Pharmacology of orismilast, a potent and selective PDE4 inhibitor

There remains an unmet need for oral medications that are safe and efficacious for long-term management of chronic inflammatory skin diseases (CISD). Inhibition of phosphodiesterase 4 (PDE4) can modulate a broad range of pro-inflammatory cytokines that play a major role in CISD pathogenesis. Orismilast is a second generation PDE4 inhibitor in clinical development for CISD treatment.The objective of this study was to examine the PDE4 enzymatic activity and anti-inflammatory effects of orismilast in vitro, ex vivo, and in vivo.The PDE1-11 enzymatic activity of orismilast was tested in vitro using a single concentration of 308 nM orismilast. The PDE4 selectivity and inhibitory potency was further examined in a radiometric assay. Orismilast was tested on human whole blood and human peripheral blood mononuclear cells (PBMC) to determine effects on its cytokine secretion and inhibition profile ex vivo. Orismilast was orally administered in a murine model of chronic oxazolone-induced ear skin inflammation. Ear thickness, a marker of inflammation, and inflammatory cytokines were analysed.Orismilast selectively inhibited PDE4 and demonstrated potent inhibition of PDE4B and PDE4D subtype splice variants in vitro. Orismilast inhibited whole blood and PBMC production of tumour necrosis factor α (TNFα), and the secretion of T-helper (Th)1 (TNFα and IFNγ), Th17 (IL-22 and IL-23), and Th2 (IL-4, IL-5, and IL-13) related cytokines in PBMC. In vivo, 10 and 30 mg/kg doses of orismilast significantly reduced ear thickness and inflammation markers (p < 0.0001, respectively).Orismilast displayed selective and potent PDE4 inhibition and broad-spectrum anti-inflammatory activity in several pre-clinical models. The results of the study support clinical development of oral orismilast as a novel treatment option for CISD including psoriasis, atopic dermatitis, and hidradenitis suppurativa.