Development of an LC-MS/MS assay to analyze a lipid-conjugated siRNA by solid phase extraction (SPE) in mouse plasma and tissue using a stable isotope labeled internal standard (SILIS).

BACKGROUND

Oligonucleotide therapeutics (ONTs) are a rapidly growing class of drug, with 20+ approved drugs on the market and more undergoing preclinical and clinical investigation for various indications. Many groups in the field are appending chemical modifications to modulate tissue specificity. Conjugation of long-chain fatty acids to siRNA molecules increases the hydrophobicity of the analyte and poses analytical challenges for extraction and LC-MS.

RESULTS

We report the development and optimization of an SPE extraction method for a lipid-conjugated siRNA. To improve assay quantitation by LC-MS, a stable isotope label internal standard (SILIS) was evaluated that enabled robust quantitation with high accuracy and precision (±5% in most cases).

CONCLUSION

We demonstrate the performance of the assay in mouse plasma and tissue homogenates and apply the assay to the determination of tissue exposure and plasma PK profile for a novel lipid-conjugated siRNA molecule and suggest that a SILIS quantitation approach should be standard practice in siRNA bioanalysis.