PK/PD Study of Zanubrutinib in Primary Chronic Lymphocytic Leukemia Patients
Authors: Xu Zhenshu , Weng Ping , Xu Shujuan , Huang Yun , Guo Guangyao , Yu Zezhong , Lin Jie , Liu Liping , Pan Renyao , Wang Changgui , Chen Xi , Bai Yumenglin 
Published: December 2024

Introduction
Chronic lymphocytic leukemia (CLL) is a clonal proliferative neoplasm of mature B lymphocytes characterized by a specific immunophenotype. Zanubrutinib, a novel BTK inhibitor, has limited experience in China, and its metabolic profile is still unclear in patients with primary CLL, with large inter- and intra-individual variations in pharmacokinetic and pharmacodynamic (PK/PD) profiles, which have resulted in distinct therapeutic efficacy and toxicity, and therefore an in-depth individualized dosing study of this drug is urgently needed. Therefore, there is an urgent need for in-depth studies on the individualized administration of the drug, especially on the changes in the concentration of the drug in lymphocytes, which is the key to directly exerting the pharmacological effects of the drug. To elucidate the pharmacodynamic material basis and mechanism of action of zanubrutinib, and then to promote the use of zanubrutinib for the first-line treatment of CLL, and to provide a scientific basis.
Methods
Six blank plasma samples from different sources were used for selectivity investigation. Before and 2 h after the next dose of zanubrutinib, 1-2 mL of anticoagulant blood samples were collected, centrifuged at 3500 rpm (1200 g) for 10 min at 4℃, and the supernatant plasma samples were sealed and stored in a refrigerator protected from light at -80℃ until analysis. The peak location and peak area of zanubrutinib LLOQ samples were compared to observe whether there was interference with zanubrutinib and the marked peaks in blank blood samples.
Results
Blank plasma showed no interference peaks at both zanubrutinib and internally marked peaks, indicating that endogenous substances in blank plasma did not interfere with the determination of target compounds. Zanubrutinib and internal standard had symmetrical peaks and well separated, with retention times of 2.51 min and 2.59 min, respectively. The standard curve and the lower limit of quantification of zanubrutinib had a good linear relationship in the range of 1～1000 ng/mL, the regression equation was y = 0.00237 x + 1.92× 10-3 (R2= 0.9942，1/x2), the lower limit of quantification was 1 ng/mL, and the signal-to-noise ratio of the lower limit of quantification was &gt;10. Analysis of TDM monitoring results: A total of 39 TDM results of zanubrutinib in 28 patients after clinical administration of zanubrutinib to reach a steady state showed that the mean trough concentration of zanubrutinib was 5.82±15.86 ng/mL (CV: 272.69%), the average peak concentration was 160.62±207.58 ng/mL (CV: 129.24%).
Conclusions
We successfully established a rapid, accurate and reproducible assay for the drug concentration in plasma and lymphocytes of zanubrutinib, which can be used for routine analysis of clinical samples, and better guide the efficacy testing of zanubrutinib treatment in CLL patients. A stable PK/PD model was constructed, with strong predictive ability to provide basic data for the next step of quantitative screening of factors influencing drug absorption.
Key words：Chronic lymphocytic leukemia; PK/PD; Zanubrutinib;