Quantitative analysis of the cyclic peptide GG-8-6 in rat plasma using LC-MS/MS and its application to a pharmacokinetic study

Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related death worldwide. The discovery of new anticancer compounds is of great significance. GG-8-6, cyclo-(Val1-Leu2-Pro3-Ile4-Leu5-Leu6-Leu7-Val8-Leu9), a new synthetic cyclic peptide, might be a potential candidate for developing new anti-HCC drugs. GG-8-6 shares no structural homology to current anti-HCC drugs. Therefore, it was necessary to develop a quantitative method for the determination of GG-8-6 in vivo. Herein, a simple, specific and sensitive liquid chromatographic method with tandem mass spectrometric detection (LC-MS/MS) was developed and validated for the analysis of GG-8-6 in rat plasma. GG-8-6 and the internal standard (IS), A6, cyclo-(Val1-Leu2-Pro3-Ala4-Leu5-Leu6-Leu7-Val8-Leu9), were extracted from rat plasma by ethyl acetate. Chromatographic separation was performed on an Agilent Eclipse XDB-C18 column (4.6 × 150 mm, 5 μm) with a mobile phase consisting of acetonitrile-water containing 0.1% formic acid (90:10, v/v) with isocratic elution at a flow rate of 0.5 mL/min for 8.0 min. Multiple reaction monitoring (MRM) mode was performed with ion pairs of m/z: 974.8 → 861.8 for GG-8-6 and 932.7 → 819.8 for A6. The selectivity, matrix effects, recovery, intra- and inter-day precision and accuracy were validated with acceptable results in accordance with the US Food and Drug Administration guidelines. The calibration curve was linear (r2 > 0.99) over a concentration range of 1-1000 ng/mL with a lower limit of quantification (LLOQ) of 1 ng/mL. The method was successfully applied to the pharmacokinetic study of GG-8-6 in rats.