Discovery of a novel deaminated metabolite of a single-stranded oligonucleotide in vivo by mass spectrometry.

Aim: A novel single-stranded deaminated oligonucleotide metabolite resulting from a REVERSIR™ oligonucleotide was discovered and identified in monkey liver after subcutaneous administration. Results & methodology: REVERSIR-A and its metabolites were extracted from biological matrices by solid phase extraction and analyzed using LC coupled with high-resolution MS under negative ionization mode. A novel 9-mer metabolite of REVERSIR-A, resulting from deamination of the 3' terminal 2'-O-methyl-adenosine nucleotide to 2'-O-methyl-inosine, was discovered at significant levels in monkey liver. The metabolite's identity was confirmed by LC-MS/MS. Conclusion: This report describes the first observation of a long-chain deaminated metabolite of a single-stranded REVERSIR oligonucleotide in vivo in monkey liver.