Study On Anti-cancer And Anti-inflammatory Mechanism Of Isoliquiritigenin And Its Analogs

Compared with normal cells,cancer cells exhibit increased ROS levels to maintain their malignant phenotypes such as uncontrolled proliferation,invasion,and metastasis.Thus,cancer cells as a kind of already stressed cells are more vulnerable to further ROS production.This favours a prooxidant strategy to design anticancer agents because they are capable of selectively killing cancer cells by ROS production.Additionally,chronic inflammation is closely involved in development of cancer,thus developing anti-inflammatory agents is crucial for cancer chemoprevention and chemotherapy.Natural products with extraordinarily diverse chemical scaffolds provide an important source of inspiration for designing anticancer agents.Isoliquiritigenin(ISL),isolated from the roots of licorice,is a chalcone-based Michael acceptor molecule with a wide range of pharmacological effects despite of its structural simplicity.It has been identified as a promising anticancer agent by targeting ROS signaling.However its structural determinants and mechanisms underlying its anticancer activity remain to be elucidated.For example,whether its activity is Michael acceptor unit-dependent? How do hydroxyl groups on the two aromatic A and B rings influence its activity? How do ROS mediate death of cancer cells? Accordingly,we synthesized ISL and its analogs where the reduced analogs(ISL-1 and ISL-5)and the others(ISL-2,ISL-3 and ISL-4)were used to probe influence of Michael acceptor unit and hydroxyl groups on its activity,respectively.On this basis,we tried to find more potent anticancer and anti-inflammatory agents than this parent ISL,and explored their action mechanisms.The main contents are summarized as follows:(1)We selected initially human hepatoma HepG2 cells as a model to probe the structural determinants for cytotoxicity of ISL.It was found that the Michael acceptor unit is indispensible for recapitulating cytotoxicity observed for ISL,2-and 4-OH on the aromatic A ring contribute to its Michael acceptor-dependent activity but 4'-OH on the aromatic B ring weakens its activity.ISL-2 surfaced as a lead exhibiting more potent cytotoxicity than this parent ISL.This molecule failed to induce apoptosis of HepG2 cells,but arrested the cell cycle in the G2/M phase by up-regulation of P21 and down-regulation of Cdc25 C and Cdk1 in a Michael acceptor-dependent but ROS-independent fashion.(2)The same structure-activity relationship(SAR)as described in HepG2 cells was observed in human fibrosarcoma HT1080 cells.Among the test molecules,ISL-2 displayed the most cytotoxicity against HT1080 cells with the IC50 value of 14.5 ?M.Mechanistic study uncovers that and this molecule induces G2/M phase arrest and mitochondria-dependent apoptosis in a Michael acceptor-and ROS-dependent fashion.(3)Employing RAW264.7 cells stimulated by lipopolysaccharide(LPS)as a model of inflammation,we identified ISL-2 as the novel and promising anti-inflammatory agent displaying better activity than the parent ISL.Mechanistic investigaton implies that by virtue of its Michael acceptor,ISL-2 exert anti-inflammatory activity through inhibiting IKK/I?B-NF-?B signaling pathway,which was achieved at various stages by blocking MAPKs activation,preventing phosphorylation of IKK?/?,stabilizing the suppressor protein IkB?,and interfering with subsequent nuclear translocation of NF-?B,an important signal transduction factor in the inflammatory response,and final expression of iNOS and COX-2 stimulated by LPS.