The synthesis and biological evaluation of desepoxyisotedanolide and a comparison with desepoxytedanolide.

The tedanolides are biologically active polyketides that exhibit a macrolactone constructed from a primary alcohol. Since polyketidal transformations only generate secondary alcohols, it has been hypothesized by Taylor that this unique lactone could arise from a postketidal transesterification. In order to probe this hypothesis and to investigate the biological profile of the putative precursor of all members of the tedanolide family, we embarked on the synthesis of desepoxyisotedanolide and its biological evaluation in comparison to desepoxytedanolide. The biological experiments unraveled a second target for desepoxytedanolide and provided evidence that the proposed transesterification indeed provides a survival advantage for the producing microorganism.

The marine polyketide myriaporone 3/4 stalls translation by targeting the elongation phase.

Myriaporone 3/4, a cytotoxic polyketide, has been reported as an inhibitor of eukaryotic protein synthesis. However, the mechanism by which it inhibits translation was unknown. Here we show that myriaporone 3/4 stalls protein synthesis in the elongation phase by inducing phosphorylation of eukaryotic elongation factor 2. The phosphorylation results from direct binding of myriaporone 3/4 to eukaryotic elongation factor 2 kinase. Our study also shows that myriaporone 3/4 in the nanomolar range inhibits in vitro tube formation by endothelial cells without being cytotoxic. In general, myriaporone 3/4 was at least 300 times less toxic to primary cells than to tumor cells.

Screening of small molecules affecting mammalian P-body assembly uncovers links with diverse intracellular processes and organelle physiology.

Processing bodies (P-bodies) are cytoplasmatic mRNP granules containing non-translating mRNAs and proteins from the mRNA decay and silencing machineries. The mechanism of P-body assembly has been typically addressed by depleting P-body components. Here we apply a complementary approach and establish an automated cell-based assay platform to screen for molecules affecting P-body assembly. From a unique library of compounds derived from myxobacteria, 30 specifically inhibited P-body assembly. Gephyronic acid A (GA), a eukaryotic protein synthesis inhibitor, showed the strongest effect. GA also inhibited, under stress conditions, phosphorylation of eIF2α and stress granule formation. Other hits uncovered interesting novel links between P-body assembly, lipid metabolism, and internal organelle physiology. The obtained results provide a chemical toolbox to manipulate P-body assembly and function.

An improved route to (+)-tedanolide and analysis of its subtle effects controlling conformation and biological behaviour.

The improved synthesis of the antitumor compound (+)-tedanolide is described through an aldol coupling of bis-ketone 7. This modification shortens the synthetic steps in the endgame and provides rapid access to this biologically important natural product. Additionally, it serves as a probe in order to unravel the conformational effects that impede or enable its successful synthesis. Having this way access to des-epoxy-tedanolide, its biological characterization surprisingly unravelled the mode of action to resemble candidaspongiolide rather than deoxytedanolide.

Cytotoxic and antivascular 1-methyl-4-(3-fluoro-4-methoxyphenyl)-5-(halophenyl)-imidazoles.

A series of 1-methyl-4,5-diphenylimidazoles 6 with various patterns of m-halogen substitution at the 5-phenyl ring were tested for cytotoxicity in cancer and nonmalignant cell lines and for their capacity to prevent tube formation in HUVEC cultures. Unlike the monofluoro and difluoro derivatives 6a and 6e, the monobromo and diiodo analogs 6c and 6h were strongly cytotoxic and inhibited the polymerization of tubulin and the tube formation by HUVEC. The dibromo derivative 6g displayed a unique selectivity for KB-3-1 cervix and PC-3 prostate cancer cells. It also inhibited the tube formation by HUVEC and the polymerization of tubulin which is indicative of its potential antiangiogenic activity in solid tumors.

Copy-choice recombination during mitochondrial L-strand synthesis causes DNA deletions.

Mitochondrial DNA (mtDNA) deletions are associated with mitochondrial disease, and also accumulate during normal human ageing. The mechanisms underlying mtDNA deletions remain unknown although several models have been proposed. Here we use deep sequencing to characterize abundant mtDNA deletions in patients with mutations in mitochondrial DNA replication factors, and show that these have distinct directionality and repeat characteristics. Furthermore, we recreate the deletion formation process in vitro using only purified mitochondrial proteins and defined DNA templates. Based on our in vivo and in vitro findings, we conclude that mtDNA deletion formation involves copy-choice recombination during replication of the mtDNA light strand.

Investigations on the mode of action of gephyronic acid, an inhibitor of eukaryotic protein translation from myxobacteria.

The identification of inhibitors of eukaryotic protein biosynthesis, which are targeting single translation factors, is highly demanded. Here we report on a small molecule inhibitor, gephyronic acid, isolated from the myxobacterium Archangium gephyra that inhibits growth of transformed mammalian cell lines in the nM range. In direct comparison, primary human fibroblasts were shown to be less sensitive to toxic effects of gephyronic acid than cancer-derived cells. Gephyronic acid is targeting the protein translation system. Experiments with IRES dual luciferase reporter assays identified it as an inhibitor of the translation initiation. DARTs approaches, co-localization studies and pull-down assays indicate that the binding partner could be the eukaryotic initiation factor 2 subunit alpha (eIF2α). Gephyronic acid seems to have a different mode of action than the structurally related polyketides tedanolide, myriaporone, and pederin and is a valuable tool for investigating the eukaryotic translation system. Because cancer derived cells were found to be especially sensitive, gephyronic acid could potentially find use as a drug candidate.

Synthesis of simplified tedanolide analogues--connecting tedanolide to myriaporone and gephyronic acid.

Southern belles! Simplified analogues of tedanolide, a natural product with picomolar activity against a range of tumor cell lines, were synthesized and evaluated for potency in mammalian cancer cells. The truncated analogues were found to retain significant activity in vitro (23 µmol mL(-1) for the example shown) compared with the parent compound tedanolide (0.33 nmol mL(-1)), and represent potential leads for the development of novel anticancer agents.

Novel peptidomimetic compounds containing redox active chalcogens and quinones as potential anticancer agents.

Many types of cancer cells are associated with a disturbed intracellular redox balance and oxidative stress (OS). Among the various agents employed to modulate the intracellular redox state of cells, certain redox catalysts containing quinone and chalcogen moieties have shown considerable promise. Passerini multicomponent reaction has been developed for the synthesis of agents combining two, three or even four redox centers in one molecule in a good yield. When incubated with cancer cells these agents inhibited cell proliferation and induced apoptotic cell death. Interestingly, some of these redox active compounds exhibited quite low toxicity with normal cells. The cause was obviously OS, which was reflected by significant decrease in reduced glutathione, subsequently cell cycle arrest and induction of apoptosis.