Conicasterol displays marked cytotoxic activity against human breast adenocarcinoma cell line (MCF-7) with the IC50 value of 6.23 ug/mL.

As a part of our continuing work to find out bioactive lead molecules from marine invertebrates, the CHCl3 fraction of the organic extract of the Red Sea sponge Theonella mirabilis showed cytotoxic activity in our primary screen. Bioassay-guided purification of the active fractions of the sponge's extract resulted in the isolation of two new glycerides, mirabolides A and B (1 and 2), together with the reported 4-methylene sterols, Conicasterol (3) and swinhosterol B (4). The structures of the compounds were assigned by interpretation of their 1D (1H, (13)C), 2D (COSY, HSQC, HMBC, ROESY) NMR spectral data and high-resolution mass determinations.