GSE136634
Clinical and biological implications of target occupancy in chronic lymphocytic leukemia treated with acalabrutinib
Inhibition of the B-cell receptor pathway, and specifically of Bruton tyrosine kinase (BTK), is a leading therapeutic strategy in chronic lymphocytic leukemia (CLL). Target occupancy has been measured as a pharmacodynamic parameter in clinical studies of covalent BTK inhibitors. However, the kinetics of BTK turnover, which determines occupancy, and the relationship between occupancy, pathway inhibition and clinical outcomes remains undefined. This randomized phase 2 study investigated the safety, efficacy, and pharmacodynamics of a selective BTK inhibitor acalabrutinib at 100 mg twice daily or 200 mg once daily in 48 patients with relapsed/refractory or high-risk treatment naïve CLL. Acalabrutinib was well tolerated and yielded an overall response rate (ORR) of partial response or better of 95.8% (95% CI 78.9%, 99.9%) and an estimated progression-free survival (PFS) rate at 24 months of 91.5% (95% CI 70.0%, 97.8%) with twice daily dosing and an ORR of 79.2% (95% CI 57.9%, 92.9%) and an estimated PFS rate at 24 months of 87.2% (95% CI 57.2%, 96.7%) with once daily dosing. BTK resynthesis was faster in CLL than in healthy volunteers. Twice daily dosing maintained higher BTK occupancy and achieved more potent pathway inhibition compared to once daily dosing. Additional follow-up is required to address the impact of dosing schedule and BTK occupancy on long-term clinical outcomes. Overall design: RNA sequencing of CD19+ peripheral blood mononuclear cells and lymph node core biopsies before and during treatment with acalabrutinib ACP = acalabrutinib BID = twice daily QD = once daily D3/4/5 = day 3/4/5 of treatment C1/6 = after cycle 1/6 of treatment