metabolites, their inspirational structural scaffolds and the possible role of micro-organism associants in their biosynthesis. Also important are the increasing concerns regarding the collection of reef invertebrates for the discovery process. The case examples considered here will be useful to insure that future research to unearth bioactive invertebrate-derived compounds will be carried out in a sustainable and environmentally conscious fashion. Our account begins with some observations pertaining to the natural history of these organisms. Many still believe that a serious obstacle to the ultimate development of a marine natural product isolated from coral reef invertebrates is the problem of compound supply. Recent achievements through total synthesis can now be drawn on to forcefully cast this myth aside. The tools of semisynthesis of complex natural products or insights from SAR efforts to simplify an active pharmacophore are at hand and demand discussion. Equally exciting is the prospect that invertebrate-associated micro-organisms may represent the next frontier to accelerate the development of high priority therapeutic candidates. Currently in the United States there are two FDA approved marine-derived therapeutic drugs and two others that are often cited as being marine-inspired. This record will be examined first followed by an analysis of a dozen of our favorite examples of coral reef invertebrate natural products having therapeutic potential. The record of using complex scaffolds of marine invertebrate products as the starting point for development will be reviewed by considering eight case examples. The potential promise of developing invertebrate-derived micro-organisms as the starting point for further exploration of therapeutically relevant structures is considered. Also significant is the circumstance that there are some 14 sponge-derived compounds that are available to facilitate fundamental biological investigations.