Anti-Inflammatory Evaluation of Pyrazino[2,1-b]quinazoline-3,6-dione Derivatives Inspired by Fiscalin B

Background/Objectives: Chronic inflammatory skin diseases are frequently associated with pruritus, in which the neurokinin-1 receptor (NK1R) and its ligand substance P (SP) play a central role. The development of compounds combining anti-inflammatory and antipruritic effects represents a promising therapeutic strategy. This study aims to identify fiscalin B derivatives as anti-inflammatory agents with high affinity to NK1R using an integrated in silico and in vitro approach. Methods: A library of fiscalin B derivatives was screened through molecular docking against NK1R to identify high-affinity ligands. Selected compounds were further evaluated using in silico ADMET and toxicity predictions. In vitro assays were conducted in HaCaT keratinocytes, RAW264.7 macrophages, and NIH/3T3 fibroblasts to assess cytotoxicity, nitric oxide production, inflammatory proteins expression, and cell migration. Results: Docking studies identified several derivatives with predicted binding affinities comparable to or exceeding those of aprepitant, a well-established NK1R antagonist. Several compounds, particularly 2, 3, 4, 6, and 7, reduced lipopolysaccharide-induced nitric oxide production to 41–51% without relevant cytotoxicity. This effect was associated with reduced iNOS protein levels, suggesting modulation of inflammatory pathways rather than direct nitric oxide scavenging. Most compounds showed positive safety profiles, although in silico analysis indicated limited biodegradability and potential aquatic toxicity. Conclusions: The fiscalin B derivatives, 2, 3, and 4, demonstrate potential as anti-inflammatory agents, in vitro, and as NK1R high affinity ligands, in silico. These findings support their potential as lead compounds for topical therapies for inflammatory skin disorders associated with pruritus, although further optimization and validation are required.