Pharmacological Profile of Difamilast, a Novel Selective Phosphodiesterase 4 Inhibitor, for Topical Treatment of Atopic Dermatitis

Synthetic approaches and clinical application of representative small-molecule inhibitors of phosphodiesterase

Phosphodiesterases (PDEs) constitute a family of enzymes that play a pivotal role in the regulation of intracellular levels of cyclic nucleotides, including cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Dysregulation of PDE activity has been implicated in diverse pathological conditions encompassing cardiovascular disorders, pulmonary diseases, and neurological disorders. Small-molecule inhibitors targeting PDEs have emerged as promising therapeutic agents for the treatment of these ailments, some of which have been approved for their clinical use. Despite their success, challenges such as resistance mechanisms and off-target effects persist, urging continuous research for the development of next-generation PDE inhibitors. The objective of this review is to provide an overview of the synthesis and clinical application of representative approved small-molecule PDE inhibitors, with the aim of offering guidance for further advancements in the development of novel PDE inhibitors.

Cost-Effectiveness Study of Difamilast 1% for the Treatment of Atopic Dermatitis in Adult Japanese Patients

INTRODUCTION

Difamilast has proven to be an effective treatment for the treatment of atopic dermatitis (AD) in Japan, but its cost-effectiveness remains unknown. Therefore, the objective of the current study was to determine the cost-effectiveness of difamilast 1% compared with delgocitinib 0.5% in Japanese adult patients with moderate-to-severe AD and compared with placebo in Japanese adult patients with all-severity AD from a Japanese public health-care perspective.

METHODS

The analysis was conducted using a cost-effectiveness model from the Japanese public health-care perspective. This model had four health states ("clear," "mild," "moderate," and "severe") defined according to the Eczema Area and Severity Index score. The time horizon of the analysis was 1 year. Because the analysis period was short, no discount rate was applied. The proportions of patients previously estimated by the anchored matching-adjusted indirect comparison were implemented in the model. The model was further populated with data from the literature. The main model outcomes were quality-adjusted life-years (QALY), costs, and outcomes, including the incremental cost-effectiveness ratio. All prices were stated in JPY at the price level from 2018 April to 2019 March. One-way sensitivity analysis and probabilistic sensitivity analysis (PSA) were performed to assess the robustness of the results.

RESULTS

In the base case, the cost-effectiveness of difamilast 1% compared with delgocitinib 0.5% and placebo was JPY 827,054/QALY and JPY 1,518,657/QALY, respectively. The PSA showed that the cost-effectiveness of difamilast 1% compared with delgocitinib 0.5% and placebo had a 66.6% and 99.6% probability of being below the JPY 5 million/QALY threshold, respectively.

CONCLUSION

The results suggest that difamilast 1% is a more cost-effective treatment option compared with delgocitinib 0.5% in Japanese adult patients with moderate-to-severe AD and compared with placebo in adult patients with all-severity AD from a Japanese public health-care perspective.

Matching-Adjusted Indirect Comparison of the Efficacy and Safety of Difamilast 1% and Delgocitinib 0.5% in Patients with Moderate-to-Severe Atopic Dermatitis

BACKGROUND

Atopic dermatitis (AD) is a chronic condition with an increasing incidence in Japan. Difamilast and delgocitinib are both new topical drugs for AD proven to be efficacious and safe in phases 2 and 3 clinical trials in Japan. However, there are no head-to-head trials comparing their efficacy and safety. The aim of this study was to determine the proportion of patients by severity and compare the clinical efficacy and safety of difamilast with delgocitinib among patients with moderate-to-severe AD using a matching-adjusted indirect comparison (MAIC).

METHODS

Phase 3 clinical trials of difamilast and delgocitinib for treating AD were included. The trials had similar designs but differed in baseline population characteristics. Anchored MAIC was used to align the baseline characteristics and calculate clinical outcomes. The primary outcome was to determine severity stages of the proportion of patients with AD through Eczema Area and Severity Index (EASI), while the secondary outcome included comparing other clinical efficacy and safety of difamilast with delgocitinib.

RESULTS

A total of 340 patients were selected (170 each received difamilast and placebo) from the difamilast trial, with 158 (106 received delgocitinib; 52 received placebo) from the delgocitinib trial for the analysis. After matching patients from the difamilast trial with those from the delgocitinib trial, the effective sample sizes (ESS) reduced to 32.7-43.3% of the original difamilast (treatment/placebo) patients. At week 4, the ESS in the difamilast group demonstrated no statistically significant differences in the distribution of AD severity stages, as per EASI scores, compared with the delgocitinib group. In addition, no significant differences were found in modified EASI (mEASI) scores, mEASI 50 and 75 scores, and safety outcomes between the two treatments.

CONCLUSIONS

The anchored MAIC analysis indicates that difamilast treatment, like delgocitinib, is a useful option for the treatment of patients with moderate-to-severe AD in Japan.

[Phosphodiesterase 4 inhibitors in dermatology : Role in the treatment of skin diseases]

BACKGROUND

Chronic inflammatory skin diseases are of great social and medical importance and require effective drug therapy. Phosphodiesterase 4 (PDE4) inhibitors represent a possible therapeutic option by regulating inflammatory processes. PDEs cause the release of proinflammatory cytokines by interfering with signaling pathways. The PDE4 inhibitors apremilast (treatment of psoriasis and Behçet's disease), roflumilast (treatment of chronic obstructive pulmonary disease), and crisaborole (treatment of atopic dermatitis) are currently approved in Europe.

PSORIASIS

Apremilast is used for second-line treatment of plaque psoriasis and psoriatic arthritis and has a favorable side effect profile. Topical PDE4 inhibitors are currently being researched and have not yet been approved by the European Medicines Agency (EMA).

ATOPIC DERMATITIS

The topical PDE4 inhibitor crisaborole was approved by the EMA in 2020 as a topical treatment alternative to glucocorticoids and calcineurin inhibitors. Although the substance has shown good tolerability in studies and also alleviates the accompanying itching, it did not find its way onto the German market. BEHçET'S DISEASE: Apremilast is approved for the treatment of Behçet's disease in adults with refractory, severe oral ulcers.

OUTLOOK

Case studies have also demonstrated the efficacy of systemic PDE4 inhibition in other skin diseases (including blistering autoimmune dermatoses, lichen planus, and acantholytic genodermatoses). The substances are also being researched and used to treat extracutaneous inflammatory diseases.

An Interim Report of a Phase 3, Long-Term, Open-Label Study to Evaluate Efficacy and Safety of Difamilast Ointment in Japanese Infants with Atopic Dermatitis

INTRODUCTION

Difamilast is the first selective phosphodiesterase 4 inhibitor approved for atopic dermatitis (AD) in Japan. A phase 3, 52-week, open-label study is ongoing to establish efficacy and safety of difamilast ointments in infants with AD aged 3 to < 24 months because a clinical study has not been conducted in this population.

METHODS

This study consisted of a 4-week primary evaluation period in which difamilast 0.3% ointment was applied twice daily to Japanese infants aged 3 to < 24 months (n = 41) and an ongoing 48-week long-term extension period in which difamilast 0.3% or 1% ointment was applied based on existing symptoms. The data on efficacy and safety of difamilast were obtained as of an interim report in the study period.

RESULTS

The response rate in Investigator's Global Assessment score was 45.0% at week 1, which was maintained at 56.1% at week 4 and 63.4% at the interim report. Infants achieved the response rate in Eczema Area and Severity Index 75 (improvement of ≥ 75%) of 47.5% at week 1, which further improved to 82.9% at week 4 and 78.1% at the interim report. Adverse events (AEs) were reported in 22 (53.7%) infants in the primary evaluation period: of those the most frequent AE was nasopharyngitis (19.5%) followed by dermatitis contact (7.3%). As of the interim report, 36 (87.8%) infants experienced AEs: of those, nasopharyngitis (70.7%) and gastroenteritis (22.0%) were most frequently observed. The total AEs were mostly mild or moderate in severity. No investigational medicinal product-related AEs and no AEs leading to discontinuation were reported.

CONCLUSION

Difamilast ointments applied twice daily to Japanese infants with AD aged 3 to < 24 months is effective and well tolerated as of the interim report in the study period. The final results will be reported in the near future.

CLINICAL TRIAL REGISTRATION

Clinical Trials. gov identifier: NCT05372653.

PDE4D: A Multipurpose Pharmacological Target

Phosphodiesterase 4 (PDE4) enzymes catalyze cyclic adenosine monophosphate (cAMP) hydrolysis and are involved in a variety of physiological processes, including brain function, monocyte and macrophage activation, and neutrophil infiltration. Among different PDE4 isoforms, Phosphodiesterases 4D (PDE4Ds) play a fundamental role in cognitive, learning and memory consolidation processes and cancer development. Selective PDE4D inhibitors (PDE4Dis) could represent an innovative and valid therapeutic strategy for the treatment of various neurodegenerative diseases, such as Alzheimer's, Parkinson's, Huntington's, and Lou Gehrig's diseases, but also for stroke, traumatic brain and spinal cord injury, mild cognitive impairment, and all demyelinating diseases such as multiple sclerosis. In addition, small molecules able to block PDE4D isoforms have been recently studied for the treatment of specific cancer types, particularly hepatocellular carcinoma and breast cancer. This review overviews the PDE4DIsso far identified and provides useful information, from a medicinal chemistry point of view, for the development of a novel series of compounds with improved pharmacological properties.

Topical Application of a PDE4 Inhibitor Ameliorates Atopic Dermatitis through Inhibition of Basophil IL-4 Production

Phosphodiesterase 4 inhibitors have been approved for the treatment of atopic dermatitis. However, the cellular and molecular mechanisms underlying their therapeutic effect remain to be fully elucidated. In this study, we addressed this unsolved issue by analyzing the action of difamilast, a novel phosphodiesterase 4 inhibitor, on an oxazolone-induced skin allergic inflammation commonly used as a mouse model of atopic dermatitis. Topical application of difamilast ameliorated skin inflammation in association with reduced IL-4 expression even when the treatment commenced 4 days after the initiation of oxazolone challenge, showing its therapeutic effect on atopic dermatitis. IL-4-deficient mice displayed milder skin inflammation than did wild-type mice, and the difamilast treatment had little or no further therapeutic effect. This was also the case in mice depleted of basophils, predominant producers of IL-4 in the skin lesion, suggesting that difamilast may act on basophils. Notably, basophils accumulating in the skin lesion showed highly upregulated expression of Pde4b encoding the B subtype of the phosphodiesterase 4 family. Difamilast suppressed IL-4 production from basophils activated in vitro, at least in part, through inhibition of ERK phosphorylation. Taken together, difamilast appeared to ameliorate atopic dermatitis inflammation through the suppression of basophil IL-4 production in the skin lesion.

The use of essential oils in atopic dermatitis: a review

Atopic dermatitis (AD) has become a common childhood disease that affects a large number of children worldwide and has become a chronic skin disease that causes huge economical and psychological damage to the whole family. Despite the use of steroids, immunosuppressants, and various topical preparation, the prognosis is still poor. Hence, this review aimed to explore the potential of using essential oils (EO) as an active ingredient in managing AD. The review was completed by using Pubmed, Scopus, and Medline to search for relevant articles that study the pathophysiology of AD, the properties of EO, the use of EO in managing AD, and the suitable advanced formulation to incorporate EO. From the review conducted, it was concluded that EO have huge potential in managing AD and can be used as complimentary therapeutic agents in AD treatment. Scientists and industries should venture into commercializing more topical products with EO to help manage AD more effectively.

Preclinical pharmacokinetic investigation of the bioavailability and skin distribution of HY-072808 ointment, a novel drug candidate for the treatment of atopic dermatitis, in minipigs by a newly LC-MS/MS method

HY-072808 is a novel phosphodiesterase 4 inhibitor clinically used for topical atopic dermatitis treatment. Cytochrome P450 enzymes are involved in transforming it into major metabolite ZZ-24. An efficient UPLC-MS/MS method was established to detect HY-072808 and ZZ-24 in plasma and skin tissues of minipigs.One-step protein precipitation was performed with acetonitrile. Subsequently, elution was served with a methanol and water gradient containing 0.1% formic acid for 3.5 min. The plasma and skin tissue concentrations of HY-072808 and ZZ-24 showed good linearity from 0.200 to 200 ng/mL.The experimental minipigs exhibited low systemic exposure and bioavailability of 3.1-7.6% after transdermal application of 1-4% HY-072808 ointment. Multiple topical administrations over seven consecutive days showed a minor accumulation in systemic exposure, with accumulation factors of 2.3 and 4.0 for HY-072808 and ZZ-24, respectively.The distribution of HY-072808 ointment among different cortical layers in minipigs was studied for the first time. Following transdermal application of 2% HY-072808 ointment, the concentration in plasma and skin tissues in the order of epidermis > dermis > subcutaneous tissue ≈ subcutaneous muscle ≈ plasma; at 48 h after the administration, the epidermis and dermis still had a high concentration of the drug.