Metabolite profiling of chemically modified oligonucleotides in rat liver homogenates using hydrophilic interaction liquid chromatography-high resolution mass spectrometry

Abstract

Chemically modified oligonucleotide is a rapidly emerging field of biotherapeutics. The evaluation of the metabolic stability of therapeutic oligonucleotides is critical. The current methods are limited to the ion-pairing reversed phase chromatographic techniques. Due to complex chemical modifications of therapeutic oligonucleotides and diverse structural changes in their metabolites, comprehensive metabolite profiling is still challenging. Therefore, an alternative analytical method for the metabolism study of oligonucleotides is urgently needed. In this study, a novel hydrophilic interaction liquid chromatography-high resolution mass spectrometry (HILIC-HRMS) method was developed and applied to the metabolism study of two chemically modified oligonucleotides, i.e., N11-GalNAc (phosphorothioate, 2′-F, 2′-OMe, and 3′-GalNAc) and N9 (phosphorothioate, 2′-F), in rat liver homogenates. Highly broad retention of metabolites on the HILIC column was achieved, with truncated metabolite having a single nucleotide being detected. A stepped normalized collisional energy (NCE) in HRMS led to characteristic c/y, d/y, and b/y fragment ion series, and diagnostic fragment ions for linker and GalNAc, which covered the whole sequence of oligonucleotides. A total number of twenty-seven and twenty-nine metabolites were identified in rat liver homogenates for N11-GalNAc and N9, respectively, by using the isotopic envelope of the precursor ion and stepped NCE-based sequence mapping data. The time-dependent production of metabolites was observed. The UCU sequence with the uniform 2′-F modification on ribose was identified as the major metabolic site for N11-GalNAc, and the phosphodiester bonds between nucleosides involving unmodified uracil were identified as the metabolic soft sites for N9. The developed HILIC-HRMS method provided a high coverage of various oligonucleotide metabolites. Characteristic fragment ions enable sequence mapping and therefore unambiguous metabolite identifications. This approach can be broadly applicable to the metabolism study of chemically modified oligonucleotides and the identification of their metabolic soft sites.