| This research focuses on the active constituent plumbagin from Chinese Traditional Medicine Plumbago zeylanica.A series of original creative investigations have been accomplished and some significant outcomes obtained through the strategy of the overlapping of different disciplines, including natural medicine chemistry,coordination chemistry,pharmacology and bioinorganic chemistry.1.Twenty macroelements and microelements were analyzed in the leaves, stems and roots of Plumbago Zeylanica grown in Guangxi province by inductively coupled plasma atomic emission spectrometric(ICP-AES).The results provide useful data for discussing the relationship between the elemental contents in Chinese Traditional Medicine and its activities.2.Basing on natural medicine chemistry,utilizing chromatography method,plumbagin,an anticancer effective constituent of Plumbago Zeylanica and the other two compounds identified as droserone andβ-sitosterol were isolated from the ethanol extract of Plumbago Zeylanica.Their structures were identified by IR,NMR,ESI-MS spectroscopies,and the crystal structure of plumbagin was further confirmed by single crystal X-ray diffraction analysis.3.A series of metal complexes have been synthesized using plumbagin as main ligand.Firstly,twenty plumbagin complexes and its sodium salt, including transition metal,alkali metal,alkaline earth metal and rare earth metal complexes,have been synthesized and structurally determined by elemental analyses,IR,UV,1HNMR,13CNMR and EI-MS spectroscopic methods.The crystal structures of six metal complexes and plumbgin were determined by single crystal X-ray diffraction analysis.Compounds 1-7 are the complexes of plumbagin with Cu(Ⅱ),Co(Ⅱ),Ni(Ⅱ),Zn(Ⅱ),Mn(Ⅱ), Ca(Ⅱ)and Mg(Ⅱ).In complex 1,Cu(Ⅱ)can be described as a four-coordinated square planar geometry.Compound 8 is the sodium salt of plumbagin and exists as ionic compound.Compounds 9-16 are the rare earth complexes of plumbagin with La(Ⅲ),Y(Ⅲ),Dy(Ⅲ),Sm(Ⅲ),Gd (Ⅲ),Nd(Ⅲ),Er(Ⅲ)and Eu(Ⅲ).Compound 17 is binuclear Y(Ⅲ) complex.18 is mononuclear Y(Ⅲ)complex with plumbagin and another ligand from Plumbago Zeylanica.Compounds 19-21 are the ternary complexes with plumbagin and 2,2'-bpy and phen as assistant ligand.In 19, the geometry of Cu(Ⅱ)can be described as five-coordinated distorted square pyramid that exists in a dimer through the weak bonding(Cu...O),and 1-D chain structure is formed by intermolecular hydrogen bonds.Compounds 20 and 21 are dinuclear Zn(Ⅱ)complexes with six-coordinated octahedral geometry and 1-D chain structure.In compound 21,the 2-D structure is formed by intermolecular hydrogen bonds,while the 3-D structure byπ-πstacking interaction.4.The antitumour activites in vitro of the synthesized metal complexes with plumbagin have been investigated.Utilizing MTT methods assayed the antitumour activities in vitro of plumbagin and its fourteen metal-based compounds against ten tumor cell lines,including NIC-460,7860,BEL7404, MCF-7,MGC803,HCT116,HepG2,LOVO,CNE2 and CNE1.It was found that compounds 1,2,19 were the most potent compounds which exhibited remarkably activities against the five cell lines(7860, MCF-7,HCT116,HEPG2,CNE2)compared with the free plumbagin and CCDP,especially against 7860(IC50,3.42μM,2.26μM,2.52μM, respectively).Compound 19 showed a significant activity towards NIC-460 (IC50,1.97μM),which is 20 times stronger than that of CCDP.Compounds 3, 4 showed remarkably activities towards 7860(IC50,2.3μM, 2.29μM).Compounds 7,9,10,11,12,13 showed remarkably activities towards BEL7404(IC50,2.9μM,6.11μM,10.98μM,5.06μM,9.10μM); Compounds 5,7,8,12 better cytotoxic activities towards NIC-460(IC50, 13.36μM,8.1μM,17.27μM,6.98μM).Furthermore,the time- and dosagedependent relationships exist between the inhibition rates of tumor cells and the complexes.In the same time,the inhibitory rates of the tested cells enhance with the concentration of complexes increasing,and the same results are also found under the same concentration.Also,the inhibitory rates of most of complexes against the tested cells are stronger than that of the free ligand and CCDP.5.The bioinorganic chemistry studies on the interactions between metal complexes of plumbagin and DNA have been accomplished.The interactions of plumbagin and its 14 active complexes with calf thymus DNA in tris buffer have been investigated by UV-vis Absorption,Fluorescence Spectroscopy, Circular Dichroism and Cyclic Voltammetry measurements.The main absorption peaks of plumbagin and its complexes display red-shift and hypochromicity with CT-DNA addition,which implys the intercalation mode between the complexes and the double helix of CT-DNA,and the binding constant Kb was found to be in the range of 103-104 M-1(but the Kb value of complex 8 is 5.82×102 M-1due to ionic compound).Moreover,the analysis of the CD and CV spectroscopy,as well as the results of quenching fluorescence and isosbestic point for DNA-EB system with plumbagin and its complexes addition further supported the intercalation mode.Also,the results indicate that the complexes exhibit different DNA-binding affinity,which may be one of the reasons that complexes show different antitumour activities against some cell lines.Therefor,the results suggest that the possible anti-tumor mechanism of the complexes might exist to interfere with DNA replication through the intercalation binding mode,despite the targets maybe involving protein or other molecules.The results herein obtained will provide scientific references for the design and synthesis of the metal-base drugs from effective constituents of Chinese Traditional Medicine,and the research on the synergistic antitumour effects from effective constituents and metal ions.Also,it is significant to elucidate the antitumour action mechanism of plumbagin and its complexes,and quinone antitumour drugs as well as developing the analogous drugs.
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