Pirtobrutinib preclinical characterization: a highly selective, non-covalent (reversible) BTK inhibitor

Abstract

Bruton tyrosine kinase (BTK), a nonreceptor tyrosine kinase, is a major therapeutic target for B-cell driven malignancies. However, approved covalent BTK inhibitors (cBTKi) are associated with treatment limitations due to off-target side effects, suboptimal oral pharmacology, and development of resistance mutations (eg, C481) that prevent inhibitor binding. Here we describe the preclinical profile of pirtobrutinib, a potent, highly selective, non-covalent (reversible) BTK inhibitor. Pirtobrutinib binds BTK with an extensive network of interactions to BTK and water molecules in the adenosine triphosphate (ATP)-binding region and shows no direct interaction with C481. As a result, pirtobrutinib inhibits both BTK and BTK C481 substitution mutants in enzymatic and cell-based assays with similar potencies. In differential scanning fluorimetry studies, BTK bound to pirtobrutinib exhibited a higher melting temperature than cBTKi-bound BTK. Pirtobrutinib, but not cBTKi, prevented Y551 phosphorylation in the activation loop. These data suggest pirtobrutinib uniquely stabilizes BTK in a closed, inactive conformation. Pirtobrutinib inhibits BTK signaling and cell proliferation in multiple B-cell lymphoma cell lines and significantly inhibits tumor growth in human lymphoma xenografts in vivo. Enzymatic profiling showed pirtobrutinib was highly selective for BTK in >98% of the human kinome, and in follow-up cellular studies pirtobrutinib retained >100-fold selectivity over other tested kinases. Collectively, these findings suggest pirtobrutinib represents a novel BTK inhibitor with improved selectivity and unique pharmacologic, biophysical and structural attributes with the potential to treat B-cell driven cancers with improved precision and tolerability. Pirtobrutinib is being tested in phase 3 clinical studies for a variety of B-cell malignancies.

A Review of Resistance Mechanisms to Bruton’s Kinase Inhibitors in Chronic Lymphocytic Leukemia

“…Pirtobrutinib is a potent, highly selective ncBTKi that enables it to break through resistance to cBTKi. Due to its unique structure, pirtobrutinib reversibly links to the ATP binding site of BTK without the involvement of C481 [58]. Therefore, pirtobrutinib remains active in both the C481-mutated and wild-type BTK, overcoming the major mechanism of resistance to cBTKi.…”

Advances in the treatment of relapsed/refractory marginal zone lymphoma

“…Pirtobrutinib is a potent, non-covalent (reversible), highly selective inhibitor of both BTK and C481 mutant BTK. Pirtobrutinib functions by binding to BTK via an extensive network of interactions with water molecules in the ATP binding region, rather than directly interacting with the C481 site, demonstrating potential to overcome resistance to covalent BTK inhibitors ( 58 , 59 ). On January 27, 2023, the FDA expedited approval of pirtobrutinib for the treatment of R/R MCL patients who have received at least two lines of systemic therapy, including BTK inhibitors ( 60 ).…”

Amino-Pyrazoles in Medicinal Chemistry: A Review

“…Very recently, Eli Lilly launched the new 5AP Pirtobrutinib (Jaypirca™, Figure 9), approved to treat mantle cell lymphoma (MCL), on the market [71][72][73][74][75][76]. In detail, this (S)-5amino-3-(4-((5-fluoro-2-methoxybenzamido)methyl)phenyl)-1-(1,1,1-trifluoropropane-2-yl)-1H-pyrazole-4 carboxamide is a reversible inhibitor of Bruton Kinase (BTK), a nonreceptor tyrosine kinase, that represents a major therapeutic target for B-cell-driven malignancies.…”