Abstract 3519: The polyphenolic ellagitanin vescalagin is a specific inhibitor of the alpha isoform of human DNA topoisomerase II
Authors: Auzanneau Céline , Montaudon Danièle , Jacquet Rémi , Elkaoukabi-Chaibi Assia , Quideau Stéphane , Giorgi Francesca De , Ichas François , Pourquier Philippe 
Published: February 2011

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 (&gt;80% inhibition), whereas vescalagin and methylvescalagin specifically targeted top2a with a reduced effect on top2b (&lt;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.