MILAN – Janus kinase (JAK) inhibitors have clear science supporting their use in alopecia areata, and an increasing number of positive studies demonstrate their efficacy in regrowing hair, Brett King, MD, PhD, said at the World Congress of Dermatology.
Although not yet specifically approved for , said Dr. King, associate professor of dermatology at Yale University, New Haven, Conn.
“JAK inhibitors are very much within our reach for the treatment of severe alopecia areata,” Dr. King said in an oral presentation on therapeutic advances for alopecia. “We need to follow the science,” he added. “We would not be here telling a story about JAK inhibitors and these other agents without very bright scientists, so we really have to applaud the people who made this the focus of their research.”
JAK science
The science supporting JAK inhibitors can be traced back to a 2014 report by Angela M. Christiano, PhD,, Raphael Clynes, of Columbia University, New York, and others showing that alopecia areata is driven by cytotoxic T lymphocytes, and is reversed by inhibition of the JAK/STAT pathway in mouse models of disease (Nat Med. 2014 Sep;20[9]:1043-9). Those investigators also reported near-complete regrowth of hair in three patients who received oral ruxolitinib, an inhibitor of JAK1 and JAK2, hinting at the potential clinical importance of this targeted approach.
As Dr. King explained, secretion of interleukin (IL)-15 from the hair follicle endothelial cell activates CD8+NKG2D+ T cells leading to secretion of interferon (IFN)-gamma, which has a receptor on the hair follicle epithelial cell, activating that cell to secrete more IL-15.
“IL-15 and IFN-gamma both signal through the JAK/STAT pathway,” he said. “There are over 50 cytokines that signal through the JAK/STAT pathway, including IFN-gamma and IL-15, and on binding their receptor at the cell surface, they pass the baton, if you will, to the JAK enzymes, of which there are 4 members – JAK1, 2, 3 and tyrosine kinase 2. These enzymes subsequently pass the baton to STAT, and STAT translocates to the nucleus, where transcription occurs and disease happens. So we have an opportunity then with a small molecule JAK inhibitor to mediate disease, such that if we give this person a JAK inhibitor, they should regrow hair.”
JAK data
A number of studies of JAK inhibitors support that science, including an open-label study of 66 patients treated with the JAK1/3 inhibitor tofacitinib twice daily (JCI Insight. 2016 Sep 22;1[15]:e89776). About one-third experienced a 50% or greater improvement from baseline, as measured by the severity of alopecia tool (SALT) score over 3 months of treatment, with adverse events limited to grade 1-2 infections, according to the authors, which included Dr. King.
Around the same time, results of an open-label study with ruxolitinib, a JAK1/2 inhibitor, were published showing that 9 of 12 patients had complete or near complete scalp hair regrowth over 6 months of treatment, he said.
In a subsequent retrospective study of 90 patients treated with tofacitinib, about 66%-70% of patients experienced regrowth of hair, depending on the dose received. However, that study also showed that hair regrowth was unlikely in patients with complete or near complete scalp hair loss for 10 years or more, Dr. King said. An additional study showed that tofacitinib may be effective in adolescents as in adults, or even more effective, he added, while another found that low-dose ruxolitinib was as effective as higher dose ruxolitinib for the treatment of severe alopecia areata.
News earlier in 2019 surrounded the results of two randomized, double-blind placebo controlled trials, reported at the annual American Academy of Dermatology meeting in Washington, DC, showing efficacy for investigational oral JAK-targeted agents, a JAK 1/2 inhibitor (CTP-543), and a TYK2/JAK1 inhibitor (PF-06700841) and a JAK3 inhibitor (PF-06651600).
“I think this really is the near future of alopecia areata treatment,” Dr. King said.
No success yet for topical JAKs
One area where JAK inhibitors have not shined yet is in topical formulations. In a pilot study of tofacitinib 2% ointment, only 1 of 10 patients had significant scalp hair growth, while a study of topical ruxolitinib was stopped early and results have not yet been reported, according to Dr. King. “As dermatologists, we’re always interested in topical therapy for skin disease, but I’m not sure that alopecia areata is a disease for which topical JAK inhibitors will be effective,” he said.
Dr. King reported disclosures related to Aclaris Therapeutics, Concert Pharmaceuticals, Dermavant Sciences, Eli Lilly, Pfizer, Regeneron, and Sanofi Genzyme.