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

PDE4 inhibitors are expected to be anti-inflammatory agents based on their mechanism of action, but the application of this drug class is limited by a narrow therapeutic window due to adverse effects associated with gastrointestinal function. Difamilast, a novel selective phosphodiesterase 4 (PDE4) inhibitor, demonstrated significant efficacy without adverse reactions such as nausea and diarrhea in patients with atopic dermatitis (AD) and was recently approved in Japan. In this study, we investigated the pharmacological and pharmacokinetic properties of difamilast to provide nonclinical data to help understand the clinical effects. Difamilast selectively inhibited recombinant human PDE4 activity in assays. The IC50 of difamilast against PDE4B, a PDE4 subtype that plays an important role in the inflammatory response, was 0.0112 µM, representing a 6.6-fold decrease compared with the IC50 against PDE4D (0.0738 µM), a subtype that can trigger emesis. Difamilast inhibited TNF-α production in human (IC50 = 0.0109 µM) and mouse (IC50 = 0.0035 µM) peripheral blood mononuclear cells and improved skin inflammation in a mouse model of chronic allergic contact dermatitis. These effects of difamilast on TNF-α production and dermatitis were superior to those of other topical PDE4 inhibitors: CP-80633, cipamfylline, and crisaborole. In pharmacokinetic studies using miniature pigs and rats, the concentrations of difamilast in the blood and brain after topical application were not sufficient to support pharmacological activity. This nonclinical study contributes to explain the efficacy and safety of difamilast with a sufficient therapeutic window in the clinical trials. SIGNIFICANCE STATEMENT: This is the first report on the nonclinical pharmacological profile of difamilast ointment, a novel topical PDE4 inhibitor that demonstrated utility in clinical trials in patients with atopic dermatitis. Difamilast, which has high PDE4 selectivity (especially for the PDE4B subtype), ameliorated chronic allergic contact dermatitis in mice after topical application, with a pharmacokinetic profile in animals that suggests few systemic side effects; thus, difamilast is a promising new therapeutic treatment for atopic dermatitis.

Protection of human corneal epithelial cells from TNF-α-induced disruption of barrier function by rebamipide.

PURPOSE: TNF-α disrupts the barrier function of cultured human corneal epithelial (HCE) cells. We investigated the effects of the cytoprotective drug rebamipide on this barrier disruption by TNF-α as well as on corneal epithelial damage in a rat model of dry eye. METHODS: The barrier function of HCE cells was evaluated by measurement of transepithelial electrical resistance. The distribution of tight-junction (ZO-1, occludin) and adherens-junction (E-cadherin, ß-catenin) proteins, and the p65 subunit of nuclear factor-κB (NF-κB) was determined by immunofluorescence microscopy. Expression of junctional proteins as well as phosphorylation of the NF-κB inhibitor IκB-α and myosin light chain (MLC) were examined by immunoblot analysis. A rat model of dry eye was developed by surgical removal of exorbital lacrimal glands. RESULTS: Rebamipide inhibited the disruption of barrier function as well as the downregulation of ZO-1 expression, and the disappearance of ZO-1 from the interfaces of neighboring HCE cells induced by TNF-α. It also inhibited the phosphorylation and downregulation of IκB-α, the translocation of p65 to the nucleus, the formation of actin stress fibers, and the phosphorylation of MLC induced by TNF-α in HCE cells. Treatment with rebamipide eyedrops promoted the healing of corneal epithelial defects as well as attenuated the loss of ZO-1 from the surface of corneal epithelial cells in rats. CONCLUSIONS: Rebamipide protects corneal epithelial cells from the TNF-α-induced disruption of barrier function by maintaining the distribution and expression of ZO-1 as well as the organization of the actin cytoskeleton. Rebamipide is, thus, a potential drug for preventing or ameliorating the loss of corneal epithelial barrier function associated with ocular inflammation.