Detection of the phosphorothioate oligonucleotide fomivirsen using a ligase detection reaction with polymerase chain reaction

This study aimed to develop a simple and sensitive detection method for fomivirsen, a 21-nucleotide phosphorothioate oligonucleotide used as a nucleic acid medicine, using a ligase detection reaction. A ligation probe was designed to hybridize with fomivirsen and polymerase chain reaction (PCR) primers, with a deoxyuridine part between the primer binding sites. The probe was ligated to a circular product by Taq DNA ligase, and the resulting product was converted to a linear form through the removal of the uracil base using uracil DNA glycosylase. The linear product was then quantified using real-time PCR. The developed method could detect 0.025–6.4 nM of fomivirsen in water and HeLa genomic DNA solutions and 0.6–160 nM of fomivirsen in mouse serum in combination with an extraction method based on alkalinization and neutralization. This method could be useful for not only detecting fomivirsen but also other functional oligonucleotides composed of phosphorothioate oligonucleotides. In summary, this study presents a practical and effective approach to the detection of the nucleic acid medicine fomivirsen.