Insights into the potential of picoplanktonic marine cyanobacteria strains for cancer therapies – Cytotoxic mechanisms against the RKO colon cancer cell line

• Two picocyanobacterials strains revealed anticancer activity in RKO colon carcinoma cells.
• Chemically characterized fractions of Cyanobium sp. and Synechocystis salina were tested.
• Cyanobium sp. altered protein networks, which extended from endoplasmic reticulum stress to proteasome degradation.
• Exposure to Synechocystis salina induced apoptosis and resulted in a cell cycle arrest at the G2/M transition.
• Bioactive compounds present in fractions targeted cancer cells via different molecular mechanism.

PurposeIn this work, we analysed the potential of picoplanktonic marine cyanobacteria strains as a source of anticancer compounds by elucidating the cytotoxic mechanisms of an ethyl acetate fraction of Cyanobium sp. (LEGE06113) and the Synechocystis salina (LEGE06155) on the RKO colon adenocarcinoma cell line.MethodsCytotoxicity was analysed by MTT. Effects on cells were evaluated by mRNA expression of cell cycle and apoptotic genes, flow cytometry (cell cycle), qualitative and quantitative fluorescence microscopy (apoptosis), and quantitative proteomics.ResultsIC50 values were 27.01 and 8.03 μg/ml for Cyanobium sp., and 37.71 and 17.17 μg/ml for Synechocystis salina, after 24 h and 48 h, respectively. Exposure to the Cyanobium sp. fraction increased 2.5 fold BCL-2 mRNA expression (p < 0.05), and altered proteins (13, p < 0.05) belonged to apoptosis (PSMA5, PSMA7, TPT1, UBE2K), cell cycle (EIF4E, PCNA), cellular metabolism (AHSG, GLO1, ATP5H, HSP90AB1, NME1, HNRNPC) and cell structure (KRT10). Exposure to the Synechocystis salina fraction decreased 2fold CCNB1 mRNA expression (p < 0.05). Accordingly, flow cytometry demonstrated a decrease of cells in the G0/G1 and S phase (p < 0.05), indicating a cell cycle arrest at the G2/M transition. Fluorescence microscopy confirmed a higher level of apoptosis compared to the solvent control group (p < 0.01). Altered proteins (6, p < 0.05) belonged to apoptosis (HSPD1, UBE2K), protein metabolism (PKM, PDIA3) and cell structure (KRT10, KRT1).ConclusionSince induction of cytotoxicity is a very broad parameter, the study demonstrates the potential of picocyanobacteria to produce bioactive compounds that target cancer cells via different molecular mechanisms.