Definition

An orally bioavailable, brain-penetrant, selective, small molecule inhibitor of Bruton’s tyrosine kinase (BTK), with potential immunomodulatory and anti-inflammatory activities. Upon oral administration, BTK inhibitor SAR442168 is able to cross the blood-brain barrier and inhibits the activity of BTK both peripherally and in the central nervous system (CNS). This prevents the activation of the B-cell antigen receptor (BCR) signaling pathway, and the resulting immune activation and inflammation. The inhibition of BTK activity also prevents microglial inflammatory signaling in the CNS, and the resulting immune activation, neuroinflammation and neurodegeneration. BTK, a cytoplasmic tyrosine kinase and member of the Tec family of kinases, plays an important role in B lymphocyte development, activation, signaling, proliferation and survival. In addition to B cells, BTK is also expressed in innate immune cells, including macrophages and microglia, and plays an important role in the regulation of microglial inflammatory signaling.