Characterization of the bisintercalative DNA binding mode of a bifunctional platinum-acridine agent

Abstract

The DNA interactions of PT-BIS(ACRAMTU) ([Pt(en)(ACRAMTU)2](NO3)4; ACRAMTU = 1-[2-(acridin-9-ylamino)ethyl]-1,3-dimethylthiourea, en = ethylenediamine), a bifunctional platinum–acridine conjugate, have been studied in native and synthetic double-stranded DNAs and model duplexes using various biophysical techniques. These include ethidium-DNA fluorescence quenching and thermal melting experiments, circular dichroism (CD) spectroscopy and plasmid unwinding assays. In addition, the binding mode was studied in a short octamer by NMR spectroscopy in conjunction with molecular modeling. In alternating copolymers, PT-BIS(ACRAMTU) shows a distinct preference for poly(dA-dT)2, which is ∼3-fold higher than that of ACRAMTU. In the ligand-oligomer complex, d(GCTATAGC)2·PT-BIS(ACRAMTU) (complex I*), PT-BIS(ACRAMTU) increases the thermal stability of the B-form host duplex by ΔTm > 30 K (CD and UV melting experiments). The agent unwinds pSP73 plasmid DNA by 44(±2)° per bound molecule, indicating bisintercalative binding. A 2-D NMR study unequivocally demonstrates that PT-BIS(ACRAMTU)'s chromophores deeply bisintercalate into the 5′-TA/TA base pair steps in I*, while the platinum linker lies in the minor groove. An AMBER model reflecting the NMR results shows that bracketing of the central AT base pairs in a classical nearest neighbor excluded fashion is feasible. PT-BIS(ACRAMTU) inhibits DNA hydrolysis by BstZ17 I at the enzyme's restriction site, GTA↓TAC. Possible consequences for other relevant DNA–protein interactions, such as those involved in TATA-box-mediated transcription initiation and the utility of the platinum-intercalator technology for the design of sequence-specific agents are discussed.

Structural basis for DNA cleavage by the potent antiproliferative agent (–)-lomaiviticin A

“…Strong intranucleotide contacts were observed between T5 H6 and T13 H6 and both H5′ and H5′′ of their respective carbohydrate residues, suggesting that 1 substantially disrupts the orientation of the central bases. Notably, these NOE contacts were not observed in earlier studies that used an identical duplex and acridinium-or fluorenone-based intercalative ligands (27,31). These latter ligands were shown to bind by a typical intercalative mode and the differences between these complexes and that formed from 1 suggest a novel mode of association.…”

Metal complex interactions with DNA

“…172 Upon binding to B-DNA, these complexes have demonstrated the ability to induce Hoogsteen base-pair formation, 172 unwind the helix by 44 o and increase thermal stability by over 30K 176. 172 Upon binding to B-DNA, these complexes have demonstrated the ability to induce Hoogsteen base-pair formation, 172 unwind the helix by 44 o and increase thermal stability by over 30K 176.…”

Preparation and Characterization of Cobalt (II)- Complexes of 4-Hydroxybenzaldehyde Semicarbazone and Amino Acid Esters Ligands

“…Coordination compounds of mixed ligands were of a considerable importance in the field of metalloenzymes and biological activities in addition to other purpose [21][22][23][24][25][26]. Hence a large number of coordination compounds containing mixed ligands with transition and non-transition metal ions have been reported recently [27][28][29][30].…”