Tight binding of the antitumor drug ditercalinium to quadruplex DNA.

The structural selectivity of the DNA-binding antitumor drug ditercalinium was investigated by competition dialysis with a series of nineteen different DNA substrates. The 7H-pyridocarbazole dimer was found to bind to double-stranded DNA with a preference for GC-rich species but can in addition form stable complexes with triplex and quadruplex structures. The preferential interaction of the drug with four-stranded DNA structures was independently confirmed by electrospray mass spectrometry and a detailed analysis of the binding reaction was performed by surface plasmon resonance (SPR) spectroscopy.

DNA sequence recognition by the antitumor drug ditercalinium.

The antitumor drug ditercalinium is a rare example of a noncovalent DNA-binding ligand that forms bisintercalation complexes via the major groove of the double helix. Previous structural studies have revealed that the two connected pyridocarbazolium chromophores intercalate into DNA with the positively charged bis(ethylpiperidinium) linking chain oriented to the wide groove side of the helix. Although the interaction of ditercalinium with short oligonucleotides containing 4-6 contiguous GC base pairs has been examined in detail by biophysical and theoretical approaches, the sequence preference for ditercalinium binding to long DNA fragments that offer a wide variety of binding sites has been investigated only superficially.

Effects of cationic charge on three-dimensional structures of intercalative complexes: structure of a bis-intercalated DNA complex solved by MAD phasing.

We characterize intercalative complexes as either "high charge" and "low charge". In low charge complexes, stacking interactions appear to dominate stability and structure. The dominance of stacking is evident in structures of daunomycin, nogalamycin, ethidium, and triostin A/echinomycin.

Asymmetry and dynamics in bis-intercalated DNA.

The bis-intercalator ditercalinium (NSC 366241), composed of two 7 H-pyridocarbazoles linked by a bis(ethylpiperidinium), binds to DNA with a binding constant greater than 10(7) M-1. One distinctive aspect of the 3-D X-ray structure of a DNA-ditercalinium complex is its asymmetry. We propose here that the activity of ditercalinium may be related to structural polymorphism and dynamic conversion between conformers.

Fate of a fluorescent inhibitor of endopeptidase-24.11 using enzyme-expressing MDCK cells. Modification of its cellular processing with a monoclonal antibody.

Neutral endopeptidase-24.11 (NEP) is a membrane-bound zinc metallopeptidase which cleaves biologically active peptides such as the enkephalins and atrial natriuretic peptide. Using the specific and fluorescent thiol inhibitor of the enzyme, N-[fluoresceinyl]-N'-[1-(6-(3-mercapto-2-benzyl-1-oxopropyl)-amino-1- hexyl]-thiocarbamide (FTI), the fate of the inhibitor-enzyme complex was investigated by videomicrofluorimetry using MDCK epithelial cells expressing the rabbit peptidase thanks to a retroviral expression vector.