Bruton Tyrosine Kinase Inhibition Decreases Inflammation and Differentially Impacts Phagocytosis and Cellular Metabolism in Mouse- and Human-derived Myeloid Cells.

Bruton tyrosine kinase (BTK) is a kinase expressed by various immune cells and is often activated under proinflammatory states. Although the majority of BTK-related research has historically focused on B cells, understanding the role of BTK in non-B cell populations is critical given myeloid cells also express BTK at comparable levels. In this study, we investigated and compared how BTK inhibition in human and murine myeloid cells alters cell phenotype and function. All experiments were performed using two BTK inhibitors (evobrutinib and tolebrutinib) that are currently in late-stage clinical trials for the treatment of multiple sclerosis. Assays were performed to assess the impact of BTK inhibition on cytokine and microRNA expression, phagocytic capacity, and cellular metabolism. In all cells, both evobrutinib and tolebrutinib significantly decreased phosphorylated BTK and LPS-induced cytokine release. BTK inhibition also significantly decreased the oxygen consumption rate and extracellular acidification rate in myeloid cells, and significantly decreased phagocytosis in murine-derived cells, but not human macrophages. To further elucidate the mechanism, we also investigated the expression of microRNAs known to impact the function of myeloid cells. BTK inhibition resulted in an altered microRNA expression profile (i.e., decreased miR-155-5p and increased miR-223-3p), which is consistent with a decreased proinflammatory myeloid cell phenotype. In summary, these results provide further insights into the mechanism of action of BTK inhibitors in the context of immune-related diseases, while also highlighting important species-specific and cell-specific differences that should be considered when interpreting and comparing results between preclinical and human studies.