Janus kinase inhibitor
Janus kinase inhibitors also known as JAK inhibitors are a type of medication that functions by inhibiting the activity of one or more of the Janus kinase family of enzymes (JAK1, JAK2, JAK3, TYK2), thereby interfering with the JAK-STAT signaling pathway. These inhibitors have therapeutic application in the treatment of cancer and inflammatory diseases.
Mechanism of action
Cytokines 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 (JAK) family of enzymes for signal transduction. Hence drugs that inhibit the activity of these Janus kinases block cytokine signalling.
The first JAK inhibitor to reach clinical trials was tofacitinib. Tofacitinib is a specific inhibitor of JAK3 (IC50 = 2 nM) 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 (IC50 = 100 nM) and JAK2 (IC50 = 20 nM) which in turn blocks IFN-γ and IL-6 signalling and consequently Th1 cell differentiation.
- Ruxolitinib against JAK1/JAK2 for psoriasis, myelofibrosis, and rheumatoid arthritis. Approved by the U.S. Food and Drug Administration (FDA) in November 2011 for myelofibrosis.
- Tofacitinib (tasocitinib; CP-690550) against JAK3 for psoriasis and rheumatoid arthritis. US FDA approved in November 2012 for rheumatoid arthritis.
In clinical trials
- Baricitinib (LY3009104, INCB28050) against JAK1/JAK2 starting phase IIb for rheumatoid arthritis
- CYT387 against JAK2 for myeloproliferative disorders
- GLPG0634 against JAK1, for RA and Crohn's disease
- GSK2586184 against JAK1, for Psoriasis and ulcerative colitis, but discontinued in SLE 
- Lestaurtinib against JAK2, for acute myelogenous leukemia (AML)
- Pacritinib (SB1518) against JAK2 for relapsed lymphoma and advanced myeloid malignancies, chronic idiopathic myelofibrosis (CIMF)
- TG101348 against JAK2; phase I results for myelofibrosis are published
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- Vaddi K, Sarlis NJ, Gupta V (November 2012). "Ruxolitinib, an oral JAK1 and JAK2 inhibitor, in myelofibrosis". Expert Opin Pharmacother 13 (16): 2397–407. doi:10.1517/14656566.2012.732998. PMID 23051187.
- "Ruxolitinib (Jakafi) for myelofibrosis". Med Lett Drugs Ther 54 (1387): 27–8. April 2012. PMID 22469651.
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- Zerbini CA, Lomonte AB (May 2012). "Tofacitinib for the treatment of rheumatoid arthritis". Expert Rev Clin Immunol 8 (4): 319–31. doi:10.1586/eci.12.19. PMID 22607178.
- "Incyte Earns $19M Milestone from Lilly on Start of Phase IIb Trial with RA Candidate". Genetic Engineering & Biotechnology News. 2010-10-20.
- "Safety and Efficacy Study of CYT387 in Primary Myelofibrosis (PMF) or Post-polycythemia Vera (PV) or Post-essential Thrombocythemia (ET)". ClinicalTrials.gov. U.S. National Institutes of Health. 2012-03-09.
- Pardanani A, Lasho T, Smith G, Burns CJ, Fantino E, Tefferi A (August 2009). "CYT387, a selective JAK1/JAK2 inhibitor: in vitro assessment of kinase selectivity and preclinical studies using cell lines and primary cells from polycythemia vera patients". Leukemia 23 (8): 1441–5. doi:10.1038/leu.2009.50. PMID 19295546.
- Shabbir M, Stuart R (March 2010). "Lestaurtinib, a multitargeted tyrosine kinase inhibitor: from bench to bedside". Expert Opin Investig Drugs 19 (3): 427–36. doi:10.1517/13543781003598862. PMID 20141349.
- Hart S, Goh KC, Novotny-Diermayr V, Hu CY, Hentze H, Tan YC, Madan B, Amalini C, Loh YK, Ong LC, William AD, Lee A, Poulsen A, Jayaraman R, Ong KH, Ethirajulu K, Dymock BW, Wood JW (November 2011). "SB1518, a novel macrocyclic pyrimidine-based JAK2 inhibitor for the treatment of myeloid and lymphoid malignancies". Leukemia 25 (11): 1751–9. doi:10.1038/leu.2011.148. PMID 21691275.
- "A Phase 1/2 Study of Oral SB1518 in Subjects With Chronic Idiopathic Myelofibrosis". ClinicalTrials.gov. U.S. National Institutes of Health. 2012-04-19.
- Pardanani A, Gotlib JR, Jamieson C, Cortes JE, Talpaz M, Stone RM, Silverman MH, Gilliland DG, Shorr J, Tefferi A (March 2011). "Safety and efficacy of TG101348, a selective JAK2 inhibitor, in myelofibrosis". J. Clin. Oncol. 29 (7): 789–96. doi:10.1200/JCO.2010.32.8021. PMID 21220608. Lay summary – NCI Cancer Bulletin.