SUNY at Albany
June 19-23, 2001
Interaction of DNA Molecules in the Presence of DNA Topoisomerase I inhibitor Topotecan
Camptothecin (CPT) and its analogs, including topotecan (TPT), inhibit eukaryotic DNA topoisomerase I (topo I) and thus exhibit antitumor activity. The preference for supercoiled DNA is a peculiarity of CPT interaction with DNA (1).
The TPT interaction with calf thymus DNA in solutions of low ionic strength was studied by fluorescence, circular dichroism, and linear flow dichroism. The data obtained indicate that TPT forms two types of complex with DNA (2). The S-shaped curve of the linear dichroism dependence on DNA concentration for TPT-DNA complexes shows that DNA molecules interact with each other during formation of one of these complexes. The constant of interaction with each other of two TPT-filled DNA molecules was determined to be approximately 104 M-1 (per base pair) in 1 mM cacodylate buffer, pH 6.8, 20°C.
Intermolecular complexes formed by linear DNA in the low ionic strength solutions in the presence of TPT and containing several DNA molecules can serve as a model of interaction of compounds of the CPT family with supercoiled DNA. In fact, in the supercoiled DNA remote parts of one and the same molecule may be drawn together to interact in the presence of TPT, i.e., form a complex similar to that studied by us. It is known that eukaryotic topo I and topo II preferably bind two distant parts of supercoiled DNA and can also bind to the contact sites of two linear DNAs (3). Thus, the topo I activity modulation by TPT may be due to the formation of a complex between TPT and different sites of one and the same DNA molecule. Possibly, the biological purpose of the CPT family compounds is hidden just in this peculiarity - preferable binding to supercoiled DNA molecules when binding to linear ones is low.References and Footnotes
S.A. Streltsov, A.L. Mikheikin and Yu.D. Nechipurenko
Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, 119991 Moscow, Russia