Activity And Mechanism Of Multi-conjugated Resveratrol Analogs And Curcuminoids As Antioxidants And Cancer Chemopreventive Agents

Reactive oxygen species (ROS), as a double-edged sword, not only play an important role in cell signaling pathway as a second messenger, but have the potential to cause cellular damage. Excessive production of ROS (oxidative stress) can induce cell membrane lipids, DNA and protein oxidative damage, leading to cancer, aging and degenerative diseases. However, the intake of dietary antioxidants can be effective in the prevention and treatment of these diseases due to their ability to neutralize ROS. In my dissertation, several series of analogs with natural antioxidants and cancer chemopreventive agents such as resveratrol and curcumin as the lead compounds were designed and synthesized by elongating their conjugated links, and their antioxidant, prooxidant and cancer chemopreventive activities were investigated. In addition, their structure-activity relationship (SAR) and the detail mechanisms were also discussed. The main creative results are as follows:1. From a free radical chemistry point of view, the high free radical-scavenging activity (antioxidant activity) of phenolic compounds relies on the resonance stabilization of the resulting phenoxyl radicals. Therefore, we constructed eight hydroxystilbenoid compounds with elongation of the conjugated links of resveratrol via the Wittig-Horner reaction, in which six analogs (compounds B2-B6 and C1) were new compounds, and evaluated their antioxidant, cytotoxic and apoptosis-inducing activities. To the best of our knowledge, it is the first time to systematically compare the biological effects of hydroxystilbenoid compounds with elongation of the conjugated links. Our results suggest that elongation of the conjugated links is an important strategy to improve antioxidant activity of resveratrol analogs including hydrogen atom- or electron-donating ability in homogeneous solutions and anti-haemolysis activity in heterogeneous media. Most impressively, C3, a triene bearing 4,4’-dihydroxy groups, surfaced as an important lead compound, displaying remarkably increased cytotoxic, and apoptosis-inducing activities against cancer cells by comparison with resveratrol.2. As the instability of curcumin under physiological conditions, we selected two series enone analogs of curcumin with changes in aryl substitution pattern and central methylene structure, and evaluated their stability in PBS (pH 7.4), antioxidant, cytotoxic, apoptosis-inducing activities and their effect on the cell cycle. The main findings are as follows:(a) The stability of curcumin analogs depends not only on substitution pattern on the aromatic ring, but also on changes in the central methylene structure; (b) Phenolic hydroxyl group of curcumin analogs plays a major role in the ABTS·+-scavenging reaction, and their enolic hydroxyl group also contributes the reaction; (c) Compared to curcumin, the compounds with more potent cytotoxicity show increased stability, and compound 9 with 5-carbon linker exhibited increased stability, cytotoxic and apoptosis-inducing activities by comparision with curcumin; (d) Cytotoxicity of curcumin analogs is related to the accumulation of cells in the G2/M phase of cell cycle.3. It is believed that the active methylene group of curcumin contributes to its instability under physiological conditions. Therefore, we synthesized two curcumin analogs 13 and 14, in which twoα,β-unsaturated carbonyl moieties (Michael reaction acceptor) and two o-methoxyl phenol units were retained, but the methylene group was omitted by Knoevenagel condensation and insertion of the benzene ring, respectively. It was found that compounds 13 and 14 exhibited remarkably increased stability, lipophilicity as well as cytotoxic, apoptosis-inducing and cell cycle arrest activities against HepG2 cells compared with curcumin. They could induce the cytotoxicity and apoptosis in HepG2 cells through the increase of intracellular ROS levels (prooxidant action) and the loss ofΔΨm. More importantly, the high cytotoxic and apoptosis-inducing activities of 13 and 14 are obviously due to their high prooxidant activity. Furthermore, we evaluated their electron-transfer ability by ABTS’+-scavenging experiment and oxidative potential determination, and eletrophilicity (Michael reaction acceptor activity) using UV-visible spectroscopy, NMR and MS. It was found that 13 was most active as a Michael reaction acceptor among the compounds examined. This outcome is in accordance with its highest cytotoxic, apoptosis-inducing activities, suggesting that Michael reaction acceptor activity plays an important role in promoting the formation of ROS and changing cellular redox state. Although substantiation of this prooxidant-mediated apoptosis mechanism will require further studies, our results provide important information for design of curcumin-oriented and prooxidant-based cancer chemoprevention agents.To sum up, our data provide theoretical and experimental evidences for design of resveratrol-and curcumin-oriented cancer chemoprevention agents.