Cytotoxic Constituents of the Vietnamese Sea Snail Monodonta labio (Linnaeus, 1758)

Background: Marine molluscs, the most diverse species in ocean, have been recognized as a good source of bioactive compounds. Monodonta labio is a species of top snail belonging to the family Trochidae (class Gastropoda, phylum Mollusca). This is one of the least investigated species with few alkaloids and aminoalkylphosphonyl cerebrosides isolated and identified to date. Methods: We used various chromatographic methods to isolate compounds from the acetone extract of sea snail Monodonta labio. Spectroscopic experiments were used to elucidate the structures of isolated compounds. The cytotoxic activity against three human cancer cell lines as carcinoma (A-549), hepatocellular carcinoma (Hep3B), and cervical adenocarcinoma (Hela) was evaluated by an MTT assay. Results: Two new tetrahydropyran derivative diastereoisomers; namely monodontins A (1) and B (2), together with twelve known compounds as rivularin A (3), 2-hydroxy-1-(4-hydroxyphenyl)-1,4-pentanedione (4), L-thymidine (5), thymine (6), 5β,6-epoxy-cholestan-3β-ol (7), melithasterol A (8), 5α,6α-epoxy-3β,7α-dihydroxycholest-8(14)-ene (9), cholesta-3β,5α,6β-triol (10), cholest-7-ene-3β,5α,6β-triol (11), cholest-5-ene-3β,7β-diol (12), cholest-5-ene-3β,7α-diol (13), and 3β-hydroxycholesta-5,8-dien-7-one (14), were isolated from the acetone extract of sea snail Monodonta labio. Among the isolated compounds, compound 3 exhibited the most potent cytotoxic activity on A-549 cell line with an IC50 value of 0.04±0.01 μM and strong effect on Hep3B cell line with an IC50 value of 0.82±0.13 μM. Compounds 4 and 8 showed selective and strong activity against only A-549 cell line (IC50 = 1.92±0.79 and 2.14± 0.16 μM). Conclusion: The obtained results suggested that the constituents from Monodonta labio contained potent cytotoxic compounds and might be potential candidates for further molecular mechanism-of-action studies.