Development and validation of a bioanalytical method for quantification of LNA-i-miR-221, a 13-mer oligonucleotide, in rat plasma using LC-MS/MS

LNA-i-miR-221, a 13-mer oligonucleotide, is a new miR-221 inhibitor that could be used as a novel drug for multiple myeloma. Herein, an ion-pair reversed phase liquid chromatography-tandem mass spectrometry (LC-MS/MS) method has been developed and validated for the quantification of LNA-i-miR-221 in rat plasma. Plasma samples were prepared with an initial phenol/chloroform/isoamyl alcohol liquid-liquid extraction followed by a solid phase extraction. Chromatographic separation was performed with a gradient system on a HALO C18 column using hexafluoro-2-propanol/triethylamine buffer and methanol as mobile phase at a flow rate of 0.4 mL/min. Under these conditions LNA-i-miR-221 and the analogue internal standard are co-eluted at 1.2 min. The detection was carried out in multiple reaction monitoring (MRM) mode using a negative electrospray ionization (ESI) interface. The assay showed a good linearity within the calibration range 10-10000 ng/mL. The precision, accuracy, and recovery values were found to be <15% (<20% at LLOQ), 100 ± 15%, and 97.6-103.7%, respectively. This method was successfully applied to measure the concentrations of LNA-i-miR-221 in plasma samples following the intravenous administration during a 4-week toxicity study in rats.