Originally known as GRN163L, imetelstat sodium (imetelstat) is a 13-mer N3’—P5’ thio-phosphoramidate (NPS) oligonucleotide that has a covalently bound 5’ palmitoyl (C16) lipid group. The proprietary nucleic acid backbone provides resistance to the effect of cellular nucleases, thus conferring improved stability in plasma and tissues, as well as significantly improved binding affinity to its target. The lipid group enhances cell permeability to increase potency and improve pharmacokinetic and pharmacodynamic properties.

The compound has a long residence time in bone marrow, spleen and liver. Imetelstat binds with high affinity to the template region of the RNA component of telomerase, resulting in direct, competitive inhibition of telomerase enzymatic activity, rather than elicit its effect through an antisense inhibition of protein translation. Imetelstat is administered by intravenous infusion.