Research On Chemopreventive Activity And Mechanisms Of Resveratrol Analogues Based On The Double Bond Modifications

Despite decades of research, the treatments of malignant tumors still remain a formidable challenge for public health. Although chemotherapy has been practiced to combat cancer, an increasing trend of chemoresistance and the recurrence of secondary tumors put chemotherapy at the back foot in the fight against cancer. In this context, the search for natural agents with high efficacy and low toxicity as chemopreventive, chemotherapeutic and chemosensitized agents is a key in cancer treatment. One of the promising dietary phytochemicals with chemopreventive and chemotherapeutic potential is resveratrol (3,5,4’-trihydroxystilbene), which has first been isolated from the roots of white hellebore and subsequently identified in various food sources including grapes, peanuts, mulberries, etc. and in more than 70 other plant species. However, the potential use of resveratrol in clinical application has been hindered by its short biological half-life and low bioavailability. The limitations of resveratrol have prompted interest in designing novel resveratrol analogs with improved activities and pharmacologic properties. In this thesis, several resveratrol analogues based on the double bond modifications were synthesized and their related chemopreventive activities were investigated. In addition, their structure-activity relationship and detailed molecular mechanisms were also discussed. The main findings and innovations are as follows:(1) Five hydroxylated phenanthrene compounds as "cis-configuration-fixed" resveratrol analogues differing in the number and the position of the hydroxyl groups were designed and synthesized. Their antioxidant activity was studied by ferric reducing antioxidant power,2,2-diphenyl-l-picrylhydrazyl free radical-scavenging, and DNA strand breakage-inhibiting assays, corresponding to their electron-donating, hydrogen-transfer and DNA-protecting abilities, respectively. In the above assays, their activity depends significantly on the number and the position of the hydroxyl groups, and most of them are more effective than resveratrol. Noticeably, compound 9b (2,4,6-trihydroxyl phenanthrene) with the same hydroxyl group substitutions as resveratrol, is superior to the reference compound, highlighting the importance of extension of the conjugation over multiple aromatic-rings. Similar activity sequences were obtained in different experimental models, but the appreciable differences could contribute detailed insights into antioxidant mechanisms. Based on these results, the hydroxylated phenanthrenes may be considered as a novel type of resveratrol-directed antioxidants.(2) Numerous studies have supported the conclusion that methylated resveratrol analogues increased metabolic stability, most importantly, improved some of their major biological activities.3,5,4’-trimethoxy-trans-stilbene (TM), methoxylated instead of hydroxylated at positions 3,5, and 4’in resveratrol, has been shown to possess improved biological activities and pharmacokinetic properties. To identify the influence of rigidity, flexibility and configuration on its biological activity, several methoxylated resveratrol analogues with changing different configuration and modifying the double bond linkages were constructed. Among the compounds investigated,3,5,4’-trimethoxy-cis-stilbene (ZTM) was the most active with IC50 values of 1.8 μM against the growth of NCI-H460 cells. Flow cytometry studies showed that this compound arrested cell cycle in the G2/M phase. Immunocytochemistry revealed this compound effectively inhibited tubulin polymerization. Docking of compounds with tubulin suggested that these compounds occupy the colchicine binding site.(3) The affinity of a drug toward plasma proteins is an important issue when determining its overall pharmacokinetic profile. The interaction between three series of resveratrol analogs and human serum albumin (HSA) was studied by surface plasmon resonance (SPR) analysis. Structure-activity relationship study provides the important information that the 3,5-OH and double bond functionalities of resveratrol are both essential to its binding with HSA, and the elongation of the conjugated links further improves the binding. Interestingly, resveratrol glucuronide metabolites turned out to be more excellent HSA ligands than its parent molecule. Molecular modeling method suggested that resveratrol analogs could bind within the site I of HSA and the hydrophobic interaction is the predominant binding force.(4) The mode of cisplatin-resistant human ovarian cell line SKOV3/DDP was chosen to probe the ability of resveratrol and curcumin analogs to act as chemosensitizers to cisplatin. An enhanced response of cisplatin-resistant cells to combination treatments of cisplatin and 4,4’-dihydroxystilbene or mono-carbonyl curcumin analogues, was observed. The combination index (CI) for the combination of 12μM cisplatin with 15μM 4,4’-dihydroxystilbene or the mono-carbonyl curcumin analog is 0.394 and 0.395, respectively, clearly indicating a synergistic interaction against cell proliferation. This provides a paradigm in development of resveratrol and curcumin analogs as multidrug resistance reversal agents. However, the detailed cellular mechanism is unclear and needs further study.