34S-SIL of PCSK9-Active Oligonucleotide as Tools for Accurate Quantification by Mass Spectrometry.

Stable isotope labeling (SIL) of active pharmaceutical ingredients (API) is a well-established technique for the accurate quantification of small-molecule drugs. As the scope of active ingredients is expanding into areas of larger molecules, such as oligonucleotides (ONs), the development of new quantification techniques is critical. Herein, we describe the analysis of a 34S-SIL anti-PCSK9 gapmer-type antisense ON. A new method for the quantification of this API in complex biological matrices was developed and applied to mouse, dog, and monkey tissue homogenates, which gave improved accuracy and reproducibility compared with the use of auxiliary ONs as internal standard.