CD spectra of (DNA-TOEPyP4) + ZnTOEPyP4, (DNA-ZnTOEPyP4) + TOEPyP4, and DNA + (TOEPyP4-ZnTO- EPyP4) complexes have been studied. It is shown that CD spectra of these triple complexes significantly differ from the DNA-TOEPyP4 and DNA-ZnTOEPyP4 double complex spectra, and they are not sum of these double complexes. Especially some strong differences in CD spectra of the triple and double complexes were observed when both porphyrins were added simultaneously into the DNA solution. In this case, ZnTOEPyP4 revealed a dominant influence on CD spectrum form. Zn-porphyrin also caused a strong intensity of positive band at 416 nm and a negative band at 437 nm when it was added into solution containing the DNA-TOEPyP4 complex. On the basis of obtained data, it was supposed that the observed significant changes in CD spectra of triple complexes were connected to an altered DNA conformation initiated by intercalation of porphyrin TOEPyP4 into GC-rich sites. The melting process analysis of the double complexes was carried out. The mechanisms of individual and joint influence of the porphyrins on DNA, and influence of binding modes on stability of these complexes are also discussed.
Among ligands, a special attention is paid to the water soluble cation meso-tetra(4-N-oxyethylpyridil) porphyrins-TMPyP4 type porphyrins-because it is minimal toxic. It predominantly accumulates in tumor cells and binds to G-quadruplex of telomeric DNA [1,2], and defends it from high telomerase activity detaining growth of transformed cells in case of many leukemic diseases [3,4]. Its metal complexes can induce DNA strand cleavage at deoxyribose residues and initiate apoptosis of cancer cells [
The obtained results gave us a possibility to deeper understanding of TMPyP binding mechanism, including TMPyP binding to DNA in vitro and in situ, which is very important for understanding influence on chromatin DNA in live cells. In the given work we tried to characterize the joint influence of two different conformational conditions of TOEPyP4-plane porphyrin and its nonplane Zn-complex. TOEPyP4 is an analogue of TMPyP, according to its physical and chemical properties [14,15].
These investigations are important from medical point of view, because in case of many diseases, DNA in vivo may be attacked simultaneously not only by endogenes and exogenes porphyrins free from metals, but also by metal-containing porphyrins, some small proteins, as well as transition metal ions that can change the binding mode of porphyrins to DNA [3,16,17]. This can change the therapeutic effect of the drug, especially in case of photodynamic therapy. Therefore, we think that it is very important to know the mechanisms of combined influence of intercalating and non-intercalating (outside binding) porphyrins on DNA.
The water-soluble meso-tetra(4-N-oxyethylpyridil) porpyrin (TOEPyP4) and its Zn-containing analogue was synthesized in ESU according to the method described in work [