Apolipoprotein C3 (Apo C3) LNA/DNA gapmer was evaluated under various stress and formulation conditions for the purpose of its development as a potential biotherapeutic for low density lipoprotein (LDL) lowering. Using ion-pairing (IP) reversed-phase (RP) liquid chromatography ultra-high resolution (UHR) tandem mass spectrometry (IP-RPLC-MS/MS), a combination of accurate mass measurements and collision-induced dissociation enabled in-depth characterization of Apo C3 LNA/DNA oligonucleotide, in particular the inherent impurities following synthesis and degradation products after exposure to stress conditions. In this study, oligonucleotide samples were stressed under different pH and UV exposure conditions. The primary impurities in Apo C3 LNA/DNA were losses of nucleotide moieties from both the 5'- and 3'-terminus leading to n-1, n-2, etc. species. Desulfurization and depurination were observed in Apo C3 LNA/DNA after a week under UV light stress conditions at low pH. Guanine oxidation and dimerization were the primary degradation products detected under UV light exposure for 1 week at high pH. The effect of antioxidants on the levels of these degradation products was evaluated under neutral pH conditions. In the presence of all antioxidants, levels of guanine oxidation and desulfurization under tested conditions were the same as those in the unstressed sample, except for sodium ascorbate. The thorough understanding of the Apo C3 LNA/DNA oligonucleotide structure, its impurities, and degradation products laid the foundation for the successful formulation development of this novel biotherapeutic modality.
Keywords: characterization by LC/MS/MS; formulation of LNA/DNA; locked nucleic acids.