Studies On The Synthesis, Characterization And Antitumor Activity Of The Schiff Base Complexes

Schiff base and its metal complexes have been proved to have biological activities, such as anti-cancer, antibacterial, and interactions with DNA, which causes widespread concern in the scientific community. In recent years, several reports on anti-tumor activity of the Schiff base metal complexes have been published. However, there are rarely reports about the mechanism of Schiff base metal complexes as the proteasome inhibitor to induce apoptosis in cancer cells. As an important way for degradation of eukaryotic cells, Ubiquitin-proteasome pathway (UPP) causes wide concern in the treatment of tumor. UPP is the major proteolytic mechanism which plays a critical role in the degradation of the proteins involve in the cell cycle control and tumor growth, such as cyclin-dependent kinases, P53 , Bax, IκB and so on. Specified block the UPP, then inhibiting the degradation of such protein should have profound effects on tumor cells proliferation and cause cells to undergo apoptosis. So the proteasome inhibitor is useful compound to targeting this pathway in cancer therapy.In this dissertation, we synthesis several Schiff base metal complexes, then use proteasome activity and MTT assay to got several copper and zinc Schiff base complexes which can inhibit 26S proteasome activity and proliferation ability in cancer cell lines. The mechanism of these complexes to inhibit proteasome and induce apoptosis in MDA-MB-231 and Jurkat T cancer cells were studied, and make sure the antitumor target of those complexes is proteasome. The details of the contents are as follows,(1) 11 taurine Schiff base complexes were synthesized, and theirs proteasome inhibit activity were studied. The results showed that all of the copper complexes could inhibit the 26S proteasome activity, MTT assay showed that only taurine Schiff base copper phen complex (Y6) have anti-proliferation activity in cancer cells. Y6 potently inhibits chymotrypsin-like activity of purified 20S, the IC50 is 12μM. The experiment also showed that Y6 potently inhibits chymotrypsin-like activity of 26S proteasome and induce apoptosis in human breast cancer MDA-MB-231 in dose and time dependent manner; Trypan blue assay showed that Y6 could induce cell death in dose dependent manner, and Y6 potently inhibits activity of 26S proteasome and induce apoptosis in leukemia Jurkat T cells in dose and time dependent manner. The mechanism of Y6 induce apoptosis in these two cancer cells are same. Our results strongly suggest that Y6 are potent proteasome inhibitors.(2)The novel Schiff base ligand (KL) which is derived from 3,5-dibromotyrosine and o-vanillin has been prepared, and it's 5 complexes have been synthesized. Those ligand and complexes were characterized by elemental analysis, IR spectroscopy, UV spectroscopy, TG-DTG analysis and molar conductance analysis. The suggested structure of the complexes are confirmed to be[CuL (CH₃COO)(CH₃OH)]·2H₂O,[ZnL (CH₃COO)(CH₃OH)]·H₂O,[CdL (CH₃COO) (CH₃OH)]·H₂O,[La LNO₃] NO₃·H₂O,[SmLNO₃] NO₃·H₂O.The kinetic equations of thermal decomposition for complexes and the corresponding kinetic parameters were gained.The detail are as follows, The thermal decomposition kinetic function of [CuL(CH₃COO)(CH₃O H)]·2H₂O in step 3 may be expressed as f(α)=1/3(1-α)[-ln(1-α)]-2, and the kinetic equation of thermal decomposition may be expressed as dα/dt = A·e-E/RT·f(α) = 1/3A·e-E/RT (1-α)[-ln (1-α)]-2,E = 327.03 kJ/mol,lnA =55.24,r = 0.9952,â–³S≠=-209.48J/mol·K,â–³G≠=112.58 kJ/mol.The thermal decomposition kinetic function of [ZnL (CH₃COO)(CH₃OH)]·H₂O in step 2 may be expressed as f(α)=1/3(1-α)[-ln(1-α)]-2, and the kinetic equation of thermal decomposition may be expressed as dα/dt = A·e-E/RT·f(α) = 1/3A·e-E/RT (1-α)[-ln(1-α)]-2,E = 471.70 kJ/mol,lnA =82.58,r = 0.968,â–³S≠=-436.19J/mol·K,â–³G≠=-220.45 kJ/mol.The thermal decomposition kinetic function of [SmLNO₃] NO₃·H₂O in step 2 may be expressed as f(α)=1/4(1-α) [-ln(1-α)]-3, and the kinetic equation of thermal decomposition may be expressed as dα/dt = A·e-E/RT·f(α) = 1/4 A·e-E/RT (1-α) [-ln(1-α)]-3,E = 295.98 kJ/mol,lnA =88.68,r = 0.9899,â–³S≠=-486.68 J/mol·K,â–³G≠=-21.95 kJ/mol.The fluorescence property of ligand(KL) and part of it's complexes were studied. The excitation and emission peak wavelengths(λex/λem) of the schiff base ligand KL is 286nm/505 nm, and the complexes of [CuL (CH3COO)(CH3OH)]·2H2O, [ZnL(CH3COO)]·H2O, [La LNO3] NO3·H2O are 373nm/444 nm, 285nm/500 nm, 375nm/478nm. Compared with the ligand, the excitation peaks and the emission peak of [CuL (CH3COO)(CH3OH)]·2H2O have changed, and the fluorescence quenched; the excitation peaks and the emission peak of [ZnL(CH3COO)]·H2O and [La LNO3] NO3·H2O almost same as the ligand, and still have strong fluorescence.(3) The anticancer activity of ligand (KL) and copper complex [CuL (CH3COO)(CH3OH)]·2H2O (Z1) were studied. The results showed that this complex could inhibit the chymotrypsin- like activity of proteasome and induce apoptosis in highly metastatic MDA-MB-231 breast cancer cells. The mechanism of how the complex induce apoptosis are same as taurine copper Schiff base complex (Y6).(4) The Schiff base ligands (B2, B7) which are derived from o-vanillin, salicylaldehyde with o-phenylenediamine and the mixture of the copper(or zinc) with the ligands have been prepared. The activity of proteasome inhibition and the apoptosis induction in human breast cancer MDA-MB-231 and leukemia Jurkat T cells by the mixture were studied. All the results showed that both copper and zinc mixture could inhibit proteasome and induce apoptosis in human breast cancer MDA-MB-231 and leukemia Jurkat T cells, the copper mixture a little more potent than the zinc mixture; and the calpain protein which plays a critical role in apoptosis involve in both metal mixture induce apoptosis. Compared the ability of proteasome inhibition and apoptosis induction in Jurkat T cells by the mixtures - copper with two different ligands( B2 and B7) .The results showed that the structure of the ligands could effect theirs ability to carry metal ions.(5)The mechanism of copper inhibit proteasome were studied. The results showed that both Cu(I)and Cu(II) can inhibit purified 20S proteasome activity, the Cu(I) a little more potent than Cu(II), the purified 20S proteasome can reduce Cu(II) to Cu(I), the hydrogen radical scavenger can partially protect the Cu(II) inhibit the purified 20S proteasome activity, hydrogen radical scavenger is one of reactive oxygen species (ROS), furthermore, treatment of MDA-MB-231 breast cancer cells with copper complex resulted in the production of reactive oxygen species (ROS), which make sure the ROS is one of the reason about copper inhibit proteasome activity.(6)The crystal of Schiff base 2-(2-hydroxy-3-methoxy benzaldehyden)- aminobenzothiazole (C15H12N2O2S) was obtained. The molecular structure of 2-(2-hydroxy-3- methoxy benzaldehyden)- aminobenzothiazole is calculated using the density functional theory (DFT) with the gradient corrected B3LYP method. All calculations are performed using the Gaussian 03 program package. The crystal structure of the compound is totally optimized. The energies and components of molecular orbital (HOMO and LUMO), natural population, NBO and stabilization energy were calculated. All data obtained from the calculations are consistent with those gained from the determination, which means the calculation model is stabilized. The possible three chemistry activities atom (N(28), O(29), O(31)) were predicted, that means those three atoms are easy to react with metal. The results of the calculation give a theory direction on the rational design and synthesis of metal–directed complexes in coordination chemistry.