Marine organisms are rich sources of polycyclic pigments. Pyridoacridine alkaloids are an important class of marine-derived heteroaromatic pigments, many of which possess cytotoxic activity. Amphimedine (1), isolated from an Amphimedon sp. sponge,1 constitutes the first example of this type of alkaloid from a marine organism. Pyridoacridines are not exclusive to sponges (phylum Porifera) and have been reported from other marine phyla, such as Urochordata, Cnidaria, and Mollusca.2 In the search for new anticancer metabolites from marine animals, our research group recently published the isolation of neoamphimedine from a Philippine Xestospongia sp. and Xestospongia cf. carbonaria from Micronesia.3 Neoamphimedine (2) is a new topoisomerase II inhibitor that induces catenation of plasmid DNA by mammalian topoisomerase II. We now report the isolation and structural elucidation of a new pyridoacridine alkaloid, deoxyamphimedine (3), along with amphimedine (1) and neoamphimedine (2), from two specimens of a Xestospongia sp., collected from the Philippines and Palau. Comparative bioactivity studies reveal that, unlike amphimedine (1) and neoamphimedine (2), deoxyamphimedine (3) appears to damage DNA through the production of reactive oxygen species.