Preclinical characterization of pirtobrutinib, a highly selective, noncovalent (reversible) BTK inhibitor

Bruton tyrosine kinase (BTK), a nonreceptor tyrosine kinase, is a major therapeutic target for B-cell-driven malignancies. However, approved covalent BTK inhibitors (cBTKis) are associated with treatment limitations because of 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, noncovalent (reversible) BTK inhibitor. Pirtobrutinib binds BTK with an extensive network of interactions to BTK and water molecules in the adenosine triphosphate binding region and shows no direct interaction with C481. Consequently, 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 cBTKis, prevented Y551 phosphorylation in the activation loop. These data suggest that 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 that 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 that 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.

IL-23 and IL-2 activation of STAT5 is required for optimal IL-22 production in ILC3s during colitis

Signal transducer and activator of transcription (STAT) proteins have critical roles in the development and function of immune cells. STAT signaling is often dysregulated in patients with inflammatory bowel disease (IBD), suggesting the importance of STAT regulation during the disease process. Moreover, genetic alterations in STAT3 and STAT5 (e.g., deletions, mutations, and single-nucleotide polymorphisms) are associated with an increased risk for IBD. In this study, we elucidated the precise roles of STAT5 signaling in group 3 innate lymphoid cells (ILC3s), a key subset of immune cells involved in the maintenance of gut barrier integrity. We show that mice lacking either STAT5a or STAT5b are more susceptible to Citrobacter rodentium-mediated colitis and that interleukin-2 (IL-2)- and IL-23-induced STAT5 drives IL-22 production in both mouse and human colonic lamina propria ILC3s. Mechanistically, IL-23 induces a STAT3-STAT5 complex that binds IL-22 promoter DNA elements in ILC3s. Our data suggest that STAT5a/b signaling in ILC3s maintains gut epithelial integrity during pathogen-induced intestinal disease.

LAG3+ Regulatory T Cells Restrain Interleukin-23-Producing CX3CR1+ Gut-Resident Macrophages during Group 3 Innate Lymphoid Cell-Driven Colitis

Interleukin-22 (IL-22)-producing group 3 innate lymphoid cells (ILC3) maintains gut homeostasis but can also promote inflammatory bowel disease (IBD). The regulation of ILC3-dependent colitis remains to be elucidated. Here we show that Foxp3+ regulatory T cells (Treg cells) prevented ILC3-mediated colitis in an IL-10-independent manner. Treg cells inhibited IL-23 and IL-1β production from intestinal-resident CX3CR1+ macrophages but not CD103+ dendritic cells. Moreover, Treg cells restrained ILC3 production of IL-22 through suppression of CX3CR1+ macrophage production of IL-23 and IL-1β. This suppression was contact dependent and was mediated by latent activation gene-3 (LAG-3)-an immune checkpoint receptor-expressed on Treg cells. Engagement of LAG-3 on MHC class II drove profound immunosuppression of CX3CR1+ tissue-resident macrophages. Our study reveals that the health of the intestinal mucosa is maintained by an axis driven by Treg cells communication with resident macrophages that withhold inflammatory stimuli required for ILC3 function.

Recombinant Helicobacter bilis protein P167 for mouse serodiagnosis in a multiplex microbead assay

Infection of mice with Helicobacter bilis is widespread in research and commercial mouse colonies. Therefore, sensitive, specific, and high-throughput assays are needed for rapid and accurate testing of mice in large numbers. This report describes a novel multiplex assay, based on fluorescent microbeads, for serodetection of H. bilis infection. The assay requires only a few microliters of serum to perform and is amenable to a high-throughput format. Individual microbead sets were conjugated to purified, H. bilis-specific, recombinant proteins P167C and P167D and bacterial membrane extracts from H. bilis and Helicobacter hepaticus. For detecting H. bilis infection in the microbead multiplex assay, P167C and P167D provided significantly higher sensitivities (94 and 100%, respectively) and specificities (100 and 95%, respectively) than membrane extract (78% sensitivity and 65% specificity). Microbead multiplex assay results were validated by enzyme-linked immunosorbent assay. Purified recombinant proteins showed low batch-to-batch variation; this feature allows for ease of quality control, assay robustness, and affordability. Thus, recombinant antigens are highly suitable in the multiplex microbead assay format for serodetection of H. bilis infection.