Rémi Jacquet

The polyphenolic ellagitannin vescalagin acts as a preferential catalytic inhibitor of the α isoform of human DNA topoisomerase II.

Polyphenolic ellagitannins are natural compounds that are often associated with the therapeutic activity of plant extracts used in traditional medicine. They display cancer-preventing activity in animal models by a mechanism that remains unclear. Potential targets have been proposed, including DNA topoisomerases II (Top2). Top2α and Top2β, the two isoforms of the human Top2, play a crucial role in the regulation of replication, transcription, and chromosome segregation. They are the target of anticancer agents used in the clinic such as anthracyclines (e.g., doxorubicin) or the epipodophyllotoxin etoposide. It was recently shown that the antitumor activity of etoposide was due primarily to the inhibition of Top2α, whereas inhibition of Top2β was responsible for the development of secondary malignancies, pointing to the need for more selective Top2α inhibitors. Here, we show that the polyphenolic ellagitannin vescalagin preferentially inhibits the decatenation activity of Top2α in vitro, by a redox-independent mechanism. In CEM cells, we also show that transient small interfering RNA-mediated down-regulation of Top2α but not of Top2β conferred a resistance to vescalagin, indicating that the α isoform is a preferential target. We further confirmed that Top2α inhibition was due to a catalytic inhibition of the enzyme because it did not induce DNA double-strand breaks in CEM-treated cells but prevented the formation of Top2α- rather than Top2β-DNA covalent complexes induced by etoposide. To our knowledge, vescalagin is the first example of a catalytic inhibitor for which cytotoxicity is due, at least in part, to the preferential inhibition of Top2α.

Binding of Filamentous Actin and Winding into Fibrillar Aggregates by the Polyphenolic C-Glucosidic Ellagitannin Vescalagin†

Herein we describe the effects of the C-glucosidic ellagitannin vescalagin (1, Figure 1a), a polyphenolic natural product readily available from fagaceous woody plant sources, such as oak (Quercus sp.), on actin, one of the most abundant structural proteins in eukaryotic cells. Monomeric globular actin (G-actin) subunits assemble through an adenosine triphosphate (ATP) dependent process into polymeric fibrillar actin (F-actin) filaments, which are further ordered into three-dimensional architectures to establish the functional actin cytoskeleton. A dynamic equilibrium between the G-actin and F-actin states continuously ensures the adaptation of the actin cytoskeleton during its various roles in controlling cell shape, cytokinesis, motility, adhesion, and gene expression. Natural products have been key players in probing the role of actin by perturbing the assembly and/or disassembly of actin filaments. The bicyclic heptapeptide fungal metabolite phalloidin and the cyclodepsipeptide sponge or microbial metabolites jasplakinolide and chondramide C bind to F-actin and inhibit depolymerization by strengthening actin–actin

Biological activity of ellagitannins: Effects as anti-oxidants, pro-oxidants and metal chelators

Ellagitannins are a subclass of hydrolysable tannins that have been suggested to function as defensive compounds of plants against herbivores. However, it is known that the conditions in the digestive tracts of different herbivores are variable, so it seems reasonable to anticipate that the reactivities and modes of actions of these ingested defensive compounds would also be different. A previous study on a few ellagitannins has shown that these polyphenolic compounds are highly oxidizable at high pH and that their bioactivity can be attributed to certain structural features. Herein, the activities of 13 ellagitannins using the deoxyribose assay were measured. The results provided information about the anti-oxidant, pro-oxidant and metal chelating properties of ellagitannins. Surprisingly, many of the tested ellagitannins exhibited pro-oxidant activities even at neutral pH and only moderate to low radical scavenging activities, although the metal chelating capacities of all tested ellagitannins were relatively high.

Remarkable Biomimetic Chemoselective Aerobic Oxidation of Flavano‐Ellagitannins Found in Oak‐Aged Wine

Under the auspices of Bacchus! Acutissimins, natural flavano-ellagitannins, occur in oak-aged wine as a result of a diastereoselective condensation reaction of the flavan-3-ol catechin, a component of grapes, with the C-glucosidic ellagitannin vescalagin, found in oak. The acutissimins are further converted into natural mongolicains and analogues of camelliatannin G in a remarkably chemoselective fashion by simple aerobic oxidation.

Hemisynthesis and Structural and Chromatic Characterization of Delphinidin 3-O-Glucoside–Vescalagin Hybrid Pigments

During red wine maturation in the presence of oak wood, reactions involving anthocyanins and ellagitannins might affect wine organoleptic properties such as color and astringency. In this work, the condensation reaction between myrtillin (delphinidin 3-O-glucoside) and vescalagin has been performed to determine the behavior of this anthocyanin in this kind of reaction and to assess the possible impact of such a reaction in wine color modulation. Two different hybrid pigments have been hemisynthetized and characterized by HPLC-DAD-MS and NMR spectroscopy. These pigments have been identified as 1-deoxyvescalagin-(1β→8)-myrtillin (major) and 1-deoxyvescalagin-(1β→6)-myrtillin (minor). The minor pigment could be formed both by the condensation reaction and by a regioisomerization process from the major pigment. Moreover, the chromatic properties of these pigments have been studied and compared to those of myrtillin. The hybrid pigments showed an important bathochromic shift (ca. 20 nm) in the maximum absorbance wavelength and lower molar absorption coefficients.

Abstract 3519: The polyphenolic ellagitanin vescalagin is a specific inhibitor of the alpha isoform of human DNA topoisomerase II

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC Polyphenolic ellagitanins are natural structurally complex molecules that are often associated with the therapeutic activity of plant extracts used in traditional medicine. Studies have reported their cancer-preventing activity in animal models at concentrations found in diets. In vitro, some derivatives display cytotoxic activities at micromolar concentrations and induce apoptosis by a mechanism which remains unclear. Potential targets have been proposed, including topoisomerases (top) I and II, which are involved in the regulation of DNA topology during replication, transcription and chromosome segregation. The two human isoforms of top2: top2 alpha (top2a) and top2 beta (top2b) are the target of anticancer agents such as doxorubicin or etoposide. It is known that antitumoral activity of etoposide is primarily due the inhibition of the alpha isoform whereas inhibition of the beta isoform is primarily responsible for the development of secondary malignancies, pointing to the need for more selective top2a inhibitors. Here, we report the differential activity on top2a and top2b of new polyphenolic ellagitanins: vescalagin, methylvescalagin, acutissimin B (acuB) and epiacutissimin B (epiacuB). Using kinetoplast DNA as a substrate, we showed that top2a-mediated decatenation was strongly inhibited by all 4 derivatives at 1 µM concentration, whereas no significant inhibition of top2b could be seen. When used at 10 µM, acuB and epiacuB inhibited both isoforms and were even more active on top2b (>80% inhibition), whereas vescalagin and methylvescalagin specifically targeted top2a with a reduced effect on top2b (<20% inhibition). Vescalagin could also specifically poison top2a in treated CEM cells, since it could induce an increase in covalent top2a-DNA but not top2b-DNA cleavage complexes as detected by the immuno complex of enzyme (ICE) assay. We showed that top2a mutated CEM-VM1 etoposide-resistant cells were also resistant to vescalagin, but were still sensitive to ICRF193 suggesting that vecsalagin is a top2a poison. Using alkaline elution technique we also showed that treatment of CEM cells with 50 µM vescalagin (2h) did not induce detectable double-strand breaks conversely to etoposide. This was confirmed by the absence of gH2AX detection. Surprisingly, vescalagin could induce a significant amount of single-strand breaks. Whether generation of these single-strand breaks is mediated by top2a poisoning and is the cause of cell growth inhibition remains to be investigated. Together our preliminary data identified vescalagin as a new potent and specific top2a poison that could be used as a lead to generate alternative top2 inhibitors with reduced chances to develop secondary malignancies. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3519.