Synthesis And Bioactivities Of A Series Of Metal Complexes Of Symmetrical Pyrrole-polyamide Dimers

It is known that some anti-cancer drugs that are clinically used exert their activities by recognizing, binding, and cleaving DNA. Therefore, metal complexes with high affinities and sequence specificities toward DNA have been attracting considerable interest from medicinal chemists. For example, the first metal complex cisplatin for the treatment of cancer binds to DNA of tumor cells to interfere with the synthesis of DNA, inhibits tumor cell division and exerts antitumor activity. However, it has side effects. Therefore, identification of metal complexes with few side effects, drug resistance, and high efficacy has been a hot research topic during the past decades.The interaction of a metal-based cleaving molecule with DNA includes two steps. Firstly, the molecule recognizes and binds to DNA through non-covalent interactions. Secondly, it cleaves DNA. Pyrrole polyamides can bind to the minor groove of double-stranded DNA with high affinities and sequence specificities through non-covalent interactions, therefore they were chosen as a recognition system of metal complexes. Dimeric pyrrole polyamides 1-4 were designed and synthesized. Their Cu(Ⅱ) metal complexes, that is, 1@Cu2+,2@Cu2+,3@Cu2+ and 4@Cu2+ were prepared from Ligands 1-4 and Cu(II) ion, and their DNA-cleaving, binding and antitumor activities were examined. The results are summarized below.Firstly, a dimeric pyrrole-polyamide analog 1 was synthesized and characterized on the basis of NMR (1H and 13C), MS (ESI and HR) and IR. The linker of compound 1 is a poiyether chain. Its copper complex, i.e., 1@Cu2+ was characterized on the basis of ESl-MS and UV-Vis. Agarose gel electrophoresis (GE) study of the cleavage of plasm id pBR322 DNA by 1@Cu2+ indicated that 1@Cu2+ was capable of efficiently converting pBR322 DNA into open circular DNA at pH 7.0 and 37℃, most probably via an oxidative mechanism. The maximal catalytic rate constant kmax and Michaelis constant KM of 1@Cu2+ were estimated to be 5.61 h-1 and 7.3 mM, respectively. Ethidium bromide (EB) displacement experiments indicated that 1@Cu2+ showed moderate binding affinity toward calf-thymus (CT) DNA, and its binding constant Ka was (8.75±1.31)×104 M-1. Viscosity experiment indicated that 1@Cu2+ interacted with CT-DNA, possibly via a mixed mode of intercalation and electrostatic interaction. MTT assay showed that 1@Cu2+ displayed inhibitory activities toward the proliferation of lung adenocarcinoma A549, hepatoma hepg2. and gastric-carcinoma NCI-N87 cells. It had the strongest inhibitory effect on gastric-carcinoma cells NCI-N87 with the EC50 value being 10.52 μM.Secondly, two new dimeric dipyrrole-polyamide analogs 2 and 3 were synthesized and fully characterized by NMR (1H and 13C), MS (ESI and HR) and IR. The linker of compound 2 is triethylenetetramine, whereas that of compound 3 is spermine.1H NMR, spectrophotometric titration, ESI-MS and IR indicated that compounds 2 and 3 formed 1:1 complexes with Cu2+ ion (i.e.,2@Cu2+ and 3@Cu2+). Agarose GE studies indicated that 2@Cu2+ and 3@Cu2+ were capable of efficiently converting pBR322 DNA into open circular and linear forms under physiological conditions, most probably via an oxidative mechanism. The maximal catalytic rate constant kmax and Michaelis constant KM were estimated to be 1.49 h-1 and 0.101 mM for 2@Cu2+, and 1.41 h-1 and 0.072 mM for 3@Cu2+, respectively. The overall catalytic activities were estimated to be 14.76 h-1·mM-1 for 2@Cu2+ and 19.63 h-1·mM-1 for 3@Cu2+, respectively. EB displacement experiment indicated that 2@Cu2+ and 3@Cu2+ showed moderate binding affinity toward CT DNA. The binding constant Ka of 3@Cu2+ was slightly greater than that of 2@Cu2+. MTT assay showed that 2@Cu2+ and 3@Cu2+ displayed inhibitory activities toward the proliferation of lung adenocarcinoma A549, hepatoma hepg2, and gastric-carcinoma NC1-N87 cells. They had the strongest inhibitory effect on gastric-carcinoma cells NCI-N87.Thirdly, a new dimeric dipyrrole-polyamide analog 4 was synthesized and fully characterized on the basis of NMR (1H and 13C). MS (ESI and HR) and 1R. Spectrophotometric titration, ESI-MS and conductivity measurements indicated that compound 4 formed a 1:1 complex with Cu2+ ion (i.e.,4@Cu2-). Agarose GE studies indicated that 4@Cu2+ was capable of efficiently converting pBR322 DNA into open circular and linear forms under physiological conditions, most probably via an oxidative mechanism. The maximal catalytic rate constant kmax and Michaelis constant KM of 4@Cu2+ were estimated to be 14.3 h-1 and 0.60 mM. respectively. The overall catalytic activity of 4@Cu2+ was estimated to be 23.9 h-1·mM-1. EB displacement experiment indicated that 4@Cu2+ showed moderate binding affinity toward CT DNA, and its binding constant Ka was (6.43±0.75)×105 M-1. MTT assay showed that 4@Cu2+ displayed inhibitory activities toward the proliferation of lung adenocarcinoma A549, hepatoma hepg2, and gastric-carcinoma NCI-N87 cells. It had the strongest inhibitory effect on gastric-carcinoma cells NCI-N87 with the EC50 value being 12.72 μM.In summary, we have synthesized four novel symmetrical pyrrole polyamides and their metal complexes with promising binding and cleaving properties. The present results indicate that one more pyrrole subunit at each end can enhance the binding affinities and the cleaving activities, and that the length of the linkers can modulate the DNA cleaving activity. These four novel metal-based cleaving complexes may provide useful guidance for future rational design of more effective DNA-cleaving agents with a view toward new drug discovery.