Janus kinase (JAK) is a family of intracellular, non-receptor tyrosine kinases that transduce cytokine-mediated signals via the JAK-STAT pathway. They were initially named "just another kinase" 1 and 2, but were ultimately published as "Janus kinase". The name is taken from the two-faced Roman god of beginnings, endings and duality, Janus, because the JAKs possess two near-identical phosphate-transferring domains. One domain exhibits the kinase activity, while the other negatively regulates the kinase activity of the first.
A tyrosine kinase is an enzyme that can transfer a phosphate group from ATP to the tyrosine residues of specific proteins inside a cell. It functions as an "on" or "off" switch in many cellular functions.
The JAK-STAT signaling pathway is a chain of interactions between proteins in a cell, and is involved in processes such as immunity, cell division, cell death and tumour formation. The pathway communicates information from chemical signals outside of a cell to the cell nucleus, resulting in the activation of genes through a process called transcription. There are three key parts of JAK-STAT signalling: Janus kinases (JAKs), signal transducer and activator of transcription proteins (STATs), and receptors. Disrupted JAK-STAT signalling may lead to a variety of diseases, such as skin conditions, cancers, and disorders affecting the immune system.
Signal transducer and activator of transcription 5 (STAT5) refers to two highly related proteins, STAT5A and STAT5B, which are part of the seven-membered STAT family of proteins. Though STAT5A and STAT5B are encoded by separate genes, the proteins are 90% identical at the amino acid level. STAT5 proteins are involved in cytosolic signalling and in mediating the expression of specific genes. Aberrant STAT5 activity has been shown to be closely connected to a wide range of human cancers, and silencing this aberrant activity is an area of active research in medicinal chemistry.
Tyrosine-protein kinase JAK3 is a tyrosine kinase enzyme that in humans is encoded by the JAK3 gene.
Janus kinase 2 is a non-receptor tyrosine kinase. It is a member of the Janus kinase family and has been implicated in signaling by members of the type II cytokine receptor family, the GM-CSF receptor family, the gp130 receptor family, and the single chain receptors.
JAK1 is a human tyrosine kinase protein essential for signaling for certain type I and type II cytokines. It interacts with the common gamma chain (γc) of type I cytokine receptors, to elicit signals from the IL-2 receptor family, the IL-4 receptor family, the gp130 receptor family. It is also important for transducing a signal by type I (IFN-α/β) and type II (IFN-γ) interferons, and members of the IL-10 family via type II cytokine receptors. Jak1 plays a critical role in initiating responses to multiple major cytokine receptor families. Loss of Jak1 is lethal in neonatal mice, possibly due to difficulties suckling. Expression of JAK1 in cancer cells enables individual cells to contract, potentially allowing them to escape their tumor and metastasize to other parts of the body.
Interleukin-2 receptor subunit beta is a protein that in humans is encoded by the IL2RB gene. Also known as CD122; IL15RB; P70-75.
Lestaurtinib is a tyrosine kinase inhibitor structurally related to staurosporine. This semisynthetic derivative of the indolocarbazole K252a was investigated by Cephalon as a treatment for various types of cancer. It is an inhibitor of the kinases fms-like tyrosine kinase 3 (FLT3), Janus kinase 2 (JAK2), tropomyosin receptor kinase (trk) A (TrkA), TrkB and TrkC.
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.
Ruxolitinib, sold under the brand names Jakafi and Jakavi, is a medication for the treatment of intermediate or high-risk myelofibrosis, a type of myeloproliferative disorder that affects the bone marrow, polycythemia vera (PCV) when there has been an inadequate response to or intolerance of hydroxyurea, and steroid-refractory acute graft-versus-host disease. It was developed and marketed by Incyte Corp in the US under the brand name Jakafi, and by Novartis elsewhere in the world, under the brand name Jakavi.
Fedratinib, sold under the brand name Inrebic, is a medication used to treat myeloproliferative diseases including myelofibrosis. It is used in the form of fedratinib hydrochloride and is an orally available semi-selective inhibitor of Janus kinase 2 (JAK-2). Fedratinib acts as a competitive inhibitor of protein kinase JAK-2 with IC50=6 nM; related kinases FLT3 and RET are also sensitive, with IC50=25 nM and IC50=17 nM, respectively. Significantly less activity was observed against other tyrosine kinases including JAK3 (IC50=169 nM). In treated cells the inhibitor blocks downstream cellular signalling (JAK-STAT) leading to suppression of proliferation and induction of apoptosis. It was approved by FDA on 16 August 2019.
Momelotinib (INN, formerly GS-0387, CYT-387) is an inhibitor of Janus kinases JAK1 and JAK2, acting as an ATP competitor with IC50 values of 11 and 18 nM, respectively. The inhibitor is significantly less active towards other kinases, including JAK3 (IC50 = 0.16 μM).
Baricitinib, sold under the brand name Olumiant among others, is a drug for the treatment of rheumatoid arthritis (RA) in adults whose disease was not well controlled using RA medications called tumor necrosis factor (TNF) antagonists. It acts as an inhibitor of janus kinase (JAK), blocking the subtypes JAK1 and JAK2. The drug is approved for use in the European Union and the United States.
Pacritinib (INN) is a macrocyclic Janus kinase inhibitor that is being developed for the treatment of myelofibrosis. It mainly inhibits Janus kinase 2 (JAK2) and Fms-like tyrosine kinase 3 (FLT3). The drug was in Phase III clinical trials as of 2013.
Oclacitinib is a veterinary medication used in the control of atopic dermatitis and pruritus from allergic dermatitis in dogs at least 12 months of age. Chemically, it is a synthetic cyclohexylamino pyrrolopyrimidine janus kinase inhibitor that is relatively selective for JAK1. It inhibits signal transduction when the JAK is activated and thus helps downregulate expression of inflammatory cytokines. While oclacitinib is effective, its long-term safety is currently unknown.
Upadacitinib, sold under the brand name Rinvoq, is a Janus kinase (JAK) inhibitor medication for the treatment of moderately to severely active rheumatoid arthritis in adults where methotrexate did not work well or could not be tolerated. It was approved for medical use in the United States and in the European Union in 2019, and was developed by the biotech company AbbVie.
Janus kinase 3 inhibitors, also called JAK3 inhibitors, are a new class of immunomodulatory agents that inhibit Janus kinase 3. They are used for the treatment of autoimmune diseases. The Janus kinases are a family of four nonreceptor tyrosine-protein kinases, JAK1, JAK2, JAK3, and TYK2. They signal via the JAK/STAT pathway, which is important in regulating the immune system. Expression of JAK3 is largely restricted to lymphocytes, while the others are ubiquitously expressed, so selective targeting of JAK3 over the other JAK isozymes is attractive as a possible treatment of autoimmune diseases.
Abrocitinib is a Janus kinase inhibitor drug which is currently under investigation for the treatment of atopic dermatitis. It was developed by Pfizer.
Zotiraciclib (TG02) is a potent oral spectrum selective kinase inhibitor for the treatment of cancer. It was discovered in Singapore by S*BIO Pte Ltd and falls under the category of small molecule macrocycles. It crosses the blood brain barrier and acts by depleting Myc through the inhibition of cyclin-dependent kinase 9 (CDK9). It is one of a number of CDK inhibitors under investigation; others targeting CDK9 for the treatment of acute myeloid leukemia include alvocidib and atuveciclib. Myc overexpression is a known factor in many cancers, with 80 percent of glioblastomas characterized by this property. Zotiraciclib has been granted orphan drug designation by the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA) for the treatment of gliomas.
