Synthesis, Biological Evaluation and Mechanistic Insights of Natural-Product-Inspired Rubrolide Analogues as Antitumor Agents

Abstract

Rubrolides belong to marine derived γ-aromatic butenolides family, which is a steadily growing class of marine natural products with diverse biological properties, especially, antitumor activity. Most of the studies on rubrolides were focused on the discovery of new compounds and preliminary screening of cytotoxic activity, and there were rare reports about their anti-tumor mechanisms and structure-activity relationship. In this work, a series of new rubrolides derivatives were synthesized and characterized, and their cytotoxic activities were screened by MTT assay. Compounds 1, and4,5, 7, 8, 9 all exhibited excellent anti-proliferative activities, especially, compound 7 showed broad-spectrum cytotoxic activity against six tumor cell lines, with IC50 values mostly ranging from 5 μM to 0.01 μM. Their structure-activity relationship indicated that the presence of para-methoxy substitution on the phenyl ring and amino/hydroxy substitutions on the benzyl phenyl ring could enhance the anti-tumor activity of rubrolides derivatives.  Further mechanistic analysis revealed that compound 7 was capable of penetrating HCT116/Hela cells and entering the endoplasmic reticulum, subsequently upregulating the PERK/CHOP pathway, inducing ER stress, elevating intracellular reactive oxygen species (ROS) levels, and ultimately triggering apoptosis in tumor cells. Additionally, compound 7 could upregulate the expression of Cyclin B1 protein, arresting the cell cycle at the G2/M phase. In vivo studies showed that liposomal delivery of compound 7 exhibited potent anti-tumor efficacy against Hela xenograft tumors. Based on above results, marine natural rubrolides derivatives have great potential to be developed as novel antitumor drug lead compounds.

Note:
Funding Information: This work was partially supported by Taishan Scholar Project (tsqn202211112), National Natural Science Foundation of China (82273969, 82073888), Shandong Provincial Natural Science Foundation (ZR2021LSW011), Natural Science Foundation of Shandong Province (ZR2023MH134) and TCM science and technology project of Shandong Province (Q-2023105).

Declaration of Interests: The authors declare no conflict of interest, financial or otherwise.

Ethics Approval Statement: The use of animals was approved by the Ethics Committee of Animal Experimentation of Yantai University (protocol number 20231221) according to the Code of Ethical Conduct for Animal Care and Use.

Keywords: Marine natural products, Rubrolides, derivatives, synthesis, anti-tumor activity, ER stress, apoptosis