Background Several studies have been reported previously on the bioactivities of different extracts of marine
molluscs. Therefore, we decided to evaluate the cytotoxic and antimicrobial activities of S. pharaonis ink as a highly
populated species in the Red Sea. We extracted the flavonoids from the ink and analyzed their composition. Then we evaluated systematically the cytotoxic and antimicrobial properties of this extract. A pharmacokinetic study was also conducted using SwissADME to assess the potential of the identified flavonoids and phenolic compounds from the ink extract to be orally active drug candidates.

Results Cytotoxic activity was evaluated against 5 cell lines (MCF7, Hep G2, A549, and Caco2) at different
concentrations (0.4 μg/mL, 1.6 μg/mL, 6.3 μg/mL, 25 μg/mL, 100 μg/mL). The viability of examined cells was reduced by the extract in a concentration-dependent manner. The highest cytotoxic effect of the extract was recorded against A549 and Hep G2 cancer cell lines cells with IC50 = 2.873 and 7.1 μg/mL respectively. The mechanistic analysis by flow cytometry of this extract on cell cycle progression and apoptosis induction indicated that the extract arrests the cell cycle at the S phase in Hep G2 and MCF7, while in A549 cell arrest was recorded at G1 phase. However, it causes G1 and S phase arrest in Caco2 cancer cell line. Our data showed that the extract has significant antimicrobial activity against all tested human microbial pathogens. However, the best inhibitory effect was observed against Candida albicans ATCC 10,221 with a minimum inhibitory concentration (MIC) of 1.95 μg/mL. Pharmacokinetic analysis using Swiss ADME showed that most flavonoids and phenolics compounds have high drug similarity as they satisfy Lipinski’s criteria and have WLOGP values below 5.88 and TPSA below 131.6 Å2.

Conclusion S. pharaonis ink ethanolic extract showed a promising cytotoxic potency against various cell lines and
a remarkable antimicrobial action against different pathogenic microbial strains. S. pharaonis ink is a novel source
of important flavonoids that could be used in the future in different applications as a naturally safe and feasible
alternative of synthetic drugs.

Keywords Flavonoids, Red Sea, Cytotoxicity, Cephalopods, Antimicrobial activity