DNA oligomers are attracting attention as functional molecules driven in cells due to their high biocompatibility. In this study, we attempted to construct a drug that expresses its drug effect under photoirradiation conditions only in the presence of a target gene by changing the interaction between quencher and photosensitizer using structural change.
In the system, we designed a 20-mers hairpin DNA (H-ODN) and introduced a photosensitizer (ruthenium complex: Ru), and a quencher (cyclooctatetraene: COT), at both ends of H-ODN, which usually forms a hairpin-type structure. When H-ODN forms hairpin-type structure, the efficiency of singlet oxygen production is low, because of rapid energy transfer from Ru to COT. On the other hand, when target RNA complementary to H-ODN is present in the cells, H-ODN changes to a double-stranded structure. Thus, Ru and COT are separated from each other and singlet oxygen is generated upon photoirradiation. In this study, we selected a tumor-associated microRNA: miR-21 as an intracellular target and characterized the behavior of H-ODNs.
After the synthesis of H-ODNs using phosphoramidite method, we examined whether the structural change of H-ODN changes the excited state of Ru generated by photoirradiation. When H-ODN was excited in the absence of target strand, weak phosphorescence of Ru around 600 nm was observed. On the other hand, addition of the complementary strand resulted in an enhancement of the emission. We also measured the phosphorescence emission of 1O2 and found that 1O2 generation from H-ODN in double-stranded structure was more efficient than that from hairpin-type H-ODN. The quantum yield for generation of 1O2 from double-stranded H-ODN and hairpin-type H-ODN were 0.11 and 0.02, respectively. Thus, generation of 1O2 was regulated by the conformational change of H-ODN.