Metal Ion-Condensed DNA Nanoparticle Library: Phase Separation and Transition and Antisense Therapy Applications

DNA condensation has long been investigated as a fundamental cellular activity and is known to be driven by the mediation of diverse condensing agents. The phase behaviors of DNA during condensation are particularly interesting because the complicated molecular structure of natural nucleotides fundamentally allows electrostatic, coordinate covalent, and various other secondary interactions with the condensing agents. Recently, metal ion (Mⁿ⁺)-induced DNA condensation has emerged as a powerful approach to synthesizing nanoparticulate DNA structures suitable for therapeutic gene delivery. However, how the DNA phase changes during Mⁿ⁺-induced DNA condensation has rarely been observed and is not understood yet. In this study, a library of Mⁿ⁺-condensed DNA nanoparticles (Mⁿ⁺-CDNPs) was established using 30 different types of Mⁿ⁺s, and their phase behaviors during condensation were elucidated using spherical nucleic acids (SNAs) as electron microscopic labels. Importantly, the phase transition and separation of DNA were demonstrated to be driven by the Mⁿ⁺s into either the growth of individual DNA particles or the fission of bulky DNA aggregates. Pt²⁺ and Eu³⁺ were chosen as model systems for the demonstration. The hard and soft acid nature of Mⁿ⁺ is presumably the underlying driving force of these phase transitions. In addition, the Mⁿ⁺-controlled anticancer therapeutic efficiency of the Mⁿ⁺-CDNP library as a state-of-the-art gene delivery platform was demonstrated even for unmodified antisense oligonucleotides in association with the potential toxicity of the Mⁿ⁺s released from the Mⁿ⁺-CDNPs. This comprehensive study of the Mⁿ⁺-dependent condensation of nucleic acids provides profound insights into the chemistry of the nucleic acid-Mⁿ⁺ interactions and the reliable theragnostic applications of Mⁿ⁺-CDNPs as functional nucleic acid nanostructures.