antagomiRs

Antagomirs are chemically engineered antisense oligonucleotides designed to silence endogenous microRNAs (miRNAs) in vivo. They are typically complementary to a mature miRNA sequence and are modified to enhance stability and uptake, often including a phosphorothioate backbone, 2'-O-methyl or other sugar modifications, and a hydrophobic moiety such as cholesterol to improve delivery. In use, antagomirs are administered systemically to bind the target miRNA, thereby preventing incorporation of the miRNA into the RNA-induced silencing complex (RISC) and reducing miRNA activity. The bound miRNA may be sequestered or degraded, leading to upregulation of miRNA target genes.

Antagomirs are usually 21–23 nucleotides in length and designed to be complementary to the mature miRNA sequence. Their chemical modifications increase stability in biological fluids and tissue uptake, enabling in vivo silencing of the target miRNA, often with notable activity in liver after systemic administration.

History and scope: The term antagomir originated from a study by Krutzfeldt and colleagues in 2005–2006, which demonstrated cholesterol-conjugated, chemically modified antisense oligonucleotides that could suppress miR-122 in mice and produce metabolic effects. Since then, antagomir-like molecules have been used to study miRNA function and have been explored as potential therapeutics in diseases linked to miRNA dysregulation.

Limitations and considerations: Challenges include off-target effects, immune stimulation, toxicity, and delivery limitations that vary by tissue and dosing. Antagomirs are part of a broader landscape of miRNA inhibitors that includes locked nucleic acid (LNA) antisense oligos and miRNA sponges, each with distinct properties and applications.