Synthesis, Biological Evaluation, and Mechanistic Insights of Rubrolide Analogues as Antitumor Agents

Marine natural products and their analogues have as of now been acknowledged as an important source of bioactive molecules for the treatment of cancer. Rubrolides, a unique group of <i>γ</i>-butenolides derived from marine microorganisms, have shown strong cytotoxic activity against various tumor cells. In this study, we synthesized and characterized 21 rubrolide analogues (including 16 new compounds) and investigated their antitumor activities in order to screen more active molecules and elucidate their mechanism of action. Primary MTT assay showed that compounds <b>1</b> and <b>4</b>-<b>9</b> all exhibited excellent antiproliferative activities. In particular, compound <b>7</b> showed broad-spectrum cytotoxic activity against six tumor cell lines, with IC₅₀ values mostly ranging from 2.5 to 0.2 μM. Further mechanistic studies revealed that compound <b>7</b> could penetrate HCT116 and Hela cells, localize in the endoplasmic reticulum, and upregulate the PERK-eIF2α-CHOP pathway, inducing ER stress and increasing intracellular reactive oxygen species (ROS) levels to ultimately trigger apoptosis in tumor cells. Additionally, compound <b>7</b> was found to upregulate Cyclin B1 protein expression, causing cell cycle reticulum at the G₂/M phase. <i>In vivo</i> studies further demonstrated that liposomal delivery of compound <b>7</b> exhibited a potent antitumor efficacy against Hela xenograft tumors. Based on these results, marine-derived rubrolide analogues show significant potential as novel lead compounds for antitumor drug development.