Development of a Novel Scintillation Proximity Competitive Hybridization Assay for the Determination of Phosphorothioate Antisense Oligonucleotide Plasma Concentrations in a Toxicokinetic Study

A novel scintillation proximity competitive hybridization assay was developed for determining plasma concentrations of compound 4003W94, a 15-base phosphorothioate antisense deoxyribonucleotide that is currently under preclinical evaluation for the treatment of restenosis following coronary artery angioplasty. The principle of the assay involves the hybridization binding of antisense (4003W94) to a biotinylated sense oligonucleotide to form a double-stranded nucleic acid complex on the surface of scintillation proximity beads derivatized with streptavidin. As in a competitive radioimmunoassay, there is an inverse relationship between the amount of radioactivity in the final binding complex and the amount of 4003W94 present in the sample being analyzed. Because this is a homogenous assay, no physical separation of bound from free radioligand is necessary. Conventional cross-reactivity studies with either 3′- or 5′-deletion oligomers of 4003W94 indicated that cross-reactivity generally decreased with each base deletion. The assay was used to determine plasma concentrations of 4003W94 equivalents in rhesus monkeys during an exploratory 14-day toxicity study. This method conceivably could be adapted for use as an effectivein vitroscreening tool for the identification of potential antisense oligonucleotide drug candidates or as a diagnostic tool for the detection of pathological disorders.