New polyhydroxy sterols:: Proteasome inhibitors from a marine sponge Acanthodendrilla sp.

Seven new polyhydroxylated sterols, as well as the known agosterols A, C, and D-2 (8-10), were isolated from a marine sponge Acanthodendrilla sp. as proteasome inhibitors. Their structures were elucidated on the basis of their spectral data, and they were characterized as agosterol congeners, which had been initially isolated from a marine sponge Spongia sp. and reported to reverse multidrug resistance in tumor cells. Among them, agosterol C (9) most strongly inhibited chymotrypsin-like activity of the proteasome with an IC50 value of 10 mug/mL.