DDRE-08. A BIOANALYTICAL LC-MS/MS ASSAY TO QUANTIFY TOTAL AND UNBOUND LY3214996, ABEMACICLIB AND ITS ACTIVE METABOLITES IN HUMAN PLASMA, CEREBROSPINAL FLUID AND HUMAN GLIOBLASTOMA

BACKGROUND Here, we report on our development and validation of a sensitive and rapid LC-MS/MS method for the determination of total and unbound concentrations of ERK inhibitor LY3214996, CDK4/6 inhibitor abemaciclib and its M2 and M20 active metabolites in human plasma, cerebrospinal fluid and human glioblastoma tissue. METHODS Analytes were extracted from patient plasma, CSF and glioblastoma homogenate samples by protein precipitation with methanol. Four levels of quality controls were used during validation. The method was validated according to FDA guidelines and CAP/CLIA regulations. Equilibrium dialysis was performed to determine unbound fraction of four analytes in plasma and brain tissue. The detection was performed on Sciex QTRAP 6500+ mass spectrometer in positive electrospray ionization mode. RESULTS The method was validated over a concentration range from 0.2-500 nmol/L for all four analytes. The analytical separation was optimized on Phenomenex Kinetex™ F5 column with total run time of 3.8 min using gradient elution. For all the analytes the maximum coefficient of variation for intra- and inter-day precision was 12.0% and the accuracy was within 90.2-119.7% in all matrixes. The analytes are stable in plasma and brain homogenate for at least 19 hours and 6 hours at room temperature (RT), respectively. Stability of stock and working solutions was demonstrated for at least 15 hours (RT) and 28 days (2-8°C). The unbound fraction of the analytes in pooled human plasma and brain were determined to be 0.371 and 0.065 for LY3214996, 0.026 and 0.013 for abemaciclib, 0.052 and 0.008 for M2, 0.024 and 0.021 for M20, respectively. CONCLUSIONS A bioanalytical method to quantify LY3214996, abemaciclib and its M2 and M20 metabolites is successfully developed and validated. The method is currently applied to evaluate plasma pharmacokinetics and CNS penetration of LY3214996 and abemaciclib in recurrent glioblastoma patients in an ongoing Phase 0 clinical trial (NCT04391595).