The potential of JAK inhibitors
The family of JAKs is composed of four tyrosine kinases, JAK1, JAK2, JAK3, and TYK2, that are involved in the JAK signaling pathway, which regulates normal hematopoiesis (or blood making), inflammation, immune function, and some growth processes. Dysregulation of the immune function and its effector molecules, cytokines, makes use of the JAK signaling pathway and has been associated with a number of diseases, including RA, psoriasis and other chronic inflammatory diseases.
A growing body of clinical data suggests that the level of selectivity of a JAK therapeutic is highly correlated to its efficacy and safety profile. For example, JAK1 is known to interact with the other JAKs to transduce cytokine-driven pro-inflammatory signaling, which leads to inflammation in human tissues. Therefore, inhibition of JAK1 is believed to be of therapeutic benefit for a range of inflammatory conditions as well as for other diseases driven by JAK-mediated signal transduction. In contrast, inhibition of the other three kinases (JAK2, JAK3, and TYK2) may not be required for the anti-inflammatory effect, whereas their inhibition may contribute to side effects. For example, inhibition of JAK2 has been linked to anemia, and inhibition of JAK3 to immunosuppression. Non-selective JAK inhibitors have been shown to increase low-density lipoprotein, or LDL. Therefore, we believe the desired efficacy and safety profile of any JAK inhibitor is directly linked to the selectivity of the product.
In November 2012, Xeljanz®1Xeljanz® is a registered trademark for an approved RA medicine of Pfizer. was approved by the U.S. Food and Drug Administration, or FDA, as the first and only JAK inhibitor for RA approved for commercial sale in the United States. Xeljanz is intended for the treatment of adult patients with RA who have had an inadequate response to, or who are intolerant of, MTX. Xeljanz is a small molecule suitable for oral administration and has strong binding affinity for JAK3 and JAK1, and weaker affinity for JAK2. The safety and effectiveness of Xeljanz were evaluated in seven clinical trials in adult patients with moderately to severely active RA. In all of the trials, patients treated with Xeljanz experienced improvement in clinical response and physical functioning compared to patients treated with placebo. However, the use of Xeljanz has been associated with a range of side effects, including anemia (reduced hemoglobin levels) and elevations in both liver enzyme and lipid levels. For example, in controlled clinical trials for Xeljanz, dose-related elevations in lipid parameters (total cholesterol, LDL cholesterol, high-density lipoprotein, or HDL, cholesterol, triglycerides) were observed at one month of exposure, including a 15% increase in LDL cholesterol in the Xeljanz 5 mg twice daily arm, the approved dosage in the United States. Accordingly, Galapagos believes there continues to be a significant unmet medical need in RA and other inflammatory diseases for an orally administered approach with a more favorable side effect profile.