Binding of Protoporphyrin IX and its H- and J-aggregates by Porphyrin-Binding Aptamer – Novel Candidates for Photosensitizer Delivery Systems and Method for Supporting Supramolecules

抄録

The formation of protoporphyrin IX (PPIX) H- and J-aggregates and the interactions between porphyrin-binding aptamer (PBA), monomeric PPIX, and PPIX aggregates were comprehensively studied. The present study reveals for the first time that PBA can capture one or more PPIX molecules upon interaction with H- and J-aggregates forming the common novel complex, with the absorption maximum at 412 nm. This complex could not be prepared even by adding excess amount of monomeric PPIX to PBA. The titration experiments, and the denaturation and subsequent annealing of the resulting complex suggested the equilibrated interaction between PBA and H- or J-aggregates, and the affinity constants K_as were determined as 1.4 × 10⁵ M^-1 and 5.0 × 10⁴ M^-1, respectively. From the standpoint of clinical applications, the aptamer sequence having affinity for cancer cells bound to the PBA sequence may be effective for drug delivery system of photodynamic therapy and diagnosis because the resulting complexes are sufficiently stable at body temperature to reach the target and are not too stable to release one or more PPIXs near cancer cells. From the standpoint of supramolecular chemistry, moreover, the present results may be useful for the immobilization of the porphyrin aggregates on the electrode or sensor surface using DNA aptamers for the practical applications.