Russell G. Kerr

Biosynthetic studies of the alkaloid, stevensine, in a cell culture of the marine sponge Teichaxinella morchella

The biosynthetic origin of stevensine, a C11N5 sponge alkaloid, has been investigated using a cell culture composed of archaeocytes from the sponge Teichaxinella morchella (Porifera: Demospongiae: Axinellidae). Histidine and ornithineproline were identified as amino acid building blocks of stevensine.

Marine natural products as therapeutic agents

The marine environment has been shown to provide a source of great diversity of chemical structures with promising biological activities. A growing number of these compounds are entering clinical trials and thus, the impact of this field on the biomedical industry is increasing. The majority of recent patents discussing marine natural products have focused on the discovery of antitumour agents with the antiviral and anti-inflammatory areas receiving significantly less attention. The phylum Porifera is the source of the greatest number of metabolites described in recent patents. The review is organised phylogenetically and will provide a description of the patent literature in the field of marine natural products focussing on the period 1996 to April 1999.

Identification of anti-inflammatory diterpenes from the marine gorgonian Pseudopterogorgia elisabethae

Analysis of the terpene metabolites of Pseudopterogorgia elisabethae collected from the Florida Keys has resulted in the identification of a novel hydroxyquinone, elisabethadione (1), as well as new pseudopterosins and seco-pseudopterosins. Anti-inflammatory assays indicate that elisabethadione is more potent than the well characterized pseudopterosin A and E. This report also describes the co-occurrence of pseudopterosins and seco-pseudopterosins, diterpenes with amphilectane and serrulatane skeletons, respectively. This together with our previously described isolation of elisabethatriene as the sole diterpene cyclase product in P. elisabethae suggests that the amphilectane and serrulatane families of diterpenes are derived from the same geranylgeranyl diphosphate cyclase product.

Radioactivity-Guided Isolation and Characterization of the Bicyclic Pseudopterosin Diterpene Cyclase Product from Pseudopterogorgia elisabethae

Abstract The intermediate representing the first committed step in the pseudopterosin biosynthetic pathway has been discovered using a radioactivity-guided isolation. This diterpene cyclase product was identified from a cell-free extract of the marine soft coral, Pseudopterogorgia elisabethae, which was incubated with 3H-geranylgeranyl diphosphate. Structural studies of the compound have revealed an unexpected bicyclic skeleton suggesting that the pseudopterosins are related to the seco-pseudopterosins through a common bicyclic intermediate. In addition, the intermediacy of this metabolite in pseudopterosin biosynthesis has been confirmed utilizing a cell-free extract of P. elisabethae.

Comparative proteomic analysis of matched primary and metastatic melanoma cell lines.

Identification of the biochemical pathways involved in the transformation from primary to metastatic melanoma is an area under intense investigation. A 2DE proteomics approach has been applied herein to the matched patient primary and metastatic melanoma cell lines WM-115 and WM-266-4, respectively, to better understand the processes that underlie tumor progression. Image analysis between samples aligned 470 common gel spots. Quantitative gel analysis indicated 115 gel spots of greater intensity in the metastatic line compared with the primary one, leading to the identification of 131 proteins via database searching of nano-LC-ESI-Q-TOF-MS/MS data. This more than tripled the number of proteins previously shown to be of higher abundance during melanoma progression. Also observed were 22 gel spots to be of lesser intensity in the metastatic line with respect to the primary one. Of these gel spots 15 proteins could be identified. Numerous proteins from both groups had not been reported previously to participate in melanoma progression. Further analysis of one protein, cyclophilin A, confirmed that this protein is expressed at higher levels in metastatic melanoma compared with primary melanoma and normal fibroblasts. Overall, this study expands our knowledge of protein modulation during melanoma stages, and suggests new targets for inhibitor development.

Cytotoxic and antimicrobial activity of pseudopterosins and seco-pseudopterosins isolated from the octocoral Pseudopterogorgia elisabethae of San Andrés and Providencia Islands (Southwest Caribbean Sea).

To expand the potential of pseudopterosins and seco-pseudopterosins isolated from the octocoral Pseudopterogorgia elisabethae of San Andrés and Providencia islands (southwest Caribbean Sea), we report the anti-microbial profile against four pathogenic microorganisms (Staphylococcus aureus, Enterococcus faecalis, Pseudomonas aeruginosa and Candida albicans) and report a more complete cytotoxic profile against five human cells lines (HeLa, PC-3, HCT116, MCF-7 and BJ) for the compounds PsG, PsP, PsQ, PsS, PsT, PsU, 3-O-acetyl-PsU, seco-PsJ, seco-PsK and IMNGD. For the cytotoxic profiles, all compounds evaluated showed moderate and non-selective activity against both tumor and normal cell lines, where PsQ and PsG were the most active compounds (GI50 values between 5.8 μM to 12.0 μM). With respect to their anti-microbial activity the compounds showed good and selective activity against the Gram-positive bacteria, while they did not show activity against the Gram-negative bacterium or yeast. PsU, PsQ, PsS, seco-PsK and PsG were the most active compounds (IC50 2.9–4.5 μM) against S. aureus and PsG, PsU and seco-PsK showed good activity (IC50 3.1–3.8 μM) against E. faecalis, comparable to the reference drug vancomycin (4.2 μM).

Diketopiperazines as Advanced Intermediates in the Biosynthesis of Ecteinascidins

Abstract The diketopiperazines of phenylalanine, tyrosine and DOPA have been synthesized from 14 C-labeled amino acids and tested as intermediates in the biosynthesis of the ecteinascidins. Biosynthetic experiments were performed using an enzyme preparation of the tunicate Ecteinascidia turbinata, the source of the ecteinascidins. Tyrosine and DOPA diketopiperazines were both transformed to the ecteinascidins whereas the diketopiperazine of phenylalanine was not modified. It is now apparent that the biosynthesis of the ecteinascidins is initiated by the condensation of tyrosine to its cyclic dipeptide followed by a subsequent oxidation to the diketopiperazine of DOPA.

Antimicrobial organometallic dendrimers with tunable activity against multidrug-resistant bacteria

Multidrug-resistant pathogens are an increasing threat to public health. In an effort to curb the virulence of these pathogens, new antimicrobial agents are sought. Here we report a new class of antimicrobial organometallic dendrimers with tunable activity against multidrug-resistant Gram-positive bacteria that included methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium. Mechanistically, these redox-active, cationic organometallic dendrimers induced oxidative stress on bacteria and also disrupted the microbial cell membrane. The minimum inhibitory concentrations, which provide a quantitative measure of the antimicrobial activity of these dendrimers, were in the low micromolar range. AlamarBlue cell viability assay also confirms the antimicrobial activity of these dendrimers. Interestingly, these dendrimers were noncytotoxic to epidermal cell lines and to mammalian red blood cells, making them potential antimicrobial platforms for topical applications.

An assessment of natural product discovery from marine (sensu strictu) and marine-derived fungi

The natural products community has been investigating secondary metabolites from marine fungi for several decades, but when one attempts to search for validated reports of new natural products from marine fungi, one encounters a literature saturated with reports from ‘marine-derived’ fungi. Of the 1000+ metabolites that have been characterized to date, only approximately 80 of these have been isolated from species from exclusively marine lineages. These metabolites are summarized here along with the lifestyle and habitats of their producing organisms. Furthermore, we address some of the reasons for the apparent disconnect between the stated objectives of discovering new chemistry from marine organisms and the apparent neglect of the truly exceptional obligate marine fungi. We also offer suggestions on how to reinvigorate enthusiasm for marine natural products discovery from fungi from exclusive marine lineages and highlight the need for critically assessing the role of apparently terrestrial fungi in the marine environment.

Chemical dereplication of marine actinomycetes by liquid chromatography-high resolution mass spectrometry profiling and statistical analysis

Discovery of novel bioactive metabolites from marine bacteria is becoming increasingly challenging, and the development of novel approaches to improve the efficiency of early steps in the microbial drug discovery process is therefore of interest. For example, current protocols for the taxonomic dereplication of microbial strains generally use molecular tools which do not take into consideration the ability of these selected bacteria to produce secondary metabolites. As the identification of novel chemical entities is one of the key elements driving drug discovery programs, this study reports a novel methodology to dereplicate microbial strains by a metabolomics approach using liquid chromatography-high resolution mass spectrometry (LC-HRMS). In order to process large and complex three dimensional LC-HRMS datasets, the reported method uses a bucketing and presence-absence standardization strategy in addition to statistical analysis tools including principal component analysis (PCA) and cluster analysis. From a closely related group of Streptomyces isolated from geographically varied environments, we demonstrated that grouping bacteria according to the chemical diversity of produced metabolites is reproducible and provides greatly improved resolution for the discrimination of microbial strains compared to current molecular dereplication techniques. Importantly, this method provides the ability to identify putative novel chemical entities as natural product discovery leads.