Antitumor activity of hierridin B, a cyanobacterial secondary metabolite found in both filamentous and unicellular marine strains

Cyanobacteria are widely recognized as a valuable source of bioactive metabolites. The majority of such compounds have been isolated from so-called complex cyanobacteria, such as filamentous or colonial forms, which usually display a larger number of biosynthetic gene clusters in their genomes, when compared to free-living unicellular forms. Nevertheless, picocyanobacteria are also known to have potential to produce bioactive natural products. Here, we report the isolation of hierridin B from the marine picocyanobacterium Cyanobium sp. LEGE 06113. This compound had previously been isolated from the filamentous epiphytic cyanobacterium Phormidium ectocarpi SAG 60.90, and had been shown to possess antiplasmodial activity. A phylogenetic analysis of the 16S rRNA gene from both strains confirmed that these cyanobacteria derive from different evolutionary lineages. We further investigated the biological activity of hierridin B, and tested its cytotoxicity towards a panel of human cancer cell lines; it showed selective cytotoxicity towards HT-29 colon adenocarcinoma cells.

PNL, MC and VR acknowledge funding from FCT – Foundation for Science and Technology (SFRH/BPD/70233/2010, BTI/PTDC/MAR/102638/2008/2010- 025 and SFRH/BD/80153/2011, respectively). This research was partially supported by the European Regional Development Fund (ERDF) through the COMPETE - Operational Competitiveness Programme and national funds through FCT, under the projects PEst-C/MAR/LA0015/2011, PTDC/MAR/102258/2008 and PTDC/ MAR/102638/2008. WHG acknowledges funding from the National Institutes of Health CA100851. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.