Pirtobrutinib is a small molecule, noncovalent inhibitor of BTK. BTK is a signaling protein of the B-cell antigen receptor (BCR) and cytokine receptor pathways. In B-cells, BTK signaling results in activation of pathways necessary for B-cell proliferation, trafficking, chemotaxis, and adhesion. Pirtobrutinib binds to wild type BTK and BTK harboring C481 mutations, leading to inhibition of BTK kinase activity. In nonclinical studies, pirtobrutinib inhibited BTK-mediated B-cell CD69 expression and inhibited malignant B-cell proliferation. Pirtobrutinib showed dose-dependent anti-tumor activities in BTK wild type and BTK C481S mutant mouse xenograft models. On January 27, 2023, the Food and Drug Administration (FDA) granted accelerated approval to pirtobrutinib (Jaypirca, Eli Lilly and Company) for relapsed or refractory mantle cell lymphoma (MCL) after at least two lines of systemic therapy, including a BTK inhibitor.

Ibrutinib is an orally bioavailable Bruton's tyrosine kinase (BTK) inhibitor indicated for the treatment of mantle cell lymphoma (MCL) patients that previously received at least one therapy. The drug was jointly developed by Janssen Biotech and Pharmacyclics. Ibrutinib selectively binds to Cys-481 residue in the allosteric inhibitory segment of BTK (TK/SH1 domain), and irreversibly blocks its enzymatic activity thus preventing B-cell activation and signaling, totally blocking the B-cell receptor and cytokine receptor pathways. This leads to an inhibition of the growth of malignant B cells that overexpress BTK. Apart from mantle cell lymphoma Ibrutinib is approved for the treatment of chronic lymphocytic leukemia and Waldenstrom Macroglobulinemia.