Janus kinase inhibitor


Janus kinase inhibitors, also known as JAK inhibitors or jakinibs, are a type of medication that functions by inhibiting the activity of one or more of the Janus kinase family of enzymes, thereby interfering with the JAK-STAT signaling pathway.
These inhibitors have therapeutic application in the treatment of cancer and inflammatory diseases such as rheumatoid arthritis. There is interest in their use for various skin conditions. JAK3 inhibitors are attractive as a possible treatment of various autoimmune diseases since its functions is mainly restricted to lymphocytes. Development for a selective JAK3 inhibitors are ongoing.

Mechanism of action

s play key roles in controlling cell growth and the immune response. Many cytokines function by binding to and activating type I and type II cytokine receptors. These receptors in turn rely on the Janus kinase family of enzymes for signal transduction. Hence drugs that inhibit the activity of these Janus kinases block cytokine signalling.
More specifically, Janus kinases phosphorylate activated cytokine receptors. These phosphorylated receptors in turn recruit STAT transcription factors which modulate gene transcription.
The first JAK inhibitor to reach clinical trials was tofacitinib. Tofacitinib is a specific inhibitor of JAK3 thereby blocking the activity of IL-2, IL-4, IL-15 and IL-21. Hence Th2 cell differentiation is blocked and therefore tofacitinib is effective in treating allergic diseases. Tofacitinib to a lesser extent also inhibits JAK1 and JAK2 which in turn blocks IFN-γ and IL-6 signalling and consequently Th1 cell differentiation.
One mechanism is that the blocking of Jak-dependent IL-23 reduces IL-17 and the damage it causes.

Molecule design

Some JAK1 inhibitors are based on a benzimidazole core.

Examples

Approved compounds