Simultaneous quantification of siRNA antisense and sense strands by hybrid liquid chromatography-mass spectrometry

BACKGROUND: Most oligonucleotide bioanalytical assays currently only quantify the pharmacologically-active antisense strand, though there have been recent efforts to simultaneously quantify the sense strand using hybridization ELISA or solid phase extraction LC-MS. Hybrid LC-MS, which offers both high sensitivity and specificity unlike the currently used platforms, has not been applied to quantify both siRNA strands simultaneously. MATERIALS & METHODS: A hybrid LC-MS assay utilizing LNA capture probes was developed and applied to quantify both strands of a 21-mer lipid-conjugated siRNA (SIR-3) using tandem mass spectrometry (MS/MS). A similar approach using high-resolution mass spectrometry (HRMS) was also evaluated. RESULTS: The final LC-MS/MS method was capable of quantifying both strands of SIR-3 at concentrations between 0.600 and 1000 ng/mL in cynomolgus monkey tissue homogenates with acceptable accuracy and precision. The LC-HRMS assay demonstrated similar sensitivity and assay performance as the LC-MS/MS assay. CONCLUSIONS: Overall, this manuscript presents orthogonal methods to existing siRNA bioanalytical workflows that with high sensitivity and specificity can provide greater information about the concentration and biotransformation of an siRNA analyte.