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

Marine\nnatural products and their analogues have as of now been\nacknowledged as an important source of bioactive molecules for the\ntreatment of cancer. Rubrolides, a unique group of <i>γ</i>-butenolides derived from marine microorganisms, have shown strong\ncytotoxic activity against various tumor cells. In this study, we\nsynthesized and characterized 21 rubrolide analogues (including 16\nnew compounds) and investigated their antitumor activities in order\nto screen more active molecules and elucidate their mechanism of\naction. Primary MTT assay showed that compounds <b>1</b> and <b>4</b>–<b>9</b> all exhibited excellent antiproliferative\nactivities. In particular, compound <b>7</b> showed broad-spectrum\ncytotoxic activity against six tumor cell lines, with IC<sub>50</sub> values mostly ranging from 2.5 to 0.2 μM. Further mechanistic\nstudies revealed that compound <b>7</b> could penetrate HCT116\nand Hela cells, localize in the endoplasmic reticulum, and upregulate\nthe PERK-eIF2α-CHOP pathway, inducing ER stress and increasing\nintracellular reactive oxygen species (ROS) levels to ultimately trigger\napoptosis in tumor cells. Additionally, compound <b>7</b> was\nfound to upregulate Cyclin B1 protein expression, causing cell cycle\nreticulum at the G<sub>2</sub>/M phase. <i>In vivo</i> studies\nfurther demonstrated that liposomal delivery of compound <b>7</b> exhibited a potent antitumor efficacy against Hela xenograft tumors.\nBased on these results, marine-derived rubrolide analogues show significant\npotential as novel lead compounds for antitumor drug development.