Abstract
Chronic lymphocytic leukemia (CLL) is a clinically heterogeneous disease that originates from dysfunctional B lymphocytes. Abnormal B cell receptor (BCR) signaling has been linked to the proliferation and survival of B cell malignancies such as CLL. The treatment landscape of these lymphomas has been revolutionized by the use of targeted therapies against proteins like Bruton’s tyrosine kinase (BTK), Phosphoinositide 3-kinases (PI3K), and B cell lymphoma 2 (BCL-2). Among the three, targeting BTK has the longest track record of effectiveness in the treatment of CLL. Nevertheless, lifelong treatment exposure leads to the emergence of on-target resistance mutations contributing to the challenge that CLL remains an incurable disease.
This study delves into the discovery and characterization of BTK mutations that cause resistance to BTK inhibitors. In our studies, we utilized data from bulk and single-cell genomic analyses that identified a series of acquired BTK mutations in a cohort of CLL patients that relapsed on the phase I/II clinical trial of pirtobrutinib, a next generation non-covalent BTK inhibitor. The data revealed mutations (BTK V416L, A428D, M437R, T474I, L528W) that occur at critical residues within the catalytic kinase domain of BTK. Utilizing our cellular assays, we found that these mutations were causative of resistance to the non-covalent BTK inhibitor pirtobrutinib and that several BTK mutations conferred resistance to both covalent and non-covalent BTK inhibitors.Taken together, our findings suggest that kinase-impaired mutations in BTK can still activate downstream signaling pathways through interactions with surrogate kinases.