Cytotoxic furanosesquiterpenoids and steroids from Ircinia mutans sponges

Abstract

Context: Ircinia mutans Wilson (Irciniidae) is a sponge with antimicrobial and cytotoxic constituents.

Objective: Our objective was to characterise the cytotoxic constituents of two seasonal collections of I. mutans.

Materials and methods: The sponges were extracted in methanol-dichloromethane and their constituents were purified and characterised using column chromatography, GC-MS, 1 D and 2 D NMR. Anti-proliferative activities of the compounds, were evaluated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric assay (0.25-100 μg/mL, 72 h) against leukaemia (MOLT-4), breast (MCF-7) and colon cancer (HT-29) human cells.

Results: Three furanosesquiterpoids; furodysin (1), ent-furodysinin (2) and furoircin (3) and ten sterols were characterised in I. mutans, for the first time. Cholesterol (4), cholesta-5, 7-dien-3β-ol (5) and ergosterol (6) were determined in the sponge from the winter collections, while cholesta-5, 22-dien-3β-ol (7), 24-methyldesmosterol (8), campesterol (9), stigmasterol (10), γ-ergostenol (11), chondrillasterol (12) and γ-sitosterol (13) were detected in the summer samples. The steroids from the winter collection exhibited cytotoxic activity with IC₅₀ values of 13.0 ± 0.9, 11.1 ± 1.7 and 1.1 ± 0.4 µg/mL, against the mentioned cancer cell lines, respectively, while those from the summer sample, showed greater activity, IC₅₀ = 1.1 ± 0.2 μg/mL against MOLT-4. The purified steroids showed potent MOLT-4 cytotoxic activity, IC₅₀ values = 2.3-7.8 µg/mL.

Discussion and conclusion: The present study suggests that I. mutans is a rich source of cytotoxic steroids, and introduces 3 as new natural product. Considering the high cytotoxic activity of the steroids, these structures could be candidates for anticancer drug development in future research.

Keywords: Furanosesquiterpenes; cholesterol; ergosterol; marine sponge; stigmasterol; γ-sitosterol.

Figure 1.

Structures of furodysin (1), furodysinin (2), and furoircin (3) isolated from Ircinia mutans.

Figure 2.

Structures of steroids identified from Ircinia mutans.

Figure 3.

HPLC chromatograms of the subfraction FS6-10- F25-29 (steroids fraction) isolated from I. mutans (summer sample).

Figure 4.

GC-MS chromatograms of FH2-FH5 of the HPLC semi-purified compounds 4–13 from FS6-10- F25-29 (steroids fraction) isolated from I. mutans (summer sample).

Figure 5.

Cytotoxic activity of compounds isolated from I. mutans collected in winter (A) and summer (B) against three human cancer cell lines. Values are presented as mean ± S.E.M. of 3–5 experiments. *Compound 1w was not active against MOLT-4 and MCF-7 cell lines; IC₅₀ > 100 µg/mL. **Compounds 4–13 were not tested against MCF-7 and HT-29 cell lines.

Figure 6.

Cytotoxic activity of RP4-HPLC purified steroids isolated from I. mutans (summer sample) against human lymphoblastic leukaemia cell line. Values are presented as mean ± S.E.M. of 3-5 experiments. FH2: Compounds: 5, 6, 7 and 8, FH3: compound 4, FH4: compounds 4, 9, 10, 11 and 12; FH5: compound 13. Based on statistical analysis, cytotoxic activity of FH2 has significant difference with other fractions (p < 0.05) while FH4 and FH5 were not significantly different compared to that of cisplatin as a positive control (p > 0.05).