In the search for novel therapeutics, antisense oligonucleotide (ASO) analogs have been a major focus of research for over 40 years. They use the antisense strategy, namely they have a nucleic acid base sequence that is complementary to a portion of a specific mRNA that is produced in the cell, or to a viral RNA, in order to selectively inhibit gene expression. Oligonucleotides need to be chemically modified to stabilize them against hydrolysis by endogenous nucleases. Until now several

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... othioate (PS) oligonucleotide analogs have been approved by the FDA for human use. This article seeks to provide a history of this subject to date.