Vestigation Of Interactions Of Sp1Zinc Finger Protein With Latinum-based Anti-cancer Drugs

Although DNA is widely accepted as a primary target for platinum-based anti-cancer drugs, more and more evidence indicates that proteins play important roles in determining the overall toxicity profile via affecting the cellular process of platinum compounds, such as drug uptake and distribution, DNA repair processes. Proteomics studies reveal that the expressions of a large number of proteins are influenced by the treatment of platinum-based drugs, suggesting that platinum drugs could interfere with the transcription process. Zinc finger proteins are the most abundant DNA binding proteins in human transcription factors. The conserved Cys residues in the zinc coordination site are the potential binding site of platinum complexes.In this thesis, we have investigated the reactions between Sp1zinc finger protein and platinum complexes. Variours platinum compounds with different ligands and coordination geometries were used in order to obtain the information about how ligands and coordination geometries regulated the reactivity to Spl. Results indicate that the trans platinum thiazole complex (trans-PtTz) possesses the high reactivity towards Sp1zinc finger protein among all platinum complexes used in this work. The mechanism of thiazole ligand has been analyzed in the regulation of the activity of platinum complex to the Sp1zinc finger protein. In addition, we found that the reducing agent TCEP can significantly promote the reaction of cisplatin with Sp1zinc finger protein.In the chapter1, the structures and functions of zinc finger proteins and the molecular mechanisms of platinum-based antitumor drugs have been reviewed. The presents the overview of the classification and the functions of zinc fingers, the structure-activity relationship of antitumor platinum complexes, the role of proteins in the mechanism of antitumor platinum complexes and zinc finger proteins as the potential therapeutic target for platinum-based anti-cancer drugs.In the chapter2, the reactions of Spl zinc finger protein have been carried out with platinum complexes featuring different ligands and coordination geometries. Results show that the trans platinum thiazole complex exhibits the highest reactivity to the Spl zinc finger protein, while other platinum compounds are much less reactive. Results from CD spectra and NMR spectra indicate that trans-PtTz can effectively disrupt the secondary structure of the Sp1protein zinc finger. We also found that trans-PtTz can effectively inhibit the binding of Spl transcription factor to the hCtrl promoter DNA sequence. Since the intact Zinc finger structure is necessary for Spl transcription factor trafficking from cytoplasm to nucleus, trans-PtTz can prevent such process via disturbing the Spl zinc finger structure.Based on the discovery in the chapter2, we further investigated the role of ligand in regulating the reactivity of platinum complexes towards Spl zinc finger protein. Results indicate that the high reactivity does not mainly result from the π stacking interaction between thiazole ligand and Spl protein. Since thiazole has a free coordination site (S atom) which differs from pyridine, we further investigated role of the thiazole-S atom in the reaction of trans-PtTz with Spl protein and found that the free coordination site in aromatic ligand can actually promote the reaction. This discovery explains the high reactivity of tran-PtTz towards Spl zinc finger protein and provides fundamental information for designing platinum complexes toward oncoproteins.In chapter4, we investigated the effect of Tris-(2-carboxyethyl)phosphine(TCEP) on the interaction between Spl zinc finger protein and cisplatin. It has been previously reported that cisplatin can effectively disrupt the zinc finger structure and result in the zinc ejection. However, cisplatin is really inert to the Spl zinc finger. Further incastigations reveal that the reducing agent TCEP plays an important role in promoting the reaction of cisplatin with Sp1zinc finger protein. Mechanistic study reveals that the TCEP can coordinates to cisplatin and the strong trans effect of P enhances the reactivity of ciaplatin. The findings suggests that cellular molecules might significantly affect the activity of cisplatin via strong trans effects.