The use of natural products as chemotherapeutic agents is well established. However, many are associated with undesirable side effects, including high toxicity and instability. Previous reports on the cytotoxic activity of
pyrroloiminoquinones isolated from Latrunculid sponges against
cancer cell lines revealed extraordinary activity at IC50 of 77nM for discorhabdins. Their general lack of selectivity against the
cancer and normal cell lines, however, precludes further development. In this study, extraction of a South African Latrunculid sponge produced three known
pyrroloiminoquinone metabolites (14-bromodiscorhabdin C (5),
Tsitsikammamine A (6) and B (7)). The assignment of the structures was established using standard 1D and 2D NMR experiments. To mitigate the lack of selectivity, the compounds were loaded onto
gold nanoparticles synthesized using the aqueous extract of a brown seaweed, Sargassum incisifolium (sAuNPs). The cytotoxicity of the metabolites alone, and their sAuNP conjugates, were evaluated together with the known
anticancer agent doxorubicin and its AuNP conjugate. The compound-AuNP conjugates retained their strong cytotoxic activity against the MCF-7 cell line, with >90% of the
pyrroloiminoquinone-loaded AuNPs penetrating the cell membrane. Loading cytotoxic natural products onto AuNPs provides an avenue in overcoming some issues hampering the development of new anticancer drugs.