Cytotoxic scalarane-type sesterterpenes from the Saudi Red Sea sponge Hyrtios erectus.

The CHCl3/MeOH extract of the marine sponge Hyrtios erectus showed cytotoxicity against three cancer cell lines HepG2, A549, and PC-3 with IC50 0.055, 0.044, and 0.023 μg/ml, respectively. The CH2Cl2 soluble fraction afforded three scalarane sesterterpenes (1-3) along with a cholestane derivative (4) and an indole alkaloid (5). Chemical structures were established by spectroscopic techniques and comparison with data reported in the literature. Scalarinol (1) was found as a new metabolite, while heteronemin (2) and 12-O-deacetyl-19-deoxyscalarin (3) are known compounds. 1-3 exhibited cytotoxic activity against the cancer cell lines with IC50 values ranging from 14 to 230 μM. The molecular affinity to the DNA was employed as marker to examine the proposed mechanism of cytotoxic activities. Compound 2, with IC50 28 μg/ml, displayed the highest affinity to the DNA.