New bioactive pyrrole alkaloid isolated from the Saudi Red Sea sponge <i>Stylissa carteri</i> with potential anticancer property against human lung adenocarcinoma cell line, and possible mechanisms

Chemical investigation of a MeOH extract of the Red Sea sponge <i>Stylissa carteri</i>, offered a new bromopyrrole alkaloid named stylisinone (<b>1</b>) along with other eight pyrrole alkaloids. The structures were established by comprehensive spectroscopic analyses of NMR and MS, as well as by comparison with the literature. The <i>in vitro</i> anticancer activity of the isolated alkaloids was evaluated against human cancer cell lines, HepG2, MCF-7, LS513, A549, and THP1, and BM as normal mice cells. The results showed that stylisinone had the highest cytotoxicity against the A549 cell line, with IC₅₀ values at 24.08 µM, respectively. The new metabolite stylisinone caused strong cell cycle arrest at sub G1 and G2/M (22.43-fold and 2.28-fold, respectively), indicating its potential as an antitumor agent. Furthermore, stylisinone showed a marked increase in Annexin V-FITC necrotic cells (from 1.23 to 21.38%), making this molecule an attractive candidate for further mechanism of action studies.