Binding of cationic porphyrins and metalloporphyrins to the human transferrin for photodynamic therapy of tumors

In photodynamic therapy (PDT) of tumors, targeted therapy is one of the most successful directions. The goal of the present work was to study the formation of new potential photosensitizers, based on transferrin (Tf) and cationic porphyrins, for targeted binding with transferrin receptors of cancer cells. We studied non-covalent binding of three cationic porphyrins 1) meso-tetra [4-N-(2'-oxyethtyl) pyridyl] porphyrin (TOEt4PyP) 2) Zn-TOEt4PyP and 3) Zn-mesotetra [4-N- butyl pyridyl] porphyrin (Zn-TBut4PyP) with human transferrin by absorption and fluorescent spectroscopy as well as by gel filtration methods. It was shown that the investigated porphyrins and metalloporphyrins bind stably enough to the protein molecule. It was found that the porphyrins having Zn ion in porphyrin core as well as the peripheral OH - groups are linked better to the transferrin molecules. It can be apparently explained by Zn coordination with transferrin amino acids and the formation of the hydrogen bonds between OH - groups of the porphyrin and transferrin amino acids. It was shown that, for the transferrin-porphyrin complexes, singlet oxygen luminescence is significantly decreased due to the presence of transferrin amino acids which are efficient quenchers of singlet oxygen.