Design, Synthesis And Antitumor Activities Of Natural Product Piperlongumine Derivatives

Piperlongumine (PL), an alkaloid, isolated from the fruit of Long pepper, Piper Longum., is a naturally occurring small molecule product with multiple pharmacological activities. It selectively targets and kills tumor cell but leaves normal cell intact. In spite of the low solubility, unclear mechanism of action and others shortcomings, among the multivalent effects, the potential of PL as novel antitumor agent has gained increasing attention recently.According to the theory of Michael acceptor, the isostere and scaffold hopping strategies were used for the structure modification of PL. Forty-nine new six-ring PL derivatives had been synthesized by the modification of C2/C7and benzene-ring of PL. These derivatives were evaluated for in vitro cytotoxicities against cancer cells by MTT assay. The results showed the trimethoxyl group on benzene-ring of PL was not essential to biological activities. Piperlongumine derivatives with halogen substituent as electrophilic group at C2position of showed higher potent activities than piperlongumine. To our surprise, morphine substituents as nucleophilic group at C2substituted piperlongumine were uniformly less than piperlongumine. It was noted that the all the active compounds revealed modest selectivity for human lung normal cells MRC-5and human fetal lung normal cells WI38.On the basis of the favorable in vitro activity and selectivity for normal cells, compounds PL-4and PL-23were selected for further in vivo antitumor activity studies on human lung cancer A549xenograft model. Using DOX as a reference drug, compounds PL-4and PL-23suppressed tumor growth by48.58%and54.62%compared to38.31%of PL. In addition, there is no obvious weight loss in animals treated with compounds PL-4and PL-23.Furthermore, we designed seven-ring lactam PL derivatives based on the design strategy of hCPT and SAR of PL derivatives. Thirty-one new seven-ring PL derivatives were prepared and were evaluated for in vitro cytotoxicities against cancer cells by MTT assay. The results showed all of them were favorable of increasing cellular toxicities. Compound PL-51showed excellent antitumor activities in vitro. In addition, PL-51also indicated potent antitumor activities in vivo with suppressed tumor growth by46.93%on Saos-2cancer xenograft model.The mechanism study of antitumor action found that PL derivatives with high activities showed the characters of multiple targets. PL treatment not only increased the ROS levels in cancer cells, but also acted on multiple kinases such as IRAK and mTOR. Except for increasing ROS levels in tumor cells, compound PL-5can induce the expression of MDM2protein. Compound PL-23was found not to elevate cellular levels of ROS, but it can inhibit mTOR kinase. Meanwhile, it acts on p53-MDM2, NF-κB and Keapl-Nrf2signal pathways. Cell apoptosis and cell cycle assays showed that compounds can induce cell apoptosis and cell cycle arrest. These results showed PL derivatives is a kind of multiple targets of antitumor compounds which is worthy of further study.