|This article is outdated. (November 2012)|
|Systematic (IUPAC) name|
|Trade names||Xeljanz, Jakvinus|
|Licence data||US FDA:|
|Metabolism||Hepatic (via CYP3A4 and CYP2C19)|
|Mol. mass||312.369 g/mol|
Tofacitinib (trade names Xeljanz and Jakvinus, formerly tasocitinib, CP-690550) is a drug of the janus kinase (JAK) inhibitor class, discovered and developed by Pfizer. It is currently approved for the treatment of rheumatoid arthritis (RA) in the United States and Russia, and is being studied for treatment of psoriasis, inflammatory bowel disease, and other immunological diseases, as well as for the prevention of organ transplant rejection. Tofacitinib was not approved by the European regulatory agencies because of concerns over efficacy and safety.
It is an inhibitor of the enzyme janus kinase 3 (JAK3), which means that it interferes with the JAK-STAT signaling pathway, which transmits extracellular information into the cell nucleus, influencing DNA transcription.
Recently it has been shown in a murine model of established arthritis that tofacitinib rapidly improved disease by inhibiting the production of inflammatory mediators and suppressing STAT1-dependent genes in joint tissue. This efficacy in this disease model correlated with the inhibition of both JAK1 and 3 signaling pathways, suggesting that tofacitinib may exert therapeutic benefit via pathways that are not exclusive to inhibition of JAK3.
The potential significance of JAK3 inhibition was first discovered in the laboratory of John O'Shea, an immunologist at the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health (NIH). In 1994, Pfizer was approached by the NIH to form a public-private partnership in order to evaluate and bring to market experimental compounds based on this research. Pfizer initially declined the partnership but agreed in 1996, after the elimination of an NIH policy dictating that the market price of a product resulting from such a partnership would need to be commensurate with the investment of public taxpayer revenue and the "health and safety needs of the public." The drug discovery, preclinical development, and clinical development of tofacitinib took place exclusively at Pfizer.
In November 2012, the U.S. Food and Drug Administration (FDA) approved tofacitinib for treatment of rheumatoid arthritis. Once on the market, rheumatologists complained that the $2,055 a month wholesale price was too expensive, though the price is 7% less than related treatments.
Phase II clinical trials tested the drug in RA patients that had not responded to DMARD therapy. In a tofacitinib monotherapy study, the ACR score improved by at least 20% (ACR-20) in 67% of patients versus 25% who received placebo; and a study that combined the drug with methotrexate achieved ACR-20 in 59% of patients versus 35% who received methotrexate alone. In a psoriasis study, the PASI score improved by at least 75% in between 25 and 67% of patients, depending on the dose, versus 2% in the placebo group.
The most important side effects in Phase II studies were increased blood cholesterol levels (12 to 25 mg/dl LDL and 8 to 10 mg/dl HDL at medium dosage levels) and neutropenia. Phase III trials testing the drug in rheumatoid arthritis started in 2007 and are scheduled to run until January 2015.
In April 2011, four patients died after beginning clinical trials with tofacitinib. According to Pfizer, only one of the four deaths was related to tofacitinib.
By April 2011, three phase III trials for RA had reported positive results.
In November 2012, the U.S. FDA approved tofacitinib "to treat adults with moderately to severely active rheumatoid arthritis (RA) who have had an inadequate response to, or who are intolerant of, methotrexate." A boxed warning that goes along with this approval warns patients that they are at higher risk of opportunistic infections, tuberculosis, cancers and lymphoma.
Combination with methotrexate
Tofacitinib is taken in combination with or without methotrexate.
In June 2014, scientists at Yale have successfully treated a male patient afflicted with alopecia universalis. The patient was able to grow a full head of hair, eyebrows, eyelashes, facial, armpit, genitalia and other hair. No side effects were reported in the study. 
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