This chapter provides an overview of the pathogenesis of atopic dermatitis and the key mediators that are of therapeutic interest.
As we acquire more knowledge into the pathogenesis of atopic dermatitis, we will be able to use more targeted treatments
The two most recently Food and Drug Administration–approved medications are dupilumab and crisaborole.
There are a number of topical and systemic novel and emerging targeted therapies for atopic dermatitis.
Despite promise of these new drug therapies, potential gaps include limited head-to-head trials, lack of subgroup analysis, and high cost.
This chapter is intended to discuss novel and emerging pharmaceutic treatments for patients affected by atopic dermatitis (AD). It will give a brief overview of the proposed mechanism of each treatment, the major side effects, and the most recent clinical data from trials and studies. We hope to provide a comprehensive overview of the new treatments available for AD and to make clinicians better informed about the particular strengths and weaknesses of each drug. It should also be noted that many of these treatments are still in development and may not be available for clinical use, and we encourage readers to follow up on the updated results of the trials and studies listed throughout each section. A summary of the medications can be found in Table 23.1 .
|Name||Topical/systemic||Manufacturer||Result||Phase||Major adverse events|
|Dupilumab||Systemic||Regeneron||Favorable||Conjunctivitis, keratitis, nasopharyngitis|
|Tralokinumab||Systemic||AstraZeneca||Favorable||3||Upper respiratory tract infection (URTI), headache|
|Lebrikizumab||Systemic||Dermira/Eli Lilly||Favorable||3||URTI, headache, nasopharyngitis|
|Omalizumab||Systemic||Novartis||Variable||N/A||Injection site reaction, URTI, malignancies|
|Ligelizumab||Systemic||Novartis||Unfavorable||2||Injection site reaction, URTI|
|Nemolizumab||Systemic||Galderma||Favorable||3||Nasopharyngitis, URTI, asthma-related exacerbations|
|Tofacitinib||Systemic||Pfizer||Favorable||2||Neutropenia, lymphopenia, herpes-zoster-associated encephalitis, appendicitis, pericoronitis, skin infection|
|Barticitinib||Systemic||Eli Lilly||Favorable||2||Neutropenia, lymphopenia, herpes-zoster-associated encephalitis, appendicitis, pericoronitis, skin infection|
|Abrocitinib||Systemic||Pfizer||Favorable||3||Neutropenia, lymphopenia, herpes-zoster-associated encephalitis, appendicitis, pericoronitis, skin infection|
|Upadacitinib||Systemic||AbbVie||Favorable||3||Infection, neutropenia, hepatic disorder, URTI, acne, headache, nasopharyngitis, diarrhea|
|Delgococitinib||Topical||LEO Pharma||Favorable||2||Infection, neutropenia, URTI, acne, nasopharyngitis, hepatic disorder|
|Tacrolimus||Topical||Accord Healthcare||Variable||Skin infection, application pain|
|Pimecrolimus||Topical||Novartis||Variable||Skin infection, application pain|
|Apremilast||Systemic||Celgene||Favorable||2||Diarrhea, weight loss|
|Ustekinumab||Systemic||Janssen Biotech Inc.||Favorable||2||Infusion reaction, nasopharyngitis, URTI, malignancies|
|Tapinarof||Topical||Dermavant Sciences||Favorable||2||Folliculitis, contact dermatitis|
|JNJ 39758979||Systemic||Janssen Biotech Inc.||Unfavorable||2||Neutropenia|
|DS107||Topical, Systemic||DS Biopharma||Favorable||2||N/A|
|Aprepitant||Systemic||Merck Ltd.||Unfavorable||Leukopenia, hypotension|
|Serlopitant||Systemic||Menlo Therapeutics||Unfavorable||2||Nasopharyngitis, URTI|
Sustained barrier defects generated by filaggrin mutations, decreased ceramide synthesis, scratching, increased serine protease activity, and prolonged exposure to reduced environmental humidity result in epidermal dysfunction and allow for penetration of allergens found in pollen, microbes, and food ( ). In response to allergens, trauma, and inflammation, keratinocytes release inflammatory mediators such as interleukin-25 (IL25), IL33, thymic stromal lymphopoietin (TSLP), and pollen-associated lipid mediators (PALMs), which, along with presentation of allergens by dendritic cells, stimulate a T helper type 2 (Th2)-driven immune response ( ). TSLP receptor activates STAT1, STAT3, STAT5/JAK1, and JAK2, which are important for Th2 cell differentiation ( ).
These Th2 cells subsequently produce cytokines and chemokines, including IL4, IL5, IL13, and tumor necrosis factor-α (TNF-α), which stimulate B-cell class switching, immunoglobulin E (IgE) production, and eosinophil survival; induce proliferation of leukocyte adhesion molecules; and direct circulating lymphocytes, macrophages, and eosinophils to cutaneous sites of inflammation ( ). IL4 has been strongly associated with AD and requires numerous agents in the JAK-STAT pathway, including JAK1, JAK3, STAT3, STAT5, and STAT6 to enact its effects ( ). IgE contributes to AD pathogenesis through mast cell activation and subsequent release of preformed mediators such as histamine, IL4, and IL13, as well as through increased expression of FCεRI on Langerhans and dendritic cells, which results in further Th2 activation ( ). Mast cells also stimulate further IgE synthesis by B cells, upregulate integrins on Langerhans cells, and suppress IL12 production by dendritic cells, leading to polarization to the Th2 subtype ( ). Th2 cells also release IL31, which has been associated with higher disease severity, pruritus, chemotaxis of inflammatory cells, and induction of proinflammatory molecules by eosinophils through the JAK-STAT pathway ( ). Eosinophils release various cytokines and chemokines such as IL16, IL12, transforming growth factor-β (TGF-β), and IL13 ( ). The JAK-STAT pathway, through STAT6-mediated gene regulation, also stimulates B-cell differentiation, IgE class switching, and major histocompatibility complex (MHC) class II production ( ).
Similar to the JAK-STAT pathway, JAK-spleen tyrosine kinase (SYK) pathways have also been associated with AD pathogenesis by mediating IL17R-proximal signaling complex formation, which is responsible for upregulation of CCL20 in keratinocytes ( ). CCL20 has been found to attract immature dendritic cells and effector T cells into the dermis of inflamed skin ( ). SYK activation has also been implicated in B-cell survival, degranulation of mast cells, antigen presentation in dendritic cells, and proinflammatory cytokine production by macrophages ( ).
Th17 cells have also been implicated in the pathogenesis of AD as an enhancer, and an increased percentage of Th17 in blood correlates with the severity of AD ( ). Th17 cells release IL17, which enters the inflamed dermis and stimulates keratinocytes to produce proinflammatory cytokines and chemokines, including GM-CSF, TNF-α, IL8, and CXCL10 ( ). Patients with chronic AD have also been found to have increased blood levels of IL22-producing T cells ( ). IL22 induces keratinocyte proliferation and epidermal proliferation, and increased levels of IL22 are correlated with AD disease severity ( ).
Phosphodiesterase (PDE) functions to hydrolyze cyclic adenosine monophosphate (cAMP), and higher levels of PDE activity have been associated with increased IgE synthesis and IL4 production ( ). Increased PDE activity is seen in leukocytes of patients with AD and is thought to contribute to increased serum levels of IL10 and prostaglandin E2 ( ). IL12, which is stimulated by Th2-type cells, is thought to polarize naïve T cells to Th1-type cells and terminate Th2-type cytokine patterns ( ). A switch from Th2 cells to a predominantly Th1 cell response has been associated in the chronic and late phases of AD ( ). Increased levels of IL12, mRNA, and interferon-gamma (IFN-γ) (which are produced by Th1 cells) in AD lesions have also been linked to chronic AD ( ).
Pruritus in AD is caused by numerous mediators, including histamine, neuropeptides, neurotransmitters, cytokines, proteinases, and arachidonic acid derivatives ( ). Histamine induces IL13 and IL31 production and activates sensory neurons, primarily through histamine-1 receptors (H 1 R) and histamine-4 receptors (H 4 R) ( ). Through H 4 R, histamine also activates mast cells, basophils, and eosinophils ( ). One potent releaser of histamine from mast cells is compound 48/80, which, upon injection, has been shown to cause itching in mice ( ). Similarly, increased concentrations of substance P, a neuropeptide that induces itching through neurokinin receptors (NK1R,) and neuropeptide Y are present in patients with AD ( ).
Peroxisome proliferator-activated receptor gamma (PPAR-γ) is a type of nuclear receptor that has an increased expression in the monocytes and T lymphocytes of AD patients and is responsible for keratinocyte differentiation and permeability barrier homeostasis ( ).
Dihomo-γ-linolenic acid (DGLA) is a fatty acid that has been found to be significantly lower in the serum of patients with AD than in healthy volunteers ( ). DGLA is also metabolized into antiinflammatory eicosanoids, and oral administration of DGLA in mice prevents the development of AD by suppressing the activation of mast cells and keratinocytes ( ).
Recalcitrant and moderate to severe AD often require systemic treatment. Immunosuppressants such as methotrexate, cyclosporine A, mycophenolate mofetil, and azathioprine have traditionally been used; however, significant side effect profiles can limit their long-term use. Newer immunomodulators (i.e., biologics and small-molecule inhibitors) selectively target specific cytokines and regulators involved in AD pathogenesis and have much more desirable side effect profiles.
Currently, the only Food and Drug Administration (FDA)–approved biologic medications for AD are dupilumab and crisaborole. There are a number of new and promising treatments currently under investigation. This chapter provides a summary and review of systemic therapies that target specific mediators involved in the pathogenesis of AD and its related symptoms. Included are those therapies that have been specifically approved for AD, those undergoing clinical trials, and those that have demonstrated efficacy to a significant degree.
Treatments targeting pathogenic cytokines
Dupilumab is currently the only FDA-approved systemic immunomodulator indicated for AD. It is fully a monoclonal antibody that inhibits IL4 and IL13 receptors by binding to the α-subunit shared by these receptors ( ). In two phase 3, randomized, double-blind, placebo-controlled, parallel-group trials of identical design involving a total of 1379 adults with moderate to severe AD refractory to topical treatment, significantly more patients who received dupilumab 300 mg subcutaneously every other week for 16 weeks reached the primary endpoint of an Investigator Global Assessment (IGA) score of 0 (clear) or 1 (almost clear) (38% and 36% for the dupilumab group vs. 10% and 8% for the placebo group, P < .001 for both comparisons vs. placebo) ( ). Furthermore, an improvement of 75% or more on Eczema Area and Severity Index (EASI-75) (which measures erythema, induration, papulation, and edema; excoriations, and lichenification) was achieved by significantly more patients who received dupilumab compared to patients receiving placebo (51% and 44% for the dupilumab group vs. 15% and 12% for the placebo group, P < .001 for both groups compared to placebo). Additionally, patients who completed this trial were able to enter an ongoing maintenance trial, a phase 3, randomized, double-blind, placebo-controlled, parallel-group trial involving 422 patients who were rerandomized in a 2:1:1:1 ratio to receive their original regimen of 300 mg dupilumab weekly or every 2 weeks, a less frequent regimen of 300 mg every 4 or 8 weeks, or placebo for 36 weeks ( ). More patients who continued to receive dupilumab every week or every 2 weeks maintained EASI-75 response compared to those taking dupilumab every 4 weeks, 8 weeks, or placebo (71.6%, 58.3%, 54.9%, 30.4%, respectively; P < .001) ( ). A phase 3, nonrandomized, open-label, single-group assignment of dupilumab in adult patients who have participated in previous dupilumab clinical trials is currently ongoing ( ). In terms of side effects, dupilumab has been associated with an increased incidence of ocular surface diseases such as conjunctivitis and keratitis ( ).
Tralokinumab is a fully monoclonal IgG4 monoclonal antibody that binds to and neutralizes the effects of IL13 via inhibition of signal transduction ( ). In a phase 2b, randomized, double-blinded, placebo-controlled, parallel assignment, dose-ranging study involving 204 adults with moderate to severe AD lasting longer than 1 year, participants were randomized in a 1:1:1:1 ratio to receive placebo or tralokinumab (45, 150, or 300 mg) subcutaneously every 2 weeks for 12 weeks, with a 10-week follow-up period ( ). At 12 weeks, more patients who were treated with 300 mg of tralokinumab were found to have a significantly improved change in EASI score compared to patients who received placebo (adjusted mean difference = −4.94, P = .01). Additionally, improvements in IGA response rates were associated with increasing doses of tralokinumab, with the greatest absolute percentage difference from placebo being observed in participants who received 300 mg of tralokinumab (26.7% vs. 11.8%, P = .06). Patients treated with 300 mg of tralokinumab also had significant improvements in SCORAD, Dermatology Life Quality Index, and pruritus numeric rating scale versus placebo. Two randomized, double-blind, placebo-controlled, parallel assignment, phase 3 clinical trials involving 780 patients being given tralokinumab and/or placebo for 52 weeks are currently ongoing or completed, but results are not yet available ( ).
Lebrikizumab is a humanized monoclonal antibody that binds to IL13 and inhibits signal transduction by blocking IL13α1/IL4Rα heterodimerization ( ). In a randomized, placebo-controlled, double-blind, phase 2 study of 209 adults with moderate to severe AD who were treated with lebrikizumab 125 mg single dose, lebrikizumab 250 mg single dose, lebrikizumab 125 mg every 4 weeks for 12 weeks, or placebo every 4 weeks for 12 weeks, significantly more patients treated with lebrikizumab 125 mg every 4 weeks achieved EASI-50 at week 12 of the study compared to patients receiving placebo every 4 weeks (82.4% vs. 62.3%, P = .26) ( ). Additionally, the percentage of patients who achieved an IGA of 0 or 1 and the number of patients with SCORAD-50 was higher at week 12 in all lebrikizumab groups compared with placebo. A phase 2, randomized, double-blind, placebo-controlled, dose-ranging trial for lebrikizumab in 280 adult patients with moderate to severe atopic eczema lasting longer than 1 year was completed in 2019, but results are not yet available ( ). Two phase 3, randomized, double-blind, placebo-controlled, parallel-group studies involving 400 child and adult patients with moderate to severe AD being treated with lebrikizumab monotherapy are currently recruiting and are expected to be completed in 2021 ( ).
Nemolizumab is a humanized monoclonal antibody against IL34 receptor A and inhibits signaling of IL31, which plays a role in pruritus ( ). In a phase 2, randomized, double-blind, placebo-controlled, multicenter, 12-week trial of 264 adults with moderate to severe AD refractory to topical glucocorticoids or topical calcineurin inhibitors who were given subcutaneous nemolizumab at a dose of 0.1 mg, 0.5 mg, or 2 mg per kilogram of body weight, or placebo every 4 weeks, or 2 mg nemolizumab/kg every 8 weeks with placebo given at week 4, there was significant dose-dependent reduction in pruritus from baseline as measured by the pruritus visual-analogue scale (VAS); reductions of 43.7%, 59.8%, and 63.1% were seen in the 0.1 mg/kg, 0.5 mg/kg, and 2.0 mg/kg groups, respectively, compared to a 20.9% reduction seen with the placebo ( P = .002, P < .001, P < .001) ( ). Participants treated with nemolizumab also experienced significant reductions in pruritus verbal rating scale, improvements in EASI score and SCORAD, and improvements in mean percentage changes from baseline in sleep disturbance-VAS (−52.3%, −59.1%, and −62.6% for 0.1 mg/kg, 0.5 mg/kg, and 2.0 mg/kg vs. –31.9% with placebo). A follow-up study in which patients continued their previous nemolizumab dose every 4 weeks or every 8 weeks for 52 weeks in a double-blind extension found that there were maintained or decreased pruritus VAS scores from week 12 to week 64 in patients randomized to receive nemolizumab, with the greatest improvement occurring in the 0.5 mg/kg group ( ). Mean percentage change from baseline in EASI score, SCORAD score, and sleep disturbance-VAS scores were also maintained or decreased from week 12 to week 64. Patients who received placebo in the previous study and switched to nemolizumab at week 12 experienced a favorable response to treatment in pruritus VAS score by week 16 and maintained this response through week 64. A phase 2, randomized, double-blind, multicenter, parallel-group, placebo-controlled, dose-ranging study of 351 adults with moderate to severe AD who were randomized into a nemolizumab 10 mg group, nemolizumab 30 mg group, nemolizumab 90 mg group, and a placebo group found that percent change from baseline in EASI at week 24 was −72.2%, −73.4%, −69.2%, and −58.4%, respectively, and demonstrated reductions in EASI scores that were statistically significant for nemolizumab compared to placebo for the 10 mg and 30 mg treatment groups ( P = .051, P = .016), but not for the 90 mg treatment group ( P = .322) ( ). A phase 2, multicenter, open-label, single-group clinical trial to assess the safety of nemolizumab in adolescents with AD is currently recruiting ( ).
Ustekinumab, which is approved for the treatment of plaque psoriasis, is a fully humanized monoclonal antibody that neutralizes IL12 and IL23 by targeting the shared p40 subunit, causing regulation of Th1 and Th17/Th22 responses ( ). In a phase 2, double-blinded, placebo-controlled, crossover study of 32 adult patients with moderate to severe chronic AD who were given subcutaneous ustekinumab (45 mg and 90 mg per injection for patients weighing <100 kg or >100 kg, respectively) or placebo at weeks 0, 4, and 16 with a crossover at weeks 16, 20, and 32, for 40 weeks, the ustekinumab group achieved higher SCORAD50 response at 12 weeks, 16 weeks, and 20 weeks compared to placebo, but the difference was not statistically significant ( ). In a phase 2, randomized, double-blind, placebo-controlled, multicenter, parallel-group study of 79 adult Japanese patients with severe or very severe AD who were given 45 mg or 90 mg ustekinumab or placebo subcutaneous injections at 0 weeks and 4 weeks with a primary efficacy endpoint in percent change from baseline in EASI score at week 12, ustekinumab treatment demonstrated nonsignificant improvement in least-square mean change from baseline EASI score at week 12 (45 mg: −38.2, P < .95; 90 mg: −39.8%, P < .81; vs. placebo: −37.5%) and nonsignificant improvements in IGA, EASI-50, and EASI-75 ( ).
Risankisumab is another anti-IL23 humanized IgG monoclonal antibody that has been approved by several countries for treatment of moderate to severe plaque psoriasis ( ). A phase 2, multicenter, randomized, double-blinded, placebo-controlled, parallel assignment study of 155 children and older adults with moderate to severe AD receiving double-blind placebo for 16 weeks followed by risankizumab dose 1 or 2 for 24 weeks is currently ongoing and is estimated to be completed in April 2021 ( ).
Secukinumab is a recombinant human monoclonal antibody that selectively targets IL17A and prevents its binding to the IL17 receptor, causing neutralization of the proinflammatory cytokine cascade ( ). In a case report of an adult male with severe refractory AD, administration of subcutaneous secukinumab 300 mg caused a 66% improvement in SCORAD and marked improvement in erythema and pruritus after 16 weeks of treatment ( ). A phase 2, randomized, double-blind, parallel-assignment pilot study of 41 adult participants with moderate to severe AD receiving secukinumab (300 mg SQ every 2 weeks) has been completed, but results are not yet available, and a phase 2, randomized, placebo-controlled, parallel-assignment, double-blind study of 45 adult participants receiving secukinumab (300 mg SQ every 2 weeks) is currently recruiting ( ).
Fezakinumab (ILV-094) is a fully human monoclonal antibody against IL22, which promotes keratinocyte proliferation and upregulation of antimicrobial peptides in the epidermis ( ). In a phase 2a, randomized, double-blind, placebo-controlled, multicenter clinical trial of 60 adult patients with moderate to severe AD who were given IV fezakinumab (600 mg loading dose, 300 mg every 2 weeks) or placebo for 10 weeks, patients who had severe AD and received fezakinumab experienced significant reductions in SCORAD compared to placebo at 12 weeks (21.6 vs. 9.6, P = .029) and at 20 weeks (27.4 vs. 11.5, P = .010), as well as improvements in IGA versus placebo (0.7 vs. 0.3, P = .34) ( ). However, there were less significant reductions in SCORAD, BSA, and IGA observed in patients with moderate AD receiving fezakinumab compared to those with severe AD. In a phase 2a, randomized, placebo-controlled, multicenter clinical trial of 59 adult participants who were given IV fezakinumab (600 mg loading dose, 300 mg every 2 weeks) or placebo every 10 weeks, it was found that participants treated with fezakinumab experienced significantly greater reversal of the AD genomic profile versus placebo (25.3% vs. 10.5% at 4 weeks, P = 1.7 × 10 −5 ; 65.5% vs. 13.9% at 12 weeks, P = 9.5 × 10 −19 ) ( ).
Treatments targeting pathogenic antibodies: Anti-IgE
Omalizumab is a humanized anti-IgE IgG monoclonal antibody that prevents the binding of IgE to FCεRI and CD23 on B cells, causing a reduced number of FCεRI on basophils and reduced IgE synthesis by B cells, resulting in decreased expression of proinflammatory cytokines such as IL5, IL8, and IL13 ( ). Omalizumab has demonstrated significant efficacy in both pediatric and adult patients with AD ( ). However, several studies have also demonstrated no improvement of disease with omalizumab therapy, and it is hypothesized that lack of filaggrin mutations and lower elevations of total serum IgE are associated with a favorable response to omalizumab ( ).
Ligelizumab is another anti-IgE monoclonal antibody that binds to the Cε3 domain of IgE and inhibits the binding of free IgE to mast cells and basophils. Two randomized, placebo-controlled, double-blind clinical trials of 183 adults with a history of atopy found that ligelizumab demonstrated greater of suppression of serum IgE and IgE bound to mast cells and basophils compared to omalizumab ( ). Similarly, a double-blind, randomized, placebo-controlled, parallel-group multicenter study in 37 adult subjects with mild allergic asthma comparing the effects of ligelizumab to omalizumab found that there were was a greater inhibition of skin prick test response with ligelizumab compared to omalizumab ( P < .0001) ( ). A phase 2, randomized, double-blinded, placebo-controlled, parallel-group, proof of concept study of 22 adult participants with moderate to severe AD has been completed, but results have not yet been published (A study evaluating the safety and efficacy of QGE031 in atopic dermatitis patients, 2017).
Treatment targeting immune cells: Anti-CD20
Rituximab is a chimeric monoclonal anti-CD20 antibody that causes decreased immunomodulatory functions and loss of antigen presenting capability by B cells ( ). An open-label pilot study of four women and two men with severe AD who were refractory to topical corticosteroid and/or calcineurin inhibitor therapy were given two doses of 1000 mg of rituximab, 2 weeks apart ( ). All patients experienced significant improvement of AD lesions within 4 to 8 weeks of treatment, as measured by their EASI scores (29.4 ± 4.3 at baseline vs. 8.4 ± 3.6 at 8 weeks, P < .001), and EASI scores remained low at weeks 16 and 24. There was also a reduction of spontaneous IL13 production by peripheral blood mononuclear cells ex vivo (25.7 ± 5.7 pg/mL vs. 5.5 ± 4.1 pg/mL, P = .18), indicating a reduction of activated T cells in blood. Skin histology following treatment was notable for decreased hyperkeratosis, acanthosis, spongiosis, and dermal inflammatory cells. In a case study of three adult patients with severe AD unresponsive to standard therapy, patients experienced a reduction in peripheral blood CD19+ B-cell numbers following rituximab treatment, but they did not experience significant clinical benefit as measured by EASI ( ).
Treatments targeting immune signaling: JAK-STAT/JAK-SYK
Systemic JAK inhibitors
Tofacitinib is a small-molecule janus kinase-1 (JAK1) inhibitor that inhibits cytokines directly and leads to attenuation of JAK-STAT signaling in keratinocytes ( ). In a phase 2a, multisite, randomized, double-blind, vehicle-controlled, parallel-group study, 69 adults with mild to moderate AD were randomized 1:1 to 2% tofacitinib or vehicle ointment twice daily for 4 weeks ( ). Percentage change from baseline at week 4 in EASI score was significantly greater for the tofacitinib group compared to vehicle (−81.7% vs. 29.9%, P < .001), and a greater proportion of patients treated with tofacitinib had a Physician’s Global Assessment (PGA) of clear or almost clear compared to those on placebo (73% vs. 22%, P < .05). In a case series of six adult patients with moderate to severe AD refractory to standard therapy, 5 mg of oral tofacitinib administered twice daily in five patients and 5 mg once daily in one patient for 29 weeks significantly decreased body surface area of dermatitis, with improvement in erythema, edema/papulation, excoriation, lichenification, pruritus, decreased sleep loss, and a decrease in the composite scoring of AD (SCORAD) index by an average of 54.8% ( P < .05) during the initial 4 to 14 weeks ( ). This improvement was maintained with a subsequent reduction of 66.6% ( P < .05) observed during weeks 8 to 29 of treatment.
A phase 3, multicenter, open-label study of baricitinib, a selective JAK1/2 inhibitor approved for rheumatoid arthritis treatment, in 300 adult patients with moderate to severe AD is currently recruiting ( ). Likewise, a phase 3, multicenter, randomized, double-blind, placebo-controlled, parallel-group, outpatient study evaluating the safety and efficacy of baricitinib in 465 pediatric patients with moderate to severe AD is also recruiting ( ).
A phase 2b, randomized, double-blind, placebo-controlled, parallel, multicenter, dose-ranging study of abrocitinib, a JAK1 inhibitor, in adults with moderate to severe AD in 267 adult patients with moderate to severe AD randomized into 10 mg, 30 mg, 100 mg, 200 mg of abrocitinib once daily, and placebo groups for 12 weeks found that a statistically significantly greater percentage of patients in the 100 mg and 200 mg treatment groups achieved grades of clear or almost clear on the IGA scale, with improvement of two grades or more compared to placebo ( P = .0184, P = .0032). Patients in the 100 mg and 200 mg treatment groups also achieved more EASI-75 responses than patients in the placebo group ( P = .004, P < .001) ( ). A phase 3, randomized, double-blind, placebo-controlled, multicenter study of adolescents with moderate to severe AD treated with abrocitinib and a phase 3, randomized, double-blind, placebo-controlled, parallel group multicenter study to evaluate PF-0496582 monotherapy in participants over age 12 years with moderate to severe AD are also recruiting ( ).
Gusacitinib is an oral dual inhibitor of JAK and SYK kinases. In a phase 1b, randomized, double-blind, placebo-controlled multicenter study of 36 adult patients with moderate to severe AD who were given ASN002 (20 mg, 40 mg, or 80 mg) or placebo once daily for 28 days, significantly higher proportions of patients who received ASN002 (40 mg or 80 mg daily) achieved EASI-50 (100% and 83%, P = .003 and P = .03, respectively) at day 29 compared to placebo; no significant difference was seen between the 20 mg group and the placebo group ( ). Patients in the 40 mg group also experienced a significant decrease in change from baseline in BSA at day 29 (−21.6, P = .03) compared to placebo, and a significant decrease from baseline in weekly average pruritus numeric rating scale in the 80 mg group at day 29 (−4.7, P = .01) compared to placebo. A phase 2b, randomized, double-blind, placebo-controlled, parallel-assignment study to evaluate efficacy, safety, tolerability, and pharmacokinetics of ASN002 in adults with moderate to severe AD is ongoing ( ).
Upadacitinib is an oral JAK-1 inhibitor originally developed for the treatment of rheumatoid arthritis. It has a higher selectivity for JAK-1 over JAL-2 and JAK-3, and thus has a better safety profile with limited hematologic abnormalities such as cytopenia ( ). In a phase 2, randomized, parallel-assignment, placebo-controlled study of 166 participants with moderate to severe AD who were randomized in a 1:1:1:1 ratio to receive upadacitinib 7.5 mg, 15 mg, 30 mg, or placebo for 16 weeks, investigators found that there was a significantly higher improvement from baseline in the upadacitinib treatment groups compared to the placebo group as measured by EASI score (39%, P = .03; 62%, P < .001; and 74%, P < .001 vs. placebo 23%, respectively), with a dose-response relationship ( ). A phase3, randomized, double-blind, parallel-group, placebo-controlled study evaluating the safety and efficacy of upadacitinib in 847 adult and adolescent participants with moderate to severe AD who were given upatacinib 15 mg, upadacitinib 30 mg, or placebo for 16 weeks found that those in the 15 mg and 30 mg treatment groups demonstrated significant improvement as measured by EASI scores ( ); 70% of participants in the 15 mg treatment group and 80% of participants in the 30 mg treatment group achieved EASI-75 at week 16, compared to 16% in the placebo group ( P < .001). Patients in both treatment groups also experienced significantly greater improvement in Worst Pruritus Numerical Rating Scale (NRS) compared to placebo (52%, 60%, 12%, P < .001, respectively), and experienced significantly greater improvement in IGA-AD scores compared to patients in the placebo group (48%, 62%, 8%, P < .001, respectively). There is a phase 3, randomized, double-blind, active controlled study in which 692 participants will be given oral upadacitinib for 24 weeks and placebo injections for 22 weeks or dupilumab injections for 22 weeks and placebo tablets for 24 weeks ( ).
JAK inhibitors have been associated with a number of adverse effects, including polyneuropathy, pancytopenia, dermatologic infections, increases in serum high-density lipoprotein, low-density lipoprotein, and total cholesterol, and gastrointestinal complaints ( ).
Topical JAK inhibitors
Delgocitinib is a topical JAK inhibitor that inhibits JAK1, JAK2, JAK 3, and tyrosine kinase 2 ( ). A phase 2, randomized, double-blind, vehicle-controlled study of 103 pediatric patients randomized in a 1:1:1 ratio to receive 0.25% or 0.5% delgocitinib ointment or a vehicle ointment for 4 weeks demonstrated that at the end of treatment, mEASI scores in both delgocitinib groups were significantly more reduced compared to the vehicle group (0.25% group: −54.2%, P < .001; 0.5% group: −61.8%, P < .001) ( ). In a phase 2, randomized, vehicle-controlled, intergroup comparison study involving 327 adult patients assigned to a vehicle group, delgocitinib 0.25% group, delgocitinib 0.5% group, delgocitinib 1% group, delgocitinib 3% group, and a tacrolimus group twice daily for 4 weeks found that changes in the least-squares mean percentage from baseline in mEASI scores for the delgocitinib 0.25%, 0.5%, 1%, and 3% groups were −41.7%, −57/1, −72.9%, and −12%, respectively, which were signifi-cantly reduced compared to the vehicle group ( P < .001). As of 2020 there have been no head-to-head trials comparing topical JAK inhibitors to other nonsteroidal antiinflammatory pharmaceuticals in patients with AD.
A phase 1, nonrandomized, parallel-assignment, open-label, pilot pharmacokinetic study of ruxolitinib (JAK1/2 inhibitor) phosphate cream, in 60 pediatric patients with AD is currently active ( ).
A phase 2, randomized, dose-ranging, vehicle-controlled and triamcinolone 0.1% cream-controlled study to establish safety and efficacy of ruxolitinib phosphate cream in adults with AD has also been completed, but results are not yet available ( ).
Tacrolimus and pimecrolimus are calcineurin inhibitors that bind to FK506-binding protein (FKBP), thereby inhibiting the activation of calcineurin and its downstream signaling pathway; this results in decreased production of inflammatory cytokines ( ). Tacrolimus and pimecrolimus have the same mechanisms of action, but pimecrolimus has an altered skin penetration profile ( ). A meta-analysis of 12 independent randomized clinical trials comparing topical calcineurin inhibitors to topical corticosteroids in the treatment of AD in pediatric and adult patients found that there were similar improvements (81% vs. 71%, P = .01) and treatment success (72% vs. 68%, P = .04) ( ). The number of adverse events and adverse events related to treatment was higher in patients treated with calcineurin inhibitors compared to those treated with corticosteroids (adverse events: 74% vs. 64%, P = .02; adverse events related to treatment: 11% vs. 8%, P = .002).
Crisaborole is a topical antiinflammatory PDE4 inhibitor that causes inhibition of proinflammatory and T-cell cytokine production ( ). In two identically designed, vehicle-controlled, double-blind studies (AD-301 and AD-302), 1522 patients age 2 years and older with AD were given crisaborole ointment twice daily for 28 days or a vehicle ( ). Patients treated with crisaborole achieved higher Investigator’s Static Global Assessment (ISGA) scores at day 29 compared to those treated with vehicle (AD-301: 32.8% vs. 25.4%, P = .38; AD-302: 31.4% vs. 18.0%, P < .001). A phase 4, multicenter, open-label safety study of crisaborole ointment in 137 children age 3 months to less than 24 months with mild to moderate AD has been completed, but results are not yet available ( ).
Apremilast is an oral PDE4 inhibitor approved for the treatment of adults with moderate to severe psoriasis and psoriatic arthritis ( ). A phase 2, double-blind, placebo-controlled trial of 185 patients with moderate to severe AD who received apremilast 30 mg twice daily, 40 mg twice daily, or placebo for 12 weeks found that at week 12, patients who received apremilast 40 mg twice daily showed significantly greater improvement from baseline in EASI score compared to patients who received placebo (−31.6% vs. −11%, P < .04) ( ). Tissue biomarker data in patients taking apremilast 40 mg twice daily also showed substantial reductions in epidermal hyperplasia and inflammatory markers. Of note, those taking apremilast 30 mg twice daily did not experience statistically significant changes in EASI score versus placebo and did not have notable changes in inflammatory biomarkers. In a case series of four adults with AD since childhood who were treated with apremilast for 10 weeks to 9 months, there was clearance or reduction of eczematous papules, erythema, plaques, and pruritus ( ).
Initially developed for treatment of irritable bowel syndrome, asimadoline is a peripherally acting κ-opioid agonist that has also been found to inhibit the itch caused by compound 48/80 ( ). A phase 2, randomized, double-blind, single-group assignment study evaluating the efficacy of asimadoline in adults with AD with pruritus is completed, but results are not yet available ( ).
Aryl hydrocarbon receptor (AhR) agonists
Tapinarof (5-[(E)-2-phenylethenyl]-2-[propan-2-yl] benzene-1, 3-diol) is a nonsteroidal, fully synthetic, hydroxylated stilbene compound classified as an AhR modulating agent that binds and activates the AhR, causing downregulation of proinflammatory cytokine expression and impacting barrier gene expression in human keratinocytes ( ). In a phase 1, open-label, two-cohort sequential study that assessed the pharmacokinetics, safety, and efficacy of tapinarof in 11 adults with moderate to severe AD, administration of tapinarof (1% or 2%) resulted in at least 50% total EASI by day 21 and a decrease in pruritus ( ). In a phase 2, randomized, double-blind, vehicle-controlled, six-arm, multicenter trial of 247 adult patients with AD who were given tapinarof 1% twice daily, tapinarof 1% once daily, tapinarof 0.5% twice daily, tapinarof 0.5% once daily, vehicle twice daily, or vehicle once daily, the rate of treatment success, as measured by IGA score, with tapinarof 1% twice daily was statistically significantly higher than the rate with vehicle twice daily (53% vs. 24%, α = 0.05 level) ( ).
Anti-H4 receptor (H4R)
JNJ 39758979 [(R)-4-(3-amino-pyrrolidin-1-yl)-6-isopropyl-pyrimidin-2-ylamine] is an H4R antagonist that has demonstrated effectiveness in reducing pruritus in healthy subjects ( ). In a phase 2a, randomized, double-blind, placebo-controlled, multicenter, parallel-group study of 88 Japanese adults with moderate AD who were administered one JNJ-3975879 (100 mg and 300 mg) or placebo, decreases in median EASI were observed (−3.7 and −3.0, respectively), but these changes were not significant compared to placebo (−1.30, P = 1.672 and 0.1992, respectively) ( ). The trial was also prematurely discontinued due to side effects of neutropenia.
In a phase 2, randomized, double-blind, placebo-controlled, parallel group study, 98 adult participants with moderate to severe AD were administered adriforant (30 mg orally daily) for 8 weeks ( ). This study has been completed, but results are not yet available.
Dihomo-γ-linolenic acid (DGLA)
DS107 is an agent containing DGLA ( ). In a phase 2a, randomized, placebo-controlled, parallel assignment trial of 102 adult participants with moderate to severe AD who received oral DS107 or placebo, patients administered DS107 experienced a statistically significant decrease in IGA compared to placebo ( P = .57) as well as a statistically significant reduction of itch assessed by VAS compared to placebo ( P = .015) ( ). In a phase 2b, randomized, double-blind, multicenter, vehicle-controlled study in which 326 patients with mild to moderate AD were given DS107 cream (1% and 5%) or placebo, patients receiving DS107 experienced a dose-dependent response in IGA and EASI-75, and those administered 5% DS107 cream achieved statistically significant changes in both IGA and EASI-75 ( P = .029 and .019, respectively) ( ). A phase 2, randomized, double-blind, placebo-controlled, parallel assignment study to assess efficacy and safety of oral DS107 in adult patients with moderate to severe AD is currently recruiting ( ).
Neurokinin-1 receptor (NK1-R) antagonist
NK1-R antagonists prevent the interaction between NKR-1 and substance P, which is involved in the pathogenesis of nonhistaminergic pruritus ( ). Aprepitant is an oral NK1-R antagonist approved for treatment of nausea during chemotherapy ( ). In a prospective study of 20 patients with chronic pruritus refractory to therapy who were treated with aprepitant 80 mg for 3 to 13 days, patients experienced a significant decrease in pruritus intensity on the VAS (8.4 at baseline vs. 4.9 after treatment, P < .001) ( ). In an open, randomized trial of 39 patients with moderate to severe AD who were given aprepitant 80 mg daily for 7 days (n = 19) or topical treatment alone (n = 20), there were significant reductions in SCORAD (40.5–32.0, P < .01), mean VAS (5.5–3.8, P < .05), and scratching movements (77.3–48.3, P < .05) in the aprepitant group ( ). However, these reductions were not significant when compared to the control group.
Serlopitant is a NK1-R antagonist developed for chronic use in treatment of overactive bladder ( ). In a phase 2, randomized, double-blind, parallel-group, placebo-controlled, multicenter, dose finding and efficacy study of 222 adult participants with pruritus lasting longer than 6 weeks refractory to antihistamines and steroids who were given serlopitant (0.25 mg, 1 mg, or 5 mg) or placebo once daily for 6 weeks, participants taking 1 mg and 5 mg of serlopitant experienced a dose-dependent decrease in VAS pruritus score compared to placebo ( P = .022 and P = .13, respectively) ( ). Mean overall Dermatology Life Quality Index (DQLI) was also lower in treatment groups, although statistically significant improvements were only seen in the 1 mg group. In a phase 2, randomized, double-blind, placebo-controlled, parallel assignment study of 484 adults and adolescents with pruritus who were given daily oral doses of serlopitant (1 mg or 5 mg) or placebo for 6 weeks, there was no significant decrease in Worst Itch Numeric Rating Scale (WI-NRS) score in either treatment group ( P = .11 and P = .17, respectively) by the end of the treatment period ( ).
In a phase 2, randomized, double-blind, placebo-controlled multicenter study of 168 adult subjects with chronic, AD-associated pruritus refractory to antihistamine and corticosteroids, participants were either given placebo or oral tradipitant (VLY-686), another NK1-R, for 8 weeks ( ). Subjects receiving trapiditant experienced significantly greater improvement on the worst itch VAS scale (−44.2 vs. −30.6, P = .019), the total SCORAD index (−21.3 vs. −13.6, P = .008), objective SCORAD (−13.3 vs. −7.2, P = .005), Clinician Global Impression of Change (CGI-C) (2.6 vs. 3.3, P = .007), Patient Global Impression of Change (PGI-C) itch (2.6 vs. 3.2, P = .025), and PGI-C AD (2.7 vs. 3.5, P = .007) compared to placebo ( ). An earlier phase 2, randomized, double-blind, placebo-controlled, proof of concept study in 69 adult participants with AD and chronic pruritus who were given oral tradipitant or placebo for 4 weeks also demonstrated significant improvement in VAS for itch from baseline for patients who received tradipitant ( P < .0001) ( ; ). However, the change was not significant compared to placebo. A phase 3, randomized, double-blind, placebo-controlled, parallel-assignment, efficacy study of tradipitant in adult patients with chronic pruritus and AD is currently recruiting ( ).
Rosiglitazone is a PPAR-γ agonist approved for treatment of type 2 diabetes mellitus that has been shown to inhibit TLSP-induced dendritic cell maturation and reduce severity of skin lesions and scratching behavior in mice ( ). In a case series of six patients with severe AD, the addition of rosiglitazone (2–4 mg PO twice daily) to treatment with corticosteroids, antihistamines, and/or calcineurin inhibitors caused a BSA reduction of more than 65% in five patients and a decreased number of flares compared with baseline ( ).
Traditional therapies for AD are limited to immunosuppressants whose use can be limited by harmful and unwanted side effects. The development of targeted treatments offers safer and more specific options. Although many of the therapies mentioned in this chapter have shown much promise, only two, crisaborole and dupilumab, have been approved by the FDA for use in AD patients. Furthermore, these new treatment options are often expensive and costly. As of January 2020, the list price for Dupixent is $3019.50 for a 4-week supply ( ). To usher in this new era of AD therapy, further large-scale, randomized, placebo-controlled, double-blind, multicenter trials are needed to determine efficacy and safety. More research into the specific mediators and their receptors involved in the pathogenesis of AD may also be beneficial so that further potential therapies can be developed and tested in head-to-head trials and subanalyses, and evaluated among different patient demographics. It is also necessary to conduct large-scale trials in pediatric populations due to the significantly higher prevalence of AD in this population ( ). Finally, trials involving a combination of target-specific treatments would be very valuable to determine drug interactions. Table 23.1 summarizes the list of currently available and emerging targeted treatment medications for AD.