Scytonemin extracted from Lyngbya aestuarii exhibits anti-cancer activity: involvement of c-Myc pathway inhibition

The increasing incidence of cancer-related morbidity and mortality underscores the urgent need for novel, less toxic therapeutic options. In this study, we isolated scytonemin from the marine cyanobacterium Lyngbya aestuarii. Its identification was confirmed through an absorption peak at 384 nm and MALDI-TOF MS analysis showing a [M + H]⁺ ion at m/z 545.838, consistent with its oxidised form (C₃₆H₂₀N₂O₄). Scytonemin demonstrated significant cytotoxicity against breast cancer cell lines MDA-MB-231 and MCF-7, with IC₅₀ values of 8 μM and 4 μM, respectively, while remaining non-toxic to human peripheral blood lymphocytes (HPBLs). The compound rapidly induced caspase-dependent intrinsic apoptosis within 2 h, with apoptotic effects magnifying at 24 and 48 h. Molecular docking and reporter gene assays revealed that scytonemin inhibits two critical proteins associated with cancer progression c-Myc and Polo-like kinase 1 (PLK1). These results suggest that scytonemin holds promise as a lead compound for the development of targeted anti-cancer therapies.