Mechanism Studies Of Platinum Complexes In Antitumor And Inhibition Of Aβ Aggregation

Inspired by the discovery of the anticancer application of cisplatin, numorous platinum complexes have been synthesized. The mechanism studies of cisplatin have also drawn great attention. It is widely accepted that DNA is the ultimate target of cisplatin, however, only a small amount of cellular platinum forms DNA adducts. Proteins also play important roles in the drug uptake, cellular distribution, drug detoxification, DNA repair and drug efflux. Since cisplatin does not have selectivity in DNA types, the reaction of proteins determined the side-effects and resistance of platinum drugs. Additionally, platinum phenanthroline complexes have been found to inhibit Aβ aggregation and reduce Aβ-caused neurotoxicity, and were considered as potential therapeutic agents for the treatment of Alzheimer’s disease.The mechanisms of platinum complexes in anticancer and the inhibition of Aβ aggregation have been studied in dissertation. We studied interactions between platinum complexes and biomolecules (proteins and DNA), including following three topics:(1) The reactions of mono functional platinum complex with DNA in the presence of sulfur containing molecules (methionine, peptide and protein). Results indicate that thioether binding mediates monofunctional platinum antitumor reagents to trans configuration in DNA interactions.(2) The reactions of cisplatin and oxaliplatin with the second transmembrane domain (TM2) of CTR1. Moreover, the role of platinum transfer from N terminus to TM2was discussed. Results suggest that CTR1plays different roles in the drug uptake for the two platinum compounds. Meanwhile, we also studied copper competing reactions between CTR1and albumin.(3) The inhibition mechanism of platinum phenanthroline complexes in Aβ aggregation. The results reveal the dual role of PtCl2(phen) in the inhibition of Aβ aggregation:noncovalent interactions and Aβ platination.Chapter1is a review section, which summerized the mechanisms of platinum anticancer drugs, including the structure/activity relationships of platinum complexes, cellular uptake and transport of the drug to the nucleus and the related toxicity and resistance. Meanwhile, the relationship between copper transporters and platinum containing drugs were also discussed.In chapter2, the reactions of cis-[Pt(NH3)2(py)Cl]Cl (cDPCP) with nucleic acids (GMP and DNA) in the presence of methionine were investigated using NMR, HPLC and ESI-MS. Met first bound with cDPCP forming two adducts, cis-[Pt(NH3)2(py)(Met)]Cl2and trans-[Pt(NH3)(py)(Met)Cl]Cl at different pH value solution. These adducts could further react with DNA and produce the same ternary products trans-[Pt(NH3)(py)(Met)(DNA)], which was also the reaction product of trans-[PtCl2(NH3)(py)] with Met and DNA. The results indicate that methionine binding converts monofunctional platinum complex to trans configuration adducts. Similar reactions were also observed in sulfur-containing peptides (CTR1-N8, H7) and proteins (Albumin, Histone1). These results suggest that the action of monofunctional platinum complexes may correlate to the mechanism of trans geometry complexes in the cellular process.In chapter3, we studied reactions of cDDP and oxaliplatin with N8and TM2. The major adduct [Pt+TM2]Cl2of cDDP with TM2was confirmed by ESI-MS. Furthermore, minor product [Pt(NH3)2+TM2]Cl2was also observed. The reaction of oxaliplatin with TM2yielded [Pt(DACH)+TM2]Cl2. For platinum transfer reaction, TM2is able to substitute the platinum from cDDP/N8adduct [PtCl+N8]Cl, but unable to react with the oxaliplatin/N8adducts [Pt(DACH)+N8]Cl2. This observation reveals the different function of CTR1in the cellular uptake of cisplatin and oxaliplatin.In chapter4, the interactions between Cu2+/Cu+and the N-terminal domain of CTR1(CTR11-16, CTR11-55) were investigated using mass spectra and EPR. The results showed that the binding of multiple Cu2+ions occured in NH2-MDH (ATCUN) and histidine-rich domain of CTR11-16/CTR11-55. The binding constant of Cu2+in CTR11-16/CTR11-55is about one order of magnitude lower than that in HSA. Cu+was prefer to bind to Met-rich motifs of CTR11-16/CTR11-55with relatively high affinity. Meanwhile, we also investigated copper transfer from HSA and histidine to N-terminal domain of CTR1. The result shows that albumin and histidine may be as copper transporters in the blood.In chapter5, the mechanism of PtCl2(phen) inhibiting Aβ aggregation was studied in detail. The phenanthroline ligand could induce noncovalent interaction between Aβ peptide and platinum complexes, leading to rapid Aβ platination. Multiple products were generated in the reaction, in which His6/His14chelation was preferentially formed. Coordination of Asp7, His13, and Lys16was also detected in other products. The majority of products were monoplatinated adducts with binding of the [Pt(phen)] scaffold, which impeded intermolecular interactions between Aβ peptides. Noncovalent interactions were confirmed by the interaction between peptide and [Pt(phen)2]Cl2. Although cisplatin did not react with Aβ1.16, it was suggested that it reacted at Met35of full length Aβ. These results indicate that the binding sites and the nature of products are important for the inhibition activities.Since platinum binds to the Cu(Ⅱ) binding sites and platinum has strong coordination to the Aβ peptide. PtCl2(phen) can release copper ions from Cu2+-Aβ complexes. Surprisingly, in the reaction of copper-bound Aβ peptide, the phenanthroline ligand was also released from platinum atom forming the products [Pt(DMSO)+Aβ1-16] and [2Pt(DMSO)+Aβ1-16]. These products were clearly different to the products from apo-Aβ. These results suggest that copper ions also play an important role in the phen liberation process.