Montagna Symposium 2017 - Janus Kinase inhibitors for treatment of alopecia areata

Abstract

The advancement of genetic and pre-clinical studies has uncovered the mechanisms involved in the pathogenesis of alopecia areata (AA). The development of targeted therapies using small molecules blocking specific pathways for the treatment of AA is underway. By repurposing FDA-approved small molecule JAK inhibitors as treatments for AA, it has been demonstrated that JAK inhibitors can effectively reverse hair loss in patients with moderate to severe AA. In this review, we summarize and discuss the current pre-clinical and clinical studies on JAK inhibitors, as well as the prospects of using JAK inhibitors for the treatment of AA.

Introduction

Alopecia areata (AA) is a form of non-scarring, hair loss that is mediated by inflammatory mechanisms. With a prevalence of about 1.7–2.1%, AA is one of the most common autoimmune diseases in the USA (Strazzulla et al., 2018b). The development of AA is indiscriminate among genders and ethnicities with initial onset often occurring before age 30. AA typically begins as small, well-defined patches of hair loss on the scalp or beard that may spontaneously remit without intervention, however, AA relapses in about 30% of cases. Discrete AA patches can grow larger and coalesce to form more extensive hair loss that covers the entire scalp (alopecia totalis; AT) or the entire body (alopecia universalis, AU) (Strazzulla et al., 2018b). Spontaneous remission is rarely observed in patients with AT or AU. Currently, there are no treatments for AA that offer durable responses or permanent reversal of hair loss.

Identification of lymphocytic infiltrates in AA lesions gave rise to the hypothesis that there is an autoimmune attack on hair follicles (HFs), which is likely a consequence of loss of immune privilege, mediated by immune T cells (Paus et al., 2018). Currently, the primary therapeutic approaches in treating AA include non-specific broad immunosuppressant medications, given systemically or locally, to dampen immune cell attack, or contact sensitizers to re-direct autoimmune attack, however, broad non-specific immunosuppression can lead to adverse events. Specifically, topical and intralesional corticosteroids are associated with undesirable side-effects such as local skin atrophy, telangiectasias, and striae, while systemic corticosteroid side effects include acne, adrenal suppression, weight gain, insomnia, and glucose intolerance. Due to the non-specific nature of this treatment, efficacy of immunosuppression and contact sensitization is highly variable from patient to patient. Many of the broad T cell antagonist medications, immunosuppressants, and biologic drugs did not achieve desirable hair regrowth in AA, potentially because they were not directed at key drivers of disease etiology (Strazzulla et al., 2018a).

Our recent genetic studies on AA revealed genetic similarities between AA and other autoimmune diseases such as rheumatoid arthritis and type I diabetes (Betz et al., 2015, Petukhova et al., 2010). AA has been associated with other dermatologic and autoimmune diseases such vitiligo, atopic dermatitis, allergic rhinitis, and autoimmune thyroid disease (Chu et al., 2011, Drucker et al., 2017, Lee et al., 2014). Genome-wide association studies (GWAS) studies in AA also revealed risk alleles in AA patients that identified previously unreported genes and pathways as potential biomarkers or therapeutic targets, such as ULBP3 (a “danger” signal and ligand of NKG2D) and CD8⁺ expressing NKG2D T cells IL15, IFNy, and JAK-STAT signaling pathways, among others (Betz et al., 2015, Moftah et al., 2016, Petukhova et al., 2010, Xing et al., 2014). With the recent advancements in genetic techniques, immunological assays, and the development of robust mouse models of AA, such as the C3H/HeJ strain for preclinical research (Gilhar et al., 2016), significant breakthroughs in understanding the mechanism of AA have been made.

The JAK-STAT signaling pathway in the initiation and progression of AA emerged as a major driver of disease pathogenesis, which provided a strong rationale for the clinical investigation of small molecule Janus Kinase (JAK) inhibitors. Some of these medications have already been FDA-approved for the treatment of other diseases such as rheumatoid arthritis (tofacitinib, a pan-JAK inhibitor) and myelofibrosis (ruxolitinib, a JAK1/2 inhibitor) (O’Shea and Plenge, 2012). For this review, we will focus on the rationale and evidence of using JAK inhibitors as a treatment for AA and discuss ongoing clinical research and future prospects for JAK inhibitors.

JAK-STAT signaling

The Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway is an intracellular signaling pathway upon which many different pro-inflammatory signaling pathways converge (Damsky and King, 2017). JAKs are intracellular cytoplasmic tyrosine kinases that signal in pairs and transduce cytokine signaling from membrane receptors via STAT factors to the nucleus (Vanhoutte et al., 2017). Cytokines are critical for immunoregulation, but also play a major role in the immunopathogenesis of autoimmune disease (Schwartz et al., 2016). The JAK-STAT pathway is utilized by cytokines including interleukins (ILs), interferons (IFNs) and other molecules such as growth factors and hormones to transmit signals from the cell membrane to the signaling (Damsky and King, 2017, Paus et al., 2018). Upon engagement of extracellular ligands, intracellular JAK proteins become activated and phosphorylate STAT proteins, which dimerize and then translocate into the nucleus to directly regulate gene expression (Damsky and King, 2017, O’Shea et al., 2015, Schwartz et al., 2016). For example, an interferon-gamma (IFNy) receptor interact with JAK1 and JAK2, upon the binding of IFNy, the JAKs phosphorylate STAT1 and STAT2, which subsequently translocate into the nucleus and activate downstream gene expression (Erduran et al., 2017).

There are four known JAKs, including JAK1, JAK2, JAK3 and tyrosine kinase 2 (TYK2). JAK1 commonly mediates signals for a range of inflammatory diseases, whereas JAK2 mediates signaling for a range of cytokines mainly in the context hematopoiesis. JAK3 activity is restricted to the lymphoid lineage (Vanhoutte et al., 2017), and loss of function mutations in JAK3 cause severe combined immunodeficiency syndrome. In contrast, gain of function mutations in JAKs can act as oncogenes in a variety lymphoproliferative disorders and hematologic malignancies (Damsky and King, 2017). Different combinations of JAKs form a dimer on different cytokine receptors with one of the 7 members of STATs (STAT1–4, STAT5a, STAT5b, STAT6), facilitating downstream effects of cytokine receptors upon ligand binding.

JAK inhibitors are a class of immunomodulatory drugs

Two JAK inhibitors are approved by the Food and Drug Administration (FDA) for use in the US (ruxolitinib, tofacitinib), and one is approved for veterinary use (oclacitinib). These JAK inhibitors each target multiple JAKs with different levels of specificity(O’Shea et al., 2013). Ruxolitinib was FDA approved for the treatment of myelodysplastic disorders and is selective for JAK1/2 (Damsky and King, 2017). Tofacitinib was an FDA approved JAK inhibitor for the treatment of rheumatoid arthritis, and inhibits JAK1, JAK2, and JAK3, but most potently inhibits JAK3 (Vanhoutte et al., 2017). Baricitinib is in clinical trials for rheumatoid arthritis, psoriasis, and atopic dermatitis and is selective for JAK1/2 (O’Shea et al., 2015). Oclacitinib is a pan-JAK inhibitor and is used for atopic dermatitis treatment in dogs (O’Shea et al., 2015).

Repurposing of JAK inhibitors in alopecia areata and preclinical assessment

We and others demonstrated that IFNy and IL15 signaling play a crucial role in AA development and disease maintenance, in both humans and the C3H/HeJ mouse model of AA (Divito and Kupper, 2014, Xing et al., 2014). IFNy primarily signal through JAK1/2 and IL15 mostly through JAK1/3, providing the rationale to use JAK inhibitors to specifically block the inflammatory response resulting from the activation of these receptors (O’Shea and Plenge, 2012, O’Shea et al., 2015, Xing et al., 2014).

Our preclinical assessments using ruxolitinib and tofacitinib as a systemic treatment in the C3H/HeJ mouse model of AA showed therapeutic promise, since both drugs prevented the induction of AA via skin grafting method (Xing et al., 2014). We also investigated topical JAK inhibitor treatment daily on mice with longstanding AA, and showed localized hair regrowth in as little as 4 weeks. The skin of treated mice showed a marked decrease of CD4, CD8, MHC Class I and II, as well as a decreased number of CD8+/NKG2D+ cells (Xing et al., 2014). In a separate study, we used daily topical treatment with 0.5% baricitinib and showed significant hair regrowth in 6 weeks and reduction of inflammatory infiltrates in C3H/HeJ mice (Jabbari et al., 2015). There are now multiple JAK-specific inhibitors being investigated in human clinical trials using both topical and oral formulations (Table 1).

Table 1.

Current status of clinical trials of treatment of alopecia areata with JAK inhibitors listed on clinicaltrials.gov.

Trial Listing	Identifier	Molecule	Recruiting	Location	Study Type	AA type	Start Date
A Study of ATI-50002 Topical Solution for the Treatment of Alopecia Areata	NCT03354637	Topical JAK inhibitor	Yes	Multicenter	Phase 2; RCT with Placebo; 120 Subjects	Moderate to severe (SALT 30-95%)	Nov 28, 2017
Safety and Pharmacokinetic Study of ATI-50002 in Subjects With Alopecia Universalis (AU) and Alopecia Totalis (AT)	NCT03315689	Topical JAK inhibitor	Yes	Multicenter	Phase 2; RCT with Placebo; 12 Subjects	Moderate to severe (AT/AU)	Oct 20, 2017
Study to Evaluate the Safety and Efficacy of CTP-543 in Adult Patients With Moderate to Severe Alopecia Areata	NCT03137381	Oral JAK inhibitor	Yes	Multicenter	Phase 2; RCT with Placebo; 90 Subjects	Moderate to severe	May 2, 2017
Study To Evaluate The Efficacy And Safety Profile Of PF-06651600 And PF-06700841 In Subjects With Alopecia Areata	NCT02974868	Oral JAK inhibitor	Active, not recruiting	Multicenter	Phase 2; RCT with Placebo; 143 Subjects	Moderate to severe	Nov 29, 2016
Topical Tofacitinib for the Treatment of Alopecia Areata and Its Variants	NCT02812342	Oral Tofacitinib	Active, not recruiting	Yale University	Phase 2; Open label; 10 Subjects	Moderate to severe (>50% SALT to AT/AU)	June 24, 2016
Study To Evaluate The Efficacy Of Tofacitinib In Moderate To Severe Alopecia Areata, Totalis And Universalis	NCT02299297	Oral Tofacitinib	Active, not recruiting	Columbia University	Phase 2; Open label; 15 Subjects	Moderate to severe (AT/AU)	Nov 24, 2014
LEO 124249 Ointment in the Treatment of Alopecia Areata	NCT02561585	Topical JAK inhibitor	Completed	Icahn/Mount Sinai and North Western University	Phase 2; RCT with Placebo; 31 Subjects	Moderate to severe (SALT >30%, AT/AU)	Sept 28, 2015
Tofacitinib for the Treatment of Alopecia Areata and Its Variants	NCT02312882	Oral Tofacitinib	Completed	Stanford University	Phase 2; Open label; 40 Subjects	Moderate to severe (>50% SALT to AT/AU)	Dec 9, 2014
Tofacitnib for the Treatment of Alopecia Areata and Variants	NCT02197455	Oral Tofacitinib	Completed	Yale University	Phase 2; Open label; 30 Subjects	Moderate to severe (>50% SALT to AT/AU)	July 22, 2014
Pilot Study to Evaluate the Efficacy of Ruxolitinib in Alopecia Areata	NCT01950780	Oral Ruxolitinib	Completed	Columbia University	Phase 2; Open label; 12 Subjects	Moderate to severe (SALT 30-95%)	Sept 25, 2013
A Study With INCB018424 Phosphate Cream Applied Topically to Subjects With Alopecia Areata (AA)	NCT02553330	Topical Ruxolitinib	Terminated	Multicenter	Phase 2; RCT with Placebo; 90 Subjects	Partial or complete AA	Sept 17, 2015

Treatment of AA in humans using JAK inhibitors

There have been many clinical studies of JAK inhibitor efficacy in treating AA, most of which used oral medications and a few studies using topical formulations (Table 2) (Kennedy Crispin et al., 2016, Mackay-Wiggan et al., 2016, Wang et al., 2018). The oral formulations had dramatic outcomes with hair regrowth in about 67–75% of patients in several studies (Kennedy Crispin et al., 2016, Mackay-Wiggan et al., 2016). Oral formulations are generally very easy to take for patients, leading to increased compliance and hair regrowth. Tofacitinib can be taken once or twice a day in either the 5mg or 11mg dosing. However, it is difficult to achieve high concentrations of JAK inhibitor through oral dosing. In some of the most difficult to treat cases, topical formulation may provide opportunities for higher local concentrations to target the disease causing lymphocytic infiltrate.

Table 2.

Case reports of JAK inhibitors as a treatment for alopecia areata.

	Type of study	Treatment	Number of patients	Response rate	Length of treatment
(Jabbari et al., 2018)	Open-label, single-arm	Tofacitinib, 5mg BID then TID	12	91%	11-64 weeks
(Kennedy Crispin et al., 2016)	Open-label, single-arm	Tofacitinib, 5 mg BD	66	32% of patients had at least 50% regrowth	3 months
(Mackay-Wiggan et al., 2016)	Open-label, single-arm	Ruxolitinib, 20 mg BD	12	75% of patients had at least 50% regrowth	3-6 months
(Liu et al., 2017)	Retrospective	Tofacitinib, 5 mg BD	90	77% of patients had at least 50% regrowth 20% complete response	Median, 12 months (4-18 months)
(Ibrahim et al., 2017)	Retrospective	Tofacitinib, 5 mg BD	13	53.8% of patients had at least 50% regrowth	Mean, 4.2 moths (1-9 months)
(Craiglow et al., 2017)	Retrospective	Tofacitinib, 5 mg BD	13 (adolescents)	76.9% of patients had response with median 100% regrowth (20% to 100%)	Median, 5 months (2-16 months)
(Xing et al., 2014)	Case report	Ruxolitinib, 20 mg BD	3	Complete regrowth	3-5 months
(Craiglow and King, 2014)	Case report	Tofacitinib, 10 mg AM, 5 mg ON	1 (AU)	Complete regrowth	8 months
(Higgins et al., 2015)	Case report	Ruxolitinib, 20 mg BD for CMC	1	Complete regrowth at 3 months	6 months
(Jabbari et al., 2015)	Case report	Baricitinib, 7 mg AM, 4 mg ON for CANDLE	1	Complete regrowth	9 months
(Pieri et al., 2015)	Case report	Ruxolitinib, 20 mg BD for ET	1 (AU)	Complete regrowth	10 months
(Gupta et al., 2016)	Case report	Tofacitinib, 5 mg BD	2 (AU)	Complete regrowth in both patients	8 months
(Harris et al., 2016)	Case report	Ruxolitnib, 20 mg BD	1	85% regrowth, maintained 12 weeks after cessation	6 months
(Dhayalan and King, 2016)	Case report	Tofacitinib, 5 mg BD	3	Improvement in nail dystrophy, 2 of 3 experienced hair regrowth	5-6 months
(Scheinberg and Ferreira, 2016)	Case report	Tofacitinib, 5 mg BD	2 (AU)	Partial regrowth	9 months
(Ferreira et al., 2016)	Case report	Tofacitinib, 5 mg BD	1 (AU)	Complete regrowth and improvement in nail changes	10 months
(Anzengruber et al., 2016)	Case report	Tofacitinib, 5 mg BD with MTX 15 mg/week	1 (AU)	Transient regrowth, relapsed	6 months
(Vandiver et al., 2017)	Case report	Ruxolitinib up to 30 mg/day	2 (AA, AT)	Complete regrowth	13-14 months
(Mrowietz et al., 2017)	Case report	Tofacitinib, 10 mg OD for PsA	1 (AU)	Complete regrowth	9 months
(Erduran et al., 2017)	Case report	Tofacitinib, 10 mg AM, 5 mg ON	1 (AU)	Complete regrowth	6 months
(Bayart et al., 2017)	Case report	Tofacitinib (2% topical) Ruxolitinib (1% and 2% topical)	6 (adolescents)	3 of 6 partial regrowth, 1 complete regrowth	3-12 months

There are several case studies that demonstrated improvement of AA in patients who received JAK inhibitors for other diseases such as psoriasis, CANDLE syndrome, vitiligo, essential thrombocytopenia, and mucocutaneous candidiasis (Craiglow and King, 2014, Harris et al., 2016, Higgins et al., 2015, Jabbari et al., 2015, Pieri et al., 2015). While detailed mechanistic studies were not performed in these case studies, a common theme here is the involvement of autoimmune/autoinflammatory disorders or gain-of-function mutation in JAK-STAT signaling pathway.

Topical JAK Inhibitors

While oral JAK inhibitors demonstrated high efficacy in humans with moderate to severe AA, systemic treatments may yield unwanted long-term side-effects. Topical application JAK inhibitors may be a desirable treatment option for AA, since it will localize the effect of JAK inhibition to the site of application. Topical JAK inhibitors reversed AA in C3H/HeJ mice with well-established AA within 4 weeks (Xing et al., 2014). We have tested multiple formulations of topical JAK inhibitors in the C3H/HeJ mouse model and showed efficacy, however, topical JAK inhibitors for human trials will need to be formulated differently to compensate for the thickness of human skin, since murine skin is thinner and easier to penetrate. Currently, there are no topical formulations of JAK inhibitors that yield satisfactory results. Bayart (2017) reported in a small retrospective study of 6 pediatric patients, 4 showed regrowth after topical application with different combinations of tofacitinib and ruxolitinib (Bayart et al., 2017). There were no serious adverse effects observed in these patients, however due to the scale of the study and the lack of uniformed treatment regiment, the efficacy of the topical formulations used cannot be confirmed yet. If the efficacy can be confirmed in a larger clinical trial with appropriate design, topical JAK inhibitors may be preferable for children with AA because of the potential advantages in the safety profile with long-term use.. There have been two phase-2 randomized controlled trials initiated by Incyte Corporation (NCT02553330, terminated) and LEO Pharma (NCT02561585, completed no published results). No results from these trials were published, as such, the efficacy of cannot be determined. Currently, the trials initiated by Aclaris Therapeutics are recruiting (NCT03354637 and NCT03315689), therefore, the efficacy of topical JAK inhibitors remains undetermined.

In clinical practice, AA frequently recurs after a patient stops taking oral JAK inhibitors. Some patients require higher oral doses of JAK inhibitors to achieve initial full regrowth, up to 5mg tofacitinib three times a day. Once regrowth has been achieved, maintenance doses could potentially be titrated down to maintain hair growth or transitioned to a topical regiment. However, to maintain regrowth after use of JAK inhibitors, patients will likely need to continue the medication indefinitely to maintain full regrowth. Ideally, a transition to a topical formulation in patients that have achieved full hair regrowth would be more sustainable.

Considerations for using JAK inhibitors

Using topical formulation would mitigate side effects of oral JAK inhibitors, such as increased risk of some cancers and infection. Interferons and NK cells are important in tumor surveillance and blockade of their action by JAK inhibition increases the risk of cancer development. The rate of lymphoma or lymphoproliferative disorders with tofacitinib in RA was 0.07 per 100 patient years (O’Shea et al., 2013).

The most common adverse events while taking tofacitinib are bacterial, mycobacterial, fungal and viral infections, increases in serum creatinine, thrombocytopenia, hypercholesterolemia, and neutropenia. Three patients were reported to have pulmonary tuberculosis (TB) after tofacitinib, including those who had previous negative TB screening. Increased frequency of non-disseminated Herpes zoster has been reported. The half life is short and if infections occur the drug can be stopped, and the immunomodulatory effect is transient. Also at doses exceeding the recommended dosage of 5mg twice daily, tofacitinib was also associated with anemia (Vanhoutte et al., 2017). The potential side effects of prolonged treatment of JAK inhibitors have not been evaluated.

Promise of JAK inhibitors in dermatology

Research efforts into small molecule JAK inhibitors currently focused targeting the JAK/STAT pathways essential in AA. Also, with more specific targeting, medication side effects and off target downstream effects will be limited. With further research into the specific target pathways, information on ways to improve durability of treatment will emerge. Furthermore, the cost of JAK inhibitor medications is a barrier to treatment for many patients, because JAK inhibitors are used in off-label indications for the treatment of AA.

JAK inhibitors can also be delivered orally, making them easier for patient administration and compliance. JAK inhibitors are also effective because they can simultaneously target multiple pathogenic pathways identified in AA such as type I and type II IFN receptor pathways (Freyschmidt-Paul et al., 2006, Ghoreishi et al., 2010, Xing et al., 2014). Small molecule inhibitors can also be formulated topically which will decrease the systemic effect and potential adverse reactions that can be associated with oral JAK inhibitor treatment.

JAK inhibitors may hold promise in treating other inflammatory skin conditions such as vitiligo, psoriasis, scarring alopecias, or atopic dermatitis, by blocking JAK/STAT-mediated inflammatory signaling. Delivery vehicle and individual JAK/STAT pathway targeting will be important in these applications, which also hold promise for the future treatment of a wide range of inflammatory skin conditions.