[Energy of interaction in actinomycin-nucleotide complexes]

Variety of different compounds has been used for delivery of antibiotics to the tumor cells. In this work, using the highly sensitive spectrophotometry, the natural complexes of heterocyclic antibiotic actinomycin D (AMD) with such possible curriers like purine and pyrimidine nucleotides as well as fragmented DNA and phospholipid liposomes were studied. The antibiotic is not only adsorbed on the surface of purine clusters, but also is embedded in them. The antibiotic is especially well integrated into the unwound DNA regions. Embedding is accompanied by a long-wavelength shift in the absorption spectrum. The magnitude of the shift was used for calculation of the interaction energy. In the case of AMD with caffeine and adenosine, the value of energy is 2.4 and 2.7 kcal/mol and in the case of guanosine and fragmented DNA--considerably higher: 3.3 and 3.7 kcal/mol. It can be assumed that guanosine, adenosine, caffeine, and the fragmented DNA could serve as carriers of antibiotic.