Validation of a sensitive assay for thiocoraline in mouse plasma using liquid chromatography-tandem mass spectrometry

A sensitive high-performance liquid chromatography-tandem mass spectrometry assay for thiocoraline, an anti-tumor depsipeptide, in mouse plasma is described. Echinomycin, a quinoxaline peptide, was used as an internal standard. Thiocoraline was recovered from the mouse plasma using protein precipitation with acetonitrile and followed by solid-phase extraction of the supernatant. The mobile phase consisted of methanol (0.1% formic acid)-water (0.1% formic acid) (90:10, v/v). The analytical column was a YMC C(18). The standard curve was linear from 0.1 to 50 ng/ml (R(2)>0.99). The lower limit of quantitation was 0.1 ng/ml. The assay was specific based on the multiple reaction monitoring transitions at m/z 1157-->215 and m/z 1101-->243 for thiocoraline and the internal standard, echinomycin, respectively. The mean intra- and inter-day assay accuracies remained below 5 and 12%, respectively, for all calibration standards and quality control (QC) samples. The intra- and inter-day assay precisions were less than 11.4 and 9.5% for all QC levels, respectively. The utility of the assay was demonstrated by a pharmacokinetic study of i.v. (bolus) thiocoraline on CD-1 mice. Thiocoraline was stable in mouse plasma in an ice-water bath for 6 h and for three freeze-thaw cycles. The reconstituted thiocoraline after extraction and drying sample process was stable in the autosampler for over 24 h. The assay was able to quantify thiocoraline in plasma up to 48 h following dose. Pharmacokinetic analysis showed that thiocoraline has distinct pharmacokinetic profiling when dosed in different formulation solutions. The assay is currently used to measure thiocoraline plasma concentrations in support of a project to develop a suitable formulation with a desirable pharmacokinetic profile.