A validated HPLC-MS/MS method for the quantification of systemic mifepristone after subcutaneous application in mice

Mifepristone (RU486, MIF) is a synthetic steroidal hormone with progesterone and glucocorticoid receptor antagonistic characteristics. MIF is commonly used for pharmalogical abortions, but also for the treatment of endometrial and endocrine disorders. The goal of the study was to establish and validate a targeted HPLC-MS/MS method for the quantification of MIF and one of its active metabolites metapristone (MET) in plasma after subcutaneous implantation of slow-release MIF pellets in female BALB/c mice. Additionally, we aimed to apply the analytical method to tissue of several organs to understand the tissue-specific distribution of both analytes after release into systemic circulation. Sample preparation comprised a simple liquid-liquid extraction with diethylether and required 100 μl of plasma or homogenates of approximately 50 mg of tissue. The presented HPLC-MS/MS method showed high sensitivity with baseline separation of MIF, MET, and the internal standard levonorgestrel within a run time of only 8.0 minutes and comparable limits of quantification for plasma and tissue homogenates ranging from 40 pg ml^-1 to 105 pg ml^-1 for MIF and MET. The presented study is suitable for murine plasma and tissues and can be easily applied to human samples.