Janus kinase inhibitors in autoimmune diseases

Abstract

Biological therapies directed at proinflammatory cytokines have irrevocably changed the landscape of treatment of rheumatoid arthritis (RA) and other autoimmune diseases. With the advances in our knowledge in cytokine signalling, the question emerges whether targeting intracellular signalling might also be a safe and efficacious strategy. Janus kinases or Jaks are critical for a large family of cytokines and the first Jak inhibitors has been approved by the FDA. It is therefore timely to consider this new category of drugs and reflect on their potential roles, present and future, in the treatment of RA and related disorders.

Figures

Figure 1

Usage of different Jaks by various cytokines

Figure 2. Jakinibs block multiple aspects of cytokine signaling

Cytokine binding to its cognate receptor leads to phosphorylation of the intracellular domain of the tyrosine kinase receptor by specific Jaks. STATs are then recruited, bind to the receptor and become phosphorylated by Jaks. This results in STAT dimerization, translocation, and regulation of gene transcription. Cytokines also activate the PKB (Akt) and mTOR. Though not carefully studied, it is highly likely that blocking proximal cytokine signals will disrupt all downstream pathways. ** Also referred to as AKT.

Figure 3

Impact of inhibiting various Jaks on signaling by selected cytokines