Determination of GTI-2040, a novel antisense oligonucleotide, in human plasma by using HPLC combined with solid phase and liquid–liquid extractions

GTI-2040 is a 20-mer phosphorothioate oligonucleotide complementary to the mRNA of the R2 subunit of ribonucleotide reductase (RNR). It is under clinical development as an anti-cancer agent. A reverse phase high-performance liquid chromatograph (HPLC) method was established for the quantitative analysis of GTI-2040 in human plasma. Plasma samples were prepared with an initial solid-phase extraction (SPE) followed by a liquid–liquid extraction step. HPLC analysis was performed with a gradient system on a Waters XTerra®MS C18 column. The mobile phase consisted of acetonitrile–tetrabutyl ammonium hydrogen sulfate (TBAS) buffer (pH 9.0, 20 mM) at a flow rate of 1.0 ml/min, and the detector was set at a wavelength of 260 nm. A cationic pairing reagent, tetrabutyl ammonium hydrogen sulfate was added during plasma sample clean-up with solid-phase extraction, resulting in significant improvement in extraction recovery. In addition, TBAS addition to the mobile phase improved the peak symmetry of GTI-2040. This method was successfully used in the analysis of GTI-2040 in clinical plasma samples.