Sequence-specific binding of antitumour bisquaternary ammonium heterocycles to DNA and inhibition of polymerase activity in vitro.

Ten bisquaternary ammonium heterocycles (BQA) active against experimental tumours were investigated for possible sequence-selective binding to DNA. Footprinting analyses indicated that several bound preferentially to dAdT runs consisting of at least four base pairs. Shortening of one or two spacer groups between the aromatic rings of the ligands (by replacement of CONH with NH) emerged as a prerequisite for sequence-specific binding. Other relevant factors concerned the overall shape of the ligands and the relative position of their positive charges. Footprinting plots evaluated for the BQA compound SN 6132 on the 167mer EcoRI-RsaI restriction fragment from plasmid pBR322 yielded the highest individual binding constant for the symmetrical base sequence AATTTAA, with approximate K(A) = 2.0 x 10(6)/M. Polymerase-catalysed syntheses of DNA and RNA in vitro were inhibited by all BQA derivatives, but the inhibition was much more pronounced with the sequence-specific binders SN 6999 and SN 6132 than with the non-specific ligand SN 6113.

Anthracycline antibiotics. Interaction with DNA and nucleosomes and inhibition of DNA synthesis.

We report studies of the interaction of four anthracycline antibiotics, iremycin (IM), daunomycin (DM), aclacinomycin A (AM), and violamycin B1 (VM), with naked DNA, nucleosomal core particles, and 175 base pair (bp) nucleosomes lacking histone H1. In all cases the binding strength increases in the order IM less than DM approximately AM less than VM. The binding substrates increased in affinity for the drugs in the following order: core particles less than 175-bp nucleosomes less than DNA. The apparent DNA length increment per drug bound decreases in the progression IM greater than DM greater than AM greater than VM, the same serial order as is characterized by increasing binding affinity. Dichroism amplitude measurements show that for all drugs the long-wavelength absorbance transition moment is tilted by 26-29 degrees relative to the plane perpendicular to the helix axis; this angle probably corresponds to the long axis tilt of the intercalated chromophore. Finally, it was found that the ability of the drugs to inhibit DNA synthesis by Escherichia coli DNA polymerase I increases in the same order as their binding affinity.

(dA-dT) dependent inactivation of the DNA template properties by interaction with netropsin and distamycin A.

The inhibitory effect of the polypeptide antibiotics netropsin and distamycin A on DNA dependent nucleic acid synthesis has been shown to be related to the base composition of the template DNA. A number of natural DNA's of quite different dA-dT content as well as poly (dI-dC)-poly (dI-dC), poly (dA-dT)-poly (dA-dT), poly (dA) - poly (dT) and poly (dG) - poly (dC) has been studied as templates in DNA and in part in RNA polymerase reaction. The highest binding efficiency of netropsin existing for (dA-dT) - containing DNA polymers and the less pronounced interaction with the (dI-dC)-containing polymer shown by the melting and CD spectrral behaviour of the complexes are entirely reflected in the template inactivation. The same is evident for distamycin A. However, in contrast to netropsin the antibiotic distamycin A exhibits some binding tendency to poly (dG) - poly (dC). Binding effects of a netropsin derivative to DNA and (dA-dT) -containing polymers suggest the importance of hydrogen bonds of the peptide groups in the complex formation.

Effects of the antibiotic resistomycin on the synthesis of macromolecules.

Resistomycin preferentially inhibits RNA synthesis in comparison to DNA and protein synthesis in intact bacterial cells. Studies with cell-free systems have shown that the antibiotic interferes with DNA and RNA synthesis, while protein synthesis is inhibited to a much lesser extent. Detailed studies in cell-free systems indicate an interaction of resistomycin with DNA- and RNA polymerase. In the case of RNA polymerase this was proved by CD measurements, whereas no interaction of the antibiotic with DNA, RNA, and homopolynucleotides could be found. One can conclude that the binding of the antibiotic to RNA polymerase is the basis for its interference with RNA synthesis.