Development and validation of LC-MS/MS methods for the measurement of ribociclib, a CDK4/6 inhibitor, in mouse plasma and Ringer's solution and its application to a cerebral microdialysis study

- Novel LC-MS/MS methods for the quantitation of ribociclib in mouse plasma and Ringer's solution were developed and validated.
- Mouse plasma samples were extracted using solid phase extraction method, no extraction was required for the Ringer's solution samples.
- These methods were successfully applied for the determination of ribociclib concentration in preclinical samples obtained from cerebral microdialysis studies.

LC-MS/MS methods to measure ribociclib in mouse plasma and Ringer's solution were successfully developed and validated. Reverse phase chromatography was performed with gradient elution using C18 (100A, 50 × 4.6 mm, 3 μ) and C8-A (50 × 2.0 mm, 5 μ) columns for plasma and Ringer's samples, respectively. Mouse plasma samples were extracted using solid phase extraction method, whereas no extraction was required for the Ringer's solution samples. Analytes were detected using positive ion MRM mode. The precursor to product ions (Q1 → Q3) selected for ribociclib and d6-ribociclib were (m/z) 435.2 → 252.1 and 441.2 → 252.1, respectively. The linear range of quantification of ribociclib was 62.5-10,000 ng/ml for plasma method and 0.1-100 ng/ml for Ringer's solution method. The results for the inter-day and intra-day accuracy and precision of quality control samples were within the acceptable range. The lower limit of quantitation (LLOQ) for plasma and Ringer's samples were 62.5 ng/ml (S/N > 30) and 0.1 ng/ml (S/N > 13), respectively, whereas the limit of detection (LOD) was 6.9 ng/ml (S/N > 7) and 0.05 ng/ml (S/N > 3), respectively. The developed methods were successfully applied to the analysis of ribociclib in mouse plasma and dialysate samples collected during a cerebral microdialysis study of ribociclib in a non-tumor bearing mouse.